New interpretation of vertically aligned gypsum fabrics: Implications for gypsum depositional environments and diagenesis

Conference · Tue May 01 00:00:00 EDT 1990 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:6866897

Rosen, M R ^[1]; Warren, J K ^[2]

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1. Curtin Univ. of Technology, Perth, Western Australia (Australia)
2. National Centre for Petroleum Geology and Geophysics, Adelaide, South Australia (Australia)

Gypsum and anhydrite fabrics in trenches and deep 500-m cores from Bristol Dry Lake, California, exhibit a vertical alignment of crystals similar to the fabric seen in bottom-nucleated brine pond gypsum. However, geochemical and sedimentologic evidence indicates that the gypsum formed in Bristol Dry Lake precipitated as a diagenetic displacive mineral within the sediment where groundwater saturated with respect to gypsum recharges around the playa margin (groundwater seepage gypsum). Evidence for displacive growth of gypsum comes from (1) the geometry of the deposit, (2) stable isotopic data and the water chemistry of the brine, and (3) inclusions of matrix that follow twin planes and completely surround crystals as they grow. Because the fabrics and textures of this diagenetic gypsum formed by groundwater in playa settings are similar to those of primary gypsum formed in a brine pond, it is necessary to refine the criteria for the distinction between subaerial, groundwater, and subaqueous gypsum. When compared to the features observed in a Holocene subaqueous gypsum deposit (Marion Lake, Australia) and a Holocene subaerial deposit (Abu Dhabi sabkha), the following criteria can be used to distinguish between the three different types of gypsum deposits: (1) amount of matrix, (2) geometry of the deposit, (3) gypsum crystal size and orientation, (4) distribution of matrix and fluid inclusions within individual crystals, and (5) fabric of the matrix around the gypsum. Distinguishing between subaqueous and groundwater gypsum may be difficult. However, sufficient mesoscale differences exist such that, in most cases, the different gypsum types can be resolved from core slabs and thin sections. These criteria may be applied in ancient examples even after gypsum has been converted to anhydrite.

• OSTI ID: 6866897
• Report Number(s): CONF-900605-; CODEN: AABUD
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (USA), Vol. 74:5; Conference: Annual convention and exposition of the American Association of Petroleum Geologists, San Francisco, CA (USA), 3-6 Jun 1990; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
GYPSUM
DEPOSITION
DIAGENESIS
ANHYDRITE
BRINES
CALIFORNIA
GEOCHEMISTRY
GROUND WATER
QUATERNARY PERIOD
ALKALINE EARTH METAL COMPOUNDS
CALCIUM COMPOUNDS
CALCIUM SULFATES
CENOZOIC ERA
CHEMISTRY
FEDERAL REGION IX
GEOLOGIC AGES
HYDROGEN COMPOUNDS
MINERALS
NORTH AMERICA
OXYGEN COMPOUNDS
SULFATE MINERALS
SULFATES
SULFUR COMPOUNDS
USA
WATER
580000* - Geosciences