Insights into the Origin of Natural Gas Reservoirs in the Devonian System of the Marsel Block, Kazakhstan

The genetic type and accumulation model of the Devonian reservoirs in the Marsel Block remain unclear, despite decades of exploration history. According to the well testing, logging interpretations and sample testing results, the Devonian natural gas reservoir in the Marsel Block has five typical characteristics:(1) It is obvious that the traps contain continuous gas accumulations. Not only the apexes of the structures are enriched in natural gas, but also the slopes and depressions contain gas accumulations.(2) The gas reservoirs are classified as tight reservoirs, but there are also reservoirs with high porosity and permeability in some areas.(3) The general negative or low-pressure in the gas reservoir is obvious, although the pressure in the target layers of some wells is close to normal.(4) The yields of single wells in the Devonian reservoir are quite different: some wells have low yields or are dry, whereas the gas production from high-yield wells has reached 700 000 m3/day.(5) The gas-water relationship is complicated: there is no obvious gas-water interface, but the water-producing layer is generally located at the apexes of structures. Research and analysis have shown that using the model of the conventional gas reservoirs genetic type can only explain the characteristics of parts of the gas reservoir, while the model of accumulation in a deep-basin gas reservoir cannot fully explain the distribution characteristics of the Devonian reservoir. However, the model of accumulation in a stacked complex continuous oil and gas reservoir can reasonably explain the geological and distribution characteristics of the Devonian reservoir. Moreover, the predicted gas distribution along a cross-section of the reservoir is also in agreement with the geological background and tectonic environment of the Marsel Block, therefore, the genetic type of the Devonian natural gas reservoir in the Marsel Block is a stacked complex continuous tight-gas reservoir. Finally, by comprehensively analyzing the source rock, reservoir and cap rocks, as well as the structural characteristics, it is verified that Devonian in the Marsel Block has favorable geological conditions for formation of a superimposed continuous tight gas reservoir.

Biostratigraphy,Microfacies,Sedimentary Environments and Sequence Stratigraphy of the Late Devonian-Carboniferous Deposits at the Anarak Section,Central Iran

The Late Devonian-early Carboniferous deposits of the Anarak section in northeastern Isfahan,Central Iran,evaluated based on conodont biostratigraphy,sedimentary environment and sequence stratigraphy.According to the field observations,five lithological units were identified.Investigating the conodont fauna of the Late Devonian-Carboniferous(Mississippian-Pennsylvanian)deposits of Bahram,Shishtu,and Qaleh(Sardar 1)formations in Anarak section led to the identification of 67 species of 18 conodont genera,and accordingly 22 conodont biozones were differentiated.The correlation of sea-level change curves,regarding to the conodont biofacies with the global sea-level curve,demonstrates the relative correlation in the mentioned times due to the shallow condition of the central Iran basin compared to the European and American basins.The microfacies analysis led to the identification of 12 microfacies related to the open sea,bioclastic barrier,lagoon and tidal flat sub-sedimentary environments in a homoclinal carbonate ramp environment.Based on sequence stratigraphy studies,three 3rd order sequences were identified.The first sequence,which is of the Late Devonian(upper part of the Bahram Formation,32.5 m),the second sequence(12.5 m)is the Late Devonian(uppermost part of the Bahram Formation),and the third sequence(68 m)is the early Carboniferous(the Shishtu I Formation).

粤北地区“南华系”沉积时代的重新厘定:来自碎屑锆石年代学的证据

粤北地区横跨湘桂赣和武夷两个地层分区,大地构造上位于华夏地块西部,介于武夷、云开两个微陆块之间。粤北南华纪地层是研究华夏地块新元古代晚期构造演化等问题的重要载体,但该地区南华系的确定和划分较大程度上依赖与周边省份相应岩石地层的岩性组合和层序的对比,而周边省份的相应岩石地层单位的认识近年来发生较大的变化,因此,粤北地区“南华系”的重新厘定显得极为必要。本文对粤北地区原定为“南华系”大绀山组和活道组开展碎屑锆石U-Pb年代学研究,获得最年轻一组锆石加权平均年龄分别为422±4 Ma和430±4 Ma。结合岩性组合、区域地质调查研究成果及文献数据,暂将该地区原定的南华系厘定为下泥盆统。碎屑锆石年龄谱显示,其与周边地区泥盆系均具有450~420 Ma、1000~900 Ma以及~2450 Ma为主的锆石年龄显示,且在800~550 Ma之间形成复杂的次级峰值,可能指示了相似的物源。综上,建议在开展华夏地块新元古代构造演化等研究中,需首先对南武夷-云开地区南华系的沉积层位做细致的认定。

景泰县三眼井铜矿地质特征及找矿标志

三眼井铜矿属于沉积再造层控型砂岩铜矿,赋存于上泥盆统沙流水群紫红色砂砾岩的不完全退色层及断层破碎带中,呈似层状、透镜状、脉状,主要受褶皱或构造破碎蚀变岩带控制。结合三眼井铜矿的地质特征,分析其找矿标志,以更好地开发砂岩型铜矿资源。

Late Silurian to Early Devonian Palynomorphs from Qujing,Yunnan,Southwest China

Well-preserved and diversified spores,cryptospores,and acritarchs have been recorded from a relatively continuous sequence that encompasses the Silurian-Devonian boundary in Qujing, Yunnan,southwest China.Four spore assemblage zones from Late Silurian to Early Devonian in age are proposed based on the first appearance datum（FAD）of characteristic spore species.In ascending stratigraphic order,they are Ambitisporites dilutus-Apiculiretusispora synorea（DS;Late Ludfordian to Early Pridoli）,Synorisporites verrucatus-Apiculiretusispora plicata（VP;Pridoli）,Apiculiretusispora minuta-Leiotriletes ornatus（MO;Lochkovian）,and Verrucosisporites polygonalis-Dibolisporites wetteldorfensis（PW;Pragian）.The acritarch assemblage from the upper part of the Yulongsi Formation,the Xiaxishancun Formation,and the lower-middle parts of the Xitun Formation indicates an age of Late Silurian.Based on palynological evidence,the upper part of the Yulongsi Formation is considered Late Ludfordian to Early Pridoli in age;the Xiaxishancun Formation is believed to be Pridoli in age;the Xitun Formation is considered Late Pridoli to Early Lochkovian in age;the Guijiatun Formation is considered Lochkovian in age;and the Xujiachong Formation is Late Lochkovian to Pragian in age.The Silurian-Devonian boundary is recognized between the VP and the MO spore biozones,and occurs within the middle part of the Xitun Formation.

Evolutionary Significance of Pylentonemid Radiolarians and Their Late Devonian Species from Southwestern Tianshan,China

A group of radiolarian fossils with a complete morphological gradient of increasing polarization are reported from upper Devonian successions in southwestern Tianshan, China. Specifically, the important transitional mophotypes, Pylentonema transitorum sp. nov., Archocyrtium medium sp. nov. and Quadrapesus transitivus sp. nov, were found. Based on the fact that the new transitional radiolarian fossils resemble more closely to pylentonemids （cyrtoid nassellarians） than to entactinids （spumellarians） in morphology, they are assigned to pylentonemids. Pylentonemids share characters of both the Nassellaria （e.g., horned cephalis, basal opening with pylome） and Spumellaria （e.g., system of trabecular spicules）, and they are thus of evolutionary significance. The evolutionary trend from spumellarians to nassellarians is characterized by （1） internal spicule： from simple trabecular spicules to complicate components （A;Ir,II;D;V;Lr,Li;MB）; （2） polarization of the radiolarian tests due to rearrangment of spine, from radial to an axial symmetry; （3） the gradual formation of a basal opening （aperture, pylome, or podome）; and the transition from a pseudopylome, a primative pylome with a narrow margin on the outer shell, to a true pylome rimmed with a narrow, elevated impermite wall.

Soft-sediment Deformation Structures Related to Earthquake from the Devonian of the Eastern North Qilian Mts.and Its Tectonic Significance

Devonian in the North Qilian orogenic belt and Hexi Corridor developed terrestrial molasse of later stage of foreland basin caused by collision between the North China plate and Qaidam microplate. The foreland basin triggered a intense earthquake, and formed seismites and earthquake-related soft-sediment deformation. The soft-sediment deformation structures of Devonian in the eastern North Qilian Mts. consist of seismo-cracks, sandstone dykes, syn-depositional faults, microfoids （micro-corrugated lamination）, fluidized veins, load casts, flame structures, pillow structures and brecciation. The seismo-cracks, syn-depositional faults and microfolds are cracks, faults and folds formed directly by oscillation of earthquake. The seismic dykes formed by sediment instilling into seismic cracks. Fluidized veins were made by instilling into the seismo-fissures of the fluidized sands. The load casts, flame structures and pillow structures were formed by sinking and instilling caused from oscillation of earthquake along the face between sandy and muddy beds. The brecciation resulted from the oscillation of earthquake and cracking of sedimentary layers. The seismites and soft-sediment deformations in Devonian triggered the earthquake related to tectonic activities during the orogeny and uplift of North Qilian Mts.

A Middle-Upper Devonian Boundary Section in the Open Platform,Platform Margin Facies of Guilin,South China

The Caiziyan Middle and Upper Devonian boundary section is located approximately 30 km northeast of Guilin. It hosts relatively abundant benthic and common-rare pelagic fossils, including brachiopods, corals, tentaculites, and conodonts, which may serve as a better suitable section for pelagic and neritic stratigraphic correlation. In this section, 10 ＂standard＂ conodont zones are recognized across the Givetian-Frasnian boundary, including, in descending order, the Lower hassi Zone, punctata Zone, transitans Zone, the Upperfalsiovalis Zone, the Lowerfalsiovalis Zone, disparilis Zone, the Upper hermanni-cristatus Zone, the Lower hermanni-cristatus Zone, the Upper varcus Zone, and the Middle varcus Zone, all of which are defined by the first occurrence of their defining conodont species. The Middle-Upper Devonian （Givetian-Frasnian） boundary is defined by the first occurrence of Ancyrodella pristina in accordance with the Global Stratotype Section and Point （GSSP）, which is assigned at 6.2m above the base of bed 19 in the Caiziyan section.

Upper Devonian and Lower Carboniferous Sequence Stratigraphy of South China

In South China four depositional sequences are recognized in the upper part of Upper Devonian and Tournaisian. They are named SQ0 SQ1, SQ2 and SQ3 in ascending order. SQ0 is Strunian (uppermost Devonian), and the other three Tournaisian in age. These four depositional sequences appear to correlate fairly well with the four sequence recognized in Europe, North America and other areas. This may suggest that these sequences are synchronous depos- its resulted from the eustatic changes. The present study on sequence stratigraphy, biostratigraphy and event stratigraphy indicates that in neritic facies areas of South China, the Devonian-Carboniferous boundary, matching the boundary between Siphonodella praesulcata zone and S. sulcata zone in pelagic facies areas, is not only higher than the top of the Cystophrentis zone, but also higher than the top of the Devonian-Carboniferous boundary event bed. In neritic facies areas, the Devonian-Carbonifrerous boundary is marked by the most distinct transgressive surface within the Cystophrentiseudouralina interval zone, i. e. at the base of the TST of the SQ1. This boundary coincides with the top surface of the event bed resulted from the eustatic fall, and approximately corresponds to the basal part of Rseudouralina assemblage zone.

Devonian Sea-Level Change Rhythms in South China and Coupling Relationships Among the Earth-spheres

Twenty orthosequences and their corresponding sea-level change (SLC) cycles have been recognized in the Devonian overlying the Caledonian unconformity, of which 9, 5.5 and 5.5 occurred in the Lower, Middle and Upper Devonian respectively. They can be grouped into 4 orthosequence sets, in which the maximum flooding surfaces lie in the sulcutus Zone (D12), perbonus Zone (D13), Middle and Upper varcus Zone (D22) and gigas Zone (D21) respectively. Four instant palaeogeographical reconstructions of South China have been made in the Emsian and Givetian. Devonian sea-level change rhythms of South China can be divided into 3 categories: the autorhythmic, the worldwide and regional allorhythmic, and the coupling-rhythmic. They developed respectively in the Famennian, Pragian, Eifelian, Lochkovian, Emsian, Givetian, Frasnian and the F / F (between the Frasnian and Famennian) event. The cause of the worldwide allorhythmic SLC of the Pragian and Eifelian under comparatively dry, warm and tranquil conditions may be related to the pulsating expanding and contracting of the oceanic basin volume or the earth volume pulsation, rather than the common glaciation and plate tectonism. The coupling-rhythmic SLC related to the F/ F event is a sensitive indicator of the interaction between terrestrial and extraterrestrial factors, and coordinated action among the earth-spheres.

Two Zosterophyll Plants from the Lower Devonian(Lochkovian)Xitun Formation of Northeastern Yunnan,China

Two zosterophyll plants are described from the Lower Devonian （Lochkovian） Xitun Formation of Qujing, Yunnan, China. Xitunia spinitheca gen. et sp. nov. has stalked sporangia laterally attached on the axis in a helical arrangement. Sporangia are dorsoventrally flattened and composed of two unequal valves; the adaxial valve is round in face view, while the abaxial valve is larger than the former, triangular or wedge-shaped, and radially bears long spiny appendages along the distal margin. Xitunia shows new variation of sporangial morphology within the zosterophylls. Zosterophyllum minorstachyum sp. nov. has K-shaped branchings at the basal parts and small-sized terminal spikes, which consist of round to elliptical sporangia arranged helically. This paper provides new data on the diversity of plant types during Lochkovian when rare vascular plants were reported. As for various species of Zosterophyllum in South China, their apparent evolutionary trend of features from the Late Silurian to Early Devonian （Emsian） is discussed.

Devonian to Triassic Successions of the Changning-Menglian Belt,Western Yunnan,China

Phanerozoic strata are distributed in several north-south trending zones in the central part of the Changning-Menglian Belt. Four types of Devonian to Triassic stratigraphic successions can be identified: (1) elastics with limestone lenses in the mid-section, changing up-section into alternations of fine elastics and cherts; (2) elastics with chert intercalations and limestone lenses, and topped by Permian basic volcanics; (3) elastics-basic volcanics-carbonates-clastics; and (4) limestones, dolomitic limestones-dark gray thin-bedded limestones, argillaceous limestones, mudstones and siliceous mudstones. Devonian to Triassic cherts occur in different horizons and different zones from east to west. These cherts are usually transitional to their neighboring elastics. There is no continuous Devonian to Middle Triassic chert sequence in the central zone of the Changning-Menglian Belt as Liu et al. (1991,1993) reported. Volcanics and the overlying carbonates described by some workers as 'seamount' sequences are more likely to have formed in a marine environment on continental crust. Succession (4) is newly recognized in the area from Menglai to Yong'an in Cangyuan County and further north to Padi of Gengma County. Basalts, cherts and elastics also appear in this area. Mid-Triassic (very probably Ladinian) radiolarians extracted from bedded cherts in the Ganzhejidi section indicate that they are in higher stratigraphic positions. The change from bedded cherts via siltstones to thick-bedded sandstones with thin-bedded fine intercalations in the Ganzhejidi section and (some other outcrops along the road from Cangyuan to Gengma) suggests a fundamental change of sedimentary environment caused by a rapid increase of a large quantity of detritus supply. These siliciclastic sediments are possibly syn-orogenic deposits.

Atrypid Brachiopods from the Upper Devonian Wangchengpo Formation(Frasnian)of southern Guizhou,China—Extinction Patterns in the Frasnian of South China

The Wangchengpo Frasnian section of Dushan County contains two atrypid brachiopod assemblages. The lower is characterized by the Atryparia （Costatrypa） dushanensis fauna that appears at the base of the Hejiazhai Member approximately in the falsiovalis to transitans conodont zones： the upper is characterized by the Radiatrypa yangi fauna, which appears in the Lujiazhai Member approximately correspondent with the hassi to Upper rhenana conodont zones. Atrypid brachiopods, together with other brachiopods from the Dushan section show that the Hejiazhai Member is of Frasnian age. Preliminary analyses of Frasnian atrypid brachiopods from sections of South China indicate that there are nine genera and subgenera including Atryparia （Costatrypa）, Kyrtatrypa, Spinatrypa, lsospinatrypa, Spinatrypina, lowatrypa, Desquamatia （Desquamatia）. Desquamatia （Seratrypa）, and Radiatr）pa. Atrypid species diversity did not change much through the Frasnian. On a regional scale in South China, most atrypid species went extinct prior to the Frasnian/Famennian boundary. At any specific locality or section, these atrypids became extinct about 20-40 m below the Frasnian/Famennian （F/F） boundary, within the linguiformis conodont Zone, marking this as the major extinction level. Three new atrypid species are described： Atryparia （Costatrypa） dushanensis, lowatrypa pseudobodini, and Radiatrypa yangi.

Ramp facies in an intracratonic basin:A case study from the Upper Devonian and Lower Carboniferous in central Hunan,southern China

Detailed studies on Late Devonian to Early Carboniferous carbonate rocks in central Hunan, southern China have led to the recognition of 25 lithofacies which can be grouped into： （I） inner ramp peritidal platform, （2） inner ramp organic hank and mound, （3） mid ramp, （4） outer ramp, and （5） shelf basin facies associations. The peritidal platform facies association dominates the Zimenqiao Formation （Namurian A or late Datangian） and is characterized by gypsum and dolostone-containing sequences, indicating a peritidal platform environment. The other four facies associations dominate the Menggongao Formation （late Famennian）, Liujiatang Formation （Tournaisian or Yangruanian）, Shidengzi Formations （early Visean or early Datangian）. Five upward-shallowing cycles were distinguished in these three Formations. The predominant facies associations developed in each Formation demonstrate an overall transgression-regression cycle in the Late Devonian to Early Carboniferous in central Hunan. The overall transgressive sequence was preserved in the Shaodong, Menggongao, and Liujiatang Formations, and the overall regressive sequence was preserved in the Liujiatang, Shidengzi, Ceshui and Zimenqiao Formations.

A New Lycopsid, Zhenglia radiata gen. et sp. nov., from the Lower Devonian Posongchong Formation of Southeastern Yunnan, China, and Its Evolutionary Significance

A new plant, Zhenglia radiata gen. et sp. nov., from the Posongchong Formation （Early Devonian, Pragian age） of the Wenshan District of southeastern Yunnan Province, China is a small herbaceous lycopsid. The aerial branches divide into foliar and fertile stems. The arrangement of the leaf bases on the stem shows lepidodendroid-like phyllotaxy. Possibly the leaf base bears a ligulate pit. The microphyll consists of a swollen, decurrent base, and an entire, linear lamina. The fertile axis is composed of sporophylls arranged helically, forming a compact area similar to cone-like structure. Each sporophyll consists of a widened lateral extension and a distal lamina. The ovoid-elongate sporangia are attached adaxially on the surface of sporophylls. Based on morphological similarities, especially the undivided microphylls, the style of phyllotaxy, the form of the cone-like structures and sporangia, the new lycopsid Zhenglia radiata is placed in the order Protolepidodendrales and a possible evolutionary relationship with the arborescent lycopsids of the Late Devonian and Carboniferous is considered.

On the Devonian-Carboniferous Boundary in Neritic Facies Areas of South China:A Viewpoint of Integrated StratigraPhy

Biostratigraphical data indicate that in the neritic facies areas of South China, the Devonian -Carboniferous boundary (DCB), matching the boundary between conodont Siphonodella praesulcata zone and S. sulcata zone, should be drawn between rugose coral Cystophrentis zone and Pseudouralina zone, i.e. the Cystophrentis\ Pseudouralina inter val-zone. The top of the sea level fall event bed near the DCB is lower than the boundary between S. praesulcata and S. sulcata zones, but higher than the top of the Cysto phrentis zone. Sequence stratigraphical study shows that the sea level fall event bed near the DCB constitutes the shelf margin system tract (SMST) of a depositional sequence (SQ1) in both neritic and pelagic facies areas. The top surfaces of SMST of SQ1 is slightly lower than the base of S. sulcata zone in the pelagic facies areas. In neritic facies areas of South China, therefore, the Devonian - Carboniferous boundary is marked by the most distinct transgressive surface within the Cystophrentis\ Pseudouralina interval-zone, i.e. the base of the TST of SQ1. This boundary coincides with the top surface of the event bed resulted from the eustatic fall, and approximately corresponds to the base of Pseudouralina assemblage zone.

Geochemical Anomaly at the Devonian/Carboniferous Boundary, Huangmao, Gnangxi, China

The abundances of nearly 40 elements, Ir included, have been measured using radio-chemical and instrumental neutron activation analysis (RNAA and INAA) across a Devonian/Carboniferous (D/C) boundary section at Huangmao, Guangxi, China. The Ir anomaly has been found in the D/C boundary bed. Its peak value is 156 ppt, richer by a factor of 12 than that in the underlying strata. Besides, as with Ir, other siderophile and chalcophile elements such as Au. Ni. Co. As and Sb are also enriched. The cause for the abundance anomalies of Ir and other elemets is discussed. Neither volcanic eruption nor extraterrestrial impact can explain it satisfactorily. The real mechanism for the anomalies awaits further study.

Devonian Sequence Stratigraphy and Relative Sea Level Changes in Longmenshan Area, Sichuan

The Longmenshan area is located at the western margin of Yangtze platform, where the Devonian is composed of clastic rocks, mixed clastic-carbonate rocks and carbonate rocks in ascending order, and was formed in the marine environment from nearshore to outer shelf. Based on a study of six sections the Devonian in Longemenshan area is divided into 18 sequences and 5 sequence sets. The maximum transgressive high in the Devonian of this area occurred in Early Frasnian, corresponding to asymmetricus zone. The boundaries among the sequence sets are roughly corresponding to the bottom boundaries of Ⅰa',Ⅰc',Ⅱa, and Ⅱd in the Devonian of West Europe and North America, respectively. The frequencies of the relative sea level changes in this area vary in different periods, but can be correlated with those in the other regions of the world.

Archaeopteris halliana from the Late Devonian(Famennian)of Anhui Province,China

New materials from the Upper Devonian （Famennian） Wutong Formation of Chizhou District, Anhui Province, South China, allow description of fertile and sterile characters of Archaeopteris halliana. This plant has penultimate axes attached by sterile leaves and paired ultimate branches in the same ontogenetic spiral. Sterile leaves are narrowly cuneate in shape and bear distal margins dissected deeply. These leaves are spirally arranged on sterile ultimate axes. Non-laminated sporophylls occur spirally on the ultimate axes and bifurcate once or twice. Elongate sporangia with longitudinal dehiscence are borne adaxially below or above the dividing points of the sporophylls. Despite the leaf shape resembling that of Archaeopteris macilenta, our plant is assigned to A. halliana because of its non-laminated sporophylls. Fertile characters should be given priority or enough consideration in identifying species of Archaeopteris.

Phylogeny of Devonian Lycopsids Inferred from Bayesian Phylogenetic Analyses

To investigate the phylogeny of early lycopsids,cladistic analyses using both parsimony and Bayesian approaches are presented,with a data matrix of 33 morphological characters across 25 taxa. The resulting parsimony and Bayesian trees showed overall similarities in tree topologies.In the Bayesian tree,the Protolepidodendrales and the heterosporous lycopsids are recognized as two monophyletic groups,and within the latter group,the Isoetales sensu lato forms a subclade.This topology implies that the acquisition of a ligulate character evolved twice in the lycopsids,once in the protolepidodendralean Leclercqia Banks et al.,and once in the heterosporous lycopsid clade. Phylogenetic positions of several lycopsid plants previously reported from the Mid-Upper Devonian of South China,which have uncertain ordinal affinities,were estimated by the cladistic analyses;cf. Longostachys Xue et Hao,Longostachys Zhu et al.,Monilistrobus Wang et Berry,and Yuguangia Hao et al.fall well within the Isoetales clade,as earliest members of this order,while Minostrobus Wang and Wuxia Berry et al.are nested within the basal part of the heterosporous lycopsids.Bayesian analyses are a very useful approach in systematic studies and can be applied in analyzing paleobotanical data sets as well.