Through the Seismic Looking Glass: Challenges of Using Reflections as Geomorphic Surfaces
Seismic interpreters commonly conceptualize seismic-reflection volumes as 3D images of the Earth. Utilizing photographic approaches to interpreting sedimentary successions usually overlooks the impacts that rock properties can have on the resulting imagery. Thus, distinguishing single and composite geomorphic features are commonly not considered in many interpretations, leading to misperceptions and intermingling of chronostratigraphic and lithostratigraphic features. Seismic resolvability and detectability also complicate seismic-image interpretation. Here we use geomorphic and stratigraphic records of constructional and degradational fluvial features in the Gulf of Thailand (GoT) and the Mediterranean, respectively, to elucidate issues of scale and rock-property effects on geologic interpretations of seismic datasets. We compare seismic data with similar dominant frequencies of a well-imaged Quaternary aggradational succession from the GoT with upper Miocene degradational accumulations from the Mediterranean. We find that bounding reflections from the GoT largely approximate composite and diachronous features, whereas those from the Mediterranean delineate single and synchronous ones. Yet at substantially higher frequencies (i.e., with sparker datasets), reflections approximate timelines and are represented as finer-scale features through changes in impedance. Diligent use of forward synthetic models can confirm and constrain stratigraphic interpretations of single and composite geomorphic features. Our findings show that quantifying scales of the bounding features and rock properties, rather than resolving deposit interiors, are an essential first step to interpreting any seismic dataset, especially when they are used as image proxies for reservoir analogs.
AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017