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Results for “Chemostratigraphy”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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6 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2020

The Role of Diagenesis at Vera Rubin Ridge in Gale Crater, Mars, and the Chemostratigraphy of the Murray Formation as Observed by the Chemcam Instrument

The Mars Science Laboratory (MSL) Curiosity rover explored Vera Rubin ridge (VRR) in Gale crater, Mars, for almost 500 sols (Mars days) between arriving at the ridge on sol 1809 of the mission in September 2017 and leaving it on sol 2302 upon entering the Glen Torridon area south of the ridge. VRR is a topographic ridge on the central mound, Aeolis Mons (Mt. Sharp), in Gale crater that displays a strong hematite spectral signature from orbit. In-situ observations on the ridge led to the recognition that the ridge-forming rocks belong to the Murray formation, the lowermost exposed stratigraphic unit of the Mt. Sharp group, that was first encountered at the Pahrump Hills location. Including VRR rocks, the Murray formation, interpreted to be primarily deposited in an ancient lacustrine environment in Gale crater, is more than 300 m thick. VRR itself is composed of two stratigraphic members within the Murray formation, the Pettegrove Point member overlain by the Jura member. The Pettegrove Point member overlies the Blunts Point member of the Murray formation. Areas of gray coloration are observed in the Jura member predominantly, but also in the Pettegrove Point member. Generally, gray areas are found in local topographic depressions, but contacts between red and gray rocks crosscut stratigraphy. Additionally, cm-scale dark concretions with very high iron-content are commonly observed in gray rocks, typically surrounded by a lighttoned zone that is conversely depleted in iron. A key goal for the VRR campaign was to characterize geochemical variations in the ridge-forming rocks to investigate the role of primary and diagenetic controls on the geochemistry and morphology of VRR. Here, we present observations by the ChemCam instrument on VRR and compare these to the full Murray formation chemostratigraphy. This work was recently submitted to a special issue of JGRPlanets that detail the full VRR campaign.

Frydenvang, J.↗
NASA NTRS1998

A Vendian-Cambrian boundary succession from the northwestern margin of the Siberian Platform: stratigraphy, palaeontology, chemostratigraphy and correlation

Siberia contains several key reference sections for studies of biological and environmental evolution across the Proterozoic-Phanerozoic transition. The Platonovskaya Formation, exposed in the Turukhansk region of western Siberia, is an uppermost Proterozoic to Cambrian succession whose trace and body fossils place broad limits on the age of deposition, but do not permit detailed correlation with boundary successions elsewhere. In contrast, a striking negative carbon isotopic excursion in the lower part of the Platonovskaya Formation permits precise chemostratigraphic correlation with upper-most Yudomian successions in Siberia, and possibly worldwide. In addition to providing a tool for correlation, the isotopic excursion preserved in the Platonovskaya and contemporaneous successions documents a major biogeochemical event, likely involving the world ocean. The excursion coincides with the palaeontological breakpoint between Ediacaran- and Cambrian-style assemblages, suggesting a role for biogeochemical change in evolutionary events near the Proterozoic Cambrian boundary.

Non-NASA Center↗
NASA NTRS2008

Chemostratigraphy and Fe Mineralogy of the Victoria Crater Duck Bay Section: Opportunity APXS and Moessbauer Results

Meridiani Planum is a vast plain of approximately horizontally bedded sedimentary rocks composed of mixed and reworked basaltic and evaporitic sands containing secondary, diagenetic minerals [e.g., 1-5]. Because bedding planes are subparallel to topography, investigation of contiguous stratigraphy requires examining exposures in impact craters. Early in the mission (sols 130-317), Opportunity was commanded to do detailed study of exposed outcrops in Endurance crater, including the contiguous Karatepe section at the point of ingress. Just over 1000 sols later and roughly 7 km to the south, the rover is being commanded to do a similar study of the Duck Bay section of Victoria crater. Here we report on the preliminary results from the Alpha Particle X-ray Spectrometer (APXS) and Moessbauer instruments.

Mittlefehldt, D. W.↗
NASA NTRS1992

Latest Proterozoic stratigraphy and earth history

Novel biostratigraphic and chemostratigraphic data furnish an improved framework for stratigraphic correlation of the Proterozoic Eon as well as tools for a chronostratigraphic division of the late Proterozoic. It is argued that, in conjunction with geochronometric data, protistan microfossils and isotope geochemistry can furnish a means for an eventual integration of the latest Proterozoic Eon. Attention is given to the emerging methodologies of fossil protists and prokaryotes and of isotopic chemostratigraphy.

Knoll, Andrew H.↗
NASA NTRS2000

Learning to tell Neoproterozoic time

In 1989, the International Commission on Stratigraphy established a Working Group on the Terminal Proterozoic Period. Nine years of intensive, multidisciplinary research by scientists from some two dozen countries have markedly improved the framework for the correlation and calibration of latest Proterozoic events. Three principal phenomena--the Marinoan ice age, Ediacaran animal diversification, and the beginning of the Cambrian Period--specify the limits and character of this interval, but chemostratigraphy and biostratigraphy based on single-celled microfossils (acritarchs), integrated with high-resolution radiometric dates, provide the temporal framework necessary to order and evaluate terminal Proterozoic tectonic, biogeochemical, climatic, and biological events. These data also provide a rational basis for choosing the Global Stratotype Section and Point (GSSP) that will define the beginning of this period. A comparable level of stratigraphic resolution may be achievable for the preceding Cryogenian Period, providing an opportunity to define this interval, as well, in chronostratigraphic terms--perhaps bounded at beginning and end by the onset of Sturtian glaciation and the decay of Marinoan ice sheets, respectively. Limited paleontological, isotopic, and radiometric data additionally suggest a real but more distant prospect of lower Neoproterozoic correlation and stratigraphic subdivision.

NASA Discipline Exobiology↗
NASA NTRS1995

Neoproterozoic variations in the C-isotopic composition of seawater: stratigraphic and biogeochemical implications

The recent proliferation of stratigraphic studies of delta 13C variation in carbonates and organic C in later Neoproterozoic and basal Cambrian successions (approximately 850-530 Ma) indicates a strong oscillating trend in the C-isotopic composition of surface seawater. Alone, this trend does not adequately characterize discrete intervals in Neoproterozoic time. However, integrated with the vectorial signals provided by fossils and Sr-isotopic variations, C isotope chemostratigraphy facilitates the interbasinal correlation of later Neoproterozoic successions. Results of these studies are evaluated in terms of four stratigraphic intervals: (1) the Precambrian/Cambrian boundary, (2) the post-Varanger terminal Proterozoic, (3) the late Cryogenian, and (4) the early Cryogenian. Where biostratigraphic or radiometric data constrain the age of Neoproterozoic sedimentary sequences, secular variations in C and Sr isotopes can provide a level of stratigraphic resolution exceeding that provided by fossils alone. Isotopic data place strong constraints on the chemical evolution of seawater, linking it to major tectonic and paleoclimatic events. They also provide a biogeochemical framework for the understanding of the initial radiation of macroscopic metazoans, which is associated stratigraphically, and perhaps causally, with a global increase in the burial of organic C and a concomitant rise of atmospheric O2.

NASA Discipline Exobiology↗