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Devonian
Kinds of Devonian Selected AbstractsDEVONIAN CARBONATES OF THE NIGEL PEAK AREA, ROCKY MOUNTAINS, CANADA: A FOSSIL PETROLEUM SYSTEM?JOURNAL OF PETROLEUM GEOLOGY, Issue 3 2008J. Köster In this study we report on Devonian (Frasnian , Famennian) limestones and dolostones exposed near Nigel Peak in the Main Ranges of the Canadian Rocky Mountains. These carbonates are a proximal facies of the Southesk-Cairn Carbonate Complex. The investigated strata are stratigraphically equivalent to the oil- and gas bearing Nisku Formation in the subsurface of the Western Canada Sedimentary Basin, about 300 km to the east. The rocks were investigated by polarisation and cathodoluminescence microscopy, total organic carbon analysis, Rock-Eval pyrolysis, solid bitumen reflectance measurements, gas chromatography and fluid inclusion analysis. Thin section analyses showed that silt-grade quartz and saddle dolomite increase upward from the base of the stratigraphic section, and that porosities are generally low. This is due to reduction of pore space due to early cementation and extensive dolomitization. Cathodoluminescence identified up to four generations of calcite cements. TOC values ranged from 0.2 to 2.4 %. Rock-Eval pyrolysis of carbonate samples resulted in measurable S1 peaks but not S2 peaks, indicating that there was no residual petroleum generation potential. Organic petrographic analyses identified dispersed kerogen and migrabitumen, and calculated vitrinite reflectance values were around 4 % on average which implies peak temperatures of 234,262 °C (due to deep burial) or 309,352 °C (due to short term hydrothermal heating). Fluid inclusion data indicates at least one pulse of hot fluids with elevated homogenization temperatures of > 300 °C, and this may explain the high thermal maturity of the studied rocks. [source] THE EXTRAORDINARY TRILOBITE FENESTRASPIS (DALMANITIDAE, SYNPHORIINAE) FROM THE LOWER DEVONIAN OF BOLIVIAPALAEONTOLOGY, Issue 4 2009DAVID J. HOLLOWAY Abstract: The hitherto poorly known, monotypic trilobite genus Fenestraspis from the Lower Devonian of Bolivia is revised and its original assignment to the Synphoriinae supported. The thoracic morphology of the genus remains very poorly known. Fenestraspis is morphologically unusual because of the development of extensive fenestrae in the pleural region of the pygidium and apparently of the thorax; the presence of upwardly directed spines on the cephalon, thorax and pygidium; and the exceptionally large and highly elevated eyes with the palpebral rim projecting outwards above the visual surface. The function of the fenestrae remains uncertain. If they formed openings in the body of the trilobite in life they may have allowed circulation of oxygenated water to the limb exites so that respiration could have been maintained while the trilobite was enrolled. If they were covered with a flexible membrane, they may have been secondary respiratory structures or had a sensory function. The Synphoriinae is regarded as a subfamily of the Dalmanitidae rather than as an independent family of the Dalmanitoidea as proposed by some authors. The type species of the poorly known monotypic genus Dalmanitoides from the Lower Devonian of Argentina is illustrated photographically for the first time and compared with Fenestraspis. [source] PATTERNS OF EVOLUTION AND EXTINCTION IN THE LAST HARPETID TRILOBITES DURING THE LATE DEVONIAN (FRASNIAN)PALAEONTOLOGY, Issue 1 2009KENNETH J. McNAMARA Abstract:, Late Devonian (Frasnian) harpetid trilobites have hitherto only been described from the western side of the Protethys Ocean, in what is now Europe and North Africa, as well as from Gondwana-derived northwestern Kazakhstan (Mugodjar). However, late Frasnian strata in the Canning Basin, Western Australia, that were deposited on the eastern side of this ocean, contain a rich harpetid fauna. Described herein are two new harpetids: Eskoharpes gen. nov. and Globoharpes gen. nov., within which are placed six species: E. palanasus sp. nov., E. wandjina sp. nov., E. boltoni sp. nov., E. guthae sp. nov., G. teicherti sp. nov. and G. friendi sp. nov. The ontogenetic development of E. palanasus, E. wandjina and G. teicherti are described, including the first unequivocal harpetid protaspis. Globoharpes exhibits evidence of sexual dimorphism in the development of a pronounced preglabellar boss in some specimens. This structure is thought to have functioned as a brood pouch. Such structures have previously only been described in Cambrian and Ordovician trilobites, and never before in harpetids. It is suggested that the characteristic harpetid fringe functioned as a secondary respiratory structure. The Eskoharpes lineage shows evolutionary trends that mirror changes seen in ontogenetic development of the youngest species, suggesting the operation of peramorphic processes. This is the first record of heterochrony in harpetids and the first documented example of peramorphosis in Devonian trilobites. These harpetids demonstrate a stepped pattern of extinction during the late Frasnian, probably related to the effects of the two Kellwasser biocrises that have been well documented in European Frasnian sections. Highly vaulted species of Eskoharpes and the strongly vaulted Globoharpes became extinct at the Lower Kellwasser Event. The flatter species of Eskoharpes became extinct at the base of the Upper Kellwasser Event shortly prior to the Frasnian/Famennian boundary. The extinction of these harpetids, along with contemporaneous forms from Europe, which are also discussed herein, marks the end of the trilobite order Harpetida worldwide. [source] THE GENUS GIGANTASPIS HEINTZ, 1962 (VERTEBRATA, HETEROSTRACI) FROM THE LOWER DEVONIAN OF SPITSBERGENPALAEONTOLOGY, Issue 2 2007VINCENT PERNEGRE Abstract:, Material collected in 1969 by the CNRS-MNHN expedition to Spitsbergen includes a new species of Gigantaspis, G. minima, which is the smallest known species of this genus. The revision of Gigantaspis leads to the inclusion of Zascinaspis laticephala Blieck and Goujet in this genus. The phylogenetic analysis presented herein suggests that Gigantaspis is close to Zascinaspis, as suggested by Blieck. Moreover, it is also close to generalized representatives of the Protaspididae. Their shared character states allow the definition of a possible ancestral morphotype for the Protaspididae. [source] LATE DEVONIAN (FAMENNIAN) LUNGFISHES FROM THE CATSKILL FORMATION OF PENNSYLVANIA, USAPALAEONTOLOGY, Issue 6 2006MATT FRIEDMAN Abstract:, Occurrences of fossil lungfishes (Dipnoi: Sarcopterygii) in the Famennian Catskill Formation of Pennsylvania are reviewed. A nearly complete dermal skull roof is assigned to a new genus and species, Apatorhynchus opistheretmus. Other recently discovered lungfish specimens include an incomplete postcranium similar to that of the Frasnian genus Fleurantia, a small parasphenoid of uncertain affinities, and isolated toothplates. Previously described dipnoan remains from the Catskill Formation include a partial skull roof of Soederberghia groenlandica, toothplates assigned to several species of Dipterus, a putative rostral or symphysial region placed in the problematic form taxon Ganorhynchus, and sedimentary structures interpreted as burrows. The toothplates attributed to Dipterus are indeterminate and are placed in open nomenclature, while the specimen identified as Ganorhynchus is not convincingly dipnoan. The status of the burrows remains uncertain pending the discovery of lungfish remains within these or similar structures in Catskill deposits. The distinct ichthyofaunas within the Catskill Formation and their lungfish components are briefly reviewed. Lungfishes are found in the Holoptychius - and Bothriolepis -dominated faunas common in the Catskill succession, as well as in the compositionally distinctive Red Hill assemblage. Many of the Devonian continental faunas that contain tetrapods also include long-snouted, denticle-bearing lungfishes (,rhynchodipterids', fleurantiids, or both). The composition of Late Devonian ichthyofaunas may have predictive qualities that will allow researchers to identify localities likely to produce the remains of early tetrapods. [source] A NEW SPECIES OF BRITTLESTAR (OPHIUROIDEA, ECHINODERMATA) FROM THE HUNSRÜCK SLATE (LOWER EMSIAN, LOWER DEVONIAN) OF GERMANYPALAEONTOLOGY, Issue 5 2006ALEXANDER GLASS Abstract:,Lapworthura lehmanni, a new species of ophiuroid, is described from four specimens from the Lower Devonian Hunsrück Slate of Germany. It is the only known ophiuroid in the Hunsrück Slate with paired but unfused ambulacrals, and it exhibits unique rows of spine-bearing dorsal arm ossicles. The genus Lapworthura Gregory was previously known only from the Ordovician of Scotland and the Silurian of England and Australia. [source] First record of the brachiopod Lingulella waptaensis with pedicle from the Middle Cambrian Burgess ShaleACTA ZOOLOGICA, Issue 2 2010Sandra Pettersson Stolk Abstract Pettersson Stolk, S., Holmer, L. E. and Caron, J -B. 2010. First record of the brachiopod Lingulella waptaensis with pedicle from the Middle Cambrian Burgess Shale. ,Acta Zoologica (Stockholm) 91: 150,162 The organophosphatic shells of linguloid brachiopods are a common component of normal Cambrian,Ordovician shelly assemblages. Preservation of linguloid soft-part anatomy, however, is extremely rare, and restricted to a few species in Lower Cambrian Konservat Lagerstätten. Such remarkable occurrences provide unique insights into the biology and ecology of early linguloids that are not available from the study of shells alone. Based on its shells, Lingulella waptaensis Walcott, was originally described in 1924 from the Middle Cambrian Burgess Shale but despite the widespread occurrence of soft-part preservation associated with fossils from the same levels, no preserved soft parts have been reported. Lingulella waptaensis is restudied herein based on 396 specimens collected by Royal Ontario Museum field parties from the Greater Phyllopod Bed (Walcott Quarry Shale Member, British Columbia). The new specimens, including three with exceptional preservation of the pedicle, were collected in situ in discrete obrution beds. Census counts show that L. waptaensis is rare but recurrent in the Greater Phyllopod Bed, suggesting that this species might have been generalist. The wrinkled pedicle protruded posteriorly between the valves, was composed of a central coelomic space, and was slender and flexible enough to be tightly folded, suggesting a thin chitinous cuticle and underlying muscular layers. The nearly circular shell and the long, slender and highly flexible pedicle suggest that L. waptaensis lived epifaunally, probably attached to the substrate. Vertical cross-sections of the shells show that L. waptaensis possessed a virgose secondary layer, which has previously only been known from Devonian to Recent members of the Family Lingulidae. [source] New arthrodires (Family Williamsaspididae) from Wee Jasper, New South Wales (Early Devonian), with comments on placoderm morphology and palaeoecologyACTA ZOOLOGICA, Issue 2009Gavin C. Young Abstract Two new arthrodire species represented by articulated trunk armours from the Early Devonian (Emsian) limestones of the Burrinjuck area are placed in a new genus Elvaspis (E. tuberculata, E. whitei), assigned to the Family Williamsaspididae. On new evidence of the dermal neck-joint and shape of the median dorsal plate this family is reassigned from the Phlyctaeniina to the Brachythoraci. The strongly ornamented post-branchial lamina of the trunk armour relates to a recent hypothesis that special post-branchial denticles in placoderms are homologous to pharyngeal denticles of crown-gnathostomes rather than modified external tubercles. Variable development of the post-branchial lamina and its ornament in different placoderm subgroups, with specific resemblance to the external ornament characteristic of that subgroup, indicates that modification of normal external dermal ornament is the most parsimonious interpretation. A comparison of fish diversity in modern and ancient tropical reef environments is consistent with an equilibrium model for species diversification through time. [source] Enameloid microstructure in the oldest known chondrichthyan teethACTA ZOOLOGICA, Issue 2009H. Botella Abstract Previous studies on tooth enameloid microstructure in several chondrichthyan taxa spanning the phylogeny of the group provided support for the homology of chondrichthyan tooth enameloid. This hypothesis requires that a single crystallite enameloid (SCE) monolayer must be present in the teeth of the most primitive chondrichthyan. However, the dental microstructure of the earliest sharks has yet to be investigated. We have studied the tooth enameloid microstructure of the two oldest tooth-bearing shark species currently known, Leonodus carlsi Mader (1986) and Celtiberina maderi Wang (1993), from the lowermost Lochkovian (Lower Devonian) of Spain. Our study demonstrates the presence of a SCE monolayer in the teeth of both species. These results show that a superficial cap of SCE is present in the oldest shark teeth known, which suggest its presence in the most basal chondrichthyans. [source] The braincase of the chondrichthyan Doliodus from the Lower Devonian Campbellton Formation of New Brunswick, CanadaACTA ZOOLOGICA, Issue 2009John Maisey Abstract The braincase of the late Lower Devonian (Emsian) chondrichthyan Doliodus is described for the first time. Its postorbital process is extended ventrally and probably enclosed part of the infraorbital sensory canal, as in some placoderms. Doliodus has a shark-like dentition, but its upper anterior tooth files were supported by the internasal cartilage of the braincase, not by the palatoquadrates. Modern selachian jaws and dentitions are not representative of primitive crown-group gnathostomes because they display a mixture of conserved and derived character states. Separation of the palatoquadrates by the internasal cartilage is probably a primitive condition for crown-group gnathostomes. Continuity of the upper dental arcade across the ethmoid region may represent a synapomorphy of chondrichthyans and some acanthodians (the condition is not found in placoderms or osteichthyans). Exclusion of the arcade from the ethmoid region is probably apomorphic within elasmobranchs. Doliodus has curious bar-like, paired subcranial ridges ending posteriorly at the hyomandibular articulation. These superficially resemble visceral arch infrapharyngohyals fused to the floor of the braincase, adding circumstantial palaeontological support to the old proposal that parts of visceral arches may be incorporated into the gnathostome braincase, although it seems more plausible that they formed in the lateral margins of the embryonic parachordal or hypotic lamina. [source] An enigmatic gnathostome vertebrate skull from the Middle Devonian of BoliviaACTA ZOOLOGICA, Issue 2009Alan Pradel Abstract A new taxon, Ramirosuarezia boliviana n. gen., n. sp. is erected for a single, articulated jawed fish (gnathostome) skull from the Middle Devonian (Eifelian) Icla Formation of Bolivia. The specimen displays an elasmobranch-like braincase, but lacks unambiguous elasmobranch and even chondrichthyan characters, although its peculiar tooth-bearing ,labial' elements evoke certain stem-holocephalans. Its endoskeletal elements seem lined with either perichondral bone or non-prismatic calcified cartilage, but show no evidence of endochondral bone. Although devoid of large dermal bones and scales, R. boliviana shares with certain ,ostracoderms', placoderms and holocephalans the lack of an otico-occipital fissure, but lacks a hypophysial fenestra. Certain features (elongated braincase, ,labial elements', sharp denticles and teeth) are also suggestive of the equally enigmatic coeval stensioellids, once regarded as either primitive placoderms or stem holocephalans. The jaws are armed with platelets that bear blunt to pointed and sharp teeth, in which synchrotron radiation microtomography yields evidence of a large pulp cavity, a possibly osteichthyan-like character. No character clearly supports affinities of R. boliviana to any of the currently known major gnathostome groups. Tenuous hints suggest a relationship to the enigmatic fossil Zamponiopteron, from the Eifelian of Bolivia, known by peculiar calcified ,fin plates' and isolated shoulder girdles. [source] A new tooth-plated lungfish from the Middle Devonian of Yunnan, China, and its phylogenetic relationshipsACTA ZOOLOGICA, Issue 2009Tuo Qiao Abstract A new genus and species of tooth-plated lungfish, Sinodipterus beibei gen. et sp. nov., is described from the Qujing Formation (Middle Devonian, late Eifelian) of Zhaotong, Yunnan, China. The new form resembles Dipterus in the skull table, but differs in its tooth-plate: cosmine-like tissue absent near the midline, tooth rows fewer in number (7 to 8) and less divergent radiating, and no reparative dentine layers. Phylogenetic analysis of Devonian lungfish based on a dataset of 150 characters and 33 taxa indicates that the new taxon is more crownward than Dipterus and the clade comprising Adololopas, Sorbitorhynchus and Pillararhynchus. Our results agree broadly with previous cladistic solutions. Diabolepis is placed as a sister group to all other Devonian lungfish. The species referred to Chirodipterus fail to form a monophyletic group. The result shows a large number of convergences corresponding to early radiation of lungfish compressed in time. [source] Heddleichthys, a new tristichopterid genus from the Dura Den Formation, Midland Valley, Scotland (Famennian, Late Devonian)ACTA ZOOLOGICA, Issue 2009Daniel Snitting Abstract A new tristichopterid genus, Heddleichthys, from the Famennian of Scotland is described based on material previously assigned to a number of different genera, including Glyptopomus, Gyroptychius and Eusthenopteron. The validity of the new genus is established by a discussion of the reasons for the invalidity of the previous assignments. Heddleichthys is characterized by a combination of derived and primitive tristichopterid features. Derived features include the presence of symphyseal dentary fangs and premaxillary pseudofangs, a diamond-shaped symmetric caudal fin, a low posterodorsal expansion of the maxilla, and a posteriorly positioned kite-shaped pineal series. Primitive features include a postorbital and jugal contribution to the orbital margin and a parasphenoid with a ventral keel. External dermal bones are rather poorly preserved in the referred material, with few easily discernible sutures. The holotype specimen, a three-dimensionally preserved skull, was scanned by computed tomography to reveal well-preserved internal dermal bones, including entopterygoids, vomers and parasphenoid. There is no preserved endoskeletal material. As the first representative of derived tristichopterids described from Britain, Heddleichthys lends support to the idea that faunal dispersion between Gondwana and Laurussia in the Late Devonian was widespread. Derived tristichopterids have been described from all continents except South America. In contrast, the basal tristichopterids Eusthenopteron and Tristichopterus are still only described from Laurussia. [source] Bite marks as evidence of predation in early vertebratesACTA ZOOLOGICA, Issue 2009Oleg A. Lebedev Abstract Study of lifetime bite traces on agnathans and fish (or gnathostomes) from Ukraine, Estonia, Latvia and north-western and central European Russia reveals evidence of predator,prey relationships in communities of Devonian age. Numerous bite traces on skeletal parts of agnathan pteraspidiforms and psammosteiforms, placoderm arthrodires and antiarchs and sarcopterygian porolepiforms and osteolepiforms are described. Evidence of healing shows that prey organisms responded to predation by reconstruction of damaged skeletal elements. Ichthyofaunistic analysis is used to establish possible predators. The most probable predators in the Middle and Late Devonian communities are sarcopterygian porolepiforms and osteolepiforms. Predatory tetrapods become evident during the Famennian. Global analysis of aquatic predators during the Silurian,Devonian interval shows a gradual increase in species numbers with time. During the Late Silurian, only ischnacantid acanthodians, early osteichthyans and sarcopterygians are known to belong to this trophic group. By the end of the Devonian this list is complemented by chondrichthyans, arthrodires, porolepiform, osteolepiform, struniiform and rhizodontiform sarcopterygians and tetrapods. Only Devonian agnathans show no predatory groups. In sarcopterygians, predatory dentitions, which developed according to more or less the same pattern, show little change during the Devonian. [source] Evolution of morphogenesis in 360-million-year-old conodont chordates calibrated in daysEVOLUTION AND DEVELOPMENT, Issue 6 2008Jerzy Dzik SUMMARY Highly rhythmic increments of crown tissue are identifiable in conodont oral apparatus elements from the Late Devonian of the Holy Cross Mountains, Poland; individual laminae being of thickness comparable with daily increments of vertebrate tooth enamel and fish otoliths. Abundant occurrence of such specimens enables bed-by-bed (stratophenetic) studies of the process of evolution at the population level and quantitative presentation of the evolution of ontogeny in the sampled geological section covering several million years. The morphologic transformation is expressed as expansion of a juvenile asymmetry to later stages of the ontogeny and in decrease of the mature element width, which was due to a change of the mineral tissue secretion rate. It was not just a simple extension of a juvenile character into the later stage of the ontogeny (heterochrony) but rather a true developmental novelty. The evolution was gradual and very slow. The proposed quantitative approach to growth increments in the mineral skeleton of ancient chordates introduces real-time units to evolutionary developmental studies connected with direct paleontological evidence on the course of evolution. [source] The fate of the homoctenids (Tentaculitoidea) during the Frasnian,Famennian mass extinction (Late Devonian)GEOBIOLOGY, Issue 3 2006DAVID BONDArticle first published online: 18 AUG 200 ABSTRACT The homoctenids (Tentaculitoidea) are small, conical-shelled marine animals that are among the most abundant and widespread of all Late Devonian fossils. They were a principal casualty of the Frasnian,Famennian (F-F, Late Devonian) mass extinction, and thus provide an insight into the extinction dynamics. Despite their abundance during the Late Devonian, they have been largely neglected by extinction studies. A number of Frasnian,Famennian boundary sections have been studied, in Poland, Germany, France, and the USA. These sections have yielded homoctenids, which allow precise recognition of the timing of the mass extinction. It is clear that the homoctenids almost disappear from the fossil record during the latest Frasnian ,Upper Kellwasser Event'. The coincident extinction of this pelagic group, and the widespread development of intense marine anoxia within the water column, provides a causal link between anoxia and the F-F extinction. Most notable is the sudden demise of a group, which had been present in rock-forming densities, during this anoxic event. One new species, belonging to Homoctenus is described, but is not formally named here. [source] Ancient hydrocarbon seeps from the Mesozoic convergent margin of California: carbonate geochemistry, fluids and palaeoenvironmentsGEOFLUIDS (ELECTRONIC), Issue 2 2002K. A. Campbell Abstract More than a dozen hydrocarbon seep-carbonate occurrences in late Jurassic to late Cretaceous forearc and accretionary prism strata, western California, accumulated in turbidite/fault-hosted or serpentine diapir-related settings. Three sites, Paskenta, Cold Fork of Cottonwood Creek and Wilbur Springs, were analyzed for their petrographic, geochemical and palaeoecological attributes, and each showed a three-stage development that recorded the evolution of fluids through reducing,oxidizing,reducing conditions. The first stage constituted diffusive, reduced fluid seepage (CH4, H2S) through seafloor sediments, as indicated by Fe-rich detrital micrite, corroded surfaces encrusted with framboidal pyrite, anhedral yellow calcite and negative cement stable isotopic signatures (,13C as low as ,35.5, PDB; ,18O as low as ,10.8, PDB). Mega-invertebrates, adapted to reduced conditions and/or bacterial chemosymbiosis, colonized the sites during this earliest period of fluid seepage. A second, early stage of centralized venting at the seafloor followed, which was coincident with hydrocarbon migration, as evidenced by nonluminescent fibrous cements with ,13C values as low as ,43.7, PDB, elevated ,18O (up to +2.3, PDB), petroleum inclusions, marine borings and lack of pyrite. Throughout these early phases of hydrocarbon seepage, microbial sediments were preserved as layered and clotted, nondetrital micrites. A final late-stage of development marked a return to reducing conditions during burial diagenesis, as implied by pore-associated Mn-rich cement phases with bright cathodoluminescent patterns, and negative ,18O signatures (as low as ,14, PDB). These recurring patterns among sites highlight similarities in the hydrogeological evolution of the Mesozoic convergent margin of California, which influenced local geochemical conditions and organism responses. A comparison of stable carbon and oxygen isotopic data for 33 globally distributed seep-carbonates, ranging in age from Devonian to Recent, delineated three groupings that reflect variable fluid input, different tectono-sedimentary regimes and time,temperature-dependent burial diagenesis. [source] The Ridgeway Conglomerate Formation of SW Wales, and its implications.GEOLOGICAL JOURNAL, Issue 1 2007The end of the Lower Old Red Sandstone? Abstract The Devonian Old Red Sandstone Ridgeway Conglomerate Formation crops out in Pembrokeshire, SW Wales. It was deposited as part of a dryland alluvial fan, axial fluvial valley deposystem. It conformably overlies the mid Lochkovian Freshwater West Formation and probably predates deposition of the Lower Cosheston Group Mill Bay Formation indicating an Early Devonian (latest Lochkovian to earliest Pragian) age, rather than a Middle Devonian age as suggested by previous workers. It therefore represents the youngest preserved formation of the Milford Haven Group south of the Ritec Fault. The Formation thickens drastically into the Ritec Fault, indicating its control on sedimentation. The half-graben topography initiated deposition of a hangingwall alluvial fan that was sourced from a southerly Lower Palaeozoic/Precambrian provenance within the present-day Bristol Channel. The Formation is heterolithic in nature, with deposits on the fan reflecting a mixture of processes. Conglomerates were deposited primarily by laterally extensive sheetfloods, and as bars in low-relief, laterally accreted channels. Sandstones were also predominantly deposited by sheetfloods. Gritty mudrocks in comparison demonstrate deposition by cohesive debris flows. The fan prograded northward and interfingered with a low-gradient, high-sinuosity fluvial channel system dominated by inclined and non-inclined heterolithic stratification. Thinly laminated mudstone and sandstone interbeds were deposited in ephemeral fan-toe and axial valley lakes that may have developed during sub-humid climatic episodes. The lacustrine heterolithic association has associated matgrounds and possible ,algal roll-up' structures. Calcretized peetee structures and root traces comprise a lake margin calcrete association. Fan gravels prograded into the axial fluvial valley during periods of increased sediment flux that may represent semi-arid conditions and/or episodes of tectonic activity. Calcretes of varying development were established in both the fan and axial valley zones. Calcretes with lower stages of development are more proximal to the Ritec Fault reflecting decreased soil residence times and high deposition rates within the axial valley. More strongly developed soil profiles on the fan may indicate sequence boundaries associated with low sediment flux, or increased soil residence time due to active fan-channel migration (the pedofacies concept). Groundwater calcretes have sharp-based and layer-bound calcrete profiles. Gully-bed cements are locally developed within the fan gravels. Copyright © 2007 John Wiley & Sons, Ltd. [source] Carbonate melting and peperite formation at the intrusive contact between large mafic dykes and clastic sediments of the upper Palaeozoic Saint-Jules Formation, New-Carlisle, QuebecGEOLOGICAL JOURNAL, Issue 1 2006P. Jutras Abstract The base of an upper Palaeozoic graben-fill in eastern Canada was affected by mafic dyke intrusions shortly after deposition, resulting in the formation of peperite. Complex magma,sediment interactions occurred as the melts mingled with the wet and poorly consolidated clastic material of this sedimentary basin, which is separated from underlying rocks by the Acadian unconformity (Middle Devonian). As a result of these interactions, the mafic rocks are strongly oxidized, albitized and autobrecciated near and above the unconformity, where blocky juvenile clasts of mafic glass and porphyritic basalt have mingled with molten or fluidized sediments of the upper Palaeozoic Saint-Jules Formation, forming a peperite zone several metres thick. In contrast to most peperite occurrences, the New-Carlisle peperites are associated with the tip of dykes rather than with the sides of sills or dykes. We argue that more heat can be concentrated above a dyke than above a sill, as the former provides a more efficient and focused pathway for heated waters to invade the poorly consolidated host sediments. Superheated groundwaters that issued from the sides of the dykes appear to have promoted melting of carbonate components in calcareous sedimentary rock clasts of the Saint-Jules Formation, locally generating carbonate melts that contributed to the mingling of juvenile and sedimentary clasts in the peperite. Copyright © 2005 John Wiley & Sons, Ltd. [source] SHRIMP zircon and EPMA monazite dating of granitic rocks from the Maizuru terrane, southwest Japan: Correlation with East Asian Paleozoic terranes and geological implicationsISLAND ARC, Issue 3 2008Masahiro Fujii Abstract The Maizuru terrane, distributed in the Inner Zone of southwest Japan, is divided into three subzones (Northern, Central and Southern), each with distinct lithological associations. In clear contrast with the Southern zone consisting of the Yakuno ophiolite, the Northern zone is subdivided into the western and eastern bodies by a high-angle fault, recognized mainly by the presence of deformed granitic rocks and pelitic gneiss. This association suggests an affinity with a mature continental block; this is supported by the mode of occurrence, and petrological and isotopic data. Newly obtained sensitive high mass-resolution ion microprobe (SHRIMP) zircon U,Pb ages reveal the intrusion ages of 424 ± 16 and 405 ± 18 Ma (Siluro,Devonian) for the granites from the western body, and 249 ± 10 and 243 ± 19 Ma (Permo,Triassic) for the granodiorites from the eastern body. The granites in the western body also show inherited zircon ages of around 580 and 765 Ma. In addition, electron probe microanalysis (EPMA) monazite U,Th,total Pb dating gives around 475,460 Ma. The age of intrusion, inherited ages, mode of occurrence, and geological setting of the Siluro,Devonian granites of the Northern zone all show similarities with those of the Khanka Massif, southern Primoye, Russia, and the Hikami granitic rocks of the South Kitakami terrane, Northeast Japan. We propose that both the Siluro,Devonian and Permo,Triassic granitic rocks of the Northern zone are likely to have been juxtaposed through the Triassic,Late Jurassic dextral strike-slip movement, and to have originated from the Khanka Massif and the Hida terrane, respectively. This study strongly supports the importance of the strike-slip movement as a mechanism causing the structural rearrangement of the Paleozoic,Mesozoic terranes in the Japanese Islands, as well as in East Asia. [source] One-dimensional thermal modelling of Acadian metamorphism in southern Vermont, USAJOURNAL OF METAMORPHIC GEOLOGY, Issue 6 2000T. R. Armstrong One-dimensional thermal (1DT) modelling of an Acadian (Devonian) tectonothermal regime in southern Vermont, USA, used measured metamorphic pressures and temperatures and estimated metamorphic cooling ages based on published thermobarometric and geochronological studies to constrain thermal and tectonic input parameters. The area modelled lies within the Vermont Sequence of the Acadian orogen and includes: (i) a western domain containing garnet-grade pre-Silurian metasedimentary and metavolcanic rocks from the eastern flank of an Acadian composite dome structure (Rayponda,Sadawga Dome); and (ii) an eastern domain containing similar, but staurolite- or kyanite-grade, rocks from the western flank of a second dome structure (Athens Dome), approximately 10 km farther east. Using reasonable input parameters based on regional geological, petrological and geochronological constraints, the thermal modelling produced plausible P,T paths, and temperature,time (T ,t) and pressure,time (P,t) curves. Information extracted from P,T ,t modelling includes values of maximum temperature and pressure on the P,T paths, pressure at maximum temperature, predicted Ar closure ages for hornblende, muscovite and K-feldspar, and integrated exhumation and cooling rates for segments of the cooling history. The results from thermal modelling are consistent with independently obtained pressure, temperature and Ar cooling age data on regional metamorphism in southern Vermont. Modelling results provide some important bounding limits on the physical conditions during regional metamorphism, and indicate that the pressure contemporaneous with the attainment of peak temperature was probably as much as 2.5 kbar lower than the actual maximum pressure experienced by rocks along various particle paths. In addition, differences in peak metamorphic grade (garnet-grade versus staurolite-grade or kyanite-grade) and peak temperature for rocks initially loaded to similar crustal depths, differences in calculated exhumation rates, and differences in 40Ar/39Ar closure ages are likely to have been consequences of variations in the duration of isobaric heating (or ,crustal residence periods') and tectonic unroofing rates. Modelling results are consistent with a regional structural model that suggests west to east younging of specific Acadian deformational events, and therefore diachroneity of attainment of peak metamorphic conditions and subsequent 40Ar/39Ar closure during cooling. Modelling is consistent with the proposition that regional variations in timing and peak conditions of metamorphism are the result of the variable depths to which rocks were loaded by an eastward-thickening thrust-nappe pile rooted to the east (New Hampshire Sequence), as well as by diachronous structural processes within the lower plate rocks of the Vermont Sequence. [source] DEVONIAN CARBONATES OF THE NIGEL PEAK AREA, ROCKY MOUNTAINS, CANADA: A FOSSIL PETROLEUM SYSTEM?JOURNAL OF PETROLEUM GEOLOGY, Issue 3 2008J. Köster In this study we report on Devonian (Frasnian , Famennian) limestones and dolostones exposed near Nigel Peak in the Main Ranges of the Canadian Rocky Mountains. These carbonates are a proximal facies of the Southesk-Cairn Carbonate Complex. The investigated strata are stratigraphically equivalent to the oil- and gas bearing Nisku Formation in the subsurface of the Western Canada Sedimentary Basin, about 300 km to the east. The rocks were investigated by polarisation and cathodoluminescence microscopy, total organic carbon analysis, Rock-Eval pyrolysis, solid bitumen reflectance measurements, gas chromatography and fluid inclusion analysis. Thin section analyses showed that silt-grade quartz and saddle dolomite increase upward from the base of the stratigraphic section, and that porosities are generally low. This is due to reduction of pore space due to early cementation and extensive dolomitization. Cathodoluminescence identified up to four generations of calcite cements. TOC values ranged from 0.2 to 2.4 %. Rock-Eval pyrolysis of carbonate samples resulted in measurable S1 peaks but not S2 peaks, indicating that there was no residual petroleum generation potential. Organic petrographic analyses identified dispersed kerogen and migrabitumen, and calculated vitrinite reflectance values were around 4 % on average which implies peak temperatures of 234,262 °C (due to deep burial) or 309,352 °C (due to short term hydrothermal heating). Fluid inclusion data indicates at least one pulse of hot fluids with elevated homogenization temperatures of > 300 °C, and this may explain the high thermal maturity of the studied rocks. [source] ORDOVICIAN,PERMIAN PALAEOGEOGRAPHY OF CENTRAL EURASIA: DEVELOPMENT OF PALAEOZOIC PETROLEUM-BEARING BASINSJOURNAL OF PETROLEUM GEOLOGY, Issue 3 2003V. A. Bykadorov In this paper, we discuss three petroleum-bearing basins of Palaeozoic age in Central Eurasia,the Precaspian, Tarim and Chu-Sarysu Basins. We make use of recently-published palaeogeographic maps of the Central Eurasian region, six of which are presented here (Late Ordovician, Early-Middle Devonian, Late Devonian, Early Carboniferous, Early Permian and Late Permian). The maps illustrate the development through the Palaeozoic of the Palaeoasian and Palaeotethys Oceans; of the East European, Siberian and Tarim cratons; and of the Kazakhstan and other microcontinental blocks. The Kazakhstan block formed during the Late Ordovician and is a collage of Precambrian and Early Palaeozoic microcontinents and island arcs. It is surrounded by collisional foldbelts (Ob-Zaisan, Ural-Tianshan and Junggar-Balkhash) which formed in the Late Carboniferous , Permian. We believe that the formation of a stable Kazakhstan block is not consistent with the existence of the previously-identified "Kipchak arc" within the Palaeoasian ocean, or (as has previously been proposed) with activity on this arc up to the end of the Palaeozoic. The oil and gas potential of the Precaspian, Tarim and Chu-Sarysu Basins depends to a large extent on their tectonic stability during the Palaeozoic and subsequent time. The Precaspian Basin has been stable since the Cadomian orogeny (Early Cambrian) and is known to have major hydrocarbon potential. The Tarim Basin (NW China) has somewhat lower potential because the margins of the Tarim continental block have been affected by a series of collisional events; that margin with the Palaeotethys Ocean, for example, was active during the Late Palaeozoic. The Chu-Sarysu Basin on the Kazakhstan block is the least stable of the three and contains only minor gas accumulations. [source] POST-DRILLING ANALYSIS OF THE NORTH FALKLAND BASIN, PART 1: TECTONO-STRATIGRAPHIC FRAMEWORKJOURNAL OF PETROLEUM GEOLOGY, Issue 3 2000P. C. Richards Six wells were drilled in the extensional North Falkland Basin in 1998. The wells encountered a Devonian to Cenozoic stratigraphy dominated by thick Mesozoic syn- and post-rift successions. Although most previously published models predicted that the succession would most likely be of marine origin, it is in fact predominantly terrestrial; marine conditions did not become established in the basin until the Late Cretaceous. The oldest rocks recorded are Devonian and these were penetrated in only one well. The overlying succession comprises: a fluvio-lacustrine, early syn-rft interval of ?mid-Jurassic to Tithonian age; a late syn-rift fluvio-lacustrine interval of Tithonian to Berriasian age; a rift-sag transitional unit of Berriasian to Valanginian age; an early post-rift lacustrine unit of Valanginian to early Aptian age; a middle post-rift, transgressive unit of Aptian to Albian age; a late post-rift, terrestrial to marine unit of Albian to early Palaeocene age; and a post-up lift thermal subsidence unit of Palaeocene to Recent age. Much of the sediment appears to have been derived from volcanic and/or metamorphic terranes, probably located to the north or NW of the basin. As well as the volcanic material which occurs in the ground mass and as lithoclasts in many of the units, some volcaniclastic rocks and minor amounts of ashfall tufls are observed, particularly within the late syn-rift succession. [source] Eigenshape analysis of ammonoid suturesLETHAIA, Issue 2 2010TAKAO UBUKATA Ubukata, T., Tanabe, K., Shigeta, Y., Maeda, H. & Mapes, R.H. 2009: Eigenshape analysis of ammonoid sutures. Lethaia, Vol. 43, pp. 266,277. A morphometric method based on eigenshape analysis is proposed for characterizing the morphospace of widely varied ammonoid suture shapes. The analysis requires initially the placement of a suture line in an x,y coordinate system, with the ventral and umbilical extremes located on the x -axis. Series of x- and y -coordinates along the suture line are used as descriptors. The coordinate data are summarized into the two largest principal components using eigenshape analysis. A total of 115 species belonging to six ammonoid orders, spanning from the Devonian to the Cretaceous, was utilized in the present analysis. The analysis, using y -coordinate data, revealed differences in morphological variation in suture shape among taxa within the Mesozoic ammonitids: the Lytoceratina and Ammonitina were characterized by small negative values of the first eigenshape scores, whereas the Phylloceratina (the sister group of the Lytoceratina plus Ammonitina), as well as the Triassic ceratitids and Palaeozoic ammonoids, have a wide range of the first eigenshape scores. The pattern of data obtained from many different ammonoid species, as plotted on eigenshape axes in the morphospace constructed based on y -coordinate data, reveals a plesiomorphic aspect of suture shape in some phylloceratine species with respect to other ammonitids. ,Ammonoids, eigenshape analysis, morphometrics, suture line. [source] Soft-tissue imprints in fossil and Recent cephalopod septa and septum formationLETHAIA, Issue 4 2008CHRISTIAN KLUG Several soft-tissue imprints and attachment sites have been discovered on the inside of the shell wall and on the apertural side of the septum of various fossil and Recent ectocochleate cephalopods. In addition to the scars of the cephalic retractors, steinkerns of the body chambers of bactritoids and some ammonoids from the Moroccan and the German Emsian (Early Devonian) display various kinds of striations; some of these striations are restricted to the mural part of the septum, some start at the suture and terminate at the anterior limit of the annular elevation. Several of these features were also discovered in specimens of Mesozoic and Recent nautilids. These structures are here interpreted as imprints of muscle fibre bundles of the posterior and especially the septal mantle, blood vessels as well as the septal furrow. Most of these structures were not found in ammonoids younger than Middle Devonian. We suggest that newly formed, not yet mineralized (or only slightly), septa were more tightly stayed between the more numerous lobes and saddles in more strongly folded septa of more derived ammonoids and that the higher tension in these septa did not permit soft-parts to leave imprints on the organic preseptum. It is conceivable that this permitted more derived ammonoids to replace the chamber liquid faster by gas and consequently, new chambers could be used earlier than in other ectocochleate cephalopods, perhaps this process began even prior to mineralization. This would have allowed faster growth rates in derived ammonoids. [source] Histological structure of the cancellous bone layer in Bothriolepis canadensis (Antiarchi, Placodermi)LETHAIA, Issue 3 2005CAROLE BURROW The Placodermi are extinct basal gnathostomes which had extensive dermal and perichondral bone, but which lacked the endochondral bone which characterizes the more derived bony fishes. Thin sections of bone from a specimen of the antiarch placoderm Bothriolepis canadensis, from the Escuminac Formation (Frasnian, Upper Devonian), Québec, Canada, reveal that part of the cancellous layer in its dermal and endoskeletal bone formed from perichondral bone trabeculae growing around cartilage spheres. The resultant structure mimics that of osteichthyan endochondral bone. The layout and dimensions of this polygonal mosaic patterning of the bone trabeculae and flattened cartilage spheres resemble those of the prismatic layers of calcified cartilage in chondrichthyans. If the lack of endoskeletal bone in chondrichthyans is a derived character, then the structure identified in B. canadensis could represent a ,template' for the formation of prismatic calcified cartilage in the absence of bone. [source] A quantitative comparison of the ontogeny of two closely-related Upper Devonian phacopid trilobitesLETHAIA, Issue 2 2005CATHERINE CRÔNIER The best insight into the development of Devonian phacopids has been obtained from Trimerocephalus lelievrei Crônier & Feist, 1997, a Famennian phacopine from Morocco, where changes in size and shape have been quantified. In this study, a morphometric approach has been used: (1) to retrodeform and then establish patterns of morphological variation in a well preserved but tectonically deformed assemblage belonging to another phacopine species Weyerites ensae (Richter & Richter, 1926), a Famennian phacopine from Thuringia, and (2) to establish patterns of developmental and evolutionary changes within two closely related species: Weyerites ensae and Trimerocephalus lelievrei. The method of retrodeformation using a set of discrete points presumed to be homologous on all studied individuals, has demonstrated that the next analyses are possible on the retrodeformed material as compared to the undeformed material. Morphometric analysis based on outline analysis has permitted demonstration of progressive shape change in agreement with ontogenetic ordination and a comparison of changes in size and shape in Weyerites ensae. The main changes in shape appear to occur in the meraspid period, whereas increase in size takes place mainly in the holaspid period. This pattern, already reported for Trimerocephalus lelievrei, can be generalized for phacopine trilobites from the Late Devonian. Moreover, the comparison of the two ontogenetic trajectories has shown that most of the differences are related to ,structural' changes, probably linked to a relative pre- post-displacement. The results suggest that ecological adaptation may be studied by examining the changes in development that occur within species through time and space. [source] A trace fossil assemblage from fluvial Old Red deposits (Wood Bay Formation; Lower to Middle Devonian) of NW-Spitsbergen, SvalbardLETHAIA, Issue 2 2004MAX WISSHAK From the fluvial Old Red Sandstone (ORS) of the Lower to Middle Devonian Wood Bay Formation (NW-Spitsbergen), a diverse trace fossil assemblage, including two new ichnotaxa, is described: Svalbardichnus trilobus igen. n., isp. n. is interpreted as the three-lobed resting trace of an early phyllocarid crustacean (Rhinocarididae). Cruziana polaris isp. n. yields morphological details that point towards a trilobite origin. This occurence of presumably marine trace makers in a fluvial red bed sequence raises the question of whether we are dealing with marine ingressions that are not sedimentologically expressed, with homeomorphy, or with an adaptation of marine groups to non-marine environments. [source] A scratch circle origin for the medusoid fossil KullingiaLETHAIA, Issue 4 2002SÖREN JENSEN Kullingia is considered a key taxon in demonstrating the presence of terminal Proterozoic-early Cambrian chondrophorine hydrozoans. However, Kullingia concentrica from the Lower Cambrian of northern Sweden possesses several features that show that it is not a body fossil but that it was formed by current or wave-induced rotation of an anchored tubular organism, possibly a sabelliditid. A scratch circle interpretation applies also to several other reports of Lower Cambrian Kullingia, including Kullingia delicata from the Chapel Island Formation of Newfoundland. Given the considerable number of problematic fossils that have been interpreted as chondrophorines, it is difficult to put an age on the oldest fossil chondrophorines, but it may be as late as the Devonian. Overall, scratch circles appear to be rarely preserved. The occurrence of these scratch circles in Lower Paleozoic storm deposits is probably related to low levels of bioturbation that enhanced both the likelihood of formation and preservation of these structures. [source] | ||||||||||||||||||||||||||||