T65 Future Leaders in Paleontology

Sunday, 22 September 2024
1:30 PM - 5:30 PM
207A

BIOGEOGRAPHICAL IMPLICATIONS OF GASTROPOD MOLLUSKS OF THE BRIGHTSEAT FORMATION (PALEOCENE: DANIAN) OF MARYLAND

Paper number: T65-11
Program: Technical Sessions
Time: 4:00 PM – 4:15 PM

Authors

Abstract

The Brightseat Formation, exposed near the inner margin of the Salisbury Embayment in Maryland and Virginia, represents the earliest Paleocene sediments that outcrop in this region of the northern Atlantic Coastal Plain. The formation is placed within the middle part of the Danian stage (~64 Ma), as defined by the presence of the Chiasmolithus danicus calcareous nannofossil Zone (NP3). While a number of studies have investigated the microfauna of the Brightseat, no similarly thorough evaluation has been afforded to the shallow-shelf marine macrofauna. This study provides the first extensive taxonomic treatment of the gastropods, collected largely from now-inaccessible Brightseat localities near the original type section in the lower Potomac River Valley, east of Washington, D.C. The diverse gastropod fauna of the Brightseat Formation consists of 52 species or forms – 25 of which are described as new – that are assigned to 41 genera distributed among 18 families. By abundance, the fauna is dominated by 6 species of the suspension-feeding family Turritellidae, which proportionally comprise over 60% of the individuals in the assemblage.

The Brightseat gastropods include a mixture of genera indicative of both Northern Mild-Temperate (NMT) and Southern Warm-Temperate (SWT) affinities. In overall taxonomic composition, the Brightseat fauna more strongly resembles the Danian to Selandian shelf faunas of West Greenland, Denmark, and Belgium, within the NMT marine zoogeographic province, than it does contemporaneous faunas to the southwest in Texas, Mississippi, and Alabama, on the northern margin of the SWT province. The mixture of elements of differing biogeographic affinities suggests that the Brightseat gastropods flourished on a portion of the eastern North American continental shelf situated within a zone of overlapping, though unequal, northern and southern interchange.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-403659

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