Wheeler Diagram Analysis of Cenozoic Sequence Stratigraphy, Texas Gulf Coast Basin Margin
Cenozoic strata along the northwest (Texas) margin of the Gulf of Mexico Basin comprise a minimum of 50 recognizable third- and fourth-order, mostly type-1, depositional sequences. When placed in a chronostratigraphic “Wheeler chart,” which is based on microfossil-defined ages of unconformity-bounded sequences and internal maximum flooding surfaces, the strata are displayed in a highly visual, regional, stratigraphic temporal framework.
Early Paleogene sequences are principally type 2, deposited in response to initially high rates of subsidence in the basin. Therefore, exploring for deep-water, off-shelf reservoirs in the earliest Cenozoic sequences will probably not be highly successful because these sequences exhibit only on-shelf, lowstand, shelf-margin systems tracts. Younger Paleogene and Neogene/Holocene sequences are mostly type 1, demonstrating that shelf edges subsided at rates less than that of falling eustatic sea level. Type-1 cycles, responsible for on-shelf incised-valley erosion and deposition of off-shelf lowstand systems, constitute important petroleum reservoirs in the basin. Consequently, it is possible to predict growth-faulted intraslope subbasins that were filled by lowstand depositional systems and difficult-to-locate, subsalt, lowstand, basin-floor-fan targets, which generally occur basinward of type-1 notched shelf edges.
This Wheeler chart demonstrates that construction of these displays is an important stratigraphic goal for sedimentary basin analysis because the chart allows documentation of the defined stratigraphic framework with which to improve knowledge of synchronous events in a basin’s geologic history. It also provides a framework for understanding distribution of hydrocarbon reservoirs, as well as total petroleum systems.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009