Estructuras sedimentarias inducidas por obstáculos en los lagos someros efímeros de Lillo (Toledo) y Racetrack (EEUU)estudio comparativo

Abstract

In this work, we describe and analyse the formation of erosional and depositional marks produced around obstacles (stones) by unidirectional currents in Racetrack playa (Death Valley, USA) and in three playa-lakes of La Mancha (central Spain). These structures are associated with long and curvilinear grooves lefts behind by stones (sailing stones). The common association of these erosional and/or depositional marks with different biotic features (microbial mat fragments, gas bubbles, pores, organic matter, etc.) is also documented. Given the extremely shallow and flat nature of the playa lakes, the occurrence of erosion marks on its surface, especially the long furrows left by rocks, is not yet fully understood and remains controversial. Through continued and detailed morphological, sedimentary, meteorological and hydrodynamic studies, as well as comparative morphological analyses carried out in Racetrack, the formation of such structures is reconstructed. Obstacle marks form around protruding objects that act as obstacles to the water flow. Eventually, the turbulence can be strong enough to remove and transport the object (rock) in one or more successive stages, which causes the formation of a groove. The recognition of obstacle-induced sedimentary structures, thus, may provide helpful information in reconstructing palaeoenvironments, especially in gypsum rocks.