Dinoflagellate cysts of the La Meseta Formation (middle to late Eocene), Antarctic Peninsula: implications for biostratigraphy, palaeoceanography and palaeoenvironment

Abstract

Dinoflagellate cyst assemblages recovered from the La Meseta Formation cropping out in Seymour Island, Antarctic Peninsula, are studied herein and their distribution is compared with the biostratigraphic scheme available for the Palaeogene of the Southern Ocean and other high-latitude regions. In this way, the La Meseta Formation is dated as middle Lutetian to Priabonian (46.2–36 Ma), which differs from the age provided by other fossils, isotopes and also with the magnetostratigraphic scheme recently performed for the unit. The dinoflagellate cyst data support the proposal of ocean circulation patterns on the South American Shelf prior to the opening of Drake Passage. Assemblages from the La Meseta Formation contain Antarctic-endemic taxa which are also dominant in several circum-Antarctic sites, located south of 45° S. Their distribution reflects an ocean-circulation scheme with wide clockwise gyres surrounding Antarctica that were disrupted as a consequence of the deepening and definitive apertures of the Tasmanian Gateway and Drake Passage towards the Eocene/Oligocene transition. The palaeoenvironmental inference based on the S/D ratio (sporomorphs versus dinoflagellate cysts) and the P/G ratio (peridinioid versus gonyaulacoid dinoflagellate cysts) suggests an overall trend through the section from marine-dominated assemblages with poorly productive waters in the lower part of the section to more terrestrially dominated assemblages with increasing productivity in the upper part of the unit, reflecting a shallowing trend to the top.

Phylogeny of the Eocene Antarctic Tapetinae Gray, 1851 (Bivalvia, Veneridae) from the La Meseta and Submeseta formations

“…58.4 Ma) and the lower Lutetian (ca. 45.8 Ma) (Marenssi, 2006;Ivany et al, 2008;Montes et al, 2013Montes et al, , 2019a, although recent research proposed a late early Eocene (Crame et al, 2014) or middle Eocene age (Douglas et al, 2014) at the beginning of deposition, Amenábar et al (2019) determined a middle Lutetian to Priabonian age . This unit includes mudstones and sandstones with interbedded conglomerates, and it is organized into seven allomembers (Marenssi et al, 1998a): Valle de Las Focas, Acantilados I, Acantilados II, Campamento, Cucullaea I, Cucullaea II, and Submeseta.…”

Probing the Ecology and Climate of the Eocene Southern Ocean With Sand Tiger Sharks Striatolamia macrota

“…The relative stratigraphic position of TELMs has been agreed upon, but absolute age models of TELMs have changed over time. We adopt the age model from Douglas et al (2014) and Amenábar et al (2020) based on their biostratigraphic analysis of the endemic group of dinocyst taxa referred to as "transantarctic fauna." The lower TELMs (2-3) are determined to be no older than Middle Eocene based on the presence of Enneadocysta diktyostila (first occurrence calibrated to Chron C20r at~45 Ma) and Arachnodinium antarcticum and Hystricosphaerodoim truswelliae (last occurrences during Chron C18n at~38 Ma) (Amenábar et al, 2020;Douglas et al, 2014 (Amenábar et al, 2020;Douglas et al, 2014).…”

“…The Upper La Meseta Fm. (TELM 5) is less well constrained but includes diagnostic dinocyst occurrences of E. diktyostila , Alterbidinium distinctum , Brigantedinium spp ., Lejeunecysta spp ., and Selenopemphix nephroides and indicate an age ranging from 41–37 Ma (Amenábar et al, 2020; Douglas et al, 2014). Shark occurances, including † S. macrota , are rare in the overlying Submeseta Fm.…”

Earliest fossils of giant-sized bony-toothed birds (Aves: Pelagornithidae) from the Eocene of Seymour Island, Antarctica

“…A combination of age-dating methods, such as strontium isotopes, magnetostratigraphy, and lithostratigraphy, indicate that the La Meseta Formation is early to middle Eocene in age and the Submeseta Formation is middle to late Eocene in age 18,19 . However, studies of dinoflagellate cysts support a middle to late Eocene age for the La Meseta Formation 20,21 . We refer to the dates generated from the combined methodology 19 in Fig.…”

“…4 ). Depending on the geochronological methods used, the humeral fragment is of a similar age to the Submeseta specimens (the combined methodology of Montes et al 19 ) or the La Meseta specimens (following Amenábar et al 21 ).…”