Intercontinental Correlation Research Articles

The first continuous δ13C record across the Late Silurian Lau Event on Gotland, Sweden

The positive δ13C excursion associated with the Late Silurian Lau Event is recognized globally and is the most prominent carbon isotope excursion of the Phanerozoic. We present new δ13C data (195 samples) and the first continuous carbon isotope stratigraphy across the stratigraphic range of this bioevent based on two drill cores from Gotland, the informal type area for the Lau Event. The positive δ13C anomaly reaches a peak value of 9.01‰ in an interval correlated to the Icriodontid conodont Zone in the upper Eke Formation, an interval with generally impoverished fauna and strongly dominated by one single conodont species, Panderodus equicostatus, and a mass-occurrence of oncoids. The distinct morphology of this Late Ludfordian Carbon Isotope Excursion, including a well-defined rising limb, a plateau and a falling limb can be used for intercontinental correlation of the strata.

Conodont biostratigraphy and global correlation of the middle Darriwilian-lower Sandbian (Ordovician) Las Aguaditas Formation, Precordillera of San Juan, Argentina

Middle Darriwilian to lower Sandbian conodonts were recorded from the Las Aguaditas Formation at its type section in the Argentine Precordillera. A total of 9,974 conodont specimens were recovered from 46 carbonate samples, which represent 68 species of 38 genera. A biostratigraphic study verified a middle Darriwilian age for the interval spanning the contact between the San Juan and the Las Aguaditas formations. The following zones are determined in the study section: the Lenodus variabilis Zone, with the Periodon gladysae and Paroistodus horridus subzones following the Precordilleran scheme; the L. variabilis, Yangtzeplacognathus crassus, and the Eoplacognathus pseudoplanus zones with the Microzarkodina hagetiana and M. ozarkodella subzones, and the Pygodus anserinus Zone, according to the Scandinavian scheme; the Periodon macrodentatus Zone, with the Histiodella sinuosa, H. holodentata and H. cf. holodentata subzones, and the P. zgierzensis Zone with the H. kristinae Subzone that correlates the North American scheme. A stratigraphic gap was recognized between the lower and middle members of the Las Aguaditas Formation. It comprises the Eoplacognathus suecicus and Pygodus serra zones, and the lower subzone of the Pygodus anserinus Zone. The variation of conodont diversity through the study section conforms to shallowing and deepening patterns, which accompanies the changes of the provenance lithology. Three conodont assemblages were quantitatively recognized: a) Diverse conodont association, b) Low diversity conodont association and c) Recovery phase association. We propose to use the North American biozonal scheme of conodonts for the Central Precordillera because of the affinity of documented index taxa, which provides a more accurate intercontinental correlation for the global Middle Ordovician Series.

Intercontinental correlation of organic carbon and carbonate stable isotope records: evidence of climate and sea‐level change during the Turonian (Cretaceous)

AbstractCarbon (δ13Corg, δ13Ccarb) and oxygen (δ18Ocarb) isotope records are presented for an expanded Upper Cretaceous (Turonian–Coniacian) hemipelagic succession cored in the central Bohemian Cretaceous Basin, Czech Republic. Geophysical logs, biostratigraphy and stable carbon isotope chemostratigraphy provide a high‐resolution stratigraphic framework. The δ13Ccarb and δ13Corg profiles are compared, and the time series correlated with published coeval marine and non‐marine isotope records from Europe, North America and Japan. All previously named Turonian carbon isotope events are identified and correlated at high‐resolution between multiple sections, in different facies, basins and continents. The viability of using both carbonate and organic matter carbon isotope chemostratigraphy for improved stratigraphic resolution, for placing stage boundaries, and for intercontinental correlation is demonstrated, but anchoring the time series using biostratigraphic data is essential. An Early to Middle Turonian thermal maximum followed by a synchronous episode of stepped cooling throughout Europe during the Middle to Late Turonian is evidenced by bulk carbonate and brachiopod shell δ18Ocarb data, and regional changes in the distribution and composition of macrofaunal assemblages. The Late Turonian Cool Phase in Europe was coincident with a period of long‐term sea‐level fall, with significant water‐mass reorganization occurring during the mid‐Late Turonian maximum lowstand. Falling Δ13C (δ13Ccarb – δ13Corg) trends coincident with two major cooling pulses, point to pCO2 drawdown accompanying cooling, but the use of paired carbon isotopes as a high‐resolution pCO2 proxy is compromised in the low‐carbonate sediments of the Bohemian Basin study section by diagenetic overprinting of the δ13Ccarb record. Carbon isotope chemostratigraphy is confirmed as a powerful tool for testing and refining intercontinental and marine to terrestrial correlations.

Latest Devonian to earliest Carboniferous conodont and carbon isotope stratigraphy of a shallow‐water sequence in South China

AbstractTo improve regional and intercontinental correlation of the uppermost Devonian–lowermost Carboniferous, we examined the conodont faunas and carbon isotopic records of the Tangbagou Formation in the Qilinzhai section, southern Guizhou, South China. The Tangbagou Formation is a succession of mixed carbonate–siliciclastic rocks that accumulated on a shallow‐water platform under normal marine conditions. Seven conodont zones for shallow‐water biofacies in South China, theCl.gilwernensis–Cl.unicornisZone, thePo.spicatusZone, theSi.homosimplexZone, theSi.sinensisZone, theSi.eurylobataZone, thePs.multistriatusZone and thePo.co.porcatusZone in ascending order, are recognized in the Tangbagou Formation. Although apparently limited in its value for global correlation, this conodont zonation is more applicable to shallow‐water biofacies in South China. Carbonate samples have yielded carbon isotopic signatures consistent with those recorded in Euroamerica sections, in particular showing four distinct characteristics: (1) the peak values of Hangenberg Carbon Isotope Excursion (HICE) during the latest Devonian, (2) a minor positive shift (P1) in theSi.homosimplexZone during the early Tournaisian, (3) a second minor positive shift (P2) in theSi.sinensisZone and (4) the middle Tournaisian Carbon Isotope Excursion (TICE) in the middle part of the Tangbagou Formation. The similarity in peak values (~5.5‰) and magnitude of TICE for the Qilinzhai and Belgian sections indicates that the Euro‐asia δ13Ccarbtrends may reflect the changes in global mean ocean δ13CDIC, rather than having been overprinted by local carbon cycling. Integration of conodont biostratigraphy and δ13C stratigraphy provides a powerful tool for stratigraphic correlation. Copyright © 2015 John Wiley & Sons, Ltd.

The middle lower Cambrian (Ovetian)Lunagraulosn. gen. from Spain and the oldest trilobite records

AbstractThe type material ofAgraulos antiquusSdzuy, 1961 from the La Herrería Formation, northern Spain, is revised together with additional material and included in the new genusLunagraulos. The stratigraphical range ofLunagraulos antiquus(Sdzuy, 1961) – occurring below that of the trilobite species of the generaLunolenus,MetadoxidesandDolerolenusin the type locality of Los Barrios de Luna in the province of León, northern Spain – and the accompanying ichnofossil assemblage demonstrate an Ovetian age (lower part of Cambrian Stage 3, currently being discussed by the International Subcommission on Cambrian Stratigraphy) for this species. Moreover, the trilobiteLunagraulos tamamensisn. gen. n. sp. is found in the Tamames Sandstone near the village of La Rinconada in the province of Salamanca, central Spain. The biostratigraphical position of this new taxon and its accompanying ichnoassemblage is also analysed and assigned to the lowermost Ovetian Stage. The genusLunagraulosis therefore the oldest agraulid found in the fossil record. The exceptional presence ofLunagraulosin a marine coarse siliciclastic succession – a facies rather typical for the ichnofossilsCruzianaandRusophycus, some of the oldest signs of trilobite activity – suggests that first trilobite representatives may have inhabited high- to middle-energy, marine environments. This hypothesis may also explain both the taxonomic and biostratigraphic heterogeneity of the first trilobite genera appearing across the world, due to preservation problems in this type of facies. Comparison of theLunagraulos biostratigraphy with other coeval Spanish fossil assemblages allows us to propose its intercontinental correlation with the oldest records of currently known trilobites.

Reply to Comment on “Zircon U–Th–Pb dating using LA-ICP-MS: Simultaneous U–Pb and U–Th dating on the 0.1 Ma Toya Tephra, Japan”

The province of Jämtland, central Sweden, records a well-preserved but very thin suite of the Lower–Middle Ordovician cool-water carbonates. In this study we present the first carbon isotope profile for these strata on the basis of whole-rock samples from the Brunflo 2 core. The studied succession is 41.55 m thick and includes, in ascending order, the Bjørkåsholmen Formation, Latorp Limestone, Tøyen Shale, and the Lanna, Holen, and Segerstad limestones. We identify two distinct positive δ13C excursions that can be used for intra- as well as inter-continental correlations. A positive excursion in the Tøyen Shale probably correlates to the mid-late Floian and the Oepikodus evae Zone in Baltica and Precordillera, and the Reutterodus andinus Zone in North America. A continuous increase in δ13C values through the upper Holen Limestone and the preserved part of the overlying Segerstad Limestone is interpreted as the rising limb of the Middle Darriwilian Isotope Carbon Excursion (MDICE), an important tie-point for the global correlation of the Jämtland strata. Negative δ13C values associated with the Latorp Limestone may correlate with similar low values in the late Tremadocian and early Floian of the Argentine Precordillera and the Shingle Pass and Ibex sections in North America.

Lower–Middle Ordovician δ13C chemostratigraphy of western Baltica (Jämtland, Sweden)

The province of Jämtland, central Sweden, records a well-preserved but very thin suite of the Lower–Middle Ordovician cool-water carbonates. In this study we present the first carbon isotope profile for these strata on the basis of whole-rock samples from the Brunflo 2 core. The studied succession is 41.55m thick and includes, in ascending order, the Bjørkåsholmen Formation, Latorp Limestone, Tøyen Shale, and the Lanna, Holen, and Segerstad limestones. We identify two distinct positive δ13C excursions that can be used for intra- as well as inter-continental correlations. A positive excursion in the Tøyen Shale probably correlates to the mid-late Floian and the Oepikodus evae Zone in Baltica and Precordillera, and the Reutterodus andinus Zone in North America. A continuous increase in δ13C values through the upper Holen Limestone and the preserved part of the overlying Segerstad Limestone is interpreted as the rising limb of the Middle Darriwilian Isotope Carbon Excursion (MDICE), an important tie-point for the global correlation of the Jämtland strata. Negative δ13C values associated with the Latorp Limestone may correlate with similar low values in the late Tremadocian and early Floian of the Argentine Precordillera and the Shingle Pass and Ibex sections in North America.

Exotic trilobites from the Lower–Middle Cambrian boundary interval in Morocco and their bearing on the Cambrian Series 3 lower boundary

The Moroccan Atlas ranges provide sections which not only permit fine-scale biostratigraphic analysis of the basal part of the Middle Cambrian by means of typical West Gondwanan faunal elements, but also include exotic trilobites well known from other Cambrian continents or at least extremely rare in West Gondwana. Such trilobites often permit intercontinental correlation that significantly improves the framework for the traditional Lower–Middle Cambrian boundary interval and leads to a fairly robust correlation table. Other “exotic” trilobites are rare findings of new taxa with mosaic patterns of morphological characters, which therefore remain problematic in consideration of their systematic position. This case study illustrates and (re)describes the trilobites Granularaspis bommeli n. sp., Shergoldiella vincenti Geyer, Palaeoworld 15: 348–359, 2006, Onchocephalites permingeati (Termier and Termier, Paleontologie marocaine. Tome 2. Invertebres de l'Ere primaire. Fasc. 4: Annelides, Arthropodes, Echinodermes, Conularides et Graptolithes. Notes et Memoirs de la Service geologique du Maroc 79, and Coll. Actualites scientifiques vol 1095 Hermann & Cie, Paris, pp 282, 1950), Eoptychoparia tafilaltensis n. sp., Oreisator tichkaensis Geyer and Malinky, J Paleontol 71(4): 620–637, 1997 and Cambroproteus lemdadensis n. gen., n. sp. from the Moroccan Atlas ranges. These species partly belong to genera previously known from outside West Gondwana only, and all of them provide new and unexpected clues for faunistic relationships from West Gondwana into other Cambrian continents and distinctly supplement the picture of the organismic diversity for the basal Middle Cambrian in the region.

Cenomanian To Campanian Carbon Isotope Chemostratigraphy from the Western Interior Basin, U.S.A

Abstract Late Cretaceous carbon isotope curves generated for localities in Europe, Asia, and the deep-sea records have provided the foundation for development of a contiguous, intercontinental chemostratigraphic framework. Despite the development of carbon isotope records from selected stratigraphic intervals in the Western Interior Basin, however, a comprehensive δ13C record comparable to those developed in Europe and Asia, and from ODP sites, had not yet been completed. This study reports a new, high-resolution Cenomanian to Campanian carbon isotope record for the central Western Interior Basin of North America that makes a key contribution to the intercontinental correlation. The curve is correlated to the well-developed molluscan biostratigraphic framework for the Western Interior Basin, as well as a revised geochronology based on integration of new radioisotopic dating and astrochronology developed in the same core records from where the δ13C data were derived. The new δ13C record reflects not only major perturbations in the global carbon cycle, such as the mid-Cenomanian Event and the Cenomanian–Turonian Ocean Anoxic Event 2, but also smaller excursions that have been recognized in records from Europe and Asia. This shows that the Western Interior shallow epeiric sea was not isolated for any appreciable part of Cenomanian to early Campanian time—it consistently recorded changes in the global marine carbon cycle observed elsewhere. A critical attribute of the chemostratigraphic dataset produced in this study is its linkage with a revised Late Cretaceous time scale. Assignment of revised ages to Western Interior carbon isotope events that are globally expressed will allow export of the improved time scale to localities within and outside the Western Interior where similar carbon isotope records have been generated. This chronostratigraphic tool will allow a number of stratigraphic and geochemical hypotheses to be more rigorously tested.

δ 13C chemostratigraphy in the Lower–Middle Ordovician succession of Öland (Sweden) and the global significance of the MDICE

Based on the Tingskullen drillcore, we present the first continuous carbon isotope stratigraphy from the Lower–Middle Ordovician “orthoceratite limestone” of Öland, Sweden. The extremely condensed Tremadocian and Floian stages include large gaps as well as the Ceratopyge Regressive Event and the widespread Evae transgression accompanied by prominent shifts in the δ 13C record. The Dapingian and Darriwilian stages are characterised by low sedimentation rates and a relatively complete sedimentary record. A total of 99 whole-rock samples were analysed for carbon isotope geochemistry from the Ordovician part of the succession (46 m thick). The most striking anomaly detected is the middle Darriwilian isotope carbon excursion (MDICE) that appears unusually well developed and complete for the region, and thus forms an important proxy for intercontinental correlation of the succession.

The Cambrian–Ordovician transition in dysoxic facies in Baltica — diverse faunas and carbon isotope anomalies

The Cambrian–Ordovician boundary interval in Scandinavia is characterized by largely endemic trilobite species and fossil-meager intervals within the Alum Shale Formation. Previous investigations of this interval in Scandinavia, based on drill cores, are rather sketchy. In order to characterize the faunal signature in a largely dysoxic setting during this time interval, as well as providing biostratigraphic and chemostratigraphic data valuable for intercontinental correlation, a small strip in the outskirts of the village Södra Sandby in Scania, southern Sweden, was excavated. Nearly 5m of the Cambrian–Ordovician boundary strata, largely represented by alum shale, were exposed and the profile was meticulously investigated for fossil content and lithological characteristics and sampled for δ13Corg analyses. The uppermost Cambrian in Sweden has previously been described as barren of fossils; however, the present study reveals a rather diverse fauna, including lingulid brachiopods, trilobites, protoconodonts, paraconodonts and euconodonts in the uppermost 1.6m of the Furongian. The first appearance datum of planktic graptolites is represented by a single shale surface covered by specimens of Rhabdinopora flabelliforme parabola at 1.74m above the base of the section and roughly corresponds to the Cambrian–Ordovician boundary. The conodont fauna includes several cordylodids important for intercontinental correlation. The Södra Sandby section δ13Corg data were coupled with isotope data from two Scanian drill cores, Håslöv-1 and Tosterup-2, in order to compile a composite isotope curve spanning the uppermost Ctenopyge linnarssoni Trilobite Zone in the Furongian to the upper R. flabelliforme parabola Graptolite Zone in the Lower Ordovician (Lower Tremadocian). Two isotope shifts from baseline values, observed at the base of the Peltura paradoxa Trilobite Zone and the lower part of the Peltura transiens Trilobite Zone, respectively, can be correlated with contemporaneous shifts in other parts of the world. The former, a negative shift of approximately 0.4–0.7‰, corresponds to the widely documented Top of Cambrian carbon isotope Excursion (TOCE) and the latter, a positive shift of approximately 1‰, corresponds to an as-yet-unnamed excursion at the base of the Cordylodus proavus Conodont Zone. In terms of faunal content and isotopic signals, the present study represents the first detailed description of the Cambrian–Ordovician boundary interval in Baltica. The relatively diverse fauna recorded suggests that the dysoxic environment was not a serious inhibitor for marine life. Globally, no isotope values significantly different from background values have been reported at the Cambrian–Ordovician boundary. This is confirmed by the present study; however, as the base of the Ordovician GSSP lacks meaningful isotope data, global correlation of this important boundary is problematic.

Darriwilian (Middle Ordovician) δ13Ccarb chemostratigraphy in the Precordillera of Argentina: Documentation of the middle Darriwilian Isotope Carbon Excursion (MDICE) and its use for intercontinental correlation

Although documented from Estonia, Latvia, Sweden, eastern North America, and China, the Middle Ordovician (Darriwilian) positive δ13C excursion known as the MDICE has previously not been recognized with certainty in South America. The most promising region in South America for detailed Middle Ordovician carbon isotope research is the Precordillera of western Argentina, where there are many excellent exposures of biostratigraphically well-dated carbonate successions spaning the Tremadocian through Sandbian stratigraphic interval. For this project, we collected numerous isotope and conodont samples from the middle Darriwilian Las Chacritas and Aguaditas formations at their type localities, which yielded important biostratigraphic data as well as informative δ13Ccarb values. In the E. pseudoplanus Zone in the upper half of the Las Chacritas Formation, there is a relatively modest but distinct δ13Ccarb excursion. Because its stratigraphic position and magnitude closely agree with the MDICE in other parts of the world, we recognize it as the first firm record of this excursion in South America. The fact that the δ13Ccarb curve from the Las Aguaditas Formation shows no such excursion is due to the existence of a stratigraphic gap between the Lower and Middle Members of this formation that cuts out the excursion interval. The Precordilleran MDICE is used for detailed long-range correlations with successions in Baltoscandia, Newfoundland, and China illustrating the usefulness of also this δ13Ccarb excursion as a global stratigraphic tool. A recent proposal of a greatly extended chronostratigraphic range of the Table Head Group on Newfoundland is rejected based on well-established biostratigraphic evidence.

Late Ordovician Ostracods of the Girvan District, South-West Scotland

The Late Ordovician ostracod fauna recorded from the Girvan district, south-west Scotland, comprises 54 species from 26 genera and 15 families, but includes 22 species described in open nomenclature and a further 17 that are considered as nomina dubia. The ostracods include representatives of the podocope suborders Palaeocopina, Binodicopina, Leiocopina and Metacopina, and the new genera and species Danemestrinus scotus n. gen. et sp., Leperditella girvanensis n. sp. and Krausella jonesiana n. sp. are described. The fauna includes several species that allow inter-continental correlation with the Late Ordovician succession of North America, including the Sandbian species Eurychilina sunbloodensis, Balticella deckeri, Baltonotella parsispinosa and Hippula ventrospinosa. The Katian species Kinnekullea comma has correlative value between Scotland, Ireland, England and the East Baltic. Biogeographically, the Girvan ostracod fauna of Sandbian age shows strong affinities at species-level with the fauna of palaeocontinental Laurentia, but from the early Katian onwards there are species level links with the Baltic region, and some common taxa at generic and species-level with palaeocontinental Avalonia.

Misinterpreting by localism: transposing European geology and tectonics onto Jamaica and the Antilles

Abstract ‘Localism’ occurs when geologists are most influenced by data with which they are familiar, applying it to new, but not necessarily appropriate, areas of study. Jamaica has been particularly prone to localist interpretations. Henry T. De la Beche (1796–1855) mapped eastern Jamaica in 1823–1824, and made lithostratigraphic comparisons between Jamaica and Europe that were the first attempt at intercontinental correlation. He correlated the Jamaican succession on the basis of lithological similarity to rocks in Europe. Charles A. Matley (1866–1947) is best remembered for his mapping in North Wales. He was geologist to the second geological survey of Jamaica in 1921 and developed the Basal Complex hypothesis which envisaged a geological structure analogous to that of North Wales, where the deformed Mona Complex underlies the Lower Palaeozoic succession. Matley thus provided a ‘factual’ basis for theories that the Antillean islands were the peaks of a foundered continent. Charles T. Trechmann (1885–1964) was the principal opponent of the Basal Complex hypothesis, not recognising evidence for old basement in Jamaica. His ‘answer’ was the Theory of Mountain Uplift, based on gravitational tectonics, but Trechmann's theory was comparable to the earlier fixist theories of tectonics that he learnt as a student.

Furongian (Cambrian) agnostoids of Scandinavia and their implications for intercontinental correlation

AbstractOut of the 14 agnostoid species/subspecies so far recorded from the Furongian of Scandinavia, seven are excellent biostratigraphical indices and important for correlation between Baltica and other palaeocontinents.Glyptagnostus reticulatus,Aspidagnostus lunulosusandAgnostus(Homagnostus)obesusfirst appear at the base of theG.reticulatusZone, allowing a precise correlation of the base of the Paibian Stage into Scandinavia.Tomagnostella orientalisandPseudagnostus cyclopygeappear near the base of theParabolina brevispinaZone, suggesting a correlation with the uppermost Paibian through the lowermost Jiangshanian stages.Lotagnostus americanus andPseudagnostus rugosushave an intercontinental distribution and their first appearance in Scandinavia allows for a correlation with one of the most favourable levels for defining the base of Cambrian provisional Stage 10. In the Furongian of Scandinavia, agnostoids are conspicuously assembled in three different intervals: the lowerGlyptagnostus reticulatusZone, the lowerPseudagnostus cyclopygeZone and theLotagnostusamericanusthrough lowerTrilobagnostus holmizones. The agnostoid-barren and largely unfossiliferous succession separating the lower and middle agnostoid-bearing intervals can be explained by means of subsequent dissolution of the calcareous fauna and/or a hostile environment. The middle agnostoid-bearing interval is succeeded by an anomalous succession dominated by the orthide brachiopodOrusia lenticularis, reflecting a regressive event coupled with increasing levels of oxygen at the sediment/water interface. This shallowing evidently resulted in unfavourable conditions for agnostoids.

A new occurence of the genus Tonkinella in northern Spain and the Middle Cambrian intercontinental correlation

The genus Tonkinella is a typical polimeroid trilobite in lower Middle Cambrian rocks from Vietnam, Canada, U.S.A., India, Korea, Siberia, China and Argentina. It has recently been found in the Mediterranean region (Iberian Chain, northeastern Spain). In this paper we refer the finding of Tonkinella aff. breviceps in the Leonian (lower Middle Cambrian) of the Cantabrian Mountains (northern Spain), analysing its stratigraphical position, fossil assemblages, biochronology and utility for intercontinental correlation. The presence of this taxon allows us to make a more accurate correlation between the Middle Cambrian biochronological scales of Laurentia, the Mediterranean area and China.

Proposal of a reference section and point for the Cambrian Series 2–3 boundary in the Mediterranean subprovince in Murero (NE Spain) and its intercontinental correlation

The classical lower‐middle Cambrian boundary is approximately equivalent with the boundary of the Cambrian Series 2 and 3, which is now in the process of definition by the International Subcommission on Cambrian Stratigraphy. Currently, there are two oryctocephalid trilobite species first appearance data (FAD) that are suggested as possible markers of this level: Ovatoryctocara granulata Tchernysheva, 1962 and Oryctocephalus indicus (Reed, 1910), respectively. Until now neither of these two species has been recorded in the Mediterranean subprovince or Baltica. As a result, in these regions a level potentially correlating with either the FAD of Ovatoryctocara granulata or Oryctocephalus indicus has to be located using the available bio‐, isotope‐, and event‐stratigraphy data.Carbon isotope signatures reveal global oceanic perturbations adjacent to the Cambrian Series 2 and Series 3 (former lower‐middle Cambrian) boundary. This event, first called the Valdemiedes Event (it was defined in Murero, NE Spain; Liñán et al., 1993a), caused a noticeable extinction of trilobites, mostly olenellids and protolenids (which were replaced in some regions by paradoxidids), as well as an almost complete extermination of some other early Cambrian marine animals. Both isotope and palaeontological evidence show that the disappearance of olenellids in Laurentia, protolenids in Siberia and the appearance of the first Acadoparadoxides in Western Gondwana, Baltica, Avalonia, and Siberia, which was formerly thought to be a series of diachronous regional perturbations, were nearly contemporaneous events. Features of a global ecological crisis and faunal replacement being taken together with a pronounced global δ13Corg negative excursion would serve as the best indicator of the lower boundary of the Cambrian Series 3 and Stage 5 in the Mediterranean subprovince and is correlatable with the Ovatoryctocara granulata FAD. Another δ13Corg negative excursion followed by a positive shift occurs at a slightly younger level, which coincides with a transgression maximum and roughly is coeval with the Oryctocephalus indicus FAD, also proposed as a possible base of the Cambrian Series 3. Copyright © 2011 John Wiley & Sons, Ltd.

Scandinavian Isograptids (Graptolithina, Isograptidae): Biostratigraphy and Taxonomy

SUMMARY The Lower–Middle Ordovician of Scandinavia is largely dominated by endemic Atlantic Province graptolite faunas, which are useful only for local biostratigraphy and paleoecology, but are difficult for correlation on an inter-continental scale. Isograptids, regarded as essential for inter-continental biostratigraphic correlations in the Lower–Middle Ordovician due to their wide palaeobiogeographic distribution, have rarely been recorded from the region. The Scandinavian Tøyen Shale and Bogo Shale formations bear a number of isograptids that range in age from the late Floian to the early Darriwilian, and these provide a good tool for inter-continental correlations of this interval. Isograptus caduceus norvegicus Monsen and Isograptus spinosus Spjeldnaes are interpreted as possible tetragraptid species. The following biostratigraphically important Isograptus species from Scandinavia are described as new: Isograptus spjeldnaesi n. sp., Isograptus rigidus n. sp. Isograptus mobergi n. sp. and Scandinavian zonal names in the Dapingian are revised accordingly.

An intercontinental correlation of the mid-Neoproterozoic Eastern Indian tectonic zone: evidence from the gneissic clasts in Elan Bank conglomerate, Kerguelen Plateau

The Kerguelen Plateau is a submarine, Cretaceous Large Igneous Province in the southern Indian Ocean. Drilling on Elan Bank, a western salient of the Kerguelen Plateau, yielded a ~26 m section of fluvial conglomerate intercalated with basalt. Chemical dating of monazite within garnet and matrix monazite in metapelitic clasts from the conglomerate indicates that high-grade metamorphism of the pelitic protolith occurred between 785 ± 12 and 694 ± 18 Ma. A calculated P–T pseudosection indicates that the observed core-to-inner rim compositional zoning in garnet is consistent with P/T decrease from 10.2 kb/760°C to 6.2 kb/560°C. In an Early Cretaceous paleogeographic reconstruction, the Elan Bank drill site is located on a SSW continuation of the Eastern Indian Tectonic Zone (EITZ), a 876–784 Ma, NNE–SSW metamorphic belt with sinistral shear zones in eastern India. The retrograde P–T path of the Elan Bank metapelitic clast overlaps with that of the EITZ metapelite, and the Elan Bank monazite chemical dates and previously determined 824–675 Ma U–Pb isotope monazite dates by the TIMS method are remarkably similar to the monazite chemical dates from the EITZ metapelites and high-grade metamorphic rocks from the eastern margin of the Eastern Ghats Belt. Based on the demonstrable affinity of metamorphic, geochronologic, and spatial data, this study concludes that the EITZ was likely a continuous, ~1,800–km-long tectono-metamorphic belt in the Rodinia supercontinent stretching from eastern India through the Eastern Ghats to the basement of Elan Bank and probably to the Rayner Complex of East Antarctica.

Ammonites of the genus Peltoceratoides Spath, 1924 from the Oxfordian of Kachchh, western India

Forty-three ammonites from the Kachchh Basin in western India have been assigned to seven taxa belonging to the genus Peltoceratoides sPAth, 1924. The two most abundant morphospe- cies Peltoceratoides (Peltoceratoides) constantii and Peltoceratoides (Parawedekindia) arduennen- sis are commonly considered as the macro- and microconch, respectively of a single biospecies. The taxa are important for intrabasinal as well as intercontinental correlation due to their wide geographic range during the Early Oxfordian. The specimens occur in beds, which had been assigned to the Cor- datum Zone, but also reworked in the so-called Dhosa Conglomerate Bed, which contains an array of ammonites from different ammonite zones.