| Deltas have long been of human interest from the land resource as well as the petroleum exploration point of view. However, fades architecture of deltaic deposits is relatively poorly understood compared to their fluvial and deepwater counterparts.; Outcrop and high-resolution seismic studies show that prograding delta deposits consist of seaward-dipping, offlapping clinoform strata. Despite this, many studies of Quaternary deltas with a few widely-spaced cores commonly depict sharp fades boundaries, similar to the "lithostratigraphic-correlation" originally shown by Scruton (1960). The method of bedding correlation (i.e. "chronostratigraphic-correlation") derived from geometries observed in outcrops and seismic examples, is applied to re-correlate several of these Quaternary cores. The new correlations are potentially more useful in modeling bed-scale growth of deltas and 3-D fluid flow behavior of deltaic reservoirs and aquifers.; Architectural-element analysis is applied to determine the basic building-blocks of a Cretaceous delta at the top of the upper Turonian Wall Creek Member exposed along the western flanks of the Powder River Basin, Wyoming. Cliff sections show an upward-coarsening fades succession displaying basinward dipping clinoform strata and interpreted to represent a prograding delta deposit. Five orders of bounding surfaces bind six facies architectural elements within prodelta and delta front deposits. These elements are prodelta fines (PF), frontal splay (FS), channel (CH), storm sheet (SS), tidally modulated deposit (TM), and bar accretion (BA). Seasonal to decadal river floods are thought to represent the main building phases of the delta, producing elements CH, FS, and BA. During intervening periods, the delta is reworked by waves, storms, and tides, producing mainly elements SS and TM. Because of the complex interactions of river effluents with waves, storms and tides the delta is interpreted as mixed-influenced.; Bed-scale variation of ichonological signatures within the above deltaic deposits are correlated with inferred short and long-term changes in depositional processes. These changes reflect various proportions of river, flood, wave, storm, and tide influences. Bioturbation Index (BI) values of the strata were presented in a novel way as continuous line curve, called "BI log". Trend analysis of BI log, when integrated with the ichnofacies approach, helps to delineate evolutionary history, and paleogeography of deltaic deposits. |
