Middle Permian Limestone Research Articles

Alteration effects of karstification and hydrothermalism on middle Permian Qixia formation at the Wulong section, South China

Middle Permian Qixia Formation in the southwestern region of Sichuan (SW China) has experienced multiphase fluidisation, resulting in an unclear understanding of the reservoir reconstruction effect. In this study, a systematic analysis of the Qi2 member in Wulong Town was carried out by combining field outcrop petrology and geochemistry. The results demonstrated that multiple sets of crystalline dolomite-bioclastic limestone cycles were stacked vertically in the Qi2 member, accompanied by the development of fractures and karst channels. The dolomite was mainly composed of silty-fine dolomite (D1) and recrystallised dolomite (D2). Furthermore, obvious multiphase dolomitic cements (Cd1-Cd2) were present in the fractures and pores. Early karst is known to have lithologic mutation surface development and karst channel development at the top of several secondary cycles. The vadose silt dolomites (Cd1) having karst channels developed dull luminescence under cathode luminescence (CL). Both the geochemical indicators of elements and rare earth element (REE) content indicated dysoxic-oxic environmental conditions. The hydrothermal solution displayed tectonic carniole characteristics in the strata burial stage. Fractures and pores were filled with hydrothermal minerals such as coarse dolomites-saddle dolomites (Cd2, with some caused by recrystallisation of the Cd1 hydrothermal solution) and fluorites. Coarse dolomites-saddle dolomites developed dull-red luminescence with a bright-red rim under CL and their δ18OVPDB values were more negative than those of middle Permian limestone samples. Both the geochemical indicators of elements and REE content indicated the suboxic-anoxic environmental conditions. Karstification had minor constructive impact on the reservoir of the Qi2 member in Baoxing in southwestern Sichuan. Most products of karstification were distributed as fillings in channels. Aside from creating certain networked fractures, the hydrothermal solution was mainly filled with hydrothermal minerals along the fractures, pores and early karst channels. Karst and the hydrothermal solution mainly damaged the middle and upper parts of the middle Permian Qixia Formation in Southwest Sichuan. The impact of episodic fluid on the restoration of the carbonate reservoir was mainly restricted by channels for fluid migration and thickness differences among the reservoir. However, certain thick-layered and massive crystalline dolomite may hold promise for exploration.

Evolution of the North Qiangtang Block in the late Paleozoic: Paleomagnetism and its tectonic implications

Understanding of the geodynamic evolution of the Tethyan realm cannot be complete without paleogeographical reconstructions of the North Qiangtang Block (NQB) that occupies a central position in Tibet. However, the reliability of such a reconstruction for the Paleozoic still requires substantial improvement. In this paper, we present paleomagnetic results obtained from the Middle Permian limestones and Upper Permian volcanic rocks in the Tanggula area, aiming to provide precise constraints on the NQB kinematics during the geodynamic evolution of the Tethys realm. Combined with other available paleomagnetic data from the NQB, our results suggest that the block was stably located at ∼24°S for a long time before the Middle Permian, started to drift rapidly northward in the Middle Permian, and reached ∼8.4°S in the Late Permian. The NQB continued drifting rapidly northward during the Triassic until merging with the southern margin of Eurasia in the Late Triassic. We reviewed new and available paleomagnetic and geological data and proposed a revised model for the tectonic evolution of the eastern Tethys realm. The NQB likely belonged to a ribbon-like separate continental archipelago in the middle of the Paleo-Tethys Ocean during the early−late Paleozoic. The Cimmerian continent, including the South Qiangtang Block (SQB), rifted away from the northern margin of Gondwana and drifted northward to ∼22°S in the Middle Permian. The continent approached or partially collided with the NQB, resulting in the rapid northward movement of the NQB and the formation of the Longmuco−Shuanghu suture between the NQB and SQB.

Middle Permian ostracod fauna from the Khao Khad Formation (Indochina Terrane), Central Thailand

Permian ostracods are reported for the first time from the Wordian (Middle Permian) Khao Khad Formation of Saraburi Group (Lopburi Province, Central Thailand). The ostracod fauna consists of 18 species belonging to 11 genera including Bairdia, Bohlenatia,Liuzhinia, Silenites, Acratia, Bairdiacypris, Basslerella, Aurigerites, Microcheilinella, Paraparchites and Shemonaella. The studied Khao Khad Limestone, which are rich in fusulinids, gastropods, ostracods, bivalves and brachiopods, was deposited in a shallow carbonate platform on the western margin of the Indochina Terrane. The ostracod assemblage is typically Palaeo-Tethyan and similar to faunas from the other Lower to Middle Permian limestones in central Thailand.

Mixed seawater and hydrothermal sources of nodular chert in Middle Permian limestone on the eastern Paleo-Tethys margin (South China)

Middle Permian limestone and marl of the Maokou Formation deposited along the eastern Paleo-Tethys margin (South China) host abundant chert nodules that formed in association with the global Permian Chert Event (PCE). An enhanced understanding of the origin of the chert may help elucidate Middle Permian oceanic and diagenetic conditions. However, the mechanisms responsible for the formation of chert, especially the source of silica, remain controversial. Maokou chert nodules, which are made up of quartz and subordinate calcite, hematite, pyrite, and fluorite, and rimmed by F-bearing sepiolite laminae, appear to have formed mainly by the replacement of precursor nodular limestone by silica. The nodular limestone may have formed by differential compaction of interbedded limestone and marl, after which carbonate was replaced gradually outward from nodule centers by dissolved silica released from the dissolution of siliceous skeletal grains (including spicules and radiolarians) in host marl during early diagenesis. The introduction of high-T hydrothermal fluids into ocean water is evidenced by the presence of F-bearing minerals (fluorite and sepiolite), a hybrid rare earth element (REE) + Y pattern, and a wide range of δ30Si values (−0.4‰ to +0.7‰) documented from the Maokou nodular chert. Conservative estimation indicated that Middle Permian seawater may have had a δ30Si composition (+0.7‰ to +1.8‰) similar to that of modern open ocean water, suggesting that seawater was the dominant silica source of nodular chert. Mixing calculations based on REE + Y geochemistry suggest additional contributions of ca. 0.05–0.2% high-T hydrothermal fluid and ca. 1–10% of continental-derived freshwater to ocean water. Such increased influx of silica to seawater may have been related to the early rifting induced by Emeishan volcanism and intensified chemical weathering during an interglacial period, which played an important role in promoting the flourishing of siliceous organisms and subsequent chert enrichment during the Middle Permian.

A palaeomagnetic study of the Middle Permian and Middle Triassic limestones from Shan State, Myanmar: Implications for collision of the Sibumasu Terrane and Indochina Terrane

We report herein a new palaeomagnetic study on the Middle Permian and Middle Triassic limestones from Shan State of eastern Myanmar, aiming to resolve the spatial location of the Sibumasu Terrane during the collision of tectonic blocks in Southeast Asia and to constrain the timing of convergence between the Sibumasu Terrane and Indochina Terrane. Based on the rock magnetic and palaeomagnetic experiments, three stable characteristic remnant magnetizations are recognized from limestone specimens of Middle Permian and Middle Triassic age. The characteristic Component C of the Middle Permian limestone passed the fold test at 95% confidence level, indicative of a pre‐folding origin. The mean direction of this component is D = 10.7°, I = 17.9° (κ = 130.3, α95 = 10.8°) before and D = 13.7°, I = −25.3° (κ = 1894.9, α95 = 2.8°) after tilt correction, corresponding to a palaeomagnetic pole at 254.1°E, 53.2°N (A95 = 1.7°). This suggests that the Sibumasu Terrane was placed at a palaeolatitude of ~13.0°S during the Middle Permian. The Component C separated from the Middle Triassic samples also passed the fold test with a mean direction of D = 207.3°, I = −8.3° (κ = 12.9, α95 = 6.2°) before tilt correction and D = 205.6°, I = −33.5° (κ = 27.1, α95 = 4.2°) after tilt correction, corresponding to a palaeomagnetic pole at 187.3°E, 65.8°N (dp/dm = 2.7°/4.8°). This implies that the Sibumasu Terrane was located at a palaeolatitude of ~18.3°N during the Middle Triassic. Based upon the detailed palaeomagnetic analysis, this study supports the view that the collision of the Sibumasu Terrane and Indochina Terrance occurred during or before the Middle–Late Triassic times.

The giant Upper Yangtze Pb–Zn province in SW China: Reviews, new advances and a new genetic model

In the western margin of the Yangtze Block, SW China, the Emeishan large igneous province (ELIP) is spatially associated with >400 carbonate-hosted epigenetic Pb–Zn deposits. These deposits form the giant Upper Yangtze Pb–Zn metallogenic province with >20 Mt base metals. In the southeastern part of this province, the important Pb–Zn deposits include those of the Yinchangpo, Yunluhe, Maozhachang, Tianqiao, Banbanqiao, Mangdong, Shaojiwan, Liangyan, Qingshan, Shanshulin, Nayongzhi and Guanziyao deposits. Sulfide ore bodies in these deposits are (i) hosted in late Ediacaran to middle Permian limestone, dolomitic limestone and dolostone; (ii) structurally controlled by reverse fault-anticline tectonic systems; and (iii) spatially associated with the ELIP flood basalts and mafic dikes, and early Permian, early Carboniferous and early Cambrian organic matter-rich black shales. C–O isotopic compositions suggest that dolostone and limestone, mantle-derived rocks of the ELIP, and sedimentary organic matters supplied C–O to the hydrothermal systems through water/rock (W/R) interaction. New and existing S isotopic compositions of sulfides imply multiple sources of S and the reduction of sulfate through both abiotic thermochemical (TSR) and bacterially mediated (BSR) processes. Zn isotopes indicate that the sources of Zn were most likely related to the ELIP with various contributions from sediments and basements locally. Pb isotope signatures are suggestive of derivation of Pb from basements and sedimentary rocks with variable influences from the ELIP. Sr isotopes support that mantle-derived rocks, sediments and basements were involved in Pb–Zn mineralization, and they have various contributions in different deposits. We consider that the Pb–Zn deposits in the Upper Yangtze province are the mixed products of multiple S species-bearing solutions and metal-rich fluids, both of which were derived from, flowed through or interacted with multiple lithostratigraphic units in the western Yangtze Block. The change of tectonic regimes from extension to compression after eruption of basalts of the ELIP, and then to extension during Early Mesozoic, facilitated extraction, migration, and excretion of ore-forming metals and associated fluids. Mixing of fluids and reduction geochemical barrier activated TSR, causing cyclical carbonate dissolution, CO2 degassing and recrystallization (namely carbonate buffer). All these processes triggered continuous precipitation of huge amounts of hydrothermal minerals. Underplating and eruption of ELIP basalts provided heat flow, fluids and volatiles, whereas the basalts acted as an impermeable and protective layer, and even as ore-hosting rocks. These Pb–Zn deposits have spatial and genetic association with igneous activities of the ELIP, and are characterized by high ore grades (>10 wt% Pb + Zn), high concentrations of associated metals (e.g. Cu, Ag, Ge, and Cd), and medium-low temperatures (usually < 300 °C) and salinities (commonly < 20 wt% NaCl equiv.), all of which are significantly different from those of typical Mississippi Valley-type (MVT) deposits. Hence, the carbonate-hosted epigenetic Pb–Zn deposits in the Upper Yangtze metallogenic province representing to a new type of Pb–Zn deposits that are hosted in platform carbonate sequences and formed within compressional zones of passive margin tectonic settings.

Evolution of sedimentary facies and fossil communities in the Middle Permian Maokou Formation in Zigui County, Hubei Province, South China

A geological event that happened at the end of the Middle Permian resulted in different levels of erosion in a shallow-water platform of South China, which led to diverse geological records in different sections. The Lianziya section in western Hubei Province of South China has a well-exposed stratigraphic sequence of the late Middle Permian rocks with abundant fossils and sedimentary facies types, providing new evidences for understanding the evolution of marine biota and environment in the late Middle Permian. Our study shows that four fossil communities can be recognized with the change of sedimentary facies in the late Middle Permian: Foraminiferal–algal community, phylloid algal community, bryozoan community and Ungdarella community. The foraminiferal–algal community is dominated by fusulinids and calcareous algae, but was soon replaced by the phylloid algal community. With an increase of terrestrial input, the phylloid algal community was again replaced by the bryozoan community. Near the end of the Middle Permian, with a decrease of terrestrial input, the bryozoan fossil community disappeared while the Ungdarella community became dominant. A 10 cm-thick weathered crust occurred at the top of the Middle Permian limestone, marking a large amplitude fall in sea-level and the beginning of a terrestrial erosion stage. The sedimentary facies and fossil community changes in the Lianziya section indicates that the Middle Permian crisis was a gradual process while the sea-level fall mainly occurred in the latest Middle Permian.

Characteristics and exploration prospects of Middle Permian reservoirs in the Sichuan Basin

In recent years, encouraging progress has been made in the Middle Permian natural gas exploration in the Sichuan Basin – numerous wells have obtained high-yield industrial gas flows in the dolomite porous reservoir sections in the Middle Permian Maokou Formation and the Qixia Formation, making the Middle Permian one of the most realistic replacement strata at present. In order to clarify the further exploration prospect of the basin, the Middle Permian depositional settings and prospective reservoir types were analyzed. The results show that: (1) the depositional environment was predominately open, shallow water; the paleogeomorphology was high in the west and low in the east, with bioclastic flat reservoirs more extensive in the middle-west part than the east part; crustal extension made Middle Permian deposits have good conditions for thermal water deposition and hydrothermal alteration; and (2) the prospect reservoirs for exploration were shoal facies dolomite porous reservoir of the Qixia Formation, thermal water dolomite porous reservoir and karst reservoir of the Maokou Formation, thus, dolomite porous reservoir was the most perspective target in the Middle Permian. It is concluded that Middle Permian limestone source rocks have large hydrocarbon generation intensity in the northern part of Western and Central Sichuan Basin and have the material basis for the formation of large-medium gas fields; the thick dolomite reservoir of the Qixia Formation in the Western Sichuan Basin is the most prospective reservoir in the Middle Permian; three types of reservoirs are distributed in the Central Sichuan Basin, and they are superimposed vertically with large exploration potential; Jiange–Nanchong–Fengdu region is located in the thermal sub-basin zone, where the thermal water dolomite reservoir of the Maokou formation is pervasive and superimposed on the karst reservoir of the Maokou Formation, showing good natural gas exploration prospects.

Mineralogy, geochemistry, and genesis of lateritic bauxite deposits in the Wuchuan–Zheng'an–Daozhen area, Northern Guizhou Province, China

The lateritic bauxite deposits in the Wuchuan–Zheng'an–Daozhen area, Northern Guizhou Province, are hosted by the Liangshan Formation which unconformably overlies the Lower–Middle Silurian mud-shale and the Upper Carboniferous limestone and underlies the Middle Permian limestone. From the bottom upward, the deposits are generally composed of brick-red, yellow-brown, and gray bauxite horizons. Diaspore, boehmite, kaolinite, smectite and hematite are the major mineral components in the bauxite ores with small amounts of gibbsite, illite, goethite, pyrite, anatase, zircon, quartz and feldspar. The textural features of ores suggest that the bauxite has an authigenic origin but locally underwent transportation and re-deposition. Geochemical investigations indicate that the immobile elements like Al, Ti, Zr, Cr, Hf, Nb, Ta and Th were obviously enriched during bauxitization. Factors such as the type of parent rock, pH variation in weathering solutions, adsorption processes, groundwater chemical characteristics, Fe concentration variation in the weathering profiles, leaching degree of minerals, and geochemistry of elements have played a significant role in the distribution of trace and rare earth elements during weathering of the lateritic bauxite. The bauxites may have a close genetic relationship with the Hanjiadian mud shale and the Huanglong limestone in view of their similar chondrite-normalized REE patterns, Zr/Hf and Nb/Ta ratios. However, field observations and geochemical data suggest that the precursors of bauxites are complex and the main components of precursors are basic igneous rocks possibly from the Neoproterozoic basic igneous rocks and the Mesoproterozoic basic–ultrabasic intrusions in the Yangtze Block.

Carbonate Sedimentation in a Permian High-Latitude, Subpolar Depositional Realm: Queensland, Australia

High-latitude carbonate rocks that formed in subpolar Paleozoic oceans contain critical information about past climate, but they are neither well documented nor fully understood. Lower and middle Permian limestones that were deposited in such paleoenvironments at 45°S to 55°S along the southeastern margin of Gondwana are now exposed in eastern Australia. Such carbonates constitute a small but important and well-preserved part of the siliciclastic glacigene succession in the Bowen Basin from southern and central Queensland. Cleanest limestones accumulated on topographic highs in the eastern (seaward) parts of the basin that were isolated from siliciclastic sediment input from the western craton. Shallow-water deposits are composed of large eurydesmid bivalves, spiriferid and productid brachiopods, bryozoans, infaunal and epifaunal benthic foraminifers, calcareous sponge spicules, and abundant crinoids in the form of locally cross-bedded rudstones and grainstones. Deeper-water, muddy carbonates are dominated by bryozoans, crinoids, and productids (shells and spines). Deepest-water sediments are argillaceous floatstones or shales containing fenestrate bryozoans, thin-walled productids, and siliceous sponge spicules. When integrated with recent studies of coeval sedimentary rocks along the 2000-km-long paleocontinental margin, a clear pattern of sedimentation emerges wherein deposition took place in similar settings during three discrete periods of deglaciation: late Sakmarian, late Artinskian, and Wordian. All of the carbonates are distinguished by a low-diversity, high-abundance heterozoan biota with no phototrophs and express a recurring deepening-upward stratigraphic motif that is interpreted to reflect rising sea level accompanying glacial meltdown. They also record a strong poleward gradient of increasing ice-rafted debris, increasing skeleton size, decreasing invertebrate diversity, decreasing epifaunal calcareous benthic foraminifers, and reduction in crinoids; glendonites are confined to siliciclastic sediments deposited during glacial periods. Comparison with coeval northern hemisphere carbonates indicates a strong parallelism of facies and depositional systems. This study helps to establish these deposits as a template for a global Paleozoic high-latitude carbonate facies model.

Foraminiferal fauna and lithofacies of Middle Permian limestone blocks in the middle course of Kuma River (Osakama), southern margin of the Chichibu Terrane in west Kyushu, Japan

ABSTRACT Middle Permian (Midian in the Tethyan standard scale) foraminifers of 34 species assignable to 27 genera were identified in erratic limestone blocks collected on the left bank of the middle course of the Kuma River (Osakama), west Kyushu, Japan, where four species of fusulinoideans have been reported. These blocks are thought to have been derived from a small limestone contained in basaltic rocks embedded within uppermost Jurassic mudstone along the southern margin of the Chichibu Terrane (Sambosan Terrane). An Osakama foraminiferal fauna in comparison with contemporaneous faunas known from the Jurassic to Early Cretaceous terranes of Japan and in relation to the limestone lithology are described and discussed in this paper. The Osakama fauna is characterized by dominant occurrence of a newly proposed species Yabeina osakamensis contained in weakly dolomitized gray limestone consisting of fusulinoidean crinoidal bioclastic packstone/grainstone with lithic clasts of limestone. The limestone lithol...

Middle Permian foraminifers of the Izuru and Nabeyama Formations in the Kuzu area, Tochigi Prefecture, Japan Part 1. Schwagerinid, neoschwagerinid, and verbeekinid fusulinoideans

The Middle Permian Izuru and Nabeyama Formations in the Kuzu area, Tochigi Prefecture are composed of thick basaltic rocks and fossiliferous partly dolomitized limestone. Fusulinoidean biostratigraphy is first established in these two formations, and the stratigraphic distribution of the 30 species of fusulinoideans distinguished from 70 localities is shown. The Izuru and Nabeyama Formations are biostratigraphically subdivided into the lower Parafusulina nakamigawai, the middle Parafusulina yabei, and the upper Parafusulina tochigiensis zones. The first zone is correlated to the Parafusulina nakamigawai Zone of the basal part of the Akasaka Limestone. The middle part of the third zone corresponds to the upper part of the Neoschwagerina craticulifera Zone to the lower part of the Neoschwagerina margaritae Zone of the Akasaka Limestone based on the occurrence of Gifuella amicula. More precise correlation of the Parafusulina yabei and Parafusulina tochigiensis zones will be possible when biostratigraphic zonation by schwagerinids is made clear in relation to the stratigraphic range of neoschwagerinids in Middle Permian limestones of the Jurassic terrane of Japan. Seven species of Parafusulina including two new species, P. shimotsukensis and P. tochigiensis, and Pseudodoliolina ozawai and Gifuella gifuensis are described and discussed herein.

Middle Permian Limestone on Pacific Side of Alaska Peninsula: GEOLOGICAL NOTES

Middle Permian Limestone on Pacific Side of Alaska Peninsula: GEOLOGICAL NOTES