. Bulletin. Natural history; Natuurlijke historie. 96 PEABODY MUSEUM BULLETIN 44. Fig. 46. Detail of wavy algal bedding, Alcova Limestone Member, Milne Ranch, southern flank of Muddy Mountain, Natrona County, Wyoming. Carbonate Minerals These are, of course, the major mineralogic components of the Alcova, which has been variously described as a limestone, a dolomitic limestone, and a dolomite (Branson and Branson 1941; Carini 1964; Love 1957; Picard 1978; etc.). Both calcite and dolomite occur in the Alcova Member, but their proportional ratios vary widely with geographic position. Considering
. Bulletin. Natural history; Natuurlijke historie. 96 PEABODY MUSEUM BULLETIN 44. Fig. 46. Detail of wavy algal bedding, Alcova Limestone Member, Milne Ranch, southern flank of Muddy Mountain, Natrona County, Wyoming. Carbonate Minerals These are, of course, the major mineralogic components of the Alcova, which has been variously described as a limestone, a dolomitic limestone, and a dolomite (Branson and Branson 1941; Carini 1964; Love 1957; Picard 1978; etc.). Both calcite and dolomite occur in the Alcova Member, but their proportional ratios vary widely with geographic position. Considering the unit as a whole, however, and particularly where it is structurally undeformed, calcite is by far the dominant constituent. This is the case at all known Corosaurus localities and Figure 48 presents the pattern results of X-ray powder diffraction analysis on a typical sample from Muddy Mountain, Natrona County (associated with YPM 41037). The powdered rock sample allows random orientation of crystal faces, permitting simple analysis under the Bragg equation and accurate distinction between calcite and dolomite. The Bragg equation stipulates that X = 2d sin d, where d is the spacing in angstroms between the molecular layers of a mineral, 6 is half the angle between the diffracted and incident X-radiation, and X is the wavelength of the incident X-radiation. Standard copper K-alpha radiation (wavelength of A) was used. When molecular spacing data for calcite and dolomite obtained from Berry (1974) was applied, the scanning run of 26° to 33° for 26 (Fig. 48) indicates an intense diffraction peak for pure calcite (d = A) at approximately ° with no dolomite diffraction (approximately 31°). Small amounts of quartz and feldspar are also indicated. The origin of the primary Alcova calcite is presumed to have been fourfold. Initial calcite sediment was probably deposited as a micritic, phytochemical pre- cipitate amid the prominent fabric of stromatolitic alga
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