The deltaic nature of Amazon shelf sedimentation

Abstract

Research Article| April 01, 1986 The deltaic nature of Amazon shelf sedimentation C. A. NITTROUER; C. A. NITTROUER 1Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina 27695 Search for other works by this author on: GSW Google Scholar S. A. KUEHL; S. A. KUEHL 1Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina 27695 Search for other works by this author on: GSW Google Scholar D. J. DEMASTER; D. J. DEMASTER 1Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina 27695 Search for other works by this author on: GSW Google Scholar R. O. KOWSMANN R. O. KOWSMANN 2CENPES/PETROBRAS, Rio de Janeiro, Cep. 21910, Brazil Search for other works by this author on: GSW Google Scholar Author and Article Information C. A. NITTROUER 1Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina 27695 S. A. KUEHL 1Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina 27695 D. J. DEMASTER 1Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina 27695 R. O. KOWSMANN 2CENPES/PETROBRAS, Rio de Janeiro, Cep. 21910, Brazil Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1986) 97 (4): 444–458. https://doi.org/10.1130/0016-7606(1986)97<444:TDNOAS>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 Tools Icon Tools Get Permissions Search Site Citation C. A. NITTROUER, S. A. KUEHL, D. J. DEMASTER, R. O. KOWSMANN; The deltaic nature of Amazon shelf sedimentation. GSA Bulletin 1986;; 97 (4): 444–458. doi: https://doi.org/10.1130/0016-7606(1986)97<444:TDNOAS>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 Despite the annual discharge of more than a billion tons of sediment by the Amazon River, the sedimentary environment near the river mouth has little subaerial expression and thus does not meet the classic definition of a delta. The river mouth, however, is not an estuary, either. These observations raise a major question as to what type of sedimentary environment the Amazon river mouth represents.Seismic stratigraphy has been examined on the continental shelf at the mouth of the Amazon River using high-frequency (3.5-kHz) seismic records from about 6,000 km of ship track. These records demonstrate three regions. (1) <40-m water depth—topset strata composed primarily of muddy sediment with sandy interbeds that dip gently and diverge seaward; stratification (sandy interbeds) that becomes less predominant northwestward along the dispersal system. (2) ∼40- to ∼60-m water depth—foreset strata that dip relatively steeply (but <1°) and converge seaward. (3) ∼60- to ∼100-m water depth—bottomset strata that form a thin, acoustically transparent layer of mud, which is burying sandy bedforms on the surface of a basal (transgressive) sand layer. The large-scale structure which the deposits of these regions create is a sigmoidal clinoform. Fine-scale sedimentary structures have been examined from the inner continental shelf using X-radiographs of about 140 cores (box cores and large gravity cores). These X-radiographs reveal: (1) physically stratified sand near the river-mouth bar, (2) interbedded mud and sand (in the shelf adjacent to the river mouth, and (3) faintly laminated and mottled mud surrounding the interbedded deposits. This fine-scale stratification resembles deposits of (respectively) the distributary-mouth bar, distal bar, and prodelta observed for the Mississippi and other deltas.The Amazon River has built a subaqueous feature which stretches for hundreds of kilometres offshore and alongshore from its mouth. The feature is prograding seaward and accreting upward, and it contains fine-scale stratification typical of classic deltas. The feature forming at the mouth of the Amazon is a subaqueous delta; it differs from classic deltas primarily in its lack of subaerial expression. Subaqueous deltas, such as the Amazon, represent the general case of a major river entering an energetic oceanic regime. 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.