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Hydrothermal origin of Devonian conical mounds (kess-kess) of Hamar Lakhdad Ridge, Anti-Atlas, Morocco

D. Mounji, P. A. Bourque and M. M. Savard
Hydrothermal origin of Devonian conical mounds (kess-kess) of Hamar Lakhdad Ridge, Anti-Atlas, Morocco
Geology (Boulder) (December 1998) 26 (12): 1123-1126


Various interpretations have been proposed for the origin of peculiar cone-shaped, finely crystalline, Devonian carbonate mounds of the Hamar Lakhdad Ridge, Anti-Atlas, Morocco, ranging from shallow-water reefs to deep-water mud mounds, formed by biogenic and/or hydrodynamic processes. This study is the first integrated sedimentological and geochemical analysis of these structures. The mounds are cone shaped, steep sided, circular to subelliptical in plan view, and exhibit internal crude bedding parallel to the mound's outer surface. They occur in a cluster of 48 mounds on top of a volcanic massif. Stable isotope analyses of first-stage isopachous nonluminescent cement have yielded marine values. In contrast, the finely crystalline carbonate that makes up the bulk of the mound and the internally sedimented mud between crusts of early marine cements have significantly lower delta (super 18) O values, whereas values of delta (super 13) C are similar to those of the early marine cement. Strontium isotope ratios also clearly distinguish the nonluminescent early marine cements from the finely crystalline material. The (super 87) Sr/ (super 86) Sr values for the former (0.707 934-0.709 392) are in or near the Devonian marine range, whereas the ratios for the latter (0.708 515-0.709 656) indicate a more radiogenic Sr source. On the basis of their lithology, architecture, isotope geochemistry, and clustered occurrence on top of a volcanic pile, we propose that the finely crystalline material that forms the mounds and the intermound beds was precipitated from hydrothermal fluids, and that accretion of the material was driven by hydrothermal venting.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 26
Serial Issue: 12
Title: Hydrothermal origin of Devonian conical mounds (kess-kess) of Hamar Lakhdad Ridge, Anti-Atlas, Morocco
Affiliation: Universite Laval, Departement de geologie et de genie geologique, Quebec City, QC, Canada
Pages: 1123-1126
Published: 199812
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
Accession Number: 1999-000448
Categories: Sedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
N27°40'00" - N32°04'60", W13°15'00" - W02°00'00"
Secondary Affiliation: Geological Survey of Canada, CAN, Canada
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 199901
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