Ellen Thomas

Biogeography of the Late Paleocene Benthic Foraminiferal Extinction

Ellen Thomas — Mon, 27 Jun 2011 12:28:54 PDT

During the Late Paleocene Thermal Maximum (LPTM) benthic foraminifera at middle bathyal and greater depths suffered extinction of 30-50% of species during a few thousand years. Extinction was less severe at neritic to upper bathyal depths, where temporary changes in faunal composition prevailed. Pre-extinction deep-sea faunas were cosmopolitan and diverse, and contained heavily calcified species. Immediate post-extinction faunas were more variable geographically, exhibited low diversity, and were dominated by thin-walled calcareous or agglutinated taxa, possibly because CaCO3 dissolution increased globally from neritic to abyssal depths just before the extinction. These assemblages were dominated either by long-lived taxa such as Nuttallides truempyi or by buliminid taxa, the latter accompanied by agglutinants in some areas. Faunas dominated by N. truempyi were common in the South Atlantic and at lower bathyal through upper abyssal depths in the Indian Ocean, and might indicate oligotrophic conditions as well as increased corrosiveness. Buliminid-dominated faunas might indicate high rates of deposition of organic matter or low-oxygen conditions. Such faunas were common globally along continental margins, and locally co-occurred with sedimentologic or planktonic faunal indicators of high productivity. In the bathyal central Pacific, however, buliminid dominated faunas co-occurred with planktonic faunas suggesting oligotrophy, and they could reflect low-oxygen conditions resulting from sluggish ocean circulation, oxidation of dissociated methane hydrates, or warming of bathyal-abyssal waters caused by a change in deep-sea circulation. Alternatively, they could indicate that the faction of organic matter reaching the seafloor increased as a result of decreased oceanic oxygenation. The latest Paleocene benthic extinction thus was complex, and factors such as changes in deep-sea circulation, increased CaCO3 corrosiveness. increased temperatures, decreased oxygenation and changes in the patterns of high productivity may have contributed to its severity.

Productivity Control of Fine Particle Transport to Equatorial Pacific Sediment

Ellen Thomas — Thu, 08 Apr 2010 08:23:33 PDT

Upper Cretaceous and Lower Paleogene Benthic Foraminifera from Northeastern Mexico

Ellen Thomas — Thu, 01 Apr 2010 08:24:58 PDT

The Cretaceous ⁄ Tertiary Boundary: Sedimentology and Micropalaeontology at El Mulato Section, NE Mexico

Ellen Thomas — Thu, 01 Apr 2010 08:24:54 PDT

Warming the Fuel for the Fire: Evidence for the Thermal Dissociation of Methane Hydrate During the Paleocene-Eocene Thermal Maximum

Ellen Thomas — Thu, 01 Apr 2010 08:24:54 PDT

Balancing the Deglacial Global Carbon Budget: The Hydrate Factor

Ellen Thomas — Tue, 30 Mar 2010 08:44:31 PDT

Benthic Foraminiferal Faunal Turnover Across the Cretaceous/Tertiary Boundary at Agost (Southeastern Spain): Paleoenvironmental Inferences

Ellen Thomas — Tue, 30 Mar 2010 08:44:30 PDT

Indian Ocean High-productivity Event (10–8 Ma): Linked to Global Cooling or to the Initiation of the Indian Monsoons?

Ellen Thomas — Tue, 23 Mar 2010 08:50:15 PDT

An Ocean View of the Early Cenozoic Greenhouse World

Ellen Thomas — Tue, 16 Feb 2010 08:26:33 PST

Cretaceous/Paleogene Boundary Bathyal Paleo-Environments in the Central North Pacific (DSDP Site 465), the Northwestern Atlantic (ODP Site 1049), the Gulf of Mexico and the Tethys: The Benthic Foraminiferal Record

Ellen Thomas — Tue, 16 Feb 2010 08:26:33 PST

Uppermost Maastrichtian benthic foraminiferal assemblages (N 63 Am) are diverse, indicating mesotrophic conditions in lower bathyal DSDP Hole 465A (Hess Rise, central North Pacific), in 4 lower bathyal land sections in central-East and Northeastern Mexico, and in the upper to middle bathyal Agost section (Tethys area, Southeastern Spain). They indicate more eutrophic conditions in lower bathyal ODP Hole 1049C (Blake Nose, Northwestern Atlantic). Benthic foraminifers did not suffer significant extinction at the K/Pg boundary, but diversity and heterogeneity of the assemblages and the percentage of infaunal morphogroups decreased drastically in all sections, with the exception of DSDP Hole 465A where the percentage of infaunal taxa increased. These faunal changes probably reflect the effect on the benthic faunas of a widespread decrease in the food supply to the sea floor, as a result of the collapse of primary productivity at the K/Pg boundary. The decrease in food supply apparently affected the benthic faunas least at more eutrophic NW Atlantic ODP Site 1049 and at Pacific DSDP Site 465, which is distal from the impact site of the K/Pg bolide on the Yucatan Peninsula. At these sites the faunas recovered within the Parvulorugoglobigerina eugubina Biozone (~ 100 ky), although diversity and heterogeneity remained low through the early Danian, possibly indicating environmental stress. This stress might be related to a high or fluctuating food supply by primary producers that could not easily be used by the benthos, such as various bloom species of dinoflagellates. Benthic assemblages recovered more slowly (~ 300 ky) in the Mexican and Spanish sections. Low oxygen conditions after the K/Pg boundary could be inferred from the benthic assemblages at Agost (Southeastern Spain) only. A short episode of hypoxia, however, may be obscured at Pacific DSDP Hole 465A by drilling disturbance, and in the Mexican sections and Hole 1049C by incomplete sections due to downslope transport. Benthic foraminiferal assemblages thus appear to have been affected by the collapse of primary productivity at the K/Pg boundary to a different extent in different regions, and took different lengths of time for their recovery after the boundary.

Cenozoic Mass Extinctions in the Deep Sea; What Disturbs the Largest Habitat on Earth?

Ellen Thomas — Tue, 02 Feb 2010 08:26:37 PST

Deep-sea benthic foraminifera live in the largest habitat on Earth, constitute an important part of its benthic biomass and form diverse assemblages with common cosmopolitan species. Modern deep-sea benthic foraminiferal assemblages are strongly influenced by events affecting their main food source, phytoplankton (bentho-pelagic coupling). Surprisingly, benthic foraminifera did not suffer significant extinction at the end of the Cretaceous, when phytoplankton communities underwent severe extinction. Possibly, bentho-pelagic coupling was less strong than today in the warm oceans of the Cretaceous – Paleogene, because of differences in the process of food transfer from surface to bottom, or because more food was produced below the photic zone by litho-autotrophs. Alternatively, after the end Cretaceous extinction the food supply from the photic zone to the sea floor recovered in less time than previously thought. In contrast, deep-sea benthic foraminifera underwent severe extinction (30-50% of species) at the end of the Paleocene, when planktic organisms show rapid evolutionary turnover, but no major extinction. Causes of this benthic extinction are not clear: net extinction rates were similar globally, but there is no independent evidence for global anoxia or dysoxia, nor of globally consistent increase or decrease in productivity, or of carbonate dissolution. The extinction might be linked to a global feature of the end-Paleocene environmental change, i.e., rapid warming. Cenozoic deep-sea benthic faunas show gradual faunal turnover during periods of pronounced cooling and increase in polar ice volume: the late Eocene-early Oligocene, the middle Miocene and the middle Pleistocene. During the latter turnover, taxa that decreased in abundance during the earlier two turnovers became extinct, possibly because of increased oxygenation of the oceans, or because of increased seasonality in food delivery. The Eocene-Oligocene was the most extensive of these turnovers, and bentho-pelagic coupling may have become established at that time.

Emendation of the Genus Streptochilus Broennimann and Resig, 1971 (Foraminifera) and New Species from the Lower Miocene of the Atlantic and Indian Oceans

Ellen Thomas — Tue, 02 Feb 2010 08:26:37 PST

Deep Sea Environments Across the Cretaceous/Paleogene boundary in the eastern South Atlantic Ocean

Ellen Thomas — Tue, 02 Feb 2010 08:26:36 PST

The Palaeocene-Eocene Thermal Maximum Super Greenhouse: Biotic and Geochemical Signatures, age Models and Mechanisms of Climate Change

Ellen Thomas — Thu, 28 Jan 2010 10:42:16 PST

Surviving mass extinction by bridging the benthic/planktic divide

Kate F. Darling et al. — Thu, 28 Jan 2010 10:42:15 PST

Evolution of planktic organisms from benthic ancestors is commonly thought to represent unidirectional expansion into new ecological domains, possibly only once per clade. For foraminifera, this evolutionary expansion occurred in the Early–Middle Jurassic, and all living and extinct planktic foraminifera have been placed within 1 clade, the Suborder Globigerinina. The subsequent radiation of planktic foraminifera in the Jurassic and Cretaceous resulted in highly diverse assemblages, which suffered mass extinction at the end of the Cretaceous, leaving an impoverished assemblage dominated by microperforate triserial and biserial forms. The few survivor species radiated to form diverse assemblages once again in the Cenozoic. There have, however, long been doubts regarding the monophyletic origin of planktic foraminifera. We present surprising but conclusive genetic evidence that the Recent biserial planktic Streptochilus globigerus belongs to the same biological species as the benthic Bolivina variabilis, and geochemical evidence that this ecologically flexible species actively grows within the open-ocean surface waters, thus occupying both planktic and benthic domains. Such a lifestyle (tychopelagic) had not been recognized as adapted by foraminifera. Tychopelagic are endowed with great ecological advantage, enabling rapid recolonization of the extinction-susceptible pelagic domain from the benthos. We argue that the existence of such forms must be considered in resolving foraminiferal phylogeny.