Recent progress in the bio- and chronostratigraphic understanding of the upper Frasnian (Upper Devonian) sedimentary sequences in Armenia

Over 30 depositional sequences have been identified in the Paleozoic and lower Mesozoic of the Ghadames basin of eastern Algeria, southern Tunisia, and western Libya. Well logs and lithologic information from more than 500 wells were used to correlate the 30 sequences throughout the basin (total area more than 1 million km{sup 2}). Based on systematic change in the log response of strata in successively younger sequences, five groups of sequences with distinctive characteristics have been identified: Cambro-Ordivician, Upper Silurian-Middle Devonian, Upper Devonian, Carboniferous, and Middle Triassic-Middle Jurassic. Each sequence group is terminated by a major, tectonically enhanced sequence boundary that is immediately overlain (except for the Carboniferous) by a shale-prone interval deposited in response to basin-wide flooding. The four Paleozoic sequence groups were deposited on the Saharan platform, a north facing, clastic-dominated shelf that covered most of North Africa during the Paleozoic. The sequence boundary at the top of the Carboniferous sequence group is one of several Permian-Carboniferous angular unconformities in North Africa related to the Hercynian orogeny. The youngest sequence group (Middle Triassic to Middle Jurassic) is a clastic-evaporite package that onlaps southward onto the top of Paleozoic sequence boundary. The progressive changes from the Cambrian to themore » Jurassic, in the nature of the Ghadames basin sequences is a reflection of the interplay between basin morphology and tectonics, vegetation, eustasy, climate, and sediment supply.« less

The Kolyvan–Tomsk folded zone (KTFZ) represents part of the Central Asian Orogenic Belt (CAOB). The KTFZ is mainly composed of detrital Late Palaeozoic sedimentary deposits, with minor intrusions. Detrital zircon geochronology on the Upper Devonian to Lower Permian sedimentary sequences of the KTFZ and the associated Gorlovo foreland basin yields four age peaks, reflecting the magmatic events in the source terranes. These events consist of (a) a minor Neoproterozoic peak (0.9–0.7 Ga), (b) a significant Early Palaeozoic peak (550–460 Ma), with a maximum at 500 Ma, and two well‐defined Late Palaeozoic peaks during (c) the Middle–Late Devonian (385–360 Ma) and (d) the Carboniferous–Early Permian (360–280 Ma), with a maximum at 320 Ma. Older zircons (>1 Ga) are quite rare in the sampled sedimentary sequences. Slightly negative εNd values and associated relatively young Nd model ages were obtained (εNd(T) = −0.78, T (DM) ~1.1 Ga for Upper Devonian sandstones, εNd(T) = −1.1, T (DM) ~1.1 Ga for Lower Permian sandstones), suggesting only minor contribution of ancient continental crust to the main sedimentary units of the KTFZ. All intrusive and volcaniclastic rocks on the contrary are characterized by high positive εNd(T) values in the range of 3.78–6.86 and a Late Precambrian model age (T (DM) = 581–916 Ma), which corroborates its juvenile nature and an important depleted mantle component in their source. The oldest unit of the KTFZ, the Bugotak volcanic complex formed at the Givetian–Early Frasnian transition, at about 380 Ma. Upper Devonian detrital deposits of the KTFZ were formed in the Early Palaeozoic accretion belt of the Siberian continent and specifically in a passive continental margin environment. Deposits of the Gorlovo foreland basin, adjoining the KTFZ, were accumulated as a result of erosion of the Carboniferous–Early Permian volcanic rocks, which are now buried under the Meso–Cenozoic sedimentary cover of the West Siberian Basin. The magmatic events, recorded in the KTFZ zircon data, correspond to the most significant magmatic stages that affected the western part of the CAOB as a whole.

Pinnoputamen erikfluegeli and Sycidium aff. volborthi magnum from Akkuyu (Southern Taurides) are the first Palaeozoic charophytes reported from Turkey, and their presence emphasises the world-wide distribution of Sycidiales during the Middle and Upper Devonian. Both species occur in the upper part of the Akkuyu Section of late Givetian through early Frasnian age, based on combined biostratigraphical data. The sedimentary sequence mainly consists of reefal limestones and silt-/sandstones, partly intercalated with shales. In these nearshore deposits, charophytes and open marine fossils, notably brachiopods and conodonts, are found associated. With reference to identical primordial structures of vegetative and reproductive organs both in extant and Palaeozoic forms, and account taken of the prerequisite environmental conditions (such as salinity, light intensity, and nature of substratum), the mode of life in Palaeozoic charophytes was certainly similar to that of modern ones. By a critical review of other fossil occurrences interpreted as marine, we conclude that an allochthonous origin is most probable for the charophytes of the Akkuyu Section.

The Dafulou and Huile vein and stratabound cassiterite–sulfide deposits and sheeted ore veins at the Kangma cassiterite–sulfide deposit are located in the eastern part of the Dachang tin field. These deposits are hosted in a sedimentary sequence containing significant concentrations of organic matter in the form of Lower Devonian calcareous black shales and hornfels. These rocks together with the younger intrusion of Longxianggai granite (91±2 Ma) actively participated in the formation of Sn-polymetallic deposits. The following three major stages have been distinguished in stratiform and vein-type orebodies at Dafulou, Huile and Kangma: stage I (cassiterite, pyrrhotite, arsenopyrite, tourmaline, carbonate), stage II – main sulfide stage (quartz, cassiterite, arsenopyrite, pyrrhotite, sphalerite, stannite, pyrite, carbonates) and stage III (native Bi, galena, electrum, sulfosalts). Stage IV (post-ore), recognized at Huile is represented by barren carbonates and zeolites. Whole rock geochemistry has revealed that at Dafulou, Bi and Cu correlate strongly with S, whereas V and Pb correlate well with Corg (organic carbon). The similar distribution patterns of selected elements in average slightly mineralized low-Ca black shales indicate a fluid composition similar for all deposits studied. Studies of graphitization of the organic matter in black shales adjacent to orebodies indicate that d(002) and FWHM (full width in half maximum)/peak height values gradually decrease in the following sequence: Dafulou deposit → Kangma deposit → Huile deposit. The pyrolysate of wall rocks at the Dafulou deposit is relatively enriched in asphaltenes and maltenes (55.6–72.0% of the pyrolysate) comparable with pyrolysate obtained from more distal black shales (19.2–28.5%). Typical GC-MS spectra of pyrolysate from distal black shales are dominated by alkanes in the n-C15 to n-C25 range, aromatic molecules being represented mostly by alkyl-naphthalenes. In contrast, only traces of aliphatic hydrocarbons in the n-C14 to n-C18 range and elemental sulfur were identified in pyrolysates from pyrrhotitized wall rocks. The earliest fluid inclusions of the studied system occur in the quartz–tourmaline–cassiterite assemblage of stage I at Dafulou. These inclusions are H2O–CO2–CH4-rich, with 10 to 20 vol% of aqueous phase. P–T conditions of the trapping of inclusions are estimated to be up to 400 °C and 1.3 to 2.0 kbar (between 5.0 and 7.5 km under lithostatic pressure). In contrast, the presence of a low density gaseous CO2–CH4 phase indicates relatively low pressures during the formation of the breccia-type quartz–calcite–cassiterite–sulfide mineralization (stage II), when P–T conditions probably reached approx. 380 to 400 °C and 0.6 kbar (up to 6 km under hydrostatic pressure). Fluid inclusion data and oxygen isotope thermometry indicate that cassiterite–sulfide ores of the main sulfide stage (stage II) formed from aqueous-carbonic fluid (CO2/CH4 =≈10) at temperatures of up to 390 °C at Dafulou and in a temperature range of 250 to 360 °C at Huile and 260 to 370 °C at Kangma. The δ34S values of sulfides from Dafulou range mostly between –1 and –6‰, whereas sulfides from the Kangma and Huile deposits are characterized by more negative δ34S values (between –8 and –11‰, and between –9 and –12‰, respectively). These data suggest that bacteriogenic sulfides of black shales were a dominant source of reduced sulfur for epigenetic (vein and replacement) mineralization. Oxygen isotopic compositions of five quartz-cassiterite pairs from Dafulou and Huile show a relatively narrow range of calculated oxygen isotope temperatures (250–320 °C, using the equation of Alderton 1989) and high δ18Ofluid values between +8 and +10‰ (SMOW), which are in agreement with fluid derivation from and/or high temperature equilibration with the Longxianggai granite. The carbon and oxygen isotope composition of carbonates reflects variable carbon sources. Stage I calcite is characterized by narrow ranges of δ13C (–7.0 to –9.5‰ PDB) and δ18O (+15.0 to +17.5‰ SMOW). This calcite shows ubiquitous deformation, evidenced by intense development of twins. Fluid compositions calculated at 330 °C for the Dafulou and Huile deposits and at 270–300 °C for the Kangma deposit (δ18Ofluid between +10.0 and +11.5‰ SMOW, δ13Cfluid between –5.5 and –7.5‰ PDB), agree with fluid derivation from and/or equilibration with the peraluminous, high-δ18O Longxianggai granite and suggest a significant influence of contact metasedimentary sequences (carbon derived from decomposition and/or alteration of organic matter of calcareous black shales). The δ13 C values of organic matter from the Lower to Upper Devonian host rocks at the Dafulou deposit (–24.0 and –28.0‰) fit with a marine origin from algae. However, organic matter adjacent to the host rock-ore contact displays a slight enrichment in 13C. The organic carbon from the Huile and Kangma deposits is even more 13C enriched (-24.6 to –23.5‰). The most heavy δ13 C values (–16.5‰) were detected in hornfels sampled at the contact of the Upper Devonian sediments with the Longxianggai granite. The δ13C data broadly correlate with the degree of structural ordering (degree of graphitization) of organic matter, which indicates that both variables are related to thermal overprint.

Upper Devonian to Lower Carboniferous strata of the Campwyn Volcanics of east central Queensland preserve a substantial sequence of first‐cycle volcaniclastic sedimentary and coeval volcanic rocks that record prolonged volcanic activity along the northern New England Fold Belt. The style and scale of volcanism varied with time,producing an Upper Devonian sequence of mafic volcano‐sedimentary rocks overlain by a rhyolitic ignimbrite‐dominated sequence that passes upward into a Lower Carboniferous limestone‐bearing sedimentary sequence. We define two facies associations for the Campwyn Volcanics. A lower facies association is dominated by mafic volcanic‐derived sedimentary breccias with subordinate primary mafic volcanic rocks comprising predominantly hyaloclastite and peperite. Sedimentary breccias record episodic and high energy, subaqueous depositional events with clastic material sourced from a mafic lava‐dominated terrain. Some breccias contain a high proportion of attenuated dense, glassy mafic juvenile clasts, suggesting a syn‐eruptive origin. The lower facies association coarsens upwards from a lithic sand‐dominated sequence through a thick interval of pebble‐ to boulder‐grade polymict volcaniclastic breccias, culminating in facies that demonstrate subaerial exposure. The silicic upper facies association marks a significant change in eruptive style, magma composition and the nature of eruptive sources, as well as the widespread development of subaerial depositional conditions. Crystal‐rich, high‐grade, low‐ to high‐silica rhyolite ignimbrites dominate the base of this facies association. Biostratigraphic age controls indicate that the ignimbrite‐bearing sequences are Famennian to lower‐mid Tournaisian in age. The ignimbrites represent extra‐caldera facies with individual units up to 40 m thick and mostly lacking coarse lithic breccias. Thick deposits of pyroclastic material interbedded with fine‐grained siliceous sandstone and mudstone (locally radiolarian‐bearing) were deposited from pyroclastic flows that crossed palaeo‐shorelines or represent syn‐eruptive, resedimented pyroclastic material. Some block‐bearing lithic‐pumice‐crystal breccias may also reflect more proximal subaqueous silicic explosive eruptions. Crystal‐lithic sandstones interbedded with, and overlying the ignimbrites, contain abundant detrital volcanic quartz and feldspar derived from the pyroclastic deposits. Limestone is common in the upper part of the upper facies association, and several beds are oolitic (cf. Rockhampton Group of the Yarrol terrane). Overall, the upper facies association fines upward and is transgressive, recording a return to shallow‐marine conditions. Palaeocurrent data from all stratigraphic levels in the Campwyn Volcanics indicate that the regional sediment‐dispersal direction was to the northwest, and opposed to the generally accepted notion of easterly sediment dispersal from a volcanic arc source. The silicic upper facies association correlates in age and lithology to Early Carboniferous silicic volcanism in the Drummond (Cycle 1) and Burdekin Basins, Connors Arch, and in the Yarrol terranes of eastern Queensland. The widespread development of silicic volcanism in the Early Carboniferous indicates that silicic (rift‐related) magmatism was not restricted to the Drummond Basin, but was part of a more substantial silicic igneous province.

Rhythmic continental sequences characterize the proximal Genesee Group (Upper Devonian) in southeastern New York, which are interpreted as the remnant elements of a sequence of coastal-plain and upland fluvial deposits. A rhythm consists of a braided pattern of coarse conglomeratic channel-fill, a composite of point-bar, channel-fill, and overbank sandstones, and overbank, mudflat, and general flood plain accumulations of siltstones and mudrocks. Widespread lateral variability, rapid vertical change, channel depths of more than 30 feet, and textural mapping suggest a significant fall-line scarp close to the east of the present outcrop limit. Various aspects of the natural rhythmic sequences of the Genesee Group have been synthesized and examined using simulation techniques.

Research subject. Terrigenous rocks of the Sargaevo stage of sedimentation in various structural-facies settings within the Tsilma area (Middle Timan). Material and methods. The composition, structural features of rocks, and the species diversity of spores of higher plants were studied in the most complete natural outcrops proposed as a stratotype of the Paladinskaya Formation – a new straton of the Sargaevo age in the Middle Timan. Over a large area of the region, the deposits contain very few remains of fossil fauna, often indifferent. As a result, palynostratigraphy was selected as the main biostratigraphic method. Results. In the Middle Timan, a new straton, the Paladinskaya Formation, is described, which characterizes the Sargaevo stage of sedimentation in various structural-facies settings within the Tsil’ma area. The new straton has clear lithological and detailed palynological characteristics; a description of the limitotypes was performed.At present, the Paladinskaya Formation is the most complete sequence of Early Frasnian sedimentation in the European North-East of Russia, where it was possible to record regional responses to the global Frasnes event and to determine the position of the controversial level of the boundary between the Middle and Upper Devonian. Conclusions. The name “Ust’e Yarega” Formation in the Middle Timan cannot be considered valid, since it is a homonym of the sediments of the same age in the South Timan. The section is represented mainly by continental, rather than marine, deposits. A new name for the identifed formation is proposed – “Paladinskaya” with a description of the stratum section and limitotype.The Paladinskaya Formation is characterized by subcomplexes of spores (А and Б) of the regional miospore zone Cristatisporites pseudodeliquescens, which made it possible to correlate the marine and continental deposits of the Early Frasnian on the territory of the entire Timan-Pechora region and establish its exact position in the stratigraphic scheme of the Devonian.

The Upper Devonian sedimentary sequences of Central Armenia, which mainly consist of shallow water, mixed carbonate-siliciclastic deposits, contain abundant and diverse brachiopods that are dominated by spiriferides. Based on newly collected material from the lower Famennian Aramazdospirifer orbelianus brachiopod zone (coeval to the Palmatolepis crepida conodont zone) of Armenia, we here introduce two new cyrtospiriferid genera and fully document their type species, including their intraspecific variability. Pentagonospirifer n. gen. is a monospecific genus assigned to the subfamily Cyrtospiriferinae that is currently known only from the lower Famennian of Armenia; it is likely that its type species, P. abrahamyanae n. sp., evolved from the species Cyrtospirifer verneuili sensu Abrahamyan, known from the Frasnian and lower Famennian of Armenia. The second new genus, Tornatospirifer n. gen., is assigned to the subfamily Cyrtiopsinae and defined on the basis of one of the most biostratigraphically valuable cyrtospiriferid species, namely T. armenicus n. comb., described previously from the lower Famennian Aramazdospirifer orbelianus Zone of Armenia. It is likely that it evolved from a Frasnian ancestral stock of Tiocyrspis Sartenaer, known from northwestern Europe, which probably migrated during the early Frasnian to the north Gondwanan margin. A neotype is selected for Abrahamyan's species because the type material is lost. Epibionts (Cornulites, Hederella) attached to brachiopods are also documented for the first time from the Upper Devonian of Armenia.UUID: http://zoobank.org/923d232f-cd6a-48bb-8a05-27c689058b65.

The Frasnian–Famennian (Upper Devonian) siliciclastic sedimentary sequences of the Ertych section, located in south-central Armenia, yielded a relatively diverse and well-preserved marine phytoplankton assemblage consisting of acritarchs and prasinophytes. The former are represented by 19 species belonging to 10 genera; the latter comprise six species (five genera). This constitutes the first report of marine organic-walled phytoplankton from the Upper Devonian successions of the South Armenian Block, then part of the northern Gondwanan continental margin. Comparison of the examined assemblage with others documented from elsewhere in Gondwana (e.g. Iran, Africa, South America, Australia), central and east Asia (South China, Tarim, Junggar), Variscan Terranes (Iberia, Armorica), and Laurussia (e.g. North America), establishes a close palaeobiogeographical affinity of the Armenian material with assemblages preserved in the Alborz Mountain Range, Iran. The presence in our material of several index acritarch species in palynomorph zones from the Eastern Alborz Mountains, Iran, signifies correlation with the late Frasnian–early Famennian interval, confirming previous results based on miospores. Furthermore, our observations provide additional data on previously suggested palaeobiogeographical patterns of Late Devonian organic-walled phytoplankton, supporting a closer affinity between floras from central to north-western Gondwana with those of Laurussia compared with those of higher palaeolatitudes (e.g. South America). Indeed, the assemblage from the Ertych section contains species evidently restricted to warm-temperate and arid climate belts.

The central Carnic Alps contain continuous sedimentary carbonate sequences that extend through the Devonian and lowermost part of the Carboniferous. Some sediments were deposited near mean sea level; other cephalopod-bearing facies were laid down in deeper water. Red mottled cephalopod limestones are continuous into the Upper Devonian. Grey cephalopod limestones, containing derived shallow-water calcarenites, occur in the Devonian and grade upwards into turbidite-free cephalopod limestones of Early Carboniferous age. These deep-water limestones are characterized by evidence of early lithification and solution, and by the presence of a characteristic fauna. Interpretation of their depositional depth is based on present-day compensation depths for aragonite and calcite: the original sediments apparently resembled modern pelagic oozes. Sedimentological and palaeontological criteria indicate a progressive deepening of the basinal areas accompanied by continuous growth of platform carbonates at the basin edge until Late Devonian time when the shallow-water areas subsided.

Top seal development in the shale-dominated Upper Devonian Catskill Delta Complex, western New York State

Mudstones, which represent more than 80% of the sedimentary rock record by volume, have increasingly been targeted for investigation as they have become essential to the petroleum industry to meet the domestic and global demand for oil and gas. Mudstones can serve not only as petroleum source rocks, but also as reservoirs that store substantial petroleum reserves. The advancements in drilling and well stimulation that have led to the development of resources in places like the Upper Devonian to Lower Mississippian Bakken Formation, Upper Devonian Marcellus Formation, and Upper Cretaceous Eagle Ford Shale have transformed our understanding of the heterogeneity of mudstone lithologies both stratigraphically and laterally (Percy and Pedersen, 2020). While such observations have significantly impacted our accepted interpretations of depositional environments and sequence stratigraphic frameworks for mudstones, the majority of these studies have focused on proximal locales where variability in terrigenous derived sediment can be more easily evaluated (Li and Schieber, 2020; Percy and Pedersen, 2020; Laurin et al., 2019). In this study, we present an integrated lithologic (from core and thin section) and geochemical (bulk organic and inorganic analyses) facies evaluation of mudstones comprising the Late Cretaceous Greenhorn Formation in the USGS #1 Portland Core collected near Pueblo, Colorado (Dean and Arthur, 1998), including those that were deposited during Oceanic Anoxic Event 2 (OAE 2). The distribution of facies is evaluated to track how variability in the depositional environments and play elements vary stratigraphically throughout the formation.

During the Late Devonian, sediments deposited in shallow marine, brackish, and tidal mud-flat environments accumulated in west-central Colorado. This sedimentary sequence comprises the Chaffee Group, which is divided into two formations; the lower third, the Parting Formation, consists predominantly of detrital rocks; the upper two thirds of the group, the Dyer Formation, is composed of carbonate rocks. The Parting Formation is divided into three stratigraphic units, designated A, B, and C, in ascending order. Unit A is chiefly quartzose sandstone. Unit B is composed of four persistent beds which, in ascending order, are shale, thin dolomite, shale, and sandy dolomite or dolomitic sandstone that contains dolomite pebbles. Unit C consists of lenses and beds of quartzose sandstone, sandy shale, and sandy dolomite. On the east and northeast all three units change in facies to quartzose sandstone. The Parting Formation is principally a transgressive sequence, but the middle dolomite bed and the top bed of unit B represent regressive phases. The source for the detrital sediments was a crystalline highland flanked by sedimentary rocks, located east and northeast of the study area. This highland persisted throughout Chaffee deposition, but yielded more detritus to the Parting Formation. The maximum advance of the Devonian sea occurred during upper Parting and lower Dyer deposition. The Dyer Formation is a regressive carbonate sequence that can be divided into two carbonate members. The lower member consists of dark-gray, dolomitic, fossiliferous limestone, and herein is named the Broken Rib Member. The upper member consists of light-gray dense, stromatolitic dolomite, and herein is named the Coffee Pot Member. The Broken Rib Member apparently reflects deposition in a sublittoral environment. The stromatolites of the Coffee Pot Member are interpreted as having formed by the trapping and binding action of blue-green algae, which grew in the littoral zone. Intraformational breccias formed by the disruptive action of waves on desiccation polygons are associated with the stromatolites.

The Tafilalt is one of a number of generally unexplored sub‐basins in the eastern Anti‐Atlas of Morocco, all of which probably underwent a similar tectono‐stratigraphic evolution during the Palaeozoic Era. Analysis of over 1000 km of 2‐D seismic reflection profiles, with the interpretation of ten regional seismic sections and five isopach and isobath maps, suggests a multi‐phase deformation history for the Palaeozoic‐aged Tafilalt sub‐basins. Extensional phases were probably initiated in the Cambrian, followed by uniform thermal subsidence up to at least the end of the Silurian. Major extension and subsidence did not begin prior to Middle/Upper Devonian times. Extensional movements on the major faults bounding the basin to the north and to the south took place in synchronisation with Upper Devonian sedimentation, which provides the thickest part of the sedimentary sequence in the basin. The onset of the compressional phase in Carboniferous times is indicated by reflectors in the Carboniferous sequence progressively onlapping onto the Upper Devonian sequence. This period of compression developed folds and faults in the Upper Palaeozoic‐aged strata, producing a structural style characteristic of thin‐skinned fold and thrust belts. The Late Palaeozoic units are detached over a regional décollement with a northward tectonic vergence. The folds have been formed by the process of fault‐propagation folding related to the thrust imbricates that ramp up‐section from the décollement. Copyright © 2007 John Wiley & Sons, Ltd.

We demonstrate how lithological and mechanical stratification of Ediacaran–Carboniferous sedimentary package governs strain partitioning in the Lublin Basin (LB) which was incorporated in the marginal portion of the Variscan fold-and-thrust belt. Based on the geometry of seismic reflectors, the pre-Permian–Mesozoic sedimentary sequence was subdivided into two structural complexes differing in structural style. The lower one reveals forelandward-vergent imbrication, while the upper one comprises fold train, second-order deformations, and multiple local detachments. Lithological composition of the upper structural complex controlled geometry, kinematics, and position of compressional deformations in stratigraphic profile. System of foreland-vergent thrusts which links lower and upper detachment developed due to efficiency of simple shear operating in heterogeneous clastic-carbonate-evaporitic strata of the Lower–Upper Devonian age. Internal homogeneity promoted the formation of conjugate sets of thrusts in Silurian shales and Upper Devonian limestones. Structural seismic interpretation combined with sequential restoration revealed localised thickening of Devonian strata and up to 5% difference in length of Devonian horizons. This mismatch is interpreted as a manifestation of distributed shortening, including layer-parallel shortening (LPS), which operated before or synchronously to the initiation of folding. The amount of distributed strain is comparable with numbers obtained in external parts of other fold-and-thrust belts. The outcomes derived from this study may act as a benchmark for studying variability in a structural style of multilayered sequences which were incorporated in the external portion of other fold-and-thrust belts.