Early Middle Pennsylvanian Research Articles

Vegetation dynamics in the Early–Middle Pennsylvanian coal swamps of the Nord-Pas-de-Calais Coalfield, France

During recent years, different studies have focused on characterising plant diversities in the Carboniferous environments of the Variscan Foreland. One of these areas, the Nord-Pas-de-Calais Coalfield, has a Namurian–Westphalian sequence that has historically yielded abundant evidence of vegetation change, but to date, little attention has been paid to its macrofloral diversity dynamics. Here we show, for the first time, a comprehensive characterisation of the diversity changes and macroevolutionary patterns from this coalfield. The results show evidence of low levels of species richness during the Namurian, followed by an exponential diversification at the base of Westphalian. Duckmantian–Bolsovian species diversity continues to progressively increase, suggesting relatively stable conditions at that time. Maximum species richness is observed at the mid-Bolsovian followed by a major depletion during the Asturian. Overall, this pattern is quite similar to that seen in other parts of the Variscan Foreland. However, we see Nord-Pas-de-Calais vegetation diversified earlier than those in the British parts, probably because the dynamics of marine incursions and lacustrine conditions delayed its development in the latter areas. Furthermore, we also see the Asturian decline of the Nord-Pas-de-Calais coal swamp occurred later than in other basins, such as in the Pennines, Ruhr, and South Wales. This scenario suggests that the collapse of this biome was probably caused by increased sediment influx and reduced subsidence, resulting from the northwards migration of the Variscan Mountains. This further supports other studies in Europe advocating that climate change was at most only a subsidiary factor in the collapse of the Pennsylvanian coal swamp biomes.

Identifying sources of non-unique detrital age distributions through integrated provenance analysis: An example from the Paleozoic Central Colorado Trough

AbstractTo address the longstanding issue of provenance interpretation of non-unique detrital zircon age populations, we integrated zircon U-Pb, rare earth element (REE), and εHf(t) data from upper Paleozoic strata in the northern Central Colorado Trough and Cambrian intrusions with petrography, paleocurrent data, and structural and stratigraphic observations. This data set indicates that Cambrian sediment was shed by multiple local sources instead of distant sources hundreds of kilometers away, and it reveals a detailed history of tectonic drainage reorganization in the northern Central Colorado Trough during Ancestral Rocky Mountain deformation. During the Early–Middle Pennsylvanian, Cambrian detrital zircons were a minor constituent of northern Central Colorado Trough sediment. However, during the Late Pennsylvanian–early Permian, westward advancement of the adjacent Apishapa Uplift deformation front precipitated drainage reorganization, which resulted in an episode of dominant Cambrian detrital zircon sourcing. Paleocurrent and petrographic data indicate that the source of Cambrian detritus was shed by an igneous rock body that was ≤15 km northeast of the depocenter, which has since been eroded away or mantled by Tertiary volcanic rocks. The addition of zircon petrochronology to the data set applied here was critical in confirming this hidden source of detritus and elucidating the compositional characteristics of that igneous rock. Zircon εHf(t) provided a regional provenance indicator of a western Laurentian affinity, and REE composition aided in discriminating possible local sources of Cambrian zircon. Furthermore, this work serves as a case study of a dominant Cambrian detrital zircon signature sourced from outside of the wellknown Amarillo-Wichita Uplift, and it has implications for the interpretation of such detrital spectra in the context of a direct-from-basement source or the recycling of Cambrian zircon-dominated rocks. In summary, we demonstrate the utility of this multi-provenance proxy approach in interpreting a complex structural history of a dynamic hinterland and concomitant drainage reorganization through an in-depth investigation into the basin record.

From widespread Mississippian to localized Pennsylvanian extension in central Spitsbergen, Svalbard

Abstract. In the Devonian–Carboniferous, a rapid succession of clustered extensional and contractional tectonic events is thought to have affected sedimentary rocks in central Spitsbergen, Svalbard. These events include Caledonian post-orogenic extensional collapse associated with the formation of thick Early–Middle Devonian basins, Late Devonian–Mississippian Ellesmerian contraction, and Early–Middle Pennsylvanian rifting, which resulted in the deposition of thick sedimentary units in Carboniferous basins like the Billefjorden Trough. The clustering of these varied tectonic settings sometimes makes it difficult to resolve the tectono-sedimentary history of individual stratigraphic units. Notably, the context of deposition of Mississippian clastic and coal-bearing sedimentary rocks of the Billefjorden Group is still debated, especially in central Spitsbergen. We present field evidence (e.g., growth strata and slickensides) from the northern part of the Billefjorden Trough, in Odellfjellet, suggesting that tilted Mississippian sedimentary strata of the Billefjorden Group deposited during active (Late/latest?) Mississippian extension. WNW–ESE-striking basin-oblique faults showing Mississippian growth strata systematically die out upwards within Mississippian to lowermost Pennsylvanian strata, thus suggesting a period of widespread WNW–ESE-directed extension in the Mississippian and an episode of localized extension in Early–Middle Pennsylvanian times. In addition, the presence of abundant basin-oblique faults in basement rocks adjacent to the Billefjorden Trough suggests that the formation of Mississippian normal faults was partly controlled by reactivation of preexisting Neoproterozoic (Timanian?) basement-seated fault zones. We propose that these preexisting faults reactivated as transverse or accommodation cross faults in or near the crest of transverse folds reflecting differential displacement along the Billefjorden Fault Zone. In Cenozoic times, a few margin-oblique faults (e.g., the Overgangshytta fault) may have mildly reactivated as oblique thrusts during transpression–contraction, but shallow-dipping, bedding-parallel, duplex-shaped décollements in shales of the Billefjorden Group possibly prevented substantial movement along these faults.

Placas columnares de crinoides del Carbonífero de la región de Santiago Ixtaltepec, Municipio de Nochixtlán, Oaxaca; consideraciones estratigráficas y paleobiogeográficas

Eleven crinoid columnal morphotypes of Mississippian and Pennsylvanian ages found in different stratigraphic levels of the Santiago (informal unit) and Ixtaltepec formations in outcrops in the Santiago Ixtaltepec region, municipality of Nochixtlan, Oaxaca, are reported and described. Axilinucrinus angustus is proposed as a new morphogenus and new morphospecies. Cyclocaudex insaturatus and Floricyclus welleri have been found in middle Mississippian (Meramecian-Chesterian?) strata from the upper member of the Santiago formation. Lomalegnum cf. L. hormidium, Axilinucrinus angustus and one indeterminate genus are present in middle-late Mississippian (Meramecian-Chesterian) strata of the Ixtaltepec Formation. Pentagonomischus cf. P. plebeius and Cyclocion distinctus occur in earlymiddle Pennsylvanian (Morrowan-Desmoinesian) strata of the Ixtaltepec Formation. Cylindrocauliscus fiski and Cyclocaudex typicus are morphotypes with a broad distribution throughout the carboniferous section of Nochixtlan. A strong similarity exists between all of the parataxa from Oaxaca and those reported from lower Mississippian-middle Pennsylvanian faunas of the Mid-Continent region of the central eastern United States.

An ultrastructural investigation of early Middle Pennsylvanian megaspores from the Illinois Basin, USA

Four megaspore genera: Cystosporites, Rotatisporites, Zonalessporites, and Valvisisporites were isolated from palaeokarst fill deposits of early Middle Pennsylvanian age, hosted within Ordovician limestones at Central Quarry in Central, Kendall County, Illinois, U.S.A. Five uncompacted megaspore species were identified and studied using scanning and transmission electron microscopy (SEM and TEM). The species Valvisisporites sculptus Bhardwaj is emended based on improved morphological and new ultrastructural data. The genus Pseudovalvisisporites Lachkar is recognized as a junior synonym of Valvisisporites. The ontogenetic development of aborted and functional Cystosporites diabolicus megaspores is investigated and the timing of sporopollenin deposition in both the exine and massa is reported. In Carboniferous megaspores, the importance of detailed investigation of the periapertural region is emphasized by the discovery of fusiform lamellate thickenings in Valvisisporites and Rotatisporites. The taxonomic and systematic importance of these features are considered in light of the otherwise highly conserved ultrastructure that is recognized in many lycopsid megaspores of this age.

Tetrapod Footprint Biostratigraphy and Biochronology

Tetrapod footprints have a fossil record in rocks of Devonian-Neogene age. Three principal factors limit their use in biostratigraphy and biochronology (palichnostratigraphy): invalid ichnotaxa based on extramorphological variants, slow apparent evolutionary turnover rates and facies restrictions. The ichnotaxonomy of tetrapod footprints has generally been oversplit, largely due to a failure to appreciate extramorphological variation. Thus, many tetrapod footprint ichnogenera and most ichnospecies are useless phantom taxa that confound biostratigraphic correlation and biochronological subdivision. Tracks rarely allow identification of a genus or species known from the body fossil record. Indeed, almost all tetrapod footprint ichnogenera are equivalent to a family or a higher taxon (order, superorder, etc.) based on body fossils. This means that ichnogenera necessarily have much longer temporal ranges and therefore slower apparent evolutionary turnover rates than do body fossil genera. Because of this, footprints cannot provide as refined a subdivision of geological time as do body fossils. The tetrapod footprint record is much more facies controlled than the tetrapod body fossil record. The relatively narrow facies window for track preservation, and the fact that tracks are almost never transported, redeposited or reworked, limits the facies that can be correlated with any track-based biostratigraphy. A Devonian-Neogene global biochronology based on tetrapod footprints generally resolves geologic time about 20 to 50 percent as well as does the tetrapod body fossil record. The following globally recognizable time intervals can be based on the track record: (1) Late Devonian; (2) Mississippian; (3) Early-Middle Pennsylvanian; (4) Late Pennsylvanian; (5) Early Permian; (6) Late Permian; (7) Early-Middle Triassic; (8) late Middle Triassic; (9) Late Triassic; (10) Early Jurassic; (11) Middle-Late Jurassic; (12) Early Cretaceous; (13) Late Cretaceous; (14) Paleogene; (15) Neogene. Tetrapod footprints are most valuable in establishing biostratigraphic datum points, and this is their primary value to understanding the stratigraphic (temporal) dimension of tetrapod evolution.

FORAMINIFERAL EVIDENCE FOR THE AGE OF EXOTIC BLOCKS WITHIN THE KOPRÍA MÉLANGE, RHODOS (GREECE)

Blocks embedded within the Kopria Melange of western Rhodos yield well-preserved, abundant microfossils including early Middle Pennsylvanian fusulinacean faunas represented by species belonging to the genera Eoschubertella, Profusulinella, Pseudostaffella and Ozawainella. A less diagnostic fauna mainly composed of the genus Paraachaediscus and an undetermined species of Howchinia has been also recorded and referred to a probable Mississippian age.This tropical to subtropical microfauna with Urals-Paleotethyan paleobiogeographic affinity provides new constraints for the paleogeographic interpretation of the Aegean region during the still poorly understood transition from the Variscan to the Alpine deformational cycle. In one olistolith, fusulinid-bearing strata are underlain by a basal conglomerate horizon whose composition indicates both recycled orogenic provenance and significant chemical weathering in a warm, humid climate. Sedimentologic and petrographic data, combined with the age and Urals-Paleotethyan affinity of the microfossil assemblages, are evidence for a major transgression that coincided in time with the end of the Variscan Orogeny. This may suggest original deposition of the melange on the northern European margin of Paleotethys, although a southern origin be ruled out. Subsequent accretion to the External Hellenides, on the southern, Gondwanan margin of Paleotethys, could have taken place during the Eo-Cimmerian orogeny at the end of the Middle Triassic, shortly before the opening of the Pindos Basin.

Metalliferous coals of the Westphalian A Joggins Formation, Cumberland Basin, Nova Scotia, Canada: petrology, geochemistry, and palynology

Five coals of Westphalian A (early Middle Pennsylvanian) age were sampled from the Joggins Formation section exposed along Chignecto Bay at Joggins, Nova Scotia. Coal beds along the bay were mined beginning in the early 17th century, yet there have been few detailed published investigation of the coal beds of this classic section. The lowermost coal, the Upper Coal 28 (Upper Fundy), is a high-vitrinite coal with a spore assemblage dominated by arboreous lycopsid spores with tree ferns subdominant. The upper portions of the coal bed have the highest ratio of well-preserved to poorly-preserved telinite of any of the coals investigated. Coal 19 (“clam coal”) has 88% total vitrinite but, unlike the Fundy coal bed, the telinite has a poor preservation ratio and half the total vitrinite population comprises gelocollinite and vitrodetrinite. The latter coal bed is directly overlain by a basin-wide limestone bed. The Lower Kimberly coal shows good preservation of vitrinite with relatively abundant telinite among the total vitrinite. The Middle Kimberly coal, which underlies the tetrapod-bearing lycopsid trees found by Lyell and Dawson in 1852, exhibits an upward decrease in arboreous lycopod spores and an upward increase in the tree fern spore Punctatisporites minutus. Telinite preservation increases upwards in the Middle Kimberly but overall is well below the preservation ratio of the Upper Fundy coal bed. The coals all have high sulfur contents, yielding up to 13.7% total sulfur for the lower lithotype of the Upper Fundy coal bed. The Kimberly coals are not only high in total and pyritic sulfur, but also have high concentrations of chalcophile elements. Zinc, ranging up to 15,000 ppm (ash basis), is present as sphalerite in fusain lumens. Arsenic and lead each exceed 6000 ppm (ash basis) in separate lithotypes of the Kimberly coals. Together these data are consistent with elevated pH in planar mires. The source of the elemental enrichment in this presumed continental section is enigmatic.

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).

96/00022 Organic geochemical characterization of some Carboniferous coal seams of Zonguldak Basin (NW Turkey)

The Manchester coal bed in eastern Kentucky is the stratigraphically lowest coal in Kentucky that is both laterally continuous and of consistent mineable thickness. The Manchester coal bed occurs in the lower part of the Breathitt Formation, in an interval between the underlying Corbin Sandstone and the overlying Betsie Shale, both of which are also aerially widespread units. The Manchester is early Middle Pennsylvanian in age and is equivalent with the middle Morrowan of the Eastern Interior Basin and the late Westphalian A of western Europe. Increment samples were collected from the western and eastern outcrop and mining areas of the Eastern Kentucky Coal Field and were analyzed palynologically, petrographically and geochemically to compare and contrast the two areas.In the western part of the Eastern Kentucky Coal Field, the Manchester coal bed is uniform in occurrence and composition. The bed is consistently 0.61–0.92 m (2–3 ft) thick, and generally is devoid of inorganic partings. Palynologically, the coal in this area is largely dominated by Lycospora, the dispersed spore of many of the large lycopsid trees (e.g., Lepidodendron and Lepidophloios) and, to a lesser extent, Granasporites medius (representing Diaphorodendron and Synchysidendron). Petrographically, the coal contains high percentages of vitrinite macerals and correspondingly low percentages of liptinite and inertinite macerals. Most of the increments from this area studied are generally low in ash yield ( >5%) and sulfur content ( < 1%), although terminal coal layers are frequently higher in ash ( > 10%) and occasionally sulfur ( > 1%).In the eastern part of the coal field the Manchester coal bed is typically thicker ( > 3 ft, 1 m), but usually occurs as a coal zone with intercalated coal beds and clastic units. Palynologically, the coal in this area contains increased percentages of small lycopsid, small (seed?) ferns, calamites, and cordaites. Petrographically, the coal is higher overall in liptinite and inertinite macerals. Ash yields in the eastern sample area are generally low ( < 10%), an exception being some high-ash durain bands. Overall sulfur contents also are low (typically < 1%).The western samples are interpreted as having formed in a well protected, generally flooded, mire. A consistent water cover would provide a favorable environment for arboreous lycopsid growth and proliferation, and also inhibit oxidation of the peat surface, thus promoting the formation of a high vitrinite content coal.The eastern samples are also interpreted as having formed in a mire that was well protected most of the time, giving rise to thick sequences of low-ash, low-sulfur coal. Intermittent inundation by extra-swamp waters, carrying sediment in this area, resulted in the development of a multiple coal zone (i.e., several peat-forming events with intervening clastic deposition), in contrast to a single peat-forming event in the western area. Surficial peat exposure was more frequent in the eastern area, which allowed for increased microbial degradation of the peat and subsequent formation of inertinite macerals upon conversion to bituminous coal. This condition might also accelerate charring of the peat surface by wildfire.

Palynologic, petrographic and geochemical characteristics of the Manchester coal bed in Eastern Kentucky

The Manchester coal bed in eastern Kentucky is the stratigraphically lowest coal in Kentucky that is both laterally continuous and of consistent mineable thickness. The Manchester coal bed occurs in the lower part of the Breathitt Formation, in an interval between the underlying Corbin Sandstone and the overlying Betsie Shale, both of which are also aerially widespread units. The Manchester is early Middle Pennsylvanian in age and is equivalent with the middle Morrowan of the Eastern Interior Basin and the late Westphalian A of western Europe. Increment samples were collected from the western and eastern outcrop and mining areas of the Eastern Kentucky Coal Field and were analyzed palynologically, petrographically and geochemically to compare and contrast the two areas. In the western part of the Eastern Kentucky Coal Field, the Manchester coal bed is uniform in occurrence and composition. The bed is consistently 0.61–0.92 m (2–3 ft) thick, and generally is devoid of inorganic partings. Palynologically, the coal in this area is largely dominated by Lycospora, the dispersed spore of many of the large lycopsid trees (e.g., Lepidodendron and Lepidophloios) and, to a lesser extent, Granasporites medius (representing Diaphorodendron and Synchysidendron). Petrographically, the coal contains high percentages of vitrinite macerals and correspondingly low percentages of liptinite and inertinite macerals. Most of the increments from this area studied are generally low in ash yield ( >5%) and sulfur content ( < 1%), although terminal coal layers are frequently higher in ash ( > 10%) and occasionally sulfur ( > 1%). In the eastern part of the coal field the Manchester coal bed is typically thicker ( > 3 ft, 1 m), but usually occurs as a coal zone with intercalated coal beds and clastic units. Palynologically, the coal in this area contains increased percentages of small lycopsid, small (seed?) ferns, calamites, and cordaites. Petrographically, the coal is higher overall in liptinite and inertinite macerals. Ash yields in the eastern sample area are generally low ( < 10%), an exception being some high-ash durain bands. Overall sulfur contents also are low (typically < 1%). The western samples are interpreted as having formed in a well protected, generally flooded, mire. A consistent water cover would provide a favorable environment for arboreous lycopsid growth and proliferation, and also inhibit oxidation of the peat surface, thus promoting the formation of a high vitrinite content coal. The eastern samples are also interpreted as having formed in a mire that was well protected most of the time, giving rise to thick sequences of low-ash, low-sulfur coal. Intermittent inundation by extra-swamp waters, carrying sediment in this area, resulted in the development of a multiple coal zone (i.e., several peat-forming events with intervening clastic deposition), in contrast to a single peat-forming event in the western area. Surficial peat exposure was more frequent in the eastern area, which allowed for increased microbial degradation of the peat and subsequent formation of inertinite macerals upon conversion to bituminous coal. This condition might also accelerate charring of the peat surface by wildfire.

Marginovatia, a mid-Carboniferous genus of linoproductid brachiopods

Marginovatiais proposed as a new genus of small North American linoproductid brachiopods that developed a narrow shelf around the anterior and anterolateral margin of the visceral disc in the brachial valve and a corresponding small flange in the pedicle valve interior. When the valves closed, these structures fit together and helped seal off the visceral cavity. This genus first appeared in the Late Mississippian (late Meramecian), continued through the Early and earliest Middle Pennsylvanian (Morrowan), and may have continued into the early Middle Pennsylvanian (Atokan). In addition to the type species,Productus inflatusvar.minorSnider, seven species are assigned to this genus:Marginovatia aureocollisn. sp.,M. catinulusn. sp.,Linoproductus duodenariusEaston,M. eurekensisn. sp.,M. manardensisn. sp.,Productus(Linoproductus)semicubiculusBell, andL. pumilusSutherland and Harlow. An eighth species, identified asMarginovatiaaff.M. pumila(Sutherland and Harlow), occurs in rocks of probable middle to late Morrowan or Atokan age in southeastern Alaska.

Sedimentology, Petrology, and Reservoir Characteristics of Lower Strawn Sandstone, Bent Tree Field, Hardeman County, Texas: ABSTRACT

Reservoir sandstones of the lower Strawn Formation (early Middle Pennsylvanian) in the Bent Tree field of Hardeman County, Texas, are coarse to fine-grained, texturally submature arkoses. Cores show the sandstones to have been deposited in 1.5-4.5 m thick fining-upward successions of aggraded or prograded bar units. Each bar unit has a sharp erosional base overlain by cross-bedded, coarse-grained, conglomeratic sandstone, which, in turn, is overlain by medium to fine-grained, horizontally bedded or ripple-bedded sandstone. The coarse conglomeratic sandstones are interpreted to represent deposition in main channels of a braided fluvial system that were progressively filled by aggrading and prograding bars. The interbedded, finer grained, more immature sandstones appear to have been deposited in auxiliary channels or swales, or in proximal overbank settings. The detrital framework grain suite of the reservoir sandstones averages 47% quartz, 30% feldspars, 19% igneous rock fragments, and 4% sedimentary rock fragments. The source of these sands was a plutonic/cratonic igneous massif with minor exposures of older sedimentary strata, and was probably the ancestral Wichita Mountains. Diagenesis has significantly affected the petrographic and reservoir properties of the lower Strawn sandstones, primarily through the in-situ alteration of detrital feldspathic grains and by the precipitation of authigenic quartz overgrowths,more » chlorite clay, and carbonate cements.« less

Evolution of the Ordovician through Middle Pennsylvanian carbonate shelf in east-central California

Carbonate shelf rocks marked by various sedimentary features suggesting intertidal to supratidal deposition or bearing rich, benthic faunas and their corresponding slope and basin rock sequences containing planktic fossils and sediment-gravity-flow deposits have been identified in the Inyo Mountains–Argus Range region of east-central California for all of the Paleozoic from Ordovician through Middle Pennsylvanian. Four major depositional sequences, each beginning with a marine transgression and all but the third ending with a progradation, were developed representing (1) Early Ordovician into Early Silurian time, (2) Early Silurian into earliest Middle Devonian time, (3) Middle to Late Devonian time and (4) Early to middle Late Mississippian time. A period of basinal infilling in the Late Mississippian was followed by a fifth major marine transgression in the Early Pennsylvanian. The carbonate shelf itself evolved from a homoclinal ramp in the Ordovician to an accretionary rimmed margin by the Early Devonian. This margin was drowned, probably in the Middle Devonian; by the Early Mississippian, a new homoclinal ramp had been developed. Before the end of the Mississippian, this ramp became distally steepened and then was transformed into an accretionary rimmed margin. The Early to Middle Pennsylvanian marine transgression gave rise to still another homoclinal carbonate ramp. Subsidence of ∼2,300 m occurred between Early Ordovician and Middle Pennsylvanian time in the area immediately east of the Inyo Mountains. It increased westward to probably >3,500 m at the edge of the Owens Valley as the continental margin subsided and bent downward ∼1° between Early Ordovician and middle Late Mississippian time. As a result of subsidence and relatively low rates of sedimentation, the water depth in the western part of the study area increased from close to sea level at the beginning of the Ordovician to as much as 3,000 m in the Late Mississippian. Because of higher rates of sediment accumulation and lower rates of subsidence in the eastern part of the region, shallow-water environments were maintained throughout most of this time interval; even so, the shelf-slope break retreated at least 45 km southeastward from Middle Ordovician to middle Late Mississippian time and at least 35 km farther southeastward by Middle Pennsylvanian time.

Changing patterns of Pennsylvanian coal-swamp vegetation and implications of climatic control on coal occurrence

Improved regional and interregional stratigraphic correlations of Pennsylvanian strata permit comparisons of vegetational changes in Euramerican coal swamps. The coal-swamp vegetation is known directly from in situ coal-ball peat deposits from more than 65 coals in the United States and Europe. Interpretations of coal-swamp floras on the basis of coal-ball peat studies are extended to broader regional and stratigraphic patterns by use of coal palynology. Objectives of the quantitative analyses of the vegetation in relation to coal are to determine the botanical constituents at the peat stage and their environmental implications for plant growth and peat accumulation. Morphological and paleoecological analyses provide a basis for deducing freshwater regimes of coal swamps. Changes in composition of Pennsylvanian coal-swamp vegetation are quire similar from one paralic coal region to another and show synchrony that is attributable to climate. Paleobotany and paleogeography of the Euramerican province indicate a moist tropical paleoclimate. Rainfall, runoff and evapotranspiration were the variable climatic controls in the distribution of coal-swamp vegetation, peat accumulation and coal resources. In relative terms of climatic wetness the Pennsylvanian Period is divisible into five intervals, which include two relatively drier intervals that developed during the Lower-Middle and Middle-Upper Pennsylvanian transitions. The climate during Early Pennsylvanian time was moderately wet and the median in moisture availability. Early Middle Pennsylvanian was drier, probably seasonally dry-wet; late Middle Pennsylvanian was the wettest in the Midcontinent; early Late Pennsylvanian was the driest; and late Late Pennsylvanian was probably the wettest in the Dunkard Basin. The five climatic intervals represent a general means of dividing coal resources within each region into groups with similar botanical constituents and environments of peat accumulation. Regional differences in basinal geology and climate were significant variables, but the synchronous control of paleoclimate was of primary importance.

Tectonics of Western Permian Basin: ABSTRACT

The Permian basin of west Texas and southeastern New Mexico probably originated in late Precambrian time as a shallow geosynclinal trough on the southern edge of the North American craton. The extreme southern part of the region formed part of a subduction trough. By Late Cambrian time the seas in the southern part of the trough had advanced over part of the craton, and Paleozoic sedimentation began. Perhaps in late Precambrian a north-facing salient of the trough developed into an aulacogen with lateral dextral movement along steep faults in what later became the eastern part of the Delaware basin. During early and middle Paleozoic time the region was tectonically quiet. However by Middle Mississippian the Precambrian zones of weakness were reactivated and the Delaware and Midland subbasins began to form. At the same time the Marathon-Ouachita trough began to deepen. In early Middle Pennsylvanian time active tectonism with stresses from the northeast formed a small mountain chain between the two subbasins, on the site of the Central Basin platform. In later Pennsylvanian and Early Permian time renewed tectonism resulted in low-angle thrusting of early Paleozoic rocks northward from the Marathon trough. At the same time there was renewed vertical movement on the ancient lateral faults which formed the eastern edge of the Delaware basin. Middle and Late Permian was a quiet time tectonically with the only movement being slight subsidence, probably due to differential compaction in the basins. This regime continued through the early Mesozoic. By Early Cretaceous, however, a major change in paleogeography resulted in an advance of the sea over the region which was by then securely welded to the craton. The area was protected from severe deformation during the Laramide orogeny by the beam effect of the Matador and Amarillo uplifts on the north and the east-west folds of the Marathon belt on the south. Tectonic activity since the early Tertiary has been minimal. Tectonic style in the Delaware basin is characterized by eastward tilt in the Permian and younger rocks. The older rocks are folded and cut by steeply dipping faults. The Central Basin platform style comprises supertenuous draped structures in the younger rocks. These overlie closed folds with steeply dipping faults in the older rocks which trend north-northwest. The Midland basin contains en echelon faults and extension fracturing, reflecting moderate movement. The extreme southern part of the Permian basin consists of deep folded troughs bounded by thrust faults. The trend of these structures forms a large angle with the trends of the Central Basin platform. The long interval of tectonic stability in the region since the early Permian has undoubtedly contributed to the maturation and accumulation of the oil and gas resources of the basin. End_of_Article - Last_Page 762------------

Tectonic History of Boothia Uplift and Cornwallis Fold Belt, Arctic Canada

The Boothia uplift is an elongate northerly extension of crystalline rocks of the Precambrian shield into the Canadian Arctic Archipelago. The structural grain of the crystalline rocks which comprise the uplift is northerly. This causes the uplift to have an over-all northerly trending elongate outline. Proterozoic to Upper Devonian sediments, which overlie and closely flank the Boothia uplift, form the Cornwallis fold belt. The structure of the Cornwallis fold belt is the result of movements of the underlying Boothia uplift, and for this reason the fold belt also has both a northerly structural grain and outline. Together, the uplift and the fold belt extend at least 600 miles, striking diametrically across the Arctic lowlands and Franklinian miogeosyncline. At various times since the Precambrian, the Boothia uplift has risen, lifting the Cornwallis fold belt with respect to flanking areas. Movements are dated from erosion surfaces and unconformities on the uplift and in the fold belt. In the southern part, the uplift is a simple arch, whereas in the northern, it is predominantly a horst, with a lesser amount of arching. Near-vertical faults bordering the Boothia uplift become high-angle reverse faults toward the surface, presumably the result of lateral spreading of the uplifted area. Such faulting commonly is exposed at the boundary of the uplift in the Arctic lowlands. However, in the much thicker, commonly incompetent succession of the miogeosyncline fold belt, structure is reflected as asymmetrical folding of the Cornwallis fold belt Published model experiments with fine, dry sands, in which a horst-shaped block was uplifted, have steep reverse faults at the boundaries, and strongly resemble the northern part of the Boothia uplift. A mobile belt encompassing the Boothia uplift and Cornwallis fold belt moved periodically, having six documented times of uplift relative to the flanking areas. These uplifts occurred in (1) Precambrian, (2) pre-Middle Cambrian, (3) mid-Early Devonian, (4) late Early to early Middle Devonian, (5) mid-Late Devonian, and (6) Pennsylvanian or Early Permian times. Submergence following the mid-Early Devonian and the late Early to early Middle Devonian uplifts was the result of widespread regional submergence rather than relative depression of the mobile belt alone. The nature of the submergence which followed the other uplifts is unknown. Thus, in the geologic record, the Boothia uplift and Cornwallis fold belt have risen six times with respect to the flanking regions. However, although t ey were covered by sediments at various times and have narrow normal-faulted zones of down-dropped blocks, they do not appear to have sunk as a unit with respect to the flanking regions.

Revision of Upper Paleozoic Nomenclature, Banff Area, Alberta, Canada: GEOLOGICAL NOTES

The succession at Highwood Pass was previously misinterpreted. The Storm Creek is directly overlain by beds containing early Middle Pennsylvanian fossils, and is underlain by clastic rocks bearing Morrowan fossils. It is equivalent to the type Tunnel Mountain formation. The Norquay is not equivalent to the type but corresponds to the Todhunter member of the Tunnel Mountain clastic rocks. The Tunnel Mountain is not equivalent to the type Tunnel Mountain, but is typical of carbonate rocks of the Etherington formation with a high Chesteran fauna. Thus the Stenopora zone is not Permian in age but Lower Pennsylvanian, and the Plagioglypta canna zone as shown by fusulinids is early Middle Pennsylvanian in age, not Permian. The Rocky Mountain group is divided into 3 formations. From the top down these are: the Ishbel formation (new name) of Permian age, the Kananaskis formation (new name) of early Middle Pennsylvanian age, and the Tunnel Mountain formation (restricted) of Lower Pennsylvanian age, which includes Tunnel Mountain clastic rocks only.