Late Campanian–Maastrichtian Ammonite Fauna from Seymour Island (Antarctic Peninsula)

Abstract

One of the richest and best preserved late Campanian-Maastrichtian ammonite faunas of the world occurs within the Lopez de Bertodano Formation on Seymour Island. The excellent exposure of this sequence has offered an opportunity for detailed stratigraphic study of the fauna, providing a stratigraphic control unavailable for most other Southern Hemisphere strata of similar age.Ammonites are restricted to the Cretaceous portion of the Lopez de Bertodano Formation, becoming more abundant and increasing in diversity within a 600-m interval below the Cretaceous-Tertiary boundary. The ammonite-rich levels are divided into three zones (from oldest to youngest: Pachydiscus ootacodensis, P. riccardi and P. ultimus zones), extending from the late Campanian-Maastrichtian to the latest Maastrichtian.The taxonomic study of this fauna shows a predominance of endemic taxa of the family Kossmaticeratidae, including the species Maorites tuberculatus Howarth, M. seymourianus (Kilian and Reboul), M. densicostatus (Kilian and Reboul), M. weddelliensis n. sp., Grossouvrites gemmatus (Huppe) and Gunnarites bhavaniformis (Kilian and Reboul). These taxa, together with the members of the family Desmoceratidae Kitchinites (Kitchinites) darwini (Steinmann) and K. (K.) laurae n. sp., are mostly restricted to the margins of the Late Cretaceous Weddellian Province that extended from southern South America to Australia.Cosmopolitan genera described in this work become more abundant up section and include the species Anagaudryceras seymouriense n. sp., Zelandites varuna (Forbes), Pseudophyllites loryi (Kilian and Reboul), Diplomoceras lambi Spath, Pachydiscus (Pachydiscus) ootacodensis (Stoliczka), P. (P.) riccardi n. sp. and P. (P.) ultimus n. sp.

Late cretaceous Cephalopoda (Mollusca) from the Takatika Grit, Chatham Islands, southwest pacific

“…38 DISCUSSION: Late Cretaceous ammonites with large (up to 350 mm) diameters; the predominantly smooth shells with differentially strong ribs on the periphery, narrow umbilicus, and compressed whorls are uniquely Pachydiscus. However, the apparent lack of ornamentation and unique sutural pattern of these specimens delineate it from other congeneric taxa described within the Late Cretaceous of New Zealand and Antarctica (Marshall 1926;Henderson 1970;Macellari 1986). Nevertheless, the specimens are too incomplete for assignment to species level.…”

“…Nevertheless, the specimens are too incomplete for assignment to species level. Pachydiscus riccardi Macellari, 1986, from the late Maastrichtian of Seymour Island, Antarctic Peninsula, has affinities to the Chatham Island specimens; both species exhibit comparable size; inflated, involute whorl profiles; vertical umbilical walls; broad, rounded venter; and complex, florid sutural traces. Furthermore, the cephalopod described here has vestiges of well-spaced radial ribs, a feature that bestows an affinity to P. riccardi, which bears weak ribs and umbilical nodes.…”

“…Pachydiscus has not been identified previously within the Chatham Islands despite the region's paleoposition and depositional setting of a shallow marine environment on the eastern margin of Gondwana (juxtaposed to Marie Byrd Land) in the Late Cretaceous ). This observation is thought to be the result of collection bias rather than a paleoecological limitation, as this genus is moderately well represented in the Late Cretaceous fossil record of New Zealand and West Antarctica, and has an almost cosmopolitan distribution, save the western interior of the United States of America and Canada, and Greenland (Henderson 1970;Macellari 1986 Macellari, 1986. Partial, right-lateral view of phragmacone showing sutures on lower part; TM8323 (GNS), diameter (predicted) = c. 350 mm, width c. 70 mm (Early Haumurian Stage), (refer to main scale bar for Fig.…”

Intermittent euxinia in the high-latitude James Ross Basin during the latest Cretaceous and earliest Paleocene

“…A robust age model has been developed for the LBF based on biostratigraphy (Macellari, 1986;Huber, 1988;Bowman et al, 2012;Witts et al, 2015), chemostratigraphy (primarily strontium isotopes; McArthur et al, 1998), and magnetostratigraphy (Tobin et al, 2012), as well as the presence of an iridium (Ir) anomaly at the K-Pg boundary (Elliot et al, 1994; see Witts et al, 2016 for more details). This has confirmed the Maastrichtian-Danian age of the succession, and also the high rate of sedimentation during the Cretaceous-Paleogene interval (10-20 cm/kyr), with the entire sequence on SI likely deposited in b4 million years (Tobin et al, 2012;Bowman et al, 2013).…”

Calcareous nannofossils from the Santa Marta Formation (Upper Cretaceous), northern James Ross Island, Antarctic Peninsula

“…The biostratigraphy of the Marambio Group has been studied in fairly good detail using ammonites, which have good records in several sections on Vega, James Ross, Snow Hill and Seymour islands (Riccardi, 1980;Olivero, 1984Olivero, , 1992Olivero, , 2012Macellari, 1986Macellari, , 1988Pirrie et al, 1991Pirrie et al, , 1997Scasso et al, 1991;Olivero and Medina, 2000).…”