At the toe of the Llandovery slope-apron system lie a series of lobes. The best exposed forms the first sequence of the Ystrad Meurig Grits. Built of sets of coarsening/thickening upward and thinning/fining upward bed cycles, these reflect topographic compensation as low aspect distributary channels swept across the lobe surface. Flows ponded behind the Ystwyth Fault forming pervasive convolute lamination. Palaeocurrent analysis reveals a complex history of flow pattern and process partitioning. Medium to thick bedded sands at the acme of coarsening upward cycles present flute marks paralleling the Ystwyth Fault, whereas cross-lamination from thin bedded intervals continue northwest in the direction of regional palaeoslope. This suggests the topography presented by the fault was subtle, steering higher concentration distributary channel flows into parallelism but not affecting thicker, more dilute flows. A small subset of south-easterly palaeocurrents originate from collapse of flows ramping up the fault's back. The lobe is topped by a basin-wide hemipelagic drape. The second sequence of Ystrad Meurig Grits then builds in front, and to the northeast of the Ystwyth Fault, the original topographic depression having been filled.
The lobes, and related leveed channels, of the early Silurian Welsh Basin are analogous to stratigraphically trapped fan plays of the Tertiary North Sea.
Stratigraphic forward modelling of synthetic shelf/basin transects allows to analyze the fundamental influence of specific controls on shelf development. Tested physical parameters include: amplitudes of 3rd and 2nd order sea-level changes, tectonic and total subsidence, carbonate and pelagic production rates, initial bathymetry.
Punctuated progradation and backstepping, little aggradational phases, well developed lowstand wedges, and steep slope gradients characterize shelf/basin transitions influenced by high-amplitude sea-level changes. Prevailing aggradation, little progradational and backstepping phases, shelf margin wedges and ramp to distally steepened ramp development characterize shelf/basin transitions influenced by low-amplitude sea-level changes. Models of changes in accommodation should be based on sea-level changes and rates of total subsidence, i.e. include compaction, flexural loading and isostatic rebound. Compaction processes in the buried subsurface represent a major component of changes in accommodation space for specific stratigraphic intervals in the basin fill. The volumes of carbonate sediment deposited in a specific time increment are more important that carbonate production rates measured in vertical direction. Volumes of sediment deposited depend on (1) the carbonate production rate at a specific depth, (2) the shelf surface at this depth level and in the photic zone; (3) the accommodation space available along the shelf/basin transition; (4) water energy (currents, wind), that influences the redistribution of carbonate sediment. Shifts in the carbonate factory depend very much on rates of sea-level changes and on the preexisting bathymetric profile. An important feedback process exists between changes in accommodation and the volume of sediment deposited on the shelf/basin transition. Accommodation initially controls the volume of sediment that can be deposited. Once deposited, sediment triggers changes in the thickness of the water column, increased flexural loading and increased compaction of buried subsurface sediments. This results in further increased rates of accommodation and consequently larger volumes of sediment that can be deposited. When the initial bathymetric profile shows low relief, rates of changes in accommodation are small to moderate and sediment production allows long-term keep up, the influence on shelf geometries will be strong and long-term. When the initial bathymetric profile shows high relief, rates of changes in accommodation are high and keep-up is restricted to landward parts of the shelf/basin transition, the influence on shelf geometries will be small and short-term.
Quantification of the physical controls on shelf/basin transitions requires an approach of combined reverse basin modelling and forward stratigraphic modelling. 2D reverse basin modelling considering the whole basin fill between top basement and the level of maximum burial depths should precede stratigraphic forward modelling. It provides realistic approximations for tectonic subsidence, com-paction-induced subsidence, flexural loading and sediment flux which are an essential input for 2D and 3D stratigraphic forward modelling.
A thin, barite-bearing, carbonate unit overlies Neoproterozoic - Cambrian glaciogenic units throughout W Africa. The origin of this unit and similar «cap dolomites» around the world is the subject of avid discussion. We report preliminary results of a petrographic and isotopic study on such a <5 m thick cap from Jbéliat, near Atar, Mauritania, which drapes snugly 7-10 m wide polygons, characteristic of a cold, arid climate, which themselves overly continental tillites. The Jbéliat cap has a complex history of early deformation with sheet, polygonal and tepee dessication cracks, and secondary brecciation related to subaerial exposure and groundwater-seawater mixing, and chicken-wire textures suggestive of an occasionally evaporitic environment. Barite is present as syndiagenetically contorted veins, radially structured balls (up to 20 cm), clusters of acicular crystals or domal stromatolites. These stromatolites retain their original lamination defined by inclusions of chert and calcite and from their texture are likely to be abiogenic precipitates rather than algal in origin. Above the cap (and the surface of brecciation) is found a thin (30-50 cm), strongly indurated and laterally extensive violet bed comprising imbricated pebbles of volcanic glass, calcite cement, glauconite and acicular barite crystals, which forms the base of <100 m of siltstones and silexites of partly volcanic origin. Carbon isotope values vary in the Jbéliat 'cap' from -3.7‰ to + 3.8‰ (n = 20) with highest values from calcitic pisoids and the violet bed. Positive 13C values have never been reported from Sturtian or Marinoan age 'caps' or correlative sections in Senegal (unpubl. data). Therefore, barring a major hiatus between the base and the top of the Jbéliat cap, it seems unlikely that such high values reflect open seawater. Several of the Jbéliat barites have also been analysed geochemically: sulphur isotope values range between 21.4‰ and 45.6‰ (n = 6) averaging close to Neoproterozoic - Cambrian seawater (28‰). Sequential leaching of the barites allowed us to constrain the Sr isotopic compositions of both the barite and the calcite inclusions. Initial mild acid leaches which dissolved calcite produced consistently more radiogenic 87Sr/86Sr ratios (0.7084; n = 3) than later, pure barite leaches (0.7078; n = 5). Correlative successions from Senegal and Guinea contain fossils of the Early Cambrian (Aldanella attleborensis, chancellorids, sponges, foraminifera), during which time seawater 87Sr/86Sr decreased from 0.7085 to 0.7080. Thus, it would appear that the calcite inclusions retain a seawater 87Sr/86Sr composition. The 87Sr/86Sr ratio of the barites, at 0.7078 (the same as a correlative barite from Mali), is significantly lower than that for seawater for the period between 550 and 280 Ma. Therefore, another less radiogenic source of Sr, probably the volcanism which formed the overlying and synsedimentary volcaniclastics, appears to have contributed to the Sr isotope composition and, by inference, the origin of the barites.
The striated surface at Bigganjargga was first described by Reusch (1891) who interpreted it as glacial scouring of a lithified sandstone (the Veinesbotn Formation in recent nomenclature).
Later, Føyn (1937), Rosendahl (1945) and Bjørlykke (1967) stated that the Bigganjargga pavement is part of a regional unconformity between the "older" and "younger" sandstones of Finnmark. This idea was supported by the regional work by Edwards (1975). However, the glacial origin of this surface was questioned and the tillite was considered to be contemporaneous with the underlying sandstone by some authors in the 1960s and recently by Jensen and Wulff-Pedersen (1996).
Studies on the famous Reusch outcrop in 1998 led to the following important new observations: 1) The classical surface is flat and subhorizontal only on above the high-tide level. At the intertidal zone, covered by algae, it forms part of the western margin of a smoothly irregular channel with a minimum depth of 0.8 m and a width of over 5 m. The channel margin disappears east into the sea. 2) A single 10 x 80 cm, almost in situ, sandstone fragment of the Veinesbotn type along with other smaller ones occur at the very basal part of the channel. 3) The main channel axis, scours, and ridges are parallel to older striae on the classical surface and those in Handelsnes, Skjåholmen and Vieranjarga. 4) Solitary faint striae of the younger set occur within the channel. 5) At the Bigganjargga outcrop site the unconformity surface rises from sea level to the altitude of 2 m and erodes 5 trough cross-bedded sets of the underlying Veinesbotn Formation to the distance of 30 m. 6) The unconformity can be followed 500 m to the west where it occurs at the altitude of c. 10 m and separates the distinguishably trough-cross-bedded fluvial to shallow-marine Veinesbotn sandstone from the massive and parallel-bedded turbiditic Smalfjord sandstone (cf. Bjørlykke, 1967, Fig. 5). These observations prove that the palaeosurface at Bigganjargga is part of the regional "pre-tillitic" unconformity, which was carved into the consolidated "older Finnmarkian sandstones". It clearly belongs to Bjørlykke's (1967, Figs. 2 and 3) glacially scoured Varangerfjord palaeovalley system and represents its deepest parts, but not necessarily the very bottom.
Bjørlykke K, Norges Geol. Undersøkelse, 251, 18-44, (1967).
Føyn S, Norsk Geol. Tidsskrift, 17, 65-164, (1937).
Edwards MB, Sedimentology, 22, 75-94, (1975).
Jensen PA & Wulff-Pedersen E, Geol. Mag, 133, 137-145, (1996).
Reusch H, Norges Geol. Undersøkelse, 1, 78-85, (1891).
Rosendahl H, Norsk. Geol. Tidsskrift, 25, 327-349, (1945).
The holotype and numerous specimens of the species Entosphaeroides irregularis (Maithy, 1975) deriving from the type-layer in the Bushimay Supergroup (Upper Precambrian from eastern Kasai, Zaire) have been studied in detail. The description of the species has been precised and a comparison with the holotype of the species E. bilinearis (Maithy, 1975) and "Palaeomycrocystis schopfii" (Maithy, 1975) has been performed.
These two previous species seem to belong to the E. irregularis species.
Different morphological and theoretic stages of destruction of the species E. irregularis are proposed. These stages has been found (this work and Baudet, 1987) in the same layer under the names of Taeniatum sp. (isolate sheath), Chlorogloeaopsis zairensis (Maithy, 1975) and Glenobotrydion kanskiensis (Maithy, 1975) (cylindrical agglomerate of cells, without sheath; without or with central body in the cells), Palaeoanacystis psilata (Maithy, 1975), Myxococcoides verrucosa (Maithy, 1975), M. Zairensis (Maithy, 1975), Synsphaeridium sp. (shapeless agglomerate of cells, without sheath) and finally Sphaeromorphs from gena, Leiosphaeridia and ?Archaeodiscina (isolate cells). The important points of similarity between all these species well confirm the idea they are different pieces of Entosphaeroides irregularis, suggesting a connection between some Acritarchs Sphaeromorphs species with Cyanophyta as a part of them.
As a consequence, the value of some morphological criteria for these Acritarchs which can be criteria for separing real species or for separing only growing stages of a same species are examined. Moreover, the planktonic characteristic usually assumed for Acritarchs are discussed as regard this link with this assumed benthic Cyanophyta.
Baudet D, Geol. Journ. Thematic Issue, 22, 121-137, (1987).
Maithy PK, The Paleobotanist, 22, 133-149, (1975).
The processes by which non biomineralised tissues are preserved in the fossil record are of interest to geochemists, mineralogists and palaeobiologists. Taphonomic models can be constrained by identifying the mineralogical phases in which these tissues have been replicated. However, this is usually a destructive technique, for example, involving the production of a thin section.
Electron Probe Microanalysis usually requires samples to be polished and subsequently coated in order to produce for example, a homogenous x-ray map of a homogenous material. It is, however, possible to interpret x-ray maps from unpolished and uncoated material in terms of mineralogy. Two principal characteristics of analysing such samples need to be addressed. Firstly, sample charging must be minimised by reducing the accelerating potential of the electron beam until the sample reaches a charge-neutral state - this may preclude the analysis of some elements. Secondly, additional effects of surface roughness can be eliminated by applying a subtraction of an x-ray continuum map free from characteristic x-rays, generated over the same sample area. Energy dispersive x-ray mapping is preferred to wavelength dispersive mapping as the geometrical constraints of wavelength dispersive spectrometers will exacerbate the effects of surface roughness of a sample.
The value of this technique has been demonstrated in an investigation of the diagenesis of selected fossils from the Burgess Shale (Stephen Formation: Middle Cambrian) of British Columbia, Canada (Orr, Briggs and Kearns 1998). As many Burgess Shale fossils are of soft-bodied organisms, this world famous Konservat-Lagerstätte is important to our understanding of early metazoan evolution; however, the mode of preservation of Burgess Shale-type fossils has remained unresolved. The fossils are preserved as a combination of organic carbon films and sheet silicates of illitic and micaceous composition. Elemental mapping confirms that there are contrasts between the chemistry of the sheet-silicates that define the fossils and those of the matrix. This confirms, for the first time, that the former are authigenic and precipitated onto the template provided by the decaying organism. Variations in the compositions of the clay minerals in different parts of the fossils were controlled by contrasts in the chemistry of the decaying tissues. The composition of the decaying tissues may have controlled binding or precipitation of minerals directly. Alternatively, the control may have been indirect and occurred via the sequential precipitation of different clay minerals in tandem with the decay of progressively more recalcitrant tissues. Bacterially-mediated authigenesis of clay minerals is a plausible, but unproven, mechanism by which either process could have occurred.
Orr PJ, Briggs DEGB & Kearns SL, Science, 281, 1173-1175, (1998).
A detailed foraminiferal distribution from bed by bed collecting of the Russian Platform, Mangyshlak penninsula and SW Crimea is studied. The present citeria for defining the Santonian/Campanian and Campanian/Maastrichtian boundaries by means of planktic and benthic Foraminifera are discussed. A biostratigraphical analysis of the Santonian - Maastrichtian interval and correlation with NW German basins are proposed. Authors received the next conclusions. 1. The proposed benthic foraminiferal zonal scheme for the Late Santonian-Maastrichtian of the EPA was created on the basis of analysis of zonal schemes and zonal assemblages of different regions of the eastern and western EPA, particularly of the Mangyshlak-Precaspian Basin and the NW German Basin. 2. This scheme is very detailed: it comprises 18 biostratigraphical units, 13 zones and 5 subzones. 3. Most of the zones are very widely applicable. They can be followed throughout the EPA, and some of them areal so recognised throughout the adjacent areas. 4. The benthic zonal scheme is 2 - 3 times more detailed then the planktic. 5. The scheme is based on the phylogenetic lineages of foraminiferal genera. Some evolutionary events of phylogenetic development of Stensioina, Bolivinoides, Bolivina and other genera can be determinated both in Europe as well as in Asia, Africa, North America, Australia and in the oceans. 6. On the basis of peculiarities of the geographical distribution of the benthic foraminifera in the Late Santonian - Maastrichtian, the EPA can be subdivided into two palaeobiogeographical provinces: West European and East European. The first was linked with the North Sea and North Atlantic, and, to a lesser degree, with Tethys. The second had restricted connection with the Arcto-Boreal West Siberian Sea through the Turgai Strait, and was continuously linked with Tethys. 8. The appearance of some of the stratigraphically important benthic species and all of the planktic species reflect different abiotic palaeogeographic events: eustatic transgression and connection between the EPA Basin and Tethys, North Atlantic, and the Boreal-Arctic West Siberian Sea through the Turgai Strait, which was formed during the later part of the Late Campanian. More open and freer connection between the East European Province, and the Arcto-Boreal West-Siberian Sea through the Turgai Strait was established during the Late Maastrichtian.
The early Jurassic was a time of rapidly rising sea-level and is associated with the extensive spread of anoxic bottom waters. Sea-level rise across the Pliensbachian-Toarcian boundary culminates in the falciferum zone of the Toarcian and is one of the best authenticated eustatic events in the Jurassic. This major transgressive pulse is marked by apparent deepening in marine sequences and associated with the deposition of organic rich shales. The development of anoxia coincides with a notable period of mass extinction of the marine fauna. High resolution sampling and study of the microfaunas through several sequences in the U.K. confirm that benthic foraminiferal faunas were similarly affected by an early Toacian falciferum zone event. Samples were analysed from Pliensbachian-Toarcian mudstone, clay and shale sequences of the Dorset Coast, the Midlands and the Yorkshire coast. The sections studied show distinct changes in assemblages across the Pliensbachian-Toarcian boundary and in the basal zones of the Toarcian. The foraminiferal data from the U.K. successions is compared to other successions in France and Germany. In an analysis of all the successions one can determine the rates of extinction, the rapid appearance of opportunistic 'disaster' taxa, and the final re-emergence of the stable fauna of the of the Toarcian.
Upper Turonian to lower Campanian planktonic foraminiferal assemblages from ODP Holes 762C and 763B, drilled on the Exmouth Plateau (Southeastern Indian Ocean), were investigate for biostratigraphic and paleobiogeographic purpose. During the Late Cretaceous the studied holes were located close to 50°S and for the first time a complete record of mid-high latitudes Cretaceous planktonic foraminiferal fauna was obtained. Results showed that several taxa including some of the low latitude marker species display a different vertical distribution. On the other hand, other species overlooked at low latitudes such as Heterohelix papula exhibit restricted ranges that appear to be useful for biostratigraphic correlations. The stratigraphic ranges of Globotruncana ventricosa, a low latitudes marker species, Globigerinelloides impensus and Hedbergella sliteri, both endemic species of high latitudes, are discussed. The total range of Falsotruncana maslakovae and the partial range of Marginotruncana marianosi have been used to identify two new biozones for the interval between the extinction of Helvetoglobotruncana helvetica and the first appearance of Dicarinella asymetrica. A planktonic foraminiferal biozonation for the mid-high latitude is tentatively proposed at a regional scale and compared with the zonal scheme previously used for the circum-Antarctic region and with the low latitude standard zonation.
During the Jurassic coccolithophorids and calcareous dinoflagellate cysts provide the largest amount of carbonate to the sediments. Various studies (Noël & Busson, 1990; Erba, 1992; Mattioli, 1997) have shown that, at different stages in the Mesozoic, a contrast exists between limestone and marlstone assemblages respectively dominated by calcareous dinoflagellates and coccoliths. These variations of assemblage composition are generally interpreted as changes in productivity. During the Middle-Upper Jurassic period, the species diversity is characteristically low and the assemblages are worldwide dominated by one coccolithophorid family: the Watznaueriaceae. The dominance of this family over other coccoliths began at the Aalenian/Bajocian boundary, when Watznaueriaceae radiated. They replaced the calcareous dinoflagellate cyst Schizosphaerella spp. as carbonate producer, while the abundance of Schizosphaerella spp. sensibly decreased. Coccolithophorids composed then the pelagic calcareous fraction in limestones and marls. The contrast between limestones and marls is expressed by variations of species diversity and size of the taxa in coccolith assemblages: limestones contain poorly diversified, small-sized assemblages of coccoliths and marls yield diversified, normal-sized assemblages (Busson et al., 1997).
The present study is focused on the genus Watznaueria which dominates in the Middle-Upper Jurassic assemblages. Middle to Upper Jurassic sections have been studied in southeastern France, central Italy and southern Germany. They belong to different palaeogeographical domains and present variable lithologies, show that the dominance of Watznaueria spp. is not a consequence of selective diagenesis. Preliminary results show that the assemblages are composed of ten dominant species of the genus Watznaueria which are highly resistant to diagenesis and with a comparable preservational potential. Quantitative analyses on several species evidence a dominance of W. britannica, W. manivitae with subordinated W. barnesae in the marl-limestone alternations. Watznaueria britannica occurs with several morphotypes, differing by size dimensions, shape and length of the central area and of the bridge. Statistical analyses are applied on the abundance and distribution of the most common species and of the different morphotypes in limestones and marls. The scope of this approach is to test wheather or not morphological or abundance variations reflect palaeoceanographic primary fluctuations.
Noël D, Busson G, Sci. Géol, 43, 63-93, (1990).
Erba E, Riv. Ital. Paleonto. Stratigr, 97, 455-484, (1992).
Mattioli E, Palaeogeogr. Palaeclimatol. Palaeoecol, 130, 113-133, (1997).
Busson G, Noël D, Cornée A, Bull. Soc. Géol. Fr, 168, 601-609, (1997).
The Maastrichtian ostracods recovered from ODP Holes 1049B, 1050C and 1052E on the Blake Nose, Western North Atlantic, were investigated. The three sites are located on a depth transect encompassing middle to lower bathyal, Late Cretaceous palaeodepths. Hole 1052E, which is the shallowest site, yielded only rare ostracods in the early Maastrichtian G. falsostuarti-G. gansseri Zone. The species richness, abundance and faunal density were in average considerably higher in the late Maastrichtian R. fructicosa and A. mayaroensis Zones of Hole 1052E, possibly, at least partly, as a result of palaeoceanographical changes that were also responsible for the disappearance of the inoceramid bivalves on this location. According to MacLeod (1994), inoceramids were adapted to warm, oxygen-deficient conditions with low populations of burrowing organisms and exclusion of shell-crushing predators. Their extinction was possibly a consequence of the global change in oceanic circulation during which warm, oxygen-poor bottom water was replaced by more vigorously circulating, cool, oxygenated Antarctic bottom water (MacLeod, 1994). A palaeobathymetrical comparison among the late Maastrichtian ostracod assemblages recorded from Holes 1049B, 1050C and 1052E shows that the faunal density and mean number of taxa is inversely correlated with palaeodepth. However, the dominance of the platycopid genus Cytherella increases with palaeodepth. A dominance of platycopids may signify environmental stress related to low oxygen content (Whatley 1991). The dominance of the benthic foraminifer Nuttalides trumpey in the Late Cretaceous of Holes 1049B and 1050C provides additional evidence of oxygen deficiency. From a total of 28 genera recorded from Holes 1049B, 1050C and 1052E, 15 were previously recorded from Hole 689B, a high latitude hole in the Southern Ocean, and demonstrate that many ostracod genera display a wide latitudinal distribution in the Late Cretaceous deep sea, although more geographically restricted genera seem also present as is analogous to modern and Tertiary oceans.
MacLeod KG, Geology, 22, 139-142, (1994).
Whatley R, Journal of Micropalaeontology, 10, 181-185, (1991).
Significant stratigraphic variation may be observed in the elemental and isotopic compositions of pelagic sediments and their constituent fossils. Such variation may be attributed to various environmental factors, including elemental fluxes, carbonate and siliciclastic supply, marine productivity, biotic composition, water temperature and salinity, redox conditions, water depth and sedimentation rates. Interpretation of chemostratigraphic variation is, therefore, rarely straight-forward.
The Cenomanian stage represents one of the best documented periods of eustatic sea-level rise in the geological record. We have studied stratigraphic variation in the elemental composition of chalks deposited during the Cenomanian transgression, in an attempt to identify geochemical criteria that can be employed as indices of sea-level change and can provide a basis for sequence stratigraphic analysis. The Cenomanian in southern England is particularly suitable for such a study because: (1) sediments consist of a uniform succession of dm-scale alternations of chalks and marls; (2) burial depths have remained shallow, so sediments retain high porosities, contain little cement, and retain oxygen isotope values close to Cretaceous seawater; (3) a comprehensive sequence stratigraphic model has been proposed recently (Robaszynski et al., 1998). Samples were collected at metre-intervals through a 100-m-thick succession exposed at Culver Cliff, Isle of Wight. Desalinated samples were dried, ground, dissolved in nitric acid following fusion with lithium-metaborate, and analysed by ICP-AES. Selected samples were leached with acetic acid and analysed to estimate the contribution of the non-carbonate fraction to the bulk chemistry.
Geochemical profiles display a close correspondence to the sequence stratigraphic model. Manganese is the most sensitive and robust indicator of sea-level change, with a broad decline in bulk Mn-contents occurring through the Cenomanian. However, no clear correlation exists between lithology and Mn content. In general, large negative excursions on Mn profiles coincide with sequence boundaries. Low values of Mn are recorded in shelf margin wedges, increasing values occur in the transgressive system tracts, with maxima possibly corresponding to maximum flooding surfaces. Decreasing values characterise highstand systems tracts. By contrast, a major positive Mn excursion characterises the uppermost Cenomanian - lowest Turonian, interpreted to represent a shelf-margin wedge and transgressive systems tract. However, this interval is coincident with Oceanic Anoxic Event 2, a period of reduced oceanic oxygenation, when redox conditions would have played a major role in controlling Mn chemistry.
Variation in Mg, Sr and Fe also shows some correspondence to the sequence stratigraphy. Strontium provides a more robust indicator than the other two elements. However, non-carbonate associated elements, particularly Si, Ti, and Zr, when normalised to Al, provide good independent evidence of sequence boundary positions and systems tract identification. Our study demonstrates that elemental chemostratigraphy provides a powerful new tool in the development of sequence stratigraphic models from pelagic successions.
Robaszynski F, Gale A, Juignet P, Amédro F & Hardenbol J, SEPM Spec. Publ, 60, 363-386, (1998).
For the first time, mosasaur genera have been identified from Late Cretaceous deposits on Vega and Seymour islands, east of the Antarctic Peninsula. Recent expeditions to Antarctica sponsored by the United States National Science Foundation and the Instituto Antartico of Argentina have resulted in the first mosasaur specimens that may be identified to generic levels. We have found three genera, Mosasaurus, Leiodon, and Plioplatecarpus from the Sandwich Bluff Member of the Lopez de Bertodano Formation.
Mosasaurs are squamates that had adapted to an aquatic environment during the Late Cretaceous. Although their late appearance in the Age of Reptiles might suggest restricted geographic ranges, these marine reptiles have now been found on every continent. Even so, mosasaurs have often been considered to be rather endemic, even at a generic level, throughout the world. Undoubtedly, this situation evolved as a result of isolation of workers on separate continents and upon a relative paucity of specimens. However, the associated genera identified from Antarctica have also been recorded in South America, North America, Africa, and Europe. Therefore, these highly mobile aquatic reptiles appear to have obtained a cosmopolitan distribution in a relatively short time during the end of the Cretaceous.
The (pelagic) Massignano section in central Italy has been ratified as the GSSP for the Eocene/Oligocene (E/O) boundary at meter 19 of the total 22.9 m. Thus, unfortunately only some 4 m of lowermost Oligocene is exposed at the GSSP site. To extend the lower Oligocene record at Massignano, the MASSICORE was drilled about 110 m south of the stratotype section (Lanci et al., 1996). The correlation of the core with the Massignano quarry (GSSP) section indicates that the E/O boundary in the MASSICORE occurs at a depth of 19.2 m (dated at 33.7 ± 0.5 Ma; Lanci et al., 1996), and that hence, an additional 15 m of lower Oligocene strata was recovered.
Detailed dinoflagellate cyst zonation of the E/O transition interval in the Mediterranean area indicates that the E/O boundary GSSP correlates to the middle part of the classic (marginal marine) Priabonian type section in northeast Italy (Brinkhuis & Biffi, 1993; Brinkhuis, 1994), thus placing the classic Priabonian/Rupelian boundary (and E/O boundary) now in the lowermost Oligocene. These, and other results from the Priabonian type area prompted Brinkhuis and Visscher (1995) to suggest that the E/O GSSP was unsuitably placed, and proposed alternative horizons, for example the TA4.3/4.4 third order sequence boundary of Haq et al. (1988), close to the extinction of the dinoflagellate cyst Areosphaeridium diktyoplokus.
To further elucidate the early Oligocene history in central Italy, we analyzed 100 samples taken between 39.42 and 1.15 m of the MASSICORE palynologically, emphasizing dinoflagellate cysts. Our data indicate cooler conditions and lowstand across the E/O boundary GSSP, followed by transgression and a brief warmer interval during the earliest Oligocene. Subsequently, our record indicates that a more pronounced cooler and lowstand period occurred. The corresponding sequence boundary may well be correlated to the TA4.3/4.4 boundary, occurring just below the last occurrence of Areosphaeridium diktyoplokus. These results are well-correlatable to those from the Priabonian type area, and once again stress that this 'cooling/sequence stratigraphic' concept of the E/O boundary enables and facilitates world-wide recognition, and that hence, the position of the E/O GSSP should be reconsidered.
Brinkhuis, H & Visscher, SEPM Spec. Publ, 54, 295-304, (1995).
Brinkhuis, H, Palaeogeogr. Palaeoclimatol. Palaeooecol, 107, 121-163, (1994).
Brinkhuis, H & Biffi, U, Mar. Micropalaeontol, 22, 131-183, (1993).
Haq, BU, Hardenbol, J, & Vail, PR, Soc. Econ. Paleont. Miner., Spec. Publ, 42, 71-108, (1988).
Lanci, L, Lowrie W & Montanari A, Earth Planet. Sci. Lett, 143, 37-48, (199).
Extensive shallow-water carbonates are deposited today along continental margins at mid-to high latitudes (beyond 30 degrees) in temperate and cold-water environments. Their ancient counterparts are commonly found throughout the geologic record. Despite their abundance, the factors which control their growth and development are not as well understood as those controlling their warm-water equivalents. In addition, warm-water and cool-water carbonates are often found superimposed in the geologic record, but the factors controlling these alternations remain speculative.
Benthic and planktonic foraminifera from pelagic sections adjacent to the cold-water carbonate platforms successions can be used as paleoenvironmental proxies for the external factors, such as eustasy, climate, circulation patterns, nutrients concentration, and tectonic, which control the development of cool-water carbonate bodies.
In this study, we examined a deep-water section (Palazzolo Section) outcropping in the Palazzolo Acreide area in southeastern Sicily. This section, which spans the interval from the middle to the early late Miocene, consists of packstone to wackestone strata deposited in an outer shelf setting (Tellaro Formation) passing into shallow-water carbonate beds (Palazzolo Formation). A micropaleontological study of the benthic and planktonic foraminifera and Bolboforma (protophyta, incertae sedis) and stable isotope analysis of 3 foraminiferal species (Dentoglobigerina altispira, Globigerina bulloides and Uvigerina striatissima) were performed on samples from this section. Preliminary data on the foraminiferal and Bolboforma assemblage composition and the isotope record indicate that temperate or cool-water conditions and/or coastal upwelling dominated in the Palazzolo area during the middle and early late Miocene. Our interpetation of the data suggest that these pelagic paleoenvironmental conditions may have strongly affected the development of the shallow-water benthic communities and, therefore, also fundamentally controlled the evolution of the carbonate system.
This study demonstrates the application of microfossils for paleoceanographic reconstructions in cool-water environments. As with warm-water sequences, marker species can be used for age determination, their assemblages record the paleoenvironmental conditions and their chemical composition can be used as a tracer of the water mass conditions.
Alfred Wegener Institute for Polar and Marine Research, Columbusstraße, 27568 Bremerhaven, Germany
The Sea of Okhotsk, a marginal sea of the North Pacific Ocean, is unique for its recent sediments because it produces radiolarian signals in surface sediments that are similiar to those known from northern and southern high-latitude glacial oceans. Thus, the processes in the Sea of Okhotsk that lead to the modern deposition of glacial-type radiolarian assemblages may represent a potential anlogue for past glacial conditions in both, the northern and the southern high latidudes. Radiolarian assemblages in the sediment record represent well established tools for the reconstruction of hydrographic surface water conditions in the past (e.g. paleotemperatures). Of special interest in our study is the radiolarian taxon Cycladophora davisiana, that contributes up to 40 - 50% of the radiolarian assemblages in glacial sediments from northern and southern high-latitudes oceans and represents an important stratigraphic marker for the delineation of glacial time intervals.
In this study we present the first results of a detailed study of radiolarian assemblages from surface sediment and plankton samples taken during two expeditions with LV Lavrentiev into the Sea of Okhotsk in 1996 and 1998. In order to describe the radiolarian assemblages distributed in surface sediments of the Sea of Okhotsk the data base was treated with a Q-mode factor analysis and the obtained results were compared with the depth habitat of living radiolarians obtained from vertical plankton hauls in relation to modern hydrographic data. We expect that the investigations of the radiolarian assemblages collected in the water column and from surface sediments of the Sea of Okhotsk will allow a better understanding of the environmental conditions linked with the production of glacial indicator species and thus will lead to considerable improvement of the reconstruction of the paleoceanographic conditions in glacial high-latitude oceans (reduction of no-analog situations) and in the Sea of Okhotsk.
Vegetation is sensitive to climatic conditions; fossil pollen records are thus used as evidence for floral pattern changes linked with climatic shifts. Such an approach applied to west European/Mediterranean Pliocene-Pleistocene series has generated a paradigm in which abundant pollen of Artemisia (a principal constituent of steppe landscapes) is correlative to glacial episodes. Our recent study carried out on uppermost Pliocene series on Zakynthos island (Ionian sea, eastern Mediterranean) reveals a behaviour opposite to the model mentioned above, as Artemisia peaks are coeval with interglacial phases. This unusual behaviour of Artemisia pollen with respect to glacial/interglacial cycles led us to consider the differences in species behaviour within the Artemisia group (fossil Artemisia pollen has generally not been identified to species heretofore). Our review of ecological conditions of some Maghrebian Artemisia species shows extremely large ranges of temperature and humidity. Palaeoclimatic interpretations based on Artemisia s.l. abundances thus require caution. The new evidence that Artemisia pollen peaks from the Zakynthos Pliocene indicate interglacials has major implication for our understanding of the complexity of palaeoclimatical patterns.
The objective of the BRGM's project " Morphogenese fluviale " is to reconstruct fluvial dynamics of the Middle Loire river during Holocene and to quantify the relative impact of climatic variability compared to human activities.
The aim of the first phase was to determine the geometry of sedimentary bodies. Holocene deposits of Middle Loire are mainly constituted by sand and gravel beds and clayey channel fillings sometimes associated with peat. A project specific data base partially derived from the BSS (national base of borehole data) has been constituted, all collected data are integrated in a GIS.
A stratigraphy is established on the basis of morphological observations (from field data, aerial photographs), lithological data from the BSS and 50 new exploring drilling, and analysis of basement incisions below alluvial deposits (up to 10 levels are distinguished). The oversimplified concept of one post glacial phase of incision and one phase of filling is invalidated in this area of Middle Loire. In fact, during Holocene, incision and deposition are highly polyphased. In the aim to characterise sandy deposits and the geometry and nature of filling of channels, 40 km of electromagnetic profiles (EM31, EM34) were realised. After post-processing, electric resistivity maps were constructed. Destructive holes were realised to test and control geophysical interpretations. Electro-magnetism permits the detection of unknown channel structures, where they are totally masked by younger loam deposits, demonstrating interest of the method (Gourry et al. 1999).
Actual work consists of dating and characterising clay and peat deposits from 13 cores extracted from channel fillings (up to 5 m of thickness by 10 to 30 m of width).A high resolution sampling has been performed for palynologic investigation, 14C AMS dating, sedimentological and geochemical analysis. Archaeological observations furnish supplementary elements for absolute chronology.
The estimation of the volume of deposits and of sedimentation rates for the different phases will permit a 3D reconstruction of the evolution of the Middle Loire valley during Holocene. This reconstruction will be compared with climatic and anthropic triggers.
This BRGM project is part of French CNRS' PIR "Environnement, vie et Société: Interactions Homme- milieu dans le bassin versant de la Loire" and the " Projet Collectif de Recherche" "Géoarchéologie de la Loire Moyenne et de ses marges".
Gourry et al, Inversion of Slingram electromagnetic data for alluvial sediments mapping, J. Conf. Abs, 4, (1999).
The Dead-Sea and northern Wadi-Araba area are clothed with alluvial and lacustrine deposits that have accumulated in the rift valley over the Late Quaternary. The chronology of deposition of the various alluvium and lake level variations is constrained by various techniques: exposure of cobbles to cosmic rays (based on in situ produced 10Be), U/Th on aragonite, 14C on a driftwood and a shell, and morphologic dating of a terrace riser. In northern Wadi Araba, the rift valley is mainly floored with large alluvial fans and pediments of Pleistocene age (Q2). As indicated by the exposure ages of suficial cobbles, the bulk of alluvium was probably deposited between 140 10Be ky and the late Pleistocene transgression of the Lisan evidenced by overlying lacustrine sediments dated at roughly 30 ky B.P. by U/Th on aragonite. Cosmic ray exposure of cobbles collected on overlying beach ridges indicates that lake Lisan rose to -150 m b.s.l after ca 18 ka B.P.. The ridge material consists mainly of remobilized Pleistocene gravel indicating little sediment supply to the pediment during most of the cold-dry Lisan period. During the Lisan period subaquatic fan-deltas were deposited along the margin of the Dead Sea at the mouth of the major streams. The Lisan lake retreated abruptly, after about ca 12 ka B.P., leaving numerous wave-cut shorelines carved into the talus apron and terraces on top of the Late Pleistocene fan delta at the base of the rift flanking the Dead-Sea. A gravel veneer prograded (Q3a) on top of Lisan lacustrine material after about ca 15 ka B.P.. After the Younger Dryas dry spell, that possibly lead to total shrinkage of the lake, wetter conditions than today prevailed between about ca 10.5 ka B.P and ca 7 ka B.P. maintaining a lacustrine level that probably rose to a maximum of about 280 m b.s.l. at the end of this period. Smaller fan-deltas were then deposited into the previously dissected Late Pleistocene fan-deltas. Most fans along the Dead-Sea margin show about the same Holocene sequence with two major episodes of fluvial aggradation, Q3b and Q3c. These fan terraces were probably laid down during period of low lake level. Q3b was probably deposited between about ca 7.0 ka and ca 6.2 ka B.P.. Beach-bars were built on top of Q3b during a subsequent lake transgression (dated between 6.2 and 4.4 ka B.P.) up to 350 m b.s.l.. Q3c was deposited between ca 4.4 ka and ca 2.0 ka B.P. The lake level rose to 375 m b.s.l. again after Q3c deposition as indicated from overlying beach bars and transgressive lacustrine deposits (dated to ca 1960-1715 a B.P.) This record is consistent with boreholes data that indicate one major episode of lake transgression around ca 4.8 ka, marked by clay-rich fine sediments with some aragonite, and two periods of predominantly fluvial gravel depositions. The observed correlation between periods of low stand of the lake level and fluvial aggradation does not reflect any base-level control. It probably simply reflect synchronous changes of fluvial regime and of the lake hydrologic balance forced by climate changes. This study provides a synthetic and simple frame to interpret ages of geomorphic features around the Dead-Sea. Topographic profiles run across a terrace riser between Q3b and Q3a show a degree of erosion of 9-15 m2 consistent with an early-middle Holocene age. Assuming a ca 7.0 - 6.2 ka B.P age range for abandonment of Q3b we derive a mass diffusivity between 0.8 and 2.4 m2/kyr. This range is consistent with estimates obtained elsewhere from comparable scarps in arid environment.
We study simple geomorphologic systems composed of an alluvial fan and its catchment. In such closed systems, mass transfers are simple and measurable and, as such, can be used to put quantitative constraints on existing models of erosion. Using topographic maps at a scale of 1/100,000 and SPOT panchromatic images from northwestern Tibet, in a region along the Altyn Tagh fault which we suppose homogeneous in climatic and tectonic conditions, we have calculated the volume V of several alluvial fans and the area A of their catchment ranging in size from 10 to 104 km2. We observe a non-linear correlation: V <alpha> A0.75. This exponent 0.75 is approximately equal to the ratio between the logarithms of the bifurcation ratio Rb and the surface ratio Ra of the basin river networks, as defined by Horton and Strahler. It can be shown that the cumulative length of channels in a drainage basin is also approximately proportional to A(ln Rb/ln Ra). This suggests that the volume V of the alluvial fan is proportional to the cumulative length of channels in the basin. This in turn is compatible with a uniform flux of sediments along the whole network, independent on the river order.
Detection of paleosurfaces of mountainous areas plays a major role in calculations and estimations concerning the speed of denudation, uplift history and sediment budget. Digital elevation models (DEM) provide a perfect database for the computation of surface features that might be a part of a paleosurface. Sometimes the envelope of the actual surface may indicate a previous erosion plane. Although the DEM dataset used to detect these features contain all information needed to calculate the envelope, the results depend on the data selection and on the used interpolation method.
Our method is based on the local histogram calculation for a given window size. For the modeling a 100 m pixel-size DEM of the Eastern Alps was used. Since the results derived from the computed envelope (such as volume of the sediments actually missing from valleys) are heavily influenced by any relatively small fluctuation in the fitted surface, we payed special attention to the error propagation throughout the whole process. The statistic approach in envelope calculation ensures that we can estimate the error bar of the derived values for sediment budget and erosion rate approximation.
The statistic properties of the peak points had been studied to characterize the similarities and differences in geomorphic appearance of the geological units on the actual surface. The horizontal and vertical distribution of the data show strong correlation with the tectonic units, therefore the interpolated envelope surface is correlated with the geological setting. This dependency points out that the envelope fragments of the different geological structures have different peak level parameters (namely their height average and standard deviation). Although the envelope found to be flat or gently sloping, some peaks of the actual surface rise remarkably above the fitted surface. These areas are relatively small, therefore statistically insignificant, but may represent local tectonic or geomorphic disturbances.
In a few cases the automatic segmentation of the envelope surface based on these parameters derived purely from the DEM dataset outlines the tectonic units. This segmentation also allows the estimation of the sediment mass missing from the valleys for each geological unit.
These results combined with geological evidence (e.g. sediment mass budget) make possible to determine the erosion rates and uplift history of the different geological units and can give valuable information for palinspastic reconstructions.
Pyroclastic rocks represent an increasing proportion of eruptives during magmatic differentiation controlled by anhydrous phases, as differentiation of co-genetic rock-suites in Central Italy. Central Italian potassium-rich pyroclastics are easily altered by hydration and alkali-ion disturbances. Magmatic geochemistry can only be presented by ratios of immobile elements. The ratio MgO/TiO2 shows good positive and negative correlations with incompatible and compatible elements, respectively, for a large data set from the volcanic centers in Central Italy.
The ratio Al2O3/SiO2 has strong r2=0.96 and 0.92 positive correlations with MgO/TiO2 in the co-genetic rock-suites of Sabatini and Vulsini. Lightly altered samples from a compositionally zoned pyroclastic cooling-unit defines a narrow correlation in the MgO/TiO2vs.Al2O3/SiO2 diagram and this provides information on the differentiation pattern of a single magma. Al2O3/SiO2 ratios are very sensitive to plagioclase fractionation and the correlations in ultrapotassic rock-suites is evidence that plagioclase fractionation has no effect on major element chemistry. Even the most evolved rocks appears to evolve by clinopyroxene only. In contrast, the Central Italian lower potassium rock-suites (LK- or K-series) has been calculated (Appelton, 1972) to differentiate by gabbro fractionation. Lower potassium series is thus predicted to be uncorrelated in diagrams of MgO/TiO2vs.Al2O3/SiO2 and this diagram could be a parameter to distinguish ultrapotassic magmas from lower potassium series.
Future investigations of co-eruptive pyroclastics has the potential to precisely define the geochemical range in which correlations cease in the MgO/TiO2vs.Al2O3/SiO2 diagram, and, by extrapolation, constrain melting in source-rock mineralogy.
Appleton JD, J. Petrol, 13, 425-456, (1972).
Paleoceanographic studies of last glacial sediment records proximal to the Barents Sea continental margin and interior Arctic Ocean records have revealed significant differences in environmental proxies. Recent studies have shown that during the Last Glacial Maximum (LGM) relatively warm and saline surface/subsurface Atlantic Water travelled as far as to the N. Barents Sea continental margin (as it does during the present). Earlier studies, on the other hand, have suggested that a huge ice shelf covered the interior Arctic Ocean during the LGM. Major contrasts in the glaciological, oceanic, and atmospheric parameters affecting the surface ocean character and depositional pattern can explain this difference. In order to map out gradients and understand paleocirculation modes better we have studied new cores from the SW Eurasian Basin and the NE Greenland continental margin and integrated the information with other studies. It appears that a basic parameter as sedimentation rates dropped rather abruptly by a factor of 10 at about 84°N far from the continental margins. Moreover, the trace of the saline, isotopically heavy Atlantic water mass, also known from the Nordic Seas, surprisingly can be followed as far as up to 84°N in the Eurasian Basin. From here and further northwards there seems to be a steady decline of planktic oxygen isotope values. South of 84°N a 'high productivity peak' of planktic foraminifers can be traced over the whole Fram Strait and the SW Eurasian Basin. The content of subpolar planktic foraminifera species reveals positive summer temperatures of the near suface water masses in the whole SW Eurasian Basin. We support the idea of polynya formation and upwelling of Atlantic Waters driven by katabatic winds off the ice sheets sitting on the continetal margins adjacent to the SW Eurasian Basin. A meridional circulation pattern with a much higher degree of Atlantic Water recirculation in the SW Eurasian Basin and export as a Proto East Greenland Current may explain the pattern of paleoenvironmetal proxies. It seems likely that the Transpolar Drift system as we know it today we not existing, and that a massive ice cover limited planktic production and ice abblation rates over the interior Arctic Ocean.
Raised beaches correlation's are not evident without accurate stratigraphical record and dating; it rises difficulties to rebuild eustatic curve for the Channel coasts and the Dover Strait dynamic. Moreover this sector of Europe is characterised by strong geological contrasts. It is controlled by two main geological boundaries: in the North, the Variscan Overthrust correspond roughly to the position of the Dover Strait and in the South, the Northern Branch of the Southern Brittany Shearing Zone. These two boundaries border a domain, which seems to behave rather homogeneously at a large scale under control of plate tectonic (long wavelength deformations), despite the cross cuting by the prolongation of the Channel and North Sea grabens and the existence of main hercynian faults as the Bray Fault. Today, north and south of this "Channel" region, shores are subsiding. All platforms were initially cut mostly during the Late Miocene (late Serravalian-Tortonian) in relation with more steep thermal gradient on the N. Atlantic and seem to have been re-trimmed several times especially by shore-ice rafting since OIS 9. Episodic uplift movements have mostly controlled the opening status of the Dover Strait, especially after the Messinian and after the Early Quaternary events, by reactivating Variscan structures: it enlights the malacofaunal and foraminifers data, the change in river patterns in N. France and Belgium and paleosols record within and outside the Boulonnais. Since the 400 ka BP crisis and global cooling, supplementary deformations were induced by glacio-isostatic deformations and clustered seismic activity in the area during the phase of ice sheet building. The evidence of 8 different transgressions (ESR and TL dating) in the Channel-Strait regions, from OIS 13 to the end of OIS 5 shows the complexity of the sea-level record in a region unstable for isostatic and neotectonic reasons. The sea apparently rose to about the same level of stand at OIS 11, 9 and 7. On the background of tectonic movements, glacio-isostatic and glacio-eustatic relative displacement of the sea-level have modify coastal position and temporarily modify the intensity of tidal currents. Dover Strait re-opening is a recent feature evidenced by faunal, mineralogical and erosionnal evidence: it results from enhanced subsidence of the northern part of the variscan front and the emptying of the pre-existing Loburg Deep. Neotectonic related on varisc structure reactivation still prevails on glacio-isostatic deformation and basin subsidence.
The Vienna Basin is situated within the Alpine - Carpathian mountain chain, between the Eastern Alps and the Western Carpathians. It represents a polyhistoric basin with the Neogene to Quaternary sedimentary fill, deposited in various types of basins in relation to the paleotectonic development of the orogen. Subtropical and humid climate with paleotropical elements of geoflora has been indicated at the Sarmatian/Pannonian boundary. Vegetation assemblages with dominating Pinuspollenites Abiespollenites, Tsugaepollenites, Piceapollis, Cedripites and Alnipollenites, Ulmipollenites, Myricipites subdominance on the basin margin indicates a warm-temperate and humid climate around the sedimentary area during the Early Pannonian. The lowstand period with marshes and lagoons at the basin margins caused the increased pollen portion of Chenopodiaceae and swamp vegetation elements Inaperturopollenites, Nyssaepollenites, less Myricipites in the pollenspectra. The increased pollen portion of Ericaceae points to a fluvial influence. The accumulation of Chenopodiaceae in the interfluve areas indicates probably the local saline swampy environment during the relatively fallen sea level. The Middle Pannonian pollen analyses data with prevailing Alnipollenites, Betula type, Myricipites, Nyssaepollenites coastal vegetation on the basin margin, indicate a temperate and more humid climate. In the Upper Pannonian pollenspectra are spores less frequent and represented by Leiotriletes, Laevigatosporites, Sellaginela, Verucatosporites. Among Gymnospermae the most frequent were pollen of the genus Pinuspollenites, Piceapollis, Inaperturopollenites, Abiespollenites, Cedripites, Tsugaepollenites. Angiospermae were the most frequent, especially the pollen of Salix, Carya, Myrica, Betula, Momipites, Quercus, Ilex, Juglans, Oleoidearumpollenites, Ulmus, Carpinus, Fagus, Tilia. Salixipollenites div. sp. and various herb species, especially grasses from Graminidites sp., dominated over the others species. Other herb species comprised: Chenopodiaceae, Asteraceae, Ericipites and others ranged to NAP (nonaboreal pollen). In all samples prevailes AP (aboreal pollen) group. Some of the samples was rich in halophytic taxa, mainly Chenopodiaceae. Probably this accumulation of the Chenopodiaceae indicates the local salty swampy process following the regresion of the sea.
Jurassic strata in Sweden are restricted to the southernmost province of Scania and adjacent offshore areas where they were deposited in the north-eastern part of what is at present defined as the Danish Basin. The deposition in Scania was strongly influenced by tectonic movements along the Sorgenfrei-Tornquist Zone and the Fennoscandian Border Zone. Relative sea-level changes played a significant role in the distribution and evolution of sedimentary facies. In these marginal facies more or less the entire Jurassic system is represented in outcrops and boreholes, though exposures are to be found only in Scania and on the island of Bornholm.
Previous work has included definition of stratigraphical units (bio- and lithostratigraphy), sedimentology of deltaic and floodplain deposits, structural geology and tectonic evolution of Scania. Special studies have focused on palaeosols, diagenesis and paleontology (e.g. foraminifers, ostracodes, ammonites, vertebrates, ichnology, macrofloras and palynomorphs).
Recent and current research includes a sedimentological synthesis, documentation of new temporary outcrops, subsurface mapping, hydrocarbon assessment, palaeoclimate studies and vertebrate systematics (sharks).
To further develop knowledge and understanding of Jurassic geology in Sweden, a specific group has been formed in 1998. The overall aim is to integrate results from multidiciplinary investigations and to put them into a regional context especially with respect to stratigraphic correlation and basin evolution. Planned studies include volcanic impact, tectonic control, aspects of sequence stratigraphy, subsurface mapping and regional correlation.
The locality is situated near Hajnacka village in the Rimavská Sobota district, Southern Slovakia. The fossiliferous sequence this Villafranchian locality, which has been deposited in a smalll limnic basin, consists mainly from fine grained, tuffaceous and poorly indurated sediments (silty sands, tuffites and pyroclastic debrits). The fossiliferous deposits are limited to two areas near Hajnacka village: the fossil localities Hajnacka I. and II. (Fejfar et al. 1990). The excavated fauna includes remains of Lamellibranchiata (Anodonta), fishes (Tinca furcata, Scardinus? erythrophthalmus, Esox sp.), reptiles (Chelydra aff. decheni, Emys orbicularis), birds (Mergus sp.) and mammals (Prospalax priscus, Baranomys loceyi, Mimomys (Cseria) stehlini, Mimomys (Mimomys) hajnackensis, Trogontherium minus, Lutra sp., Parailurus hungaricus, Hyaena cf. perrieri, Tapirus arvernensis, Dicerorhinus jeanvireti, Muntiacus sp., Anancus arvernensis, Mammut borsoni, etc. The overlying loessic sediments have contained remains of quaternary vertebrate fauna (woolly rhins, elephant, Microtus and Clethrionomys) (Fejfar et al. 1990). The fossil flora includes especially remains of taxa Torreya fejfari, Ulmus braunii, Carpinus sp., Tilia cf. platyphyllos and Buxus pliocaenica. On the basis these fossil plant remains was determined a thermophile forest environment (Fejfar et al. 1990). Acorrdingly to key-fossils (Tapirus arvernensis, Anancus arvernensis, Mammut borsoni, Dicerorhinos jeanvireti, Mimomys (Cseria) stehlini and Mimomys (Mimomys) hajnackensis), the vertebrate fauna of Hajnacka has placed in MN 16a, the hajnackensis-zone of the Borsodia - Dolomys-stage (=Lower Villafranchian). Paleozoogeographical affinitis with the south-east Asiatic area are given by the presence of Parailurus hungaricus and Muntiacus sp. The Hajnacka section is from sedimensts correlated with the early Gauss magnetic chron (3-3.5 Ma) (Lindsay et al.1997). The locality was discovered in 1863. Since this year, many geologists and paleontologists, have been dealed with this locality. The new research of this locality has started in summer 1996 and excavations will continue up to year 2000.
Fejfar O, Heinrich WD & Heintz E, Quartarpalaontologie, 8, 47-70, (1990).
Lindsay EH, Opdyke ND & Fejfar O, Paleogeography, Paleoclimatology, Paleoecology, 133, 205-226, (1997).
The most representative section of Jurassic deposits was penetrated by well 24-Nylydz drilled in the river Pojeg basin. In the wells 10-Setra and 20-Koda the sections are reduced. The deposits of Sysola suite, represented by quartz sands with cross-bedding, are lying at the base of Jurassic sequence. They are overlayed by planar-bedding sands with large amount of mica. L.A. Duriagina has examined palinocomplex with predominant of Disaccites, subdominant Cyathidites, Sciadopityspollenites, from the upper part of this section from 24-well. There are also some forms of Gleicheniidites, Classopolis. This complex is typycal for the Batonian deposits of Vychegda oil shale basin. Two complexes of foraminifera have been recognized in the overlaying unit of dark-gray clays. The main part of the section is characterized by Haplophragmoides infracalloviensis Dain, Recurvoides ventosus (Chab.), Lenticulina tatariensis Mjatl., Guttulina tatariensis Mjatl.. Kutsevella calloviensis Jak., Lenticulina polonica (Wisn.), L. uhligi (Wisn.) were determined in the upper part of the section. Both complexes are typical for the Callovian deposits of Sysola oil shale region, the first one characterizing Lower - Middle Callovian deposits, the second one - Upper Callovian sediments. Greenish-gray clays with glauconite overlay the Callovian sediments unconformably. There are many fragments of Belemnoidea, Ammonoidea and Pelecipoda. Four complexes of foraminiferas have been determined from these clays. Lenticulina russiensis (Mjatl.), L. brueckmanni (Mjatl.), Nodosaria samaraensis Mjatl., Ophthalmidium strumosum (Gumb.) Epistomina nemunensis Grig.; above them Lenticulina russiensis (Mjatl.), L. suprajurassica (Schwag.), Epistomina nemunensis Grig. and numerous Epistomina uhligi Mjatl. were identified from the lower part of the section. These complexes are correlated accordingly with foraminifera association from the Middle and Upper Oxfordian of Russian platform, where their age was determined by Ammonoidea. Lenticulina sublenticularis (Schwag.), L. simplex (Kubl. et Zw.), Epistomina praetatariensis (Umansk.), E. aff. unzhensis Azb. have been recognized in the upper part of section. The complex with predominance of Pseudolamarckina pseudorjasanensis Dain appeared at the top of the layer. According to the first complex, the age of deposits was identified as Lower Kimmeridgian (based on the correlation with the similar complex of Kostroma). The second one is characterizing the Upper Kimmeridgian deposits of Sysola oil shale region. The Oxford-Kimmeridgian deposits are changed by Middle-Volgian oil shale-bearing rocks up the section. These rocks are characterized by two complexes of foraminifera. The complex with Lenticulina biexcavata (Mjatl.) could be observed in the kerogen-containing deposits. The other-one (with Lenticulina infravolgaensis-Saracenaria pravoslavlevi) could be find in the carbonaceous clays. The stratigraphic level of these complexes - zone Dorsoplanites panderi - is well-known. The foraminifera complex of Virgatites virgatus was examined from the unit of gray calcareous siltstones, overlying the Sysola suite in well 10. Lenticulina ponderosa Mjatl., L. ivantchuki Dain, L. muensteri (Furs. et Pol.), Marginulina formosa Mjatl. were well-known from the deposits of zone virgatus from the Middle Volgian of sediments Sysola oil shale region.
Mammalian remains have been obtained in the result of excavations of Zveroboy rockshelter, situated on eastern slope of Polar Ural. Tafonomic characters of the bone material, such as lack of artefacts, traces of gnawing and acid erosion suggest that the rockshelter must have been used by predators as lair. Bone remains of Lepus timidus are represented by all sceleton elements with predominance of teeth and distal parts of limbs. Three lithological horizons are distinguished in the rockshelter section. Radiocarbon date 4000 BP have been obtained for lower part of stratigrafically lowest layer 3. Remains of Lepus timidus, Alopex lagopus, Vulpes vulpes, Martes sp. and Mustela erminea are found in layer 3. The presence of Martes sp. suggests the existence of forest biotops in this time. Remains of Alopex lagopus and Vulpes vulpes are approximately of the same quantity. Sediments of overlaying layer 2 comprise bone remains of Lepus timidus, Alopex lagopus, Vulpes vulpes, Ursus arctos, Martes sp., Gulo gulo, Mustela erminea, Mustela sibirica and Rangifer tarandus. Share of Martes sp. sharply decreases. Lepus timidus, Alopex lagopus, Rangifer tarandus becomes predominate. Remains of Alopex lagopus considerebly prevail over Vulpes vulpes in quantity. Layer 1 is represented by sediments deposited in front of rockshelter entrance. Remains of Lepus timidus, Alopex lagopus and Rangifer tarandus are predominate. Bones of Alopex lagopus prevail over ones of Vulpes vulpes in quantity.
Differences between faunas in taxa composition and proportions of remains reflect the retreat of forest zone border in last 4000 BP.
Several specimens belonging to twenty-five species of agglutinated foraminifera were analysed with EDS (Energy Dispersion X-ray Spectrometry) method. The main goal of this research is to improve the knowledge about texture and mineralogic composition of agglutinated tests. The EDS method has been merely applied to recent fauna, but not to the fossil record.
Thirteen sections belonging to epiligurian successions (Northern Apennines), covering the cronostratigraphic interval between the Middle Eocene and Lower Miocene, were analysed in their foraminiferal content.
The collected data show how the agglutinated species analysed are selective in their grain and cement composition, grain size and shape. Some groups of species are recognize on the basis of test features:-species with silica cement and dominant feldspar (K-feldspar and Plagioclase) and quartz grains (e.g. Cyclammina cancellata, Ammodiscus cretaceus, Recurvoides spp., Trochamminoides spp., Rhabdammina spp.). In these forms the cement appears dishomogeneous, lumpy with an irregular distribution, alternated with empty spaces, probably originally filled with organic matter;-species with calcite cement and dominant albite grains (e.g. Vulvulina spp., Tritaxia szaboji, Eggerella bradyi, Dorothia spp.);-species with abundant cement, fine-grained texture and selected grains in size and composition (e.g. Vulvulina spp., Karreriella spp. and Dorothia spp.);-species with scarce cement, coarse-grained texture and non selected grains (e.g. Hyperammina elongata, Astrorhiza spp.);-species with cement only (e.g. Glomospira charoides).
All the analyzed species agglutinate inorganic grains only, while the recent ones take also organic fragments from the environment. They are sponge spicules, radiolarian tests, diatoms, coccoliths etc.
Another attempt of this study is to focalize the relationship between the test features of agglutinated foraminifera and the paleoenvironmental condition through the correlation of several parameters related to:
-the sediment composition (difractometric analysis);
-CaCO3 content in the sample;
-foraminiferal content (morphotype analysis of benthic foraminifera and paleobathymetric indexes).
The Arabian Gulf is that part of the Tethys sedimentary belt between South East Turkey and Oman. Its southestern part has excellent exposures of Tertiary sedimentary sequences and allow detailed micropalaeontological study to be developed. The samples examined were from 8 different localities and represented by 4 formations, these are the Muthaymimah, Pabdeh, Dammam and Asmari Formations. Carbonates, some clastics rocks and evaporites are the major constituents of these rock units.
Lithologically, these deposits are dominated by microcrystaline to cryptocrystaline limestones ranging between biomicrite to poorly washed biosparite and unsorted biosparite. The porosity types in these sediments are variable in origin between primary depositional (intergranular and intragranular) and secondary compaction and solution (mouldic type). The evaluation of porosity can be described as fair to good and the percentage of the rock consisting of foraminiferan tests is often high. The preservation is variable also, but is mostly fair and some times perfect. These carbonates include a combination of abundent larger foraminifera, and calcareous red algae. This combination as well as the broken nature of most of these faunas and floras indicate that the deposition was in warm waters of an inner to outer shelf environment with some currents, range in depth between 0-130 m and in area of relatively high salinity. The microbiota and microfacies are typical of Palaeocene, Eocene, and Oligocene. The use of European stages names for divisions of the Tertiary of the Arabian Gulf region were difficult to apply. However, the Letter classification of the Tertiary of the East Indies has been followed in the current study and 6 Letter Stages (LS) have been distinguished and defined based on the presence of 60 different genera and species of larger foraminifera and associated calcareous microfossils. The presence of Nummulites deserti group suggests LS Ta1 (Upper Palaeocene), the N. globulus group refers to LS Ta2 (Lower Eocene), the LS Ta3 (Middle Eocene) is represented by N. gizehensis-lyelli group and associated with Discocyclina cf. partti, Asterocyclina cuvillieri, and A. cf. subtaranellei, the LS Tb (Upper Eocene) is marked by the presence of N. chavannesi, N. fabianii group and associated with D. sella, Asterigerina routla, Pellatispira orbitodea, A. asterisca, Actinocyclina radians. For the LS Tc and Td (Lower Oligocene) are mainly charactaraized by the presence of N. fichteli-intermedius group and N. vascus.
In conclusion, the rock units in the study area range in age from Lower Palaeocene to Lower Oligocene. The Muthaymimah Formation ranges between Lower Palaeocene to Middle Eocene. The Dammam Formation ranges between Middle to Upper Eocene. The Pabdeh Formation ranges from Lower to Upper Eocene and the Asmari Formation is Lower Oligocene in age.
The Microcodium Formation outcrops discontinuously in the Italian-French Maritime Alps along a wide unconformity (Jurassic to Senonian) at the distal margin of the early Tertiary Alpine foreland basin. It is formed by several lithofacies, such as disorganised conglomerates, massive or laminated sandstones, lagoonal siltstones and marlstones (Sturani, 1969; Campredon, 1977). It is overlain by shallow marine limestones of the transgressive Nummulitic Limestones Formation and it is interpreted as the infills to a set of paleovalleys cut into the subcrop (Gupta, 1997).
Along the meridian of Ventimiglia we recognized a small lower alluvial fan delta system, located at the outlet of a paleovalley, prograding into the sea, that laterally becomes a sandy coastal system. The basal surface is quite erosional and locally exhibits reddening, Microcodium structures and the development of carbonate nodules in the Upper Cretaceous substratum; this indicates that the basal surface was pedogenically modified as a result of subaerial exposure. Tipically, we found well-rounded and heterometric conglomerates both as result of turbolent floods and short time deposition from streamfloods. The reconstruction of geometric features and the analysis of relationships between conglomerates and sandstones induce to locate the fan delta system in the NW of the area, with transition southward and eastward to sandy coastal system. This latter is formed of coarse-grained sandstones with beach facies (trough cross bedding, low-angle lamination) and middle to upper shoreface facies (massive sandstones with burrows). On the basis of sedimentary structures and fabrics (laminasets arrangement, imbricated pebbles, maximum grain-size decreasing from north to south) we inferred a stream provenance from N-NW.
Sturani C, Boll. Soc. geol. It, 88, 363-379, (1969).
Campredon R, Mém. h. sér. Soc. géol. Fr, 9, 1-199, (1977).
Gupta S, Journal of Sedimentary Research, 67, 1030-1043, (1997).
Holocene deposits in northeastern Europe are widely distributed and form a high floodland and the upper II and I overfloodland terrace 1-15 m high. The deposits are represented by ancient lake, floodland and river bed alluvium. 60 sections were studied by diatom and palynologic analysis in the basins of the rivers Vychegda and Rogovaya. The periods in Holocene were distinguished based on palynologic analysis. Diatom assemblages were found in 11 sections. They comprise 276 taxa 37 genera. The results indicated the changes of environments during Holocene.
1. The Boreal period (9200-8000 years ago). Diatom assemblages were various and rather abundant. Benthonic diatoms dominated (species of genera Epithemia, Fragilaria, Pinnularia, Navicula). Plankton species were not numerous. Boreal species prevailed early in the period, but at the end the number of northern species increased which is indicative of colder climatic conditions. The assemblages are typical of shallow stagnant basins.
2. The Atlantic period (8000-5000 years ago). At the beginning of the period diatom assemblages were poor; later, during a climatic optimum, they were replaced by various and abundant complexes. Species of genera Eunotia, Fragilaria, Pinnularia, Navicula were diverse. The share of plankton species increased. More than half of the species were boreal. The diatom flora reflects greater depths and warmer conditions.
3. The Subboreal period (5000-2300 years ago). Diatom assemblages were poor. The overgrowing and bottom diatoms dominated (species of genera Eunotia, Fragilaria, Hantzschia). The number of northern forms increased. The assemblages suggest shallow basins under colder conditions.
Ongoing geodynamic processes during the Alpine orogeny constantly created more space for terrestrial ecosystems to develop. Clastic sediments of Tertiary age in the Eastern Alps are mostly confined to intra-montane and molasse basins and are often associated with small-scale coal-bearing strata, or to a lesser extent with oil shale-bearing lacustrine series. Palynofloras, organic facies and sedimentological data extracted from different clastic basin fills of the Eastern Alps are now used to reconstruct ancient palaeo-habitats, including the sedimentary environment, edaphic conditions, the types and distribution of the ancient vegetation cover and, as far as possible, climatic conditions. All this information combined gives us an insight into how terrestrial ecosystems worked and how plant diversity/bioproductivity and, but not least, the preservation potential of plant derived organic carbon in coal-bearing or oil shale strata was controlled. Case studies and reconstructions of various habitats from different time slices (Upper Paleocene/Lower Eocene, Oligocene, Lower, Upper Miocene) have been investigated. A few simple relations emerge: plant fossil bearing sedimentary rocks are generally restricted to the lacustrine and fluvial facies and therefore the bio-habitats reflected have mostly a lowland wetland character and represent the azonal vegetation. In contrast, elements of both the zonal and azonal vegetation types are present in palynofloras. Plant diversity in wetlands varies considerably, depending on the hydrological and edaphic conditions: long hydroperiods and poor soil conditions lead to a decrease in diversity and vice versa. High biodiversity apparently occurred in "transitional and zonal vegetation" of transitional environments (nutrient rich and better drained) and may have led to a high net primary production of biomass, but not necessarily to the storage of organic matter in the sediments (except soil humus). In wetlands environments, vegetation types were less diverse and primary production was presumably (with exceptions in the lacustrine realm) not as high, but the preservation potential of plant derived organic matter increased with prolonged hydroperiods and resulting oxygen depletion. We suggest that long term carbon storage in Tertiary sedimentary rocks of Austria was primarily controlled by neither the degree of bio-diversity nor the productivity of the biohabitats, but by the hydrological and sedimentological conditions.
The Triassic Otter Sandstone of the Sherwood Group outcrops along the coastline in south Devon, England. The outcrops are up to 70 m high and extending more than 10 km along the coast (Lorsong and Atkinson, 1995). The sadstone dips about 5° to the east. This gentle dip give us an excellent opportunity to examine the 100 m thick Otter Sandstone, only disturbed by normal faults, with a throw of 1 - 20 meter. The Otter Sandstones rests conformably on Lower Triassic fluvial conglomerates, the Budleigh Salterton Pebble Beds. The lower part of the Otter Sandstone is dominated by aeolian dune deposits and the upper part is dominated by multistorey and singlestorey channel deposits. Paleopedosol horizons are seen in several places with vertical root casts and sheet calcretes. The Otter Sandstone grades into the Mercia Mudstone, which is dominated by playa lake deposits. We have concentrated our studies on the upper fluvial part of the Otter Sandstone. The Sherwood Sandstone Group (formerly Bunter Sandstone) is the principal hydrocarbon reservoir in the Wessex Basin, hosting the giant Wytch Farm oil field and similar accumulations (Lorsong and Atkinson, 1995). This gives us a lot of subsurface data, used for correlation between reservoir and outcrops. We have used several different methods of analyzing the continental sandstone. Samples for ICP-AES, ICP-MS and heavy mineral analysis has been collected, for each 0.5 m. The cliff-section has been gamma ray logged, with a spectral gamma ray tool, using a sampling distance of 0.2 m. The sampling and geochemical work, has given us the following results:
- The close sampling using the spectral gamma ray tool gives information about the distribution of potassium, uranium and thorium, at such a detailed level, that correlation between facies change and change in element distribution is possible. The overall gamma ray log from the examined outcrops has been correlated to the Wytch Farm reservoir, situated 80 km east of the cliff section.
- The overall changes in geochemistry are the result of changes in provenance. The same changes are seen in the Wytch Farm data. This shows that correlation between outcrop and borehole data, based on geochemistry is a useful tool in the petroleum geology. The more detailed geochemical variations are due to changes in sedimentary facies, which facilititates facies evaluation based on borehole data. Different elements are concentrated in the paleopedosol horizons.
This work shows how integration of geochemistry, heavy minerals and spectral gamma ray data provides good constrain in establishing a high resolution stratigraphy, which could be a powerfull tool for chemo-steering in producing hydrocarbon fields.
Lorsong, JA and Atkinson, CD, Sedimentology and Stratigraphy of Lower Triassic Alluvial Deposits, East Devon Coast. Petroleum Group, The Geological Society of London, pp 52, (1995).
The Muth Formation is part of the huge sedimentary succession of the so called Tethyan Zone at the northern margin of the Indian plate ranging from Precambrian to Eocene age. The formation mainly comprising characteristic white quartzarenites has been traced throughout the whole NW Himalayas, from Kashmir to Nepal. The ages for the Muth Formation given in the literature range between Upper Silurian to Middle Devonian. In the Pin Valley the Tethyan sediments form a well exposed SW-vergent fold belt. The Muth Formation in this area varies in thickness between some 380 m (Mikkim) and 260 m (Muth). The formation shows a sharp lower contact (probably a disconformity) to shallow marine dolomites of the Pin Formation. The upper contact to the overlying Lipak Formation displays a gradual transition. In the Pin Valley a foreshore/backshore depositional environment is assumed for the Muth Formation. The average grain-size varies very little and commonly ranges in the fine middle to middle sand size. There are hardly any other minerals than quartz present in thin section. Sections of the at the first glance monotonous Muth Formation in the Pin valley near Mikkim and Muth reveal diversified sedimentary structures in the aquartz-renite. The most important variation which can be used for correlation within the quartzites is a dolomitic horizon in the uppermost 1/3 of the formation. Below this dolomitic horizon the pure arenites can be divided in two facies associations. The lower one shows sub-horizontally laminated beds alternating with common tangential, concave-up cross-stratification with set thickness averaging 0.5-1 m and palaeo-current directions to SE. The which displays palaeo-current directions to NNE consists of large-scale cross-beds up to 4.5 m in thickness alternating with thinner sub-horizontally laminated beds. Arthropod trackways are abundant in the upper facies association but rare anywhere else. Water-escape structures like spring pits, sand volcanoes and sand dykes are present everywhere in the section, but they accumulate below the dolomitic horizon. In the section at Muth well exposed cones and tubes of sand volcanoes appear directly below the dolomitic horizon. Field observation possibly imply that the underlying sand has been sealed by fine-grained dolomite prior to the formation of the sand volcanoes. These water-escape structures could indicate tectonic instability near the beginning of the transgression of the overlying Lipak Formation.
The Lacustrine Oligocene Carbonate Basin represented by the strata of Carinao Formation is here pesented. Microfacies are described and depositional environment is inferred. The outcrops of the Carinao Formation crop out at the western edge of Sierra de Tecka (43º 10'-43º40'S Lat. and 70º69'W Long.), Chubut Province, NW Extraandean Patagonia. Limestone facies and microfacies of Carinao Formation represent distinct lacustrine environments: bioherms, ponds and fluvial channels. Eight bioherms facies were distinguished: Stromatolites with fenestral fabric, Radial dome microbialite, Microbialite with radial dendrite macrofabric, Microbialite showing fenestral fabric, Pinnacle stromatolites, Laminae microbialite, Microbialite with occasional fenestras and Microbialite mudstone interlayered with intrabioclastic wackestone. The bioherms show different shapes. Some are elongated bars parallel to the paleoshore and resistant to the wave agitation, other are coalescent structures, or are mushroom-shaped. In cross section they show several successive growth phases. The pond microfacies consists of: peloidal grainstone and intraclastic floastone. In this environment the energy differs from moderate to high, with wave agitation. The ponds constitute the boundary of the microbial forms. The fluvial channel microfacies are composed of bioclastic grainstones, biointraclastic grainstone, intraclastic grainstone and floastone. At the northern part of the basin, the very thick fluvial deposits represent channels, which diverge southwards, making up a distributary channel system. On the channel surface current ripples, mud cracks, bird foot prints and casts of sole marks are common. The microfossil association contains Eucypris sp., Limnocythere sp. and Candona sp., characteristic ostracods of fresh water environments and they are frequent in the ponds and fluvial channels facies. During the Oligocene, part of the Northwestern Chubut Province was characterized by the development of a shallow lacustrine basin with an important organic activity, which allow the carbonate precipitation. In this environment organosedimentary structures were formed, considered as the result of the accretion of the activity of benthic microbial communities. The bioherms recorded different hydrodynamic cycles in the paleolake, with consecutive rain-off periods interrupted by phases of stability. Among these build ups, the water circulation was free and occasionally formed ponds supplied by fluvial waters. The carbonate sequence would reflect the different contraction and expansion cycles of the lake, controlled by the climatic variations.
Many volcanoclastic layers are interbedded in the Oligocene marly successions that extensively crop out in the Tertiary Piemonte Basin (NW Italy). These volcaniclastic products, characterized by a peralkaline composition, contain mineral suitable for radiometric age determination. The description of these layers is reported in Cadoppi et al. (1999).
Two sections from the SE sector of the Tertiary Piemonte Basin (Garbagna and Sottovalle) have been selected for an integrated study concerning calcareous plankton biostratigraphy (planktonic foraminifera and calcareous nannofossils), 40Ar/39Ar geochronology and magnetostratigraphy. This work have different purposes:- to characterize the main Oligocene calcareous plankton bioevents and to calibrate them to the magnetostratigraphic scale; - to define the age of the peralkaline volcanism.
The preliminary analyses on calcareous nannofossil and planktonic foraminiferal associations allowed to refer the study sections respectively to Zone CP18 and CP19a (Okada & Bukry, 1980) and to Zone P20, P21 and P22 (Spezzaferri, 1994), corresponding to Lower Oligocene p.p. and to Upper Oligocene p.p.
40Ar/39Ar analyses on biotite samples were performed on two volcaniclastic layers of the Garbagna section. Biotite 97 show an integrated age of 29.6 ± 0.16 Ma and a plateau age at 29.4 ± 0.15 Ma. Biotite 117 show a quite flat age spectrum with an integrated age at 28.4 ± 0.16 Ma and a plateau age of 28.5 ± 0.06 Ma according with its higher stratigraphic position. 40Ar/39Ar dating of volcaniclastic layers interbedded in the more continuous Sottovalle section are in progress.
The Sottovalle section is sampled and presently studied also for magnetostratigraphy.
The new geochronological and magnetostratigraphical data could allow to better constrain the Oligocene biochronology.
Cadoppi et al., J. Conf. Abs., 4, (1999)
Okada H & Bukry D, Mar. Micropaleont, 5, 321-325, (1980).
Spezzaferri S, Paleontogrph. Ital, 81, 1-117, (1994).
The uppermost Arenig is represented by Volkhov Formation in Ladoga - Glint area. It corresponds to the most part of Didymograptus hirundo graptolite Zone. Five lithotypes of rocks one can distinguish in the Formation. One of the keys for interpretation of the sediment formation is the position and shape of glauconite grains. They exist in all of the lithotypes. There are two different cases of glauconite. The first one is dark-green in colour and oval in shape. The size of the grains varies from fine-grained up to the coarse-grained. The first type grains are reworked and oxidised to different degree. The second type glauconite is fine-grained, light-green in colour. It incrustates the surface of hard grounds and infauna burrows. It also appears between recrystallised carbonate grains. This glauconite seems to be predominant and has diagenetic origin. An abundance of the first type glauconite results from partial rewashing of the primary sediment and/or from additional input from the shallow parts of the basin. The presence of the second type glauconite marks sedimentary breaks. The sedimentary gaps (hard grounds) are numerous. They have sharp surfaces coloured by limonite and marked by the glauconite. The interval between two adjacent boundaries usually does not exceed 1 cm and often they reworks each other. Clay material content increases and bioclasts content decreases (they become better sorted) upward the section. Typical signs of tempestites (sorting, ripples, etc.) are not well-developed, except one layer, where gradual sorting is presented. The great extension of layers does not confirm coastal currents because of the ripple absence and the great content of muddy component. The deposition of the Volkhov Formation in the region took place under shallow water conditions, intensive water activity. High accumulation rates alternated with the low one (hard grounds formation). Redeposition of the sediment was a cycling process, which was controlled by the high-order sea level fluctuations.
The present study is focused on the lower member of the Cañadón Asfalto Formation, which crops out near to Cerro Cóndor (69º 07'-69º 10' W; 43º 17'- 43º 26' S), Chubut Province, Argentina. A general model of the ancient lake shore with an associated magmatic event is proposed here. The facies zonation for the lake shore is inferred through microfacies analysis and several field data. The volcanic rocks were characterized by stratigraphic relationships and petrographic studies. The volcanic sedimentary cycle of Cañadón Asfalto Formation, Callovian-Oxfordian in age, is the result of different stages in the evolution of the extensional Cañadón Asfalto-Somuncura Basin with a half graben geometry. Two stratigraphic members compose this formation: the lower consist of lacustrine limestones interbedded with basalt and pyroclastic rocks. The upper member is characterized by lacustrine shales with conchostracans, debris flows deposits and fluvial deltaic sandstones, including pyroclastic levels and some basaltic flows at the top. The high lake level deposits alternate with broad playa lake interbeds. The lake deposits allow three subenvironments to be defined. 1) The suprattidal subenvironment is represented by sabka and palustrine facies. Sabka facies are best exposed at the SW area. It shows mudstones with thin levels of interbedded gypsum, mudcracks often filled by this mineral, and chicken wire mesostructure. Palustrine facies are developed behind the bioherm belt. They are composed of microbialitic mudstone and wackestone with pedogenetic peloids, roots and insects eggs, interlayered with mudflat shales with conchostracans. 2) The eulittoral subenvironment is characterized by biohermal belt facies, microbialite mudstone/wackestone with sauropod remains and araucaria pines. Intraclastic grainstone microfacies are present as well. Facies types of biohermal carbonates are: stromatolitic mudstones with wackestone levels, stratiform stromatolites and hemispherical stromatolites with chalk covers. 3) The infralittoral subenvironment is conspicuous in the NW Cerro Cóndor area. The microfacies comprise oncoidal floastone, packstone/wackestone and mudstone with "varves" lamination and fossil fishes. Basalt flows domain in the lower member of the formation, and they are interlayered with carbonates; meanwhile, a more explosive volcanic event is recorded in the upper member. The basalts show high alteration, green and red colors, and vesicles filled by carbonate and chlorite. Other flows are well preserved and are characterized by columnar jointing. They are poorly aphyric, with intersertal to subophytic textures. Mineralogy is composed of plagioclase, clynopyroxene (titanoaugite), olivine, apatite and opaque minerals. Some pyroclastic levels occur as a result of ash falls during the carbonate sedimentation. They appear like yellow, thin layers of glassy tuff and tufites with organic remains.
The Barremian/Aptian boundary was determined by means of integrated bio- and magnetostratigraphy for the first time in the terrigenous sections of Middle Povolzhie region (Ulianovsk - Saratov region, Russian Platform). The boundary coincides with the sedimentary break and with the disappearance of Barremian belemnite faunas according to the new data. The Upper Barremian contains two belemnite zones. The upper zone is Oxyteuthis lahuseni Zone, which was recognised by Baraboshkin (1998). The position of the Zone corresponds to I. depressa Zone of the NW Europe (Mutterlose, 1983). The lower Zone is Oxyteuthis germanica Zone. It was not recognised before in the Russian Platform sections. It contains belemnite assemblages from O. germanica Zone of the NW Europe, being good biostratigraphical marker. The first appearance of Aptian ammonite Deshayesites forbesi is 25-30 m above boundary. Therefore, the boundary was defined by the first appearance of Pseudoceratium eisenackii dinocyst. The data are completed by the recognition of M0 magnetic Chrone, which was found directly above the last occurrence of Barremian belemnites. Tracing of M0 Zone allows to discover the disappearance of significant part of Aptian succession in Ulianovsk Povolzhie region.An integrated bio- and magnetostratigraphical data provides a good correlational link with NW Europe and Mediterranean sections.The work was done with the financial support of MGGA and RBSF (Grants 97-05-65567 and 98-05-64195).
Baraboshkin EY, Zbl. Geol. Palaeont, I, 11/12, 1131-1147, (1998).
Mutterlose J, Palaeontogr. A, 180, 1-3, 90, (1983).
The " Estratos No Denominados" is an upper Cretaceous sedimentary-pyroclastic sequence, which crops out in the northwestern area of the Kotick Point, James Ross Island, Antarctica. This lithological unit shows a lenticular geometry, and overlays turbidite deposits assigned to the Kotick Point Formation (Aptian-Albian). The lithology and internal structure of the "Estratos No Denominados" differentiate them from the underlying rocks. Lithofacies and petrography analysis were carried out and a genetic model is proposed. Two stratigraphic sections are studied: the first, located 2 km south of the Kotick Point; and the second, in the Kotick Point coastal cliffs. The thickness of the " Estratos No Denominados" reaches 100 m. The physical, structural and petrographical features allow six lithofacies to be defined; 1) Lapilli Tuff and Tuff; 2) Pumiceous to Lithic Lapillite; 3) Orthoconglomerates; 4) Conglomeradic Sandstone and Sandy Tuff Conglomerate; 5) Tuff Sandstone and Tufite 6) Silty Claystones. The volcanic lithofacies show different proportion of pyroclastic components, and textural relation reflecting the genetic processes. Vitroclasts (30 to 70%) are represented by pumices, "fiammes", and glass shards. Lithoclasts (5 to 30%) derived from volcanic rocks, rhyolites, andesites and pyroclastic rocks, and in lesser amount sandstone and pelites. They show similar composition in all the lithofacies. Crystals (10 to 15%) consist of plagioclase, quartz, biotite, alkaline feldspar, and scarce pyroxene, zircon, and opaque minerals. Polymictic orthoconglomerates contain pebbles constituted by rhyolites, quartzites, sandstones, ignimbrites and shales. The proposed depositional environment correspond to braided submarine fan systems with an important pyroclastic participation, related to the contemporaneous volcanism of the Antarctic Peninsula magmatic arc. Debris flows, high concentrated turbidite currents, ash falls, and pyroclastics flows, are considered the main depositional processes in the area. The pyroclastic components are the result of a plinian eruption. Ashes are transported by wind and deposited as ash falls in the sea. In many cases, afterwards, they are redeposited by gravitational flows. The collapse of the eruptive column originates pyroclastic flows rich in pumices which come into the sea as massive and laminar flows, mirrored in Lapilli Tuff and Tuff lithofacies.
New nannopaleontologic results are presented as a first attempt to establish the Cretaceous-Paleogene boundary of the Neuquen Basin, Northern Patagonia, Argentina, through microfossils and megafossils. Five geologic sections analyzed consist of the Liu Malal section (SE Mendoza Province), Opaso, Barranca de Jagüel, and Puesto Sin Nombre sections (SW Neuquen Province), and Cerros Bayos section (La Pampa Province). Quantitative and semiquantitative analyses have been carried out on calcareous nannofossils in the well-exposed and continuous marine Liu Malal, Opaso, Barranca de Jagüel and Puesto Sin Nombre sections. The lithologies consist of marls, siltstones, fine-grained sandstones and sparse grainstones, deposited in outer-inner-shelf environments. In previous studies these rocks have been assigned to the Jagüel and Roca Formations, and they have been considered as Late Cretaceous-Paleocene in age, on the basis of their foraminifera and invertebrates. In the five sections, more than 58 coccoliths species have been recognized, and two nannofossil associations has been differentiated. One is an upper Maastrichtian chalk belonging to Zones CC25 and CC26 of Sissingh (1977); the second, with lower diversity, is Danian in aging Zones NP1-NP3 of Martini (1971). Maastrichtian species include: Micula murus, Cribrosphaerella daniae, Cribrosphaerella ehrembergii, Arkhangelskiella cymbiformis, Arkhangelskiella specillata, Eiffellithus gorkae, Eiffellithus turriseiffelii, Predicosphaera cretacea, Predicosphera spinosa, Micula decussata, Ahmuellerella octoradiata, Kamptnerius magnificus, Lithraphidites carniolensis, Retecapsa crenulata, Ellipsagelosphaera britannica, Watznaueria barnesae, among others. The main Danian species are: Biantholithus sparsus, Cruciplacolithus primus, Cruciplacolithus tenuis, Cruciplacolithus asymmetricus, Cyclagelosphaera reinhardtii, Markalius inversus, Micrantholithus attenuatus, Micrantholithus pinguis, Micrantholithus vesper, Neochiastozygus modestus, Thoracosphaera operculata, Thoracosphaera saxea, Hornibrookina teuriensis, Chiasmolithus danicus, Nodosella elegans, Thoracosphaera crassa, Neochiastozygus modestus, Neochiastozgus perfectus and Toweius africanus. In the Cerros Bayos section is recorded for the first time in Argentina the transition between the Micula murus Zone (latest Maastrichtian) and the Biantholithus sparsus (earliest Danian), based on the LO of Micula murus and the FO of Biantolithus sparsus. In the Liu Malal section are detected a thoracosphaerid and micrantholithid bloom at the base of the marine danian sediments; these are progressively replaced by Toweius africanus and Neochiastozygus modestus near to the top of the sequence. A remarkable and anomalous reworked Hauterivian nannoflora was detected in these danian samples and monitored through counting. This unusual association belongs to the Agrio Fm., and is probably due to tectonism and uplift of Cretaceous rocks on the western flanks of the basin, a sea-level fall during the latest Maastrichtian-earliest Danian, unroofing Cretaceous rocks in the provenance, or a combination of these factors. A more precise delineation of the K/P boundary in this region is still in progress, based on closer sample spacing. This will help to establish the first known locality that records the K/P in the Northern Patagonia, Argentina.
Sissingh W, Geol. Mijnbow, 56 (1), 37-65, (1977).
Martini E, Proc. II Plank. Conf. Roma, (A. Farinacci, ed). Ed. Tecnoscienza, 2, 739-785, (1971).
Puesto Araya Formation (Sinemurian - Pliensbachian), a sag deposit of a rifted back-arc basin (Manceda & Figueroa, 1995), is featured by strongly changing facies, thickness and age. Lithofacies and taphofacies analysis was carried out to interpret the depositional system and paleogeographical features of pliensbachian deposits along 3 biostratigraphically controlled sections: Puesto Araya (type locality), Las Chilcas (10 km farther west) and Arroyo Peuquenes (50 km farther southwest). Three facies assemblages (Tidal Assemblage TA, Shoreface Assemblage SA and Offshore-Transition Zone Assemblage OTA) were recognized.
TA includes channelized bipolar cross-bedded sandstones and tabular sandstones showing tidal cross-bedding and mud drapes, trough cross-bedding, swash stratification, plane lamination and parting lineation. TA is interpreted as fillings of shallowing upwards tidal inlets and subtidal sand dunes set in a barrier island-lagoon system (or a partially closed estuary).
SA comprises multievent massive shelly sandstones and amalgamated hummocky cross-stratified (HCS) sandstones, trough-cross bedded and minor massive fine sandstones, pavements of (epi and in) fauna in life position and massive shelly sandstones with clumps of brachiopods. SA is a set of shoreface storm and fair-weather deposits.
OTA shows alternating HCS sandstones with storm event shell beds, massive and normally graded - plane laminated fine sandstones, pavements of epifauna in life position, massive shelly sandstones with clumps of brachiopods and minor massive pelites. OTA is interpreted as storm and fair-weather beds deposited around storm wave base.
Generally TA is covered by SA and then by OTA. This fining- and thinning-upward succession records the upward replacement of multievent storm shell beds by event storm beds following a trend of increasing depth or distance from shore. The scheme and paleocurrents from flute marks, trough axes, wave-ripples and oriented shells (medias between 221,2° and 296°