Synthetic Cyclic Stratigraphy: ABSTRACT

Abstract

There are many examples of cyclic stratigraphy in the sedimentary record. Cyclothems have amplitudes of a few tens of meters. They are often attributed to sea level changes caused by glaciations. Assuming modern glaciations to be applicable, the expected period ^tgr would be about 105 years and sea level would be expected to rise rapidly by about 100 m and then to fall slowly. We have modeled this cycle by an instantaneous rise in sea level (h) following by a linear fall. In order to generate cyclic stratigraphy, this cyclic sea level change must be superimposed either on a long-term sea level increase or upon tectonic subsidence; we model either with a constant velocity uo. The thickness of each sedimentary cycle is uo^tgr. We also consid r constant velocity limits on the rates of sedimentation us and erosion rate ue. We have determined the age-depth relations in sedimentary cycles, the lengths of hiatuses, and the water depths as functions of the nondimensional parameters h/uo^tgr, us/uo, and ue/uo. By specifying horizontal variations of the nondimensional parameters, we have generated synthetic seismic stratigraphy. This stratigraphy is characterized by toplap and pinch-out. Observed seismic stratigraphy has been interpreted in terms of cyclic sea level changes End_Page 559------------------------------ with a slow rise in sea level followed by a rapid fall with periods ranging from 1 to 200 m.y. We have modeled these cycles in a similar way with a linear rise in sea level followed by an instantaneous drop. The resulting synthetic stratigraphy is characterized by extensive onlap in this case. End_of_Article - Last_Page 560------------