Rapid flooding of the northern argentine shelf during the late glacial: paleoecological and geochronological constrains

LAPRIDA, CECILIA; DÍAZ, GERMÁN; GARCÍA CHAPORI, NATALIA; MARIA, SOFÍA PLASTANI ; VIOLANTE, ROBERTO

Mar del Plata

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

INIDEP

During the Last Glacial Maximum (LGM), the Argentine Continental Shelf (ACS) wassubaerially exposed. Subsequent sea level increase produced a complex sedimentarysequence. However, sedimentary sequences spanning the time between the LGM andthe 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 isstill speculative in many aspects. Here we analyze a sedimentary core from northernACS (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 thedominance of Cyprideis salebrosa indicates fresh to brackish water continentalenvironments, probably related with the Colorado river paleosystem; foraminifera werealso recovered. This apparent contradiction suggests that the LG continentalenvironments 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 andsupport reworking, while fragile forms are absent. Thereafter, between 15-14,1kyr BP,the dominance of limnocytherids and well preserved Ammonia becarii indicate fluvioestuarine,mixohaline conditions. Full marine estuarine conditions prevailed between14,1-13,8kyr BP, as evidenced by the dominance of Perissocitheridea whitensis.Continental ostracods gradually disappear since 13,8kyr BP in coincidence with a 54cm-thick shelly concentration, indicating that a rapid sea level rise occurred. The shellbed includes marine macroinvertebrates which combined with taphonomic featuresindicate deposition in the lower shoreface, and marks the end of the Pleistocenesedimentation. 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 sectionassigned to the LG was deposited during a rapid sea-level rise contemporaneous tothe Meltwater Pulse 1A, when the highest rates of post-glacial sea-level rise occurredworldwide. During this period, much sediment was supplied to the present outer shelfsince our data imply a sediment accumulation rate of 17yr/cm between 16,5-13,8kyrBP, increasing to 36yr/cm between 13.8-12.7kyr BP when the shelly concentration wasdeposited.