Outcrop and forward modelling analysis of ice-house cyclicity and reservoir lithologies

摘要

Combined outcrop and forward modelling studies were employed to improve upon conceptual sequence stratigraphic models of carbonate platform facies architecture during ice-house climate periods. The studied outcrops were chosen to reflect carbonate deposition in a range of sedimentary basin types of similar age (Moscovian) the Paradox Basin (Utah, USA), the Orogrande Basin (New Mexico, USA) and the Moscow-Mezen Basin (Arkhangel'sk Oblast, Russia). Results of outcrop studies were compared and contrasted with results of a one-dimensional stratigraphic forward model, designed to incorporate and test likely controls on carbonate icehouse systems. Outcrop studies and microfacies interpretation of the Honaker Trail Section (Paradox Basin) reveals no evidence of a sedimentary hierarchy, despite previous interpretation. Existing qualitative conceptual models of a sedimentary hierarchy are found to be flawed and an improved quantitative definition of a sedimentary hierarchy is presented. Results of numerical forward modelling suggest that the existence of a rigorously identifiable sedimentary hierarchy in the stratigraphic record is highly improbable. Comparison of sedimentary stacking patterns between the Orogrande Basin, the Moscow-Mezen Basin and numerical simulations suggest that although sedimentary cyclicity is highly likely to be forced by glacio-eustatic sea-level oscillations, the stacking patterns and intra-cycle facies distributions are controlled primarily by subsidence regime of the basin. Generally, it can be said that the best reservoir facies (net-to-gross thickness of grainstone) development will occur in moderately to rapidly subsiding extensional basins and moderately subsiding foreland basins. The absence of peritidal facies within ice-house carbonate successions is a sedimentological distinction between ice-house and green-house periods. Numerical forward modelling reveals that peritidal facies are developed during ice-house periods but because of their position within accommodation cycles tend to have low preservation potential.