Tectonic and Depositional Controls on Syn-Rift Carbonate Platform Sedimentation
Steven L. Dorobek, 2008. "Tectonic and Depositional Controls on Syn-Rift Carbonate Platform Sedimentation", Controls on Carbonate Platform and Reef Development, Jeff Lukasik, J.A. (Toni) Simo
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All scales of tectonic deformation influence the location, sizes, shapes, and internal stratigraphy of carbonate platforms that form in active rift settings. Normal and oblique-slip faults bound the tectono-geomorphologic features that are typically found across rift settings. These fault-bounded structural elements can provide substrates for shallow-water carbonate platforms if they are submerged to shallow water depths. Thus, the incremental and long-term growth of tectonic structures, and interactions between surface processes and carbonate depositional systems that develop around or on top of these structures, determines nearly all stratigraphic aspects of syn-rift carbonate platforms.Isolated carbonate platforms are the most common type of platforms in active rift settings because they form on fault–bounded syn-rift highs. Steeply dipping fault scarps and tilted to flat-topped depositional surfaces control where shallow-marine carbonate deposition is possible. Fault scaling laws and rules for fault growth, spacing, and linkage/interaction are important for understanding the internal stratal patterns within syn-rift carbonate platforms. Footwall highs are common nucleation sites for carbonate platforms, although paleo-wind directions and siliciclastic supply to adjacent depocenters also influence facies distributions, platform morphology, and overall stratigraphic development. Active fault displacements and related surface deformations during platform growth can control platform-margin locations, facies distributions across fault-bounded basement highs, siliciclastic–carbonate interactions (especially in updip fault-bounded depocenters), and the internal growth stratal patterns within syn-rift platforms. Wedge-like growth stratal patterns within syn-rift isolated platforms are characteristic of half-graben structural elements and are well documented in outcrop and subsurface examples. Flexural uplift of footwall margins of large, fault-bounded horsts is also documented by stratal relationships from syn-rift isolated platforms that build on horst highs. Syn-rift thermal subsidence may influence where carbonate facies are distributed across the rift system, as well as timedependent accumulation rates for each platform.Syn-rift carbonate platform strata can form important petroleum reservoirs within rift-basin systems. They also provide critical records for understanding the tectonic evolution and depositional history of rift systems.
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Controls on Carbonate Platform and Reef Development
Carbonate platforms and reefs emerge, grow and die in response to intrinsic and extrinsic mechanisms forced primarily by tectonics, oceanography, climate, ecology and eustasy. These mechanisms, or controls, create the physical, biological and chemical signals accountable for the myriad of carbonate depositional responses that, together, form the complex depositional systems present in the modern and ancient settings. If we are to fully comprehend these systems, it is critical to ascertain which controls ultimately govern the “life cycle” of carbonate platforms and reefs and understand how these signals are recorded and preserved. Deciphering which signals produce a dominant sedimentological response from the plethora of physical and biological information generated from superimposed regional to global-scale controls is critical to achieving this goal. With this understanding, it may be possible to extract common time- and space-independent depositional responses to specific mechanisms that may, ultimately, be used in a productive sense. Extensive research on a wide variety of carbonate platform and reefal systems in the past few decades has provided the foundation and understanding necessary to take carbonate research to a new level. With assistance from rapidly advancing computer software and an increasing use of cross-disciplinary integration, carbonate research is shifting from description and morphological analysis towards a science that is more focused on the assessment of process and genetic relationships. The aim of this special publication is to present a cross section of recent research that shows this evolution from a variety of perspectives and scales using examples distributed throughout the Phanerozoic.