Late Triassic Age Research Articles

Geology and exploitation of kaolin deposits in the Bidor area, Peninsular Malaysia

The kaolin deposits of more than 50 million tonnes and distributed over 70 sq km occur in the Bidor area, Peninsular Malaysia. They are believed to have been formed hydrothermally. The area is underlain by Paleozoic metasediments which are intruded by the Changkat Rembian granite of Late Triassic age. Argillization is pervasive, affecting both the metasediments and the southern half of the Changkat Rembian granite which is intensely sheared. The residual kaolin deposits derived from the alteration of granitic and metasedimentary rocks may be distinguished by their field, physical, chemical and mineralogical characteristics. Kaolin of granitic parent rock is generally characterized by relict granitic texture, high grit and lower clay content compared to metasedimentary kaolin. The granitoid kaolin generally has a higher brightness. Quartz, in vein and granular forms, is the most predominant non-clay mineral common to both types of deposits. In the clay mineral fraction, the assemblage consists mainly of kaolinite and trace to small amounts of illite. montmorillonite/vermiculite, quartz and feldspar. However, in places, illite predominates over kaolinite in some residual metasediments to form illite deposits. It was mining of placer tin which led to the exposure of most of the kaolin deposits. Quartz veins/ stringers carrying tourmaline and cassiterite with occasional wolframite and gold have been found in the Changkat Rembian granite and along its contact with the metasediments. Though the genetic rela­ tionship between gold, tin and tungsten mineralization and argillization is uncertain, temporally argillization is the youngest. The Malaysian kaolin industry originated in the 1930s from this area. Currently. there are about a dozen processing plants which produce more than two-thirds of Malaysia's kaolin output of about 50,000 tonnes per annum. Both wet and dry processes are used to produce various grades of kaolin for ceramic, paper, paint, plastics and rubber industries. The most refined kaolin produced is of paper-filler grade.

Triassic olivine-normative diabase from Northumberland Strait, eastern Canada: implications for continental rifting

Two intervals of mafic igneous rocks were encountered within a Silurian to Carboniferous sequence in an exploratory offshore well located in the Gulf of St. Lawrence, eastern Canada. Geochemical and radiometric analyses show that the lower mafic rocks are Early Silurian continental tholeiite lavas, with their radiogenic clock thermally reset during the Late Devonian. The upper igneous interval consists of several dikes of high-alumina diabase characterized by flat, relatively unenriched REE spectra and a positive Eu anomaly. This diabase resembles olivine tholeiites. Two K/Ar dates suggest a Late Triassic age for these intrusions. The dike composition differs from that of known Late Triassic and Early Jurassic continental tholeiites nearby in Nova Scotia, which are associated with a late stage of continental rifting. The Triassic – Early Jurassic igneous activity shows a pattern of geochemical evolution that we relate to mantle upwelling.

Facetted garnets formed by etching. Examples from sandstones of Late Triassic age, South Germany

ABSTRACTDetrital garnets from the Upper Triassic (Keuper) of southern Germany have well developed facets where they occur in calcite‐cemented sandstone. The grains belong to the pyralspite series and have a homogeneous chemical composition, without any zonation is revealed by microprobe analyses. It is concluded that the large facets are caused by etching during diagenesis and not by authigenic overgrowth. High calcium contents of the pore fluids may have been important in the formation of these garnet facets.

Late Triassic paleogeography of the southern Cordillera: The problem of a source for voluminous volcanic detritus in the Chinle Formation of the Colorado Plateau region

The Upper Triassic Chinle Formation of the Colorado Plateau contains voluminous volcanic detritus evidently derived from a source to the south. Volcanic rocks exposed in southern Arizona and northern Sonora have been assumed to represent this source terrane, but U-Pb isotopic geochronology and regional stratigraphic correlations indicate that these volcanic rocks are distinctly younger than the Chinle, and thus not a source for the volcanic detritus in the Chinle. Igneous rocks of known or possible Late Triassic age in Nevada, California, or northeastern Mexico are possible sources, but a clearly defined source terrane for the volcanic detritus in the Chinle has not been identified. Tectonic removal of the source terrane by rifting or strike-slip offset, though not proven, is a possibility.

Late Triassic, arc-related, potassic igneous rocks in the North American Cordillera

Igneous rocks of Late Triassic age are widespread in the Cordillera of western North America and, except in Wrangellia, consist of subduction-related plutonic and volcanic suites. Many of these, including those in the Stikinia, Quesnellia, Rattlesnake Creek, and Jackson terrenes and in southern California, are clinopyroxene rich and belong to high-potassium and shoshonitic rock series, features that are generally absent from older and younger igneous rocks in the same terranes. The Late Triassic subduction-related rocks are exposed in two discontinuous belts that lie east and west of the Cache Creek terrane in Canada and correlative melange terranes farther south. Stratigraphic and structural data suggest that these belts were spatially separate magmatic arcs in Late Triassic time. Tectonic implications of this analysis include an explanation of Middle Jurassic Cordilleran deformation as the result of collision of the western with the eastern belt, absence of Late Triassic links between Stikinia and Quesnellia, disassociation of Stikinia with terranes in northwestern Nevada, and tentative correlation of the Wallowa (Seven Devils) terrane with Stikinia rather than Wrangellia.

Depositional Environments and Sedimentology of Vinita Beds, Richmond Basin, Virginia: ABSTRACT

The Carnian (middle to late Middle Triassic Age) Richmond basin of northeast Virginia is the oldest of the exposed Newark rift basins of the eastern seaboard. These basins formed during the Mesozoic divergence of the continents. As presently defined, the Richmond basin is a large synclinal feature measuring 32 mi (53 km) long by 8 mi (13 km) wide, and is located west of Richmond, Virginia, and east of Amelia, Virginia. Sediments of the Richmond basin have been assigned to the Richmond Group and have been stratigraphically subdivided into the following informal units, oldest to youngest: coarse boulder breccias, coal measures, Vinita Beds, and Otterdale Sandstone. The Vinita Beds are composed of arkosic sandstones, shales, siltstones, and minor amounts of coal, and are mineralogically immature. They are composed of angular to subrounded rock fragments, quartz, and feldspars, and are highly micaceous and kaolinitic. In places, feldspars make up as much as 50% of the rock. Sandstones and conglomerates are cross-bedded and channeled, and shales and siltstones are thinly laminated. The Vinita Beds are rich in fossil fish, branchiopods, and plant fragments. These rocks were deposited in braided streams as well as in paludal and possible lacustrine environments in a humid and heavily vegetated setting. End_of_Article - Last_Page 275------------

Origin and tectonic evolution of the Maclaren and Wrangellia terranes, eastern Alaska Range, Alaska

Major portions of the eastern Alaska Range, south of the Denali fault, in the McCarthy, Nabesna, Mount Hayes, and eastern Healy quadrangles, consist predominantly of the Maclaren and Wrangellia tectono-stratigraphic terranes. The Maclaren terrane consists of the Maclaren Glacier metamorphic belt and the regionally deformed and metamorphosed East Susitna batholith. The Maclaren Glacier metamorphic belt is composed of argillite, metagraywacke, and sparse andesite flows that are progressively regionally metamorphosed from lower greenschist facies to middle amphibolite facies near the East Susitna batholith. The East Susitna batholith is composed of gabbro, quartz diorite, granodiorite, and sparse quartz monzonite. Isotopic ages are as old as a K-Ar hornblende age of 87.5 m.y., possibly reset, and a U-Pb zircon age of 70 m.y. The batholith is intensely deformed and regionally metamorphosed under conditions of the middle amphibolite facies. The Wrangellia terrane is divided into two subterranes: (1) the Slana River subterrane, composed of late Paleozoic andesite to dacite flows, tuff, limestone, and argillite, unconformably overlying massive basalt flows of the Triassic Nikolai Greenstone, Late Triassic limestone, and younger Mesozoic flysch; and (2) the Tangle subterrane, a deeper-water equivalent of the Slana River subterrane, composed of late Paleozoic and Early Triassic aquagene tuff, chert, minor andesite tuff and flows, limestone, unconformably overlying pillow basalt and massive basalt flows of the Triassic Nikolai Greenstone, and Late Triassic limestone. Both subterranes are intruded by locally extensive gabbro and diabase dikes and by cumulate mafic and ultramafic sills. Less extensive terranes (two) are the Clearwater terrane, a sequence of intensely deformed chlorite schist, muscovite schist, marble, and greenstone of Late Triassic age; and an unnamed terrane of ultramafic and associated rocks of presumable Paleozoic or Mesozoic age. Each terrane or subterrane generally has (1) a distinctive time-stratigraphic sequence reflecting a unique geologic history; (2) a missing provenance for bedded sedimentary or volcanic rocks; and (3) bounding thrust or strike-slip faults, interpreted as accretionary sutures. The Maclaren and Wrangellia terranes are juxtaposed along the Broxson Gulch thrust, which consists of an imbricate series of north-dipping thrust faults. Paralleling the Broxson Gulch thrust, a few kilometres to the south, is the north-dipping Eureka Creek thrust, along which are juxtaposed the Slana River and Tangle subterranes. The Maclaren terrane is correlated with the Kluane Schist and the Ruby Range batholith in the southern Yukon Territory, which represent the northward extension of the Taku and Tracy Arm terranes. If correct, this correlation defines a minimum displacement of the Maclaren terrane along the Denali fault of ∼400 km. The Maclaren terrane is interpreted to have formed in a synorogenic Andean-type arc setting on the west margin of Mesozoic North America in the middle to late Mesozoic and early Cenozoic. The Wrangellia terrane is interpreted to have initially formed in an island-arc setting during the late Paleozoic. Subsequently in the Late Triassic, the Wrangellia terrane underwent rifting near the paleoequator, with formation of the Nikolai Greenstone and associated mafic and ultra-mafic igneous rocks. In the middle and late Mesozoic, Wrangellia migrated toward, and was accreted during, the middle Cretaceous to the Maclaren terrane along the Broxson Gulch thrust. Subsequent dispersion of both the Maclaren and Wrangellia terranes along the Denali fault and the Broxson Gulch thrust commenced during the early Tertiary and continues through the present.

Triassic plant Megafossils from the Tiki Formation, South Rewa Gondwana Basin, India

Plant megafossils are for the first time described from the Tiki Formation. The specimens are from two regions, Janar River Section, near Harai and Son River Section, near Giar, Shahdol District, Madhya Pradesh.
 From the Janar River Section Lepidopteris madagascariensis Carpentier, Dicroidium hughesii (Feistmantel) Gothan, D. zuberi (Szajnocha) Archangelsky, D. sp., Xylopteris sp., Sphenobaiera janarensis Pal sp. nov. and Baiera sp. have been described. On the basis of this assemblage an Early Upper Triassic age has been suggested for Janar River beds.
 Son River Section, near Giar has yielded Lepidopteris strombergensis (Seward) Townrow, Dicroidium giarensis Pal sp. nov., D. coriaceum (Johnston) Townrow, D. zuberi (Szajnocha) Archangelsky, D. sp. cf. D. odontopteroides (Morris) Gothan, Elatocladus denticulatus Pal sp. nov., E. raoi Pal sp. nov., Pagiophyllum bosei Pal sp. nov., Yabiella indica Pal sp. nov. and Desmiophyllum singhii Pal sp. nov. Beside these, a few impressions of equisetaceous stem, leaf-sheath and nodal diaphragm have also been described. A Late Upper Triassic age has been proposed for the beds exposed in the Son River.

Paleozoic volcanic assemblages and volcanogenic massive sulfide deposits near Tulsequah, British Columbia

New fossil, structural, and lithological evidence shows that the dominantly andesitic terrane near the junction of the Taku and Tulsequah rivers, northwestern British Columbia, is a proximal facies, roughly age equivalent to late Paleozoic tuffaceous and argillaceous sedimentary rocks exposed near Tatsamenie Lake, rather than of Late Triassic age as previously mapped. Fusulinids from the Tulsequah sequence are Middle Pennsylvanian, whereas the limestones at the top of the Paleozoic section near Tatsamenie Lake are of Permian age. The Tulsequah sequence hosts the Tulsequah Chief, Big Bull, and Ericksen – Ashby massive sulfide deposits, which arc associated with small bodies of rhyolite.

New records and taxa of Permian and Triassic fossils from New Caledonia and New Zealand

Five taxa including one new genus and three new species, are described from marine sequences of the Permian-Triassic Téremba Group and Baie de St Vincent Group of west coast New Caledonia. Taxa described include a conulariid, Paraconularia caledonica sp. nov. and a bivalve Trabeculatia trabeculum (Waterhouse) of Late Permian age and a brachiopod Psioidiella parisi sp.nov., a bivalve Ouamouia grantmackiei gen. et sp.nov. and an indeterminate plesiosaur of Late Triassic age. Recognition of most of these taxa from sequences in both New Caledonia and New Zealand strengthens faunal and biostratigraphic correlations between the two.

Vega Field and Potential of Ragusa Basin, Offshore Sicily: ABSTRACT

Vega, the largest single oil field in the Mediterranean Sea, is located between the southeastern coast of Sicily and the Island of Malta. The field lies entirely in Italian waters. Its discovery in October 1980 was based on interpretation of a very poor-quality seismic survey which, nevertheless, roughly outlined a relatively small structure. A limestone and dolomite fractured reservoir of the Inici, or Siracusa Formation, of Late Jurassic age, may contain in excess of 1 billion bbl of heavy crude (15.5 API) within a productive area of approximately 10,000 acres (4,000 ha.). Reservoir properties are excellent, with permeabilities in darcys. The field extends northwest-southeast for 8.5 mi (14 km) and averages 1.7 mi (3 km) in width, according to the 3D seismic survey (2,0 0 km) shot soon after the discovery well was drilled. The gross oil column reaches approximately 820 ft (250 m). The southeasternmost part of the Vega structure is not yet completely defined, and an additional 3D seismic survey is in progress. Should the new seismic results confirm expectations, the Vega structure could extend over 10 mi (17 km). The deepest formation reached by wells in the Ragusa basin is the Taormina Formation (dolomite of Middle to Late Triassic age) to which the Ragusa, Gela, Ponte Dirillo, and Piano Lupo oil fields are linked. The overlying Streppenosa Formation (Late Triassic to Early Jurassic age) is represented by bituminous shale with limestone development at the bottom (basal Streppenosa or Noto Member), which produces in the Mila and Irminio fields. The overlying Inici reservoir consists of dolomite and underlain by limestone in the southwestern part of the basin, and entirely of limestone in the northwestern portion of the basin. The Inici Formation represents the platform facies of the open-sea Villagonia and Giardini sediments. The Cammarata-Pozzillo (discovered in 1959), Perla (1979), Vega (1980), and Prezioso (1983) heavy crude oil fields are related to this formation. The Vega structure lies across the edge of the Inici carbonate platform. The northeastern flank appears to be controlled mainly by the facies variation between the Inici and Villagonia Formations. The southwestern flank seems, rather, to be controlled by dip. The potential for discovery of other fields similar to Vega in the Ragusa basin is excellent. End_of_Article - Last_Page 1206------------

Speculations on the Mesozoic Plate tectonic evolution of eastern China

Several orogenic belts transecting eastern China are the sites of former convergent plate margins, although there have been varying views on the collisional framework of individual continental blocks, styles of convergence at these zones, and the timing of respective collisions. A tectonic study of eastern China, Mongolia and the southern Soviet Far East indicates the collision of the South China Block with a combined North China‐Northeast China Fold Zone Block in the Late Triassic‐Early Jurassic, their collective suturing to Eurasia in the Late Jurassic‐Early Cretaceous, followed by the Sikhote Alin‐Japan Block in the Mid to Late Cretaceous. The evidence is as follows: (1) A linear belt of Late Triassic‐Early Cretaceous granites and granodiorites trends east from the Qinlingshan through the Dabieshan to the Huaiyang massif. Ophiolites, flysch, subduction zone mélange, a paired metamorphic belt indicating north dipping subduction and marine strata of Carboniferous to Late Triassic age from the Qinlingshan define the suture between the North and South China Blocks, (2) A sinuous belt of ultramafics, blueschists, silicic to intermediate magmatism and west and north vergent folds and thrusts trend from the west margin of the Ordos Basin through central Inner Mongolia and along the east Great Khingan Range to the Amur River. Coupled with a Mid Jurassic‐Early Creataceous unconformity a suturing of eastern Chinese blocks to Eurasia along this zone is suggested, (3) A fold and thrust belt with ultramafics, flysch, blueschists and subduction zone mélange along the Ussuri River in northeast China indicates the suturing of the Sikhote Alin‐Japan Block to Eurasia along a west dipping subduction zone in the Mid to Late Cretaceous. Similarly, a tectonic study of southern China and Southeast Asia has revealed a complex regional mosaic of suture‐bounded terrains which nucleated about the eastern, western and southern margins of the Yangtze Craton during the Late Triassic and Early Jurassic. The evidence is as follows: (4) A north–south trending belt of ophiolites, blueschists, calc‐alkaline volcanics and subduction zone mélange, including granites, granodiorites and strongly deformed marine strata all of Late Triassic age exposed in the Longmenshan of Sichuan merge with the Kekexilishan ophiolite zone into the Ailaoshan‐Tengtiaohe ophiolite and blueschist belt in central Yunnan along which the Songban‐Ganzi Complex and the Shan‐Thai‐Malaya Block join the Craton, and (5) A southeastern prolongation of the Ailaoshan‐Tengtiaohe belt bifurcates into the southeast trending Konvoi zone of northern Vietnam and the north‐south trending Pak Lay‐Luang Prabang zone of Laos and eastern Thailand. Zones of ophiolite, calc‐alkaline volcanics and strong Late Triassic deformation, they separate the Indosinia and Shan‐Thai‐Malaya Blocks from the Craton respectively. These findings differ significantly from previous interpretations of a Late Paleozoic consolidation of South‐Eastern Asia as well as disputing the existence of a true Pangea.

A glauconitic clay-mineral from a speleological deposit of late triassic age

An interstratified glauconite-smectite is recorded from a speleological deposit of Rhaetian age near Bristol, G. B. The mineral is similar to glauconitic material recorded from non-marine or brackish environments and its occurrence is compatible with the proposal that the fissure deposits formed in a transitional fresh-water/saline environment.

Lower Jurassic Radiolaria, San Hipolito, Formation, Vizcaino Peninsula, Baja California Sur: ABSTRACT

End_Page 568------------------------------Lower Jurassic radiolarian faunas recovered from the sandstone member of the San Hipolito Formation, Baja California Sur, indicate a younger age for much of this member than previously assumed. The San Hipolito Formation, exposed at Punta San Hipolito on the Vizcaino Peninsula, consists of 2,400 m (7,875 ft) of marine sedimentary rocks. The oldest member, a Halobia-bearing green chert, lies on pillow basalts and is successively overlain by limestone, breccia, and sandstone members. Upper Triassic (upper Karnian? and/or lower Norian to lower upper Norian) radiolarians have been described from the chert member. The hemipelagic pelecypod Monotis cf. M. subcircularis (Gabb) of Late Triassic (late Norian) age is found in the upper part of the limestone member. The uppermost member of the San Hipolito Formation, a volcaniclastic sandstone 1,840 m (6,035 ft) thick, previously yielded only poorly preserved radiolarians, and was inferred to be of Late Triassic age. In this study, well-preserved radiolarians were not recovered from the sandstone and tuff beds. Thin limestone beds at the very base of the sandstone member contain a unique radiolarian fauna with some forms similar to Triassic radiolarians described from Austria and Italy. Discoidal limestone concretions and thin limestone beds from the top of the lower part of the sandstone member yielded abundant, well-preserved Lower Jurassic radiolarians. No ammonites are found in association with the San Hipolito Lower Jurassic radiolarians, but the radiolarians are similar to Lower Jurassic radiolarian faunas from British Columbia and Oregon, for which excellent ammonite biostratigraphy is available. Based on the occurrence of the radiolarian genera Canoptum, Droltus, Bagotum, Canutus, Hsuum, Lupherium and Pseudoheliodiscus, a Pliensbachian and/or Toarcian age is assigned to the top of the lower part of the sandstone member of the San Hipolito Formation. The continuation of radiolarian studies in British Columbia, Oregon, and Baja California will provide a basis for further elaboration and refinement of a Lower Jurassic radiolarian zonation. End_of_Article - Last_Page 569------------

The ophiolitic North Fork terrane in the Salmon River region, central Klamath Mountains, California

The North Fork terrane is an assemblage of ophiolitic and other oceanic volcanic and sedimentary rocks that has been internally imbricated and folded. The ophiolitic rocks form a north-trending belt through the central part of the region and consist of a disrupted sequence of homogeneous gabbro, diabase, massive to pillowed basalt, and interleaved tectonitic harzburgite. U-Pb zircon age data on a plagiogranite pod from the gabbroic unit indicate that at least this part of the igneous sequence is late Paleozoic in age. The ophiolitic belt is flanked on either side by mafic volcanic and volcaniclastic rocks, limestone, bedded chert, and argillite. Most of the chert is Triassic, including much of Late Triassic age, but chert with uncertain stratigraphic relations at one locality is Permian. The strata flanking the east side of the ophiolitic belt face eastward, and depositional contacts between units are for the most part preserved. The strata on the west side of the ophiolitic belt are more highly disrupted than those on the east side, contain chert-argillite melange, and have unproven stratigraphic relation to either the ophiolitic rocks or the eastern strata. Rocks of the North Fork terrane do not show widespread evidence of penetrative deformation at elevated temperatures, except an early tectonitic fabric in the harzburgite. Slip-fiber foliation in serpentinite, phacoidal foliation in chert and mafic rocks, scaly foliation in argillite, and mesoscopic folds in bedded chert are consistent with an interpretation of large-scale anti-formal folding of the terrane about a north-south hinge found along the ophiolitic belt, but other structural interpretations are tenable. The age of folding of North Fork rocks is constrained by the involvement of Triassic and younger cherts and crosscutting Late Jurassic plutons. Deformation in the North Fork terrane must have spanned a short period of time because the terrane is bounded structurally above and below by Middle or Late Jurassic thrust faults. The North Fork terrane appears to contain no arc volcanic rocks or arc-derived detritus, suggesting that it neither constituted the base for an arc nor was in a basinal setting adjacent to an arc sediment source. Details of the progressive accretion and evolutionary relationship of the North Fork to other terranes of the Klamath Mountains are not yet clear.

Découverte de Dipneustes triasiques( Ceratodontiformes, Dipnoi) dans la formation de Cenger («Arkoses rouges) du Taurus lycien (Turquie occidentale)

Red arkosic sandstones (Cenger Fm.) are known atthe Paleozoic-Mesozoic boundary in some allochtonous series of the lycian Taurus ( de Graciansky, 1972). A small vertebrate fauna discovered near the base of the formation mainly contains fish remains among which Ptychoceratodus and Arganodontidae, represented by teeth plates of young individuals. The Late Triassic age of this faunal assemblage sets an upper limit for orogenic movements that are now known in the south-anatolian Taurus.

Halobia(Bivalvia, Triassic) and a gastropod from Torlesse Supergroup rocks of Wellington, New Zealand

Abstract Halobia lilliei Marwick is recorded from a stream boulder in the Hutt River, probably of local origin. It indicates an Oretian (Karnian) age and confirms a Late Triassic age determination for at least some Torlesse Supergroup rocks in the Wellington-Hutt Valley area. An indeterminate gastropod is described from another locality within the same rocks.

The stratigraphy of the Torlesse rocks of the Mt Somers area (S81) mid-Canterbury

Abstract Pre-Cretaceous basement in the Mt Somers area consists of Torlesse Supergroup rocks of prehnite-pumpellyite facies which are here subdivided into the Mt Taylor Group (Middle-Late Triassic; new group), the Clent Hills Group (Middle-Late Jurassic; amended group), and undifferentiated Torlesse Supergroup. Mt Taylor Group is further subdivided into three new formations: (a) Fingers Formation (Kaihikuan-?Oretian (Ladinian-?Carnian) of late Middle to perhaps early Late Triassic age) of medium-coarse-grained sandstone and minor interbedded alternating sandstone-siltstone sequences containing the key fossils Daonella sp., Praegonia sp., and Spiriferina cf. abichi Oppel. Part of this formation consists of distinctive massive, white, micaceous, coarse-grained feldsarenite with dark calcareous spheroidal concretions. (b) Pudding Hill Formation (Middleearly Late Triassic) a flysch-like sequence of alternating dark grey, fine sandstone and siltstone turbidites, and contains the tube fossil Torlessia mackayi Bather. This formation appears to interdigitate with the Fingers Formation. (c) Balmacaan Formation (Kaihikuan (Ladinian), late Middle Triassic), a fine- to mediumgrained sandstone and siltstone sequence containing conglomerate beds. The key fossil of this formation is Agonisca corbiensis Fleming. Balmacaan Formation appears to be a near-shore (proximal) deposit, Fingers Formation an intermediate reworked deposit, and Pudding Hill Formation a distal turbidite deposit of a continental shelf submarine fan. A west to east palaeoslope is suggested. Undifferentiated Torlesse rocks, of probable Triassic age, occur in the area. These unfossiliferous rocks are lithologically similar to the Mt Taylor Group and in particular to the Balmacaan Formation but in places grade into a phyllite or cataclasite, apparently related to faulting. The Clent Hills Group contains both non-marine and marine sequences with probable gradations between the two. A late Jurassic (Puaroan) age is indicated by the presence of Inoceramus cf. gracilis Holdhaus and Buchia sp. indet., but other marine fossil assemblages indicate a possible range of Middle-Late Jurassic (Temaikan-Puaroan). Conglomerate channel deposits containing tree trunks, and siltstone beds containing well preserved plant remains are a conspicuous feature of the formation. The Clent Hills Group is interpreted as a deltaic sequence.

Triassic turtle remains from northeastern Thailand

ABSTRACT Fragments of dermal bones referable to an undetermined aquatic chelonian have been discovered in the Huai Hin Lat Formation near the Chulabhorn Dam, northeastern Thailand. In the same area, this formation has also yielded ostracodes, semionotid actinopterygians, lungfishes (Ceratodus), capitosaurids (Cyclotosaurus), and phytosaurs, all suggestive of a Late Triassic (possibly Norian) age. The turtle remains are the first hitherto recorded from the Triassic of Asia, but it is still undecided whether they can be referred to one of the taxa known from the Triassic of Germany or belong to a new taxon. They resemble corresponding parts of post-Triassic chelydrid and thalassemydid turtles.

An association ofTorlessiaand late Middle—early Upper Triassic fossils at Pudding Hill Stream, central Canterbury

Abstract Marine invertebrates of late Middle-early Upper Triassic age are associated in redeposited sediments with tubes of Torlessia at Pudding Hill Stream near Mount Hutt, central Canterbury. Bryozoans, taxodont bivalves, Plicatula, brachiopods including Mentzeliopsis, gastropods and crinoids are preserved in more or less fragmentary form in the coarse (granule-sized) bases of graded units, some of which contain Torlessia tubes in their finer-grained upper parts. The mode of occurrence suggests emplacement by subaqueous flow of both the tubes and the shelly remains. Contemporaneity of the tubes and the other fossils is certain and time equivalence of Pudding Hill Formation and Fingers Formation to the west is established. An east-facing palaeoslope seems likely for the Rangitata-Ashburton catchment area for at least part of Triassic time.