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Fan-deltas and braid deltas: Varieties of coarse-grained deltas

1987; Geological Society of America; Volume: 99; Issue: 3 Linguagem: Inglês

10.1130/0016-7606(1987)99 2.0.co;2

1943-2674

John G. McPherson, Ganapathy Shanmugam, R. J. Moiola,

Methane Hydrates and Related Phenomena

Research Article| September 01, 1987 Fan-deltas and braid deltas: Varieties of coarse-grained deltas JOHN G. McPHERSON; JOHN G. McPHERSON 1Mobil Research and Development Corporation, Dallas Research Laboratory, P.O. Box 819047 Dallas, Texas 75381 Search for other works by this author on: GSW Google Scholar GANAPATHY SHANMUGAM; GANAPATHY SHANMUGAM 1Mobil Research and Development Corporation, Dallas Research Laboratory, P.O. Box 819047 Dallas, Texas 75381 Search for other works by this author on: GSW Google Scholar RICHARD J. MOIOLA RICHARD J. MOIOLA 1Mobil Research and Development Corporation, Dallas Research Laboratory, P.O. Box 819047 Dallas, Texas 75381 Search for other works by this author on: GSW Google Scholar Author and Article Information JOHN G. McPHERSON 1Mobil Research and Development Corporation, Dallas Research Laboratory, P.O. Box 819047 Dallas, Texas 75381 GANAPATHY SHANMUGAM 1Mobil Research and Development Corporation, Dallas Research Laboratory, P.O. Box 819047 Dallas, Texas 75381 RICHARD J. MOIOLA 1Mobil Research and Development Corporation, Dallas Research Laboratory, P.O. Box 819047 Dallas, Texas 75381 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1987) 99 (3): 331–340. https://doi.org/10.1130/0016-7606(1987)99 2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation JOHN G. McPHERSON, GANAPATHY SHANMUGAM, RICHARD J. MOIOLA; Fan-deltas and braid deltas: Varieties of coarse-grained deltas. GSA Bulletin 1987;; 99 (3): 331–340. doi: https://doi.org/10.1130/0016-7606(1987)99 2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Two types of coarse-grained deltas are recognized: fan-deltas and braid deltas. Fan-deltas are gravel-rich deltas formed where an alluvial fan is deposited directly into a standing body of water from an adjacent highland. They occupy a space between the highland (usually a fault-bounded margin) and the standing body of water. In contrast, braid deltas (here introduced) are gravel-rich deltas that form where a braided fluvial system progrades into a standing body of water. Braid deltas have no necessary relationship with alluvial fans, as exemplified by fluvioglacial braid deltas. Braid deltas have previously been classified as fan-deltas even though the geomorphic and sedimentologic settings of the two systems can be vastly different. Braid deltas are a common present-day geomorphic feature and are abundant in the geological record.Fan-deltas and braid deltas can be distinguished in the rock record by distinctive subaerial components of these depositional systems; the shoreline and subaqueous components of both are similar. Fan-delta sequences have a subaerial component that is an alluvial-fan facies comprising interbedded sheetflood, debris-flow, and braided-channel deposits. Fan-deltas produce small (a few tens of square kilometres), wedge-shaped bodies of sediment, commonly displaying high variability in paleocurrent patterns and abrupt changes in facies. The deposits are generally very coarse grained (with large out-sized clasts), very poorly sorted, matrix-rich, polymictic, heterolithic, partially cemented by penecontemporaneous carbonate, and have low porosity and permeability. Braid-deltas, in contrast, have a subaerial component consisting entirely of braided-river or braidplain facies. Their deposits display better sorting, roundness, and clast orientation than do fan-delta sediments; they lack a muddy matrix; they display size grading and bar migration; they commonly have a sheet geometry with high lateral continuity (tens to hundreds of square kilometres); and they exhibit moderate to high porosity and permeability. Valuable paleogeographic and tectonic information concerning the proximity of highlands and major fault zones may be misinterpreted or lost if these two coarse-grained deltaic systems are not differentiated. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.