Lower Middle Pennsylvanian Research Articles

Bashkirian-Moscovian (Lower–Middle Pennsylvanian) conodonts from the Amazonas Basin, northern Brazil: Biostratigraphy, biofacies, and paleobiogeographic significance for Western Gondwana

Bashkirian-Moscovian (Lower to Middle Pennsylvanian) Itaituba Formation is well exposed in the Itacimpasa Quarry at the southern platform of the Amazonas Basin, northern Brazil. An abundant and diverse conodont fauna was recovered from this predominantly carbonate formation, with a total of 19 species belonging to 8 genera identified. The following species were documented and systematically described for the first time in the basin: Declinognathodus marginodosus, Declinognathodus donetzianus, Idiognathoides postsulcatus, Idiognathoides fossatus, Diplognathodus benderi, Adetognathus spathus, and Idioprioniodus conjunctus, providing significant stratigraphic and environmental insights into the Bashkirian-Moscovian boundary (BMB) interval. The Declinognathodus marginodosus – Neognathodus atokaensis (upper Bashkirian Stage) and the Declinognathodus donetzianus – Diplognathodus ellesmerensis (lower Moscovian Stage) zones are recognized. The distribution of conodonts studied through cluster analysis reveals the conodont biofacies Idiognathodus/Adetognathus and Declinognathodus/Idiognathoides biofacies. Changes in these conodont biofacies are interpreted as the result of a marine ingression event in Western Gondwana during the BMB interval. The fauna recorded in the studied section shows affinities with conodont faunas reported from Paleo-Tethys Ocean regions indicating a faunal connection of this ocean with the Panthalassa in Western Gondwana. These findings contribute significantly to the refinement of the biostratigraphy and paleobiogeography of the Bashkirian-Moscovian boundary interval in the Amazonas Basin and Western Gondwana.

U–Pb age constraints on the protolith, cooling and exhumation of a Variscan middle crust migmatite complex from the Central Iberian Zone: insights into the Variscan metamorphic evolution and Ediacaran palaeogeographic implications

The Figueira de Castelo Rodrigo–Lumbrales Anatectic Complex (FCR-LAC) located in the Central Iberian Zone of the European Variscan Belt is delimited by two shear zones, which have been interpreted as constraining its exhumation. New U–Pb zircon and apatite ages for the migmatites allowed us to obtain a peak metamorphic age of the anatectic complex (316.8 ± 2.0 Ma), and to estimate fast cooling (7–54°C Ma –1 ) and fast exhumation (0.2–1.3 mm a −1 ) after a vertical displacement of c. 6–9 km. Our results show a similar zircon age distribution between migmatites and the Excomungada Formation from the host Ediacaran–Cambrian Douro–Beiras Supergroup. Although the existence of an inherited zircon population lasting c. 500 Ma, absent in the metasedimentary units, suggests the contribution of Ollo de Sapo magmatic rocks during the Lower–Middle Pennsylvanian melting events. Detrital zircon ages of the Pinhão Formation (Douro Group) have contrasting sources to units from the Beiras Group, which may indicate the presence of a barrier that prevented older detrital components from reaching the Douro basin. However, at odds with what has been postulated before, such a barrier must have been placed farther south of the FRC-LAC, and thus not coincident with the Juzbado–Penalva do Castelo shear zone. Supplementary material: A full description of the stratigraphy and lithologies (Supplementary 1 and 2, respectively); the analytical conditons of the LA-ICP-MS analyses (Supplementary Material 3); the U–Pb zircon and apatite data of the FCR-LAC migmatites and the U–Pb detrital zircon data of the DBSG (Supplementary Material 4) are available at https://doi.org/10.6084/m9.figshare.c.6002006

A new species of palaeosiphonocladal algae Kamaena gigantea from the Lower–lowermost Middle Mississippian sediments of the Donbas (Upper Tournaisian–Lower Visean)


 
 
 
 A new species of green paleosiphonocladаl algae Kamaena gigantea from the Lower–lowermost Middle Mississippian sediments of the Donbas has been described. This species was distinguished from other representatives of the genus Kamaena Antropov by its extremely large size, tortuous shape of the thallus and convex partitions. The species belongs to an artificial taxonomic unit of the Kamaenae Shuysky tribe, 1985 , of the family Palaeoberesellaceae Mamet et Roux , a systematic grouping which is still controversial. The attribution of this family to green siphonocladal algae is controversial and quite conditional, the opinions of different authors being based on personal vision, and varying in range from the plant to the animal kingdom. A characteristic feature of the family is the tubular shape , the segments of which are connected by partitions with a large central pore, sometimes with additional small pores. The thallus wall (fossilized remains of the body) is porous or non-porous and has simple or branched pores. It has been emphasized that study of Paleoberezellides in thin sections, the sometimes fuzzy images of the typical material in publications and ignorance of other researchers’ publications have caused confusion and led to the selection of an unreasonably large number of genera and species within the family. It has been noted that in previous works, representatives of this species were mistakenly identified as Anthracoporellopsis Maslov, a genus characteristic of the Lower–Middle Pennsylvanian sediments. This erroneous definition was based mainly on general external similarity, a poorly illustrated description of the type species, and did not take into account the morphological features that were characteristic for the genus. It has been found that representatives of the new species had a rather limited stratigraphic distribution: the Upper Tournaisian (Dokuchaevskian horizon) and the Lower Visean (Hlybokian–Sukhinskian horizons), and the most similar specimens found in the Ural region in underlying Tournaisian sediments were, unfortunately, poorly illustrated and smaller in size and had a narrower thallus. It has been noted that a characteristic feature of the tribe Kamaenae Shuysky, 1985 was the tubular shape, its inter-segmental partitions were perpendicular to the walls and were at the approximately same interval from each other. It has been pointed out that representatives of the new species were found mainly in grainstones, packstones, and wackstones − organogenic-detrital limestones along with such groups of microfauna as echinoderms and ostracods, isolated spicules of sponges and remains of worms. The material for illustrations was mainly taken from the borehole74 (near the village of Rodnikove, Starobeshiv district, Donetsk region) , which most fully revealed the Lower–Middle Pennsylvanian deposits of the southern part of the Donbas. The knowledge of the systematic composition of the Early Carboniferous algoflora has been expanded. This has helped us to conclude that the tribe Kamaeneae Shuysky, 1985 ,includes 6 genera and at least 22 species that were found in the layers from the Early Devonian to the Early Visean of the Lower Carboniferous.
 
 
 

Influence of magmatic fluids on the organic and inorganic fractions of coals from the Peñarroya-Belmez-Espiel Basin (Spain)

The study of coals affected by magmatic intrusions is important from a geological point of view, in order to understand how heat and magmatic fluids could affect the organic and inorganic fractions as well as the properties of the coals. These fluids may lead to an enrichment of trace elements and heavy metals of environmental concern or serve as unconventional sources of critical elements. Therefore, the objective of this study is to investigate the organic and inorganic fractions of Peñarroya-Belmez-Espiel Basin (PBEB) (Spain) coals in order to verify whether changes of the petrography, chemical composition, mineralogy, and inorganic geochemistry have taken place. The PBEB corresponds to a Carboniferous intramontane basin filled with a Middle Mississippian to Lower-Middle Pennsylvanian sedimentary succession with coal-bearing units. Two main successive depocentres (extended from NW to SE) were recognized and in which bituminous and anthracite coals, as well as natural cokes occur. Petrographic analysis, ultimate and proximate analysis, scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDS) analysis, inductively coupled plasma-optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) analysis were carried out for the purpose of this study. The sampling consisted of a selected set of nine samples of bituminous coals, ten samples of anthracites and three samples of natural cokes. The results show that the organic fraction of bituminous and anthracite coals is mainly made up of vitrinite. Although the minerals identified in the two depocentres vary, they mainly consist of quartz and clay minerals in both cases. Authigenic kaolinite and epigenetic mineralization related to thermal events that occurred in the basin were observed in the anthracites. Natural coke shows isotropic and fine mosaic textures, and signs of epigenetic mineralization. The trace element content of the coal samples was compared with the values established for world hard coals and an enrichment of Cs, in bituminous and anthracite coals, and of Hg in natural cokes, was observed. The occurrence of REY in bituminous coals is related to the detrital sedimentary source, whereas in anthracite the epigenetic and thermal effects may have also been involved. In natural cokes, the REY content is probably associated with the original coal. Mercury enrichment in natural cokes may be associated with magmatic fluids and explained by Hg volatilization, its capture in natural coke pores and subsequent precipitation.

Paleohydrology and Machine-Assisted Estimation of Paleogeomorphology of Fluvial Channels of the Lower Middle Pennsylvanian Allegheny Formation, Birch River, WV

Rivers transport sediments in a source to sink system while responding to allogenic controls of the depositional system. Stacked fluvial sandstones of the Middle Pennsylvanian (Desmoinesian Stage, ~310 – 306 Ma) Allegheny Formation (MPAF) exposed at Birch River, West Virginia exhibit change in sedimentary structure and depositional style, reflecting changes in allogenic behavior. Paleohydrologic and numerical analysis were used to quantify geomorphological and paleohydrologic variations reflected by MPAF fluvial deposits with the goal of understanding the controls on resulting fluvial sandstone architecture in these different systems. Channel body geometry, sedimentary structures, and sandstone grain size distribution were used to reconstruct the paleoslope and flow velocity of the MPAF fluvial systems. In order to enhance paleohydrological estimates, machine learning methods including multiple regression and Support Vector Regression (SVR) algorithms were used to improve the dune height, and channel depth estimated from cross-set thickness. Results show that the Channel depths of the lower MPAF beneath the Lower Kittanning coal beds tend to decrease upsection; this decrease may reflect a transition from fluvial systems formed in a humid ever-wet climate to fluvial systems formed in less humid, seasonally wet, semi-arid climate. Paleohydraulic estimations enabled the evaluation of hydraulic changes in the fluvial depositional systems of the Appalachian Basin during the Desmoinesian stage. Paleoslope estimates indicated that the slope was low which indicated that the fluvial gradient response was not driven by the effect of tectonic subsidence or uplift and sea-level change.

Productidinid brachiopods (Strophomenata, Productida), including Martinezchaconia luisae new genus and new species of Linoproductidae, from the Carboniferous of Santiago Ixtaltepec region, Oaxaca, Southeast México

We describe three brachiopod species of the Suborder Productidina from the Ixtaltepec Formation, Carboniferous of the north of Oaxaca State, southern Mexico, found in peri-reef deposits. Stegacanthia bowsheri and Undaria sp. are members of the families Sentosiidae and Monticuliferidae respectively and were found in strata of the Visean (Middle Mississippian). Martinezchaconia luisae, new genus and species of the Family Linoproductidae, was recollected in Bashkirian-Moscovian (Lower-Middle Pennsylvanian) strata. The respective ages are inferred from the index species of brachiopods associated with the productidines herein described.

Lower–Middle Pennsylvanian strata in the North American midcontinent record the interplay between erosional unroofing of the Appalachians and eustatic sea-level rise

Lower–Middle Pennsylvanian strata in the North American midcontinent record the interplay between erosional unroofing of the Appalachians and eustatic sea-level rise

Sequence Stratigraphic and Tectono-Stratigraphic Successions, Ozark Shelf, Tri-State Region, Southern Midcontinent

The southern Ozark region, Arkansas, Missouri, and Oklahoma occupies the southern border of the North American craton. Its sedimentary succession preserves a complete Wilson Cycle reflecting the Late Precambrian-Cambrian rifting of Rodinia into the Laurussian and Gondwanan landmasses that opened the Iapetus Ocean Basin during the Late Cambrian-Middle Mississippian. The basin was closed during the Late Mississippian-Middle Pennsylvanian by the collision of Laurussia with Gondwana. During the Late Cambrian through the Middle Pennsylvanian, the Ozark Shelf, including its gently sloping, Northern Arkansas Structural Platform (NASP) and adjacent ramp, records both transgression and regression by epeiric seas as well as regional tectonism that can be recognized as five Tectono-Stratigraphic Successions (TS) and correlated readily with the Sloss Cratonic Sequences. The TS record comprises at least 33 named formations with a potential thickness >2926m (9600ft). However, both eustatic and tectonic sea-level rise and fall also produced regional surfaces of erosion that punctuated deposition, and the preserved thickness on the NASP is significantly less. The five distinct, but related, Tectono-stratigraphic Successions in the Paleozoic record are (TS1) Late Precambrian-Middle Cambrian, (TS2) Upper Cambrian-lowest Ordovician, (TS3) Lower Ordovician-Lower Devonian, (TS4) Middle Devonian-Upper Mississippian, and (TS5) Lower-Middle Pennsylvanian. TS1, a pre-Late Sauk Sequence, is the least well-known succession, consisting of emplaced igneous and low-ranked metasedimentary bodies and pre-Lamotte sedimentary rocks. TS2, Late Sauk Sequence, is potentially >937m (3075ft) of dolomites and sandstones. TS3, Tippecanoe Sequence, is the penultimate thickest interval, possibly >1257m (4125ft) of dolomites, limestones, shales, and supermature sandstones. TS4, Kaskaskia Sequence, measures at least 736m (2416ft). The final TS5, Lower Absaroka Sequence of first cycle sandstones with variable amounts of mrfs, and shales is the thickest interval, >1267m (4160ft) and may exceed 7620m (25,000ft) in the adjacent Arkoma Basin.

Taphofacies of Lower-Middle Pennsylvanian marine invertebrates from the Monte Alegre and Itaituba formations, part of the outcropped marine sequence of the Tapajós Group (Southern Amazonas Basin, Brazil) – regional palaeoecological models

One of the most relevant characteristics of the Pennsylvanian shallow-water carbonates of the Amazonas Basin is its diverse and well preserved invertebrate fossiliferous assemblages. In order to better understand the origin of these fossil concentrations, taphonomic data were obtained along well exposed areas of the uppermost part of the Monte Alegre Formation and basal part of the Itaituba Formation, which, based on conodonts, fusulinids and palynomorphs is of Atokan age. The taphonomic data focused on invertebrate organisms were supported by petrographic analysis. The understanding of the stacking pattern of the strata in the studied section allowed the identification of five type taphofacies, which contributed in the development of regional palaeoecological models, expressed as block-diagrams. These characterize the distribution of the environmental parameters, the composition of the faunal associations and the distribution and amplitude of the taphonomic processes that created the taphonomic signatures of the bioclastic elements throughout the supratidal to lower intertidal/deep subtidal depositional environments pertinent to the studied depositional environment. The regional palaeoecological models here presented are related to the particularities of the depositional environments of the studied rocks and are exclusive for the characterization of this intracratonic basin set influenced by high frequency climatic variations. Lithofacies, biofacies and taphofacies associations also reflect depositional conditions pertinent to the studied regional context, differing from the elements observed in modern intracratonic contexts analogous to the one studied, from different sedimentary basins around the world. Therefore, invertebrate taphonomy, supported by the analysis of sedimentary facies, fulfills the purposes recommended in this work, demonstrating its potential as a tool for palaeoecological analysis in the Pennsylvanian outcropping section in the southern platform of the Amazonas Basin.

Re–Os age for the Lower–Middle Pennsylvanian Boundary and comparison with associated palynoflora

The Betsie Shale Member is a relatively thick and continuous unit that serves as a marker bed across the central Appalachian basin, in part because it includes an organic-rich shale unit at its base that is observable in drill logs. Deposited during a marine transgression, the Betsie Shale Member has been correlated to units in both Wales and Germany and has been proposed to mark the boundary between the Lower and Middle Pennsylvanian Series within North America. This investigation assigns a new Re–Os date to the base of the Betsie and examines the palynoflora and maceral composition of the underlying Matewan coal bed in the context of that date. The Matewan coal bed contains abundant lycopsid tree spores along its base with assemblage diversity and inertinite content increasing upsection, as sulfur content and ash yield decrease. Taken together, these palynologic and organic petrographic results suggest a submerged paleomire that transitioned to an exposed peat surface. Notably, separating the lower and upper benches of the Matewan is a parting with very high sulfur content (28wt.%), perhaps representing an early marine pulse prior to the full on transgression responsible for depositing the Betsie. Results from Re–Os geochronology date the base of the Betsie at 323±7.8Ma, consistent with previously determined age constraints as well as the palynoflora assemblage presented herein. The Betsie Shale Member is also highly enriched in Re (ranging from 319.7 to 1213ng/g), with high 187Re/188Os values ranging from 3644 to 5737 likely resultant from varying redox conditions between the pore water and overlying water column during deposition and early condensing of the section.

Carboniferous tetrapod footprints from the Lublin Basin, SE Poland

Evidence of tetrapod footprints is scarce in the Carboniferous rocks of Europe and only a dozen sites have been found. Here is presented the first description of the Carboniferous tetrapod traces collected from the Bogdanka Coal Mine, Lublin Basin, south-eastern Poland. The footprints occur in reddish, white-gray sandstone or black-brown siltstone-mudstone, fluvial and lacustrine in origin, of the Westphalian A and B (about 315 and 310 Ma, lower-middle Pennsylvanian) of the Lublin Formation. Based on the study of 19 specimens (isolated and usually poorly preserved manus or pes imprints), I discern two distinct types of tetrapod footprints and also problematic traces (or scratches) made by swimming tetrapods. Footprints are assigned to the two ichnotaxa: Batrachichnus–Limnopus plexus and aff. Pseudobradypus isp. Traces described as Tetrapoda indet. A–C represent poorly preserved footprints, which are similar to the ichnogenera Ichniotherium, Dimetropus and Attenosaurus. The described trace fossils were produced by small amphibians (temnospondyls) and medium-sized amniotes (reptiliomorphs and reptiles). The tetrapod ichnofauna from the Bogdanka Coal Mine is similar in composition to Pennsylvanian ichnofaunas from Europe and North America.

A new genus and four new species of cladid crinoids from the Carboniferous of Oaxaca State, Mexico

Eight cladid (Subclass Cladida) crinoids are described from the Carboniferous Ixtaltepec Formation of Oaxaca State, southern Mexico. Most of the material consists of external and internal moulds of cups, arms and the proximal parts of the stem. Ekteinocrinus mixteca sp. nov. is assigned to the Order Dendrocrinida; newly recognized taxa in the Order Poteriocrinida include Stipecrinus splendidus gen. et sp. nov., Hydriocrinus amplus sp. nov. and Aesiocrinus profundus sp. nov. Cosmetocrinus sp., Contocrinus cf. kingi, an indeterminate Scytalocrinidae and a cup probably belonging to the Family Stellarocrinidae are also described. Stipecrinus splendidus sp. nov. and Cosmetocrinus sp. are Middle–Upper Mississippian (Visean–Serpukhovian), the other crinoids being Lower-Middle Pennsylvanian (Bashkirian–Moscovian). The present study reveals a strong similarity, expressed in terms of palaeobiodiversity, between the Oaxaca crinoids and those reported from Mississippian–Pennsylvanian faunas from the central-east region of North America. This similarity is also evident in the composition of the associated non-echinoderm fauna.http://zoobank.org/urn:lsid:zoobank.org:pub:347E74B9-82EB-49B8-BA16-61A65835CA5E

Latest Paleozoic–early Mesozoic structures in the central Oaxaca Terrane of southern Mexico: deformation near a triple junction

Paleozoic rocks in the Oaxaca Terrane of southern Mexico occur as two outliers (Rio Salinas and Santiago Ixtaltepec) unconformably overlying the 1-Ga Oaxaca Complex. They consist of the Upper Cambrian–Lower Ordovician Tiñu Formation, Mississippian Santiago Formation, lower–middle Pennsylvanian Ixtaltepec Formation and the unfossiliferous Yododeñe Formation of presumed Permian or younger age. These Paleozoic rocks have been deformed by several sets of structures. Three moderately westerly-dipping, bedding-parallel shear zones displaying dextral kinematic indicators (C–S fabrics, curvilinear isoclinal folds, en-echelon boudinage, en-echelon veins, and strained amygdales) occur along the boundaries between the Tiñu and Santiago formations, between the Santiago and Ixtaltepec formations, and within the Ixtaltepec Formation in the Santiago Ixtaltepec outlier. The bedding and these bedding-parallel shear zones are deformed by N–S, upright-asymmetric, subhorizontal folds accompanied by a slaty or spaced cleavage, that are in turn deformed by several sets of kink bands: subhorizontal and steeply dipping E–W, NW–SE and NE–SW. In the northern part of the Santiago Ixtaltepec outlier, the stratigraphy, bedding-parallel shear zones and slaty cleavage are displaced by NW–SE normal faults, all of which are truncated by the angular unconformity at the base of the Cretaceous, which brackets their age as post-Early Permian and pre-Cretaceous. Geometric correlation of the major N–S folds with E-vergent thrusting of the Oaxacan Complex over the Juarez Terrane suggests that they are older than Middle Jurassic. No age constraints are available for the kink and chevron folds; however, most may be related to Laramide structures in the overlying Cretaceous rocks. Unfolding the major structures in the Paleozoic rocks reorients the bedding-parallel shear zones to subhorizontal detachment shear zones or faults with a top-to-the-north sense of displacement. They may be related to either gravity sliding following amalgamation of Pangea, extensional rifting of the Yucatán Peninsula from southern Laurentia or intra-arc rifting associated with a Permo–Triassic arc within southern Mexico. The major N–S fold structures and E-vergent thrusting of the Oaxacan Complex over the Juárez Terrane may represent a response to (1) convergent subduction of the Kula and/or Farallon plates beneath western Mexico, (2) migration of a Gulf of Mexico–Yucatan–South America triple junction.

Channel-fill coal beds along the western margin of the Eastern Kentucky Coal Field

Four channel-filling coal beds from the lower part of the Breathitt Formation (lower Middle Pennsylvanian, late Westphalian A) were examined palynologically, petrographically and geochemically to determine the paleoenvironmental conditions under which these peats accumulated. These results were then compared with detailed sedimentological analyses of the strata overlying the coal in the channels to see if any genetic relationship between coal composition and the origin of the overburden could be drawn. All four of the coal beds used in this study are located in the western-most part of the Eastern Kentucky Coal Field and occur at, or near, the Early Pennsylvanian unconformity (0–30 m). Lycospora and Densosporites (and related crassicingulate taxa, e.g. Cristatisporites , Cingulizonates and Radiizonates) dominate the studied assemblages, with Granulatisporites (and related trilete, sphaerotriangular genera, e.g. Leiotriletes and Lophotriletes), Laevigatosporites and Schulzospora being common accessory genera. Petrographically, all four coals contain high percentages of vitrinite macerals (avg. 78.6% mineral matter free), moderate amounts of liptinite (or exinite) macerals (avg. 14.9%, mmf) and low percentages of inertinite macerals (avg. 6.5%, mmf). Strata above the coals consist of dark, carbonaceous shales, and heterolithic strata that exhibit varying degrees of bioturbation. Commonly occurring trace fossils include Arenicolites, Monocraterion, Planolites and Skolithos. Although marine-influenced strata, as determined from detailed sedimentology and ichnology (the study of trace fossils), covers all four coal beds, they are not uniformly high in total total sulfur content as might be expected. Rather they are extremely variable, ranging from 1–9% (dry basis) total sulfur. Ash yields are also variable ranging from 6.2–54.3% (dry basis). It is probable that the origin of the very first sediments covering the peat, as well as the amount of brackish water influence during peat accumulation, were important factors in determining the total sulfur content of the resultant coal. Initial sedimentation of fresh water clays and silts may have acted as a barrier to downward percolation/diffusion of sulfate bearing waters, or may have served as a site for sulfide formation, thereby keeping the total sulfur content of the underlying coal low. If initial sedimentation was of brackish or marine origin, as indicated by bioturbated laminae directly above the coal, or if the peat was subject to frequent brackish or marine water influence during accumulation, then sulfide generation might proceed unchecked, resulting in high sulfur coal.

Lower and lower Middle Pennsylvanian coal palynofloras, southwestern Virginia

Lower and lower Middle Pennsylvanian coals, recovered from an exploratory drilling program in southwestern Virginia, were analyzed for their palynomorph content. Results show them to be dominated by spores produced by arboreous lycopsids. Lycospora pellucida and Lycospora pusilla generally are the most common species, with others, namely Lycospora granulata, L. micropapillata and Lycospora orbicula being locally abundant. Densosporites, Cristatisporites, Radiizonates and Cingulizonates, representing small lycopsids, and Granulatisporites, produced by small ferns, and perhaps some pteridosperms typically are sub-dominant taxa. The recovered palynofloras are similar in overall composition making individual coal bed identification and correlation very difficult, if not impossible. However, the introduction and extinction of a few forms do assist the correlation of packages of strata, on both an intra- and interbasinal scale. Dictyotriletes bireticulatus is first observed in basal Lee Formation strata, at about the level of the Cove Creek coal bed. Radiizonates aligerans and R. striatus also appear more abundantly at this level, although some forms have been observed in older, Pocahontas Formation coals. This level essentially coincides with the Namurian C/Westphalian A boundary, based on plant megafossil evidence. Laevigatosporites minor, L. vulgaris, Endosporites globiformis, E. zonalis and Granasporites medius are first seen consistently just above the Sewell coal bed. Radiizonates aligerans, R. striatus and Densosporites irregularis are last seen in the early Middle Pennsylvanian, at about the level of the Splash Dam coal bed. Schulzospora rara occurs throughout Early and early Middle Pennsylvanian strata, and is last seen in the Manchester coal. The Manchester is directly overlain by the Betsie Shale, a widespread marine unit; the base of the Betsie marks the Westphalian A/B contact. When compared with palynomorph assemblage zonations published for the Western Interior, and Eastern Interior Basins, Early and early Middle Pennsylvanian palynofloras from the Central Appalachian Basin compare most favorably with early Morrowan strata. Analysis of bench samples indicates that Lycospora typically dominates basal and middle portions of Early and early Middle Pennsylvanian coals. More terminal layers often contain higher percentages of Granulatisporites (and related trilete, sphaerotriangular genera, e.g. Lophotriletes, Acanthotriletes, Deltoidspora) and Densosporites (and related trilete, crassicingulate genera, e.g. Cristatisporites, Cingulizonates, Radiizonates). This temporal change is consistently observed and may primarily reflect a water table change within the paleomires from consistently high (covered with water or at least water-logged most of the time) to intermittently low (occasional substrate exposure).

Lower and lower Middle Pennsylvanian fluvial to estuarine deposition, central Appalachian basin: Effects of eustasy, tectonics, and climate

Interpretations of Pennsylvanian sedimentation and peat accumulation commonly use examples from the Appalachian basin because of the excellent outcrops and large reserve of coal (>100 billion metric tons) in the region. Particularly controversial is the origin of Lower and lower Middle Pennsylvanian quartzose sandstones; beach-barrier, marine-bar, tidal-strait, and fluvial models all have been applied to a series of sand bodies along the western outcrop margin of the basin. Interpretations of these sandstones and their inferred lateral relationships are critical for understanding the relative degree of eustatic, tectonic, and climatic controls on Early Pennsylvanian sedimentation. Cross sections utilizing >1000 subsurface records and detailed sedimentological analysis of the Livingston Conglomerate, Rockcastle Sandstone, Corbin Sandstone, and Pine Creek sandstone (an informal member) of the Breathitt Group were used to show that each of the principal quartzose sandstones on the margin of the central Appalachian basin contains both fluvial and marginal marine facies. The four sandstones are fluvially dominated and are inferred to represent successive bed-load trunk systems of the Appalachian foreland. Base-level rise and an associated decrease in extra-basinal sediment at the end of each fluvial episode led to the development of local estuaries and marine reworking of the tops of the sand belts. Each of the sand belts is capped locally by a coal, regardless of whether the upper surfaces of the sand belts are of fluvial or estuarine origin, suggesting allocyclic controls on deposition. Peats were controlled by a tropical ever-wet climate, which also influenced sandstone composition through weathering of stored sands in slowly aggrading braidplains. Recurrent stacking of thick, coarse-grained, fluvial deposits with extra-basinal quartz pebbles; dominance of bed-load fluvial–lowstand deposits over mixed-load, estuarine-transgressive deposits; thinning of sand belts around tectonic highs and along faults; cratonward shift and amalgamation of successive sand belts on the margin of the basin; and truncation of successive sand belts toward the fault-bound margin of the basin are interpreted as regional responses to Alleghenian tectonism, inferred to have been the dominant control on accommodation space and sediment flux in the Early Pennsylvanian basin.

Rhythmic Sedimentation in a Mixed Tide and Wave Deposit, Hazel Patch Sandstone (Pennsylvanian), Eastern Kentucky Coal Field

ABSTRACT The Hazel Patch sandstone is an informal unit of the lower Middle Pennsylvanian Breathitt Formation, which is locally dominated by facies containing alternating sand and shale layers, or rhythmic bedding. Three types of rhythmites are defined. Cyclic rhythmites show a sinusoidal vertical stacking trend of thickening and thinning laminae, amalgamated rhythmites show partially or possibly cyclic trends that have been reworked or erosively truncated by overlying formsets, and noncyclic rhythmites show only random thickness distribution and no evidence of original cyclicity. Lower in the sandstone, noncyclic rhythmites are associated with swaly to quasi-planar bedding, even bedding, and ripples with rounded crests, and are inferred to have formed in response to storm waves and combined flows. Higher in the sandstone, noncyclic, amalgamated, and cyclic rhythmites are present in association with herringbone stratification and pinstripe laminae, and are inferred to have formed under the influence of tidal currents. Cyclic tidal rhythmites are present near the base of a shallow channel deposit. These rhythmites contain sandstone-shale couplets indicative of presumed diurnal tides, 11-12 laminae cycles indicative of neap-spring tidal sedimentation, and 25-27 laminae cycles indicative of lunar monthly sedimentation. Upward and laterally within the channel trunc tion of neap-cycle laminae by spring-cycle ripples, and a loss of continuous clay drapes in amalgamated rhythmites, led to preservation of only monthly or greater depositional cycles. Vertical facies trends in the sandstone are interpreted to indicate upward shallowing from a wave-influenced outer estuarine or shallow shelf environment to an intertidal sand flat to an exposed low-lying coast upon which peats accumulated. The fact that cyclic rhythmites were preserved only in a shallow channel, stratigraphically near the middle of the mail may indicate that accommodation space and a medial estuarine position with little wave reworking and bioturbation controlled the preservation of the various orders of cycles.

Lower-Middle Pennsylvanian Gobbler Formation: Isotopic Constraints on Temperature, Water-Rock Ratio, and Timing of Burial Diagenesis: ABSTRACT

The Lower-Middle Pennsylvanian Gobbler Formation is a 250 m-thick, cyclic limestone sequence deposited in the Orogrande basin of south-central New Mexico. meteoric diagenesis during episodic sub-aerial exposure of cycle tops produced meteoric calcite trends within individual cycles (constant {delta}{sup 18}O, variable {delta}{sup 13}C). Subsequent burial diagenesis proceeded in a closed system (W/R = 1-3), as shown by preservation of high-frequency variation in {delta}{sup 13}C and limited isotopic variation between host rocks and coexisting cements. As a consequence of variable burial depths (0.8 km on shelves to 1.6 km in basin center), some locales were subjected to higher burial temperatures, increasing the {delta}{sup 18}O depletion of burial precipitates. Inter- and intrasectional trends in {delta}{sup 18}O with respect to burial depth permit estimation of ambient geothermal gradients at the time of burial stabilization. Such isotopic trends demonstrate elevated geothermal gradients (90{degree}-120{degree}C/km), while a strong correlation between section-average {delta}{sup 18}O values and end-Virgilian overburden thicknesses implies completion of burial stabilization around this time. The timing of geothermal gradient elevation and burial stabilization was not coincidental but probably was linked to rapid subsidence of the Orogrande basin during the Virgilian Epoch. Such isotopic trends offer considerable potential for studying basinal thermal regimes during burialmore » diagenesis.« less

Foraminiferal characterization of the Morrowan/Atokan (lower Middle Pennsylvanian) boundary: Discussion and reply

Research Article| June 01, 1987 Foraminiferal characterization of the Morrowan/Atokan (lower Middle Pennsylvanian) boundary: Discussion and reply: Reply JOHN R. GROVES JOHN R. GROVES 1Amoco Production Company, P.O. Box 800, Denver, Colorado 80201 Search for other works by this author on: GSW Google Scholar Author and Article Information JOHN R. GROVES 1Amoco Production Company, P.O. Box 800, Denver, Colorado 80201 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1987) 98 (6): 746. https://doi.org/10.1130/0016-7606(1987)98<746:FCOTAL>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation JOHN R. GROVES; Foraminiferal characterization of the Morrowan/Atokan (lower Middle Pennsylvanian) boundary: Discussion and reply: Reply. GSA Bulletin 1987;; 98 (6): 746. doi: https://doi.org/10.1130/0016-7606(1987)98<746:FCOTAL>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract No Abstract Available. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Foraminiferal characterization of the Morrowan/Atokan (lower Middle Pennsylvanian) boundary: Discussion and reply

No Abstract Available. The article discussed appeared in the Bulletin , v. 97, p. 346–353.