Characterization of deltaic sediment bodies based on in situ CPT/CPTU profiles: A case study on the Llobregat delta plain, Barcelona, Spain

摘要

This article describes a preliminary study on the Llobregat delta, Spain, which includes the construction of a 3D model from cone penetration tests (CPT) and piezocone tests (CPTU) in order to establish the architectural stacking pattern of deltaic sediment bodies. The sediment facies identified from boreholes have been characterized by using their mechanical behaviour and have been used to identify the depositional sequence of the Llobregat delta. Within the general architectural frame, flood plain silts and silty sands, crevasse sands, fluvial channel sands, sand ridges, delta front silts and clays, and prodelta silts and clays have been characterized as a function of cone tip resistance (qc) and sleeve friction (fs). From the sediment facies characterization, a depositional sequence constituted by three systems tracts is proposed. The sequence is divided into: a lowstand systems tact (LST) represented by fluvial gravels, a transgressive systems tact (TST) constituted by a fining-upward sequence with a thin sand sheet below silts and clays, and the highstand systems tract (HST) represented by three prograding wedges displaying coarsening-upward sequences. We emphasize the simplicity, speed, high spatial resolution and low cost of CPT/CPTU grids as a new tool enabling us to reconstruct the three-dimensional structure of deltaic environments for sedimentological and stratigraphical purposes.