THE FIRST BIVALVE BURROW FROM THE QUATERNARY OF ARGENTINA PRODUCED BY SOLEN TEHUELCHUS. WITH A DISCUSSION ON THE VALIDITY OF OBLONGICHNUS

CARVALHO C.N.D; CECILIA LAPRIDA,; CRISTIAN PEREYRA

La Plata

Jornada; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2019

APA

Oblongichnus (Haouz, Lagnaoui, Silantiev, 2018) is a purported biogenic structure produced by soft-bottom dwellers from the middle Permian of Russia. This burrow comprises molds of an oblong to recurved elongated and multioriented bivalve. We describe here for the first time a new ichnospecies of the Oblongichnus from wavy and flaser lithofacies belonging to the transgressive marine Destacamento Río Salado Member of the Canal de Las Escobas Formation. This lithostratigraphic unit was dated by 14C on Solen tehuelchus Hanley, 1842 valves indicating an age of 6725 ± 35 AP (KIA 33511). The burrows are preserved as concave epireliefs, almond to elliptical in plain view and differ from ichnospecies of Lockeia by the high depth:length: width ratio and the lining along the widest margin. The burrows are referred to as Oblongichnus in the general appearance of the contour and longitudinal section, they are also very deep, sub-rectangular in lateral longitudinal view, and no longer than 4 cm in the observed specimens. In some cases, valves of Solen tehuelchus are still present in their burrows. These burrows occur associated to callianassid burrows, a diverse parautochthonous and allochthonous molluscan fauna, and a complete skeleton of a fur seal. This finding indicates the validity of Oblongichnus but suggests the need to define new ichnospecies. It is also important in the understanding of the sedimentary dynamics of the early-mid-Holocene transgression in the Salado Basin. Thus, burrows preserved with their producers are extremely good indicators of the depositional conditions in fine sequencestratigraphy analysis.