LACUSTRINE SEDIMENTATION IN THE DIAPIR-CONTROLLED MIOCENE BICORB BASIN, EASTERN SPAIN

The Miocene Bicorb Basin is a small elongated basin developed by norma l faulting of a thick Jurassic-Cretaceous carbonate succession and sub sequent diapirism of Upper Triassic mudstones and evaporites. The basi n fill comprises a sequence over 650 m thick formed by two units. The lower, alluvial unit consists of a complex alternation of conglomerate s, sandstones, mudstones, and minor lacustrine limestones. The upper u nit comprises marginal alluvial and lacustrine deposits in which seven lacustrine facies associations have been distinguished, The inner lac ustrine deposits comprise mudstones and carbonates with minor evaporit ic deposits. At the northeast and southwest basin edges, alluvial inpu ts led to the development of delta and fan-delta environments where sa ndstone and conglomerate deposits dominate, The latter stages of the l ake evolution are represented by an expansive thick limestone sequence which close to the NW fault-bounded margin pass laterally to breccias , The hierarchical arrangement of the upper unit shows five different orders of sequences. The first-order sequence defines a major vertical trend of lake expansion whereas three second-order sequences are link ed to major flooding-expansion episodes. All these sequences are relat ed to the tectonic evolution of the diapir. Metre-scale, third- and fo urth-order sequences and fifth-order sequences, which consist of finel y laminated rhythmite deposits probably record climatically forced pro cesses. The diapir-graben system evolution and the climatic variations have exerted major controls on the sequential arrangement and evoluti on of the lacustrine system. Both factors have also strongly influence d the changes in the gastropod assemblages. (C) 1998 Elsevier Science B.V. All rights reserved.