Geology Pub Date : 2024-03-28 DOI: 10.1130/g52005.1

Joel Gombiner, J. Lesemann

引用次数: 0

Bedrock rivers are steep but not narrow: Hydrological and lithological controls on river geometry across the USA 基岩河流陡峭但不狭窄：美国各地河流几何形状的水文和岩性控制因素

Geology Pub Date : 2024-03-27 DOI: 10.1130/g51627.1

James Buckley, Rebecca A. Hodge, Louise J. Slater

{"title":"Bedrock rivers are steep but not narrow: Hydrological and lithological controls on river geometry across the USA","authors":"James Buckley, Rebecca A. Hodge, Louise J. Slater","doi":"10.1130/g51627.1","DOIUrl":"https://doi.org/10.1130/g51627.1","url":null,"abstract":"Bedrock rivers are commonly expected to have steeper and narrower channels than alluvial rivers. However, understanding of bedrock river characteristics has largely been based on small samples of sites in specific climates and upland locations. We provide the first systematic assessment of bedrock and alluvial river channel characteristics for 1274 sites across a broad climatic gradient. We assess whether the width, width-to-depth ratio, and slope of bedrock channels differ from those of alluvial channels and the extent to which these differences are correlated with drainage area, mean annual flow (QMAF), grain size, and lithology. We find that bedrock channels occur at all drainage areas. For the same drainage area, bedrock channels are wider and steeper than alluvial channels. They also have a higher mean annual precipitation and hence QMAF, which likely causes the increased width. After accounting for differences in QMAF, both bedrock and alluvial channels have similar hydraulic scaling. Lithology affects both types of channels in a similar way, with channels on sedimentary lithologies being wider and less steep compared to those on igneous-metamorphic lithologies. Overall, our findings raise new questions about the evolution of bedrock river channels and pave the way for more accurate landscape evolution modeling.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140377630","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

Rehydrated glass embayments record the cooling of a Yellowstone ignimbrite 再水化的玻璃嵌入物记录了黄石燃爆岩的冷却过程

Geology Pub Date : 2024-03-26 DOI: 10.1130/g51905.1

K. Befus, James O. Thompson, Chelsea M. Allison, A. Ruefer, Michael Manga

引用次数: 0

Ice? Salt? Pressure? Sediment deformation structures as evidence of late-stage shallow groundwater in Gale crater, Mars 冰？盐？压力？沉积物变形结构是火星盖尔陨石坑晚期浅层地下水的证据

Geology Pub Date : 2024-03-22 DOI: 10.1130/g51849.1

S. G. Banham, Amelie L. Roberts, Sanjeev Gupta, Joel M. Davis, Lucy M. Thompson, D. M. Rubin, G. Paar, K. Siebach, W. Dietrich, A. Fraeman, A. Vasavada

{"title":"Ice? Salt? Pressure? Sediment deformation structures as evidence of late-stage shallow groundwater in Gale crater, Mars","authors":"S. G. Banham, Amelie L. Roberts, Sanjeev Gupta, Joel M. Davis, Lucy M. Thompson, D. M. Rubin, G. Paar, K. Siebach, W. Dietrich, A. Fraeman, A. Vasavada","doi":"10.1130/g51849.1","DOIUrl":"https://doi.org/10.1130/g51849.1","url":null,"abstract":"Persistence of near-surface water during the late evolution of Gale crater, Mars, would have been fundamental for maintaining a habitable environment. Sedimentation in aqueous conditions is evident during the early stages of crater infilling, where accumulation of lower Mount Sharp group strata is characterized by fluviolacustrine sedimentary rocks. The basal unit of the Siccar Point group—the Stimson formation—which unconformably overlies the Mount Sharp group and represents conditions postdating the exhumation of Aeolis Mons, is characterized by accumulation of aeolian strata under arid conditions. Water was largely absent near the surface during its deposition. At the Feòrachas outcrop, discovery of soft sediment deformation structures in aeolian Stimson strata challenges the notion that Gale crater was devoid of water during its later depositional phase. We identified deformed wind-rippled and vertically laminated sandstones, hosted within erosion-resistant ridges forming boxwork patterns. Broadly, these structures are diagnostic of water (as liquid or as ice) in the shallow subsurface. Comparison with Earth analogues suggests formation by subsurface fluid escape, freeze-thaw processes, or evaporite deformation. Regardless of the mechanism, these structures signify the presence of water at or near the surface much later than previously documented and may extend the habitability window in Gale crater.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140213322","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

Exceptional preservation of a marine tapeworm tentacle in Cretaceous amber 白垩纪琥珀中海洋绦虫触手的特殊保存情况

Geology Pub Date : 2024-03-22 DOI: 10.1130/g52071.1

Cihang Luo, Harry W. Palm, Yuhui Zhuang, E. Jarzembowski, Thet Tin Nyunt, Bo Wang

{"title":"Exceptional preservation of a marine tapeworm tentacle in Cretaceous amber","authors":"Cihang Luo, Harry W. Palm, Yuhui Zhuang, E. Jarzembowski, Thet Tin Nyunt, Bo Wang","doi":"10.1130/g52071.1","DOIUrl":"https://doi.org/10.1130/g52071.1","url":null,"abstract":"Parasites are ubiquitous in extant ecosystems but rarely preserved in the geological record, especially parasitic worms (helminths). One such group is Cestoda (tapeworms), a specialized endoparasitic group of platyhelminths (flatworms). They have a complex lifecycle with at least two hosts, infecting all major groups of vertebrates. However, their fossil record is extremely sparse due to their soft tissue and concealed habitats, with the only widely accepted example before the Quaternary being eggs discovered in a shark coprolite from the Permian. The lack of body fossils greatly hampers our understanding of their early evolution. We report a slender, armed fossil from mid-Cretaceous Kachin (Myanmar) amber (ca. 99 Ma). This fossil displays unique external (armature pattern) and internal (partially invaginated tentacle and rootless hooks) features that are most consistent with the tentacles of extant trypanorhynch tapeworms that parasitize marine elasmobranchs (mainly sharks and rays). Our study thus probably provides not only the first partial body fossil of a tapeworm, but also arguably the most convincing body fossil of a flatworm. In addition, the exquisite invaginated tentacle inside the fossil highlights that amber can preserve the internal structure of helminths. Remarkably, nearly all extant trypanorhynchs are endoparasites of marine elasmobranchs, thus our study provides an exceptional example of a marine endoparasite trapped in terrestrial amber.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140218504","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

Oman as a fragment of Ediacaran eastern Gondwana 阿曼是埃迪卡拉纪东冈瓦纳的一个片段

Geology Pub Date : 2024-03-21 DOI: 10.1130/g51989.1

Irene Gómez-Pérez, Andrew C. Morton, Hussam Al Rawahi, Dirk Frei

{"title":"Oman as a fragment of Ediacaran eastern Gondwana","authors":"Irene Gómez-Pérez, Andrew C. Morton, Hussam Al Rawahi, Dirk Frei","doi":"10.1130/g51989.1","DOIUrl":"https://doi.org/10.1130/g51989.1","url":null,"abstract":"Comprehensive U-Pb detrital zircon geochronology of Ediacaran sandstones from Oman indicates that they originated from Neoproterozoic basement with a peak magmatic age of ca. 850−780 Ma (Tonian), with lesser Paleoproterozoic and Ediacaran sources and renewed magmatic input starting at ca. 550 Ma. Comparison with detrital zircons from the Arabian-Nubian and NW Indian Shields supports an eastern Gondwana affinity for the Ediacaran succession of Oman. Tonian basement sediment sources are present in Oman. Sources for older Paleoproterozoic zircons (ca. 2500 and 1800 Ma) are not found in Oman but are known from the cratonic Indian Shield. The signal of the main magmatic events of the juvenile Arabian-Nubian Shield, peaking at ca. 640−620 Ma, is rare or absent in the Ediacaran rock succession of Oman. However, deformed Ediacaran clastic units with an Arabian-Nubian Shield affinity occur in western Oman. Influx of latest Ediacaran−early Cambrian zircons (550−525 Ma) is interpreted as due to final Cambrian Angudan/Malagasy orogeny-related magmatism.\u0000 These results, together with new ages for volcano-sedimentary terranes in the subsurface of SW Oman and seismic observations, support the interpretation that the Ediacaran succession of Oman was deposited along the western, passive margin of the Greater Indian Shield, on the eastern (east and west in this paper refer to present-day coordinates) side of the Mozambique Ocean. Oman then collided with the Arabian-Nubian Shield in the early Cambrian, when the Angudan/Malagasy orogeny led to final consolidation of Gondwana. Our data support the inference that the youngest and final suture between the Indian and Arabian Shields lies in the subsurface of Oman along the early Cambrian western deformation front.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140221025","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

Disconformity-controlled hydrothermal dolomitization and cementation during basin evolution: Upper Triassic carbonates, UAE 盆地演化过程中的错构控制热液白云石化和胶结作用：上三叠统碳酸盐岩，阿联酋

Geology Pub Date : 2024-03-21 DOI: 10.1130/g51990.1

H. Mansurbeg, M. Alsuwaidi, D. Morad, S. Morad, M. Tiepolo, S. Shahrokhi, I. Al-Aasm, H. Koyi

{"title":"Disconformity-controlled hydrothermal dolomitization and cementation during basin evolution: Upper Triassic carbonates, UAE","authors":"H. Mansurbeg, M. Alsuwaidi, D. Morad, S. Morad, M. Tiepolo, S. Shahrokhi, I. Al-Aasm, H. Koyi","doi":"10.1130/g51990.1","DOIUrl":"https://doi.org/10.1130/g51990.1","url":null,"abstract":"Petrography, fluid-inclusion microthermometry, stable isotope analyses, and radiometric (206Pb/238U) dating of Upper Triassic dolostones, saddle dolomite, and quartz and calcite cements were used to constrain the timing and conditions of dolomitization and cementation in the context of the tectonic evolution of a basin in the northern United Arab Emirates. Dolomitization (ca. 152.4 Ma) and precipitation of saddle dolomite (ca. 146.8 Ma), calcite (ca. 144.6 Ma), and quartz cements are attributed to focused synrifting flow of hot basinal brines into grain-supported limestones in which permeability was enhanced by incursion of meteoric waters beneath a disconformity surface. Another calcite cement generation (ca. 99.7 Ma) was formed by flow of hot brines during tectonic compression related to the obduction of Oman ophiolites in the Late Cretaceous. Thus, this paper provides new insights into (1) stratigraphic controls on and timing of hydrothermal (hot basinal brines) dolomitization, (2) the origin of closely associated intraformational limestones and dolostones, and (3) linkages between diagenesis and thermochemical modifications of basinal brines during tectonic evolution of sedimentary basins.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140221832","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

Polymorphic transformations of titanium oxides contribute to economic uranium mineralization in sandstone 钛氧化物的多态转化促进了砂岩中的经济铀矿化

Geology Pub Date : 2024-03-20 DOI: 10.1130/g51982.1

Shuo Yin, Zhaobin Yan, Jiali Fu, Wen Zhang, Hong Liu, Fei Xia, Qingfei Wang

{"title":"Polymorphic transformations of titanium oxides contribute to economic uranium mineralization in sandstone","authors":"Shuo Yin, Zhaobin Yan, Jiali Fu, Wen Zhang, Hong Liu, Fei Xia, Qingfei Wang","doi":"10.1130/g51982.1","DOIUrl":"https://doi.org/10.1130/g51982.1","url":null,"abstract":"Sandstone-hosted uranium (U) deposits provide a significant U resource for nuclear energy worldwide. Driven by redox reactions, tetravalent uranium-bearing minerals are commonly associated with reductants (e.g., pyrite and organic matter). However, numerous observations have revealed that tetravalent uranium-bearing minerals can spatially coexist with chemically stabilized titanium oxides in sandstone-hosted U deposits, requiring a complementary mechanism to interpret these findings. We present a new model based on in situ texture, trace-element content, and titanium isotopic ratio, as well as polymorph type and related transformation for titanium oxides from the Yaojia Formation of the southwestern Songliao Basin in northeast China. Specifically, in our model, abundant nanopores were generated during the spontaneous transformation of anatase to rutile, producing a porous material for hexavalent U adsorption. Facilitated by a U-rich source rock, adsorbed U in porous titanium oxide from the lower Yaojia Formation was up to several thousand parts per million. In order to minimize surface energy, a subsequent decrease in surface area by merging small pores is inevitable. When the evolved surface area was small enough, hexavalent U would be desorbed and subsequently transformed to tetravalent U by local reductants, forming uraninite nanoparticles on the surface of U-rich rutile with relatively large pores. Our newly proposed mechanism not only contributes to a better understanding of economic U mineralization in sandstone, but also suggests that U occurred as uranium oxide instead of brannerite in sandstone-hosted U deposits, providing a nano-mineralogical perspective required for industrial processing.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140226171","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

Modification of Archean cratons in southern Africa with foundered segments dropped into the shallow lower mantle 南部非洲奥陶纪火山口的改造与落入浅层下地幔的创始地段

Geology Pub Date : 2024-03-19 DOI: 10.1130/g52023.1

Jiaji Xi, Youqiang Yu, Dapeng Zhao, Jiashun Hu

引用次数: 0

Exothermic reactions and 39Ar−40Ar thermochronology: Hydration leads to younger apparent ages 放热反应与 39Ar-40Ar 热年代学：水合作用导致表观年龄变小

Geology Pub Date : 2024-03-13 DOI: 10.1130/g51776.1

Simon Schorn, E. Moulas, Kurt Stüwe

{"title":"Exothermic reactions and 39Ar−40Ar thermochronology: Hydration leads to younger apparent ages","authors":"Simon Schorn, E. Moulas, Kurt Stüwe","doi":"10.1130/g51776.1","DOIUrl":"https://doi.org/10.1130/g51776.1","url":null,"abstract":"Retrogression and hydration commonly affect large swaths of Earth’s crust, causing variable degrees of chloritization, sericitization, and/or serpentinization. Hydration is a strongly exothermic process that partially opens isotopic systems, thereby distorting the recorded apparent ages and cooling histories of reworked terranes. Using a simple one-dimensional numerical model involving heat released at variable temperatures to simulate exothermic hydration, we track the cooling histories for rocks that exhume from depth. The calculated cooling paths are used to quantify apparent 39Ar−40Ar ages in muscovite, biotite, and feldspar considering 40Ar production and diffusive Ar loss. For fluid incorporation relative to chloritization of ∼10%, ∼50 kJ of latent heat are released per kilogram of rock. For this scenario and exhumation rates between 1 mm·yr−1 and 4 mm·yr−1, muscovite grains ≤100 µm in diameter yield apparent ages that are younger by up to 10%, but always exceeding the typical uncertainty of Ar dating. Biotite and feldspar display a similar distortion, even for large grains of ∼1 mm in size. The relative younging effect increases to >30% with enthalpy released, exhumation rate, and decreasing grain size, with younging reaching a maximum for hydration at approximately the nominal closure temperature of the respective thermochronometers. Using published data sets (from Sifnos, Greece, and Tian Shan, China), we suggest that rejuvenation of apparent mica ages is consistent with diffusive Ar loss due to exothermic hydration during exhumation. Our method applies to any thermally activated process, like element exchange in mineral thermometers or fission-track annealing, provided heat is released close to the characteristic closure temperature. This extends to processes beyond hydration, such as shear heating or localized magma emplacement, making our results pertinent for diverse thermochronometers and temperature-sensitive methods across a broad range of conditions.","PeriodicalId":503125,"journal":{"name":"Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140245165","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

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