The Arabian Basin is an ideal area to study past monsoon variations because of the strong link between summer monsoon wind strength and wind-driven upwelling. The sediments in this area have been studied extensively in order to unravel the orbital phase relationships of monsoonal climate. These studies revealed an exceptional large phase lag between summer insolation and the precession related maxima in summer monsoon intensity of approximately 6-8 kyrs. Summer monsoon proxies such as the upwelling foraminifer G. bulloides, Ba/Al ratio and the organic carbon content of the sediment reach maxima several kyrs after minimum ice volume, indicated by the oxygen isotope record. To explain this large phase lag several mechanisms have been suggested such as a prolonged snow cover of the Tibetan Plateau during early summer, latent heat supply from the Southern hemisphere and the length of the upwelling season. Recent high resolution studies of Arabian Sea monsoon climate showed a high degree of variability of summer and winter monsoon intensity on a sub-Milankovitch time scale, which can be linked to similar high frequency climatic changes originally known from the Greenland ice cores. In this talk we will show that the sub-Milankovitch variability in the monsoonal proxy records and oxygen isotopes are in phase, in contrast to the precession forcing. This suggests that the intensity of the monsoon system on this time scale is (close to) in phase with climatic changes such as recorded in the ice cores.
For the tropical Pacific Ocean, there is a long ongoing debate whether or not productivity in surface waters was enhanced during glacial times. We studied a north-south oriented sediment core transect from the eastern equatorial Pacific perpendicular to the east-west elongated zone of high productivity near the equator (time frame 0 - 1.3 Ma), to add a new perspective to this question. In the upper part of the water column, steep gradients presently occur in nutrient concentration, temperature, and oxygen saturation, from near the equator in the north (ODP site 846) to the Peru Basin (sites 243, 184, and 217) in the south. Sedimentary records of 18O and 13C from both planktonic and benthic foraminifera, organic carbon, alkenone sea-surface temperatures (SST), barium, and phosphor, reveal a complex interaction between the South Equatorial Current which is the major westward flowing current of the equatorial upwelling system, and the Peru Current which transports colder, nutrient-rich water from high latitudes. At first glance, our data suggests that the meridional upwelling gradient from the Peru Basin to the north was stronger during glacials (stronger South Equatorial Currernt relative to Peru Current), indicative for increased productivity at the equator. During interglacials, meridional gradients were lower at the southern boundary, indicative for lower equatorial productivity. Maximum ice volume coincides with maximum organic carbon and minima in alkenone SST, whereas maxima in carbonate and phosphor lag behind by 20-30 kyr.
Analytical results for physical properties in long sediment cores (100 m and 200 m) from Lake Baikal indicates that the climate of the deep continental interior cooled gradually, with periodic changes, over the past 3.5 Myr. Major climato-limnological changes during the interval occurred at about 2.5-2.8, 1.7-1.9, and 0.8-1.1 Ma, which were close to times of major geomagnetic polarity reversals (Matuyama/Gauss, Olduvai, Jaramillo + Matuyama/Brunhes). The longest period found here is nearly 1,000 kyr, which may correspond to the periodicity of fluctuation in solar insolation. It also seems to be related to geomagnetic field intensity. Other long-term period found is about 400 kyr, which corresponds to a Milankovitch parameter of eccentricity. The period was clearly seen before 1.0 Ma, though it was not so clear afterwards. These results suggest that changes in solar insolation were closely related to long-term environmental changes also in the continental interior.
The climate fluctuations of the late Pliocene were simulated using the LLN-2D model. It was forced by the astronomically derived insolation and by scenarios for the CO2 concentration. The model simulations support the geological evidence that significant Northern Hemisphere ice sheets started to develop between 2.75 and 2.55 Myr BP (Raymo et al., 1992). More precisely when CO2 concentration becomes lower than about 360 ppmv the Milankovitch forcing may explain the suddenness and the timing of the entrance into the Ice Age during the late Pliocene (Li et al., 1998). Contrary to the late Pleistocene the late Pliocene ice age corresponds to an orbital forcing with high eccentricity and high amplitude of the obliquity.
On the other hand spectral analysis was performed on the simulated ice volume: the spectrum changes according to the chosen CO2 scenario. The simulated ice volume is dominated by a 100-kyr period when CO2 is fixed to 220 ppmv; it is dominated by a 41-kyr period when a pre-industrial CO2 concentration of 280 ppmv is used. Eventually a linearly decreasing CO2 concentration (from 320 ppmv at 3 Myr BP to 220 ppmv at the LGM) shows a spectrum dominated by the 41 kyr period before 1 Myr BP and by the 100 kyr period after 1 Myr BP, in agreement with the sedimentary records (Berger et al., 1998; Imbrie et al., 1993). In this case the transition is also accompanied by an increase of the ice volume.
Berger A, Li XS & Loutre MF, Quaternary Science Reviews, (1998).
Imbrie J, Berger A, Boyle EA, Clemens SC, Duffy A, Howard WR, Kukla G, Kutzbach J, Martinson DG, McIntyre A, Mix AC, Molfino B, Morley JJ, Peterson LC, Pisias NG, Prell WL, Raymo ME, Shackleton NJ & Toggweiler JR, Paleoceanography, 8(6), 699-735, (1993).
Li XS, Berger A, Loutre MF, Maslin MA, Haug GH & Tiedemann R, Geophys. Res. Lett, 25(6), 915-918, (1998).
Raymo ME, Hodell D & Jansen E, Paleoceanography, 7, 645-672, (1992).
We studied shallow water limestones of an Upper Bashkirian (Mid-Pennsylvanian) carbonate platform in Asturias (Northern Spain) for their sedimentologic and paleoceanographic record. The successions are built by few meters to tens of meters thick shoaling-upward cycles of which few reached the supratidal due to very rapid basement subsidence. The stable oxygen and carbon isotope composition was determined on matrix bulk subsamples with a 0.25 to 0.5 meter spacing in three sections of 50 to 80 meter length. The resulting oxygen isotope curves show a sawtooth-pattern cyclicity with a maximum amplitude of three to four permille that strongly resembles glacial-interglacial patterns of the Pleistocene. The carbon isotope curves also displays regular fluctuations with maximum amplitudes of two permille. There is, with few exceptions, no evidence for early or burial diagnetic destructive overprinting of the primary isotope composition. Detailed investigation of the litho-, and bioclast distribution also indicates that the facies pattern does not controls the stable isotope values. Assuming the isotope fluctuations to reflect Milankovitch orbital parameter cyclicity the oxygen isotope is dominated by the 400 kyr cycle whilst the carbon isotope curve reflects the 100 kyr cycle. This time frame is in agreement with estimates of sedimentation rates based on biostratigraphic (benthic foraminifera) age data.
Tidal rhythmites consist of interbedded sandstone-siltstone and mudstone laminations preserved either as horizontal layers or as foresets. Such rhythmites serve as high-resolution depositional records from which it is possible to deduce absolute sedimentation rates, paleoclimates and lunar orbital shapes.
Within the middle-Pennsylvanian Breathitt Group in Kentucky, several 15-metre thick, delta-front rhythmite intervals contain Neap-Spring cycles comprised of up to 28 clay-draped sandstones (Adkins and Eriksson, in press). Individual sandstone beds, which range in thickness from 0.5 to 20 cm, commonly occur as thick-thin pairs. These pairs are interpreted as daily laminae produced during both the dominant and subordinate ebb tidal cycles. Where rhythmite deposits preserve several months of continuous sedimentation, successive Neap-Spring cycles display a thick-thin relationship reflecting unequal lunar perigean and apogean tides. Estimated accumulation rates ranged in general between 20 and 100 cm per Neap-Spring cycle, but locally reached 20 cm per day in the most proximal deltaic environments.
The upper Mississippian Pride Shale in West Virginia preserves a hierrarchical record of tidal and climatic periodicities (Miller and Eriksson, 1997). Sub-millimeter-thick, fine-grained sandstone/shale or siltstone/shale couplets are interpreted as the product of prodeltaic suspension settling associated with individual ebb tidal flows. Up to 17 couplets systematically thicken and thin within millimeter- to centimeter-thick bundles interpreted as Neap-Spring cycles. Successive Neap-Spring cycles display a thick-thin relationship compatible with unequal perigean and apogean tides associated with the anomalistic month. Decimeter-scale cycles in the Pride Shale are manifested by the progressive upward thickening and thinning of up to 18 Neap-Spring cycles. This bundling is considered to reflect an annual climatic (mosoonal) signature in which during the monsoon more sand was supplied to the delta for redistribution by ebb flows than during the inter-monsoon. Decompacted annual cycle thicknesses indicate that accumulation rates for the Pride Shale ranged between 3 and 20 cm per year but locally reached up to 60 cm per year.
The 3.2 billion year-old Moodies Group in the Barberton Greenstone Belt, South Africa contains the oldest preserved record of tides in the form of bimodal-bipolar cross bedding, lenticular, wavy and flaser bedding, and fine-scale alternation of sandstone and mudstone laminations on cross-bed foresets. Detailed analysis of a tidal sandwave deposit in the lower Moodies Group reveals a hierarchy of semi-diurnal, bi-monthly and monthly tidal periodicities that provides the first terrestrial rock record-based constraints on the origin of the Moon. Thick-thin pairs of foresets reflect deposition by semi-diurnal dominant and subordinate tidal currents, respectively. Cyclic variations in foreset thicknesses reflect waxing and waning of tidal current velocities consistent with Neap-Spring-Neap cyclicity. Alternating thicker and thinner Neap-Spring-Neap cycles are comparable to anomalistic, perigean and apogean signatures. Tidal cyclicity recognized in the Moodies sandwave deposit is comparable to that recorded in modern tidal settings and identified in the Carboniferous rock record. Such cyclicity is compatible with a near-circular lunar orbit at 3.2 Ga that is inconsistent with the lunar capture model but favors the impact model for the origin of the Moon.
Miller, DJ and Eriksson, KA, Late Mississippian prodeltaic rhythmites in the Appalachian Basin: a hierarchical record of tidal and climatic periodicities. Journal of Sedimentary Research, B67, 653-660, (1997).
Adkins, RM and Eriksson, KA, Rhythmic sedimentation in a mid-Pennsylvanian delta front succession, Four Corners Formation (Breathitt Group), eastern Kentucky: a near complete record of daily, semi-monthly and monthly tidal periodicities. SEPM Spec. Publ. 61, (in press).
Recent attempts to tune geological timescales to Milankovitch-type cycles rely on matching features in proxy records to astronomically calculated obliquity and precession cycles. They often use tuning targets such as the 65°N summer insolation curve. It has been shown (Laskar 1993) that the exact position of insolation peaks in time depends on the parameters chosen for dynamical ellipticity and tidal dissipation (the Earth model). Hence a better knowledge of these parameters is needed before precise timescales for the pre Pliocene can be developed using traditional methods (Lourens, 1996).
High quality geological records that have been tuned to an astronomical target have been published from both the Pacific (especially ODP Leg 138; Shackleton et al., 1995) and the Atlantic (especially ODP Leg 154; Shackleton and Crowhurst, 1997) although two different astronomical solutions have been used for the two studies. We have re-examined these data sets to place them in a consistent time scale, and to improve signal-to-noise ratio by stacking different data sets. Our objective is to optimise the separation in the data of that variability that is independent of the chosen Earth model (the amplitude modulation of the precession and obliquity components, extracted by complex demodulation) from the components that do depend on the chosen Earth model (the mean frequencies for obliquity and climatic precession). This operation can be performed iteratively on older sequences to optimise the astronomical solution for longer time intervals.
Laskar J, Joutel F & Boudin F, Astron. Astrophys., 270, 522-533, (1993).
Laskar J, Icarus, 88, 266-291, (1990).
Lourens LJ et al, Paleoceanography, 11, 391-413, (1996).
Shackleton NJ & Crowhurst S, Proc. ODP Sci. Res, 154, 69-82, (1997).
Shackleton NJ et al, Proc. ODP Sci. Res, 138, 73-101, (1995).
Recently, we established an APTS for the Late Miocene (6.7-9.7) based on cyclically bedded sequences in the Mediterranean. The astronomical ages of the Messinian polarity reversals are much older (up to 166 kyr) than expected from CK95. Because the previous APTS covered the last 5.3 m.y., we still have a "Messinian gap" from 5.3 to 6.7 Ma. This gap is caused by the notoriously complex history of the Mediterranean during the so-called "Messinian salinity crisis" and the deposition of less-favourable sediments (diatomites and evaporites) during this time interval. However, most of these Messinian sediments display a very clear sedimentary cyclicity what makes them especially suitable for cyclostratigraphic calibration to the astronomical curves. Field observations indicate that the cyclicity in the Messinian diatomites and evaporites are related to precession/insolation with an average periodicity of 21 kyr. We will present the results of our detailed integrated stratigraphic studies on various sections located throughout the Mediterranean. This will close the "Messinian gap" and, for the first time, provide an accurate and reliable time frame for the Mediterranean Messinian in which several important paleoceanographic and tectonic events are now accurately dated.
Our study focuses on stable isotope analysis on planktonic and benthonic foraminiferal tests from ODP Site 925 on the Ceara Rise (western tropical Atlantic). This site is located at 3041 m waterdepth, i.e. well above the CCD. We have analyzed carbon- and oxygen-isotope ratios in Globigerinoides trilobus (surface-dweller), Menardella (Globorotalia) multicamerata/limbata (deeper dwelling) and Nuttalides umbonifera (benthonic) covering a time-period of 800 ka from 5.85-5.25 Ma. Our results include the first high-resolution (~ 4-5 ka) planktonic stable isotope records straddling the Miocene/Pliocene boundary, as most other deep sea sites either experience hiatuses or non-preservation during this interval. The most outstanding feature in our records is a prominent surface warming to a temperature peak at about 5.53 Ma. Immediately before this, benthonic 18O values are very positive, reflecting stages TG12 and TG14 as recorded in ODP Site 846 of the eastern equatorial Pacific. As in Site 846, interglacial benthonic 18O values are systematically lighter after this event than before. Coincident with this warming we also note a change in both planktonic 13C records from a very low to a higher frequency signal. The benthonic carbon ratios however remain rather constant over this incident, with the only remarkable feature being significantly lighter values at the beginning of the investigated period.The warming at 5.54 Ma can be linked with the LO of Discoaster quinqueramus. Hilgen et al. (1995) constrained the age of evaporite sequences in land-based sections of the Mediterranean by astronomical tuning. They dated the Miocene/Pliocene-boundary at 5.33 Ma and the base of the Upper Evaporites at 5.52 Ma. The scale of the warming (and likely sealevel rise) that we document at 5.54 Ma is so great, it is likely to have affected events in the Mediterranean.
Hilgen FJ, Krijgsman W, Langereis CG, Lourens LJ, Santarelli A Zachariasse WJ, Earth and Planetary Science Letters, 136, 495-510, (1995).
Results from a high-resolution integrated study of two sections of late Miocene age (Oued Akrech and Ain El Beida) located at the Atlantic site of the Rifian Corridor in NW Morocco are presented. The sections consist of continuous sedimentary sequences of alternating reddish and whithish marls. The integrated stratigraphy of Oued Akrech (OA) allows the section to be correlated in detail to time-equivalent sections in the Mediterranean and shows that the sedimentary cycles are dominantly precession controlled. Characteristics in the cycle pattern allow OA to be tuned to the astronomical record, indicating that the reddish layers are time-equivalent to Mediterraneans apropels. The section spans the Tortonian/Messinian boundary and has been proposed to define the Messinian GSSP. The integrated stratigraphy of Ain El Beida (AEB) allows this section to be astronomically tuned as well, showing that it covers one million year from 6.47 to 5.46 Ma. A high-resolution quantitative planktonic foraminiferal study focussed on the relationship between faunal patterns and the sedimentary cyclicity. The reddish layers are characterized by an increase in the relative abundance of Globigerinoides spp., dextral forms of Neogloboquadrina acostaensis and Globorotalia scitula and the white levels by an increase in Globorotalia margaritae and sinistral forms of N. acostaensis. The t-test reveals that other species and/or groups of species are related to the lithology as well: Globigerinoides spp., Globoquadrina altispira, Gq. venezuelana, Globigerina falconensis, G. na apertura, and Hastigerina spp. are related to the red layers; Neogloboquadrina total and sinistral, G. nanepenthes, G. lia juanai, G. lia margaritae s.l., and the Sea Surface Productivity (SSP) values to the white layers. In addition, the stableisotopic composition of benthic and planktonic foraminifers has been analysed; the 18O shifts to lighter values in the reddish layers in both the planktonic as well as the benthic record.
The most important prerequisite to distinguish between autocyclicity and allocyclicity is an excellent age control, preferably of long and continuous successions. Such an age control is often lacking in studies of continental deposits therefore allocyclic forcing cannot be demonstrated and an autocyclic control is favoured. This situation also holds for studies of continental successions in Spain. However, recent studies with an excellent age control suggest that allocyclicity related to astronomically induced climate oscillations is present (Krijgsman et al. 1996). Clearly, an unambiguous demonstration of allocyclicity is mandatory as it has far reaching implications for the interpretation of rhythmic alternations in continental successions.In the vicinity of Orera village (Calatayud Basin, NE Spain), an extraordinary cyclic succession of distal alluvial fan-floodplain, lacustrine and palustrine sediments of middle Miocene age is developed. The sections comprise grey, occasionally red, clays and dolomitic marls alternating with white palustrine carbonates. In the succession, sedimentary cycles can be recognised at four different scales varying from basic small-scale cycles up to large scale cycle patterns. Cyclostratigraphy and magnetostratigraphy of several subsections were used to construct the composite time-stratigraphic record. The magnetostratigraphy was correlated to the Geomagnetic Polarity Time Scale (GPTS) of Cande & Kent (1995:CK95), providing an age of 10.7 to 12.8 Ma for the entire succession. Colour measurements of the sedimentary cycles proved an excellent tool for an objective recognition of these different scales of sedimentary cycles. Spectral analysis of the colour data set resulted in several peaks with frequencies similar to the periodicity of earth's orbital parameters. The average periodicity of the basic small-scale cycles arrives at about 23 kyr implying that these cycles are related to the earth's orbital cycle of precession. The large-scale cycles, characterised by the intervals of well developed small-scale cycles with distinct carbonate beds alternated with more clay-rich with less well defined small-scale cycles, are related to the 100 and 400 kyr eccentricity cycles. The sedimentary cycles were correlated to the eccentricity, precession and summer insolation curves of Laskar 93, thereby assuming that the carbonates represent higher lake levels and thus correspond to precession minima and eccentricity maxima. This correlation provides astronomical ages for the individual sedimentary cycles and for the polarity reversals whereby the latter results in an extension of the Astronomical Polarity Time Scale (APTS) into the middle Miocene. For the last 10 Ma the APTS has been constructed on the basis of cyclic marine successions (Hilgen, 1991b; Shackelton et al., 1996)
Krijgsman W, Garces M, Langereis CG, van Dam J, van der Meulen AJ, Agusti J & Cabrera L, Earth Plant. Sci. Lett, 142, 367-380, (1996).
Cande SC & Kent DV, J. Geoph. Res, 100, 6093-6095, (1995).
Hilgen FJ, Earth Planet. Sci. Lett, 107, 349-368, (1991b).
Shackleton NJ, Crowthrust S, Hagelberg T, Pisias NG & Schneider DA, Proc. ODP, Sci. Res, 138, 73-101, (1996).
Mesozoic carbonate platforms of Southern Italy are thick and well stratified bodies, resulting from Late Tertiary deformation of the Southern Tethyan Continental Margin. They formed mostly in shallow ramp, open to restricted lagoon and peritidal/supratidal settings, and show a prevailingly cyclic organization, consisting of m-scale shallowing upward units. This cyclicity is demonstratably controlled by the Earth's orbital perturbations (evidences from individual cycle duration, hierarchical organization, numerical analysis of their sedimentological and petrophysical features). The genetic mechanisms of the cyclicity have a clear climatic dictator (allocyclicity), that is coupled with eustatic oscillation revealed by emersion-related features. We present here a case-history from the Aptian of the Campania region (Southern Italy) where 3 sections for a total of 250 m have been studied at cm-scale: Serra Sbregavitelli (Central Matese Mountains, 160 m, Upper Aptian-lower Albian), Monte Faito (Sorrento Peninsula, 55 m, upper Aptian-Lower Albian) and Monte Tobenna (Picentini Mountains, 35 m, Upper Aptian); the latter two outcrop at about 100 km SSE of the former. The three sections show a hierarchical organization of the elementary cycles in bundles and superbundles, that may be related respectively to the Earth's short and long orbital Eccentricity oscillation, while the elementary cycles mostly appear to correspond to the Precession or to a combination of Precession and Obliquity periodicities. In these successions the stratal pattern shows a dominant aggradational configuration, where the thickness of cycles, bundles and superbundles is environmentally controlled, the thicker cycles being those formed in more open settings and vice-versa. If analysed in terms of sequence stratigraphy, the superbundles show well recognizable system tracts that, maximum flooding surfaces and sequence boundaries that are used to obtain chronostratigraphic diagrams. The latter may show cycle omission at bundle or superbundle level like in the cases of Monte Tobenna and Monte Faito sections, while at Serra Sbregavitelli we recognize a smaller number of gaps and a good matching with the Tethyan pelagic C-isotopic curve. Using appropriate biostratigraphic and isotopic markers, we have also correlated the Serra Sbregavitelli section with the two distant sections of Monte Tobenna and Monte Faito. The correlation appears possible at the scale of bundles of cycles and sometimes also at elementary cycle level.
The Red Sea is a semi-enclosed sea which communicates with the Indian Ocean through a narrow and shallow sill (~110 m) located north of the Bab-el-Mandeb strait. Its hydrological conditions are sensitive to evaporation/precipitation balance and to variations in the incoming flux of upper water from the Indian Ocean. At the Last Glacial Maximum, reduced exchanges with Indian Ocean (lowering of sea level) and increased evaporation/precipitation ratio over the Red Sea resulted in the increase of surface water salinity with values reaching up to 53‰ (Hemleben et al., 1996). During the Holocene, an increase in climate humidity and surface water exchanges with the Indian Ocean lead to the lowering of surface water salinity. The stronger stratification of the water column and poor ventilation of deep water masses resulted in the deposition of a sapropelic layer, which appears to be synchronous with sapropelic event S1 from the eastern Mediterranean Sea (Rossignol Strick, 1987; Thunell et al., 1988, Almogi-Labin et al., 1991).
The 15 m long piston core MD921017 (19°38.37N, 38°09.16E) retrieved during cruise MD73-Red Sea of the R/V Marion Dufresne covers the last 465 kyr. Over this time interval, there are 11 layers with total organic content (TOC) above 0.4%, reaching up to 1.7%. They deposited during periods of light 18O values which correspond to lowered surface salinities in the reconstruction from Hemleben et al. (1996). Organic matter is mostly from continental origin (with numerous wood fragments), suggesting that high TOC values could result not only from better preservation on the sea bottom (stronger stratification) but also from increased river discharge of continental organic material.
Based on 18O isotopic stratigraphy (G. ruber), we show that 7 of these 11 proto-sapropelic layers appear to be synchronous with sapropelic events observed in Mediterranean Core KC01B (Rossignol-Strick et al., 1998). We suggest that the common driving mechanism for these organic-rich events deposited synchroneously in Mediterranean and Red seas, is the increase of monsoon-related rainfalls over east Africa during periods of strong low-latitude insolation forcing. The dominant 23 kyr-1 frequency observed in the TOC record of Core MD921017 strengthen this hypothesis. Secondary spectral peaks are found at 1/100 and 1/33 kyr-1. The 1/33 kyr-1 frequency can be related to ~1/30 kyr-1 frequency observed in various monsoon-related records from the Indian Ocean (Bassinot et al., 1994) and explained as non-linear response of low-latitude climate to insolation forcing at the Milankovitch periods. The occurrence of 1/100 kyr-1 frequency is not yet fully explained but could indicate a response to glacio-eustatic sea level oscillations. Based on our results, we will discuss possible interactions of sea level changes and evaporation/precipitation balance on the sedimentation of organic matter in the Red Sea.
Almogi-Labin A, Hemleben C, Meischner D & Erlenkeuser H, Paleoceanography, 6, 83-98, (1991).
Bassinot F, Labeyrie L, vincent E, Quidelleur X, Shackleton N & Lancelot Y, EPSL, 126, 91-108, (1994).
Hemleben C, Meischner D, Zhan R, Almogi-Labin A, Erlenkeuser H & Hiller B, Paleoceanography, 11, 147-156, (1996).
Rossignol-Strick M, Paleoceanography, 2, 333-360, (1987).
Rossignol-Strick M, Paterne M, Bassinot F & Emereis KC, Nature, 392, 269-272, (1998).
Thunell RC, Locke SM & Williams DF, Nature, 334, 601-604, (1988).
The bathyal Aptian-Albian Scisti a Fucoidi of central Italy are pervaded by hierarchical cycles. These were studied by means of gray-scale scans of image-processed photographs of the Piobbico core. The cyclicity is expressed mainly in fluctuations in pelagic carbonate production, fluctuations in sediment oxydation and fluctuations in what appears to have been air-born soot, evidence of forest fires. Accumulation rates varied as does the preservation of cyclicity, but segments in which clarity of the "100 ka" signal allows tuning have yielded spectra essentially identical to those of the present-day orbital cycles, including the double modes for the ca. 100 ka eccentricity and for the precession. Higher frequencies of obliquity and precession cycles reflect the change in the earth's spin rate.Variations in the strength of the obliquity signal suggest that polar influences on this near-tropical region was episodic. The (chemical) evidence for soot, and carbon-rich turbidites in the Atlantic sea-floor suggest that fires played a large role in the Mid-Cretaceous world, and that oxygen levels in the Mid-Cretaceous atmosphere may have been high.
The investigation of the Upper Cretaceous and Lower Palaeocene of Russian craton and southern adjacent areas such as SW Crimea and SW Caucasus resulted in establishment of 9 types of periodites in carbonate (marl-marl (1); marl-limestone (2); limestone-limestone (3); marl-chalk (4) and chalk-chalk (5) cycles), terrestrial-carbonate (sandstone, sand-calcareous sandstone, sand (6); sandstone, sand-marl (7); clay-marl, limestone (8) cycles) and siliceous-carbonate successions (opoka-marl (9) cycles). Carbonate turbidites (Caucasus), periodites (mostly Russian craton and Crimea, Caucasus) and transitional turbidite-periodite successions (Caucasus) were observed. All stages of the Upper Cretaceous and Lower Palaeocene in the Caucasus contain limestone-marl-sandstone carbonate turbidites. At the same time in all regions of investigation intervals with arrhythmic, chaotic bedding were founded. Rhythmicity below and above K/T boundary was observed in all investigated regions.
Cenomanian rocks include periodites of types: 6 (Russian craton), 1-3 (Crimea) and clay-marl periodites inside the «black shale» (Bonarelli level) in the Crimea and Caucasus.
Turonian successions contain periodites of second type (Lower Turonian of the Crimea) and fifth type (Upper Turonian of the Russian craton). Lower Turonian rocks of the Russian craton and Upper Turonian-Coniacian rocks of the Crimea are arrhythmic.
Coniacian rocks contain periodites of 5 and 9 types (Russian craton). Santonian periodites of 2, 5, 9 types were observed on the Russian craton. Santonian rocks in the SW part of the Crimea are absent.
Campanian rocks include periodites - types: 4, 5, 9 (Russian craton); 1, 8 (Crimea).
Maastrichtian stage is characterized by presence of: periodites - types: 4, 5, 9 (Russian craton); 1, 6, 7 (Crimea) and 2 (Caucasus); carbonate turbidites and transitional turbidite-periodite successions (Caucasus).
Lower Palaeocene deposits are presented by periodites of 8 and 9 type.
Second order cycles can be distinguished in Maastrichtian rocks of the Russian craton and Crimea. They are presented by cyclic variations of rhythmic and arrhythmic levels in the succession (type 5, Lower Maastrichtian, Russian craton) or by possibility of uniting groups of rhythms into new cycles due to lithologic characteristics (all types, Crimea).
It should be noted that the rich diversity of rhythmicity is observed in the Cenomanian and Maastrichtian. At the same time arrhythmic successions are typical for Turonian-Coniacian deposits of the Russian craton and the Crimea. The origin of periodites is connected with cycles of dilution, solution and bioproduction which are the components of 10 paleogeographic models. The climatic variations caused by Milancovitch cycles resulted in the appearance of different kinds of rhythmicity in the Upper Cretaceous and Lower Palaeocene rocks of the Russian craton, SW Crimea and SW Caucasus.
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