Early Eocene calcareous nannofossils of the Punta Torcida

CUCINIELLO, CARLOS D.; BEDOYA AGUDELO, ERIKA LORENA; PÉREZ PANERA, JUAN PABLO; OLIVERO, EDUARDO

Athens

Congreso; 16 International Nannoplankton Association Meeting; 2017

International Nannoplankton Association

Calcareous nannofossil assemblages from a 105m-thickpartial section at the type locality of the Punta Torcida Formation,Austral Basin are presented. The section consistsof dark gray siltstones that are interbedded with thin graysandstones. According to the planktonic foraminiferal andradiolarian record, the Torcida has an early Eocene age(planktonic foraminifera Zones E5-E7: 49?52.2Ma), andthe micropaleontological assemblage records the ETM-3(Eocene thermal maximum)(Malumián & Jannou, 2010;Jannou, 2012; Malumián et al., 2014). There were highrelative abundances of the genera Toweius, Reticulofenestra,and Pontosphaera in the organic rich siltstones. This,in association with diatoms, radiolarians, and planktonicforaminifera, suggests eutrophic sea surface waters andan outer shelf paleoenvironment. The lower part of theprofile (samples 742-1 to 742-3) yielded an assemblagedominated by Toweius spp., Chiasmolithus bidens, and theholococcolith Lanternithus simplex, which assigned it toZone NP11. Sample 742-2 had a relatively higher speciesrichness and abundance and together with the presence ofDiscoaster kuepperi, Sphenolithus moriformis, and Sphenolithusorphanknollensis might reflect the ETM-2 paleoclimaticevent (Fig. 1). In the middle part of the section(samples 742-4 to 744-3), assemblages were assigned toZone NP12, which contained the first appearance of thegenus Reticulofenestra. This agrees with the older appearanceof the genus in the southern high latitudes (Schneideret al., 2011; Shepherd & Kulhanek, 2016). The youngersamples in this section yielded a high relative abundanceof Discoaster kuepperi, and this sudden reappearanceis interpreted as the ETM-3 (Agnini et al., 2006; 2014).In the upper part (samples 744-4 to 744-7), nannofossilassemblages were assigned to Zone NP13, and Reticulofenestraspp. thrived to the detriment of Toweius spp. Thisnannofossil event has been observed worldwide (Schneideret al., 2011) and coincides with a climatic coolingtrend after the early Eocene climatic optimum (EECO).