Características sedimentológicas, secuenciales y tectoestratigráficas del Triásico de Cantabria y norte de Palencia.

Abstract

The Triassic System is represented widely and thickely in outcrops of Cantabria (Santander) and north of Palencia that form the western part of thc Basque-Cantabrian region in north Spain (Fig. 1). It uneonformably overlies Permian or Carboniferous materials and consists of the three characteristie facies of the Germanie Trias. The Euntsandstein shows an important development, mainly in the Central zone (Reinosa Sector), where it reaches a thickness of neariy 1,000 m. Three depositional macrosequences of alluvial and fluvial sediments (Units 1, 2 and 3), are recognized (Fig. 2), alí of them thinning and fining up in character. Jts deposition took place in a W-E orientated tectonie graben (Figs. 3 ané 4), which was enlarged progressively as a result of repeated back-faulting (Fig. 5). The Buntsandstein is followed by the Muschelkalk, up to 100 m thick, with shalloxv marine calcareous facies, in turn overlied by the Reuper, of lagoonal clays with evaporites, with ophitic intrusions. Inmediately after the Keuper sedimentation, compresive N-S movements created W-E folds that were partially eroded along its axis. There, the carbonates of the Uppermost Triassic-Lowermost Jurassie uncoformably overlie older Triassic materials (Fig. 6). The boundary faults of the graben in which the Buntsanéstein was acumulated can be related to a major system of simple shear produced by a NW-SE sinistral shear couple, mostly acting along the NW-SE orientated fault liries of Ventaniella and Bilbao (Fig. 7). A change in the relative rate of movement, or even complete inversion from sinistral to dextral, could account for the folding phase of the final triassic (Fig. 8). The geodinamie pattern postulated for the creation of the Buntsandstein graben is in good agrcement with the strike-slip regime invoked for the triassic rift of the Bay of Biscay (sinistral), and with the contemporaneous movements of individualization of the Iberian subplate (ZIEGLER, 1982). 1.