Geology Pub Date : 2024-05-02 DOI: 10.1130/g52131.1

Youwei Wang, T. F. Baars, J. Storms, A. Martinius, P. Gingerich, H. Abels

{"title":"Long-eccentricity pacing of alluvial stratigraphic architecture in the Eocene Bighorn Basin, Wyoming, USA","authors":"Youwei Wang, T. F. Baars, J. Storms, A. Martinius, P. Gingerich, H. Abels","doi":"10.1130/g52131.1","DOIUrl":"https://doi.org/10.1130/g52131.1","url":null,"abstract":"Alluvial stratigraphy builds up over geologic time under the complex interplay of external climatic and tectonic forces and internal stochastic processes. This complexity makes it challenging to attribute alluvial stratigraphic changes to specific factors. Geological records indicate pronounced and persistent climatic changes during the Phanerozoic, while the effects of these changes on alluvial stratigraphy remain insufficiently documented. We provide evidence for 405 k.y. long-eccentricity climate forcing of alluvial stratigraphy in the lower Eocene Willwood Formation of the Bighorn Basin, Wyoming (USA). Two ∼90-m-thick intervals, characterized by a relative paucity of sand, dominance of sinuous-river channels, and floodplain sediments with better-developed paleosols, coincide with eccentricity maxima as determined through integrated stratigraphic methods. These intervals are interspersed with three contrasting intervals, marked by relatively high sand content, prevalent braided-river channels, and less-developed paleosols, corresponding to eccentricity minima. A comprehensive genetic model that integrates climate, source-to-sink system, and alluvial dynamics to explain these findings remains to be elucidated. Given the consistent presence of the 405 k.y. eccentricity cycle throughout Earth’s history, it is plausible to infer that its influence may be discernible across a wide array of alluvial stratigraphic records.","PeriodicalId":503125,"journal":{"name":"Geology","volume":"3 7","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141020713","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Niobium ore genesis in a capsule 胶囊中的铌矿石成因

Geology Pub Date : 2024-04-25 DOI: 10.1130/g52169.1

A. Williams-Jones, O. Vasyukova, A.V. Kostyuk

引用次数: 0

Alkenone-derived estimates of Cretaceous pCO2 白垩纪 pCO2 的烯酮估计值

Geology Pub Date : 2024-04-23 DOI: 10.1130/g51939.1

Weimin Si, Joseph B. Novak, Nora Richter, P. Polissar, Ruigang Ma, Ewerton Santos, Jared Nirenberg, Timothy D. Herbert, Marie-Pierre Aubry

引用次数: 0

Excessive subsidence of oceanic basins caused by recycled oceanic crust in the mantle source: A new perspective on the oceanic topography within Southeast Asia 地幔源中的再生洋壳导致大洋盆地过度下沉：东南亚海洋地形的新视角

Geology Pub Date : 2024-04-23 DOI: 10.1130/g52079.1

Fan Yang, Xiao-Long Huang, Yi‐Gang Xu, Le Zhang, Peng‐Li He, Yang Yu, Liang Liu

引用次数: 0

Identifying and characterizing missing source orogens for syn-orogenic basins based on detrital accessory mineral U-Pb geochronology and trace element geochemistry 根据非晶质附属矿物 U-Pb 地球年代学和痕量元素地球化学确定并描述同源盆地的缺失源造山运动

Geology Pub Date : 2024-04-18 DOI: 10.1130/g52212.1

Lijun Wang, Shoufa Lin, W. Xiao, J. Hanchar, William J. Collins, Donald W. Davis, C. Yakymchuk, Guangfu Xing, Zhijun Niu, D. Xiang, C. V. van Staal, Qǐháng Wú

{"title":"Identifying and characterizing missing source orogens for syn-orogenic basins based on detrital accessory mineral U-Pb geochronology and trace element geochemistry","authors":"Lijun Wang, Shoufa Lin, W. Xiao, J. Hanchar, William J. Collins, Donald W. Davis, C. Yakymchuk, Guangfu Xing, Zhijun Niu, D. Xiang, C. V. van Staal, Qǐháng Wú","doi":"10.1130/g52212.1","DOIUrl":"https://doi.org/10.1130/g52212.1","url":null,"abstract":"Identifying source orogens for syn-orogenic sediments in dispersed fragments of a supercontinent provides key information on the tectonic evolution of the orogens involved in supercontinent assembly and on paleogeographic reconstruction. An approach using U-Pb geochronology and trace elements of multiple detrital minerals including zircon, rutile, apatite, and monazite has major advantages over detrital zircon studies alone. Application of this multi-pronged approach to Ediacaran and Cambrian clastic sedimentary rocks from the West Cathaysia terrane of the South China block demonstrates that these rocks were deposited in two distinct, but overlapping, syn-orogenic basins related to the assembly of eastern Gondwana. The Ediacaran rocks have detritus likely sourced from the Paterson-Petermann orogen (PPO) in Australia, and the dominant 650−600 Ma populations and trace element compositions of detrital rutile and apatite indicate a significant Ediacaran thermal and high-pressure metamorphic event in the orogen. The appearance of Cambrian and Tonian detrital rutile and apatite populations in the Cambrian rocks indicates derivation from a different source orogen characterized by multiple thermal events, most likely the Kuunga-Pinjarra orogen (KPO). Our data suggest that West Cathaysia was located adjacent to both the PPO and the KPO and support the hypothesis that the PPO was a collisional, rather than a long-lived post-Grenvillian intraplate, orogen. Our data also suggest a poly-metamorphic history for the poorly preserved northern part of the KPO and a larger expanse of Greater India.","PeriodicalId":503125,"journal":{"name":"Geology","volume":" 9","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140688726","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

A little mica goes a long way: Impact of phyllosilicates on quartz deformation fabrics in naturally deformed rocks 云母的作用可大可小植硅体对天然变形岩石中石英变形结构的影响

Geology Pub Date : 2024-04-16 DOI: 10.1130/g52053.1

R. Gottardi, Gabriele Casale, J. Economou, Kristen Morris

{"title":"A little mica goes a long way: Impact of phyllosilicates on quartz deformation fabrics in naturally deformed rocks","authors":"R. Gottardi, Gabriele Casale, J. Economou, Kristen Morris","doi":"10.1130/g52053.1","DOIUrl":"https://doi.org/10.1130/g52053.1","url":null,"abstract":"Quartz deformation fabrics reflect stress and strain conditions in mylonites, and their interpretation has become a mainstay of kinematic and structural analysis. Quantification of grain size and shape and interpretation of textures reflecting deformation mechanisms can provide estimates of flow stress, strain rate, kinematic vorticity, and deformation temperatures. Empirical calibration and determination of quartz flow laws is based on laboratory experiments of pure samples; however, pure quartzite mylonites are relatively uncommon. In particular, phyllosilicates may localize and partition strain that can inhibit or enhance different deformation mechanisms. Experimental results demonstrate that even minor phyllosilicate content (<15 vol%) can dramatically alter the strain behavior of quartz; however, few field studies have demonstrated these effects in a natural setting.\u0000 To investigate the role of phyllosilicates on quartz strain fabrics, we quantify phyllosilicate content and distribution in quartzite mylonites from the Miocene Raft River detachment shear zone (NW Utah, USA). We use microstructural analysis and electron backscatter diffraction to quantify quartz deformation fabrics and muscovite spatial distribution, and X-ray computed tomography to quantify muscovite content in samples with varying amounts of muscovite collected across the detachment shear zone. Phyllosilicate content has a direct control on quartz deformation mechanisms, and application of piezometers and flow laws based on quartz deformation fabrics yield strain rates and flow stresses that vary by up to two orders of magnitude across our samples. These findings have important implications for the application of flow laws in quartzite mylonites and strain localization mechanisms in mid-crustal shear zones.","PeriodicalId":503125,"journal":{"name":"Geology","volume":"1 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140697618","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Oligocene melting of subducted mélange and its mantle dynamics in northeast Asia 东北亚渐新世俯冲熔块的熔化及其地幔动力学

Geology Pub Date : 2024-04-12 DOI: 10.1130/g52115.1

Ke-Chun Hong, Feng Wang, Si-Wen Zhang, Wenxian Xu, Yi‐Ni Wang, De-Bin Yang

{"title":"Oligocene melting of subducted mélange and its mantle dynamics in northeast Asia","authors":"Ke-Chun Hong, Feng Wang, Si-Wen Zhang, Wenxian Xu, Yi‐Ni Wang, De-Bin Yang","doi":"10.1130/g52115.1","DOIUrl":"https://doi.org/10.1130/g52115.1","url":null,"abstract":"Melting of subducted mélange can potentially transport mass from the slab-mantle interface to the mantle wedge in subduction zones. The mélange diapir model was primarily proposed from the results of laboratory experiments and thermodynamic modeling. However, the melting mechanisms of mélange diapirs in subduction zones remain unclear. To further constrain the mantle dynamics of a mélange diapir, we studied Oligocene alkaline intermediate rocks on the northeast Asian continental margin. We report whole-rock geochemical and Sr-Nd-Pb-Mg-Zn isotope data and show that these rocks formed by partial melting of mélange. We conclude that a diapir was the mechanism for Oligocene melting of the mélange. We also identified younger rocks formed by melting of mélange in the eastern part of northeast Asia, implying an eastward shift in such magmatism since the Oligocene. Our results and the tectonic setting indicate that melting of mélange diapirs occurred preferentially during tectonic transitions, such as the formation of a back-arc basin triggered by trench-perpendicular mantle flow. The low-viscosity mantle with an incompressible stress field triggered melting of the mélange diapirs. Interactions occurred between the mélange diapirs and carbonated peridotites, constraining the depth of mélange-mantle interactions to the asthenosphere, which is deeper than the depth inferred in previous studies.","PeriodicalId":503125,"journal":{"name":"Geology","volume":"11 12","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140710544","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Evidence for ca. 1 Ga hypervelocity impact event found in northwest Greenland 格陵兰岛西北部发现约格陵兰岛西北部发现约 1 Ga 超高速撞击事件的证据

Geology Pub Date : 2024-04-12 DOI: 10.1130/g51876.1

William R. Hyde, G. G. Kenny, S. Jaret, Joseph A. MacGregor, Pierre Beck, M J Whitehouse, N. K. Larsen

{"title":"Evidence for ca. 1 Ga hypervelocity impact event found in northwest Greenland","authors":"William R. Hyde, G. G. Kenny, S. Jaret, Joseph A. MacGregor, Pierre Beck, M J Whitehouse, N. K. Larsen","doi":"10.1130/g51876.1","DOIUrl":"https://doi.org/10.1130/g51876.1","url":null,"abstract":"There are likely many undiscovered impact structures on Earth, but several challenges prevent their detection, including possible concealment beneath large ice sheets. In recent years, geophysical, geochemical, and microphysical evidence has mounted for a ca. 58 Ma impact structure under the Hiawatha Glacier, northwest Greenland. Here, we report evidence for a second, much older hypervelocity impact event in this region, recorded in an impact melt rock sample collected from a glaciofluvial deposit in Inglefield Land. Secondary ion mass spectrometry U-Pb analyses of shock metamorphosed zircon grains yielded a previously unrecorded, Proterozoic best estimate impact age of 1039 ± 16 Ma (mean square of weighted deviates = 2.9). Based on Archean−Proterozoic target rock U-Pb ages obtained from unshocked zircon grains and the location of the melt rock sample along the ice margin, we suggest this sample was derived from a hypervelocity impact structure farther inland, concealed by the Greenland Ice Sheet. This study demonstrates the ability to uncover new impact events in some of the most inaccessible areas on Earth and the possibility of sampling multiple impact structures from one location when examining ex situ material. Our results have implications for current and future Martian and lunar returned samples that demonstrably bear complex impact histories.","PeriodicalId":503125,"journal":{"name":"Geology","volume":"82 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140709148","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Bank strength variability and its impact on the system-scale morphodynamics of the upper Amazon River in Brazil 堤岸强度变化及其对巴西亚马逊河上游系统尺度形态动力学的影响

Geology Pub Date : 2024-04-09 DOI: 10.1130/g51862.1

Muriel Z.M. Brückner, R. Aalto, Jim Best, Renato Paes de Almeida, A. Nicholas, Phil Ashworth, Marco Ianniruberto

{"title":"Bank strength variability and its impact on the system-scale morphodynamics of the upper Amazon River in Brazil","authors":"Muriel Z.M. Brückner, R. Aalto, Jim Best, Renato Paes de Almeida, A. Nicholas, Phil Ashworth, Marco Ianniruberto","doi":"10.1130/g51862.1","DOIUrl":"https://doi.org/10.1130/g51862.1","url":null,"abstract":"Large anabranching rivers form channels in sediments of varying strength, resulting from erosional and depositional processes that act over geological time scales. Although bank strength variability is known to affect channel morphodynamics, its impact on the migration of large sand-bed rivers remains poorly understood. We report the first in situ measurements of bank strength from an ∼100-km-long reach of the Solimões River, the Brazilian Amazon River upstream of Manaus. These show that cohesive muds in Pleistocene terraces along the river’s right margin have bank strengths as much as three times greater than Holocene floodplain deposits composing the left bank. Image analysis suggests these resistant outcrops determine channel-bar dynamics: channel widening and bar deposition are inhibited, which lowers planform curvature and reduces erosion of the opposing bank. Planform analysis of the 1600-km-long Solimões River between 1984 and 2021 shows that where the channel is associated with Pleistocene terraces, lower rates of bank erosion and bar deposition are evident. Heterogeneity in bank strength is thus a first-order control on the large-scale morphodynamics of the world’s largest lowland river.","PeriodicalId":503125,"journal":{"name":"Geology","volume":"75 S1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140723373","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Subsidence-induced early doming at a large ignimbrite caldera 大型火成岩破火山口的沉降诱发早期穹隆

Geology Pub Date : 2024-04-05 DOI: 10.1130/g52130.1

Peter W. Lipman

引用次数: 0

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