Can deepwater bottom currents generate clinothems? An example of a large, asymmetric mounded drift in Upper Jurassic to Lower Cretaceous sediments from northwestern Australia

Abstract

Abstract Clinoforms and clinothems are ubiquitous in shallow marine and shelf margin environments, where they show remarkable seaward progradation trends. Consensus holds that these features do not form in deepwater settings. This study describes an example of a large, asymmetric mounded deposit formed in Upper Jurassic to Lower Cretaceous sediments along the Exmouth Plateau (offshore northwestern Australia). Although it formed in deepwater environments, the deposit has previously been interpreted to reflect either a deltaic or shelf margin system based on clinoform and clinothem geometries. We support that this deposit shares similarities with a delta drift that evolved into a large, mounded drift (~180 km in length, ~120 km in width, and up to ~1.7 km in sedimentary thickness) that exhibits two migration trends: one westward and the other northeastward. Three evolutionary phases are proposed: (1) an onset drift stage (ca. 146.5–143.5 Ma); (2) a growth drift stage (ca. 143.5–138.2 Ma); and (3) a burial stage (ca. 138.2 Ma), which marks the completion of the drift and a shift in depositional style. The drift asymmetry and clinoform orientations indicate the influence of a northward-flowing water mass with two main cores. Our analysis thus suggests that bottom currents can create complex deposits with geometries that resemble clinothems in deepwater environments.