Giovanni Camanni, Efstratios Delogkos, Stefano Tavani, Ester Piegari, Muhammed Kösen
The reactivation of deep-seated, throughgoing strike-slip faults produces highly segmented fault zones at shallower levels, yet how displacement is partitioned among segments as the fault grows remains poorly constrained. We address this by examining a ∼160-m-long section of the East Anatolian fault surface rupture of the Mw 7.8 2023 Kahramanmaraş strike-slip earthquake (Turkey). The rupture offsets meter-spaced ridges and furrows in a ploughed field, providing a unique opportunity for detailed displacement measurements, which were obtained from an orthophoto and a digital elevation model (DEM) built for this study. The surface rupture consists of ten primary segments separated by nine restraining stepovers and is associated with a 3-D strain field dominated by ∼3.5 m of left-lateral offset. Displacement patterns allow us to derive a new model for strike-slip fault growth in which deformation is asymmetric and controlled by the 3-D structure of the fault—specifically, by the position of the underlying fault relative to shallow fault segments. Initially, displacement is accommodated by contraction within restraining stepovers. With increasing displacement, fault segments located closer to the trace of the underlying fault consistently accumulate greater displacement. This asymmetry is facilitated by enhanced synthetic rotation within stepovers. With further displacement, the higher-displacement segment bounding a stepover becomes dominant, while the other one is bypassed and layer rotation ceases. These results not only improve fault growth models but could also inform seismic hazard models and impact industrial applications dealing with subsurface faulted reservoirs.
{"title":"Asymmetric growth of strike-slip faults controlled by 3-D fault structure: Insights from the Mw 7.8 2023 Kahramanmaraş (Turkey) earthquake","authors":"Giovanni Camanni, Efstratios Delogkos, Stefano Tavani, Ester Piegari, Muhammed Kösen","doi":"10.1130/g53724.1","DOIUrl":"https://doi.org/10.1130/g53724.1","url":null,"abstract":"The reactivation of deep-seated, throughgoing strike-slip faults produces highly segmented fault zones at shallower levels, yet how displacement is partitioned among segments as the fault grows remains poorly constrained. We address this by examining a ∼160-m-long section of the East Anatolian fault surface rupture of the Mw 7.8 2023 Kahramanmaraş strike-slip earthquake (Turkey). The rupture offsets meter-spaced ridges and furrows in a ploughed field, providing a unique opportunity for detailed displacement measurements, which were obtained from an orthophoto and a digital elevation model (DEM) built for this study. The surface rupture consists of ten primary segments separated by nine restraining stepovers and is associated with a 3-D strain field dominated by ∼3.5 m of left-lateral offset. Displacement patterns allow us to derive a new model for strike-slip fault growth in which deformation is asymmetric and controlled by the 3-D structure of the fault—specifically, by the position of the underlying fault relative to shallow fault segments. Initially, displacement is accommodated by contraction within restraining stepovers. With increasing displacement, fault segments located closer to the trace of the underlying fault consistently accumulate greater displacement. This asymmetry is facilitated by enhanced synthetic rotation within stepovers. With further displacement, the higher-displacement segment bounding a stepover becomes dominant, while the other one is bypassed and layer rotation ceases. These results not only improve fault growth models but could also inform seismic hazard models and impact industrial applications dealing with subsurface faulted reservoirs.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"36 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145807417","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Lidya G. Tarhan, Thomas H. Boag, Boriana Kalderon-Asael
The Ediacara Biota—Earth’s earliest fossilized ecosystems of complex, macroscopic organisms—has played a key role in shaping understanding of the transition between the Precambrian and early Paleozoic radiations of animal diversity. The majority of Ediacara Biota Lagerstätten are exceptionally preserved in the distinctive Ediacara style as three-dimensional casts and molds in sandstones. However, the factors responsible for the fossilization of these soft-bodied organisms—in particular, for their preservation in compositionally immature sandstones and heterolithic strata—remain debated. In this study, we investigate the taphonomic importance of clay minerals in fostering Ediacara-style fossilization in classic Ediacara Biota fossil assemblages in Newfoundland and northwestern Canada. Using a combination of electron microscopy, X-ray diffraction, and major and trace element and lithium isotope analyses, we describe evidence for both detrital and early diagenetic clay minerals associated with these fossils. In particular, we document iron- and magnesium-rich clays, including chamosite and other chlorite-group minerals, which may reflect an authigenic precursor such as berthierine, a mineral that has also been implicated in other modes of exceptional preservation. Lithium isotope data corroborate the importance of detrital and marine authigenic clays in shaping the moldic preservation of these fossils. These results provide a broader view of potential drivers of the Ediacara-style fossil record and suggest that authigenic clay mineralization may have shaped multiple windows of exceptional fossilization across the Neoproterozoic−Paleozoic transition.
{"title":"Authigenic clays shaped Ediacara-style exceptional fossilization","authors":"Lidya G. Tarhan, Thomas H. Boag, Boriana Kalderon-Asael","doi":"10.1130/g53967.1","DOIUrl":"https://doi.org/10.1130/g53967.1","url":null,"abstract":"The Ediacara Biota—Earth’s earliest fossilized ecosystems of complex, macroscopic organisms—has played a key role in shaping understanding of the transition between the Precambrian and early Paleozoic radiations of animal diversity. The majority of Ediacara Biota Lagerstätten are exceptionally preserved in the distinctive Ediacara style as three-dimensional casts and molds in sandstones. However, the factors responsible for the fossilization of these soft-bodied organisms—in particular, for their preservation in compositionally immature sandstones and heterolithic strata—remain debated. In this study, we investigate the taphonomic importance of clay minerals in fostering Ediacara-style fossilization in classic Ediacara Biota fossil assemblages in Newfoundland and northwestern Canada. Using a combination of electron microscopy, X-ray diffraction, and major and trace element and lithium isotope analyses, we describe evidence for both detrital and early diagenetic clay minerals associated with these fossils. In particular, we document iron- and magnesium-rich clays, including chamosite and other chlorite-group minerals, which may reflect an authigenic precursor such as berthierine, a mineral that has also been implicated in other modes of exceptional preservation. Lithium isotope data corroborate the importance of detrital and marine authigenic clays in shaping the moldic preservation of these fossils. These results provide a broader view of potential drivers of the Ediacara-style fossil record and suggest that authigenic clay mineralization may have shaped multiple windows of exceptional fossilization across the Neoproterozoic−Paleozoic transition.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"161 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145765170","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Rocio Jaimes-Gutierrez, Lucas Vimpere, David J. Wilson, Patrick Blaser, Philip A.E. Pogge von Strandmann, Thierry Adatte, Swapan Sahoo, Sébastien Castelltort
Silicate weathering regulates Earth’s long-term climate by removing atmospheric CO2. Understanding changes in weathering regimes and rates is key to predicting climate response time scales. We investigated the reactivity of the North American source-to-sink system and the chemical weathering regime during the Paleocene−Eocene Thermal Maximum (PETM). We measured the detrital lithium isotope composition (δ7Li) in a deep-marine sediment core from the Gulf of Mexico, tracking changes in the formation of clay minerals, alongside neodymium isotopes (εNd), to constrain sediment provenance. We find a buffered negative δ7Li excursion during the PETM body, likely reflecting the mixing of neoformed and reworked clays from continental floodplains, followed by a stronger negative δ7Li excursion during the recovery phase. This pattern aligns with the continental Bighorn Basin (Wyoming, USA) δ7Li record, indicating rapid propagation of enhanced weathering and erosion fluxes in response to the PETM, which would have contributed to efficient CO2 drawdown.
{"title":"Lithium isotopes reveal enhanced weathering fluxes in North America during the Paleocene−Eocene Thermal Maximum","authors":"Rocio Jaimes-Gutierrez, Lucas Vimpere, David J. Wilson, Patrick Blaser, Philip A.E. Pogge von Strandmann, Thierry Adatte, Swapan Sahoo, Sébastien Castelltort","doi":"10.1130/g53708.1","DOIUrl":"https://doi.org/10.1130/g53708.1","url":null,"abstract":"Silicate weathering regulates Earth’s long-term climate by removing atmospheric CO2. Understanding changes in weathering regimes and rates is key to predicting climate response time scales. We investigated the reactivity of the North American source-to-sink system and the chemical weathering regime during the Paleocene−Eocene Thermal Maximum (PETM). We measured the detrital lithium isotope composition (δ7Li) in a deep-marine sediment core from the Gulf of Mexico, tracking changes in the formation of clay minerals, alongside neodymium isotopes (εNd), to constrain sediment provenance. We find a buffered negative δ7Li excursion during the PETM body, likely reflecting the mixing of neoformed and reworked clays from continental floodplains, followed by a stronger negative δ7Li excursion during the recovery phase. This pattern aligns with the continental Bighorn Basin (Wyoming, USA) δ7Li record, indicating rapid propagation of enhanced weathering and erosion fluxes in response to the PETM, which would have contributed to efficient CO2 drawdown.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"3 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145746673","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Tülay Kaya-Eken, Yasuo Ogawa, Yoshiya Usui, Takafumi Kasaya, M. Kemal Tunçer, Yoshimori Honkura, Naoto Oshiman, Masaki Matsushima, Weerachai Siripunvaraporn
Reliable knowledge of the crustal properties beneath the North Anatolian fault (NAF), seismically silent for more than 250 years beneath the Marmara Sea (MS), is crucial for understanding seismic hazard and mitigating the potential for disaster on an enormous scale. In the present work, the first three-dimensional inverse modeling performed on a magnetotelluric dataset of the MS has unveiled localized weak and locked fault segments along this shear deformation zone. Low-resistivity regions along the northern branch of the NAF beneath the Central and Çınarcık-Imralı basins are likely attributed to the presence of fluids, which may represent a fault zone conductor in a fractured zone and can explain the densely populated microseismicity. These low-resistivity anomalies surrounded by higher resistivity structures imply that the segmented, multi-branched NAF system extends beneath the MS, following the Intra-Pontide suture zone. The resistive anomalies, between the Central and Çınarcık basins, along with those at the western and eastern extremities of the MS, presumably signify regions of stress accumulation, shedding light on the ongoing processes of fault mechanics at play in this critical region.
{"title":"3-D electromagnetic imaging of highly deformed fluid-rich weak zones and locked section of the North Anatolian fault beneath the Marmara Sea","authors":"Tülay Kaya-Eken, Yasuo Ogawa, Yoshiya Usui, Takafumi Kasaya, M. Kemal Tunçer, Yoshimori Honkura, Naoto Oshiman, Masaki Matsushima, Weerachai Siripunvaraporn","doi":"10.1130/g52995.1","DOIUrl":"https://doi.org/10.1130/g52995.1","url":null,"abstract":"Reliable knowledge of the crustal properties beneath the North Anatolian fault (NAF), seismically silent for more than 250 years beneath the Marmara Sea (MS), is crucial for understanding seismic hazard and mitigating the potential for disaster on an enormous scale. In the present work, the first three-dimensional inverse modeling performed on a magnetotelluric dataset of the MS has unveiled localized weak and locked fault segments along this shear deformation zone. Low-resistivity regions along the northern branch of the NAF beneath the Central and Çınarcık-Imralı basins are likely attributed to the presence of fluids, which may represent a fault zone conductor in a fractured zone and can explain the densely populated microseismicity. These low-resistivity anomalies surrounded by higher resistivity structures imply that the segmented, multi-branched NAF system extends beneath the MS, following the Intra-Pontide suture zone. The resistive anomalies, between the Central and Çınarcık basins, along with those at the western and eastern extremities of the MS, presumably signify regions of stress accumulation, shedding light on the ongoing processes of fault mechanics at play in this critical region.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"34 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145704187","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Kemi Ashing-Giwa, Jonathan L. Payne, Erik A. Sperling
In the wake of the end-Permian mass extinction, bivalves replaced articulate brachiopods as the dominant benthic marine filter-feeders, despite morphological and ecological similarities. Several factors have been suggested as drivers of the extinction’s selectivity, including competition, ocean acidity, CO2 poisoning, and differing reproductive potential. The spread of sulfidic water (euxinia) has been proposed as a general kill mechanism, but its physiological selectivity has not been investigated. Survival studies of the co-occurring bivalve Glycymeris septentrionalis and articulate brachiopod Terebratalia transversa from San Juan Island, Washington, USA, were carried out in anoxic and euxinic environments at 13.7, 16, and 22 °C. In colder anoxic conditions without sulfide, the brachiopod exhibited greater survival than the bivalve, but at higher temperatures, the bivalve generally outlasted the brachiopod, and by a greater margin in euxinia. The alignment between physiological tolerance in experimental settings and survival patterns in the paleontological record indicates that euxinia may have played a role in end-Permian extinction severity and selectivity, serving as an additional stressor in already warm, oxygen-depleted oceans.
{"title":"Investigating the response of Glycymeris septentrionalis (Bivalvia) and Terebratalia transversa (Brachiopoda) to euxinia: Implications for mass extinctions","authors":"Kemi Ashing-Giwa, Jonathan L. Payne, Erik A. Sperling","doi":"10.1130/g53911.1","DOIUrl":"https://doi.org/10.1130/g53911.1","url":null,"abstract":"In the wake of the end-Permian mass extinction, bivalves replaced articulate brachiopods as the dominant benthic marine filter-feeders, despite morphological and ecological similarities. Several factors have been suggested as drivers of the extinction’s selectivity, including competition, ocean acidity, CO2 poisoning, and differing reproductive potential. The spread of sulfidic water (euxinia) has been proposed as a general kill mechanism, but its physiological selectivity has not been investigated. Survival studies of the co-occurring bivalve Glycymeris septentrionalis and articulate brachiopod Terebratalia transversa from San Juan Island, Washington, USA, were carried out in anoxic and euxinic environments at 13.7, 16, and 22 °C. In colder anoxic conditions without sulfide, the brachiopod exhibited greater survival than the bivalve, but at higher temperatures, the bivalve generally outlasted the brachiopod, and by a greater margin in euxinia. The alignment between physiological tolerance in experimental settings and survival patterns in the paleontological record indicates that euxinia may have played a role in end-Permian extinction severity and selectivity, serving as an additional stressor in already warm, oxygen-depleted oceans.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"5 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145704186","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Bryan A. Black, Patrick T. Pringle, James W. Vallance
New dating of lahar-killed trees underscores volcano hazards in the Puget Sound metropolitan area. Beginning as a landslide from the west flank of Mount Rainier, Washington, USA, the Electron Mudflow, which was the largest lahar of the last millennium, swept more than 60 km down the Puyallup River drainage into areas now densely populated. Wiggle matching of seven radiocarbon ages from buried, bark-bearing Douglas-fir (Pseudotsuga menziesii) trees brackets the mudflow’s age between 1477 and 1522 CE with 99.7% certainty. To narrow this date, we applied dendrochronology crossdating on samples collected from 21 trees killed by the lahar, measuring 86 time series for statistical verification. The four bark-bearing trees died the same year while the final rings in all other trees had decayed, exposing rings formed in earlier years. When averaged together, the crossdated measurements form a 475 yr master chronology that was correlated against absolutely dated tree-ring chronologies in the region. The Electron chronology best matched with chronologies from low-elevation sites, especially a Douglas-fir chronology from Vancouver Island, Canada, to show that the Electron trees died in 1507 CE. Latewood in the final ring was beginning to form, indicating the mudflow likely occurred in the late-summer months. What caused the Electron Mudflow is unknown, but this precise date will help to assess possible relationships with other events, assist in interpreting Indigenous narratives about the mudflow, and increase awareness of potential lahar hazards.
{"title":"Forest-floor burial in 1507 by the largest Mount Rainier lahar of the past millennium","authors":"Bryan A. Black, Patrick T. Pringle, James W. Vallance","doi":"10.1130/g53721.1","DOIUrl":"https://doi.org/10.1130/g53721.1","url":null,"abstract":"New dating of lahar-killed trees underscores volcano hazards in the Puget Sound metropolitan area. Beginning as a landslide from the west flank of Mount Rainier, Washington, USA, the Electron Mudflow, which was the largest lahar of the last millennium, swept more than 60 km down the Puyallup River drainage into areas now densely populated. Wiggle matching of seven radiocarbon ages from buried, bark-bearing Douglas-fir (Pseudotsuga menziesii) trees brackets the mudflow’s age between 1477 and 1522 CE with 99.7% certainty. To narrow this date, we applied dendrochronology crossdating on samples collected from 21 trees killed by the lahar, measuring 86 time series for statistical verification. The four bark-bearing trees died the same year while the final rings in all other trees had decayed, exposing rings formed in earlier years. When averaged together, the crossdated measurements form a 475 yr master chronology that was correlated against absolutely dated tree-ring chronologies in the region. The Electron chronology best matched with chronologies from low-elevation sites, especially a Douglas-fir chronology from Vancouver Island, Canada, to show that the Electron trees died in 1507 CE. Latewood in the final ring was beginning to form, indicating the mudflow likely occurred in the late-summer months. What caused the Electron Mudflow is unknown, but this precise date will help to assess possible relationships with other events, assist in interpreting Indigenous narratives about the mudflow, and increase awareness of potential lahar hazards.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"133 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145704185","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Anne-Sofie C. Ahm, Philip Fralick, John A. Higgins
Earth’s long-term climate is closely tied to the formation of carbonate sediments in the ocean, driving the ocean’s ability to moderate atmospheric CO2 levels. It has been hypothesized that in the Precambrian, this process was controlled by a “hidden” deep-sea carbonate sink. However, our results indicate that shallow-marine platforms have been the dominant mode of carbonate formation since the Mesoarchean. This conclusion is based on Ca isotopes from 2.8 Ga carbonates, which constrain the Ca isotope value of Mesoarchean seawater to −0.5‰ relative to modern values, strikingly similar to pre-Mesozoic values and suggesting that carbonate deposition mainly was confined to shallow-water platforms until the evolution of pelagic calcifiers in the Mesozoic.
{"title":"As it ever was: Calcium isotope constraints on Mesoarchean seawater chemistry","authors":"Anne-Sofie C. Ahm, Philip Fralick, John A. Higgins","doi":"10.1130/g53945.1","DOIUrl":"https://doi.org/10.1130/g53945.1","url":null,"abstract":"Earth’s long-term climate is closely tied to the formation of carbonate sediments in the ocean, driving the ocean’s ability to moderate atmospheric CO2 levels. It has been hypothesized that in the Precambrian, this process was controlled by a “hidden” deep-sea carbonate sink. However, our results indicate that shallow-marine platforms have been the dominant mode of carbonate formation since the Mesoarchean. This conclusion is based on Ca isotopes from 2.8 Ga carbonates, which constrain the Ca isotope value of Mesoarchean seawater to −0.5‰ relative to modern values, strikingly similar to pre-Mesozoic values and suggesting that carbonate deposition mainly was confined to shallow-water platforms until the evolution of pelagic calcifiers in the Mesozoic.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"79 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145704184","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
B.V. Ribeiro, V. Jakobsson, C.L. Kirkland, R.A. Spikings, A. Zametzer, W.D.A. Rickard, S. Centrella, N.E. Timms, A.J. Cavosie, M. Danišík
Bolide impacts can have profound effects on Earth, causing biogeochemical changes that may obliterate, initiate, or even diversify life. Thus, identifying and dating impact structures, especially in ancient rocks, can provide crucial temporal context for understanding the role of impacts in Earth’s evolution. We present novel characterization of muscovite from shocked pegmatites of the Yarrabubba structure in Western Australia. Shocked muscovite developed kink bands that underwent chemical modification, increasing the celadonite content, interpreted to be coeval with the impact event. In situ Rb−Sr (2463 ± 25 Ma) and 40Ar/39Ar dates (ca. 2464 Ma; probability peak) from low-strain, chemically unmodified muscovite overlap with zircon U−Pb dates (2440 ± 16 Ma) of pegmatite crystallization. Conversely, in situ 40Ar/39Ar dates from high-strain, celadonite-enriched lamellae define a complex age spectrum with a ca. 2266 Ma probability peak, overlapping the Yarrabubba impact age. Our findings indicate that muscovite, a major crustal mineral, can retain unique microstructural and geochemical features formed during impact metamorphism, and that targeted 40Ar/39Ar analysis can provide a reliable upper limit for the impact age.
{"title":"Microstructural and geochemical response of muscovite to impact metamorphism","authors":"B.V. Ribeiro, V. Jakobsson, C.L. Kirkland, R.A. Spikings, A. Zametzer, W.D.A. Rickard, S. Centrella, N.E. Timms, A.J. Cavosie, M. Danišík","doi":"10.1130/g53895.1","DOIUrl":"https://doi.org/10.1130/g53895.1","url":null,"abstract":"Bolide impacts can have profound effects on Earth, causing biogeochemical changes that may obliterate, initiate, or even diversify life. Thus, identifying and dating impact structures, especially in ancient rocks, can provide crucial temporal context for understanding the role of impacts in Earth’s evolution. We present novel characterization of muscovite from shocked pegmatites of the Yarrabubba structure in Western Australia. Shocked muscovite developed kink bands that underwent chemical modification, increasing the celadonite content, interpreted to be coeval with the impact event. In situ Rb−Sr (2463 ± 25 Ma) and 40Ar/39Ar dates (ca. 2464 Ma; probability peak) from low-strain, chemically unmodified muscovite overlap with zircon U−Pb dates (2440 ± 16 Ma) of pegmatite crystallization. Conversely, in situ 40Ar/39Ar dates from high-strain, celadonite-enriched lamellae define a complex age spectrum with a ca. 2266 Ma probability peak, overlapping the Yarrabubba impact age. Our findings indicate that muscovite, a major crustal mineral, can retain unique microstructural and geochemical features formed during impact metamorphism, and that targeted 40Ar/39Ar analysis can provide a reliable upper limit for the impact age.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"168 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145674287","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Calum M. Lyell, Finlay M. Stuart, James I. Shaw, Adrian J. Boyce, Jonathan Cloutier
Orogenic gold vein deposits are an economically important, well-documented mineralization class with limited consensus regarding the role of juvenile magmatism in their genesis. Here we use He isotopes to determine the contribution of mantle heat in driving the ore fluids responsible for major gold deposits in the Laurentian Caledonides of Britain and Ireland, including all active mines (Cononish, Curraghinalt, and Cavanacaw), many of which are tentatively classed as orogenic. The 3He/4He of fluids in Au-bearing sulfides (0.09−3.3 Ra) require a significant contribution from exsolved magmatic volatiles, implying that mantle heat is intrinsic to ore formation. The largest deposit, Curraghinalt, formed from the hottest ore fluids with the highest proportion of magmatic He during the Grampian Event. The smaller late-Caledonian deposits precipitated from cooler fluids with lower 3He/4He. Ore-fluid 3He/4He does not correlate with sulfide δ34S (−1.9−9.1‰) reflecting multiple crustal S sources. A positive correlation between the maximum 3He/4He and Au reserve implies that gold was sourced from mafic mantle melts generated by post-subduction processes during the Caledonian orogeny.
{"title":"The role of mantle melting and associated granitoid magmatism in the genesis of orogenic gold in the Laurentian Caledonides","authors":"Calum M. Lyell, Finlay M. Stuart, James I. Shaw, Adrian J. Boyce, Jonathan Cloutier","doi":"10.1130/g54161.1","DOIUrl":"https://doi.org/10.1130/g54161.1","url":null,"abstract":"Orogenic gold vein deposits are an economically important, well-documented mineralization class with limited consensus regarding the role of juvenile magmatism in their genesis. Here we use He isotopes to determine the contribution of mantle heat in driving the ore fluids responsible for major gold deposits in the Laurentian Caledonides of Britain and Ireland, including all active mines (Cononish, Curraghinalt, and Cavanacaw), many of which are tentatively classed as orogenic. The 3He/4He of fluids in Au-bearing sulfides (0.09−3.3 Ra) require a significant contribution from exsolved magmatic volatiles, implying that mantle heat is intrinsic to ore formation. The largest deposit, Curraghinalt, formed from the hottest ore fluids with the highest proportion of magmatic He during the Grampian Event. The smaller late-Caledonian deposits precipitated from cooler fluids with lower 3He/4He. Ore-fluid 3He/4He does not correlate with sulfide δ34S (−1.9−9.1‰) reflecting multiple crustal S sources. A positive correlation between the maximum 3He/4He and Au reserve implies that gold was sourced from mafic mantle melts generated by post-subduction processes during the Caledonian orogeny.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"101 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145674182","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Rowan C. Martindale, Sinjini Sinha, Travis N. Stone, Tanner Fonville, Stéphane Bodin, François-Nicolas Krencker, Peter Girguis, Crispin T.S. Little, Lahcen Kabiri
Wrinkle structures are often interpreted to be formed by photosynthetic microbial mats. They are rare in Phanerozoic marine subtidal environments because animal activity typically destroys mats or biofilms before lithification. We report wrinkle structures in lower Toarcian (Lower Jurassic) turbidites from the Tagoudite Formation in Morocco. These wrinkles are consistent with those from shallower deposits; however, given their paleodepth (∼200 m), it is unlikely they were formed by photoautotrophic communities. Modern turbidites are known to host chemosynthetic communities, often with extensive microbial mat formation. We propose the Tagoudite Formation wrinkles were formed by chemosynthetic communities, and the sedimentological, geochemical, and hydrographical conditions of the turbidites excluded grazers, allowing wrinkle structure lithification. Wrinkle structures occur in Cambrian, Silurian, Devonian, and Jurassic turbidites, and we posit that chemosynthetic mats growing on turbidity deposits represent a previously dismissed, underappreciated, or unrecognized mode of preservation. The chemosynthetic mat−induced wrinkle paradigm has significant implications; this taphonomic window for wrinkle preservation in turbidites expands the range of environments where these microbially induced sedimentary structures form and the communities that made them. Wrinkles in turbidites also represent new possibilities for the study of chemosynthetic ecosystems in deep time.
{"title":"Chemosynthetic microbial communities formed wrinkle structures in ancient turbidites","authors":"Rowan C. Martindale, Sinjini Sinha, Travis N. Stone, Tanner Fonville, Stéphane Bodin, François-Nicolas Krencker, Peter Girguis, Crispin T.S. Little, Lahcen Kabiri","doi":"10.1130/g53617.1","DOIUrl":"https://doi.org/10.1130/g53617.1","url":null,"abstract":"Wrinkle structures are often interpreted to be formed by photosynthetic microbial mats. They are rare in Phanerozoic marine subtidal environments because animal activity typically destroys mats or biofilms before lithification. We report wrinkle structures in lower Toarcian (Lower Jurassic) turbidites from the Tagoudite Formation in Morocco. These wrinkles are consistent with those from shallower deposits; however, given their paleodepth (∼200 m), it is unlikely they were formed by photoautotrophic communities. Modern turbidites are known to host chemosynthetic communities, often with extensive microbial mat formation. We propose the Tagoudite Formation wrinkles were formed by chemosynthetic communities, and the sedimentological, geochemical, and hydrographical conditions of the turbidites excluded grazers, allowing wrinkle structure lithification. Wrinkle structures occur in Cambrian, Silurian, Devonian, and Jurassic turbidites, and we posit that chemosynthetic mats growing on turbidity deposits represent a previously dismissed, underappreciated, or unrecognized mode of preservation. The chemosynthetic mat−induced wrinkle paradigm has significant implications; this taphonomic window for wrinkle preservation in turbidites expands the range of environments where these microbially induced sedimentary structures form and the communities that made them. Wrinkles in turbidites also represent new possibilities for the study of chemosynthetic ecosystems in deep time.","PeriodicalId":12642,"journal":{"name":"Geology","volume":"6 1","pages":""},"PeriodicalIF":5.8,"publicationDate":"2025-12-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145664939","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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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