The Devonian Period experienced the proliferation of vascular plants and had the highest levels of carbonate production, reef-building, and marine faunal diversity in the Paleozoic Era, which led to a diverse biostrati-graphic record. While the presence of extensive reef systems is a characteristic feature of many Devonian deposits worldwide, this aspect is relatively subdued in northwestern South America. Instead, the Devonian stratigraphy of Colombia and Venezuela is characterized by marine faunas and flora which altogether point to a connection between Laurussia and Gondwana.Despite these biostratigraphic pieces of evidence, paleogeographic reconstructions of northwestern Gondwana are challenging. For these reasons in this contribution, we summarize the current knowledge of metamorphic, plutonic, and sedimentary Devonian rocks from northwestern Brazil to Venezuela along with our new results to propose paleogeographic evolution during Early, Middle, and Late Devonian time.Devonian sedimentation in northwestern Gondwana took place under an extensional tectonic regime widely documented at the current Eastern Cordillera and Llanos basin in Colombia delineating a Devonian back-arc basin, shaped by normal and dextral strike-slip en echelon faults. Paleontological data discloses to ages ranging from Pragian to Frasnian for the Devonian sedimentary rocks in northwestern Gondwana deposited during a transgression along a north-south trending epicontinental basin, on top of a Proterozoic-Early Paleozoic metamorphic basement. During Eifelian-Givetian times, the build-up of a carbonate platform indicates the maximum flooding surface of the basin. Finally, during the Frasnian-Fammenian, a regressive cycle characterized by coastal facies indicates a period of uplift possibly linked with the first stages of western Pangaea amalgam-ation and the Rheic Ocean closure. Recently, published U-Pb detrital zircon geochronology from Devonian sediments of Colombia basins sug-gests a protracted active margin during Paleozoic times, with near-zero lag times between zircon crystallization and sedimentation. These provenance constraints appear to contradict Devonian magmatic quiescence in northwestern Gondwana. In contrast, south of the Macarena Range in the structural domain of the Guiana Shield, Devonian sedimentary rocks exclusively yield Proterozoic zircon inheritance.Observed changes in detrital zircon provenance suggest, 1) A Devonian magmatic arc in the Oaxaquia, Mix-teca, or Maya blocks, was likely the source of detritus to Devonian basins in northern Colombia and Venezuela, and 2) A paleogeographic control must have prevented the interconnection of northern Devonian sediment routing systems with their southern counterparts in the Guiana Shield. In this scenario, basement highs within the Guiana Shield vicinity likely acted as paleogeographic barriers compartmentalizing Devonian sedimentary basins in northwestern Gondwana.

Devonian orthotetides from South America have often been uncritically assigned to a limited number of broadly described species. Schellwienella clarkei n. sp. is described from the Ponta Grossa Formation, Parana Basin, southern Brazil. These brachiopods had been identified as Schuchertella agassizi. Schellwienella clarkei n. sp. differs from Schuchertella agassizi on the basis of shell structure, dental plates, and cardinalia. UUID: http://zoobank.org/90ebc242-42c3-4bd7-9b63-461df05b6f28

Palynological investigation carried on the samples from the Unit 1 of the Sappington Formation (Upper Famennian, Montana, USA) reveals a presence of rich phytoplankton and microflora assemblages. The presence of spheroidal vesicles approx. 20 mu m in diameter having a rigid smooth wall and frequently arranged in clusters connected by an external coating are proposed as a new taxon named Involusphaeridium gutschicki gen. et sp. nov. The coating on individual vesicles and colonies of I. gutschicki gen. et sp. nov. suggests a link with algal or fungal groups but also, with the eggs of arthropods. Hence, it is considered as incertae sedis (acritarch group). (C) 2020 Elsevier B.V. All rights reserved.

The Toregua Formation in northern Bolivia comprises a continuous succession of sedimentary rocks containing two glacial intervals related to the onset of the Late Paleozoic Ice Age (LPIA). The provenance and depositional tectonic setting of the Upper Devonian-Mississippian (lower) and Pennsylvanian (upper) glacial intervals are separated by non-glacial deposits observed in the Manuripi X-1 and Pando X-1 drill cores, from which petrography, geochemistry, detrital zircon U-Pb and monazite Th-U-total Pb dating are described. Zircon age spectra of sandstone clasts and diamictite indicate an upward change in provenance. Zircon age data from the lower glacial interval yielded age groups at 700-500 Ma, 1300-900 Ma and 2200-1820 Ma, while the monazite gave ages in the range of 600-500 Ma. These age populations correspond to the Guapore Shield and/or the Arequipa Massif. Detrital zircon from the upper glacial interval has a significant age population at 330-300 Ma that reflects prominent input from the Eastern Cordillera. The maximum depositional age of the upper glacial interval was constrained to ca. 308 Ma. Provenance discrimination diagrams, based on major element geochemistry and trace element ratios, suggest that the glacial and non-glacial sediments were mainly sourced from felsic source rocks. The moderate to high chemical index of alteration (CIA < 81) and mineralogical index of alteration (MIA = 81-90 values), abundance of siderite clasts and dominance of kaolinite and abraded zircon grains (without correlation between age and zircon roundness) indicate that the lower glacier incorporated material from older sedimentary covers. In the upper glacial interval, the lower CIA (70) and MIA (71) values and the abundance of plagioclase and detrital zircon grains with preserved euhedral shape < 400 Ma suggest that local volcanic rocks in addition to sedimentary covers were eroded.

For the first time, Late Devonian palynofacies analyses of the Lower Sappington shale units U1A─D was carried out at Peak 9559 (Sacajawea) and Ainger Lake in the Bridger Range of Montana. Diagnostic spore species Apiculiretusispora verrucosa, Diducites mucronatus and D. versabilis allowed the correlation of our U1A-D with the European Late Famennian A. verrucosa-V. hystricosus Palynozone. The first appearance of Gorgonisphaeridium winslowiae in U1 is the oldest record before the inception of Retispora lepidophyta. Four palynofacies correlative with U1A-D and new findings of invertebrates and microfossils allow the interpretation of paleoenvironmental changes. Amorphous organic matter, marine phytoplankton and pyrite in black shales of U1A-B indicate anoxic bottom conditions occurred in offshore marine environments. An erosional fossiliferous phosphatic lag above these units confirms a regional SB. U1C black shales composed by AOM, marine and terrestrial phytoplankton, land–derived remains and pyrite reveal shallower, dysoxic-anoxic, brackish water environments. A thin layer at the base of Unit 1D yielded AOM and marine phytoplankton and low terrestrial input indicating dysoxic-anoxic conditions were maintained. The lack of organic matter and the presence of invertebrates and microfossils in a thin green fossiliferous mudstone supports the establishment of normal, oxygenated marine conditions maintained in the basal Middle Sappington Member (U2). These two thin units are not part of the underlying anoxic black shale (U1A-B) sequence as commonly was over-simplified. Instead, they are part of a transgressive interval with the basal Middle Sappington. A correlation of the U1 shale interval is established with the global multiphase Dasberg Event.

This study documents the occurrence of atmospheric dust from Pennsylvanian carbonates of the Copacabana Formation, recovered in core (Mobil-Oxy Manuripi X-1) from the Madre de Dios basin (Bolivia), within southern mid-latitudes (similar to 35 degrees S) of western Gondwana. The Copacabana Formation spans Pennsylvanian-Early Permian time, and thus formed coeval with and in relative proximity to ice centers and associated glacial deposits located at southern paleolatitudes in adjoining regions of Gondwana (e.g. the Parana, Tarija, and Paganzo basins in Brazil, southeastern Bolivia, and Argentina, respectively). In Pennsylvanian time carbonate deposition of the Copacabana Formation occurred on a ramp isolated from fluvial-deltaic influx, and thus siliciclastic material in this system reflects atmospheric input. The study interval comprises a series of upwardly shallowing successions 1-3 m thick ranging from open marine ramp facies to more restricted inner-ramp facies, commonly capped by horizons of microkarsted and/or red mudstone reflecting subaerial exposure of the carbonate ramp. These horizons mark abnormal exposure and are interpreted to record glacial lowstands. Dust recovered from throughout the study section varies from similar to 1 to 43 wt% in carbonate facies and is quartzo-feldspathic. Grain size modes range from <1 to 97 gun, with coarser intervals generally corresponding to peak dust content (wt%), and high-frequency sequence (glacial-stage) boundaries. Provenance indicates two discrete sources of atmospheric input-a western volcanic arc source and eastern continental source, recording both westerly (zonal) and easterly (katabatic) wind directions. The western (volcanic) source records zonal westerlies expected at this mid-latitude (similar to 35 degrees S) locality. In contrast, easterly winds suggest the influence of katabatic winds associated with Gondwanan ice centers. The most likely dust-sourcing regions are the periglacial to proglacial regions of the Gondwanan ice sheets. Non-volcanic peaks in dust occur most commonly associated with subaerial exposure surfaces; this, together with mass accumulation rate estimations suggest that atmospheric dust loading peaked during glacial stages. (C) 2018 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Cratonic depositional systems in the Central Montana Trough involve the Devonian-Carboniferous boundary (DCB), and reflect both subtle regional epeirogeny and significant global glacioeustatic controls. A palynologic analysis of the upper Three Forks, Sappington and lower Lodgepole formations was carried out at the classic Logan Gulch location in Horseshoe Hills. The lower Trident Member of Three Forks Formation yielded low-diversity cosmopolitan, long ranging phytoplankton and few spores species (LAs1), attributed to the middle Famennian. The upper part of the same green seaway shale yielded only leiosphaerids and Botryococcus (LAs2), along with an external mold of a clymenid ammonoid. Age-diagnostic spores Retispora lepidophyta, Verrucosisporites nitidus and Vallatisporites vallatus from middle Sappington siltstone (LAs3) indicated a Strunian LN Zone. Two more assemblages from upper Cottonwood Canyon Member (LAs4) and false Bakken (LAs5), in the lower Lodgepole Formation yielded scarce, poorly preserved spores. The presence of Waltzispora polita in LAs4 indicated a Tournaisan-Visean age.

Largely terrestrial Pennsylvanian strata (Macharetí and Mandiyutí groups) in Bolivia and northern Argentina contain a brief marine incursion. Dominated by glacio-fluvial and glacial diamictites, much of the thick succession is peri-glacial in origin and deposited within a basin with paleohighs. In southernmost Bolivia (Balapuca section), new discoveries of poorly preserved orthotetacean brachiopods (Derbyoides sp.) document the marine systems. Without the brachiopod, co-occurrence of numerous in situ gastropods (Mourlonia balapucense), with all ontogenetic growth stages, could not be confirmed as marine. Palynomorphs corresponding to the TB Zone di Pasquo stratigraphically below the megafossil occurrence place the age of the assemblage in the Kasimovian/Gzhelian Stage. Many units show extensive recycling of Devonian and Mississippian palynomorphs (Retispora lepidophya, and others) and a brachiopod demonstrate pre-Gzhelian erosion and high energy deposition in diamictites during deposition of the Tarija Formation, and through much of the succession. This brief marine transgression in this basin corresponds to regionally more long-lived marine transgressions in western Argentina, characterized by the Tivertonia-Streptorhynchus Fauna (Moscovian-Gzhelian) linked with the beginning of a global major sea level rise as an interlude in the Gondwana glaciations. The marine transgression exceeded isostatic rebound. Further in Bolivia, the transgression from the north produced the Copacabana Formation carbonates. Coeval siliciclastics of the San Telmo Formation in the south show contrasting in lithologic facies and faunal composition as a result of thermal barriers (warm – cold waters).