ABSTRACT: Systems tracts are linkages of contemporaneous depositional systems that accumulate under specific conditions of accommodation and sediment supply. They are identified by their stratal stacking pattern and position within the sequence. In practice, it is often difficult to assign accurately relative sea-level position to stacking patterns. Observations also show that systems tracts may succeed each other in different orders, not necessarily according to the prediction of an ideal model. The purpose of this study is to analyze the quantitative conditions for different possible combinations of systems tractswithin a cycle of relative sea-level change. Icehouse and greenhouse eustatic trends, active and passive tectonics, and varying depositional rates are considered as conditions. The systems tracts were defined based on the rate of accommodation change and depositional rate.Our quantitative calculations revealed that if the tectonics is active and the basement motion-time curve is segmented with sharp turning points between segments, eight possible successions of systems tracts may occur. If the basement motion is transitional between segments of subsidence and uplift, six scenarios are possible. Only three possible combinations of systems tracts can form in a sea-level cycle if the basement tectonics is passive. Variable depositional rate alone can be responsible for four different combinations of systems tracts under similar accommodation conditions. These combinations of systems tracts may occur primarily in greenhouse world. Eustasy under icehouse climatic conditions has rapid rates of change (up to 4000 m/myr), which are likelymany times faster thanwhat subsidence/uplift rates realistically can reach.As a consequence, only the full series of systems tract in the order of forced regression-lowstand normal regression-transgression-highstand normal regression can be predicted in icehouse, although the thickness of systems tracts in the real rock record may be rather small because of the fast rate of sea-level change.
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