Calcareous Microfossils Research Articles

Paleocene–Eocene palaeoenvironmental conditions of the main phosphorite deposits (Chouabine Formation) in the Gafsa Basin, Tunisia

A detailed sedimentary section of the marine Chouabine Formation in the palaeogeographic Gafsa Basin, south-western Tunisia, was investigated in order to characterize environmental and depositional conditions focusing on the interval that spans the Paleocene–Eocene transition. We did stable isotope analyses of bulk sediments. Both phosphorite and carbonate yielded relatively similar isotopic compositions; while marls show observable trends, with negative shifts in both δ13Cinorg and δ18O values at the Paleocene–Eocene transition.The diversity of the calcareous microfossils is low. The presence of few environmentally tolerant small benthic foraminifera and the absence of planktic forms indicate a restricted palaeoenvironment subject to variation in salinity and temperature. The ostracod fauna is more diverse and is rather comparable to Paleocene and PETM (Paleocene–Eocene thermal maximum) assemblages in northwest Tunisia. While all these microfossils demonstrate various diagenetic features (i.e., phosphatization, secondary mineral overgrowths and infills), the different groups retain distinct stable isotopic compositions, suggesting partial preservation of signatures derived from their respective ecological niches.Few organic-rich layers below the negative δ13C shift yielded dinoflagellate assemblages with the common forms of Adnatosphaeridium sp., Operculodinium sp., Spiniferites spp. and Thalassiphora sp. The rare presences of Apectodinium-complex agree with depositional age prior to the PETM.The combined data emphasize that most of the Chouabine Formation in the Gafsa Basin was deposited during the late Paleocene. The most negative isotopic values from marls are believed to represent the onset of PETM or pre-PETM record, and the related perturbation of the carbon cycle in shallow water deposits in Tunisia.

Cool tropics in the Middle Eocene: Evidence from the Changchang Flora, Hainan Island, China

The middle Eocene (Lutetian–Bartonian, 48.6–37.2Ma) near-equatorial megafossil flora from swamp and lacustrine facies of the lower Changchang Formation, Hainan Island, South China (19.631463°N, 110.445049°E) is highly diverse (>200 taxa) dominated by an unusual mixture of angiosperms typical of modern temperate, subtropical and tropical evergreen and deciduous forms. It is also rich in palms. Multivariate analysis of the architecture of minimally transported woody dicot leaves reveals a mean annual air temperature (MAT) of ~22±4.7°C with a marked thermal seasonality range of ~21°C. The year-round humid climate lacked any monsoonal signature. The overall climate signal is compatible with the growth characteristics exhibited by fossil wood, but is warmer than the climate signal derived from pollen and spores using Co-existence Analysis. Corrections for possible palaeoelevation of the basin bring the megafossil-derived MAT estimate in line with 54–52Ma sea surface and soil temperatures obtained from the Gulf Coast, USA, (palaeolatitude ~30°N) using multiple geochemical proxies and supports the claim that the low latitude Eocene climate was not uniformly warm. This challenges previous conclusions based on ∂18O analysis of unaltered calcareous microfossils. Our air temperature data also adds to the challenge of understanding heat transport away from the equator to higher latitudes during ‘hothouse’ climate regimes.

Cell geometry records the physiological responses of coccolithophores to Paleogene climate change

The physiology and ecology of the calcifying marine phytoplankton group coccolithophores are expected to be susceptible to future changes in environmental conditions forced by increasing atmospheric carbon dioxide and temperature (e.g., Fabry et al., 2008). A key trait of the physiological state of a phytoplankton cell is cell size (e.g., Finkel et al., 2007), which we have captured from exquisitely preserved fossil coccospheres in biometric measurements of coccolith length, coccosphere size and number of coccoliths per coccosphere (Fig. 1). Our exquisitely preserved calcareous microfossils are obtained from sites where post-depositional alteration of the calcite is virtually absent. Typically these sites contain hemipelagic, clay-rich lithologies with high sedimentation rates that rapidly encapsulate calcareous microfossils, isolating them within an impermeable matrix (Bown et al., 2008). These sediments contain a remarkably high diversity of fossil coccolithophores and an unusually high abundance of intact coccospheres, where the original spherical-subspherical cell covering of coccoliths is completely preserved, instead of the typical disarticulation into loose coccoliths. The pristine preservation of fragile and taxonomically important central-area structures in coccoliths combined with the preservation of very small (<3μm)coccolithsenablesustostudycoccospheregeometry across a wide variety of Paleogene taxa at species level. We present material from Tanzania (Nicholas et al., 2006), New Jersey (Miller et al., 1998) and Californian (John et al., 2008) continental shelf environments, where the shallow water depth minimized water-column disaggregation and dissolution and the shelf setting promoted high sedimentation rates. The thick sequence of clay-rich oozes at deep-sea Labrador Sea site ODP 647A (Firth, 1989) has also yielded diverse coccospheres that illustrate a high-latitude North Atlantic Eocene assemblage. Intact fossil coccospheres can be interpreted on a cellular level through analogy with the cellular geometry of their modern counterparts (Gibbs et al., 2013). This facilitates an unprecedented insight into the cellular physiology of cells that are millions of years old and its link to population-level responses to climate change. Our biometric data (following Fig. 1; Gibbs et al., 2013 and Henderiks, 2008) reveals the cellular growth and calcification response of more than 30 coccolithophore species to long-term variability in sea-surface conditions during the Paleogene greenhouse interval, between 66 and 34 million years ago. Cell geometry from abundant coccospheres of the common Paleogene genera

Retreat of the West Antarctic Ice Sheet from the western Amundsen Sea shelf at a pre- or early LGM stage

Recent palaeoglaciological studies on the West Antarctic shelf have mainly focused on the wide embayments of the Ross and Amundsen seas in order to reconstruct the extent and subsequent retreat of the West Antarctic Ice Sheet (WAIS) since the Last Glacial Maximum (LGM). However, the narrower shelf sectors between these two major embayments have remained largely unstudied in previous geological investigations despite them covering extensive areas of the West Antarctic shelf. Here, we present the first systematic marine geological and geophysical survey of a shelf sector offshore from the Hobbs Coast. It is dominated by a large grounding zone wedge (GZW), which fills the base of a palaeo-ice stream trough on the inner shelf and marks a phase of stabilization of the grounding line during general WAIS retreat following the last maximum ice-sheet extent in this particular area (referred to as the Local Last Glacial Maximum, ‘LLGM’). Reliable age determination on calcareous microfossils from the infill of a subglacial meltwater channel eroded into the GZW reveals that grounded ice had retreated landward of the GZW before ∼20.88 cal. ka BP, with deglaciation of the innermost shelf occurring prior to ∼12.97 cal. ka BP. Geophysical sub-bottom information from the inner-, mid- and outer shelf indicates grounded ice extended to the shelf edge prior to the formation of the GZW. Assuming the wedge was deposited during deglaciation, we infer the timing of maximum grounded ice extent occurred before ∼20.88 cal. ka BP. This could suggest that the WAIS retreat from the outer shelf was already underway during or even prior to the global LGM (∼23–19 cal. ka BP). Our new findings give insights into the regional deglacial behaviour of this understudied part of the West Antarctic shelf and at the same time support early deglaciation ages recently presented for adjacent drainage sectors of the WAIS. If correct, these findings contrast with the hypothesis that initial deglaciation of Antarctic Ice Sheets occurred synchronously at ∼19 cal. ka BP.

Correlation and paleoenvironments of middle Paleogene marine beds based on dinoflagellate cysts in southwestern Patagonia, Argentina

An understanding of paleonvironmental and paleoceanographic evolution of the Southwestern Atlantic Ocean during the Palaeogene is prevented by the lack of precise tools to date and correlate the sedimentary units. Palynological samples collected in the upper portion of the Man Aike Formation, which crops out southern Lago Argentino area, in the southwest of the Austral Basin (50°21′45″S–72°14′30″W), contain well preserved marine organic dinoflagellate cysts, which are potentially important biostratigraphic and paleoenvironmental indicators. Herein we describe the composition of the Man Aike Formation's dinoflagellate cyst assemblages and compare them to similar assemblages collected in the same basin in the upper member of the Río Turbio Formation using Compositional Statistical Analysis. The dinoflagellate cyst assemblages from the upper part of the Man Aike Formation are highly correlated to the assemblages from the upper member of the Río Turbio Formation from outcropping sections (51°31′13″S–72°15′11″W) and with the lower part of sediment cores drilled by Yacimientos Carboníferos Fiscales in the Río Turbio Formation area. These dinoflagellate cyst assemblages show a very low correlation with the assemblages from the upper part of the Yacimientos Carboníferos Fiscales's cores. The comparison of our results with the high-resolution Southern Pacific Ocean dinoflagellate cyst zonation for the late Palaeocene to late Eocene allow us to date some of the dinoflagellate events recorded in formations of southwestern Patagonia. The assemblages from the Man Aike Formation and the lower part of the upper member of the Río Turbio Formation relate to the zones SPDZ11 and SPDZ12 and are assigned to the mid-middle Eocene (late Lutetian to early Bartonian). The biostratigraphy proposed herein constrains the age of the Man Aike Formation and equivalent units based on calcareous microfossil data, mollusks affinities and 87Sr/86Sr isotopic values to an age ranging between ∼42 and 39 Ma. The assemblages from the upper part of the upper member of the Río Turbio Formation relate to the SPDZ13 Zone, which corresponds to the late Eocene (early Priabonian). The dinoflagellate cyst assemblages indicate that they were under the influence of relatively warm, marine open waters in an inner-shelf environment for the lower part of the sections. In the upper part of the sections, the assemblages suggest shallow marine waters associated with coastal areas and high trophic levels, possibly as a result of freshwater inputs.

Chemical and minero-petrographic features of Plio-Pleistocene fine-grained sediments in Calabria, southern Italy

The composition of Plio-Pleistocene fine-grained sediments from different areas of Calabria (southern Italy), have been studied to unravel the interplay of provenance. The use of multivariate statistical methods (e.g., PCA) based on biplot, allows for the discrimination of different groups of sediments. The general chemical composition of the fine-grained samples reflects the mineralogical variation observed in the sediments, which are composed of phyllosilicates, quartz, calcite, dolomite and feldspars. The I-S mixed layers, 10 A-minerals (illite and micas) are the most abundant phyllosilicates, chlorite and kaolinite are present in variable amounts, and smectite and chlorite/smectite mixed layers are presents in trace amounts. These chemical and mineralogical variations are also confirmed by SEM analysis, which also demonstrates that phyllosilicates are characterized by open and folded structures with generation of neoformed clay minerals. Provenance proxies and element ratios testify greater input of felsic source rocks, with lack of a marked mafic-ultramafic detritus input for all studied sediments, and the minero-petrographical features of the studied fine-grained sediments. These chemical and mineralogical variations are also confirmed by SEM analysis showing abundant phyllosilicate minerals for Groups 1 (Crotone Basin) and 2 (Crati Graben) and high content of quartz and feldspars grains for Group 4 (Catanzaro Graben) samples, probably due to abundant siliciclastic input coming from plutonic-metamorphic source and associated Mesozoic to Miocene sedimentary sources (Sila and Serre Massifs), and abundant calcium-carbonate phases mainly related to the presence of planktonic calcareous microfossils (Globigerina and coccoliths) for Groups 3 (southern Ionian coast) and 5 (southern Tyrrhenian coast).Furthermore, paleogeographic reconstructions characterized by re-establishment of open-marine conditions in the Mediterranean following the Messinian salinity crisis at the beginning of the Pliocene, play an important role. A progressive increase in the connectivity of Mediterranean sub-basins with the Atlantic (e.g., subbasins at the south of the Catanzaro Strait, characterized by normal water supply) and Paratethys (e.g., sub-basins at the north of the Catanzaro Strait, characterized by freshwater supply) can be envisaged during the Neogene period; this paleogeographic reconstruction may also explain the different composition among the studied samples.

The Black Sea Dating Game and Holocene Marine Transgression

Dating of major sea-level changes using shells or calcareous microfossils is prone to errors in semi-enclosed marine environments where inputs of seawater and river water vary over time and space. The need to refine mollusc-based age estimates for the rate of the Holocene marine transgression in the Black Sea is the focus of multiple palaeoceanographic and archaeological studies. This ongoing “dating game” seeks to clarify conflicting evidence for a hypothetical catastrophic marine flood that forced the emigration of Neolithic farmers from the shores of a Holocene freshwater lake in the Black Sea. The potential importance of confirming or rejecting this megaflood hypothesis has led to multiple attempts at refining the chronology of the marine transgression and quantifying the palaeosalinity of the Black Sea surface water during the Holocene. Here we report that six new AMS radiocarbon ages of 8890 ± 50 to 8450 ± 40 yr BP were obtained for wood, grass and sedge leaves from peat layers in Core 342 at 33.16 - 32.71 m below present sea level on the Ukrainian Shelf. These plant materials provide critical new ages for quantifying Black Sea carbon reservoir issues. The accuracy of our new AMS wood/peatages is independently supported by palynochronological correlation. The ages of our plant materials have ~100 years precisionandare ~420 - 520 years younger than those previously reported for unsorted detrital peat in Core 342. Paired mollusc—wood ages for brackish—freshwater Dreissena polymorpha shell from detrital peat also shows that an inaccuracy of >1120 yr can arise for shells during times when carbon reservoir values in the semi-isolated, brackish-water Black Sea could depart significantly from global average. Our revised sea level curve shows a gradual early Holocene transgression from water depths of -45.9 to -32.8 m, with initial Mediterranean inflow by 8.9 ka BP.

Microorganisms in the Zone of Submarine Volcanic Eruptions at 535-513 Ma

New anatomical features revealed in some Early Cambrian calcareous microfossils suggest comparison with Rhodophyta (red algae), which makes it possible to define their taxonomic position. A taxonomically rich Early Cambrian paleobiocoenosis has been discovered in northern Tien Shan, which exemplifies the existence on earth at 535-513 Ma (million years) of morphologically complex fungiform microorganisms and red algae in a shallow-water biotope where environmental conditions favorable for life were created as a result of submarine volcanic eruptions.

Glacial history and paleoceanography of the southern Yermak Plateau since 132 ka BP

The southern Yermak Plateau (YP) is situated at the entrance to the Arctic Ocean in the narrow Marginal Ice Zone (MIZ) between the Polar and Arctic Fronts, north-west of Svalbard. A gravity core JM10-02GC has been analysed in order to reconstruct paleoceanographic conditions and the movement of the sea ice margin as well as the glacier ice conditions of the Svalbard–Barents Sea Ice Sheet (SBIS) during the Last Interglacial–Glacial cycle. The distribution of planktic and benthic foraminifera, planktic and benthic oxygen and carbon isotopes and variations in ice-rafted debris (IRD) has been investigated. The sediment core covers the time interval from the Marine Isotope Stage (MIS) 6/5e transition (Termination II, c. 132 ka BP) to the early Holocene. During Termination II (TII), the SBIS retreated and the sea ice margin was in distal position whereas during MIS 5 to MIS 4 the sea ice margin was close to the core site. Several core intervals interpreted as representing MIS 5e, MIS 5c, MIS 5a, MIS 3 and MIS 1 were barren of calcareous microfossils whereas the intervals representing MIS 4 and MIS 2 were characterised by high productivity (HP) of planktic and benthic foraminifera. These “glacial” HP zones were associated with the open water conditions resulting from the advection of Atlantic Water (AW) and retreat of the sea ice margin. The barren zones during MIS 5, MIS 3 and MIS 1 resulted from the proximity of the sea ice margin whereas during MIS 2 the likely cause was an advance of the SBIS.

Late Holocene sedimentation and hydrologic development in a shallow coastal sinkhole on Great Abaco Island, The Bahamas

It remains poorly understood how sea level drives environmental change and hydrographic development in coastal karst basins (underwater caves, sinkholes, blueholes, etc.) over millennial timescales. It was previously hypothesized that coastal karst basins (CKBs) transition from vadose, to littoral, then anchialine, and finally submarine environments as sea-level rise inundates coastal karst landscapes, but the initial flooding event of CKBs remains challenging to sample. Runway Sinkhole hosts a modern anchialine ecosystem located ∼225 m from Great Abaco Island coastline in The Bahamas, and its shallow water depth (∼1.8 mbsl) permits an investigation into the early environmental evolution and hydrographic development in a CKBs after inundation by sea-level rise. Four sediment cores were collected from Runway Sinkhole, and late Holocene environmental change was reconstructed with benthic foraminiferal paleoecology, organic matter geochemistry (OM%, δ13Corg, and C:N), X-radiography, and radiocarbon dating. Despite some uncertainties associated with the chronology, it appears that Holocene sea-level rise initially flooded Runway Sinkhole and created a littoral environment at least by ∼3.9 ka, whereafter a detrital peat deposit accumulated in the sinkhole. This detrital peat had a high organic matter content (mean 88%), a δ13Corg value indicative of organic matter derived from C3 plants including mangroves (−28‰), and an unknown calcareous microfossil suggestive of a non-marine habitat in the sinkhole. A shift to carbonate sand deposition, organic matter with more marine-influenced δ13Corg values (−23‰), and expansion of euryhaline (Bolivina striatula, Elphidium poeyanum, and Triloculina bermudezi) and anchialine (Physalidia simplex and Conicospirillina exleyi) benthic foraminifera at ∼1.2 ka marks the onset of modern anchialine environmental conditions at the sediment–water interface (∼1.8 mbsl). These results suggest that relative sea-level rise in the Bahamas forced environmental change in Runway sinkhole at ∼1.2 ka, and indicate that peat deposits in coastal sinkholes must be verified as in-situ before being utilized as sea-level indicators.

Quaternary history of sea ice in the western Arctic Ocean based on foraminifera

Sediment cores from the Northwind Ridge, western Arctic Ocean, including uniquely preserved calcareous microfossils, provide the first continuous proxy record of sea ice in the Arctic Ocean encompassing more than half of the Quaternary. The cores were investigated for foraminiferal assemblages along with coarse grain size and bulk chemical composition. By combination of glacial cycles and unique events reflected in the stratigraphy, the age of the foraminiferal record was estimated as ca 1.5 Ma. Foraminiferal abundances, diversity, and composition of benthic assemblages, especially phytodetritus and polar species, were used as proxies for sea-ice conditions. Foraminiferal Assemblage Zone 2 in the Lower Pleistocene indicates diminished, mostly seasonal sea ice, probably facilitated by enhanced inflow of Pacific waters. A gradual decrease in ice-free season with episodes of abrupt ice expansion is interpreted for the Mid-Pleistocene Transition, consistent with climatic cooling and ice-sheet growth in the Northern Hemisphere. A principal faunal and sedimentary turnover occurred near the Early–Middle Pleistocene boundary ca 0.75 Ma, with mostly perennial sea ice indicated by the overlying Assemblage Zone 1. Two steps of further increase in sea-ice coverage are inferred from foraminiferal assemblage changes in the “Glacial” Pleistocene by ca 0.4 and 0.24 Ma, possibly related to hemispheric (Mid-Brunhes Event) and Laurentide ice sheet growth, respectively. These results suggest that year-round ice in the western Arctic was a norm for the last several 100 ka, in contrast to rapidly disappearing summer ice today.

Biogenic and detrital-rich intervals in central Arctic Ocean cores identified using x-ray fluorescence scanning

X-ray fluorescence (XRF) scanning of sediment cores from the Lomonosov Ridge and the Morris Jesup Rise reveals a distinct pattern of Ca intensity peaks through Marine Isotope Stages (MIS) 1 to 7. Downcore of MIS 7, the Ca signal is more irregular and near the detection limit. Virtually all major peaks in Ca coincide with a high abundance of calcareous microfossils; this is particularly conspicuous in the cores from the central Arctic Ocean. However, the recorded Ca signal is generally caused by a combination of biogenic and detrital carbonate, and in areas influenced by input from the Canadian Arctic, detrital carbonates may effectively mask the foraminiferal carbonates. Despite this, there is a strong correlation between XRF-detected Ca content and foraminiferal abundance. We propose that in the Arctic Ocean north of Greenland a common palaeoceanographic mechanism is controlling Ca-rich ice-rafted debris (IRD) and foraminiferal abundance. Previous studies have shown that glacial periods are characterized by foraminfer-barren sediments. This implies that the Ca-rich IRD intervals with abundant foraminifera were most likely deposited during interglacial periods when glaciers left in the Canadian Arctic Archipelago were still active and delivered a large amount of icebergs. At the same time, conditions were favourable for planktic foraminifera, resulting in a strong covariance between these proxies. Therefore, we suggest that the XRF scanner’s capability to efficiently map Ca concentrations in sediment cores makes it possible to systematically examine large numbers of cores from different regions to investigate the palaeoceanographic reasons for the calcareous microfossils’ spatial and temporal variability.Keywords: Foraminifera; Arctic Ocean; IRD; calcareous microfossils; XRF scanning(Published: 7 February 2013)Citation: Polar Research 2013, 32, 18386, http://dx.doi.org/10.3402/polar.v32i0.18386

Using Cathodoluminescence Spectroscopy of Cretaceous Calcareous Microfossils to Distinguish Biogenic from Early-Diagenetic Calcite

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.

Rare calcareous microfossils from Middle Miocene strata, Weddell Sea off Antarctic Peninsula

AbstractThe calcareousmicrofossil assemblage from Middle Miocene strata of SHALDRIL Site NBP0602A−5D consists of benthic foraminifera, ostracods, bivalves, and gastropods, and is interpreted as shallow−water. It appears to be reworked but its age is probably similar to the age of the host sediment, which contains only rare, fragmented, agglutinated foraminifera. Most of the calcareous taxa are of uncertain taxonomic affiliation, due to the scarcity of Ceno− zoic microfossils of this age fromWest Antarctica, and also the very different paleohabitat of this now extinct assemblage.

Pennsylvanian (Late Carboniferous) calcareous microfossils from Cedro Peak (New Mexico, USA). Part 1: Algae and Microproblematica

At Cedro Peak (Manzanita Mountains, central New Mexico), the Pennsylvanian succession is divided into four formations: Sandia, Gray Mesa, Atrasado, and lower part of Bursum. The sampled limestones of the Gray Mesa and Atravasado formations yielded three age distinctive fossil assemblages: (a) latest Atokan/early Desmoinesian; (b) late early Desmoinesian, and (c) middle Virgilian. The calcareous algae, incertae sedis algae and cyanobacterial-foraminiferal consortia are described here. The following new taxa are named: Epimastoporaceae n. fam.; Anthracoporellopsis novamexicana n. sp.; Tubiphytidae n. fam.; and Latitubiphytes n. gen.

Calcareous microfossils from the Karakatty Formation (Lower Cambrian) of the Northern Tien Shan

Lower Cambrian calcareous microfossils that preserved monospores and basal attachment organs with rhizoids have been discovered in jaspers of the Karakatty Formation of the Northern Tien Shan. A new genus, Koroleviphyton Kolosov, is established in the red algae division Rhodophyta with the type species K. attenuescens (Kolosov, 1983).

Astronomical calibration of upper Campanian–Maastrichtian carbon isotope events and calcareous plankton biostratigraphy in the Indian Ocean (ODP Hole 762C): Implication for the age of the Campanian–Maastrichtian boundary

An integrated framework of magnetostratigraphy, calcareous microfossil bio-events, cyclostratigraphy and δ13C stratigraphy is established for the upper Campanian–Maastrichtian of ODP Hole 762C (Exmouth Plateau, Northwestern Australian margin). Bulk-carbonate δ13C events and nannofossil bio-events have been recorded and plotted against magnetostratigraphy, and provided absolute ages using the results of the cyclostratigraphic study and the recent astronomical calibration of the Maastrichtian. Thirteen carbon-isotope events and 40 nannofossil bio-events are recognized and calibrated with cyclostratigraphy, as well as 14 previously published foraminifer events, thus constituting a solid basis for large-scale correlations. Results show that this site is characterized by a nearly continuous sedimentation from the upper Campanian to the K-Pg boundary, except for a 500kyr gap in magnetochron C31n. Correlation of the age-calibrated δ13C profile of ODP Hole 762C to the δ13C profile of the Tercis les Bains section, Global Stratotype Section and Point of the Campanian–Maastrichtian boundary (CMB), allowed a precise recognition and dating of this stage boundary at 72.15±0.05Ma. This accounts for a total duration of 6.15±0.05Ma for the Maastrichtian stage. Correlation of the boundary level with northwest Germany shows that the CMB as defined at the GSSP is ~800kyr younger than the CMB as defined by Belemnite zonation in the Boreal realm. ODP Hole 762C is the first section to bear at the same time an excellent recovery of sediments throughout the upper Campanian–Maastrichtian, a precise and well-defined magnetostratigraphy, a high-resolution record of carbon isotope events and calcareous plankton biostratigraphy, and a cyclostratigraphic study tied to the La2010a astronomical solution. This section is thus proposed as an excellent reference for the upper Campanian–Maastrichtian in the Indian Ocean.

Changes in the hydrological cycle in tropical East Africa during the Paleocene–Eocene Thermal Maximum

The Paleocene–Eocene Thermal Maximum (PETM), at ca. 55.8Ma, is one of the most studied instances of past greenhouse gas-induced global warming. As such, it provides a rich opportunity to examine the impact of such global change on local climates. The effects of increased continental and sea surface temperatures on local precipitation and humidity during the PETM remain poorly constrained and studies reveal complex, regional differences; whilst some localities appear to experience a net increase in humidity, others exhibit the opposite. Crucially, there are few records of hydrological change from tropical regions. Recent onshore drilling expeditions in Tanzania have yielded expanded sedimentary sections, deposited in a marine environment, that span much of the Late Cretaceous and Paleogene and show exceptionally good preservation of both calcareous microfossils and organic matter. The PETM interval has previously been constrained by both biostratigraphy and carbon isotopic records and spans ca. 7m of section. Lipid distributions, including various terrestrial, marine and bacterial biomarkers and their hydrogen isotopic compositions, as well as mineralogy, were used to examine East African vegetation and hydrological responses to the global change occurring at the PETM. Although total organic carbon contents decrease, the concentrations of both higher plant (n-alkanes, n-alkanoic acids) and soil bacterial (glycerol dialkyl glycerol tetraethers) biomarkers increase dramatically at the onset of the PETM negative carbon isotope excursion (CIE), suggesting an increased discharge of fluvial sedimentary organic matter. Similarly, mineralogical indicators of terrestrial input – including Ti/Al and Si/Al ratios, quartz contents and, notably, the proportion of kaolinite – also increase at the onset of the CIE. However, higher plant leaf wax n-alkanes (C27, C29 and C31) become more deuterium-enriched throughout the same interval, suggesting a more arid and/or hotter, rather than a more humid, environment. This evidence collectively suggests an East African early PETM climate characterised by overall hot and arid conditions punctuated by intense, perhaps seasonal, precipitation events. These data match observations from other locations at mid-latitudes, suggesting that the humid climate often suggested for the PETM was not globally widespread.

Microfósiles Calcáreos No Marinos y Semillas de la Formación Piedra Clavada (Albiano) en su área Tipo, Provincia de Santa Cruz, Argentina

Non-marine calcareous microfossils (ostracods and charophytes) and primitive angiosperm seeds (Carpolithus sp.) from the Piedra Clavada Formation (early Albian to early late Albian) in its type area, at Quebrada Don Nielsen section, Santa Cruz Province, Argentina are described and illustrated for the first time. The microfauna suggests a marshy lagoon paleoenvironment. Affinities with Lower Cretaceous microfossil assemblages from the Golfo San Jorge Basin are included.

Spatio-lateral continuity of hurricane deposits in back-barrier marshes

Sedimentological and micropaleontological analysis of fifteen 3-m gouge-auger cores revealed a lack of spatio-lateral continuity for paleohurricane deposits from the back-barrier marshes of Folly Island, South Carolina. The offshore-indicative calcareous microfossil content of some storm deposits was taphonomically altered or destroyed, and in many cases cores taken 10 m apart provided significantly different storm records. In several low-marsh cores, where bioturbation is more intense, storm deposits were completely unrecognizable using foraminifer or sedimentological analyses. In nearly all cores the sedimentary record of storm deposits was more extensive than the record produced using foraminifers, and, as a result, the sedimentary proxy produced shorter hurricane return periods. While offshore-indicative foraminifers in the salt marshes behind Folly Island are good indicators of their original source and mode of deposition (storm current transport from the shelf by overwash, storm inlet, or via Lighthouse Inlet), their susceptibility to destruction from bioturbation and dissolution suggests that they provide a less accurate or less complete record of storm frequency than previously thought.