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Previous studies of Cretaceous sedimentary rocks have used multi-proxy correlation methods to suggest eustatic change, modulated by the c. 400 kyr long eccentricity rhythm. Although numerous authors have inferred eustatic changes on shorter timescales, none have demonstrated synchronous sea-level changes in separate basins on different plates, thousands of kilometres apart. Our study integrates basin-scale, three-dimensional sequence architecture, molluscan biostratigraphy, and carbon-isotope chemostratigraphy to demonstrate synchronous sea-level changes in upper Turonian to lower Coniacian shallow-marine clastic successions in the Western Canada Foreland Basin, and the Bohemian Cretaceous Basin. Depositional sequences in both basins are plotted in a common time domain using an astronomically calibrated age model, allowing direct comparison. In both basins, at least seven major transgressive events can be shown to be synchronous within the limits of combined biostratigraphic and chemostratigraphic resolution. ‘Major’ and ‘minor’ sequences of late Turonian age appear to have been paced, respectively, by the long (c. 400 kyr) and short (c. 100 kyr) eccentricity cycles. In contrast, early Coniacian sequences evidence pacing by the c. 38 kyr obliquity rhythm. Stratal architecture suggests that sequences developed in response to eustatic changes of c. 14–20 m at average rates ranging 0.08 to >1.3 m/kyr. At a time of ‘warm greenhouse’ climate, sea-level change of this magnitude and timescale may not be explicable entirely as a result of thermal- and aquifer-eustasy, and hence glacio-eustasy may also have been a contributing factor.

The Early Turonian interval represents a unique confluence of climatic and oceanographic conditions including peak surface temperatures, high greenhouse-gas concentrations and maximum Phanerozoic s...

In a well-exposed succession of Cenomanian through lower Turonian strata at Pecinov (Bohemian Cretaceous Basin, Czech Republic), a detailed study of ammonite and inoceramid assemblages was undertaken for the first time and combined with a revision of physical and carbon-isotope stratigraphy. The upper Cenomanian part of the OAE2 interval yielded a relatively rich ammonite assemblage containing Metoicoceras geslinianum (d'Orbigny, 1850), Calycoceras (Calycoceras) naviculare (Mantell, 1822), Pseudocalycoceras angolaense (Spath, 1931), Lotzeites aberrans (Kossmat, 1895), Euomphaloceras septemseriatum (Cragin, 1893), Sciponoceras gracile (Shumard, 1860), Allocrioceras annulatum (Shumard, 1860) and ?Puzosia sp. Inoceramid bivalves include Inoceramus pictus J. de C. Sowerby, 1829, Inoceramus sp. aff. Mytiloides praeturonicus Troger, 2015 and Inoceramus cf. bohemicus Leonhard, 1897 in the Cenomanian part of the succession. The subspecies concept of the Inoceramus pictus group is modified here. The occurrence of Mytiloides puebloensis Walaszczyk and Cobban, 2000 indicates the lowermost Turonian Watinoceras devonense Zone. Earlier interpretation of the positive carbon-isotope excursion is refined here and a combined bio- and chemostratigraphic correlation is presented to successions from the Western Interior Seaway and the British Chalk.

Foraminiferal assemblages were studied as part of a multi-proxy dataset from an expanded record of Late Turonian hemipelagic deposition obtained from the Bch-1 research borehole in the Bohemian Cretaceous Basin (Central Europe). Based on fluctuations in the Si/Al ratio, precession-paced cyclicity (18–23 kyr) is recognized in the studied interval and interpreted to reflect changes in seasonality. This study focuses on relationships between the astronomically controlled lithological cyclicity and the composition of foraminifera assemblages, together with variation in other parameters (geochemical, geophysical, palynological) that may provide further information about palaeoenvironmental change on a precession time scale. Spearman correlation enables the foraminiferal assemblages to be divided into three clusters. These clusters are interpreted to reflect palaeoenvironmental patterns that result from variation in nutrient supply and in surface water salinity, driven by changes in seasonality. The “Lenticulina – Gyroidinoides – agglutinated foraminifera” cluster dominated during periods of decreased seasonality and alternated with the “Cibicides – spiral unkeeled planktics” cluster (lower part of study interval) or the “Gavellinela – Praebulimina – spiral keeled + biserial planktics” cluster (upper part of study interval) coincident with the presumed seasonality maxima. Replacement of the Gavelinella cluster by the Cibicides cluster may reflect a longer-term trend of seasonality changes or changes in food supply. The observed low foraminiferal abundance and low planktic/benthic ratio during the seasonality maxima indicates that these were times of more intense rainfall, increased clastic supply and surface water turbidity, and more pronounced salinity fluctuations.

During the latest Turonian – early Coniacian time, a succession of sand-rich, Gilbert-type deltas was deposited along the faulted margin of the Bohemian Cretaceous Basin (BCB, Central Europe), fining along depositional dip into prodeltaic heterolithic facies and offshore mudstones to marlstones. The active tectonic setting with accelerated subsidence and supply rates contributed to deposition and preservation of an expanded record showing otherwise insufficiently known parts of the Turonian-Coniacian (T–C) boundary interval. In this study a combination of detailed biostratigraphy, genetic sequence stratigraphy, and carbon isotope chemostratigraphy is employed to characterize the T–C boundary in the northern part of the BCB, in both nearshore and offshore facies. The basis of the biostratigraphic framework was the establishment of the same succession of inoceramid bivalves and other molluscan marker taxa and bioevents as that in Salzgitter-Salder (Germany) and Slupia Nadbrzezna (Poland). All the faunal markers from the Mytiloides scupini through Cremnoceramus crassus crassus inoceramid zones were found both in the nearshore and offshore facies. The linkage of biostratigraphic and carbon isotope-stratigraphic data to a regional stratigraphic picture, as well as to individual outcrop and core sections, provides an important new database for further study of the boundary interval, with a direct link to the transgressive-regressive history of the nearshore depositional systems. Therefore it is proposed here that the T–C interval in the BCB complements the Salzgitter-Salder and Slupia Nadbrzezna sections and together with them constitutes a broader type region for definition of the T–C boundary.

Carbon sources and sinks are key components of the climate feedback system, yet their response to external forcing remains poorly constrained, particularly for past greenhouse climates. Carbon-isotope data indicate systematic, million-year-scale transfers of carbon between surface reservoirs during and immediately after the Late Cretaceous thermal maximum (peaking in the Cenomanian-Turonian, circa 97–91 million years, Myr, ago). Here we calibrate Albian to Campanian (108–72 Myr ago) high-resolution carbon isotope records with a refined chronology and demonstrate how net transfers between reservoirs are plausibly controlled by ~1 Myr changes in the amplitude of axial obliquity. The amplitude-modulating terms are absent from the frequency domain representation of insolation series and require a nonlinear, cumulative mechanism to become expressed in power spectra of isotope time series. Mass balance modeling suggests that the residence time of carbon in the ocean-atmosphere system is—by itself—insufficient to explain the Myr-scale variability. It is proposed that the astronomical control was imparted by a transient storage of organic matter or methane in quasi-stable reservoirs (wetlands, soils, marginal zones of marine euxinic strata, and potentially permafrost) that responded nonlinearly to obliquity-driven changes in high-latitude insolation and/or meridional insolation gradients. While these reservoirs are probably underrepresented in the geological record due to their quasi-stable character, they might have provided an important control on the dynamics and stability of the greenhouse climate.

Turonian strata of the Bohemian Cretaceous Basin, Central Europe, preserve a basin-scale record of shoreline transgressions and regressions, previously interpreted to have been strongly influenced by short-term eustatic cycles. Here, nearshore siliciclastic strata in two separate sub-basins are correlated to a multi-stratigraphic dataset generated from a new research core (Bch-1) drilled in offshore marine sediments of the central basin. A high-resolution δ13Corg record from Bch-1 is presented along with major- and minor-element proxies, TOC, carbonate content, terrestrial to marine palynomorph ratios, and detailed macro- and microfossil biostratigraphy. The 400 m thick Turonian through Lower Coniacian interval permits correlation to the highest-resolution C-isotope curves available: all carbon-isotope events demonstrated by δ13Ccarb studies in the British Chalk, NW Germany and other reference sections in Europe are recognized in the δ13Corg curve from Bch-1. A number of short-term, basin-wide regressions in the Bohemian Cretaceous Basin, most likely reflecting eustatic falls, show a recurrence interval of 100 kyr or less. This is an order of magnitude shorter than the timing of sea-level falls inferred from the New Jersey margin and the Apulian platform, interpreted to be driven by glacioeustacy. The estimated magnitude of the Bohemian Basin sea-level falls, typically 10–20 m and generally < 40 m, indicates that the 2.4 Myr period suggested by others to generate 3rd-order cycles, is too long to be the principal cycle generating unconformities in rapidly-subsiding basins, where the rate of eustatic fall must exceed the subsidence rate. Unconformities in low-accommodation settings such as passive margins most likely represent amalgamated records of multiple cycles of sea-level fluctuations of 100 kyr scale, recognizable only in high-resolution datasets from expanded successions. Comparison of the δ13C excursions to the interpreted sea-level record has not yielded a clear causal link. A long-term ‘background’ δ13C cycle shows a duration close to the 2.4 Myr long-eccentricity cycle, and shorter-term (1 Myr scale) highs and lows in δ13C appear to broadly correspond to intervals characterised by more pronounced short-term sea-level highs and lows, respectively. However, on the scale of intermediate to short-term δ13C fluctuations, no systematic relationship between δ13C and sea-level change can be demonstrated.

A series of prominent carbon-cycle perturbations, indicated by carbon-isotope excursions of up to 2‰, marked climatic and oceanographic changes that followed the peak mid-Cretaceous greenhouse. The nature and forcing mechanisms of these changes remain poorly understood, partly due to the lack of a detailed temporal control in this interval. Here we present an orbitally calibrated time scale, which is based on hemipelagic rhythmites in the Bohemian Cretaceous Basin, and which can be linked to the established chronostratigraphic framework using inoceramid biostratigraphy and carbon-isotope signature. In the new age model, the Late Turonian, defined by the first occurrence of I. perplexus below and the first occurrence of C. deformis erectus above, spans 1.56 ( ± 0.07 ) Myr . When anchored to the newly refined age of the Turonian–Coniacian boundary ( Sageman et al., in press ), the onset of the Late Turonian is 91.31 ( ± 0.45 ) Ma . Inoceramid zones I. perplexus and M. scupini span 0.76 ( ± 0.05 ) Myr and 0.80 ( ± 0.05 ) Myr , respectively. A time-domain record of carbon-isotope variations was obtained by pinning published δ13Ccarb data to the orbital time scale using 9 biostratigraphic and carbon-isotope markers. The timing of major carbon-isotope excursions suggests a link to 405-kyr eccentricity changes and, in the early Late Turonian, to ∼100 kyr eccentricity variations. However, over 80% of the variance in the Late Turonian δ 13 C occurs at longer (million-year) scales. The key features of the δ13Ccarb signature, including the amplified long-term variance, can be reproduced with simple models of orbitally driven isotopic mass balance. At a constant carbon-isotope fractionation, the best fit to the δ13Ccarb signature is obtained with enhanced organic burial at high eccentricity (in accordance with monsoonal forcing of organic accumulation in the low-latitude Atlantic and/or buildup of low-latitude, terrestrial carbon reservoirs). Alternative solutions should consider changing carbon-isotope fractionation due to pCO2 and/or nutrient-flux changes.

Lower to Middle Turonian deposits within the Bohemian Cretaceous Basin (Central Europe) consist of coarse-grained deltaic sandstones passing distally into fine-grained offshore sediments. Dune-scale cross-beds superimposed on delta-front clinoforms indicate a vigorous basinal palaeocirculation capable of transporting coarse-grained sand across the entire depth range of the clinoforms (ca 35 m). Bi-directional, alongshore-oriented, trough cross-set axes, silt drapes and reactivation surfaces indicate tidal activity. However, the Bohemian Cretaceous Basin at this time was over a thousand kilometres from the shelf break and separated from the open ocean by a series of small islands. The presence of tidally-influenced deposits in a setting where co-oscillating tides are likely to have been damped down by seabed friction and blocked by emergent land masses is problematic. The Imperial College Ocean Model, a fully hydrodynamic, unstructured mesh finite element model, is used to test the hypothesis that tidal circulation in this isolated region was capable of generating the observed grain-size distributions, bedform types and palaeocurrent orientations. The model is first validated for the prediction of bed shear stress magnitudes and sediment transport pathways against the present-day North European shelf seas that surround the British Isles. The model predicts a microtidal to mesotidal regime for the Bohemian Cretaceous Basin across a range of sensitivity tests with elevated tidal ranges in local embayments. Funnelling associated with straits increases tidal current velocities, generating bed shear stresses that were capable of forming the sedimentary structures observed in the field. The model also predicts instantaneous bi-directional currents with orientations comparable with those measured in the field. Overall, the Imperial College Ocean Model predicts a vigorous tide-driven palaeocirculation within the Bohemian Cretaceous Basin that would indisputably have influenced sediment dispersal and facies distributions. Palaeocurrent vectors and sediment transport pathways however vary markedly in the different sensitivity tests. Accurate modelling of these parameters, in this instance, requires greater palaeogeographic certainty than can be extracted from the available rock record.

The Oligo‐Miocene Most Basin is the largest preserved sedimentary basin within the Eger Graben, the easternmost part of the European Cenozoic Rift System (ECRIS). The basin is interpreted as a part of an incipient rift system that underwent two distinct phases of extension. The first phase, characterised by NNE–SSW‐ to N–S‐oriented horizontal extension between the end of Eocene and early Miocene, was oblique to the rift axis and caused evolution of a fault system characterised by en‐echelon‐arranged E–W (ENE–WSW) faults. These faults defined a number of small, shallow initial depocentres of very small subsidence rates that gradually merged during the growth and linkage of the normal fault segments. The youngest part of the basin fill indicates accelerated subsidence caused probably by the concentration of displacement at several major bounding faults. Major post‐depositional faulting and forced folding were related to a change in the extension vector to an orthogonal position with respect to the rift axis and overprinting of the E–W faults by an NE–SW normal fault system. The origin of the palaeostress field of the earlier, oblique, extensional phase remains controversial and can be attributed either to the effects of the Alpine lithospheric root or (perhaps more likely because of the dominant volcanism at the onset of Eger Graben formation) to doming due to thermal perturbation of the lithosphere. The later, orthogonal, extensional phase is explained by stretching along the crest of a growing regional‐scale anticlinal feature, which supports the recent hypothesis of lithospheric folding in the Alpine–Carpathian foreland.

The Bohemian Cretaceous Basin combines features of a shallow-water (mostly

The Early Miocene Bilina Palaeodelta consists of fluvio-deltaic and lacustrine clastics deposited along the south-eastern margin of the extensional Most Basin, part of the Eger Graben in north Bohemia (Czech Republic). The Bilina succession shows evidence of repeated advances of an axial deltaic system across a thick accumulation of organic material and clay in the hangingwall of an active fault. Exposures up to ca 4·5 km long in the Bilina open-cast mine help bridge the gap between seismic scale and typical outcrop scale of observation and thus allow the relationships between small-scale and basin-scale stratal geometries to be evaluated. The Bilina Palaeodelta deposits include sand-dominated, fluvial channel fills and heterolithic sheets interpreted as delta plain strata, sand-dominated mouth-bar wedges and heterolithic sheets of prodeltaic deposits, passing distally into lacustrine clays. The depositional environment is interpreted as a fluvial-dominated, mixed-load, lacustrine delta with a high degree of grain-size segregation at the feeder-channel mouths. On the largest temporal and spatial scales, variable tectonic subsidence controlled the overall advance and retreat of the delta system. The medium-term transgressive-regressive history was probably driven by episodes of increased subsidence rate. However, at this temporal scale, the architecture of the deltaic sequences (deltaic lobes and correlative lacustrine deposits) was strongly affected by: (i) compaction of underlying peat and clay which drove lateral offset stacking of medium-term sequences; and (ii) growth of a fault-propagation fold close to the active Bilina Fault. At the smallest scale, the geometries of individual mouth bars and groups of mouth bars (short-term sequences) reflect the interaction among sediment loading, compaction and growth faulting that produced high-frequency relative lake-level fluctuations and created local accommodation at the delta front.

This study presents an integrated sedimentological and geochemical analysis of the Lower Permian Rudnik member — the most extensive lacustrine deposits in the Krkonose Piedmont Basin. Grey to black and variegated lacustrine mudstones, laminites and carbonates of the Rudnik member have a lateral extent of more than 400 km 2 . In the studied sections four facies associations were recognised: A) anoxic offshore, B) suboxic to oxic offshore, C) nearshore and mudflat, and D) slope deposits. In the northern part of the E–W elongated basin, anoxic to suboxic organic-rich offshore lacustrine facies dominate and form a succession up to 130 m thick. Fan-delta and turbidite facies occur locally along the faulted northern basin margin. The central part of the basin is occupied by anoxic to oxic offshore facies interfingering with nearshore carbonate and mudflat facies of the low-gradient lacustrine margin. In the central part of the basin, the thickness of the lacustrine deposits of the Rudnik member reaches up to 60–70 m. In the southern part of the basin fluvial and alluvial plain facies dominate and alternate with minor lacustrine nearshore facies. The lateral facies distribution indicates that subsidence along the northern basin fault was the main mechanism generating the asymmetric infill geometry in the basin's half-graben setting. The δ 1 8 O values of primary and early diagenetic calcite range between − 11.0‰ and + 1.3‰ (V-PDB) and δ 1 3 C values between − 5.1‰ and + 3.7‰; most of the data fall within the range of freshwater limestones. Coarser-grained pure microspar laminae show more positive δ 1 3 C values in comparison to clayey organic-rich micrite laminae, and are interpreted as a record of bioinduced precipitation during seasonal eutrophication. The obtained δ 1 3 C TOC values range from − 29.0‰ to − 24.0‰, the total organic carbon (TOC) content from 0.26% to 23%. Maceral analysis and Rock-Eval pyrolysis indicate that most of the samples contain a mixture of aquatic and terrestrial organic matter, but two minor, distinctive groups of samples with algally-dominated and terrestrially-dominated organic matter composition, respectively, were also found. The study of vertical changes in boron content in the clay fraction of the lacustrine mudstones shows that high lake level stages were periods of lower salinity with the lowest boron contents (from 73 to 268 ppm), and periods of falling lake level were followed by significant increases in salinity with much higher boron values (293–603 ppm). Lake-level fluctuations of the Rudnik lacustrine system, which are recorded by shallowing-up units of sedimentary facies within most of the sections throughout the basin, can also be traced within the monotonous black shale dominated sections, where no sedimentological evidence of these lake level changes exists. Good indicators for such changes seem to be the δ 1 8 O and δ 1 3 C values of primary calcite, δ 1 3 C TOC and HI. These lake level fluctuations are interpreted as driven by climatic oscillations in the order of tens of thousands years, which could reflect climatic changes connected with the last glaciation event of Gondwana.

The record of aeolian processes was studied in Early Triassic sandstones of the upper part of the Bohdasin Formation, NE Bohemia, an isolated erosional relict of a Triassic fluvial–aeolian succession in the Sudetes block of the Bohemian Massif (central Europe). The aeolian system exposed in the Devět Křižů quarry near Cervený Kostelec provides a significant addition to the generally poorly preserved record of Early Triassic palaeoclimate and palaeowind regime in central Europe. Two mutually interbedded facies occur in the aeolian succession: (1) dune facies comprising cross-strata that show interdune, reactivation and superimposition bounding surfaces, and (2) interdune facies, formed by horizontally stratified, commonly mud-draped sandstones, which display a number of indicators of damp to wet conditions and fluctuations in water table. The succession of the Devět Křižů Sandstones is interpreted as a record of migration and climb of dunes with intervening interdune flats, which replaced an underlying fluvial system. It is likely that a coeval fluvial system existed near the Devět Křižů dune field, providing available sand in dry periods and flooding in wet periods. Dominant palaeowind directions are southwestward and northward in present-day coordinates. Repeated reversals of palaeowind direction, interpreted as seasonal, are recorded in changes in the internal structure of the cross-strata (reworking and reactivation) in the dune migration direction. At least some episodes of dune reworking occurred simultaneously with episodes of water-table rise. A drying-upward trend in the aeolian succession is interpreted from evidence for increased availability of sand through time. The upward transition from a braided fluvial to a wet, drying-upward aeolian system within the Bohdasin Formation represents a shift toward maximum aridity of the palaeoenvironment, which marks also the peak arid conditions in the long-term palaeoclimatic evolution of the Carboniferous–Triassic succession of the Sudetes region, and correlates with the establishment of aeolian settings in other regions of central Europe during the Early Triassic. The record of changing palaeowind directions, documented in several cases to have been coupled with episodes of rapid rise in water table, is taken as evidence for pronounced climatic seasonality and brings additional support to the models predicting strong monsoonal circulation during the Early Triassic, affecting particularly the eastern subequatorial coast of Pangaea and adjoining regions.

A delay in the onset of sedimentation during fault-related subsidence at a basin margin can occur in both extensional settings, where footwall tilting may cause a diversion of drainage patterns, and in strike-slip basins, where a source area may be translated along the basin margin. The ‘initial depth’ created by this delay acts as pre-depositional accommodation and is a partly independent variable. It controls the geometry of the first stratal units deposited at the basin margin and thus modifies the response of the depositional system to subsequent, syndepositional changes in accommodation. In systems with a sharp break in the depositional profile, such as the topset edge in coarse-grained deltas, the initial depth controls the foreset height and therefore the progradational distance of the topset edge. The topset length, in turn, influences topset accommodation during cyclical base level variations and therefore is reflected in the resulting stacking patterns at both long- and short-term time scales. In the simplified cases modelled in this study, it is the relationship between the initial depth and the net increase in depth over the interval of a relative sea-level cycle (ΔH) that governs long- and short-term stacking patterns. In situations where the initial depth is significantly larger than ΔH, the topset accommodation of the first delta is insufficient to contain the volume of sediment of younger sequences formed during subsequent relative sea-level cycles. Therefore, the depositional system tends to prograde over a number of relative sea-level cycles before the topset area increases so that the long-term stacking pattern changes to aggradation. Stacking patterns of high-frequency sequences are influenced by a combination of topset accommodation available and position of the short-term relative sea-level cycles on the rising or falling limb of a long-term sea-level curve. This determines whether deposits of short-term cycles are accommodated in delta topsets or foresets, or in both. Variations in stacking pattern caused by different initial depths may be misinterpreted as due to relative sea level or sediment supply changes and it is necessary to consider initial bathymetry in modelling and interpretation of stacking patterns, especially in fault-bounded basins.

The succession of the Peruc and Korycany Members in the Pecinov quarry, Bohemia, reflects the interplay of 4th-order sea-level fluctuations, of approximately 100–120 ka periodicity, and a long-term (3rd-order) sea-level rise of the late middle through early late Cenomanian. The succession studied includes deposits of a shallow, gravelly braided river (unit 1), tide-influenced braided river (unit 2), supratidal marsh (unit 3), tidal flat (unit 4) and ebb-tidal delta to estuary mouth fill (unit 5). Units 1–5 are interpreted as parasequences of a single depositional sequence; units 1–4 together make up a transgressive systems tract and unit 5 is a highstand deposit, capped by a sequence boundary. The presence of deciduous plants attests to a certain degree of seasonality of the climate. The mixing of thermophile and temperate vegetation, together with the presumed palaeolatitudinal position of the Bohemian Massif, suggests a generally slightly semi-arid (i.e., seasonally wet) regional climatic conditions during the deposition of units 1–5; substrates in local habitats in alluvial valleys and estuary margins were damp due to high local water table. The plant habitat of the alluvial valley (units 1 and 2) was characterized by the Myrtophyllum assemblage, which included an angiosperm-dominated gallery forest and shrubs on braid bars and islands. The transition between fluvial and coastal environments was characterized by a taxodioid backswamp forest (the Ceratostrobus assemblage). Coastal vegetation (i.e., the marsh habitats of unit 3 and the upper part of unit 5), changes distinctly between the two units, although both represent similar facies of high intertidal to supratidal origin. The Frenelopsis assemblage of unit 3, representing shrubby marsh vegetation growing seaward of the Ceratostrobus forest, differs strongly from the more xerophytic Sphenolepis assemblage of unit 5, characterized by herbaceous pteridophytes growing in the marsh in front of a coastal taxodioid forest. We explain the differences between units 3 and 5 by the different sequence-stratigraphic position of the two units: a high groundwater table and eutrophic substrate of the transgressive systems tract (unit 3) compared with a lower or falling regional water table and oligotrophic substrate during the late highstand systems tract (unit 5). Thus, temporal changes in coastal plant assemblages of the Pecinov section do not merely reflect lateral shifts of facies belts, but show that similar depositional environments in different systems tracts hosted very different floras.

Relationships between geochemical anomalies, sea-level change and other events were studied in the Cenomanian–Turonian boundary interval in the Pecinov quarry in southwestern part of the Bohemian Cretaceous Basin (Czech Republic). A major 3rd-order sea-level rise at the base of the late Cenomanian M. geslinianum Zone was followed by deposition of organic-enriched mudstones in a succession of parasequences, deposited in response to high-frequency (4th-order) sea-level fluctuations and recording a stepwise decrease in bottom oxygenation towards intensely dysaerobic conditions. A complex δ13C excursion occurs in total organic matter of the late Cenomanian deposits. A sequence boundary of latest Cenomanian age in the Pecinov section is correlated to a global sea-level fall during the N. juddii Zone. A renewed sea-level rise occurred during the early Turonian W. coloradoense Zone and reached maximum flooding during the M. nodosoides Zone. During the early Turonian, bottom waters were generally aerobic, and the positive δ13C excursion waned early in the W. coloradoense Zone. The magnitude of the δ13C excursion, more than 4‰, is approximately the same as in North America and Northern Africa, confirming that it was controlled by a global paleoceanographic mechanism. The absence of anoxia and a δ13C anomaly during the peak flooding of early Turonian age suggests that widespread deposition of organic-enriched deposits, as well as the positive shift in δ13C generally did not depend on the absolute elevation of sea level but, rather, on the area of newly flooded land during transgression. Abrupt, small-scale shifts in δ13C towards higher values coincide with the flooding surfaces of parasequences and may reflect either regional changes in the proportion of marine and terrestrial organic matter or rapid global changes in isotopic composition of marine organic matter related to high-frequency sea-level changes. Abundances of Ir, Sc, Cr, V and other elements previously reported as forming anomalous concentrations in the boundary interval showed no enrichment in the Bohemian section. This is most probably due to the large distance of the depositional site from the presumed volcanic source of element-enriched deep waters in the proto-Caribbean region. Anomalous concentration of Mn at the base of the Turonian deposits was caused by diagenetic incorporation of Mn into siderite.

The sedimentary record across the Cenomanian-Turonian boundary in Bohemia confirms the crucial role of eustasy as the driving force of the Cenomanian-Turonian anoxic event. The late Cenomanian siltstone facies of the Peruc-Korycany Formation was deposited after major sea-level rise at the beginning of the Metoicoceras geslinianum Zone (above the UZA 2.4/2.5 3rd-order sequence boundary of Haq et al. , 1988). Increasing depletion in oxygen during the late Cenomanian is reflected in dark, pyrite-rich siltstones characterized by low C/S ratios and progressive deterioration of benthic foraminiferal assemblages. Small-scale steps in sea-level rise followed by oxygen depletion during the M. geslinianum Zone can be correlated between the Bohemian Cretaceous and the Plenus Marls of SE England. This indicates that the impingement of oxygen-poor waters on the European shelf, which reached inland as far as the Bohemian Massif, was driven by eustasy even at the level of 4th-order cyclicity. The late Cenomanian part of the global δ 13 C anomaly is in part overprinted by diagenesis, and in part falls within a stratigraphic hiatus between the upper M. geslinianum and the Neocardioceras juddii Zones. A record of a waning δ 13 C anomaly helped to assign the basal Bila Hora Formation to the early Turonian W. coloradoense Zone. The basal Bila Hora carbonates reflect a major early Turonian sea level rise and waning of dysaerobic conditions.

Palaeoenvironments inferred from stable carbon isotope ratios of fossil plants collected from various environments of the Cenomanian of Bohemia were compared with palaeobotanical and sedimentological data to test the use of isotope ratios as a record of local palaeoenvironments and fossil-plant ecology. A number of isotope and biogeochemical patterns suggested that stable carbon isotope ratios in the Cenomanian plants from Bohemia have not been significantly affected by diagenesis. Stable carbon isotope ratios of the palaeoflora from one of the sections studied were used as a reference for a non-stressed habitat since both sedimentological and palaeobotanical evidence suggested that the fossil flora underwent no environmental stresses that could have influenced its δ13C values. Comparisons of δ13C values of the other palaeofloras with that of the reference section, allowed inference of the palaeoenvironmental stresses undergone by fossil plants. These palaeoenvironmental patterns deduced from 13C/12C ratios are in agreement with the palaeoenvironments previously reconstructed by sedimentological and palaeobotanical studies. Combining evidence from those studies with isotope data provided detailed insights into the palaeoecology of the plants studied. Finally, stable carbon isotope ratios allowed precise characterisation of the ecology of the best-represented species of the deposits studied, the ginkgoalean plant Eretmophyllum obtusum and the conifer Frenelopsis alata, which were quite common in the salt-marsh environments in Europe during the Cenomanian. Hence, stable carbon isotope ratios can help in evaluating the environmental stresses undergone by fossil plants and the combination of these results with palaeobotanical and sedimentological data can provide detailed insights into fossil-plant ecology.