Sedimentology in metamorphic rocks,the Willyama Supergroup,Broken Hill,Australia

In the upper greenschist to granulite grade rocks of the Willyama Supergroup at Broken Hill, Australia, earlier recognition of metamorphosed graded bedding in siliciclastic metasedimentary rocks led to interpretations of these rocks as deep-water turbidites. However, graded beds can also be deposited in shelfal environments below storm wave base. This study identified other tempestite features including wave oscillation ripples, hummocky cross-stratification and swaley cross-stratification indicating that deposition took place above the wave base of the larger storms.

Albitised metasedimentary rocks of the upper Thackaringa Group show structures such as swaley cross-stratification typical of shallow-water conditions above fair-weather wave base. Deposition of the Broken Hill Group commenced with muddy Allendale Metasediments conformable on the Thackaringa Group. The Ettlewood Calc-Silicate Member, originally a dolomitic, siliceous sediment, is interpreted as coastal sabkha indicating onset of a marine transgression. The Parnell Gneiss represents a volcanic or volcaniclastic interruption, heralding gradually increasing input of sand in the Freyers Metasediments reaching a maximum in middle Freyers Metasediments, followed by an abrupt reversion to mud, still influenced by wave action. An open marine shelf is interpreted, possibly 30 m deep (no more than 100 m) in the final stage of a developing rift. The Broken Hill Group terminated with the massive Hores Gneiss volcanic unit.

Sedimentation of the siliciclastic Sundown Group took place in similar conditions, commencing with a muddy interval overlying the Hores Gneiss. The shallowing produced by ～90 m thickness of volcanic/volcaniclastic Hores Gneiss was compensated by subsidence.

Paragon Group deposition commenced with substantial black mud, resulting from isolation from the sand supply and probably isolation from the sea. A fresh connection to the sea led first to the deposition of dolomitic carbonate (King Gunnia Calc-Silicate Member), then to deposition of parallel-laminated fine sand below wave base (upper Cartwrights Creek Metasediments), followed by ripple cross-laminated sand above wave base (Bijerkerno Metasediments). The Dalnit Bore Metasediments show abundant very thin graded silt–mud units possibly deposited below storm wave base, and thicker units of stacked wave oscillation ripples deposited above the wave base of larger storms.

The Broken Hill orebody is hosted by altered Broken Hill Group metasedimentary rocks deposited at water depths of ～30 m. Unless the ore fluid temperature was less than 150°C, it is likely that the orebody formed below the seafloor: at such shallow-water depths, the confining pressure would be inadequate to suppress boiling of hotter rising hydrothermal fluids.     

白布勘探区龙潭组沉积环境及成煤条件分析

贵州大方县白布勘探区煤系地层龙潭组为海陆交互相沉积,厚度177～211m,含煤21～36层,煤层总厚18.04～30.29m,可采煤层6层。根据岩性、岩相特征自下而上分为3段,下段为潟湖—潮坪相沉积,并在大部分地区形成泥炭沼泽,形成了可采的33、28号煤层;中段为三角洲相,泥岩沼泽相多在三角洲分流河道间的湖沼区及湖波浪带基础上发育而成,煤层层位稳定,厚度不大;上段为潮坪三角洲相,该期构造活动趋于平稳,形成的煤层层位稳定,厚度大,6中煤0.39～6.88m,7号煤0～3.09m。三段厚度比较接近,反映该区晚二叠世期间地壳沉降均衡。沉积环境差异是本区成煤条件的主要控制因素。     

Geology of coal bearing Palaeogene sediments,onshore Torquay Basin,Victoria

New mapping at Anglesea coal mine, and coal resource and deep groundwater drilling have provided new perspectives on the economically important Eastern View Group coal bearing sedimentary succession in the onshore Torquay Basin. In the Anglesea Syncline, the upper 35 m thick brown coal seam of the Eastern View Group is overlain by a low angle unconformity. Units overlying the coal seams include high energy, cross cutting sand channels of the Boonah Formation and lower energy channel and interchannel systems of the overlying Salt Creek and Anglesea Formations. The mine section can be correlated from borehole data with the Eastern View Group and Demons Bluff Group exposed in coastal cliff sections along the adjacent Anglesea to Torquay coast. Recently drilled coal and groundwater exploration bores provide new data on the extent of the coal measures in the Anglesea area, and details of the underlying Tertiary succession that include typical Otway Basin units such as the Pember Mudstone and Pebble Point Formations. The stratigraphy below the coal measures suggests that the Otway Ranges were not present during Palaeogene times. The rank of the brown coals on and around the Otway Ranges is higher than any other Tertiary coals in onshore Victoria, and they preserve similar patterns of rank distribution to the high rank black coals in the underlying Lower Cretaceous Otway Group. Evidence for large overburden thicknesses is lacking, and the high ranks may have been augmented by higher than normal geothermal gradients in the Early Tertiary. Comparisons between the observed depositional cycles, sequence stratigraphic cycles, and worldwide coastal onlap curves suggest that the observed disconformity boundaries are sequence boundaries that provide a chronostratigraphic framework. Sequences present may include TB4.1–4.5 in the overburden units, and TB 2.4–3.6 in the coal bearing interval.     

U–Pb geochronology and palynology from Lopingian (upper Permian) coal measure strata of the Galilee Basin,Queensland, Australia

This study presents the first chemical abrasion-isotope dilution thermal ionisation mass spectrometry (CA-IDTIMS) U–Pb zircon ages from tuffs in Lopingian (upper Permian) strata of the Galilee Basin, Queensland and reassigns the B coal-seam to the ‘Burngrove Formation equivalent.’ Five Lopingian tuffs were dated: four from the CRD Montani-1 drill hole including three from the ‘Fair Hill Formation equivalent’ (255.13 ± 0.09, 254.41 ± 0.07 and 254.32 ± 0.10 Ma) and one from the ‘Burngrove Formation equivalent’ (252.81 ± 0.07 Ma, approximately the age of the Yarrabee Tuff in the adjacent Bowen Basin); and a single tuff from the Black Alley Shale in the GSQ Tambo-1-1A drill hole (254.09 ± 0.06 Ma). In the Galilee Basin, all three units are constituents of the Betts Creek Group, here formally elevated in nomenclatural status from the Betts Creek beds. On the western margin of the basin, the group thins, and the ‘J and K’ seams (formerly known as the Crossmore and Glenaras sequences, respectively) in the GSQ Muttaburra-1 drill hole have been interpreted through palynology as Cisuralian–early Guadalupian (spore-pollen assemblage APP3.2). This corroborates the exclusion of the ‘J and K’ seams from the overlying Lopingian Betts Creek Group (spore-pollen assemblage APP5), and the underlying lower to mid-Cisuralian Aramac Coal Measures (spore-pollen assemblage APP2.2), which represent the uppermost unit of the Joe Joe Group. It is proposed that the ‘J and K’ seams are restricted to a depocentre in the Hulton–Rand structure. The recognition of these strata containing APP3.2 spore-pollen assemblages suggests that the mid-Permian hiatus is locally reduced to 12–13 My from 30 Ma (where the ‘J and K’ seams are absent). The results of the radiometric dating and palynological analysis in the Galilee Basin support the proposed, albeit informal stratigraphy, that is given in terms of equivalents of formational units in the Bowen Basin and on the intervening Springsure Shelf.     

Pre-Cenozoic geology of the Latrobe Valley Area—onshore Gippsland Basin,S.E. Australia

In 2010–2011, a well on the uplifted northern edge of the Latrobe Valley (Yallourn North-1A) cored a 550 m section of mostly arenaceous sediments from the Lower Cretaceous Tyers River Subgroup. A follow-up core-hole (Yallourn Power-1) aimed at extending the Tyers River Subgroup section some 5 km south into the Latrobe Valley instead encountered Paleozoic basement rocks immediately below Cenozoic coal measures. From a re-examination of earlier coal and groundwater bore results, and new interpretations from gravity, seismic and magneto-telluric (MT) surveys, there is a significant area of Paleozoic basement rock that may underlie the whole northern Latrobe Valley area. The uplifted Yallourn North Lower Cretaceous sediments are a separate basin entity herein named the Monash trough. It appears they are separate from the main Lower Cretaceous Strzelecki Group Basin sediments on the southern side of the Latrobe Valley. Attributes of the Monash trough may underlie the main Strzelecki Basin, but this remains to be substantiated by further drilling. The intervening subcrop of Paleozoic basement rocks is herein named the Glengarry basement block. It shows characteristic gravity, MT and seismic features covering some 200 km² of the northern Latrobe Valley area. The boundary between the Glengarry basement block and Strzelecki Basin approximates to the Princes Highway. It is uncertain whether structural separation of the Monash trough from the main Strzelecki Basin always existed, or whether uplift and stripping of Cretaceous rocks over the Glengarry basement block occurred in post-Cretaceous but pre-Cenozoic times. Comparative rank and maturity indices indicate a greater depth of burial of the Glengarry basement block than what exists today, whereas less stripping and loss of section have occurred to the Monash trough. Cretaceous sediments of the Tyers River Subgroup (Rintouls Creek Formation, Tyers Conglomerate) in the Monash trough are dominated by mudstones, siltstones with lesser quartzose sandstones, conglomerates and thin coals. The sediments are over 300 m thick and are conformably overlain by 100 m of volcaniclastic sediments typical of the main Strzelecki Group, in turn overlain by nearly 100 m of Cenozoic coal measures. New detailed spore–pollen dating of Yallourn North-1A cores indicates that all Cretaceous sediments in the Monash trough are Barremian in age. This revises the traditional Neocomian age assigned to the formation. High total organic carbon levels in the 100 m-thick mudstones of the Locmany Member in the Rintouls Creek Formation constitute a mature petroleum source rock worthy of future hydrocarbon exploration.     

Matt Wilson structure: record of an impact event of possible Early Mesoproterozoic age,Northern Territory

The Matt Wilson structure is a circular 5.5 km-diameter structure in Early Mesoproterozoic or Neoproterozoic rocks of the Victoria Basin, Northern Territory. It lies in regionally horizontal to gently dipping Wondoan Hill and Stubb Formations (Tijunna Group) and Jasper Gorge Sandstone (Auvergne Group). An outer circumferential syncline with dips of 5?–?40° in the limbs surrounds an intermediate zone with faulted sandstone displaying horizontal to low dips, and a central steeply dipping zone about 1.5 km across. Several thrust faults in the outer syncline appear to indicate outward-directed forces. The central zone, marked by steeply dipping to overturned Tijunna Group and possibly Bullita Group sandstone and mudstone, indicates uplift of at least 300 m. The rocks are intensely fractured with some brecciation, and contain numerous planar to subtly undulating surfaces displaying striae which resemble shatter cleavage. Thin-sections of sandstone from the central area show zones of intense microbrecciation and irregular and planar fractures in quartz, but no melt-rocks have been identified. The planar fractures occur in multiple intersecting parallel sets typical of relatively low-level (5?–?10 GPa) shock-pressure effects. Alternative mechanisms, i.e. igneous intrusion, carbonate collapse, diapirism and regional deformation processes, have been discounted. The circular nature, central uplift, faulting, shatter features and planar fractures are all consistent with an impact origin. The Matt Wilson structure is most likely a deeply eroded impact structure in which the more highly shocked rocks of the original crater floor have been removed by erosion. Estimates of the age of the Auvergne and Tijunna Groups range from Early Mesoproterozoic (which we favour) to Late Neoproterozoic. Early Cambrian Antrim Plateau Volcanics near the impact structure show no signs of impact effects, allowing the age of impact to be constrained between Early Mesoproterozoic and Early Cambrian. The presence of widespread soft-sediment deformation features, apparently confined to a single horizon in the Saddle Creek Formation some 700?–?1000 m stratigraphically higher in the Auvergne Group than the rocks at the impact site, and apparently increasing in thickness towards the Matt Wilson structure, lead us to speculate that this probable event horizon is related to the impact event: if correct the impact occurred during deposition of the Saddle Creek Formation.     

Permo-Carboniferous coal measures in the Qinshui basin: Lithofacies paleogeography and its control on coal accumulation

The Qinshui basin in southeastern Shanxi Province is an important base for coalbed methane exploration and production in China. The methane reservoirs in this basin are the Carboniferous and Permian coals. Their thickness is strongly controlled by the depositional environments and the paleogeography. In this paper, sedimentological research was undertaken on the outcrop and borehole sections of the Taiyuan and Shanxi formations in the Qinshui basin and the basin-wide lithofacies paleogeography maps for these two formations have been reconstructed. The Taiyuan Formation is composed of limestones, aluminous mudstones, siltstones, silty mudstones, sandstones, and mineable coal seams, with a total thickness varying from 44.9 m to 193.48 m. The coal seams have a thickness ranging between 0.10 and 16.89 m, averaging 7.19 m. During the deposition of the Taiyuan Formation, the northern part of the basin was dominated by a lower deltaic depositional system, the central and southern parts were dominated by a lagoon environment, and the southeastern corner was occupied by a carbonate platform setting. Coal is relatively thick in the northern part and the southeastern corner. The Shanxi Formation consists of sandstones, siltstones, mudstones, and coals, with the limestones being locally developed. The thickness of the Shanxi Formation is from 18.6 m to 213.25 m, with the thickness of coal seams from 0.10 to 10 m and averaging 4.2 m. During the deposition of the Shanxi Formation, the northern part of the Qinshui basin was mainly dominated by a lower deltaic plain distributary channel environment, the central and southern parts were mainly an interdistributary bay environment, and the southeastern part was occupied by a delta front mouth bar environment. The thick coals are distributed in the central and southern parts where an interdistributary bay dominates. It is evident that the thick coal zones of the Taiyuan Formation are consistent with the sandstone-rich belts, mainly located in the areas of the northern lower deltaic plain and southeastern barrier bar environments, whereas the thick coal zones of the Shanxi Formation coincide with the mudstone-rich belts, located in the areas of the central and southern interdistributary bay environments. Translated from Journal of Palaeogeography, 2006, 8(1): 43–52 [译自: 古地理学报]     

Conceptual models for short‐eccentricity‐scale climate control on peat formation in a lower Palaeocene fluvial system,north‐eastern Montana (USA)

Fluvial systems in which peat formation occurs are typified by autogenic processes such as river meandering, crevasse splaying and channel avulsion. Nevertheless, autogenic processes cannot satisfactorily explain the repetitive nature and lateral continuity of many coal seams (compacted peats). The fluvial lower Palaeocene Tullock Member of the Fort Union Formation (Western Interior Williston Basin; Montana, USA ) contains lignite rank coal seams that are traceable over distances of several kilometres. This sequence is used to test the hypothesis that peat formation in the fluvial system was controlled by orbitally forced climate change interacting with autogenic processes. Major successions are documented with an average thickness of 6·8 m consisting of ca 6 m thick intervals of channel and overbank deposits overlain by ca 1 m thick coal seam units. These major coal seams locally split and merge. Time‐stratigraphic correlation, using a Cretaceous–Palaeogene boundary event horizon, several distinctive volcanic ash‐fall layers, and the C29r/C29n magnetic polarity reversal, shows consistent lateral recurrence of seven successive major successions along a 10 km wide fence panel perpendicular to east/south‐east palaeo‐flow. The stratigraphic pattern, complemented by stratigraphic age control and cyclostratigraphic tests, suggests that the major peat‐forming phases, resulting in major coal seams, were driven by 100 kyr eccentricity‐related climate cycles. Two distinct conceptual models were developed, both based on the hypothesis that the major peat‐forming phases ended when enhanced seasonal contrast, at times of minimum precession during increasing eccentricity, intensified mire degradation and flooding. In model 1, orbitally forced climate change controls the timing of peat compaction, leading to enhancement of autogenic channel avulsions. In model 2, orbitally forced climate change controls upstream sediment supply and clastic influx determining the persistence of peat‐forming conditions. At the scale of the major successions, model 2 is supported because interfingering channel sandstones do not interrupt lateral continuity of major coal seams.     

阳泉矿区含煤地层沉积环境及其对煤层厚度分布控制

阳泉矿区煤系地层形成于海陆交互相的过渡环境,其煤层的形成、赋存、厚度变化、分布均受沉积环境的控制和影响。根据分析成煤环境、预测煤层赋存变化情况,为煤炭资源补勘和开采生产提供指导     

Lithofacies attributes, depositional system and diagenetic properties of the Permian Gharif Formation from Haushi–Huqf area, Central Oman

Over 70 m thick interbedded sandstone, siltstone and claystone of the upper member of the Gharif Formation are exposed in western Huqf area in Oman Interior Sedimentary Basin. The Gharif Formation, particularly its upper member hosts major hydrocarbon reservoir in the subsurface of the Oman Interior Sedimentary Basin. The upper member of the Gharif Formation is comprised of interbedded thick sandstone, siltstone, carbonaceous clays and intraformational conglomerates. The sandstone lithofacies, on average, constitute 10 m thick multistoreyed sequences, which are composed internally of 2–3 m thick and 100 s of metres across vertically and laterally amalgamated sandstone bodies. Two major types of sandstones (types 1 and 2) are identified on the basis of their lithofacies association and internal architecture. The type 1 sandstone constitutes the lower part of the member and is comprised of pebbly to coarse-grained, planar and trough cross-bedded sandstone, plane bedded sandstone and pebble lags at the base of major sandstone bodies. The cross-beds are, on average, 30 cm thick exhibiting a dominant paleoflow direction towards NW (280–300° N). It is interpreted to be deposited by low sinuosity braided streams. The type 2 sandstone constitutes the upper part of the member and is comprised of medium-grained sandstone, trough to low angle plane bedding associated with lateral accretion surfaces. It is commonly interbedded with carbonaceous clays. Silicified plant fragments are commonly distributed in the upper part of the sandstone. Interbedded clays and siltstones are red, mottled and extensively bioturbated due to root burrows. It is interpreted to be deposited by high sinuosity meandering streams. In the uppermost part of the section, several dark grey to black carbonaceous clay/coal beds with plant matter are interbedded with sandstone and red clay indicating development of swampy conditions during onset of the coastal setting in the uppermost part of the formation. About 30 cm thick bioclastic sandstone deposited by the marine coastal bars mark transition from the Gharif Formation to carbonate dominated Khuff Formation. The sandstone of the Gharif Formation is arkosic in composition. Very small amount of cement and negligible compaction of constituent grains in sandstone indicates shallow burial before uplift.     

On the geodynamics of the Alpine collisional granitoids from Central Anatolia: petrology,age and isotopic characteristics of the granitoids of the Ekecikdağ Igneous Association (Aksaray/Turkey)

Granitoids of the Ekecikda? Igneous Association (Central Anatolia/Turkey) are products of collisional–post-collisional magmatism in the Ekecikda? area. These granitoids are granodiorite, microgranite and leucogranite. Field relations of granodiorites with microgranites is obscured, but leucogranites intrude both rock types. Mean zircon laser ablation (LA)-ICP-MS ²⁰⁶Pb-²³⁸U ages of granodiorites and microgranites are 84.52 ± 0.93 Ma and 80.7 ± 1.6 Ma, respectively, and age of leucogranites is suggested as 80 Ma, based on field relations combined with ²⁰⁶Pb/²³⁸U and Rb-Sr ages. Crystallisation temperatures of granodiorites, microgranites and leucogranites are 728°C-848°C, 797°C-880°C, 704°C-809°C, respectively.

Geochemical characteristics including Sr-Nd isotopic evidences infer a non-cogenetic character, as there is a high crustal contribution in I-type granodiorite sources, a crustal source with insignificant and significant mantle inputs in S-type microgranites and leucogranites, respectively. LA-ICP-MS Lu-Hf isotope data from zircons reveal their crustal nature (εHf_(t): ?1.3 ± 0.5 to ?8.8 ± 0.5). Crustal melting linked to the Alpine thickening during the Late Cretaceous led to formation of heterogeneous sourced granitoids with crustal dominated sources in the Ekecikda? area. Understanding of the nature and evolution of collisional Ekecikda? granitoids is not only important to put contribution in the geodynamic evolution of Central Anatolia and surrounding Alpine area, but also to better understand systematics of collisional magmatic systems.     

ON MANGANIFEROUS FORMATIONS AND THE METALLOGENY OF MANGANESE,PAPER I. VOLCANOGENIC-SEDIMENTARY MANGANIFEROUS FORMATIONS

The article describes Carboniferous and Lower Liassic coal measures in Franz Josef Land, and a "2-ft coal bed" at the base of the Carboniferous motley sandstones observed by Fisher in Cook Cliffs at the south end of Prince George Land. Until recently the Cook Cliffs coal was identified by Dibner as "Paleozoic redeposited in Upper Triassic time." Later Dibner reassigned the coal and related beds to the Upper Triassic. Some doubt on this age is cast by the fact that the only coals on Spitzbergen are Lower Carboniferous. Ye. M. Andreyeva studied the coal's spores and found only Lower and Middle Carboniferous species. Traveling southeast of Wilczek Land in 1935, Yermolayev recovered coals he believed to be Paleozoic. Based on these finds, there is a strong likelihood of Paleozoic coals on Franz Josef Land. The Upper Triassic Vasil'yevsk Formation contains Noric to Rhaetic plants and spores. At Goristyy Cape (Champ Island) two brown coals occur; one is 1 m thick; 55 m higher is a 2-m bed coked at the top by an overlying basalt flow. The petrography of the coals is discussed. The Tegetthof Formation, based on its plant fossils, is Lower Liassic, compatible with sections on Spitzbergen. Next higher are Aalenian siltstones, Bathonian and sandy limestones with Volgian clams. Still higher are Lower Cretaceous volcanics with intercalated sandstones, shales and coals, divisible into the Tikhaya Cove Formation and Salisbury Formation. Altogether there are 13 coal beds in Franz Josef Land, ranging from Carboniferous up into the Lower Cretaceous (with 9 coal beds). Interesting petrographic details are included.—B. N. Cooper.     

Subduction-related 200 Ma Talun metagranite,SE Taiwan: an age constraint for palaeo-Pacific plate subduction beneath South China Block during the Mesozoic

Various tectonic models have been proposed to account for the widely distributed igneous activities in the southeastern part of the South China Block (SCB) during the Triassic–Jurassic period. One of the major contending debates is on the timing of initiation of the palaeo-Pacific plate subduction under the SCB, due to lack of unequivocal evidence for arc magmatism during the period in this region.

The 191 ± 10 Ma (N = 5, MSWD = 12) calc-alkalic high-K I-type Talun metagranite occurs in the southern Tailuko belt of the Tananao metamorphic complex, Taiwan. In terms of age, this metagranite belongs to the Early Yanshanian igneous activity in the southeastern part of the SCB. However, its geographic position does not accord with the well-known general oceanward younging trend of the Yansnanian igneous rocks. In view of the large age uncertainty reported, this metagranite is redated in this study. Some zircons of this metagranite are high in U content and are metamict. Zircons with low U contents are analysed by SHRIMP yielding a more precise age of 200 ± 2 Ma (N = 10, MSWD = 4). In particular, the εHf(t) of these dated zircons ranges from +4.5 to +12.9. The metagranite mainly consists of quartz, K-feldspar, plagioclase, with minor amounts of garnet, biotite, zircon, apatite, and pyrrhotite. Chlorite and calcite are secondary phases overprinted by the later tectonic event(s). Its initial Sr isotope compositional range is 0.70473–0.70588, and εNd(t), +2.4 to +3.6. The results demonstrate that the genesis of this metagranite could be attributed to the assimilation-fractionation of a depleted mantle-derived basaltic magma, which was most likely related to arc magmatism. The present study therefore offers key evidence that during the Mesozoic, the palaeo-Pacific plate subduction underneath the SCB would have taken place no later than the very early Jurassic.     

Controls on the accumulation of coal and on the development of anastomosed fluvial systems in the Cretaceous Dakota Formation of southern Utah

Alluvial strata of the Cretaceous Dakota Formation of southern Utah are part of a transgressive systems tract associated with a foreland basin developed adjacent to the Sevier orogenic belt. These strata contain valley fill deposits, anastomosed channel systems and widespread coals. The coals constitute a relatively minor part of the Dakota Formation in terms of sediment volume, but may represent a substantial amount of the time represented by the formation. The coals are separated by clastic units up to 20 m thick. The stratigraphically lowest clastic unit of the Dakota Formation lies above an unconformity cut into Jurassic rocks. Incised valleys associated with the unconformity are up to 12 m deep. Two discrete episodes of valley fill sedimentation are recognized, including a lower sandstone unit with conglomerate layers, and an upper, discontinuous, coal-bearing unit. After the valleys filled, the area became one of low relief where extensive mires formed. Peat accumulation was interrupted at least three times by deposition of clastic sediment derived from the west. The clastic units consist of sandstone, mudstone or heterolithic ribbon bodies, stacked tabular sandstones, and laminated mudstones, and contain minor coal beds less than 0·35 m thick. Ribbon bodies are 1–9 m thick and 15–160 m wide, have pronounced basal scours, and are filled with both lateral and vertical accretion deposits. An anastomosed channel complex is suggested by the large number of coeval channels of varying dimensions, the variation in the structure and grain size of channel fills, and the presence of abundant tabular sandstones interpreted as crevasse splays. Although some sandstone bodies have well developed lateral accretion surfaces, the overall ribbon geometry indicates that mature meandering streams were not well developed. This is in contrast to modern anastomosed systems, which are commonly thought to be a transitional morphology caused by avulsion of a meander belt to a new position on its floodplain. Rather than being a transitional channel pattern related to river avulsion, the anastomosed channels of the Dakota Formation may have formed part of a large inland delta that episodically invaded widespread mires. The mires developed during periods when clastic influx was reduced either by high rates of subsidence close to the thrust belt or by deflection of rivers by emergent thrusts.     

阳泉—井陉一带石炭二叠纪煤田的沉积环境探讨

 本文运用现代沉积学的理论与方法,分析了位于华北晚古生代聚煤区中北带的阳泉,井陉煤田含煤岩系的岩相类型、沉积环境及古地理演化。提出,阳泉、井陉一带石炭纪中、晚期及早二叠世早期沉积的古地理类型均属滨海平原型,北部边缘的阴山古陆为聚煤区陆源碎屑沉积物的主要供给区,同时,五台、太行、吕梁隆起区也可提供部分陆源碎屑沉积物。     

Fault‐related folding: Tulcumba Ridge,western New England

An overturned angular fold in the Currabubula Formation at Tulcumba Ridge has a north‐south axial trace exposed along the western side of this ridge. The geometry and position of this fold adjacent to the Mooki Thrust is consistent with its formation as a fault‐propagation fold involving a thrust step‐up angle of ～ 30° from a décollement. Overturned strata also occur adjacent to the Mooki Thrust near the Rocky Creek Syncline to the north and to the south on Gunnan Ridge and in the Werrie Syncline. Overturning of strata in these areas may be the result of fault‐propagation folding. It is suggested that folding in the Tamworth Belt involves thin‐skinned deformation that is dominantly fault‐related.     

辽西八道壕煤盆地层序地层与成煤环境分析

辽西黑山—彰武地区分布有一系列早白垩世断陷成因的陆相盆地,其中以八道壕煤盆地含煤性最好。本次工作在八道壕煤矿深部勘探区,采用二维地震、钻探、测井等对八道壕组进行了层序地层和成煤环境分析。八道壕组可分为三个三级层序,下部第1层序（Sq1）为冲积扇注入湖盆形成的水下扇—扇三角洲沉积体系,湖侵域和高位域各含一个煤组,湖侵域退积的水下扇边缘和高位域扇三角洲前缘都有厚煤层发育。早期冲积扇自盆地西南注入湖盆,煤层发育在断陷较深的中北部,自西侧盆缘断裂附近向东超覆。Sq1湖侵域的煤层比高位域的煤层分布面积要大。盆地南部冲积扇主体部位粗碎屑岩增多,上、下煤组的煤层均向南变薄尖灭。由于物源区构造抬升冲积扇向湖盆的进积作用加剧,八道壕组中上部第2、3层序粗碎屑沉积物增多,湖盆水域面积缩小,煤层不再发育。     

豫西陕渑煤田山西组煤层形成环境和聚煤特征

本文以宏观沉积学研究方法为主，辅助进行室内岩矿签定，编制沉积断面图和各种等值线图，在此基础上讨论了山西组煤层的沉积环境。并对煤层与聚煤沉积环境间的关系进行讨论。研究结果表明，泥炭沉积前和沉积期的沉积环境是影响煤层厚度和煤质的主要原因，泥炭沉积后的沉积环境仅在局部地区影响煤厚分布，而后期构造对煤厚影响程度较小。     

内蒙古二连盆地群晚中生代煤盆地的类型和聚煤特征

本文对内蒙古东北部二连盆地群晚中生代煤盆地的类型、充填样式和聚煤特征进行了讨论,并结合盆地的沉积序列,对其构造演化进行了探讨。     

平朔露天矿太原组11^#和9^#煤层的沉积环境分析

平塑露天矿的露采煤层,即１１＾＃和９＾＃煤层是上石炭统太原组Ⅱ－Ⅲ层段扇三角洲－泻湖及扇三角洲－潮坪环境的产物。厚４ｍ的１１＾＃煤层形成于扇三角洲－潮坪环境中,厚１５ｍ的９＾＃煤层形成了扇三角洲平原,扇三角洲前缘（北西部）以及覆水较深的泻湖（中南部）环境中。