Architectural Elements Versus Geomorphological Units: Building Blocks of Ancient and Modern Depositional Systems

Gani, M. Royhan¹ (1) University of Utah, Salt Lake City, UT

Knowledge of stratal architecture is the key for reservoir characterization and modeling, and depends heavily on modern and ancient analogs. In architectural studies, ancient successions are usually treated with architectural elements, whereas modern systems are commonly characterized with geomorphological units. With the advent of seismic geomorphology, ancient systems are increasingly characterized with morphological units in the subsurface where possible. While the concepts of architectural elements and geomorphological units are both useful, the distinction between the two is warranted. Architectural element is a single stratum or a package of strata, regarded as the smallest but meaningful unit (i.e. building blocks) enclosed by through-going surfaces, of a depositional system. Architectural element commonly represents part of a geomorphological unit, which is defined by distinct topographic character. In modern depositional environments important sandy geomorphological units include channels, bars, large bedwaves, and splays. These morphological units migrate and/or grow to produce architectural elements in the rock record. Importantly, the 3D shape of an architectural element could be significantly different than that of a parent morphological unit, depending on how the morphological unit evolves, deposits, and is modified through geologic time. For example, a migrating U-shaped channel may produce a tabular-sand. However, in some cases geomorphological units may be completely preserved in the rock record. In a case study, the architectural elements (e.g., frontal splay, channel, storm sheet, tidally-modulated deposit, bar accretion) of a Cretaceous delta are identified in the outcrop and corresponding geomorphological units are shown from modern deltas using remote sensing images.