Middle Ordovician (Whiterockian-Chazyan) trilobites from the Sunblood Formation, District of Mackenzie

The Middle Ordovician Sunblood Formation in the South Nahanni River area, District of Mackenzie, comprises mainly limestones and dolostones of intertidal and shallow subtidal origin as indicated by the presence of desiccation polygons, fenestral fabric, and oncolites. The study of well preserved, silicified trilobites from low diversity, Bathyurus-dominated, Nearshore Biofacies faunas of Whiterockian and Chazyan age collected in six stratigraphic sections through the Sunblood Formation permits the recognition of three new Whiterockian zones, and two previously established Chazyan zones. The Bathyurus mackenziensis, Bathyurus sunbloodensis, and Bathyurus margareti zones (Whiterockian), together with the Bathyurus nevadensis and Bathyurus granu/osus zones (Chazyan) represent the Nearshore Biofacies components of a dual biostratigraphic scheme that considers both temporal and spatial distribution patterns, and are compositionally distinct from faunas in correlative strata around North America that represent other biofacies. Twenty-six species belonging to eighteen genera are described and illustrated. Ludvigsenella ellipsepyga is established as a new bathyurine genus, in addition to four new species of Bathyurus : Bathyurus mackenziensis, Bathyurus sunbloodensis, Bathyurus margareti and Bathyurus acanthopyga. Other genera present are: Basilicus, Isote/us, ///aenus, Bumastoides, Fail/eana, Phorocepha/a,Ceraurinella, Acanthoparypha, Xystocrania, Cydonocephalus, Ectenonotus, Pseudomera, Encrinuroides, Calyptaulax, Amphilichas and Hemiarges.

Investigating the Death of the Early Paleozoic Moyero River Geomagnetic Superchron: Middle Ordovician Paleomagnetism from Estonia

Flat-lying Early and Middle Ordovician limestones exposed on the North margin of Estonia provide key insights into the early Paleozoic biosphere and climatic history of the Baltic Platform, and potentially offer a site for calibrating the duration of the proposed Moyero River Reversed Superchron. Past paleomagnetic analyses on these rocks have been focused primarily on determining paleomagnetic pole positions and have been hampered by relatively weak remanent magnetizations. We therefore applied techniques of the Rock and Paleomagnetic Instrument Development (RAPID) consortium using thin-walled, low-noise quartz glass sample holders on an automatic system to enhance magnetostratigraphic resolution. Our results, based on over 300 oriented core samples spanning the stratigraphic interval from the Volkhov stage, up through the Lasnamägi stage, confirm previous work isolating a stable characteristic magnetization of reversed polarity, and furthermore confirm the presence of an interval of magnetically Reversed polarity spanning an interval of at least 15 million year duration. In addition, we recognize a magnetic overprint of presumed Normal polarity held in antiferromagnetic phases, of presumed Permian age, based on the apparent polar wander path given by (Plado et al., 2010).

Sedimentology and taphonomy of storm-generated shell beds from the Verulam formation (Ordovician), Lakefield and Gamebridge quarries, Southern Ontario, Canada /

The Verulam Formation (Middle Ordovician) at the Lakefield Quarry and Gamebridge Quarry, southern Ontario, is comprised of five main lithofacies. These include shoal deposits consisting of Lithofacies 1, winnowed crinoidal grainstones and, shelf deposits consisting of: Lithofacies 2, wackestones, packstones, grainstones, and rudstones; Lithofacies 3, laminated calcisiltites; Lithofacies 4, nodular wackestones and mudstones; and, Lithofacies 5, laminated mudstones and shales. The distribution of the lithofacies was influenced by variations in storm frequency and intensity during a relative sea level fall. Predominant convex-up attitudes of concavo-convex shells within shell beds suggest syndepositional reworking during storm events. The bimodal orientations of shell axes on the upper surfaces of the shell beds indicates deposition under wave-generated currents. The sedimentary features and shell orientations indicate that the shell beds were deposited during storm events and not by the gradual accumulation of shelly material. Cluster and principal component analysis of relative abundance data of the taxa in the shell beds, interbedded nodular wackestones and mudstones, and laminated mudstones and shales, indicates one biofacies comprised of three main assemblages: a strophomenid (Sowerbyelladominated) assemblage, a transitional mixed strophomenid-atrypid assemblage and an atrypid (Zygospira-dominatQd) assemblage. The occurrence of the strophomenid, the strophomenid-atrypid and atrypid assemblages were controlled by storm-driven allogenic taphonomic feedback.

Paragenetic history of the Ordovician Trenton Group carbonates, Southwestern Ontario

Geochemical examination of the rock matrix and cements from core material extracted from four oil wells within southwestern Ontario suggest various stages of diagenetic alteration and preservation of the Trenton Group carbonates. The geochemical compositions of Middle Ordovician (LMC) brachiopods reflect the physicochemical water conditions of the ambient depositional environment. The sediments appear to have been altered in the presence of mixed waters during burial in a relatively open diagenetic microenvironment. Conodont CAl determination suggests that the maturation levels of the Trenton Group carbonates are low and proceeded at temperatures of about 30 - 50°C within the shallow burial environment. The Trenton Group carbonates are characterized by two distinct stages of dolomitization which proceeded at elevated temperatures. Preexisting fracture patterns, and block faulting controlled the initial dolomitization of the precursor carbonate matrix. Dolomitization progressed In the presence of warm fluids (60 75°C) with physicochemical conditions characteristic of a progressively depleted basinal water. The matrix is mostly Idiotopic-S and Idiotopic-E dolomite, with Xenotopic-A dolomite dominating the matrix where fractures occur. The second stage of dolomitization involved hydrothermal basinal fluid(s) with temperatures of about 60 - 70°C. These are the postulated source for the saddle dolomite and blocky calcite cements occurring in pore space and fractures. Rock porosity was partly occluded by Idiotopic-E type dolomite. Late stage saddle dolomite, calcite, anhydrite, pyrite, marcasite and minor sphalerite and celestite cements effectively fill any remaining porosity within specific horizons. Based on cathode luminescence, precipitation of the different diagenetic phases probably proceeded in open diagenetic systems from chemically homogeneous fluids. Ultraviolet fluorescence of 11 the matrix and cements demonstrated that hydrocarbons were present during the earliest formation of saddle dolomite. Oxygen isotope values of -7.6 to -8.5 %0 (PDB), and carbon isotope values of - 0.5 and -3.0 %0 (PDB) from the latest stage dog-tooth calcite cement suggest that meteoric water was introduced into the system during their formation. This is estimated to have occurred at temperatures of about 25 - 40°C. Specific facies associations within the Trenton Group carbonates exhibit good hydrocarbon generating potential based on organic carbon preservation (1-3.5%). Thermal maturation and Lopatin burial-history evaluations suggest that hydrocarbons were generated within the Trenton Group carbonates some time after 300 Ma . Progressively depleted vanadium trends measured from hydrocarbon samples within southwestern Ontario suggests its potential use as a hydrocarbon migration indicator on local (within an oilfield) and on regional scales.

The Ordovician system in the Xainza region, north Tibet

Lithostratigraphy, biostratigraphy of the Ordovician Xainza area, northern division and correlation divided of approximates of the early as of Ordovician of Tetragraptus (Paratetragraptus)-Didymograptus (Corymbograptus) deflexus combination of Middle Ordovician Michelinoceras elongatum- combination with Sinoceras chinese and the Late Ordovician Michelinoceras huangnigang-Columenoceras priscum combination band. Early Ordovician strata author from 2000 to 2001 making Xainza County Sheet 1:250000 regional geological survey newly discovered, is the oldest strata of reliable fossils based in northern Tibet. Especially Tetragraptus (Paratetragraptus) approximatus discovery, not only to expand the distribution of it in our geographic area Early Ordovician strata the similar stratigraphic correlation international biological basis.

The paper deals with the classification and correlation of lithostratigraphy and biostratigraphy of the Ordovician System in the Xainza region, North Tibet. Based on fossils, the Ordovician System is divided into several biozones as follows: Tetragraptus (Paratetragraptus) approximatus Didymograptus (Corymbograptus) deflexus graptolite assemblage of Early Ordovician, The sediments of Early Ordovician is discovered recently by authors during 2000~2001 when making the geological surveying 1:250000 scale of Xainza county, Which has been the oldest stratum based on fossils up to now in northern Tibet. What is more, the discovery of Tetragraptus (Paratetragraptus) approximatus enlarges its geographical distribution in our nation as well as provides biology evidence to international correlation of the Ordovician in Xainza county.

Discovery of the Early Ordovician strata in Xianza County, Tibet and its significance

There is no any sediments contain fossils which formed earlier than Middle Ordovician in northern Tibet yet. It is very important whether have developed the Cambrian to Early Ordovician sedimentary strata. During geological mapping of Xainza County in 2000, Tetragraptus approximatus, the typical one of graptolite belts which cosmepolitically distributed in the Arenigian of Early Ordovician, was collected from the so-call Pre-Sinian Nianqingtanggula Group. So there is developped the Early Ordovician sediments and we have established Zakang Formation and Taduo Formation which perfected the Plaeozoic sequences in northern Tibet. According to these, we can realize tectonic control, palaeogeographrc pattern as well as palaeobiogeographic distribution of the Qinghai-Tibet Plateau in the early Paleozoic and also provided the materials to the cosmepolitical biostratigraphic contrast.

Palynostratigraphy of Ordovician strata, Canning Basin, Western Australia. Part One: acritarchs and prasinophytes

This paper is the initial part of a comprehensive bipartite monograph of palynomorphs (viz., acritarchs, prasinophyte phycomata, and chitinozoans) that are represented profusely in marine lower Palaeozoic strata of the Canning Basin, Western Australia. The prime aim is to establish a palynologically based zonal scheme for the Ordovician sequence as represented in five cored boreholes drilled through the Lower to Middle Ordovician strata of the central-northeastern Canning Basin. These strata embrace the Oepikodus communis through Phragmodus-Plectodina conodont zonal interval and comprise (in ascending order) the Willara, Goldwyer, and Nita formations, of inferred early Arenig to Llanvirn age. All three formations contain moderately diverse and variably preserved palynomorphs. The palynomorph taxa, detailed systematically in the current Part One of this monograph, comprise 66 species of acritarchs and six of prasinophytes. Of these, two species of prasinophytes and 11 of acritarchs are newly established: Cymatiosphaera meandrica and Pterospermella franciniae; Aremoricanium hyalinum, A. solaris, Baltisphaeridium tenuicomatum, Gorgonisphaeridium crebrum, Lophosphaeridium aequalium, L. aspersum, Micrhystridium infrequens, Pylantios hadrus, Sertulidium amplexum, Striatotheca indistincta, and Tribulidium globosum. Pylantios (typified by P. hadrus), Sertulidium (typified by S. amplexum), and Tribulidium (typified by T globosum); are defined as new acritarch genera. Three new combinations are instituted: Baltisphaeridium pugiatum (PLAYFORD & MARTIN 1984), Polygonium canningianum (COMRAZ & PENIGUEL 1972), and Sacculidium furtivum (PLAYFORD & MARTIN 1984); and Ammonidium macilentum PLAYFORD & MARTIN 1984 and Sacculidium furtivum (PLAYFORD & MARTIN 1984) are emended. An appreciable number of palynomorph species are not formally named owing to lack of sufficient or adequately preserved specimens; others are compared but not positively identified with previously instituted species. The ensuing Part Two of this study will complete the systematic-descriptive documentation, i.e., chitinozoans, and evaluate the Canning Basin palynoflora in terms of its chronological and stratigraphic-correlative significance.

Palynostratigraphy of Ordovician strata, Canning Basin, Western Australia. Part Two: chitinozoans and biostratigraphy

This second and concluding part of a comprehensive palynological study of the Lower to Middle Ordovician succession of the central-northeastern Canning Basin completes the systematic documentation of the palynomorphs, i.e., chitinozoans, and formulates a palynostratigraphic zonation scheme embracing all three constituent formations of this investigation, viz., the Willara, Goldwyer, and Nita formations. A total of 21 species of chitinozoans (five genera), detailed systematically herein, are identified. Although chitinozoan recovery per sample proved variable, the following species occur fairly persistently in the productive samples: Belonechitina micracantha, Conochitina subcylindrica, C. poumoti, C. langei, Calpichitina windjana, and Rhabdochitina magna. Five, stratigraphically successive acritarch/prasinophyte assemblage zones, ranging in age from early Arenig through late Llanvirn, are proposed as follows (ascending order): Athabascaella rossii Assemblage Zone (corresponding to the lower Willara Formation; and dated as early-mid Arenig); Comasphaeridium setaricum Assemblage Zone (upper Willara and lowermost Goldwyer; late Arenig-earliest Llanvirn); Sacculidium aduncum Assemblage Zone (lower Goldwyer; early Llanvirn); Aremorica-nium solaris Assemblage Zone (middle and lower upper Goldwyer; mid Llanvirn); and Dactylofusa striatogranulata Assemblage Zone (upper Goldwyer and lower Nita; late Llanvirn). Four chitinozoan assemblage zones, stratigraphically coinciding (within the limits of sampling) with the acritarch/prasinophyte zones, comprise (in ascending order): Lagenochitina combazi Assemblage Zone (equivalent to the A. rossii and L. heterorhabda Assemblage Zones); Conochitina langei Assemblage Zone; Conocbitina subcylindrica Assemblage Zone; and Belonecbitina micracantha Assemblage Zone. Chronostratigraphic assignments are based principally on associated conodont and graptolite faunas. Whereas the acritarch/prasinophyte zones bear scant similarities to those established globally elsewhere, the chitinozoan zones show significant affiliations with those known from Laurentia.

碳酸盐岩缝洞型储层地球物理响应特征及预测方法研究

Proven by the petroleum exploration activities, the karsts-fissure reservoir in carbonate rocks is significant to find out the large scale oil & gas field. They are made up of the four reservoir types: karsts-cave, karsts-crack, crack-cave and fracture-pore-cave. Each reservoir space and each reservoir bed has different features of reservoir heterogeneity and small scale of pore-crack-cave. The fracture-cave reservoir in carbonate rocks is characteristic by multi-types and long oiliness well. The reservoir shape is controlled by the irregular pore-crack-cave. The development level of fracture and karst-cave is the key element of hydrocarbon enriching, high productivity and stable production. However, most of Carbonate formation are buried deeply and the signal-ration-noise of seismic reflection are very low. It is reason why the fracture-cave reservoir are difficult to be predicted effectively. In terms of surveyed and studied lots of the former research outcome, The author applied the methods of synthetical reservoir geophysical prediction from two ways including macrosopic and microcomic technics in terms of the reservoir-cap condition, geophysics and geology feature and difficulty of prediction in carbonate rocks. It is guiden by the new ideas of stratigraphy, sedimentology, sedimentography, reservoir geology and karst geology. The geophysics technology is key technics. In aspects of macroscopic studies, starting off the three efficiencies of controlling the reservoir distribution including sedimental facies, karst and fracture, by means of comprehensive utilization of geology, geophysics, boring well and well log, the study of reservoir features and karst inside story are developed in terms of data of individual well and multiple well. Through establishing the carbonate deposition model, karstic model and fracture model, the macro-distribution laws of carbonatite are carried out by the study of coherence analysis, seismic reflection feature analysis and palaeotectonics analysis. In aspects of microcosmic studies, starting off analysis in reservoir geophysical response feature of fracture and karst-cave model according to guidance of the macroscopic geological model in carbonate reservoir, the methods of the carbonate reservoir prediction are developed by comprehensively utilization of seismic multi-attribution intersection analysis, seismic inversion restricted by log, seismic discontinuity analysis, seimic spectrum attenuation gradient, moniliform reflection feature analysis and multiparameter karst reservoir appraisement.Through application of carbonate reservoir synthetical geophysics prediction, the author r successfully develops the beneficial reservoir distribution province in Ordovician of Katake block 1in middle Tarim basin. The fracture-cave reservoir distributions are delineated. The prospect direction and favorable aims are demonstrated. There are a set of carbonate reservoir prediction methods in middle Tarim basin. It is the favorable basic technique in predicting reservoir of the Ordovician carbonate in middle Tarim. Proven by exploration drilling, the favorable region of moniliform reflection fracture and pore-cave and cave-fracture in lower-middle Ordovician are coincidence with the region of hydrocarbon show. It’s indicated that the reservoir prediction methods described in the study of Ordovician carbonate formation are feasible practicably.

Caratterizzazione geo-petrografica, petrologica e geochimica di rocce anatettiche del nord Sardegna

The High Grade Metamorphic Complex (HGMC) of Variscan basement of north Sardinia is characterized by the widespread of migmatites. This study is focused on two localities of NE Sardinia (Porto Ottiolu and Punta Sirenella) where ortho- and para-derivates migmatites outcrop. A geological and structural survey was carried out, leading to the realization of a geological schematic map of Punta Sirenella area. Several samples of different rocks were collected for petrographic, micro-structural minero-chemical and geochemical analyses. In the Porto Ottiolu area three main deformation phases have been identified; D1, characterized by tight folds with sub-horizontal axes, rarely preserved in paragneisses; D2, that produce a pervasive foliation oriented N100° 45°SW marked by biotite and sillimanite blastesis and locally transposed by shear zone oriented N170°; D3, late deformation phase caused symmetric folds with sub-horizontal axes with no axial plane schistosity. Leucosomes form pods and layers along S2 schistosity but also leucosomes along shear zones have been observed. In the Punta Sirenella area, three main deformation phases have been identified; D1, is manifested by the transposition of centimeter-sized leucosomes and is rarely observed in paragneisses were produce open folds with sub-vertical axes; D2, NW-SE oriented on whose XY plane three mineralogical lineation (quartz+plagioclase, fibrolite+quarz and muscovite) lie; D3, a ductile-brittle deformation phase that produce a mylonitc S3 foliation that locally become the most evident schistosity in the field oriented N140° steeply dipping toward NE. In both areas, leucosomes of sedimentary-derived migmatites are generally trondhjemitic pointing out for a H2O fluxed melting reaction, but also granitic leucosomes have been found, produced by muscovite dehydration melting. Leucosomes of migmatitic orthogneiss instead, have granitic compositions. Migmatization started early, during the compressional and crustal thickening (sin-D1, pre-D2) and was still active during exhumation stage. For each studied outcrop of migmatite pseudosections for the average mesosome composition have been calculated; these pseudosections have been used to model the P-T conditions of anatexis on the basis of the melt volume (%) of melt, Si/Al and Na/K molar ratios, modal content of garnet and Si content in metamorphic white mica. Further pseudosections have been calculated for the average composition of leucosomes in order to define the P-T conditions of the end of the crystallization through intersection of solidus curve and isopleths of Si content in white mica and/or XMg ratio in biotite. Thermodynamic modeling on ortho- and sedimentary-derived migmatites of Punta Sirenella yield P-T conditions of 1.1-1.3 GPa - 670-740°C for migmatitic event and 0.75-0.90 GPa - 660-730°C for the end of crystallization. These conditions are fit well with previous studies on adjacent rocks. Modeling of Porto Ottiolu ortho- and sedimentary-derived migmatites yield P-T conditions of 0.85-1.05 GPa - 690-730°C for migmatitic event and 0.35-0.55 GPa - 630-690°C strongly affected by re-equilibration during exhumation, expecially for crystallization conditions. Geochemical analyses of samples belonging to Porto Ottiolu and Punta Sirenella orthogneisses show a strong link with those of other orthogneisses outcropping in NE Sardinia (for instance, Lode-Mamone and Golfo Aranci) that are considered the intrusive counterparts of middle-Ordovician metavolcanics rocks outcropping in the Nappe Zone. Thus, the studied ortogneiss bodies, even lacking radiometric data, can be considered as belonging to the same magmatic cycle.

Geology of the Gander Group, Gander River Ultramafic Belt and Davidsville Group in the Jonathan's Pond - Weir's Pond Area, northeast Newfoundland /

The study area is situated in NE Newfoundland between Gander Lake and the north coast and on the boundary between the Gander and Botwood tectonostratigraphic zones (Williams et al., 1974). The area is underlain by three NE trending units; the Gander Group, the Gander River Ultramafic Belt (the GRUB) and the Davidsville Group. The easternmost Gander Group consists of a thick, psammitic unit composed predominantly of psammitic schist and a thinner, mixed unit of semipelitic and pelitic schist with minor psammite. The mixed unit may stratigraphically overlie the psammitic unit or be a lateral facies equivalent of the latter. No fossils have been recovered from the Gander Group. The GRUB is a terrain of mafic and ultramafic plutonic rocks with minor pillow lava and plagiogranite. It is interpreted to be a dismembered ophiolite in thrust contact with the Gander Group. The westernmost Davidsville Group consists of a basal conglomerate, believed deposited unconformably upon the GRUB from which it was derived, and an upper unit of greywacke and slate, mostly of turbidite origin, with minor limestone and calcareous sandstone. The limestone, which lies near the base of the unit, contains Upper Llanvirn to Lower Llandeilo fossils. The Gander and Davidsville Groups display distinctly different sedimentological , structural and metamorphic histories. The Gander Group consists of quartz-rich, relatively mature sediment. It has suffered three pre-Llanvirn deformations, of which the main deformation, Dp produced a major, NE-N-facing recumbent anticline in the southern part of the study area. Middle greenschist conditions existed from D^ to D- with growth of metamorphic minerals during each dynamic and static phase. In contrast, the mineralogically immature Davidsville Group sediment contains abundant mafic and ultramafic detritus which is absent from the Gander Group. The Davidsville Group displays the effects of a single penetrative deformation with localized D_ and D_ features, all of which can be shown to postdate D_ in the Gander Group. Rotation of the flat Gander S- into a subvertical orientation near the contact with the GRUB and the Davidsville Group is believed to be a Davidsville D^ feature. Regional metamorphism in the Davidsville Group is lower greenschist with a single growth phase, MS . These sedimentological, structural and metamorphic differences between the Gander and Davidsville Groups persist even where the GRUB is absent and the two units are in contact, indicating that the tectonic histories of the Gander and Davidsville Groups are distinctly different. Structural features in the GRUB, locally the result of multiple deformations, may be the result of Gander and/or Davidsville deformations. Metamorphism is in the greenschist facies. Geochemical analyses of the pillow lava suggest that these rocks were formed in a back-arc basin. Mafic intrusives in the Gander Group appear to be the result of magraatism separate from that producing the pillow lava. The Gander Group is interpreted to be a continental rise prism deposited on the eastern margin of the Late Precambrian-Lower Paleozoic lapetus Ocean. The GRUB, oceanic crust possibly formed in a marginal basin to the west, is believed to have been thrust eastward over the Gander Group, deforming the latter, during the pre-Llanvirnian, possibly Precambrian, Ganderian Orogeny. The Middle Ordovician and younger Davidsville Group was derived from, and deposited unconformably on, this deformed terrain. Deformation of the Davidsville Group occurred during the Middle Devonian Acadian Orogeny.

Structural, stratigraphic and geochemical studies of the Horwood Peninsula - Gander Bay Area, Northeast Newfoundland /

The Horwood Peninsula - Gander Bay area is located at NE Newfoundland in the Botwood Zone (Williams et a1., 1974) or in the Dunnage Zone (Williams, 1979) of the Central Mobile Belt of the Newfoundland Appalachians. The area is underlain by Middle Ordovician to possible Lower Silurian rocks of the Davidsville and Indian Islands Groups, respectively. Three conformable formations named informally : the Mafic Volcanic Formation, the Greywacke and Siltstone Formation and the Black Slate Formation, have been recognized in the Davidsville Group. The Greywacke and the Black Slate Formations pass locally into a Melange Formation. From consideration of regional structure and abundant locally-derived mafic volcanic olisto- 1iths in the melange, it is considered to have originated by gravity sliding rather than thrusting. Four formations have been recognized in the Indian Islands Group. They mainly contain silty slate and phyllite, grey cherty siltstone, green to red micaceous siltstone and limestone horizons. Repetition of lithological units by F1 folding are well-demonstrated in one of formations in this Group. The major structure in this Group on the Horwood Peninsula is interpreted to be a synclinal complex. The lithology of this Group is different from the Botwood Group to the west and is probably Late Ordovician and/or Early Silurian in age. The effects of soft-sediment deformation can be seen from the lower part of the Davidsville Group to the middle part of the Indian Islands Group indicating continuous and/or episodic slumping and sliding activities throughout the whole area. However, no siginificant depOSitional and tectonic break that could be assigned to the Taconian Orogeny has been recognized in this study. Three periods of tectonic deformation were produced by the Acadian Orogeny. Double boudinage in thin dikes indicates a southeast-northwest sub-horizontal compression and main northeast-southwest sub-horizontal extension during the D1 deformation. A penetrative, axial planar slaty cleavage (Sl) and tight to isocJ.ina1 F1 folds are products of this deformation. The D2 and D3 deformations formed S2 and S3 fabrics associated with crenulations and kink bands which are well-shown in the slates and phyllites of the Indian Islands Group. The D2 and D3 deformations are the products of vertical and northeast-southwest horizontal shortening respectively. The inferred fault between the Ordovician slates (Davidsville Group) and the siltstones (Indian Islands Group) suggested by Williams (1963, 1964b, 1972, 1978) is absent. Formations can be followed without displacement across this inferred fault. Chemically, the pillow lavas, mafic agglomerates, tuff beds and diabase dikes are subdivided into three rock suites : (a) basaltic komatiite (Beaver Cove Assemblage), (b) tholeiitic basalt (diabase dikes), (c) alkaline basalt (Shoal Bay Assemblage). The high Ti02 , MgO, Ni contents and bimodal characteristic of the basaltic komatiite in the area are comparable to the Svartenhuk Peninsula at Baffin Bay and are interpreted to be the result of an abortive volcano-tectonic rift-zone in a rear-arc basin. Modal and chemical analyses of greywackes and siltstones show the trend of maturity of these rocks increasing from poorly sorted Ordovician greywackes to fairly well-sorted Silurian siltstones. Rock fragments in greywackes indicate source areas consisting of plagiogranite, low grade metamorphic rocks and ultramafic rocks. Rare sedimentary structures in both Groups indicate a southeasterly provenance. Trace element analyses of greywackes also reveal a possible island-arc affinity.

Biogeochemistry of Paleozoic brachiopods from New York State and Ontario

A comprehensive elemental, isotopic and microstructural analyses was undertaken of brachiopod calcites from the Hamilton Group (Middle Devonian), Clinton Group (Middle Silurian) and Middle to Upper Ordovician strata of Ontario and New York State. The majority of specimens were microstructurally and chemically preserved in a pristine state, although a number of specimens show some degree of post-depositional alteration. Brachiopod calcites from the Hamilton and Clinton Groups were altered by marine derived waters whereas Trenton Group (Middle Ordovician) brachiopods altered in meteorically derived fluids. Analysis of the elemental and isotopic compositions of pristine Hamilton Group brachiopods indicates there are several chemical relationships inherent to brachiopod calcite. Taxonomic differentiation of Mg, Sr and Na contents was evident in three co-occuring species from the Hamilton Group. Mean Mg contents of pristine brachiopods were respectively Athyris spiriferoides (1309ppm), Mucrospirifer mucronatus (1035ppm) and Mediospirifer audacula (789ppm). Similarly, taxonomic differentiation of shell calcite compositions was observed in co-occuring brachiopods from the Clinton Group (Middle Silurian) and the Trenton Group (Middle Ordovician). The taxonomic control of elemental regulation into shell calcite is probably related to the slightly different physiological systems and secretory mechanisms. A relationship was observed in Hamilton Group species between the depth of respective brachiopod communities and their Mg, Sr and Na contents. These elements were depleted in the shell calcites of deeper brachiopods compared to their counterparts in shallower reaches. Apparently shell calcite elemental composition is related to environmental conditions of the depositional setting, which may have controlled the secretory regime, mineral morphology of shell calcite and precipitation rates of each species. Despite the change in Mg, Sr and Na contents between beds and formations in response to environmental conditions, the taxonomic differentiation of shell calcite composition is maintained. Thus, it may be possible to predict relative depth changes in paleoenvironmental reconstructions using brachiopod calcite. This relationship of brachiopod chemistry to depth was also tested within a transgressiveregressive (T-R) cycle in the Rochester Shale Formation (Middle Silurian). Decreasing Mg, Sr and Na contents were observed in the transition from the shallow carbonates of the Irondequoit Formation to the deeper shales of the lowest 2 m of Rochester Shale. However, no isotopic and elemental trends were observed within the entire T-R cycle which suggests that either the water conditions did not change significantly or that the cycle is illusory. A similar relationship was observed between the Fe and Mn chemistries of shell calcite and redox/paleo-oxygen conditions. Hamilton Group brachiopods analysed from deeper areas of the shelf are enriched in Mn and Fe relative to those from shallow zones. The presence of black shales and dysaerobic faunas, during deposition of the Hamilton Group, suggests that the waters of the northern Appalachian Basin were stratified. The deeper brachiopods were marginally positioned above an oxycline and their shell calcites reflect periodic incursions of oxygen depleted water. Furthermore, analysis of Dalmanella from the black shales of the Collingwood Shale (Upper Ordovician) in comparison to those from the carbonates of the Verulam Formation (Middle Ordovician) confirm the relationship of Fe and Mn contents to periodic but not permanent incursions of low oxygen waters. The isotopic compositions of brachiopod calcite found in Hamilton Group (813C; +2.5% 0 to +5.5% 0; 8180 -2.50/00 to -4.00/00) and Clinton Group (813C; +4.00/00 to +6.0; 8180; -1.8% 0 to -3.60/ 00) are heavier than previously reported. Uncorrected paleotemperatures (assuming normal salinity, 0% 0 SMOW and no fractionation effects) derived from these isotopic values suggest that the Clinton sea temperature (Middle Silurian) ranged from 18°C to 28°C and Hamilton seas (Middle Devonian) ranged between 24°C and 29°C. In addition, the isotopic variation of brachiopod shell calcite is significant and is related to environmental conditions. Within a single time-correlative shell bed (the Demissa Bed; Hamilton Group) a positive isotopic shift of 2-2.5% 0 in 013C compositions and a positive shift of 1.0-1.50/00 in 0180 composition of shell calcite is observed, corresponding with a deepening of brachiopod habitats toward the axis of the Appalachian Basin. Moroever, a faunal succession from deeper Ambocoelia dominated brachiopod association to a shallow Tropidoleptus dominated assocation is reflected by isotopic shifts of 1.0-1.50/00. Although, other studies have emphasized the significance of ±20/oo shifts in brachiopod isotopic compositions, the recognition of isotopic variability in brachiopod calcite within single beds and within depositional settings such as the Appalachian Basin has important implications for the interpretation of secular isotopic trends. A significant proportion of the variation observed isotopic distribution during the Paleozoic is related to environmental conditions within the depositional setting.