Journal articles on the topic 'Subaerial weathering'
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1
Potts, Richard. "Temporal span of bone accumulations at Olduvai Gorge and implications for early hominid foraging behavior." Paleobiology 12, no. 1 (1986): 25–31. http://dx.doi.org/10.1017/s0094837300002955.
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Bones of mammals exhibit progressive stages of weathering during their time of subaerial exposure. Consequently, the study of bone weathering in fossil assemblages may help to assess the period represented by an accumulation of bones. Stages of bone decomposition due to subaerial weathering have been identified in assemblages of fossil macromammals from Olduvai Gorge, Tanzania. A modern bone assemblage collected by spotted hyenas is used to devise a method for recognizing attritional accumulations of bones from weathering characteristics. This method, which involves study of long bone diaphyses, is applied to Plio-Pleistocene faunal assemblages from Olduvai, 1.70–1.85 ma old. Previous work indicates that early hominids had an important role in the collection of fauna at five of the six sites studied. It is shown that animal bones were accumulated at each site over a period of probably 5–10 yr or more. The length of this period, along with other taphonomic evidence, suggests that the processes of bone aggregation at these sites differed from those at the short-term campsites of modern, tropical hunter-gatherers.
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Tsekhovskii, Yu G., В. А. Bogatyrev, and V. V. Zhukov. "Lithogenesis on peneplaned сontinented platform of Kazakhstan and Siberia during the Cretaceous-Paleogene boundary epoch." LITOSFERA, no. 1 (March 17, 2019): 5–29. http://dx.doi.org/10.24930/1681-9004-2019-19-1-5-29.
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Research subject. The inner structure, composition, and genesis of the poorly studied formation of weathering crusts are studied with reference to peneplaned platform territories in Kazakhstan and Siberia during the Cretaceous-Paleogene boundary epoch. This formation hosts many valuable minerals, such as bauxite, iron ores, refractory clays, etc., thereby attracting much research attention. Materials and methods. The results were obtained following a series of long-term studies and a review of available data recently obtained on the weathering crust formation in the territories of Kazakhstan and Siberia. The methods of lithological facies and formation analysis were used, along with the separate studies of the eluvial material – weathering crusts in erosion areas and intra-formation weathering horizons in accumulation areas. Results. The weathering crust formation in the study area is shown to comprise two kinds of rock mass: siliceous-kaolinite ones forming erosion-tectonic depressions and kaolinite-bauxite ones forming karst depressions. The inner structure, composition, and genesis of both rock mass units are studied in detail, with all their sedimentation stages being analyzed. The sedimentation process is traced from the preparation of the material in weathering crusts at erosion areas to the deposition of this material and its post-sedimentation transformations (mostly with the involvement of subaerial diagenesis) in depressions. Detailed information is presented on subaerial diagenesis, which deserves further studies. Conclusions. This publication is the frst to present detailed information on the inner structure, composition and genesis of the ancient formation of weathering crusts produced in hot humid climate on peneplaned land territories. It is confrmed that the processes underpinning this formation – starting with the preparation of the material and ending with its accumulation in depressions – were different from those typical of modern orogenic environments. This conclusion extends the current understanding of the forms and nature of ancient lithogenetic processes.
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Liu, Jiacheng, Joseph R. Michalski, and Mei-Fu Zhou. "Intense subaerial weathering of eolian sediments in Gale crater, Mars." Science Advances 7, no. 32 (August 2021): eabh2687. http://dx.doi.org/10.1126/sciadv.abh2687.
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After over 8 years of successful surface operations on Mars, the Curiosity rover has revealed much about the environment in Gale crater. Despite early observations of a lacustrine environment, few of the subsequent deposits exhibit demonstrable lacustrine character. We suggest instead that most of the stratigraphic section explored to date can be best explained as eolian and/or volcaniclastic sediments subaerially chemically weathered by acidic precipitation in a reduced atmosphere. Most of the deposits in Gale crater seemingly did not form in an ancient lake, but the results nonetheless shed considerable light on ancient climate, environmental change, and the astrobiology of Mars. Discoveries by Curiosity provide a critical piece to Mars’ global alteration puzzle.
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Dąbski, Maciej. "Rock surface micro−roughness, Schmidt hammer rebound and weathering rind thickness within LIA Skálafellsjökull foreland, SE Iceland." Polish Polar Research 35, no. 1 (March 1, 2014): 99–114. http://dx.doi.org/10.2478/popore-2014-0008.
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Abstract : Glacially abraded basaltic rock surfaces found within a Little Ice Age (LIA) fore− land of Skálafellsjökull (SE Iceland) were studied at eight sites of different age applying different weathering indices. They include surface micro−roughness parameters measured with the Handysurf E35−B electronic profilometer - a new tool in geomorphology, Schmidt hammer rebound (R−values) and weathering rind thickness. Values of these indices obtained from study sites exposed to subaerial weathering for more than ca. 80 years are significantly different than those from younger moraines closer to the glacier snout. Despite a wide scatter of readings within each study site, there is a significant correlation between the ages and the values of the indices. It is concluded that the micro−roughness parameters provided by the Handysurf E35−B profilometer, Schmidt hammer R−values and weathering rind thickness are robust indices of rock surface deterioration rate in short time−scales. There is mounting evidence that rock surface undergoes relatively rapid weathering during first decades since deglaciation.
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Roerdink, Desiree L., Yuval Ronen, Harald Strauss, and Paul R. D. Mason. "Emergence of felsic crust and subaerial weathering recorded in Palaeoarchaean barite." Nature Geoscience 15, no. 3 (February 24, 2022): 227–32. http://dx.doi.org/10.1038/s41561-022-00902-9.
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Alfimova, Nadezhda A., Alexey A. Novoselov, Vjacheslav A. Matrenichev, and Carlos Roberto de Souza Filho. "Conditions of subaerial weathering of basalts in the Neoarchean and Paleoproterozoic." Precambrian Research 241 (February 2014): 1–16. http://dx.doi.org/10.1016/j.precamres.2013.09.013.
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Mitchell, R. H. "Mineralogy of stalactites formed by subaerial weathering of natrocarbonatite hornitos at Oldoinyo Lengai, Tanzania." Mineralogical Magazine 70, no. 4 (August 2006): 437–44. http://dx.doi.org/10.1180/0026461067040344.
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AbstractStalactites formed by the chemical weathering of natrocarbonatite lava decorate the roofs of hollow inactive hornitos at Oldoinyo Lengai, Tanzania. The stalactites are composed principally of trona with lesser and very variable amounts of nahcolite, (NaHCO3), thermonatrite (Na2CO3.H2O), aphthitalite [(K,Na)3Na(SO4)2], kogarkoite [Na3(SO4)F], schairerite [Na21 (SO4)7F6Cl], halite and sylvite. Stalactites are considered to form by the evaporation of Ca-free highly alkaline brines seeping from the altered lavas which form the roofs of the hornitos. The principal subaerial weathering products of natrocarbonatite, i.e. pirsonnite, gaylussite, shortite and calcite are not found in the stalactites and are retained in the altered lavas of the homito roof. Fluorine required for the formation of kogarkoite and schairerite is derived from the decomposition of fluorite at high pH (>10). Sulphur is derived from the decomposition of gregoryite.
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Dąbski, Maciej. "Application of the Handysurf E-35B electronic profilometer for the study of weathering micro-relief in glacier forelands in SE Iceland." Acta Geologica Polonica 65, no. 3 (September 1, 2015): 389–401. http://dx.doi.org/10.1515/agp-2015-0018.
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AbstractThis article presents the results of weathering micro-roughness measurements performed with the use of a Handy-surf E-35B electronic profilometer, a new tool in geomorphological studies. Measurements were performed on glacially abraded basaltic surfaces within the Little Ice Age (LIA) glacial forelands of Hoffelsjökull, Fláajökull, Skálafellsjökull and Virkisjökull in Iceland. Results show a statistical increase in micro-roughness in a direction from the glacial termini to LIA moraines. However, a major change in the micro-roughness of basaltic surfaces only occurs during the first 80 to 100 years since the onset of subaerial weathering. Increase in rock surface micro-roughness is accompanied by an increase in weathering rind thickness and a decrease in Schmidt hammer R-values. Micro-roughness measurements with the use of the Handysurf E-35B can provide insights into initial rates of rock surface micro-relief development. The use of this instrument as a relative dating technique is limited to fine-grained rocks and decadal time-scales of weathering because of the limited range of measureable micro-relief amplitude.
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Lowe, Donald R., Janice L. Bishop, Damien Loizeau, James J. Wray, and Ross A. Beyer. "Deposition of >3.7 Ga clay-rich strata of the Mawrth Vallis Group, Mars, in lacustrine, alluvial, and aeolian environments." GSA Bulletin 132, no. 1-2 (May 2, 2019): 17–30. http://dx.doi.org/10.1130/b35185.1.
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Abstract The presence of abundant phyllosilicate minerals in Noachian (>3.7 Ga) rocks on Mars has been taken as evidence that liquid water was stable at or near the surface early in martian history. This study investigates some of these clay-rich strata exposed in crater rim and inverted terrain settings in the Mawrth Vallis region of Mars. In Muara crater the 200-m-thick, clay-rich Mawrth Vallis Group (MVG) is subdivided into five informal units numbered 1 (base) to 5 (top). Unit 1 consists of interbedded sedimentary and volcanic or volcaniclastic units showing weak Fe/Mg-smectite alteration deposited in a range of subaerial depositional settings. Above a major unconformity eroded on Unit 1, the dark-toned sediments of Unit 2 and lower Unit 3 are inferred to represent mainly wind-blown sand. These are widely interlayered with and draped by thin layers of light-toned sediment representing fine suspended-load aeolian silt and clay. These sediments show extensive Fe/Mg-smectite alteration, probably reflecting subaerial weathering. Upper Unit 3 and units 4 and 5 are composed of well-layered, fine-grained sediment dominated by Al-phyllosilicates, kaolinite, and hydrated silica. Deposition occurred in a large lake or arm of a martian sea. In the inverted terrain 100 km to the NE, Unit 4 shows very young slope failures suggesting that the clay-rich sediments today retain a significant component of water ice. The MVG provides evidence for the presence of large, persistent standing bodies of water on early Mars as well as a complex association of flanking shoreline, alluvial, and aeolian systems. Some of the clays, especially the Fe/Mg smectites in upper units 1 and 2 appear to have formed through subaerial weathering whereas the aluminosilicates, kaolinite, and hydrated silica of units 3, 4, and 5 formed mainly through alteration of fine sediment in subaqueous environments.
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Viehmann, Sebastian. "Hf-Nd Isotopes in Archean Marine Chemical Sediments: Implications for the Geodynamical History of Early Earth and Its Impact on Earliest Marine Habitats." Geosciences 8, no. 7 (July 16, 2018): 263. http://dx.doi.org/10.3390/geosciences8070263.
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The Hf-Nd isotope systems are coupled in magmatic systems, but incongruent Hf weathering (‘zircon effect’) of the continental crust leads to a decoupling of the Hf-Nd isotope systems in low-temperature environments during weathering and erosion processes. The Hf-Nd isotope record was recently dated back from the Cenozoic oceans until the Archean, showing that both isotope systems were already decoupled in seawater 2.7 Ga ago and potentially 3.4 Ga and 3.7 Ga ago. While there might have existed a hydrothermal pathway for Hf into Archean seawater, incongruent Hf weathering of more evolved, zircon-bearing uppermost continental crust that was emerged and available for subaerial weathering accounts for a significant decoupling of Hf-Nd isotopes in the dissolved (<0.2 µm) and suspended (>0.2 µm) fractions of Early Earth’s seawater. These findings contradict the consensus that uppermost Archean continental crust was (ultra)mafic in composition and predominantly submerged. Hence, Hf-Nd isotopes in Archean marine chemical sediments provide the unique potential for future research to trace the emergence of evolved continental crust, which in turn has major implications for the geodynamical evolution of Early Earth and the nutrient flux into the earliest marine habitats on Earth.
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White, Art F., and Michael F. Hochella. "Surface chemistry associated with the cooling and subaerial weathering of recent basalt flows." Geochimica et Cosmochimica Acta 56, no. 10 (October 1992): 3711–21. http://dx.doi.org/10.1016/0016-7037(92)90164-e.
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Meixnerová, Jana, Joel D. Blum, Marcus W. Johnson, Eva E. Stüeken, Michael A. Kipp, Ariel D. Anbar, and Roger Buick. "Mercury abundance and isotopic composition indicate subaerial volcanism prior to the end-Archean “whiff” of oxygen." Proceedings of the National Academy of Sciences 118, no. 33 (August 9, 2021): e2107511118. http://dx.doi.org/10.1073/pnas.2107511118.
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Earth’s early atmosphere witnessed multiple transient episodes of oxygenation before the Great Oxidation Event 2.4 billion years ago (Ga) [e.g., A. D. Anbar et al., Science 317, 1903–1906 (2007); M. C. Koehler, R. Buick, M. E. Barley, Precambrian Res. 320, 281–290 (2019)], but the triggers for these short-lived events are so far unknown. Here, we use mercury (Hg) abundance and stable isotope composition to investigate atmospheric evolution and its driving mechanisms across the well-studied “whiff” of O2 recorded in the ∼2.5-Ga Mt. McRae Shale from the Pilbara Craton in Western Australia [A. D. Anbar et al., Science 317, 1903–1906 (2007)]. Our data from the oxygenated interval show strong Hg enrichment paired with slightly negative ∆199Hg and near-zero ∆200Hg, suggestive of increased oxidative weathering. In contrast, slightly older beds, which were evidently deposited under an anoxic atmosphere in ferruginous waters [C. T. Reinhard, R. Raiswell, C. Scott, A. D. Anbar, T. W. Lyons, Science 326, 713–716 (2009)], show Hg enrichment coupled with positive ∆199Hg and slightly negative ∆200Hg values. This pattern is consistent with photochemical reactions associated with subaerial volcanism under intense UV radiation. Our results therefore suggest that the whiff of O2 was preceded by subaerial volcanism. The transient interval of O2 accumulation may thus have been triggered by diminished volcanic O2 sinks, followed by enhanced nutrient supply to the ocean from weathering of volcanic rocks causing increased biological productivity.
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Parnell, John, Kirsty Macleod, and Malcolm J. Hole. "Carbon dioxide drawdown by Devonian lavas." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 105, no. 1 (March 2014): 1–8. http://dx.doi.org/10.1017/s1755691014000152.
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ABSTRACTLower Devonian volcanic rocks in the northern British Isles, especially Scotland, show extensive evidence for contemporaneous subaerial weathering. Basalt and andesite lavas were altered to red iron oxides, commonly accompanied by calcite. Measurement of carbonate contents in 104 samples over a region of 100,000 km2 show an average of 13% calcite. Weighted for outcrop thickness, this represents an estimated 7.3×1016 moles CO2, extracted from surface waters and ultimately the atmosphere. The time frame for this drawdown is difficult to constrain, but complete weathering of a one-metre unit over 1000 years would involve CO2 consumption comparable with the highest rates determined in modern basaltic watersheds. These data demonstrate that volcanic activity can be a major sink, as well as a source for CO2, and provide a data set for modelling of CO2 flux during episodes of volcanic activity in the geological record. The high capacity of the Devonian lavas for CO2 drawdown emphasises the potential of basalts for CO2 sequestration.
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Christian Smoot, N. "Mass wasting and subaerial weathering in guyot formation: the Hawaiian and Canary Ridges as examples." Geomorphology 14, no. 1 (October 1995): 29–41. http://dx.doi.org/10.1016/0169-555x(95)00035-4.
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Pokines, James T., Rebecca E. King, Deborah D. Graham, Amanda K. Costello, Donovan M. Adams, Jennifer M. Pendray, Kushal Rao, and Donald Siwek. "The effects of experimental freeze-thaw cycles to bone as a component of subaerial weathering." Journal of Archaeological Science: Reports 6 (April 2016): 594–602. http://dx.doi.org/10.1016/j.jasrep.2016.03.023.
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Kennedy, David M., Ryan Paulik, and Mark E. Dickson. "Subaerial weathering versus wave processes in shore platform development: reappraising the Old Hat Island evidence." Earth Surface Processes and Landforms 36, no. 5 (October 20, 2010): 686–94. http://dx.doi.org/10.1002/esp.2092.
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Al Hatrushi, Salim Mubarak. "Morphology of the Raised Shore Platforms along the Coastline between Daghmar and Dhabab, Sultanate of Oman." Journal of Arts and Social Sciences [JASS] 8, no. 2 (July 15, 2017): 13. http://dx.doi.org/10.24200/jass.vol8iss2pp13-24.
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Raised shore platforms, are rocky surfaces formed by wave action and subaerial weathering during global high sea level stands. The present height of the raised shore platforms is attributed to several factors, mainly to eustatic sea level changes, isostatic changes in the relative level of land and sea, and vertical tectonic activities. The aim of this study is to investigate the detailed morphology of the raised shore platform along the rocky coastline between Daghmar and Dhabab, in the southeastern part of Muscat Governorate. The study also intends to establish a tentative chronology of the raised shore platforms development. The methodology is based on field observation and documentation, along with satellite and aerial photographs analysis. The results have shown that the study area has a sequence of five successive, well developed raised shore platforms and well preserved, except the platform at 10m altitude which is only found in isolated fragments. The formation of the raised shore platforms has been affected by a number of constructive factors including tectonic activity, and destructive factors such as fluvial action and subaerial weathering. No absolute dating has been reported or can be obtained from the study area, due to its erosional nature. However, dating from the shorelines adjacent to the study area, ranging in heights from 3 to 15m above sea level, revealed a narrow range of 26,400 to 29,600 years. This period coincides with the last glaciations when the sea level was at about 75m below the present level, and thus did not match with the altitudes of the platforms. This suggests that the platforms could be belong to the last interglacial high sea level, when the sea level stood at about 6m above the present level. Based on this scenario, the study concludes that the coastline of the study area has not experienced any significant uplift during the Late Quaternary.
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Samolczyk, Mary A., James W. Vallance, Joel F. Cubley, Gerald D. Osborn, and Douglas H. Clark. "Geochemical characterization and dating of R tephra, a postglacial marker bed in Mount Rainier National Park, Washington, USA." Canadian Journal of Earth Sciences 53, no. 2 (February 2016): 202–17. http://dx.doi.org/10.1139/cjes-2015-0115.
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The oldest postglacial lapilli–ash tephra recognized in sedimentary records surrounding Mount Rainier (Washington State, USA) is R tephra, a very early Holocene deposit that acts as an important stratigraphic and geochronologic marker bed. This multidisciplinary study incorporates tephrostratigraphy, radiocarbon dating, petrography, and electron microprobe analysis to characterize R tephra. Tephra samples were collected from Tipsoo Lake and a stream-cut exposure in the Cowlitz Divide area of Mount Rainier National Park. Field evidence from 25 new sites suggests that R tephra locally contains internal bedding and has a wider distribution than previously reported. Herein, we provide the first robust suite of geochemical data that characterize the tephra. Glass compositions are heterogeneous, predominantly ranging from andesite to rhyolite in ash- to lapilli-sized clasts. The mineral assemblage consists of plagioclase, orthopyroxene, clinopyroxene, and magnetite with trace apatite and ilmenite. Subaerial R tephra deposits appear more weathered in hand sample than subaqueous deposits, but weathering indices suggest negligible chemical weathering in both deposits. Statistical analysis of radiocarbon ages provides a median age for R tephra of ∼10 050 cal years BP, and a 2σ error range between 9960 and 10 130 cal years BP.
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DA ROSA, ÁTILA AUGUSTO STOCK, NUNO LAMAS VALENTE PIMENTEL, and UBIRATAN FERRUCIO FACCINI. "Paleoalterações e Carbonatos em Depósitos Aluviais na Região de Santa Maria, Triássico Médio a Superior do Sul do Brasil." Pesquisas em Geociências 31, no. 1 (June 30, 2004): 3. http://dx.doi.org/10.22456/1807-9806.19561.
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Five types of paleo-weathering and carbonate precipitation were recognized in fine-grained deposits of the Alemoa Member, Santa Maria Formation, Middle to Upper Triassic of southern Brazil. The fauna and flora found in these lithologies are important dating tools, but only in a generic way, misleading the time involved in periods of deposition and non deposition. The identified types of deposits are (i) reddish mudstones, with none or little paleo-weathering, (ii) mottled mudstones, with incipient pedogenesis, mainly mottling, destratification, animal and vegetal colonization, (iii) carbonate veins, with more evidences of exposure and root action, (iv) carbonate siltstones/sandstones, where restricted fluvial deposits are cemented by phreatic carbonate, and (v) carbonate nodules and lenses, in which small lenses of a very compact calcrete are at the top and in the center of carbonated siltstone/sandstone beds, distinguished by its crystalinity, hardness and brighter color. The recorded microfacies point to a cyclic variation of the mainly high phreatic level, forming cracks and pedotubules (pedogenesis) filled with carbonate and Fe and Mn oxides (phreatic). The identification of five distinct pedofacies and the stratigraphic correlation in the sedimentary package of the Alemoa Member (base, middle or topmost position) suggest a probable association of paleo-weathering processes and vertebrate preservation. Near channel facies, mainly at the base and top, present smaller exposure periods and higher variations on the phreatic level, and consequently, the best preserved vertebrate fossils. On the other hand, facies which are far from the channel, record more subaerial exposure and more significant phreatic variation, leading to more advanced (although still incipient) paleo-weathering and carbonate precipitation, and to a worst fossil preservation.
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Park, Yuem, Nicholas L. Swanson-Hysell, Scott A. MacLennan, Adam C. Maloof, Mulubrhan Gebreslassie, Marissa M. Tremblay, Blair Schoene, et al. "The lead-up to the Sturtian Snowball Earth: Neoproterozoic chemostratigraphy time-calibrated by the Tambien Group of Ethiopia." GSA Bulletin 132, no. 5-6 (October 17, 2019): 1119–49. http://dx.doi.org/10.1130/b35178.1.
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Abstract The Tonian-Cryogenian Tambien Group of northern Ethiopia is a mixed carbonate-siliciclastic sequence that culminates in glacial deposits associated with the first of the Cryogenian glaciations—the Sturtian “Snowball Earth.” Tambien Group deposition occurred atop arc volcanics and volcaniclastics of the Tsaliet Group. New U-Pb isotope dilution–thermal ionization mass spectrometry (ID-TIMS) dates demonstrate that the transition between the Tsaliet and Tambien Groups occurred at ca. 820 Ma in western exposures and ca. 795 Ma in eastern exposures, which is consistent with west to east arc migration and deposition in an evolving back-arc basin. The presence of intercalated tuffs suitable for high-precision geochronology within the Tambien Group enable temporal constraints on stratigraphic data sets of the interval preceding, and leading into, the Sturtian glaciation. Recently discovered exposures of Sturtian glacial deposits and underlying Tambien Group strata in the Samre Fold-Thrust Belt present the opportunity to further utilize this unique association of tuffs and carbonate lithofacies. U-Pb ID-TIMS ages from zircons indicate that Tambien Group carbonates were deposited from ca. 820 Ma until 0–2 m.y. before the onset of the Sturtian glaciation, making the group host to a relatively complete carbonate stratigraphy leading into this glaciation. New δ13C and 87Sr/86Sr data and U-Pb ID-TIMS ages from the Tambien Group are used in conjunction with previously published isotopic and geochronologic data to construct newly time-calibrated composite Tonian carbon and strontium isotope curves. Tambien Group δ13C data and U-Pb ID-TIMS ages reveal that a pre-Sturtian sharp negative δ13C excursion (referred to as the Islay anomaly in the literature) precedes the Sturtian glaciation by ∼18 m.y., is synchronous in at least two separate basins, and is followed by a prolonged interval of positive δ13C values. The composite Tonian 87Sr/86Sr curve shows that, following an extended interval of low and relatively invariant values, inferred seawater 87Sr/86Sr rose ca. 880–770 Ma, then subsequently decreased leading up to the ca. 717 Ma initiation of the Sturtian glaciation. These data, when combined with a simple global weathering model and analyses of the timing and paleolatitude of large igneous province eruptions and arc accretion events, suggest that the 87Sr/86Sr increase was influenced by increased subaerial weathering of radiogenic lithologies as Rodinia rifted apart at low latitudes. The following 87Sr/86Sr decrease is consistent with enhanced subaerial weathering of arc lithologies accreting in the tropics over tens of millions of years, lowering pCO2 and contributing to the initiation of the Sturtian glaciation.
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PRADO, MAURÍCIO, JOSÉ TADEU MAXIMINO MIRRAS FERRON, EVANDRO FERNANDES DE LIMA, ARTUR CEZAR BASTOS NETO, VITOR PAULO PEREIRA, ORLANDO RENATO RIGON MINUZZI, and RONALDO PIEROSAN. "Caracterização Petrográfica e Geoquímica da Parte Leste do Granito Europa, Distrito Mineiro de Pitinga, AM." Pesquisas em Geociências 34, no. 1 (June 30, 2007): 77. http://dx.doi.org/10.22456/1807-9806.19464.
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The important mineral deposits of the Pitinga Mine, in the Amazonian region are related to A-type granites intruded in the Iricoumé Group. The Europa granite is one of these A-type rocks, intruded in the Iricoumé Group, which is represented by subaerial vulcanoclastic rocks (crystal-rich ignimbrites, thin massive tuffs and siltic tufaceous arenites) and minor hipabissal rhyolites. The volcanic rocks were probably generated in a caldera environment. The Europa granite is an alkali-feldspar peralkaline granite (hipersolvus) without genetic relationship with to the volcanic rocks of the Iricoumé Group, but it could have been generated during the resurgence stages. The petrographic and geochemical data attest that fractional crystallization process was the principal mechanism during the crystallization, which led to the generation of two different granitic facies. The Nb soil anomalies overprinted on the more differentiated facies are related to the astrophillite weathering.
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Mushkin, Amit, Amir Sagy, Eran Trabelci, Rivka Amit, and Naomi Porat. "Measuring the time and scale-dependency of subaerial rock weathering rates over geologic time scales with ground-based lidar." Geology 42, no. 12 (December 2014): 1063–66. http://dx.doi.org/10.1130/g35866.1.
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Fernández-Remolar, D. C. "The subsurface and surface acidic system of Río Tinto: Sulfur and iron transfer from underground weathering to subaerial precipitation." Geochimica et Cosmochimica Acta 70, no. 18 (August 2006): A171. http://dx.doi.org/10.1016/j.gca.2006.06.343.
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Ruibal, Constantino, Laura Selbmann, Serap Avci, Pedro Martin-Sanchez, and Anna Gorbushina. "Roof-Inhabiting Cousins of Rock-Inhabiting Fungi: Novel Melanized Microcolonial Fungal Species from Photocatalytically Reactive Subaerial Surfaces." Life 8, no. 3 (July 15, 2018): 30. http://dx.doi.org/10.3390/life8030030.
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Subaerial biofilms (SAB) are an important factor in weathering, biofouling, and biodeterioration of bare rocks, building materials, and solar panel surfaces. The realm of SAB is continually widened by modern materials, and the settlers on these exposed solid surfaces always include melanized, stress-tolerant microcolonial ascomycetes. After their first discovery on desert rock surfaces, these melanized chaetothyrialean and dothidealean ascomycetes have been found on Mediterranean monuments after biocidal treatments, Antarctic rocks and solar panels. New man-made modifications of surfaces (e.g., treatment with biocides or photocatalytically active layers) accommodate the exceptional stress-tolerance of microcolonial fungi and thus further select for this well-protected ecological group. Melanized fungal strains were isolated from a microbial community that developed on highly photocatalytic roof tiles after a long-term environmental exposure in a maritime-influenced region in northwestern Germany. Four of the isolated strains are described here as a novel species, Constantinomyces oldenburgensis, based on multilocus ITS, LSU, RPB2 gene phylogeny. Their closest relative is a still-unnamed rock-inhabiting strain TRN431, here described as C. patonensis. Both species cluster in Capnodiales, among typical melanized microcolonial rock fungi from different stress habitats, including Antarctica. These novel strains flourish in hostile conditions of highly oxidizing material surfaces, and shall be used in reference procedures in material testing.
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Scuderi, L. A., L. D. McFadden, and J. R. McAuliffe. "Dendrogeomorphically derived slope response to decadal and centennial scale climate variability: Black Mesa, Arizona, USA." Natural Hazards and Earth System Sciences 8, no. 4 (August 18, 2008): 869–80. http://dx.doi.org/10.5194/nhess-8-869-2008.
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Abstract. A major impediment to an understanding of the links between climate and landscape change, has been the relatively coarse resolution of landscape response measures (rates of weathering, sediment production, erosion and transport) relative to the higher resolution of the climatic signal (precipitation and temperature on hourly to annual time scales). A combination of high temporal and spatial resolution dendroclimatic and dendrogeomorphic approaches were used to study relationships between climatic variability and hillslope and valley floor dynamics in a small drainage basin in the Colorado Plateau of northeastern Arizona, USA Dendrogeomorphic and vegetation evidence from slopes and valley bottoms, including root exposure, bending of trunks, change in plant cover and burial and exhumation of valley bottom trees and shrubs, suggest that the currently observed process of root colonization and rapid breakdown of the weakly cemented bedrock by subaerial weathering, related to periodic dry/wet cycle induced changes in vegetation cover, has lead to a discontinuous, climate-controlled production of sediment from these slopes. High-amplitude precipitation shifts over the last 2000-years may exert the largest control on landscape processes and may be as, or more, important than other hypothesized causal mechanisms (e.g. ENSO frequency and intensity, flood frequency) in eroding slopes and producing sediments that ultimately impact higher order drainages in the region. Current vegetation response to a prolonged drought over the past decade suggests that another major transition, incorporating vegetation change, slope erosion, sediment production and subsequent valley floor deposition, may be in its initial phase.
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Dey, Sumit, Prabir Dasgupta, Kaushik Das, and Abdul Matin. "Neoproterozoic Blaini Formation of Lesser Himalaya, India: Fiction and Fact." GSA Bulletin 132, no. 11-12 (March 16, 2020): 2267–81. http://dx.doi.org/10.1130/b35483.1.
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Abstract The long-conceived idea of the glacial origin of Blaini diamictite of Lesser Himalayan Neoproterozoic succession reached its maxima when the diamictites and capping pink limestone were attributed to the Neoproterozoic Snowball Earth event and its aftermath, respectively. Occurrences of diamictite-limestone association in two different levels have also been correlated with the Sturtian and Marinoan glaciations. Critical review, however, reveals that the interpretations of the glacial origin of diamictites are not well founded. The diamictite-limestone association, which occurs at the lower part of a thick, light brown shale unit and laterally grades into light brown shale, primarily indicates episodic surge events in an otherwise tranquil condition favorable for hemipelagic sedimentation. The lithology, bed geometry, internal organization, and disposition of the diamictite bodies suggest deposition of debris flow fan lobes along fault scarps in a rift setting. Emplacement of subaqueous debris flows is indicated by the associated deposits of entrained turbidity currents. The limestone also bears the signature of claciturbidites. The appearance of diamictite bodies and associated limestone in two distinct levels is not a stratigraphic disposition; on the contrary, the deposits were dislocated and repeated by two successive regional thrust faults. The Chemical Index of Alteration (CIA) values of the light brown shale and the matrix of the diamictites indicate that these sediments formed through prolonged subaerial weathering. The events leading up to development of the rift system and evidence of prolonged weathering within the basin-fill sediments are consistent with supercontinental break up, the prologue of Snowball Earth.
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Zheng, Zhuo, and Qianyu Li. "Vegetation, Climate, and Sea Level in the Past 55,000 Years, Hanjiang Delta, Southeastern China." Quaternary Research 53, no. 3 (May 2000): 330–40. http://dx.doi.org/10.1006/qres.1999.2126.
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AbstractPollen in Quaternary deposits from the subtropical Hanjiang Delta records three major phases in the local vegetation and climate history during the last 55,000 yr: (1) a prevalent cool-to-temperate and humid climate at ca. 24,000 14C yr B.P. is indicated by abundant pollen of temperate trees including conifers; (2) between 20,000 and 15,000 14C yr B.P., a cold, dry environment was associated with low sea level during the last glaciation, leading to subaerial exposure, weathering, and interruption of sedimentation, as well as departure from the region of Dacrydium and Sonneratia; (3) a short-term expansion of grassland at ca. 10,300 14C yr B.P. reduced the predominant Lauraceae-Fagaceae evergreen forest, possibly corresponding to the Younger Dryas cooling. The combined data indicate a maximum sea-level rise in the mid-Holocene (7500–4000 14C yr B.P.) and a marine influence in the late Pleistocene at 45,000–20,000 14C yr B.P. The Holocene warming, however, did not bring back moisture-sensitive taxa, indicating high seasonal aridity probably caused by renewed monsoon conditions.
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Hall, A. J., A. E. Fallick, V. Perdikatsis, and E. Photos-Jones. "A model for the origin of Al-rich efflorescences near fumaroles, Melos, Greece: enhanced weathering in a geothermal setting." Mineralogical Magazine 67, no. 2 (April 2003): 363–79. http://dx.doi.org/10.1180/0026461036720102.
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Efflorescences in the geothermal field of SE Melos, Greece, contain significant amounts of hydrated Al sulphate, alunogen, which could represent the Melian alumen exploited in Roman times and commended by Pliny. The efflorescences at subaerial fumaroles are explained as follows: Sulphur crystallizes on oxidation of H2S emanating from depth. Weathering produces sulphuric acid enhancing groundwater alteration of volcanic rocks. The high geothermal gradient and arid climate stimulate efflorescences. Salts are recycled during wet and dry weather leading to Al-enrichment on loss of Fe(II,III) and other cations. δ34S‰ V-CDT values for sulphur in fumarole sublimates, solfatara soils and ‘veins’ range from —0.3 to 6.4‰, mean 3.8‰ (n = 8) while Al, Ca and Mg-sulphates in diverse settings range from —4.1 to 6.8‰ (n = 16). The values for sulphur indicate that the initial H2S had an igneous source and the signature is largely inherited by the sulphates.This study aims to underpin research into the exploitation of industrial minerals in the Roman period. When searching for early alumen workings, areas with evidence of acid sulphate alteration (white rocks) and sulphurous fumarole activity should be investigated.
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Costa, Newton. "GEOQUÍMICA DO PERFIL LATERÍTICO DE OUTEIRO (BELÉM-PARÁ)." Boletim do Museu de Geociências da Amazônia 9, no. 1 (June 30, 2022): 1–55. http://dx.doi.org/10.31419/issn.2594-942x.v92022i1a7ncc3.
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The Amazon region has, in all its immensity, abundant occurrences of laterites. These laterites, a product resulting from subaerial tropical weathering processes, keep records and important information about the environmental transformations experienced by the region. The Outeiro Island, inserted in this context, presents in its cliffs, good exposures of this lithological type. In this work these laterites are described as a function of the texture, closely related to the granulometry of the Barreiras Sediments, involved in the lateritization process. In them, the soil horizons, concretionary, mottled and remains of the mother rock and/or substrate are identified. The predominant mineralogy in the horizons in this profile is quartz and kaolinite, occurring in the concretionary horizon a large amount of hematite and goethite and muscovite in the most basal portion. The heavy minerals identified were, in order of abundance, staurolite, tourmaline, kyanite, zircon and rutile. The chemistry is characterized by high levels of SiO2, ranging from top to bottom from 90% to 51% and high levels of Fe and Al in the concretionary horizon and of Fe in the bedrock, not characterizing, however, a complete chemical differentiation, proving the immature nature of the profile. Keywords: Soils; concrecionary; mottled; kaolinite; hematite.
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Lü, Xiuxiang, Weiwei Jiao, Xinyuan Zhou, Jianjiao Li, Hongfeng Yu, and Ning Yang. "Paleozoic Carbonate Hydrocarbon Accumulation Zones in Tazhong Uplift, Tarim Basin, Western China." Energy Exploration & Exploitation 27, no. 2 (April 2009): 69–90. http://dx.doi.org/10.1260/0144-5987.27.2.69.
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Diverse types of marine carbonate reservoirs have been discovered in the Tazhong Uplift, Tarim Basin, and late alteration of such reservoirs is obvious. The marine source rocks of the Cambrian-lower Ordovician and the middle-upper Ordovician provided abundant oil and gas for hydrocarbon accumulation. The hydrocarbons filled various reservoirs in multiple stages to form different types of reservoirs from late Caledonian to early Hercynian, from late Hercynian to early Indosininan and from late Yanshanian to Himalayan. All these events greatly complicated hydrocarbon accumulation. An analysis of the discovered carbonate reservoirs in the Tazhong Uplift indicated that the development of a reservoir was controlled by subaerial weathering and freshwater leaching, sedimentation, early diagenesis, and alteration by deep fluids. According to the origin and lateral distribution of reservoir beds, the hydrocarbon accumulation zones in the Tazhong area were identified as: karsted reservoirs, reef/bank reservoirs, dolomite interior reservoirs, and hydrothermal reservoirs. Such carbonate hydrocarbon accumulation zones are distributed mainly in specific areas of the Tazhong uplift, respectively. Because of differences in the mechanism of reservoir formation, the reservoir space, capability, type and distribution of reservoirs are often different in different carbonate hydrocarbon accumulation zones.
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Broz, Adrian P. "Organic Matter Preservation in Ancient Soils of Earth and Mars." Life 10, no. 7 (July 16, 2020): 113. http://dx.doi.org/10.3390/life10070113.
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The emerging field of astropedology is the study of ancient soils on Earth and other planetary bodies. Examination of the complex factors that control the preservation of organic matter and other biosignatures in ancient soils is a high priority for current and future missions to Mars. Though previously defined by biological activity, an updated definition of soil as planetary surfaces altered in place by biological, chemical or physical processes was adopted in 2017 by the Soil Science Society of America in response to mounting evidence of pedogenic-like features on Mars. Ancient (4.1–3.7 billion year old [Byr]) phyllosilicate-rich surface environments on Mars show evidence of sustained subaerial weathering of sediments with liquid water at circumneutral pH, which is a soil-forming process. The accumulation of buried, fossilized soils, or paleosols, has been widely observed on Earth, and recent investigations suggest paleosol-like features may be widespread across the surface of Mars. However, the complex array of preservation and degradation factors controlling the fate of biosignatures in paleosols remains unexplored. This paper identifies the dominant factors contributing to the preservation and degradation of organic carbon in paleosols through the geological record on Earth, and offers suggestions for prioritizing locations for in situ biosignature detection and Mars Sample Return across a diverse array of potential paleosols and paleoenvironments of early Mars. A compilation of previously published data and original research spanning a diverse suite of paleosols from the Pleistocene (1 Myr) to the Archean (3.7 Byr) show that redox state is the predominant control for the organic matter content of paleosols. Most notably, the chemically reduced surface horizons (layers) of Archean (2.3 Byr) paleosols have organic matter concentrations ranging from 0.014–0.25%. However, clay mineralogy, amorphous phase abundance, diagenetic alteration and sulfur content are all significant factors that influence the preservation of organic carbon. The surface layers of paleosols that formed under chemically reducing conditions with high amounts of iron/magnesium smectites and amorphous colloids should be considered high priority locations for biosignature investigation within subaerial paleoenvironments on Mars.
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Andriani, G. F., N. Walsh, and R. Pagliarulo. "The influence of the geological setting on the morphogenetic evolution of the Tremiti Archipelago (Apulia, Southeastern Italy)." Natural Hazards and Earth System Sciences 5, no. 1 (January 3, 2005): 29–41. http://dx.doi.org/10.5194/nhess-5-29-2005.
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Abstract. The Tremiti Archipelago (Southern Adriatic Sea), also called Insulae Diomedae from the name of the Greek hero who first landed there, is an area of high landscape and historical value. It is severely affected by significant geomorphologic processes dominated by mass movements along the coast that constitute the most important and unpredictable natural hazard for the population and cultural heritage. Coastal erosion is favoured by the peculiar geological and structural setting, seismic activity, weathering, development of karst processes, and wave action. The present paper reports on descriptive and qualitative evaluation of the factors controlling landslides and coastline changes based on medium-term in situ observation, detailed surface surveys at selected locations since 1995, and historic and bibliographic data. The Tremiti Archipelago is part of an active seismic area characterised by a shear zone separating two segments of the Adriatic microplate that have shown different behaviour and roll back rates in the subduction underneath the Apennines since middle Pleistocene. Although coastal morphology can be basically considered to be the result of wave action, the continual action of subaerial processes contributes effectively to the mechanism of shoreline degradation. Weathering mainly affects the marly calcisiltites and calcilutites of the Cretaccio Fm. and the friable and low cemented calcarenites and biomicrites of the San Nicola Fm. The cliffs are characterised by different types of failure such as lateral spreads, secondary topples, rock falls and slides. At the Isle of San Nicola, landslides are controlled by the contrast in competence, shear strength and stiffness between the Pliocene re-crystallised dolomitic calcarenites and calcisiltites and the Miocene marly calcilutites and calcisiltites. At the Isles of San Domino and Caprara rock falls are attributed to the undercutting of waves at the base of the cliffs.
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Ruban, Dmitry A. "Complexity and Geoheritage Importance of Granite Pseudokarst from the Belaya River Gorge (Western Caucasus)." Geosciences 12, no. 4 (April 15, 2022): 175. http://dx.doi.org/10.3390/geosciences12040175.
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New investigations in the Western Caucasus contribute to the understanding of granite pseudokarst (sensu lato) and megaclasts linked to river erosion. A plot on the bank of the Belaya River (Mountainous Adygeya, Western Caucasus) was selected to examine diverse and abundant pseudokarst features (small rock basins, hollows, potholes, and channels) and large clasts. Morphological analysis of these features clarifies their general characteristics and genetic interpretations. Pseudokarst features can be classified into two major categories, namely the relatively small (<1 m) and large (>1 m) features. Potholes, which are usually 1–3 m in size, are the most characteristic features occurring on two levels, i.e., on steep walls of the gorge (half-filled with river water) and on slightly inclined surfaces of a terrace-like landform (subaerial exposure). In both cases, their walls from the side of the river are broken. Apparently, these potholes were formed on the river bottom. Subsequent incision of the gorge elevated potholes and the river has eroded them from one side. Apparently, some pseudokarst features are related to macroturbulent flood flows and granite weathering. Due to its scientific uniqueness and aesthetic attractiveness, this granite pseudokarst constitutes geoheritage, which can be exploited for the purposes of geoscience research and geotourism development.
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Campbell, James A., Michael J. Ryan, and Jason S. Anderson. "A taphonomic analysis of a multitaxic bonebed from the St. Mary River Formation (uppermost Campanian to lowermost Maastrichtian) of Alberta, dominated by cf. Edmontosaurus regalis (Ornithischia: Hadrosauridae), with significant remains of Pachyrhinosaurus canadensis (Ornithischia: Ceratopsidae)." Canadian Journal of Earth Sciences 57, no. 5 (May 2020): 617–29. http://dx.doi.org/10.1139/cjes-2019-0089.
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Scabby Butte is an isolated exposure of Upper Cretaceous (uppermost Campanian to lowermost Maastrichtian) strata of the St. Mary River Formation. These rocks have produced a diverse assemblage of both terrestrial and aquatic vertebrates, although hadrosaurid and ceratopsid dinosaurs represent the largest component by volume. Almost all of these dinosaur remains were collected from a single bonebed (Site 2) at Scabby Butte and have been referred to the hadrosaurid Edmontosaurus regalis Lambe, 1917 and the ceratopsid Pachyrhinosaurus canadensis Sternberg, 1950. This study presents a quantitative taphonomic reanalysis of the originally published data, providing new information previously overlooked and important information about the age-class structure of the dinosaur fauna preserved at the site. Site 2 is a lag deposit with a minimum number of 11 individuals (two ceratopsid, nine hadrosaurid), with three-quarters of the material being adult-sized based on size-class analysis. Most elements have undergone moderate to severe breakage and abrasion, and are completely disarticulated, suggesting that they were transported from where they died; post-mortem scavenging is also a possibility, as evidenced by the presence of tooth marks and trample marks on several elements. Burial took place soon after scavenging, as there is little evidence of subaerial weathering.
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Gall, Quentin. "Precambrian paleosols in Canada." Canadian Journal of Earth Sciences 29, no. 12 (December 1, 1992): 2530–36. http://dx.doi.org/10.1139/e92-200.
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Although at least 38 Precambrian paleosols have been reported in Canada, few have received the attention afforded most other geological phenomena. The most intensively studied of these are widely distributed Early Proterozoic paleosols associated with the sub-Huronian and Matonabbee (new name) unconformities. Criteria that have been most useful in identifying Precambrian paleosols in Canada include macrostructures (ascending protolith disruption, saprolith, and corestones), micromorphology (sepic texture and peds), mineralogical changes (dissolution, transformation), geochemical signatures (ascending depletion of some elements, characteristic weathering indices), and distinctive colour contrast. Diagenetic mechanical and geochemical overprinting of the paleosols, evident in many Canadian examples, includes paleosol compaction, veins cutting pedogenic features, and widespread alkali and alkaline earth element metasomatism. Metamorphism and deformation also tend to mask pedogenic features, as attested by the scarcity of documented occurrences of medium- to high-grade metamorphosed Precambrian paleosols in Canada. The recognition of other Precambrian paleosols in metamorphosed terranes could be aided by systematic detailed studies of rocks beneath unconformities to assess geochemical gradients in metamorphic minerals rich in Si, Al and Fe. Geochronological constraints on Precambrian paleosol development might reinforce previously proposed stratigraphic correlations, suggest new correlations, and serve to delimit times and areas of relative tectonic stability and subaerial exposure.
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Pevehouse, Katie J., Dustin E. Sweet, Branimir Šegvić, Charles C. Monson, Giovanni Zanoni, Stephen Marshak, and Melanie A. Barnes. "Paleotopography controls weathering of Cambrian-age profiles beneath the Great Unconformity, St. Francois Mountains, SE Missouri, U.S.A." Journal of Sedimentary Research 90, no. 6 (June 5, 2020): 629–50. http://dx.doi.org/10.2110/jsr.2020.33.
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ABSTRACT Precambrian (1.4 to 1.5 Ga) granite and rhyolite in the St. Francois Mountains at the northeast corner of the Ozark Plateau in Missouri has been altered down to a depth up to 8 meters below the Great Unconformity (the contact between Paleozoic sedimentary rock and underlying Precambrian). Petrographic, geochemical, and mineralogic data indicate that at least two events generated this alteration: 1) surficial weathering due to subaerial exposure of the granite before Cambrian burial—this material is preserved as a paleosol; and 2) alteration due to reaction with basinal fluids channeled along the unconformity from nearby sedimentary basins long after burial by Paleozoic strata. To assess the variation between surficial weathering and basinal fluid alteration, we measured and sampled for petrologic, geochemical, and mineralogic data in the rock at and just below the Great Unconformity at three paleoelevations. Whole-rock geochemical oxide and X-ray diffraction data indicate that K-metasomatism and highly crystalline illite occurred in each profile. The K increase reflects crystallization of authigenic feldspar and illite from basinal fluids that were channeled along the Great Unconformity during younger Paleozoic fluid-flow events. Each profile also exhibits an upward increase in altered feldspar crystals and highly crystalline kaolinite, and an upward decrease in Ca and Na. Such changes reflect soil formation due to reaction with meteoric water before Cambrian burial, indicating that the altered granite was a paleosol before Paleozoic basinal fluid-flow events. Notably, the paleosol at the highest paleoelevation displays the least amount of paleoweathering and the paleosol at the lowest displays the greatest amount of paleoweathering. These results demonstrate that not only can characteristics of the paleosol just below the Great Unconformity be recognized in the St. Francois Mountains, despite subsequent alteration, but also it is possible to detect variations in soil thickness that were controlled by slope steepness and, therefore, water availability and/or soil creep or failure. This spatial relationship is compatible with studies of modern soils which indicate that soil character varies with position on a slope.
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Hofmann, Axel, Robert Bolhar, Paul Dirks, and Hielke Jelsma. "The geochemistry of Archaean shales derived from a Mafic volcanic sequence, Belingwe greenstone belt, Zimbabwe: provenance, source area unroofing and submarine versus subaerial weathering." Geochimica et Cosmochimica Acta 67, no. 3 (February 2003): 421–40. http://dx.doi.org/10.1016/s0016-7037(02)01086-4.
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Frey, Holli M., Kathryn J. Szramek, Matthew R. Manon, and Matthew T. Kissane. "Slow chemical weathering in a semiarid climate: Changes in the mineralogy and geochemistry of subaerial lava flows in the Deschutes River Basin, central Oregon." Chemical Geology 347 (June 2013): 135–52. http://dx.doi.org/10.1016/j.chemgeo.2013.04.002.
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Michniewicz, Aleksandra. "Tors in Central European Mountains – are they indicators of past environments?" Bulletin of Geography. Physical Geography Series 16, no. 1 (June 18, 2019): 67–87. http://dx.doi.org/10.2478/bgeo-2019-0005.
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Abstract Tors represent one of the most characteristic landforms in the uplands and mountains of Central Europe, including the Sudetes, Czech-Moravian Highlands, Šumava/Bayerischer Wald, Fichtelgebirge or Harz. These features occur in a range of lithologies, although granites and gneisses are particularly prone to tor formation. Various models of tor formation and development have been presented, and for each model the tors were thought to have evolved under specific environmental conditions. The two most common theories emphasised their progressive emergence from pre-Quaternary weathering mantles in a two-stage scenario, and their development across slopes under periglacial conditions in a one-stage scenario. More recently, tors have been analysed in relation to ice sheet extent, the selectivity of glacial erosion, and the preservation of landforms under ice. In this paper we describe tor distribution across Central Europe along with hypotheses relating to their formation and development, arguing that specific evolutionary histories are not supported by unequivocal evidence and that the scenarios presented were invariably model-driven. Several examples from the Sudetes are presented to demonstrate that tor morphology is strongly controlled by lithology and structure. The juxtaposition of tors of different types is not necessarily evidence that they differ in their mode of origin or age. Pathways of tor remodelling and degradation under subaerial conditions are identified and it is argued that processes of tor formation and development are ongoing. Thus, tors are not reliable indicators of past environments, because they are considerably influenced by both geological factors, such as lithology and structure, and geomorphological factors such as hillslope setting..
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Bond, Philip L., Greg K. Druschel, and Jillian F. Banfield. "Comparison of Acid Mine Drainage Microbial Communities in Physically and Geochemically Distinct Ecosystems." Applied and Environmental Microbiology 66, no. 11 (November 1, 2000): 4962–71. http://dx.doi.org/10.1128/aem.66.11.4962-4971.2000.
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ABSTRACT This study presents population analyses of microbial communities inhabiting a site of extreme acid mine drainage (AMD) production. The site is the inactive underground Richmond mine at Iron Mountain, Calif., where the weathering of a massive sulfide ore body (mostly pyrite) produces solutions with pHs of ∼0.5 to ∼1.0. Here we used a suite of oligonucleotide probes, designed from molecular data recently acquired from the site, to analyze a number of microbial environments by fluorescent in situ hybridization. Microbial-community analyses were correlated with geochemical and mineralogical data from those environments. The environments investigated were within the ore body and thus at the site of pyrite dissolution, as opposed to environments that occur downstream of the dissolution. Few organism types, as defined by the specificities of the oligonucleotide probes, dominated the microbial communities. The majority of the dominant organisms detected were newly discovered or organisms only recently associated with acid-leaching environments. “Ferroplasma” spp. were detected in many of the communities and were particularly dominant in environments of lowest pH and highest ionic strength.Leptospirillum spp. were also detected in many slime and pyrite-dominated environments. In samples of an unusual subaerial slime, a new uncultured Leptospirillum sp. dominated.Sulfobacillus spp. were detected as a prominent inhabitant in warmer (∼43°C) environments. The information gathered here is critical for determining organisms important to AMD production at Iron Mountain and for directing future studies of this process. The findings presented here also have relevance to the microbiology of industrial bioleaching and to the understanding of geochemical iron and sulfur cycles.
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He, Chipeng, Longbin Sha, Dongbo Zhao, Lu Dai, Zheng Li, Jiabing Tang, Xianfu Li, and Dongling Li. "Sedimentary Environmental Evolution of the Western Taiwan Shoal Area since the Late Pleistocene." Journal of Marine Science and Engineering 9, no. 10 (October 19, 2021): 1150. http://dx.doi.org/10.3390/jmse9101150.
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A new pollen analysis and major and trace element contents were conducted on a 40 m long gravity core recovered from the Taiwan Shoal (sand ridges), south of the Taiwan Strait, beginning in the Late Pleistocene. The changes in the pollen assemblage and concentration represent the climate change around the Taiwan Shoal and the strength of the Zhe-Min Coastal Current, whereas variations in major and trace element contents can imply the source of the sediments in the Taiwan Shoal, which are correlated with the rise or fall of the sea level with increased marine dinoflagellate cysts. The interval of 40–30 m was characterized by high pollen and spore concentrations, and evergreen Quercus was dominant taxon, which indicates a warm sedimentary environment, and the surrounding area of the Taiwan Shoal were covered by a tropical and subtropical broad-leaved forest. There were no pollen and spores from 30–24 m, which indicates a strong hydrodynamic sedimentary environment, and most of the Taiwan Shoal might have been experience subaerial exposure. The interval of 24–17 m was characterized by the reappearance of pollen and spores, as well as marine dinoflagellate cysts and foraminifera, suggesting the climate was warm and wet in the study area and an apparent marine sedimentary environment with relatively high sea level. Deciduous Quercus dominated the interval of 17–12 m, which indicated that the climate was relatively cool, corresponding to the end of Marine isotope stages3 (MIS3) to the Last Glacial Maximum accompanied by weathering and denudation. Above 12 m, the low pollen concentration with increased marine dinoflagellate cysts and foraminifera abundance suggested a marine sedimentary environment in the Taiwan Shoal. The high concentrations in Pinus corresponds to Holocene high sea level.
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Näslund, Jens-Ove. "Landscape development in western and central Dronning Maud Land, East Antarctica." Antarctic Science 13, no. 3 (September 2001): 302–11. http://dx.doi.org/10.1017/s0954102001000438.
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Large-scale bedrock morphology and relief of two key areas, the Jutulsessen Nunatak and the Jutulstraumen ice stream are used to discuss glascial history and landscape development in western and central Dronning Maud Land, Antarctica. Two main landform components were identified: well-defined summit plateau surfaces and a typical alpine glacial landscape. The flat, high-elevation plateau surfaces previously were part of one or several continuous regional planation surfaces. In western Dronning Maud Land, overlying cover rocks of late Palaeozoic age show that the planation surface(s) existed in the early Permian, prior to the break-up of Gondwana. A well-develoment escarpment, a mega landform typical for passive continental margins, bounds the palaeosurface remnants to the north for a distance of at least 700 km. The Cenozoic glacial landscape, incised in the palaeosurface and escarpment, is exemplified by Jutulsessen Nunatak, where a c. 1.2 km deep glacial valley system is developed. However, the prominent Penck-Jutul Trough represents some of the deepest dissection of the palaeosurface. This originally tectonic feature is today occupied by the Jutulstraumen ice stream. New topographic data show that the bed of the Penck-Jutul Trough is situated 1.9±1.1 km below sea level, and that the total landscape relief is at least 4.2 km. Today's relief is a result of several processes, including tectonic faulting, subaerial weathering, fluvial erosion, and glacial erosion. It is probable that erosion by ice streams has deepened the tectonic troughs of Dronning Maud Land since the onset of ice sheet glaciation in the Oligocene, and continues today. An attempt is made to identify major events in the long-term landscape development of Dronning Maud Land, since the break-up of the Gondwana continent.
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Neil, David. "Weathering rates of a subaerially exposed marble in eastern Australia." Zeitschrift für Geomorphologie 33, no. 4 (December 27, 1989): 463–73. http://dx.doi.org/10.1127/zfg/33/1989/463.
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Manyuk, Volodymyr V. "New data on geology of the Rybalsky Quarry, unique object of geological heritage of Global Significance." Journal of Geology, Geography and Geoecology 30, no. 1 (April 9, 2021): 100–121. http://dx.doi.org/10.15421/112110.
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Among the great variety of geological relics of Ukraine, one of the most attractive is the Rybalsky Quarry, located in the city of Dnipro, and well known outside Ukraine. First of all, it is famous for the Mandrykivski Layers exposed in one of the ridges of the Quarry back in the 1970s, although there are many other important peculiarities of the geological structure of the Quarry which attract scientists from Ukraine, Germany, France, Netherlands, Russia and other countries. There are full data on the history of discovery and survey of the Mandrykivski Layers from their discovery by Valerian Domger in 1882 to current studies that reveal various aspects of geological structure of the Quarry, the results of study of different groups of fossil fauna, compare them with the fauna of the Paris Upper Eocene basin and other well- known locations. Particularly in the Rybalsky Quarry, thanks to the author`s efforts, the Layers received the status of “layers with geographic name”, as confirmed by the decision of Cenozoic Commission of the National Stratigraphic Committee of Ukraine in 2001. New fragments of the section of subaerial and subaqueous deposits of the Quaternary deposits were found and their composition, structure and complete stratigraphic content were studied. The research allows us to consider it typical for the Middle Prydniprovia. Fluvioglacial and lake-glacial deposits of the Dnipro glaciations in the Quarry exposed for the second time in 25 years, but this is the first time when their genetic origin, position in the section and lithological-facies peculiarities were determined. Thick layer of sands embedded on the roof of the Mandrykivski Layers were identified to the fifth or Hadzhybeiska terrace of the Dnipro, in the upper part of which there were notable siliceous-clayey-ferruginous formations or lateral crust (ferruginous crusts). The studies of the layer of brown-green and red-brown clays in the roof of the Mandrykivski layers allows us to presume their marine origin. In this case, they are underwater weathering crust (terra rossa) developed in the process of halmyrolysis or are the product of dissolution of carbonate silt enriched with detritus of mollusks, corals and other inhabitants of the warm Mandrykivske Sea.
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Garzanti, Eduardo, Giovanni Vezzoli, Sergio Andò, Mara Limonta, Laura Borromeo, and Christian France-Lanord. "Provenance of Bengal Shelf Sediments: 2. Petrology and Geochemistry of Sand." Minerals 9, no. 10 (October 19, 2019): 642. http://dx.doi.org/10.3390/min9100642.
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The Bangladesh lowlands are traversed by the largest sediment flux on the planet. Detritus generated mostly in Himalayan highlands and conveyed through the Ganga–Brahmaputra rivers and Meghna estuary reaches the Bay of Bengal, where it forms a composite deltaic system. This study integrates the vast existing database on Ganga–Brahmaputra sediments of all grain sizes from clay to sand with new petrographic, mineralogical, and geochemical data on estuarine and shallow-marine sands. A large spectrum of compositional signatures was used to: (i) assess the relative supply of the Ganga and Brahmaputra rivers to estuarine and shelfal sediments; (ii) define the compositional variability of estuarine sediments and the impact exerted by hydraulic sorting and climate-related chemical weathering on provenance signals; (iii) define the compositional variability of shelf sediments and the potential hydrodynamic segregation of fast-settling heavy minerals in coastal environments and of slow-settling platy micas on low-energy outer-shelf floors; (iv) consider the potential additional mud supply from the western subaerial part of the delta formerly built by the Ganga River; and (v) draw a preliminary mineralogical comparison between fluvio-deltaic sediments and turbidites of the Bengal–Nicobar deep-sea fan, thus tracing sediment dispersal across the huge sedimentary system extending from Tibet to the equatorial Indian Ocean. All investigated mineralogical and geochemical parameters, as well as Sr and Nd isotope ratios and clay–mineral assemblages, showed a clear prevalence in sediment supply from the Brahmaputra (60–70%) over the Ganga (30–40%). Heavy-mineral suites and Sr and Nd isotope fingerprints of Bengal shelf sediments are nearly identical to those of the Brahmaputra River and Meghna estuary, also because the Brahmaputra carries almost twice as many Ca-plagioclase grains and heavy minerals including epidote than the Ganga, and these minerals control the large majority of the Sr and Nd budgets. The experience gained in modern settings can be directly extrapolated only to the recent past, because sediments older than the late Pleistocene and buried more than a few hundred meters begin to lose less durable ferromagnesian minerals by selective chemical dissolution, which makes quantitative estimates progressively less robust in more deeply buried older strata.
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Lagabrielle, Yves, Alain Chauvet, Marc Ulrich, and Stéphane Guillot. "Passive obduction and gravity-driven emplacement of large ophiolitic sheets: The New Caledonia ophiolite (SW Pacific) as a case study?" Bulletin de la Société Géologique de France 184, no. 6 (November 1, 2013): 545–56. http://dx.doi.org/10.2113/gssgfbull.184.6.545.
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Abstract The 300 km long allochthonous sheet of oceanic mantle forming the New Caledonia ophiolite displays three specific characters: 1) the ophiolite pile lacks concordant sheeted dykes and pillow basalt layers; 2) the ophiolite, refered to as the Peridotite nappe, is thrusted over the basaltic formations of the Poya terrane which are classicaly thought to originate from a different oceanic environment; 3) The basal contact of the ultramafic sheet is remarkably flat all along New-Caledonia and the Peridotite nappe has not been thickened during obduction, rather it experienced significant extension. This suggests that the peridotites have not been emplaced by a tectonic force applied to the rear. New petrological and geochemical results obtained from mantle rocks finally show that the Poya terrane may originate from the same oceanic basin as the peridotites. In this article, we consider such possible cogenetic links and we propose a simple model for the obduction of the New Caledonia ophiolite in which the Poya basalts represent the original cover of the Peridotite nappe. We infer that continuous uplift of the subducted units buried beneath the oceanic lithosphere in the northern part of New Caledonia drove passive uplift of the ophiolite and led to erosion and to initiation of sliding of the basaltic layer. During the Priabonian (latest Eocene), products of the erosion of the basaltic layer were deposited together with sediments derived from the Norfolk passive oceanic margin. These sediments are involved as tectonic slices into an accretionary wedge formed in response to plate convergence. The volcaniclastic sedimentation ends up with the emplacement of large slided blocks of basalts and rafted mafic units that progressively filled up the basin. Obduction process ended with the gravity sliding of the oceanic mantle sheet, previously scalped from its mafic cover. This process is contemporaneous with the exhumation of the HP-LT units of Pouebo and Diahot. Gravity sliding was facilitated by the occurrence of a continuous serpentine sole resulting from metasomatic hydratation of mantle rocks, which developed during the uplift of the Norfolk basement and overlying Diahot and Pouébo units. Progressive emersion of the obducted lithosphere allowed subsequent weathering under subaerial, tropical conditions.
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Gyokche, M. I., and A. V. Plyusnin. "THE NEPSKY-1 IMPACT CRATER AND ITS FILL DEPOSITS ON THE BASEMENT ROOF OF THE SIBERIAN PLATFORM." Geodynamics & Tectonophysics 11, no. 4 (December 15, 2020): 710–21. http://dx.doi.org/10.5800/gt-2020-11-4-0502.
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In the Earth studies, discoveries and investigations of impact craters buried beneath thick sediments are sporadic so far and may still remain inefficient, unless geophysical surveys of the areas of interest are initiated. Such studies can provide useful data to develop the knowledge about cosmic events of the past geological eras, as well as contribute to industrial development of the areas. It is known that an impact crater is filled with layered deposits that create specific sequences and are generally thicker that deposits outside the crater. We have investigated a Precambrian crater located in the southern part of the Nepa-Botuoba anteclise of the Siberian platform. This impact crater called Nepsky-1 was discovered by seismic surveys using the common depth point method (CDPM). In our study, we used the geological and geophysical deep-drilling data of three wells, including gamma-ray and neutron logs and lithological core descriptions. With reference to the concepts of regional geological conditions, we reconstructed the conditions of sedimentation in the study area based on a comprehensive analysis of the structural and textural features of the rocks, and logging and seismic survey data. By processing and interpretation of the CDPM 3D seismic survey data, we obtained the structural images and cross-sections of the impact crater and analysed the thickness of its fill deposits. The Nepsky-1 crater is a bowl-shaped structure with a rim composed of allogenic breccia. In the area around the crater, fault systems are detected. Based on the core sample analysis, we identified the lithological members of the crater and its rim and described them in detail. Active compensation with lacustrine-delta sediments took place in the Nepa period of the late Vendian. By the end of the Tira time, the crater was completely leveled up. In our study, we obtained the first data on the structure of the crater section of the Vendian deposits. Sedimentation in the study area was controlled by the sea level changes. The main terrigenous productive horizons are confined to sandstones that accumulated during the sea level low stand, and found at the bottoms of the lower and upper Nepa subsuites, as well as at the bottoms of the lower and upper Tira subsuites. It is established that the study area was tectonically active in the late Tira time. As a result, the sediments filling the crater were removed to subaerial conditions, and the edges of the allogenic breccia rim were partially destroyed and formed granite breccia outgrowths observed in the rim’s cross-section. We conclude that in the Nepa and Tira times, tectonic vertical movements initiated relatively fast weathering and transportation of the terrigenous material from the adjacent hills into the sedimentation basin. The Nepsky-1 crater gives evidence of meteorite bombing of the Siberian paleocontinent in Precambrian. Finding similar crater structures can be reasonably expected in the study region. Considering the increased thicknesses of crater fill deposits, buried craters are promising potential for discovering oil-source and overlying seal rocks, which is important for petroleum industry.
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Bucholz, Claire E., and Christopher J. Spencer. "Strongly Peraluminous Granites across the Archean–Proterozoic Transition." Journal of Petrology 60, no. 7 (June 7, 2019): 1299–348. http://dx.doi.org/10.1093/petrology/egz033.
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Abstract Strongly peraluminous granites (SPGs) form through the partial melting of metasedimentary rocks and therefore represent archives of the influence of assimilation of sedimentary rocks on the petrology and chemistry of igneous rocks. With the aim of understanding how variations in sedimentary rock characteristics across the Archean–Proterozoic transition might have influenced the igneous rock record, we compiled and compared whole-rock chemistry, mineral chemistry, and isotope data from Archean and Paleo- to Mesoproterozoic SPGs. This time period was chosen as the Archean–Proterozoic transition broadly coincides with the stabilization of continents, the rise of subaerial weathering, and the Great Oxidation Event (GOE), all of which left an imprint on the sedimentary rock record. Our compilation of SPGs is founded on a detailed literature review of the regional geology, geochronology, and inferred origins of the SPGs, which suggest derivation from metasedimentary source material. Although Archean and Proterozoic SPGs are similar in terms of mineralogy or major-element composition owing to their compositions as near-minimum melts in the peraluminous haplogranite system, we discuss several features of their mineral and whole-rock chemistry. First, we review a previous analysis of Archean and Proterozoic SPGs biotite and whole-rock compositions indicating that Archean SPGs, on average, are more reduced than Proterozoic SPGs. This observation suggests that Proterozoic SPGs were derived from metasedimentary sources that on average had more oxidized bulk redox states relative to their Archean counterparts, which could reflect an increase in atmospheric O2 levels and more oxidized sedimentary source rocks after the GOE. Second, based on an analysis of Al2O3/TiO2 whole-rock ratios and zircon saturation temperatures, we conclude that Archean and Proterozoic SPGs formed through partial melting of metasedimentary rocks over a similar range of melting temperatures, with both ‘high-’ and ‘low-’temperature SPGs being observed across all ages. This observation suggests that the thermo-tectonic processes resulting in the heating and melting of metasedimentary rocks (e.g. crustal thickening or underplating of mafic magmas) occurred during generation of both the Archean and Proterozoic SPGs. Third, bulk-rock CaO/Na2O, Rb/Sr, and Rb/Ba ratios indicate that Archean and Proterozoic SPGs were derived from partial melting of both clay-rich (i.e. pelites) and clay-poor (i.e. greywackes) source regions that are locality specific, but not defined by age. This observation, although based on a relatively limited dataset, indicates that the source regions of Archean and Proterozoic SPGs were similar in terms of sediment maturity (i.e. clay component). Last, existing oxygen isotope data for quartz, zircon, and whole-rocks from Proterozoic SPGs show higher values than those of Archean SPGs, suggesting that bulk sedimentary 18O/16O ratios increased across the Archean–Proterozoic boundary. The existing geochemical datasets for Archean and Proterozoic SPGs, however, are limited in size and further work on these rocks is required. Future work must include detailed field studies, petrology, geochronology, and constraints on sedimentary source ages to fully interpret the chemistry of this uniquely useful suite of granites.
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Park, Yuem, Pierre Maffre, Yves Goddéris, Francis A. Macdonald, Eliel S. C. Anttila, and Nicholas L. Swanson-Hysell. "Emergence of the Southeast Asian islands as a driver for Neogene cooling." Proceedings of the National Academy of Sciences 117, no. 41 (September 24, 2020): 25319–26. http://dx.doi.org/10.1073/pnas.2011033117.
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Steep topography, a tropical climate, and mafic lithologies contribute to efficient chemical weathering and carbon sequestration in the Southeast Asian islands. Ongoing arc–continent collision between the Sunda-Banda arc system and Australia has increased the area of subaerially exposed land in the region since the mid-Miocene. Concurrently, Earth’s climate has cooled since the Miocene Climatic Optimum, leading to growth of the Antarctic ice sheet and the onset of Northern Hemisphere glaciation. We seek to evaluate the hypothesis that the emergence of the Southeast Asian islands played a significant role in driving this cooling trend through increasing global weatherability. To do so, we have compiled paleoshoreline data and incorporated them into GEOCLIM, which couples a global climate model to a silicate weathering model with spatially resolved lithology. We find that without the increase in area of the Southeast Asian islands over the Neogene, atmosphericpCO2would have been significantly higher than preindustrial values, remaining above the levels necessary for initiating Northern Hemisphere ice sheets.
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Winsor, Kelsey, Kate M. Swanger, Esther Babcock, Rachel D. Valletta, and James L. Dickson. "Rock glacier characteristics serve as an indirect record of multiple alpine glacier advances in Taylor Valley, Antarctica." Cryosphere 14, no. 1 (January 2, 2020): 1–16. http://dx.doi.org/10.5194/tc-14-1-2020.
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Abstract. The geomorphic record indicates that alpine glaciers in the McMurdo Dry Valleys of southern Victoria Land, Antarctica, appear to advance during interglacial periods in response to ice-free conditions in the Ross Sea. Few records of these advances are preserved and/or subaerially exposed, complicating the interpretations of regional glacier response to climate changes. Here, we present geophysical and geochemical analyses of a rock glacier that originates from icefalls fed by alpine Doran Glacier in central Taylor Valley. The rock glacier exhibits a trend of increased weathering of granitic clasts via ventifaction and grussification down-flow. Meltwater ponds on the rock glacier exhibit variable salinity that ranges from freshwater to higher than seawater, with the highest salinity pond near the rock glacier toe. Ground-penetrating radar analyses reveal the feature to possess a primarily clean ice interior, with layers of englacial debris. Stable isotopic data from three ice cores support a glacial origin for the ice within the rock glacier. These data suggest that the current morphology of the rock glacier is the result of multiple events of increased ice contribution caused by advances of Doran Glacier, which is the main source of ice to the rock glacier. We therefore demonstrate the potential of ice-cored rock glaciers to record multiple advances and retreats of Dry Valley glaciers, permitting the interpretation of glacial responses to Pleistocene and Holocene climate change even where direct records are not present.