Mediterranean Messinian Salinity Crisis: constraints from a coeval marginal basin, Sorbas, southeastern Spain

Abstract

The extent, timing and effects of Late Miocene desiccation and evaporite deposition in the Mediterranean Sea remain controversial. Marginal basins containing Messinian (5.3–7.1 Ma) sequences now exposed onland supplement information from the deep Mediterranean, but have evaporites of a variety of ages. Some of these Messinian evaporites pre-date, and others post-date, deep desiccation. None appears to be exactly coeval with those of the deep Mediterranean. In the Betic Cordillera of southern Spain, basins (e.g. Granada Basin) far from the present-day Mediterranean lost connection with the Mediterranean due to uplift ∼1 Ma before the Salinity Crisis, and have marine evaporites of early, not late, Messinian age. In contrast, basins such as the Sorbas Basin in southeastern Spain, adjacent to the present-day Mediterranean, record events directly reflecting the course of the Salinity Crisis. The Sorbas Basin retained marine connection with the western Mediterranean up until evaporative drawdown in the mid-Messinian and was rapidly reflooded immediately afterwards. The Sorbas Messinian sequence is up to 320 m thick. It is complete and normal marine, except for an incised basinwide erosion surface overlain by a 130 m thick gypsum deposit. We propose that this surface marks the interval of deep desiccation of the adjacent Mediterranean basin. Erosion occurred shortly after 5.9 Ma and the irregular unconformity has relief of at least 240 m, confirming Mediterranean drawdown significantly below the Atlantic level. Sorbas gypsum deposits overlie the unconformity and are intercalated with marls estimated at ∼5.5 Ma containing normal marine Messinian biotas. These gypsum deposits therefore post-date deep desiccation and formed in a silled basin immediately following marine reflooding. They mark the end of the Salinity Crisis and are overlain by 70 m of normal marine sediments containing unreworked foraminifers of latest Messinian age. This succession demonstrates that the Salinity Crisis occurred faster and was completed sooner than previously believed. It took place within ∼0.4 Ma (time-scale of Berggren et al., 1995b, is ∼0.2 Ma on the time-scale of Baksi, 1993) and was completed before the end of the Messinian. This corrects previous views that the Salinity Crisis continued until the Early Pliocene. There is no evidence in the Sorbas Basin for brackish `Lago Mare' conditions, and the normal marine biotas that directly precede and follow drawdown rebut earlier suggestions of prolonged salinity effects.