Disentangling Sea Level, and Sediment Supply Signals From The Panther Tongue Parasequence

Abstract

To assess, and validate the most recent interpretations on the Panther Tongue\rq{}s depositional history we use the conceptual process-response model, 2Dstratsim. The focus of this study is on the Ksp040 parasequence which reflects the wave-dominated shoreface along the southern Wasatch Plateau. The associated Panther Tongue delta to the north is considered as the dominant sediment source for the Ksp040 parasequence. As a result of the complex 3D nature of the individual Panther Tongue delta lobes it is infeasible to correlate it to a 2D simulated profile of 2Dstratsim. Before field data is used in the 2Dstratsim model, the model is first brought to a workable level through debugging, and rewriting of the C++ source code. Then the model uses parameterised equations together with user implemented input signals in a forward routine to generate a cross-sectional profile of a shoreface on a linear decreasing initial surface. This forward routine is used through inversion techniques to automatically correlate measured, and simulated logs with the data format average grain-size to depth. By generating a best match between these logs, the forcing signals of the geologic environment are disentangled. To disentangle the forcing signals of the Panther Tongue first the cross-sectional diagram of the Panther Tongue\rq{}s shoreface is modified to prepare it for a visual correlation to the simulated cross-sections based on observed bedset characteristics. Then, the measured average grain-size log data is digitised to enable a detailed correlation calculation between the measured, and simulated logs. New tools are added to examine the model\rq{}s output graphically, in addition existing ones are enhanced. Four forward scenarios are created based on the bedset characteristics of the shoreface to set preliminary parameters, and constrain the statistical functions of the inversion routine. This improves the automated correlation procedure between the measured logs and the simulated logs. The forward scenarios use two different geologic settings, with, and without back-barrier formation on the shoreface profile. These settings are again subdivided into a scenario where solely the sea level is changed to match the simulated profile to the measured cross-sectional diagram. The other scenario primarily uses fluctuations in the sediment supply to match the cross-sections, and uses the sea level to a minimal extent. In the inversion scenario the model is matched to the simulated logs of the forward scenario, that was created without back-barrier formation, and only changes in sea level. Because the model requires additional work to generate a profile from the field measured logs. This issue is related to the stability and sensitivity of the 2Dstratsim model, the difference in average grain-size classification between the model and the field, and the gaps in the individual measured logs. Thus, 2Dstratsim can be used to create sedimentary environments using the forward routine. The model is also able to use its inversion routine to automatically recreate sedimentary environments to a limited extent as no geologic constraints are considered in this routine. Therefore, there is no assurance that the final result is geologically plausible. Additionally, extensive preliminary work is required to use the inversion routine.