Meteoric Stabilization and Preservation of Limestone Within Late Proterozoic Beck Spring Dolomite of Eastern California

William G. Zempolich, B. H. Wilkinson, K. C. Lohmann

Petrographic and geochemical study of limestone, silicified carbonate, and dolostone indicates that meteoric diagenetic processes and paleogeographic position played important roles in the stabilization and preservation of limestone within the pervasively dolomitized Beck Spring Dolomite.

Three relic limestone occurrences are found interbedded with dolostone and siliciclastics along the southwestern margin of the Amargosa basin in the vicinity of Saratoga Spring, Death Valley National Monument. The uppermost occurrence is 8 m thick and is found just below siliciclastics of the Kingston Peak Formation. The lower two occurrences are discontinuous laminated micrites. The upper limestone section contains pisolite, oolite, and micrite. Pisolite and oolite contain concentric, neomorphic, deformed, and leached grains. These grains possess up to 1,800 ppm strontium. Cements found within ooid and pisoid grainstone include microdolomite-rich isopachous columnar calcite and pore-filling equant calcite cement. Deformed pisoids found at the top of the section display elephantine fa ric; leached pisoids found at the base commonly exhibit passive flow within fluid escape structures. Isotopic compositions of calcitic components show ¹³C enrichment (-0.7 to 4.9 ^pmil PDB) with stratigraphic depth accompanied by relatively uniform depleted ¹⁸O (-9 to 11^pmil PDB).

Silicified and hematite-cemented pisolite is found interbedded with limestone and dolostone in an incomplete section located in the Saddle Peak Hills, just east of Saratoga Spring. Here, micro to coarse crystalline chert laminae completely replace pisoid grains. Partial silicification of calcitic pisoid grains from Saratoga Spring occurs as thin concentric layers within neomorphic equant crystals. Elsewhere, dolostone infrequently contains leached ooids filled by marine cement, and pores filled by successive generations of marine cement and interbedded crystal silt.

We conclude that Beck Spring marine cement allochems precipitated as aragonite and high-magnesium calcite. In the vicinity of Saratoga Spring, these metastable mineralogies were dissolved, eroded, stabilized to calcite, and replaced by silica through interaction with meteoric waters. Early stabilization of limestone components along the margin of the Amargosa basin apparently decreased susceptibility to subsequent dolomitization.

AAPG Search and Discovery Article #91024©1989 AAPG Pacific Section, May 10-12, 1989, Palm Springs, California.