Reconstrucción de la evolución diagenética de la formación arrecifal de Torrecilla en Cameros (Kimmeridgiense Inferior) durante el desarrollo de la discontinuidad situada a techo (Puerto de Bigornia, provincia de Soria, España)

Abstract

Detailed petrography, and fine-scale geochemical and isotopic analysis of diagenetic phases of the Kimmeridgian reefal Torrecilla en Cameros Formation of Northern Iberian Ranges indicate a complex history of early meteoric diagenesis. This reefal succession underwent extensive alteration by meteoric waters prior to the deposition of the overlying Tithonian-Berriasian continental deposits. Although the continental facies are separated from the reefal unit by a single unconformity, a record o f three distinct episodes of alteration by meteoric waters, infused at this single hiatal surface, is preserved in the succession of calcite cements present within the underlying reefal unit. The first episode of meteoric alteration resulted in the precipitation of a first generation of calcite (Cement I). Two later generations (Cement II and III) were emplaced throughout the reefal unit. Although similar in petrography to Cement I, these phases are distinct in their isotopic composition, reflecting changes in the regional climate of the Iberia during the early Tithonian. Overlying continental units, in turn, record yet another episode of alteration by meteoric waters as non-ferroan calcite cements formed within the lacustrine limestones. These cements are also distinct based on their petrographic and geochemical character.