Geology topics

David K. Watkins

Publications and source records attributed to David K. Watkins.

4 recordsLinked to original sources

USGS2022

Evolution and taxonomy of the Paleogene calcareous nannofossil genus Hornibrookina

The genus Hornibrookina consists of enigmatic calcareous nannofossils that first appeared shortly after the K-Pg mass extinction. Due to their relative paucity in most published sections, specimens of this genus have not been previously studied in detail and their paleobiogeographic preferences and evolutionary history have been poorly understood. Biostratigraphic and morphometric analyses of Hornibrookina specimens from outcrops and cores from the Atlantic Ocean, the North Sea, the Southern Ocean, the Indian Ocean, North America, South America, Africa, and New Zealand resulted in a comprehensive and detailed documentation of this group of calcareous nannofossils. Biostratigraphic ranges for each species are refined and a hypothetical evolutionary lineage for this genus is proposed. Two new species (Hornibrookina gracila and Hornibrookina indistincta), two new combinations (Hornibrookina elegans and Hornibrookina australis arca) and one new subspecies (Hornibrookina australis australis) are described. Morphometric analyses prove that Hornibrookina edwardsii and Hornibrookina teuriensis are distinctly different species with biostratigraphically useful ranges. Hornibrookina apellanizii is shown to be invalid.

Micropaleontology↗

USGS2022

Regression of the Tethys Sea (central Asia) during middle to late Eocene: Evidence from calcareous nannofossils of western Tarim Basin, NW China

Calcareous nannofossil assemblages from middle to upper Eocene sediments of the western Tarim Basin indicate two important episodes of marine incursion into the basin. The first episode represents a period of shallowing upward in the Wulagen Formation, which is dated as Zone CNE13 (Lutetian) by the co-occurrence of Discoaster bifax, Chiasmolithus solitus , and common Reticulofenestra umbilicus . The presence of a diverse assemblage of discoasters in the basal Wulagen suggests deposition occurred in oligotrophic, warm water with a connection to the open ocean. Progressive shallowing over time led to the formation of a restricted basin in which only Coccolithus pelagicus could survive . The second major episode of marine incursion is preserved in the middle part of the Bashibulake Formation, which is dated as Zone CNE17 (Bartonian/Priabonian) based on the presence of common Cribrocentrum erbae . The interval between the two marine incursions was dominated by subaerial exposure and evaporation, resulting in the deposition of gypsum at the top of the Wulagen Formation. Although maximum regression at the end of the Lutetian is followed by sea-level rise at the beginning of the Bartonian globally, it is clear that local tectonics played a crucial role in regional marine incursions into the Tarim Basin during deposition of the Wulagen Formation.

Western Tarim Basin↗

USGS2012

Calcareous nannofossil assemblage changes across the Paleocene-Eocene thermal maximum: Evidence from a shelf setting

Biotic response of calcareous nannoplankton to abrupt warming across the Paleocene/Eocene boundary reflects a primary response to climatically induced parameters including increased continental runoff of freshwater, global acidification of seawater, high sedimentation rates, and calcareous nannoplankton assemblage turnover. We identify ecophenotypic nannofossil species adapted to low pH conditions ( Discoaster anartios, D. araneus, Rhomboaster spp.), excursion taxa adapted to the extremely warm climatic conditions ( Bomolithus supremus and Coccolithus bownii ), three species of the genus Toweius ( T. serotinus, T. callosus, T. occultatus ) adapted to warm, rather than cool, water conditions, opportunists adapted to high productivity conditions ( Coronocyclus bramlettei, Neochiastozygus junctus ), and species adapted to oligotropic and/or cool‐water conditions that went into refugium during the PETM ( Zygrablithus bijugatus, Calcidiscus? parvicrucis and Chiasmolithus bidens ). Discoaster anartios was adapted to meso- to eutrophic, rather than oligotrophic, conditions. Comparison of these data to previous work on sediments deposited on shelf settings suggests that local conditions such as high precipitation rates and possible increase in major storms such as hurricanes resulted in increased continental runoff and high sedimentation rates that affected assemblage response to the PETM.

Marine Micropaleontology↗

USGS1997

The Blake Nose Cretaceous-Paleogene (Florida Atlantic margin, ODP Leg 171 B): An exemplar record of the Maastrichtian-Danian transition

During ODP Leg 171B, devoted to the analysis of the Blake Plateau margin in front of Florida, 16 holes have been drilled in 5 distinct sites. The sites have documented a sedimentary succession ranging in age from Aptian to Eocene. Emphasis has been put on critical periods, comprising the Paleocene-Eocene transition, the Cretaceous-Tertiary boundary which has been cored in excellent conditions, the middle Maastrichtian extinctions and the Albian anoxic episodes.

Comptes Rendus de l'Academie des Sciences - Serie ↗