Diagénesis temprana meteórica de la Formación Torrecilla en Cameros (Kimmeridgiense inferior; Preriff) y de los carbonatos de la base del GrupoTera (Tithónico; Sinriff) en el sector de Soria. Cuenca de Cameros. N. España

Abstract

The last marine Jurassic episode of sedimentation in the Soria area corresponds to the deposition of the Torrecilla en Cameros Fm. during Lower Kimmeridgian. This formation is mainly composed by sandstones, coral reefs and oolites, and is overlain by the Tithonian continental sediments (clays, conglomerates, sandstone and lacustrine and palustrine limestones) of the Âgreda Afm. (Tera Croup). The limit between both units corresponds to an edaphic surface overlain by a ferruginous crust. Associated to the subaerial exposure of the Torrecilla en Cameros Fm. during Upper Kimmeridgian, and prior to the deposition of Âgreda Afm., marine aragonite was dissolved. Both primary and secondary porosity were then cemented by meteoric non-ferroan calcite. Isotopic composition of this calcite ranges between -3.7 and -7.3 ‰ in δ13C and -4.7 and -5.9 ‰ in δ18. Carbonates situated at the base of the Âgreda Afm. correspond to some layers of palustrine limestones as well as conglomerates, basically composed by lacustrine and oolitic pebbles. The isotopic composition of both palustrine limestones and limestone pebbles is very similar to the isotopic composition of the meteoric cement precipitated in the Torrecilla en Cameros Fm. This suggests that the climatic conditions and the isotopic composition of the meteoric waters were very similar during precipitation of meteoric calcite in both Torrecilla en Cameros Fm. and the base of the Âgreda Afm.