--> Platform Controls on Basin Sedimentation: The Role of Paleotopography and Relative Sea Level, La Rellana Platform and Agua Amarga Basin, Cabo de Gata, Southeast Spain

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Platform Controls on Basin Sedimentation: The Role of Paleotopography and Relative Sea Level, La Rellana Platform and Agua Amarga Basin, Cabo de Gata, Southeast Spain

Abstract

Typical depositional models for resedimented deepwater carbonates fail to reflect the impact of platform topography on sediment redistribution. This study focuses on a 2-dimensional coastal exposure perpendicular to the margin of the Rellana platform and builds upon work done in the Agua Amarga basin (Cabo de Gata region, Southeast Spain) to demonstrate the interaction of paleotopography and sea level on sediment redistribution into the basin. The results counter the highstand shedding model and focus on proximity of the reefal margin to a steep basin margin. The Rellana platform developed on Neogene volcanic substrate that features a drainage divide separating a steep-dipping (~15 °) south slope from a shallow-dipping (~5 °) north slope. The shallow-dipping north slope steepens to 25° distally (1.3 km N of the drainage divide) and defines the basin margin. It eventually flattens as it reaches the basin floor. The Rellana platform formed the southern rim above the Agua Amarga basin for approximately 4.5 km and was a major source for carbonate accumulations. Seven sequences on the platform document the evolution of the platform from a heterozoan ramp, to photozoan reef to a shallow marine microbial/oolitic system. Basinal deposits consist of grainy heterozoan-dominated shallow-water deposits, hemi-pelagic and pelagic deep-water deposits, carbonate/volcanic breccias, as well as high- and low-density turbidites. During the platform reef phase, the initial reef margin was near the steep basin margin, and margin sourced coarse breccias accumulated in the basin. During a subsequent sea-level rise, the reef margin stepped backward resulting in backstepping of basinal breccias and an increase in fine grained basin deposits. Highstand reef progradation towards the basin margin resulted in an increase of coarse grained, mostly sediment gravity flow deposits in the basin. As sea level fell, reefs continued to prograde and downstep toward the basin resulting in increasing amounts of coarse-grained basinal deposits, including breccias, that progressively stepped toward the basin center. Our results show that proximity of the reef margin to the basin margin increases the volume of coarse material deposited in the basin. This runs counter to the highstand-shedding model and indicates an alternative timing for deposition of coarse-grained basinal sediments.