Isotopic Composition of Carbonate Facies in Formations of the Upper Triassic Chinle Group, Four Corners Area, Southwestern United States
نویسندگان
چکیده
Carbonates of the Ojo Huelos Member of the San Pedro Arroyo Formation include ostracodal limestones, brecciated micritic limestones, vuggy, mottled limestones, peloidal graistones/packstones, pisolitic rudstones and nodular limestones. These lithofacies record deposition in lacustrine, palustrine and alluvial environments. Lacustrine (ostracodal) limestones are isotopically heaviest, with nodular limestones, palustrine limestones and peloidal/pisolitic limestones all progressively depleted. We interpret isotopic depletion as a consequence of exposure to atmospheric and soil-derived CO2 during pedogenic reworking of lacustrine-derived carbonate. Comparison of the Ojo Huelos carbonates to the isotopic composition of similar lithofacies from the Owl Rock Formation (Chinle Group) assists in elucidating the role of pedogenesis in development of the carbonate fabrics in the Ojo Huelos Member. Distinct differences in the isotopic composition of lacustrine and palustrine carbonates from the two formations may or may not reflect differences in climate during deposition.
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Calcareous paleosols of the Upper Triassic Chinle Group, Four Corners region, southwestern United States: Climatic implications
Paleosols are prominent features of the Upper Triassic Chinle Group. The oldest (Carnian-age) formations of the Chinle Group (Zuni Mountains and Shinarump Formations) contain kaolinitic paleosols that display gley features but generally lack calcretes. Paleosols of the (Upper Carnian) Blue Mesa Member of the Petrifi ed Forest Formation are mostly mature Alfi sols that have distinctive horizonat...
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