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1. The Late Paleogene Çankırı Basin of Türkiye: The geologic record of lithospheric foundering beneath the Central Anatolian Plateau

   https://doi.org/10.1130/B38453.1  

   Campbell, CF; Taylor, MH; Mueller, MA; Licht, A; Ocakoğlu, F; Beard, KC (November 2025, Geological Society of America Bulletin)

   We hypothesized that the Çankırı Basin of Türkiye records lithospheric foundering beneath the Central Anatolian Plateau in Late Paleogene time. Geologic mapping and stratigraphic sections supplemented by detrital zircon U-Pb and Hf isotopic analyses demonstrate that a 7500 km2 saline lake developed within a 125 × 75 km box-fold along the İzmir-Ankara-Erzincan Suture Zone at ca. 37.5 Ma. Lacustrine environments mark the transition from polymodal to bimodal detrital zircon age spectra during the onset of a trend toward crustal εHf(t) values. Such geologic and geochemical changes are consistent with subsidence above thickening lithosphere. At ca. 32.5 Ma deposition transitioned to volcanogenic-alluvial, fluvial, and lacustrine environments along the northern margin of the Çankırı Basin. Detrital zircon from such deposits return to polymodal age spectra and record a 15-unit εHf(t) mixing array. Such changes are consistent with unroofing and multi-source melting during isostatic rebound above foundering lithosphere. Today, the Çankırı Basin resides within an elliptical ~750-m-high topographic depression that is bisected by the north-northeast flowing Kızılırmak River and surrounded by rugged landscapes reaching elevations of ~1500 m. Such radial physiographic symmetry exhibits a wavelength of ~250 km (50,000 km2) and further defines the Sarıcakaya-Kızılırmak and Yeşilırmak-Kızılırmak river drainage divides. Indeed, both drainage divides are underlain by a slow shear wave velocity geophysical anomaly. Thus, the geomorphological expression of drip tectonics endures today. Our results, therefore, demonstrate that upper plate lithospheric removal along the İzmir-Ankara-Erzincan Suture Zone began in Late Paleogene time and is tied to the ongoing development of the Central Anatolia Plateau. 

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2. Early to middle Eocene (50–43 Ma) Xianqian Basin in central Tibet: Archives of arid paleoenvironments and a southward plateau uplift trend

   https://doi.org/10.1130/B38437.1  

   Ma, Anlin; He, John JY; Hu, Xiumian; Kapp, Paul; Wang, Youwei; Wang, Jordan W; Li, Lin; Liang, Wendong; Wang, Xuetian; Li, Keran (November 2025, Geological Society of America Bulletin)

   Abstract Sedimentary basins provide valuable records of local surface uplift and paleoenvironment. While previous studies have inferred that the Qiangtang terrane in the Tibetan interior has been at high elevation since at least the Eocene, direct evidence from well-dated basins within the Qiangtang terrane remains scarce. Here, we present integrated stratigraphic, sedimentologic, paleontologic, and provenance data from the Maerguo Formation in the Xianqian Basin, southwestern Qiangtang. U-Pb dating of tuff zircons and lacustrine carbonate indicates that the Maerguo Formation was deposited between ca. 50 Ma and 43 Ma, establishing an Eocene record for central Tibet’s paleoenvironmental, tectonic, and topographic evolution. The Maerguo Formation consists of >1900 m of well-exposed strata that comprise five distinct units from bottom to top: Em1 (lower conglomerates); Em2 (fluvial red beds); Em3 (lower fine-grained lacustrine red beds); Em4 (upper lacustrine unit); and Em5 (upper conglomerates). Growth strata developed synchronously with a north-dipping thrust along the northern margin of the Xianqian Basin, while the southern part of the basin dips gently and lies unconformably above Mesozoic strata. Multiproxy provenance data indicate sediment sources from surrounding sedimentary and volcanic rocks, with sediments derived from more localized metamorphic rocks and Jurassic granitoids to the north becoming dominant during the deposition of units Em4 and Em5 in the northern basin. The presence of abundant gypsum in Em3, lacustrine carbonate in Em3 and Em4, and small, narrow, elongate leaf fossils in Em4 indicates an arid environment. These findings indicate that the Xianqian Basin was a short-lived, arid, internally drained system that terminated well before the peak expansion of Cenozoic basins along the Bangong-Nujiang suture to the south. The integrated paleogeographic reconstruction suggests that surface uplift of the Tibetan Plateau progressed southward from its interior since the Eocene. This Tibetan uplift pattern may have been driven by lithospheric removal and associated crustal shortening and thickening, beginning in the central Qiangtang terrane. 

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3. Stratigraphic Context and Preliminary Taphonomy of Mammalian Fossil Assemblages from Stewart Valley, Nevada

   https://doi.org/10.1130/abs/2025AM-8792  

   Loughney, Katharine (January 2025, Geological Society of America)

   The Stewart Valley in eastern Nevada is one of the numerous basins of the Basin and Range province that formed through extensional tectonics during the Miocene. The Gilbert Andesite and Stewart Valley Group (~16–11 Ma) comprise volcanic, volcaniclastic, lacustrine, and fluvial deposits that represent the evolution of a localized lake system in a volcanically active region. These units preserve abundant plant, insect, and vertebrate fossils for which Stewart Valley is well known. Fossil localities in the basin formed within and at the margins of a lake system that expanded and contracted over time, with different fossil assemblages forming in relation to lake transgressions and regressions. Based on results from stratigraphic simulations of extensional-basin fossil records, preservation quality and taphonomic mode are predicted to vary cyclically with lake-level fluctuations. Plant, insect, and fish assemblages are preserved in thin-bedded tuffaceous or cherty shales and siltstones representing deposits in a relatively deep-water lake that was intermittently stratified. Mammalian and small-vertebrate fossils occur at localities representing fluvial and lake-margin deposits, and taphonomic features of the assemblages vary taxonomically and with facies. The majority of bones are disarticulated and isolated; material from small vertebrates have lower amounts of weathering and abrasion than material from large mammals. Preliminary taphonomic assessment of mammalian material from Stewart Valley indicates that assemblages are time averaged and accumulated in a low-aggradation marginal lacustrine setting. Preservation quality of terrestrial vertebrate assemblages may vary in relation to changes in lake-level: increasing in localities forming during early lake-level rise and decreasing through slowing lake-level rise in association with increased indications of reworking and subaerial exposure 

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4. Pleistocene shifts in Great Basin hydroclimate seasonality govern the formation of lithium-rich paleolake deposits

   https://doi.org/10.1016/j.quascirev.2024.108747  

   Bhattacharya, Tripti; Brennan, Peter R; Ibarra, Daniel E; Gagnon, Catherine A; Butler, Kristina L; Terrazas, Alexa; Miller, Shaw; Munk, Lee Ann; Boutt, David F; Feng, Ran; et al (July 2024, Quaternary Science Reviews)

   Southwestern North America is currently experiencing a multidecadal megadrought, with severe consequences for water resources. However, significant uncertainty remains about 21st century precipitation changes in this semi-arid region. Paleoclimatic records are essential for both contextualizing current change, and for helping constrain the sensitivity of regional hydroclimate to large-scale global climate. In this paper, we present a new 2.8 Ma to present compound-specific isotopic record from Clayton Valley, the site of a long-lived paleolake in the southern Great Basin. Hydrogen and carbon isotopes from terrestrial plant leaf waxes provide evidence of past shifts in rainfall seasonality as well as ecosystem structure, and help contextualize the formation of this lithium-rich lacustrine basin. Our results suggest that regional hydroclimates underwent a substantial reorganization at the Plio-Pleistocene boundary, especially between 2.6 and 2.0 Ma. In this interval, a reduced latitudinal temperature gradient in the North Pacific likely resulted in a northward shift in storm tracks, and a reduction in winter rainfall over the southern Great Basin. This occurred against a background of increased summer rainfall and a greater accumulation of lithium in the lake basin. Our interpretation is corroborated by a compilation of Plio-Pleistocene north Pacific sea surface temperature records, as well as an isotope-enabled model simulation. Overall, these results suggest that past shifts in rainfall seasonality helped set the stage for the development and dessication of lithium-rich lacustrine deposits. 

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5. Loess in the Lodeve? Exploring the depositional character of the Permian Salagou Formation, Lodeve Basin (France).

   https://doi.org/doi:10.1130/abs/2018AM-317628  

   Pfeifer, Lily S. (October 2018, Geological Society of America Abstracts with Programs)

   Permocarboniferous strata of basins proximal to the Central Pangaean Mountains in France archive regional paleoequatorial climate during a unique interval in geological history (late Paleozoic Pangaean assembly, ice age collapse, megamonsoon inception). The voluminous (estimated 2 km) succession of exclusively fine-grained redbeds that composes the Permian Salagou Formation (Lodéve Basin, France) has been interpreted as recording either lacustrine or fluvial settings. We present preliminary field data to explore the hypothesis that these deposits record eolian transport, and ultimate deposition as either loess or in a shallow lacustrine environment. Fieldwork includes ~1000 m of section described at dm-scale, and magnetic susceptibility measured at 0.5 m intervals, from sections strategically located in both proximal and distal areas, and from all stratigraphic levels of the unit to assess spatial and temporal variations. These data indicate that the lower and middle Salagou Formation is dominated by internally massive, red mud-siltstone with no evidence of channeling. Up-section, a higher frequency of ripples, rare hummocky cross stratification, and mudcracks record the presence of shallow water, but with no channeling, nor units of grain size exceeding very fine-grained sand. Randomly-oriented slickensides at various localities in the mid-upper Salagou may represent incipient pedogenesis. The lack of evidence for channels and other fluvial features casts doubt on a fluvial interpretation. A lacustrine interpretation is consistent with local evidence of shallow water. However, in the absence of fluvial transport indicators, large volumes of entirely fine-grained material that were delivered to the Lodéve basin call for eolian transport, and thus a loess or shallow lacustrine interpretation. The documentation of voluminous paleoloess in eastern equatorial Pangea during the Permian could reflect the influence of glaciation associated with the Variscan highlands. Together with previous studies that detail Permian loess in western equatorial Pangea, this work impacts our understandingof the global Late Paleozoic climate system and presents a need to reevaluate modeling parameters (e.g. equatorial mountain glaciation, atmospheric dust loading). 

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