Abstract
AbstractSedimentation regimes on the Great Barrier Reef margin often do not conform to more conventional sequence stratigraphic models, presenting difficulties when attempting to identify key processes that control the margin's geomorphological evolution. By obstructing and modifying down‐shelf and down‐slope flows, carbonate platforms are thought to play a central role in altering the distribution and morphological presentation of common margin features. Using numerical simulations, we test the role of the carbonate platforms in reproducing several features (i.e., paleochannels, shelf‐confined fluvial sediment mounds, shelf‐edge deltas, canyons, and surface gravity flows) that have been described from observational data (seismic sections, multibeam bathymetry, sediment cores, and backscatter imagery). When carbonate platforms are present in model simulations, several notable geomorphological features appear, especially during lowstand. Upon exposure of the shelf, platforms reduce stream power, promoting mounding of fluvial sediments around platforms. On the outer shelf, rivers and streams are re‐routed and coalesce between platforms, depositing shelf‐edge deltas and incising paleochannels through knickpoint retreat. Additionally, steep platform topography triggers incision of slope canyons through turbidity currents, and platforms act as conduits for the localized delivery of land and shelf‐derived sediments to the continental slope and basin. When platforms are absent from the topographic surface, the model is unable to reproduce many of these features. Instead, a more typical “reciprocal‐type” sedimentation regime arises. Our results demonstrate the essential role of carbonate platform topography in modulating key bedload processes. Therefore, they exert direct control on the development of various geomorphological features within the shelf, slope, and basin environments.
Highlights
Submarine geomorphology provides a crucial window into the myriad of hydrodynamic, sedimentary, biological, and climatic processes that operate on continental margins over geological timescales
We test the role of the carbonate platforms in reproducing several features that have been described from observational data
Australia's Great Barrier Reef margin is the world's largest extant mixed carbonate‐siliciclastic system, and while it hosts many features that are ubiquitous in both siliciclastic‐ and carbonate‐dominated settings, the margin repeatedly deviates from conventional styles of geomorphological development that are predicted by these end‐member scenarios (Dunbar et al, 2000; Dunbar & Dickens, 2003b)
Summary
Submarine geomorphology provides a crucial window into the myriad of hydrodynamic, sedimentary, biological, and climatic processes that operate on continental margins over geological timescales. The processes that form features such as paleochannels, submarine canyons, sediment gravity flows, and submarine fans are well understood within a typical sequence stratigraphic framework, which heavily emphasizes the role of eustatic sea level position in mediating source‐to‐sink sediment transport in what are typically THRAN ET AL. Gaps between the platforms (or “inter‐reef passages” at highstand), are believed to act as conduits for deposition of coarse‐grained sediments on the slope and in the basin (Puga‐Bernabéu et al, 2014; Symonds et al, 1983; Webster et al, 2012)
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