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1. Microbial and Geochronologic Constraints on the Neogene Paleotopography of Northern Tibetan Plateau

   https://doi.org/10.1029/2018GL081505  

   Zhuang, Guangsheng; Zhang, Yi Ge; Hourigan, Jeremy; Ritts, Bradley; Hren, Michael; Hou, Mingqiu; Wu, Minghao; Kim, Bumsoo (February 2019, Geophysical Research Letters)

   Abstract High topography is the manifestation of the balance between deep and surficial erosional processes. Hence, reconstructions of paleotopography are critical for disentangling records of orogenesis and climate. Here we used a new approach by combining detrital zircon U‐Pb geochronology and tetraether‐based paleothermometry to characterize the Neogene paleotopography of Northern Tibetan Plateau. Detrital zircon U‐Pb data reveal that the Qilian Shan has been uplifted, providing sediments to bounding basins since circa 15.8 Ma. The paleothermometry studies show warm temperatures for paleosols (<12.4–9.5 Ma and 3.7–2.0 Ma) and low temperatures for lacustrine facies (12.4 Ma and 9.5–3.7 Ma). We interpret the different temperatures to reflect the in situ production of tetraethers under warm temperatures within the basin (paleosols) versus terrestrial inputs from high and cold drainage to the paleolake (lacustrine facies). The study supports a topography with significant relief in the Northern Tibetan Plateau since 12.4 Ma. 

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2. Dating lacustrine carbonate strata with detrital zircon U-Pb geochronology

   https://doi.org/10.1130/G48070.1  

   Finzel, Emily S.; Rosenblume, Justin A. (November 2020, Geology)

   null (Ed.)

   Abstract Carbonate lacustrine strata in nonmarine systems hold great potential for refining depositional ages through U-Pb dating of detrital zircons. The low clastic sediment flux in carbonate depositional environments may increase the relative proportion of zircons deposited by volcanic air fall, potentially increasing the chances of observing detrital ages near the true depositional age. We present U-Pb geochronology of detrital zircons from lacustrine carbonate strata that provides proof of concept for the effectiveness of both acid-digestion recovery and resolving depositional ages of nonmarine strata. Samples were collected from Early Cretaceous foreland basin fluvial sandstone and lacustrine carbonate in southwestern Montana (USA). Late Aptian–early Albian (ca. 115–110 Ma) maximum depositional ages young upsection and agree with biostratigraphic ages. Lacustrine carbonate is an important component in many types of tectonic basins, and application of detrital zircon U-Pb geochronology holds considerable potential for dating critical chemical and climatic events recorded in their stratigraphy. It could also reveal new information for the persistent question about whether the stratigraphic record is dominated by longer periods of background fine-grained sedimentation versus short-duration coarse-grained events. In tectonically active basins, lacustrine carbonates may be valuable for dating the beginning of tectonic subsidence, especially during periods of finer-grained deposition dominated by mudrocks and carbonates. 

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3. Chronostratigraphy of Miocene strata in the Berkeley Hills (California Coast Ranges, USA) and the arrival of the San Andreas transform boundary

   https://doi.org/10.1130/GES02650.1  

   Gerasimov, Stacey H; Hodgin, Eben B; Crowley, James L; Swanson-Hysell, Nicholas L (January 2024, Geosphere)

   Miocene strata of the Claremont, Orinda, and Moraga formations of the Berkeley Hills (California Coast Ranges, USA) record sedimentation and volcanism during the passage of the Mendocino triple junction and early evolution of the San Andreas fault system. Detrital zircon laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) age spectra indicate a change in sedimentary provenance between the marine Claremont formation (Monterey Group) and the terrestrial Orinda and Moraga Formations associated with uplift of Franciscan Complex lithologies. A sandstone from the Claremont formation produced a detrital zircon chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) maximum depositional age of 13.298 ± 0.046 Ma, indicating younger Claremont deposition than previously interpreted. A trachydacite tuff clast within the uppermost Orinda Formation yielded a CA-ID-TIMS U-Pb zircon date of 10.094 ± 0.018 Ma, and a dacitic tuff within the Moraga Formation produced a CA-ID-TIMS U-Pb zircon date of 9.974 ± 0.014 Ma. These results indicate rapid progression from subsidence in which deep-water siliceous sediments of the Claremont formation were deposited to uplift that was followed by subsidence during deposition of terrestrial sediments of the Orinda Formation and subsequent eruption of the Moraga Formation volcanics. We associate the Orinda tuff clast and Moraga volcanics with slab-gap volcanism that followed the passage of the Mendocino triple junction. Given the necessary time lag between triple junction passage and the removal of the slab that led to this volcanism, subsidence associated with ca. 13 Ma Claremont sedimentation and subsequent Orinda to Moraga deposition can be attributed to basin formation along the newly arrived transform boundary. 

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4. High-latitude ice and climate control on sediment supply across SW Gondwana during the late Carboniferous and early Permian

   https://doi.org/10.1130/B35852.1  

   Griffis, N.; Montañez, I.; Mundil, R.; Heron, D. Le; Dietrich, P.; Kettler, C.; Linol, B.; Mottin, T.; Vesely, F.; Iannuzzi, R.; et al (February 2021, GSA Bulletin)

   null (Ed.)

   Abstract The response of sediment routing to climatic changes across icehouse-to-greenhouse turnovers is not well documented in Earth's pre-Cenozoic sedimentary record. Southwest Gondwana hosts one of the thickest and most laterally extensive records of Earth's penultimate icehouse, the late Paleozoic ice age. We present the first high-resolution U-Pb zircon chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) analysis of late Paleozoic ice age deposits in the Kalahari Basin of southern Africa, which, coupled with existing CA-ID-TIMS zircon records from the Paraná and Karoo Basins, we used to refine the late Paleozoic ice age glacial history of SW Gondwana. Key findings from this work suggest that subglacial evidence in the Kalahari region is restricted to the Carboniferous (older than 300 Ma), with glacially influenced deposits culminating in this region by the earliest Permian (296 Ma). The U-Pb detrital zircon geochronologic records from the Paraná Basin of South America, which was located downstream of the Kalahari Basin in the latest Carboniferous and Permian, indicate that large-scale changes in sediment supplied to the Paraná were contemporaneous with shifts in the SW Gondwana ice record. Gondwanan deglaciation events were associated with the delivery of far-field, African-sourced sediments into the Paraná Basin. In contrast, Gondwanan glacial periods were associated with the restriction of African-sourced sediments into the basin. We interpret the influx of far-field sediments into the Paraná Basin as an expansion of the catchment area for the Paraná Basin during the deglaciation events, which occurred in the latest Carboniferous (300–299 Ma), early Permian (296 Ma), and late early Permian (<284 Ma). The coupled ice and detrital zircon records for this region of Gondwana present opportunities to investigate climate feedbacks associated with changes in freshwater and nutrient delivery to late Paleozoic ocean basins across the turnover from icehouse to greenhouse conditions. 

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5. Stratigraphic and geochronologic investigation of the Muddy Creek Basin: Implications for the Eocene tectonic evolution of southwest Montana, USA

   https://doi.org/10.1130/B37268.1  

   Thoresen, Haley E; Cassel, Elizabeth J; Smith, M Elliot; Stockli, Daniel F; Jicha, Brian R (February 2024, Geological Society of America Bulletin)

   Sedimentary basins record crustal-scale tectonic processes related to the construction and demise of orogenic belts, making them an invaluable archive for the reconstruction of the evolution of the North American Cordillera. In southwest Montana, USA, the Renova Formation, considered to locally represent the earliest accumulation following Mesozoic−Cenozoic compressional deformation, is widespread but remains poorly dated, and its origin is debated. Herein, we employed detrital zircon U-Pb and (U-Th)/He double dating and sanidine 40Ar/39Ar geochronology in the context of decimeter-scale measured stratigraphic sections in the Renova Formation of the Muddy Creek Basin to determine basin evolution and sediment provenance and place the basin-scale record within a regional context to illuminate the lithospheric processes driving extension and subsidence. The Muddy Creek Basin is an extensional half graben in southwest Montana that is ∼22 km long and ∼7 km wide, with a >800-m-thick sedimentary package. Basin deposition began ca. 49 Ma, as marked by multiple ignimbrites sourced from the Challis volcanic field, which are overlain by a tuffaceous fluvial section. Fluvial strata are capped by a 46.8 Ma Challis ignimbrite constrained by sanidine 40Ar/39Ar dating. An overlying fossiliferous limestone records the first instance of basinal ponding, which was coeval with the cessation of delivery of Challis volcanics−derived sediment into the Green River Basin. We attribute initial ponding to regional drainage reorganization and damning of the paleo−Idaho River due to uplift and doming of the southern Absaroka volcanic province, resulting in its diversion away from the Green River Basin and backfilling of the Lemhi Pass paleovalley. Detrital zircon maximum depositional ages and sanidine 40Ar/39Ar ages show alternating fluvial sandstone and lacustrine mudstone deposition from 46 Ma to 40 Ma in the Muddy Creek Basin. Sediment provenance was dominated by regionally sourced, Challis volcanics−aged and Idaho Batholith−aged grains, while detrital zircon (U-Th)/He (ZHe) data are dominated by Eocene cooling ages. Basin deposition became fully lacustrine by ca. 40 Ma, based on an increasing frequency of organic-rich mudstone with rare interbedded sandstone. Coarse-grained lithofacies became prominent again starting ca. 37 Ma, coeval with a major shift in sediment provenance due to extension and local footwall unroofing. Detrital zircon U-Pb and corresponding ZHe ages from the upper part of the section are predominantly Paleozoic in age, sourced from the Paleozoic sedimentary strata exposed in the eastern footwall of the Muddy Creek detachment fault. Paleocurrents shift from south- to west-directed trends, supporting the shift to local sources, consistent with initiation of the Muddy Creek detachment fault. Detrital zircon maximum depositional ages from the youngest strata in the basin suggest deposition continuing until at least 36 Ma. These data show that extension in the Muddy Creek Basin, which we attribute to continued lithospheric thermal weakening, initiated ∼10 m.y. later than in the Anaconda and Bitterroot metamorphic core complexes. This points to potentially different drivers of extension in western Montana and fits previously proposed models of a regional southward sweep of extension related to Farallon slab removal. 

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