Aragonite loss in a cold-water coral mound; mechanisms and implications

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doi: 10.1111/j.1365-3091.2010.01178.x
Author(s): Frank, Tracy D.; Titschack, Jürgen; Thierens, Mieke
Author Affiliation(s): Primary:
University of Nebraska, Department of Geosciences, Lincoln, NE, United States
Other:
Friedrich-Alexander-Universität Erlangen-Nurnberg, Germany
University College Cork, Ireland
Volume Title: Sedimentology
Source: Sedimentology, 58(3), p.670-690. Publisher: Wiley-Blackwell, Oxford, United Kingdom. ISSN: 0037-0746 CODEN: SEDIAT
Note: In English. 62 refs.; illus., incl. 2 tables, 4 plates, sketch map
Summary: Selective dissolution of aragonitic grains is emerging as a volumetrically significant process that affects a broad range of modern carbonate settings. This study explores mechanisms and implications of aragonite loss in Challenger Mound, a giant cold-water coral (Lophelia pertusa) mound of Pleistocene age, which lies on the continental slope off southwest Ireland. A comprehensive sampling scheme allowed the integration of petrographic data with geochemical analyses of sediment and pore water. The mound remains virtually unlithified and consists of stacked, fining-upward cycles of silty coral floatstone-rudstone and bafflestone grading into wackestone. Whereas calcitic grains appear unaltered, aragonitic grains are corroded and fragmented. Aragonite dissolution is attributed to organic matter oxidation at/near the sediment-water interface and, at greater depths, to the initial stages of bacterially mediated sulfate reduction, when alkalinity production is outpaced by the generation of H+. Pore water profiles indicate that undersaturated waters are diffusing towards the mound interior from two centers of sulfate reduction: one located in the upper 10 m of the sediment column and a second that lies below an erosional unconformity which marks the base of the mound. Continued aragonite dissolution is expected to gradually lower the diagenetic potential of the Challenger Mound and delay lithification until deep burial, when solution-compaction processes come into play. Despite a fundamental role in predestining the final taphonomic and textural characteristics of Challenger Mound, the processes described here are expected to leave little trace in the geological record due to a lack of cementation and calcitization. Assuming that similar processes have been active throughout the Phanerozoic, results imply that the understanding of diagenetic processes in carbonate systems may be incomplete. Abstract Copyright (2010), International Association of Sedimentologists.
Year of Publication: 2011
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 24 Surficial Geology, Quaternary Geology; Algal mounds; Algal structures; Aragonite; Atlantic Ocean; Biogenic structures; Carbonate rocks; Carbonates; Cenozoic; Challenger Mound; Depositional environment; Diagenesis; Expedition 307; Floatstone; IODP Site U1317; IODP Site U1318; Integrated Ocean Drilling Program; Marine environment; North Atlantic; Northeast Atlantic; Paleo-oceanography; Pleistocene; Porcupine Seabight; Quaternary; Rudstone; Sedimentary rocks; Sedimentary structures
Coordinates: N512300 N512300 W0114300 W0114300
N512600 N512600 W0113300 W0113300
Record ID: 2011044367
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from John Wiley & Sons, Chichester, United Kingdom