COUPLED PALEOGEOGRAPHIC PATTERNS IN LATE CRETACEOUS, SHALLOW-MARINE BODY AND TRACE FOSSILS FROM ANTARCTICA

OLIVERO E.B.; LOPEZ CABRERA, M.I

Mendoza

Congreso; 4th International Palaeontological Congress; 2014

IPA - CONICET MENDOZA

Late Cretaceous mollusks from the Marambio Group, James Ross Basin, NE Antarctic Peninsula, record a long cooling trend of seawater temperatures from the Coniacian/Santonian (~18C°) to the Maastrichtian (~8C°). Accompanying this trend are remarkable shifts in the biogeographic distribution of pelagic (ammonites) and benthic (bivalves) faunas. A strong biogeographical contrast is apparent between nearly cosmopolitan or Indo Pacific Santonian faunas and Southern Gondwanarestricted mid Campanian-Maastrichtian ones. The pelagic elements of the latter are characterized by radiation and dominance of the stenothermal kossmaticeratid ammonites and early extinction of the scaphitid, nostoceratid, and baculitid ammonites; and the benthic fauna by the early extinction of inoceramid and most trigoniid bivalves. Here we document and discuss accompanying changes in fossil behavior, expressed by complex spreite burrows that are mostly restricted to southern highlatitudes. The 3 km-thick Marambio Group records a variety of deltaic, estuarine, storm-influenced, and shelfal fine-grained deposits bearing ichnological suites characteristic of the proximal and distal Cruziana ichnofacies. Typical Upper Cretaceous ichnogenera that are well-known elsewhere in the world include: 1) for the proximal and archetypal Cruziana ichnofacies, Asterosoma, Chondrites, Nereites, Ophiomorpha, Phycodes, Phycosiphon, Planolites, Rhizocorallium, Rosselia, Schaubcylindrichnus, Scolicia, Taenidium, Teichichnus and Thalassinoides; and 2) for the distal Cruziana ichnofacies, the addition of large specimens of Stelloglyphus, Zoophycos, and restricted horizons with graphoglyptids. Among these a distinctive group of complex spreite burrows appears at different times with increasing diversity and dominance, including Paradictyodora antarctica (Santonian); P. antarctica and Tasselia ordamensis (late early Campanian); P. antarctica, T. ordamensis, and Euflabella singularis (mid Campanian); P. antarctica, T. ordamensis, E. singularis and Euflabella multiplex (late Campanian); and P. antarctica, T. ordamensis, E. singularis; E. multiplex, Euflabella radiata, Patagonichnus stratiformis and Patagonichnus thalassiformis (Maastrichtian). These complex spreite burrows are shallow-tier fodinichnia, but some of their producers were also trophic generalists, living on detritus from the burrowed sediment, fresh detritus from the surface, and bacterial gardening. Except for T. ordamensis, which is poorly known outside Antarctica and Tierra del Fuego, the rest of these spreite burrows appears to be restricted to southern high paleolatitudes. By the Late Cretaceous, the James Ross Basin was already positioned at its present latitude of about S64° and we hypothesize that high paleolatitudes, resulting in strong seasonal variations in primary production, and cooling, both favored the appearance of specialized strategies and behaviors offering a causal explanation for the observed concurrent paleogeographical restrictions in the pelagic and benthic faunas and trace fossils.