When the levee breaks: Visualization of a deepwater crevasse splay in Late Cretaceous in Exmouth Basin Offshore Western Australia

Abstract

“The present is the key to the past” is a foundational geologic concept that helps us contextualize buried subsurface features in current geologic analogs. As seismic interpreters, the generation of the geologic model should be unbiased, yet as humans our unconscious biases are expected, and we sometimes overlook anomalous reflection patterns in our seismic data that do not fit the model. As a result, we often disservice ourselves when we overlook these characteristics, potentially ignoring additional geologic context. These anomalous geoforms or funny-looking things (FLTs) may provide further geologic context and aid us in solving the geologic model if included. Crevasse splay on a continental slope marine environment is described and analyzed using attributes, seismic inversion, and voxel-based classification. We discuss possible causes that may have triggered the break of the levee on the Exmouth Basin during the Early Eocene and why a crevasse splay on a steep slope is an FLT. A possible explanation is that the presence of preexisting faults beneath said feature is the likely culprit for a levee break that created the crevasses splay. Thus, in contrast with the Led Zeppelin song about why the levee breaks, it is equally important to understand the preexisting faults when analyzing sediment supply. In addition, this highlights the importance of integral stratigraphic sequence interpretation — from deep to shallow — to understand geology in a full context. Geologic feature: Crevasse splays and distributary channels Seismic appearance: Mounded high-amplitude reflection with hummocky low-amplitude internal reflection on vertical section, subparallel overlapping sinuous features on seismic attribute horizon slice Alternative interpretation: Mass-transport deposit, avulsion node; channel overbank Formation: The Wilcox Formation Age: Early Eocene-Late Paleocene Location: Offshore Western Australia Seismic data: Stybarrow 2008 M4D MSS obtained by the Geoscience Department of Australia Analysis tools: Coherence, multispectral coherency, principal curvature (K1 and K2), acoustic seismic inversion, flatness and curvedness, CNN automatic fault interpretation, and spectral decomposition