Paleocene–Eocene Thermal Maximum Interval Research Articles

Shallow-water carbonate responses to the Paleocene–Eocene thermal maximum in the Tethyan Himalaya (southern Tibet): Tectonic and climatic implications

This study presents a detailed stratigraphic record of the Paleocene–Eocene Thermal Maximum (PETM) in the Gamba area of the Tethyan Himalaya, a carbonate-platform succession originally deposited along the southern margin of the eastern Tethys Ocean. The Paleocene-Eocene boundary interval is marked by a negative carbon isotope excursion at the boundary between members 3 and 4 of the Zongpu Formation. The succession is erosionally truncated at this surface, which is overlain by an intraformational carbonate conglomerate, and only the upper part of the PETM interval is preserved. Foraminiferal assemblages of Shallow Benthic Zone 4 are present below the conglomerate bed, but are replaced by assemblages of Shallow Benthic Zone 6 above the conglomerate. Depositional facies also change across this surface; below the disconformity, floatstones and packstones containing nummulitid forams record progressive transgression in an open-marine environment, whereas restricted or lagoonal inner-ramp deposits containing Alveolina and Orbitolites are typical above the disconformity. The prominent negative excursion observed in the δ13C of whole-rock carbonate (−1.0‰ at Zongpu, −2.4‰ at Zengbudong) and organic matter (−24.7‰, at Zengbudong) is correlated to the characteristic PETM carbon isotope excursion. This major negative excursion in shallow-marine carbonates may have partly resulted from syndepositional alteration of organic matter. The erosional unconformity can be constrained to the lower PETM interval (between 56 and 55.5Ma), and is identifiable throughout the Tethyan Himalaya. This widespread disconformity is attributable to tectonic uplift associated with the southward migration of an orogenic wave, originated 3±1Ma earlier in the middle Paleocene at the first site of India-Asia continent-continent collision. A possible eustatic component of the pre-PETM sea-level fall, which resulted in the excavation of incised valleys filled during the subsequent sea-level rise when the conglomerate bed was deposited, remains to be assessed.

Response of calcareous nannofossils to the Paleocene-Eocene thermal maximum from a shelf section in Jordan

Abstract The Paleocene-Eocene Thermal Maximum (PETM) is known as an approximately 200 kyr long lasting interval of extreme global warming accompanied by major alterations in the ocean-atmosphere system. These include a negative carbon isotope excursion, intense carbonate dissolution and biotic changes of marine floras and faunas. The current study reports the response of calcareous nannofossils across the Paleocene-Eocene boundary in a paleoshelf setting in Jordan (core OS-28), clearly marked by a negative δ 13 C org excursion and the occurrence of characteristic “excursion taxa” (e.g., Discoaster araneus , Rhomboaster spp., Coccolithus bownii ). While this section suffers from intense dissolution at the onset of the event and the peak of the isotopic excursion, it retains well-preserved, diverse nannofossil assemblages from the pre-PETM, PETM recovery and post-PETM intervals. These assemblages are dominated by two taxa of inferred mesotrophic affinities ( Coccolithus pelagicus , Toweius spp.) and show only low abundances of oligotrophic taxa ( Discoaster spp., Fasciculithus spp., Sphenolithus spp.). Overall, there appear to be only relatively low-level changes in the general assemblage composition across the PETM. During the post-PETM, however, there was a gradual decrease in relative abundance of C. pelagicus and Toweius spp. This decline co-coccured with a relative increase of Coccolithus bownii and Coccolithus foraminis , and in its later phase was accompanied by an increase in the relative abundance of Sphenolithus spp. These changes, indicate a possible shift towards less fertile conditions following the hyperthermal event. The relatively muted signal of biotic change associated with the PETM interval at this site was partly a consequence of poor preservation within the key sequence of the studied core. On the other hand, the low signal may also be indicative for local environment processes, such as variations in riverine sourced nutrients, salinity, turbidity. Operating on a regional scale, these local factors overrode the direct and indirect temperature signals that are the dominant control on nannofossil communities across the PETM in open ocean sites. Finally, the assemblages from the Jordan section highlight further the overall spatial heterogeneity in reported responses of shelf area communities to the PETM interval. These heterogeneities have been observed in shelf assemblages from Tanzania, New Jersey and the Tethyan margins, which again points to the strong influence of regional controls like river input in more marginal settings.

A massive input of coarse-grained siliciclastics in the Pyrenean Basin during the PETM: the missing ingredient in a coeval abrupt change in hydrological regime

Abstract. The Paleocene–Eocene thermal maximum (PETM) is represented in numerous shallow and deep marine sections of the south–central and western Pyrenees by a 2–4 m thick unit (locally up to 20 m) of clays or marly clays intercalated within a carbonate-dominated succession. This unit records a massive input into the Pyrenean Gulf of fine-grained terrestrial siliciclastics, attributed to an abrupt hydrological change during the PETM. However, the nature of such a change remains controversial. Here we show that, in addition to fine-grained deposits, large volumes of coarse-grained siliciclastics were brought into the basin and were mostly accumulated in incised valleys and in a long-lived deep-sea channel. The occurrence of these coarse-grained deposits has been known for some time, but their correlation with the PETM is reported here for the first time. The bulk of the incised valley deposits in the PETM interval are cross-bedded sands and pebbly sands, almost exclusively made of quartz. The criteria for indicting a relation to the PETM include their stratigraphic position between upper Thanetian and lower Ilerdian marine carbonates, organic carbon isotope data, and a high percentage of kaolinite in the clay matrix. The axially flowing deep-sea channel existed throughout Paleocene times in the Pyrenean Basin, within which coarse-grained calciclastic and siliciclastic turbidites were accumulated. This Paleocene succession is capped by thickly bedded quartz sandstones and pebbly sandstones, probably deposited by hyperpycnal flows, which are here assigned to the PETM based on their stratigraphic position and organic carbon isotopic data. The large and simultaneous increase in coarse- and fine-grained terrestrial siliciclastics delivered to the Pyrenean Gulf during the PETM is attributed to an increased intra-annual humidity gradient. During the PETM a longer and drier summer season facilitated the erosion of landscapes, whereas a dramatic enhancement of precipitation extremes during the wet season led to intensified flood events, with rivers carrying greater volumes of both bed and suspended loads. This scenario argues against the possibility that PETM kaolinites indicate a coeval warm and humid climate in northern Spain. Instead, the kaolinite reflects the erosion of thick Cretaceous lateritic profiles developed on the Hercynian basement.

Calcareous Nannofossils Boistratigraphy and Paleoecology of the Late Paleocene/Early Eocene of Wadi Nukhul, Westcentral Sinai, Egypt

The calcareous nannofossil biozones NP7/8 through NP12 were identified from the Esna and base of the Thebes formations at Wadi Nukhul, westcentral Sinai. The Subzone NP9a spans the lower part of Esna Formation. The Zone NP10 is easily differentiated into 4 subzones (a-d). The NP9/NP10 zonal boundary can be identified at the level of increase frequency of Neochiastozygus junctus. Zone NP11 occupies the topmost part of the Esna Formation and the base of the Thebes Formation indicating conformable relation between them. The Paleocene/Eocene boundary is traced between the NP9a/NP9b subzonal boundary which is marked by the first- appearances of Rhomboaster spp. It is located at the basal part of the Esna Formation and conforms lithologic change from blackish calcareous shale to brown calcarenite. On the basis of nannofossils, the Paleocene Eocene Thermal maximum (PETM) interval can be divided into two parts (lower and upper). The major assemblage shift across the P/E boundary suggests a change from colder, more productive surface waters to warmer, more oligotrophic conditions. Above the PETM interval, the niche of Fasciculithus spp. was filled by Neochiastozygus juncts and Rhabdolithus solus, the cooler and more eutrophic taxa.

Biostratigraphy and Geochemistry of Upper Paleocene - lower Eocene Oceanic Red Beds from the Zagros Mountains, SW Iran

Oceanic Red Beds studied are well known in the upper Cretaceous (CORBs, i.e. Cretaceous Oceanic Red Beds), but their presence and genesis have hitherto not been intensively discussed for equivalent Paleogene deposits. We describe a red to purple shale interval from the Pabdeh Formation, Zagros basin, Iran, which can be assigned to Late Paleocene to Early Eocene age, nannofossil zones NP9-NP12. Parts of the purple marl interval within NP9/NP10 coincide with the PETM (Paleocene-Eocene Thermal Maximum) interval. Coccolithus pelagicus, Sphenolithus moriformis, Sphenolithus orphanknollensis, and Toweius ssp. are dominant in nannofossil assemblages in this interval, and PETM event taxa such as Discoaster araneus appear. Based on whole rock geochemistry and microfossil assemblages, the red to purple marls were deposited in an oligotrophic environment with low nutrient (Ba) values, and were accompanied by a shift to more oxic conditions and low amount of TOC in an oceanic basin. Low amount of major elements like Si, Al and Fe indicates low terrestrial input and relatively high amount of CaO (biogenic element) emphasizes the open sea and pelagic deposition of the shale. Warm deep water can be inferred by the presence of the dinoflagellate taxa Impagidinium and nannoplankton taxa, Discoaster. As a result, the purple shale can be considered as typical Paleogene ORBs in the Zagros basin deposited under very similar conditions as well studied Tethyan Cretaceous oceanic red beds.

Calcareous nannofossils of the Paleocene–Eocene transition in four sections from Egypt

A detailed analysis of calcareous nannofossil assemblages was carried out across the Paleocene-Eocene transition in four outcrops in Egypt (the Gebel Matulla, Markha, El-Quss Abu Said, and Gebel Duwi sections) that span the Discoaster multiradiatus (NP9) to Discoaster binodosus (NP11) zones. The Paleocene-Eocene (P/E) boundary is placed in the lower part of the Esna Shale Formation based on the LOs of the Calcareous Nannofossil Excursion Taxa (CNET or RD) that define the base of NP9b. The studied sections are considered complete and document the Paleocene-Eocene Thermal Maximum (PETM). The occurrences of long-armed and asymmetrical discoasters (e.g., D. araneus, D. anartios) and rhomboasters (e.g., R. intermedia, R. bitrifidia, and R. spineus) are characteristic of the PETM interval. A sharp decrease in the diversification of Fasciculithus is noted at the onset of PETM. The abundance of Zygrhablithus bijugatus increases and corresponds with the dramatic decline in the oligotrophic Fasciculithus above the Paleocene/Eocene boundary and appears to be a significant global event. The Discoaster, Fasciculithus, and Rhomboaster species reflect relatively warm and, probably, oligotrophic surface waters. A minor hiatus in most of the studied sections near the upper part of Zone NP10 has been recorded in many parts of the world and reflects a global sea level drop.

MANGANESE-BEARING RHIZOCRETIONS IN THE WILLWOOD FORMATION, WYOMING, U.S.A.: IMPLICATIONS FOR PALEOCLIMATE DURING THE PALEOCENE-EOCENE THERMAL MAXIMUM

Changes in the stratigraphic distribution of manganese (Mn)-bearing columnar structures interpreted as rhizocretions indicate a shift in paleohydrological conditions in the Bighorn Basin during the Paleocene–Eocene Thermal Maximum (PETM). While most studies agree that significant warming occurred during the PETM, interpretations differ as to the effects of warming on the paleohydrologic regime. The columns consist of sand and silt cemented by calcite that also contains black, Mn-bearing nodules. The rhizocretions are typically vertically oriented and range from a few cm to over 50 cm in diameter and up to 75 cm tall. They are interpreted to have formed in the rhizospheres of relatively large root systems. The rhizocretions are restricted to intervals, showing only weak paleopedogenic development, that are interpreted as crevasse-splay or avulsion deposits. While such deposits are present throughout the study section at Polecat Bench in the northern Bighorn Basin, Wyoming, the Mn-bearing rhizocretions are found only below and above the PETM interval and within the initial carbon isotope excursion (CIE) marking the onset of the PETM. The abundance of black, Mn-rich nodules (< 1 cm in diameter) in the rhizocretions and presence of other pedogenic features indicate that the soils in which the plants were growing underwent seasonal flooding and repeated redox alternations. Their distribution in similar host deposits throughout the study interval, except for the main body of the PETM, supports climate as the driving factor in preservation of the Mn-bearing rhizocretions. The Mn-bearing rhizocretions support recent studies that suggest transient drying in northern Wyoming during the PETM.

Toward a better understanding of Paleocene-Eocene Thermal Maximum: A multidisciplinary record from Dababiya GSSP, Luxor, Egypt

The Paleocene-Eocene thermal maximum (PETM) shows an extraordinary drop in both δ 13 Ccarb and δ 13 Corg values, suggesting that a massive amount of 12 C-rich carbon dioxide was released into the atmosphere in a very short time (on the order of few hundred ky). The Dababiya GSSP (Luxor, Egypt) is thought to be the most complete known PETM section. The expanded sedimentary record of the Dababiya GSSP improves our understanding of the processes leading to the PETM events. Our multiproxy dataset, which includes geochemistry, mineralogy, micropaleontology and sedimentology, provided the following crucial clues for the PETM interval at Dababiya GSSP (Fig. 1). The Dababiya GSSP is deposited in the deepest part of an asymmetric submarine channel as indicated by the paleotopography, and absence of uppermost Paleocene and lowermost Eocene sediments from the Eastern section located 25m away from the main GSSP outcrop (Fig.1). At 50 m to the NW, the sediment beds thin out and finally disappear at about 150 m from the main GSSP outcrop. Thus, the Dababiya GSSP represents a localized expanded PETM sequence with a maximum extent of about 200m. At the GSSP, the PaleoceneEocene boundary (PEB) coincides therefore with a sequence Toward a better understanding of Paleocene-Eocene Thermal Maximum: A multidisciplinary record from Dababiya GSSP, Luxor, Egypt

The Paleocene-Eocene thermal maximum in the Arctic Beaufort-Mackenzie Basin -- Palynomorphs, carbon isotopes and benthic foraminiferal turnover

Abstract Examination of samples from exploration wells in the Arctic Beaufort-Mackenzie Basin has resulted in the documentation of the global Paleocene-Eocene thermal maximum (PETM) interval in 6 out of 12 wells examined. The PETM, a brief period of extreme global warming at about 55 Ma, occurs within the upper part of the deltaic-influenced Aklak Sequence. The PETM was recognized primarily by the occurrence of the dinoflagellate cyst Apectodinium augustum — globally associated with the PETM. Thermophilic pollen, e.g. Intratriporopollenites (Tilia) and Platycaryapollenites, are also associated with the PETM in the Beaufort-Mackenzie Basin wells. Carbon isotope analyses from one well, Natiak O-44, indicate a carbon isotope (δ13C) excursion of about −0.72‰ associated with the A. augustum acme. This excursion is low relative to continental settings for the PETM, but closer to some oceanic values. In Natiak O-44, the PETM interval is unusually thick, at about 100 m. This is consistent, however, with rapid deltaic sedimentation of the Aklak Sequence (nearly 5 km thick). A comparison of palynological and foraminiferal data indicates that the index foraminifera Reticulophragmium boreale becomes extinct at approximately the PETM interval. Furthermore, there is a pronounced foraminiferal turnover at or near the PETM. The turnover is apparently of circum-Arctic extent and caused by the extreme global warming and oceanic change of the Paleocene-Eocene transition. Recognition of the PETM in the Beaufort-Mackenzie Basin provides an important chronostratigraphic datum in complex deltaic sediments that are typically difficult to date precisely.

Unraveling the Paleocene-Eocene thermal maximum in shallow marine Tethyan environments: the Tunisian stratigraphic record

Despite the increasing understanding of the Paleocene-Eocene thermal maximum (PETM) in open marine environments, shallow marine settings remain relatively unexplored. We investigated an upper Paleocene to lower Eocene shallow-water sequence near Kalaat Senan in Tunisia (Sidi Nasseur and Wadi Mezaz sections) in order to generate a stratigraphic framework of the PETM in a shallow marine fine-grained siliciclastic setting of the Southern Tethys. These sections expose the top part of the El Haria Formation (Fm.), the Chouabine Fm. and the lower part of the limestone bearing El Garia Fm., covering the upper Paleocene- lower Eocene (NP9a to NP11). The PETM interval is situated near the top of the El Haria Fm. and the re- gional stratigraphy is compared to the well-known Egyptian setting. The isotope record of total organic car- bon (δ 13 Corg) reveals the characteristic negative carbon isotope excursion (CIE), comparable to the δ 13 Corg record of the Global Boundary Stratotype Section and Point of the Eocene at Dababiya (Egypt). Although the Tunisian PETM interval is quite expanded, no anomalous beds are observed and only the CIE core is part- ly represented as the top part of the PETM is truncated. In addition to a well-expressed CIE, the position of the Paleocene-Eocene boundary is supported by the appearance of nannoplankton (Discoaster araneus) and foraminiferal (e. g. Acarinina multicamerata) marker taxa. Furthermore, ostracode and benthic foraminifer- al turnovers coincide with the onset of the PETM and are characterized by the disappearance of many com- mon Paleocene taxa (e. g. Frondicularia aff. phosphatica) in this area. The lowest occurrences of Alo- copocythere attitogonensis and Buntonia? tunisiensis (ostracodes), Reophax sp. 1 (benthic foraminifera) and Fasciculithus tonii (calcareous nannoplankton) may be applicable for regional correlation. These results in- dicate that characteristic PETM taxa evolved and/or dispersed immediately after the main δ 13 Corg shift.

Dwarfing of ostracodes during the Paleocene–Eocene Thermal Maximum at DSDP Site 401 (Bay of Biscay, North Atlantic) and its implication for changes in organic carbon cycle in deep-sea benthic ecosystem

The Paleocene–Eocene Thermal Maximum (PETM) has been held up as a past analog to future environmental change and presents the opportunity to study climate impacts on marine communities. During the PETM, deep-sea benthic foraminifers decreased their body-size and increased their productivity, metabolic rates, and food consumption in response to abruptly increasing temperature and changing surface water productivity. Here we find that three species of marine ostracodes – part of the multicellular benthos – also experienced a reduction in body-size in response to PETM warming in the Northeast Atlantic. Positive correlations between ostracode body-size and benthic foraminiferal oxygen isotope data indicate that reduced body-sizes were caused by high temperature during the PETM. Dwarfing of ostracodes during the PETM interval suggests that their food consumption rates, and lifetimes, were less than those of ostracodes in the pre-PETM interval. This interpretation is based upon previous studies that show that food consumption and ostracode lifetimes both decrease as ostracodes increase their growth rates under higher temperatures. Estimates of body volume, temperature, and individual abundance suggest a decline in lifetime metabolic rate in ostracode individuals during the core of the PETM. In addition there is also a decrease in biomass flux in the whole ostracode community at this time. The decline in biomass flux at the community level suggests major changes in the energy flow and carbon cycling in deep-sea benthic ecosystem and the reduction of organic carbon flux between the ostracode community and sediments during the PETM. The decline in ostracode carbon flux stands in contrast with previous interpretations that carbon cycling by benthic foraminifera increased during the PETM. Hence, our data suggest that the benthic community response to the PETM was not uniform between different taxonomic groups.

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.

Perturbation of a Tethyan coastal environment during the Paleocene–Eocene thermal maximum in Tunisia (Sidi Nasseur and Wadi Mezaz)

Despite the large number of studies on the Paleocene–Eocene thermal maximum (PETM), the knowledge of environmental and biotic responses in shallow marine environments remains quite poor. Benthic foraminiferal assemblages of the Sidi Nasseur and Wadi Mezaz sections in Tunisia were studied quantitatively and the paleoecologic interpretations provide new insights into the complex relationship between PETM global warming and perturbations of shallow marine settings. These sections expose upper Paleocene to lower Eocene shales and marls of the El Haria Formation up to the phosphate layers of the Chouabine Formation underlying the El Garia limestones. The Sidi Nasseur section contains a more complete and expanded Paleocene–Eocene boundary interval compared to Wadi Mezaz, although being truncated at the top. The Wadi Mezaz section contains a more complete post-PETM interval. The studied interval can be subdivided into a sequence of 4 biofacies, representing respectively a latest Paleocene biofacies, two PETM biofacies and one post-PETM Eocene biofacies.The latest Paleocene biofacies 1 consists of numerous calcareous benthic foraminifera (e.g. Anomalinoides midwayensis, Frondicularia aff. phosphatica and various Bulimina and Lenticulina species), abundant non-calcareous taxa (Haplophragmoides) and rare planktic foraminifera, indicating a slightly hypersaline eutrophic inner neritic to coastal environment, regularly interrupted by oxygen deficiency (moderate dysoxia). During the latest Paleocene, this highly productive environment shallowed as indicated by the increasing abundances of A. midwayensis. The variable dominance of non-calcareous agglutinated taxa in biofacies 1 indicates post-mortem dissolution effects. The TOC δ13Corg record reveals a sharp negative excursion, marking the base of the Eocene. In general, the absence of lithologic changes, an increasing sedimentation rate and absence of reworking indicate that the initial part of the PETM is complete and expanded in the Sidi Nasseur section. A sharp faunal turnover coincides with this negative δ13Corg excursion and is characterized by the disappearance or diminution of common Paleocene taxa in this area. During the PETM, benthic foraminifera are less abundant and consist of opportunistic non-calcareous taxa together with deeper dwelling (middle neritic) lagenids and buliminids (biofacies 2 and 3). Planktic foraminifera, dominated by flat-spired Acarinina (mainly A. multicamerata), become more abundant, as observed in many open marine sequences worldwide. All these faunal parameters suggest more stressed probably severe dysoxic sea floor conditions within a transgressive phase during the onset of the PETM. An estimation of the total duration of the Sidi Nasseur PETM interval is difficult to establish, yet the lack of recovery carbon isotope values suggests that the preserved PETM interval reflects only a part of the CIE “core”. The top of the PETM interval is truncated due to local (?) erosion during the early Eocene. The Eocene recovery fauna is mainly composed of Lenticulina and Stainforthia species (biofacies 4), indicating restricted coastal to hyposaline lagoonal eutrophic conditions, distinctly different from earlier environmental conditions.

Transient dwarfism of soil fauna during the Paleocene-Eocene Thermal Maximum.

Soil organisms, as recorded by trace fossils in paleosols of the Willwood Formation, Wyoming, show significant body-size reductions and increased abundances during the Paleocene-Eocene Thermal Maximum (PETM). Paleobotanical, paleopedologic, and oxygen isotope studies indicate high temperatures during the PETM and sharp declines in precipitation compared with late Paleocene estimates. Insect and oligochaete burrows increase in abundance during the PETM, suggesting longer periods of soil development and improved drainage conditions. Crayfish burrows and molluscan body fossils, abundant below and above the PETM interval, are significantly less abundant during the PETM, likely because of drier floodplain conditions and lower water tables. Burrow diameters of the most abundant ichnofossils are 30-46% smaller within the PETM interval. As burrow size is a proxy for body size, significant reductions in burrow diameter suggest that their tracemakers were smaller bodied. Smaller body sizes may have resulted from higher subsurface temperatures, lower soil moisture conditions, or nutritionally deficient vegetation in the high-CO(2) atmosphere inferred for the PETM. Smaller soil fauna co-occur with dwarf mammal taxa during the PETM; thus, a common forcing mechanism may have selected for small size in both above- and below-ground terrestrial communities. We predict that soil fauna have already shown reductions in size over the last 150 years of increased atmospheric CO(2) and surface temperatures or that they will exhibit this pattern over the next century. We retrodict also that soil fauna across the Permian-Triassic and Triassic-Jurassic boundary events show significant size decreases because of similar forcing mechanisms driven by rapid global warming.

Large terrestrial and marine carbon and hydrogen isotope excursions in a new Paleocene/Eocene boundary section from Tanzania

Recent onshore drilling expeditions in Tanzania have yielded sediments spanning much of the Late Cretaceous and Paleogene which show exceptionally good preservation of both calcareous microfossils and organic matter. The interval of the Paleocene–Eocene Thermal Maximum (PETM) was recovered at Tanzania Drilling Project (TDP) Site 14, in 2004. The PETM interval was identified using planktonic foraminifer and nannofossil biostratigraphy. Carbon isotopic measurements of planktonic foraminifera from the genus Subbotina show a maximum measured negative shift in δ 13C values of approximately 4.5‰, which is significantly larger than has been observed for most deep sea foraminifer records. Higher plant derived n-alkanes yield a ca. 6.5‰ negative shift through the same interval. As carbon isotope fractionation in higher plants varies amongst taxa and is influenced by humidity, it is possible that this remarkably large shift in the n-alkane δ 13C values records environmental and vegetation changes as well as changes in the δ 13C value of the ocean–atmosphere reservoir. However, dramatic increases in humidity appear to be unlikely as higher plant biomarker δD values shift to higher rather than lower values. Taken together, the records suggest that the magnitude of the carbon isotope excursion (CIE) in the ocean–atmosphere reservoir may have been larger than has generally been accepted. This has important implications for the source and quantity of 13C-depleted carbon released at the PETM.

Paleoclimatic Implications of Crayfish-Mediated Prismatic Structures in Paleosols of the Paleogene Willwood Formation, Bighorn Basin, Wyoming, U.S.A.

Abstract Paleosols at Polecat Bench, northern Bighorn Basin, Wyoming, show prismatic structures not previously described in the Paleogene Willwood Formation. Prisms are densely spaced 15–50 mm diameter cylinders with vertical to slightly sinuous paths up to 400 mm long, subangular to rounded vertical faces, and slightly concave to convex tops. Prism exteriors are coated commonly by < 1-mm-thick clay films; exteriors also commonly show knobby and striated surficial morphologies. Prismatic structures are nearly exclusive to thin-bedded (< 1 m thick) compound paleosols composed of red to red-purple sandy mudrock overlying gray to green-gray heterolithic units composed chiefly of fine-grained sandstone. In addition to prismatic structures, these paleosols are characterized by large gray mottles, slickensides, and calcareous rhizocretions which crosscut or more typically follow prism exteriors. The architectural and surficial morphology of the soil prisms suggest strongly that these are pedogenically modified freshwater crayfish burrows of the ichnospecies Camborygma litonomos. At Polecat Bench, an ~ 40 m interval of the Willwood Formation records a transient episode of global warming known as the Paleocene–Eocene Thermal Maximum (PETM). The PETM interval is characterized by a series of predominantly red, cumulative paleosol profiles and increased soil carbonates. Prismatic soil structures and crayfish burrows are rare or absent in cumulic paleosols typical of the PETM, whereas they are locally abundant in red compound paleosols outside the PETM interval. The changes in paleosol morphology and a sharp decrease in crayfish burrows within the PETM interval suggest significantly improved soil-drainage conditions and lower water tables on the Willwood floodplain during the global warming event.

Size variations of the calcareous nannofossil taxon Discoaster multiradiatus ( Incertae sedis) across the Paleocene–Eocene thermal maximum in ocean drilling program holes 690B and 1209B

Size measurements of the calcareous nannofossil taxon Discoaster multiradiatus were carried out across the Paleocene–Eocene Thermal Maximum (PETM) in Ocean Drilling Program Holes 690B (Maud Rise, Weddell Sea) and 1209B (Shatsky Rise, Pacific Ocean). Morphometric investigations show that D. multiradiatus specimens are generally larger at ODP Site 1209 than at ODP Site 690. A limited increase in size of D. multiradiatus is recorded at ODP Site 1209, whereas significant enlargements characterize ODP Site 690. Preservation is comparable at both sites: nannofossils are moderately preserved with some evidence of etching/overgrowth in the PETM interval. Yet, D. multiradiatus variations do not correlate with preservation state and morphometric data most likely represent primary signals rather than diagenetic artifacts. There is a direct relationship between D. multiradiatus size and paleotemperatures: largest specimens are coeval with global warming associated with the PETM, inferred to result from excess atmospheric CO 2 due to (partial) oxidation of massive quantities of methane. Size increases and largest specimens of D. multiradiatus occur at different stratigraphic levels within PETM at ODP Sites 690 and 1209. A marked shift in diameter size was observed at the onset and peak of the Carbon Isotopic Excursion (CIE) at ODP Site 690, but only at the end of CIE and initial recovery interval at ODP Site 1209. This diachroneity is puzzling, but indeed correlates well with reconstructed changes in surface and thermocline water masses temperature and salinity in the PETM interval at low and high latitudes. The presumed high concentrations of carbon dioxide seem to have not influenced the morphometry of D. multiradiatus. The major size increase of D. multiradiatus in the CIE of ODP Site 690 could represent the migration of larger-sized allochtonus specimens that moved from peri-equatorial/subtropical areas to higher latitudes during the warmest interval of the PETM, although no direct evidence of distinct populations/subpopulations has been obtained from the frequency diagrams. As a result, we infer that D. multiradiatus is a proxy of water masses stratification and might be used for deriving temperature–salinity–nutrient conditions in the mixed layer and thermocline and their dynamics.

Relationship of Floodplain Ichnocoenoses to Paleopedology, Paleohydrology, and Paleoclimate in the Willwood Formation, Wyoming, During the Paleocene-eocene Thermal Maximum

Vertical changes in distribution, abundance, and ichnodiversity of ichnocoenoses in alluvial deposits of the Willwood Formation suggest significantly drier moisture regimes in the Bighorn Basin, Wyoming, during the Paleocene–Eocene Thermal Maximum (PETM), a transient period of global warming. The Willwood Formation at Polecat Bench contains an abundant assemblage of ichnofossils, including various types of rhizoliths and invertebrate trace fossils, such as Naktodemasis bowni, Camborygma litonomos, Edaphichnium lumbricatum, cf. Cylindricum isp., cf. Planolites isp., cf. Steinichnus, and cocoon traces. These comprise six distinct ichnocoenoses, which are categorized as dominantly terraphilic, hygrophilic, or hydrophilic based on the inferred moisture regimes of their most abundant ichnofossil morphotypes and associated pedogenic features, including other trace fossils and rhizoliths. The interpreted moisture regimes correlate well with the paleoenvironments of their host lithofacies, as inferred from sedimentology and paleopedology. Outside the PETM interval at Polecat Bench, abundant avulsion deposits and thin, compound paleosols containing hygrophilic and hydrophilic ichnocoenoses suggest frequent depositional events and predominantly poor to imperfect soil-drainage conditions. Within the PETM interval, thick, cumulative paleosol profiles with abundant terraphilic to hygrophilic ichnocoenoses suggest significantly improved drainage conditions. Lithofacies and ichnocoenoses above the PETM interval are not significantly different from those below the interval, indicating a return to pre-PETM moisture regimes. These conclusions support previous studies that suggest the Bighorn Basin experienced transient drying during this interval. This study demonstrates that ichnocoenoses and their ichnopedologic associations can be used to refine paleohydrologic and paleoclimatic generalizations inferred from paleoclimate models.

Transient drying during the Paleocene–Eocene Thermal Maximum (PETM): Analysis of paleosols in the bighorn basin, Wyoming

The Paleocene Eocene Thermal Maximum (PETM) was a transient episode of global warming that occurred at the Paleocene/Eocene boundary. The event is marked by a sharp decline in carbon isotope values that is globally recognized from marine and continental sections. The negative isotope excursion has been attributed to the release of methane hydrates from oceanic sediments. Although studies concur that temperatures rose during the PETM, changes in precipitation are not well understood. Alluvial paleosols in the Bighorn Basin that span the PETM interval contain a continuous and highly resolved record of climate including information on precipitation. They show a significant but transient decrease in precipitation at the onset of the PETM but a gradual return to pre-PETM levels by the end of the interval. The paleosols also show additional, although less dramatic, wet/dry cycles within the PETM interval that may correspond to precessional cycles that have been identified in the marine record of the PETM. This study counters interpretations of increased precipitation for Wyoming at this time and shows the importance of detailed case studies of continental strata to test climatic generalizations and models that have been developed for PETM precipitation patterns.

Nannofossil assemblage fluctuations during the Paleocene–Eocene Thermal Maximum at Sites 213 (Indian Ocean) and 401 (North Atlantic Ocean): palaeoceanographic implications

The Paleocene–Eocene Thermal Maximum (PETM) was an abrupt global warming event at ∼55 Ma. This event had profound effects on the biosphere. Quantitative investigations of calcareous nannofossil assemblages were performed across the PETM, at Deep Sea Drilling Project Site 213, in the tropical Indian Ocean, and Site 401, in the Bay of Biscay, North Atlantic Ocean, at a temperate latitude. Calcareous nannofossil assemblages from both sites show major changes before, during, and after the PETM. Fluctuations at Site 213 are affected by selective dissolution of the least robust taxa. By contrast, assemblages in the lower part of the PETM at Site 401 show less diagenetic alteration and display high abundances of genera such as Discoaster, Fasciculithus, and Ericsonia. These taxa reflect relatively warm and, probably, oligotrophic surface waters. Abundances of the genus Chiasmolithus, an indicator of relatively cool and eutrophic waters, decreased dramatically. The upper portion of the PETM is characterized by an increase in the abundance of Toweius spp. and Zygrhablithus bijugatus, interpreted as a return to cooler and more eutrophic conditions. The elimination of Fasciculithus was probably due to competition with the holococcolith species, Z. bijugatus, which occupied the same ecological niche. The occurrences of long-armed and asymmetrical Discoaster species such as Discoaster araneus, Discoaster anartios, and Discoaster okadai, and Rhomboaster species, such as Rhomboaster calcitrapa and Rhomboaster cuspis, are characteristic of the PETM interval.