Conodonts in Ordovician Chronostratigraphy

The great importance of conodonts in Ordovician chronostratigraphy is shown by the fact that conodonts are used for the definition of two of the seven global stages, and seven of the 18 stage slices, now recognized within this system

The Global Stratotype Section and Point (GSSP) for the base of the Katian Stage of the Upper Ordovician Series at Black Knob Ridge, Southeastern Oklahoma, USA

The International Subcomission on Ordovician Stratigraphy (ISOS) of the International Commission on Stratigraphy (ICS) recently defined the base of the global Upper Ordovician Series to be at the first appearance datum (FAD) of the graptolite species Nemagraptus gracilis in the Fågelsång GSSP in southern Sweden. This designation recognized the tremendous utility for global correlation of the first appearance of a cosmopolitan taxon that occurs within a consistent succession of other first appearance datums (e.g., Finney and Bergström, 1986; Bergström et al., 2000). Current efforts by the ISOS have focused on subdividing the Upper Ordovician into three stages and choosing appropriate levels and stratotypes for the bases of the middle and upper of these stages. The purpose of the present report is to describe the GSSP of the middle stage, for which the name Katian Stage was approved by the ISOS and ratified by the ICS in 2006 (Bergström et al., 2006). For a recent review of the long process of developing the new subdivisions of the Ordovician, see Finney (2005)

An Ordovician Global Reference Section Recently Selected in Oklahoma

Ordovician fossil faunas are characterized by a marked biogeographic differentiation that results in a minimal similarity between most North American faunas and those of major Ordovician areas elsewhere in the world. This provincial distribution of most fossils has led to establishment of different schemes of fossil-based regional stages in, for instance, North America, Baltoscandia, China, and the British Isles. Because these chrono-stratigraphic units have been largely based on shelly fossils with distributions restricted to a particular region, it has been impossible in most cases to establish a precise international correlation of these regional stages. Furthermore, some general terms, such as the Middle Ordovician;\u27 have a vastly different stratigraphic scope in different parts of the world causing confusion among stratigraphers and non-stratigraphers alike. Indeed, in view of the fact that many of today\u27s geology studies are of more than regional nature, there has been an urgent need for an international chronostratigraphic classification

Ordovician K-bentonites in the Argentine Precordillera: relations to Gondwana margin evolution

Ordovician K-bcn Ionites have now been recorded from >20 localities in the vicinity of the Argentine Prccordillera. Most occur in I he eastern thrust belts, in the San Juan Limestone and the overlying the Gualcamayo Formation, but a few ash beds are known also from the central thrust belts. The oldest occur in the middle Arenig t. victorias iunatus grnplolite (Oe. evae conodont) Zone, and the youngest in the middle Llanvirn P. etegans (P. .tuecicas) Zone. Mineralogical characteristics, typical of other Ordovician K-bentonites, include a matrix of illite/smectite mixed-layer clay and a typical felsic volcanic phenocryst assemblage: biotite, beta-form quartz, alkali and plagioclase feldspar, apatite, and zircon, with lesser amounts of hornblende, clinopyroxene, tilanilc and Fe-Ti oxides. The proportions of the mineral phases and variations iii their crystal chemistry are commonly unique to individual (or small groups of) K-benlonite beds. Glass melt inclusions preserved in quartz are rhyolitic in composition The sequence is unique in its abundance of K-benlonite beds, but a close association between the Precordillera and other Ordovician sedimentary basins cannot be established.Theash distribution is most consistent with palacogeographical reconstructions in which early Ordovician drifting of the Precordillera occurred in proximity to one or more volcanic arcs, and with eventual collision along the Andean margin of Gondwana during the mid-Ordovician Ocloyic event of the Famalinian orogeny. The Puna-Famatina terrane northeast of the Precordillera might have served as the source of the K-bcnlonite ashes, possibly in concert with active arc magmatism on the Gondwana plate itself.Centro de Investigaciones Geológica

Clustering patients on the basis of their individual course of low back pain over a six month period

<p>Abstract</p> <p>Background</p> <p>Several researchers have searched for subgroups in the heterogeneous population of patients with non-specific low back pain (LBP). To date, subgroups have been identified based on psychological profiles and the variation of pain.</p> <p>Methods</p> <p>This multicentre prospective observational study explored the 6- month clinical course with measurements of bothersomeness that were collected from weekly text messages that were sent by 176 patients with LBP. A hierarchical cluster analysis, Ward's method, was used to cluster patients according to the development of their pain.</p> <p>Results</p> <p>Four clusters with distinctly different clinical courses were described and further validated against clinical baseline variables and outcomes. Cluster 1, a "stable" cluster, where the course was relatively unchanged over time, contained young patients with good self- rated health. Cluster 2, a group of "fast improvers" who were very bothered initially but rapidly improved, consisted of patients who rated their health as relatively poor but experienced the fewest number of days with bothersome pain of all the clusters. Cluster 3 was the "typical patient" group, with medium bothersomeness at baseline and an average improvement over the first 4-5 weeks. Finally, cluster 4 contained the "slow improvers", a group of patients who improved over 12 weeks. This group contained older individuals who had more LBP the previous year and who also experienced most days with bothersome pain of all the clusters.</p> <p>Conclusions</p> <p>It is possible to define clinically meaningful clusters of patients based on their individual course of LBP over time. Future research should aim to reproduce these clusters in different populations, add further clinical variables to distinguish the clusters and test different treatment strategies for them.</p