Record of the Messinian Salinity Crisis in the SW Mallorca area (Balearic Promontory, Spain)

Abstract

The current interpretation of the Messinian Salinity Crisis (MSC) involves the deposition of the so-called “peripheral or marginal” evaporites in onshore basins, as well as the erosion of the margins and the formation of thick evaporites in the deep parts of the basins. The present study focuses on intermediate depth basins, i.e. located between the onshore outcrops and the deep basins. Indeed, the Balearic Promontory shows small stepped basins filled with MSC deposits between its western extremity on the Alicante shelf and its eastern end around the Menorca block. New and already available seismic reflection profiles and onshore data allow us to investigate the nature and geometrical relationships of these deposits in the area between the islands of Ibiza and Mallorca. Our observations suggest the existence of three MSC-related units in this area. The lowermost transparent seismic unit can be interpreted as a 100 to 200-m-thick salt layer deposited in the deepest part of the Central Mallorca Depression. These evaporites pass laterally and upward into a thin-bedded seismic unit, which could be lithologically equivalent to the Upper Evaporites of the deep basins. All around the borders of the Central Mallorca Depression, this bedded seismic unit onlaps a Slope Unit which shows bedded to chaotic and rafted facies. The Messinian continental shelf is eroded and incised by a valley extending from the Palma onshore area to the Mallorca downslope domain. Our results suggest the presence offshore of at least two generations of diachronous MSC deposits. The observation of salt on a continental high and the widespread MSC deposits on the margins of the Central Mallorca Depression call into question the location of halite preferentially in the deep abyssal basins and the significance of the deep basin MSC units that onlap onto the Margin Erosional Surface (MES), as observed all around the passive margins of the Northwest-Mediterranean Basin. The dual terminology used for peripheral/deep MSC evaporites cannot be applied to any of the MSC units found in the study area.