Correlation of the lower devonian rocks of australasia

Alkali basaltic rocks from the Southern Highlands, N.S.W., contain oxide phases of both high and low pressure origin. The two phases are readily distinguished using chemical and textural criteria.

Chemical data for low‐pressure Fe‐Ti oxides indicate that oxygen fugacities of the host lavas range from 10‐^12.8 to 10‐⁸ atm at 950° to 1110°C. In most cases, the oxygen fugacities of the individual lava flows appear to be principally a function of temperature and intrinsic chemical equilibria existing at the time of formation of the basaltic liquid. However, some relatively differentiated flows shows a high degree of oxidation due to volatile enrichment with fractionation. Rare glassy flows show dendritic crystallization of Fe‐Ti oxides. Most flows in which abundant olivine was the first phase to be precipitated also contain Cr‐rich spinels associated, and apparently coeval, with the earliest‐crystallizing olivine.     

Correlation of the upper devonian rocks of Australia

A heavy mineral concentrate from the undeformed Mundi Mundi Granite N of Broken Hill yielded very few zircons. U‐Th‐Pb measurements on microgram fractions of those extracted showed no indication of the stock's true 1500–1600 Ma intrusive event but revealed something inherited and of an age probably greater than 2 Ga. These zircons, either survivors of those inherited from the magma source or accidental inclusions from the wall rocks, may either represent sedimentary accumulations in the lower Willyama Supergroup with an older craton source i.e. provenance, or indicate the presence of a pre‐Willyama Supergroup basement. Considerable loss of Pb from the zircons is deduced to have occurred at (1) the time of granite intrusion, (2) in the lower Palaeozoic, and, (3) in the case of ²⁰⁸Pb, probably right up to recent time.     

High-temperature carbidization of carboniferous rocks

Processes of thermal metamorphism of carboniferous rocks have been studied experimentally. The conditions of high-temperature interaction of shungite carbon with components of the contained rocks, leading to formation of carbide compounds, have been determined. The results of this investigation contribute to the works on searching for new raw material for prospective material production.     

Fluvial sedimentation in the lower carboniferous of Clew Bay,County Mayo,Ireland

A succession of about 300 m of fluvial sediments from the Lower Carboniferous of northwest Ireland is described and interpreted. A lower, mainly red, formation contains fluvial channel deposits dominated by flat laminated sandstone. These are separated by interbedded sandstones and mudrocks with local caliche horizons and abundant mudcracks interpreted as levee and flood basin deposits. An upper, mainly non-red, formation contains fluvial channel deposits with common trough cross-stratification and epsilon cross-stratification also separated by interbedded sandstones and mudrocks. Evidence of desiccation is less common in the uppermost beds which pass transitionally upwards into marine sediments.The change in fluvial channel style is interpreted as due to increasing sinuosity and permanence of flow which may have been partly temporally and partly spatially controlled. The predominance of coarse sediments is thought to be largely controlled by limited subsidence. The Lower Carboniferous transgression was the major overall control of alluviation.     

Stratigraphy and sedimentology of lower carboniferous (Dinantian) boreholes from West Co. Meath,Ireland

The 2-km deep Athboy Borehole (1439/2) together with the lower part of boreholes EP30 and N915 form a standard type section for strata of Dinantian (Courceyan to Asbian) age in west Co. Meath. Above a thin basal red-bed siliciclastic sequence, the marine Courceyan shelf succession is almost 600 m thick. It comprises the Liscartan, Meath, and Moathill Formations of the Navan Group and the Slane Castle Formation of the succeeding Boyne Group. The shallow-water limestones include micrites, oolites, and sandy bioclastic packstones and grainstones with subordinate skeletal wackestones and shales. Lateral facies changes from north to south in the Navan area suggest deepening across a shelf towards a depocentre further to the south around Trim. The deeper-water Waulsortian Limestones of late Courceyan to Chadian age (Feltrim Formation, ca. 213 m thick) form a series of five sheet-like mudbanks, interbedded with generally thin units of nodular crinoidal limestones and shales. The mudbanks are formed of bryozoan-rich peloidal wackestones and lime-mudstones with phase C and D components. Rare soft-sediment breccias occur at the bottom and top of banks. The succeeding Fingal Group commences with a thin interval (3–20 m) of black shales, laminated packstones, and micritic limestones of Chadian age, the Tober Colleen Formation. This is followed by the Lucan Formation (Chadian to Asbian) predominantly of laminated and graded calciturbidites, laminated sandstones, cherts, and black shales, which is over 1300 m thick. Ten sedimentary units have been informally defined, based on lithofacies and facies associations. The oldest unit, the Tara Member, is characterized by proximal debris-flow breccia deposits and nodular mudstones. A thick bioturbated micrite and shale unit (Ardmulchan Member) in the middle of the formation is overlain directly by a coarse oolitic and crinoidal grainstone unit (Beauparc Member). Near the top of the formation is a distinctive unit of coarse-grained laminated sandstones and shales (Athboy Member). The highest rocks in the Borehole are clean thickly-bedded limestones of the Asbian Naul Formation (>90 m thick). The youngest Dinantian strata in the area, the Brigantian Loughshinny Formation, marks a return to shale-dominant basin sedimentation. The significance of this work lies in the fact that the Athboy borehole is the longest continuously cored borehole in the Carboniferous of Ireland and provides a continuous sedimentary and biostratigraphic record for the northern part of the Dublin Basin. Foraminiferal biozones (Cf2–Cf6) have been recognized in this and in borehole N915, and Stage boundaries identified, which can be applied throughout the Basin. The sedimentary record for the Lucan Formation indicates four tectonic pulses during the Viséan, in the late Chadian/early Arundian, mid-Arundian, Holkerian, and late Holkerian/early Asbian.     

The lower carboniferous (dinantian) of the Swords area: Sedimentation and tectonics in the Dublin Basin,Ireland

The litho- and biostratigraphy of the Lower Dinantian succession in a deeper part of the Dublin Basin is described. The sub-Waulsortian Malahide Limestone Formation (emended) is described fully for the first time, and has proved to be very much thicker than was previously suspected, in excess of 1200 m. Succeeding the ‘Lower Limestone Shale’ unit, which is transitional from the underlying Old Red Sandstone facies, the following six new members are recognized: Turvey Micrite Member, Swords Argillaceous Bioclastic Member, St. Margaret's Banded Member, Huntstown Laminated Member, Dunsoghly Massive Crinoidal Member and Barberstown Nodular Member (top). The Malahide Limestone Formation is overlain by ‘Waulsortian’ limestones of the Feltrim Limestone Formation (new name) which form overlapping and isolated mudmounds with complex relationships with their enclosing non-mound facies. Though very much thicker, the Courceyan succession is comparable with that elsewhere on the south side of the Basin, and is part of the Kildare Province (Strogen and Somerville 1984). Isopach maps for the region show that this province and the North Midlands are separated by the deepest part of the Dublin Basin, named the ‘East Midlands Depocentre’, in which a shale-dominant facies is present. The top of the ‘Waulsortian’ is of early Chadian age. Formations younger than this are dominated by basinal calcareous shales (Tober Colleen Formation) and by storm deposits and calciturbidites with appreciable terrigenous input from the east (Rush Formation). The Courceyan main shelf conodont biozones are also greatly thickened in this area. The Pseudopolygnathus multistriatus Biozone (> 300 m thick) is succeeded by a very thick (> 900 m) Polygnathus mehli Biozone. The base of the Chadian is considered to occur below the top of the Feltrim Limestone Formation and, although equivocal, may be diagnosed in the Dublin Basin by the first appearance of the problematic microfossil Sphaerinvia piai and a primitive form of the calcareous alga Koninckopora. In the late Courceyan, the Swords area was part of a gently sloping shelf extending northwards into the basin. During deposition of the Feltrim Limestone Formation there was major deepening and there is evidence of initial break up of the Dublin Basin by faulting into separate blocks. By Chadian time the Basin was definitely subsiding by fault displacements and basinal limestones contain shallow water faunas and littoral sand and pebbles derived by turbidite flows from the margins of the higher blocks. The early subsidence was apparently by pure flexure, but in the Viséan the Dublin Basin was fault-controlled, differing from the adjacent Shannon Basin in having both margins strongly faulted.     

Amphibole and chlorite in mafic and ultramafic rocks in the lower crust and upper mantle

Stabilities of amphibole and chlorite in mafic and ultramafic compositions have been considered in the model system CaO+MgO+Al₂O₃+SiO₂+H₂O. From topological arguments two petrogenetic grids have been constructed. Although available experimental data in CMASH are compatible with the grid in which amphibole reacts out before chlorite in model ultramafic compositions for the pressure range 6 to 15 kbar, naturally observed mineral assemblages and some experimental data in more complex systems favour the other grid in which chlorite reacts out before amphibole at all pressures. This discrepancy between natural and model systems is due to differential movement of the dehydration equilibria of the two hydrates reflecting the variation of activity of H₂O or of components other than CMASH.     

The devonian and carboniferous volcanism of the peloritan mountains (sicily) and the evolution of palaeozoic basins in the calabrian-peloritan arc

Volcanic rocks from three Palaeozoic low-grade metamorphic sequences of different age from the Peloritan Mountains, Sicily, have been analysed for major and trace elements. On the basis of the relative abundances of certain comparatively immobile elements (especially Zr, Ti, Nb, and Y) the petrogenetic affinities of the volcanic rocks in each area have been established. The Fiumara Fitalia sequence contains Lower Devonian within-plate alkaline basalts, the Ogliastrello sequence contains Upper Devonian continental within-plate calc-alkaline basalts and the Randazzo-Floresta road sequence contains Lower Carboniferous calc-alkaline basalts probably of island arc affinity. When account is taken of their stratigraphic positions, geochemical characteristics of the volcanic rocks indicate Devonian extensional conditions and Lower Carboniferous compressional conditions. Evidence for Lower Devonian extension is present in several circum-Mediterranean basins (i.e. Calabria, Sardinia, Carnic Alps). In the Peloritan Mountains, as well as in Calabria and Sardinia, extensional conditions were already present in the Cambro-Ordovician. The compression in the Calabrian-Peloritan Arc was probably related to a period of subduction during the Hercynian orogeny and resulted in the closure of the basins in the Carboniferous.     

Lower carboniferous (Dinantian) stratigraphy and structure in the Kingscourt Outlier,Ireland

Logging of 55 recent boreholes, together with remapping, has resulted in a fundamental reassessment of the stratigraphy and sedimentology of the Dinantian Kingscourt Outlier. Despite the present isolated position of the outlier within the Longford-Down Massif, the Kingscourt rocks are an integral part of the Dublin Basin succession. The newly defined Ardagh Platform marks the most northerly limit to basinal sedimentation in the Dinantian Dublin Basin. The Courceyan is a typical but thinner, north Dublin Basin succession with two new formal units: the Rockfield Sandstone Member and the Kilbride Formation. The latter, a coarse-grained, well washed limestone of latest Courceyan to early Chadian (late Tournaisian) age is the shallow water equivalent of the Feltrim Formation (Waulsortian facies), which is absent in the outlier. The Courceyan interval in the north of the outlier is markedly attenuated. In the succeeding Chadian-Brigantian interval basinal facies predominate in the south, but on the Ardagh Platform an almost complete coeval Viséan shallow water sequence is found. A new platform unit (Deer Park Formation) of latest Asbian to Brigantian age is defined in the Ardagh area. The Dee Member (Chadian) is newly defined for the lower part of the basinal Tober Colleen Formation and the Altmush Shale Member is formally defined for the upper part of the Loughshinny Formation. Two major structures dominate the Kingscourt Outlier: the NE-SW trending Moynalty Syncline in the south and the N-S trending Kingscourt Fault. Both are Hercynian structures, but probably represent reactivated Caledonide basement-controlled structures. Dinantian syn-depositional faulting is indicated in both the Courceyan (‘Kingscourt Sag’) and Chadian-Asbian. The latter period of faulting in the Ardagh area separates platform facies in the north from basinal facies to the south. In the late Asbian, platform facies with carbonate build-ups prograded south into the basin as far south as Nobber, but in the latest Asbian to Brigantian, basinal facies extended northwards over the collapsed platform margin.     

Stratigraphy of upper Viséan carbonate platform rocks in the Carlow area,southeast Ireland

The stratigraphy of the upper Viséan (Asbian to Brigantian) carbonate succession in southeast Ireland is revised on the basis of seven quarry and two borehole sections. Six lithological units have been distinguished, two units (units 1 and 2) in the upper Asbian Ballyadams Formation, and four units (units 4 to 6) in the Brigantian Clogrenan Formation (both formations are dated precisely using foraminiferans, calcareous algae and rugose corals). The boundary between the Ballyadams and Clogrenan formations is redefined 19 m below the horizon proposed by the Geological Survey of Ireland, and thus, lithological characteristics of both formations are redescribed. The upper part of the Ballyadams Formation is characterized by well‐developed large‐scale cyclicity, with common subaerial exposure surfaces. Fine‐ to medium‐grained thin‐bedded limestones with thin shales occur in the lower part of cycles, passing up into medium‐grained pale grey massive limestones in the upper part. The Clogrenan Formation is composed mainly of medium‐ to coarse‐grained thick limestone beds with variable presence of shales; but no large‐scale cyclicity. There is a decrease in the number of subaerial exposure surfaces towards the top of the formation and common chert nodules; macrofauna occurs mostly concentrated in bands. The six units recognized in the Carlow area are comparable with other units described for the same time interval (Asbian–Brigantian) from south and southwest Ireland, demonstrating the existence of a stable platform for most parts of southern Ireland, controlled principally by glacioeustatics. Copyright © 2004 John Wiley & Sons, Ltd.     

Facies and faunal changes in the Ludlovian rocks of Aymestrey,Herefordshire

The Aymestrey area displays changes in facies, faunas and thicknesses which can be related to its position on the shelf edge during later Silurian times. The Wenlock Limestone becomes an alternation of limestones and mudstones. The Lower and Middle Elton Beds, however, are substantially similar to their development at Ludlow. The Upper Elton Beds and the Bringewood Beds thin westwards within the area, probably due to non-deposition or erosion on a ridge at the hinge between shelf and basin. The most striking change is the rapid westward passage of the Aymestry Limestone facies of the Upper Bringewood Beds into siltstones, which are considered to be shallow-water deposits and not basinal. The Leintwardine Beds exhibit a westward thickening, and slumping is developed in the Lower Leintwardine Beds; the faunas relate more to the basin facies than to the shelf. The Whitcliffe Beds thicken markedly westwards but retain their shallow-water characteristics.     

Thermal maturity of the lower carboniferous Horton group, Nova Scotia

The Thermal Alteration Index (TAI) obtained from spore colouration is a useful maturity indicator that may be obtained from palynological preparations. Thermal maturity is an important parameter in determining the hydrocarbon potential of the Lower Carboniferous lacustrine and fluviatile sediments of the Horton Group, and coeval rocks, of Nova Scotia. Samples studied from fifty-two separate localities indicate a wide range in thermal maturity from low (TAI 2 to 3) to high (TAI 4 to 5?). Variation in depth of burial was probably the main factor responsible for the regional differences in thermal maturity. The thickness of Horton sedimentation varied considerably in a series of half grabens, as did the overburden of post-Tournaisian Lower Carboniferous, Upper Carboniferous, Permian and possibly Triassic rocks.The organic matter in most samples is composed of exinous (Type II) and woody and coaly material (Types III and IV). Locally in a few localities amorphous algal material (Type I) consisting of Botryococcus sp. is common. The composition of the organic matter and the thermal maturity data suggest that in most of the study area rocks of the Horton Group are in the dry gas generation zone, although in some areas oil generation may have taken place; in a few localities where the thermal maturity is high the organic matter has been altered beyond the dry gas preservation limit.     

Some geochemical aspects of sedimentary rocks in proximity of coals, sydney coalfield (upper carboniferous), cape breton island, nova scotia, canada

Channel samples of roof and seat rocks (lutites, siltstone)) of 10 successional coals, in addition to red mudstone and calcareous siltstones, have been collected from the Sydney Coalfield, Nova Scotia. The channel samples are confined to within 150 cm above the top of coals, and to within 20 cm below the bottom of coals. Whole-rock and trace-elemental analyses are reported: wt. % of oxides of Si, Al, total Fe, Ca, Mg, Na, K, T1, Mn; and ppm's for Cu, Ni, Pb, Zn, Cr, Co, Ga, V, As, U, and Th, respectively. Th/U ratios, organic carbon and carbonate carbon of selected roof rock samples are also reported.The comparatively small stratugraphic mean variations of Na₂/K₂O and Na₂O/Al₂O₃ are open to interpretation but may indicate either a common sedimentary source, or a similar diagenetic history during basin development. Assumed is that the oxide ratios originated from detrital feldspars and clays. The probability model for uranium is Pearson's Type VII curve. The relationship between uranium (thorium) and (assumed) organic calcite in selected calcareous siltstones is examined. Stratigraphic variation of the geochemistry is assumed to be cycle-controlled, excepting probably As, V, and Cu,which under the stated conditions are amenable to mathematical modeling (of sedimentary cycles).     

Facies relationships in the Upper Devonian-Lower Carboniferous of southwest Ireland and adjacent regions

In southwest Ireland 2,500 m of Upper Famennian to basal Namurian marine sandstones and mudstones, the Cork Beds, overlie rocks of Old Red Sandstone facies. Coastal exposures of the Cork Beds are interpreted as showing gradual upward change from alluvial strata, through thick subtidal and shelf sediments to pyritic muds. A review of recent palaeontological evidence shows that the thick shallow marine part of the Cork Beds is older than the major development of lime-stones north of the Cork Harbour—Kenmare Une, whose equivalents to the south are in the condensed basinal sediments. The Lower Carboniferous portion of the Cork Facies is shown to be thicker in South Cork than in West Cork. In Lower Carboniferous times a positive area–the Glandore High–separated two sub-basins with different depositional histories. Six palaeogeographic maps are used to demonstrate the progressive shift of facies belts as Lower Carboniferous marine transgression progressed. Finally, brief comparison is made with rocks of the same age in southwest England.     

Transition from basin-plain to shelf deposits in the carboniferous flysch of Southern Morocco

In the Jebilet Palaeozoic inlier, 20 km north of Marrakech, there are extensive exposures of Carboniferous flysch deposits. Although there are some structural complications due to over-riding nappes with associated chaotic breccias, one clearly unbroken succession from basin-plain turbidites to shallow-marine deposits can be examined. The succession is more than 2 km thick and is dated as Upper Viscan in the uppermost part.The lowermost unit of B- and C-based turbidites shows no sequential organisation and is interpreted as a typical basin-plain association. Above this are similar turbidites arranged in thickening-upward sequences that may represent outer-fan or base-of-slope deposits. Succeeding these are thin-bedded turbidites with interbedded units formed by mass movement that represent a slope deposit. The overlying lenticular-bedded facies resembles previously described overflow deposits of submarine-fan channels, but is here interpreted as comprising storm-generated deposits on the outer shelf/upper slope. These deposits are genetically linked with the overlying parallel-laminated sandstones with irregular-rippled tops for which a storm-surge origin is suggested. The upper part of the succession shows cross-bedded, oolitic, bioclastic, sandy limestones with bipolar current structures sandwiched between low-energy siltstones containing thin-graded silt/sand beds. These are collectively interpreted as shelf deposits that formed under different depths due to transgressive-regressive events.The sequence differs from many described in the literature in that there is an absence of most submarine-fan facies. Locally a NNE-SSW basin strike is proposed with a basin margin to the ESE, but there is at present little control on regional palaeogeography.     

西天山伊犁地区石炭纪火山岩地球化学特征及构造环境

伊犁板块南北缘广泛发育石炭纪火山岩.其中阿希、巩乃斯和恰西石炭纪火山岩主要由玄武岩、安山玄武岩、玄武粗安岩、粗安岩和粗面岩组成,为基性-中性-酸性连续岩系,以中基性岩为主;它们多为钙碱性岩;轻稀土较重稀土元素富集,富集大离子亲石元素Rb,Ba,Th,U,K,相对亏损高场强元素Nb,Ta,Ti,具有大陆边缘火山岛弧火山岩亲缘性.其可能形成于准噶尔洋向南俯冲于伊犁板块之下的大陆边缘岛弧环境,伊犁板块南缘火山岩也有可能产出于南天山洋向伊犁-中天山板块之下俯冲的岛弧环境.     

Site selectivity of a lower carboniferous boring organism infesting a crinoid

The position of a boring in a cup of the disparid crinoid Synbathocrinus conicus Phillips from Clitheroe, England, suggests various inferences concerning the ecology of the pit-forming organism. The crinoid cup shows a growth deformity, indicating it must have been alive when infested. The boring is at a triple suture between the E and A ray radials and the EA interray basal, presumably one of five equally weak points on the cup. This site is well removed from the anus and would have been an ideal point of attachment for a filter feeding organism, being well elevated, upcurrent and protected.