The cañadón de las vacas-rincón del buque area: preliminary correlations with other santacrucian (Early Miocene, Patagonia) localities

VIZCAÍNO, S. F.; BARGO, M. S.; FERNICOLA, J. C.; CUITIÑO, J. I.; TRAYLER, R.; KOHN, M. J.; KAY, R. F.; TOLEDO, N.; MUÑOZ, N. A.

General Roca, Río Negro

Congreso; XI Congreso de la Asociación Paleontológica Argentina; 2016

Thearea of Cañadón de las Vacas (CV) and adjacent Rincón del Buque (RB) (SoutheastSanta Cruz Province) includes outcrops of the continental Santa Cruz Formation(SCF), rich in fossil vertebrates of Santacrucian Age (Early Miocene). Theoutcrops extend for some 28 km from N to S from (50° 31? 45? S; 69° 7? 52? W)to (50° 46? 37? S; 69° 10? 1? O). In total, they comprise a section ~170 m inthickness overlying the marine Monte León Formation. The section is exposedalmost completely and continuously in CV and more discontinuously in RB.Previous Ar/Ar dates from CV framed much of the section between 17.4 Ma (tuffCO, near the base) and 16.9 Ma (tuff TB, in the upper third of the section).New U/Pb dates render provisionally slightly older ages for these levelsbetween 17.69 Ma (CO) and 16.83 (TB). Together with recently published datesfrom outcrops of the SCF along the Río Santa Cruz, they allow correlation ofthe CO-TB section at CV with the basal and middle levels of the section atBarrancas Blancas at Río Santa Cruz. The levels above TB would correlate withthe higher levels at Barrancas Blancas and the most basal part of the sectionat Segundas Barrancas Blancas. The lower part of the CO-TB section at CV andthe underlying levels would correlate with the higher levels at Río Bote, nearLago Argentino, ~190 km to the West. Overall, the CV-RB area enables intensivesampling for fossil vertebrates, in progress, particularly important for thehigher levels, which are virtually inaccessible in classic cliffs of thecoastal localities of the SCF south of Río Coyle. The vertebrate fossilassemblage and the new radiometric ages obtained in CV and RB will allowaccurate biostratigraphic correlations of middle and upper levels of the SCFalong the Santa Cruz and Chalía rivers and the western Andean localities aswell. They also will constrain paleoenvironmental and paleoecological changesin time