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239 results on '"Whitehouse A"'

48. Sample-scale carbon isotopic variability and diverse biomass in the Paleoproterozoic Zaonega Formation, Russia

Author

Yuangao Qu, Alenka E. Črne, Mark A. van Zuilen, Aivo Lepland, Martin J. Whitehouse, and Anthony E. Fallick

Subjects
chemistry.chemical_classification, Biomass (ecology), 010504 meteorology & atmospheric sciences, δ13C, Great Oxygenation Event, Geochemistry, chemistry.chemical_element, Geology, 010502 geochemistry & geophysics, 01 natural sciences, Carbon cycle, chemistry, Stratigraphy, Geochemistry and Petrology, Isotopes of carbon, Organic matter, Carbon, 0105 earth and related environmental sciences
Abstract

The stratigraphic record of organic matter in the c. 1.97 Ga Zaonega Formation (ZF), Onega Basin, northwestern Russia, exhibits a distinct negative δ13C excursion (δ13Corg from −25 to −40‰ VPDB), which was previously interpreted either to reflect a disturbance in the global carbon cycle after the Great Oxidation Event, or to have been caused by an increase in basinal methanotrophic activity. In order to assess the nature of primary biomass and the effects of post-depositional alteration, we here report the sample-scale carbon isotopic characteristics of organic matter in two drill cores from the ZF, covering 500 m of stratigraphy, by using secondary ion mass spectrometry (SIMS). The results confirm that the organic matter has to a large extent preserved the primary isotopic signatures, whereas secondary effects are limited (

Published
2018

49. Preliminary detrital zircon signatures from the southern Asir terrane, Saudi Arabia: A link to Yemen or the Nubian Shield?

Author

Victoria Pease, Ellen Kooijman, Martin J. Whitehouse, and Frank A. Robinson

Subjects
geography, geography.geographical_feature_category, 010504 meteorology & atmospheric sciences, Volcanic arc, Geochemistry, Pyroclastic rock, Geology, Crust, 010502 geochemistry & geophysics, 01 natural sciences, Gondwana, Basement (geology), Geochemistry and Petrology, Accretion (geology), 0105 earth and related environmental sciences, Zircon, Terrane
Abstract

The Arabian Shield comprises early Neoproterozoic to Cambrian (∼850–530 Ma) tectonostratigraphic terranes formed by the closure and accretion of juvenile volcanic arcs and back-arc basins associated with Gondwana assembly. Unlike the Nubian Shield which preserves crustal isotopic signatures, the Arabian Shield is distinctly juvenile with the exception of the Paleoproterozoic (∼1800–1670 Ma) Khida subterrane in Saudi Arabia and the terranes of Yemen. This study presents the first combined zircon U-Pb, O and Hf isotope data of metavolcanic and metasedimentary rocks from southwestern most Saudi Arabia, near the Yemen border – a region thought to contain some of the oldest (>815 Ma) lithologies in Saudi Arabia, including the Atura Formation and the Tayyah Belt. One volcaniclastic metasediment sample from the Atura Formation yields zircon U-Pb age peaks of 741, 672, 646 Ma (n = 131), δ18O(V-SMOW) ranging from 4.6 to 8.3‰ and ɛHf (t) from +7.7 to +12.5. Two samples from the Tayyah Belt include an older metasandstone and a late intruding granitic dyke which provides a minimum age for the Tayyah Belt. The former yields two significant U-Pb peaks of 812 (n = 8) and 999 (n = 6) Ma, δ18O and ɛHf (t) values ranging from 4.4 to 9.6‰ and −10.1 to +12.4, respectively; the later yields a concordia age of 645.8 [±1.7] Ma (n = 29), δ18O ranging from 5.7 to 6.6‰, and ɛHf (t) of +5.9 to +9.6. The zircon age and juvenile Hf signatures from the Atura Formation are consistent with the synorogenic phase in the Shield. Sedimentation was likely associated with arc volcanism during the previously documented eastward phase of accretion at ∼740–640 Ma and the closure of the Mozambique Ocean. In contrast, the data from the texturally more mature Tayyah Belt metasediment indicate a more distal, and more evolved crustal input at the time of sediment deposition which is unusual for the Saudi Arabian Shield. Consequently, the Tayyah metasediments are likely sourced from areas with greater continental affinity, such as the cratonic basement and/or reworked crust of the Sahara metacraton in NE Africa.

Published
2018

50. U-Pb age distribution recorded in zircons from Archean quartzites in the Mt. Alfred area, Yilgarn Craton, Western Australia

Author

Jeremy J. Bellucci, Robert T. Pidgeon, Ross Kielman, Alexander A. Nemchin, and Martin J. Whitehouse

Subjects
education.field_of_study, 010504 meteorology & atmospheric sciences, Archean, Population, Geochemistry, Geology, Greenstone belt, Yilgarn Craton, 010502 geochemistry & geophysics, 01 natural sciences, Geochemistry and Petrology, Clastic rock, education, 0105 earth and related environmental sciences, Zircon, Gneiss, Terrane
Abstract

The U-Th-Pb isotopic data from detrital zircon grains from five samples of Archean quartzite from the Mt. Alfred area of the Illaara greenstone belt in the Yilgarn Craton of Western Australia are presented in this study. The zircon grains are typically fractured and contain both irregular and oscillatory zoned internal structures as revealed by cathodoluminescence imaging. Concordant 207Pb/206Pb ages range between 3109 ± 17 and 3918 ± 16 Ma (2σ), with three main age peaks at ca. 3640, 3690 and 3760 Ma. Older 207Pb/206Pb ages up to 4067 ± 5 Ma are strongly affected by at least one recent disturbance event, however one single-grain discordia yields an upper intercept age of 4107 ± 12 (MSWD = 1.2). A further sixteen zircon grains with multiple analyses define discordia that suggest U-Pb disturbance events in the Neoarchean and the Mesozoic, the latter as a result of invasive low temperature weathering solutions. The notable lack of grains with ages less than ∼3.6 Ga in the Mt. Alfred detrital zircon population differentiates it from other quartzite samples from both the Illaara Formation and the Eoarchean zircon-bearing metasedimentary rocks of the Narryer Terrane. Also, the limited spread of zircon ages between 3640 and 3760 Ma suggests a relatively uniform and possibly local source region. However, no rocks of this age have been found in the Youanmi Terrane. This implies either the distal transport of similarly aged clastic sediments at 3.1 Ga from the Narryer Gneiss Complex (NGC) to the Mt. Alfred area, or the previous existence of NGC-like rocks near the Illaara greenstone belt that are either not currently recognised or have since been destroyed.

Published
2018

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