ABSTRACT

This paper describes a computer model based on algorithms that simulate processes of carbonate sediment production, deposition, erosion and redeposition, and sequence stratigraphy of carbonate platforms. We use the exceptionally well-exposed cliff sections through the reef-rimmed Miocene carbonate platform of Mallorca, Spain, to test the ability of our program to simulate an outcropping stratigraphy.

When an outcrop-derived sea level curve and the average Holocene rates of production and erosion are used in our model, we can precisely match the natural and the synthetic stratigraphies. In addition, we can reconstruct the nonoutcropping parts of the platform. This modeling indicates the ability of our program to simulate the sequence stratigraphy, stratal geometries, and facies of a real carbonate platform. In addition, this modeling strongly suggests that the processes for which we have no field evidence and that we are not modeling, i.e., compaction, differential subsidence, and three-dimensional sedimentary processes, are unimportant factors in the development of the Llucmajor Platform of Mallorca.

The model is then used to explore and bracket some of the rates of different processes considered to be important in controlling the development of this late Miocene platform. Carbonate production and a decrease in production from the reefal margin into lagoonal areas have important controls on slope progradation rates and drowning of lagoons. When model-matching stratal geometries and sea level curves, one can establish a precise relationship between rates of sea level rise and rates of production. However, the solution is not unique in that production rates may be doubled and the sea level curve periodicity halved, and the same result is achieved. Both outcrop and modeling data indicate that rates of sea level rise never exceeded production rates. Therefore, production and accommodation were limited by sea level. One consequence of this is that erosion rates are very important in controlling the carbonate stratigraphy. With a constrained sea level curve, erosion rates are refined from the modeling of the Mallorca outcrops by the levels of erosion surfaces generated during sea level falls. The outcrops and the modeling also indicate that the bulk of the carbonate production and platform progradation occurs during the transgressive and highstand periods rather than during periods of falling sea level. Condensed sections characterize lowstands and not transgressions. This and other features of the Mallorca platform illustrate the inapplicability of many published carbonate sequence stratigraphic models. Modeling has contributed to three advances in our analysis of this carbonate platform. First, this method is probably the best way to study the many effects that the different controlling parameters have on platform evolution. Second, if some parameters can be quantified from field analysis, then other parameters can be bracketed from modeling. Third, this method strongly suggests that the parameters we are not modeling have no important control on platform evolution. Accurate forward modeling of carbonate stratigraphies allows petroleum geologists to independently test sequence stratigraphic interpretations, reconstruct partially exposed or imaged carbonate stratigraphies, locate and quantify the cross sections of likely reservoir facies, illustrate the development and likely interconnections of reservoir facies, and predict stratigraphies around a basin margin.

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