Early Chesterian Research Articles

Mississippian mud rocks of the eastern Great Basin: Stratigraphy, tectonic significance, and hydrocarbon potential

A thick succession of Mississippian mud rocks in the eastern Great Basin has historically been identified as the Chainman Shale and interpreted as a foreland basin deposit associated with the Antler orogeny. Our work shows that this section is two distinct mud-rock units separated by a Late Mississippian unconformity. The Gap Wash Formation is identified as the mud rock below the unconformity, and Chainman Shale is restricted to mud rock above the unconformity. Poor exposure, sparse age control, and limited lithologic contrast have hampered identification and correlation of the mud-rock units. New research identifies subtle differences in rock type, and mineralogical and source-rock analyses show that the two formations have contrasting characteristics. These are associated with petrophysical properties that can be correlated across the region. The data show that the Gap Wash Formation has significantly more organic carbon and better pyrolysis results than the Chainman Shale. The Gap Wash also has mineralogy that could make it more suitable for treatment as a shale reservoir. The new understanding of Mississippian mud rocks in the Great Basin can focus future hydrocarbon exploration. The mud-rock units record regional Mississippian paleogeographic evolution. The Gap Wash Formation was deposited into accommodation space created by the loading of the continental margin during the Antler orogeny. The Chainman Shale was deposited in a successor basin that formed in response to resumed continental margin contraction in the late Meramecian to early Chesterian and is not clearly associated with the Antler orogeny.

Hydrothermal, Biogenic, and Seawater Components in Metalliferous Black Shales of the Brooks Range, Alaska: Synsedimentary Metal Enrichment in a Carbonate Ramp Setting

Trace element and Os isotope data for Lisburne Group metalliferous black shales of Middle Mississippian (early Chesterian) age in the Brooks Range of northern Alaska suggest that metals were sourced chiefly from local seawater (including biogenic detritus) but also from externally derived hydrothermal fluids. These black shales are interbedded with phosphorites and limestones in sequences 3 to 35 m thick; deposition occurred mainly on a carbonate ramp during intermittent upwelling under varying redox conditions, from suboxic to anoxic to sulfidic. Deposition of the black shales at ~335 Ma was broadly contemporaneous with sulfide mineralization in the Red Dog and Drenchwater Zn-Pb-Ag deposits, which formed in a distal marginal basin. Relative to the composition of average black shale, the metalliferous black shales ( n = 29) display large average enrichment factors (>10) for Zn (10.1), Cd (11.0), and Ag (20.1). Small enrichments (>2–<10) are shown by V, Cr, Ni, Cu, Mo, Pd, Pt, U, Se, Y, and all rare earth elements except Ce, Nd, and Sm. A detailed stratigraphic profile over 23 m in the Skimo Creek area (central Brooks Range) indicates that samples from at and near the top of the section, which accumulated during a period of major upwelling and is broadly correlative with the stratigraphic levels of the Red Dog and Drenchwater Zn-Pb-Ag deposits, have the highest Zn/TOC (total organic carbon), Cu/TOC, and Tl/TOC ratios for calculated marine fractions (no detrital component) of these three metals. Average authigenic (detrital-free) contents of Mo, V, U, Ni, Cu, Cd, Pb, Ge, Re, Se, As, Sb, Tl, Pd, and Au show enrichment factors of 4.3 × 103 to 1.2 × 106 relative to modern seawater. Such moderate enrichments, which are common in other metalliferous black shales, suggest wholly marine sources (seawater and biogenic material) for these metals, given similar trends for enrichment factors in organic-rich sediments of modern upwelling zones on the Namibian, Peruvian, and Chilean shelves. The largest enrichment factors for Zn and Ag are much higher (1.4 × 107 and 2.9 × 107, respectively), consistent with an appreciable hydrothermal component. Other metals such as Cu, Pb, and Tl that are concentrated in several black shale samples, and are locally abundant in the Red Dog and Drenchwater Zn-Pb-Ag deposits, may have a partly hydrothermal origin but this cannot be fully established with the available data. Enrichments in Cr (up to 7.8 × 106) are attributed to marine and not hydrothermal processes. The presence in some samples of large enrichments in Eu (up to 6.1 × 107) relative to modern seawater and of small positive Eu anomalies (Eu/Eu* up to 1.12) are considered unrelated to hydrothermal activity, instead being linked to early diagenetic processes within sulfidic pore fluids. Initial Os isotope ratios (187Os/188Os) calculated for a paleontologically based depositional age of 335 Ma reveal moderately unradiogenic values of 0.24 to 0.88 for four samples of metalliferous black shale. A proxy for the ratio of coeval early Chesterian seawater is provided by initial (187Os/188Os)335 Ma ratios of four unaltered black shales of the coeval Kuna Formation that average 1.08, nearly identical to the initial ratio of 1.06 for modern seawater. Evaluation of possible sources of unradiogenic Os in the metalliferous black shales suggests that the most likely source was mafic igneous rocks that were leached by externally derived hydrothermal fluids. This unradiogenic Os is interpreted to have been leached by deeply circulating hydrothermal fluids in the Kuna basin, followed by venting of the fluids into overlying seawater. We propose that metal-bearing hydrothermal fluids that formed Zn-Pb-Ag deposits such as Red Dog or Drenchwater vented into seawater in a marginal basin, were carried by upwelling currents onto the margins of a shallow-water carbonate platform, and were then deposited in organic-rich muds, together with seawater- and biogenically derived components, by syngenetic sedimentary processes. Metal concentration in the black shales was promoted by high biologic productivity, sorption onto organic matter, diffusion across redox boundaries, a low sedimentation rate, and availability of H2S in bottom waters and pore fluids.

Early Carboniferous Nautiloids from the Ruddell Shale Member in Arkansas, Midcontinent North America

Abstract. An early Chesterian (early Carboniferous; Late Mississippian) nautiloid fauna is described from the Ruddell Shale Member of the Moorefield Formation in Arkansas, Midcontinent North America. It consists of the three orthocerids, Euloxoceras buffalowallowense sp. nov., Mitorthoceras perfilosum Gordon and Moorefieldoceras yochelsoni gen. et sp. nov., and the two nautilids, Tylonautilus sp. and Peripetoceras milleri sp. nov. Reexamination of M. perfilosum, the type species of the genus, provides grounds for emendation of the generic concept emphasizing the supracentral position of the siphuncle. Moorefieldoceras is differentiated from comparable genera by its relatively rapid shell expansion, prominent annulations with a distinct ventral sinus, and relatively large siphuncle diameter with a central to subcentral position.

Upper Mississippian (Lower Carboniferous) carbonate stratigraphy and syndepositional faulting reveal likely Ouachita flexural forebulge effects, eastern Kentucky, U.S.A.

Stratigraphic analysis of late Middle to early Late Mississippian (Early Carboniferous; late Meramecian–early Chesterian) carbonates in east-central and northeastern Kentucky, U.S.A., shows six unconformity-bound sequences. The earliest, late Meramecian, St. Louis sequence shows a relatively uniform distribution and a typical eastward Appalachian gradient along the ENE-trending outcrop belt on the western margin of the Appalachian Basin. However, abrupt uplift and exposure of deeper water St. Louis deposits, indicated by erosional thinning and well-developed exposure features, at the Meramecian–Chesterian transition signal inception of regional early Chesterian uplift that intensively altered the nature and distribution of the five overlying early Chesterian carbonate sequences. Uplift was related to the syndepositional reactivation of WNW-trending basement faults that broke up the St. Louis platform and generated a mosaic-like distribution of the overlying five sequences due to structurally related erosional incision and paleoslope change to the southwest. These early Chesterian events coincide with a major phase of northeast-directed Ouachita Orogeny on the southern margin of Laurussia and concomitant forebulge migration to the ENE. Modeling of regional stress distribution, as well as timing and location during bulge migration, strongly indicate that a migrating Ouachita bulge reactivated basement structures and generated the noted stratigraphic anomalies in eastern Kentucky and nearby areas. The likelihood of low-amplitude flexural waves, like the Ouachita bulge, migrating across areas where they were not previously considered, has major implications for understanding structural, stratigraphic, and eustatic anomalies in supposedly stable cratonic areas far removed from active tectonism.

Phylogenetics, systematics, paleoecology, and evolution of the trilobite generaPaladinandKaskiafrom the United States

Late Mississippian and earliest Pennsylvanian trilobite faunas of North America are dominated by thePaladinandKaskiaclades. Phylogenetic analysis of middle Carboniferous species of these clades demonstrates the close ancestral relationship between these groups. TheKaskiaclade consists of eight species:K. chesterensisWeller, 1936,K. osagensis(Cisne, 1967),K. longispina(Strong, 1872),K. wilsoni(Walter, 1924),K. genevievensis(Walter, 1924),K. rosei(Cisne, 1967),K. gersnain. sp., andK. rollinsin. sp.KaskiaWeller, 1936 ranges from late Osagean to middle Chesterian (early Visean-early Serpukhovian) and is restricted to cyclothemic shelf and nearshore deposits. Species ofKaskiaappear to have evolved in areas of shallow water and high environmental stress. ThePaladinclade consists of 12 species including previously named speciesP. morrowensis(Mather, 1915),P. girtyianusHahn and Hahn, 1970,P. rarusWhittington, 1954,P. helmsensisWhittington, 1954, andP. moorei(Branson, 1937). New species belonging to this clade arePaladin moorefieldensisn. sp.,P. pleisiomorphusn. sp.,P. imoensisn. sp.,P. mangerin. sp., andP. wapanukaensisn. sp. This group ranges from the early Chesterian to early Morrowan (late Viseanlate Bashkirian). Species ofPaladinappear to be confined to outer shelf shelf-edge and off-shelf facies where presumably deeper water environments existed. This is manifested in their paleogeographic distribution, which is paleoenvironmentally controlled.

Depositional Settings, Correlation, and Age of Carboniferous Rocks in the Western Brooks Range, Alaska

The Kuna Formation (Lisburne Group) in northwest Alaska hosts the Red Dog and other Zn-Pb-Ag massive sulfide deposits in the Red Dog district. New studies of the sedimentology and paleontology of the Lisburne Group constrain the setting, age, and thermal history of these deposits. In the western and west-central Brooks Range, the Lisburne Group includes both deep- and shallow-water sedimentary facies and local volcanic rocks that are exposed in a series of thrust sheets or allochthons. Deep-water facies in the Red Dog area (i.e., the Kuna Formation and related rocks) are found chiefly in the Endicott Mountains and structurally higher Picnic Creek allochthons. In the Red Dog plate of the Endicott Mountains allochthon, the Kuna consists of at least 122 m of thinly interbedded calcareous shale, calcareous spiculite, and bioclastic supportstone (Kivalina unit) overlain by 30 to 240 m of siliceous shale, mudstone, calcareous radiolarite, and calcareous lithic turbidite (Ikalukrok unit). The Ikalukrok unit in the Red Dog plate hosts all massive sulfide deposits in the area. It is notably carbonaceous, is generally finely laminated, and contains siliceous sponge spicules and radiolarians. The Kuna Formation in the Key Creek plate of the Endicott Mountains allochthon (60–110 m) resembles the Ikalukrok unit but is unmineralized and has thinner carbonate layers that are mainly organic-rich dolostone. Correlative strata in the Picnic Creek allochthon include less shale and mudstone and more carbonate (mostly calcareous spiculite). Conodonts and radiolarians indicate an age range of Osagean to early Chesterian (late Early to Late Mississippian) for the Kuna in the Red Dog area. Sedimentologic, faunal, and geochemical data imply that most of the Kuna formed in slope and basin settings characterized by anoxic or dysoxic bottom water and by local high productivity. Shallow-water facies of the Lisburne Group in the Red Dog area are present locally in the Endicott Mountains allochthon and throughout the Kelly River allochthon and consist of the Utukok and Kogruk Formations. The Utukok Formation is an impure limestone with disseminated and interbedded noncarbonate mud and quartz-rich silt and sand. Clean carbonate predominates in the overlying Kogruk Formation but has been widely altered to dolostone and chert. Deep-water strata, similar to that in the Kuna Formation, overlie and grade laterally into shallow-water rocks in the Endicott Mountains allochthon and compose the uppermost Lisburne in the Kelly River allochthon. The Utukok Formation is mainly Osagean but its base is Kinderhookian (early Early Mississippian) in the highest plates of the Kelly River allochthon. The Kogruk Formation is mostly Meramecian but partly Osagean and early Chesterian in some areas. We interpret inner to middle platform settings for most of the Utukok and Kogruk Formations. Deep-water, locally phosphatic facies of the uppermost Lisburne Group formed during a platform-drowning event of regional extent that began in the late Meramecian. In the Howard Pass area, ~120 to 250 km to the east, the Lisburne Group includes an array of shallow- and deep-water facies that correspond well in age and general depositional environment to those in the Red Dog area but differ in some details. Deep-water strata are generally thinner, include less carbonate, and formed in settings that were deeper and/or had less detrital input. Shallow-water deposits are less extensive, contain less quartz silt and sand, and formed chiefly in middle and outer platform settings. Paleogeographic reconstructions imply that carbonate platforms flanked the Kuna basin to the north and south in the west but flourished chiefly north of the basin in the east. These platforms provided carbonate and perhaps some siliciclastic detritus to the basin; siliciclastic detritus could also have come from older strata underlying the platforms and/or from the Endicott delta to the north. Carbonate turbidite deposition in the Kuna basin occurred chiefly during middle Osagean and late Meramecian-early Chesterian times and ceased when adjacent platforms drowned. A combination of local and eustatic factors probably controlled the timing of detrital input to the basin and the demise of the adjoining carbonate platforms. Platform inundation is roughly coeval with the onset of barite precipitation and sulfide mineralization, implying that regional extension was a significant component of all three events. High productivity, locally thick calcareous turbidite fill, and proximity to restricted, shallow-water carbonate platform environments are aspects of the Kuna basin that appear to have been important in forming the giant Red Dog deposits. Conodont color alteration indices of the Lisburne Group in the Red Dog area and much of the Howard Pass area are mostly 2.5 to 3.5 and indicate temperatures of 110° to 200°C. Such temperatures are typically produced by burial depths of 3,500 to 5,500 m. Because Pennsylvanian-Cretaceous strata above the Lisburne Group are less than 1,500 m thick, tectonic burial and/or an elevated geothermal gradient are needed to explain the conodont color alteration index data.

Widespread effects of middle Mississippian deformation in the Great Basin of western North America

Stratigraphic analyses in central and eastern Nevada reveal the importance of a deformation event in middle Mississippian time that caused widespread deformation, uplift, and erosion. It occurred between middle Osagean and late Meramecian time and resulted in deposition of both synorogenic and postorogenic sediments. The deformation resulted in east-west shortening, expressed as east-vergent folding and east-directed thrusting; it involved sedimentary rocks of the Antler foredeep as well as strata associated with the Roberts Mountains allochthon. A latest Meramecian to early Chesterian unconformity, with correlative conformable lithofacies changes, postdates this deformation and occurs throughout Nevada. A tectonic highland—created in the middle Mississippian and lasting into the Pennsylvanian and centered in the area west and southwest of Carlin, Nevada—shed sediments eastward across the Antler foreland, burying the unconformity. Post oro genic strata are late Meramecian to early Chesterian at the base and are widespread throughout the Great Basin. The tectonism therefore occurred 20 to 30 m.y. after inception of the Late Devonian Antler orogeny, significantly extending the time span of this orogeny or representing a generally unrecognized orogenic event in the Paleozoic evolution of western North America. We propose a revised stratigraphic nomenclature for Mississippian strata in Nevada, based on detailed age control and the recognition of unconformities. This approach resolves the ambiguity of some stratigraphic names and emphasizes genetic relationships within the upper Paleozoic section. We take advantage of better stratigraphic understanding to propose two new stratigraphic units for southern and eastern Nevada: the middle Mississippian Gap Wash and Late Mississippian Captain Jack Formations.

Subsurface Sequence Stratigraphy of Early Chesterian (Mississippian) Mixed Carbonates and Siliciclastics, Illinois Basin : ABSTRACT

Subsurface Sequence Stratigraphy of Early Chesterian (Mississippian) Mixed Carbonates and Siliciclastics, Illinois Basin : ABSTRACT

Mississippian Stratigraphy and Tectonics of East-Central Nevada: Post-Antler Orogenesis

High-resolution stratigraphic studies in the Diamond Mountains are revealing details of tectonic deformation and basin filling that post-date the emplacement of the Antler allochthon and predate the Sonoma orogeny. Antler foreland-basin strata were deformed, uplifted, and eroded in the middle Mississippian, and a late Mississippian successor basin was established that persisted into the Pennsylvanian. The Antler peripheral foreland basin of eastern Nevada formed in the early Mississippian as a result of obduction of an accretionary prism onto the western edge of the North American craton. This basin filled with submarine-fan sediments shed from the west that range in age from late Osagean to middle Meramecian or slightly younger. In the Diamond Mountains, these strata are deformed into open folds, and are truncated by a regional unconformity. The unconformity documents an uplift and erosion event in the late Meramecian that the authors have called the Diamond mountain phase of deformation. Oldest strata above the unconformity are early Chesterian. Renewed subsidence in Chesterian time resulted in formation of a wide and shallow successor basin, bounded on the west by the relict Antler highland, and on the east by a siliciclastic shelf and the craton margin. This successor basin was filled with recycledmore » Antler foreland sediments and intrabasinal shelf carbonates. Reworked antler clastics were distributed throughout the basin by a system of mainly south-flowing fluvial and deltaic distributaries. This mixed clastic/carbonate basin persisted well into the Pennsylvanian.« less

Anomalous Morrowan-Chesterian Correlations in Western Anadarko Basin: ABSTRACT

Fossils recovered from cores of a thin lignitic shale and a coal in two widely separated wells in the western Anadarko basin show that the shale and coal beds are time-equivalent. Spore-pollen assemblages from the two intervals are identical and indicate a late Morrowan age. Coal from one well in the western Oklahoma Panhandle is from an interval generally considered as late Morrowan; the lignitic shale from a well near Liberal, Kansas, however, is from rocks widely accepted as early Chesterian--almost Meramecian. Considering that there is a span of several million years between early Chesterian and late Morrowan, two possible interpretations are presented. Either (1) identical spore-pollen assemblages are not sufficient evidence to distinguish between early Chesterian and late Morrowan or (2) some rocks currently accepted as of Chesterian age in the western Anadarko basin actually are limestone-shale facies of the Morrow Formation, and the relation between Morrowan sandstone-shale and Chester limestone-shale would not be one of onlap on an unconformable surface but, instead, a major facies change. In the two wells the interval between the Meramecian St. Genevieve Limestone and the Atokan 13-finger limestone is nearly equal and analysis of the geologic history of this interval lends support to the facies interpretation. Either interpretation is provocative and could have economic consequences. End_of_Article - Last_Page 551------------

Local and Interregional Distribution of Late Paleozoic Cephalopods: ABSTRACT

Despite the ability of cephalopods to move freely through the sea, their geographic distribution patterns tend to be restricted. Many genera but few species were widely distributed in the past. In fact, it is by means of distribution patterns at the generic level that most interregional correlations based on cephalopods are made. Carboniferous ammonoids common to strata on both sides of the Atlantic Ocean in the Northern Hemisphere include: Protocanites lyoni (Meek and Worthen) in the late Kinderhookian and late Tournaisian; Goniatites crenistria Phillips in the late Meramecan and late Visean; G. granosus Portlock and Neoglyphioceras subcirculare (Miller) in the early Chesterian and late Visean; Eumorphoceras bisulcatum Girty, Anthracoceras paucilobum (Phillips), and Delepinoceras bressoni Ruzhentsev in the late Chesterian and early Namurian; Branneroceras branneri (Smith) in the Morrowan, middle Namurian, and Bashkirian; and Politoceras politum (Shumard) in the Desmoinesian and Westphalian C. These few species constitute the principal pegs on which the correlation framework is hung. Apparent lack of species common to both sides of the Atlantic in Late Pennsylvanian and Permian deposits may result from more complicated sutures, which make differentiation in these ammonoids easier to establish. Nautiloids generally tend to have greater stratigraphic ranges than ammonoids, but some were just as restricted stratigraphically and equally distributed geographically as some ammonoids. A few coleoids also had moderately extensive geographic ranges. Factors that probably influenced cephalopod distribution include swimming and feeding habits, reproduction, buoyancy, sea-water properties (pH, salinity, other chemical features of the sea water, and prevailing currents), physical barriers, and type of bottom. End_of_Article - Last_Page 615------------

Carboniferous and Permian Stratigraphy of the Oquirrh Basin, Northwestern Utah: ABSTRACT

The Oquirrh basin, the dominant element in the late Paleozoic history of northwestern Utah and adjacent areas, first developed near the eastern margin of the Cordilleran miogeosyncline in medial Mississippian time. From then until the medial Permian, it existed continuously with alternate times of extension and contraction, the extensions being generally northwestward toward central Idaho and southwestward toward northeastern Nevada. Times of increased tectonism, which appear to be represented in accentuation of subsidiary basins and rise of marginal positive areas, with attendant contraction of the sea, were Meramecian and early Chesterian, Morrowan-Lampasan, Missourian-Virgilian, and early Wolfcampian. Times of decreased tectonism with less rapid depression and wider sp eading of the marine waters were Desmoinesian and Leonardian-early Guadalupian. Particularly noteworthy are the Logan-Milligen sub-basin of early Chesterian time, the main basin in Wolfcampian time, and the Diamond Creek and Lower Park City sub-basins of late Wolfcampian and early Leonardian time. In the latter, dolomite, red and buff sandstone, and anhydrite were deposited to notable thicknesses. The eastern margin of the Oquirrh basin was exceptionally abrupt and the remarkable change of facies exhibited there is accentuated by overthrusting which has moved the basin facies tens of miles eastward on to the shelf facies. End_of_Article - Last_Page 2612------------