Ines Wendler | Universität Bremen (original) (raw)

Papers by Ines Wendler

This review provides a synopsis of ongoing research and our understanding of the fundamentals of ... more This review provides a synopsis of ongoing research and our understanding of the fundamentals of sea-level change today and in the geologic record, especially as illustrated by conditions and processes during the Cretaceous greenhouse climate episode. We give an overview of the state of the art of our understanding on eustatic (global) versus relative (regional) sea level, as well as long-term versus short-term fluctuations and their drivers. In the context of the focus of UNESCO-IUGS/IGCP project 609 on Cretaceous eustatic, short-term sea-level and climate changes, we evaluate the possible evidence for glacio-eustasy versus alternative or additional mechanisms for continental water storage and release for the Cretaceous greenhouse and hothouse phases during which the
presence of larger continental ice shields is considered unlikely. Increasing evidence in the literature suggests a correlation between long-period orbital cycles and depositional cycles that reflect sea-level fluctuations, implying a globally synchronized forcing of (eustatic) sea level. Fourth-order depositional sequences seemto be related to a ~405 ka periodicity,whichmost likely represents long-period orbital eccentricity control on sea level and depositional cycles. Third-order cyclicity, expressed as time-synchronous sea level falls of ~20 to 110 m on ~0.5 to 3.0 Ma timescales in the Cretaceous, are increasingly recognized as connected to climate cycles triggered by longterm astronomical cycles that have periodicity ranging from ~1.0 to 2.4 Ma. Future perspectives of research on greenhouse sea-level changes comprise a high-precision time-scale for sequence stratigraphy and eustatic sealevel changes and high-resolution marine to non-marine stratigraphic correlation.

The major states, in which Earth's climate operates, i.e., icehouse, greenhouse and hothouse, are... more The major states, in which Earth's climate operates, i.e., icehouse, greenhouse and hothouse, are epochs of tens of
millions of years. These states set long-termboundary conditions that need to be considered for climate and sea level interpretations. This paper summarizes the conceptual models for hydrological cycling derived from the characteristics of these three climate states. While glacio-eustatic forcing of sea-level changes under icehouse climate conditions is fairly well understood, the drivers of eustatic sea-level fluctuations under greenhouse conditions remain enigmatic. This lack of understanding may be related to incoherencies in the current ideas about the impact of accelerated hydrological cycling on sea level under greenhouse climate conditions.
As an example for a greenhouse climate, we review evidences that link proxies for climate and sea level for the intensely studied, but controversially discussed, mid-Cretaceous sea-level history. Based on sequence stratigraphy and a recently published high-precision timescale, we demonstrate that the late Middle Turonian Pewsey δ13C isotope maximum represents a major transgression, not a regression as previously stated, which conflicts with the interpretation of a co-occurring δ18O maximum to reflect a short glacial episode. This contradiction can be solved by the concept, presented here, that dominance of aquifer-eustasy characterized sea-level forcing during the Turonian greenhouse climate, despite a possible, though contentious, sporadic presence of minor ice sheets. The effects of temperature and ice volume both lead to a pronounced δ18Ocarb maximum during glacio-eustatic regressions. In contrast, the opposing effects of temperature and groundwater volume on oxygen-isotope fractionation lead to a δ18Ocarb maximum during aquifer-eustatic transgressions. We suggest that, throughout Earth history, both aquifer-eustatic and glacio-eustatic forcing formed a combined sea-level response, with dominance of aquifer-eustasy being typical for the greenhouse climate mode. During the icehouse mode, aquifer-eustasy apparently remains active as a background process, but is outpaced by the glacio-eustatic effect.

Cyclic fluctuations in global sea level during epochs of warm greenhouse climate have remained en... more Cyclic fluctuations in global sea level during epochs of warm greenhouse climate have remained enigmatic, because absence or subordinate presence of polar ice during these periods precludes an explanation by glacioeustatic forcing. An alternative concept suggests that the water-bearing potential of groundwater aquifers is equal to that of ice caps and that changes in the dynamic balance of aquifer charge versus discharge, as a function of the temperature-related intensity of the hydrological cycle, may have driven eustasy during warm climates. However, this idea has long been neglected for two reasons: 1) the large storage potential of subsurface aquifers
was confused with the much smaller capacity of rivers and lakes and 2) empirical data were missing that document past variations in the hydrological cycle in relation to eustasy.
In the present study we present the first empirical evidence for changes in precipitation, continental weathering intensity and evaporation that correlate with astronomically (long obliquity) forced sea-level cycles during the warmest period of the Cretaceous (Cenomanian–Turonian). We compare sequence-stratigraphic data with changes in the terrigenous mineral assemblage in a low-latitude marine sedimentary sequence from the equatorial humid belt at the South-Tethyan margin (Levant carbonate platform, Jordan), thereby avoiding uncertainties from land–ocean correlations. Our data indicate covariance between cycles in weathering and sea level: predominantly chemical weathering under wet climate conditions is reflected by dominance of weathering products (clays) in deposits that represent sea-level fall (aquifer charge N discharge). Conversely, preservation of weathering-sensitive minerals (feldspars, epidote and pyroxenes) in transgressive sediments reflects decreased continentalweathering due to dryer climate (aquifer discharge N charge). Based on our results
we suggest that aquifer-eustasy represents a viable alternative to glacio-eustasy as a driver of cyclic 3rd-order sea-level fluctuations during the middle Cretaceous greenhouse climate, and it may have been a pervasive process throughout Earth history.

Despite many advances in sea-level research, the nature of cyclic eustatic sea-level fluctuations... more Despite many advances in sea-level research, the nature of cyclic eustatic sea-level fluctuations during warm periods without, or with much reduced, polar ice remains enigmatic. Recently published δ18O records from extremely well-preserved Turonian microfossils from Tanzania do not support the contentious idea of glacioeustatic control of global sea-level changes during the warmest period of the Cretaceous. For the same locality (site TDP 31) we reconstruct relative sea-level changes based on sequence stratigraphy and integration of sedimentology, microfacies, geochemistry, and micropaleontology. Four local sequence boundaries (SBs TuTz1–4) are recognized: at the base, middle, and top of the Helvetoglobotruncana helvetica Zone and in the Late Turonian.
The lowstands are characterized by increased grain size, enhanced organic carbon flux, faunal assemblage changes, and bulk δ13Corg and foraminiferal δ13Cf and δ18Of minima. Strong benthic and planktic foraminiferal turnovers above the top Middle Turonian SB TuTz3 probably reflect shallowing (from upper slope to outer shelf) and/or eutrophication.
The TDP 31 age model is refined through inter-regional comparison of planktic foraminiferal ranges and δ13C records from three other South-Tethyan localities (ODP Holes 762C and 763B, Exmouth Plateau, and the Guru section, Tibet). This age model enables correlation of the regressive events at a global scale and suggests that, within stratigraphic uncertainty, the TDP 31 depositional sequences are synchronous with the global Turonian third-order sequences and are likely driven by eustasy. These correlations, together with recent astrochronological and radiometric dating, indicate a considerably younger age (91.17 ± 0.52 Ma) for the top H. helvetica Zone than currently assumed, resulting in zonal duration of 2.35 ± 0.52 myr. Foraminiferal stableisotope data fromTDP 31 indicate slight surface- and bottom-waterwarming during the regressions and possibly a minor surface-water salinity decrease,which is inconsistentwith glacio-eustatic forcing of Turonian third-order sea-level cycles and is more in line with the model of aquifer-eustasy.

The 2009 Tanzania Drilling Project (TDP) expedition to southeastern Tanzania cored a total of 572... more The 2009 Tanzania Drilling Project (TDP) expedition to southeastern Tanzania cored a total of 572.3 m of sediments at six new mid-Cretaceous to mid-Paleocene boreholes (TDP Sites 36, 37, 38, 39, 40A, 40B). Added to the sites drilled in 2007 and 2008, the new boreholes confirm the common excellent preservation of planktonic and benthic foraminifera and calcareous nannofossils from core samples that will be used for biostratigraphy, volutionary studies, paleoceanography and climatic reconstructions from the Tanzanian margin, with implications elsewhere. The new sites verify the presence of a relatively expanded Upper Cretaceous succession in the region that has allowed a new stratigraphic unit, named here as the Lindi Formation (Fm), to be formally defined. The Lindi Fm (upper Albian to Coniacian), extending ~120 km between Kilwa and Lindi, comprises a 335-m-thick, outer-shelf to upper-slope unit, consisting of dark gray claystone and siltstone interbeds, common finely-laminated intervals, minor cm thick sandstones and up to 2.6% organic carbon in the Turonian. A subsurface, composite stratotype section is proposed for the Lindi Fm, with a gradational top boundary with the overlying Nangurukuru Fm (Santonian to Maastrichtian) and a sharp bottom contact with underlying upper Albian sandstones. The section cored at TDP Sites 36 and 38 belongs to the Lindi Fm and are of lower to middle Turonian age (planktonic foraminifera Whiteinella archaeocretacea to Helvetoglobotruncana helvetica Zones and nannofossils subzones UC6b ± UC7). The lower portion of TDP Site 39 (uppermost part of the Lindi Fm) is assigned to the lower to upper Coniacian (planktonic foraminifera Dicarinella concavata Zone and nannofossils zone UC 10), while the remaining part of this site is attributed to the Coniacian–Santonian transition and younger Santonian (planktonic foraminifera D. asymetrica Zone and upper part of nannofossils zone UC10). TDP Site 37 recovered relatively expanded (150 m thick), monotonous calcareous claystones from the lower to upper Maastrichtian (planktonic foraminifera Pseudoguembelina palpebra to Abathomphalus mayaroensis Zones and nannofossils zones UC19 to UC20aTP) that were separated by a hiatus and/or a faulted contact from overlying brecciated carbonates of the Selandian (middle Paleocene: PF Zone P3 and nannofossil zone NP5). The lower portion of TDP Sites 40A and 40B recovered sandstones and conglomerates barren of microfossils. Their overlying parts were assigned to incomplete sections of the nannofossil zones NC6A to NC8 (uppermost Barremian to lower Albian). Benthic foraminiferal assemblages allowed the Barremian to lower Aptian to be identified in TDP Sites 40A and 40B, while the upper Aptian to middle Albian (Hedbergella trocoidea to Ticinella primula Zones) were assigned using planktonic foraminifera. Cores recovered at TDP 39 (Coniacian–Santonian) and at TDP Sites 40A and 40B (Barremian–middle Albian) represent the first time that these two intervals have been continuously cored and publicly documented in Tanzania. Bulk sediment isotope records generated for the new sites show lower d18Ocarb values in the Turonian and Santonian (~-3.5‰ to -5‰) than in the Maastrichtian (~-3‰), a situation consistent with extreme global warmth in the older intervals and cooling toward the end of the Cretaceous. Also, similar to Turonian sites from previous TDP expeditions, a negative d13Corg excursion was detected across the W. archaeocretacea – H. helvetica boundary of TDP Site 36 (close to, but above, the Cenomanian-Turonian boundary). This excursion probably responded to local processes in the region, but it is unknown whether they were related to the recovery phase from Ocean Anoxic Event 2.

An evaluation of the global synchronicity and duration of “3rd-order” sea-level fluctuations duri... more An evaluation of the global synchronicity and duration of “3rd-order” sea-level fluctuations during the Cretaceous greenhouse has been hampered by poor constraints on potential climatic and tectonic drivers, and limitations of geochronology and chronostratigraphic correlation. To provide insight into the nature of such sea-level fluctuations, here we present a new Late Cretaceous record from the Jordanian Levant Platform, comprising a detailed physical-, bio-, chemo- and sequence stratigraphy. Carbonate content of these strata reflects overall sequence stratigraphic development, and demonstrates a dramatic 3rd-order-scale cycle that is also apparent in the δ13C record. Updated radioisotopic constraints and astrochronologic testing provide support for the inference of an ~ 1 million year long sea-level oscillation associated with this 3rd-order cycle, which likely reflects a long-period obliquity (1.2 Myr) control on eustasy and stratigraphic sequence development, linked to the global carbon cycle. The observation of cyclic sea-level fluctuations on this time scale suggests sustained global modulation of continental fresh-water-storage. The hypothesized link between astronomical forcing and sea-level forms a baseline approach in the global correlation of sequence boundaries.

Climate variability is driven by a complex interplay of global-scale processes and our understand... more Climate variability is driven by a complex interplay of global-scale processes and our understanding of them depends on sufficient temporal resolution of the geologic records and their precise inter-regional correlation, which in most cases cannot be btained with biostratigraphic methods alone. Chemostratigraphic correlation based on bulk sediment carbon isotopes is increasingly used to facilitate high-resolution correlation over large distances, but complications arise from a multitude of possible influences from local differences in biological, diagenetic and physico-chemical factors on individual δ13C records that can mask the global signal. To better assess the global versus local contribution in a δ13C record it is necessary to compare numerous isotopic records on a global scale. As a contribution to this objective, this paper reviews bulk sediment δ13Ccarb records from the Late Cretaceous in order to identify differences and similarities in secular δ13C trends that help establish a global reference δ13C record for this period. The study presents a global-scale comparison of twenty δ13C records from sections representing various palaeo-latitudes in both hemispheres and different oceanic settings from the Boreal, Tethys, Western Interior, Indian Ocean and Pacific Ocean, and with various diagenetic overprinting. The isotopic patterns are correlated based on independent dating with biostratigraphic and paleomagnetic data and reveal good agreement of the major isotope events despite offsets in absolute δ13C values and variation in amplitude between the sites. These differences reflect the varying local influences e.g. from depositional settings, bottom water age and diagenetic history, whereas the concordant patterns in δ13C shifts might represent δ13C fluctuations in the global seawater dissolved inorganic carbon. The latter is modulated by variations in organic matter burial relative to re-mineralization, in the global-scale formation of authigenic carbonate, and in partitioning of carbon between organic carbon and carbonate sinks. These variations are mainly controlled by changes in climate and eustasy. Additionally, some globally synchronous shifts in the bulk δ13Ccarb records could result from parallel variation in the contribution of authigenic carbonate to the sediment. Formation of these cements through biologically mediated early diagenetic processes is related to availability of oxygen and organic material and, thus, can be globally synchronized by fluctuations in eustasy, atmospheric and oceanic oxygen levels or in large-scale oceanic circulation. Because the influence of early diagenetic cements on the bulk δ13Ccarb signal can, but need not be synchronized, chemostratigraphy should not be used as a stand-alone method for trans-continental correlation, and especially minor isotopic shifts have to be interpreted with utmost care. Nevertheless, the observed consistency of the δ13C correlations confirms global scale applicability of bulk sediment δ13C chemostratigraphy for the Late Cretaceous, including sediments that underwent lithification and burial diagenesis such as the sediments from the Himalayan and Alpine sections. Limitations arise from increased uncertainties (1) in sediments with very low carbonate content, (2) from larger δ13C variability in sediments from very shallow marine environments, (3) from unrecognized hiatuses or strong changes in sedimentation rates, and (4) in sections with short stratigraphic coverage or with few biostratigraphic marker horizons.

The combination of chemostratigraphy with biostratigraphy and magnetostratigraphy substantially increases the precision and temporal resolution of inter-regional correlations and helps overcome problems that arise from differences in biostratigraphic schemes, facies or provincialism of key fossils. By using an iterative approach to stepwise increase precision of the correlations, isochroneity of first and last occurrences of marker species versus chemostratigraphy is tested, which helps to improve biostratigraphic zonations, to assess zonal boundary ages and to identify useful criteria for defining Late Cretaceous stage boundaries, many of which are still not formally defined. The presented correlations indicate a consistent position for most planktic foraminifer zonal boundaries relative to corresponding isotope shifts during the mid-Cretaceous sea-level high, whereas diachroneity appears to be more pronounced during the Late Campanian and Maastrichtian global sea-level fall. A similar pattern is observed for trans-continental consistency in the δ13C shifts. Graphic correlation of isotopic shifts, magnetostratigraphic and biostratigraphic events among the compared sections is used to detect hiatuses or relative changes sediment accumulation rates and visualizes consistency or offsets of individual biostratigraphic markers relative to chemo- and magnetostratigraphy. Finally, an attempt of a global average δ13C stack is presented for the Turonian through Maastrichtian.

Turonian (93.5- 89 Ma) oxygen isotopic measurements from exceptionally well preserved foraminifer... more Turonian (93.5- 89 Ma) oxygen isotopic measurements from exceptionally well preserved foraminifera from Tanzania support hot greenhouse conditions at this time and are remarkably stable across millions of years of deposition. Over 1000 individual analyses representing 8 planktic and 11 benthic taxa from two sites show consistent values and interspecies rank ordering across the ~2 m.y. time interval studied. Planktic taxa typically have δ18O values between -4.0 and -4.5‰V-PDB, suggesting surface water temperatures between 33°C and 35°C in the subtropical Indian Ocean using standard assumptions for the isotopic composition of the Cretaceous ocean. Benthic foraminifera (6 aragonitic and 5 calcitic taxa) also show constant interspecies offsets with the calcitic species ranging between -1.5 and -2.5‰V-PDB, suggesting upper slope bottom water temperatures between ~17 and 26°C. Absence of a coordinated positive δ18O excursion anywhere within the Turonian sections studied negates a key prediction for the greenhouse glacial hypothesis. Combined with other Turonian tropical temperature estimates and estimated pCO2 levels of 1000 ppm, these data suggest a climate sensitivity expressed as temperature change for a doubling of pCO2 to be ~6°C.

The interpretation of δ18O and δ13C analyses of extinct foraminifera is hampered by insufficient ... more The interpretation of δ18O and δ13C analyses of extinct foraminifera is hampered by insufficient knowledge on the contribution of environmental versus biological factors on the measured values. We present single-species stable isotope data for 18 benthic and 11 planktic foraminiferal species and one calcareous dinoflagellate cyst species from a Turonian equatorial record measured on samples collected in SE Tanzania. All microfossils analyzed were excellently preserved and results are compared to isotopic measurements from bulk sediment of the same material. Remarkably low intra-specific variability (standard deviations <0.2‰) across the studied interval and consistently large benthic / planktic offsets in δ18O (~2.8‰) and δ13C (~1.5‰) indicate absence of major long-term environmental fluctuations and presence of a well stratified water column. Stratigraphic isotopic trends show small shifts that are parallel in all studied benthic species (with the exception of the δ13C record of Lenticulina species), but within-sample inter-specific offsets reflect a combination of habitat differences and species-specific isotopic disequilibrium fractionation. Among planktic taxa closely related taxa tend to have similar isotopic values. Biserial taxa have the lowest δ18O values (~-4.7‰) but also have relatively low δ13C values (~1.6‰) indicating that, for the assumption of a surface water habitat, additional metabolic effects need to be involved, which supports the concept of their opportunistic life style. Among trochospiral planktics the keeled taxa with compressed chambers have slightly higher δ18O (~-4.2‰) and lower δ13C (~2.3‰) values than taxa with globular chambers (~-4.4‰ and ~2.4‰, respectively), suggesting differences in habitat or in peak seasonal abundance. Benthic taxa are subdivided into three isotopically distinct groups with differences reflecting mineralogy, life strategy and habitat; Group I: aragonitic taxa (Epistomina, Colomia africana), Group II: calcitic trochospiral taxa with isotopic values seemingly close to equilibrium (Berthelina berthelini, Oridorsalis umbonatus, Lingulogavelinella globosa, Lingulogavelinella convexa) and Group III: calcitic taxa with low δ18O values and large scatter in δ13C values (Lenticulina). Four other benthic species show values between Groups II and III.

The wealth and consistency of data, especially for benthic taxa, permits refined conclusions. The five studied species of Epistomina have a similar isotopic signature and are inferred to form their aragonitic shells with close to equilibrium values. Small isotopic offsets are seen among species that differ in orientation of the septal foramen, but no offsets are seen that seem to co-vary with test shape or ornamentation. The conical species C. africana has δ18O values ~0.2‰ lower and δ13C values ~0.7‰ lower than species of Epistomina. The latter offset probably reflects an infaunal habitat for C. africana. Epistomina and Group II species are recommended for paleoenviromental studies. Mono-specific Lenticulina δ18O values may be used if increased by correction factors of 0.4‰ to 0.9‰, but this taxon’s low and variable δ13C values are interpreted to reflect incorporation of respiratory CO2, possibly combined with fast growth rates related to opportunism, rather than equilibrium with benthic dissolved inorganic carbon. The observed stability of inter-specific isotopic offsets suggest disequilibrium isotopic effects are relatively consistent for many taxa in this section, and correction factors are proposed that may help to generate more robust Upper Cretaceous foraminiferal isotopic records. However, δ18O / δ13C covariance in some benthic inter-specific comparisons suggest offsets might vary with changes in temperature, food supply or other factors so the appropriateness of the correction factors should be confirmed before being applied at different sites. Similarities between the observed single-species isotopic patterns from this and other studies are used to present a summarizing scheme of influences on the stable isotopic composition in foraminiferal tests. By applying the new insights from our study to data from other Cretaceous studies we demonstrate that the selection of species for isotopic analysis and understanding these signals are critical to the outcome of paleoceanographic interpretations.

Extraordinarily well-preserved pithonellid microfossils (calcitarchs, “calcispheres”) from the Tu... more Extraordinarily well-preserved pithonellid microfossils (calcitarchs, “calcispheres”) from the Turonian of Tanzania reveal previously unknown morphological traits, crystallographic patterns, and chemical signatures, providing new insight to this enigmatic group of microfossils. Using combined transmitted-reflected light microscopy, scanning electron microscope imagery, electron microprobe elemental analysis and stable isotope geochemistry the present study reveals four new aspects of the genus Pithonella: 1) An affinity with cyst-forming organisms, potentially the dinoflagellates, is indicated by presence of a hatch opening and corresponding operculum. 2) The pristine outer wall architecture consists of thin, smooth shingle-shaped plates with regular rows of slit-shaped pores and an apical sub-angular or circular pore. This primary surface pattern is significantly different from previous descriptions of an outer wall consisting of “parquet shaped” prismatic crystal rows; this latter surface pattern is formed by secondary overgrowth. 3) The crystallographic pattern of the inner wall is crypto-crystalline. 4) Unaltered pithonellids reveal a calcite chemistry characterized by comparably high Mg-contents, relatively enriched stable carbon isotope values, and stable oxygen values indicating a surface water habitat. Based on these previously unseen traits the diagnosis of the genus Pithonella is revised. A new species, Pithonella diconica, is described from the lower-middle Turonian sediments of Tanzania.

A comparative cathodoluminescence (CL) spectroscopic study of extraordinarily well-preserved vers... more A comparative cathodoluminescence (CL) spectroscopic study of extraordinarily well-preserved versus diagenetically altered Turonian (~92 Ma before present) calcitic and aragonitic microfossils was performed to document the cathodoluminescence characteristics of two common Cretaceous carbonate producers, foraminifera and calcareous dinoflagellates. Unaltered specimens reveal a conspicuous peak in the blue CL band at ~400 nm that has rarely been previously reported for biogenic carbonates. We interpret this luminescence as an indicative feature of the primary bio-mineralized shells of calcareous dinoflagellates and foraminifera. Orange luminescence as the second important CL emission band (~620 nm) in calcite generally increases with diagenetic cement overgrowth and recrystallization but can also be present in unaltered material. Thus, orange CL of biogenic calcite is not an unequivocal diagenetic indicator. Accordingly, spectroscopic investigation of both the ~400 and ~620 nm peaks represents a more objective criterion to evaluate the degree
of diagenetic alteration. The ratio of relative intensities of the blue CL versus orange CL can provide a semiquantitative measure with relative intensity ratios blue:orange >2 occurring in the least diagenetically altered microfossils. Comparison of unaltered specimens of separate species reveals elemental differences that potentially indicate species-specific biomineralization or habitats.

The 2008 Tanzania Drilling Project (TDP) expedition recovered common planktonic foraminifera (PF)... more The 2008 Tanzania Drilling Project (TDP) expedition recovered common planktonic foraminifera (PF), calcareous nannofossils (CN) and calcareous dinoflagellates with extraordinary shell preservation at multiple Cenomanian–Campanian sites that will be used for paleoclimatic, paleoceanographic, and biostratigraphic studies. New cores confirm the existence of a more expanded and continuous Upper Cretaceous sequence than had previously been documented in the Lindi and Kilwa regions of southeastern coastal Tanzania. This TDP expedition cored 684.02 mat eight Upper Cretaceous sites (TDP Sites 28–35) and a thin Paleocene section (TDP Site 27). TDP Sites 29, 30, 31 and 34 together span the lowermost Turonian to Coniacian (PF Whiteinella archaeocretacea to Dicarinella concavata Zones and CN Zones UC6a–9b), with TDP Site 31 being the most biostratigraphically complete Turonian section found during TDP drilling. A discontinuous section from the Santonian–upper Campanian (PF D. asymetrica to Radotruncana calcarata Zones and CN Zones UC12–16) was collectively recovered at TDP Sites 28, 32 and 35, while thin sequences of the lower Cenomanian (PF Thalmanninella globotruncanoides Zone and CN subzones UC3a–b) and middle Paleocene (Selandian; PF Zone P3a and CN Zone NP5) were cored in TDP Sites 33 and 27, respectively. Records of δ13Corg and δ13Ccarb from bulk sediments generated for all the Cretaceous sites show largely stable values through the sections. Only a few parallel δ13Corg and δ13Ccarb shifts have been found and they are interpreted to reflect local processes. The δ18Ocarb record, however, is consistent with Late Cretaceous cooling trends from the Turonian into the Campanian. Lithologies of these sites include thick intervals of claystones and siltstones with locally abundant, finely-laminated fabrics, irregular occurrences of thin sandstone layers, and sporadic bioclastic debris (e.g., inoceramids, ammonites). Minor lithologies represent much thinner units of up to medium-grained, massive sandstones. The %CaCO3 (5–40%) and %Corg (0.1–2%) are variable, with the highest %CaCO3 in the lower Campanian and the highest %Corg in the Turonian. Lithofacies analysis suggests that deposition of these sediments occurred in outer shelf-upper slope, a setting that agrees well with inferences from benthic foraminifera and calcareous dinoflagellates.

A new, 430 m long and mostly continuous Upper Cretaceous section from southern hemisphere low pal... more A new, 430 m long and mostly continuous Upper Cretaceous section from southern hemisphere low paleolatitudes in the Tethys Himalaya (Guru, Tibet) is presented. The lithology, microfacies and fossil contents of the Guru section indicate a continuous shallowing trend from open oceanic conditions at the slope during the Turonian to shallow marine inner shelf environments in the Maastrichtian, interrupted by short periods of stagnation or slight deepening. Strong variations in sedimentation rates and contents of carbonate, quartz, organic carbon and sulfur appear to reflect a combination of regional and global processes. On regional scale, the patterns of varying clastic sediment supply seem to be related to the fast northward drift of the Indian plate from the temperate climate belt in the Turonian and Coniacian, crossing the arid zone during the Santonian and early Campanian, and passing into the tropical humid belt in the late Campanian. On global scale, similar sedimentary changes as in Guru with a transition from clay-rich Turonian sediments to Coniacian carbonates are found in other regions of the world, suggesting an additional influence of global oceanic and climatic factors. Intervals of omission, erosion and reworking in upper Coniacian and lower Campanian sediments of the Guru section appear to coincide with global sea-level lowstands.
Well preserved planktic foraminifera occur over most of the Guru section and provide good biostratigraphic control for correlation of stable carbon and oxygen isotopes with data from the reference section for the boreal white chalk in northern Germany at Lägerdorf-Kronsmoor and with the English Chalk reference section, showing detailed correlation of bulk sediment carbon isotopes and comparable trends in oxygen isotopes. The Campanian and Maastrichtian carbon isotope fluctuations can be related to cyclic variations in carbonate content at Lägerdorf-Kronsmoor which are thought to be driven by long eccentricity. This indicates orbital forcing of both carbonate accumulation and carbon isotope signature, most likely mediated by global sealevel changes. The possibility of detailed δ13C correlation from boreal sections of the northern hemisphere to a low-latitude section of the southern hemisphere allows for global correlation with an accuracy not achieved by biostratigraphic methods so far. It further enables linking of microfossil and macrofossil biozones, facilitating precise comparison of shallow and deep water sections, which is essential for the improvement of our understanding of timing, causes and effects of climatic and oceanographic processes.

Two new species, Tubulogenerina turonica and Colomia africana, are described from the Turonian of... more Two new species, Tubulogenerina turonica and Colomia africana, are described from the Turonian of Tanzania, and the genus Colomia is emended. The genus Tubulogenerina was originally thought to have originated in Europe in the early Eocene. Our discovery of T. turonica indicates that the roots of the genus reach back to the middle Cretaceous, and argues against a previous conclusion that it originated in temperate European regions. A tropical/subtropical site of origination would be consistent with the observation that most Tubulogenerina species inhabited warm, shallow-water environments. Tubulogenerina turonica has a relatively simple morphology, suitable as a starting point for morphological trends in the genus during the Cenozoic, thus supporting its status as a plausible ancestral species. In clay-rich middle Cretaceous sediments from Tanzania, foraminifera are exceptionally well preserved, and assemblages include a number of aragonitic taxa, including Colomia africana. This new species is distinguished from others of the genus by its aperture and toothplate structure and its dominantly biserial test without a well-developed uniserial growth stage. Morphologic similarities, however, indicate the close evolutionary relationship with other species of Colomia, so the genus is emended accordingly. Sufficient numbers of C. africana were found in multiple samples to characterize its stable carbon and oxygen isotope values relative to another aragonitic species (Epistomina chapmani) and calcitic species (Berthelina berthelini) from the same material. Results show an expected offset between calcitic and aragonitic tests that is partially explained by differential fractionation factors, but suggests vital or microhabitat effects contribute to values measured on C. africana.

The 2007 drilling season by the Tanzania drilling project (TDP) reveals a much more expanded Uppe... more The 2007 drilling season by the Tanzania drilling project (TDP) reveals a much more expanded Upper Cretaceous sequence than was recognized previously in the Lindi region of southern Tanzania. This TDP expedition targeted recovery of excellently preserved microfossils (foraminifera and calcareous nannofossils) for Late Cretaceous paleoclimatic, paleoceanographic and biostratigraphic studies. A total of 501.17 m of core was drilled at six Upper Cretaceous sites (TDP Sites 21, 22, 23, 24, 24B and 26) and a thin Miocene Pleistocene section (TDP Site 25). Microfossil preservation at all these sites is good to excellent, with foraminifera often showing glassy shells and consistently good preservation of small and delicate nannofossil taxa. In addition to adding to our knowledge of the subsurface geology, new surface exposures were mapped and the geological map of the region is revised herein. TDP Sites 24, 24B and 26 collectively span the upper Albian to lower-middle Turonian (planktonic foraminiferal Planomalina buxtorfi–Whiteinella archaeocretacea Zones and calcareous nannofossil zones UC0a–UC8a). The bottom of TDP Site 21 is barren, but the rest of the section represents the uppermost Cenomanian–
Coniacian (W. archaeocretacea–Dicarinella concavata Zones and nannofossil zones UC5c–UC10). Bulk organic δ13C data suggest recovery of part of Ocean Anoxic Event 2 (OAE2) from these four sites. In the upper part of this interval, the lower Turonian nannofossil zones UC6a–7 are characterized by a low-diversity nannoflora that may be related to OAE2 surface-water conditions. TDP Site 22 presents a 122-m-thick, lower-middle Turonian (W. archaeocretacea - Helvetoglobotruncana helvetica Zones) sequence that includes the nannofossil zones UC6a(-7?), but invariable isotopic curves. Further, a lower to upper Campanian (Globotruncana ventricosa–Radotruncana calcarata Zones and nannofossil subzones
UC15bTP–UC15dTP) succession was drilled at TDP Site 23. Lithologies of the new sites include thin units of gray, medium to coarse sandstones, separating much thicker intervals of dark claystones with organicrich laminated parts, irregular silty to fine sandstone partings, and rare inoceramid and ammonite debris. These lithofacies are interpreted to have been deposited in outer shelf and upper slope settings and indicate relatively stable sedimentary conditions during most of the Late Cretaceous on the Tanzanian margin.

A one-meter-thick marine red bed (Cretaceous oceanic red beds, CORBs) is reported from Early Turo... more A one-meter-thick marine red bed (Cretaceous oceanic red beds, CORBs) is reported from Early Turonian sediments associated with the Levant carbonate platform in central Jordan. These CORBs are of regional significance, in that deposits similar in facies and age are present in various sections of the Levant carbonate platform farther southwest in the Sinai. The red bed represents a rare shallow marine counterpart to the widely known deeper marine CORBs. The onset of sedimentation of these brick-red marls in a shallow sea (shallow subtidal) of the southern Tethys margin is shown to be synchronous with the Tethys-wide onset of marine red beds in oceanic settings in the latest Early Turonian. The transition into red marls marks a significant change in sedimentation from marly, gypsum-rich clay, representing lowstand deposits below, into a sequence including massive platform limestone beds forming a transgressive systems tract above the red bed. The sedimentary conditions on the Levant platform during red-bed deposition show some similarities to its deeper marine counterparts on the Northern Tethys margin: they are related to strongly fluctuating sedimentation rates, and they follow periods of high marine productivity, which occurred in the aftermath of OAE2. It is obvious that both strong synsedimentary fluctuations in water depth and accumulation rate and significant early and late evaporite diagenesis influenced the investigated section, so the cause of the red coloring is likely to be not solely a synsedimentary feature. The time-equivalent onset of shallow marine red beds and deep marine red beds in the Early Turonian indicates that both share common global prerequisites regardless of the paleobathymetry.

A section from the Ultrahelvetic units of Upper Austria comprises the transition from light-gray,... more A section from the Ultrahelvetic units of Upper Austria comprises the transition from light-gray, upper-bathyal to middlebathyal carbonates of Early Turonian age towards red-colored carbonates of the Middle Turonian. The total-organic-carbon content is very low throughout the section, but benthic foraminifera associations, especially high abundance of Tappanina laciniosa, indicate repeated phases of enhanced organic-matter flux and decreased oxygen concentrations at the seafloor. The overlying reddish layers are enriched in iron oxides and hydroxides and pyrite and may represent paleo–redox fronts that were related to periods of well oxygenated bottom waters, reduced sedimentation rates, and degradation of organic matter in the underlying sediments. Cyclic sedimentary packages consist of four marlstone–limestone couplets with upward-increasing bedding thickness, red carbonates at the base, and a gray limestone bed at the top. Based on carbon isotope stratigraphy, these packages reflect the 400 kyr eccentricity cycle, with the four marlstone–limestone couplets representing the 100 kyr cycle. Three 400-kyr-cycle boundaries are preceded by horizons with high T. laciniosa abundance and are followed by a paleo-redox front and red-bed deposition. Thus, there is indication of the temporary presence of a local oxygen-minimum zone during enhanced production at the end of each 400 kyr cycle, possibly linked to sea-level fluctuations. Organic-carbon fluxes seem to have decreased immediately above the cycle boundaries. Recycling of organic carbon could be responsible for the distinct carbon-isotope minima at the base of each cycle. Accumulation rates based on our orbital model suggest a switch from relatively uniform sedimentation rates in the Early Turonian to cyclic fluctuations of sedimentation rates in the Middle Turonian. The occurrence of three 400 kyr cycles between the main carbon-isotope excursions points to a 1.2 Myr periodicity, which may reflect the Earth’s long obliquity cycle. A long-term
increase in bottom-water aeration from the Early to the Middle Turonian is evident from the increasing dominance of red sediments.

New stable carbon and oxygen isotope data from an Upper Cretaceous section in Tibet are presented... more New stable carbon and oxygen isotope data from an Upper Cretaceous section in Tibet are presented, and compared to carbon isotope records from England, Italy, and Germany. Together with a stratigraphic reinterpretation of published carbon isotope data from a nearby section in Tibet, our data can surprisingly well be correlated with the European sections. This indicates that, similar to the distinct positive carbon isotope excursion at the Cenomanian-Turonian boundary, also the broad positive carbon isotope shift in the middle-late Coniacian and early Santonian reflects a major perturbation of the carbon cycle on a global scale, even though organic-rich sediments related to the OAE3 appear to be mainly restricted to the Atlantic Ocean and adjacent basins. The data further show that, apart from the broad Coniacian- Santonian carbon isotope excursion, also isotopic shifts on a smaller scale in the Turonian and Coniacian, such as the Round Down, Pewsey, and Hitchwood Events, can be correlated over both hemispheres. This demonstrates that the development of global oceanic anoxic conditions and associated burial of large amounts of organic carbon do not constitute a prerequisite for globally reflected carbon isotopic shifts. The data from Tibet support the concept of a relation between main carbon isotope excursions and major sea-level variations. Cyclic fluctuations of geochemical and lithological parameters are likely to be orbitally driven. These cycles appear to be preferably reflected in the sediments during periods of lower or variable sea-level, whereas the ocean-atmosphere system seems to have operated in a different mode during long phases of high, stable sea-level, as during the Coniacian-Santonian OAE3.

CORBs are described from a north–south transect from the passive European margin with the Helveti... more CORBs are described from a north–south transect from the passive European margin with the Helvetic–Ultrahelvetic shelf and continental slope through the Alpine Tethys, including the Rhenodanubian Flysch Zone into the southern, tectonically active margin of the Austro-Alpine microplate, including the Northern Calcareous Alps. In the Helvetic (shelf) and Ultrahelvetic (slope) part of the European margin, the proportion of CORBs in the Upper Cretaceous successions increases significantly with increasing water depth and increasing pelagic character. In the Ultrahelvetic units of Upper Austria (Rehkogelgraben, Buchberg), CORBs define a continuous red interval from the Lower Turonian to the Lower Campanian. The onset of CORB deposition in the Ultrahelvetic Zone corresponds to a major change in paleoceanographic conditions from anoxic during the Late Cenomanian OAE 2 to highly oxic during the Early to Middle Turonian. In the Rhenodanubian Flysch, hemipelagic red and green shales alternate with turbiditic siltstones and minor sandstones in the Upper Aptian–Lower Cenomanian Lower Varicolored Marls, the Coniacian–Lower Campanian Seisenburg Formation, and the uppermost Campanian Perneck Formation. CORBs in the Rhenodanubian Flysch are controlled mainly by tectonic events and sea-level changes, and occur during times of transgressions, low clastic input, and low turbidite frequencies. In the Austro-Alpine Northern Calcareous Alps, CORBs occur from the Santonian onwards in the upper parts of transgressive sequences of the Gosau Group, e.g., in the Tiefenbach and the Dalsenalm sections. In areas where clastic input was low, CORB deposition continued up into the Maastrichtian. Based on these data a peak of oceanic red beds is inferred for the middle Santonian–Early Campanian time interval. Prerequisites for CORB sedimentation are low clastic input, low sedimentation rates, and increasing paleo–water depth. CORBs can be classified as a variation of three end members: clayey CORBs, consisting mainly of terrigenous clay minerals; calcareous CORBs, mainly pelagic limestones; and siliceous CORBs, consisting mainly of biogenic SiO2.

Several transitions of Lower to Middle Turonian pelagic marl–limestone-cycles into Oceanic Red Be... more Several transitions of Lower to Middle Turonian pelagic marl–limestone-cycles into Oceanic Red Beds were studied at high resolution to gain a better understanding of the Tethyan marine system before and during red bed initiation and development. Samples were analysed for mineralogy, geochemistry, and stable isotope composition. In particular, carbonate geochemistry of diagenetically largely unaltered calcite was used to explore palaeoceanographic changes in the western Tethys. Principal component analysis of carbonate chemical data showed that the development of red coloured pelagic sediments is accompanied by a shift towards highly oligotrophic conditions in the surface ocean as well as a decrease in hydrothermal activity. The formation of red beds is most likely associated with a shift towards more oxic conditions in basins with black shale deposits that eventually resulted in enrichment of thiophile elements in the entire basin. Depletion in nutrients (most likely phosphate) and red bed deposition followed the maximum flooding in the Early Turonian. Highly productive marsh areas from the proximal European shelf were reworked and supplied nutrients during transgression. A gradual nutrient depletion during sea level highstand might be the cause of significantly diminished nutrient availability. Carbonate production in this low latitude setting was influenced by orbital variation in insolation (20 ka cycle). Stable carbon isotope stratigraphy reveals low sedimentation rates (between 1 and 7 mm/kyr) and a duration of episodes of Cretaceous ocenic red bed deposition between 30 and 360 kyrs.

Resolving questions on the amplitude, timing and ultimate causes of sea-level change during the C... more Resolving questions on the amplitude, timing and ultimate causes of sea-level change during the Cretaceous greenhouse world requires high precision in correlating sections on a global scale and an understanding of the proxies used for reconstructing sea-level shifts. In addition to the traditionally used biostratigraphy, the increased availability of chemo- and magnetostratigraphic data during the past years now enables comparison of sections that are dated with different biostratigraphic schemes and to correlate them with higher resolution than with biostratigraphy alone. However, these techniques also make us increasingly aware of a number of problems that involve inconsistencies in taxonomic concepts, rare occurrence or selective preservation of key taxa or their true diachroneity in the sedimentary record. The discovery of exquisitely preserved Late Cretaceous sediments from Tanzania not only offers a chance for studying the geochemistry of minimally altered Cretaceous microfossils but also opens a window into the rich world of structural details that are typically not preserved in Cretaceous microfossils. The added amount of detail in many cases calls into question existing taxonomic concepts and sometimes requires profound taxonomic revisions that often have considerable importance for biostratigraphy. A study of a Turonian drill Site from Tanzania further indicates that benthic foraminifera and other proxies that are used for reconstructing past sea-level give conflicting results, pointing to the need to revise some of the traditionally used concepts of proxy interpretation for sea-level reconstruction in the Cretaceous.

While in the present icehouse episode sea level apparently is controlled dominantly by the waxing... more While in the present icehouse episode sea level apparently is controlled dominantly by the waxing and waning of polar ice caps, this controlling factor is controversial when it comes to sea level fluctuation during the Cretaceous greenhouse episode. Controversy exists because ice played a much smaller role and was only temporarily present on just one pole. Yet global sea level kept fluctuating at rates comparable to the icehouse mode. The amount of water in the global oceans in fact seems to have alternated following a consistent cyclic beat regardless of which mode, icehouse or greenhouse. So, what could have controlled sea level during the greenhouse mode? Here we follow this question by examining cyclic global stable isotope data that are correlated to sea level cycles deposited during the Cenomanian-Turonian peak greenhouse period. A sedimentary succession from Jordan that represents a Cretaceous shelf environment was analyzed. Mineralogical cycles in this section are associated with the cycles of fluctuating global sea level and suggest a cyclic pattern in continental weathering. Given the potential of water storage on land in groundwater aquifers, the observed signal could explain sea level changes due to a process that doesn’t require ice caps for water storage.

Paleoclimatic greenhouse conditions of the mid-Cretaceous are still far from being understood as ... more Paleoclimatic greenhouse conditions of the mid-Cretaceous are still far from being understood as evidenced by the controversy on glaciations during the Turonian – one of the warmest periods of the Mesozoic. Absolute paleotemperature estimates and reconstructions of stability or fluctuation of climate and sea-level critically depend on high-resolution records of well-preserved fossil material. We present a data compilation of grain-size, foraminiferal assemblages and single-species stable isotopes from Turonian clayey siltstones with exceptionally well-preserved microfossils that were drilled in Tanzania and represent a low-latitudinal record. The data indicate stable environmental conditions during the Early and most of the Middle Turonian, arguing against a glaciation during that period. In the uppermost H. helvetica Zone and lower M. schneegansi Zone (Middle/Late Turonian), two phases of simultaneous shifts in benthic foraminifera associations, an increase in grain-size and sifts in foraminiferal d13C appear to reflect a stepwise shallowing in relative sea-level, which is supported by a dramatic increase in planktic biserial foraminifera during the second phase. A change in foraminiferal preservation at this level precludes interpretation of d18O data, but absence of simultaneous d18O shifts in benthic and planktic foraminifera during the first phase does not support the glaciation hypothesis as a cause for the regression.

Calcitic reproduction cysts of extinct Cretaceous algae (pithonellid calcitarchs) at unprecedente... more Calcitic reproduction cysts of extinct Cretaceous algae (pithonellid calcitarchs) at unprecedented pristine preservation from a unique microfossil-lagerstätte reveal new biomineralization styles. We discovered delicate, laminated architectures consisting of ply-like and interwoven structures that represent a complexity previously unknown from unicellular eukaryotes. In contrast, similar interwoven structures are seen e.g. in mammal tooth enamel suggesting that the constructive solution needed to mold normally brittle mineral components into durable material has a common principle pervading all nature. In the case of reproductive cysts, i.e. capsules that carry new life, such structures provide a balance of strength and flexibility needed for protection. Additionally, the low-density crystallite-pattern may have prevented the cysts from sinking to water depths from which the organisms could not recover on excystment. These are two characteristics potentially also desired in technical materials so that mimicking the structure of pithonellid calcitarchs could provide a solution to create durable yet flexible crystalline fabrics. Our findings suggest that despite of extensive paleontological research the knowledge of biomineralization styles of otherwise well-known fossil shells is incomplete. What are the reasons? Using cathodoluminescence-spectral analysis (CL) of the bio-mineralized calcite the unique preservation-state of the fossils studied here can be quantitatively proven by a dominance of the blue CL-band. This CL-feature is rare in fossil material whereas a dominant orange CL-band is common. Consequently, most fossils are altered strongly enough that their original bio-mineralized structures remain hidden due to the homogenizing effects of recrystallization. Like in the case of the pithonellid calcitarchs, these recrystallized structures can be easily mistaken as being original biominerals because the fossil-shape is intact. Therefore, if never found un-altered, their pristine shell-structures that reveal the original functionality of the biomineralogical fabric - useful in biomimetics - can be missed. This emphasizes an immense value of fossil-lagerstätten such as the Tanzanian Turonian studied here in the frame of the Tanzanian Drilling Project (TDP).

GSA, 2011

A major component of Turonian marine sediments are calcareous particles, commonly called “calcisp... more A major component of Turonian marine sediments are calcareous particles, commonly called “calcispheres” (Pithonelloideae; genera Pithonella, Bonetocardiella) which represent algal reproduction states. The taxonomy of these microfossils is based on the operculum (an opening) shape and size being the highest hierarchical criterion – particularly in calcareous dinoflagellate cyst taxonomy. Wall crystal architecture is the second-most important criterion. We found evidence that these key-traits of taxonomic classification of algal cysts are subject to spectacular re-crystallization during carbonate diagenesis. Here we show a comparison between pristine Pithonelloideae from material recovered by the Tanzanian Drilling Project with Pithonelloideae from the Chalk (northern France). The preservation-states of these two materials differ tremendously so that it is impossible that both represent the original bio-mineralogical wall-architecture equally. However, both have been used in detailed wall-crystallographic analyses resulting in taxonomic description. We find a gradual crystallographic transition from the “Tanzanian preservation” to the “chalk preservation”. Importantly, opercula in the Tanzanian material are preserved to an unbelievable degree of SEM-microscopic detail. These observations shed new light on species distinction; “lumping” formerly separated species and revising the existing classification scheme. Furthermore, the exceptional preservation of the Tanzanian material allows for CL-spectral study and geochemical measurements that enable unprecedented insight into the paleoecology of Pithonelloideae.

Geological Society of America Abstracts with Programs, Vol. 43, No. 5, p. 659

Upper Cretaceous sediments recovered during the Tanzania Drilling Project from 2007 to 2009 inclu... more Upper Cretaceous sediments recovered during the Tanzania Drilling Project from 2007 to 2009 include long intervals with exceptionally well preserved planktic and benthic foraminifera providing an excellent sample base for generating stable carbon and oxygen isotopic records as well as other geochemical data. Our study examines inter-species variation in stable isotopic values and their relation to the shell carbonate geochemistry and preservation by applying a combination of light-microscope and SEM imaging with microprobe and cathodoluminescence-based geochemical analyses. Our goal is to evaluate which species are best suited for studies of stable isotopes and temperature reconstructions in the Cretaceous. We present results from a Turonian sequence with relatively stable environmental conditions as inferred from minimal variation in intra-specific d13C and d18O values across the section. The studied material contains abundant and diverse benthic foraminifer assemblages that indicate an outer shelf to upper slope paleodepth. We performed single species d13C and d18O measurements for 18 calcareous benthic and 10 planktic species. Cross plots of d13C and d18O show distinct offsets between clusters of data points for individual species, reflecting a combination of differences in habitat and disequilibrium fractionation due to metabolic effects or an infaunal mode of life. Offsets in d18O between two groups of trochospiral planktic foraminifera apparently reflect water depth-related differences in temperature during their lifetime. An expected offset is observed between benthic species with aragonitic versus calcitic tests, but systematic offsets among aragonitic species indicate that micro-habitat or vital effects also influence measured values. The lowest d13C values among the calcitic benthic foraminifera were observed for species of the genus Lenticulina. Because we did not observe differences in their preservation relative to other benthic species, the isotope results suggest a strong influence of metabolic effects on isotopic fractionation for Lenticulina species. Among the calcitic benthic species studied the two species Berthelina berthelini and Lingulogavelinella convexa appear to have close-to-equilibrium values and are preferred for paleoenvironmental reconstructions.

Geological Society of America Abstracts with Programs, Vol. 43, No. 5, p. 376., 2011

In this study, we evaluate potential cyclic sea level changes during the Cenomanian and Turonian,... more In this study, we evaluate potential cyclic sea level changes during the Cenomanian and Turonian, spanning ~6 million years of time, through a new analysis of sequence stratigraphic stacking patterns of the Levant Platform in Jordan. This Tethyan carbonate platform preserves a relatively complete stratigraphic record through the interval, as indicated by biostratigraphy and new carbon isotope data, and also provides a clear imprint of sea level fluctuation as evidenced in sedimentologic structures and geochemistry (e.g., wt. % CaCO3). Application of the Average Spectral Misfit method for astrochronologic testing (Meyers and Sageman, 2007) to wt. % CaCO3 data confirms orbital influence on sedimentation through the OAE 2 interval, where data resolution is sufficient to resolve precession, obliquity and eccentricity components. This analysis also reveals a strong 1.2 Ma rhythm in wt. % CaCO3 and δ13C data, which demarcates the "3rd-order" sequence boundaries immediately above and below the C/T boundary, and is consistent with a long-period obliquity influence on sea level and the carbon cycle. "Minimal tuning" exercises provide additional evidence to support the presence of a pervasive 1.2 Ma pacing for all five sequence boundaries present in the section, in each case coupled to a 1.2 Ma cycle in the δ13C data. In the Oligocene, a 1.2 Ma obliquity cycle has been shown to be related to carbon cycle events, 3rd-order sea level fluctuations and glacial periodicity. We consider possible drivers for this long-period linkage between orbital cycles, sea level, and the carbon cycle during the Cretaceous greenhouse, a time during which continental ice sheets are expected to be either ephemeral or non-existent. Our mineralogic assemblage data from the Levant Platform indicates systematic changes in weathering patterns that are consistent with variable freshwater transport between the ocean and land, supporting the hypothesis that freshwater storage in aquifers played an important role in modulating eustacy.

GSA

Calcispheres constitute the second-most abundant calcareous microfossils of many Late Cretaceous ... more Calcispheres constitute the second-most abundant calcareous microfossils of many Late Cretaceous rocks and show significant spatial and temporal blooms, the most important of which is the Late Cenomanian - Early Turonian global calcisphere bioevent associated with OAE2. Because of their common appearance calcispheres could give substantial paleo-ecological information if their taxonomic affinities would be better known. However, a lack of morphological features limits our understanding of what these microfossils actually are. The most common calcispheres belong to the genus Pithonella. They are 20 to 180 micrometers in diameter and have been interpreted as calcareous cysts of dinoflagellates. However, the dinoflagellate cyst nature of Pithonelloideae has been controversial due to their lack of dinoflagellate-specific features. Unusually well-preserved Pithonelloideae are abundant in the Turonian from Tanzania. The pristine specimens reveal a number of shell-morphological features that have never been described before. Our study aims at revising the taxonomy of this complex microfossil group based on these new morphological findings. We combine light-optical imaging, SEM-imaging, cross-section study and microprobe analysis on single specimens. Most crucial to the determination of their taxonomic affinity with dinoflagellates is our discovery of an operculum-like structure that can be associated with the apical 3’ plate known from the peridinialean tabulation pattern of dinoflagellates. Furthermore, comparison between Pithonella sphaerica and the known calcareous dinoflagellate cyst Pirumella krasheninnikovii reveals striking biomineralogical similarities in wall-crystal architecture and chemistry. Such similarity hints at a common biomineralisation principle in both species. Stable oxygen isotope values of Pithonella plot with the values of planktic foraminifera suggesting a habitat of Pithonella near the water surface.

GSA

Uncertainties in reconstructing palaeotemperatures and CO2-levels in the Cretaceous mainly arise ... more Uncertainties in reconstructing palaeotemperatures and CO2-levels in the Cretaceous mainly arise from various degrees of diagenetic overprinting of most Cretaceous sediments. In the Tanzania Drilling Project exceptionally well preserved foraminiferal shells have been retrieved from Cenomanian and Turonian sediments with low carbonate and high clay content. This allows for a comparison of the primary shell material of individual species concerning their mineralogy, chemistry and stable isotopes. It further offers the unique opportunity to compare pristine shells that are glassy with slightly re-crystallized shells that are still well preserved and hollow, but appear more “frosty” or less translucent. The influence of these first processes of diagenetic alteration on the shell geochemistry and isotope signatures is studied by applying a combination of light microscope imaging, scanning electron microscope analyses, cathodoluminescence and microprobe observations. To exclude variation due to environmental factors or vital effects we compare specimens from the same sample and within the same species. Cathodoluminescence studies confirmed the presence of aragonitic shells for a number of species, testifying to the excellent preservation of the material. Their isotopic composition shows a considerable offset as compared to other benthic species. There is also a large difference in oxygen isotopes between benthic and planktic foraminifera. Slightly re-crystallized shells of benthic foraminifera show isotope values that fall within the range of variability of the species. However, the presence of cement can lead to a decrease in δ18O and becomes evident from bright orange linings under the cathodoluminescence microscope and from a rough shell surface under the SEM. Microprobe analysis reveals that manganese and iron increase in the cemented areas while strontium decreases. A similar trend is observed by comparing the shell chemistry of glassy and less translucent specimens of the same species, indicating some alteration of the primary shell material during re-crystallization.

GSA

Upper Cretaceous sediments recovered during the Tanzania Drilling Project in 2007 to 2009 reveal ... more Upper Cretaceous sediments recovered during the Tanzania Drilling Project in 2007 to 2009 reveal long intervals with exceptionally well preserved planktic and benthic foraminifera, allowing for single species carbon and oxygen isotope and geochemical analyses. We present results of an ongoing study in which we focus on the paleoceanographic and paleoclimatic history at low latitudes during the Turonian period of global warmth. The studied material contains abundant and well diversified foraminifera faunas indicating an outer shelf to upper slope position. Consistently present calcareous species are used for carbon and oxygen isotope measurements. To enhance our understanding of the stable isotope data we study intra-species offsets and their relation to carbonate geochemistry of the shells, by applying a combination of light-microscope and SEM imaging with microprobe and cathodoluminescence-based geochemical analyses. For example, various aragonitic-shelled species of the genus Epistomina show a striking offset in carbon isotopes while displaying similar values in oxygen isotopes, as compared to other benthic species. Cross plots of carbon and oxygen isotopes show distinct clustering of data points for individual species, pointing to species-specific fractionation during the foraminifer’s life time. Cross plots of the elemental shell compositions also show species-specific clusters of data points, possibly indicating primary and/or early-diagenetic mineralogical differences that potentially affect the isotopic shell chemistry apart from or along with the vital effects. The influence of diagenetic alteration is studied by comparing isotope data and geochemical composition of the shells from samples with different degrees of preservation. Our study aims at providing important information for selecting species that are suitable for studies of stable isotopes and temperature reconstructions in the Cretaceous. Furthermore, we compare single species measurements of pristine shells with isotope data from bulk sediments to assess the reliability of bulk sediment data, as they are increasingly used for chemostratigraphic correlation and reconstruction of relative temperature trends in the Cretaceous.

The sediments of the southern coastal Tanzania contain exceptionally well preserved microfossils ... more The sediments of the southern coastal Tanzania contain exceptionally well preserved microfossils and have been targeted in recent years by the “Tanzania Drilling Project” (TDP), an informal collaboration of researchers studying Cretaceous-Neogene paleoclimate. Drilling in 2007 was near Lindi, where previous TDP works had cored ~35 m of upper Campanian-lower Maastrichtian claystones and mapped upper Campanian to lower Oligocene sediments based on scarce surface exposures. During 2007, a total of 380 m of core was recovered. Three holes collectively spanned the uppermost Albian to upper Cenomanian (Planomalina buxtorfi sub-Zone to Rotalipora cushmani Zone) and include organic carbon isotopic evidence suggesting recovery of at least the base of OAE2; two holes recovered a thick sequence of the lower to middle Turonian (Whiteinella archaeocretacea to Helvetoglobotruncana helvetica Zones) with the Coniacian marker Dicarinella concavata in the highest samples; and one hole recovered the lower to upper Campanian (Globotruncanita elevata to Radotruncana calcarata Zones). Stratigraphic gaps exist in the lower Cenomanian, upper Turonian and Santonian, and the Cenomanian-Turonian boundary is not demonstrably conformable. Lithologies include thin intervals of light, coarse sandstones and sandy siltstones with occasional woody debris separating thicker intervals of dark claystone containing rare bivalves and ammonites and thin interbeds of silt to fine sandstone. Organic-rich, finely laminated claystones were also recovered at parts of the Turonian sequence. Beyond the refinements to knowledge of the local stratigraphy and subsurface geology, these results coupled with ongoing geochemical and biostratigraphic studies are being used to examine Late Cretaceous greenhouse climates. Of particular interest is the temperature history in the region, whether sedimentological and geochemical data together support Late Cretaceous glacial episodes, and how the tropical-subtropical East African shelf environment behaved during OAE2 and other Late Cretaceous events.

While the Early Cretaceous was characterised by periods of marine black shale deposition, widespr... more While the Early Cretaceous was characterised by periods of marine black shale deposition, widespread deposition of marine red beds in pelagic as well as in shallow water environments started in the Turonian, with apparent peak abundances in the Santonian to early Campanian and late Campanian to Maastrichtian. Red coloured marine sediments form when Fe is oxidised and bound in iron oxides. This chemical reaction is only possible under absence of larger amounts of organic carbon, as organic matter degradation leads to reducing conditions precluding the formation of iron oxides. Oxidation of organic carbon is mainly controlled by (1) the amount of available oxygen in the bottom- and sediment pore water, (2) the amount of organic carbon (Corg-flux) and (3) the oxygen exposure time (dependent on the sediment accumulation rate). Thus, the syn-sedimentary and early diagenetic red-ox conditions are the result of the interplay of these three factors which, in turn, are modulated by the global changes of ocean circulation and climate. The general global cooling and reorganisation of the ocean circulation in the Late Cretaceous certainly are major factors which must have had an influence on the oxygenation of the deep water. However, detailed concepts for the explanation of the formation and distribution of marine red-beds in the Upper Cretaceous are still not available.

The studied Buchberg section is part of the Ultrahelvetic units of Upper Austria which represent sedimentation on the European passive continental margin during the Cretaceous. The 7 m long profile comprises a succession of planktonic foraminifera-rich marls and limestone with a transition from grey to red colours, and was studied at high resolution for the content on benthic foraminifera as well as the mineralogical composition. The section can be assigned to nannofossil standard zones CC10 to CC12 (UC3 – UC8a). Helvetoglobotruncana helvetica is present in the grey to red transitional interval and gives evidence for an early to middle Turonian age of the marine red beds. Strontium isotope stratigraphy also confirms a Turonian age of the succession. The red sediment colour is restricted to discrete beds pointing to a syn-depositional to early diagenetic formation. It is interesting to note that the oxic conditions which lead to the red sediment colour must have established in several steps. The Buchberg section exposes alternations between red and grey marls as well as between red and grey limestone, indicating that sedimentation rate and productivity are most probably not the only factors controlling the colour distribution and that the oxygen content of the bottom water must have changed several times during this period. This can also be inferred from the changing vertical distribution patterns of benthic foraminifera in relation to the sediment colour. Very high abundance of species which are regarded to be typical for increased organic matter flux rates to the sea floor and slightly reduced oxygen levels such as Tappanina laciniosa and Praebulimina elata (Kuhnt & Wiedmann, 1995; Friedrich & Erbacher, in press) occur just before the changes from grey to red colours and are followed by peaks of pyrite, iron-hydroxides and iron-oxides. This indicates that the sediments reflect changing conditions at the sea floor which could have led to the preservation of early diagenetic red-ox fronts in the sediments.

. Oxygen and carbon isotopic data for from TDP 22 plotted relative to subsurface depth. Foraminif... more . Oxygen and carbon isotopic data for from TDP 22 plotted relative to subsurface depth. Foraminiferal zones shown to left from Huber and Petrizzo (in press). Lines go through average of values if a taxon was analyzed multiple times from the same sample. The temperature scale is appropriate for calcitic shells secreted in equilibrium with seawater having a  18 O value of -1‰ VSMOW . For aragonitic Epistomina spp., observed  18 O of values of -1‰ VPDB correspond to paleotemperature estimates of ~20°C. W