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Sedimentological and Diagenetic Constraints for the Forward Modelling of a Greenhouse High-Relief Flat-Topped Platform (Triassic, Southern Alps, Italy)

Berra, Fabrizio *1; Lanfranchi, Alessandro 1; Ronchi, Paola 2; Smart, Peter 3; Whitaker, Fiona 4
(1) Department of Earth Sciences, University of Milano, Milano, Italy.
(2) ENI, Milano, Italy.
(3) School of Geographical Sciences, University of Bristol, Bristol, United Kingdom.
(4) School of Earth Sciences, University of Bristol, Bristol, United Kingdom.

Forward simulation models provide an important tool linking studies of the present-day processes of carbonate sedimentology and diagenesis and their controlling factors, to the observed geometry, sedimentology and diagenesis of carbonate platforms in the geological record. We have simulated the coupled sedimentary and diagenetic evolution of a flat-topped Late Anisian-Early Carnian carbonate platform (Esino Lms., Southern Alps, Italy) using the forward model CARB3D+. The platform-to-basin succession studied preserves development from inception, through early aggradation and subsequent progradation (over c. 4 km) to final subaerial exposure which marks the end of carbonate deposition. Field-based reconstruction of the geometry of the platform (including platform size, paleo-bathymetry and slope profile) and facies analysis (including grain size, source areas of the sediment, accumulation rates and diagenetic evolution) provide critical constraints on model parameterisation (eg initial surface geometry, types of carbonate factory present). More importantly it also provides information for testing the model output (eg paleobathymetry, slope profiles, sediment grain size).

Model parameterization, in terms of sediment production rates and their depth dependence, sea level curves and overall rates of subsidence, has been tuned within the ranges deduced from the field data, in order to honour the field observations. As paleogeographic/paleoenvironmental reconstructions suggest that hydrodynamic conditions remained fairly constant during the 3 main phases of platform growth, the relative sea level curve was of particular importance and proved to be the main determinant of the gross architecture (eg the aggradation to progradation ratio). Modelling indicated that the maximum rates of reef, margin and interior carbonate production on this greenhouse platform (6, 3 and 1 m/ka) were slightly higher than reported for modern icehouse platforms. The modeling of diagenetic processes in the Esino Limestone (typically early-diagenetic marine cementation), allowed us to evaluate the role and rate of cementation processes on the geometry of this greenhouse carbonate platform. The good fit between the optimized model output and the field data suggests the possible use of this set of parameters for simulation of time-equivalent subsurface analogues. Finally, the forward model provides a starting point for further numerical analyses, such as simulation of fluid circulation.


AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California