Journal of Conference Abstracts

CARBONATE 3D: A Computer Model to Simulate Carbonate Platform Evolution in 3 Dimensions

Georg Warrlich (georg@gl.rhbnc.ac.uk), Dave Waltham (d.waltham@gl.rhbnc.ac.uk) & Daniel Bosence (d.bosence@gl.rhbnc.ac.uk)

Department of Geology, Royal Holloway, University of London, U.K.

Following on from the 2-dimensional forward modelling packages CARBONATE, a modelling package to reproduce and predict stratigraphic geometries and facies in 3 dimensions is being developed. The program simulates carbonate and mixed carbonate-siliciclastic stratigraphies controlled by the following sedimentary processes:

* Carbonate platform rim production dependent on water depth, restriction and sedimentation

* Carbonate platform interior production dependent on water depth and restriction and sedimentation

* Basinal sediment production and deposition

* Siliciclastic input

* Erosion, transport and redeposition of sediment dependent on currents, slope, depth and restriction

* Subaerial dissolution

From a user defined initial surface, run-time and sealevel curve, the program works out a suitable time-step size for which each process simulation is calculated. For each time-step erosion rates for areas above wavebase and on slopes steeper than a critical angle are computed, as well as a shear stress vector field (direction and magnitude of the shear stress at every point on the surface) defined by slope and currents. The eroded sediments are entrained if shear stress is greater than a critical shear stress. The sediments are then transported along the shear stress vector field and deposited if the shear stress falls below the critical shear stress. This sediment dispersal loop is applied to coarse and to fine-grained erosion products and to siliciclastic input.

The in situ carbonate production rates are then calculated dependent on waterdepth, restriction and amount of deposition of clastics and eroded sediments. Carbonate production on the platform top is simulated separately for platform interior and platform rim environments using a restriction function for each point on the platform top. This is essentially based on the distance to open marine waters.

Having calculated the sediment production, sedimentation transport and erosion rates the program accumulates sediment to produce a new surface which is used as the input surface for the next time step.

The ability of the program to reproduce stratigraphic geometries and facies in 3 dimensions is being tested on the Miocene carbonate platform at Nijar, SE Spain. Here, a reef-rimmed carbonate platform has prograded from an irregularly shaped shoreline towards an offshore volcano which developes into an atoll thus generating a complex 3 dimensional geometry. Preliminary modelling results show that CARBONATE 3D can reproduce the overall geometries and facies distribution within the estimated time interval.

Using different initial geometries, current patterns, sea level curves and production rates CARBONATE 3D is then used to test different hypotheses about the formation of the Nijar stratigraphies (like the asymmetry of carbonate growth on the volcano), which are not resolvable from field observations.

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