Distribution of accommodation space on a prograding high-relief carbonate platform (Triassic, Southern Alps of Italy) recorded by regressive facies: unraveling the contribution of compaction-induced subsidence by numerical modelling

The demise of the high-relief, steep slope, prograding Ladinian-Early Carnian carbonate platforms of the Esino Limestone (Central Southern Alps of Italy) is marked on the platform top by a subaerial exposure associated with... [ view full abstract ]

The demise of the high-relief, steep slope, prograding Ladinian-Early Carnian carbonate platforms of the Esino Limestone (Central Southern Alps of Italy) is marked on the platform top by a subaerial exposure associated with different erosional (mainly karst-related), depositional and diagenetic processes (Calcare Rosso Fm.). The exposure-related deposits consist of three major facies associations: 1) residual soils, 2 to 10 m thick, with thin lenses of conglomerates with black pebbles and, locally, weathered vulcanites; 2) chaotic breccia lenses irregularly distributed in the uppermost part of the Esino Limestone carbonate platform, interpreted as collapse breccias in karstic setting: 3) inter-supratidal carbonate cycles with dissolution and development of paleosols and tepee structures (up to 50 m thick).
Facies distribution follows the sub-environments of the underlying Esino Limestone. Facies 1 and 2 typically characterize the core of the platform, covering the underlying inner platform facies. Facies 3 instead develops toward the edge of the platform, above reef-upper slope facies of the prograding facies of the Esino Limestone. The thickness of facies 3 decreases decreases toward the core of the platform. Facies distribution reflects differences in the accommodation space and sedimentary processes from the rim (highest accommodation) to the core (reduced accommodation) of the carbonate system.
The observed changes in thickness may reflect different controlling factors: 1) tectonics, 2) differential subsidence controlled by emplacement of magmatic bodies or 3) differential subsidence controlled by the stratigraphic architecture of the Esino Limestone platform. As evidence of tectonics is not clearly recorded and the presence of volcanic bodies is only documented relatively far away from the study area, a numerical modeling for the creation of accommodation space by compaction of the basinal sediments (resedimented, fine-grained calciturbidites) during the progradation of the carbonate platform has been tested, to verify if a compaction-induced subsidence is compatible with the observed depositional architecture. Numerical models were built to simulate the evolution (aggradation and progradation) by progressively adding layers from deepest to shallowest, while compacting the underlying sediments, in order to evaluate compaction-indiced subsidence (and accommodation space for the Calcare Rosso limestone) after the deposition of the youngest strata.
The obtained results indicate that, with the used geometry and parameters, the accommodation required for the deposition of the typical facies of the Calcare Rosso can be explained by a subsidence controlled by the compaction of basinal sediments, promoting an interesting model to be tested with further investigations.