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Paleobiology of the Mesoproterozoic Billyakh Group, Anabar Uplift, Northern Siberia
- V. N. Sergeev, A. H. Knoll, J. P. Grotzinger
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- Journal:
- Journal of Paleontology / Volume 69 / Issue S39 / January 1995
- Published online by Cambridge University Press:
- 11 August 2017, pp. 1-37
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Silicified peritidal carbonates of the Mesoproterozoic Kotuikan and Yusmastakh Formations, Anabar Uplift, northeastern Siberia, contain exceptionally well-preserved microfossils. The assemblage is dominated by ellipsoidal akinetes of nostocalean cyanobacteria (Archaeoellipsoides) and problematic spheroidal unicells (Myxococcoides); both are allochthonous and presumably planktonic. The assemblage also includes distinctive mat-forming scytonematacean and entophysalidacean cyanobacteria, diverse short trichomes interpreted as cyanobacterial hormogonia or germinated akinetes, rare longer trichomes, and several types of colonial unicells. Although many taxa in the Kotuikan-Yusmastakh assemblage are long-ranging prokaryotes, the overall character of the assemblage is distinctly Mesoproterozoic, with its major features shared by broadly coeval floras from Canada, China, India, and elsewhere in Siberia.
Microfossils also occur in middle to inner shelf shales of the Ust’-Il'ya and lower Kotuikan Formations. Leiosphaerid acritarchs (up to several hundred microns in diameter) characterize this facies. As in other Mesoproterozoic acritarch assemblages, acanthomorphic and other complex forms that typify Neoproterozoic assemblages are absent.
The combination in Billyakh assemblages of exceptional preservation and low eukaryotic diversity supports the hypothesis that nucleated organisms diversified markedly near the Mesoproterozoic–Neoproterozoic boundary. The assemblages also demonstrate the antiquity of cyanobacteria capable of cell differentiation and suggest the importance of both changing peritidal substrates and evolving eukaryotes in determining stratigraphic patterns of Proterozoic prokaryotes. The permineralized assemblage contains 33 species belonging to 17 genera. Ten new species or new combinations are proposed: Archaeoellipsoides costatus n. sp., A. elongatus n. comb., A. dolichos n. comb., A. minor n. nom., A. crassus n. comb., A. major n. comb., A. bactroformis n. sp., Veteronostocale medium n. sp., Filiconstrictosus cephalon n. sp., and Partitiofilum yakschinii n. sp.
Genetic influences on hormonal markers of chronic hypothalamic–pituitary–adrenal function in human hair
- E. M. Tucker-Drob, A. D. Grotzinger, D. A. Briley, L. E. Engelhardt, F. D. Mann, M. Patterson, C. Kirschbaum, E. K. Adam, J. A. Church, J. L. Tackett, K. P. Harden
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- Journal:
- Psychological Medicine / Volume 47 / Issue 8 / June 2017
- Published online by Cambridge University Press:
- 19 January 2017, pp. 1389-1401
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Background
Cortisol is the primary output of the hypothalamic–pituitary–adrenal (HPA) axis and is central to the biological stress response, with wide-ranging effects on psychiatric health. Despite well-studied biological pathways of glucocorticoid function, little attention has been paid to the role of genetic variation. Conventional salivary, urinary and serum measures are strongly influenced by diurnal variation and transient reactivity. Recently developed technology can be used to measure cortisol accumulation over several months in hair, thus indexing chronic HPA function.
MethodIn a socio-economically diverse sample of 1070 twins/multiples (ages 7.80–19.47 years) from the Texas Twin Project, we estimated effects of sex, age and socio-economic status (SES) on hair concentrations of cortisol and its inactive metabolite, cortisone, along with their interactions with genetic and environmental factors. This is the first genetic study of hair neuroendocrine concentrations and the largest twin study of neuroendocrine concentrations in any tissue type.
ResultsGlucocorticoid concentrations increased with age for females, but not males. Genetic factors accounted for approximately half of the variation in cortisol and cortisone. Shared environmental effects dissipated over adolescence. Higher SES was related to shallower increases in cortisol with age. SES was unrelated to cortisone, and did not significantly moderate genetic effects on either cortisol or cortisone.
ConclusionsGenetic factors account for sizable proportions of glucocorticoid variation across the entire age range examined, whereas shared environmental influences are modest, and only apparent at earlier ages. Chronic glucocorticoid output appears to be more consistently related to biological sex, age and genotype than to experiential factors that cluster within nuclear families.
Tubular compression fossils from the Ediacaran Nama group, Namibia
- P. A. Cohen, A. Bradley, A. H. Knoll, J. P. Grotzinger, S. Jensen, J. Abelson, K. Hand, G. Love, J. Metz, N. McLoughlin, P. Meister, R. Shepard, M. Tice, J. P. Wilson
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- Journal:
- Journal of Paleontology / Volume 83 / Issue 1 / January 2009
- Published online by Cambridge University Press:
- 20 May 2016, pp. 110-122
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Abundant tubular macrofossils occur in finely laminated siltstones and shales of the 548–542 Ma Schwarzrand Subgroup, Nama Group, Namibia. The Nama tubes occur in both the Vingerbreek and Feldschuhhorn members commonly in dense populations and always in fine-grained, lower shore-face lithologies deposited below fair-weather wave base. The tubes are preserved mostly as compressed casts and molds that range in width from 0.6 to 2.1 mm; apparently incomplete specimens reach lengths up to 10 cm. All specimens show sinuous bending and occasional brittle fracture, indicating an original construction of strong but flexible organic matter. Feldschuhhorn specimens preserve fine longitudinal pleats or folds that record pliant organic walls, but the older Vingerbreek populations do not. Similarly, some specimens in the Feldschuhhorn Member display branching, while Vingerbreek tubes do not. The abundant Feldschuhhorn tubes are assigned to the widespread Ediacaran problematicum Vendotaenia antiqua; however, the distinctive Vingerbreek population remains in open nomenclature. The most abundant fossils in Nama rocks, these tubes resemble populations in Ediacaran successions from Russia, China, Spain, and elsewhere. Beyond their local importance, then, such tubes may turn out to be the most abundant record of Ediacaran life.
Integrated chronostratigraphy of Proterozoic–Cambrian boundary beds in the western Anabar region, northern Siberia
- Alan J. Kaufman, Andrew H. Knoll, Mikhail A. Semikhatov, John P. Grotzinger, Stein B. Jacobsen, William Adams
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- Journal:
- Geological Magazine / Volume 133 / Issue 5 / September 1996
- Published online by Cambridge University Press:
- 01 May 2009, pp. 509-533
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Carbonate-rich sedimentary rocks of the western Anabar region, northern Siberia, preserve an exceptional record of evolutionary and biogeochemical events near the Proterozoic/Cambrian boundary. Sedimentologically, the boundary succession can be divided into three sequences representing successive episodes of late transgressive to early highstand deposition; four parasequences are recognized in the sequence corresponding lithostratigraphically to the Manykai Formation. Small shelly fossils are abundant and include many taxa that also occur in standard sections of southeastern Siberia. Despite this coincidence of faunal elements, biostratigraphic correlations between the two regions have been controversial because numerous species that first appear at or immediately above the basal Tommotian boundary in southeastern sections have first appearances scattered through more than thirty metres of section in the western Anabar. Carbon- and Sr-isotopic data on petrographically and geochemically screened samples collected at one- to two-metre intervals in a section along the Kotuikan River, favour correlation of the Staraya Reckha Formation and most of the overlying Manykai Formation with sub-Tommotian carbonates in southeastern Siberia. In contrast, isotopic data suggest that the uppermost Manykai Formation and the basal 26 m of the unconformably overlying Medvezhya Formation may have no equivalent in the southeast; they appear to provide a sedimentary and palaeontological record of an evolutionarily significant time interval represented in southeastern Siberia only by the sub-Tommotian unconformity. Correlations with radiometrically dated horizons in the Olenek and Kharaulakh regions of northern Siberia suggest that this interval lasted approximately three to six million years, during which essentially all 'basal Tommotian' small shelly fossils evolved.
24 - The sedimentary rock cycle of Mars
- from Part V - Synthesis
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- By S. M. McLennan, Department of Geosciences, SUNY Stony Brook Stony Brook, NY 11794-2100, USA, J. P. Grotzinger, Geology & Planetary Sciences, California Institute of Technology MC 170-25 1200 E. California Blvd. Pasendena, CA 91125, USA
- Edited by Jim Bell, Cornell University, New York
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- Book:
- The Martian Surface
- Published online:
- 10 December 2009
- Print publication:
- 05 June 2008, pp 541-577
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Summary
Abstract
Orbital and landed missions have demonstrated that Mars possesses an extensive and diverse sedimentary rock record that is mostly ancient. Many observed or inferred processes appear familiar to sedimentary geologists but, in detail, the sedimentary record of Mars differs in fundamental ways from the terrestrial record. Mars is a basaltic planet and accordingly, the provenance of sedimentary material, including particulate debris and aqueous fluids from which chemical constituents precipitate, is composed of basalt rather than intermediate to felsic igneous compositions characteristic of terrestrial upper continental crust. Aqueous alteration, observed on Mars and studied experimentally, indicates surficial processes dominated by low pH; under acidic conditions, many chemical relationships that are characteristic of terrestrial weathering do not apply. Aluminum and Fe are far more soluble and mobile, Si mobility is limited by fluid/rock ratio and iron oxidation rates are sluggish. Low fluid/rock ratios are indicted by the observation that only the most soluble minerals (olivine, Fe-Ti oxides, phosphates, possibly pyroxene) appear to be widely involved in surface alteration with little evidence for involvement of relatively insoluble plagioclase. An intriguing result, from both global-scale orbital and detailed surface spectroscopy, and geochemistry obtained by rovers, is that evaporitic processes, leading to a wide variety of Ca-, Mg- and Fe-bearing sulfates in sedimentary rocks, alteration profiles, and soils, appear to have been common throughout Martian geological history. Investigations by Spirit and Opportunity demonstrate that classical stratigraphy and sedimentology can be accomplished on the Martian surface using remote techniques.
2 - Geological Evolution of the Proterozoic Earth
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- By Donald R. Lowe, Stanford University, Nicolas J. Beukes, Rand Afrikaans University, John P. Grotzinger, Massachusetts Institute of Technology, Raymond V. Ingersoll, University of California, Joseph L. Kirschvink, Institute of Technology, Cornelis Klein, University of New Mexico, Ian B. Lambert, Resource Assessment Commission, Australia, Ján Veizer, University of Ottawa
- Edited by J. William Schopf, University of California, Los Angeles, Cornelis Klein, University of New Mexico
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- Book:
- The Proterozoic Biosphere
- Published online:
- 04 April 2011
- Print publication:
- 26 June 1992, pp 43-80
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Summary
The Proterozoic Eon extends from 2500 to 550 Ma, from the close of the Archean to the beginning of the Cambrian. It includes three principal geochronologic divisions: Lower or Proterozoic I (2500 to 1600 Ma), Middle or Proterozoic II (1600 to 900 Ma), and Upper or Proterozoic III (900 to 550 Ma). These definitions are consistent with previous usage (Schopf 1983a) and with recommendations of the Subcommission on Precambrian Stratigraphy of the International Union of Geological Sciences (Plumb and James 1986). Although some criticism has been voiced at the use of absolute ages rather than stratigraphic or paleontologic events for subdividing Precambrian time (Cloud 1987), we find that the lack of well-developed, widespread, narrowly constrained, isochronous Precambrian biostratigraphic markers, equivalent to Phanerozoic faunal successions, presents an as yet insurmountable barrier to the establishment of globally useful Precambrian biostratigraphic subdivisions.
Systematic treatment of the geological evolution of the Proterozoic earth and similar long-term or large-scale aspects of Proterozoic history is complicated at present by our incomplete knowledge of existing Proterozoic rocks, selective preservation/obliteration of certain types of terranes, and uncertain geochronology and correlation. Many Proterozoic sequences remain essentially unstudied, especially in parts of central and northern Africa, South America, and Asia, and their stratigraphies, ages, and tectonic settings are unresolved. Information from these sequences is essential to evaluation of global patterns of Proterozoic geologic evolution, sediment recycling, and tectonics.
6 - Modern Mat-Building Microbial Communities: a Key to the Interpretation of Proterozoic Stromatolitic Communities
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- By Beverly K. Pierson, University of Puget Sound, John Bauld, Bureau of Mineral Resources, Richard W. Castenholz, University of Oregon, Elisa D'Amelio, Ames Research Center, David J. Des Marais, Ames Research Center, Jack D. Farmer, University of California, John P. Grotzinger, Massachusetts Institute of Technology, Bo Barker Jørgensen, University of Aarhus, Douglas C. Nelson, University of California, Anna C. Palmisano, Ivorydale Technical Center, J. William Schopf, University of California, Roger E. Summons, Bureau of Mineral Resources, Geology and Geophysics, Australia, Malcolm R. Walter, M. R. Walter Pty. Ltd, David M. Ward, Montana State University
- Edited by J. William Schopf, University of California, Los Angeles, Cornelis Klein, University of New Mexico
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- Book:
- The Proterozoic Biosphere
- Published online:
- 04 April 2011
- Print publication:
- 26 June 1992, pp 245-342
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Summary
Introduction
Modern microbial mats are structurally coherent macroscopic accumulations of microorganisms. Mats are widely distributed on earth. They are found in a surprisingly large number of diverse environments from the equatorial zones to both polar regions. They vary in size from extensive terrestrial and hypersaline mats that cover areas several square kilometers in extent to minute mats only a few square centimeters in area found in small thermal springs. They vary in thickness from massive accumulations measured in meters, such as those in the Persian Gulf and the Red Sea region, to thin films less than a few millimeters in thickness. In addition to being highly varied in size, modern microbial mats are also very diverse in morphology, community structure, and physiological characteristics. What do such mats have in common? Under what conditions do they form? What is the basis of their diversity? What insight do they provide, if any, to the interpretation of the widespread stromatolites of the Proterozoic?
A Terminology
Microbial mats are accretionary cohesive microbial communities which are often laminated and found growing at the sediment-water (occasionally sediment-air) interface. Most mats stabilize unconsolidated sediment. The mats are comprised of the various microorganisms that accumulate along with their metabolic products. The most conspicuous of these products is usually a copious amount of extracellular polysaccharide which helps hold the cells together to form a cohesive structure.