Sedimentary facies of Carboniferous–Permian mid-oceanic carbonates in the Changning–Menglian Belt, West Yunnan, Southwest China: Origin and depositional process

Huge carbonate rock bodies ranging in age from the Visean (Middle Mississippian/Early Carboniferous) to the Changhsingian (Lopingian/Late Permian) overlie a basaltic basement in the Changning–Menglian Belt, West Yunnan, Southwest China. These carbonates lack intercalations of terrigenous siliciclastic material throughout. These lines of evidence indicate that they formed upon an isolated and continuously subsiding mid-oceanic island (or plateau), probably of hotspot origin. The carbonates are grouped into a shallow-water carbonate platform facies regime observed in the Yutangzhai section and a relatively deep-water carbonate slope facies regime typically represented in the Longdong section. These two facies regimes developed contemporaneously as parts of a carbonate depositional system on and around a mid-oceanic volcanic edifice. The carbonate platform is subdivided into four facies, including platform-margin, shoal, lagoon, and peritidal facies. Along the measured Yutangzhai section of the platform facies regime, the vertical facies succession from the platform-margin facies into inner-platform facies such as the shoal and lagoon facies is recognized. This facies succession is explained as resulting from the progradation of the carbonate platform. Worm tubes occur as a main reef builder in platform-margin facies of the Mississippian. Their occurrence as major constituents in a high-wave-energy reef is peculiar to Carboniferous reef distributions of the world. The occurrences of other reef- and/or mound-building organisms and peritidal dolo-mudstone are almost consistent in timing with those of Panthalassan counterparts such as the Akiyoshi and Omi limestones of Japan, and probably exhibit the worldwide trend.     

江西弋阳铁砂街中元古代海底火山喷流成矿作用

江西弋阳铁砂街铜矿产于中元古代晚期海相火山岩中,矿床在大地构造环境、含矿地层建造、矿体形态、喷流岩组合、喷流岩主量－微量－稀土元素地球化学、同位素地球化学方面都具有海底火山喷流沉积的典型特征,是扬子板块、华夏板块边缘中元古代裂谷海底火山喷流沉积作用的产物。     

物探方法在临清坳陷某区块山西组沉积相分析中的应用

临清坳陷某区块缺少岩心、薄片、录井及常规测井资料。为了研究其目的层山西组沉积相对储层的控制作用,指导非常规天然气的高效开发。通过利用较少的录井岩性统计资料,结合地震物探方法,分析地震剖面特征、优选地震均方根振幅及相对波阻抗属性,确定该区目的层沉积相。通过上述地震属性研究的物探方法,确定山西组储层为河控浅水三角洲相和碳酸盐台地相,主要发育分流河道、分流间湾及局限台地沉积微相。其中三角洲相是主要的沉积相类型,分流河道是有效储层发育的主要微相类型。      

The Pongola structure of southeastern Africa: The world's oldest preserved rift?

Rocks of the Pongola Supergroup form an elongate belt in the Archean Kaapvaal Craton of southern Africa. Because these rocks exhibit many features that are characteristic of rocks deposited in continental rifts, including rapid lateral variations in thickness and character of sediments, volcanic rocks that are bimodal in silica content, coarse, basement derived conglomerates and thick sequences of shallow water sedimentary facies associations, we suggest that the Pongola Supergroup was deposited in such a rift. The age of these rocks (approximately 3.0 Ga) makes the Pongola structure the world's oldest well-preserved rift so far recognized, and comparison of the Pongola Rift with other rifts formed more recently in earth history reveals striking similarities, suggesting that the processes that formed this rift were not significantly different from those that form continental rifts today.     

Reef to island sediment connections on a Maldivian carbonate platform: using benthic ecology and biosedimentary depositional facies to examine island‐building potential

Reef islands are low‐lying accumulations of unconsolidated sediment formed from the skeletal remains of carbonate‐producing reef organisms and are therefore perceived as highly vulnerable to environmental change. However, basic elements of island composition are not well described and given their high inter‐ and intra‐basinal variability a better understanding of reef and island sedimentary environments (and the connections between them) are needed to predict future morphological response. Here, we use detailed ecological and sedimentological datasets to delineate key sediment production zones and biosedimentary depositional facies across the surface of Vabbinfaru platform, Maldives. Field measurements of platform hydrodynamics are applied to sedimentary deposits to determine the potential mobility of grains and identify transport pathways. Carbonate production was dominated by coral framework (mean: 52%) within a narrow zone on the outer reef rim (22% of platform area) resulting in coral‐rich detrital sediments (reef: 51%, island: 64%) that closely resemble living assemblages. The net transfer of sediment occurred lagoonward by wave‐driven processes leading to a decrease in grain size towards the island (R² = 0.502) which acts as a major control on depositional facies development within the lagoon. Island sediments were distinct from reefal deposits, comprising a restricted suite of durable sands (mean: 1.34?) throughout long‐term development. Our findings suggest that the production, breakdown and redistribution of coral‐derived sediment by platform currents is fundamental to future island stability at Vabbinfaru, and although alterations away from current ecological states may reduce sediment supply, the timescales over which island morphological response will occur depends upon phase lags between initial coral mortality and the conversion of this material into island‐grade sand. Copyright © 2016 John Wiley & Sons, Ltd.     

Depositional model of Early Permian reef-island ocean in Eastern Kunlun

Many fusulinid fossils have been found in thin- to middle-bedded limestones which are distributed between the Early Permian limestone hills and formerly considered as Early Triassic. The fusulinid fossils, identified asNeoshwagerina sp.,Verbeekina sp. andSchwagerina sp., can also be found in massive limestone hills. At the same time, Early Permian radiolarian chert of deep basin facies was discovered in Animaqing. All the above show that the massive limestone hills, thin- to middle-bedded limestones and radiolarian chert belong to syndeposits in Early Permian ocean. The sediments in the study area can roughly be divided into three types: shallow facies, basin facies and transitional facies. The carbonate buildup can be subdivided into massive bioclastic limestone and reef framestone. Basin facies contains thin- or middle-bedded limestone, abyssal red mudstone or ooze, blue-green mudstone and radiolarian chert. Transitional facies includes reef talus and platformal skirt facies. The Early Permian ocean in Eastern Kunlun is recognized as a kind of reef-island ocean environment according to distribution and composition of different facies. The reef-island ocean in Eastern Kunlun is characterized by reef islands (or carbonate buildups) alternating with basins, complicated sea-floor topography, sharp facial change and well-developed reefs.     

Facies architecture and Late Pliocene – Pleistocene evolution of a felsic volcanic island, Milos, Greece

The volcanic island of Milos, Greece, comprises an Upper Pliocene –Pleistocene, thick (up to 700 m), compositionally and texturally diverse succession of calc-alkaline, volcanic, and sedimentary rocks that record a transition from a relatively shallow but dominantly below-wave-base submarine setting to a subaerial one. The volcanic activity began at 2.66±0.07 Ma and has been more or less continuous since then. Subaerial emergence probably occurred at 1.44±0.08 Ma, in response to a combination of volcanic constructional processes and fault-controlled volcano-tectonic uplift. The architecture of the dominantly felsic-intermediate volcanic succession reflects contrasts in eruption style, proximity to source, depositional environment and emplacement processes. The juxtaposition of submarine and subaerial facies indicates that for part of the volcanic history, below-wave base to above-wave base, and shoaling to subaerial depositional environments coexisted in most areas. The volcanic facies architecture comprises interfingering proximal (near vent), medial and distal facies associations related to five main volcano types: (1) submarine felsic cryptodome-pumice cone volcanoes; (2) submarine dacitic and andesitic lava domes; (3) submarine-to-subaerial scoria cones; (4) submarine-to-subaerial dacitic and andesitic lava domes and (5) subaerial lava-pumice cone volcanoes. The volcanic facies are interbedded with a sedimentary facies association comprising sandstone and/or fossiliferous mudstone mainly derived from erosion of pre-existing volcanic deposits. The main facies associations are interpreted to have conformable, disconformable, and interfingering contacts, and there are no mappable angular unconformities or disconformities within the volcanic succession.Electronic Supplementary Material Supplementary material is available for this article at     

Lithostratigraphy of Permian marine sequences, Khao Pun Area, central Thailand: Paleoenvironments and tectonic history

Geologic mapping and subsurface lithostratigraphic investigations were carried out in the Khao Pun area (4 km²), central Thailand. More than 250 hand specimens, 70 rock slabs, and 70 thin sections were studied in conjunction with geochemical data in order to elucidate paleoenvironments and tectonic setting of the Permian marine sedimentary sequences. This sedimentary succession (2485 m thick) was re‐accessed and re‐grouped into three lithostratigraphic units, namely, in ascending order, the Phu Phe, Khao Sung and Khao Pun Formations. The Lower to lower Upper Permian sedimentary facies indicated the transgressive/regressive succession of shelf sea/platform environment to pelagic or abyssal environment below the carbonate compensation depth. The sedimentological and paleontological aspects, together with petrochemical and lithological points of view, reveal that the oldest unit might indicate an Early Permian sheltered shallow or lagoonal environment. Then the depositional basin became deeper, as suggested by the prolonged occurrence of bedded chert‐limestone intercalation with the local exposure of shallower carbonate build‐up. Following this, the depositional environment changed to pelagic deposition, as indicated by laminated radiolarian (e.g. Follicucullus sp.) cherts. This cryptic evidence might indicate the abyssal environment during middle Middle to early Late Permian; whereas, previous studies advocated shelf‐facies environments. Following this, the depositional condition might be a major regression on the microcontinent close to Indochina, from the minor transgressive/regressive cycles that developed within a skeletal barrier, and through the lagoon with limited circulational and anaerobic conditions, on to the tidal flat to the sheltered lagoon without effective land‐derived sediments.     

徐州大北望地区馒头组化石碳酸盐岩微相分析

江苏省徐州市大北望剖面早寒武世馒头组的碳酸盐岩地层发育较好,沉积类型多样,成岩特征明显,是研究碳酸盐岩沉积及成岩作用的理想剖面之一。文章采用微相分析的方法 ,对该剖面碳酸盐岩的生物组合、颗粒成分、基质类型及其结构等微相特征做了研究。根据颗粒类型、沉积结构和化石,本区的碳酸盐岩可以被分为3个大类和10种化石碳酸盐岩微相类型:泥晶颗粒灰岩(微相1至微相5),颗粒泥晶灰岩(微相6至微相8)和泥晶灰岩(微相9和微相10)。每一种微相对应特定的沉积环境及演化特征。综合分析表明,研究区下寒武统形成于泻湖、局限台地、开阔台地和台地边缘的浅滩环境,据此建立了沉积相模式。在徐州大北望地区进行的关于碳酸盐岩微相的研究表明早寒武世晚期的馒头组继承了早寒武世中期的特点,且海侵持续扩大的持续沉降活动。     

Englacial vs lacustrine origin of volcanic table mountains: evidence from iceland

Detailed facies analysis of hyaloclastites and associated lavas from eight table mountains and similar "hyaloclastite volcanoes" in the Icelandic rift zone contradict a rapid and continuous, "monogenetic", entirely subglacial evolution of most volcanoes studied. The majority of the exposed hyaloclastite deposits formed in large, stable lakes as indicated by widespread, up to 300-m-thick, continuous sections of deep water, shallow water and emergent facies. Salient features include extensively layered or bedded successions comprising mainly debris flow deposits, turbidites, base surge and fallout deposits consisting of texturally and compositionally variable, slightly altered hyaloclastites, as well as sheet and pillow lavas. In contrast, chaotic assemblages of coarser-grained, more poorly sorted and more strongly palagonitized hyaloclastite tuffs and breccias, as well as scoria and lava are interpreted to have formed under sub- or englacial conditions in small, chimney-like ice cavities or ice-bound lakes. Irregularly shaped and erratically arranged hyaloclastite bodies produced at variable water levels appear to have resulted mainly from rapid changes of the eruptive environment due to repeated build-up and drainage of ice-bound lakes as well as the restricted space between the ice walls. We distinguish a "deep water" facies formed during high water levels of the lake, a hydroclastic shallow water and emergent facies (leakage of the lake or growth of the volcano above the water surface). Our model implies the temporary existence of large, stable lakes in Iceland probably formed by climatically induced ice melting. The highly complex edifices of many table mountains and similar volcanoes were constructed during several eruptive periods in changing environments characterized by contrasting volcanic and sedimentary processes. Received: 10 June 1997 / Accepted: 28 July 1998     

Sequence-stratigraphic frameworks and their palaeogeographic patterns for the Permian Lopingian of the Dianqiangui Basin and its adjacent areas of Southwestern China

The Permian Lopingian in the Dianqiangui Basin and its adjacent areas is marked by the coal measures of the Wuchiapingian and the carbonate strata of the Changhsingian stages. For the Lopingian of the Dianqiangui Basin and its adjacent areas,the diversity of sedimentary facies and the obviousness of facies change provide an advantaged condition on a study of sequence stratigraphy. Approximately,the Wuchiapingian stage constitutes a third-order sequence and the Changhsingian stage forms an-other. For the Wuchiapingian stage in the study area,coal-measures were developed on the attached platform and,in addition,a special coal-measure that is composed of both limestone beds and coal beds was also developed in the central part of some isolated platforms. Grain-bank grainstones and packstones were formed on the margin of the attached platform as well as in the windward part of iso-lated platforms. For the Changhsingian stage in the study area,open-platform limestones were formed on the attached platform,while sponge-reef limestones were developed both on the margin of the at-tached platform and on the isolated platforms. The Lopingian Series is a set of basin-facies muddy shales with interbeds of silicalites in the inter-platform basin,which appears a set of the large-thick coarse clastic strata of molasses covering direct the deep-water strata from the Devonian to the Per-mian Yangsingian in the Qinzhou-Fangcheng region in the southern part of the study area. All of these features indicate the complexity of temporal-spatial facies-changes. Sequence-stratigraphic frame-works could be established,which would illustrate two types of facies-changing surfaces and dia-chronisms in the stratigraphic records,based on the combination of both biostratigraphic and chronostratigraphic materials and the regularity reflected by temporal evolutionary succession of sediments as well as spatial distributional patterns of sedimentary facies. Ultimately,features of sedi-mentary succession and palaeogeographical evolution of the Permian Lopingian in the study area are revealed clearly in a series of the panel diagrams of sequence-stratigraphic frameworks and the outline maps showing the sedimentary-facies and palaeogeography. The Permian Lopingian formed by two third-order sequences differs from the stratigraphy of the same era characterized by the constant re-gression along Euramerica. Most specially,if the end-Guadalupian mass-extinction event is genetically related to a regressive event represented by the unconformity of the first episode of the Dongwumovement in the study area,the mass-extinction event at the turn from the Permian to the Triassic is genetically related to a rapid transgressive event re-flected by the drowning unconformity in the study area. These phenomena might reveal a complex rela-tionship between mass-extinction events and trans-gressive-regressive events.     

The Permian seamount stratigraphic sequence in Chiang Mai,North Thailand and its tectogeographic significance

The widespread Permian carbonate strata outcropped in northwestern Thailand are considered as the evidence for the Late Paleozoic shallow Tethys. Our investigation, however, shows that basalt can be discovered usually under the Permian carbonate sequence in Chiang Mai-Fang area, northwestern Thailand. The basalt belongs to subalkalic basalt and potassic trachybasalt. They are characterized by high P and Ti in major elements, by high content, enriching LREE, lacking δEu anomaly in rare earth elements, and by enrichment of the large ion lithophile element (LILE) (K, Rb, Ba) and high field strength element (HFSE) (Nb, Ta, Zr) in trace elements, which can be compared with the characters of the oceanic island basalt in Three Rivers (Jinsha River, Lancang River, and Nujiang River) area, southwestern China. Therefore, the Permian carbonate in the studied area was deposited on a sea-mount, rather than on a stable carbonate platform. The oceanic basin is correlated to the Late Paleozoic ocean represented by the Changning-Menglian Belt in southwestern China and they are a major basin of the Paleo-Tethyan Archipelagoes Ocean. The result indicates nonexistence of a Shan-Thai Block in the Late Paleozoic.     

The influence of palaeoenvironment and lava flux on the emplacement of submarine, near-shore Late Permian basalt lavas, Sydney Basin (Australia)

Lava flux and a low palaeoslope were the critical factors in determining the development of different facies in the Late Permian Blow Hole flow, which comprises a series of shoshonitic basalt lavas and associated volcaniclastic detritus in the southern Sydney Basin of eastern Australia. The unit consists of a lower lobe and sheet facies, a middle tube and breccia facies, and an upper columnar-jointed facies. Close similarities in petrography and geochemistry between the basalt lavas from the three facies suggest similar viscosities at similar temperatures. Sedimentological and palaeontological evidence from the sedimentary units immediately below the Blow Hole flow suggests that the lower part of the volcanic unit was emplaced in a cold water, shallow submarine environment, but at least the top of the uppermost lava was subaerial with some palaeosol development. The lower lobe and sheet facies was emplaced on a low slope (<2°) in a lower to middle shoreface environment with water depths of 20–25 m. Lava may have transgressed from subaerial to subaqueous and was emplaced relatively passively with lava flux sufficiently high and uniform to form lobes and sheets rather than pillows. The middle unit probably originated from a subaerial vent and flowed into a shallow (10–15 m) submarine environment, and wave action probably interacted with the advancing lava front to form a lava delta. Lava flux was sufficiently high to produce well-developed, subcircular lava tubes, which lack evidence for thermal erosion. In some areas, lava ‘burrowed’ into the unconsolidated, water-saturated lava delta and sand pile to produce intrusive contacts. The upper columnar-jointed unit represents a ponded facies probably emplaced initially in water depths <5 m but whose top was subaerial.     

Sedimentary evidence for an archaean shallow-water volcanic-sedimentary facies,Eastern Pilbara Block,Western Australia

Sedimentological studies of the dominantly volcanic, ca. 3.5 b.y. Warrawoona Group, eastern Pilbara Block, Western Australia, indicate widespread shallow-water deposition. Many cherty metasediments within the ultramafic-mafic sequence represent silicified carbonate mud, sand, breccia and conglomerate, and show cross-lamination, ripple marks, scour-and-fill structures, and evidence of reworking. At North Pole, some cherty metasediments appear to be silicified and baritized gypsiferous evaporites, and contain microfossils. Felsic volcaniclastic rocks include pyroclastic deposits, cross-laminated tuffaceous metasediments and conglomerate. Subaerial volcanism apparently increased as deposition proceeded.The depositional basin was large, volcanically active and apparently shallow with subdued marginal relief. Felsic volcanoes formed topographic highs within the basin from which sheets of volcanically derived sediments interfingered with ultramafic-mafic volcanics. The Onverwacht Group of the Barberton Mountain Land, South Africa, is of similar age to the Warrawoona Group and probably represents a similar environment, but other greenstone belts may have formed in contrasting basins, possibly under differing tectonic regimes.     

Structure and evolution of Middle Permian palaeo- seamounts in Bayan Har and its adjacent area

1 Regional geology Bayan Har Middle Permian palaeo-seamounts are located in the area of Zaling Lake, near the source of Yellow River (Fig.1). The main strata outcropped in this area are Triassic sandstone and slate. Some Mid-dle Permian limestone blocks are towering above the Triassic sandstone and slate, which become one par-ticular topographical scenery in this area. These lime-stone blocks are distributed not only in Bayan Har but also in A’nyêmaqên and the southern slope of East …     

The island of Linosa (Sicily channel)

The volcanology and petrology of Linosa island are described. Linosa and Pantelleria are two quaternary volcanic islands located in the Sicily Channel, a NW-SE elongated continental rift structure of the southern Mediterranean Sea. Several hyaloclastitic rings mark the period of submarine explosive activity which formed Linosa. Lava flows and spatter cones, originated in a later period, prevented the complete destruction of this island by the sea. A typical (undersaturated) alkali basalt fractionation trend has been recognized at Linosa while Pantelleria is characterized by diflerentiation products originated from a mildly alkalic-transitional basaltic magma. These petrogenetic differences between Linosa and Pantelleria have tentatively been related to a different crustal thickness of the islands due to their tectonic location within the Sicily Channel: Linosa on a marginal area, Pantelleria just on the axis of a graben. The genesis and evolution of the Sicily Channel Rift Valley and of the associated basaltic magmatism are probably related to tensional stresses affecting the northwards migrating African plate, just behind its contact zone with the Eurasian plate.     

A Pliocene shoaling basaltic seamount: Ba Volcanic Group at Rakiraki, Fiji

At Rakiraki in northeastern Viti Levu, the Pliocene Ba Volcanic Group comprises gently dipping, pyroxene-phyric basaltic lavas, including pillow lava, and texturally diverse volcanic breccia interbedded with conglomerate and sandstone. Three main facies associations have been identified: (1) The primary volcanic facies association includes massive basalt (flows and sills), pillow lava and related in-situ breccia (pillow-fragment breccia, autobreccia, in-situ hyaloclastite, peperite). (2) The resedimented volcaniclastic facies association consists of bedded, monomict volcanic breccia and scoria lapilli-rich breccia. (3) The volcanogenic sedimentary facies association is composed of bedded, polymict conglomerate and breccia, together with volcanic sandstone and siltstone-mudstone facies. Pillow lava and coarse hyaloclastite breccia indicate a submarine depositional setting for most of the sequence. Thick, massive to graded beds of polymict breccia and conglomerate are interpreted as volcaniclastic mass-flow deposits emplaced below wave base. Well-rounded clasts in conglomerate were reworked during subaerial transport and/or temporary storage in shoreline or shallow water environments prior to redeposition. Red, oxidised lava and scoria clasts in bedded breccia and conglomerate also imply that the source was partly subaerial. The facies assemblage is consistent with a setting on the submerged flanks of a shoaling basaltic seamount. The coarse grade and large volume of conglomerate and breccia reflect the high supply rate of clasts, and the propensity for collapse and redeposition on steep palaeoslopes. The clast supply may have been boosted by vigorous fragmentation processes accompanying transition of lava from subaerial to submarine settings. The greater proportion of primary volcanic facies compared with resedimented volcaniclastic and volcanogenic sedimentary facies in central and northwestern exposures (near Rakiraki) indicates they are more proximal than those in the southeast (towards Viti Levu Bay). The proximal area coincides with one of two zones where NW-SE-trending mafic dykes are especially abundant, and it is close to several, small, dome-like intrusions of intermediate and felsic igneous rocks. The original surface morphology of the volcano is no longer preserved, though the partial fan of bedding dip azimuths in the south and east and the wide diameter (exceeding 20 km) are consistent with a broad shield.     

Large-scale Basement-involved Landslides, California Continental Borderland

— Large seafloor relief, shallow metamorphic basement, and seismic activity in the California Continental Borderland combine to produce major submarine slides capable of generating local tsunamis. The Catalina Schist basement complex of the Borderland contains melange units, faults between metamorphic facies, and foliation derived from a history of deep subduction underthrusting and subsequent tectonic exhumation along regional low-angle fault systems. Neogene volcanic and sedimentary rocks covered the exhumed metamorphic basement forming an interface with a strong contrast in material properties. Neogene transtensional block-faulting formed steep escarpments that cut through and elevated the low-angle detachment surface, providing slip surfaces with free faces susceptible to failure along the rheological boundary. Two basement-involved slope failure examples west of San Diego are described, including large block-glides and progressive rotational slumps along the steep northeast-facing Thirtymile Bank escarpment and along the southwest flank of Fortymile Bank.     

Triassic deep-marine sedimentation in the western Qinling and Songpan terrane

Triassic sequences in both the western Qinling and Songpan terrane are composed mostly of deep-marine sediments. A detailed study was carried out on main sedimentary facies of Triassic successions, showing that they resulted from diverse sedimentary processes, such as submarine debris-flows, turbidity currents, bottom-flows, suspension fallout, and fluidized sediment flows. Debris-flows are dividable into two types, gravelly and sandy debris-flows, respectively, and the sandy debris-flow deposits make up considerable portion of the Triassic successions concerned. Turbidite is characterized by occurrence of normal grading, and the whole Bouma sequences, though widely developed, are not totally attributed to true turbidity currents. The non-graded Ta division is thought to originate from sandy debris flows, whereas the rest divisions result from low-density currents or from bottom-current modification if they contain sedimentary structures related to traction currents. Four types of facies associations are distinguished within Triassic deep-marine successions: massive and thick-bedded coarse-grained facies association, medium- and thick-bedded sandstone with interlayered fine-grained facies association, interlayered thin-bedded fine-grained facies association, and syn-sedimentary slump/breccia facies association. Spatial distribution of the different facies associations suggests that Lower Triassic sedimentation occurred primarily in continental slope, submarine channels, and base-of-slope aprons in the Hezuo-Jianzha region of the western Qinling, whereas the Middle Triassic consists mainly of sedimentary facies of base-of-slope aprons and submarine incised valleys. The counterparts in the Dangchang-Diebu region, in contrast, are characterized by platform carbonates. The shallow-marine carbonates evolved into deep-marine facies since the Ladinian, indicative of rapid drowning of the Carnian carbonate platform in Middle Triassic times. Depositional history of Lower Triassic and lower portion of Middle Triassic successions in the northern Songpan terrane is similar to that of the Dangchang-Diebu region of the western Qinling, as manifested by development of Lower-early Middle Triassic shallow-marine carbonate and a rapid shift to base-of-slope apron sediments since the Ladinian.

     

Formation mechanism of in-situ volcanic reservoirs in eastern China:A case study from Xushen gasfield in Songliao Basin

A large number of in-situ volcanic reservoirs have been discovered from the Meso-Cenozoic rift basin group in eastern China.Based on drilling results in combination with geological and geophysical analysis,a case study from the Early Cretaceous Xujiaweizi fault-depression shows that the formation mechanism of in-situ volcanic reservoirs is characterized by"fault-controlled body,body-controlled facies,facies-controlled reservoir,and reservoir-controlled accumulation".In other words,deep faults control the volcanic eruption type,volcanic body,and gas reservoir distribution;the volcanic body determines the spatial distribution of volcanic facies and volcanic gas reservoir size;the volcanic facies control reservoir physical properties and effective thickness of gas formation;the volcanic reservoir properties control gas reservoir type and gas productivity.The result is useful to guiding the discovery of in-situ volcanic gas reservoirs in faulted basins in both theory and practice.