Eustasy Recording Potential of from Isolated Devonian to Pennsylvanian Carbonate Platform in a Foreland Basin Setting (Tengiz, Pricaspian Basin, Kazakhstan)

Jeroen Kenter¹ and Mitch (Paul) Harris^2
1ETC, Chevron, Voorburg, Netherlands
²ETC, Chevron, San Ramon, CA

Research drilling of continental margins over the last decade has validated a significant number, as well as the timing, of EPR sea-level events for the past 100 My. However, for the older geological record diverging sea level estimates (EPR curve, continental flooding records, planktic evolutionary records) still exist and the extraction of a reliable eustatic records remains problematic.

Tengiz field is an isolated carbonate buildup in the southeastern Pricaspian Basin, containing a complete Late Famennian to Early Bashkirian platform succession that was deposited in a relatively stable but rapidly subsiding fore land basin setting facing a thrust belt to the south. Since the Famennian, the platform aggraded and periodically back stepped resulting in approximately 1400 m (4594 ft) of relief above the Famennian platform, followed by up to 2 km (1.2 miles) of Serpukhovian progradation. Vertical trends in relative shoaling and deepening, recorded exposure and/or erosional events and biostratigraphy provide a relative sea level record of punctuated sea level falls and rises that is made up of 2nd and 3rd order sequences which are superimposed by higher (4-5th order) frequency platform cycles.

Though several of the observed sea level low stands correspond to 3rd order eustatic sequences on the EPR curve, the influence of rapid changes in the paleobathymetry of the fore land basin, which caused significant thickening of sequences and drowning in the late Devonian elsewhere in the basin, appears to have a strong influence on the regional sequence stratigraphic framework. This paper will address the interplay between subsidence and recorded sequences in such fore land basin settings.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas