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DOS SANTOS, MANOEL LUIZ, and JOSÉ CANDIDO STEVAUX. "Fáceis e associações dos depósitos rudáceos na rudáceos na Bacia do Rio Paraná em seu curso superior: uma tentativa de classificação." Pesquisas em Geociências 28, no. 2 (December 31, 2001): 171. http://dx.doi.org/10.22456/1807-9806.20284.
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This paper proposes a classification of gravel deposits in the upper Paraná River Basin based on their genesis, sedimentary facies and depositional processes. They were classified in four types: a) Upper slope oligomictic gravel (Fine and coarse-sand associations) – this deposit is associated with the origin of hydrographic basin during the Tertiary; b) Middle slope oligomictic gravel – It constitutes colluvial deposits related to present topography; c) Lower slope oligomictic gravel – this deposit is associated with present river valley; d) Polymictic gravel – deposited during the Pleistocene, it constitutes the basal sequence of the Paraná River fluvial deposits.
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Feng, Jin-Liang, Jian-Ting Ju, Feng Chen, Zhao-Guo Hu, Xiang Zhao, and Shao-Peng Gao. "Identification of a late Quaternary alluvial–aeolian sedimentary sequence in the Sichuan Basin, China." Quaternary Research 85, no. 2 (March 2016): 279–89. http://dx.doi.org/10.1016/j.yqres.2016.01.006.
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The late Quaternary sedimentary sequence in the northwestern part of the Sichuan Basin consists of five lithological units and with increasing depth include the: Chengdu Clay; Brown Clay; Red Clay; Sandy Silt; and basal Muddy Gravel. The genesis, provenance and age of the sediments, as well as the possible presence of hiatuses within this sequence are debated. Measurements of grain-size, magnetic susceptibility, quartz content, quartz δ18O values, element composition, and Sr–Nd isotopic concentrations of samples from a typical sedimentary sequence in the area provides new insights into the genesis and history of the sequence. The new data confirm that the sediments in study site are alluvial–aeolian in origin, with basal alluvial deposits overlain by aeolian deposits. Like the uppermost Chengdu Clay, the underlying Brown Clay and Red Clay are aeolian in origin. In contrast, the Silty Sand, like the basal Muddy Gravel, is an alluvial deposit and not an aeolian deposit as previously thought. Moreover, the succession of the aeolian deposits very likely contains two significant sedimentary hiatuses. Sedimentological analysis demonstrates that the source materials for the aeolian deposits in the northwestern part of the Sichuan Basin and those on the eastern Tibetan Plateau are different. Furthermore, the loess deposits on the eastern Tibetan Plateau are derived from heterogeneous local sources.
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Katamura, Fumitaka, Masami Fukuda, Nikolai Petrovich Bosikov, and Roman Vasilievich Desyatkin. "Charcoal records from thermokarst deposits in central Yakutia, eastern Siberia: Implications for forest fire history and thermokarst development." Quaternary Research 71, no. 1 (January 2009): 36–40. http://dx.doi.org/10.1016/j.yqres.2008.08.003.
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AbstractMacroscopic charcoal records from a thermokarst lake deposit in central Yakutia, eastern Siberia, were used to reconstruct the history of forest fires and investigate its relationship to thermokarst initiation. High accumulation rates of charcoal and pollen were coincident in the basal deposits of the thermokarst lake, which suggests that both were initially deposited on the forest floor and subsequently reworked and accumulated in the thermokarst depression. High charcoal and pollen accumulation rates in the basal deposits, dating to 11,000–9000 cal yr BP, also indicate that the thermokarst topography developed during the early Holocene. A lower charcoal accumulation rate after ca. 9000 cal yr BP suggests that thermokarst development has been inhibited since this time. It also indicates that a surface-fire regime has been predominant at least since ca. 9000 cal yr BP in central Yakutia.
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Wellman, Charles H. "Palynology of the ‘Lower Old Red Sandstone’ at Glen Coe, Scotland." Geological Magazine 131, no. 4 (July 1994): 563–66. http://dx.doi.org/10.1017/s0016756800012176.
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Abstract‘Lower Old Red Sandstone’ deposits preserved by cauldron subsidence at Glen Coe, Scotland have hitherto lacked secure biostratigraphical age constraint. A sporomorph assemblage recovered from basal sediments of these deposits permits age determination, despite being highly carbonized. The sporomorph assemblage is correlated with the micrornatus-newportensis Sporomorph Assemblage Biozone, indicating a late early-early late Lochkovian age (early Devonian). Sporomorph assemblages from basal sediments of the ‘Lower Old Red Sandstone’ sequence at nearby Lorne, a suggested correlative of the Glen Coe deposits, are older (latest Pridoli-earliest Lochkovian age). However, the new biostratigraphical data do not preclude the possibility that the Glen Coe and Lorne deposits are lithological correlatives and the basal sediments are diachronous.
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Yang, Ya. "Study on Sedimentary Facies of the Lower Eocene Basal Deposits in the Southeastern Part of the Jiyang Depression, Bohai Bay Basin, China." Mobile Information Systems 2022 (September 5, 2022): 1–8. http://dx.doi.org/10.1155/2022/2959031.
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Based on the analysis of cores, logging, and seismic data, this paper identifies the sedimentary facies of the basal deposits from the lower Eocene in the southeastern part of the Jiyang Depression and studies its depositional law. On this basis, a sedimentary model of the basal deposits is established. The basal sediments of the lower Eocene in the Jiyang Depression are mainly red, brown, gray, and variegated clastic rocks, which are mainly divided into Kongdian and lower Shahejie-4 Formation. It is considered that the climate during the depositional period was relatively arid, and the depositional process was greatly affected by floods. Three types of sedimentary facies were identified in the study area: proluvial fan, fan delta, and beach-bar deposition. Proluvial fans are mainly developed at the exit of the paleo gullies in the south area, and fan deltas are mainly distributed in the large gentle slope belt in the northwest, while beach bars are isolated and scattered along the lake shoreline in shallow lakes. The fan-delta and beach-bar clastic rocks are well sorted, with high compositional and textural maturity and can be used as good oil and gas reservoirs. The basal deposits in the southeast of Jiyang Depression are mainly flood-controlled sedimentary models. During the flood period, a large amount of detrital material brought by the flood was deposited in the gentle slope zone, forming the deposition of proluvial fan and fan delta, and the sand bodies at the front of the fan delta formed beach-bar deposits on its front under the transformation of waves and coastal currents. However, during the inter-flood period, only small-scale proluvial fan deposits are formed, fan delta and beach-bar sand bodies are rare.
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Sobiesiak, Matheus S., Ben Kneller, G. Ian Alsop, and Juan Pablo Milana. "Styles of basal interaction beneath mass transport deposits." Marine and Petroleum Geology 98 (December 2018): 629–39. http://dx.doi.org/10.1016/j.marpetgeo.2018.08.028.
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VILAS BÔAS, GERALDO S., FLÁVIO J. SAMPAIO, and ANTONIO M. S. PEREIRA. "The Barreiras Group in the Northeastern coast of the State of Bahia, Brazil: depositional mechanisms and processes." Anais da Academia Brasileira de Ciências 73, no. 3 (September 2001): 417–27. http://dx.doi.org/10.1590/s0001-37652001000300010.
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The Barreiras Group is a Miocene to Lower Pleistocene continental terrigenous sedimentary deposit exhibiting a large occurrence along the Brazilian coast. In the Conde region, located in the northeastern part of the State of Bahia, the sedimentological characteristics of these sediments are indicative of a deposition as gravelly and sandy bed load in braided fluvial systems, related to alluvial fans, under an arid to semi-arid climate. The basal portion of the group is dominated by a gravelly-sandy lithofacies deposited by debris flows and pseudoplastic debris flows, with lesser occurrences of subaqueous deposits, characterizing a proximal fluvial system deposition. The upper portion is made up of gravelly-sandy sediments that include subaqueous, debris flows and pseudoplastic debris flows deposits. They suggest deposition in a more distal zone as indicated by the larger occurrence of subaqueous deposits and the presence, though rare, of downstream-accretion macroforms. Besides the climate control, deposition of the Barreiras Group was strongly influenced by the intraplate tectonism, which has been affecting the South America Platform since the Middle Miocene, when neotectonism began in Brazil.
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Song, Delu, Imran Mohammed, Rupak Bhuyan, Takashi Miwa, Allison Lesher Williams, Damodar Gullipalli, Sayaka Sato, Ying Song, Joshua L. Dunaief, and Wen-Chao Song. "Retinal Basal Laminar Deposits in Complement fH/fP Mouse Model of Dense Deposit Disease." Investigative Opthalmology & Visual Science 59, no. 8 (July 10, 2018): 3405. http://dx.doi.org/10.1167/iovs.18-24133.
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Satti, Mohamed B., and John G. Azzopardi. "Amyloid deposits in basal cell carcinoma of the skin." Journal of the American Academy of Dermatology 22, no. 6 (June 1990): 1082–87. http://dx.doi.org/10.1016/0190-9622(90)70156-c.
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Passchier, Sandra, Anja L. L. M. Verbers, Frederik M. Van Der Wateren, and Frans J. M. Vermeulen. "Provenance, geochemistry and grain-sizes of glacigene sediments, including the Sirius Group, and Late Genozoic Glaciol history of the southern Prince Albert Mountains, Victoria Land, Antarctica." Annals of Glaciology 27 (1998): 290–96. http://dx.doi.org/10.3189/1998aog27-1-290-296.
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The southern Prince Albert Mountains, between David and Mawson Glaciers (75°30' to 76°S) in Victoria Land, Antarctica, comprise a series of nunataks with elevations ranging from 800m near the coast to 2300 m ~130 km inland. Geochemical and grain-size analyses of tills from these nunataks reveal three major groups of deposits: (1) coarse to medium sandy tills, found on Glaciolly streamlined summit plateaus of Kirk-pat rick Basalt above 2000 ma.s.l.., with geochemical compositions very similar to those of the underlying jurassic Kirkpatrick Basalt; (2) bimodal silty and sanely tills of the Sirius Group with Ferrar/Beacon-dominated geochemical compositions, at elevations of 1300-1600 m a.s.l. on striated summit plateaus and high-elevation terraces; (3) fine-grained tills with high SiO2 contents from ice-cored moraines at the lee sides of large nunataks. The geochemical composition of sandy tills from the highest summit plateaus suggests that valleys had not yet cut through the Kirkpatrick Basalt and into Beacon and Ferrar rocks at the time of deposition. These tills represent a phase of temperate glaciation prior to deposition of diatom-bearing Sirius Group tills. The latter were deposited after a first phase of landscape dissection as inferred from geochemical data. The fine-grained ice-cored moraines are late-Pleistocene basal tills. The presence of pre-Pliocene Glacial deposits on high mountain summits in the Prince Albert Mountains has implications for the interpretation of high-elevation Sirius Group sediments in other areas of the Transantarctic Mountains. It is possible that the “Sirius debate” has its origin in interpretations of both thin, barren pre-Pliocene deposits on high mountain summits and thick sequences of diatom-bearing deposits in valleys elsewhere in the Transantarctic Mountains. Both types of deposits are associated with the Sirius Group, but they belong to separate Glacial episodes.
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Dec, Tomasz, H. Scott Swinden, and R. Greg Dunning. "Lithostratigraphy and geochemistry of the Cottrells Cove Group, Buchans – Roberts Arm volcanic belt: new constraints for the paleotectonic setting of the Notre Dame Subzone, Newfoundland Appalachians." Canadian Journal of Earth Sciences 34, no. 1 (January 1, 1997): 86–103. http://dx.doi.org/10.1139/e17-008.
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New sedimentological, geochemical, and geochronological data from the Cottrells Cove Group in central Newfoundland provide important constraints on the nature of the Notre Dame Subzone, its tectonic setting, and the history of the Laurentian margin during the Early Ordovician. The Cottrells Cove Group forms the eastern extension of the Roberts Arm Group and correlates with the Chanceport Group on New World Island. It is represented by two volcano-sedimentary formations that occur in a complex thrust stack. The Fortune Harbour Formation consists of calc-alkalic, island-arc lavas, followed by a 1250 m thick succession of volcaniclastic deposits, radiolarian cherts, and calc-alkalic, mafic flows, which were deposited in a back-arc, basin-plain setting. The volcaniclastic deposits include felsic tuff, which has a U–Pb zircon age of 484 ± 2 Ma and an inheritance component of 2517 ± 26 Ma. These new U–Pb and Nd-isotope data suggest that the island-arc–back-arc volcanism and sedimentation in the Notre Dame Subzone developed in the vicinity of continental margin and approximately 10 Ma earlier than has previously been established. The Moores Cove Formation is undated but contains boulders of calc-alkalic basalt and is presumed to be at least in part younger than the Fortune Harbour Formation. Tholeiitic lavas, together with associated radiolarian cherts and volcaniclastic deposits, constitute the basal part of the Moores Cove Formation and may have been deposited in a back-arc environment synchronously with some parts of the Fortune Harbour Formation. They are conformably followed by an over 1200 m thick, coarsening-upward succession of lower-slope and submarine-fan deposits. The polymictic flysch, containing clasts of island-arc basalt, accompanied by other volcanic, plutonic, ultramafic, and sedimentary detritus, may record Middle or Upper Ordovician uplift and erosion of obducted arc–back-arc, volcano-sedimentary sequences and their ophiolitic substrate.
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Kogaya, Y., and K. Furuhashi. "Ultrastructural distribution of sulfated glycosaminoglycans in epithelial-mesenchymal interface of developing rat tooth germs." Journal of Histochemistry & Cytochemistry 35, no. 5 (May 1987): 585–93. http://dx.doi.org/10.1177/35.5.2435784.
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We investigated the ultrastructural distribution of sulfated glycosaminoglycans in the epithelial-mesenchymal interface of tooth germs by use of the high-iron diamine thiocarbohydrazide silver proteinate (HID-TCH-SP) staining and enzymatic digestion method. At an early stage in odontoblast differentiation, HID-TCH-SP stain deposits were sparsely distributed in the basement membrane and in the intercellular spaces. Subsequently, as formation of the initial predentin matrix began, HID-TCH-SP stain deposits were densely distributed in the interfibrillar spaces and the basement membrane. Testicular hyaluronidase digested most of those in the progenitor pre-dentin, whereas those in the region of basal lamina resisted enzymatic digestion. Testicular hyaluronidase-resistant HID-TCH-SP stain deposits were susceptible to heparitinase, indicating that the sulfated glycosaminoglycan in the basal lamina is heparan sulfate. Furthermore, the heparan sulfate tended to be regularly arranged at the sites of internal and external lamina densa. However, as progenitor pre-dentin matrix formation proceeded, the numbers of stain deposits temporarily increased and their distribution pattern became irregular, finally tending to disappear with the disruption of basal lamina.
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Badhani, Shray, Antonio Cattaneo, Stefano Collico, Roger Urgeles, Bernard Dennielou, Estelle Leroux, Florent Colin, Sebastien Garziglia, Marina Rabineau, and Laurence Droz. "Integrated geophysical, sedimentological and geotechnical investigation of submarine landslides in the Gulf of Lions (Western Mediterranean)." Geological Society, London, Special Publications 500, no. 1 (2020): 359–76. http://dx.doi.org/10.1144/sp500-2019-175.
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AbstractThe Gulf of Lions presents recurring mass-transport deposits (MTDs) within the Plio-Quaternary sediments, suggesting a long history of mass movements. The two large, surficial MTDs are located on the eastern and western levee of the Rhone canyon over an area exceeding 6000 km2 and volumes exceeding 100 km3. Both MTDs were emplaced 21 ka ago (peak of the Last Glacial Maximum), suggesting a common trigger. Here, we present a multidisciplinary high-resolution geophysical, sedimentological and in-situ geotechnical study of the source and deposit areas of both MTDs to characterize distinct expressions of sediment deformation as well as their spatial and chronological distributions. We show the internal structure of mass movements and resulting MTDs with unprecedented details that were previously represented in the conventional seismic data as transparent and chaotic facies. The combination of multidisciplinary approaches shows new insights into the nature of basal surfaces of the slope failures. In particular, we show that the basal surfaces of the failures consist of clay-rich material contrasting with the overlying turbiditic deposits, suggesting that a strong lithological heterogeneity exists within the strata. We suggest that this change in lithology between clay-rich sediments and turbiditic sequences most likely controls the localization of weak layers and landslide basal surfaces.
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Chashchin, V. V., and V. N. Ivanchenko. "Sulfide PGE–Cu–Ni and Low-Sulfide Pt–Pd Ores of the Monchegorsk Ore District (Arctic Western Sector): Geology, Mineralogy, Geochemistry, and Genesis." Russian Geology and Geophysics 63, no. 4 (April 1, 2022): 519–42. http://dx.doi.org/10.2113/rgg20214410.
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Abstract During the recent exploration of the Monchegorsk ore district (MOD) in the Arctic western sector, the platinum potential of known Cu–Ni deposits (Nittis-Kumuzhya-Travyanaya (NKT), Nyud, Ore Horizon 330 (OH330), and Terrasa) has been assessed, and new sulfide PGE–Cu–Ni deposits (Western Nittis) and manifestations (Moroshkovoe Ozero, Poaz, and Arvarench), and low-sulfide Pt–Pd deposits (Loipishnyun, Southern Sopcha, and Vuruchuaivench) have been discovered. All of them are confined to Paleoproterozoic (ca. 2.5 Ga) layered intrusions (the Monchegorsk pluton (Monchepluton) and the Monchetundra massif) and are divided into two types according to their structural position: basal, located in the marginal parts of intrusions, and reef-type (stratiform). All types of ores show Pd specialization. Platinum group minerals (PGM) have a limited composition in sulfide PGE–Cu–Ni ores and are represented by predominant Pt and Pd compounds with Bi and Te and subordinate PGE arsenides and sulfides. Low-sulfide Pt–Pd ores are characterized by a significant variety of PGM, with a predominance of PGE sulfides, bismuthide-tellurides, and arsenides. Sulfide PGE–Cu–Ni deposits and manifestations (Western Nittis, NKT, Nyud, Moroshkovoe Ozero, Poaz, and Arvarench) formed through the accumulation of base metal sulfides and PGE in immiscible sulfides and their subsequent segregation in commercial contents. The reef-type OH330 deposit and Terrasa manifestation resulted from the injection of additional portions of sulfur-saturated magma. The basal-type low-sulfide Pt–Pd deposits (Loipishnyun and Southern Sopcha) formed from residual melts enriched in ore components and fluids separated and crystallized during long-term oreforming processes. The reef-type Vuruchuaivench deposit is the result of deep fractionation of the parental magma with the formation of a sulfide liquid enriched in Cu and PGE. Significant reserves and large predicted resources of sulfide PGE–Cu–Ni and low-sulfide Pt–Pd ores are a reliable mineral resource base for the development of the mining industry in the Kola region of the Arctic western sector.
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Miramontes, Elda, Nabil Sultan, Sébastien Garziglia, Gwenael Jouet, Ewan Pelleter, and Antonio Cattaneo. "Altered volcanic deposits as basal failure surfaces of submarine landslides." Geology 46, no. 7 (June 12, 2018): 663–66. http://dx.doi.org/10.1130/g40268.1.
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Kidder, D. L., and K. Swett. "Basal Cambrian reworked phosphates from Spitsbergen (Norway) and their implications." Geological Magazine 126, no. 1 (January 1989): 79–88. http://dx.doi.org/10.1017/s0016756800006166.
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AbstractSeveral phosphatic zones are associated with the oldest remains of shelly fossils on the arctic island of Spitsbergen. The phosphate occurs as reworked nodules and layers associated with a disconformity. A gap in the acritarch biostratigraphic record supports a hiatus associated with the phosphatic zone. Palaeogeographic positions for Svalbard, both (1) as a single unit, and (2) as three isolated parts prior to Caledonian tectonism are consistent with conditions favourable to at least minimal amounts of upwelling. However, upwelling may not have been a prerequisite for development of these phosphate deposits. These phosphates were deposited in a nearshore shelf environmnt which contrasts with the outer shelf setting of many modern and recent phosphate deposits.Geochemistry of the Lower Cambrian phosphates of Spitsbergen varies with the mode of phosphate occurrence. Concretionary phosphate clasts are chemically zoned such that their centres are enriched in P2O5 and CaO and are depleted in A12O3, SiO2, and K2O. Laminated and thinly bedded phosphate shows no chemical zonation within clasts. Phosphate cements are the most pure with respect to calcium phosphate.This thin phosphatic zone of Svalbard is minor when compared with thicker and richer Lower Cambrian phosphate deposits, particularly those in the Soviet Union, Southeast Asia, and Australia. Coupled with the near absence of phosphate in some extensive Proterozoic to Lower Palaeozoic successions (e.g. western North America), this emphasizes the fact that widespread Lower Cambrian phosphate deposition was unevenly distributed. Althouth the Upper Proterozoic and Lower Cambrian are characterized by enhanced phosphogenesis, palaeogeographic position was also apparently critical to deposition of phosphatic sediments.
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Adair, R. N., and R. A. Burwash. "Evidence for pyroclastic emplacement of the Crowsnest Formation, Alberta." Canadian Journal of Earth Sciences 33, no. 5 (May 1, 1996): 715–28. http://dx.doi.org/10.1139/e96-055.
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The middle Cretaceous Crowsnest Formation west of Coleman, Alberta, is composed of bedded alkaline volcanic deposits containing heterolithic volcanic rock fragments and crystal clasts. Comparison with modern examples of subaerial pyroclastic rocks suggests that pyroclastic flows, surges, fallout of material from vertical eruption columns, and minor mud flows emplaced the deposits. Textural evidence in the form of plastically deformed volcanic fragments, chilled deposit margins, baked rock fragment margins, recrystallization, and the presence of charred wood and charred wood molds indicate emplacement at elevated temperature. Massive deposits containing a fine-grained basal zone are interpreted as the product of pyroclastic flows, whereas deposits characterized by a block-rich base overlain by a thin layer of block-depleted stratified material are interpreted as the product of density-stratified surges. Deposits exhibiting pronounced stratification were emplaced by ash-cloud surges. Thickly bedded breccias exhibiting rheomorphic textures were emplaced as vent-proximal pyroclastic flows. Deposits characterized by parallel beds and graded structures are interpreted as fallout tephra deposits, and deposition by lahars is indicated by coarse-grained beds that lack evidence for emplacement at elevated temperatures. The eruptions of the Crowsnest Formation were cyclical. An initial explosive phase generated deposits by pyroclastic flows, surges, fallout, and lahars. As an eruption progressed, it evolved into a poorly gas-charged effusive stage that emplaced coarsely porphyritic domes, plugs, spines, and vent-proximal lava flows. Subsequent eruptions destroyed the effusive vent facies deposits and produced abundant heterolithic clasts typical of the formation.
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Šimo, Vladimír, and Adam Tomašových. "Trace-fossil assemblages with a new ichnogenus in “spotted”." Geologica Carpathica 64, no. 5 (October 1, 2013): 355–74. http://dx.doi.org/10.2478/geoca-2013-0024.
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Abstract Highly-bioturbated “spotted” limestones and marls (Fleckenmergel-Fleckenkalk facies) of the Early Jurassic, which were deposited in broad and recurrent deep-shelf habitats of the Northern Tethys, are characterized by rare benthic carbonate-producing macroinvertebrates. To address this paradox, we analyse trace-fossil assemblages in a ~85 m-thick succession of Pliensbachian spotted deposits (Zliechov Basin, Western Carpathians). They are dominated by infaunal and semi-infaunal deposit-feeders, with 9 ichnogenera and pyritized tubes of the semi-infaunal foraminifer Bathysiphon, being dominated by Chondrites, Lamellaeichnus (new ichnogenus), and Teichichnus. Lamellaeichnus, represented by a horizontal basal cylindrical burrow and an upper row of stacked convex-up gutters, was produced by a mobile deposit-feeder inhabiting shallow tiers because it is crossed by most other trace fossils. We show that the spotty appearance of the deposits is generated by a mixture of (1) dark, organic-rich shallow- and deep-tier traces (TOC = 0.16-0.36), and (2) light grey, organic-poor mottled or structurless sediment (TOC = 0.09-0.22). The higher TOC in shallow-tier burrows of Lamellaeichnus demonstrates that uppermost sediment layers were affected by poor redox cycling. Such conditions imply a limited mixed-layer depth and inefficient nutrient recycling conditioned by hypoxic bottom-waters, allowed by poor circulation and high sedimentation rates in depocenters of the Zliechov Basin. Hypoxic conditions are further supported by (1) dominance of trace-fossils produced by infaunal deposit feeders, (2) high abundance of hypoxiatolerant agglutinated foraminifer Bathysiphon, and (3) high abundance of Chondrites with ~0.5 mm-sized branches. Oxygen-deficient bottom-conditions can thus simultaneously explain the rarity of benthic carbonate-producing macroinvertebrates and high standing abundance of tolerant soft-shell and agglutinated organisms in spotted deposits.
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Schellmann, Gerhard, Patrick Schielein, Wolfgang Rähle, and Christoph Burow. "The formation of Middle and Upper Pleistocene terraces (<i>Übergangsterrassen</i> and <i>Hochterrassen</i>) in the Bavarian Alpine Foreland – new numeric dating results (ESR, OSL, <sup>14</sup>C) and gastropod fauna analysis." E&G Quaternary Science Journal 68, no. 2 (July 25, 2019): 141–64. http://dx.doi.org/10.5194/egqsj-68-141-2019.
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Abstract. Until now, reliable chronological classifications based on numerical ages for many Pleistocene fluvial deposits in the Alpine Foreland were rare. In this study, new numeric data (ESR, OSL, 14C) from Middle and Upper (Late) Pleistocene Hochterrassen (high terraces) and Übergangsterrassen (transitional terraces) in the Bavarian Alpine Foreland are presented. The dating results imply that the Hochterrassen gravel sensu stricto were deposited during the penultimate glacial (MIS 6, Rissian), and that underlying older gravel accumulation are predominantly of penultimate interglacial (MIS 7, Riss–Riss interglacial) age. In some areas of the Hochterrassen in the Danube valley south of Regensburg (interglacial Hartinger Schichten, Harting layers), and in some areas of the Rainer Hochterrasse (basal gravel unit I), Hochterrassen gravels are underlain by much older interglacial gravel deposits. These interglacial basal gravel deposits illustrate that the downcutting of these valleys far away from areas of Pleistocene foreland glaciations happened predominantly during warm-temperate interglacial or late-glacial periods. One last interglacial (MIS 5e, Riss–Würm interglacial) Hochterrasse is morphologically preserved in the Isar valley. This Jüngere Moosburger Hochterrasse is composed of the Fagotienschotter (Fagotia gravel, named after the gastropod Fagotia acicularis). The next younger terraces are the Early to Middle Würmian (MIS 5d to MIS 3?) Übergangsterrassen (transitional terraces), whereas the younger one of the two Übergangsterrassen was formed most probably during the Middle Würmian (MIS 3).
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Valentine, Greg A., David C. Buesch, and Richard V. Fisher. "Basal layered deposits of the Peach Springs Tuff, northwestern Arizona, USA." Bulletin of Volcanology 51, no. 6 (September 1989): 395–414. http://dx.doi.org/10.1007/bf01078808.
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Bellas, S., and H. Keupp. "CONTRIBUTION TO THE LATE NEOGENE STRATIGRAPHY OF THE ANCIENT GORTYS AREA (SOUTHERN CENTRAL CRETE, GREECE)." Bulletin of the Geological Society of Greece 43, no. 2 (January 23, 2017): 579. http://dx.doi.org/10.12681/bgsg.11220.
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Most of the basal Neogene sediments of Crete Island (South Aegean Sea) were unconformably deposited during synsedimentary extensional tectonics and subsequent transgression on the basement. This work mainly focuses on the marine stratigraphy of south central Crete and specifically on the sedimentary deposits of the Gortys subbasin-area located in the basin of Messara. Four selected profiles north of Gortys ancient ruins (Heraklion Province) are lithostratigraphically presented. Profiles Gortys-1 and -2 (combined to one: 1+2) represent the basal Neogene deposits (older strata-commence of sedimentation) and are interpreted as of fluviatile to lagoonal origin, while profiles Gortys-4 and - 4a are considered the younger, marine development of the Gortys subbasin. Between profiles –4 and –4a are developed evaporites of the Messinian Salinity Crisis (MSC). Profiles are biostratigraphically studied and correlated on the basis of either identified macrofossils or calcareous and siliceous nannofossils. The recorded assemblages range in age from Serravallian-Tortonian to Messinian and Zanclean respectively. The good preservation and abundance of the fossil phytoplankton establishes a well-constrained biostratigraphic framework, which will further contribute to the understanding of the evolution of the Messara sedimentary basin.
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McMahon, William J., and Neil S. Davies. "Physical and biological functioning in Proterozoic rivers: evidence from the archetypal pre-vegetation alluvium of the Torridon Group, NW Scotland." Scottish Journal of Geology 56, no. 1 (October 11, 2019): 1–29. http://dx.doi.org/10.1144/sjg2019-013.
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In modern rivers, vegetation affects hydrological, geomorphological and sedimentological functioning, so extant fluvial systems can provide only partial analogues for those rivers that operated before the evolution of land plants. However, pre-vegetation rivers were the norm for the first 90% of Earth's history and so a better understanding of their sedimentary product can provide insights into both the fundamental underlying mechanisms of river behaviour and the ways in which fluvial processes operated on ancient Earth. In addition to a short review of the history of research into pre-vegetation alluvium, this paper presents a fieldwork-based case study of the later Proterozoic Torridon Group, which contains some of the most extensive and easily accessible exposures of pre-vegetation alluvium worldwide. Three alluvial architectural deposits have been recognized: (1) channel-bedform deposits (c. 80%); (2) barform deposits (c. 20%); and (3) out-of-channel deposits (≪1%). Channel-bedform deposits have erosional bases and most frequently stack vertically to form thick multistorey channel-bedform sequences. The preferential preservation of these deposits, which record the deepest parts of river channels, suggests that channel migration had a dominant control on preservation in the Torridon Group. Less frequently, channel-bedform deposits pass upwards into a genetically related barform deposit. Barform preservation in these instances is interpreted to be due to channel avulsion, which protected the barforms from reworking. Channel-bar thickness, measured from the basal erosional surface of a channel-bedform deposit to the top of its associated barform deposit, indicates minimum water depths of 1.7 to 8.0 m. Downstream-accreting barform deposits are most frequent, but lateral and upstream modes of accretion are also well represented. Dominant southeastward-palaeoflow directions imply that the Torridonian rivers were sourced from the Grenvillian Mountain Belt. The preserved architectural deposits and narrow dispersal of palaeocurrent data are explained by interpreting the Torridon Group as the alluvium of dominantly low-sinuosity rivers, with signatures recording autogenic fluvial adjustments. In the few rare instances where out-of-channel deposits are preserved, they contain fossil evidence for microbial mats, which prove that not all Proterozoic river systems were wholly abiotic. The overall characteristics of the Torridon alluvium, in terms of its ubiquitous highly tabular beds of sand-grade or coarser material, make it an archetypal example of pre-vegetation alluvium as known globally.Thematic collection: This article is part of the SJG Collection on Early-Career Research available at: https://www.lyellcollection.org/cc/SJG-early-career-research
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Smyk, Mark C., and James M. Franklin. "A synopsis of mineral deposits in the Archean and Proterozoic rocks of the Lake Nipigon Region, Thunder Bay District, Ontario." Canadian Journal of Earth Sciences 44, no. 8 (August 1, 2007): 1041–53. http://dx.doi.org/10.1139/e07-013.
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A variety of metallic and non-metallic mineral deposit types occur within Archean and Proterozoic rocks in the area encompassing the Lake Nipigon Region Geoscience Initiative. Archean deposit types include Algoma-type banded iron formation-hosted iron (e.g., Lake Nipigon iron range); volcanogenic massive sulphide copper–zinc (e.g., Onaman–Tashota belt); ultramafic intrusion-hosted chromium (e.g., Puddy–Chrome lakes); mafic to ultramafic intrusion-hosted copper–nickel – platinum group element (PGE) (e.g., Lac des Iles); and pegmatite-hosted deposits of rare metals (Li, Ta, Be), uranium, and molybdenum (e.g., Georgia Lake field, Black Sturgeon Lake, and Anderson Lake, respectively). Mesothermal lode gold deposits are prominent in the Beardmore–Geraldton camp. Superior-type iron formation occurs in Paleoproterozoic Gunflint Formation. "Red-bed" copper occurs in Mesoproterozoic Midcontinent Rift-related Osler Group volcanic and interflow sedimentary rocks. Native copper and copper sulphides occur in Mesoproterozoic Sibley Group sedimentary rocks, adjacent to ultramafic intrusions. These mafic to ultramafic intrusions, associated with Midcontinent Rift magmatism, host copper–nickel–PGE deposits (e.g., Seagull, Great Lakes Nickel). Silver-bearing veins occur in Paleoproterozoic Animikie Group sedimentary rocks in proximity to Midcontinent Rift-related mafic intrusions (e.g., Silver Islet, Silver Mountain). Lead–zinc–barite veins, uranium-bearing veins, and amethyst vein and replacement-type deposits may be cogenetic and formed at or near the unconformity between Sibley Group basal sandstone and underlying Archean granitic basement (e.g., Dorion, Black Sturgeon Lake, McTavish Township). The hydrothermal systems that produced all of these veins were probably driven by heat associated with Midcontinent rifting. Many occur in structures related to rift-bounding faults. Iron oxide – copper–gold deposits may occur near the English Bay intrusion.
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Groves, D. A., R. L. Morton, and J. M. Franklin. "Physical volcanology of the footwall rocks near the Mattabi massive sulphide deposit, Sturgeon Lake, Ontario." Canadian Journal of Earth Sciences 25, no. 2 (February 1, 1988): 280–91. http://dx.doi.org/10.1139/e88-030.
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Subaerial and shallow subaqueous mafic hyalotuffs, lava flows, and flow breccias, felsic lava flows, and pyroclastic flows and falls form a 2 km thick succession beneath the Mattabi massive sulphide deposit. The lowermost 800 m of section comprises massive to amygdaloidal mafic flows and flow breccias interlayered with repetitive sequences of thinly bedded felsic tuff: pillow lavas and hyaloclastites are absent. Amygdaloidal felsic lavas overlie the mafic flows and are locally capped by coarse explosion breccia. This breccia is believed to represent the start of mafic hydrovolcanism, which produced ash falls, surges, and flows. These pyroclastic deposits formed thin- to thick-bedded hyalotuffs that contain highly vesicular and quenched juvenile and accessory lithic fragments. Periods of water influx probably led to the construction of a tuff cone, which represents a submergent hydrovolcanic cycle.In the Mattabi area, pyroclastic flow deposits form the immediate mine footwall strata and include (i) massive basal beds and overlying bedded ash tuffs and (ii) massive pumiceous units. These deposits overlie and, to the west in the Darkwater Lake area, are intercalated with the mafic hyalotuff sequence. The morphology of the footwall volcanic rocks indicates that the Mattabi and the F-zone massive sulphide deposits formed in a shallow subaqueous environment.
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Nehyba, Slavomír, Jiří Otava, Pavla Tomanová Petrová, and Adéla Gazdová. "The foreland state at the onset of the flexurally induced transgression: data from provenance analysis at the peripheral Carpathian Foredeep (Czech Republic)." Geologica Carpathica 70, no. 3 (June 1, 2019): 241–60. http://dx.doi.org/10.2478/geoca-2019-0014.
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Abstract The Žerotice Formation recognised in a confined area NE–SE of Znojmo represents a basal member of the sedimentary succession of the southwestern margin of the Carpathian Foredeep in Moravia (Czech Republic). Two facies associations were recognised within the formation. The first one mantles the pre-Neogene basement with an irregular unconformity, reflects arid climatic conditions and deposition of episodic shallow, high-energy stream flows and/or mass flows (alluvial to fluvial deposits). The second facies association is interpreted as lagoonal to distal flood plain deposits. The barren unfossiliferous deposits of the Žerotice Formation are covered by nearshore marine Eggenburgian deposits. The boundary between these deposits represents a sequence boundary (i.e. the basal forebulge unconformity). Detailed provenance studies of successive beds below and above this sequence boundary showed differences in the source area and paleodrainage. Both the local primary crystalline rocks (Moravian and Moldanubian Unit, Thaya Batholith) and older sedimentary cover (especially Permo–Carboniferous sedimentary rocks) form the source of the Žerotice Formation. All these geological units are located only a few km away from the preserved areal extent of the deposits of the Žerotice Formation (short transport and a local source). The source areas of the overlying marine Eggenburgian beds are located far more to the W and NW in the Moldanubian and Moravian Units (longer transport, extended source area). Local confined preservation of the Žerotice Formation is preliminarily explained as connected with a tectonically predisposed paleovalley.
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Oummouch, Abdellah, Abderrahim Essaifi, Rachid Zayane, Othmane Maddi, Mohamed Zouhair, and Lhou Maacha. "Geology and Metallogenesis of the Sediment-Hosted Cu-Ag Deposit of Tizert (Igherm Inlier, Anti-Atlas Copperbelt, Morocco)." Geofluids 2017 (November 15, 2017): 1–19. http://dx.doi.org/10.1155/2017/7508484.
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The Tizert Cu-Ag deposit is the largest of a series of sediment-hosted copper deposits of the Anti-Atlas copper province in Morocco. Mineralized rocks in the deposit contain disseminated sulphides within a Late Ediacaran, dominantly siliciclastic sedimentary formation named the Basal Series. Isopach map of the Basal Series thickness shows that during the Late Ediacaran the area was composed of large subsiding zones separated by paleohighs. The ore-grade zones are well developed along basin margins adjacent to the basement paleohighs. These mineralized zones display a lateral sulphide zoning with central bornite-chalcocite zones grading outward to intermediate chalcopyrite and external pyrite zones. There is also a vertical sulphide zoning with evolution from bornite and chalcocite dominant mineralized rocks at the bottom to chalcopyrite and pyrite dominant mineralized rocks at the top of the lithostratigraphic succession. A second style of mineralization is represented by sulphide filled fractures and veins present in the Basal Series, as well as in the basement and the overlying dolomites. The similarity of the paragenetic sequences between the disseminated and the vein-hosted mineralization suggests that they may be related to the same mineralizing event, the disseminated style of mineralization being rapidly followed by the onset of the vein-style mineralization.
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Phillips, Stephen P., John A. Howell, Adrian J. Hartley, and Magda Chmielewska. "Coarse-grained meandering distributive fluvial system of the basal Cedar Mountain Formation, U.S.A." Journal of Sedimentary Research 91, no. 11 (November 22, 2021): 1188–205. http://dx.doi.org/10.2110/jsr.2020.065.
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ABSTRACT The analysis of downstream changes in ancient fluvial systems can better inform depositional models for foreland-basin systems. Herein we analyze the basal deposits of the Early Cretaceous Cedar Mountain Formation of Utah to better understand the variety of fluvial deposits present and to develop a depositional model for the Sevier foreland basin. We also evaluate the long-held interpretation of a braided origin for these deposits and document numerous examples of point-bar deposition in highly sinuous meandering rivers by analysis of large (20 to 60 km2) plan-view exposures. These plan-view exposures allow comparisons between planform and cross-sectional geometries. The study utilizes outcrop data, virtual outcrop models, and satellite imagery to develop a facies model and analyze the architecture of channel bodies in the Buckhorn Conglomerate and Poison Strip Sandstone of the Cedar Mountain Formation. We document downstream (west to east) decreases in lateral channel migration, sinuosity, channel amalgamation, grain size, and percent of fluvial channel facies (conglomerate and sandstone). Fluvial channel deposits occur arranged into larger stratal bodies: multistory–multilateral channel bodies that are dominantly composed of clast-supported conglomerate in the west to a mix of multistory, multilateral, and isolated channel bodies composed of matrix-supported conglomerate in the east. The median width of highly sinuous point bars is similar across the field area (344 m to 477 m), but the inclusion of narrower (median = 174 m), low-sinuosity bar elements in the east indicates an overall reduction in lateral channel migration and sinuosity downstream. Net-to-gross values range from 100% in much of the western outcrops to as low as 38% in the east. Paleocurrent analysis reveals a transverse (west to east) paleoflow for the study interval that merges with axial (south–north) paleoflow near the Utah–Colorado state line. We estimate 104 m3/s-scale discharge and 106 kilometer-scale drainage area for axial rivers based on paleohydraulic analysis which represents a significant part of the Early Cretaceous continental-scale drainage. The observed downstream trends in lateral channel migration, sinuosity, channel amalgamation, grain size, and net-to-gross for the basal Cedar Mountain Formation are consistent with expected trends for sinuous single-thread distributive fluvial systems and are similar to observed trends in the Jurassic Morrison Formation. Medial (Buckhorn Conglomerate) to distal (Poison Strip Sandstone) zones are preserved and span the forebulge to backbulge depozones of a foreland-basin system. Postulated deposits of the proximal distributive fluvial system have been removed during erosion of the foredeep depozone. The easternmost Poison Strip Sandstone and coeval Burro Canyon Formation represent deposits of an axial system at which western-sourced distributive fluvial systems end. Distributive fluvial systems dominate modern foreland basins, and this study suggests that they may constitute a significant proportion of ancient successions.
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Galloway, Chad A., Sonal Dalvi, Sandy S. C. Hung, Leslie A. MacDonald, Lisa R. Latchney, Raymond C. B. Wong, Robyn H. Guymer, et al. "Drusen in patient-derived hiPSC-RPE models of macular dystrophies." Proceedings of the National Academy of Sciences 114, no. 39 (September 6, 2017): E8214—E8223. http://dx.doi.org/10.1073/pnas.1710430114.
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Age-related macular degeneration (AMD) and related macular dystrophies (MDs) are a major cause of vision loss. However, the mechanisms underlying their progression remain ill-defined. This is partly due to the lack of disease models recapitulating the human pathology. Furthermore, in vivo studies have yielded limited understanding of the role of specific cell types in the eye vs. systemic influences (e.g., serum) on the disease pathology. Here, we use human induced pluripotent stem cell-retinal pigment epithelium (hiPSC-RPE) derived from patients with three dominant MDs, Sorsby’s fundus dystrophy (SFD), Doyne honeycomb retinal dystrophy/malattia Leventinese (DHRD), and autosomal dominant radial drusen (ADRD), and demonstrate that dysfunction of RPE cells alone is sufficient for the initiation of sub-RPE lipoproteinaceous deposit (drusen) formation and extracellular matrix (ECM) alteration in these diseases. Consistent with clinical studies, sub-RPE basal deposits were present beneath both control (unaffected) and patient hiPSC-RPE cells. Importantly basal deposits in patient hiPSC-RPE cultures were more abundant and displayed a lipid- and protein-rich “drusen-like” composition. Furthermore, increased accumulation of COL4 was observed in ECM isolated from control vs. patient hiPSC-RPE cultures. Interestingly, RPE-specific up-regulation in the expression of several complement genes was also seen in patient hiPSC-RPE cultures of all three MDs (SFD, DHRD, and ADRD). Finally, although serum exposure was not necessary for drusen formation, COL4 accumulation in ECM, and complement pathway gene alteration, it impacted the composition of drusen-like deposits in patient hiPSC-RPE cultures. Together, the drusen model(s) of MDs described here provide fundamental insights into the unique biology of maculopathies affecting the RPE–ECM interface.
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Nugraha, Harya D., Christopher A. L. Jackson, Howard D. Johnson, and David M. Hodgson. "Lateral variability in strain along the toewall of a mass transport deposit: a case study from the Makassar Strait, offshore Indonesia." Journal of the Geological Society 177, no. 6 (July 13, 2020): 1261–79. http://dx.doi.org/10.1144/jgs2020-071.
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Contractional features characterize the toe domain of mass transport deposits. Their frontal geometry is typically classified as frontally confined or frontally emergent. However, it remains unclear how the style of frontal emplacement and contractional strain within a mass transport deposit vary along-strike. We use bathymetry and 3D seismic reflection data to investigate the lateral variability of frontal emplacement and strain within the toe domain of the Haya Slide in the Makassar Strait, offshore Indonesia. The slide originated from an anticline flank collapse and the toe domain is characterized by a radial fold–thrust belt that reflects southwestwards emplacement. The frontal geometry of the slide changes laterally. It is frontally confined in the south and is associated with a deep, c. 200 m b.s.f. planar basal shear surface. The frontal geometry gradually changes to frontally emergent in the west, associated with a shallow, c. 120 m b.s.f., c. 3° NE-dipping basal shear surface. Strain analysis shows c. 8–14% shortening, with the cumulative throw of the thrusts increasing along-strike westwards from c. 20–40 to c. 40–80 m. We show that even minor horizontal translation of mass transport deposits (c. 1 km) can result in marked lateral variability in the frontal geometry and strain within the failed body, which may influence their seal potential in petroleum systems.
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Lauro, Soldovieri, Orosei, Cicchetti, Cartacci, Mattei, Cosciotti, Di Paolo, Noschese, and Pettinelli. "Liquid Water Detection under the South Polar Layered Deposits of Mars—a Probabilistic Inversion Approach." Remote Sensing 11, no. 20 (October 21, 2019): 2445. http://dx.doi.org/10.3390/rs11202445.
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Liquid water was present on the surface of Mars in the distant past; part of that water is now in the ground in the form of permafrost and heat from the molten interior of the planet could cause it to melt at depth. MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) has surveyed the Martian subsurface for more than fifteen years in search for evidence of such water buried at depth. Radar detection of liquid water can be stated as an inverse electromagnetic scattering problem, starting from the echo intensity collected by the antenna. In principle, the electromagnetic problem can be modelled as a normal plane wave that propagates through a three-layered medium made of air, ice and basal material, with the final goal of determining the dielectric permittivity of the basal material. In practice, however, two fundamental aspects make the inversion procedure of this apparent simple model rather challenging: i) the impossibility to use the absolute value of the echo intensity in the inversion procedure; ii) the impossibility to use a deterministic approach to retrieve the basal permittivity. In this paper, these issues are faced by assuming a priori information on the ice electromagnetic properties and adopting an inversion probabilistic approach. All the aspects that can affect the estimation of the basal permittivity below the Martian South polar cap are discussed and how detection of the presence of basal liquid water was done is described.
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Harland, T. L., and R. K. Pickerill. "Ordovician rocky shoreline deposits-the basal Trenton Group around Quebec City, Canada." Geological Journal 19, no. 3 (April 30, 2007): 271–98. http://dx.doi.org/10.1002/gj.3350190306.
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Salsabili, Mohammad, Ali Saeidi, Alain Rouleau, and Miroslav Nastev. "3D Probabilistic Modelling and Uncertainty Analysis of Glacial and Post-Glacial Deposits of the City of Saguenay, Canada." Geosciences 11, no. 5 (May 7, 2021): 204. http://dx.doi.org/10.3390/geosciences11050204.
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Knowledge of the stratigraphic architecture and geotechnical properties of surficial soil sediments is essential for geotechnical risk assessment. In the Saguenay study area, the Quaternary deposits consist of a basal till layer and heterogeneous post-glacial deposits. Considering the stratigraphic setting and soil type heterogeneity, a multistep stochastic methodology is developed for 3D geological modelling and quantification of the associated uncertainties. This methodology is adopted for regional studies and involves geostatistical interpolation and simulation methods. Empirical Bayesian kriging (EBK) is applied to generate the bedrock topography map and determine the thickness of the till sediments and their uncertainties. The locally varying mean and variance of the EBK method enable accounting for data complexity and moderate nonstationarity. Sequential indicator simulation is then performed to determine the occurrence probability of the discontinuous post-glacial sediments (clay, sand and gravel) on top of the basal till layer. The individual thickness maps of the discontinuous soil layers and uncertainties are generated in a probabilistic manner. The proposed stochastic framework is suitable for heterogeneous soil deposits characterised with complex surface and subsurface datasets.
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Hu, Guang Ming, Shun She Luo, Marjorie A. Chan, and Hong Ping Xiao. "Significance of Terrace Deposits in Fluvial Sequence Stratigraphy." Applied Mechanics and Materials 318 (May 2013): 423–27. http://dx.doi.org/10.4028/www.scientific.net/amm.318.423.
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The terrace deposits in a river valley are key records to the research of fluvial sequence stratigraphy. Terrace deposits and the basal sequence boundary comprise the half-cycle of base level fall, and the fluvial infillings belong to the half-cycle of base level rise. Thus, terrace deposits and the basal sequence boundary are part of the regressive systems tract, and should be separated from the transgressive or lowstand systems tracts in previously published littoral fluvial sequence stratigraphic models. In addition, in the upstream portions of the fluvial system where sea level cannot reach, the fluvial sequence is influenced by tectonism and/or climate. The terrace deposits can provide specific information about the main controlling factor (e.g., tectonism or climate) and its varying pattern during the half-cycle of base level fall. Because the two half-cycles of base level fall and rise are at the same stratigraphic levels and belong to the same base level cycle, it is possible to research the controlling factor and its varying pattern during the rising half-cycle, which will be significant to an inland fluvial sequence stratigraphic model. Finally, the authors assert that seeking isochronous parasequence correlation based on 4-division models (4 different systems tracts), along with the blend of sedimentology and geomorphology and diversification of models based on different controlling factors will collectively produce more robust-interpretations of fluvial sequence stratigraphy in the future.
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Melcher, Frank, and Peter Krois. "Syngenetic and diagenetic formation of ore deposits in the metamorphosed sediments of the basal Brenner Mesozoic (Stubai Valley, Austria)." Neues Jahrbuch für Geologie und Paläontologie - Monatshefte 1992, no. 4 (June 17, 1992): 207–20. http://dx.doi.org/10.1127/njgpm/1992/1992/207.
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DELPOMDOR, Franck R. A., Archange M. ILAMBWETSI, Fabricío A. CAXITO, and Antonio C. PEDROSA-SOARES. "New interpretation of the basal Bambuí Group, Sete Lagoas High (Minas Gerais, E Brazil) by sedimentological studies and regional implications for the aftermath of the Marinoan glaciation: Correlations across Brazil and Central Africa." Geologica Belgica 23, no. 1-2 (January 4, 2020): 1–17. http://dx.doi.org/10.20341/gb.2019.010.
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Along the preserved southeast border (i.e., the Sete Lagoas High) of the Bambuí basin, the Pedro Leopoldo Member, basal succession of the Sete Lagoas Formation, unconformably overlies the Archean basement, and mostly includes carbonates with thin pelite intercalations and rare ruditic deposits. One of these, the so-called Carrancas conglomerate in its type-section, has been considered one of the lowermost rudite deposits of the Bambuí basin, being frequently ascribed to a Neoproterozoic glaciation. However, our detailed study, based on facies analysis, reveals that the Carrancas conglomerate was deposited by sediment gravity flow currents within the basal Pedro Leopoldo Member. Two outcrop sections in the São José de Lapa and Vespasiano areas, including thirteen abandoned quarry-cut and cliff outcrops, display eight distinct lithofacies (LF1 to LF8) forming a shallowing-upward carbonate ramp succession. It is composed, from the base to the top, by a mixed siliciclastic-carbonate outer ramp distally bounded by a slope-outer ramp system with sediment gravity flow deposits, a deep outer ramp developed below storm-wave base environments, an outer-middle ramp with aragonite pseudomorph crystal fans developed in a CaCO3 oversaturated below storm-wave base environment in suboxic/anoxic conditions. According to published isotope data correlating δ13C trends and values in basal carbonates of the Pedro Leopoldo Member of the Sete Lagoas and Januária highs, the relatively deep outer-slope ramp mixed siliciclastic-carbonate units of the study area appear to be coeval in age with the cap dolostone of shallow-water inner ramp of the Januária High. The absence of a cap dolostone in the Sete Lagoas High could be explained by lack of accommodation space or a regional erosion due to the tectonically driven forebulge uplift of the Sete Lagoas High. The Pedro Leopoldo Member in the Sete Lagoas High was accumulated in a brine-seawater bottom waters under suboxic/anoxic conditions in the relatively deeper portion of the carbonate ramp system, whilst the cap dolostone in the Januária High was developed in oxygenated mixed layer and intermediate water near the surface water in the shallower portion of the carbonate ramp system. Such lateral variations of facies and δ13C fluctuations are similar to those recorded by the cap carbonate sequences of the basal Schisto-Calcaire/Lukala (Sub)Group in the West Congo Belt and the basal Araras Group in the Paraguay Belt, which display a similar wide range of sub-environments like the studied part of the Pedro Leopoldo Member.
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Rooyakkers, Shane M., John Stix, Kim Berlo, and Simon J. Barker. "Emplacement of unusual rhyolitic to basaltic ignimbrites during collapse of a basalt-dominated caldera: The Halarauður eruption, Krafla (Iceland)." GSA Bulletin 132, no. 9-10 (January 13, 2020): 1881–902. http://dx.doi.org/10.1130/b35450.1.
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Abstract Deposits of the ca. 110 ka Halarauður eruption of Krafla caldera (reconstructed volume = 7 ± 6 km3 dense rock equivalent) include the only spatter-rich ignimbrite known in Iceland, and an exceptionally rare lava-like basaltic ignimbrite. We present a revised stratigraphy and new whole-rock major-element data set for products of this unusual event, one of only three Quaternary ignimbrite eruptions identified in Iceland. Compositions of Halarauður products span a broad range (50.0–74.6 wt% SiO2), reflecting mixing of rhyolite with underplating basalt. Small-volume, valley-ponded, basal pumice- and spatter-bearing lithic breccias and ignimbrite (rhyolite to andesite) reflect rapid column collapse during early opening of ring-fault vents. A transition to voluminous, regionally dispersed spatter agglomerates (dacite to basaltic andesite) marks an abrupt eruptive intensification, as gas-poor magma was squeezed into a developing ring-fault system by the subsiding chamber roof. Spatial heterogeneities in ascent rates and outgassing through this variably dilated fault system caused coeval formation of collapsing plumes and spatter fountains at separate vents. Spatter was entrained into flows from the more explosive vents, which deposited proximal spatter agglomerates and more distal spatter-bearing ignimbrite. Overlying lava-like ignimbrite deposits (basaltic andesite to basalt) reflect a final opening of vents, as mafic magma from deep levels of the chamber was squeezed through a dilated ring-fault system by the subsiding roof block and erupted at uncharacteristically high mass flux. Development of a mature ring-fault conduit system during early tapping of silicic magma appears to be a prerequisite for the emplacement of welded basaltic ignimbrites, and it should be considered as a possible eruption scenario in basalt-dominated systems where silicic magma has been known to also accumulate. Poor preservation of the Halarauður deposits exemplifies the challenges of studying ignimbrite eruptions in frequently glaciated regions like Iceland, where they may be more common than the geological record suggests.
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Suarez, M., and C. M. Bell. "Upper Triassic to Lower Cretaceous continental and coastal saline lake evaporites inthe Atacama region of northern Chile." Geological Magazine 124, no. 5 (September 1987): 467–75. http://dx.doi.org/10.1017/s0016756800017040.
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AbstractEvaporites within Upper Triassic to Lower Cretaceous sequences in the Atacama region of northern Chile are interpreted as the deposits of continental and coastal saline lakes. Halite casts and finely laminated calcareous evaporites, intercalated with alluvial and fluvial sediments, are probably playa lake deposits. These continental evaporites have been recognized in Upper Triassic alluvial sediments (Cifuncho Formation), in Upper Triassic–Lower Jurassic braided river deposits (basal unit of the Pan de Azúcar Formation), and within a sequence of Lower Cretaceous aeolian, alluvial and playa lake mudflat sediments (Quebrada Monardes Formation). Lower Cretaceous evaporites between marine limestones (Lautaro Formation) and continental redbeds (Quebrada Monardes Formation) were probably deposited in coastal saline lagoons, produced during a regionally extensive marine regression.These sequences, and other similar successions in northern Chile, provide a record of almost continuous evaporite deposition, and hence of arid to semi-arid conditions, since Upper Triassic times. These conditions were primarily the result of a constant latitudinal position within the subtropical zone. A contributary factor was the geographical position of the area, initially on the west coast of Gondwanaland and subsequently on the coast of South America, with cold, northward-flowing ocean currents and offshore winds.
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DE BORBA, ANDRÉ WEISSHEIMER, and ANA MARIA PIMENTEL MIZUSAKI. "Significado Tectônico dos Depósitos de Leques Aluviais da Formação Santa Bárbara (Eo-Paleozóico) na Região de Caçapava do Sul (RS, Brasil)." Pesquisas em Geociências 29, no. 1 (June 30, 2002): 31. http://dx.doi.org/10.22456/1807-9806.19596.
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The alluvial fan deposits of Early Paleozoic Santa Bárbara Formation, located in Sul-rio-grandense Shield area of southernmost Brazil, have been analyzed here in terms of facies associations and tectonic significance. The investigated unit comprises conglomerates, sandstones, and siltstones, deposited probably under continental semi-arid climate conditions, in the post-collisional stages of Neoproterozoic Brasiliano/Pan-African Cycle. The location of the alluvial deposits suggests that the depositional locus of this sedimentary unit should probably consist of an individual and restricted fault-bounded basin, named here Santa Bárbara Basin. Its settling was controlled by the extensional and strike-slip reactivation of NE, NW, and N-S structures inherited from Brasiliano/Pan-African Cycle. Alluvial deposits located in the southwestern and northwestern borders show dominance of sheetflood processes in the alluvial fans deposition. On the other hand, the eastern border of Santa Bárbara Basin, named the “Caçapava paleohigh”, comprises the coarser alluvial deposits, with major occurrence of debris-flow features. This fact suggests a possible asymmetry of this basin. These eastern border deposits reveal, in the clast composition of the conglomerates, three main phases of denudation of “Caçapava paleohigh”. The basal conglomerates reflect a stage when this important topographic high was covered by andesites and metasedimentary rocks. Stratigraphically above, metavolcanic fragments compose the coarse deposits, while at the top of the package the conglomerate framework consists mainly of granitic clasts. This third stage reflects the exposure of the deeper parts of “Caçapava paleohigh”, and it can be positioned at the base of the unconformable Sequence III of Santa Bárbara Formation. The total inversion of braided fluvial axial filling system and the occurrence of intrabasinal debris-flow deposits suggest a strong tectonic event and possibly a significant time span at the base of Sequence III.a
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Peryt, Danuta, and Tadeusz Peryt. "Environmental changes in the declining Middle Miocene Badenian evaporite basin of the Ukrainian Carpathian Foredeep (Kudryntsi section)." Geologica Carpathica 60, no. 6 (December 1, 2009): 505–17. http://dx.doi.org/10.2478/v10096-009-0037-9.
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Environmental changes in the declining Middle Miocene Badenian evaporite basin of the Ukrainian Carpathian Foredeep (Kudryntsi section) The Kudryntsi section in West Ukraine documents a major environmental change from hypersaline to marine conditions during the Middle Miocene. There are very few (or no) specimens of foraminifers in samples of the siliciclastic series (4 m thick, with limestone intercalations) which occurs above the gypsum (and below the transgressive deposits) in the southern part of quarry. The limestone intercalations are first sparitic and microsparitic, and then become pelletal. The pelletal depositional textures are interpreted as originated in restricted environments in contrast to mixed-fossil lithoclastic packstones/grainstones overlying the siliciclastic series. The diversity of fauna increases up section. Foraminifers, bivalves, ostracods and gastropods appear first and then, additionally, brachiopods, bryozoans, crinoids, and echinoids occur. Foraminiferal assemblages are dominated by elphidiids forming 70 to 90 % of the population. The most common species are Elphidium crispum (Linné) and E. macellum (Fichtel & Moll). The limestones show a wide range of δ13C values (from -1.6 ‰ to - 18.2 ‰) and δ18O values (from -0.2 ‰ to -9.4 ‰) indicating that the cementation and some recrystallization took place in meteoric-water-dominated fluid but the restriction-controlled trend can be recognized. The siliciclastic series was deposited in an evaporitic lagoon influenced by large inflows of continental waters carrying the siliciclastic and other detrital material from the older Badenian rocks as well as from their substrate. The Kudryntsi section documents a stepwise decrease in water salinity — from ca. 150-300 ‰ during the Badenian gypsum precipitation, through ca. 80-150 ‰ during deposition of the siliciclastic series to ca. 35 ‰ during sedimentation of the basal transgressive deposits. The basal deposits originated in shallow subtidal (0-20 m) environments of normal marine salinity (30-35 ‰) and temperate to warm waters (8-18 °C) as indicated by requirements of the E. crispum association in recent seas.
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Haslett, Simon K. "An Ipswichian foraminiferal assemblage from the Gwent Levels (Severn Estuary, UK)." Journal of Micropalaeontology 16, no. 2 (October 1, 1997): 136. http://dx.doi.org/10.1144/jm.16.2.136.
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Abstract. Andrews et al. (1984) documented the occurrence of palaeo-beach deposits underlying Holocene alluvium at Llanwern, inland on the Caldicot (Gwent) Levels near Newport. These deposits at Llanwern (ST360872) lie at −3.6 to −4 m OD and were studied by Andrews et al. (1984) from borehole samples only. The sediments comprised sands and gravels with abundant intertidal and rocky shore molluscs suggesting a beach depositional setting, close to an intertidal lagoon. Locke (1971) also noted the widespread occurrence of coarse basal sands and gravels underlying the Holocene deposits of the Caldicot Levels and interpreted them as an ancient beach. Radiocarbon dates obtained from mollusc specimens yield a date of 25 450 ± 750 BP, indicating a pre-Holocene age. Amino acid racemization (AAR) studies assign these deposits to AAR Group II, oxygen isotope substage 5e, c. 120 000–130 000 BP (Andrews et al., 1984), equivalent to the Ipswichian interglacial of Great Britain.In the spring of 1991, a coarse yellow sand unit was found exposed low within the intertidal zone (c. −4–6 m OD) on the foreshore at Goldcliff, Gwent (ST374828). The unit occurs stratigraphically lower than the Holocene deposits, which at Goldcliff comprise blue/grey clay and peat of the Wentlooge Formation, deposited under brackish–freshwater conditions (Allen & Rae, 1987). This represents a similar stratigraphic succession to that observed at Llanwern by Andrews et al. (1984) some 4 km inland, and given Locke’s (1971) remarks, the probability is that the coarse yellow sand exposed at Goldcliff is a seaward . . .
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Reale, Enrico, Stephanie Groos, Ute Eckardt, Claus Eckardt, and Liliana Luciano. "New Components of ‘Basal Laminar Deposits’ in Age-Related Macular Degeneration." Cells Tissues Organs 190, no. 3 (2009): 170–81. http://dx.doi.org/10.1159/000187632.
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Molnia, Bruce F., Austin Post, and Paul R. Carlson. "20th-century glacial-marine sedimentation in Vitus Lake, Bering Glacier, Alaska, U. S. A." Annals of Glaciology 22 (1996): 205–10. http://dx.doi.org/10.3189/1996aog22-1-205-210.
Full textAbstract:
Vitus Lake, the ice-marginal basin at the southeastern edge of Bering Glacier, Alaska, U.S.A., is a site of modern, rapid, glacial-marine sedimentation. Rather than being a fresh-water lake, Vitus Lake is a tidally influenced, marine to brackish embayment connected to the Pacifie Ocean by an inlet, the Seal River. Vitus Lake consists of five deep bedrock basins, separated by interbasinal highs. Glacial erosion has cut these basins as much as 250 m below sea level. High-resolution seismic reflection surveys conducted in 1991 and 1993 of four of Vitus Lake’s basins reveal a complex, variable three-component acoustic stratigraphy. Although not fully sampled, the stratigraphy is inferred to be primarily glacial-marine units of (1) basal contorted and deformed glacial-marine and glacial sediments deposited by basal ice-contact processes and submarine mass-wasting; (2) acoustically well-stratified glacial-marine sediment, which unconformably overlies the basal unit and which grades upward into (3) acoustically transparent or nearly transparent glacial-marine sediment. Maximum thicknesses of conformable glacial-marine sediment exceed 100 m. All of the acoustically transparent and stratified deposits in Vitus Lake are modern in age, having accumulated between 1967 and 1993. The basins where these three-part sequences of “present-day” glacial-marine sediment are accumulating are themselves cut into older sequences of stratified glacial and glacial-marine deposits. These older units outcrop on the islands in Vitus Lake.In 1967, as the result of a major surge, glacier ice completely filled all five basins. Subsequent terminus retreat, which continued through August 1993, exposed these basins, providing new locations for glacial-marine sediment accumulation. A correlation of sediment thicknesses measured from seismic profiles at specific locations within the basins, with the year that each location became ice-free, shows that the sediment accumulation at some locations exceeds 10 m year−1.
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Molnia, Bruce F., Austin Post, and Paul R. Carlson. "20th-century glacial-marine sedimentation in Vitus Lake, Bering Glacier, Alaska, U. S. A." Annals of Glaciology 22 (1996): 205–10. http://dx.doi.org/10.1017/s0260305500015433.
Full textAbstract:
Vitus Lake, the ice-marginal basin at the southeastern edge of Bering Glacier, Alaska, U.S.A., is a site of modern, rapid, glacial-marine sedimentation. Rather than being a fresh-water lake, Vitus Lake is a tidally influenced, marine to brackish embayment connected to the Pacifie Ocean by an inlet, the Seal River. Vitus Lake consists of five deep bedrock basins, separated by interbasinal highs. Glacial erosion has cut these basins as much as 250 m below sea level. High-resolution seismic reflection surveys conducted in 1991 and 1993 of four of Vitus Lake’s basins reveal a complex, variable three-component acoustic stratigraphy. Although not fully sampled, the stratigraphy is inferred to be primarily glacial-marine units of (1) basal contorted and deformed glacial-marine and glacial sediments deposited by basal ice-contact processes and submarine mass-wasting; (2) acoustically well-stratified glacial-marine sediment, which unconformably overlies the basal unit and which grades upward into (3) acoustically transparent or nearly transparent glacial-marine sediment. Maximum thicknesses of conformable glacial-marine sediment exceed 100 m. All of the acoustically transparent and stratified deposits in Vitus Lake are modern in age, having accumulated between 1967 and 1993. The basins where these three-part sequences of “present-day” glacial-marine sediment are accumulating are themselves cut into older sequences of stratified glacial and glacial-marine deposits. These older units outcrop on the islands in Vitus Lake.In 1967, as the result of a major surge, glacier ice completely filled all five basins. Subsequent terminus retreat, which continued through August 1993, exposed these basins, providing new locations for glacial-marine sediment accumulation. A correlation of sediment thicknesses measured from seismic profiles at specific locations within the basins, with the year that each location became ice-free, shows that the sediment accumulation at some locations exceeds 10 m year−1.
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Mandal, Shramana, and Bhawana A. Badhe. "Malignant Transformation in a Mature Teratoma with Metastatic Deposits in the Omentum: A Case Report." Case Reports in Pathology 2012 (2012): 1–3. http://dx.doi.org/10.1155/2012/568062.
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Malignant transformation of a mature cystic teratoma (MCT) is a very rare complication with an incidence of 0.17–2%;. The most common form of malignant transformation of the MCT is squamous cell carcinoma. Other tumors arising in MCT include basal cell carcinoma, sebaceous tumor, malignant melanoma, adenocarcinoma, sarcoma, and neuroectodermal tumor. However malignant transformation with metastatic deposits in the omentum is extremely rare. The present case highlights the rarity of the occurrence of an omental deposits in a case of mature cystic teratoma with malignant transformation.
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Ampe, Carole. "The Quaternary Stratigraphy of a Section of the Sibowe River, South-West Swaziland." Afrika Focus 7, no. 3 (January 26, 1991): 225–40. http://dx.doi.org/10.1163/2031356x-00703003.
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In south-west Swaziland a river terrace along the Sibowe river is formed by active river incision. A complex profile along this terrace showing alluvial and colluvial deposits reflecting changes in environmental conditions since at least the last 30000 years is exposed. Examination of soil characteristics, relative position of the composite strata as well as river dynamics leads to a stratigraphic interpretation which has been fitted into a time frame. The basal gravel, alluvial in nature, dates from before the deposition of the Mphunga colluvium which has been deposited between 30 300 and 8490 before present. On the colluvium occurs an alluvium most probably deposited during the Early Holocene. The incision of the terrace to its present level has occurred during the Late Holocene.
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Toomey, Christopher B., Una Kelly, Daniel R. Saban, and Catherine Bowes Rickman. "Regulation of age-related macular degeneration-like pathology by complement factor H." Proceedings of the National Academy of Sciences 112, no. 23 (May 19, 2015): E3040—E3049. http://dx.doi.org/10.1073/pnas.1424391112.
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Complement factor H (CFH) is a major susceptibility gene for age-related macular degeneration (AMD); however, its impact on AMD pathobiology is unresolved. Here, the role of CFH in the development of AMD pathology in vivo was interrogated by analyzing aged Cfh+/− and Cfh−/− mice fed a high-fat, cholesterol-enriched diet. Strikingly, decreased levels of CFH led to increased sub-retinal pigmented epithelium (sub-RPE) deposit formation, specifically basal laminar deposits, following high-fat diet. Mechanistically, our data show that deposits are due to CFH competition for lipoprotein binding sites in Bruch’s membrane. Interestingly and despite sub-RPE deposit formation occurring in both Cfh+/− and Cfh−/− mice, RPE damage accompanied by loss of vision occurred only in old Cfh+/− mice. We demonstrate that such pathology is a function of excess complement activation in Cfh+/− mice versus complement deficiency in Cfh−/− animals. Due to the CFH-dependent increase in sub-RPE deposit height, we interrogated the potential of CFH as a previously unidentified regulator of Bruch’s membrane lipoprotein binding and show, using human Bruch’s membrane explants, that CFH removes endogenous human lipoproteins in aged donors. Thus, advanced age, high-fat diet, and decreased CFH induce sub-RPE deposit formation leading to complement activation, which contributes to RPE damage and visual function impairment. This new understanding of the complicated interactions of CFH in AMD-like pathology provides an improved foundation for the development of targeted therapies for AMD.
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Triantaphyllou, M. V. "CALCAREOUS NANNOFOSSIL BIOSTRATIGRAPHY OF LANGHIAN DEPOSITS IN LEFKAS (IONIAN ISLANDS)." Bulletin of the Geological Society of Greece 43, no. 2 (January 23, 2017): 754. http://dx.doi.org/10.12681/bgsg.11241.
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Spanochorion composite section (NE Lefkas) and Aghios Vassilios section (W Lefkas) have been studied semiquantitatively for their calcareous nannofossil content. The calcareous nannofossil biostratigraphy, performed at the Paxos unit atypical flysch sediments of Aghios Vassilios section, permits their biostratigraphic correlation with the uppermost part of NN4 biozone and the lower part of NN5 biozones (Martini, 1971) or MNN4b and MNN5a (Fornaciari and Rio, 1996), which chronostratigraphically point to Early Langhian age and range between 15.974 and 14.53 Ma. Τhe most interesting biostratigraphic result is the detection of the Sphenolithus heteromorphus Paracme End at the base of Aghios Vassilios section, a biohorizon that marks the basal Langhian deposits in the Mediterranean region. The mollasic sediments of Spanochorion section are more or less of the same age, ranging between 15.5 and 14.53 Ma. The biostratigraphic results of the present study reinforce the hypothesis that the molassic sediments of NE Lefkas Island behind the Ionian thrust were isochronously deposited with Paxos atypical flysch sequences deposited in front of Ionian thrust, at least until Early Langhian times.
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Luberti, Gian Marco, Francesca Vergari, Alessia Pica, and Maurizio Del Monte. "Estimation of the thickness of anthropogenic deposits in historical urban centres: An interdisciplinary methodology applied to Rome (Italy)." Holocene 29, no. 1 (October 15, 2018): 158–72. http://dx.doi.org/10.1177/0959683618804630.
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In historical urban centres, the superimposition of excavation and deposition activities over time has resulted in an irregular spatial distribution of anthropogenic deposits, which may reach considerable thicknesses. The detection of those thicknesses requires extensive investigations. Broad borehole and geophysical campaigns cost time and money, consequently at the urban-planning level, it is usual to shift to an estimation of thicknesses, which may be performed through map-algebra operations, that is, by subtracting from the modelled ground surface the elevation of the anthropogenic-deposit basal surface. The latter is implemented through the interpolation of point elevation data, which are generally provided by borehole logs. Despite the development of advanced spatial interpolation methodologies, previous modelling results in the literature show that if the process is affected by insufficient input data, it produces imprecise interpolation outputs. This paper reports an interdisciplinary methodology aiming at enhancing elevation datasets, in order to obtain more accurate digital elevation models. The increase in number and spatial distribution of input points is achieved through past-landscape analyses mainly based on elevation data given by borehole logs, available archaeological reports and historical topographic maps, these being generally available for historical urban centres. The methodology was tested in an urban sector of Rome, where significant activities have been performed for millennia particularly during the Roman Age. A reliable model of the basal surface of the anthrostrata led to a better estimation of the spatial distribution of such deposits and, in addition, revealed the original topographic surface, as modified by human activities.
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Ivanov, D. V., V. V. Ivanov, and A. V. Tolstov. "THE FEATURES OF THE INDICATOR MINERALS OF KIMBERLITES IN A NEW PIPE YANVARSKAJA (WESTERN YAKUTIA)." Proceedings of higher educational establishments. Geology and Exploration, no. 5 (October 28, 2017): 20–26. http://dx.doi.org/10.32454/0016-7762-2017-5-20-26.
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The first results of the mineral-petrographic studies of microclastes of kimberlites from the basal horizon of the Upper Paleozoic deposits of the Alakit-Markhinsky kimberlite field (Western Yakutia) have been presented. The main features of the indicator minerals of kimberlites (IMK) have been revealed. These minerals are picroilmenite, pyrope, chromspinels, phlogopite, chromdiopside and olivine. The ways of their further studying in connection with the search for kimberlite bodies have been outiined. The opening of the Yanvarskaja pipe has confirmed the correctness of the methodology for testing the basal horizons of the Upper Paleozoic deposits on the core of the wells. Minerals containing rare-earth elements (REE) have been found in the kimberlites of the new tube, which requires further research. The results of the study of the IMK of Yanvarskaja pipe serve as a supplement to the database on the Alakit-Markhinsky field and allow more reliable prediction and identification of new objects, including high-diamond ones.
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Zanchetta, Giovanni, Marta Pappalardo, Alessio Di Roberto, Monica Bini, Ilenia Arienzo, Ilaria Isola, Adriano Ribolini, et al. "A Holocene tephra layer within coastal aeolian deposits north of Caleta Olivia (Santa Cruz Province, Argentina)." Andean Geology 48, no. 2 (May 31, 2021): 267. http://dx.doi.org/10.5027/andgeov48n2-3290.
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In this paper we illustrate the stratigraphy, geochronology, and geochemistry (major, minor, trace elements and Sr-isotopes) of a Holocene tephra layer found within coastal sedimentary deposits north of Caleta Olivia (Santa Cruz Province, Argentina). The stratigraphic succession comprises beach deposits with basal erosive surface resting on the local substrate (“Formación Patagonia”) followed by a poorly developed paleosoil. The paleosoil is covered by a lenticular fine-grained (Mdφ: 5.2, 0.027 mm), well sorted (σφ: 1.2) volcanic ash layer and aeolian sands. The geochemical composition of shard fragments points to an origin from the Hudson volcano, located in the southern Andes, ca. 400 km to the west. The geochemistry, Sr-isotopes and the radiometric constraints (younger than the age of the underlying marine layer dated at ca. 4,100 a cal BP) further allow correlating this tephra with the so-called H2 eruption (ca. 3,900 a cal BP). This finding is of interest owing to the poor preservation potential of tephra within the Late Holocene sedimentary deposits of the Atlantic coast of Patagonia and represents the first finding of H2 eruption in this area, improving our knowledge of the dispersion of the fine-grained distal deposit of the Hudson volcanic explosive activity, thus allowing a better estimate of the eruptive dynamics and the risks associated with the Hudson volcano.