In Anatolia, the northern branch of Neotethys is represented by Izmir-Ankara-Erzincan (IAE) Ocean, whose fragments and associated continental entities are preserved in the IAE Suture. However, the traces of this northerly located ocean are not solely bound to the IAE Suture, but can also be found further to the south. The Mersin Mélange, situated in southern Turkey, is such a place that preserves the southerly transported remnants of the northern Neotethys. The Mersin Mélange essentially displays block-in-matrix features, with blocks/slices of different age and lithological characteristics embedded in a clastic matrix. Within the mélange, the Degirmenocagi region consists of a volcano-sedimentary sequence of middle Carnian age, which is characterized by lavas and tuffites interbedded with pelagic sedimentary lithologies. The lavas are chemically of basaltic/basaltic-andesitic composition, whereas the tuffites are of rhyolitic composition. Both lavas and tuffites display negative Nb anomalies, suggesting the involvement of subduction-related components. The high Zr/Nb and low Nb/Yb ratios (compared with normal mid-ocean ridge basalt [N-MORB]) imply a variably depleted mantle source, which has experienced previous melt extraction. The ratio-based melting systematics reflects melt generation largely dominated by spinel-facies melts. The overall geological and geochemical characteristics of the Degirmenocagi sequence suggest an oceanic backarc setting during the Carnian, which may have developed by the rifting of the Sorgun Arc. Although this new finding shows that the Triassic intraoceanic subduction is not uncommon in the Neotethys, it also strengthens a pre-Liassic opening of the northern domain (i.e., the IAE Ocean) and may further explain the longevity of the Middle–Late Triassic intraoceanic subduction in the northern Neotethys.
{"title":"Carnian (Upper Triassic) Lavas and Tuffites from the Mersin Mélange: Evidence for Intraoceanic Arc Rifting in the Northern Neotethys","authors":"Kaan Sayıt, Yavuz Bedi, U. K. Tekin, C. Okuyucu","doi":"10.1086/711000","DOIUrl":"https://doi.org/10.1086/711000","url":null,"abstract":"In Anatolia, the northern branch of Neotethys is represented by Izmir-Ankara-Erzincan (IAE) Ocean, whose fragments and associated continental entities are preserved in the IAE Suture. However, the traces of this northerly located ocean are not solely bound to the IAE Suture, but can also be found further to the south. The Mersin Mélange, situated in southern Turkey, is such a place that preserves the southerly transported remnants of the northern Neotethys. The Mersin Mélange essentially displays block-in-matrix features, with blocks/slices of different age and lithological characteristics embedded in a clastic matrix. Within the mélange, the Degirmenocagi region consists of a volcano-sedimentary sequence of middle Carnian age, which is characterized by lavas and tuffites interbedded with pelagic sedimentary lithologies. The lavas are chemically of basaltic/basaltic-andesitic composition, whereas the tuffites are of rhyolitic composition. Both lavas and tuffites display negative Nb anomalies, suggesting the involvement of subduction-related components. The high Zr/Nb and low Nb/Yb ratios (compared with normal mid-ocean ridge basalt [N-MORB]) imply a variably depleted mantle source, which has experienced previous melt extraction. The ratio-based melting systematics reflects melt generation largely dominated by spinel-facies melts. The overall geological and geochemical characteristics of the Degirmenocagi sequence suggest an oceanic backarc setting during the Carnian, which may have developed by the rifting of the Sorgun Arc. Although this new finding shows that the Triassic intraoceanic subduction is not uncommon in the Neotethys, it also strengthens a pre-Liassic opening of the northern domain (i.e., the IAE Ocean) and may further explain the longevity of the Middle–Late Triassic intraoceanic subduction in the northern Neotethys.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":"128 1","pages":"445 - 464"},"PeriodicalIF":1.8,"publicationDate":"2020-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1086/711000","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43101002","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}
Alfred Anderson, professor of geology at the University of Chicago from 1968, passed away on January 15, 2020. I met Fred in October 1982 when I first arrived as a postdocworkingwith Fred Ziegler. I beganmy postdoc before I had completed thefinal version of my dissertation. One of the components that I needed to complete was the photographing of thin sections. FredAndersonvery generously gave me access to his microscope—as he recalled in his acceptance speech of the Bowen Award in 2001— thiswas his startup package of $6.5Kwhenhe joined the faculty in 1968. It is a lovely microscope with an attached camera, and he also provided the film that I used to complete my dissertation. This simple, generous act completely typified Fred. He was a quiet, generous, self-effacing person who contributed broadly across volcanology and petrology to graduate, undergraduate, and continuing education students, to the Department of the Geophysical Sciences, and to the college. Fred was initially coeditor with BobNewton, but he later served as editor in chief of the Journal of Geology from 1984 to 2008. This is no small task, and Fred worked tirelessly and guided the journal with a steady hand for those 24 years. Fred mentored many students and postdocs, including in no particular order Guil Gualda, Dork Sahagian, Christine Skirius, Fanqiong Lu, Brett Peppard, Joe Dufek, Paul Wallace, and Stan Williams, among many others. They have gone on to successful careers, which I am sure are due in no small measure to Fred’s generous mentoring and continued support. Fredwas a gentle giantwhose acute observations, whether of hourglass bubbles in volcanic glasses or of volatile budgets in magmas, led to deep insights into volcanic eruptions and emplacement of granites. Fred received the Norman L. Bowen Award, the top award in volcanology in theworld, from the American Geophysical Union in 2001. Everyone should read the citation and Fred’s acceptance comments because they beautifully convey the
阿尔弗雷德·安德森，1968年起任芝加哥大学地质学教授，于2020年1月15日去世。1982年10月，我第一次和弗雷德·齐格勒(Fred Ziegler)一起做博士后，当时我遇到了弗雷德。我在完成论文的定稿之前就开始了我的博士后研究。我需要完成的一个组成部分是拍摄薄片。弗雷德·安德森非常慷慨地让我使用了他的显微镜——正如他在2001年鲍恩奖的获奖感言中回忆的那样——这是他1968年加入该学院时的启动资金，当时他的启动资金为6.5万美元。这是一个可爱的显微镜，附带一个相机，他还提供了我用来完成我的论文的胶卷。这个简单、慷慨的举动完全是弗雷德的典型。他是一个安静、慷慨、谦逊的人，在火山学和岩石学领域为研究生、本科生和继续教育的学生、地球物理科学系和学院做出了广泛的贡献。弗雷德最初是鲍勃·牛顿的共同编辑，但他后来在1984年至2008年期间担任《地质学杂志》的主编。这不是一项简单的任务，在那24年里，弗雷德不知疲倦地工作，坚定地指导着这本杂志。弗雷德指导了许多学生和博士后，包括Guil Gualda, Dork Sahagian, Christine Skirius, Fanqiong Lu, Brett Peppard, Joe Dufek, Paul Wallace和Stan Williams等等。他们都走上了成功的职业生涯，我相信这在很大程度上要归功于弗雷德慷慨的指导和持续的支持。弗雷德是一个温和的巨人，他敏锐的观察，无论是火山玻璃中的沙漏气泡还是岩浆中不稳定的平衡，都使他对火山爆发和花岗岩的就位有了深刻的认识。2001年，弗雷德获得了美国地球物理学会颁发的世界火山学最高奖项——诺曼·l·鲍恩奖。每个人都应该阅读引用和弗雷德的接受意见，因为他们很好地传达了
{"title":"Memorial to Alfred T. Anderson","authors":"D. Rowley","doi":"10.1086/709833","DOIUrl":"https://doi.org/10.1086/709833","url":null,"abstract":"Alfred Anderson, professor of geology at the University of Chicago from 1968, passed away on January 15, 2020. I met Fred in October 1982 when I first arrived as a postdocworkingwith Fred Ziegler. I beganmy postdoc before I had completed thefinal version of my dissertation. One of the components that I needed to complete was the photographing of thin sections. FredAndersonvery generously gave me access to his microscope—as he recalled in his acceptance speech of the Bowen Award in 2001— thiswas his startup package of $6.5Kwhenhe joined the faculty in 1968. It is a lovely microscope with an attached camera, and he also provided the film that I used to complete my dissertation. This simple, generous act completely typified Fred. He was a quiet, generous, self-effacing person who contributed broadly across volcanology and petrology to graduate, undergraduate, and continuing education students, to the Department of the Geophysical Sciences, and to the college. Fred was initially coeditor with BobNewton, but he later served as editor in chief of the Journal of Geology from 1984 to 2008. This is no small task, and Fred worked tirelessly and guided the journal with a steady hand for those 24 years. Fred mentored many students and postdocs, including in no particular order Guil Gualda, Dork Sahagian, Christine Skirius, Fanqiong Lu, Brett Peppard, Joe Dufek, Paul Wallace, and Stan Williams, among many others. They have gone on to successful careers, which I am sure are due in no small measure to Fred’s generous mentoring and continued support. Fredwas a gentle giantwhose acute observations, whether of hourglass bubbles in volcanic glasses or of volatile budgets in magmas, led to deep insights into volcanic eruptions and emplacement of granites. Fred received the Norman L. Bowen Award, the top award in volcanology in theworld, from the American Geophysical Union in 2001. Everyone should read the citation and Fred’s acceptance comments because they beautifully convey the","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":"128 1","pages":"319 - 323"},"PeriodicalIF":1.8,"publicationDate":"2020-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1086/709833","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44986693","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}
Jennifer N. Gifford, B. Platt, L. D. Yarbrough, A. O’Reilly, Mohammed Al Harthy
The Chesterian (Mississippian) Hartselle Sandstone is a tar sand exposed in the Black Warrior Basin and southern Appalachian fold belt in northern Mississippi and Alabama. Previous studies disagree about the delivery direction and relative contributions of sediment from the cratonic interior, the Appalachians, and the Ouachitas. The goal of this research is to investigate lateral trends in sedimentary and geochemical properties to provide new details about the provenance of the Hartselle. Samples were collected along a west-to-east transect and analyzed using petrography, X-ray fluorescence (XRF) geochemistry, and U-Pb detrital zircon (DZ) geochronology. Point counting indicated a major cratonic interior source with a minor recycled orogen signal. Sillimanite in the easternmost sample narrows down the potential Appalachian sources to areas of high-grade metamorphism. Petrographic observations suggest both western and eastern sources. The XRF results showed high concentrations of Ti and Mo in the westernmost sample, suggestive of a nearby terrigenous source. All of the samples had similar U-Pb DZ age distributions except for the easternmost sample, which had statistically higher proportions of Paleozoic- and Archean-aged grains (Kolmogorov-Smirnov test: p < .02). For the first time, Eoarchean and Paleoarchean grains were found in the Hartselle, indicating a likely sediment source from the Minnesota River Valley gneisses of the Superior Craton prior to Grenvillian overprinting. Based on integration of all data, we conclude that a large fluvial system draining the continental interior provided a substantial volume of sediment from the northwest. At the same time, a more dispersed drainage basin associated with the Appalachian front contributed recycled orogenic material from the northeast.
{"title":"Integrating Petrography, X-Ray Fluorescence, and U-Pb Detrital Zircon Geochronology to Interpret Provenance of the Mississippian Hartselle Sandstone, USA","authors":"Jennifer N. Gifford, B. Platt, L. D. Yarbrough, A. O’Reilly, Mohammed Al Harthy","doi":"10.1086/709700","DOIUrl":"https://doi.org/10.1086/709700","url":null,"abstract":"The Chesterian (Mississippian) Hartselle Sandstone is a tar sand exposed in the Black Warrior Basin and southern Appalachian fold belt in northern Mississippi and Alabama. Previous studies disagree about the delivery direction and relative contributions of sediment from the cratonic interior, the Appalachians, and the Ouachitas. The goal of this research is to investigate lateral trends in sedimentary and geochemical properties to provide new details about the provenance of the Hartselle. Samples were collected along a west-to-east transect and analyzed using petrography, X-ray fluorescence (XRF) geochemistry, and U-Pb detrital zircon (DZ) geochronology. Point counting indicated a major cratonic interior source with a minor recycled orogen signal. Sillimanite in the easternmost sample narrows down the potential Appalachian sources to areas of high-grade metamorphism. Petrographic observations suggest both western and eastern sources. The XRF results showed high concentrations of Ti and Mo in the westernmost sample, suggestive of a nearby terrigenous source. All of the samples had similar U-Pb DZ age distributions except for the easternmost sample, which had statistically higher proportions of Paleozoic- and Archean-aged grains (Kolmogorov-Smirnov test: p < .02). For the first time, Eoarchean and Paleoarchean grains were found in the Hartselle, indicating a likely sediment source from the Minnesota River Valley gneisses of the Superior Craton prior to Grenvillian overprinting. Based on integration of all data, we conclude that a large fluvial system draining the continental interior provided a substantial volume of sediment from the northwest. At the same time, a more dispersed drainage basin associated with the Appalachian front contributed recycled orogenic material from the northeast.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":"128 1","pages":"337 - 370"},"PeriodicalIF":1.8,"publicationDate":"2020-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1086/709700","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44903727","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}
Deschamps and Mottez (hereafter DM) argue that the Gauss-Matuyama terrestrial magnetic field reversal may have left a vanishing main dipole moment to the field for a time of order 10,000 years. They say this may have allowed an enhanced cosmic ray flux, boosting the effect we proposed in Melott and Thomas (2019). We point out that the bulk of the cosmic ray flux from a nearby supernova should be too energetic, up to a million times more energetic than the limits of deflection by the terrestrial magnetic field. In fact, only those highly energetic ones will directly reach the troposphere, relevant for cloud-to-ground lightning. From Cosmic Explosions to Terrestrial Fires?: A Discussion. F. Deschamps and F. Mottez. J. Geology 128, online ahead of print. (2020) From Cosmic Explosions to Terrestrial Fires?: A Reply A.L. Melott and B.C. Thomas. J. Geology 128, online ahead of print. (2020) From cosmic explosions to terrestrial fires? (A.L. Melott and B.C. Thomas) Journal of Geology, 127, 475-481 10.1086/703418 (2019) [arXiv:1903.01501]
{"title":"From Cosmic Explosions to Terrestrial Fires? A Reply","authors":"A. Melott, B. Thomas","doi":"10.1086/709751","DOIUrl":"https://doi.org/10.1086/709751","url":null,"abstract":"Deschamps and Mottez (hereafter DM) argue that the Gauss-Matuyama terrestrial magnetic field reversal may have left a vanishing main dipole moment to the field for a time of order 10,000 years. They say this may have allowed an enhanced cosmic ray flux, boosting the effect we proposed in Melott and Thomas (2019). We point out that the bulk of the cosmic ray flux from a nearby supernova should be too energetic, up to a million times more energetic than the limits of deflection by the terrestrial magnetic field. In fact, only those highly energetic ones will directly reach the troposphere, relevant for cloud-to-ground lightning. From Cosmic Explosions to Terrestrial Fires?: A Discussion. F. Deschamps and F. Mottez. J. Geology 128, online ahead of print. (2020) From Cosmic Explosions to Terrestrial Fires?: A Reply A.L. Melott and B.C. Thomas. J. Geology 128, online ahead of print. (2020) From cosmic explosions to terrestrial fires? (A.L. Melott and B.C. Thomas) Journal of Geology, 127, 475-481 10.1086/703418 (2019) [arXiv:1903.01501]","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":"128 1","pages":"393 - 393"},"PeriodicalIF":1.8,"publicationDate":"2020-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1086/709751","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46053455","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}
Several observational studies have revealed the explosion of a supernova in the early Pleistocene at about 100 pc from the Solar System. The proof of this explosion is based on the signature associated with Fe deposits in Earth’s sediments and on the Moon’s regolith. The supernova remnant was the cause of additional input of galactic cosmic rays (GCRs) in the Solar System. Their propagation from the supernova remnant to Earth and the effects of the associated cascades of secondary particles triggered by their interactionwith Earth’s atmosphere were analyzed by Melott and Thomas (2019). According to their study and previous works cited in their article, high-energy cosmic rays (above 1 TeV) caused a 20-fold increase of irradiation by muons on Earth’s surface and on the ocean and an order of magnitude increase of the atmospheric ionization that could have lasted more than 1,000 years. The increase in irradiation could have contributed to a minor mass extinction in the Pliocene–Pleistocene transition, 2.6 My ago. Melott and Thomas (2019) analyzed the climatic consequences of the increased atmospheric ionization leading tomore frequent lightning and, therefore, to an increase in nitrate deposition and in wildfires. Increased wildfires, evidenced by an increase in soot and carbon deposits over the relevant period, would have contributed to the transition from forest to savanna in northeastern Africa, long argued to have been a factor in the evolution of hominin bipedalism.
{"title":"From Cosmic Explosions to Terrestrial Fires? A Discussion","authors":"F. Deschamps, F. Mottez","doi":"10.1086/709750","DOIUrl":"https://doi.org/10.1086/709750","url":null,"abstract":"Several observational studies have revealed the explosion of a supernova in the early Pleistocene at about 100 pc from the Solar System. The proof of this explosion is based on the signature associated with Fe deposits in Earth’s sediments and on the Moon’s regolith. The supernova remnant was the cause of additional input of galactic cosmic rays (GCRs) in the Solar System. Their propagation from the supernova remnant to Earth and the effects of the associated cascades of secondary particles triggered by their interactionwith Earth’s atmosphere were analyzed by Melott and Thomas (2019). According to their study and previous works cited in their article, high-energy cosmic rays (above 1 TeV) caused a 20-fold increase of irradiation by muons on Earth’s surface and on the ocean and an order of magnitude increase of the atmospheric ionization that could have lasted more than 1,000 years. The increase in irradiation could have contributed to a minor mass extinction in the Pliocene–Pleistocene transition, 2.6 My ago. Melott and Thomas (2019) analyzed the climatic consequences of the increased atmospheric ionization leading tomore frequent lightning and, therefore, to an increase in nitrate deposition and in wildfires. Increased wildfires, evidenced by an increase in soot and carbon deposits over the relevant period, would have contributed to the transition from forest to savanna in northeastern Africa, long argued to have been a factor in the evolution of hominin bipedalism.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":"128 1","pages":"389 - 391"},"PeriodicalIF":1.8,"publicationDate":"2020-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1086/709750","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41347291","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}
Atef M. Kasem, S. Wise, M. Faris, S. Farouk, E. Zahran
Calcareous nannofossil, carbonate content, and δ18O and δ13C data were utilized to reveal the nature of the Paleocene-Eocene (P-E) boundary at the Gunnah section, Western Desert, Egypt. The uppermost Tarawan Formation (Fm.), Esna Fm., and the lowermost, Farafra Fm., were included in this study. Lithostratigraphically, the Esna Fm. was subdivided into the Hanadi, Dababiya Quarry, and Mahmiya Members. Three calcareous nannofossil zones (NP7/8, NP9, and NP10) and four subzones (NP9a, NP9b, NP10a, and NP10b) were recognized. The biostratigraphic significances of calcareoust nannofossil bioevents associated with the P-E boundary at the study section were discussed. The base of the Eocene was placed at the base of the Dababiya Quarry Member in coincidence with the base of subzone NP9b, which is coincident with the LOs of Rhomboaster cuspis, R. calcitrapa, R. bitrifidia, Pontosphaera pulchra, and Zygrhablithus bijugatus. However, Discoaster araneus first occurred about 3 m below the base of subzone NP9b. The global decreases of the δ13C and δ18O values and carbonate contents across the P-E boundary were documented in the Gunnah section, which represents one of the most expanded and complete P-E sequences in Egypt.
{"title":"Calcareous Nannofossil Stratigraphy across the Paleocene-Eocene Transition at the Gunnah Section, Farafra Oasis, Western Desert, Egypt","authors":"Atef M. Kasem, S. Wise, M. Faris, S. Farouk, E. Zahran","doi":"10.1086/709359","DOIUrl":"https://doi.org/10.1086/709359","url":null,"abstract":"Calcareous nannofossil, carbonate content, and δ18O and δ13C data were utilized to reveal the nature of the Paleocene-Eocene (P-E) boundary at the Gunnah section, Western Desert, Egypt. The uppermost Tarawan Formation (Fm.), Esna Fm., and the lowermost, Farafra Fm., were included in this study. Lithostratigraphically, the Esna Fm. was subdivided into the Hanadi, Dababiya Quarry, and Mahmiya Members. Three calcareous nannofossil zones (NP7/8, NP9, and NP10) and four subzones (NP9a, NP9b, NP10a, and NP10b) were recognized. The biostratigraphic significances of calcareoust nannofossil bioevents associated with the P-E boundary at the study section were discussed. The base of the Eocene was placed at the base of the Dababiya Quarry Member in coincidence with the base of subzone NP9b, which is coincident with the LOs of Rhomboaster cuspis, R. calcitrapa, R. bitrifidia, Pontosphaera pulchra, and Zygrhablithus bijugatus. However, Discoaster araneus first occurred about 3 m below the base of subzone NP9b. The global decreases of the δ13C and δ18O values and carbonate contents across the P-E boundary were documented in the Gunnah section, which represents one of the most expanded and complete P-E sequences in Egypt.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":"128 1","pages":"371 - 387"},"PeriodicalIF":1.8,"publicationDate":"2020-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1086/709359","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45671235","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. Bjornerud, Juliana E. Olsen-Valdez, Emily E. Zawacki, Drae Rogers, Kirstin Edwards, Colin Nevins
Brussels Hill in southern Door County, Wisconsin, is a localized area of faulted and brecciated bedrock in a region of otherwise undeformed lower Silurian dolostone that has been tentatively interpreted as an impact crater. The area of disturbed rock coincides with a nearly circular, 2-km-wide, flat-topped hill that stands about 40 m above the surrounding landscape. Glacial till and polished, striated surfaces on the brecciated bedrock indicate that the disturbance predated the last ice advance and suggest that the hill may have been even higher before glaciation. Anomalous, apparently intrusive bodies of glauconite-bearing sandstone within the brecciated dolostone were likely derived from Cambrian strata, which are normally 400 m in the subsurface in the area. A 103-m drill core into the center of the disturbance recovered 70 m of brecciated dolostone and shale, much of it vesicular, but with no features diagnostic of shock metamorphism. The lowest 33 m of the core sampled the upper Ordovician Maquoketa Formation, which appeared to be subhorizontal and only locally disrupted. This is puzzling, given that material from greater depth must have been brought up through this level. The fact that an area of such fragmented rock stands as a topographic high is also hard to explain. Brussels Hill may have been the site of supersonic impact, but an endogenous process such as violent fragmentation in the upper part of a diatreme cannot be ruled out.
{"title":"Brussels Hill, Door County, Wisconsin: An Enigmatic Area of Disturbed Bedrock","authors":"M. Bjornerud, Juliana E. Olsen-Valdez, Emily E. Zawacki, Drae Rogers, Kirstin Edwards, Colin Nevins","doi":"10.1086/709276","DOIUrl":"https://doi.org/10.1086/709276","url":null,"abstract":"Brussels Hill in southern Door County, Wisconsin, is a localized area of faulted and brecciated bedrock in a region of otherwise undeformed lower Silurian dolostone that has been tentatively interpreted as an impact crater. The area of disturbed rock coincides with a nearly circular, 2-km-wide, flat-topped hill that stands about 40 m above the surrounding landscape. Glacial till and polished, striated surfaces on the brecciated bedrock indicate that the disturbance predated the last ice advance and suggest that the hill may have been even higher before glaciation. Anomalous, apparently intrusive bodies of glauconite-bearing sandstone within the brecciated dolostone were likely derived from Cambrian strata, which are normally 400 m in the subsurface in the area. A 103-m drill core into the center of the disturbance recovered 70 m of brecciated dolostone and shale, much of it vesicular, but with no features diagnostic of shock metamorphism. The lowest 33 m of the core sampled the upper Ordovician Maquoketa Formation, which appeared to be subhorizontal and only locally disrupted. This is puzzling, given that material from greater depth must have been brought up through this level. The fact that an area of such fragmented rock stands as a topographic high is also hard to explain. Brussels Hill may have been the site of supersonic impact, but an endogenous process such as violent fragmentation in the upper part of a diatreme cannot be ruled out.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":"128 1","pages":"325 - 336"},"PeriodicalIF":1.8,"publicationDate":"2020-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1086/709276","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49013161","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":"Beta-blockers in heart failure patients with severe chronic kidney disease-time for a randomized controlled trial?","authors":"Rajiv Agarwal, Patrick Rossignol","doi":"10.1093/ndt/gfz187","DOIUrl":"10.1093/ndt/gfz187","url":null,"abstract":"","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":"79 1","pages":"728-731"},"PeriodicalIF":6.1,"publicationDate":"2020-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7203559/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82636604","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jared T. Freiburg, M. Holland, D. Malone, S. Malone
We present 960 detrital zircon ages from three new, deep boreholes from the Illinois Basin, USA. These zircon age spectra reveal new details of the late Paleoproterozoic through early Cambrian tectonic history of the Illinois Basin, including evidence of the timing of the development of the Reelfoot Rift and breakup of Rodinia. The oldest detrital zircon population is ~1650 Ma, older than any known age for crystalline rocks from other deep drill cores in the basin and conspicuously absent in other Cambrian strata in the region. We interpret this population to have been derived from late Paleoproterozoic crust that exists beneath the Illinois Basin and was exposed during the deposition of Cambrian strata. The principal age peak is ~1375 Ma, characteristic of igneous rocks of the Southern Granite-Rhyolite Province but also present in the St. Francois Mountains of the Eastern Granite-Rhyolite Province (EGRP). A secondary peak of ~1460 Ma detrital zircon reflects the known ages of crystalline rocks that characterize EGRP determined from along the periphery of the Illinois Basin. This population of detrital zircon in Cambrian strata may reflect a greater abundance of ~1370 Ma crust beneath the Illinois Basin than presently recognized. These data reveal that basal Cambrian sandstones in the Illinois Basin have a detrital zircon provenance that is distinct from the overlying late Cambrian arenites and that a previously unknown northern arm of the Reelfoot Rift extends into central Illinois, which is more than 300 km further north than currently mapped. The opening of the Reelfoot Rift, which was part of the broader rifting of Rodinia during the Neoproterozoic and early Cambrian, is marked by zircons, probably from Reelfoot Rift igneous rocks, that range from 540 to 525 Ma.
{"title":"Detrital Zircon Geochronology of Basal Cambrian Strata in the Deep Illinois Basin, USA: Evidence for the Paleoproterozoic-Cambrian Tectonic and Sedimentary Evolution of Central Laurentia","authors":"Jared T. Freiburg, M. Holland, D. Malone, S. Malone","doi":"10.1086/708432","DOIUrl":"https://doi.org/10.1086/708432","url":null,"abstract":"We present 960 detrital zircon ages from three new, deep boreholes from the Illinois Basin, USA. These zircon age spectra reveal new details of the late Paleoproterozoic through early Cambrian tectonic history of the Illinois Basin, including evidence of the timing of the development of the Reelfoot Rift and breakup of Rodinia. The oldest detrital zircon population is ~1650 Ma, older than any known age for crystalline rocks from other deep drill cores in the basin and conspicuously absent in other Cambrian strata in the region. We interpret this population to have been derived from late Paleoproterozoic crust that exists beneath the Illinois Basin and was exposed during the deposition of Cambrian strata. The principal age peak is ~1375 Ma, characteristic of igneous rocks of the Southern Granite-Rhyolite Province but also present in the St. Francois Mountains of the Eastern Granite-Rhyolite Province (EGRP). A secondary peak of ~1460 Ma detrital zircon reflects the known ages of crystalline rocks that characterize EGRP determined from along the periphery of the Illinois Basin. This population of detrital zircon in Cambrian strata may reflect a greater abundance of ~1370 Ma crust beneath the Illinois Basin than presently recognized. These data reveal that basal Cambrian sandstones in the Illinois Basin have a detrital zircon provenance that is distinct from the overlying late Cambrian arenites and that a previously unknown northern arm of the Reelfoot Rift extends into central Illinois, which is more than 300 km further north than currently mapped. The opening of the Reelfoot Rift, which was part of the broader rifting of Rodinia during the Neoproterozoic and early Cambrian, is marked by zircons, probably from Reelfoot Rift igneous rocks, that range from 540 to 525 Ma.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":"128 1","pages":"303 - 317"},"PeriodicalIF":1.8,"publicationDate":"2020-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1086/708432","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47476143","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 J-5 unconformity was originally described as occurring in Wyoming at the base of the Upper Jurassic Windy Hill Sandstone, where it separates the underlying Redwater Shale from the overlying Morrison Formation. The existence of this unconformity has been questioned, as has the closely coupled issue of the depositional environment of the Windy Hill Sandstone. In this article, we document the facies and architecture of the Redwater–Windy Hill–Morrison transition. Facies analysis indicates that the Windy Hill Sandstone represents a tide-dominated deltaic system that prograded northward across the shelf mudstones of the Redwater Shale, followed by the coastal plain of the Morrison Formation. The modern Han River Delta of Korea is a close analog to the Windy Hill Sandstone. The base of the Windy Hill Sandstone is not an unconformity; instead, it is conformable and time transgressive, becoming younger northward along depositional dip, implying that portions of the Redwater Shale and Morrison Formation are coeval. This reinterpretation of the J-5 unconformity in Wyoming, along with a greater appreciation of how abrupt stratigraphic contacts are formed stratigraphically, how they are recognized, and how unconformities are generated eustatically and tectonically, all suggest that a broader reappraisal of the Pipiringos and O’Sullivan unconformities is warranted. In addition, the recognition of a prograding tide-dominated delta in the highstand systems tract underscores the growing rejection of a sequence-stratigraphic paradigm that wave-dominated coasts form primarily during periods of progradation, with tide-dominated coasts being limited or favored during periods of transgression. Finally, tide-dominated deltas have been much more poorly recognized in the rock record than wave-dominated coasts and river-dominated deltas, but the previously unrecognized presence of one in the Windy Hill Sandstone suggests that other tide-dominated deltas might be similarly unrecognized in the rock record of epicontinental seas.
{"title":"The Unconformity That Isn’t: A Sequence-Stratigraphic Reinterpretation of the J-5 Unconformity and the Redwater–Windy Hill–Morrison Transition in Wyoming, USA","authors":"S. Holland, Sarah N. Wright","doi":"10.1086/708433","DOIUrl":"https://doi.org/10.1086/708433","url":null,"abstract":"The J-5 unconformity was originally described as occurring in Wyoming at the base of the Upper Jurassic Windy Hill Sandstone, where it separates the underlying Redwater Shale from the overlying Morrison Formation. The existence of this unconformity has been questioned, as has the closely coupled issue of the depositional environment of the Windy Hill Sandstone. In this article, we document the facies and architecture of the Redwater–Windy Hill–Morrison transition. Facies analysis indicates that the Windy Hill Sandstone represents a tide-dominated deltaic system that prograded northward across the shelf mudstones of the Redwater Shale, followed by the coastal plain of the Morrison Formation. The modern Han River Delta of Korea is a close analog to the Windy Hill Sandstone. The base of the Windy Hill Sandstone is not an unconformity; instead, it is conformable and time transgressive, becoming younger northward along depositional dip, implying that portions of the Redwater Shale and Morrison Formation are coeval. This reinterpretation of the J-5 unconformity in Wyoming, along with a greater appreciation of how abrupt stratigraphic contacts are formed stratigraphically, how they are recognized, and how unconformities are generated eustatically and tectonically, all suggest that a broader reappraisal of the Pipiringos and O’Sullivan unconformities is warranted. In addition, the recognition of a prograding tide-dominated delta in the highstand systems tract underscores the growing rejection of a sequence-stratigraphic paradigm that wave-dominated coasts form primarily during periods of progradation, with tide-dominated coasts being limited or favored during periods of transgression. Finally, tide-dominated deltas have been much more poorly recognized in the rock record than wave-dominated coasts and river-dominated deltas, but the previously unrecognized presence of one in the Windy Hill Sandstone suggests that other tide-dominated deltas might be similarly unrecognized in the rock record of epicontinental seas.","PeriodicalId":54826,"journal":{"name":"Journal of Geology","volume":"128 1","pages":"247 - 274"},"PeriodicalIF":1.8,"publicationDate":"2020-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1086/708433","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47028060","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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