Late Cretaceous long famine and short feast in Antarctica: Ichnological evidence from the Marambio Group

OLIVERO, E. B.; LÓPEZ CABRERA, M.I.

Idanha-a- nova

Congreso; ICHNIA 2016 IV International Ichnological Congress; 2016

Unesco International Ichnological Association

The expression long famine and short feast reflects the key role of strongseasonality in food production and structuring of modern polar marineecosystems, the origin of which has been influenced by the combination ofhigh-latitude and extreme cooling characterizing Antarctica since the latestEocene-Oligocene. Nonetheless, we present evidence that during an interval ofsignificant climatic and biotic reorganization mostly endemic Late Cretaceoustrace fossils of the Cruziana ichnofacies, Marambio Group, Antarcticarepresent behaviors reflecting a long famine and short feast scenario. Duringthe Santonian-Maastrichtian the Marambio Group record a cooling trend ofseawater temperatures from ~18C° to ~8C°, which is accompanied byremarkable shifts in the biogeography of mollusks (Olivero, 2012) andichnofossils. Consequently, typical cosmopolitan trace fossils of the Cruzianaichnofacies where progressively replaced by a suite of geographicallyrestricted complex spreite ichnofossils, dominated by Paradictyodoraantarctica, Tasselia ordamensis, Euflabella ispp., and Patagonichnus ispp. (Fig.1). Even though their complex spreite structures clearly classify them asfodinichnia important variations in their general bauplan suggest multiplefeeding strategies. The trace markers of these ichnospecies, particularly thoseof Tasselia ordamensis (Fig. 2) and Euflabella multiplex (Fig. 3), are bestinterpreted as trophic generalists, well adapted for deposit feeding, surfacedetritus feeding, and bacterial gardening (Olivero and López C., 2010, 2013).Surface detritus feeding is denoted by the relative high concentration ofcalcispheres, diatoms and foraminifers in the backfill lamellae, whereas thesystematic reworking of previous backfill laminae (negative phobotacticbehavior) supports gardening, with the upper part of each laminae being usedto culture bacteria, suggesting strategies to cope with seasonally fluctuatingfood resources and implying a Late Cretaceous long famine and short feastscenario as in the modern Antarctic fauna.