Las unidades del Jurásico superior en el sector nororiental de la Cordillera Ibérica: nuevas subdivisiones Iitoestratigráficas.

Abstract

Kimmeridgian sediments in the Iberian Chain (Eastern Spain) are mainly formed by a uniform. rithmic limestone and man interbedding (the so-called «Loriguilla Formation»). Throughout the studied area, at the NE part of Iberian Chain (Fig. 1), these sediments show some particular lithological ant! paleontological features which allow them tobe individualised as different lithostratigraphic units. Two new tcrms are erected, as new members, within Loriguilla Formation (Fig. 2): (1) Calanda Member, lower. extending widely throughout te eastern part of the studied area. It is mainly formed by a some 20 m thick rithmic interbedding of white, ammonite-bearing limestone (wackestone of fossils) ant! marts (Fig. 3). The age of tUs unit ranges from lowem Platynota to upper Acanthicum Zone. (2) Alac n Member, upper, and geographically restricted to the western part of the studied area (= Alac n ant! near arcas). It consists of a 20 m thick succession of massive white. chalky and bioclastic. highly fossiliferous limestones (packstone of bioclasts and fossils with pelloids ant! oncolites) see Fig. 4 . The age of tUs unit probably ranges from Upper Kimmeridgian to Lower Tithonian (Endoxus to? Hybonotum Zone). Numerous complementary reference sections have been studied. tbat of Molinos being specially signiflcant (Fig. 5). due to the strong reduction of thickness shown by the materials of Loriguilla Formation. A model of paleogeographie evolution is proposed (Fig. 6) br the studied area during the Kimmeridgian. A general transgressive-regressive pattemn throughout Lower to Upper Kimmeridgian can be inferred. Sedimentation takes place on an extended uniform. carbonate ramp where a small paleogeographic high (the «Amiæo-Andorra High») would be responsible for the individualisation of an outer. open shell area where ammonitebearing limestones predominate during Lower Kimmeridgian (Calanda Member). During the Upper Kimmemidgian shallow bioclastic facies are developped at the sorroundings of the paleogeographic high, (Alac n Mcmber) according to the general regression on the platform.