Global cooling accelerated by early late Eocene impacts?

Geology ◽  
2000 ◽  
Vol 28 (8) ◽  
pp. 687-690 ◽  
Author(s):  
Hubert B. Vonhof ◽  
Jan Smit ◽  
Henk Brinkhuis ◽  
Alessandro Montanari ◽  
Alexandra J. Nederbragt
Geology ◽  
2000 ◽  
Vol 28 (8) ◽  
pp. 687 ◽  
Author(s):  
Hubert B. Vonhof ◽  
Jan Smit ◽  
Henk Brinkhuis ◽  
Alessandro Montanari ◽  
Alexandra J. Nederbragt

2021 ◽  
Vol 8 (10) ◽  
Author(s):  
Cecily S. C. Nicholl ◽  
Eloise S. E. Hunt ◽  
Driss Ouarhache ◽  
Philip D. Mannion

Notosuchians are an extinct clade of terrestrial crocodyliforms with a particularly rich record in the late Early to Late Cretaceous (approx. 130–66 Ma) of Gondwana. Although much of this diversity comes from South America, Africa and Indo-Madagascar have also yielded numerous notosuchian remains. Three notosuchian species are currently recognized from the early Late Cretaceous (approx. 100 Ma) Kem Kem Group of Morocco, including the peirosaurid Hamadasuchus rebouli . Here, we describe two new specimens that demonstrate the presence of at least a fourth notosuchian species in this fauna. Antaeusuchus taouzensis n. gen. n. sp. is incorporated into one of the largest notosuchian-focused character-taxon matrices yet to be compiled, comprising 443 characters scored for 63 notosuchian species, with an increased sampling of African and peirosaurid species. Parsimony analyses run under equal and extended implied weighting consistently recover Antaeusuchus as a peirosaurid notosuchian, supported by the presence of two distinct waves on the dorsal dentary surface, a surangular which laterally overlaps the dentary above the mandibular fenestra, and a relatively broad mandibular symphysis. Within Peirosauridae, Antaeusuchus is recovered as the sister taxon of Hamadasuchus . However, it differs from Hamadasuchus with respect to several features, including the ornamentation of the lateral surface of the mandible, the angle of divergence of the mandibular rami, the texture of tooth enamel and the shape of the teeth, supporting their generic distinction. We present a critical reappraisal of the non-South American Gondwanan notosuchian record, which spans the Middle Jurassic–late Eocene. This review, as well as our phylogenetic analyses, indicate the existence of at least three approximately contemporaneous peirosaurid lineages within the Kem Kem Group, alongside other notosuchians, and support the peirosaurid affinities of the ‘trematochampsid’ Miadanasuchus oblita from the Maastrichtian of Madagascar. Furthermore, the Cretaceous record demonstrates the presence of multiple lineages of approximately contemporaneous notosuchians in several African and Madagascan faunas, and supports previous suggestions regarding an undocumented pre-Aptian radiation of Notosuchia. By contrast, the post-Cretaceous record is depauperate, comprising rare occurrences of sebecosuchians in north Africa prior to their extirpation.


2004 ◽  
Vol 83 (3) ◽  
pp. 241-248 ◽  
Author(s):  
S. Van Simaeys

AbstractThe classical problem of the nature and age of the Rupelian-Chattian (Early-Late Oligocene) unconformity in its type region is here approached using organic walled dinoflagellate cyst (dinocyst) correlations between the North Sea Basin and well-calibrated central Italian (Tethyan Ocean) sections. Useful Oligocene dinocyst events are the last occurrence ofEnneadocysta pectiniformis(~29.3 Ma), and the first occurrences ofSaturnodinium pansum(~29.4 Ma),Distatodinium biffii(~27.9 Ma) andArtemisiocysta cladodichotoma(~26.7 Ma).The latter event marks the earliest Chattian. The improved correlations indicate that the Rupelian-Chattian (R-C) boundary is associated with the so-called ‘Oligocene Glacial Maximum’. This phase of important global cooling and glacio-eustatic sea level fall is genetically related to the unconformity between the classic Oligocene stages. Subsequent global warming (so-called ‘Late Oligocene Warming Event’), induced a major sea level rise, leading e.g. to the time-transgressive deposition of the typical basal Chattian glauconitic sands. The oldest of the Chattian units have a GPTS age of-26.7 Ma. It further appears that a hiatus of ~500 kyrs spans the classic Rupelian-Chattian unconformity.


1986 ◽  
Vol 60 (4) ◽  
pp. 911-919 ◽  
Author(s):  
William P. Wall ◽  
Earl Manning

A new genus and species of amynodontid rhinoceros, Rostriamynodon grangeri, from the early Late Eocene of Inner Mongolia, People's Republic of China, is the most primitive amynodontid recognized to date. Rostriamynodon exhibits the major diagnostic characteristics of amynodontids: quadratic M3, preorbital fossa, and loss of upper and lower P1. It differs from more advanced members of the family in its long preorbital region and lower cheek tooth morphology. Comparisons with other Eocene ceratomorphs show the crucial position Rostriamynodon has in determining phylogenetic relationships between rhinocerotoids and tapiroids. Evidence is presented for the monophyly of the Rhinocerotoidea, including amynodontids.


2021 ◽  
Author(s):  
Xiangyu Li ◽  
Zhongshi Zhang ◽  
Ran Zhang ◽  
Qing Yan

<p>Geological evidence shows that the Asian inland environment experienced enhanced aridity from the Early to the Late Eocene. The underlying mechanism for this enhanced Eocene aridity in the Asian inland is still not well illustrated and varies between global cooling and early Tibetan Plateau uplift. In this report, we evaluate the climate impact of three factors, global cooling, topographic uplift and land–sea reorganization, on the enhanced Eocene aridity in Asian inland, in the perspective view from paleoclimate modeling. Paleoclimate modeling supports the Eocene aridification in Asian inland explored by paleoclimate reconstruction. Both the early uplift of Tibetan Plateau and global cooling induced by atmospheric CO<sub>2</sub> reduction contributed to the enhanced aridity in Asian inland in the late Eocene. The Eocene land sea redistribution caused the precipitation increase in Asian inland and hence didn’t contribute to the enhanced aridity there. The uplift of the central Tibetan Plateau during the early stage of the India–Asia collision is emphasized more to be responsible for the long-term Asian inland aridification during the Eocene, playing at least an equally important role as the global cooling induced by decrease in atmospheric CO<sub>2</sub>. The variation of atmospheric CO<sub>2</sub> is likely more important in modulating the regional aridity, leading to the short-term fluctuations in this Eocene Asian inland aridification.</p>


2001 ◽  
Vol 75 (2) ◽  
pp. 295-309 ◽  
Author(s):  
Geerat J. Vermeij

This paper presents a review of Cretaceous to Eocene genera and species of the Cantharus group of the buccinoidean neogastropod subfamily Pisaniinae, the description of two new genera and one new species, and a nonphylogenetic discussion of character evolution in this group. The new genus Ickarus is introduced for Tritonidea ickei Martin, 1914, from the Nanggulan beds (middle Eocene) of Java, Indonesia. Editharus (type species: Fusus polygonus Lamarck, 1803, middle Eocene of the Paris Basin, France) is a new genus with seven to nine species ranging from the early to late Eocene of Europe. Editharus is unusual in having a labral tooth formed at the angular junction between the adapical and abapical sectors of the outer lip. Editharus angulilabris from the Marinesian (early late Eocene) is a new species from the Paris Basin closely related to E. polygonus. The incidence and expression of several characters has sharply increased in the Cantharus group from the Paleogene to the Neogene. These characters include the presence of lirae (spiral ridges) on the inner side of the outer lip, the presence of a parietal tooth at the adapical end of the inner lip, and determinate growth (as inferred from a unique adult varix). These trends are also exhibited by other Cenozoic gastropod clades.


2018 ◽  
Vol 137 (1) ◽  
pp. 1-48 ◽  
Author(s):  
Pierre-Olivier Mojon ◽  
Eric De Kaenel ◽  
Daniel Kälin ◽  
Damien Becker ◽  
Claudius Marius Pirkenseer ◽  
...  

2020 ◽  
Vol 90 (3) ◽  
pp. 297-312
Author(s):  
Fikry Ibrahim Khalaf ◽  
Médard Thiry ◽  
Anthony Milnes ◽  
Rehab Alnaqi

ABSTRACT Conspicuous chert horizons occur as discontinuous bands and isolated nodules in dolostones in the Eocene Dammam Formation, which is exposed in the southeast of Kuwait. The Formation has never been deeply buried, and so chert formation is likely to have resulted from silicification processes at or near the land surface. Erosional reworking of the chert constrains its formation to a time period between the late Eocene and the Mio-Pliocene. As there is no significant source of silica in the dolostones, the chert was formed from silica imported from other sources. This process, together with the specificity of chert to particular non-bedding horizons, suggests that silicification is related to discrete locations of the groundwater table during landscape incision and resultant groundwater discharge in the region. Detailed petrographical studies demonstrate that “chertification” was initiated by precipitation of nanoglobules of silica (opal-A) from supersaturated groundwater solutions flowing through voids formed concomitantly by dissolution of dolomite. Subsequently, silica was precipitated as more crystalline forms of chalcedony, microquartz, and megaquartz from successively less saturated groundwater. The most likely mechanism for triggering the precipitation of silica is considered to be significant cooling of the groundwater as it neared the landsurface and came into contact with a cold regolith terrain. Precipitation of disordered forms of silica (opal-A) occurred at the cold front: progressively more crystalline phases formed as the host rock was warmed by the inflowing groundwater and its degree of supersaturation diminished. If our interpretation is correct, this “chertification” process could have been initiated during global cooling related to one of the glaciations recorded during Oligocene and Miocene times.


2021 ◽  
Author(s):  
Michael Amoo ◽  
Ulrich Salzmann ◽  
Matthew J. Pound ◽  
Nick Thompson ◽  
Peter K. Bijl

Abstract. Considered as one of the most significant climate reorganisations of the Cenozoic period, the Eocene-Oligocene Transition (EOT; ca. 34.44–33.65) is characterised by global cooling and the first major glacial advance on Antarctica. While in the southern high-latitudes, the EOT cooling is primarily recorded in the marine realm, the extent and effect on terrestrial climate and vegetation is poorly documented. Here, we present a new, well-dated, continuous, high-resolution palynological (sporomorph) data and quantitative sporomorph-based climate estimates recovered from the East Tasman Plateau (ODP Site 1172) to reconstruct climate and vegetation dynamics from the late Eocene (37.97 Ma) to early Oligocene (33.06 Ma). Our results indicate three major climate transitions and four vegetation communities occupying Tasmania under different precipitation and temperature regimes: (i) a warm-temperate Nothofagus-Podocarpaceae dominated rainforest with paratropical elements from 37.97–37.52 Ma; (ii) cool-temperate Nothofagus dominated rainforest with secondary Podocarpaceae rapidly expanding and taking over regions previously occupied by the warmer taxa between 37.306–35.60 Ma; (iii) fluctuation between warm temperate – paratropical taxa and cool temperate forest from 35.50–34.49 Ma, followed by a cool phase across the EOT (34.30–33.82 Ma); (iv) post-EOT (earliest Oligocene) recovery characterised by a warm-temperate forest association from 33.55–33.06 Ma. Coincident with changes in stratification of water masses and sequestration of carbon from surface water in the Southern Ocean, our sporomorph-based temperature estimates between 37.52 Ma and 35.60 Ma (phase ii) showed 2–3 °C terrestrial cooling. The unusual fluctuation between warm and cold temperate forest between 35.50 to 34.59 Ma is suggested to be linked to the initial deepening of the Tasmanian Gateway allowing eastern Tasmania to come under the influence of warm water associated with the proto-Leeuwin Current (PLC). Further to the above, our terrestrial data show mean annual temperature declining by about 2 °C across the EOT before recovering in the earliest Oligocene. This phenomenon is synchronous with regional and global cooling during the EOT and linked to declining pCO2. However, the earliest Oligocene climate rebound along eastern Tasmania is linked to transient recovery of atmospheric pCO2 and sustained deepening of the Tasmanian Gateway, promoting PLC throughflow. The three main climate transitional events across the studied interval (late Eocene–earliest Oligocene) in the Tasmanian Gateway region suggest that changes in ocean circulation due to accelerated deepening of the Tasmanian Gateway may not have been solely responsible for the changes in terrestrial climate and vegetation dynamics, but a series of regional and global events, including a change in stratification of water masses, sequestration of carbon from surface waters, and changes in pCO2 may have played vital roles.


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