Radiometrically-dated basalts from Ontong-Java and Manihiki Plateaus in the western Pacific are evidence for the simultaneous formation of these huge features between about 125-120 Ma, although widespread volcanism is not evidenced until about 123.5 Ma. Together these plateaus represent the largest volcanic event in at least the past 160 Ma of Earth history. The intervening Nova-Canton Trough rift system and several other smaller volcanic features in the present northwestern Pacific also formed concurrently or slightly later.
Several responses to these large igneous events probably resulted from accelerated hydrothermal processes delivering increased mantle effluents to the oceans. These responses occurred in the following stratigraphic order with the associated, approximate chronological ages, based in part on our improved dating of the base of the M0 magneticreversed interval (the Barremian/Aptian boundary) at 122 Ma. Nannoconid abundances began to decline, and radiolaria, planktonic foraminifera and calcareous nannofloras began to experience fluctuating abundances and speciation about 123-122.5 Ma. Metal concentrations of Co, Mn, Pb, Yb, and Cu in northern Italian sediments peaked about 122-121.5 Ma. Strontium isotope ratios began to decline at about 121.5 Ma. All of these fluctuations preceded an abrupt change in sedimentation from predominately carbonate to a more reduced, organic-carbon regime whose basal member is the Selli black shale event (OAE-1a). Changes in planktonic communities and sedimentation culminated in a nannoconid "crisis" just prior to 121 Ma and in the Selli black shale at about 121-120 Ma. A large negative excursion of X13C coincided with the beginning of the Selli event, and this rebounded into a large positive excursion peaking after the Selli event at about 120-119 Ma. Strontium isotope ratios reached minimum values at about 116-113 Ma.
These trends may have been accelerated towards their respective extrema by formation of other volcanic features that since have been subducted, or by still-existing features that have not yet been dated adequately. The formation of the Kerguelen Plateau at about 111 Ma makes it unlikely that it caused any of the above responses.
A major, volcanically induced perturbation of the environmental system is documented in the sedimentary and geochemical record of the early Aptian. The Tethyan marine sedimentary record provides informations on changes in the physical oceanography, on the response of the marine carbon system to the climate perturbation and on paleotemperature and precipitation patterns. Black shales of the Livello Selli (Oceanic Anoxic Event 1a) seem to have formed at a time of warmest temperatures, high salinity contrasts and strong upwelling in the early Aptian Tethys. They represent a peculiar greenhouse ocean circulation mode with deep water production sites probably located in highly saline low latitudes. Red, green and white limestones and marls alternating with black shales mirror different circulation modes in the Aptian Tethys. Changes in early Aptian deep water circulation patterns were coupled with an intensification of shelf currents along the northern margin of the alpine Tethys. Quartzs and, a greenhouse climate weathering product, was redistributed by shelf currents and accumulated as sediment drifts in hemipelagic settings. Phosphorite hardgrounds formed on drowned carbonate platforms further document the intensification of ocean currents along the Northern Tethyan margin. The changes in physical oceanography and in nutrient cycling at times of intensifed hydrological cycling favoured an increase in marine productivity ultimately resulting in widespread black shale formation. Changes in the global carbon cycle occurred mainly after the deposition of the Livello Selli. They were triggered by a coupled perturbation of marine organic and carbonate carbon pumps. Elevated oceanic nutrient levels favoured the organic productivity while the carbonate production rate was choked along carbonate platforms of the northern Tethyan margin, causing widespread carbonate platform drowning at a time of rising sea level. The C-isotope record serves as a proxy for described changes in marine carbon partitioning between the reduced and the oxidized carbon reservoir and it records how the biosphere succeeded in stabilising a major climate perturbation by destabilising the marine carbon system during up to millions of years.
C-isotope profiles of Barremian - Aptian shallow water carbonates from southern Italy enable correlation with the bio- and magnetostratigraphically calibrated 13/C-curves from Tethyan pelagic environments recently published by Weissert et al. (1998) and Menegatti et al. (1998). Two previously studied sections near Caserta, one at Monte Raggeto (MR) (D' Argenio et al. (1993), Raspini in prep.) and the other at Serra Sbregavitelli (SS) (Buonocunto et al. (1994)) were chosen for bulk rock 13/C-analysis. Based on green algae, benthic foraminifera and magnetostratigraphy the MR section is dated as latest Hautervian - earliest Albian while the section at SS reaches from the early Aptian into the earliest Albian. An earlier 13/C-profile of MR was published by Ferreri et al. (1997). In this study we present a higher resolved version of this section. The measured values range from 1 per mille (pm) to 4.7 pmVPDB. The C-isotope curve of MR can be split in 9 segments (MR1-9): In the lower 100 m of the MR section C-isotope values fluctuate between 1 pm and 3 pm (MR1). Above 110 m they progressively decrease from 3 pm to 1.5 pm (MR2) reaching a minimum of 1.2 pm at 140 m (MR3). After a steep increase of 2 pm (MR4) 13/C-values fluctuate between 1.8 pm and 3 pm (MR5) and then increase again to 4.5 pm at 180 m (MR6). Over an interval of 20 m, values remain around 4 pm (MR7), at 195 m they suddenly drop down to 2.5 pm (MR8). The uppermost 100 m of MR are characterized by a second positive spike reaching values of 4 per mille (MR9). The C-isotope profile of SS starts in the early Aptian with a steep decrease from 3.5 pm to 1.8 pm followed by a positive shift of more than 2 pm. Between 50 m and 100 m values drop again to 1.5 pm. In the upper 100 m a large double spike occurs showing maximum values of 4.5 pm. The global C-isotope stratigraphy in Weissert et al. 1998 shows several oscillations between 1.8 pm and 2.8 pm in the Barremian. A pronounced depression in the C-isotope profile marks the Barremian - Aptian transition while the Aptian part is characterized by two large positive spikes. This pattern is clearly reproduced at MR and at SS. Moreover, the segments MR1 to MR7 of the MR section correspond to the segments C1 to C7 of the high resolution 13/C-stratigraphy established in Tethyan pelagic limestones by Menegatti et al (1998). This allows us to define the time equivalents of the Livello Selli (OAE1a) (C4-C6 and MR4-MR6 respectively) as well as the planctonic foraminiferal zones G. blowi (C2-C6, MR2-MR6) L. cabri (C7-earliest C8) and G. ferreolensis (C8, MR8) in the platform section of MR.
Buonocunto FP, D'Argenio B@ Ferreri V, Giorn. Geol, 56/2, 179-192, (1994).
D' Argenio A, Ferreri V, Ardillo F & Buonocunto FP, Boll. Soc. GeolIt, 111, 399-407, (1992).
Ferreri V, Weissert H, D'Argenio B & Buonocunto FP, Terra Nova, 9, 57-61, (1997).
Menegatti AP, Weissert H, Brown RS, Tyson RV Farrimond P, Strasser A & Caron M, Paleoceanogr, 13/5, 530-545, (1998).
Weissert H, Lini A, Föllmi KB & Kuhn O, Paleogeogr. Paleoclimatol. Paleoecol, 137, 189-203, (1998).
The ages of sequence stratigraphic surfaces can clearly be important for determining the extent of local structural control versus regional or global influences on sequence architecture in rift settings. Unfortunately, many sedimentary facies in rift settings are difficult to correlate over even short distances. At certain times in Earth history, however, carbon-isotope excursions provide a means of global correlation. To illustrate the potential to correlate between shallow-marine clastic and pelagic carbonates a carbon-isotope curve based on terrestrial organic material has been generated from the ~300 m-thick Aptian (Lower Cretaceous) succession of the Isle of Wight (IOW), UK. The succession accumulated on the downthrow side of the synsedimentary IOW-Purbeck fault system, an important structural element of the Mesozoic Wessex Basin, and includes deposits of both regional (axial) and local (footwall-derived) sedimentary systems. Water-depth-related facies there (lagoonal, estuarine and shallow marine) are arranged cyclically which facilitates sequence stratigraphic interpretation, particularly for the lower to mid Aptian. The most marked facies shifts are associated with the development of the lowest depositional sequence in the succession, across the Barremian-Aptian boundary interval and into the middle Lower Aptian. High marine TOC values in this part of the IOW succession can be equated with the well-known Selli level of southern Europe. The carbon-isotope curve based on fossil wood collected throughout the succession (Gröcke, Hesselbo & Jenkyns, 1999) is almost identical in shape to 13Ccarb curves from Tethyan Europe and the Pacific, and the ages of positive and negative 13C excursions are biostratigraphically indistinguishable across Europe. Through the lower to mid Aptian of the IOW succession, carbon-isotopic changes occur in phase with inferred transgressions and regressions: negative 13Cwood excursions correspond to peak transgression (maximum flooding surface); positive 13Cwood excursions correspond to peak regression (sequence boundary or transgressive surface), a pattern that contrasts with many previous studies of sequences of different age. It is plausible to link the development the lowest depositional sequence in the succession (and, perhaps, also younger Aptian sequences) and the synchronous carbon-isotope excursions to emplacement of oceanic plateau basalts in the Pacific (and other) oceans.
Gröcke, Hesselbo & Jenkyns, Geology, (1999).
Despite the numerous recent works on the Barremian and Aptian stages in NW-Germany (Kemper et al., 1995) the distribution of index-foraminifers and ostracods at the boundary between the Barremian and Aptian remains problematic up to the present. The examination of several borings and sections of other outcrops especially in the eastern part of the Lower Saxony Basin resulted in a more precise definition of this boundary by means of foraminifers and ostracods. Lithologically the clays are very similar in this part of the Lower Cretaceous. Special care was taken of selecting samples from both facies types, the nearshore facies and the offshore regions. The evaluation proved that particularly the samples from the nearshore areas were reacher in microfauna. Moreover there are informations on one or two minor transgressions in the uppermost Barremian (bidentatum Zone), and at least one or more minor transgressions in the lowermost Aptian (tenuicostatus Zone). This is indicated by two genera of foraminifers which are most probably of tethyan origin: Cerobertinella Myatlyuk 1980 and Carlsiella Vespermann 1998. Both genera obviously reflect transgressive system tracts. The Barremian-Aptian boundary can be defined by the last occurrence of Veeniacythereis angulocostata Kemper 1995 and the first occurrence of Brunsvigella aptiensis (Eichenberg 1935) in both facies types nearshore as well as offshore. Further attention was payed to the first occurrence of planctonic foraminifers (Hedbergella spp.). With the exception of the boring Hoheneggelsen KB 50 these species do not occur below the characteristic so-called "Fischschiefer", a laminite of Lower Aptian age which corresponds to the OAE 1a. However in the boring Hoheneggelsen KB 50 the planctonic foraminifera were truly observed in samples of several thin laminites some metres below the Fischschiefer. Moreover it is quite interesting that the normally monotonous microfauna of the Fischschiefer includes benthonic foraminifers in several nearshore sections (Eisenkuhle, Braunschweig, Weenzen etc.).
Kemper E. et al., Geologisches Jahrbuch A, 141, 1-607, (1995).
A multidisciplinary research group has studied marine sediments of Barremian - early Aptian age in NW Germany. Disciplines and aspects involved include sedimentology, palaeogeography, calcareous nannofossils, calcispheres, palynomorphs, mineralogy, organic and inorganic geochemistry. The objectives of this multidisciplinary study were to test the interaction of biota and sediments during this critical interval and to evaluate regional and global processes which may have caused the deposition of Barremian and early Aptian muds in NW Germany, now preserved as black shales. Both biota and sediments show similar trends throughout the Barremian and earliest Aptian. Endemic evolution of marine biota (calcareous nannofossils, foraminifera, belemnites, and ammonites) coincides with the deposition of black clays and laminated sediments in the Barremian. These patterns reflect restricted conditions in a marginal epicontinental sea. The laminated sediments of the Barremian and earliest Aptian, which are rich in C-org, were deposited under anoxic conditions. Palaeontological and geochemical data indicate a major palaeoceanographic change well before the deposition of the final laminated horizon, the Fischschiefer (early Aptian, Deshayesites deshayesi Zone). A turnover of planktonic and nektonic organisms from endemic associations to homogenous cosmopolitan forms occurred in earliest Aptian times. The Barremian laminated sediments are believed to have been caused by a thermally induced stable water stratification.The early Aptian Fischschiefer is interpreted as an anoxic sediment of a stagnant environment, having been caused by a slightly reduced salinity of surface waters. Despite the stratigraphic correlation of the Fischschiefer with the global "Ocean Anoxic Event 1a" (OAE1a), we believe that the deposition of the Fischschiefer was controlled by regional factors.The turnover of marine biota, however, which occurred simultaneously both in the Tethys and in the Boreal Realm, is here considered to reflect a global signal. Increased sea-floor spreading rates, possibly related to a climatic shift, caused a shift towards pelagic conditions on a global scale. This in turn resulted in an adaptive radiation of planktonic organisms; new groups, including planktonic foraminifera, diatoms and silicoflagellates evolved. Thus, the Aptian marks i) the onset of modern marine biota, which still dominate nowadays oceans and ii) the change from siliciclastic sedimentation in pre-Aptian times to pelagic conditions in post-Aptian times.
A quantitative analyses of calcareous nannofloras carried out on the pelagic, expanded section cored at Cismon (Northern Italy) highlighted major changes in abundance and composition during the Barremian-Aptian interval. Data derive from a cm-spaced sampling of a well-constrained section dated with integrated bio-, magneto-, chemo-stratigraphy. Nannofossils were quantified in smear slides and thin sections. On each smear slide at least 300 specimens were counted, whereas all the specimens present in 1 mm2 were counted in each thin section.
In addition to low- and high-frequency fluctuations in total abundance, diversity and single taxa abundance, sharp events were detected. Marked changes in both absolute and relative abundance of nannoconids characterize the Barremian and culminate in the nannoconid crisis preceding OAE1a. Such fluctuations suggest reactions of calcareous phytoplankton to paleoenvironmental changes presumedly induced by the large igneous events connected with implacement of Ontog Java and Manihiki Plateau in the Pacific Ocean.
The sequence of nannofossil events detected at Cismon was reproduced at other locations in the Tethys and in the Pacific Ocean suggesting that changes in abundance, diversity, composition of nannofloras were induced by paleoenvironmental changes at a global scale. In particular, a speciation of coccoliths and nannoliths and a decline in nannoconid abundance occurred approximately 1 M.y. before magnetic chron M0. The wide-canal nannoconids increased in abundance and the narrow-canal nannoconids decreased in abundance in the earliest Aptian (within magnetic chron M0) and the nannoconids experienced a major crisis during OAE1a.
During a time of extremely large igneous and tectonic activity, nannoplankton reacted with a sequence of changes interpreted as the response of calcareous phytoplankton to different trophic regimes of the surface waters. We speculate that nannoconids were inhabiting the lower photic zone and bloomed when the nutricline was relatively deep. Consequently, the nannoconid decline, the increase in abundance of the wide-canal forms and the nannoconid crisis reflect increasing availability of nutrient in the upper photic zone favouring blooms of other coccoliths. Mesotrophic conditions might be direct or indirect consequences of volcanism involved in the implacement of Ontong Java and Manihiki Plateaus.
The palynological and organic geochemical analyses of the early Aptian Selli Unit (SU) (OASE 1a) of the western Tethys performed on the Cismon-Apticore provide new informations on the paleoceanography and document pronounced changes in the regional climate pattern. Based on the distribution of the POM and on geochemical parameters - four different types of organic facies (Phase M - P) are differentiated. Phase M, in the lowermost part of the Aptian section and Phase P in its uppermost part are characterized by low OM content dominated by oxidation-resistant terrestrial organic debris. Most samples of Phase N comprising the OM-rich sediments from the SU are characterized by the high abundance of AOM. However, terrestrial particles represent a considerable part of all the assemblages. The samples from the lowermost interval of the SU with abundant, fluorescent AOM are marked by the highest TOC values (max. 4.9 wt%). The biomarker Pristane/ Phytane ratio (>2), measured in one of the OM-rich samples of the SU, shows a distinct oxic influence in the depositional environment. In the samples of Phase O, following the SU, the POM is dominated by terrigenous particles. Generally, the absence of anoxia and the presence of significant amounts of marine AOM in the SU advocates enhanced primary production as the main reason for these accumulations, and the variations in preservation are related to pulses in primary production and nutrients recycling. Despite the high-productivity character of the Selli Unit black shales, both 13Ccarb and 13Corg values are not marked by a positive shift, but by an interval of unchanged values, the early Aptian positive excursion following immediately after the Selli Unit. This finding indicates that the deposition of the SU black shale had no impact on the global carbon isotope budget and/or that the "biological pump", invoked by several authors was not the dominant trigger of the positive excursion. The Early Cretaceous terrestrial assemblages of the Southern Alps reflect the intermittent influence of two major floral provinces, the Southern Laurasian province to the north and the Northern Gondwana province to the south. For the Selli Unit, warm climatic conditions are inferred from the dominance of Classopollis, the presence of pollen of southern provenience (Afropollis), and by the low 18O values. The warm climatic conditions were probably triggered by elevated atmospheric CO2 levels. For the interval above the Selli Unit, the dominance of bisaccate pollen indicates a major change in the pollen spectrum from North Gondwana to Boreal assemblages. Furthermore, the increase of the 18O values and the enhanced abundance of the coccolith E. floralis reflect a hitherto undocumented upper early Aptian cooler and more humid climate and/or a reorganisation of the Tethyan circulation pattern.
Marine sediments from different boreholes and outcrops of Barremian - Aptian age within the North West German Basin formed as the southernmost extension of the North Sea Basin have been investigated. Especially the borehole Hoheneggelsen KB 50 (Lower Saxony/Germany) recovered a unique section of Late Barremian to Early Aptian sediments.
In the North West German Basin Corg.-rich black shales occur as fine laminated Blätterton-horizons in alternation with claystones in Barremian and Early Aptian times. The black shale development culminated in the "Hauptblätterton" of Barremian age and in the "Fischschiefer" of Early Aptian age.
There are similar distribution patterns of the terrestrial palynomorphs and prasinophytes, which typically show an inverse relationships to the species diversity of dinoflagellate cysts. This reflects the changing influence of the continental system into the marine environment during Late Barremian and Early Aptian times. During deposition of the Corg-rich Blättertone of the Blätterton/Tonstein-alternation and the Fischschiefer the terrestrial input was high. Furthermore the significant freshwater runoff formed a widespread wedge of reduced salinity stratified over normal marine salinity bottom watermasses.
The organic matter contains dinoflagellate cysts, prasinophytes, bisaccate pollen and spores as well as amorphous kerogen and phytoclasts.
The investigations show a characteristic pollen/prasinophyte/dinoflagellate cyst association in the laminated, Corg-rich, dark Blättertone, deposited under anoxic conditions of seafloor-water. The minimum input of terrestrial palynomorphs is found within those sediments immediately following the Fischschiefer and indicates a sudden and remarkable change to a normal marine environment with decreased continental influence.
More than 200 different dinoflagellate species have been yielded within this partial stratigraphic sequence of Late Barremian and Early Aptian sediments. Various lithological units are characterised by different dinoflagellate cyst-associations which have been compared with associations of the tethyan sediments from Southern Germany and adjacent areas.
A growing body of evidence suggests that the mid-Cretaceous was a time of exceptional rates of sea-floor spreading and intraplate volcanism. This pulse in Earth's volcanism almost certainly caused increases in global oceanic ridge volumes, magmatic outgassing, metamorphic decarbonation reactions and atmospheric carbon dioxide levels (PCO2). Modern physical and chemical models of crust-ocean-atmosphere interaction predict that this activity caused increases in global temperatures and significant changes in the ratios of the major alkaline earth elements in sea water. However, existing 18O-palaeotemperature records suggest that low latitude sea surface temperatures (SSTs) were significantly lower than present for much of the Cretaceous. Furthermore, published estimates of mid-Cretaceous sea water Mg/Ca and Sr/Ca are of only historical interest because of their poor stratigraphic control and severe diagenetic overprinting.
Here we present new stable isotope, Mg/Ca and Sr/Ca data from texturally extremely well-preserved foraminiferal calcite from the Blake Nose (Ocean Drilling Program Leg 171B). Results suggest the following: (i) mid-Cretaceous planktonic foraminifera were, like their Cenozoic counterparts, depth stratified; (ii) these Cretaceous foraminifera lacked algal symbionts and did not undergo significant increases in depth habitat during their life cycles; (iii) previous estimates of SST for the mid-Cretaceous may underestimate true surface temperatures because of the analysis of less well-preserved specimens and sub-surface dwelling species; (iv) low-latitude western north Atlantic sea surface temperatures during the mid-Cretaceous were at least as warm as today whereas intermediate waters were significantly warmer than present; (v) Mg/Ca and Sr/Ca data from such well-preserved calcite has the potential to help constrain ancient sea water chemistry and hence, some of the important hypothesised causes and effects of mid-Cretaceous greenhouse forcing.
One of the lesser studied mid-Cretaceous oceanic anoxic events (OAE) isearly Albian OAE 1b, even as it marks an important extinction/radiation event of radiolaria and planktic foraminifera (Erbacher & Thurow, 1997, Leckie, in prep.). OAE 1b has recently been recovered during ODP Leg 171B,Sites 1049 A to C, the post cruise results of which are here compared with studies from OAE sections in southern France and Italy.
We are focussing on benthic and planktic foraminiferal changes and stable isotope variations of carbon and oxygen in both, surface and bottom waters (Erbacher et al., 1998, Erbacher & Hemleben, submitted, Erbacher et al. in prep.). A correlation of these sections from different basins and different paleo-water depths links OAE 1b to the following scenario. Comparing stablecarbon ratios of benthic and planktic foraminifers, at least two seperate water-masses must have existed throughout the entire interval studied. Aftera severe drop of stable carbon and oxygen isotopes (Clarke et al., in prep.), which probably reflects a result of a significant warming, follows arise of planktic foraminiferal carbon isotopes below the OAE. This positive excursion is paralleled by an increase of abundance of infaunal and eutrophic benthic foraminifers and indicates an enhanced flux of carbon to the sea-floor resulting from an increased oceanic productivity. A continuation of eutrophic conditions results in dysoxic to anoxic conditions during OAE 1b. The reasons for the increased productivity remains unclear as it is the case for other mid-Cretaceous OAE. However, recently, Grötsch et al. (1998) demonstrated a connection between platform drowning and positive stable carbon isotope excursions during OAE 1b.
Oxygen deficiency was interrupted by a reoxygenation event of benthic environments resulting in the return of opportunistic benthic foraminifera such as bolivinids, pleurostomelids and Pseudobolivina in the lower third of OAE 1b. Following this short event, anoxic conditions prevailed until the end of OAE 1b. Repopulation of benthic habitats after the event is slow, starting with opportunistic, oligotrophic faunas, indicating a return to mesotrophic to oligotrophic oceanic conditions. A return of a "normal" and divers pre-event benthic foraminiferal fauna does not occur until approximately 25 ky after the OAE.
Investigations of planktic foraminifers across the event (Huber, in Erbacheret al, in prep.) shows that the described scenario is matched by only few taxa. However, a lack of any deep dwelling planktic foraminifers during OAE1b has been interpreted as a result of an expanded oxygen minimum zone (Caron, in Bréhéret et al., 1986).
The two major episodes of Corg-rich black shales, namely the Selli (early Aptian) and Bonarelli (latest Cenomanian) Levels, corresponding to the anoxic Events OAE1a and OAE2, were studied for their calcareous and siliceous planktonic content in order to clarify the biotic changes associated to these extreme paleoceanographic environments.
Each episode has its own peculiarities. In particular, the Selli Level is characterized by the temporary disappearance of nannoconids among the calcareous nannofossils and a decrease in diversity among the radiolarians and planktonic foraminifers. On the other hand, the Bonarelli Level coincides with a major turnover within the radiolarians and calcareous nannofossils and the extinction of the most specialized planktonic foraminifers, the rotaliporids, abundant Heterohelix, and a bloom of calcipheres in near-shore setting. The two black shales, however, share some common features, (1) the selected decrease in diversity within the radiolarians, whose assemblages in the early to middle portion of each of them comprise only deep-dwelling genera by analogy with the modern forms; (2) in the interval immediately preceding both OAEs calcareous nannofossil assemblages are dominated by common Zygodiscus and Biscutum, index forms of high fertility, (3) although planktonic foraminifers are the most susceptible to dissolution resulting in a very scanty records, they also decrease in diversity associated with a relative increase in abundance of Leupoldina (Selli) and Schackoina (Bonarelli). While the decrease in radiolarian diversity occurs within the black shale levels, the changes, either as turnover or fluctuation in abundance, of calcareous nannoflora, and at minor extent of planktonic foraminifers, precede the acme of Corg accumulation. Depauperated radiolarian faunas characterized by deep-dwelling forms, generally in association with the max. Corg values (up to 23% t.w.) and X13C positive shift, also occur in other organic-rich black shales prior to the Selli as far back as the late Hauterivian. The changes of calcareous and siliceous plankton observed within the black shales all point to an increase in fertility in surface waters related to increased upwelling.
APTICORE at the Cismon Valley (Belluno Basin, Southern Alps) penetrated 131.8 m of pelagic limestones, marlstones and "black shales". The cored interval extends from the Upper Aptian to the lower Upper Hauterivian (about 117-130 Ma) and can be considered a "reference section" for low latitudes, containing both a complete carbonate and organic carbon record through the critical black shale intervals. Freshly cored material and logs from the Cismon drill site likely provide the most informative records.
Detailed, multidisciplinary studies are applied to point out high and low frequency changes in the lithologic, paleontologic, paleomagnetic, and geochemical records. Moderate to good preservation of calcareous and siliceous plankton and palynomorphs allowed the identification of several calcareous nannofossils, planktonic foraminiferal, radiolarian and dinoflagellate events. Magnetostratigraphy is available for the entire interval and magnetic chrons 0 through 9 were detected. Stable carbon and oxygen isotopes were analysed and chemostratigraphy of the Cismon core comprises the X13C curve. Cyclostratigraphy is based on Milankovitch cycles identified on lithologic, biotic and geochemical fluctuations. Integrated stratigraphy of the Cismon Apticore resulted in the first coherent scheme derived from direct calibration of bio-, magneto-, chemo- and cyclostratigraphy for the Hauterivian-Aptian interval.
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