GLOBAL CYCLOSTRATIGRAPHY - A MODEL OF CARBONATE GROWTH-PATTERNS

Cyclostratigraphy is the study of cyclic depositional patterns produce d by climatic and tectonic processes. A global-scale quantitative cycl ostratigraphic model is described which simulates carbonate growth pat terns controlled by tectonic and climatic processes. The model uses se ven factors simulating the effects of physical and chemical environmen ts on the deposition rates of carbonate accumulations. These factors a re sea-level change, the rate of basement subsidence, food supply (inf luence of nutrients), available sunlight, temperature, salinity and di ssolved oxygen. The factors are considered as functions of climatic an d tectonic processes. The model also integrates Milankovitch-induced s hort-term climatic changes with the long-term tectonic evolution of ba sins to examine the potential carbonate accumulation patterns. The two -dimensional computer model results provided here show that: (1) carbo nate growth patterns in different climates and under different tectoni c processes can be modelled quantitatively; (2) carbonate production i ncreases towards the equator (decreasing latitude) as the temperature and nutrition supply increase in tropical belts, and production change s because of expansion or contraction of the tropical belt in differen t climatic periods; (3) when matched with the turbidity, the model des cribes different carbonate accumulation patterns in different climatic patterns; (4) at either abnormally high or low salinity, carbonate ac cumulation rates decline sharply, and the salinity becomes normal away from the strand line; and (5) cyclic sea-level changes cause a cyclic change of carbonate accumulation. A case study is presented from the Upper Pennsylvanian of Texas. The simulation results indicate that car bonate growth patterns observed from field, well or seismic data are a ccurately modelled by the quantitative procedure given here.