Paleocene-Eocene Boundary Research Articles

Intensified bacterial productivity during the Paleocene–Eocene thermal maximum: Molecular evidence in the Tarim Basin in the eastern Tethyan realm

The investigation of bulk and molecular compositions in organic matter at the Bashibulake Section in the SW Tarim Basin, West China, across the Paleocene–Eocene boundary reveals a complex mixture of marine and terrigenous origins during the Paleocene–Eocene Thermal Maximum (PETM) in the eastern Tethys. Source-related biomarkers, such as n-alkanes, isoprenoid alkanes, steranes, hopanes and methylhopanes, exhibit diverse compositions influenced by both marine and terrigenous sources. Sterane and hopane isomer distributions, indicative of immature OM, are primarily controlled by biological configurations. Changes in compound class abundance and isomer ratios reflect variations in source inputs and depositional conditions. Elevated concentrations of n-alkanes from higher plants, along with ratios of C29-C32 moretanes/hopanes and C31/C32 homohopanes, suggest increased terrigenous OM supply during the PETM. However, the significant differences in concentration between n-alkanes from higher land plants and bacterial hopanes, coupled with the presence of 2α-methylhopanes, prevalence of C27 compounds in regular steranes, and absence of oleanane suggest a dominant aquatic bacterial contribution. The study highlights the role of enhanced continental flux and warming in stimulating microbial activity, enriching OM, a factor often overlooked by other analytical methods. The absence of carbonate carbon and low trisnorhopane isomerization provide supportive evidence of ocean acidification and carbonate dissolution during the PETM. Reduced pregnanes and tricyclic terpanes, along with low degree of hopane and sterane isomerization, indicate rising sea levels and low salinity. The findings emphasize the significance of the biomarker approach in identifying OM origin and characterizing the depositional environment in PETM-related sequences, suggesting a more substantial role of bacterial contributions than previously recognized.

PLANT COMMUNITY CHANGE ACROSS THE PALEOCENE–EOCENE BOUNDARY IN THE GULF COASTAL PLAIN, CENTRAL TEXAS

Abstract Long-term global warming during the early Paleogene was punctuated by several short-term ‘hyperthermal’ events, the most pronounced being the Paleocene–Eocene Thermal Maximum (PETM). During this long-term warming, tropical climates expanded into extra-tropical areas, creating a widespread band of thermophilic flora that reached into the paratropics, possibly as far north as mid-latitude North America in some regions. Relatively little is known about these paratropical floras, despite distribution across the North American Gulf Coastal Plain. We assess floras from the Gulf Coastal Plain in Central Texas before and after the Paleocene–Eocene boundary to define plant ecosystem changes associated with rapid global warming in this region. After the Paleocene–Eocene boundary, these floras suggest uniform plant communities across the Gulf Coastal Plain, but with high turnover rate and changes in community composition. Paleoecology and paleoclimate assessments from Central Texas Paleocene and Eocene floras suggest a warm and wet environment, indicative of tropical seasonal forest to tropical rainforest biomes. Fossil evidence from the Gulf Coastal Plain combined with the Bighorn Basin, Wyoming data suggest that early Paleogene warming helped create a paratropical belt that extended into mid-latitudes. Evaluating the response of fossil plant communities to rapid global warming has important implications for understanding and preparing for current global warming and climate change.

Paleocene–Eocene boundary in the Gabal El-Gir, east Qena, Egypt: Paleoenvironment and sequence stratigraphy interpretations

Comprehensive field, litho-, biostratigraphy, and paleoenvironmental studies of the upper Paleocene–lower Eocene (P–E) boundary interval in the Gabal El-Gir area were conducted. Two selected sections El-Gir-1 and El-Gir-2 were investigated. The prevailed paleoenvironmental conditions were discussed in the frame of the nannofossils, planktonic, and benthic foraminiferal assemblages. Benthic foraminifera assemblages indicate a remarkable turnover across the PETM. The extinction of Angulogavelinella avnimelechi at the base of the PETM represents a significant marker for the base of the benthic foraminifera extinction event at this site and other neritic sites in the Tethyan region. The dominance of calcareous planktonic excursion taxa at the base of the PETM indicates adaptation to extremely warm sea surface temperatures and low nutrient levels. Also, our data suggests that the biotic responses to environmental change in the early Eocene resembled those observed in the early Eocene hyperthermals at the nearbay Dababiya and El-Ballas sections. This could indicate that similar processes characterized the Egyptian sedimentary basin during the early Eocene. Stratigraphically, despite the limited distance between the studied sections, the Dababiya Quarry Member (DQM) in El-Gir-1 resemble those of the Global Stratotype Section and Point (GSSP) but reduced in thickness. While in El-Gir-2, the lower part of the DQM was missing. These findings could indicate that the DQM was deposited in a submarine channel. Three third-order depositional sequences were recognized covering the P–E interval. The reconstructed sea level curve shows the presence of eustatic similarities with the global sea level.

The Paleocene-Eocene transition in the Gulf of Guinea: Evidence of the PETM in the Douala basin, Cameroon

The Paleocene-Eocene Thermal Maximum (PETM) was identified for the first time in two sections (Bongue and Dibamba) from the Douala sub-basin located in the Gulf of Guinea, Cameroon. This discovery was based on a multi-disciplinary approach including biostratigraphy and occurrence of benthic and planktic foraminifera and ostracods, major and trace element contents, mercury, organic carbon isotope (δ13Corg values), total organic carbon (TOC), whole-rock and clay mineralogy. A combination of lithology, microfossil assemblage, and carbon isotope data indicate zone P5 and the top of the Paleocene enabling the definition of the Paleocene-Eocene boundary (PEB). A negative carbon-isotope excursion (CIE) spanning from the uppermost Paleocene deposits to the earliest Eocene sediments (PETM interval) shows a shift in δ13Corg values of 1.5‰ in Bongue and 3.0‰ in Dibamba. In both sections, this interval is affected by widespread acidification, as revealed by carbonate dissolution and microfossil preservation (i.e., species are dwarfed, broken, thin shelled, and with holes). The very low carbonate content and the scarcity of microfauna indicate the severity of acidification during the PETM, especially in the early Eocene where only one species was identified (Igorina broedermanni). Mercury anomalies, TOC contents, and trace element concentration ratios, point to volcanic activity linked to the Cameroon Volcanic Line (CVL) intrusive magma, and a decrease in productivity prior to the PETM. In addition to climate change, our geochemical and mineralogical data support the hypothesis that other environmental perturbations such as an increase in productivity and detrital input, as well as a decrease in bottom water oxygenation occurred during the PETM in the Douala sub-basin.

The Importance of Eurekan Mountains on Cenozoic Sediment Routing on the Western Barents Shelf

The importance of topography generated by Eocene Eurekan deformation as a sediment source for sandstones deposited on the western Barents Shelf margin is evaluated through a sediment provenance study conducted on wellbore materials retrieved from Spitsbergen and from the Vestbakken Volcanic Province and the Sørvestsnaget Basin in the southwest Barents Sea. A variety of complementary techniques record a provenance change across the Paleocene-Eocene boundary in wellbore BH 10-2008, which samples Paleogene strata of the Central Tertiary Basin in Spitsbergen. Sandstones containing K-feldspar with radiogenic Pb isotopic compositions, chrome spinel in the heavy mineral assemblage, and detrital zircons and rutiles with prominent Palaeoproterozoic and Late Palaeozoic—Early Mesozoic U-Pb age populations are up-section replaced by sandstone containing albitic plagioclase feldspar, metasedimentary schist rock fragments, a heavy mineral assemblage with abundant chloritoid, metamorphic apatite with low REE contents, metapelitic rutile with Silurian U-Pb ages and zircons with predominantly Archaean and Palaeoproterozoic U-Pb age populations. Our results clearly demonstrate the well-known regional change in source area from an exposed Barents Shelf terrain east of the Central Tertiary Basin during the Paleocene to the emerging Eurekan mountains west and north of the Central Tertiary Basin during the Eocene. Eocene sandstones deposited in the marginal basins of the southwestern Barents Shelf, which were sampled in wellbores 7316/5-1 and 7216/11-1S, contain elements of both the Eurekan and the eastern Barents Shelf provenance signatures. The mixing of the two sand types and delivery to the southwest margin of the Barents Shelf is consistent with a fill and spill model for the Central Teritary Basin, with transport of Eurekan-derived sediment east then south hundreds of kilometres across the Shelf.

Fruits of Anacardiaceae from the Paleogene of the Paris Basin, France

Premise of research. The Anacardiaceae family is distributed throughout the vegetated continents. The fossil record indicates extensive diversification of the family during the Paleogene and, in particular, during the Eocene. Despite the abundant fossil record of this period, there are only a few reliable anacardiaceous fossils in the Paris Basin. Here, we aim to document newly recognized fossils of Anacardiaceae from the Paris Basin, understand their paleoecology, and discuss their biogeographic history.Methodology. Thirty-three lignite fruits were examined from two sites, one before and one after the Paleocene-Eocene boundary (i.e., Petit Pâtis [Rivecourt] and Le Quesnoy [Houdancourt]). The specimens were photographed, and anatomy was studied using computed tomography and histological sections. Comparative analyses were undertaken using available descriptions of fossil and modern fruits of Anacardiaceae.Pivotal results. A new species, Cyrtocarpa biapertura sp. nov., is described on the basis of a unilocular fruit with two prominent apertures present on the ventral side of the endocarp, protruding into two lacunae surrounding the locule. Taphonomic analysis indicates that this plant grew close to riverbanks. Furthermore, a new record of “Lannea” europaea (Reid and Chandler) Chandler is reported for the Eocene site.Conclusions. The occurrence of Cyrtocarpa in both the Paleocene and the Eocene floras in the Paris Basin suggests similar vegetation during both time intervals. It is likely that both floras grew under similar subtropical climates. Moreover, it appears that the early Eocene shows an enrichment of the paleodiversity of Anacardiaceae and other plant families in the Paris Basin. The presence of Cyrtocarpa documents a rarely reported disjunction between the Paleogene of Europe and the recent tropical flora of South America.

Calcareous nannoplankton response model of the global warming at the Paleocene-Eocene boundary in Riben section, Northern Bulgaria

We present a model of calcareous nannoplankton response of the global warming at the PETM, based on studies of Bulgarian sections. New data acquired from forams’carbon and oxygen isotopes, as well as high-resolution quantitative study of calcareous nannofossils suggest 3 phases of the event: pre-PETM, core of PETM and recovery phase. During the core phase, a significant increase in warm-water nannofossil species was registered, as well as signs of acidification and higher salinity of the surface waters (dissolution of carbonate skeletons of nannofossils). In the recovery phase, the cold-water species from pre-event conditions gradually return, however g. Fasciculithus completely disappears.

Gypsum in diatomaceous strata of the trans-urals region: Morphology, lithogeochemistry, and genetic link to global warming at the paleocene-eocene boundary

This paper reports the geochemical, structural, and textural properties of evaporite minerals (gypsum) interbedded with from the Early Paleogene diatomite and clastics exposed in the diatomite quarry in the Kamyshlov town quarry, Trans-Urals region (Sverdlovsk Oblast, Russia). This article is the first to reveal the occurrence of these atypical minerals in local sediments for the Trans-Urals region, dating from the Paleocene to the Early Eocene. The investigated aggregates included gypsum, anhydrite, and diatomite. Gypsum crystallization occurred rapidly in the low-density non-lithified stratum of the seafloor sediment under warm conditions. Gypsum elemental composition reflects its genesis in a low bio-productivity environment strongly influenced by the influx of highly mineralized groundwater. Terrigenous influx (coarse-grained quartz and fine clay fractions) is high. As a result, radial-fibrous stellate gypsum crystals formed in the fissures that penetrated the diatomite stratum. Geochemical indicators, such as Sr/Ba ratios, show that the salinity of the watershed was variable at the onset of evaporitic conditions. Chronologically, gypsum formation is dated to the beginning of the transgressive cycle (early Eocene, the end of the Paleocene–Eocene Thermal Maximum (PETM)) or to the end of post-PETM sedimentation.

Radiolarian size and silicification across the Paleocene-Eocene boundary and into the early Eocene

The Paleocene-Eocene Thermal Maximum (PETM) was a major environmental perturbation that drove range shifts, adaptation, and faunal turnover in marine and terrestrial clades. Open ocean planktonic responses—including body size trends—have been characterized for calcareous nannoplankton, dinocysts, and planktonic foraminifera. Relatively little, however, is known about the response of radiolarians, which share life modes and phylogenetic history with planktonic foraminifera but make their tests (i.e., ‘shells’) out of silica rather than calcium carbonate. Here, we compare radiolarian assemblage changes in the Southwest Pacific with assemblages from Atlantic and Indian Ocean sites. We also measured radiolarian test size before, during, and after the PETM in a pelagic sedimentary succession at Mead Stream, South Island, New Zealand. Our results show a substantial positive shift in mean radiolarian test size at Mead Stream at the assemblage level concurrent with the onset of the PETM, primarily due to an increase in the size and relative abundance of spumellarian radiolarians. We investigate oligotrophy, elevated seawater silica concentration, and redeposition as potential drivers for this size shift. Mead Stream radiolarians remain large for 1.3 Myr, long past the recovery of the carbon isotope excursion and a return to baseline in terrigenous sedimentation, bioturbation, and benthic foraminifera diversity, leaving the ultimate cause of the observed changes in test size uncertain. We find little evidence for a uniform morphological response to the event or its aftermath across sites, particularly as relates to the relative extent of silicification of different groups of radiolarians.

Biostratigraphically significant palynofloras from the Paleocene–Eocene boundary of the USA

Pollen and spores were recovered from the Paleocene Fort Union Formation and Paleocene–Eocene Willwood Formation of the Bighorn Basin (BHB), northwestern Wyoming, USA. In many local stratigraphic sections in the BHB, the base of the Eocene has been identified by the characteristic negative carbon isotope excursion (CIE) that marks the beginning of the Paleocene–Eocene Thermal Maximum (PETM). The palynotaxa from outcrop samples were examined using light microscopy (LM) and scanning electron microscopy (SEM). Seven new species are formally described (Tricolpites vegrandis, Rousea spatium, Striatricolporites astutus, Striatopollis calidarius, Friedrichipollis geminus, Retistephanocolporites modicrassus and Retistephanocolporites pergrandis). The temporal and geographic distributions of many of these palynotaxa suggest that hotter and more seasonally dry climates facilitated their northward range shifts during the PETM from the tropics or subtropics of the USA. For the temperate palynotaxa, the hotter and seasonally dry conditions resulted in local extirpation. A re-evaluation of the palynostratigraphic schemes established for the Paleocene–Eocene boundary confirms that the first appearance of Platycarya platycaryoides denotes the Paleocene–Eocene boundary in the Rocky Mountains region. A new Striatopollis calidarius Subzone, associated with early Wasatchian (Wa) Wa-0 and Wa-R faunas, is also recognized for CIE body localities in the BHB.

Morphotype analysis and paleoecological implications of Maastrichtian - Paleogene benthic foraminifera from RCCG BH4 Borehole, Eastern Dahomey (Benin) Basin

The Maastrichtian-Eocene paleoecological conditions of eastern Dahomey (Benin) Basin were investigated using benthic foraminiferal morphotypes from the RCCG BH-4 borehole located on kilometer 46, Lagos-Ibadan Expressway, southwest Nigeria. Many previous studies on the basin and other Nigerian sedimentary basins centered on paleobathymetric studies using depth indicator benthic foraminiferal assemblages and planktic/benthic ratio. This present study attempts to categorize benthic species into morphological categories (morphotypes) based on general outline and shape, chamber arrangement, and mode of coiling, and use the distribution of the morphotypes to determine certain paleoecological conditions such as organic matter content, sediment pore water oxygen availability and sediment depositional setting. 25 ditch cutting samples subjected to the kerosene method of micropaleontological sample processing yielded few Maastrichtian – Eocene planktic species (Planoheterohelix globulosa, Morozovella acuta, Parasubbotina pseudobulloides, and Subbotina velascoensis) and fairly abundant and diverse benthic foraminiferal assemblages which we categorized into nine (9) morphotypes designated B2, B3, C1, F, H, I, J, N and Q. Six (6) of these morphotypes (B2, B3, I, J, N, and Q) are adapted to the epifaunal mode of life, while morphotypes C1, F, and H belong to the infaunal types. The dominance of the epifaunal morphotypes within the limestone Ewekoro Formation, and the underlying shaly sand unit of the Araromi Formation revealed a shallow marine (inner – middle neritic), low organic matter content, and oxygen-rich environment of deposition for these units. The infaunal morphotypes show sparse occurrence within the borehole except within the organic intercalation within the limestone unit in which 8 counts of Afrobolivina afra were recorded. The disappearance of species (faunal turnover) within the overlying shale unit (Akinbo Formation) is believed to be a response to heightened organic matter flux, reduced oxygen availability, and other climatic perturbations characteristic of the Paleocene-Eocene boundary. Eponides pseudoelevatus (morphotype N) is believed to be an opportunistic species based on the species’ continued occurrence and increased abundance within the shale unit (Akinbo Formation). The species may have recolonized the environment following improved environmental conditions that ensued after the cessation of the end Paleocene climatic perturbation.

Iron-manganese mineralization in Eocene deposits of Parashka skyba (Skybov nappe, Ukrainian Carpathians)

Formulation of the problem. Modern advances in oceanographic studies of sedimentogenesis and orogenesis open up opportunities for in-depth study of rocks by fold-nappe systems, including the Carpathian region. Review of previous research. On the territory of the Carpathians in flysch complexes researchers have mainly noted the findings of carbonates of manganese and iron nodules.At the same time, flysch complexes contain iron-manganese oxide mineralization. The purpose of the work was to study the mineral and chemical composition, morphological types of aggregates and the origin of iron-manganese mineralization (IMM) among the Eocene deposits of the Parashka skyba of Skybov nappe in the middle course of the river Opir. Methods used: Sedimentological, mineralogical, petrogeochemical and X-ray diffractometric analyzes of wall rocks and ore minerals. Results: The ore mineralization is associated with the Paleocene to Eocene transition strata, which is represented by coarse-grained turbidites and grainites of the Yamna suite and variegated fine- and medium-grained turbidites and hemipelagites of the Manyava suite. IMM are deposited in a main ore bed, ore crusts and scattered in the wall rocks. It is synchronously sedimented with deep-water deposits of the lower bathyal. The оre bed is composited of concretionary, sinter, brecciated, earthy and sooty aggregates. Concretionary morphotypes have concentric-zonal structure, which is formed by shells with different mineral composition and structural features. Crystalline secretions are observed in the nucleus. The ore substance is represented by X-ray amorphous compounds of iron and manganese hydroxides, among which are minerals of hydrothermal (pyrolusite, psilomelan, todoroquite and bersenite) and hydrogenic (vernadite, buserite) origin. Shells often have columnar, dendrіtic and colomorphic structures typical of hydrothermal formations. Differentiation of mineralization by mineral composition causes significant fluctuations in metal contents in ore aggregates (from 3 to 11.5% of Fe oxides and from 2 to 10% of Mn) and host rocks (from 1.4 to 11.5% of Fe oxides and from 0.12 to 12% Mn). This confirms the endogenous origin of ore-bearing fluids. On the diagram of the ratios of the main components of iron-manganese formations of different zones of modern oceans by E. Bonatti, the geochemical composition of the ore mineralization of the Nad’yamne variegated horizon falls into the fields of both hydrothermal and hydrothermal-hydrogen origin. Mineralogical and geochemical features of ore mineralization indicate that the main source of metals on the seabed were hydrothermal vents. Direct deposition of ore mineral phases and deposition of oxide and hydroxide compounds from metal-enriched bottom waters occurred as a result of reaction of hydrothermal fluids with seawater. The formation and functioning of the hydrothermal system was likely caused by the intensification of tectonic movements of the Laramian phase on Paleocene-Eocene boundary, which also led to restructuring and deepening of the Carpathian paleobasin. An important role in these processes was played by faults in the flysch foundation, which served as channels for circulation of hot fluids. The source of heat and metals could be deep magma, according to authors. Scientific novelty. Iron-manganese mineralization in the Eocene rocks of the Nad’yamne variegated horizon was characterized for the first time, IMM morphotypes, structural-textural, mineralogical and geochemical features of ore formations and sedimentation and petrographic features of the content rocks were described. The studied features make it possible to propose a hydrothermal model of mineral formation. Practical significance. The studied features of IMM correlate well with modern and recent formations of pelagic sedimentation. The presence of iron-manganese mineralization in the Eocene Nad’yamne variegated horizon expands the cognitive aspects of the study of the Outer Carpathian basin of the Tethys Ocean and will contribute to the study of other variegated horizons and their geochemical specialization.

Calcareous nannofossil biostratigraphy and paleoenvironmental study along the Upper Maastrichtian- Eocene sequence at Eastern and Western Deserts, Egypt

Biostratigraphy and paleoenvironment of seventy surface samples were studied based on calcareous nannofossils along the Upper Maastrichtian – Eocene sequence at Gebel Duwi and Gebel Ghanima sections, Egypt. This succession includes three rock units, arranged from base to top as follow: Dakhla, Tarawan and Esna formations. Seven calcareous nannofossil biozones have been recorded, arranged as follow: CC 25c, CC 26, NP 2/3, NP 4, NP 5, NP 6 and NP 9b, discussed and compared with their counterpart in and outside Egypt. Four present stage boundaries have been discussed; the Cretaceous/Paleogene boundary, it seems to be incomplete in the Gebel Duwi section due to the absence of the biozone NP 1. The Danian/Selandian boundary, it can be determined in the Gebel Ghanima section based on the FO of Fasciclithus tympaniformis. The Selandian/Thanetian boundary, it was difficult to trace in the Gebel Ghanima section, where the topmost part of Zone NP 6 was missed. The Paleocene/Eocene boundary, it cannot be accurately determined in the Gebel Ghanima section, owing to the presence of a small hiatus represented by the absence of the Subzone NP 9a. There is predominance in assemblages’ taxa and were relatively warm-water temperature during the Late Danian in the Gebel Duwi section and highly warm-water temperature around the Paleocene-Eocene boundary in the Gebel Ghanima section. There are two ecozones have been recognized in our study. In the Gebel Duwi, the sediments of ecozone (A) are deposited in cool-water, and transitional states between eutrophic and oligotrophic environments, while that of ecozone (B) are deposited in warm-water and also transitional states between eutrophic and oligotrophic environments. The sediments of ecozone (B) in the Gebel Ghanima are deposited in warm-water and mainly oligotrophic environments.

Bug-bitten leaves from the early Miocene of Ethiopia elucidate the impacts of plant nutrient concentrations and climate on insect herbivore communities

High-resolution paleoecological studies elucidate the effects of biotic and abiotic factors on the diversity and distribution of insect herbivory in deep time. Previous analyses of fossil leaf assemblages from intervals of significant environmental change have shown that insect damage frequency and diversity are strongly influenced by temperature and carbon dioxide levels. Similar studies that span intervals of environmental quiescence are a necessary complement and can help disentangle the relative influences of biological versus abiotic factors. The 21.73 ± 0.03 million year old (early Miocene) Mush Valley lagerstätten, Ethiopia, provides one such example. Insect damage censuses were conducted at six stratigraphic levels that span ~50,000 years and whose plant ecology has been studied in detail. A total of 2200 leaves (47 morphotypes) were examined and 35 damage types (DTs) observed. We documented variations in insect damage frequency, diversity, and composition among plant host taxa and across stratigraphic levels and tested for correlations with abiotic and biotic factors. Interspecific variations in damage frequency and diversity among host plants at Mush with >20 leaves in the damage census could not be explained solely by leaf mass per area, presence/absence of trichomes, symbiosis with nitrogen-fixing bacteria, or host plant abundance. The strongest predictor of insect herbivore damage on the bulk floras (all leaves) was the prevalence of legumes, whose symbiotic relationships with nitrogen-fixing bacteria likely made them more nutrient-rich. This pattern was also observed across the climatically-variable Paleocene-Eocene boundary in the Bighorn Basin, USA, suggesting that the soil microbiome, plant nutrient composition, and climate work synergistically in regulating insect herbivore distribution, population sizes, and feeding. • A new Miocene record of fossil insect herbivory from the African tropics. • Insect damage frequency and diversity strongly correlate to abundance of plants with N 2 -fixing symbionts. • Predicting variability in herbivore damage among fossil plant hosts is challenging.

Contribution of foraminifers in biostratigraphy and paleoecology interpretations of the basal Eocene from the phosphatic Sra Ouertaine basin, in the southern Tethys(Tunisia)

Micropaleontological, sedimentological and statistical studies were carried out on the late Paleocene-early Eocene succession of Sra Ouertaine and Dyr El Kef in Northern open phosphatic Basin of Tunisia. Based on the abundance and stratigraphic distribution of planktic foraminiferal species, five planktic zones have been recognized from the base to the top of the phosphatic layers. The El Acarinina sibaiyaensis Zone, the E2 Pseudohastigerina wilcoxensis Zone, the E3 Morozovella marginodentata Zone, the E4 Morozovella formosa Zones and the E5 Morozovella subbotinae Zone. The placement of Paleocene-Eocene boundary (PETM) is just below the base of the phosphatic interval. The ETM-2 event may be detectable in the analyzed biotic record of Sra Ouertaine.Based on benthic assemblages, abundances, cluster and multivariate statistical analyses, two biofacies were recognized for each section. The recognized ecozones are typical of warm and shallow water inner neritic setting (dominance of epifaunal fauna Anomalinoides, Dentalina and Cibicidoides associated with Frondicularia phosphatica, Trochamminoides globigeriniformis and Eponides elevatus). The paleoenvironment is eutrophic (presence of several bolivinitids and verneuilinids). For the Dyr El Kef section and P5 and E2 of Sra Ouertaine section, our records indicate that paleoenvironment is influenced by coastal upwelling without oxygen-deficiency, the paleodepth is estimated to be around 50 m. The paleoecosystem is diversified and balanced with a general tendency to stressed condition. While the upper part of Sra Ouertaine section is more eutrophic, influenced by coastal upwelling with oxygen-deficiency, the paleodepth is estimated to be less than 50 m and the ecosystem is unsettled.

Campanian-Eocene dinoflagellate cyst biostratigraphy in the Southern Andean foreland basin: Implications for Drake Passage throughflow

The tectonic opening of the Tasmanian Gateway and Drake Passage represented crucial geographic requirements for the Cenozoic development of the Antarctic Circumpolar Current (ACC). Particularly the tectonic complexity of Drake Passage has hampered the exact dating of the opening and deepening phases, and the consequential onset of throughflow of the ACC. One of the obstacles is putting key regional tectonic events, recorded in southern Patagonian sediments, in absolute time. For that purpose, we have collected Campanian-Eocene sediment samples from the Chilean sector of Southern Patagonia. Using U-Pb radiometric dating on zircons and dinoflagellate cyst biostratigraphy, we updated age constraints for the sedimentary formations, and the hiatuses in between. Thick sedimentary packages of shallow-marine and continental sediments were deposited in the foreland basin during the early Campanian, mid-Paleocene, the Paleocene-Eocene boundary interval and the middle Eocene, which represent phases of increased foreland subsidence. We interpret regional sedimentary hiatuses spanning the late Campanian, early-to mid-Paleocene, mid-Eocene and latest Eocene-early Oligocene to indicate times of reduced foreland subsidence, relative to sediment supply. We relate these changes to varying subduction rates and Andean orogeny. Dinoflagellate cyst assemblages suggest that the region was under the influence of the Antarctic-derived waters through the western boundary current of the Subpolar Gyre, developed in the southwest Atlantic Ocean and thus argues for limited throughflow through the Drake Passage until at least the latest Eocene. However, the proliferation of dinoflagellate endemism we record in the southwest Atlantic is coeval with that in the southwest Pacific, and on a species level, dinoflagellate cyst assemblages are the same in these two regions. This suggests that both regions were oceanographically connected throughout the early Paleogene, likely through a shallow opening of a restricted Drake Passage. This implies a continuous surface-water connection between the south Pacific and the South Atlantic throughout the late Cretaceous-early Paleogene.

Larger benthic foraminiferal response to the PETM in the Potwar Basin (Eastern Neotethys, Pakistan)

The Paleocene-Eocene Thermal Maximum (PETM) was the most pronounced global and transient warming event of the Cenozoic and was associated with marked changes in the biosphere, atmosphere and hydrosphere. On the basis of the large benthic foraminiferal (LBF) biostratigraphy coupled with δ13C record, the PETM event and the Paleocene-Eocene boundary are constrained in the Duleram section (Potwar Basin, Pakistan). This shallow-marine carbonate deposit offers a unique opportunity to study in detail the stratigraphic record of the PETM and its effect on LBF assemblages in the eastern Neotethyan Ocean. The ~5‰ negative carbon isotope excursion (CIE) is here used to pinpoint the Paleocene-Eocene boundary corresponding to the base of SBZ 5. The CIE is not directly associated with evident compositional changes in the LBF assemblages that are instead identified during the CIE recovery phase. The prominent LBF assemblages' changes are marked by the disappearance of Miscellanea juliettae, Miscellanea dukhani, Ranikothalia nuttalli, Ranikothalia sindensis, Daviesina tenuis, Daviesina langhami and Orbitosiphon punjabensis and by the appearance of Alveolina ellipsoidalis, Alveolina globula, Alveolina moussoulensis, Alveolina minervensis, Alveolina avellana aurignacensis, Orbitolites biplanus, Nummulites fraasi, Nummulites minervensis and miliolids that correspond to the boundary between SBZ 5 and SBZ 6. The change in the LBF assemblages during the CIE-recovery phase of PETM is attributed to enhanced continental weathering and increased temperature and organic content flux that altered the habitat from oligotrophic to eutrophic conditions. This study provides the first evidence of the PETM at shallow marine deposits in the Potwar Basin and shows that change in the LBF assemblages in response of the PETM warming event affected shallow seas bordering the eastern Neotethyan Ocean.

Testing hypotheses on signatures of precipitation variability in the river and floodplain deposits of the Paleogene San Juan Basin, New Mexico, U.S.A.

ABSTRACTMuch progress has been made in recent years towards a set of recognition criteria for river discharge variability in river channel deposits, and thus sedimentary proxies for precipitation variability. Despite this progress, there is currently no consensus on how different styles of discharge variability are reflected in river sedimentary records, and whether variable-discharge river records from different climate types can be distinguished. Herein, river discharge and precipitation variability in the Paleogene is investigated using associations between river channel and floodplain deposits across the Paleocene–Eocene boundary from the Paleocene upper Nacimiento Formation and the early Eocene San Jose Formation in the San Juan Basin, New Mexico, USA.The succession is identified as deposits of variable-discharge river systems based on shared channel-deposit characteristics with modern and ancient variable-discharge river systems and the proposed facies models, in addition to alternations of poorly drained and well-drained floodplain deposits and/or slickensides indicating alternating wet–dry cycles. A long-term stratigraphic trend toward increasingly well-drained floodplain deposits is also observed and hypothesized to indicate successively more arid conditions from the Paleocene into the early Eocene. Comparisons with modern rivers from various climate zones suggest a long-term shift from a monsoonal climate in the Paleocene, to a fluctuating subhumid climate, ultimately leading to semiarid to arid conditions in the early Eocene. These observations suggest that floodplain deposits may be a better indicator of ambient climate, whereas channel deposits are records for frequency and magnitude of high-intensity precipitation events. Therefore, the existing facies models for variable-discharge rivers that consider only channel facies may not capture critical information needed to make accurate interpretations of paleoclimatic conditions. This study also adds to a growing body of evidence from geologic records of mid-latitude Paleogene river systems suggesting increases in the magnitude or variability of river discharge coinciding with established climate perturbations.

Soil carbon degradation during the Paleocene-Eocene Thermal Maximum in the Piceance Basin, USA

The Paleocene-Eocene Thermal Maximum (PETM) warming event is marked by a negative carbon isotope excursion (CIE). The magnitude and shape of the CIE differs among carbon archives, but bulk organic carbon isotopes (δ13Corg) in terrestrial sections are often particularly variable and attenuated. Multiple lines of evidence from the Bighorn Basin, Wyoming, USA have revealed that extensive organic carbon degradation and increased refractory or allochthonous carbon inputs diminished the δ13Corg excursion magnitude. To test if this was a spatially widespread phenomenon and to understand possible underlying mechanisms, we examined the abundance of total organic carbon (%TOC) and polycyclic aromatic hydrocarbons (PAHs) as metrics of soil degradation at a neighboring terrestrial basin, the Piceance Basin in Colorado. Outcrop samples reveal both diminished %TOC and PAH concentrations across the Paleocene-Eocene boundary. Using PAHs as a proxy for intermediate refractory carbon, such as found in mineral soils, evidence from the Piceance Basin supports increased organic carbon degradation and greater proportions of refractory allochthonous carbon remaining. Correlations between %TOC and elemental oxides (e.g., Al2O3 and TiO2) suggest soil organic carbon was stabilized by its association with clay minerals. We hypothesize that decreased clay content in the soils (which reduced soil capacity to stabilize fresh carbon) and increased fluctuations in soil moisture (which destabilized older, refractory carbon), in conjunction with increased temperatures (which increased microbial decomposition rates), contributed to reduced soil organic matter preservation during the PETM. These mechanisms destabilized carbon on millennial timescales and, with sustained higher temperatures across the PETM (~150,000 years), increased soil carbon degradation persisted for tens of thousands of years.

The oldest lamprophiid (Serpentes, Caenophidia) fossil from the late Oligocene Rukwa Rift Basin, Tanzania and the origins of African snake diversity

Extant snake faunas have their origins in the mid-Cenozoic, when colubroids replaced booid-grade snakes as the dominant species. The timing of this faunal changeover in North America and Europe based on fossils is thought to have occurred in the early Neogene, after a period of global cooling opened environments and made them suitable for more active predators. However, new fossils from the late Oligocene of Tanzania have revealed an early colubroid-dominated fauna in Africa suggesting a different pattern of faunal turnover there. Additionally, molecular divergence times suggest colubroid diversification began sometime in the Paleogene, although the exact timing and driving forces behind the diversification are not clear. Here we present the first fossil snake referred to the African clade Lamprophiinae, and the oldest fossil known of Lamprophiidae. As such, this specimen provides the only potential fossil calibration point for the African snake radiation represented by Lamprophiidae, and is the oldest snake referred to Elapoidea. A molecular clock analysis using this and other previously reported fossils as calibration points reveals colubroid diversification minimally occurred in the earliest Paleogene, although a Cretaceous origin cannot be excluded. The elapoid and colubrid lineages diverged during the period of global warming near the Paleocene-Eocene boundary, with both clades diversifying beginning in the early Eocene (proximate to the Early Eocene Climate Optimum) and continuing into the cooler Miocene. The majority of subclades diverge well before the appearance of colubroid dominance in the fossil record. These results suggest an earlier diversification of colubroids than generally previously thought, with hypothesized origins of these clades in Asia and Africa where the fossil record is relatively poorly known. Further work in these regions may provide new insights into the timing of, and environmental influences contributing to, the rise of colubroid snakes.