Table of Contents for the Bulletin of Geosciences. List of articles from the latest print issue.http://www.geology.cz/bulletinen-US http://www.geology.cz/bulletin Loydell DK; Vol. 87, issue 4, pages 633 - 634
]]> http://www.geology.cz/bulletin/contents/art1355 Editorial http://www.geology.cz/bulletin/contents/art1355 Corradini C, Corriga MG; Vol. 87, issue 4, pages 635 - 650
The main conodont zonation schemes for the Přídolí and the Lochkovian presents some problems that make difficult their use in several geographical areas. Data from several sections in Sardinia and the Carnic Alps not only allow to built a regional zonation scheme for these areas, but also suggest possible solutions of global validity. In the Carnic Alps and Sardinia, the Přídolí is subdivided into three zones: eosteinhornensis s.l., Lower and Upper detortus. The latter results after the subdivision of the former detortus Zone on the basis of the Last Appearance Datum of some coniform species (Dapsilodus obliquicostatus, Coryssognathus dubius and Panderodus recurvatus) that became extinct almost simultaneously in the latest Přídolí. Daps. obliquicostatus is chosen as the marker, being the most common and easily identifiable species. In the Lochkovian six zones are discriminated: hesperius, carlsi, transitans, eleanorae, trigonicus and pandora β. The hesperius Zone, which includes the postwoschmidti subzone in its upper part, is expanded to include most of the eurekaensis zone of the “global” scheme, because the marker Oz. eurekaensis is not present. The carlsi Zone corresponds to the upper part of the eurekaensis Zone and to the lower part of the former mid-Lochkovian delta Zone (= omoalpha Zone). The rest of the Middle Lochkovian is subdivided into the three zones (transitans, eleanorae and trigonicus) already proposed in Nevada and Spain, followed by the pandora β Zone. All the zones are discussed and checked for their applicability in other palaeogeographical regions. ]]> http://www.geology.cz/bulletin/contents/art1304 http://www.geology.cz/bulletin/contents/art1304 Loydell D; Vol. 87, issue 4, pages 651 - 660
The graptolite biostratigraphy of the Rhuddanian (lower Llandovery, Silurian) of the E1-NC174 core, Murzuq Basin, Libya is described. The generally low diversity graptolite assemblages include both North African endemic taxa and cosmopolitan species. The lower part of the cored interval, below the ‘hot’ shale, is dominated by Normalograptus tilokensis, a species previously considered to be confined to the Upper Ordovician, but which almost certainly ranges into (or perhaps occurs only in) the lower Silurian. As in the BG-14 core, Jordan, the base of the ‘hot’ shale lies just above the first appearances of Neodiplograptus africanus and Normalograptus rectangularis. The latter species dominates throughout the mid Rhuddanian ‘hot’ shale interval, with the highest strata in the core, of late Rhuddanian age, yielding abundant Neodiplograptus fezzanensis. ]]> http://www.geology.cz/bulletin/contents/art1311 http://www.geology.cz/bulletin/contents/art1311 Legrand P; Vol. 87, issue 4, pages 661 - 668
In the Touat region (Algerian Sahara), the most complete Palaeozoic succession occurs to the southwest of Adrar. In the Tamest section, the Silurian comprises the Fenourine Clay and the Touat Sandstone formations. The Fenourine Clay Formation consists mostly of silty claystones of which only the upper 150m crop out. At the base of the section, bivalves occur, followed by the graptolites Saetograptus chimaera aff. salweyi (Hopkinson) and Pristiograptus cf. P. tumescens minor (Wood) which are described and figured in this paper. The overlying Touat Sandstone Formation is 170m thick. It comprises silty claystones with several lenticular, sandy beds, surmounted by a sandy, calcareous bed. At the base of the sandstone, pieces of homalonotine trilobites, brachiopods and bivalves are present. Above the base, silty claystones, a ferrugineous siltstone bed and the first Tentaculoidea occur. A conglomeratic limestone bed yielding a Pragian fauna tops the formation. The ages are as follows: the lower and middle Silurian do not crop out. The graptolites at the base of the extant section belong to the associations σ3β which characterize the Saharan Ludlow Series (g3b) (Legrand 1981, 1985). The silty, clayey beds that follow may be the equivalent of the Přídolí (g3c). The fossiliferous beds at the base of the Touat Sandstone may also be of Přídolí age, or may indicate the base of the Lochkovian (g4c). These outcrops reveal an interesting evolution in terms of facies and faunal assemblages towards the Ougarta Mountains and the Gourara to the northwest and the Azzel Matti to the southeast. ]]> http://www.geology.cz/bulletin/contents/art1305 http://www.geology.cz/bulletin/contents/art1305 Marshall C, Thomas AT, Boomer IRay DC; Vol. 87, issue 4, pages 669 - 679
High resolution δ¹³C_carb data are presented for two composite sections in England covering much of the Homerian Stage. Micrite samples collected at ˜0.5 m intervals from outcrop and core in the Dudley area, West Midlands, span the uppermost Coalbrookdale, Much Wenlock Limestone and basal Lower Elton formations. Deposition there occurred in a mid-shelf setting.Asimilar suite of samples from the Wenlock type area, Wenlock Edge, Shropshire, represents a coeval sequence deposited closer to the shelf-basin margin. The successions concerned extend from the upper lundgreni to nilssoni graptolite biozones and provide a detailed record of variation in stable carbon isotope ratios across the well-known double-peaked Homerian positive excursion (Mulde Excursion), a time of significant global biological and chemical perturbation. In the West Midlands, this excursion occurs in the Much Wenlock Limestone Formation. The lower peak (Lower Quarried Limestone Member) has δ¹³C_carb values rising to +5.5‰ VPDB. Values fall to +0.8‰ VPDB higher in the section before rising again to +4.1‰ VPDB (Nodular Beds Member). Analysis of lithofacies variation in this interval indicates two transgressive-regressive cycles, the two positive peaks of the excursion correlating with relative sea-level lows and the intervening dip with a relative sea-level high, the local expression of Johnson’s (2006) Highstand 5A. The double-peaked nature of the excursion at Dudley resembles that previously recorded for the area; however, our δ¹³C_carb values are consistently 2‰ higher, and accord more closely with values published for sections elsewhere. The lower of the two peaks found in the West Midlands cannot be identified on Wenlock Edge, where δ¹³C_carb values fluctuate somewhat around +2‰ VPDB. The upper peak, though less distinct, can be identified on Wenlock Edge with values rising to +3.8‰ VPDB. Correlations based on biostratigraphy, sequence stratigraphy and bentonite geochemistry suggest that not all changes in δ¹³C_carb occurred synchronously in the two areas studied, despite their close proximity. ]]> http://www.geology.cz/bulletin/contents/art1306 http://www.geology.cz/bulletin/contents/art1306 Sadler PM; Vol. 87, issue 4, pages 681 - 694
To correlate the burgeoning volume of biostratigraphic information available from the Silurian rocks of Baltica, it is advantageous to use numerical algorithms. Graphical correlation and related numerical methods routinely incorporate taxon range-ends and bentonites. Bentonites must be matched exactly. Local taxon ranges match or under-represent true ranges and may be stretched to fit hypotheses of correlation. Carbon isotope excursions are better handled as conservative uncertainty intervals – a new data class with properties and freedoms that are the opposite of taxon ranges. Uncertainty intervals match or over-represent truly correlative segments and inflexion points in the local series of isotopic ratios; they may be shrunk to fit correlations between sections. By these means, three fundamentally different kinds of stratigraphic information may be combined in a mutually supportive fashion without over-stating the precision of any of them. When incorporated as uncertainty intervals, Silurian isotopic excursions improve automated construction of inter-regional, ordinal time-lines of taxon first- and last-appearances at both the coarsest and finest resolution. The known succession of a few named excursions helps to stack relatively brief stratigraphic sections into their correct order in longer time-lines. The limits and details of individual excursions support some of the highest-resolution segments of optimized time-lines of individual taxon originations and extinctions. At intermediate scales, local taxon ranges are the unrivalled information source. For the best results, detailed taxon ranges, bentonite analyses and stable isotope time series need to be developed from the same rocks as often as possible. ]]> http://www.geology.cz/bulletin/contents/art1307 http://www.geology.cz/bulletin/contents/art1307 Kiipli T, Radzievičius S, Kallaste T, Kiipli E, Siir S, Soesoo A, Voolma M; Vol. 87, issue 4, pages 695 - 704
In three drill cores in Latvia and Lithuania a thin (1 cm thick) altered volcanic ash bed with high concentrations of phosphorus (up to 3%), cerium (1%), lanthanum (0.5%) and strontium (2.5%), has been found close to the Aeronian/Telychian boundary (Llandovery, Silurian, ca 438 Ma). Small, millimetre-thick lenses within the ash bed contain up to 12% P and Sr, up to 6% Ce and 3% La. These elements occur as a solid solution of goyazite-florencite mineral. Additionally, authigenic K-feldspar and kaolinite occur in this ash bed. The high concentrations of REE elements, strontium and phosphorus suggest a carbonatite source magma, but the strontium isotope ratio contradicts that origin. Such a unique composition in a volcanic ash layer is a good basis for using it as a marker horizon for correlation of sections. ]]> http://www.geology.cz/bulletin/contents/art1313 http://www.geology.cz/bulletin/contents/art1313 Munnecke A, Cramer BD, Boon DP, Kharwat R, Aiken CL, Schofield DI; Vol. 87, issue 4, pages 705 - 712
The Digital Integrated Stratigraphy Project (DISP) aims to eliminate the stratigraphical ambiguity associated with sample position within a stratigraphical section. For example, it is often impractical or impossible to compare one author’s measured section and data precisely against another author’s geographically identical measured section and data due to discrepancies in the measured thicknesses of units, variations in the assignments of litho- and chronostratigraphical terms, and/or the precise line of measured sections between authors. The DISP will provide a solution to this problem by producing a precise 3-D digital rendering of the exposure using Terrestrial Laser Scanning (TLS) LiDAR, Real-Time Kinematic (RTK) Global Navigation Satellite Systems (GNSS), overlain digital photography, and GIS software to produce a cm to mm-scale accurate digital version of a given exposure. Once available online as a permanent web-based digital resource for stratigraphy, researchers will be able to access the program and digital models of scanned exposures where they will have the means to log their sample positions directly onto the digital exposure while in the field, thus allowing unambiguous stratigraphical reference for future comparison. The Digital Integrated Stratigraphy Project represents the next generation of stratigraphical standard and can serve as the protocol for the future of high-resolution Palaeozoic Earth history research. ]]> http://www.geology.cz/bulletin/contents/art1318 http://www.geology.cz/bulletin/contents/art1318 Brett CE, Cramer BD, McLaughlin PI, Kleffner MA, Showers WJ, Thomka JR; Vol. 87, issue 4, pages 733 - 753
Recent detailed studies of the physical, bio-, and chemostratigraphy of upper Llandovery to middle Wenlock strata of the Cincinnati Arch area, primarily SW Ohio and SE Indiana and to a lesser extent west-central Kentucky, indicate a regionally extensive pattern of units, correlatable in detail over more than 30,000 sq. km. This relatively simple stratigraphy has been obscured by the development of local names and by different usage of the same name in different areas. Herein we review and update this stratigraphical succession to provide uniform nomenclature and correlation of these units throughout the study area. The units as redefined and/or extended in this study include the Lee Creek, Dayton, Osgood, Lewisburg, Massie, and Laurel formations. Extension of the unit name Salamonie Dolomite is herein discouraged south of the Salamonie type area in NE Indiana. The term Dayton Dolostone is herein redefined; it is overlain by the Osgood Formation, which is also redefined here as equivalent to Foerste’s (1897) ‘Lower Osgood Clay’. The Lewisburg Limestone/Dolostone is reintroduced here as a formal name at the rank of formation to include a thin interval of pelmatozoan-brachiopod dolomitic pack- to grainstone formerly termed ‘Middle Osgood Limestone’ in Indiana and ‘Laurel of Ohio’ (in part) in SW Ohio. The term Massie Shale, defined in SW Ohio, is extended at formation rank throughout the study area as equivalent to the ‘Upper Osgood Clay’ and unnamed shale unit of the lower part of the Laurel (subunit 2) in Kentucky. ]]> http://www.geology.cz/bulletin/contents/art1310 http://www.geology.cz/bulletin/contents/art1310 Štorch P, Schönlaub H-P; Vol. 87, issue 4, pages 755 - 766
Seven species of graptoloid graptolites are described from Hirnantian and lower Rhuddanian formations of the Austrian part of the Carnic and western Karavanke Alps. The Plöcken Formation, of latest Ordovician (Hirnantian) age, yields the biozonal index graptolite Metabolograptus persculptus in the Cellon Reference Section and, tentatively, the Feistritzgraben Section. A distinctive graptolite assemblage indicating an earliest Silurian (early Rhuddanian) age comes from the Waterfall Section near Zollnersee Hütte. Along with the presence of the biozonal index Parakidograptus acuminatus and accompanying taxa, common Rickardsograptus? bifurcus (Ye) has been recorded - for the first time outside China. The absence of Neodiplograptus lanceolatus Štorch & Serpagli, Normalograptus trifilis (Manck) and other easily recognizable lowermost Rhuddanian species which are dominant in this level throughout peri-Gondwanan Europe indicates the peculiar character of the acuminatus Biozone assemblage encountered in the Carnic Alps. ]]> http://www.geology.cz/bulletin/contents/art1350 http://www.geology.cz/bulletin/contents/art1350 Turek V, Manda Š ; Vol. 87, issue 4, pages 767 - 813
Sphooceras truncatum (Barrande, 1860), a Silurian straight-shelled cephalopod with a short finger-shaped shell, is one of a few cephalopods in which natural truncation of the apical part of the phragmocone from the rest of the conch is confirmed. Periodic natural removal of the apical part of the shell (4 to 5 phragmocone chambers) preceded formation of a terminal callus and a calcareous plug closing the septal foramen. The apical callus probably originated by fusion of the truncation septum with episeptal deposits. These structures temporarily formed the new apex on which two additional calcareous layers had been secreted. A unique specimen preserves a colour pattern in the convex apical region, which proves that the shell in Sphooceras was temporarily completely surrounded by mantle extending from the body chamber, i.e. the cephalopod was at least temporarily endocochleate. The co-occurrence of different growth stages of S. truncatum together with one type of short juvenile orthoceracone shell, with a maximum of eight phragmocone chambers and a very small subglobular initial chamber indicates that these embryonic shells may belong to Sphooceras. Two other genera are discussed, both previously included in the family Sphooceratidae: Disjunctoceras Gnoli in Kiselev, 1992 and Andigenoceras Gnoli in Kiselev, 1992. The newly discovered thickening of the apex in “Disjunctoceras” disjunctum, the type species of Disjunctoceras, indicates that this species does not differ substantially from Sphooceras and should be reassigned to this genus. Similarly, representatives of Andigenoceras also possess characteristic features of Sphooceras. Sphooceras has many features characteristic for modern cephalopods: short, thin-walled, semi-internal shell; phragmocone reduced to only a few chambers; uncalcified connecting rings; apical callus (a structure analogous to the belemnite rostrum); retractor muscle scars situated dorsally; very small protoconch without cicatrix. In some exceptionally well-preserved cephalopods with orthoceracone shell radula with seven rows of teeth were observed. All these features support the thesis that some straight-shelled cephalopods are evolutionarily closer to coleoids than nautiloids and their separation from nautiloids is legitimate. Vascular imprints on the surface of the cameral deposits provide further support for their primary origin and the existence of a cameral mantle. The character of cameral deposits in Sphooceras demonstrates that the systematic value of these structures in other straight-shelled cephalopods, a subject of controversy, has limited value. The morphology of Sphooceras also demonstrates that the boundary between endocochleate and ectocochleate cephalopods is not sharp, i.e. internalisation of the shell in cephalopods occurred repeatedly. ]]> http://www.geology.cz/bulletin/contents/art1335 http://www.geology.cz/bulletin/contents/art1335 Slavík L, Carls P; Vol. 87, issue 4, pages 815 - 832
The effects of the Lau Event on conodont faunas in shallow water environments of the Prague Synform were rather moderate in comparison with Gotland. The post-event restoration of conodont diversity following the characteristic post-siluricus faunas with diminished elements and dominated by a long-ranging stock of Delotaxis was gradual and not abrupt. This points to absence of such large gaps in the sedimentation like they had occurred below and had caused the lack of a large upper part of the siluricus Zone. Accordingly, the Bohemian conodont record of diversifying conodont faunas, starting with the entry of “slender spathognathodontids”, is comparably complete. Increased diversity and abundance of incoming conodont taxa has enabled a refinement of the regional zonal subdivision. This includes the succession of the plodowskii, latialatus, parasnajdri and crispa conodont biozones for the interval following the Lau Event in the late Ludfordian. The conodont data from Bohemia show that “Oz.” snajdri range is largely included in the overlap of Pedavis latialatus and “Ozarkodina” crispa. Accordingly, the use of the problematic stratigraphical unit - the snajdri Interval Zone as a base for the definition of a middle Ludfordian Stage Slice can be misleading. Conspicuous morphological changes in the “Ozarkodina” snadri-“Oz.” crispa stocks and in the Ozarkodina typica lineage allow refined inter-regional correlations. ]]> http://www.geology.cz/bulletin/contents/art1368 http://www.geology.cz/bulletin/contents/art1368