23 research outputs found
Nomad rover field experiment, Atacama desert, Chile 2. Identification of paleolife evidence using a robotic vehicle: Lessons and recommendations for a Mars sample return mission
This is the publisher's version, also available electronically from "http://onlinelibrary.wiley.com".During the Nomad Rover Field Experiment in the Atacama Desert (Chile), a potential fossil was identified in a boulder by the science team remotely located at NASA Ames Research Center, California. The science team requested the collecting of the boulder that was returned for laboratory analysis. This analysis confirmed the evidence of paleolife. As the first fossil identified and sampled by a remotely located science team using a rover, we use the case of sample I-250697 to describe the process, both in the field and later in the laboratory during the rock analysis, which led to the identification, characterization, and confirmation of the evidence of paleolife evidence in I-250697. We point out the lessons that this case provides for future Mars sample return missions
Multi-Taxa Isotopic Investigation of Paleohydrology In the Lower Cretaceous Cedar Mountain Formation, Eastern Utah, U.S.A.: Deciphering Effects Of the Nevadaplano Plateau On Regional Climate
We investigate the regional climatic effects of the formation of the âNevadaplanoâ 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 ÎŽ18Owvalues using established ÎŽ18OpâÎŽ18Ow and ÎŽ18OcâÎŽ18Ow relationships. At a formation scale, turtles (ÎŽ18Op â=â 14.1 to 15.7â° V-SMOW) and crocodiles (ÎŽ18Op â=â 15.0 to 19.2â°) document water compositions of â8.1 to â6.1â° and â7.7 to â4.2â°, respectively, within the zonal range for formation-scale meteoric water at 34° N paleolatitude (â7.1 to â4.8â°) established by pedogenic carbonates (ÎŽ18Oc â=â 22.0 to 23.5â° 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 ÎŽ18Op(sauropods: 19.7 to 21.9â°, ornithischians: 16.6 to 21.7â°, small theropods: 16.9 to 18.2â°, and large allosauroids: 19.1 to 20.3â°) 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 â15.5â° for ornithischians) and equal to or heavier than meteoric water for most carnivorous groups (as high as â2.0â° for allosauroids). Changes in ÎŽ18Ometeoric water, ÎŽ18Odinosaur 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 18O-enriched water (e.g., up to an average of â2.0â° from an allosauroid tooth) and extremely 18O-depleted water (e.g., â15.5â° for ornithischians) in the Ruby Ranch Member. By Mussentuchit-time, delivery of the Western Interior Seawayâdominated moisture to the region, despite continued rise of the Sevier Mountains
BerriasianâValanginian Geochronology and Carbon-Isotope Stratigraphy of the Yellow Cat Member, Cedar Mountain Formation, Eastern Utah, USA
The Early Cretaceous Yellow Cat Member of the terrestrial Cedar Mountain Formation in Utah, USA. has been interpreted as a âtime-richâ unit because of its dinosaur fossils, prominent paleosols, and the results of preliminary chemostratigraphic and geochronologic studies. Herein, we refine prior interpretations with: (1) a new composite C-isotope chemostratigraphic profile from the well-known Utahraptor Ridge dinosaur site, which exhibits ÎŽ13C features tentatively interpreted as the Valanginian double-peak carbon isotope excursion (the so-called âWeissert Eventâ) and some unnamed Berriasian features; and (2) a new cryptotephra zircon eruption age of 135.10 ± 0.30/0.31/0.34 Ma (2Ï) derived from the CA-ID-TIMS U-Pb analyses of zircons from a paleosol cryptotephra. Our interpretations of ÎŽ13C features on our chemostratigraphic profile, in the context of our new radiometric age, are compatible with at least one prior age model for the âWeissert Eventâ and the most recent revision of the Cretaceous time scale. Our results also support the interpretation that the Yellow Cat Member records a significant part of Early Cretaceous time
Berriasian–Valanginian Geochronology and Carbon-Isotope Stratigraphy of the Yellow Cat Member, Cedar Mountain Formation, Eastern Utah, USA
The Early Cretaceous Yellow Cat Member of the terrestrial Cedar Mountain Formation in Utah, USA. has been interpreted as a “time-rich” unit because of its dinosaur fossils, prominent paleosols, and the results of preliminary chemostratigraphic and geochronologic studies. Herein, we refine prior interpretations with: (1) a new composite C-isotope chemostratigraphic profile from the well-known Utahraptor Ridge dinosaur site, which exhibits δ13C features tentatively interpreted as the Valanginian double-peak carbon isotope excursion (the so-called “Weissert Event”) and some unnamed Berriasian features; and (2) a new cryptotephra zircon eruption age of 135.10 ± 0.30/0.31/0.34 Ma (2σ) derived from the CA-ID-TIMS U-Pb analyses of zircons from a paleosol cryptotephra. Our interpretations of δ13C features on our chemostratigraphic profile, in the context of our new radiometric age, are compatible with at least one prior age model for the “Weissert Event” and the most recent revision of the Cretaceous time scale. Our results also support the interpretation that the Yellow Cat Member records a significant part of Early Cretaceous time
New Geochronological Age Constraint and Chemostratigraphy for Aptian Lacustrine Strata, Cedar Mountain Formation, Utah
Abstract The Early Cretaceous is an important time of transition in Earth history, marked by a succession of oceanic anoxic events and carbon cycle perturbations that drove changes on land and in the ocean. The need for more precise geochronologic constraints in terrestrial sediments of Early Cretaceous age that record faunal and floral transitions is especially critical. The Cedar Mountain Formation (CMF) is a continental lithostratigraphic unit that hosts a trove of paleoclimate archives and important dinosaurian fossil localities. Determining the timing of deposition of CMF strata has been an ongoing effort for many years. Here, we present new lithostratigraphic and carbon isotope chemostratigraphic data along with highâprecision radiometric ages to further constrain the Ruby Ranch Member of the CMF at a unique locality referred to as âLake Carpenter,â where a thick section of dominantly lacustrine strata overlies fluvialâoverbank to palustrine strata more typical of other Ruby Ranch Member outcrops. A bentonite bed near the base of the section provides one of the most precise ages yet determined within the Ruby Ranch Member of 115.92 ± 0.14 Ma via CAâIDâTIMS UâPb analysis of zircons. The age and the trends in the carbon isotope record indicate that the Lake Carpenter sediments were deposited entirely within the late Aptian Stage. These unique new data provide an important step toward improving our understanding of the timing of Early Cretaceous evolutionary and paleoclimate events
UâPb Geochronology and Stable Isotope Geochemistry of Terrestrial Carbonates, Lower Cretaceous Cedar Mountain Formation, Utah: Implications for Synchronicity of Terrestrial and Marine Carbon Isotope Excursions
The terrestrial Lower Cretaceous Cedar Mountain Formation, Utah, is a critical archive of paleoclimate, tectonics, and vertebrate ecology and evolution. Early Cretaceous carbon cycle perturbations associated with ocean anoxia have been interpreted from this succession, as expressed in stable carbon isotopes. However, refining the timing of the observed stable isotope excursions remains a key challenge in understanding how marine anoxia affects the Earth system, and is ultimately recorded in the terrestrial realm. The geochronology and geochemistry of a terrestrial carbonate near the base of this succession, which potentially records the Ap7 global carbon isotope excursion, is studied here. Petrographic and geochemical analyses are used to test plausible mechanisms for U incorporation into the calcite lattice in this sample. Using these methods, the hypothesis that the incorporation of U was at or close to the timing of carbonate precipitation is evaluated. UâPb geochronology of calcite indicates a plausible Early Cretaceous age. However, comparison of the new UâPb ages of calcite with detrital zircon maximum depositional ages immediately beneath the studied sample indicates a disparity in the apparent sedimentation rates if both types of geochronologic information are interpreted as reflecting the timing of sediment deposition. The totality of data supports an early, and high-temperature, diagenetic timing of U incorporation, with potential for minor leaching of U in subsequent fluidârock interaction. The most likely mechanism for U transport and immobilization in these samples is hydrothermal fluidârock interaction. Therefore, the radiometric ages, and corresponding stable isotope composition of U-bearing carbonate domains in this sample, indicate early subsurface fluidârock interactions and not a record of atmosphereâsoil geochemical reactions