Abstract: Unraveling the Roles of Tectonics, Climate, and Sediment Supply Within a Sequence Stratigraphic Framework

William J. Devlin

Ongoing work in Upper Cretaceous strata of southwest Wyoming is aimed at unraveling the roles of subsidence, eustasy, climate, and sediment supply within a sequence stratigraphic framework. The role of tectonics and its effect on the stratigraphy has been discussed previously, and will only be briefly reviewed. When all tectonic factors are accounted for, including both basement-involved and regional thrust movements, there are still several orders of depositional cyclicity in the strata that cannot be directly attributed to the tectonic component.

To assess the potential contribution of climate, Gamma analysis was run on a section from the Rock Springs Uplift. Meter-scale parasequences and their associated depositional facies were the basic data input to the analysis. Spectral analyses derived from the method indicate that there is a strong precessional signal in the stratigraphic record, therefore suggesting the role of climatic forcing. The precessional insolation cycle has been tied to climatic wet and dry (monsoonal) cycles, and these cycles could be responsible for high and low sediment supply to the basin, respectively. On a parasequence scale, the bounding flooding surfaces are interpreted to be formed during times of low sediment supply (dry times), and the internal progradational facies are deposited during times of hi her sediment supply (wet times).

Parasequences in the stratigraphic section are components of fourth-order sequences that stack further into third-order sequence sets. The relative roles of longer period climate forcing and eustasy to these packages remain to be tested.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994