Journal of Sedimentary Research最新文献

{"title":"Analysis of the fluvial stratigraphic response to the Paleocene–Eocene Thermal Maximum in the Bighorn Basin, U.S.A.","authors":"A. Owen, A. Hartley, T. Hoey, A. Ebinghaus, D. Jolley, G. Weissmann","doi":"10.2110/jsr.2021.134","DOIUrl":"https://doi.org/10.2110/jsr.2021.134","url":null,"abstract":"\u0000 Geological deposits can reveal how environments of the past have responded to climate change, enabling important insights into how environments may respond to our current anthropogenically induced warming. The Paleocene–Eocene Thermal Maximum (PETM) occurred ca. 56 Ma and was a short-lived (approximately 200,000 years) global warming event (5–8°C rise). The PETM has been investigated at several terrestrial and marine localities across the globe. However, many studies are based on single successions, with very few sites being placed within a well-defined spatial and temporal context and with comparisons limited to deposits that lie immediately above and below the event. Due to the inherent variability of sedimentary systems, it is imperative that the appropriate context is provided to fully understand the impacts of climate change on landscapes and subsequent deposits. This study examines 28 locations, totaling over 4 km of recorded stratigraphy, within a newly defined quantified sedimentary basin context (Bighorn Basin, USA) to evaluate variability of fluvial response to the PETM. We show that channel-body and story thicknesses across the PETM are not statistically significantly different from deposits outside the climate event, implying that there is not a consistent sedimentary response to the climate event across the basin. Based on our large dataset we calculate that precipitation would have had to double for statistically significant changes in deposit thickness to be generated. We discuss how climatic signals may be lost due to the self-organization, spatial–temporal varied response and preservation potential in large fluvial systems. This study gives a new quantified perspective to climate events in the geologic record.","PeriodicalId":17044,"journal":{"name":"Journal of Sedimentary Research","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2023-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47706492","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Fluvial character and architecture of an outcrop using sedimentology combined with UAV-based modeling, Cretaceous McMurray Formation, NE Alberta, Canada","authors":"Derek Hayes, Scott E. Botterill, M. Ranger, M. Gingras","doi":"10.2110/jsr.2022.039","DOIUrl":"https://doi.org/10.2110/jsr.2022.039","url":null,"abstract":"It is widely accepted that most occurrences of inclined heterolithic stratification (IHS) in the rock record form by laterally accreting point bars in freshwater fluvial, tidally influenced fluvial, or tidally dominated estuary channels. Despite the widespread distribution of IHS in the subsurface and outcropping strata of the lower Cretaceous McMurray Formation, the large-scale depositional architecture and lateral facies variability of these deposits remains controversial. The relatively limited lateral extent of many of the outcrops is a challenge, particularly when point-bar deposits on the scale of hundreds of meters to kilometers are interpreted in outcrops spanning anywhere from 100 to 300 meters laterally. This has in turn led researchers to leverage other datasets such as 3-D seismic to analyze the large-scale depositional architecture of the IHS, leading to two main interpretations for the IHS in the McMurray Formation: 1) a fluvially dominated environment owing to geomorphological features comparable to those in large modern fluvial systems, or 2) an estuarine environment owing to the presence of trace fossils characteristic of marine-derived faunal colonization in brackish-water settings and strong evidence of tidal modulation. The purpose of this study is to investigate the sedimentology and depositional architecture of IHS in a unique, kilometer-wide outcrop exposure of McMurray Formation strata and compare it to IHS observed at other McMurray Formation outcrops previously interpreted as estuarine channels. This is achieved by combining traditional field-based methods with Unmanned Aerial Vehicle-based outcrop modeling to create a 3-D outcrop model to visualize and analyze large point-bar geobodies deposited in a channel upwards of 25 meters deep and 750 meters wide exposed in outcrop at Crooked Rapids of the Athabasca River, west of the City of Fort McMurray. Importantly, this methodology uses bed orientation trends, paleocurrent data, and sedimentological observations to identify and map architectural elements, which constitute an eastward-accreting point bar crosscut by a southwestward-accreting counter point bar in the outcrop. The results strongly suggest that the IHS at Crooked Rapids was deposited in a freshwater fluvial environment. When compared to IHS deposited in estuarine depositional environments, fluvial IHS is driven by seasonal river discharge as opposed to the interplay between river discharge and the extent of the tidal prism. Therefore, fluvial IHS is: 1) dominantly sandstone with very minor waning-flow siltstone interbeds resulting from erosion by the succeeding freshet phase, and 2) completely devoid of bioturbation until flat-lying bar top or overbank strata is encountered. Using 3-D outcrop modeling to supplement sedimentological and ichnological observations strengthens the interpretation of complex fluvial geobodies and increases the overall understanding of the large-scale depositional architecture of poi","PeriodicalId":17044,"journal":{"name":"Journal of Sedimentary Research","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2023-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48803166","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Environmental and microbial influence on chemistry and dolomite formation in an ancient lake, Green River Formation (Eocene), Uinta basin, Utah, U.S.A.","authors":"Maxwell Pommer, J. Sarg, F. McFarlin","doi":"10.2110/jsr.2022.016","DOIUrl":"https://doi.org/10.2110/jsr.2022.016","url":null,"abstract":"\u0000 Integrated stratigraphic, petrographic, and geochemical data allow interpretation of biogeochemical and mineralization processes in paleoenvironmental context of ancient lacustrine environments. These indicate that lake chemistry, microbial processes, and organic matter (OM) strongly influenced dolomite formation in near-surface environments throughout deposition of the Green River Formation (Eocene, Uinta basin, Utah).\u0000 The lower Green River Formation consists of interbedded fluvio-deltaic siliciclastics, paleosols, carbonate mud, coated-grain carbonates, mollusk and ostracod limestones, and microbialites all landward of profundal OM-bearing illitic mudrocks. Calcite, dolomite, Fe-dolomite, and authigenic feldspars are common. Carbonate δ18O and δ13C are covariant, and positive excursions of carbonate δ13C (up to 6.9‰ VPDB) and organic-matter δ15N (up to 13.9‰ V-AIR) occur in profundal OM-bearing mudrocks.\u0000 The upper Green River Formation consists mainly of laminated OM-lean and OM-rich dolomitic muds (i.e., “oil-shales”). Zoned dolomite crystals with Mg-calcite centers and Fe-dolomite rims are widespread in addition to authigenic feldspars and Na-carbonates. Carbonate δ13C-enrichment (up to 15.8‰ VPDB), and organic-matter δ15N-enrichment (up to 18.4‰ V-AIR) occur in these OM-rich dolomite muds. Organic-matter δ13C is relatively invariable (mean = –29.3‰ VPDB) and does not covary with carbonate δ13C.\u0000 Trends in mineralogy, organic-matter abundance, and stable isotopes result from changing hydrologic systems, paleoclimate, lake chemistry and microbial processes coincident with the Early Eocene Climate Optimum. The lower Green River Formation paleo-lake was smaller in area and volume, heavily influenced by meteoric fluvial input, variably oxygenated, and ranged from neutral and fresh to alkaline and saline. Especially in littoral environments with abundant microbialites, dolomite formed through recrystallization of precursor carbonate involving both replacement of precursor carbonate and direct precipitation as cements and overgrowths. The upper Green River Formation paleo-lake was more expansive with widespread low-oxygen, nutrient-rich, and alkaline saline environments with increased planktic organic-matter productivity. Microbial decay of organic matter in low-oxygen environments produced alkaline lake waters through methanogenesis, possible denitrification, and bacterial sulfate reduction to a limited degree. This favored precipitation of widespread dolomite, as well as Na-carbonates, authigenic feldspars, and analcime from lake water and phreatic pore water. Extracellular polymeric substances (EPS) excreted by microbial communities provided favorable nucleation sites for Mg-carbonate, allowing kinetic barriers of low-temperature dolomite formation to be overcome. Cycling of pH due to turnover of organic matter and associated microbial processes potentially bolstered EPS generation and abiotic environmental conditions favorable to dolomite p","PeriodicalId":17044,"journal":{"name":"Journal of Sedimentary Research","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2023-04-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41885647","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Multiple scours and upward fining caused by hydraulic jumps: implications for the recognition of cyclic steps in the deepwater stratigraphic record","authors":"Kenya Ono, H. Naruse, Qi-Feng Yao, Zhirong Cai, S. Fukuda, M. Yokokawa","doi":"10.2110/jsr.2021.142","DOIUrl":"https://doi.org/10.2110/jsr.2021.142","url":null,"abstract":"\u0000 Hydraulic jumps control the bypass, erosion, and depositional processes of Froude-supercritical turbidity currents, so they represent a significant process for understanding the development of submarine geomorphology. Hydraulic jumps actively occur from submarine canyons to fans, where the seafloor slope is relatively steep. Turbidites in such areas comprise large-scale bedforms called cyclic steps, and they exhibit complex internal structures, including localized erosion and the accumulation of coarse-grained fining-upward sequences. However, it is unclear which turbidity-current properties are reflected in the heterogeneous depositional characteristics and grain-size sorting of these deposits. To this end, we conducted flume experiments to reproduce deposits associated with the hydraulic jumps of surge-type flows. Turbidity-current surges were repeatedly generated in an experimental flume with a knickpoint that transitioned from a steep to a gentle slope, resulting in cyclic steps. Overall, the upstream migration of the cyclic steps produced a downstream-upward-fining succession of turbidites. However, hydraulic jumps occurred at several places over the trough to the stoss side of the step in a single flow due to the non-uniform and unsteady flow state of the surge-type turbidite succession. As a result, the reproduced succession exhibited multiple local scours and coarse-grained fill in the lower parts of the turbidites. This suggests that multiple local scours and fining-upward trends are discriminant characteristics of cyclic-step deposits formed by surge-type supercritical turbidity currents.","PeriodicalId":17044,"journal":{"name":"Journal of Sedimentary Research","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2023-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48676363","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Petrology of Bengal Fan turbidites (IODP Expeditions 353 and 354): provenance versus diagenetic control","authors":"M. Limonta, E. Garzanti, A. Resentini","doi":"10.2110/jsr.2022.071","DOIUrl":"https://doi.org/10.2110/jsr.2022.071","url":null,"abstract":"\u0000 High-resolution petrographic and heavy-mineral analyses of Bengal Fan turbidites from six cores drilled during IODP Expeditions 353 and 354 elucidate factors controlling their intersample compositional variability as a key to understanding sedimentary processes and erosional evolution of the Himalayan belt since the Miocene. Bengal Fan turbidites are feldspatho-quartzose to litho-feldspatho-quartzose with plagioclase > K-feldspar; slow-settling micas increase in abundance in very fine sand and coarse silt. The feldspar/quartz ratio and higher-rank metamorphic rock fragments notably increase from uppermost Miocene to Pleistocene deposits, which is ascribed to the onset of rapid exhumation of the Eastern Himalayan syntaxis since ∼ 5 Ma. The same trends are documented in Nicobar Fan turbidites, confirming that they belong to the same sedimentary system. Both Bengal and Nicobar fans record a pulse in mass accumulation rate at Tortonian times, when supply of sedimentary and very-low-grade metasedimentary detritus reflected accelerated exhumation of the Lesser Himalaya. In contrast to foreland-basin sediments, where ferromagnesian minerals have been completely dissolved in strata as young as Pliocene–Pleistocene, in both Bengal–Nicobar and Indus fans amphibole invariably represents about half of the moderately rich to rich transparent-heavy-mineral suite, demonstrating that amphibolite-facies Greater Himalaya metamorphic rocks were widely exposed in the Himalayan range well before the late Miocene and possibly since the late Oligocene, as indicated by a few sillimanite and kyanite grains in Bengal Fan sediments as old as 23 Ma and 28 Ma, respectively. Diagenetic dissolution strongly affected olivine and pyroxene in strata older than the middle and early Pleistocene, respectively, whereas amphibole decreases markedly through progressively older Miocene strata. Ferromagnesian minerals and sillimanite are almost completely dissolved in lower Miocene strata, where durable zircon, tourmaline, rutile, and apatite make up half of the strongly depleted heavy-mineral assemblage. Quaternary turbidites from the six studied cores have virtually the same compositional signatures, testifying to efficient homogenization by turbidite transport and reworking across the fan. Turbidites in western cores closer to peninsular India (U1444A and U1454B) are not different from those in eastern cores, indicating very minor supply from the subcontinent. Forward-mixing calculations based on integrated petrographic and heavy-mineral data indicate that sand supply from the Brahmaputra River to Quaternary turbidites was four times larger than supply from the Ganga River, indicating up to six times higher sediment yields and erosion rates in the Brahmaputra than in the Ganga catchment, largely reflecting superfast erosion of the Eastern Himalayan syntaxis.","PeriodicalId":17044,"journal":{"name":"Journal of Sedimentary Research","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2023-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48629112","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Decompositional processes of microbial carbonates in Lagoa Vermelha, Brazil","authors":"F. Shiraishi, Yusaku Hanzawa, Jiro Asada, L. Cury, A. Bahniuk","doi":"10.2110/jsr.2022.053","DOIUrl":"https://doi.org/10.2110/jsr.2022.053","url":null,"abstract":"In Lagoa Vermelha, Brazil, a lagoonal stromatolite and a saltpan microbial mat are investigated to understand the influence of environmental changes on the decomposition of microbial carbonates. The lagoonal stromatolite, composed mainly of magnesian calcite and aragonite, is developed on a dolomite-containing carbonate crust. While most stromatolites are eroded to the water surface level, some smaller, green stromatolites below the water surface retain a domal shape. The domal stromatolite surface is dominated by endolithic cyanobacteria with conspicuous microborings. In addition, microbial aerobic respiration causes carbonate dissolution in darkness, and metazoans grazing the inner surface of the stromatolite excrete fecal pellets. This suggests that the formational stage of lagoonal stromatolites has ceased and they are now decomposing, most likely because of environmental changes in recent years. The microbial mat, which is about 3 cm thick, developed in a saltpan pond precipitating carbonate and gypsum, and it contains quartz, magnesian calcite, aragonite, and gypsum. At the time of the investigation, the population of oxygenic phototrophs is low at the mat surface, and carbonate dissolution, rather than precipitation, is occurring by microbial metabolism deeper in the mat. This suggests that the formation of carbonate in the mat has ceased and is decomposing, probably due to the progressive salinity increase in the salt pan. This examination of two carbonate deposits in Lagoa Vermelha suggests that microbial metabolism is an important process for decomposing microbial carbonates in addition to grazing and microboring, and that environmental changes may alter microbial compositions from carbonate-constructive to carbonate-destructive communities.","PeriodicalId":17044,"journal":{"name":"Journal of Sedimentary Research","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2023-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44048123","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Warm acidified seawater: a dolomite solution","authors":"J. Rivers","doi":"10.2110/jsr.2022.087","DOIUrl":"https://doi.org/10.2110/jsr.2022.087","url":null,"abstract":"\u0000 The “dolomite problem” is the product of two distinct observations. First, there are massive amounts of ancient marine limestone (CaCO3) deposits that have been replaced by the mineral dolomite (MgCa(CO3)2). However, recent (Holocene and Pleistocene) marine deposits contain relatively minuscule amounts of dolomite, although the occurrence of small quantities of dolomite is observed in many modern settings, from deep marine to supratidal. Second, low-temperature synthesis of dolomite in laboratory settings has been elusive, particularly in comparison to the ease with which common marine calcium carbonate minerals (aragonite and calcite) can be synthesized. Since low-temperature solid-state diffusion can be discounted as a method for Mg incorporation into calcium carbonate (as it operates on time scales too long to matter), the replacement of CaCO3 by dolomite is one of dissolution followed by precipitation. Therefore, an often overlooked but required factor in the replacement of limestone by dolomite is that of undersaturation regarding the original calcium carbonate mineral during replacement. Such conditions could conceivably be caused by rapid dolomite growth relative to aragonite and calcite dissolution–precipitation reactions, but laboratory studies, modern systems analyses, and observations of ancient deposits all point to this possibility being uncommon because dolomite growth is kinetically inhibited at low temperature. Pressure solution by force of dolomite crystallization is a second possible driver for CaCO3 undersaturation, but requires a confining stress most likely attained through burial. However, based on petrographic observations, significant amounts of ancient dolomite replaced limestone before burial (synsedimentary dolomite), and many such platforms have not suffered any significant burial. Because these possibilities of undersaturation caused by dolomite precipitation and crystal growth can be largely discounted, the undersaturation required for “dolomitization” to proceed is most likely to be externally forced. In modern natural systems, undersaturation and selective CaCO3 dissolution in marine porewaters is very common, even in warm-water environments, being forced by the breakdown of organic matter. Such dissolution is frequently attended, to varying degrees, by precipitation of a kinetically-less-favored but thermodynamically more stable phase of CaCO3. Laboratory studies as well as observations of modern systems show that when undersaturation is reached with respect to all common marine CaCO3 phases, dolomite assumes the role of this kinetically-less-favored precipitate. This degree of undersaturation is uncommon in modern shallow marine pore systems in warm-water settings, but it was more common during times of elevated atmospheric CO2, and ocean acidification. Furthermore, because oxidation of organic matter drives dolomite formation, near-surface organic-rich deposits such as the remains of microbial mat communities,","PeriodicalId":17044,"journal":{"name":"Journal of Sedimentary Research","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2023-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49114072","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Lateral and temporal variations of a multi-phase coarse-grained submarine slope channel system, Upper Cretaceous Cerro Toro Formation, southern Chile","authors":"Guilherme Bozetti, B. Kneller, B. Cronin, P. Li, A. McArthur, Jingping Xu","doi":"10.2110/jsr.2022.020","DOIUrl":"https://doi.org/10.2110/jsr.2022.020","url":null,"abstract":"\u0000 Understanding variations in the sedimentary processes and resulting stratigraphic architecture in submarine channel systems is essential for characterizing sediment bypass and sedimentary facies distribution on submarine slopes. In the Santonian to Campanian Cerro Toro Formation, southern Chile, a coarse-grained slope system, informally known as the Lago Sofia Member, developed in a structurally controlled environment, with complex and poorly established relationships with the surrounding mud-rich heterolithic deposits.\u0000 A detailed architectural analysis of the most continuous and best-exposed channel system in the Lago Sofia Member, the Paine C channel system, provides insights on lateral facies transitions from channel axis to margin, stacked in a multi-phase sequence of events marked by abrupt changes in facies, facies associations, and architecture.\u0000 The Paine C channel system is incised into siltstones and claystones interbedded with thin-bedded very fine sandstones, interpreted to be either channel-related overbank or unrelated background deposits. The coarse-grained deposits are divided into a lower conglomeratic unit and an upper sand-rich unit. The lower conglomeratic unit can be further subdivided into three phases: 1) highly depositional and/or aggradational, dominated by thick and laterally continuous beds of clast- to matrix-supported conglomerate, herein named transitional event deposits; 2) an intermediate phase, including deposits similar to those dominant in phase 1 but also containing abundant clast-supported conglomerates and lenticular sandstones; and 3) a bypass-dominated phase, which records an architectural change into a highly amalgamated ca. 45-m-thick package composed purely of lenticular clast-supported conglomerates with local lenticular sandstones. Between the conglomeratic phases, a meter-scale package composed of interbedded thin- to medium-bedded sandstone and mudstone deposits is interpreted to drape the entire channel, indicating periods of weaker gravity flows running down the channel, with no evidence of bedload transport.\u0000 The upper sand-rich unit is divided into lower amalgamated and upper non-amalgamated phases, and represents a rapid architectural change interpreted to record an overall waning of the system. The sandstone unit laps out onto a mass-transport complex which is interpreted to have been triggered initially at the same time as major architectural change from conglomerates to sandstones.\u0000 While mindful of the fact that each system is a complete analogue only for itself, we propose a new depositional model for coarse-grained submarine channel systems, in which particular characteristics can provide significant insights into architectural heterogeneity and facies transitions in channelized systems, allowing substantial improvement in subsurface facies prediction for fluid reservoirs.","PeriodicalId":17044,"journal":{"name":"Journal of Sedimentary Research","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2023-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41519541","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Always a White Christmas in the Bahamas: temperature and hydrodynamics localize winter mud production on Great Bahama Bank","authors":"S. Purkis, A. Oehlert, T. Dobbelaere, E. Hanert, P. Harris","doi":"10.2110/jsr.2022.066","DOIUrl":"https://doi.org/10.2110/jsr.2022.066","url":null,"abstract":"\u0000 Whitings, or occurrences of fine-grained carbonate in the water column, have been observed in modern environments with salinities ranging from fresh to marine conditions, and thick deposits of lime mud are described throughout the geological record. Despite their ubiquity, the trigger for whitings has been debated for more than eighty years. Satellite data reveal that most whitings are restricted to the northwestern part of Great Bahama Bank (GBB) which occupies < 10% of the platform area. Even here, whitings are further focused. More than 35% of them occur in a zone which occupies just 1% of the platform. We propose a three-step process for the existence of this zone of peak whitings and why the whitings in it are both more frequent and larger in winter than summer. First, the temperature differential between on- and off-platform waters is highest in the winter, setting up a disparity between dissolved CO2 concentrations in the two water masses. Second, hydrodynamic mixing of these two water masses increases the degree of aragonite saturation of the platform-top waters, as colder on-platform waters with theoretically higher concentrations of dissolved gases are warmed via mixing with the warmer off-platform waters. Finally, spatial heterogeneity in the degree of aragonite saturation is higher in the winter, and the zone of peak whitings is situated in an area of locally enhanced saturation state. Hydrodynamic simulation suggests that the whitings zone is located by tidal inflow of off-platform waters across the western margin of GBB, as well as inflow from the Tongue of the Ocean to the north of Andros Island. Despite thermodynamic forcing mechanisms that predict higher frequency of whitings in the summer, the environmental, hydrodynamic, geochemical, and kinetic conditions in the whitings zone appear to support the Goldilocks configuration that enhances the formation of wintertime whitings on Great Bahama Bank. This phenomenon has implications for the interpretation of whitings mud in the geological record, including the geochemical signatures within it.","PeriodicalId":17044,"journal":{"name":"Journal of Sedimentary Research","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2023-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45380295","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The critical role of recycling of post-Grenvillian, Neoproterozoic sediments for Phanerozoic Laurentian clastic systems: evidence from detrital-zircon and -monazite geochronology and textures","authors":"D. Moecher, Steven C. Zotto, S. Samson","doi":"10.2110/jsr.2022.054","DOIUrl":"https://doi.org/10.2110/jsr.2022.054","url":null,"abstract":"\u0000 Lithic and quartz arenites of the Central Appalachian Basin deposited by late Paleozoic Laurentian fluvial systems are widely interpreted to be sourced by recycling of late Precambrian and early Paleozoic clastic sequences in the Appalachian Orogen. U-Pb and (U-Th)/He age distributions for detrital-zircon and Th-Pb age distributions for detrital-monazite, detrital-zircon and monazite textures (including detrital diagenetic monazite, which prove recycling), sandstone petrology, heavy-mineral abundances, and other detrital proxies are all accounted for by the following: 1) lithic arenite is directly sourced from late Neoproterozoic metasediments in the proximal Appalachian fold and thrust belt via transverse drainages, 2) the late Neoproterozoic sediments were recycled from early Neoproterozoic, post-Grenvillian clastic sequences, 3) Cambrian quartz arenites along the Laurentian margin were recycled from Neoproterozoic sequences with local cratonic input, 4) although dominated by sediment of ultimate Grenvillian age, quartz arenites require ∼ 40% of Paleoproterozoic and Archean input, interpreted to be recycled from late Neoproterozoic to Devonian clastic sequences of the northern Appalachians and/or southern (Scottish–Irish) Caledonides in the distal reaches of a longitudinal drainage system. Ordovician to Mississippian clastic sequences and their metamorphosed equivalents in the Appalachian crystalline core were also likely sediment sources. Quartz arenite does not result from mixing of lithic arenite with other sources because of differences in textural and compositional maturity, and in heavy-mineral characteristics. Input from the Laurentian craton, commonly cited as the source for Paleoproterozoic and Archean detrital zircon in the eastern Laurentian clastic systems, is untenable here because of: 1) the presence of Paleozoic monazite derived from Appalachian Neoproterozoic and early Paleozoic metasediments, 2) abundant detrital chromite, and 3) abundant Paleozoic detrital muscovite. Multiple recycling explains all observed sedimentologic and mineralogic characteristics of the two lithic types. Incorporation of published detrital-zircon data for Paleozoic to modern clastic sequences in eastern Laurentia reveals that Grenville-age zircons experienced at least five and potentially ten recycling events since entering the clastic system in the Neoproterozoic. Recycling also explains the abundance of quartz pebbles in conglomerates of the quartz-arenite lithofacies, and the range of detrital-muscovite 40Ar/39Ar ages in quartz arenites of the Appalachian Basin.","PeriodicalId":17044,"journal":{"name":"Journal of Sedimentary Research","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2023-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42224834","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}