Stratigraphic-forward and reactive-transport modeling of depositional and diagenetic processes in siliciclastic sandstones.

摘要

Modeling natural processes is one of the most effective ways to test the plausibility of multiple hypotheses. Numerical experiments can be set to assess different scenarios that may be responsible for development of a certain phenomenon. Reaction-Transport Modeling (RTM) is a numerical approach that permits tracking multiple species simultaneously. This can be done as a system evolves spatially and temporally. RTM was applied to understanding the mechanism under which calcite mega-concretions form. The studied geological formation was the Sierra Ladrones in the Rio Grande Rift, Albuquerque Basin near Socorro, New Mexico. Initial results of the mega-concretion study were not insightful concerning cementation mechanisms despite numerical representations of the reactions based on measured groundwater characteristics, so this project was not pursued further.;Stratigraphic-Forward Modeling (SFM) is a technique that allows for testing how stratal architecture evolves through time and space. A series of numerical experiments were set up to assess the effects of distance to sediment source and seasonally varying discharge on fluvial processes in a tropical paleoclimate. Post-depositional processes, such as the influence of burial depth on location and amount of preserved sediment also were considered. Input into SFM is based on parameters that control the physical processes through erosion, transportation, and, deposition of sediment. Cores and outcrop samples were used to constrain the range and proportion of grain size.;Experiments described above were applied on a regional scale for an area of 70 km (E-W) by 40 km (N-S). The center of this area of interest is the Mumford Hills petroleum field located in southwestern Indiana. The target of the modeling simulations is the Late Mississippian Mount Pleasant member of the Clore Formation. Available data from the literature were used to estimate the total time for accumulation of the Clore Formation at 2 Ma. Numerical values for sedimentological parameters such flow velocity, sediment concentration, and sediment flux were derived from fluvial characteristics of the Mekong River delta which was inferred to be a useful modern analogue. The selection of an analogue was based on similarity to the studied paleodepositional system in aspects such as latitude, distance to highlands, and seasonal climatic conditions. Results show that relative proportions of different grain sizes in the range of fine-grained sand to silt affect not only the amount of preserved sediment under burial, but also the location where sediment is preserved.