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.     

Lower Carboniferous (Dinantian) stratigraphy and structure of the Walterstown-Kentstown area,Co. Meath,Ireland

Stratigraphic units are defined and described for the Lower Carboniferous succession in the Walterstown-Kentstown area of Co. Meath, Ireland. A complete (unexposed) Courceyan succession from the terrestrial red bed facies of the Baronstown Formation to the Moathill Formation of the Navan Group has been penetrated in several boreholes. Although the lower part of the sequence is comparable with the Courceyan succession at Navan and Slane, the middle part of the sequence differs markedly in the Walterstown-Kentstown area and two new members, the Proudstown and Walterstown Members, are defined in the upper part of the Meath Formation. Syndepositional faulting was initiated during the Courceyan, probably in latest Pseudopolygnathus multistriatus or early Polygnathus mehli latus time. Movement on the ENE trending St. Patrick's Well Fault influenced the deposition of the Walterstown Member and the overlying Moathill Formation and was probably associated with the development of the East Midlands depocentre to the south of the area. A second episode of tectonism in the latest Courceyan or early Chadian resulted in uplift and erosion and the development of ‘block and basin’ sedimentation. Subsequent transgression of the uplifted block led to the establishment of the Kentstown Platform, bounded to the north, west and south by rocks of basinal facies. The Milverton Group (Chadian-Asbian), confined to this platform, unconformably overlies Courceyan or Lower Palaeozoic strata and is subdivided into three formations: Crufty Formation (late Chadian), Holmpatrick Formation (late Chadian-Arundian) and Mullaghfin Formation (late Arundian-Asbian). The Walterstown Fault controlled the western margin of the Kentstown Platform at this time. Contemporaneous basinal sediments of the Fingal Group (Lucan and Naul Formations) accumulated to the west of the Walterstown Fault and are much thicker than age-equivalent platform facies. Platform sedimentation ceased in latest Asbian to early Brigantian time with tectonically induced collapse and drowning of the platform; platform carbonates of the Mullaghfin Formation are onlapped northwards by coarse proximal basinal facies of the Loughshinny Formation. A distinct gravity anomaly in the Kentstown area suggests the presence of a granitoid body within the basement. The Kentstown Platform is therefore considered to have formed on a buoyant, granite-cored, footwall high analogous to the Askrigg and Alston Blocks of northern England.     

Biostratigraphy of Dinantian limestones and associated volcanic rocks in the Limerick Syncline,Ireland

Rocks of Courceyan to Brigantian age are exposed in the Limerick Syncline. However, a complete Courceyan succession is known only from two boreholes which correlate closely, both faunally and lithologically, with a standard Limerick Province succession in the Pallaskenry Borehole on the Shannon estuary. This is followed by a thick Waulsortian sequence (the newly defined Limerick Limestone Formation) of late Courceyan to early Chadian age and overlying cherty micrites (the newly defined Lough Gur Formation) of early to late Chadian age, whose top is younger to the east. The Lough Gur Formation is succeeded by lavas and tuffs of the Knockroe Volcanic Formation whose upper part is interbedded with and overlain by shallow water oolites and algal-rich bioclastic limestones of the Herbertstown Limestone Formation. The higher part of the latter is in turn interbedded with lavas and tuffs of the Knockseefin Volcanic Formation. The Herbertstown Limestone has rich and diverse coral/brachiopod and foraminiferal assemblages of late Chadian to Asbian age. Its base is markedly diachronous: late Chadian in the west of the syncline and Holkerian in the east. Both the base and top of the Knockroe Volcanic Formation are thus shown to be markedly diachronous and volcanism extends from the Chadian to early Asbian. The Knockseefin Volcanic Formation is entirely of Asbian age. The highest limestones (Dromkeen Limestone Formation) have a diagnostic late Asbian–early Brigantian fauna and are overstepped by mid-Namurian shales.     

Arundian (Dinantian) carbonate mudbanks in north-west Ireland

Arundian mudbank complexes at Pollower and Carrickbaun in north-west Ireland are described in detail. The two bank complexes developed on different fault blocks controlled and separated by the Curlew Mountain Fault system which was active during the Dinantian. The two mudbank complexes are composed predominantly of lime mudstone and wackestone textures with abundant peloids and intraclasts. Stromatactoid cavity systems in the banks are extensive and have multiple generations of geopetal internal sediment and radiaxial and bladed cryptofibrous calcite cements. These mudbanks are comparable with earlier Courceyan-Chadian deep water Waulsortian mudbanks which accumulated on carbonate ramps. Components in the Pollower bank most closely resemble those in subphotic Phase C Waulsortian banks, whereas the Carrickbaun mudbank, which possesses dasycladacean algae, intraclasts and micritized fragmented bioclasts, indicates a much shallower environment of in situ carbonate mud accumulation, comparable to the photic Phase D assemblages of Waulsortian banks. The difference in depositional setting is also reflected by their respective enclosing lithologies. The Pollower bank is surrounded by deep water black argillaceous wackestones and shales, whereas at Carrickbaun shallower water crinoidal packstones and grainstones are developed on the flanks and bank top. The Arundian mudbank complexes have many similarities with the Asbian mudbanks of north-west Ireland and as such appear to represent an important ‘stratigraphic’ link in the continuum of deep water mudbanks between the two main periods of development in the early Dinantian (Waulsortian) and late Dinantian (Asbian/Brigantian).     

Controls on the evolution and demise of Lower Carboniferous carbonate platforms,northern margin of the Dublin Basin,Ireland

Shallow water platform limestones of the Chadian–Asbian Milverton Group are restricted to the north-eastern part of the Lower Carboniferous (Dinantian) Dublin Basin. Here, they are confined to two granite-cored fault blocks, the Kentstown and Balbriggan Blocks, known to have been active during the late Dinantian. Three areas of platform sedimentation are delimited (the Kentstown, Drogheda and Milverton areas), although in reality they probably formed part of a single carbonate platform. Resedimented submarine breccias and calciturbidites (Fingal Group) composed of shallow water allochems and intraclasts sourced from the platform accumulated, along with terrigenous muds, in the surrounding basinal areas. Sedimentological evidence suggests that the Kentstown and Balbriggan Blocks possessed tilt-block geometries and developed during an episode of basin-wide extensional faulting in late Chadian time. Rotation of the blocks during extension resulted in the erosion of previously deposited sequences in footwall areas and concomitant drowning of distal hangingwall sequences. Antithetic faults on the northern part of the Balbriggan Block aided the preferential subsidence of the Drogheda area and accounts for the anomously thick sequence of late Chadian platform sediments present there. Continued subsidence and/or sea-level rise in the late Chadian–early Arundian resulted in transgression of the Kentstown and Balbriggan Blocks; carbonate ramps developed on the hangingwall dip slopes and transgressed southward with time. Subsequent progradation and aggradation of shallow water sediments throughout the Arundian to Asbian led to the development of carbonate shelves. Several coarse conglomeratic intervals within the contemporaneous basinal sequences of the Fingal Group attest to periodic increases of sediment influx associated with the development of the shelves. Sedimentological processes controlled the development of the carbonate platforms on the hangingwall dip slopes of the Kentstown and Balbriggan Blocks, though periodic increases of sediment flux into the basinal areas may have been triggered by eustatic falls in sea level. In contrast, differential subsidence along the bounding faults of these blocks exerted a strong control on the margins of the late Dinantian shelves, maintaining relatively steep slopes and inhibiting the progradation of the shelves into the adjacent basins. Tectonically induced collapse and retreat of the platform margins occurred in the late Asbian–early Brigantian. Platform sediments are overlain by coarse-grained proximal basinal facies which fine upwards before passing into a thick shale sequence, indicating that by the late Brigantian carbonate production had almost stopped as the platforms were drowned.     

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.     

The stratigraphy and sedimentology of the Ordovician Partry Group,southeastern Murrisk,Ireland

The uppermost part of the Ordovician succession in southeastern Murrisk, western Ireland, consists of coarse-grained sedimentary rocks and tuffs, the Partry Group, hitherto subdivided into the Mweelrea Formation, unconformably overlain by the Maumtrasna Formation. The age of the lower part of the succession is late Llanvirn whilst that of the upper part is unknown. Evidence is presented to show that the two formations are lateral equivalents. Consequently the Mweelrea Formation is redefined and the Maumtrasna Formation becomes redundant. The revision of the stratigraphy enables a coherent sedimentological model for the group to be proposed. The sediments of the Mweelrea Formation were deposited on alluvial fans and distally-equivalent alluvial plains and delta fans. The direction of sediment transport was towards the north and northwest.     

The Distribution of Chadian and earliest Arundian strata in North Wales: Implications for Dinantian (Carboniferous) lithostratigraphy and palaeogeography

The late Chadian Foel Formation, previously thought to be confined to the Dyserth area of North Wales, forms a poorly exposed but persistent basal unit to much of the Dinantian crop east of the Clwydian Range, necessitating a revision of the local lithostratigraphy. The formation comprises a peritidal heterolith which, together with the lowest few metres of the overlying Llanarmon Limestone, yields microfossil assemblages diagnostic of the Eoparastaffella Cf4α Subzone. Succeeding strata, containing the lowest archaediscid foraminifera, provide the first record of Cf4β assemblages from North Wales and establish an early Arundian age for these beds. The Foel Formation was deposited as an aggradational sequence on the northern flank of St. George's Land during a pulsed transgression which began in late Chadian times. The widely recognized basal Arundian transgression is represented by the contact between the Foel Formation and overlying platform carbonates. The latter overlap the Foel Formation in the southernmost part of the Clwydian crop demonstrating, for the first time, southwards onlap on the northern side of the Bala–Bryneglwys Fault System.     

The carboniferous lithostratigraphy of Southeast County Limerick,Ireland, and the origin of the shannon trough

The Carboniferous succession in southeast County Limerick, on the southeastern margin of the Shannon Trough, is Courceyan to mid-Namurian in age and over 1900 m thick. The lithostratigraphy is described in detail. Its most important aspect is the presence of two thick volcanic sequences, a Chadian one of the alkali basalt to trachyte suite and one of Asbian age dominated by limburgites and ankaramites. The associated Dinantian carbonates are of shelf or ramp facies throughout, and no fundamental division into shelf and basin facies occurs as in the Dublin and Craven Basins in early Viséan times. Rapid differential subsidence between this area and the Shannon Estuary began during deposition of the late Courceyan to early Chadian Waulsortian facies but was less marked in the remaining Viséan when much of the volcanic topography was preserved by rapid basinal subsidence. There was basinal inversion in the late Dinantian to lower Namurian, followed by renewed subsidence in mid-Namurian times. This contrasts with the continuous rapid subsidence of the area further west on the Shannon Estuary. This behaviour, together with a comparison of that of nearby Carboniferous basins such as the Dublin, South Munster, and Craven Basins, which lack substantial volcanic sequences, suggests an origin in a transtensional regime rather than one of simple crustal stretching.     

The enigma of fine-grained alluvial basin fills: the Permo-Triassic (Cumbrian Coastal and Sherwood Sandstone Groups) of the Solway Basin,NW England and SW Scotland)

The late Permian to Triassic sediments of the Solway Basin consist of a layer-cake succession of mature, predominantly fine-grained red clastics laid down in semi-arid alluvial plain to arid sabkha and saline marginal marine or lacustrine environments. The Cumbrian Coastal Group consists of Basal Clastics and Eden Shales. The Basal Clastics are thin regolith deposits resting unconformably on all-underlying units and are composed of mixtures of angular local gravel and far-transported fine to very fine-grained sands deposited as basal lag. The Eden Shales are predominantly gypsiferous red silty mudstones, with thin very fine-grained sandstone beds, and with thick marine gypsum beds at the base, deposited at a saline lake margin. The overlying Triassic Sherwood Sandstone Group consists of the Annan and Kirklinton Sandstones. The Annan Sandstones are predominantly thick-bedded, multi-storied, fine-grained mature red quartz sandstones in which coarse sand is practically absent despite channels with clay pebbles up to 30 cm in diameter. The overlying, predominantly aeolian, Kirklinton Sandstones consist of festoon cross-bedded and parallel-laminated fine-grained sandstones, almost identical to the Annan Sandstones except that mica and clay are absent. The Stanwix Shales, located above, consist of interbedded red, blue and green mudstones, siltstones, and thin very fine-grained sandstones, with gypsum layers. Although the entire succession can plausibly be interpreted as deposited in a large desert basin opening into a hypersaline marine or lacustrine embayment to the southwest, the uniformly fine-grained nature of the succession is unusual, as is the absence of paleosols, and body and trace fossils. There is almost no coarse sand even in the river channel units, and it seems likely that the basin was not only extremely arid but supplied predominantly by wind rather than water.     

Sedimentation of the Lower Cretaceous Xiagou Formation and its response to regional tectonics in the Qingxi Sag,Jiuquan Basin,NW China

Under the constraint of an isochronous sequence stratigraphic framework, sediment infill of the Xiagou Formation reflects the overall control of dynamic tectonic movements and episodic sedimentations in the Qingxi Sag. Structure reactivity during post-depositional processes could cause stratigraphic variations in longitudinal time and lateral space. This study documents sediment infill features and their response to the tectonic evolutions of the Qingxi Sag. The data sets include comparison of cores, well drilling, 3D seismic, inter-well correlation, wave impedance inversion profiles, original strata recovery data, sedimentary facies spatial evolution and their superimposition with paleogeomorphology.The Jiuquan Basin is a Mesozoic-Cenozoic superposition basin comprising an early rifting graben phase and a later compression phase. Since the Early Cretaceous, the basin has undergone four major tectonic episodes: 1) extension during the Early Cretaceous, 2) tectonic inversion caused by northwest-southeast contraction from the Late Cretaceous to the Paleocene, 3) weak extension from the Eocene to the Miocene and 4) contraction from the Miocene to the present. Therefore, the Jiuquan Basin is the product of taphrogenic, collisional and shearing movements.Seismic interpretations of sequence and maximum flooding surface divide the Xiagou Formation into three third order sequences: SQK1g₀, SQK1g₁ and SQK1g₂₊₃. Five sedimentary facies associations are identified: the shoreland plain, fan delta dominated sedimentary systems, turbidite deposits, shallow lakes and half-deep lake systems. From K1g₀ to K1g₂₊₃, decreased sandstone percentages in three fan delta areas indicate a continuously transgressive process, which shows the transition from proximal to distal sites in most statistic wells and an obvious decrease of fan delta scales. The northeast-southwest faults control the lakeward distributions of delta fronts and turbidite fans.The correspondence of sedimentary infill and its response to tectonic movements have been demonstrated in the Qingxi Sag. The more active eastern part of the northeastern boundary fault has an important influence on the northeastward migration of depocenters in the Xiagou Formation. The topography developed continuously from K1g₀ to K1g₂₊₃, but the diminished subsidence indicates the dominant geological process varying from intense fault rifting in an early period to relatively gentle and overall subsidence in a later period during the Early Cretaceous.     

Sedimentology and palynology of the Calafate Formation (Maastrichtian), Austral Basin, Southern Patagonia, Argentina

The Calafate Formation crops out in south-western Santa Cruz Province, Argentina, and displays a stacking of asymmetrical coarsening–fining-upward cycles. These cycles are interpreted as the product of short-lived transgressive-regressive events in which the coarsening upward part represents sedimentary aggradation with a stable or decreasing sea level. Sedimentological and palynological analyses indicate nearshore marine conditions. Even though the existence of an estuary or incised valley cannot be determined, this is the most probable palaeogeographic model. Based on dinoflagellate cysts, the base of the section is considered to be not older than Maastrichtian. The presence of the oyster Ambigostrea clarae (Ihering) occurring together with the dinoflagellate cyst species Manumiella druggii (Stover) Bujak and Davies and Eisenackia circumtabulata Drugg in the middle part of the section indicates an age no older than late Maastrichtian. According to sedimentological data, deposits representing the Cretaceous–Palaeogene transition would have been eroded, which is confirmed by the presence of Grapnelispora loncochensis Papú. This megaspore is a consistent component of the Maastrichtian assemblages from Patagonia.     

Late Dinantian (Lower Carboniferous) platform carbonate stratigraphy of the Buttevant area North Co. Cork,Ireland

A thick sequence of late Dinantian (Asbian–Brigantian) carbonates crop out in the Buttevant area, North Co. Cork, Ireland. A mud-mound unit of early Asbian age (the Hazelwood Formation) is the oldest unit described in this work. This formation is partly laterally equivalent to, and is overlain by, over 500 m of bedded platform carbonates which belong to the Ballyclogh and Liscarroll Limestone Formations. Four new lithostratigraphic units are described within the platform carbonates: (i) the early Asbian Cecilstown Member and (ii) the late Asbian Dromdowney Member in the Ballyclogh Limestone Formation; (iii) the Brigantian Templemary Member and (iv) the Coolbane Member in the Liscarroll Limestone Formation. The Cecilstown Member consists of cherty packstones and wackestones that are inferred to have been deposited below fair-weather wavebase. This unit overlies and is laterally equivalent to the mud-mound build-up facies of the Hazelwood Formation. The Dromdowney Member is typified by cyclic-bedded kamaenid-rich limestones possessing shell bands, capped by palaeokarst surfaces, with alveolar textures below and shales above these surfaces. The carbonates of this unit were deposited at or just below fair-weather wavebase, the top of each cycle culminated in subaerial emergence. The Templemary Member consists of cyclic alternations of subtidal crinoidal limestones capped by subtidal lagoonal crinoid-poor, peloidal limestones possessing coral thickets. Intraclastic cherty packstones and wackestones characterize the Coolbane Member, which is inferred to have been deposited below fair-weather wavebase but above storm wavebase. The early Asbian Cecilstown Member has a relatively sparse micro- and macrofauna, typified by scattered Siphonodendron thickets, archaediscids at angulatus stage and common Vissariotaxis. Conversely, macro- and microfauna is abundant in the late Asbian Dromdowney Member. Typical late Asbian macrofossils include the coral Dibunophyllum bipartitum and the brachiopod Davidsonina septosa. The base of the late Asbian (Cf6γ Subzone) is recognized by the first appearance of the foraminifers Cribrostomum lecompteii, Koskinobigenerina and the alga Ungdarella. The Cf6γ Subzone can be subdivided into two biostratigraphic divisions, Cf6γ1 and Cf6γ2, that can be correlated throughout Ireland. Relatively common gigantoproductid brachiopods and the coral Lonsdaleia duplicata occur in the Brigantian units. The base of the Brigantian stage (Cf6δ Subzone) is marked by an increase in the abundance of stellate archaediscids, the presence of Saccamminopsis-rich horizons, Loeblichia paraammonoides, Howchinia bradyana and the rarity of Koninckopora species. Changes in facies at the Cecilstown/Dromdowney Member and the Ballyclogh/Liscarroll Formation boundaries coincide closely with the changes in fossil assemblages that correspond to the early/late Asbian and the Asbian/Brigantian boundaries. These facies changes are believed to reflect major changes in relative sea-level on the Irish platforms. The sea-level variations that are inferred to have caused the facies changes at lithostratigraphic boundaries also brought in the new taxa that define biostratigraphic boundaries. Moreover, many of the Dinantian stage boundaries that are defined biostratigraphically in Great Britain, Belgium and the Russian Platform also coincide with major facies boundaries caused by regressive and transgressive episodes. The integration of detailed biostratigraphic analyses with facies studies will lead to better stratigraphic correlations of Dinantian rocks in northwest Europe. © 1997 John Wiley & Sons, Ltd.     

Depositional history of a muddy sabkha complex in the Sokoto Basin of Nigeria,West Africa

Sedimentological and stratigraphical analysis of the Sokoto Basin has resulted in recognition of four lithostratigraphic units. They are Unit A—siltstone and fine-grained sandstone; Unit B—shale and marl; Unit C—limestone and calcareous shale; and Unit D—red sandstone. Unit A represents a wadi plain system composed of desert-alluvial beds; Unit B, a mud-rich sabkha system; and Unit C, an inner-shelf carbonate system. A marine transgression from the northwest began in the Maastrichtian and reached its peak in the Palaeocene. After regression in the late Palaeocene, the area was subjected to erosion, followed by fluvial sedimentation of Unit D. Wadi plain beds and mud-rich sabkha facies of Sokoto Basin are similar to alluvial and coastal mud-flat deposits in the northwestern Gulf of California and ephemeral stream and tidal-flat sediments in Gladstone Embayment, Australia.     

Review of Lopingian (upper Permian) stratigraphy of the Galilee Basin,Queensland, Australia

The recent increase in exploration activity in the Galilee Basin, Queensland, has highlighted inconsistencies in the usage of Lopingian (upper Permian) stratigraphic nomenclature across the basin. This study utilised peer-reviewed journal, company and government publications to evaluate the current understanding of the naming conventions in use and correlated them to nomenclature in the adjacent Bowen Basin. The prominent misinterpretation is between the stratigraphic relationship and terminology of the northern and western Betts Creek beds and its eastern and southern correlatives the Bandanna Formation and Colinlea Sandstone. The correlation between the units has been assessed from a (1) lithological, (2) sedimentological and (3) coal-seam architectural perspective. The Betts Creek beds appear similar to the Colinlea Sandstone in their lithology and sedimentological character, but increased drilling data suggest the original type-sections no longer fit the heterogeneous lithology of correlated strata bearing that nomenclature. Correlation across the Springsure Shelf into the Bowen Basin suggests that the Betts Creek beds and their subdivisions are in fact equivalent to the Bandanna Formation, the Fort Cooper Coal Measures (the Burngrove and Fair Hill formations) and the Moranbah Coal Measures. A revised stratigraphic column for the Galilee Basin has been proposed to reflect this, and to suggest that a new stratigraphic unit be introduced; the ‘Fort Cooper Coal Measures equivalent’ and its subdivisions the ‘Burngrove and Fair Hill formation equivalents.’     

Sedimentation in an actively tilting half-graben: sedimentology and stratigraphy of Late Tournaisian–Viséan (Mississippian, Lower Carboniferous) carbonate rocks in south County Wexford, Ireland

The Wexford Basin (south-eastern Ireland) is a NE–SW-trending sedimentary basin containing carbonates and evaporites deposited during the Late Tournaisian and Viséan. Two separate depositional areas are defined on the basis of facies and facies associations. Sediments were deposited in inner ramp, lagoonal and peritidal environments near Rosslare, and in a more open-marine, shallow- to moderately deep-water, mid to outer ramp environment in the western area around Duncormick. Thick breccia deposits that occur in the Wexford Basin formed as a result of (i) fault movement that produced syn-sedimentary debris flows in the Late? Chadian (Breccia type I); (ii) dissolution of anhydrite/gypsum and subsequent collapse of sedimentary strata (Breccia type II); and (iii) fracturing and brecciation of porous rock caused by the movement of high temperature, late diagenetic fluids along fault planes (Breccia type III). The NE–SW facies polarity displayed by both sedimentary successions was the result of NW–SE extension and the reactivation of the NE–SW-trending Wexford Boundary Fault during the Chadian. Extension at the SE margin of the basin with downthrow to the NNW gave the basin a half-graben character. Thickening of the debris flow deposits to the SW suggests that while the half-graben was being tilted it also underwent a NE–SW block rotation due to an axial component of that normal fault.     

Ediacaran (Sinian) palaeogeographic reconstruction of the Upper Yangtze area,China, and its tectonic implications

ABSTRACT

The Ediacaran (ca. 635–541 Ma) was a critical period in Earth history, which saw a dramatic transformation in global biological, chemical and climatic conditions, making it one of the most intensively investigated time intervals worldwide. As the first mixed clastic–carbonate succession deposited on the Upper Yangtze Craton, the Ediacaran succession overlies Neoproterozoic continental rifts, and records a complex basin infill history. In this study, we focus on the tectonostratigraphic environment and basin infill process, integrating multiple data sets, including boreholes, outcrops, well correlations, seismic data, isopach maps and the spatial distribution of sedimentary facies. The Ediacaran System includes the Doushantuo Formation and overlying Dengying Formation which can be subdivided into four lithostratigraphic members (D1–D4). The Doushantuo Formation and D3 Member consist of mixed clastic–carbonate sediments, while carbonates predominate in the D1, D2 and D4 members. Intracratonic depressions and continental margin rifts dominated the Upper Yangtze area during the Ediacaran. During deposition of the Doushantuo Formation, the Upper Yangtze area contained a variety of environments, including terrigenous shorefaces, mixed tidal flats, lagoons, shelves, slopes and bathyal seas. A rimmed carbonate platform developed during deposition of the D1 and D2 members. The Deyang–Anyue Trough, which is related to post-rift subsidence in the intracratonic basin, began to develop in this interval. A relatively intense extension during deposition of the D3 Member resulted in intensification of intracratonic and continental margin rifting, creating distinct tidal flat, deep-water shelf, slope and bathyal environments. With the expansion of the Deyang–Anyue Trough during deposition of the D4 Member, the rimmed carbonate platform was divided into two segments. We suggest that the Deyang–Anyue Trough was a structurally controlled intracratonic rift-sag and likely arose from multiple episodes of rifting in the cratonic basement, as well as differential uplifting and exposure caused by the ongoing Tongwan Movement. Our model highlights the role of basement heritage on the structure and evolution of intracratonic rift-sag.     

The Cretaceous sedimentary history of the Pindos Basin (Greece)

The Cretaceous sedimentary rocks of the Pindos Zone in western Greece document the evolution of a Tethyan deep-water basin. New sedimentological and micropalaeontological studies reveal a complex basin history. Siliceous sediments with abundant radiolaria and organic-rich facies prevailed up to the early Late Cretaceous. Within the sediment-starved pre-Middle Cenomanian, marked black shale levels appear that are probably linked to oceanic anoxic events. At the change from the late Early to the early Middle Cenomanian, the sedimentary regime altered abruptly. The early Late Cretaceous is characterized by major calcareous redepositional events (orbitoline horizons) and often associated siliciclastic turbidite deposition (submarine-fan environments). In the late Late Cretaceous, carbonate supply increased rapidly, resulting in the evolution of a carbonate slope and basin-plain setting. Pelagic and allodapic limestones recorded basinwide blooms in planktonic foraminifera (elevata event) and a polyphase redepositional history that is interpreted to reflect the sensitivity of the basin to the tectonic evolution of Apulia.     

Transitional environments of the lower Maastrichtian South-Pyrenean Basin (Catalonia,Spain): The Fumanya Member tidal flat

Sedimentological, palaeontological and geochemical data provide detailed evidence of a marine-to-lagoon environmental succession around the Campanian-Maastrichtian boundary in the Ibero-Armorican domain. This regression is recorded by the succession of several environments of the south-central Pyrenees basin: open marine mixed shelf, marine restricted mixed shelf (both rudist-rich), tidal flat, lagoon and fluvial dominated. The tidal flat setting belongs to the Fumanya Member here described, which is the base of the Posa and Massana formations (Tremp Group). The Fumanya Member is 5 m thick, is built up of marly limestones and was an elongated tidal mudflat (100 km long, 25 km wide) developed in a foreland trough and was separated from the Atlantic Ocean by an island-barrier system. In the lagoon environment, marginal marine waters and continental fresh waters alternated as documented by geochemistry and fossil molluscs. The Fumanya Member is a dinosaur megatracksite, reporting the roaming activity only of sauropods in tidal flats, a likely secure area against predators. Feeding activity of these herbivores took place in the lagoonal-lacustrine environments of the Posa Formation above the Fumanya Member.