Precession-related sapropelites of the Messinian Sorbas Basin (South Spain): paleoenvironmental significance

The Sorbas Basin (Southern Spain) is a narrow and elongated basin located i n the Betic Corridor that formed the northern connection between the Atlant ic and the Paleomediterranean during the late Miocene. In the centre of the basin, about 120 m of well-preserved cyclic marine sediments crop out, ran ging in age from 7.2 to 6 Myr. These cycles make up the Abad Member and are an excellent example of precession control over sedimentation. In the uppe r part of the sequence (Upper Abad Member), the cycles include organic-rich laminated brown marls (sapropelites) alternating with homogeneous marls di splaying diatomite layers. The OM-rich laminated marls are the westernmost sapropelites of the Mediterranean. This paper is a geochemical, mineralogic al, sedimentological, and micropaleontological analysis of three cycles wit h sapropelites. The data enable us to distinguish two main climatic scenarios. The climate, which dominated each of these scenarios, regulated the sedimentology and t he physico-chemistry of the water column, resulting in the sapropelite/homo geneous marl cyclic alternations. The sapropelites developed during a clima te characterised by a long period of temperate and humid conditions that oc cur at times of precession minima. These climatic conditions changed progre ssively to a subarid and drier weather, during which homogeneous sediments were deposited. The changes between these scenarios were gradual, as expect ed from precession dynamics. Our data suggest that the change from the suba rid to the humid climate (transition from homogeneous marls to laminated sa propelites) took place at a faster rate or, at least, was recorded more rap idly by the sediments than the transition from the humid interval to the su b-arid period. (C) 2000 Elsevier Science B.V. All rights reserved.