RAPID FLOODING OF THE NORTHERN ARGENTINE SHELF DURING THE LATE GLACIAL: PALEOECOLOGICAL AND GEOCHRONOLOGICAL CONSTRAINS

CECILIA LAPRIDA; MARIA SOFIA PLASTANI; GERMAN DIAZ; ROBERTO A. VIOLANTE; NATALIA GARCÍA CHAPORI

Mar del Plata

Congreso; XVIII Congreso Latinoamericano de Ciencias del Mar COLACMAR 2019; 2019

During the Last Glacial Maximum (LGM), the Argentine Continental Shelf (ACS) was subaerially exposed. Subsequent sea level increase produced a complex sedimentary sequence. However, sedimentary sequences spanning the time between the LGM and the Holocene, the Late Glacial (LG), have been elusive and their records hard to find. Consequently, coastal environmental evolution of the northern ACS during the LG is still speculative in many aspects. Here we analyze a sedimentary core from northern ACS (SHN-T394; 40o09?S-57o14?W, 100m) which records a key period within the LG. Lithology, microfossils and radiocarbon dates indicate that the sequence between 16,5- 12,7kyr BP was mainly controlled by sea-level changes. Between 16,5-15kyr BP the dominance of Cyprideis salebrosa indicates fresh to brackish water continental environments, probably related with the Colorado river paleosystem; foraminifera were also recovered. This apparent contradiction suggests that the LG continental environments of the shelf were carved in marine sediments deposited during MIS3, when sea-level rose up to -60m, since foraminifera from these levels are robust and support reworking, while fragile forms are absent. Thereafter, between 15-14,1kyr BP, the dominance of limnocytherids and well preserved Ammonia becarii indicate fluvio- estuarine, mixohaline conditions. Full marine estuarine conditions prevailed between 14,1-13,8kyr BP, as evidenced by the dominance of Perissocitheridea whitensis. Continental ostracods gradually disappear since 13,8kyr BP in coincidence with a 54 cm-thick shelly concentration, indicating that a rapid sea level rise occurred. The shell bed includes marine macroinvertebrates which combined with taphonomic features indicate deposition in the lower shoreface, and marks the end of the Pleistocene sedimentation. Holocene is represented in the shelly sand of the uppermost 10cm, where outer shelf-upper slope foraminifera (Uvigerina striata, Globocassidulina inflata) and fully-marine ostracods were the only calcareous microfossil found. The section assigned to the LG was deposited during a rapid sea-level rise contemporaneous to the Meltwater Pulse 1A, when the highest rates of post-glacial sea-level rise occurred worldwide. During this period, much sediment was supplied to the present outer shelf since our data imply a sediment accumulation rate of 17yr/cm between 16,5-13,8kyr BP, increasing to 36yr/cm between 13.8-12.7kyr BP when the shelly concentration was deposited.