Siliciclastic sedimentation and sequence stratigraphic evolution on a storm-dominated shelf: the Lower Ordovician of the Central Iberian Zone (NE Jaen, Spain)

The Lower Ordovician of the southernmost part of the Central Iberian Zone (southern Spain) is a 1000-m thick, transgressive, largely siliciclastic succession deposited on a shallow epicontinental shelf. Facies analysis reveals lithofacies representing a variety of depositional environments, ranging from foreshore-shoreface (Facies S-0), proximal to distal parts of the shoreface (Facies S-1, S-2) proximal to distal shelf (Facies H-1, H-2, H-3) outer shelfzone or continental slope (Facies M). The vertical arrangement of the facies is characterized by the presence of high-frequency regressive cycles (partial shelf progradational sequences), themselves interrupted by strata resulting from catastrophic phenomena (storms), producing higher order autocycles of transgressive-regressive character. Major regional unconformities and the vertical distribution of the facies delineate successive genetically related units in relation to relative sea-level changes. Two second-order megacycles have been distinguished. The first of them (MCl), Tremadoc?-Lower Arenigian in age, comprises one third-order sequence (Ar-1). The lower part of the second megacycle (MC2), deposited during the Arenig-Llanvimian, displays a trangressive stratigraphic architecture. Within this megacycle, three third-order sequences are proposed (Ar-2, Ar-3, Lln-1), in which a transgressive systems tract and a highstand systems tract can be distinguished. Facies attributable to lowstand systems tracts are restricted to the base of the Ar-2 sequence, at the boundary between megacycles. (C) 2003 Elsevier B.V. All rights reserved.