Evolución paleogeográfica de los conglomerados miocenos adosados al borde norte de la Sierra de Cameros. (La Rioja)

A. MUÑOZ, G. PARDO, J. VILLENA MORALES

Abstract


Three Tectosedimentary Units (TSL! A,, A, and A,) were identified in the tertiary conglomeratic facies, which are croping out in Sierra de Yerga, Cabi Monteros and Serradero (southem margin of the Ebro Basin, adjoining the Sierra de Carneros; fig. 1). The first and third TSU have a fining upward evolution; the second one has a cyclic evolution (fining-coarsening upward). Correlation between these TSU with those established in eastern sectors of the Ebro Basin allowed us to date them.

The three TSU range from middle Aragonian to Turolian (Middle to Upper Aragonian, Upper Aragonian to Vallesian and Vallesian to Turolian, respectively). These units were deposited under compressive stress as evidenced by both, vertical evolution of sedimentary units and their relationship to active tectonic structures. Sierra de Carneros thrust affects the first and second TSI;, whereas this thrust is fossilized by the third one. This relationship shows that the age for the end of the compression was, at least, Vallesian. However, Carneros thrust maybe reached the Turolian in adecelerate way. Tmportant horizontal translation of the Sierra de Carneros thrust is detected at the diastrophic maximum which was developed at the onset of the first TSU. Alluvial fans of high transport efficiency, are associated to this horizontal translation. The source areafor these alluvial systems was mainly siliceous in composition (i. e., Purbeck-Weald facies). On the contrary, vertical translation along this trust prevails at two penods of diastrophic maximum which are located at the boundaries of both, the first and second TSU and the second and third TSU, respectively. Alluvial fans of low transport efficiency, which had mainly carbonate units in their source areas (i. e., Jurassic units), are linked to this vertical translation.


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