James E. Barrick

Cyclothem [“digital”] correlation and biostratigraphy across the global Moscovian-Kasimovian-Gzhelian stage boundary interval (Middle-Upper Pennsylvanian) in North America and eastern Europe

The long-standing difficulty of correlating Pennsylvanian strata among provincial faunal regions is resolved by effecting “digital” correlation of major glacial-eustatic cyclothems that represent high-stands when certain species achieved more global distribution than usual. In the late Moscovian–early Gzhelian (late Desmoinesian–early Virgilian) succession in the midcontinent United States, several major cyclothems are correlated, by both conodont species in common and cyclothem scale, with cyclothems in Russia (Moscow Basin) and Ukraine (Donets Basin), and the remaining cyclothems fit into the framework by position and scale. In this way the suggested event marker for the global Kasimovian-Gzhelian stage boundary (first appearance of Idiognathodus simulator ) is supported, while possible event markers for the Moscovian-Kasimovian boundary await further evaluation.

High-resolution 87Sr/86Sr chemostratigraphy of the Silurian: Implications for event correlation and strontium flux

Analyses of 87Sr/86Sr in Silurian conodonts recovered from localities in North America and Europe representing 13 of the 14 defined Silurian conodont zones provide a high-resolution record of seawater chemistry for the Silurian Period. These data, which are characterized by little or no scatter, depict several high-frequency cycles superimposed on a gradual longer term rise in 87Sr/86Sr for the Silurian. High-frequency cycles have a duration of about one conodont zone, and many correlate with sequence boundaries recognized around the world. These data provide a much higher resolution image of secular changes in 87Sr/86Sr during the Silurian and may require a rethinking of models of strontium isotope flux in marine basins.

Pt-group metal anomalies in the Lower Mississippian of southern Oklahoma

Four iridium (Pt-group elements) abundance anomalies have been found within a stratigraphic span of 3 m in the Lower Mississippian of Oklahoma. In ascending order, the first anomalies occur at the top of the Woodford Shale: Ir = 0.25 ppb, Pt = 48 ppb, Os = 7.5 ppb, and Au = 18 ppb. The anomalies occur just below a redox boundary and we suspect that the enriched elements were precipitated from sea water that contacted the organic- and sulfide-rick black shale. Two more anomalies occur in the Welden Limestone, the lower one weak and the upper one strong (Ir = 0.42 ppb, Pt = 50 ppb, Os = 0.075 ppb, and Au = 0.14 ppb). The excess Ir and Pt (also Co, As, and Ni) might have been enriched from sea water by bacteria at these two horizons. A 70-cm-thick interval of excess heavy siderophiles occurs in the overlying Caney Shale; the interval contains the following peak concentrations: Ir = 0.56 ppb, Pt =150 ppb, Os = 0.51 ppb, Co = 725 ppm, and Ni =1450 ppm. These elements vary in proportion to the Al (clay) content and we suspect that they were carried in with detrital material from erosion of ultramafic source rocks. We found no evidence of microspherules or shocked-mineral grains in any of these anomaly zones.

CONODONT SEQUENCE BIOSTRATIGRAPHY OF THE HERMOSA GROUP (PENNSYLVANIAN) AT HONAKER TRAIL, PARADOX BASIN, UTAH

Abstract In cyclical Pennsylvanian strata, conodonts find their greatest stratigraphic utility as biotic signatures of physically defined stratigraphic entities (cycles, parasequences, high frequency sequences, etc.) rather then the primary means of stratigraphic subdivision (e.g., biostratigraphic interval zones). The practice of identifying depositional entities for purposes of regional correlation on the basis of their constituent conodont faunas is herein called conodont sequence biostratigraphy. In this paper, the concept is utilized to successfully correlate Pennsylvanian cycles of the Paradox basin with their Midcontinent counterparts. The Honaker Trail section is the most accessible and well-studied succession of carbonate shelf strata in the Paradox basin. Approximately 350 m of cyclically bedded limestone, sandstone, and shale comprising 53 fifth-order cycles are exposed along the cliffs of the deeply entrenched San Juan River. Maximum transgressive facies of 19 cycles yielded Idiognathodus-Neognathodus- and/or Streptognathodus-dominated conodont faunas. Those from the Chimney Rock, Gothic, LHT-5, UHT-3, UHT-5, UHT-8, unnamed limestone, and Shafer correspond to faunas from the Verdigris, Lower Fort Scott, Altamont (Lake Neosho), Lost Branch, Hertha (Mound City), Swope (Hushpuckney), Dennis (Stark), and South Bend cycles of the Midcontinent, respectively. By extrapolation, all minor cycles of the Marmaton, Pleasanton, and Bronson Groups (except for the Critzer) also appear to have counterparts at Honaker Trail. The position of the Desmoinesian–Missourian boundary in the Honaker Trail section can be approximated using conodonts in conjunction with fusulinids. The highest Desmoinesian conodont fauna, the Idiognathodus nodocarinatus fauna, occurs in cycle UHT-3 in the lower part of the Upper Honaker Trail sequence. The highest occurrence of Beedeina occurs in the same cycle. The lowest conodont fauna with the Missourian species I. eccentricus appears two cycles higher, in cycle UHT-5. Because in the Midcontinent region a small interval of strata separates the first appearance of I. eccentricus from the base of the Missourian, we place the base of the Missourian at the base of cycle UHT-4 (bed 105) at Honaker Trail. The appearance of Streptognathodus firmus and S. pawhuskaensis in the Shafer limestone indicates that the Missourian–Virgilian boundary lies slightly above or below this stratigraphic horizon.

Swadelina new genus (Pennsylvanian Conodonta), a taxon with potential chronostratigraphic significance

Swadelina n. gen. is erected to comprise a short-ranging clade of late Desmoinesian (middle Pennsylvanian) idiognathodontid conodonts characterized by Pa elements with a deep medial trough, extensive anterior ornamentation, and an extremely short carina. The Pb elements have a small, relatively indistinct cusp, and dissimilar development of the anterior and posterior processes. Swadelina (Sw.) probably evolved through paedomorphosis from an untroughed Idiognathodus ancestor well before the appearance of similarly troughed Streptognathodus Pa elements in the Missourian (late Pennsylvanian). We currently recognize Sw. nodocarinata (Jones 1941) and Sw. neoshoensis n. sp. as component species. Swadelina occurs in both North America and Eurasia with a limited range, in strata that are otherwise characterized by pronounced provincialism. With further study of international occurrences, a species of Swadelina may provide for the definition and correlation of an appropriate GSSP stage/series boundary between the middle and upper parts of the Pennsylvanian Subsystem.

The relationship of conodont biofacies to spatially variable water mass properties in the Late Pennsylvanian Midcontinent Sea

Molybdenum and uranium enrichment factors and nitrogen isotopes suggest that an interplay of open ocean upwelling and riverine runoff led to distinct spatial and secular variations in water mass properties within the epicontinental Late Pennsylvanian Midcontinent Sea of North America. In particular, the intensity of continental runoff influenced the flux of bulk organic matter to the sediment. Benthic anoxia appears to have been controlled by the vertical density gradient in the water column associated with continental runoff combined with the advection of basinal water. Anoxic conditions were stronger in proximal (i.e., more shoreward) areas of the Midcontinent Shelf, indicating that anoxia did not develop primarily due to upwelling of nutrient-rich waters along the southern shelf margin, as previously suggested. Changes in water mass redox conditions not only drove authigenic enrichment of redox-sensitive trace elements across the basin but also had a strong effect on the spatial distribution of various conodont taxa. Our analysis suggests that the widely accepted depth-stratification model for the distribution of conodonts is incomplete. Conodont biofacies distributions seem to have been controlled by physicochemical properties of the water mass (e.g., salinity, temperature, nutrients, turbidity, and/or dissolved oxygen levels) that may correspond less directly to water depth. The proximity to terrestrial freshwater influx and the strength of anoxia/euxinia in the subpycnoclinal water mass played significant roles in the spatial and temporal distributions of conodont taxa.

Early Devonian conodonts from a limestone horizon in the Caballos Novaculite, Marathon Uplift, West Texas

Early Devonian (Lochkovian; eurekaensis Zone) conodonts occur in discontinuous limestone beds in the Caballos Novaculite at five localities in the northwestern half of the Marathon uplift, west Texas. Similar conodont faunas at all five localities indicate that the limestone beds lie at one biostratigraphic horizon within the Caballos. The upper novaculite member directly overlies the limestone horizon at one locality, giving the upper novaculite a maximum age of Lochkovian. The limestone beds are dominantly skeletal calcarenites that represent shallow-water carbonate material transported into a deeper water setting by gravity processes. Restriction of the limestones to the northwestern margin of the uplift and provenance of reworked clasts and redeposited Ordovician and Silurian conodonts suggest a North American shelf source and are evidence of the close proximity of some strata exposed in the Marathon uplift to North America in the Early Devonian. Icriodus gravesi n. sp. is described from the limestone fauna.