Lower Aptian ammonite biostratigraphy in the Maestrat Basin (Eastern Iberian Chain, Eastern Spain). A Tethyan transgressive record enhanced by synrift subsidence

Abstract

The present paper analyses the stratigraphic distribution of ammonites collected in the Lower Aptian sediments of the Maestrat Basin (E Spain). The faunal successions obtained from the systematic sampling of ten selected sections located in several sub basins led us to identify four biostratigraphic units (from base to top: Deshayesites oglanlensis, Deshayesites forbesi, Deshayesites deshayesi and Dufrenoyia furcata Zones) that are directly correlatable with the current Mediterranean standard zonation. This study further provides essential biochronologic information to accurately date the different lithostratigraphic units included in the interval studied. Thus, the upper part of the Xert Formation can be tentatively attributed to the lowermost Aptian (D. oglanlensis Zone). The Forcall Formation, which has yielded most of the ammonites, practically extends within most of the Lower Aptian. Its lower and middle parts (Cap de Vinyet and Barra de Morella Members) correspond to the upper part of the D. oglanlensis Zone and the lower part of the D. forbesi Zone, respectively. The base of the Morella la Vella Member (upper part of the Forcall Formation) includes the local record of Oceanic Anoxic Event 1a (OAE 1a) and correlates with the Roloboceras hambrovi horizon (middle/upper part of the D. forbesi Zone). The boundary between the Forcall Formation and the Villarroya de los Pinares Formation is diachronous and varies depending on the sub-basins. The base of the Villarroya de los Pinares Formation can be dated as the middle-upper part of the D. furcata Zone in the Galve, Perello and Salzedella sub-basins.