Ulicny, David¹, Lenka Spicakova¹, Jiri Laurin¹, Stanislav Cech² 
(1) Czech Academy of Sciences, Prague, Czech Republic
(2) Czech Geological Survey, Prague, Czech Republic

ABSTRACT: Evolution of Depositional Geometries of Fluvial Through Shallow-Marine Sequences, Bohemian Cretaceous Basin, Czech Republic: Interplay of Relative Sea-Level Change and Reactivation of Basement Fault Zones

In the Bohemian Cretaceous Basin of Central Europe, formed by reactivation of an intra-continental strike-slip fault system, the onset of deposition is characterized by a deepening-upward succession of fluvial, estuarine, and dominantly shallow-marine clastic systems of Cenomanian age. The Cenomanian deposition coincided with (1) the onset of subsidence along reactivated strike-slip basement fault zones, and (2) culmination of a long-term eustatic rise. Both of these controls left a signature in the geometries of the genetic sequences which were analyzed in the central part of the basin. Marine and non-marine flooding surfaces, correlated between relatively closely-spaced well logs tied to outcrop sections, provide local relative time-resolution at the level of tens of ky. Individual high-frequency sequences, superimposed on the long-term Cenomanian deepening trend, are typically thin, between 2 and 5 meters, but can be correlated along tens of kilometers. Along with the general deepening-upward trend, the temporal changes in subtle tectonic topography, coupled with the relative sea-level changes, led to transitions from fluvial to tide-dominated estuarine and subsequently to wave-dominated depositional systems. Both the palaeovalley trends and shapes of shoreline depositional systems responded to subtle movements along a reactivated conjugate system of basement strike-slip faults, which defined the distribution of source areas, sediment input paths, and shallow-marine depocenter geometries.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.