Green Mudstone Research Articles

Tremadocian (Lower Ordovician) sea-level changes and biotas on the Avalon microcontinent

The Chesley Drive Group, an Upper Cambrian-Lower Ordovician mudstone-dominated unit, is part of the Ediacaran–Ordovician cover sequence on the North American part of the Avalon microcontinent. The upper Chesley Drive Group on McLeod Brook, Cape Breton Island (previously “McLeod Brook Formation”), has two lithofacies-specific Tremadocian biotas. An older low-diversity benthic assemblage (shallow burrowers,Bathysiphon, phosphatic brachiopods, asaphid trilobites) is in lower upper Tremadocian green-gray mudstone. This wave-influenced, slightly dysoxic facies hasBathysiphon–brachiopod shell lags in ripple troughs. The upper fauna (ca. 483 +/- 1 Ma) is in dysoxic-anoxic (d-a), unburrowed, dark gray-black, upper upper (but not uppermost) Tremadocian mudstone with a “mass kill” of the olenidPeltocare rotundifrons(Matthew)—a provincial trilobite in Avalonian North America that likely tolerated low oxygen bottom waters.Scandodus avalonensisLanding n. sp. andLagenochitinaaff.conifundus(Poumot), probable nektic elements and the first upper Tremadocian conodont and chitinozoan reported from Avalon, occur in diagenetic calcareous nodules in the dark gray-black mudstone. An upper Tremadocian transition from lower greenish to upper black mudstone is not exposed on McLeod Brook, but is comparable to a coeval green-black mudstone transition in Avalonian England. The successions suggest that late late Tremadocian (probable Baltic Hunnebergian Age) sea level was higher in Avalon than is suggested from successions on other paleocontinents. The Tremadocian sea-level history of Avalon was a shoaling-deepening-shoaling sequence from d-a black mudstone (lower Tremadocian), to dysoxic green mudstone (lower upper Tremadocian), and back to black mudstone (upper upper Tremadocian).ScandodusLindström is emended, with the early speciesS. avalonensisLanding n. sp. assigned to the emended Family Protopanderodontidae.TriangulodusVan Wamel is considered a junior synonym ofScandodus. Peltocare rotundifronsis emended on the basis of complete specimens.

Jurassic-Cretaceous fluvial channel and floodplain deposits along the Karak-Kuantan Highway, central Pahang (Peninsular Malaysia)

A fluvial succession of probable Jurassic-Cretaceous age is well exposed at Km 160 along the Karak-Kuantan highway, central Pahang. Although the exact age of these rocks is unknown, the depositional environment of the rocks, and their relatively unmetamorphosed nature and low structural dips compared to surrounding rocks, suggest that they are equivalent to the 'post-orogenic' continental deposits, generally referred to as the Jurassic-Cretaceous Gagau Group. Such outcrops are rarely found preserved anywhere in Peninsular Malaysia, and if conserved, provides a good locality for the study fluvial deposits. The succession comprises fining-upward channel fill sands and muds, intercalated with red and green overbank and floodplain mudstones. There are four major sandbodies, three of which represent fining upward channel/ channel margin sands (>2 m thick), while the fourth consists of at least four tabular/sheet-like sandstones (1.5 m thick) interpreted as crevasse-splay sheet sand deposits. Their facies characteristics suggest that the sediments were deposited in a low-lying meandering channel-floodplain system. The co-existence of red and green mudstones in the floodplain facies suggest that there could be seasonal/climatic fluctuations that affected the geochemical conditions in the basin.

Dinosaur eggs and dinosaur egg-bearing deposits (Upper Cretaceous) of Henan Province, China: Occurrences, palaeoenvironments, taphonomy and preservation

The Upper Cretaceous dinosaur egg-bearing deposits in Henan Province, central China are divided into three formations in ascending order: Gaogou, Majiacun and Sigou. The Gaogou Formation belongs to alluvial fan deposits containing the fossil dinosaur egg assemblage of Faveoloolithus, Dendroolithus, Dictyoolithus, Paraspheroolithus and Longiteresoolithus. The Majiacun Formation is interpreted as braided stream to meandering stream deposits with assemblage of Ovaloolithus, Paraspheroolithus, Placoolithus, Dendroolithus, Prismatoolithus, rare Youngoolithus and Nanhiungoolithus. The Sigou Formation is shallow lacustrine/palustrine to low-sinuosity river sedimentary rocks with assemblage of Macroolithus, Elongatoolithus, Ovaloolithus and Paraspheroolithus. To date, 37 oospecies, 13 oogenera and 8 oofamilies of dinosaur eggs have been distinguished. Autochthonous dinosaur eggs are preserved in the floodplain deposits, whereas allochthonous and parautochthonous dinosaur eggs are preserved in the alluvial fans. This suggests that river floodplains are the best environments for the preservation of numerous autochthonous dinosaur eggs. The preservation of most dinosaur eggs in brown to red calcic palaeosoils, muddy siltstones or mudstones suggests that the paleoclimate of the nesting area was semiarid. The presence of gray and green mudstone and coal layers, however, indicates that there existed an ephemeral subhumid climate during the middle and Late Cretaceous. It is suggested that such a climate was favorable for the development of meandering streams in a vegetated environment.

Shallow lacustrine carbonate microfacies document orbitally paced lake‐level history in the Miocene Teruel Basin (North‐East Spain)

AbstractResults are presented of a detailed carbonate petrographic study of an Upper Miocene lacustrine mixed carbonate–siliciclastic succession in the Teruel Basin (Spain) with the aim of constraining lake‐level variability at different stratigraphic scales. Regular alternations of red to green mudstone and lacustrine limestone, termed the ‘basic cycle’, reflect lake‐level variations at the metre‐scale. In an earlier study, the basic cycle was shown to be controlled by the climatic precession cycle. Petrographic analysis made it possible to distinguish two main carbonate microfacies groups characteristic of very shallow transient and shallow permanent lake environments, respectively. In addition to the basic cyclicity, the microfacies analysis reveals lake‐level variations on a larger scale. As a consequence, the astronomical forcing hypothesis of the cyclicity in the Cascante section is explored further. A climate modelling study of orbital extremes indicates that high lake levels could relate to enhanced net winter precipitation and runoff during precession minima, consistent with Mediterranean geological data. Using this phase relationship, an astronomical tuning of the cycles is established starting from astronomical ages of magnetic reversal boundaries. Subsequently, successive basic cycles are correlated to precession minima. The tuning reveals an identical number of basic cycles in the Cascante section as precession‐related sapropel cycles in the deep marine succession at Monte dei Corvi (Italy), corroborating the precessional control of the basic cycles at Cascante. Lake‐level highstands in the large‐scale cycle identified by the microfacies analysis relate to maxima in both the ca 100 and 405 kyr eccentricity cycles, again consistent with Mediterranean geological data. Subtraction of the identified astronomically related (lake‐level) variations from the palaeoenvironmental record at Cascante indicates a shift to deeper and more permanent lacustrine environments in the upper half of the section. The cause of this shift remains unclear, but it may be linked to tectonics, non‐astronomical climate, long‐period astronomical cycles or autogenic processes.

Creep Damage Characteristics of Soft Rock under Disturbance Loads

This article focuses on the process of rock creep damage and micro-damage evolution properties of gray green mudstone under impacting disturbance load conditions for the first time using the real time computerized tomography (CT) testing technique. The results indicate that axial load comes into limit strength neighborhood, rock micro-crack links into larger crack, creep rate increases in a short time, larger plastic deformation happens; this is called disturbance accelerating creep stage. When rock is within limit strength neighborhood, there occurs creep micro-damage under smaller disturbance load. When disturbance load is larger, rock directly enters into disturbance accelerating creep stage, failure occurs instantaneously. On the basis of experimental research, the CT scanning method was used to describe the creep micro-damage of soft rock, also helpful in the prediction of roadways' service life and evaluation of geotechnical engineering stability.

Late Archaean synorogenic basins of the Eastern Goldfields Superterrane, Yilgarn Craton, Western Australia: Part II. Kurnalpi Terrane

The Penny Dam, Belches, Yilgangi, White Hills, Granny, Royal, Lucky, Brock and Wallaby Supersequences of the Kurnalpi Terrane crop out in synclines that are the erosional remnants of basins that developed as linear zones of subsidence between approximately north-trending compartment-bounding faults. Dominant sedimentary facies range from gravel-rich and sand-rich concentrated density-flow deposits to thickly and thinly bedded Bouma-type turbidites. Background deposits are black shales or laminated green mudstones, and banded iron formation is preserved in some condensed sections. Periods of non-deposition are recorded by bedded chert, which is the product of early diagenetic sea-floor silicification. The basins were separate deep-marine canyon to linear-fan systems that were linked laterally and distally by mud-rich deposits. There is only minor evidence for fault-anchored, canyon-margin slope aprons. Basin development occurred during two stages separated by a period of deformation, uplift and erosion. Sparse palaeocurrents establish sediment dispersal was to the south or southeast, indicating that uplift to the north or northwest controlled palaeoslopes. Stacking of lithofacies is aggradational, and consistent with deposition in fault-bound basins. Tectonostratigraphic equivalence with siliciclastic supersequences of the Kalgoorlie and Gindalbie Terranes is established by common depositional systems, stratigraphic styles and stratigraphic responses to tectonic forcing. Consequently, the siliciclastic supersequences represent overlap (or late-stage) basins that tied together arc-related terranes following terrane amalgamation. Similar depositional facies, aggradational styles of facies stacking and two-stage development characterise the syncollisional Plio-Pleistocene Coastal Range Basin of Taiwan. Modern analogues are the deep-marine Southern Longitudinal and Taitung Troughs off southeastern Taiwan that are being filled by synorogenic sediments derived from the Taiwan Orogen.

Proterocara argentina, a new fossil cichlid from the Lumbrera Formation, Eocene of Argentina

ABSTRACT The Lumbrera Formation is the uppermost unit of the Santa Bárbara Subgroup of the Salta Group, exposed in northwestern Argentina. It consists of fine clastic sediments of characteristic brick red color with an intercalation of green mudstone levels, which are called Faja Verde. The specimen described here was collected from the middle part of the Faja Verde II at the Alemania locality in sediments dated as Eocene. The material comprises a specimen, preserved as part and counterpart, which is assigned to a new genus and species: Proterocara argentina, gen. et sp. nov. The phylogenetic analysis to establish its position within Cichlidae was based on a matrix with 51 taxa and 91 characters. The most parsimonious tree shows P. argentina as sister group of the clade formed by the subfamilies Cichlasomatinae and Geophaginae based on three characters: articulating process of premaxilla moderately distinct, first hemal arch on last abdominal vertebra, and 13–14 pectoral-fin rays. Two autapomorphies are recognized for P. argentina: ascending arm of premaxilla as long as dentigerous arm, and dorsal lateral line on caudal fin between caudal rays D2 and D3. Extant members of the family Cichlidae live mostly in lentic freshwater bodies, corroborating the lacustrine paleo-environment assigned to this formation.

Palaeoenvironment of a Late Quaternary lacustrine–palustrine carbonate complex: Zarand Basin, Saveh, central Iran

The continental carbonate deposits of the Zarand Basin were deposited within an intra-continental strike-slip basin situated in the northwestern corner of central Iran. They consist of distal alluvial mudstones to marlstones, carbonate pond deposits, carbonate and siliciclastic-infilled channels, and lacustrine carbonates deposited within a distal alluvial–lacustrine–palustrine complex. Both sedimentological and palaeontological evidence suggest that these sediments mostly formed within an open hydrological system. The common presence of root traces, greyish green mudstones, calcareous nodulisation, mottling, and desiccation breccias indicate a palustrine setting. The carbonate deposits of the Zarand Basin were formed under an overall semi-arid climate but periods of more aridity characterised by extensive calcretization can be distinguished in the stratigraphical sections. Both tectonics and climate have contributed in controlling the sedimentation of the Zarand Basin. Archaeological and geomorphological evidence provides a unique sub-recent analogue for ancient palustrine limestones developed within an intra-continental basin under a semi-arid climatic regime. The combination of geological and archaeological data and their comparison with historical documents show that the so-called historical lake of Saveh was the remnant of the more ancient wetland system which dominated the Zarand region during the late Quaternary.

Regional paleohydrologic and paleoclimatic settings of wetland/lacustrine depositional systems in the Morrison Formation (Upper Jurassic), Western Interior, USA

During deposition of the Upper Jurassic Morrison Formation, water that originated as precipitation in uplands to the west of the Western Interior depositional basin infiltrated regional aquifers that underlay the basin. This regional groundwater system delivered water into the otherwise dry continental interior basin where it discharged to form two major wetland/lacustrine successions. A freshwater carbonate wetland/lacustrine succession formed in the distal reaches of the basin, where regional groundwater discharged into the Denver–Julesburg Basin, which was a smaller structural basin within the more extensive Western Interior depositional basin. An alkaline–saline wetland/lacustrine complex (Lake T'oo'dichi') formed farther upstream, where shallower aquifers discharged into the San Juan/Paradox Basin, which was another small structural basin in the Western Interior depositional basin. These were both wetlands in the sense that groundwater was the major source of water. Input from surface and meteoric water was limited. In both basins, lacustrine conditions developed during episodes of increased input of surface water. Inclusion of wetlands in our interpretation of what had previously been considered largely lacustrine systems has important implications for paleohydrology and paleoclimatology. The distal carbonate wetland/lacustrine deposits are well developed in the Morrison Formation of east-central Colorado, occupying a stratigraphic interval that is equivalent to the “lower” Morrison but extends into the “upper” Morrison Formation. Sedimentologic, paleontologic, and isotopic evidence indicate that regional groundwater discharge maintained shallow, hydrologically open, well oxygenated, perennial carbonate wetlands and lakes despite the semi-arid climate. Wetland deposits include charophyte-rich wackestone and green mudstone. Lacustrine episodes, in which surface water input was significant, were times of carbonate and siliciclastic deposition in scarce deltaic and shoreline deposits. Marginal lacustrine deposits include ooid and skeletal packstone–grainstone, siltstone, and sandstone. Distal lacustrine units are skeletal mudstone–wackestone, microbialites, and laminated (siliciclastic) mudstone. Differentiation between wetlands and distal lacustrine units is not always possible. Palustrine features, Magadi-type chert (MTC), and evaporites record episodes of increased aridity and exposure. Farther upstream, during deposition of the upper part of the Brushy Basin Member, the ancestral Uncompahgre Uplift imposed a barrier to shallow, eastward-flowing groundwater that discharged into the San Juan/Paradox Basin on the upstream side of the uplift. This created the closed hydrologic setting necessary for development of an alkaline–saline wetland/lacustrine complex (“Lake” T'oo'dichi'). Silicic volcanic ash, delivered by prevailing winds from calderas west and southwest of the basin, contributed to the pore-water evolution in the sediments. A distinctive lateral hydrogeochemical gradient, reflecting increasing salinity and alkalinity in the pore waters, altered the ash to a variety of authigenic minerals that define concentric zones within the basin. The basinward progression of diagenetic mineral zones is smectite→clinoptilolite→analcime±potassium feldspar→albite. The groundwater-fed wetlands were shallow and frequently evaporated to dryness. Scarce laminated gray mudstone beds record distinct episodes of freshwater lacustrine deposition that resulted from intermittent streams that carried detritus well out into the basin.

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.

Paleomagnetic Constraints on the Permian-Triassic Boundary in Terrestrial Strata of the Karoo Supergroup, South Africa: Implications for Causes of the End-Permian Extinction Event

The closure of the Palaeozoic witnessed the greatest biotic crisis in earth history. Surprisingly little is known about the effects and timing of the terrestrial counterpart of the well-described End-Permian mass extinction from known marine successions worldwide. In the present study, reliable paleomagnetic results were obtained from a PT boundary section in the terrestrial Karoo Basin of South Africa. Permo-Triassic aged mudstones from a locality in the Eastern Cape Province yielded two magnetic chrons, reverse followed by normal (with the boundary possibly close to the reversal). This extends to results from a previous study: thereby jointly identifying a R/N/R polarity pattern for this boundary interval. The PTB interval is constrained below the red mudstones of the Beaufort Group at the present locality and within reverse-magnetised green mudstone, implying a diachronic relation between the marine and terrestrial End-Permian mass extinction events.

Amphibian burrows and ephemeral ponds of the Lower Permian Speiser Shale, Kansas: evidence for seasonality in the midcontinent

Burrows attributed to the lysorophid Brachydectes elongatus occur within a green mudstone lens in the Lower Permian (Wolfcampian) Speiser Shale (Council Grove Group) of eastern Kansas. The burrow-bearing unit consists of a 100 m long lens of massive, calcareous, silty mudstone with a maximum thickness of 35 cm. The lens also contains the fossils of fish, amphibians, reptiles, charophytes ( Stomachara), and ostracodes ( Carbonita). The mudstone lens pinches out laterally into red, pedogenically modified mudstone. The burrows occur in three layers. At the top of each layer is a subaerial exposure surface indicated by rhizoliths, mudcracks, and coarse-grained lags. The mudstone lens is interpreted as the deposit of a shallow, ephemeral pond. The burrows occur in three vertically and temporally separated clusters with concentrations up to 20/m 2. The burrows show two types of architecture. Type I burrows are elongate, elliptical tubes 4–32 cm long and 2–7 cm in width. Type II burrows are short, elliptical tubes 1.5–3.5 cm in length and 2.5–5 cm in width. The burrow fill consists of a mudstone capped by sandy siltstone. Each burrow layer contains a varying number of articulated and disarticulated lysorophid skeletons within the burrows and surrounding matrix. While similar to Permian lungfish burrows, the architecture and surficial morphology of the lysorophid burrows permits their distinction even in the absence of body fossils. The occurrence of burrow layers capped by subaerial exposure surfaces and separated by layers of non-burrowed, massive mudstone indicates that burrowing occurred in response to episodic, perhaps seasonal, droughts on the Permian coastal plain. The lysorophid burrowing behavior is analogous to that of the extant amphibians Amphiuma sp. and Siren intermedia, which inhabit rivers and ponds in the southeastern USA.

The Burgess Shale arthropod Mollisonia (M. sinica new species): new occurrence from the Middle Cambrian Kaili fauna of southwest China

The Early Cambrian Chengjiang Lagerstätte, Yunnan Province, Southwest China, has become one of the most celebrated Cambrian fossil Lagerstatten not only for perhaps the earliest biota of soft-bodied organisms in the Phanerozoic (Yuan and Zhao, 1999; Zhang et aI., 2001; but see Budd and Jensen, 2000), but also for a number of significant discoveries (Shu et al., 1996a, 1996b, 1999a, 1999b, 2001), proven to be of particular importance for our understanding the Cambrian explosion. Also in Southwest China, Guizhou Province, there is a very significant, although less acclaimed, Middle Cambrian soft-bodied fauna as well, namely the Kaili fauna, which occurs in the Kaili Formation in Kaili area (Kuizhou). The age of the Kaili Formation ranges from late Early to early Middle Cambrian. Regionally, the Kaili Formation is about 222 m thick and consists of three parts. The lowermost part (late Early Cambrian, about 55 m thick) is dominated by thin, calcareous siltstone strata interbedded with limestone layers at the base. The middle part (early Middle Cambrian, ca. 123 m) consists of dark green mudstone and shale, while the uppermost part (ca. 44 m) is composed of interbedded limestone and silty shale. The Kaili fauna is derived from mudstones in the middle part of the formation (Zhao et aI., 1994; Zhu et aI., 2000).

THE BURGESS SHALE ARTHROPOD MOLLISONIA (M. SINICA NEW SPECIES): NEW OCCURRENCE FROM THE MIDDLE CAMBRIAN KAILI FAUNA OF SOUTHWEST CHINA

The Early Cambrian Chengjiang Lagerstätte, Yunnan Province, Southwest China, has become one of the most celebrated Cambrian fossil Lagerstatten not only for perhaps the earliest biota of soft-bodied organisms in the Phanerozoic (Yuan and Zhao, 1999; Zhang et aI., 2001; but see Budd and Jensen, 2000), but also for a number of significant discoveries (Shu et al., 1996a, 1996b, 1999a, 1999b, 2001), proven to be of particular importance for our understanding the Cambrian explosion. Also in Southwest China, Guizhou Province, there is a very significant, although less acclaimed, Middle Cambrian soft-bodied fauna as well, namely the Kaili fauna, which occurs in the Kaili Formation in Kaili area (Kuizhou). The age of the Kaili Formation ranges from late Early to early Middle Cambrian. Regionally, the Kaili Formation is about 222 m thick and consists of three parts. The lowermost part (late Early Cambrian, about 55 m thick) is dominated by thin, calcareous siltstone strata interbedded with limestone layers at the base. The middle part (early Middle Cambrian, ca. 123 m) consists of dark green mudstone and shale, while the uppermost part (ca. 44 m) is composed of interbedded limestone and silty shale. The Kaili fauna is derived from mudstones in the middle part of the formation (Zhao et aI., 1994; Zhu et aI., 2000).

MIDDLE TRIASSIC NEW FOSSILS OF PROTORTHOPHLEBIA TILLYARD (INSECW: MECOPTERA) FROM TONGCHUAN REGION, SHAANXI PROVINCE, CHINA

Abstract The new fossil specimens of Protorthphlebia Tillyd, 1933 collected from the Middle Triassic grayishgreen mudstone and shale of the Upper part of Lower Member, Middle Triassic Tongchuan Formation (T22t) in Tongchuan Shaanxi Province, China are reported and two new species Protorthophlebia ladinica sp.nov. and P. triassica sp.nov. are described. A key to 10 species of genus Rotorthphlebia is provided.

Alluvial-to-lacustrine systems in a pull-apart margin: southwestern Eumsung Basin (Cretaceous), Korea

Abstract In the pull-apart margin of pull-apart basins, sedimentation patterns are poorly known, compared with those in rift basins. The rhomb-shaped Eumsung Basin (Cretaceous), mid-west Korea, was formed in an overstep of the Kongju fault system and provides significant information on how sedimentary bodies dynamically filled the pull-apart margin. According to a detailed analysis of sedimentary facies, palaeoflow directions, clast compositions and downstream changes in clast size, the southwestern basin fills comprise three facies associations representing distinctive depositional environments: (1) facies association (F.A.) I (volcaniclastics-dominated alluvial fan); (2) F.A. II (alluvial plain); and (3) F.A. III (floodplain/lake). The matrix-supported and clast-supported conglomerate (F.A. I) is indicative of deposition in alluvial fans. The hollow-fill or sheetlike deposits encased in purple siltstone (F.A. II) are suggestive of channel or sheetflood deposition in an alluvial plain. The dominant purple and green mudstone (F.A. III) indicates deposition in floodplain and lacustrine environments. The distribution of facies associations represents a basinward change in depositional environments from alluvial-fan to lacustrine systems. The succession is divisible into three large-scale lateral and partly vertical units: the southernmost Ochang (∼1.5 km thick), the medial Baeti (∼1 km thick) and the northernmost Kugokri units (∼0.5 km thick), on the basis of basinal structure and changes in clast composition and lithofacies. The Ochang–Baeti transition reflects synchronous development of the alluvial-to-lacustrine systems in a pull-apart margin. This succession development is attributable to the basinal faults progressed during the basin development. The Baeti–Kugokri transition recorded the changes in clast composition and lithofacies, which was due to the progressive shifting in basinal setting from a pull-apart margin to a strike-slip margin. Unlike that of the strike-slip margins, clast composition of the pull-apart marginal fills reflects adjacent source-rock lithology. In the pull-apart margin, alluvial-to-lacustrine systems show a transverse-to-margin channel network (060°–135°), converging into the southwestern depocentre. Although the basin is of strike-slip origin, sedimentation patterns in the pull-apart margin are suggestive of relatively synchronous developments of the alluvial-to-lacustrine systems reflecting the lithology of the adjacent source rock and subsurface structure of normal-slip-dominant faults.

Biostratigraphy of the Currarie Formation on the northwestern edge of the Southern Uplands: implications for the cessation of basic volcanism

Synopsis The Currarie Formation forms part of the deep water succession near the northern margin of the Southern Uplands. It comprises red and green mudstones (distal turbidites), chert and interbedded lava and lava breccia and overlies basalt lavas. The age of the Currarie Formation is critical in providing a minimum age for the end of basic volcanism in the northernmost part of the Southern Uplands and a maximum age for the onset of northerly derived turbidite flysch. It also allows biostratigraphical correlations to be made across the Southern Upland Fault. Graptolites indicative of the lower Nemagraptus gracilis Biozone and the first record of the conodont species Protopanderodus varicostatus from the formation indicate an earliest Caradoc (early Aurelucian) age for the Currarie Formation. This dates the cessation of basic volcanism in the northernmost part of the Southern Uplands as earliest Caradoc. However, the waning of volcanism may have been diachronous, continuing into the upper TV. gracilis Biozone in the area between the Southern Upland–Glen App and Carcow faults in a succession thought to have been developed further to the south than the Currarie Formation. The onset of coarse turbidite deposition followed within the same graptolite zone marking the onset of a major phase in uplift of the Midland Valley terrane and subsidence in the Southern Uplands basin.

Sedimentology, C-S-Fe relationships and stable isotopic compositions in Devonian black mudrocks, Mackenzie Mountains, Northwest Territories, Canada

An integrated approach combining C-S-Fe relationships, stable isotopic compositions, and lithofacies characterization was utilized to constrain the palaeoenvironmental and early diagenetic conditions of Middle-Upper Devonian (Eifelian-Frasnian) mudrocks from the Mackenzie Mountains, Northwest Territories, Canada. These rocks include the Hare Indian Formation (informally subdivided into the lower Bluefish Member and the Hare Indian Upper Member), Carcajou Marker and Canol Formation. The Bluefish Member is dominated by black, laminated, organic-rich shales (TOC = 0.35–10.34 wt.%; av. 5.83 wt.) with moderate degrees of pyritization (DOP) of 0.34–0.67 (av. 0.55). These mudrocks were deposited in dysoxic marine bottom-waters that became progressively more oxygenated with time. Variations in TOC, DOP and organic matter δ 13CPDB values (−29.7% to −19.9%; av. −27.2%) are attributed to repeated clastic dilution and increased input of terrestrial organic matter in association with shallowing-upward ramp-clinothem cycles. Pyrite δ 34SCDT values (−32.7% to −18.8%; av. −24.9%) indicate an open system, bacteriogenic seawater-sulphate reduction. Conversely, the overlying Hare Indian Upper Member, characterized by clinothem facies, is composed of grey to green mudstone with minor argillaceous limestones and considerably less organic matter contents (TOC = 0.28–2.99 wt.%; δ 13C = −29.5% to −22.5%). Deposition occurred in oxic to slightly dysoxic waters (DOP = 0.20–0.54; δ 34S = −23.0% to −20.9%), depending on the palaeotopographic location along the depositional slope.A rapid rise in sea level drowned the carbonate 'ramp’ member of the Ramparts Formation and produced the thin, organic-rich Carcajou Marker. Bottom-water stagnation that resulted from subdued ramp palaeotopography produced anoxic sea bottom. Black, laminated, organic-rich shales from the Canol Formation (TOC = 1.37–6.68 wt.%) are very similar to those of the Bluefish Member, and are likewise basinal sediments. However, TOC, DOP and organic-matter δ 13CPDB values (−29.1% to −20.8%; av. −26.2%) do not show pronounced variations and indicate that low-energy, quietwater conditions persisted over relatively long, uninterrupted periods of time. High DOP values (0.72–0.93) throughout the Canol Formation suggest that deposition occurred in anoxic bottom-waters, but as basin-fill conditions continued there was a shift to a dysoxic environment (DOP = 0.55–0.65), which grades into nearshore and offshore sequences of the overlying Imperial Formation. In contrast with the Hare Indian Formation, much heavier δ 34SCDT values of pyrite in Canol mudrocks (−11.1% to +5.3%; av. −3.1%) point to bacterial sulphate reduction in a closed to semi-closed system with respect to seawater sulphate.

Stratigraphie et paléogéographie d'un bassin d'avant-arc ordovicien, Estrie-Beauce, Appalaches du Québec

Two new formations, the Frontière and Etchemin formations, have been found to lie below the Beauceville and Saint-Victor formations, the two known formations of the Magog Group. The Frontière Formation, at the base of the group, is made up of centimeter-thick beds of medium- to coarse-grained litharenite and of greyish green mudstone; the sandstone, greyish green, contains abundant felsic volcanic rock fragments and chromite grains. The Etchemin Formation is composed mostly of centimeter-thick dusky yellow green siliceous mudstone; at the base, there is also a purple mudstone, and meter-thick beds of dusky green volcaniclastic rocks rich in intermediate to felsic volcanic rock fragments and crystals of feldspar and quartz occur near its top. The Beauceville Formation consists of interbedded centimeter-thick beds of black clayslate and centimeter- to meter-thick beds of black volcaniclastic rocks. The Saint-Victor Formation consists of classic turbidite beds with few meter-thick yellowish volcaniclastic rock beds similar to those of the Beauceville Formation; the sandstone is a litharenite rich in quartz grains and sedimentary rock fragments. Most rocks of the Frontière and Etchemin formations as well as the volcaniclastic rocks of the Beauceville and Saint-Victor formations were derived from a magmatic arc located to the southeast. However, the shale of the Beauceville Formation and the turbidites of the Saint-Victor Formation were derived from an orogenic source located to the northwest. The Magog Group is located between the Saint-Daniel Mélange and the Ascot Complex interpreted as remnants of an accretionary prism and a magmatic arc, respectively. The sediments of this group were thus deposited in a fore-arc basin active during the Taconian orogeny of the Middle to Late Ordovician.

Depositional Setting and Origin of Berthierine Oolitic Ironstones in the Lower Miocene Terengganu Shale, Tenggol Arch, Offshore Peninsular Malaysia

ABSTRACT Berthierine oolitic ironstones have been found in the subsurface lower Miocene strata of the Tenggol Arch area, offshore Peninsular Malaysia. The ironstones occur within a 30 to 50 m-thick laterally extensive unit of very finely laminated to massive dark green mudstone, known as the shale. This shale unit was deposited during a regional marine transgression over the Tenggol Arch, which is a fault-bounded pre-Tertiary basement high that separates the Cenozoic intracratonic Malay and Penyu basins at the southwestern margin of the ancestral South China Sea. The oolitic ironstone beds, up to 45 cm thick, have sharp erosional bases and are composed of mainly berthierine ooids and pisoids, some terrigenous quartz-feldspar clasts, and locally, phosphatic ooids. Thicker ironstone beds occurring in the lower part of the shale unit show gradation from granule sandstone to oolitic ironstone. Sedimentological evidence suggests that the oolitic ironstones were deposited as offshore shelf storm layers. The close association of terrigenous clastic grains with the berthierine ooids suggests that these ooids were derived from lateritic soils on land. Transformation of the lateritic soil ooids into berthierine ooids, possibly via an intermediate odinite phase, took place under reducing, early diagenetic conditions. Like many other ironstone deposits described in the literature, the Terengganu ironstones were deposited during a period of sea-level highstand coincident with a marked reduction in terrigenous coarse-grained sediment influx. Palynological evidence further suggests that deposition of the Terengganu shale took place during a dry climatic phase which may have caused the reduction of terrigenous influx into the basin and promoted ironstone accumulation. Phosphatic ooids are found in the ironstones deposited near the inferred early Miocene shelf edge, and they are texturally similar to phosphatic ooids described from modern continental margins. They were probably formed during early diagenesis near the sediment-water interface under anoxic bottom conditions and then were subsequently reworked and mixed with the berthierine ooids. The occurrence of phosphatic ooids near the paleo-shelf edge suggests that the anoxic bottom conditions favorable for phosphate deposition may have been related to upwelling at the paleo-shelf margin.