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Mixed carbonate-siliciclastic record on the North African margin (Malta)—coupling of weathering processes and mid Miocene climate

Cédric M. John^,1, Maria Mutti^,1 and Thierry Adatte^,2

¹ Institut für Geologie und Paläontologie, University of Stuttgart, D-70174 Stuttgart, Germany
² Institut de Géologie, Université de Neuchâtel, CH-2007 Neuchâtel, Switzerland

We investigated rock outcrops spanning the middle Miocene, global climate-cooling step on the Maltese Islands in order to reconstruct continental weathering rates and terrigenous fluxes, as well as to explore the coupling between these later, regional climate and carbonate accumulations. Sedimentation at this location was dominated during the Oligocene and early Miocene by a transitional platform to slope carbonates but progressively switched to a clay-rich carbonate slope system in the middle Miocene. Around 13 Ma, an abrupt change toward clay-dominated marls occurred, and marl deposition persisted until the Tortonian (ca. 12 Ma), when a shallow-water carbonate ramp was reestablished. Clay mineralogy and bulk-rock oxygen isotope analyses suggest that the deposition of the Blue Clay formation was mainly caused by global climate change and related change in the rate of continental weathering.

A significant negative correlation (R² = 0.65) exists between the carbonate content and the ¹⁸O record. This, combined with the variation of mass accumulation rate of terrigenous material, suggests that shorter-term periods of globally cooler climate (Mi events) were associated with higher rates of accumulation in continental-derived material. Since during the Miocene Malta was attached to the North African Margin, we propose that the observed trends were due to a regional increase in rainfall during cooler periods, which consequently increased continental weathering and runoff. We further suggest that this pattern was linked to the perturbation of atmospheric fronts due to an increased thermal gradient during the Miocene. Thus, regional increase in rainfall might have been linked to the northward migration of the Intertropical Convergence Zone (ITCZ).

Key Words: Miocene • climate • weathering • clay mineralogy • continental margin • Malta

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