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摘要
We investigate the regional climatic effects of the formation of the %26quot;Nevadaplano%26quot; plateau during the Sevier Orogeny in an overall warming world. Paleohydrology was reconstructed from 590 individual measurements of phosphate O isotopes in continental faunas of the Lower Cretaceous Cedar Mountain Formation, Utah, U.S.A. Semi-aquatic (turtles, crocodiles) and terrestrial (dinosaurs) taxa are compared to coeval pedogenic carbonates to interpret changing water sources over time. Samples were grouped into four stratigraphic faunas (lower Yellow Cat, upper Yellow Cat, Ruby Ranch, and Mussentuchit members). Resulting isotopic values were converted to delta O-18(w) values using established delta O-18(p)-delta O-18(w) and delta O-18(c)-delta O-18(w) relationships. At a formation scale, turtles (delta O-18(p) = 14.1 to 15.7 parts per thousand V-SMOW) and crocodiles (delta O-18(p) = 15.0 to 19.2 parts per thousand) document water compositions of -8.1 to -6.1 parts per thousand and -7.7 to -4.2 parts per thousand, respectively, within the zonal range for formation-scale meteoric water at 34 degrees N paleolatitude (-7.1 to -4.8 parts per thousand) established by pedogenic carbonates (delta O-18(c) = 22.0 to 23.5 parts per thousand V-SMOW). These data suggest that, like soil carbonates, turtle and crocodile phosphate isotopes can be used as proxies for meteoric water isotopic composition. Dinosaur delta O-18(p) (sauropods: 19.7 to 21.9 parts per thousand, ornithischians: 16.6 to 21.7 parts per thousand, small theropods: 16.9 to 18.2 parts per thousand, and large allosauroids: 19.1 to 20.3 parts per thousand) values generally exceed those of semi-aquatic taxa. Using mass-balance equations for modern terrestrial animals adjusted for size and inferred dinosaur physiology, ingested water is calculated for the above dinosaur groups. On a member scale, when meteoric-water values are compared with calculated dinosaur drinking water, values are equal to or lighter than meteoric water for most herbivorous groups (as low as -15.5 parts per thousand for ornithischians) and equal to or heavier than meteoric water for most carnivorous groups (as high as -2.0 parts per thousand for allosauroids). Changes in delta O-18(meteoric water), delta O-18(dinosaur ingested water), faunal assemblages, and sedimentology, from member to member, correlate to thrusting events of the Sevier Orogeny. High elevations in the orogeny attenuated the influences of Pacific moisture, causing rainshadow-induced aridity on the leeward foreland basin during upper Yellow Cat time, and hosted seasonal snow accumulation by the end of Ruby Ranch time, as suggested by O-18-enriched water (e.g., up to an average of -2.0 parts per thousand from an allosauroid tooth) and extremely O-18-depleted water (e.g., -15.5 parts per thousand for ornithischians) in the Ruby Ranch Member. By Mussentuchit-time, delivery of the Western Interior Seaway-dominated moisture to the region, despite continued rise of the Sevier Mountains.
- 出版日期2014-11
