The Importance of the Major Variables in Sequence Stratigraphic Interpretation - Examples from the Upper Miocene - Early Pliocene of the Pannonian Basin, Hungary

Gabor A. Vakarcs

The Neogene back-arc Pannonian Basin of Hungary became isolated from the world sea at 12.7 Ma (Sarmatian/Pannonian boundary) and formed a large lake. It is an excellent area to observe the importance of the various variables affecting the development of stratal patterns and lithofacies related to sequence stratigraphy.

Relative water level changes are the major cause of the sequence development. However, the sediment supply, tectonic subsidence, and the topography of the initial depositional surface are the major controlling variables in many cases. Differences in the physiography of the basin cause a totally different sequence behavior, given the same water level fluctuation signal. In nearby sub-basins, during short time periods these lacustrine sequences are more sensitive to changes in the initial depositional profile and sediment supply then to lake level fluctuations and tectonic subsidence.

In a settings with high sediment supply, only Type-1 sequence boundaries are developed. Type-2 sequence boundaries are typically more common in low sediment supply settings. During the lowstand, slope fans are present on the lower part of the steep slopes (more than 400 m water depth, 3-5 degree dip), with slope fans and/or prograding complexes in the shallow slopes (100-400 m water depth, 1-3 degree dip) environment. Ramp geometries (less than 100 m water depth, less than 1 degree dip) were characterized by prograding complexes.

Understanding the role of the major variables within a sequence stratigraphic framework is very important for hydrocarbon exploration to predict the development of lithofacies.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California