ABSTRACTThe causes of the transition from a greenhouse to an icehouse climate during the Early Mississippian (∼359–347 Ma), Carboniferous, marking the possible onset of the Late Paleozoic Ice Age (LPIA), remain an outstanding puzzle in Earth’s climate history. This transition coincides with the mid-Tournaisian carbon isotope excursion (TICE). It is hypothesized that intensified continental silicate weathering during this period sequestered CO₂, boosted nutrients, and increased marine productivity, causing the positive TICE. However, direct evidence for enhanced continental weathering has been lacking. We present lithium isotope (δ⁷Li) data from two carbonate sections showing a ∼12‰ decline during TICE. Integrating δ⁷Li with carbon cycle models (GEOCLIM and COPSE) suggests silicate chemical weathering rates increased ∼30% with declines in weathering intensity during the TICE event, likely due to uplift or vegetation, ultimately reducing atmospheric pCO₂ by ∼1000 ppmv. This provides evidence linking enhanced chemical weathering, CO₂ drawdown, and the onset of the LPIA, shedding light on a key aspect of late Paleozoic climate change.

ABSTRACTThe Central Asia Orogenic Belt (CAOB), the largest accretionary orogenic belt in the world, has a complex history. Carboniferous–Permian magmatism in the Zhangfangshan area of China is the key to understanding the accretion orogeny and reconstructing the orogenic belt structure in the southern Beishan Orogenic Belt, which is a part of the southern margin of the CAOB. The Zhangfangshan complex is exposed in the southeast of the Beishan area and includes plagiogranite, quartz diorite, siliceous rocks, limestone, and metamorphic sandstones. We obtained weighted mean zircon 206Pb/238U ages of 351 ± 2 Ma and 338 ± 3 Ma from plagiogranite and quartz diorite in the complex, respectively. The plagiogranite yields clear negative Nb–Ta anomalies on a trace element spider diagram and εHf(t) values of +14.8 to +20.1, characteristic of depleted mantle. These results indicate that the Zhangfangshan ophiolite was formed during the early Mississippian. The quartz diorites have similar trace element and Hf isotopic compositions to O‐type adakites and high‐Mg diorites, implying the partial melting of subducted oceanic crust. The undeformed granodiorite porphyrite and diabase that intrude the Zhangfangshan complex yield mean 206Pb/238U ages of 270 ± 1 Ma and 250 ± 1 Ma, respectively, suggesting that the ocean basin represented by the Zhangfangshan ophiolite was closed before ~ 270 Ma. The diorite–granodiorite porphyrites have low Mg# (42.8–46.1) and positive εHf(t) values (+4.7 to +10.0), suggesting that they were generated from juvenile crust. The diabases have geochemical characteristics similar to the diorite porphyrite and have evolved εHf(t) values (−0.5 to +11.7) that may be related to crust–mantle mixing in their source. Based on our results and previous findings, we reveal the Late Palaeozoic evolutionary process in the southern Beishan orogenic belt.

The mid-Tournaisian carbon isotope excursion (TICE) represents the largest positive carbon isotope excursion in the late Paleozoic, coinciding with the onset of the late Paleozoic ice age (LPIA). Here, to investigate changes in the marine biological pump during the TICE, we measured barium isotopes (δ138Ba) in two marine limestone sections in the Antler foreland basin (USA). We found the largest positive δ138Ba shifts recorded in geological history, indicating increased marine export productivity in the Antler foreland basin, followed by the productivity-driven expansion of anoxia. The nearly identical stratigraphic trends, along with different absolute values in δ138Ba between the two sites, suggest spatial differences in marine biological pump intensity during the Early Mississippian. Earth system model simulations indicate that a global increase of 30% in marine export productivity is needed to explain observed changes. Our findings support the idea that an enhanced marine biological pump contributed to elevated organic carbon burial and the transition from a greenhouse climate to the LPIA.

Abstract A new genus and species of hoplostracan crustacean from Ohio, USA, Aridelocaris ohioensisn. gen., n. sp., extends the range of Hoplostraca and Sairocarididae into the Early Mississippian (Tournaisian) and echoes the Laurussian biogeographic distribution for most middle Paleozoic malacostracans. Preservation in a concretion yielded more three-dimensional preservation than seen in any other taxon of Hoplostraca and presents detail of the carapace morphology justifying a new genus. The new genus exhibits different carapace and telson morphology from the previously known genera, expanding the known morphological variation within Hoplostraca.

The transition of vertebrates from aquatic to terrestrial environments during the late Devonian to early Carboniferous marks a crucial evolutionary milestone. However, this transition remains poorly understood due to a scarcity of early tetrapod fossils during the late Devonian to early Mississippian, creating a gap in the fossil record known as Romer's Gap (~360-345 Ma). Recent discoveries have narrowed this gap, providing critical insights into early tetrapod evolution. The East Kirkton Quarry in Scotland's Midland Valley, has yielded tetrapod fossils considered early stem amphibians and amniotes. They have been proposed to be Mississippian (early Carboniferous) in age, yet data to inform their precise ages remain limited. Here, zircon grains from two tuffaceous clastic limestones and shales were dated using Laser Ablation-Inductively Couple Plasma-Mass Spectrometry (LA-ICP-MS). The study presents detrital zircon U-Pb dates, which refine the current biostratigraphy ages assigned to Westlothiana lizziae, Silvanerpeton miripedes, Balanerpeton woodi, Ophiderpeton kirktonense, Eucritta melanolimnetes, and Kirktonecta milnerae to a maximum depositional age (MDA) of 341 ± 3 Ma (±2σ, n= 7 dates), placing them in the middle-lower Visean (Holkerian-Arundian) rather than the previous assigned upper Visean (Brigantian). This revised maximum depositional age places the East Kirkton Quarry fossils within the older, critical interval of Romer's Gap, bridging a significant evolutionary time interval in the Mississippian fossil record, and allows for refining future tetrapod time trees. X-ray Fluorescence and X-ray Diffraction analyses reveal heterogeneity in the lower East Kirkton Limestone of the East Kirkton Quarry, with variations in elemental and mineralogical compositions, reflecting episodic volcanic and detrital inputs and hydrothermal activity.

Svalbard has long been thought to represent the easternmost realm of the Ellesmerian Orogeny in the late Devonian or early Mississippian (Svalbardian tectonic event). Several authors do not agree and present alternative interpretations of the observed structures in older and more recent articles. This article discusses a number of issues that, in our opinion, are not sufficiently considered in those works, but which are essential for the understanding of the Svalbardian tectonic event: (1) the possibility of re-deposited palynomorphs in the discussion of the deformational ages, (2) the age and structural setting of the crucial Adriabukta Formation in southern Spitsbergen, and (3) the presence and nature of the Svalbardian angular unconformity in central and southern Spitsbergen.

The lithofacies architecture and depositional evolution of the Lower Mississippian (Tournaisian) Pekisko Formation in the subsurface of the Hawk Hills area in northwestern Alberta have been established by integrating detailed core work and well log data. The formation is composed of skeletal-peloidal limestones and argillaceous limestones that were deposited along the northern flank of the Peace River Embayment, a semi-restricted and tectonically active oceanic re-entrant located along the western margin of Laurasia at low paleolatitude. Lithofacies associations recognized in the study area include the outer ramp to slope (LA 1), outer ramp (LA 2) and mid ramp (LA 3), which are stacked into three decameter-scale, deepening-upward and aggradational cycles that are of regional extent and have meter-scale deepening and shallowing-upward trends. A previously unrecognized paleosol horizon at the top of decameter-scale cycle 2, indicating widespread subaerial exposure of the ramp, is interpreted as a sequence boundary that divides the Pekisko and Shunda formations in the study area (and possibly elsewhere in the Peace River Embayment) into two third-order sequences, each consisting of transgressive and highstand systems tracts. The Pekisko Formation in the study area is interpreted to represent a low-energy, temperature-stratified ramp that was mainly homoclinal, but with transient, distal steepening occurring in the southern part of the study area. Ramp deposition was strongly affected by basement-fault reactivation causing differential subsidence and uplift in the Peace River Embayment. The paleogeography and paleoceanographic conditions of the embayment favored upwelling currents and development of a temperature-stratified ramp, as well as the formation of heterozoan carbonate deposits and mid ramp facies of predominantly packstones and wackestones. This depositional scenario is atypical, as most other documented examples of the Pekisko Formation and other Lower Mississippian ramp successions in western North America and western Europe are characterized by moderate to high-energy, mid to inner ramp facies deposited in open-ocean conditions. The results of this study contribute to an improved understanding of the range of depositional settings along the western margin of Laurasia during the Early Mississippian and demonstrate the applicability of the thermocline-stratified ramp model, with some modification, to ramps in semi-restricted embayments and other low energy settings.

The basement structural fabric of the Paradox basin affected sedimentary facies throughout Phanerozoic time. Continental-scale basement wrench-fault zones were rejuvenated repeatedly throughout the Paleozoic. The Paradox pull-apart evaporite basin was formed along the northwest-southeast-trending Paradox-Wichita lineament in Middle Pennsylvanian time, facilitated by basement faults of the northeast-southwest-trending Colorado lineament. Structurally controlled shoaling conditions, formed by reactivation of basement faults, fostered marine sandstone reservoirs in Late Devonian time, crinoidal buildups in the Early Mississippian, and phylloid-algae mounds in Middle Pennsylvanian time. Apparently similar basement wrench-fault zones are present in Kansas. The midcontinent rift system is a north-northeast-south-southwest-trending fault zone that was reactivated during the Paleozoic. Northwest-southeast-trending faults along the Central Kansas-Bourbon arch complex appear to have offset structures of the midcontinent rift. Both trends are interpreted to be continental-scale conjugate wrench-fault zones with sinistral displacement along the midcontinent rift and dextral displacement along the Central Kansas-Bourbon arch complex. Stratigraphic relationships suggest repeated reactivation before Pennsylvanian uplift and erosion along the major structures. In both regions major structural lineaments are associated with smaller-scale fault patterns. Reactivation of these structures through time created paleotectonic trapping conditions at several stratigraphic intervals. Evidence is accumulating in Kansas that tectonically controlled paleotopography and paleobathymetry are major predictable factors in reservoir localization. Recognition of reactivated basement structural fabrics can provide* significant constraints on reservoir characterization and modeling.

As revised here, the Chattanooga Shale of Kansas includes the basal Misener Sandstone Member overlain by informal lower, middle, and upper shale members. Present only in the subsurface, this formation underlies most of the eastern two-thirds of the state. Most of the Chattanooga Shale is Devonian in age, although the uppermost part may be Early Mississippian. The Misener Sandstone Member has an erratic distribution and is usually less than 1 m (3.3 ft) in thickness. The lower shale member is present only in south-central Kansas and is less than 15 m (49.5 ft) thick. The middle and upper shale members can be traced throughout much of the area of Chattanooga subcrop, and their combined thickness can be more than 76 m (250.8 ft). A lenticular limestone bed is present near the base of the upper shale member in central Kansas, and limestone and dolomite beds occur within the upper parts of both the middle and upper shale members in northeastern Kansas. Ferruginous oolites are present in the upper shale member in northeastern Kansas, near the contact with the overlying Mississippian carbonates. Sometimes called the Kinderhook Shale, the Chattanooga Shale of Kansas is equivalent to the Woodford Shale of Oklahoma, Texas, and New Mexico.

Burial and thermal history modeling of basins in convergent oblique-slip mobile zones: A case study of the Ardmore Basin, southern Oklahoma

Abstract The origins and primary relationships between tectono-stratigraphic units are fundamental to the terrane concept in accretionary orogens, but they are challenging to assess in metamorphic terranes. In NW British Columbia, three tectonically bounded metamorphic suites of the Yukon-Tanana terrane formed in distinct tectonic settings, based on high-spatial-resolution geochronology and immobile trace-element geochemistry. The Florence Range suite comprises late Neoproterozoic or younger to pre–latest Devonian metasedimentary rocks derived from continental crust, 360 ± 4 Ma calc-alkaline intermediate orthogneiss, and 357 ± 4 Ma amphibolite with oceanic-island basalt composition, consistent with rifting of a continental margin. The detrital signature is dominated by late Mesoproterozoic zircon, which indicates different sources than other parts of the Yukon-Tanana terrane. The Boundary Ranges suite comprises pre–Late Devonian metasedimentary rocks derived in part from a mafic source, amphibolite derived from subduction-zone metasomatized mantle, and 369 ± 4 Ma to 367 ± 7 Ma calc-alkaline felsic to intermediate orthogneiss. The Whitewater suite comprises meta-chert, graphite-rich metapelite, and amphibolite with back-arc basin basalt composition consistent with an anoxic basin near a volcanic source. Our data indicate that the Florence Range and Boundary Ranges suites were separate until at least the Early Mississippian and may have formed a composite terrane since the Permian, whereas the relationship with the Whitewater suite is uncertain. We compare the Paleozoic evolution of the Yukon-Tanana terrane in NW British Columbia with several modern analogues in the west and southwest Pacific Ocean.

Distributions of vanadyl and nickel porphyrins in the Woodford Shale and selective chelation of metal species by different tetrapyrrole configurations

Abstract The Yukon-Tanana terrane in Yukon, Canada, records Late Devonian (ca. 366–360 Ma) rifting and the onset of latest Devonian–Carboniferous arc and back-arc magmatism (ca. 360–325 Ma) in the Northern Cordillera. Detrital zircon U-Pb and Hf isotope analyses indicate that the metasedimentary basement of the Yukon-Tanana terrane was sourced in northwestern Laurentia. Sandstones in Late Devonian–Carboniferous successions generally have robust Late Devonian–Mississippian age peaks, and their Hf isotope signatures are characterized by strongly negative εHft values in Late Devonian zircons followed by progressively more juvenile εHft values in Carboniferous zircons. This Hf isotopic “pull-up” reflects the melting of Precambrian crust related to regional extension in the Late Devonian, followed by progressively more juvenile magmatism as the arc matured through the Carboniferous. Paleozoic rocks of the Tracy Arm terrane in southeastern Alaska, USA (formerly Yukon-Tanana south), have been compared with the Yukon-Tanana terrane in Yukon. Detrital zircons from the metasedimentary basement to the Tracy Arm terrane have distinct Precambrian populations that indicate sources along a different segment of the Laurentian margin compared to basement of the Yukon-Tanana terrane. Magmatism in the Tracy Arm terrane ranges from 440 Ma to 360 Ma and is characterized by an Hf isotopic “pull-down” in the Silurian to Early Devonian, followed by a “pull-up” in the Middle to Late Devonian and a second “pull-down” in the Late Devonian to early Mississippian. Thus, the Yukon-Tanana and Tracy Arm terranes record distinct pre-Carboniferous histories. Interactions between these two terranes are suggested by the influx of exotic early Mississippian clasts and detrital zircons on the Tracy Arm terrane that match sources in the Yukon-Tanana terrane.

Zonation and biofacies of the Early Mississippian conodonts from Baoshan, Yunnan, Southwest China

Abstract Mississippian rocks of the Antler foreland basin in Nevada (western United States) record its evolution in detail, clarifying the timing and tectonic significance of the Antler orogeny. Synorogenic clastic sediments mark the initiation of tectonism; they arrived in Nevada from the north or northwest in late Early Mississippian (Osagean). An orogenic highland formed in northern Nevada in late Middle Mississippian (Meramecian), producing a regional angular unconformity and terminating deposition in the Antler foreland basin. Unconformably overlying Upper Mississippian (Chesterian) rocks provide tight age control for the redefined “Antler orogeny” sensu stricto. Palinspastic restoration of Sr isotopic data reveals a projecting step in the Laurentian margin in northern Nevada. The Antler orogeny resulted from late Middle Mississippian sinistral-oblique convergence at this step. Continuing oblique convergence produced the subsequent late Paleozoic basins, structures, and unconformities in northern Nevada. The Roberts Mountains allochthon is translated material from farther north emplaced onto the margin. Its basal bounding fault, long mapped as the “Roberts Mountains thrust,” is in fact not a single continuous fault, motion on it was not synchronous, and displacement on many fault segments mapped as the Roberts Mountains thrust postdate the late Middle Mississippian. We therefore propose that the term “Roberts Mountains thrust” be abandoned. This new paradigm not only explains anomalous characteristics of the Antler orogeny but also illustrates criteria for recognizing oblique convergence at other ancient plate margins.

Revised Paleozoic depositional history of the central Rocky Mountains (Utah and Colorado)

Latest Devonian–Early Mississippian conodont biostratigraphy in the Naqing section, Guizhou, South China

ABSTRACT The Oaxacan Complex Carboniferous-Permian sedimentary cover in southern México records provenance shifts through time, reflecting the collision between Gondwana and Laurentia to amalgamate Pangea. The integration of petrological analysis and LA-ICP-MS U-Pb zircon geochronology from Santiago, Ixtaltepec and Yododeñe formations compared with adjacent terranes suggests that: (1) during the Early Mississippian, the Santiago Formation received sediments mainly from local sources such as the Oaxacan Complex and Tiñu Formation, with minor contributions from adjacent peri-Gondwana sources. The magmatic activity may have started during this time (~359–346 Ma) (2) during the Late Mississippian (Ixtaltepec Formation), detrital zircon grains of Ediacaran-Cambrian age are dominant, derived from sediments either related to the Pan-African/Brasiliano orogeny or the opening of the Iapetus Ocean; (3) during the Late Mississippian-Middle Pennsylvanian, intercalated marine volcaniclastic sandstone (Ixtaltepec Formation) provides the first record of Carboniferous arc-related volcanism reported in southern Mexico, dated between 330 and 308 Ma; (4) the early Permian Yododeñe Formation records the exhumation and erosion of the sedimentary cover during the final stage of Pangea assembly. Rhyodacitic subvolcanic sills and lavas dated at ~282–270 Ma are present throughout the succession. Volcanism and ca. 360–308 Ma detrital zircon grains could be associated with a Carboniferous magmatic arc formed by subduction of the Rheic oceanic plate beneath Gondwana. Slightly younger detrital zircon and subvolcanic rocks dated at ~300–270 Ma are linked to a western Pangea arc developed in response to the subduction of the Paleo-Pacific Ocean following Pangea assembly. Our results suggest that the Carboniferous-Permian units were deposited in a peri-arc basin, sharing sediment provenance with the Maya and Coahuila blocks, the Sierra de Juárez Complex, and northwestern South America.

Abstract A new hibbertopterid eurypterid,Cyrtoctenus bambachin. sp., is described from the Early Mississippian (Tournaisian) Price Formation of western Virginia. The same unit yields an unidentifiable stylonurine eurypterid. These are the first eurypterids documented from the Mississippian of North America, and only the fourth locality of this age anywhere in the world to yield eurypterids.UUID:http://zoobank.org/5c84d3a2-ea5a-402c-970d-9b0d867f52c7

Abstract The Yukon-Tanana terrane in the Finlayson Lake district, Yukon, represents one of the first arc–back-arc systems that formed adjacent to the Laurentian continental margin in the mid-Paleozoic. Back-arc rocks contain many large and high-grade volcanogenic massive sulfide (VMS) deposits. This study integrates U-Pb zircon geochronology, lithogeochemistry, and Hf-Nd isotopes to establish precise controls on tectonomagmatic activity adjacent to the western Laurentian margin in the Late Devonian to Early Mississippian. High-precision chemical abrasion- (CA-) ID-TIMS U-Pb zircon geochronology defines coeval arc (ca. 363.1 to 348 Ma) and back-arc (ca. 363.3 to 355.0 Ma) magmatism in the Finlayson Lake district that intruded continental crust of Laurentian affinity (e.g., Snowcap assemblage). Mafic and felsic rocks display geochemical and isotopic characteristics that are consistent with being formed from mixtures of depleted asthenosphere and enriched lithospheric mantle sources. These melts variably entrained Laurentian continental crust via high-temperature crustal melting due to basaltic underplating. The high-temperature back-arc felsic magmatism occurs at specific time periods coinciding with VMS deposits and supports previous genetic models for VMS mineralization that suggest elevated heat flow and hydrothermal circulation were due to regional-scale rift-related magmatism rather than from local subvolcanic intrusions. The short timescales and transient nature of tectonomagmatic events in the Finlayson Lake district suggest that rapid and complex subduction initiation of oceanic and continental crust fragments facilitated coeval compression, extension, and magmatism in the arc and back-arc regions. We thus reevaluate the presently accepted tectonostratigraphic framework of the Finlayson Lake district and suggest revised interpretations that shed light on VMS depositional environments and a possible broader association with the ca. 358 Ma Antler Orogeny. Results of this study have implications for incipient tectonics, magmatism, and mineralization along the western Laurentian continental margin and other orogenic belts globally.