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Petrography of finely crystalline Cenozoic dolostones as revealed by backscatter electron imaging; case study of the Cayman Formation (Miocene), Grand Cayman, British West Indies

Brian Jones and Robert W. Luth
Petrography of finely crystalline Cenozoic dolostones as revealed by backscatter electron imaging; case study of the Cayman Formation (Miocene), Grand Cayman, British West Indies
Journal of Sedimentary Research (November 2003) 73 (6): 1022-1035

Abstract

Finely crystalline Cenozoic island dolostones, like those found in the Cayman Formation on Grand Cayman, are commonly assumed to be petrographically and compositionally homogeneous. Backscatter electron images (BSEI), however, show that the constituent dolomite crystals (<100 um long and commonly <20 mm long) are commonly zoned with respect to their mol % CaCO (sub 3) content. More-over, such images allow (1) depiction of growth patterns in the constituent crystals, irrespective of their origin, (2) recognition of replacive dolomite as opposed to dolomite cement, and (3) delineation of "stratigraphic packages" in the dolomite cements that reflect different episodes of cementation. Integration of this information forms the basis for paragenetic interpretations of the dolostones. On Grand Cayman, the Miocene Cayman Formation can be divided into friable, high-porosity dolostones and hard, low-porosity dolostones. Backscatter electron images show that the hard dolostones are characterized by complex arrays of zoned dolomite cements that have occluded most of the pores. Caymanite, an internal sediment, has occluded many of the larger cavities. In contrast, the high-porosity dolostones contain little cement and no internal sediments. Precipitation of the cements and the deposition of internal sediments were related to the passage of large volumes of water through some of the dolostones. Thus, the hard, low-porosity dolostones are found in the "cap rock" of the formation, in coastal locations, and in areas close to solution-widened fractures. Conversely, the friable, high-porosity dolostones form the lower "porous unit" of the formation in the interior of the island, where the passage of water was more restricted.


ISSN: 1527-1404
EISSN: 1938-3681
Serial Title: Journal of Sedimentary Research
Serial Volume: 73
Serial Issue: 6
Title: Petrography of finely crystalline Cenozoic dolostones as revealed by backscatter electron imaging; case study of the Cayman Formation (Miocene), Grand Cayman, British West Indies
Affiliation: University of Alberta, Department of Earth and Atmospheric Sciences, Edmonton, AB, Canada
Pages: 1022-1035
Published: 200311
Text Language: English
Publisher: Society of Economic Paleontologists and Mineralogists, Tulsa, OK, United States
References: 51
Accession Number: 2004-014623
Categories: Sedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. charts, sketch map
N19°15'00" - N19°25'00", W81°30'00" - W81°04'60"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 200405
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