Jared T. Freiburg, M. Peltz, D. Willette, G. Grathoff
At the Illinois Basin–Decatur Project, a large-scale CO2 capture and geologic storage demonstration project in the saline Mount Simon Sandstone in central Illinois, three overlying and laterally continuous shale formations (the Eau Claire, Maquoketa, and New Albany) are considered confining units overlying the sandstone reservoir. The Mount Simon reservoir contains internal mudstone baffles that will influence CO2 migration pathways and future interaction with seals. Understanding the sealing properties of rock units deemed seals or confining units is vital to commercialization of geologic carbon storage. For this article, nanoscale-resolution focused ion beam scanning electron microscopy (SEM), mercury injection capillary pressure (MICP), X-ray diffraction (XRD) spectroscopy, and quantitative evaluation of minerals by SEM were used to characterize the controls on the sealing integrity of these seals and reservoir confining units. Results show that porosity and pore size generally decrease with depth, except in the carbonate-rich Maquoketa Shale. The Maquoketa contains the highest pore volume owing to abundant dolomite in the mineral matrix compared with the other mudstone and shale intervals, which are clay rich. The shallowest seal sample, the organic-rich New Albany Shale, contains the highest frequency of the smallest pore throat size and is most comparable, with respect to pore sizes and entry pressures, to the deepest black shale and primary Mount Simon reservoir seal, the Eau Claire. Point-specific MICP threshold pressure results, theoretical calculations based on a range of permeabilities, and column height calculations indicate that the internal Mount Simon mudstone and Eau Claire Shale are effective seals of CO2 in the Mount Simon reservoir.
{"title":"High-Resolution Pore Space Imaging, Mineralogical Characterization, and Sealing Capacity Estimates of Confining Units at a Geologic Carbon Storage Demonstration: The Illinois Basin–Decatur Project, USA","authors":"Jared T. Freiburg, M. Peltz, D. Willette, G. Grathoff","doi":"10.1086/722563","DOIUrl":"https://doi.org/10.1086/722563","url":null,"abstract":"At the Illinois Basin–Decatur Project, a large-scale CO2 capture and geologic storage demonstration project in the saline Mount Simon Sandstone in central Illinois, three overlying and laterally continuous shale formations (the Eau Claire, Maquoketa, and New Albany) are considered confining units overlying the sandstone reservoir. The Mount Simon reservoir contains internal mudstone baffles that will influence CO2 migration pathways and future interaction with seals. Understanding the sealing properties of rock units deemed seals or confining units is vital to commercialization of geologic carbon storage. For this article, nanoscale-resolution focused ion beam scanning electron microscopy (SEM), mercury injection capillary pressure (MICP), X-ray diffraction (XRD) spectroscopy, and quantitative evaluation of minerals by SEM were used to characterize the controls on the sealing integrity of these seals and reservoir confining units. Results show that porosity and pore size generally decrease with depth, except in the carbonate-rich Maquoketa Shale. The Maquoketa contains the highest pore volume owing to abundant dolomite in the mineral matrix compared with the other mudstone and shale intervals, which are clay rich. The shallowest seal sample, the organic-rich New Albany Shale, contains the highest frequency of the smallest pore throat size and is most comparable, with respect to pore sizes and entry pressures, to the deepest black shale and primary Mount Simon reservoir seal, the Eau Claire. Point-specific MICP threshold pressure results, theoretical calculations based on a range of permeabilities, and column height calculations indicate that the internal Mount Simon mudstone and Eau Claire Shale are effective seals of CO2 in the Mount Simon reservoir.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49573787","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}
The final closure time of the Paleozoic ocean in the Eastern Tianshan is debated, and the geotectonics are still poorly constrained; hence, research on late Paleozoic igneous rocks has important implications for the evolutionary processes involved in this area’s tectonic history. However, limited attention has been given to the volcanic rocks in the late Paleozoic strata across the Eastern Tianshan because of their rarity and identification difficulty. This article focuses on the key site of an accretionary orogen in Central Asia, the Kalatage (Shaerhu)-Dananhu–Lop Nur area, to promote the study of tectonomagmatic evolution. The interbedded volcanic rock layers in late Paleozoic strata, including volcanic edifice deposits, are mainly rhyolitic volcanic, andesitic/dacitic, and basaltic rocks. These felsic, intermediate, and mafic rocks have zircon laser ablation ICP-MS U-Pb ages of 362.5–303 Ma. Geochemically, all samples have similar primitive mantle–normalized trace-element spider diagrams and chondrite-normalized rare earth element plots. The felsic and intermediate volcanic rocks are classified as I-type rocks and formed in a volcanic arc, and the mafic rocks belong to the tholeiite series and formed in island arc (earlier) and intraplate (later) settings. By the time the mafic rocks with intraplate basalt characteristics formed at 303±13 Ma, the Paleo-Asian Ocean had completely closed, and the region had entered the intraplate evolution stage. On the basis of other findings regarding the ages of igneous rocks and synthetic analysis, the northward subduction of the Paleo-Asian oceanic slab can preferably explain the relationship between the distinctive tectonic environment and the age variation trend in the study area. The process generated subduction-, collision- and postcollision-related magmatism from the Devonian to the late Carboniferous, and after 310 Ma, the Kalatage-Dananhu–Lop Nur area synchronously underwent a tectonic transition from subduction and collision to an intracontinental environment.
{"title":"Late Paleozoic Tectonomagmatic Evolution of the Eastern Tianshan, Northwest China: Insights from Geochronology and Geochemistry of Volcanic Rocks from the Dananhu–Lop Nur Area","authors":"Xinqi Yu, Xiu Liu, Jun Hu, Wei Li, Zongxiu Wang, Weifeng Xiao","doi":"10.1086/722751","DOIUrl":"https://doi.org/10.1086/722751","url":null,"abstract":"The final closure time of the Paleozoic ocean in the Eastern Tianshan is debated, and the geotectonics are still poorly constrained; hence, research on late Paleozoic igneous rocks has important implications for the evolutionary processes involved in this area’s tectonic history. However, limited attention has been given to the volcanic rocks in the late Paleozoic strata across the Eastern Tianshan because of their rarity and identification difficulty. This article focuses on the key site of an accretionary orogen in Central Asia, the Kalatage (Shaerhu)-Dananhu–Lop Nur area, to promote the study of tectonomagmatic evolution. The interbedded volcanic rock layers in late Paleozoic strata, including volcanic edifice deposits, are mainly rhyolitic volcanic, andesitic/dacitic, and basaltic rocks. These felsic, intermediate, and mafic rocks have zircon laser ablation ICP-MS U-Pb ages of 362.5–303 Ma. Geochemically, all samples have similar primitive mantle–normalized trace-element spider diagrams and chondrite-normalized rare earth element plots. The felsic and intermediate volcanic rocks are classified as I-type rocks and formed in a volcanic arc, and the mafic rocks belong to the tholeiite series and formed in island arc (earlier) and intraplate (later) settings. By the time the mafic rocks with intraplate basalt characteristics formed at 303±13 Ma, the Paleo-Asian Ocean had completely closed, and the region had entered the intraplate evolution stage. On the basis of other findings regarding the ages of igneous rocks and synthetic analysis, the northward subduction of the Paleo-Asian oceanic slab can preferably explain the relationship between the distinctive tectonic environment and the age variation trend in the study area. The process generated subduction-, collision- and postcollision-related magmatism from the Devonian to the late Carboniferous, and after 310 Ma, the Kalatage-Dananhu–Lop Nur area synchronously underwent a tectonic transition from subduction and collision to an intracontinental environment.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48160727","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}
In 2008, Pogue and Katz reported that on granitic exposures in the Cassia City of Rocks, Idaho, the larger pans (shallow flat-floored gnammas or rock basins with overhanging sidewalls) are developed and preserved high in the local relief. They related this aspect of pan distribution to duration of exposure. This working hypothesis is tested by examining pan distribution on granitic inselbergs located on northwestern Eyre Peninsula, in semiarid southern South Australia. Pans in numbers have developed on sensibly level surfaces and have been shaped by pools of standing water. The larger—and more complex—forms are situated high in the local relief, as concluded by Pogue and Katz, but where water supply is limited to direct precipitation, by contrast with lower sites, where rainfall is augmented by runoff.
2008年，Pogue和Katz报告说，在爱达荷州Cassia City of Rocks的花岗岩暴露中，较大的平底锅(浅层平坦的岩浆或具有突出侧壁的岩石盆地)在当地的浮雕中发育并保存得很高。他们将这方面的泛分布与暴露时间联系起来。通过对位于半干旱的南澳大利亚南部艾尔半岛西北部的花岗岩inselberg上的泛盆分布进行研究，验证了这一工作假设。大量的平底锅在相当平坦的表面上形成，并由静水池形成。根据Pogue和Katz的结论，更大、更复杂的形式位于当地地势较高的地方，但那里的供水仅限于直接降水，而在较低的地方，降雨由径流增加。
{"title":"Distribution and Morphology of the Bedrock Basins Known as Pans in a Granitic Inselberg Landscape","authors":"C. Twidale","doi":"10.1086/722288","DOIUrl":"https://doi.org/10.1086/722288","url":null,"abstract":"In 2008, Pogue and Katz reported that on granitic exposures in the Cassia City of Rocks, Idaho, the larger pans (shallow flat-floored gnammas or rock basins with overhanging sidewalls) are developed and preserved high in the local relief. They related this aspect of pan distribution to duration of exposure. This working hypothesis is tested by examining pan distribution on granitic inselbergs located on northwestern Eyre Peninsula, in semiarid southern South Australia. Pans in numbers have developed on sensibly level surfaces and have been shaped by pools of standing water. The larger—and more complex—forms are situated high in the local relief, as concluded by Pogue and Katz, but where water supply is limited to direct precipitation, by contrast with lower sites, where rainfall is augmented by runoff.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44427713","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}
Here we report geochronological, geochemical, and Sr-Nd-Hf isotopic data of a basic intrusion exposed in the Jiacha area within the Tethyan Himalaya, southern Tibet. The Jiacha dikes are composed mainly of mafic rocks (gabbros). In zircon U-Pb dating of Jiacha dikes samples, the weighted mean ages of magma emplacement were determined to be 241.5±4.2 to 245.5±3.3 Ma, showing a Middle Triassic magmatic event in the eastern part of the Tethyan Himalaya. The Jiacha dikes have relatively low MgO and total alkali (K2O+Na2O) contents but high TiO2 contents, exhibit weakly fractionated rare earth element (REE) patterns with slight depletions in light REEs and no obvious Eu anomalies, and show enrichment in high field strength elements and depletion in large-ion lithophile elements. Their initial 87Sr/86Sr ratios vary in the range 0.704250–0.704321, with a positive εNd(t = 243 Ma) of +3.07 to +3.67, and their initial 176Hf/177Hf ratios vary in the range 0.282872–0.283044, with a positive εHf(t = 243 Ma) of +8.53 to +14.45. We propose that the Jiacha dikes were derived from spinel lherzolites in the mantle with no crustal contamination and underwent fractional crystallization of clinopyroxene. Considering previous studies, we propose that Jiacha dikes represent oceanic crustal products of the early evolution of the Neo-Tethys, indicating that the ocean had already begun to open in the Middle Triassic.
{"title":"Late Paleozoic to Early Mesozoic Evolution of Neo-Tethys: Geochemical Evidence from Early Triassic Mafic Intrusive Rocks in the Tethyan Himalaya","authors":"Tong Zhou, Z. Kang, Ji‐Feng Xu, Feng Yang, Rui Wang, chun-xi Shan","doi":"10.1086/722390","DOIUrl":"https://doi.org/10.1086/722390","url":null,"abstract":"Here we report geochronological, geochemical, and Sr-Nd-Hf isotopic data of a basic intrusion exposed in the Jiacha area within the Tethyan Himalaya, southern Tibet. The Jiacha dikes are composed mainly of mafic rocks (gabbros). In zircon U-Pb dating of Jiacha dikes samples, the weighted mean ages of magma emplacement were determined to be 241.5±4.2 to 245.5±3.3 Ma, showing a Middle Triassic magmatic event in the eastern part of the Tethyan Himalaya. The Jiacha dikes have relatively low MgO and total alkali (K2O+Na2O) contents but high TiO2 contents, exhibit weakly fractionated rare earth element (REE) patterns with slight depletions in light REEs and no obvious Eu anomalies, and show enrichment in high field strength elements and depletion in large-ion lithophile elements. Their initial 87Sr/86Sr ratios vary in the range 0.704250–0.704321, with a positive εNd(t = 243 Ma) of +3.07 to +3.67, and their initial 176Hf/177Hf ratios vary in the range 0.282872–0.283044, with a positive εHf(t = 243 Ma) of +8.53 to +14.45. We propose that the Jiacha dikes were derived from spinel lherzolites in the mantle with no crustal contamination and underwent fractional crystallization of clinopyroxene. Considering previous studies, we propose that Jiacha dikes represent oceanic crustal products of the early evolution of the Neo-Tethys, indicating that the ocean had already begun to open in the Middle Triassic.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46668337","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}
Yihong Tian, L. Zeng, Li-E. Gao, Yaying Wang, K. Hou, Suo‐han Tang, Chunli Guo
An Early Jurassic (∼196 Ma, laser ablation multiple-collector ICP-MS zircon U-Pb ages) suite of diabase dikes and sills has been identified within the Late Triassic Langjiexue Group, part of the Tethyan sedimentary sequence that is composed of shale and fine-grained sandstone. More primitive rocks (MgO>8.0 wt%) from this suite are characterized by mid-ocean ridge basalt–like rare earth element distribution patterns and isotope (Sr and Nd) compositions, as well as relatively high contents of mantle-compatible elements (e.g., Cr, Ni, and Co), which indicates that they were derived from partial melting of depleted mantle. Younger (∼140 Ma) mafic magmatism in the region has been proposed to represent the initial breakup of the eastern Gondwana continent and the opening of the Indian Ocean. We propose that the ∼196 Ma diabases developed in a continental extension setting and represent the products of melting of depleted mantle within or on the margin of the Neo-Tethyan Ocean.
{"title":"Early Jurassic Mafic Magmatism in the Eastern Tethyan Himalaya, Southern Tibet","authors":"Yihong Tian, L. Zeng, Li-E. Gao, Yaying Wang, K. Hou, Suo‐han Tang, Chunli Guo","doi":"10.1086/721486","DOIUrl":"https://doi.org/10.1086/721486","url":null,"abstract":"An Early Jurassic (∼196 Ma, laser ablation multiple-collector ICP-MS zircon U-Pb ages) suite of diabase dikes and sills has been identified within the Late Triassic Langjiexue Group, part of the Tethyan sedimentary sequence that is composed of shale and fine-grained sandstone. More primitive rocks (MgO>8.0 wt%) from this suite are characterized by mid-ocean ridge basalt–like rare earth element distribution patterns and isotope (Sr and Nd) compositions, as well as relatively high contents of mantle-compatible elements (e.g., Cr, Ni, and Co), which indicates that they were derived from partial melting of depleted mantle. Younger (∼140 Ma) mafic magmatism in the region has been proposed to represent the initial breakup of the eastern Gondwana continent and the opening of the Indian Ocean. We propose that the ∼196 Ma diabases developed in a continental extension setting and represent the products of melting of depleted mantle within or on the margin of the Neo-Tethyan Ocean.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45396496","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}
The Tennessee River, a primary drainage of the southern Appalachians and significant sediment source for the Gulf of Mexico, is generally considered to be the product of captures that rerouted the river from a more direct gulfward course. Sedimentary and genetic evidence indicates that a paleo-Tennessee flowed into the Mobile Basin through the late Miocene, although alternate models propose other redirections of the river. We constrain the river course’s age by dating terraces near Pickwick, Tennessee, with cosmogenic 26Al/10Be isochron burial dating. We find that the river’s present path dates to at least the early Pliocene.
{"title":"The Pliocene-to-Present Course of the Tennessee River","authors":"W. Odom, D. Granger","doi":"10.1086/719951","DOIUrl":"https://doi.org/10.1086/719951","url":null,"abstract":"The Tennessee River, a primary drainage of the southern Appalachians and significant sediment source for the Gulf of Mexico, is generally considered to be the product of captures that rerouted the river from a more direct gulfward course. Sedimentary and genetic evidence indicates that a paleo-Tennessee flowed into the Mobile Basin through the late Miocene, although alternate models propose other redirections of the river. We constrain the river course’s age by dating terraces near Pickwick, Tennessee, with cosmogenic 26Al/10Be isochron burial dating. We find that the river’s present path dates to at least the early Pliocene.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2022-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45083601","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}
The Eocene Tallahatta Formation forms part of the Tallahatta-Winona aquifer, which is part of the lower Claiborne confining unit of the Mississippi Embayment. A thorough understanding of the distribution of natural resources within the Tallahatta is limited by a lack of detailed studies at the outcrop and pore scales. In this study, we integrate particle size, petrographic, lithofacies, and geochemical analyses to interpret depositional environments, sequence stratigraphy, provenance, and diagenetic history from outcrops in Grenada County, Mississippi. Lithofacies include unprotected sand flat, tidal channel, open tidal mudflat, protected tidal flat, lower and middle shoreface, offshore transition, and offshore shelf settings. Lithofacies associations indicate that the Tallahatta consists of at least two parasequences within a falling stage systems tract (FSST). This is the first report on FSST strata from the Tallahatta Formation. Petrographic and geochemical results show that sediments were sourced from Precambrian Laurentian basement, recycled Appalachian basin sediment, and the Appalachian hinterland. Upsection changes in geochemistry represent an increase in contributions from recycled Appalachian basin sediment and progressive weathering of Acadian orogeny elements. Geochemistry also suggests that potentially economically important Ti-rich minerals are concentrated in tidal flat facies and scarce in shoreface facies. Primary porosity and bioturbation exert the greatest influence on the high porosity within many lithofacies. Early diagenesis also included detrital clay coating of framework grains, deposition of fecal pellets, minor chemical weathering, and hematite precipitation. Fecal pellets were altered to glauconite and opal cement was precipitated shortly after deposition or during early burial. Shrinkage of fecal pellets during glauconitization introduced minor moldic porosity. Limited burial produced minor physical compaction and only slightly reduced porosity. Abundant hematite precipitation during exhumation greatly decreased porosity locally.
{"title":"Sedimentological and Geochemical Analysis of the Eocene Tallahatta Formation in Northern Mississippi, USA","authors":"Husamaldeen Zubi, B. Platt, Jennifer N. Gifford","doi":"10.1086/720183","DOIUrl":"https://doi.org/10.1086/720183","url":null,"abstract":"The Eocene Tallahatta Formation forms part of the Tallahatta-Winona aquifer, which is part of the lower Claiborne confining unit of the Mississippi Embayment. A thorough understanding of the distribution of natural resources within the Tallahatta is limited by a lack of detailed studies at the outcrop and pore scales. In this study, we integrate particle size, petrographic, lithofacies, and geochemical analyses to interpret depositional environments, sequence stratigraphy, provenance, and diagenetic history from outcrops in Grenada County, Mississippi. Lithofacies include unprotected sand flat, tidal channel, open tidal mudflat, protected tidal flat, lower and middle shoreface, offshore transition, and offshore shelf settings. Lithofacies associations indicate that the Tallahatta consists of at least two parasequences within a falling stage systems tract (FSST). This is the first report on FSST strata from the Tallahatta Formation. Petrographic and geochemical results show that sediments were sourced from Precambrian Laurentian basement, recycled Appalachian basin sediment, and the Appalachian hinterland. Upsection changes in geochemistry represent an increase in contributions from recycled Appalachian basin sediment and progressive weathering of Acadian orogeny elements. Geochemistry also suggests that potentially economically important Ti-rich minerals are concentrated in tidal flat facies and scarce in shoreface facies. Primary porosity and bioturbation exert the greatest influence on the high porosity within many lithofacies. Early diagenesis also included detrital clay coating of framework grains, deposition of fecal pellets, minor chemical weathering, and hematite precipitation. Fecal pellets were altered to glauconite and opal cement was precipitated shortly after deposition or during early burial. Shrinkage of fecal pellets during glauconitization introduced minor moldic porosity. Limited burial produced minor physical compaction and only slightly reduced porosity. Abundant hematite precipitation during exhumation greatly decreased porosity locally.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2022-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46393402","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}
During the Cretaceous, the concurrence of changing paleoceanographic and paleoclimatic conditions, coupled with variations in eustatic sea level, contributed to episodes of globally widespread deposition of organic matter (OM)–rich marine sediments collectively termed oceanic anoxic events (OAEs). Here, we aim to investigate the response of a lower Aptian hemipelagic sequence from the northeastern Iberian margin in the context of OAE1a. Stable–carbon isotope (δ13Corg) data are consistent with the pattern reported for the end of carbon isotope segment C5 within OAE1a. Moreover, high sediment accumulation rates (bulk: ∼37.13 cm/ky, wet: ∼63.29 cm/ky) permit the establishment of refined details suitable for precise chemostratigraphic correlations. We recognized three distinct lithologic units. Within unit 1, variable pulses of fluvial fluxes explain the alternating lithology, with limestones depicting the least terrestrially influenced end member and marlstones representing episodes of highest terrigenous input. In the ensuing marlstone-dominated unit 2 interval, results show relatively higher OM, redox-sensitive trace elements (RSTEs), P, Fe, Al, Si, and Ti values than before, thus suggesting an increase in runoff with quasi-permanent eutrophic surface waters and continuous oxygen-deprived conditions, but without a fully anoxic phase, as benthic fauna, while relatively reduced, are present throughout. Unit 3 registers limestones impoverished in OM, Al, Si, Ti, P, and Fe, with a lower relative proportion of autochthonous to allochthonous OM, indicating a reduction in runoff and surface water fertility linked to drier climate conditions. Simultaneous changes in microfacies, with coarser packed biosparites, reduced planktonic foraminifera, and an increase in benthic taxa, imply shallowing of the basin, similar to that reported for sequences in the neighboring Basque-Cantabrian Basin synchronous with the negative δ13Corg shift heralding the end of segment C5.
{"title":"Demise of Organic Matter–Rich Facies and Changing Paleoenvironmental Conditions Associated with the End of Carbon Isotope Segment C5 of Oceanic Anoxic Event 1a in the North and Northeastern Iberian Peninsula","authors":"J. Socorro, F. Maurrasse","doi":"10.1086/718834","DOIUrl":"https://doi.org/10.1086/718834","url":null,"abstract":"During the Cretaceous, the concurrence of changing paleoceanographic and paleoclimatic conditions, coupled with variations in eustatic sea level, contributed to episodes of globally widespread deposition of organic matter (OM)–rich marine sediments collectively termed oceanic anoxic events (OAEs). Here, we aim to investigate the response of a lower Aptian hemipelagic sequence from the northeastern Iberian margin in the context of OAE1a. Stable–carbon isotope (δ13Corg) data are consistent with the pattern reported for the end of carbon isotope segment C5 within OAE1a. Moreover, high sediment accumulation rates (bulk: ∼37.13 cm/ky, wet: ∼63.29 cm/ky) permit the establishment of refined details suitable for precise chemostratigraphic correlations. We recognized three distinct lithologic units. Within unit 1, variable pulses of fluvial fluxes explain the alternating lithology, with limestones depicting the least terrestrially influenced end member and marlstones representing episodes of highest terrigenous input. In the ensuing marlstone-dominated unit 2 interval, results show relatively higher OM, redox-sensitive trace elements (RSTEs), P, Fe, Al, Si, and Ti values than before, thus suggesting an increase in runoff with quasi-permanent eutrophic surface waters and continuous oxygen-deprived conditions, but without a fully anoxic phase, as benthic fauna, while relatively reduced, are present throughout. Unit 3 registers limestones impoverished in OM, Al, Si, Ti, P, and Fe, with a lower relative proportion of autochthonous to allochthonous OM, indicating a reduction in runoff and surface water fertility linked to drier climate conditions. Simultaneous changes in microfacies, with coarser packed biosparites, reduced planktonic foraminifera, and an increase in benthic taxa, imply shallowing of the basin, similar to that reported for sequences in the neighboring Basque-Cantabrian Basin synchronous with the negative δ13Corg shift heralding the end of segment C5.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2022-02-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45682416","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}
M. Azer, A. A. Surour, A. Madani, M. Ren, A. A. El-fatah
In this work, we present new field observations, geochemical data, mineral chemistry, and interpretations from the late Neoproterozoic El-Bakriya mafic intrusion in the central Eastern Desert of Egypt to enhance our knowledge and understanding of the formation of the juvenile continental crust in the Arabian-Nubian Shield (ANS). The field relationships indicate that the gabbroic intrusion is younger than the syntectonic granodiorite but older than the postcollisional El-Bakriya granites. The El-Bakriya mafic intrusion is neither deformed nor metamorphosed and preserves typical primary mineralogical features and texture. The intrusion is composed of three main varieties of gabbro with prominent gradational contacts, namely, troctolite, olivine gabbro, and hornblende gabbro. Both megascopic and imperceptible layering is recognized in the intrusion. El-Bakriya gabbros are characterized by an enrichment in large-ion lithophile elements relative to high field strength elements and a noticeable alkaline affinity owing to fractional crystallization. Different varieties of gabbro show continuous linear composition trends in all major- and trace-element variation diagrams, indicating a cogenetic origin source. The initial magma was an alkaline mafic melt that derived from the mantle with minor crustal assimilation before its emplacement in the upper crust in a stable postcollisional cratonic setting. Mineralogical and geochemical data are combined evidence of an asthenosphere upwelling and lithosphere delamination scenario for the evolution of the El-Bakriya mafic intrusion. On the basis of geothermobarometric calculations, the gabbroic rocks crystallized at a pressure of 5–6.8 kbar and a temperature of 750°C–900°C. The petrological, geochemical, and mineralogical characteristics of the El-Bakriya mafic intrusion are akin to those of the Egyptian postcollisional younger gabbros. These gabbros are totally different from the metamorphosed oceanic and arc-related gabbros, which constitute the earlier juvenile crustal components that formed during the development of the ANS in the late Neoproterozoic.
{"title":"Mineralogical and Geochemical Constraints on the Postcollisional Mafic Magmatism in the Arabian-Nubian Shield: An Example from the El-Bakriya Area, Central Eastern Desert, Egypt","authors":"M. Azer, A. A. Surour, A. Madani, M. Ren, A. A. El-fatah","doi":"10.1086/719130","DOIUrl":"https://doi.org/10.1086/719130","url":null,"abstract":"In this work, we present new field observations, geochemical data, mineral chemistry, and interpretations from the late Neoproterozoic El-Bakriya mafic intrusion in the central Eastern Desert of Egypt to enhance our knowledge and understanding of the formation of the juvenile continental crust in the Arabian-Nubian Shield (ANS). The field relationships indicate that the gabbroic intrusion is younger than the syntectonic granodiorite but older than the postcollisional El-Bakriya granites. The El-Bakriya mafic intrusion is neither deformed nor metamorphosed and preserves typical primary mineralogical features and texture. The intrusion is composed of three main varieties of gabbro with prominent gradational contacts, namely, troctolite, olivine gabbro, and hornblende gabbro. Both megascopic and imperceptible layering is recognized in the intrusion. El-Bakriya gabbros are characterized by an enrichment in large-ion lithophile elements relative to high field strength elements and a noticeable alkaline affinity owing to fractional crystallization. Different varieties of gabbro show continuous linear composition trends in all major- and trace-element variation diagrams, indicating a cogenetic origin source. The initial magma was an alkaline mafic melt that derived from the mantle with minor crustal assimilation before its emplacement in the upper crust in a stable postcollisional cratonic setting. Mineralogical and geochemical data are combined evidence of an asthenosphere upwelling and lithosphere delamination scenario for the evolution of the El-Bakriya mafic intrusion. On the basis of geothermobarometric calculations, the gabbroic rocks crystallized at a pressure of 5–6.8 kbar and a temperature of 750°C–900°C. The petrological, geochemical, and mineralogical characteristics of the El-Bakriya mafic intrusion are akin to those of the Egyptian postcollisional younger gabbros. These gabbros are totally different from the metamorphosed oceanic and arc-related gabbros, which constitute the earlier juvenile crustal components that formed during the development of the ANS in the late Neoproterozoic.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2022-02-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44656940","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}
M. Ghoneim, A. Abdel-Karim, M. A. Anbar, Azza Nageib, S. El-shafei
Postcollisional magmatism is widely distributed in southern Sinai, the extreme northern part of the Neoproterozoic Arabian-Nubian Shield. This article deals with mineral and whole-rock chemistry of postcollisional syenogranites and associated volcanic rocks from three localities in southern Sinai: Iqna Sharay’a, Rusis-Rutig, and Um Shuki–Abu Khusheib. The studied volcanic rocks have compositions between rhyolites and dacites with minor andesite. The whole-rock chemical compositions of the investigated rock types together with the biotite chemistry are consistent with high-K calc-alkaline and alkaline/peralkaline magma. The studied syenogranites and most volcanic rocks are more akin to anorogenic alkaline within-plate environments. Only a few samples of Um Shuki–Abu Khusheib volcanic rocks display some characteristics of orogenic arc-type environments. The high-K calc-alkaline to alkaline affinity and the relative enrichments in large ion lithophile elements (especially K, Rb, and Ba) and light rare earth elements together with a significant negative Eu anomaly imply that the studied granites and volcanic rocks were generated by partial melting of lower to middle crustal materials accompanied by the underplated mafic magma produced in the lithospheric mantle (convective diffusion). This convective diffusion describes a specific scenario of active chemical interaction between mafic and silicic magmas in order to explain formation of voluminous high-K calc-alkaline and alkaline/peralkaline magmatism in postcollisional tectonic environments. The enhanced temperatures of A-type silicic magmas of more than 1000°C suggest that magma generation could occur even at the depth of the uppermost lithospheric mantle.
{"title":"Petrogenesis of Postcollisional High-K Calc-Alkaline and Alkaline Magmatism in Southern Sinai, Egypt: The Role of Crustal Anatexis Combined with Convective Diffusion","authors":"M. Ghoneim, A. Abdel-Karim, M. A. Anbar, Azza Nageib, S. El-shafei","doi":"10.1086/718832","DOIUrl":"https://doi.org/10.1086/718832","url":null,"abstract":"Postcollisional magmatism is widely distributed in southern Sinai, the extreme northern part of the Neoproterozoic Arabian-Nubian Shield. This article deals with mineral and whole-rock chemistry of postcollisional syenogranites and associated volcanic rocks from three localities in southern Sinai: Iqna Sharay’a, Rusis-Rutig, and Um Shuki–Abu Khusheib. The studied volcanic rocks have compositions between rhyolites and dacites with minor andesite. The whole-rock chemical compositions of the investigated rock types together with the biotite chemistry are consistent with high-K calc-alkaline and alkaline/peralkaline magma. The studied syenogranites and most volcanic rocks are more akin to anorogenic alkaline within-plate environments. Only a few samples of Um Shuki–Abu Khusheib volcanic rocks display some characteristics of orogenic arc-type environments. The high-K calc-alkaline to alkaline affinity and the relative enrichments in large ion lithophile elements (especially K, Rb, and Ba) and light rare earth elements together with a significant negative Eu anomaly imply that the studied granites and volcanic rocks were generated by partial melting of lower to middle crustal materials accompanied by the underplated mafic magma produced in the lithospheric mantle (convective diffusion). This convective diffusion describes a specific scenario of active chemical interaction between mafic and silicic magmas in order to explain formation of voluminous high-K calc-alkaline and alkaline/peralkaline magmatism in postcollisional tectonic environments. The enhanced temperatures of A-type silicic magmas of more than 1000°C suggest that magma generation could occur even at the depth of the uppermost lithospheric mantle.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2022-02-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46856057","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}
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