The first bivalve burrow from the quaternary of Argentina produced by solen tehuelchus. With a discussion on the validity of oblongichnus

Abstract

Oblongichnus (Haouz, Lagnaoui, Silantiev, 2018) is a purported biogenic structure produced bysoft-bottom dwellers from the middle Permian of Russia. This burrow comprises molds of anoblong to recurved elongated and multioriented bivalve. We describe here for the first time a newichnospecies of the Oblongichnus from wavy and flaser lithofacies belonging to the transgressivemarine Destacamento Río Salado Member of the Canal de Las Escobas Formation. Thislithostratigraphic unit was dated by 14C on Solen tehuelchus Hanley, 1842 valves indicating an ageof 6725 ± 35 AP (KIA 33511). The burrows are preserved as concave epireliefs, almond to ellipticalin plain view and differ from ichnospecies of Lockeia by the high depth:length:width ratio and thelining along the widest margin. The burrows are referred to Oblongichnus in the generalappearance of the contour and longitudinal section, they are also very deep, sub-rectangular inlateral 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 tocallianassid burrows, a diverse parautochthonous and allochthonous molluscan fauna and acomplete skeleton of a fur seal. This finding indicates the validity of Oblongichnus but suggeststhe need to define a new ichnospecies. It is also important in the understanding of the sedimentarydynamics of the early-mid Holocene transgression in the Salado Basin. Thus, burrows preservedwith their producers are extremely good indicators of the depositional conditions in fine sequencestratigraphy analysis.