Eocene Boundary Research Articles

Eocene to Oligocene high paleolatitude neritic record of Oi-1 glaciation in the Otway Basin southeast Australia

Multiple stable isotope investigations from upper Eocene to lower Oligocene deep-water marine sequences record the transition from global greenhouse to the icehouse conditions (Oi-1 glacial). While Southern Ocean high latitude deep sea records of this transition are well known, their shallow marine equivalents are rare and have the potential to record the eustatic and oceanic consequences of Paleogene glacial variability. The well-known high paleolatitude (~55°S) neritic carbonate sequence at Browns Creek and Castle Cove in the Otway Basin in southeast Australia spans the Eocene-Oligocene boundary. During this time the area lay on the northeastern margin of the Australo-Antarctic Gulf facing the evolving Southern Ocean. The importance of this record has been hampered by a lack of a consistent stratigraphy and contradictory microfossil interpretations. To reconcile these issues we combine new bio-, chemo- and lithostratigraphic analyses of the outcrops and a new core (Colac-2) with pre-existing data to revise the stratigraphy. This confirms the middle/upper Eocene boundary is near the base of the section. The overlying upper Eocene siliciclastic strata are truncated by an unconformity (of ~0.8 Ma in duration) and overlain by glauconitic sand (the Notrostrea greensand) deposited after ~35.9 Ma. Subsequently deepening to middle to outer neritic depths deposited cyclic carbonates. Shallowing after ~35 Ma deposited laterally variable calcareous siliciclastic facies. These strata were tilted and eroded prior to 34 Ma leading to shallow water facies that may have been subaerially exposed during uplift. Brachiopod strontium isotope dates and an 0.5‰ carbon isotope excursion above this unconformity suggests the top of the Browns Creek and the base of the Castle Cove section correlate to Eocene-Oligocene transition (EOT-1) at ~34 Ma. The subsequent persistence of positive C/O isotope values above this level records the transition to the Oi-1 glaciation at ~33.7 Ma. Strong cyclicity in the inner shelf Castle Cove limestone is interpreted to record the commencement of obliquity dominated glacio-eustacy during the Oi-1 glacial phase. The shallowing from outer to inner shelf palaeodepths from the late Eocene to the early Oligocene is likely related to the onset of cryosphere expansion, however, palaeodepth estimates are complicated by the onset of regional compressional tectonism at the Eocene/Oligocene boundary that caused localized tilting and an unconformity with possible antisiphoning effects in this near-field site.

Phylogeny and biogeography of Pachygoneae (Menispermaceae), with consideration of the boreotropical flora hypothesis and resurrection of the genera Cebatha and Nephroia

The tribe Pachygoneae consists of four genera with about 40 species, primarily distributed in tropical and subtropical Asia and America, also in Australasia and Africa. This tribe presents an ideal model to investigate the origin of the tropical and subtropical amphi-Pacific disjunction pattern. More specifically, it allows us to test whether the tropical lineages diverged earlier than the subtropical ones during the fragmentation of the boreotropical flora. In this study, we reconstructed the phylogeny of Pachygoneae using five plastid (rbcL, atpB, matK, ndhF, trnL-F) and one nuclear (26S rDNA) DNA regions. Our results indicate that Pachygoneae is not monophyletic unless Cocculus pendulus and Cocculus balfourii are excluded. We resurrected the genus Cebatha to include these two species and established a new tribe for this genus. Within Pachygoneae, the species of Cocculus are distributed in three different clades, among which two are recognized as two distinct genera, Cocculus s.str. and Nephroia resurrected, and one species is transferred into Pachygone. Our molecular dating and ancestral area reconstruction analyses suggest that Pachygoneae began to diversify in tropical Asia around the early-middle Eocene boundary (c. 48 Ma) and expanded into the New World by c. 44 Ma. In the New World, tropical Hyperbaena originated in the late Eocene (c. 40 Ma), whereas the subtropical Cocculus carolinus and Cocculus diversifolius originated later, in the early Oligocene (c. 32 Ma). These two timings correspond with the two climatic cooling intervals, which suggests that the formation and breakup of the boreotropical floral may have been responsible for the amphi-Pacific disjunct distribution within Pachygoneae. One overland migration event from Asia into Australasia appears to have occurred in the early to late Miocene.

Stratigraphy and paleoenvironment of the Lower-Middle Eocene succession in the Darnah area, northeast Libya

The stratigraphy and paleoenvironment of the Lower-Middle Eocene Apollonia Formation exposed at the northeastern and southern parts of Darnah city, northeast Libya, was studied in detail by means of foraminifera, where rich benthic and planktonic foraminiferal assemblages were recorded. Fifty-seven planktonic foraminiferal species and subspecies belonging to nineteen genera and seven families were identified and seventy-five benthic species and subspecies belonging to thirty-five genera and twenty-three families. The stratigraphic distribution of the recorded fauna in three selected surface sections enabled us to subdivide the studied succession into six planktonic and two benthic zones covering a time interval ranging from the Early to Middle Eocene. The planktonic zones were arranged from base to top as follows: Morozovella edgari, Morozovella subbotinae, Morozovella aragonensis, Acarinina pentacamerata (Early Eocene), Acarinina bullborooki and Globigerinatheka subconglobata subconglobata (Middle Eocene). The benthic zones are represented by the Anomalinoides trinitatensis (Early Eocene) and Bulimina jacksonensis (Middle Eocene). The established zones were discussed and correlated with the international standard zones and with those from neighbouring North Africa and Middle East countries. The Lower/Middle Eocene (Ypresian/Lutetian) boundary was discussed based on the zonal boundaries. The statistical analysis of the identified foraminiferal assemblages for each sample as well as the lithologic characteristics of the Apollonia Formation indicated marine middle to outer neritic setting. The high ratio of the calcareous foraminiferal assemblages and the moderate epifaunal/infaunal ratio reflect deposition in an environment of high calcium carbonate, normal salinity and low to moderate oxygenation levels.

A new stratigraphic framework and constraints for the position of the Paleocene–Eocene boundary in the rapidly subsiding Hanna Basin, Wyoming

AbstractThe Paleocene–Eocene strata of the rapidly subsiding Hanna Basin give insights in sedimentation patterns and regional paleogeography during the Laramide orogeny and across the climatic event at the Paleocene–Eocene Thermal Maximum (PETM). Abundant coalbeds and carbonaceous shales of the fluvial, paludal, and lacustrine strata of the Hanna Formation offer a different depositional setting than PETM sections described in the nearby Piceance and Bighorn Basins, and the uniquely high sediment accumulation rates give an expanded and near-complete record across this interval. Stratigraphic sections were measured for an ∼1250 m interval spanning the Paleocene–Eocene boundary across the northeastern syncline of the basin, documenting depositional changes between axial fluvial sandstones, basin margin, paludal, floodplain, and lacustrine deposits. Leaf macrofossils, palynology, mollusks, δ13C isotopes of bulk organic matter, and zircon sample locations were integrated within the stratigraphic framework and refined the position of the PETM. As observed in other basins of the same age, an interval of coarse, amalgamated sandstones occurs as a response to the PETM. Although this pulse of relatively coarser sediment appears related to climate change at the PETM, it must be noted that several very similar sandstone bodies occur with the Hanna Formation. These sandstones occur in regular intervals and have an apparent cyclic pattern; however, age control is not sufficient yet to address the origin of the cyclicity. Signs of increased ponding and lake expansion upward in the section appear to be a response to basin isolation by emerging Laramide uplifts.

Carbon isotope and mammal recovery from extreme greenhouse warming at the Paleocene–Eocene boundary in astronomically-calibrated fluvial strata, Bighorn Basin, Wyoming, USA

Massive addition of isotopically-depleted carbon to the ocean and atmosphere caused a carbon isotope excursion (CIE) and global greenhouse warming during the Paleocene–Eocene Thermal Maximum (PETM) circa 56 million years ago. The body of the CIE is followed by a recovery interval that is key to understanding Earth's capacity for carbon uptake, mechanisms of carbon uptake, and biotic responses following an extreme greenhouse warming event. Expanded terrestrial stratigraphic sections in the Bighorn Basin of Wyoming provide exceptionally high-resolution records of the CIE and can be linked directly to the mammalian fossil record.Here, we provide carbon isotope records of unprecedented resolution measured on in-situ pedogenic carbonate nodules in two parallel 8-km-spaced sections of upper Paleocene and lower Eocene fluvial sediments in the northern Bighorn Basin. We find consistent precession-driven sedimentary cycles in the two sections. Cycle thicknesses show significant lateral, and thus vertical, variation, demonstrating that astronomical age models constructed for fluvial successions require detailed sedimentary facies analysis of parallel sites.Plotting the high-resolution carbon isotope records in time using our astronomical age model for the correlated sections indicates a CIE body duration of 101 ± 9 kyr. The CIE shows an initial recovery step of +2.7 ± 1.0‰. This step occurs across the single, well-developed paleosol marker bed known as Purple-4, which represents a time interval of up to 15 kyr. The rapidity of recovery at the end of the CIE body is remarkable in light of existing hypotheses for carbon removal from the ocean–atmosphere system. Concurrent mammal finds show that the transition from faunal zone Wa-0 to faunal zone Wa-1 occurred in two steps, with a transitional Wa-R fauna preceding the CIE initial recovery step and Wa-1 fauna following the step.

Plant and insect herbivore community variation across the Paleocene-Eocene boundary in the Hanna Basin, southeastern Wyoming.

Ecosystem function and stability are highly affected by internal and external stressors. Utilizing paleobotanical data gives insight into the evolutionary processes an ecosystem undergoes across long periods of time, allowing for a more complete understanding of how plant and insect herbivore communities are affected by ecosystem imbalance. To study how plant and insect herbivore communities change during times of disturbance, we quantified community turnover across the Paleocene­–Eocene boundary in the Hanna Basin, southeastern Wyoming. This particular location is unlike other nearby Laramide basins because it has an abundance of late Paleocene and Eocene coal and carbonaceous shales and paucity of well-developed paleosols, suggesting perpetually high water availability. We sampled approximately 800 semi-intact dicot leaves from five stratigraphic levels, one of which occurs late in the Paleocene–Eocene thermal maximum (PETM). Field collections were supplemented with specimens at the Denver Museum of Nature & Science. Fossil leaves were classified into morphospecies and herbivore damage was documented for each leaf. We tested for changes in plant and insect herbivore damage diversity using rarefaction and community composition using non-metric multidimensional scaling ordinations. We also documented changes in depositional environment at each stratigraphic level to better contextualize the environment of the basin. Plant diversity was highest during the mid-late Paleocene and decreased into the Eocene, whereas damage diversity was highest at the sites with low plant diversity. Plant communities significantly changed during the late PETM and do not return to pre-PETM composition. Insect herbivore communities also changed during the PETM, but, unlike plant communities, rebound to their pre-PETM structure. These results suggest that insect herbivore communities responded more strongly to plant community composition than to the diversity of species present.

Arctic closure as a trigger for Atlantic overturning at the Eocene-Oligocene Transition

The Eocene-Oligocene Transition (EOT), approximately 34 Ma ago, marks a period of major global cooling and inception of the Antarctic ice sheet. Proxies of deep circulation suggest a contemporaneous onset or strengthening of the Atlantic meridional overturning circulation (AMOC). Proxy evidence of gradual salinification of the North Atlantic and tectonically driven isolation of the Arctic suggest that closing the Arctic-Atlantic gateway could have triggered the AMOC at the EOT. We demonstrate this trigger of the AMOC using a new paleoclimate model with late Eocene boundary conditions. The control simulation reproduces Eocene observations of low Arctic salinities. Subsequent closure of the Arctic-Atlantic gateway triggers the AMOC by blocking freshwater inflow from the Arctic. Salt advection feedbacks then lead to cessation of overturning in the North Pacific. These circulation changes imply major warming of the North Atlantic Ocean, and simultaneous cooling of the North Pacific, but no interhemispheric change in temperatures.

Species of the diatom taxa <i>Aulacodiscus</i> and <i>Trinacria</i> with biostratigraphic utility in Palaeogene and Neogene North Sea sediments

Abstract. Species of Aulacodiscus and Trinacria, two important marine diatom genera with biostratigraphic utility in offshore North Sea exploration and onshore correlation, are identified, described and emended and the North Sea microfaunal zonation scheme is revised accordingly. Occurring mainly as pyritised diatom moulds or steinkerns, detailed scanning electron microscope (SEM) analysis of several specimens, formerly in open nomenclature, has allowed the correct taxonomic identification of pyritised morphologies found to belong to the genus Aulacodiscus, including A. allorgei, A. heterostictus, A. insignis, A. singilewskyanus, A. subexcavatus and A. suspectus. The important marker species Trinacria regina is emended. SEM studies, using specimens preserved in pyrite and original silica, have shed further light on the varying forms and frustule morphology of Trinacria regina so that valves and frustules formerly thought to represent separate species are now found to be grouped within this taxon; SEM studies have shown that many of these variations represent different valves within a chain, whilst others may signify ecophenotypic variants. Emendments are therefore made to clarify the taxonomic status of different variants within T. regina, important in the Palaeocene–Eocene boundary interval onshore and offshore such as the Sele and Balder formations and the Fur Formation diatomite of Jutland, Denmark. Species of taxa formerly in open nomenclature are now assigned to Aulacodiscus insignis, which are important offshore markers in offshore late Oligocene to early Miocene sediments in northwest Europe.

Eocene Paleoseismodislocations of Mount Ak-Kaya (Belogorsk District, Crimea)

The peculiarities of the structure of Cretaceous–Eocene boundary deposits in the Belogorsk district, Central Crimea, are considered. Tectonic structures interpreted as paleoseismodislocations are revealed and described; their age, structures, and evolutionary history are characterized; the magnitude and intensity of the seismic paleoevent are estimated. The position of steeply dipping fractures in Cretaceous rocks is regular and related to the bedding along the dip and strike of the structure. Their formation was caused by transverse extension in the background of general uplift at the beginning of Eocene, coincided in time with the main folding phase in North Turkey.

The extraterrestrial impact evidence at the Palaeocene–Eocene boundary and sequence of environmental change on the continental shelf

We have identified clear evidence of an extraterrestrial impact within the onset of the carbon isotope excursion (CIE) that defines the Palaeocene-Eocene (P-E) boundary hyperthermal event (approx. 56 Ma) from several sites on the eastern Atlantic Coastal Plain and offshore. We review and update the state of the evidence for an impact at the P-E boundary, including a K-Ar cooling age of the ejecta that is indistinguishable from the depositional age at the P-E, which establishes the ejecta horizon as an isochronous stratigraphic indicator at the P-E. Immediately above the ejecta peak at the base of the coastal plain Marlboro Clay unit, we identify a sharp increase in charcoal abundance coincident with the previously observed dramatic increase in magnetic nanoparticles of soil pyrogenic origin. We therefore revisit the observed sequence of events through the P-E boundary on the western Atlantic Coastal Plain, showing that an extraterrestrial impact led to wildfires, landscape denudation and deposition of the thick Marlboro Clay, whose base coincides with the spherule horizon and CIE onset. The Sr/Ca ratio of the spherules indicates that the carbon responsible for the onset may be vaporized CaCO3 target rock mixed with isotopically light carbon from the impactor or elsewhere. Crucially, we do not argue that the impact was responsible for the full manifestation of the CIE observed globally (onset to recovery approx. 170 kyr), rather that a rapid onset was triggered by the impact and followed by additional carbon from other processes such as the eruption of the North Atlantic Igneous Province. Such a scenario agrees well with recent modelling work, though it should be revisited more explicitly.This article is part of a discussion meeting issue 'Hyperthermals: rapid and extreme global warming in our geological past'.

Paleo-environmental reconstructions of the Upper Cretaceous-Paleogene successions, Safaga, Egypt

The Late Cretaceous-Early Eocene sedimentary sequences in the Central Eastern Desert of Egypt were studied in three shallow boreholes (Wassief, Um El-Huaitat, and Mohamed Rabah). This study focuses on an integrated investigation of biostratigraphy, lithostratigraphy and some geochemical parameters, to provide important clues to the relative sea-level changes and to interpret the prevailed depositional conditions.Micropaleontological study on planktonic foraminifera allows to identify eight zones, ranging in age from Late Cretaceous to Early Eocene. Three hiatal surfaces have been recognized as evidenced by missing formaniniferal zones: The first spans the Late Maastrichtian-Danian regional unconformity. The second one is recorded in the Late Paleocene. The third one is located at the Late Paleocene-Early Eocene (Thanetian-Ypresian) boundary. The environments of the study foraminiferal parameters range from the non-marine to outer neritic-upper bathyal.Petrographically, thirteen Microfacies Types (MFT) have been recorded. Three MFTs constitute the siliciclastic facies; MFT-1; silty to sandy mudstone, MFT-2; organic-rich silty mudstone, and MFT-3; fine-grained sandstone/glauconite intercalations. Two MFTs represent a phosphorite facies which are MFT-4; phosclast packstone to phosclast grainstone and MFT-5; phosooid packstone to phosooid grainstone. Eight MFTs characterize the carbonate facies; MFT-6; non-fossiliferous lime-mudstone, MFT-7; phosphatic foraminiferal pack/grainstone, MFT-8; bioclastic foraminiferal packstone, MFT-9; bioclastic foraminiferal wackestone, MFT-10; glauconitic phosphatic foraminiferal Wack-Packstone, MFT-11; non-fossiliferous dolomitic mudstone, MFT-12; dolomitic glauconitic lime-mudstone, and MFT-13; dolomitic bioclastic wackestone. The depositional environments of the study microfacies range from the terrestrial to open marine outer neritic-upper bathyal.Geochemical parameters have been used to improve the litho- and biostratigraphic framework: the major oxides, TOC wt.% and the Chondrite-normalized REE. Based on the vertical distribution of CaO/P2O5, TiO2/CaO and cerium (Ce)-anomaly, changes in paleo-bottom water redox conditions were reconstructed and correlated with relative sea level changes. Prior to the major transgression during deposition of the Duwi Formation under reducing marine conditions, the prevailing oxic to sub-oxic bottom water terrestrial conditions during deposition of the Quseir Formation.

Ocean and climate response to North Atlantic seaway changes at the onset of long-term Eocene cooling

Around the early–middle Eocene boundary, the first occurrence of contourite drift sediments and widespread deep ocean erosion indicate changes in the North Atlantic ocean circulation. Interestingly, these changes coincide with the first steps of Cenozoic cooling from the Paleogene greenhouse climate towards the modern icehouse. The cause for this ocean circulation reorganization is poorly understood since modern water mass tracers may have worked fundamentally different in the past and the paleoceanographic proxy record is limited in both time and space. As a result, it is challenging to reliably reconstruct the climatic and tectonic boundary conditions e.g. atmospheric greenhouse gas concentration and the depth and geometry of developing and closing passages between ocean basins. In this study, we attempt to identify thresholds in tectonic gateway passages and atmospheric CO2 concentration, using the fully coupled Earth System Model COSMOS. Indeed, the simulation of Earth's past climates can unravel the physical processes driving deep-water formation in a greenhouse world. Specifically, we use COSMOS to evaluate the impact of changes in the North Atlantic gateways at the early–middle Eocene boundary on the North Atlantic Deep Western Boundary Currents under low obliquity configuration. We find that Northern Component Waters start to form when the Greenland Scotland Ridge reaches a threshold depth of deeper than 200 m, while the Arctic Ocean is still shut off from the North Atlantic. In this scenario, the relatively deep Greenland Scotland Ridge allows for sufficient inflow of warm, salty Atlantic surface waters into the Nordic Seas to initiate convection during winter cooling. Opening the seaway towards the Arctic leads to a cessation of Northern Component Water formation as it allows for inflow of brackish surface waters into the northern Nordic Seas, hindering Northern Component Water formation.

Foraminiferal response to the PETM recorded in the SW Tarim Basin, central Asia

The Paleocene/Eocene (P/E) boundary interval is the most significant climatic transition during the Cenozoic, when the PETM (Paleocene Eocene Thermal Maximum) caused rapid warming and severe fluctuation of the Earth system, especially in marine settings. The SW Tarim Basin represents a distal branch of the NE Tethys, exposing Paleocene to Eocene successions that include the Qimugen Formation and provide optimal section for investigating the P/E boundary transition. By detail field-based lithological records and the planktonic and benthic foraminiferal assemblage analysis, the P/E boundary was redefined within the black mudstone bed of the Qimugen Formation. The planktonic foraminiferal assemblages recorded in the Qimugen Formation may be subdivided into four biozones, including bioevents of Globanomalina pseudomenardii, Globanomalina luxorensis and Pseudohastigerina wilcoxensis. Planktonic foraminiferal turnover is marked by the cool water subbotinids disappearance, give way to warm water muricate taxa, co-varying with the gradual disappearance of benthic foraminifera. The foraminiferal assemblages together with other identified microfossils suggest a shallow marine environment in which transgressions related to the sea level fluctuation of the Tethyan Domain took place in the Paleocene to Eocene boundary interval.

Identification of the Paleocene–Eocene boundary in coastal strata in the Otway Basin, Victoria, Australia

Abstract. Detailed, stratigraphically well-constrained environmental reconstructions are available for Paleocene and Eocene strata at a range of sites in the southwest Pacific Ocean (New Zealand and East Tasman Plateau; ETP) and Integrated Ocean Discovery Program (IODP) Site U1356 in the south of the Australo-Antarctic Gulf (AAG). These reconstructions have revealed a large discrepancy between temperature proxy data and climate models in this region, suggesting a crucial error in model, proxy data or both. To resolve the origin of this discrepancy, detailed reconstructions are needed from both sides of the Tasmanian Gateway. Paleocene–Eocene sedimentary archives from the west of the Tasmanian Gateway have unfortunately remained scarce (only IODP Site U1356), and no well-dated successions are available for the northern sector of the AAG. Here we present new stratigraphic data for upper Paleocene and lower Eocene strata from the Otway Basin, southeast Australia, on the (north)west side of the Tasmanian Gateway. We analyzed sediments recovered from exploration drilling (Latrobe-1 drill core) and outcrop sampling (Point Margaret) and performed high-resolution carbon isotope geochemistry of bulk organic matter and dinoflagellate cyst (dinocyst) and pollen biostratigraphy on sediments from the regional lithostratigraphic units, including the Pebble Point Formation, Pember Mudstone and Dilwyn Formation. Pollen and dinocyst assemblages are assigned to previously established Australian pollen and dinocyst zonations and tied to available zonations for the SW Pacific. Based on our dinocyst stratigraphy and previously published planktic foraminifer biostratigraphy, the Pebble Point Formation at Point Margaret is dated to the latest Paleocene. The globally synchronous negative carbon isotope excursion that marks the Paleocene–Eocene boundary is identified within the top part of the Pember Mudstone in the Latrobe-1 borehole and at Point Margaret. However, the high abundances of the dinocyst Apectodinium prior to this negative carbon isotope excursion prohibit a direct correlation of this regional bio-event with the quasi-global Apectodinium acme at the Paleocene–Eocene Thermal Maximum (PETM; 56 Ma). Therefore, the first occurrence of the pollen species Spinizonocolpites prominatus and the dinocyst species Florentinia reichartii are here designated as regional markers for the PETM. In the Latrobe-1 drill core, dinocyst biostratigraphy further indicates that the early Eocene (∼ 56–51 Ma) sediments are truncated by a ∼ 10 Myr long hiatus overlain by middle Eocene (∼ 40 Ma) strata. These sedimentary archives from southeast Australia may prove key in resolving the model–data discrepancy in this region, and the new stratigraphic data presented here allow for detailed comparisons between paleoclimate records on both sides of the Tasmanian Gateway.

Wutuchelys eocenican. gen. n. sp., an Eocene stem testudinoid turtle from Wutu, Shandong Province, China

AbstractWe describe here a new turtle from the early Eocene of Wutu, Shandong Province, China. This turtle with a full row of well-developed inframarginal scutes is assigned to the basalmost testudinoids while stem testudinoids were believed to disappear by the Palaeocene–Eocene boundary. This account shows that stem testudinoids crossed this boundary in their original range. The first comprehensive phylogenetic analysis of stem and modern testudinoids performed here demonstrates that the stem testudinoids, previously placed in the family ‘Lindholmemydidae’, do not form a monophyletic group, and the two major clades of testudinoids (Emydidae and Geoemydidae+Testudinidae) split one from another well before the Palaeocene/Eocene boundary, prior to the Late Cretaceous.

Genesis of Paleocene and Lower Eocene shallow-water nodular limestone of South Tibet (China)

This paper examines the genesis of the Paleocene to Lower Eocene shallow-water nodular limestones in South Tibet. The negative carbon isotope excursion representative for the Paleocene–Eocene boundary is located in one nodular limestone bed of the Zhepure Shan Formation showing an extraordinary thickness of about 9 m, inspiring the question under which conditions these nodular limestones were formed. Based on field appearance, the shallow-water nodular limestones of Tingri and Gamba can be classified into five nodular limestone categories (Stylonodular Rock I, Nodular Rock I, Nodular Rock II, stylobedded rock and stylomottled rock) and some transitional members (stylobedded rock transitional to Stylobedded Rock II). Clay variations are assumed to be responsible for these various types of nodular limestones within the sediments. Observations of nodular limestones in South Tibet suggest that those sediments were mostly formed due to autochthonous rather than allochthonous processes. Differential diagenesis resulted in an early selective cementation of limestone nodules due to carbonate supply, while the marls were not cemented but provide the carbonate for the nodule cementation. Additionally, cemented and carbonate-rich nodules are resistant to chemical compaction, while the uncemented and clay-rich marl layers are affected by pressure solution processes due to an overburden of sediments. Additionally, a model is presented, illustrating the origin of different nodular limestones described here.

Enhanced magnetization of the Marlboro Clay as a product of soil pyrogenesis at the Paleocene–Eocene boundary?

The kaolinite-rich Marlboro Clay was deposited on the inner shelf in the Salisbury Embayment of the U.S. Atlantic margin at the onset of the carbon isotope excursion marking the 56 Ma Paleocene–Eocene boundary and is characterized by an anomalously high concentration of magnetic nanoparticles of enigmatic origin that give rise to notably intense bulk magnetization. Recent studies point to a magnetic assemblage that is dominated by single-domain magnetite particles that tend to be isolated rather than arranged in chains, the most distinguishing feature of magnetotactic bacteria fossils. On the other hand, it is very unlikely that the nanoparticles can be condensates of an impact plume given the meter-scale thickness of the Marlboro Clay. We obtained new data from a landward proximal site at Wilson Lake on the New Jersey Coastal Plain and find that the abrupt increase in magnetite nanoparticles is virtually coincident stratigraphically with the recently reported impact spherule layer at the base of the Marlboro Clay in the same core. Yet the high field magnetic susceptibility, a measure of total iron concentration, and strontium isotope values on bulk sediment, an indicator of sediment weathering provenance, are not different in the Marlboro Clay from the immediately underlying Vincentown Formation. We suggest that the distinctive magnetic properties of the Marlboro Clay originated from pyromagnetic soil enhancement by widespread wildfires on the adjoining drainage area. The pyrogenetic products were soon washed from the denuded landscape and rapidly deposited as mud-waves across the shelf, becoming the Marlboro Clay. A few percent of incinerated biomass ends up as calcite known as wood ash stone and can inherit its light carbon isotope composition. Disseminated wood ash stone entrained in the Marlboro Clay could contribute to the landward increase in amplitude of the carbon isotope excursion in bulk carbonate data. A plausible trigger for the initial conflagration is a fireball from the impact of a sizable extraterrestrial object at moderate range.

The lithologic differences between the third and fourth members of the Eocene Shahejie Formation in the Bohai Bay Basin and the associated climatic evolution

The Bohai Bay Basin straddled the Eocene boundary between arid and wet climates in eastern China. The basin was simultaneously affected by both arid and wet climates, and contemporaneous sediments developed under both extremely arid and extremely wet conditions. Data from every well drilled in the oil fields in the Bohai Bay Basin have been used to study the lower fourth member and the upper third member of the Shahejie Formation. The spatial distribution of climate indicators in the lower fourth member of the Shahejie Formation shows that the climate boundary extended from the northern Jizhong Depression to the Bozhong Depression. The portion of the basin to the north of this boundary mostly developed coalbeds, dark mudstone, and oil shale (indicative of a warm and wet climate), whereas the portion of the basin to the south of this boundary mostly developed gypsum, rock salt, and magenta dolomitic mudstone (indicative of a hot and arid climate). During the formation of the upper third member of the Shahejie Formation, the climate boundary shifted southward to the region between the southern part of the Jizhong Depression and the Jiyang Depression. The wet climate zone in the north expanded southward, and the arid climate zone in the south shrank. This shift is evident in the vertical lithologic characteristics of the members that formed before and after this shift in the climate boundary. The lithologic succession in the central part of the basin exhibits significant changes, whereas the lithologic successions in the southern and northern parts of the basin remain homogeneous and stable through time. Therefore, between the formation of the third and fourth members of the Eocene Shahejie Formation, the Bohai Bay Basin experienced a significant climate change. This change directly affected the pattern of the Eocene climate zones in eastern China and is indicative of changes in the paleoclimate zones near the Tropic of Cancer.

Zircon U-Pb ages and emplacement history of the Nodoushan plutonic complex in the central Urumieh-Dokhtar magmatic belt, Central Iran: Product of Neotethyan subduction during the Paleogene

The Nodoushan plutonic complex is composed of a wide range of felsic and mafic rocks straddling several of the major orogenic zones in Iran. Diorite porphyry, diorite, granodiorite and granite intrusives belong to the central part of the Urumieh–Dokhtar magmatic belt, which is part of the Alpine-Himalayan orogenic belt. Monzogabbroic members of the complex are instead located within the bordering Sanandaj–Sirjan magmatic-metamorphic zone. These plutons were emplaced into Permian and lower Cretaceous sedimentary units and Eocene calc-alkaline volcanic and subvolcanic rocks. New U-Pb zircon ages reveal that the plutonic complex was assembled incrementally over ca. 15m.y. during three main episodes at 40.487±0.063Ma near the Middle/Late Eocene boundary, at 30.52±0.11Ma and 30.06±0.10Ma in the Early Oligocene (Middle Rupelian) and at 24.994±0.037 and 24.13±0.19Ma in the Late Oligocene (latest Chattian). The activity recorded in the Nodoushan plutonic complex represents the final stages of subduction-related magmatism prior to the eventual Miocene collision between the Arabian and Eurasian blocks.

Sphenodus (Chondrichthyes, Neoselachii) from the Upper Cretaceous in Nakagawa Town, Hokkaido, Japan

Eight specimens of Sphenodus have been collected from the Upper Cretaceous, Coniacian of Nakagawa Town in Hokkaido, northern Japan. They are referred to as S. cf. lundgreni and Sphenodus spp. 1 and 2, and described in detail. Nearly complete specimens of Sphenodus were previously unknown from the Cretaceous in the Pacific region, and the Nakagawa specimens are the first to exhibit distinct root morphologies, which allow comparison at the species level. A review of the occurrences of this genus reveals that their distribution concentrates in the mid- to high palaeolatitude regions. This distributional pattern of Sphenodus may represent its preference for colder water and possibly explains the extinction of this genus across the Paleocene—Eocene boundary, when the thermal maximum began.