Caracterización geoquímica de facies pobremente oxigenadas en el Toarciense inferior (Jurásico inferior) del Subbético externo

Zusammenfassung

The analisys of facies and geochemistry of the Lower Toarcian (Lower Jurassic) of the Cueva del Agua section (Zegrí Fm, External Subbetic) have allowed to characterize the incidence of the Toarcian anoxic event in this area. The absence of trace fossils and foraminifera in a thinly laminated marly interval with increasing values of Mo/Al ratio, total organic carbon (TOC) and total sulphur (TS) confirm suboxic to anoxic conditions in sea-water of the bottom. Simultaneously, CO3Ca (%) and δ13C decrease whereas δ18O presents a negative excursion. This allows interpreting a perturbation in the carbon cycle and increasing temperature during the Serpentinum Zone. Overlying the thinly laminated marly interval, the Mo/Al, TOC, S and δ18O recover Pliensbachian values and trace fossils and foraminifera are registered too. These data are interpreted as the return to oxic conditions. The record of Fe and Mn oxides and oxi-hydroxides confirm the recovery of oxic conditions in the sea-bottom. Subsequent deposits of thin-bedded limestones with hummocky and cross lamination composed by micritic and radiolaritic laminae have been related to distal tempestites.