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Mixed Signals: Using Numerical Modeling to Disentangle Milankovitch Cycles in a Complicated Outcrop

Abstract

The calcarenites that make up the Late Tortonian Azagador Member in Sorbas Basin (SE Spain) were deposited in a high-energy, shallow marine environment, resulting in a succession with poor lateral continuity and an irregular stratigraphy, thereby complicating the construction of a stratigraphic age model. To mitigate this, we combined 32 logs from across the Azagador Member and normalized its stratigraphic expression using transparent image stacking and ‘marching squares’ algorithms. This novel methodology generates an unbiased, stabilized expression of the stratigraphy that is then tuned to the solar insolation target curve from Lasker et al. (2011), resulting in a stratigraphic age model of very high precision. Our tuned age model shows that the effects of precession dominated cyclicity are greatly reduced during an eccentricity minimum, temporarily causing the climatic cyclicity to shift into an obliquity controlled domain. These results link to previous work on adjacent orbitally controlled stratigraphy in the underlying Lower Azagador and the overlying Abad marls, and thus fill a gap in the chronostratigraphy of the Sorbas basin. Furthermore, astronomical tuning has shown that the deposition of a highly conformable shell debris bed, previously interpreted as a tsunamite deposit, does not coincide with the collapse of the Gordo Megabed in the adjacent Tabernas Basin as was previously proposed.