Stratigraphy, sedimentology, and paleoecology of Upper Cretaceous/Paleocene shelf-deltaic sediments of Seymour Island

Abstract

Richly fossiliferous Upper Cretaceous-Paleocene beds exposed on Seymour Island provide an excellent opportunity for a combined sedimentological-paleoecological analysis of a high-latitude shallow marine sequence. The depositional paleoenvironments of this sequence were interpreted on the basis of the stratigraphy, sedimentological analysis (including grain-size analysis) of the sediments, and auto-and synecological evaluation of the fauna present.The sequence is composed of two formations. The underlying López de Bertodano Formation (upper Campanian to Paleocene) consists of 1,190 m of gray to tan, friable, sandy, muddy siltstone, and is subdivided into 10 informal units. The lower six units (informally named the Rotularía Units) contain a depauperate macrofauna and are dominated by the annelid Rotularía. They were deposited in a shallow marine environment, near a delta or estuary. Units 7 through 10 include an abundant macrofauna (Molluscan Units). Units 7 through 9 are interpreted as progressively deeper water deposits, with Units 7 and 8 representing middle shelf facies, and Unit 9, the outer shelf facies. Macrofauna in the most offshore portion of Unit 9 is characterized by an epifaunal suspension-feeding bivalve asssemblage dominated by Pycnodonte cf. P. vesiculosa, and an increased percentage of cosmopolitan ammonites. Regressive facies appear 30 m below the inferred Cretaceous/Tertiary boundary (contact between Units 9 and 10). Unit 10 was probably deposited in a middle shelf to inner shelf environment.The overlying Sobral Formation (Paleocene) follows unconformably, and is composed of as much as 255 m of maroon, well-laminated silts at the base, followed by cleaner sandstones that become more glauconitic and crossbedded toward the top. The Sobral is not very fossiliferous and represents the filling of the basin by the progradation of a deltaic system. Units 1 and 2 are interpreted as pro-delta facies followed by clean sands of a coastal barrier (Unit 3). The uppermost Sobral (Units 4 and 5) contains the delta top facies, mostly representing the lateral accretion of distributary channels.

The oldest elasmosaurs (Sauropterygia, Plesiosauria) from Antarctica, Santa Marta Formation (upper Coniacian? Santonian–upper Campanian) and Snow Hill Island Formation (upper Campanian–lower Maastrichtian), James Ross Island

“…The Marambio Group, which crops out mostly in the James Ross Archipelago, was deposited during the upper ConiacianÁDanian interval (Macellari 1988;Ineson 1989;McArthur et al 2000;Crame et al 2004) or SantonianÁ Danian (Olivero & Medina 2000). This article follows the stratigraphy proposed by Olivero et al (2008) Crame et al (1991) (Figs.…”

The Cretaceous and Paleocene pleurotomariid (Gastropoda: Vetigastropoda) fauna of Seymour Island, Antarctica

“…Bored and abraded wood debris ranging in size up to 1 m in diameter, bivalves, and gastropods are commonly encountered throughout the sequence. The highly bioturbated nature of the sediments and the absence of primary sedimentary structures indicate that deposition was, in all likelihood, mid-shelf below effective wave-base (Macellari and Zinsmeister, 1983;Macellari, 1988). The age of the Lopez de Bertodano Formation ranges from Maastrichtian through Early Paleocene.…”

“…The upper Cretaceous and lower Paleocene sedimentary sequence of Seymour Island was described by Anderson (1906), Rinaldi et al (1978), Zinsmeister (1982a), Macellari and Huber (1982), Macellari and Zinsmeister (1983), Huber (1984), Macellari (1984Macellari ( , 1986Macellari ( , 1988, Sadler (1988), and Stilwell and Zinsmeister (1992) and consists of approximately 1600 m of gently eastward-dipping fossiliferous marine clastics. Two major stratigraphic units are recognized for the upper Cretaceous and lower Paleocene part of the sequence, the Lopez de Bertodano and Sobral formations.…”

“…formations, faunal similarities between the two units indicate that little time is missing (Elliot and Trautman, 1982;Rinaldi et al, 1978;Macellari and Zinsmeister, 1983;Macellari, 1988).…”

“…1, 2) consists of approximately 255 m (Macellari, 1988) of silty to medium-grained, wellbedded, dark brown to greenish-grey concretionary sandstone. The lower part of the Sobral Formation consists of 40-90 m of loosely consolidated greenish-grey glauconitic sandstone.…”