The Janusfjellet Subgroup (Bathonian to Hauterivian) on central Spitsbergen: a revised lithostratigraphy

The Janusfjellet Subgroup is a marine shelf to prodeltaic succession dominated by shales with subordinate siltstones and sandstones. The subgroup comprises a lower Agardhf jellet (Upper Bathonian - Berriasian) and an upper Rurikf jellet (Berriasian - Hauterivian) formation. Based on field work in central Spitsbergen the following subdivisions of the formations are proposed (units listed in ascending order).
The Agardhf jellet Formation (up to 290 m thick) contains four members: Oppdalen - a fining upwards succession from conglomerates to shales; Lardyfjellet - black paper shales; Oppdalsata - grey shales with siltstones and sandstones; and Slottsmøya - grey shales and black paper shales. Within the Oppdalen Member three beds are recognised: Brentskardhaugen - phosphoritic conglomerate; Marhøgda - glauconitic sandstones', and Drønbreen - siltstones and shales.
The Rurikfjellet Formation (thickness up to 226 m) is composed of two members: Wimanfjellet - grey and partly silty shale sequence, containing the Myklegardfjellet Bed (of plastic clays) at its base; and Ullaberget - silty and sandy shales with siltstones and sandstones.     

The type section of the Vikinghôgda Formation: a new Lower Triassic unit in central and eastern Svalbard

The Vikinghøgda Formation (250 m) is defined with a stratotype in Deltadalen-Vikinghøgda in central Spitsbergen. The Vikinghøgda Formation replaces the Vardebukta and Sticky Keep Formations of Buchan et al. (1965) and the lower part of the Barentsøya Formation of Lock et al. (1978) as extended geographically by Mørk, Knarud et al. (1982) in central Spitsbergen, Barentsøya and Edgeøya. The formation consists of three member: the Deltadalen Member (composed of mudstones with sandstones and siltstones), the Lusitaniadalen Member (dominated by mudstones with thin siltstone beds and some limestone concretions) and the Vendomdalen Member (composed of dark shales with dolomite interbeds and nodules). The Lusitaniadalen and Vendomdalen members replace the former Sticky Keep Formation/ Member in the siirne areu. The Vikinghøda Formation can be followed through central and eastern Spitsbergen to Barentøya and Edgeøya and includes all sediments between the chert-rich Kapp Starostin Formation (Permian) and the organic-rich shales of the Botneheia Formation (Middle Triassic). The subdivision into three members is also reflected in the organic carbon content and palynofacies. Upwards. each succeeding member becomes more distal, organic-rich and oil-prone than the one below.
The Vikinghøda Formation is well-dated by six ammonoid zones. although the transitional beds between the Deltadalen and Lusitaniadalen members lack age diagnostic macrofossils. Corresponding palynozonation and magnetustratigraphy have also been determined. The overall stratigraphical development correlates well with other key Triassic areas in the Arctic, although intervals in the late Dienerian and early Smithian may be condensed or missing.     

Lithological description of subcropping Lower and Middle Triasic rocks from the Svalis Dome, Barents Sea

Eleven shallow cores display 315 m of the >700 m thick Lower and Middle Triasic successional of the Svalis Dome, a Salt diapir in the central south-western Barents Sea. The Svalis Dome was uplifted in the late Mesozoic. and Trisassic rocks suherop below Quaternary till around the Upper Palaeozoic core of the dome. Deposition of the Triassic succession took place in deep shelf to basinal environments below storm wave base. The succession is dated by macrofossils and palynomorphs and can be assigned to four formations. The basal beds of the shaly greenish grey Havert Formation (Griesbachian) occur above Permian bioclastic carbonate. The Klappmyss Formation (Smithian) in the lower part contains gravity flow sands deposited as submarine fans pussible triggered by tectonic movements along the adjacent ault zones overlian by silty claystones. An organic-rich dark shale unit is here formally defined as the Steinkobbe overlain by silty claystones. An organic-rich dark shale unit is here formally defined as the Steinkobbe Formation, and was deposited in a large bight by restricted water circulation. The Snadd Formation. on top, representes a marine shelf unit deposited in front of an emerging land area in the north-east. A minimum of six higher order transgressive-regressive sequences are recognized at the Svalis Dome and these are correlated with other Arctic areas.     

Palaeomagnetism of a sequence of red beds of the Middle and Upper Sections of Pagnazo Group (Argentina) and the correlation of Upper Palaeozoic-Lower Mesozoic rocks

Palaeomagnetic data from 182 hand samples collected in a rock sequence of about 620-m of red beds of Late Palaeozoic to Early Triassic age exposed in north-western Argentina (30.3° S 67.7° W), are given.
After cleaning, the majority of the Upper Palaeozoic samples (Middle Section of Paganzo Group) show reversed polarity and yield a palaeomagnetic pole at 78° S 249° E (α₉₅= 3°). They also record a polarity transition which we have correlated with the Middle Permian Quebrada del Pimiento Normal Event. The position of the palaeomagnetic pole and the K-Ar age of a basalatic sill at the base of the sequence support this correlation.
Stable remanent magnetization has been isolated in the majority of samples from the Upper Section of the Paganzo Group; it is predominantly reversed and reveals three normal events and also three geomagnetic excursions suggesting an Illawarra Zone age (post Kiaman, Late Tatarian-Early Scythian). The palaeomagnetic pole of the reversely magnetized samples is located at 75° S 285° E(α₉₅= 13°).
The red beds involved in this study are correlated with red beds from the Corumbataí Formation (State of Paraná, Brazil) and with igneous rocks from the Quebrada del Pimiento Formation (Province of Mendoza, Argentina).
The South American Middle and Upper Permian, Upper Permian—Lower Triassic, Lower, Middle and Upper Triassic and Middle Jurassic palaeomagnetic poles reflect a quasistatic period with mean pole at 82° S 244° E, (α₉₅= 4°) which followed the South American Late Palaeozoic polar shift.     

飞仙关组紫色页岩作为矿质肥源的试验

四川盆地下三叠统飞仙关组(T_1f)紫色页岩,富含有机质、磷和多种微量元素T_1f紫色母质添加到两类基础肥力较低的紫色母质和黄壤内,种植稻麦试验后对照结果表明T_1f紫色页岩肥效显著,因此它是一种矿质肥源。     

The marine transgression in the Middle Carboniferous of Brøggerhalvøya (Svalbard)

The change from continental to marine conditions in the Middle Carboniferous on Brøggerhalvøya started at the end of the Bashkirian with short-term transgressive events at the top of the Brøggertinden Formation. Local basin subsidence was responsible for the pulsatory nature of the transgression. The establishment of a shallow marine carbonate-dominated environment is represented by the Moscovian Scheteligfjellet Member which overlies the post-Caledonian red beds of the Brøggertinden Formation. The Scheteligfjellet Member is the lowermost member of the Nordenskioldbreen Formation and shows distinct lateral facies variations. Three facies associations can be distinguished: lagoonal facies, shoal facies and open marine facies. The succeeding two members were deposited in subtidal areas of the carbonate platform. A basin subsidence event at the Carboniferous/Permian boundary was responsible for a short shift into deeper depositional environments during a time of worldwide regression. After this a continuous regression led to supratidal conditions at the top of the Nordenskioldbreen Formation.     

Palaeomagnetism and magnetostratigraphy of uppermost Permian strata, southeast New Mexico, USA: correlation of the Permian–Triassic boundary in non-marine environments

Continental red sandstone and siltstone rocks of the Dewey Lake (Quartermaster) Formation at Maroon Cliffs, near Carlsbad, New Mexico, are characterized by two components of magnetization with partially overlapping laboratory unblocking temperature spectra. Both magnetizations display high coercivities (>100 mT), probably residing in haematite. A north-directed magnetization with steep positive inclination unblocks between 100 and 650 °C, isolating a predominantly northwest-directed magnetization, with shallow inclination, of near uniform normal polarity and maximum unblocking temperatures of 680 °C.
We collected samples from 24 palaeomagnetic sites (i.e. individual beds) from a ~60 m thick section of flat-lying strata disconformably overlying carbonate and evaporite rocks of the Rustler Formation. The upper member of the Rustler Formation contains a Late Permian (early Changxingian) marine invertebrate and conodont fauna. Of the sampled sites, four yield only steep magnetizations, interpreted to be recent overprints. Eight sites did not yield well-grouped site means and were excluded from the final calculations. The formation mean (dec = 337.7°, inc = 9.2°; k = 31.6, α ₉₅ = 7.8°, N = 12 sites) defines a palaeomagnetic pole located at 55.2°N, 117.5°E, in good agreement with other Late Permian North American cratonic poles.
Correlation of the short polarity sequence of this section of Dewey Lake strata is unambiguous. Compared with the polarity stratigraphy of marine sections in Asia, and supported by isotopic age determinations on a widespread bentonite bed in Dewey Lake strata in west Texas (approximately 251 Ma) and fossil data for the underlying Rustler Formation, the magnetostratigraphy is consistent with deposition of the Dewey Lake Formation during the latest Changxingian (Late Permian) stage.     

Basin‐scale fluvial correlation and response to the Tethyan marine transgression: An example from the Triassic of central Spain

The relationships between large‐scale depositional processes and the stratigraphic record of alluvial systems, e.g. the origin and distribution of channel stacking patterns, changing architecture and correlation of strata, are still relatively poorly understood, in contrast to marine systems. We present a study of the Castillian Branch of the Permo‐Triassic Central Iberian Basin, north‐eastern Spain, using chemostratigraphy and a detailed sedimentological analysis to correlate the synrift Triassic fluvial sandstones for ~80 km along the south‐eastern basin margin. This study investigates the effects of Middle Triassic (Ladinian) Tethyan marine transgression on fluvial facies and architecture. Chemostratigraphy identifies a major, single axially flowing fluvial system lasting from the Early to Middle Triassic (~10 Ma). The fluvial architecture comprises basal conglomerates, followed by amalgamated sandstones and topped by floodplain‐isolated single‐ or multi‐storey amalgamated sandstone complexes with a total thickness up to ~1 km. The Tethyan marine transgression advanced into the basin with a rate of 0.04–0.02 m/year, and is recorded by a transition from the fluvial succession to a series of maximum flooding surfaces characterised by marginal marine clastic sediments and sabkha evaporites. The continued, transgression led to widespread thick carbonate deposition infilling the basin and recording the final stage of synrift to early‐post‐rift deposition. We identify the nonmarine to marine transition characterised by significant changes in the Buntsandstein succession with a transition from a predominantly tectonic‐ to a climatically driven fluvial system. The results have important implications for the temporal and spatial prediction of fluvial architecture and their transition during a marine transgression.     

Magnetostratigraphic investigations of the Middle Triassic Badong Formation in South China

Magnetostratigraphic sampling of the Middle Triassic Badong Formation in South China was conducted at three sections. A dual-polarity characteristic remanent magnetization (ChRM) resolved from most samples by thermal demagnetization is shown to have been acquired prior to folding. The primary nature of the ChRM is corroborated by the discovery of the same magnetic polarity at equivalent stratigraphic levels in more than one section. The relative sample VGP (virtual geomagnetic pole) latitudes define nine magnetozones for the three major constituent members of the formation. Comparison with the Mid-Triassic magnetic polarity sequence observed from the western Tethyan region appears to indicate that the bulk of the Badong Formation is Anisian in age and that Ladinian sediments are largely missing. This agrees with palaeontological and stratigraphic evidence in the region and supports the view that Ladinian regression is a major event in the geological evolution of South China, which may signal the onset of amalgamation of the Yangtze Block (YB) with the North China Block (NCB).     

The Neoproterozoic Fiq glaciation and its aftermath, Huqf supergroup of Oman

The <1.5‐km thick Fiq Member of the Ghadir Manqil Formation, Huqf Supergroup, Oman, contains a succession of Marinoan‐age glacially and non‐glacially influenced deposits overlain by a transgressive, ¹³C‐depleted, deep‐water dolostone (Hadash Formation) that deepens up into the marine shales and siltstones of the Masirah Bay Formation. The Fiq Member and Hadash–Masirah Bay Formations are well exposed in the core of the Jebel Akhdar of northern Oman and provide a valuable insight into the processes operating during a Neoproterozoic glacial epoch and its aftermath. The Fiq Member comprises seven stratigraphic units (F1–F7) of proximal and distal glacimarine, non‐glacial sediment gravity flow, and non‐glacial shallow marine facies associations. These units can be correlated over almost the entire Neoproterozoic outcrop belt (ca. 80 km) of the Jebel Akhdar. Four units contain glacimarine rainout diamictites, commonly at the top of cycles beneath strong lithofacies dislocations suggesting flooding. The units are thought to have been generated by combined glacio‐isostatic and glacio‐eustatic forcing caused by changing volumes of terrestrial glacier ice. The lateral persistence and thickness of massive diamictite units increase upwards in the stratigraphy, the youngest (F7) diamictite being abruptly overlain by the Hadash Formation. Correlation of lithofacies associations across the rift basin and palaeocurrents indicate that siliciclastic sediment and glacially entrained debris were derived from both basin margins. Open‐water conditions existed during interglacials, attested to by the presence of wave‐rippled sandstones in the western part of the basin. The Hadash carbonate also exhibits variations between east and west, showing that despite an overall deep‐water depositional setting, rift margin and intrabasinal structure continued to exert a control on facies development during the post‐glacial aftermath. Onlap of basin margins continued through the deposition of the Masirah Bay Formation. The sedimentology and stratigraphy of the Fiq Member and Hadash–Masirah Bay Formations have a number of implications for the Snowball Earth hypothesis. The overall stratigraphic evolution of the Fiq Member suggests a dynamic, temperate/polythermal style of glaciation, perhaps nucleated on uplifted continental or rift margin topography, with marine‐terminating glaciers. Some transgressions coupled to deglaciations within the Fiq glacial epoch were accompanied by minor deposition of carbonate. However, final deglaciation triggered the deposition of a <8‐m thick, deep‐water dolomite contaminated with siliciclastics, with a lithofacies assemblage still reflecting the underlying bathymetric template, followed by relatively deep marine shales and siltstones. The preservation of relatively deep marine Masirah Bay sediments above the Fiq basin margin suggests either tectonic collapse of the rift shoulder or, more likely, rapid eustatic rise accompanying deglaciation.     

Sedimentary facies,depositional processes and climatic controls in a Triassic Lake,Tanzhuang Formation,western Henan Province,China

The Middle to Upper Triassic Tanzhuang Formation represents part of the infill of the early Mesozoic Jiyuan-Yima Basin. The upper part of this stratigraphic unit records deposition within prevailing shallow lake conditions. Well-developed sequences crop out near Jiyuan, western Henan Province, central China. Six sedimentary facies clustered into two facies assemblages were recognized in the lacustrine section. Facies assemblage 1 consists of stacked coarsening-upward sequences composed, from base to top, of organic-rich shales (facies E, type I), laminated siltstones (facies A) and current-rippled laminated sandstones (facies B). Units of assemblage 1 record progradation of small mouth-bar deltas within a perennial open lacustrine system under temperate and humid conditions. Facies assemblage 2 lacks a clear vertical pattern and consists of interbedded fine-grained carbonates and siltstones (facies C); deformed and wave-reworked sandstones (facies D); organic-rich shales (facies E, type II) and clayey mudstones (facies F). The assemblage also represents a perennial, hydrologically-open, shallow lacustrine system, but characterized by strong seasonal climatic control. Water stratification probably occurred in several periods of the lake history. Pangaean megamonsoonal influence is envisaged to explain the strong seasonality imprint evidenced toward the upper part of the Tanzhuang lacustrine column.This is the fourth paper in a series of papers published in this issue on Climatic and Tectonic Rhythms in Lake Deposits.     

Microbial‐dominated carbonate platforms during the Ladinian rifting: sequence stratigraphy and evolution of accommodation in a fault‐controlled setting (Catalan Coastal Ranges,NE Spain)

The Upper Muschelkalk sedimentary record constitutes a major transgressive pulse of north‐eastern Iberia during the Ladinian. This record is arranged in two transgressive–regressive (T–R) sequences formed by two stepped microbial‐dominated carbonate ramp systems where accommodation was mainly controlled by extensional faults. This study seeks to gain new insights into how the evolution of syn‐rift subsidence controls the creation of accommodation space, the depositional styles and, especially, the palaeogeographical domains where specific microbialites developed (thrombolites and stromatolites). Thrombolite bodies (at least 40 m thick) display two types of architecture, biostromal and mud‐mounded and stromatolite bodies (at least 7 m thick) consist of tabular and domed, head‐shaped morphologies. Domed and mounded forms are usually developed during stages of increasing accommodation rates, low‐to flat‐nelief forms tend to grow in association with periods of low accommodation rates. A sea‐level fall of at least 50 m occurred at the end of the Early Ladinian leaving the platform subaerially exposed. As a result, a prominent karst with significant erosional incisions and profuse collapse breccia fillings was formed in the inner and middle ramp settings. The resultant subaerial unconformity bounds T–R sequences 1 and 2. Subsidence curves display two stages of rapid/decelerated total subsidence, constituting two discrete rift/post‐rift pulses in the large Triassic rifting period: (i) Buntsandstein – Middle Muschelkalk, and (ii) Late Muschelkalk – Imon Formation (Rhaetian). The second pulse is characterized by a rapid syn‐rift subsidence during the Late Muschelkalk, and a decelerated post‐rift subsidence throughout the deposition of Keuper facies and Imon Formation. The Late Muschelkalk rapid syn‐rift pulse of total subsidence produces gains in accommodation, which controls the development of the stromatolites and thrombolites (biostromes and mud‐mounds).     

Triassic to Early Jurassic climatic trends recorded in the Jameson Land Basin,East Greenland: clay mineralogy,petrography and heavy mineralogy

During the Early Triassic the Jameson Land Basin (Central East Greenland) was located around 30° N, in the Northern arid belt, but by the Early Jurassic was positioned at a latitude of approximately 50° N. This study examines the record of this transition through a largely continental succession using clay mineralogy, sedimentology, petrography and heavy mineralogy. The Jameson Land Basin is aligned north–south and is 280 km long and 80 km wide. Following an Early Triassic marine phase the basin was filled by predominantly continental sediments. The Early‐to‐Late Triassic succession comprises coarse alluvial clastics (Pingo Dal Formation) overlain by a succession of fine‐grained evaporite‐rich playa/lacustrine sediments (Gipsdalen Formation), indicative of arid climatic conditions. The overlying buff, dolomitic and then red lacustrine mudstones with subordinate sandstones (Fleming Fjord Formation) record reduced aridity. The uppermost Triassic grades into dark organic‐rich, and in places coaly, mudstones and buff coarse‐grained sandstones of lacustrine origin that belong to the Kap Stewart Group, which spans the Triassic–Jurassic boundary, and appear to record more humid climatic conditions. Clay mineralogy analyses highlight significant variations in the kaolinite/illite ratio, from both mudstone and sandstone samples, through the Triassic and into the earliest Jurassic. Complementary heavy mineral analyses demonstrate that the variations recognised in clay mineralogy and sandstone maturity through the Triassic–Early Jurassic succession are not a product of major provenance change or the effect of significant diagenetic alteration. The observed variations are consistent with sedimentological evidence for a long‐term trend towards more humid conditions through the Late Triassic to Early Jurassic, and the suggestion of a significant pluvial episode in the mid‐Carnian.     

Systematic palaeontology and biostratigraphy of two Early Cretaceous condensed sections from the Barents Sea

Bivalve, brachiopod and cirripede faunas from the latest Jurassic and Early Cretaceous Barents Sea boreholes 7320/3-U-l and 7425/9-U-l are systematically described and illustrated. Microfossils have also been studied and the cores arc dated on the basis of the fossil recovery. The bivalve Buchia whose zonal sequence has been used for correlation of boreal marine sections is the most important biostratigraphic marker group in the condensed Boreal Berriasian-Hauterivian intervals of these cores. A new species of cirripede Zeugmatolepas? borealis Collins sp. nov. and dinoflagellate cyst Muderongia aequicornus Århus sp. nov. are described.
The Late Jurassic fine-grained elastics of core 7320/3-U-l are overlain by about 3 m of grey dolomitic limestone of Valanginian and Hauterivian age. The lowermost part of 7425/9-U-l is represented by a latest Volgian-earliest Berriasian fossiliferous greyish green marl. It is followed by a reddish brown fossilifcrous claystone of Berriasian and perhaps partly Valanginian age. Core 7425/9-U-l also contains a mainly Valanginian greyish green marly limestone which changes into a dark grey to black limestone of Early Barremian age in its upper part. The sedimentological change from condensation to dark grey clay deposition took place in the middle Barremian H. rude-fissicostatum ammonite Zone in 7425/9-U-l and probably slightly earlier in 7320/3-U-l. This was commenced at about the same time as deposition of the inaccurately and only indirectly dated fluvio-deltaic Festningen Sandstone Member on Spitsbergen. The dark claystone may thus be a distal equivalent to this sandstone unit.     

Geochemistry of Precambrian basic igneous rocks between St. Jonsfjorden and Isfjorden, central western Spitsbergen, Svalbard

Two types of basic igneous rocks have been mapped in the middle Hecla Hoek succession in the area between St. Jonsfjorden and Isfjorden, central western Spitsbergen: the metadiabase-gabbros from the calc-argillo-volcanic formation and the Trollheimen volcanics from the quartzite-shale formation; both formations are older than the Eocambrian tilloid formation. The former has diabasic and gabbroic textures and occurs as thin discontinuous lensoid masses, while the latter exhibits definite extrusive structures with large amounts of pyroclastics and tuffs and relatively small amounts of solid lavas with abundant amygdules. Both basic rocks have been metamorphosed under the greenschist facies conditions, characterized by actinolite-epidote-biotite-albite assemblage.
The metadiabase-gabbros are moderate-high Fe tholeiites and the Trollheimen volcanics are mainly Na-alkaline, accompanied by a small amount of calk alkaline rocks. The immobile minor and trace element contents indicate that the metadiabase-gabbros are oceanic, similar to the MORB, while those of the Trollheimen volcanics show non-oceanic chemical characteristics and occur in shallow marine, shelf-shelfedge sediments.
The calc-argillo-volcanic formation reveals a shallow marine sedimentary environment and this does not conform with the oceanic nature of the metadiabase-gabbros, occurring in the formation. To overcome this disagreement, an idea of changing tectonic position is postulated to bring a shallow marine sedimentary regime onto a mid-oceanic tectonic zone. This hypothesis supports the concept of active consuming margin tectonics of the Svalbard Caledonides and explains, for example, the occurrence of the high-P metamorphic rocks in the western part of the present area.     

Evolution of salt structures in the northern Paradox Basin: controls on evaporite deposition,salt wall growth and supra‐salt stratigraphic architecture

The northern Paradox Basin evolved during the Late Pennsylvanian–Permian as an immobile foreland basin, the result of flexural subsidence in the footwall of the growing Uncompahgre Ancestral Rocky Mountain thick‐skinned uplift. During the Atokan‐Desmoinesian (～313–306 Ma) fluctuating glacio‐eustatic sea levels deposited an ～2500 m thick sequence of evaporites (Paradox Formation) in the foreland basin, interfingering with coarse clastics in the foredeep and carbonates around the basin margins. The cyclic deposition of the evaporites produced a repetitive sequence of primarily halite, with minor clastics, organic shales and anhydrite. Sediment loading of the evaporites subsequently produced a series of salt walls and minibasins, through the process of passive diapirism or downbuilding. Faults at the top Mississippian level localised the development of linear salt walls (up to 4500 m high) along a NW–SE trend. A crosscutting NE–SW structural trend was also important in controlling the evaporite facies and the abrupt termination of the salt walls. Seismic, well and field data define the proximal Cutler Group (Permian) as a basinward prograding sequence derived from the growing Uncompahgre uplift that drove salt basinwards (towards the southwest), triggering the growth of the salt walls. Sequential structural restorations indicate that the most proximal salt walls evolved earlier than the more distal ones. The successive development of salt‐withdrawal minibasins associated with each growing salt wall implies that parts of the Cutler Group in one minibasin may have no chronostratigraphic equivalent in other minibasins. Localised changes in along‐strike salt wall growth and evolution were critical in the development of facies and thickness variations in the late Pennsylvanian to Triassic stratigraphic sequences in the flanking minibasins. Salt was probably at or very close to the surface during the downbuilding process leading to localised thinning, deposition of diapir‐derived detritus and rapid facies changes in sequences adjacent to the salt wall structures.     

Trona resources in southwest Wyoming

Bedded trona (Na₂CO₃·NaHCO₃·2H₂O) in the lacustrine Green River Formation of Eocene age in the Green River Basin, southwest Wyoming, constitutes the largest known resource of natural sodium carbonate in the world. In this study, 116 gigatons (Gt) of trona ore are estimated to be present in 22 beds, ranging from 1.2 to 11 meters (m) in thickness. Of this total, 69 Gt of trona ore are estimated to be in beds containing less than 2 percent halite and 47 Gt in beds containing 2 or more percent halite. These 22 beds underlie areas of about 130 to more than 2,000 km² at depths ranging from about 200 m to more than 900 m below the surface. The total resource of trona ore in the basin for which drilling information is available is estimated to be about 135 Gt.Underveloped trona beds in the deeper southern part of the basin may be best developed by solution mining. Additional unevaluated sodium carbonate resources are present in disseminated shortite (Na₂CO₃·2CaCO₃) in strata interbedded with the trona and in shallow sodium carbonate brines in the northeast part of the basin. Estimates of the shortite and brine resources were not made.     

西南极利文斯顿岛含砾泥岩层的发现及其地质意义

西南极南设得兰群岛利文斯顿岛赫德半岛中分布的一套主要由复理石相岩石组成的低级变质沉积岩（迈尔斯陡崖组）被认为是中－ 新生代火山岩的基底（晚古生代－ 早中生代？）。以前含砾泥岩在迈尔斯陡崖组局部地点曾有零星报道,但详细的地质填图确认此地有四层含砾泥岩分布。研究表明,这些含砾泥岩可能是水下碎屑流沉积,其生成环境可能是海底扇中扇的水道。对比在南极半岛所发现有大量的含砾泥岩,则进一步表明利文斯顿岛早期地质特征可与南极半岛相比,两者在中－ 新生代岩浆弧形成之前处于相同的构造环境。     

Supradetachment to rift basin transition recorded in continental to marine deposition; Paleogene Bandar Jissah Basin,NE Oman

A transition from supradetachment to rift basin signature is recorded in the ~1,500 m thick succession of continental to shallow marine conglomerates, mixed carbonate‐siliciclastic shallow marine sediments and carbonate ramp deposits preserved in the Bandar Jissah Basin, located southeast of Muscat in the Sultanate of Oman. During deposition, isostatically‐driven uplift rotated the underlying Banurama Detachment and basin fill ~45° before both were cut by the steep Wadi Kabir Fault as the basin progressed to a rift‐style bathymetry that controlled sedimentary facies belts and growth packages. The upper Paleocene to lower Eocene Jafnayn Formation was deposited in a supradetachment basin controlled by the Banurama Detachment. Alluvial fan conglomerates sourced from the Semail Ophiolite and the Saih Hatat window overlie the ophiolitic substrate and display sedimentary transport directions parallel to tectonic transport in the Banurama Detachment. The continental strata grade into braidplain, mouth bar, shoreface and carbonate ramp deposits. Subsequent detachment‐related folding of the basin during deposition of the Eocene Rusayl and lower Seeb formations marks the early transition towards a rift‐style basin setting. The folding, which caused drainage diversion and is affiliated with sedimentary growth packages, coincided with uplift‐isostasy as the Banurama Detachment was abandoned and the steeper Marina, Yiti Beach and Wadi Kabir faults were activated. The upper Seeb Formation records the late transition to rift‐style basin phase, with fault‐controlled sedimentary growth packages and facies distributions. A predominance of carbonates over siliciclastic sediments resulted from increasing near‐fault accommodation, complemented by reduced sedimentary input from upland catchments. Hence, facies distributions in the Bandar Jissah Basin reflect the progression from detachment to rift‐style tectonics, adding to the understanding of post‐orogenic extensional basin systems.     

Sedimentation and deformation in a Pliocene–Pleistocene transtensional supradetachment basin, Laguna Salada, north-west Mexico

This study examines a thick section of Pliocene–Pleistocene sedimentary rocks exposed in the footwall of an active normal fault (Cañon Rojo fault) near its intersection with the dextral-normal Laguna Salada fault in north-western Mexico. These rocks are situated in the upper plate of an inactive strand of the Cañada David detachment fault, which is cut on the north-east by the Laguna Salada fault. The stratigraphy is divided into three unconformity-bounded sequences: (1) marine mudstone of the Pliocene Imperial Formation; (2) nonmarine Pliocene–Pleistocene redbeds, consisting of sedimentary breccia, conglomerate, conglomeratic sandstone (all un-named) and fine-grained sandstone and mudstone of the Palm Spring Formation; and (3) uncemented Pleistocene boulder gravel. Coarse deposits of the redbeds sequence were deposited in fault-bounded, high- and low-gradient alluvial fans that passed laterally into a low-energy fluvial plain of the ancestral Colorado River (Palm Spring Formation) which occupied the present-day Laguna Salada. Detailed mapping reveals convergence and lap-out of bedding surfaces in the redbeds sequence onto the west limb of a large anticline cored by Imperial Formation. These geometries, combined with fanning dips and thickening of stratigraphy into the flanking syncline, indicate that the anticline grew during deposition of the redbeds. Fold axes of the growth anticline and smaller related folds trend N to NNE, parallel to the strike of associated normal faults and perpendicular to the extension direction. Based on its orientation, large size and relationship to neighbouring structures, the anticline is interpreted to be a fault-bend fold that grew in response to slip of the upper plate over a bend in the Cañada David detachment fault during deposition in a transtensional supradetachment basin. Localized subsidence in the flanking syncline resulted in deposition of >1000 m of alluvial sediments near its intersection with the Laguna Salada fault. Sedimentary detritus is derived exclusively from the north-east (footwall) side of the dextral-normal Laguna Salada fault, indicating that topographic relief was high in the Sierra Cucapa and was subdued or negligible in the footwall of the coeval Cañada David detachment. Following deposition of the redbeds and grey gravel units, the northern part of the detachment fault was abandoned and the modern Cañon Rojo fault was initiated, producing rapid footwall uplift and erosion of previously buried stratigraphy. Slip rate on the Cañon Rojo fault is estimated to be ≈2–4 mm yr^?1 since middle Pleistocene time, similar to the late Pleistocene to Holocene rate determined in previous studies.