Sedimentary Provenance and Depositional History of Cadiz Bay (SW Spain) Based on the Study of Heavy Minerals Surface Textures

Resumen

Mineralogical and Scanning Electron Microscope (SEM) analysis was used to study heavy mineral grains present in recent marine sediments from Cadiz Bay (SW Spain) and the adjacent continental shelf, in order to establish the provenance of sediments and to determine physical and chemical processes which took place during their depositional history. Surface features analysis has been used to detect mechanical and chemical textures; euhedral, sub-euhedral and anhedral grain morphologies have been observed. Different phases or stages in the sedimentary evolution of these heavy mineral grains can be differentiated. The oldest one corresponds to eolian environments, followed by fluvial and coastal environments. The third phase is represented by chemical alterations acquired in shallow marine environments. The recent phase is characterized by presence of textures generated in pedogenic environments. Heavy mineral assemblages established in this work were compared with those found in the nearby continental areas; they are used to identify likely sediment sources. The most important source is the Iberian Massif, which provided euhedral and sub-euhedral metamorphic minerals, while the secondary sediment sources correspond to pre-orogenic formations of the Betic Cordilleras with predominance of anhedral grains of high degree of maturity. Other sediment sources are the post-orogenic Tertiary deposits present in the Guadalquivir basin and the plio-quaternary and fluvial deposits outcropping along coastal and continental areas near the bay of Cadiz