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Significance of pot and gutter casts in a Middle Triassic carbonate platform, Betic Cordillera, southern Spain



Pot casts and gutter casts are described for the first time in the lower part of the Majanillos Formation, a Middle Triassic carbonate unit located in the External Zones of the Betic Cordillera (southern Spain). Their identification, as well as their relation to tempestites, enables the better interpretation of the depositional environments and the shoreline-to-offshore facies transition on the Anisian muddy carbonate ramp of the southern Iberian Massif. The Majanillos Formation contains three members, which become progressively more marly towards the top. Well-preserved pot and gutter casts and thin intercalations of calcarenite, which are interpreted as tempestites, are abundant in the lowest member. Above the pot and gutter casts, thicker calcarenite beds, which locally contain hummocky cross-stratification, predominate. Bioturbated nodular limestones are prevalent at the top of the member. The remaining succession, which records a long-term Triassic transgressive cycle, consists mostly of fine-grained limestones deposited in very shallow-marine environments. Calcarenitic sediments only accumulated within potholes and gutters in the nearshore. They developed during storms when strong currents transported sediment to the outer shelf, where it was deposited as tempestite beds. Pot and gutter casts characterize sedimentation in the bypass zone. It is concluded that storm deposits provide important constraints for the interpretation of palaeobathymetry; it is proposed that gutter casts display a trend of increasing width/thickness ratios towards the outer shelf. The identification of these structures in marine successions elsewhere should prove useful in the interpretation of depositional environments.

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