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Neogene Gravity-driven Deformations around Gibraltar Arch Prior to the Messinian Salinity Crisis

Carlos Giraldo and Wilber Hermoza

The objective of this study is to evaluate deformation styles prior to the Messinian Salinity Crises (MSC) west and east of the Gibraltar Arch and to understand possible relationships between geodynamic setting, deformation styles and isostatic rebound of the Betic-Rif ranges. Regionally, the Gibraltar Arch is part of the Betic-Rif arcuate fold-thrust belt that resulted from collision between the Alborán, Iberian, and African plates during the early Neogene. The Gibraltar Arch isostatic rebound, in contrast to tectonic uplift, occurred prior to the Pliocene and is considered to be the main cause of disconnection between the Atlantic Ocean and the Mediterranean that led to the MSC (5.96 Ma-5.33 Ma).

2D and 3D seismic interpretation in the Gulf of Cádiz and west Alborán Sea suggest that dominant deformation styles of Neogene sediments prior to the MSC are associated with gravitational-gliding processes resulting in toe-thrusts and extensional rollovers. This gravitational deformation is related to the isostatic uplift of the Gibraltar Arch which occurred during the Middle-Late Miocene and is sealed by Pliocene strata. At least two episodes of gravity gliding processes occurred on the west Alborán side: Middle Miocene (c. 13-15 Ma) and Late Miocene (c. 7-10 Ma). In the Gulf of Cádiz a very large gravity-gliding feature known as the “Olistostrome” event is sealed by Upper Miocene sediments (c. 7-10 Ma). Active mud volcanism, triggered from Miocene overpressured shales, post-dates the MSC west and east of the Gibraltar Arch.

In the west Alborán domain the Neogene basin lies directly above the igneous-metamorphic complex known as the Alborán allochthonous. However, in the Gulf of Cádiz area the contemporaneous Neogene sediments have been deposited above the northernmost extension of the Mesozoic-Tertiary passive margin of the west African plate.

AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013