Syndepositional fault control on lower Frasnian platform evolution, Lennard Shelf, Canning Basin, Australia

Abstract

Syndepositional faulting was a major control on internal platform stratigraphy in a Frasnian reef complex on the southeastern Lennard Shelf, northern Canning Basin, Australia. By combining platform (mostly backreef) facies distributions with key stratal surfaces and biostratigraphic data, we have developed a temporal framework for the Hull Range area. Platform evolution was controlled by normal faults via an initial tilt block geometry and subsequent differential subsidence and accommodation across the platform. Three third-order, flooding surface–bounded platform phases are recorded. Basal shallow marine siliciclastic facies were deposited in topographic lows adjacent to the hanging wall and close to internal faults. Early carbonate deposition in dominantly deep subtidal environments suggests an overall ramp-style setting that deepened toward the southeast. This phase is capped by a sequence boundary represented by multiple paleokarst surfaces in the northwest that pass laterally into a major flooding surface to the southeast, above which the platform expanded toward the Mount Elma–Painted Rocks fault system. The overall stacking pattern above the sequence boundary–flooding surface is aggradational to progradational with higher-frequency shoaling trends, and locally developed exposure surfaces, related to higher-order relative sea-level changes. This second phase of platform growth ended with major flooding and a pronounced backstep of the leeward margin.