Nitrogen Contents and Isotopic Characteristics of Mesozoic and Cenozoic Granites in Northeastern China

The method of determining the nitrogen isotopic composition of granites in the northeastern part of China is described.The content and isotopic values of nitrogen released from granite samples by stepwise heating were determined as well.The results showed that the diferent areas of northeastern China hae a great difference in nitrogen content and isotopic composition.Nitrogen released from the granites is 1.64-6.23μL/g ,with the maximum at about 600℃,from rhyolite and granophyre is 108.98-755.96μL/g,with the maximum at about 900℃,It is proved that fluid is characterized by heterogeneity in the deep crust of the different areas in northeastern China.The nitrogen isotopic compositions in different ranges of temperautes are wweighted.And the nitrogen isotopic compositions in different anges of temperatures are weighted.And the nitrogen isotopic values are 9.2‰ to 17.0‰,with a variation range of 7.8‰,The nitrogen isotopic ratios may have been fractionated during degassing and the fluid released from granites is the residual component.     

大厂花岗岩年龄及成矿时代

The Dachang tin ore fields is one of the largest in China, where eassiterite-sulphide-type ore deposits occur. The ages of Dachang granites which are closely related to the ore deposits are discussed in this paper. Based on sixteen K-At biotite and one U-Pb zircon ages, it is suggested that Dachang granites were formed at 72--102 m.y.The cooling rates of Dachang granites have been estimated at 18.4℃/m.y. in the arly, 13.3℃/m.y. in the middle, and 4.5℃/m.y. in the late period.     

关于我国东南部不同时代花岗岩的年龄及分期问题的讨论

Made in the present paper is a further diseussion on the genetic relations between orogenic movements and. the formation of granitic rocks. These two major gcological processes affected one another, thus leading to the formation of the con.tincntal crust and its evolution. It seems undoubted that Hereynian granites are closely related to the Hercynian orogeny, especially in the Qinzhou Region. Based upon the geological evidence and geochronological data, the geological timescale for the granites of different ages is proposed as follows : Donganian granites --approximately from 1450 to 1300m.y.; Hsuehfengian granites--from 1000 to 650m.y. ; early-Caledonian granites--from 570 to 420 m.y. ; late-Caledonian granites from 420 to 340 m.y. ; Hercynian granites-- from 800 to 250 m.y. ; Indosinian granites--from 250 to 185 m.y. ; early-Yenshanian granites-- from 185 to 137 m.y. and late.Yenshanian granites- from 137 to 67 m.y.     

Application of Strontium Isotopic Stratigraphy to DatingMarine Sedimentary Units: A Case Study from the PermianStratotype Section in Southern China

The calibration of sedimentary rock absolute dates is one of the difficulties in sedimentological and stratigraphic research. Since strontium(Sr) resides in seawater much longer(≈106 a) than the seawater intermixing time(≈103 a), the Sr isotopic composition of global seawater is uniform at any time and results in a stable system throughout geological history,based on which a global Sr isotope composition dating database has been established for age-calibration of marine strata.The Permian stratigraphic sections in the northern part of the Upper Yangtze block, southern China, record continuous marine sediments with clear stratigraphic boundaries and is suitable for stratigraphic dating of Sr isotopes. Based on sampling and Sr isotopic compositions of Permian carbonate strata in the northern part of the Upper Yangtze, a Permian Sr isotope evolution curve was established. According to the basic principles of Sr isotope stratigraphy, the global Strontium isotope age database can be used to calibrate the Permian stratigraphic dates in the northern Upper Yangtze. The results show that the Sr isotope evolution curves for the marine carbonate rocks in the Permian stratigraphic section of the Upper Yangtze present a decreasing trend from the mid-Qixia stage(P2) to the mid-Wujiaping stage(P3), and then rise from the middle Wujiaping stage to the end of Changxing stage(P3). When the Permian Sr-isotope evolution curve is compared with the global Sr isotope evolution curve in the northern Upper Yangtze, the two are consistent in their long-term evolutionary trend, indicating that Permian global geological events are important controlling factors for the composition and evolution of Sr isotopes. The 87 Sr/86 Sr value decreased gradually in the background of large-scale regressions at the turn of middle to late Permian period, revealing that the Emeishan basalt eruption occurred near the Maokou/Wujiaping boundary(GLB). Srisotope stratigraphy dating was performed on the boundaries of the Qixia Formation/Maokou Formation, Maokou Formation/Wujiaping Formation(GLB), Wujiaping Formation/Changxing Formation(WCB) and the Permian/Triassic(PTB) using the Global Strontium Isotope Age Database. The results are 270.4 Ma, 261.2 Ma, 254.5 Ma and 249.7 Ma,respectively. Based on this, the eruption age of the Emeishan basalts is defined at about 261.2 Ma., which is more coincident with that acquired from other previous dating methods on the eruption age of the Emeishan basalts, and therefore proves that the application of Sr isotopic stratigraphy to dating marine sedimentary units is an effective method.     

Geochemical Characteristics and Genetic Types of Natural Gas in the Xinchang Gas Field, Sichuan Basin, SW China

The molecular compositions and stable carbon and hydrogen isotopic compositions of natural gas from the Xinchang gas field in the Sichuan Basin were investigated to determine the genetic types. The natural gas is mainly composed of methane (88.99%–98.01%), and the dryness coefficient varies between 0.908 and 0.997. The gas generally displays positive alkane carbon and hydrogen isotopic series. The geochemical characteristics and gas-source correlation indicate that the gases stored in the 5~(th) member of the Upper Triassic Xujiahe Formation are coal-type gases which are derived from source rocks in the stratum itself. The gases reservoired in the 4~(th) member of the Xujiahe Formation and Jurassic strata in the Xinchang gas field are also coal-type gases that are derived from source rocks in the 3~(rd) and 4~(th) members of the Xujiahe Formation. The gases reservoired in the 2~(nd) member of the Upper Triassic Xujiahe Formation are mainly coal-type gases with small amounts of oil-type gas that is derived from source rocks in the stratum itself. This is accompanied by a small amount of contribution brought by source rocks in the Upper Triassic Ma'antang and Xiaotangzi formations. The gases reservoired in the 4~(th) member of the Middle Triassic Leikoupo Formation are oil-type gases and are believed to be derived from the secondary cracking of oil which is most likely to be generated from the Upper Permian source rocks.     

Xinjiangoxylon Gen.Nov., a New Gymnosperm from the Latest Permian of China

Following the greatest known end-Permian mass extinction plants have low diversity. Lycopsids and conifers dominated on land. A new gymnosperm Xinjiangoxylon gen. nov. is proposed based on a woody stem specimen collected from the Upper Permian （latest, Changhsingian） Upper Guodikeng Formation of the Taoshuyuan section, Turpan, Xinjiang Uygur Autonomous Region, Northwest China. The decorticated stem is characterized by a complex pith, endarch primary xylem and a thick secondary xylem cylinder. Numerous petrified woods were found in the Changhsingian at this section. However, there are rare wood fossils in the Early Triassic. The abrupt decrease of fossil woods worldwide relates to the crisis at the end of the Permian. Xinjiangoxylon turpanense gen et. sp. nov. appears to represents one gymnosperm that existed in the latest Permian.     

顺5孔的磁性地层学和早松山世的北京海侵

Vertically oriented samples collected from the care S-5 in the county of Shunyi,Beijing Plain, were measured on an astatic magnetometer, after demagnetized with a peak value of 150 or 200 Oe. The results have shown that the loose sediments up to a thickness of 640 m have recorded the Brunhes-Matuyama boundary at the depth of 160m, the Matuyama-Gauss boundary at the. depth of 468 m, and the short events corresponding to the polarity events during each epoch. 28 species of foraminiferal fossils were isolated from the sample at the depth of 428 m, 31% of this fauna is composed of planktonic foraminifera. Such an assemblage in dicates the warm, shallow-water, open-sea palaeoecological environments.According to the ages of magnetostratigraphic sequences, this marina bed composed of silts and sands with foraminiferal fossils marked by classical HyaliNea baltica,has been dated to be about 2.26 re.y, B.P., approximating the age of FAD of Hyalinea baltica in the section at Santa Maria in Italy (about 2.1 m.y.B. P). Its equivalent is also found in the other coree from the Beijing Plain. From these facts, it is postulatsd that during the early Matuyama epoch, an extensive transgression took place on the Beijing Plain. A new datum level of benthonic and planktonic foraminifera marked by the appearance of Hyalinea baltica has been found in Early Matuyama strata in the Beijing Plain. The first appearance of cold forms in the Vrica Section in Italy has been dated to be about 2:4 m.y.B.P. Based upon the up-to-date reports on calcareous nannoplankton, the interval of 2.3--1.6 m.y. is a distinet alternating stage in their evolution history. The climate in the Northern Hemisphere began to become obviously colder at about 2.5 m.y. ago. From the foregoing discussion, it is reasonable to set the Pliocene-Pleistoecne boundary in the Beijing Plain at the basal limit of the Matuyama epoch (2.43 m.y.).     

Source Rocks for the Giant Puguang Gas Field,Sichuan Basin:Implication for Petroleum Exploration in Marine Sequences in South China

Detailed geochemistry studies were conducted to investigate the origin of solid bitumens and hydrocarbon gases in the giant Puguang gas field. Two types of solid bitumens were recognized： low sulfur content, low reflectance （LSLR） solid bitumens in sandstone reservoirs in the Xujiahe Formation and high sulfur content, high reflectance （HSHR） solid bitumens in the carbonate reservoirs in the Lower Triassic Feixianguan and Upper Permian Changxing formations. Solid bitumens in the Upper Triassic Xujiahe Formation correlate well with extracts from the Upper Triassic to Jurassic nonmarine source rocks in isotopic composition of the saturated and aromatic fractions and biomarker distribution. Solid bitumens in the Feixianguan and Changxing formations are distinctly different from extracts from the Cambrian and Silurian rocks but display reasonable correlation with extracts from the Upper Permian source rocks both in isotopic composition of the saturated and aromatic fractions and in biomarker distribution, suggesting that the Permian especially the Upper Permian Longtan Formation was the main source of solid bitumens in the carbonate reservoirs in the Feixianguan and Changxing formations in the Puguang gas field. Chemical and isotopic composition of natural gases indicates that the majority of hydrocarbon gases originated from sapropelic organic matter and was the products of thermal cracking of accumulated oils. This study indicates that source rock dominated by sapropelic organic matter existed in the Upper Permian and had made major contribution to the giant Puguang gas field, which has important implication for petroleum exploration in marine sequences in South China.     

GEOCHEMICAL CHARACTERISTICS OF GRANITES AND ITS STRUCTURAL GENETIC ENVIRONMENT IN THE NANDAN-HECHI METALLOGENETIC BELT, NORTHWEST GUANGXI

The Nandan-Hechi metallogenetic belt is the most important tin-polymetallic producing district in China, and is the location of the Dachang super-large tin deposit. Based on the detailed field investigation and isotopic data, the stages of magmatic activity in the Nandan-Hechi metallogenetic belt have been lined out in this paper. Through the study about the geochemical characteristics of different granites, and by using ω(Al2O3)-ω(SiO2), ω(TFeO)/[ω(TFeO) ω(MgO)]-ω(SiO2), AFM, ACF and Rb-Yb Ta, Rb-Y Nb,Ta-Yb, Nb-Y discrimination diagrams in combination with regional geological setting analysis, the authors carried out analyses about the structural environment for the formation of the granites, and discussed the structural environment and dynamic setting for the large scale mineralization in this area. Our study indicates that the majority of the granites in Nandan-Hechi metallogenetic belt belong to the POG type,while the later stage alaskite belongs to the RRG CEUG type. The granites were formed at the stage of structural transformation from postorogenic phase to intraplate setting. But the major structural environment is characterized by steady regional extension. The formation age for the granites coincides with the time for this transformation, and this translation environment is favored for large-scale metallogenesis.     

东秦岭东段花岗伟晶岩区的同位素地质年龄

26 determinations of the isotopic ages of granites and pegraatites by the K-Ar method are reported for the eastern section of the Eastern Tsinling. There may exist three periods of granites in this region, i.e., (1) late period of Early Paleozoie (420--450m.y.), (2) early period of Late Paleozoie (370-380m.y.)and (3) Mesozoic (178 m.y.) The granitic pegraatites are concentrated, in two regions-the eastern and the western regions. The western re,on is dated to be 400 m.y. Or more, and the eastern region, 370--380 m.y. Two samples of metamorphic rock from Ching-you-ho of Shangnan, Shensi and Lung-ehuan-ping of Lushi, Honan, are determined to be 451 and 453 m.y. respectively.     

On Late Triassic Floras in China and Principles for Palaeophytogeographic Regionalization

A new scheme of Late Triassic palaeophytogeographic regionalization of China is put forward on the basis of three principles given as follows:1. The palaeophytogeographic regionalization should be based on the characters of the various floras themselves. These characters include the types of the dominant floras, compositional patterns of various communities and existence of dominant genera or those genera and species characteristic of a region.2. The palaeogeographic positions of the floras in geologic time should be considered.3. The distribution of the floras was influenced in three directions——latitudinal, longitudinal and vertical——in geological time.Formerly, a number of Chinese palaeobotanists based the palaeophytogeographic regionalization only on the factor of latitude, and neglected the characters of the floras themselves and the effect of their three-directional zonation. However the discovery of the Tianqiaoling flora(located at latitude 43.5°N in NE China) rich in fossils of Dipteridaceae and Cycadophyta, indicating tropic or subtropic conditions, and a comprehensive consideration of assigning the floras of southern Tibet on the basis of palaeomagnetism, plate tectonics, etc., suggest that the palaeophytogeographic regionalization is a rather complicated subject. As the climatic conditions controlling the growth of vegetation changed in three directions one should consider not only the effect of latitudinal change(which usually causes temperature variations from south to north), but also the effect of longitudinal change(which usually brings about variations in humidity from sea to inland) and moreover the effect of vertical or elevation change(which also leads to variations in temperature and humidity). At the same time, it is also necessary to take into consideration the actual palaeogeographic positions of the floras in geologic time.Therefore, it is suggested that the Late Triassic floras in China should be grouped into three floristic regions, namely.(1) the Northern Floristic Region with the Danaeopsis-Symopteris flora,(2) the Southern Floristic Region with the Dictyophyllum-Clathropteris flora, and(3) the Yaflung Zangbo River Floristic Region. It is inferred here that the floral characters of the 3rd region are similar to those of the Dicroidium-Lepidopleris flora growing on Gondwana land at that time.     

New Schizolepis Fossils from the Early Cretaceous in Inner Mongolia, China and its Phylogenetic Position

Three Schizolepis species collected from the Lower Cretaceous layer of the Huolinhe Basin,Inner Mongolia,China are described.These fossils are Schizolepis longipetiolus Xu XH et Sun BN sp.nov.,which is a new species,Schizolepis cf.heilongjiangensis Zheng et Zhang,and Schizolepis neimengensis Deng.The new species is a well-preserved female cone,slender and cylindrical in shape.The seed–scale complexes have long petioles and are arranged on the cone axis loosely and helically.The seed scales are divided into two lobes from the base.Each lobe is semicircular or elongate ligulate in shape,widest at the middle or the lower middle part,with an obtuse or bluntly pointed apex.The inner margin is almost straight and the outer margin is strongly arched.On the surface of the lobe,there are longitudinal and somewhat radial striations from the base to the margin.The seed is borne on the adaxial surface at the base or middle of each lobe.Schizolepis was established in 1847,and,although more than twenty species have been discovered and reported,its phylogenetic position is controversial because of the imperfection of fossils.Most authors have considered there to be a close evolutionary relationship between Schizolepis and extant Pinaceae.Here,we analyze characteristics and compare Schizolepis with Picea crassifolia Kom,which is morphologically most similar to Schizolepis.The results indicate that the genus probably has a distant evolutionary relationship with extant Pinaceae.A detailed statistical analysis of the global paleogeographic distribution of Schizolepis showed that all the fossils of this genus appeared in strata ranging from the Upper Triassic to the Lower Cretaceous in the North Hemisphere,being rare in the Upper Triassic and Lower Jurassic,but being very common from the Middle Jurassic to the Lower Cretaceous,and particularly abundant in the Lower Cretaceous.According to the statistical results,we speculate that the genus originated in Europe in the Late Triassic then spread from Europe to Asia between the Late Triassic and the Late Jurassic.In the Early Cretaceous most species existed in China’s three northeastern Provinces and the Inner Mongolia Autonomous Region and adjacent areas.Combining the paleogeographic distribution of the genus with ancient climatic factors,we deduced that Schizolepis began to decline and became extinct in the Early Cretaceous,and the reason for its extinction is closely related to the icehouse climate during the Early Cretaceous.     

关于江西花岗质岩石的时代及分期

Granitic rocks are widespread n Jiangxi, constituting an important part of Nanling granites. It is snggested that they are genetieally related to ore genesis, A great deal of work had been dons by many geologists before and after liberation,but the problem concerning their age division still open to eontrovasy, The authors propose in this paper an age-division ssbeme for Jiangxi granitic rocks in an attempt to shed much light on the following problems,1, The age-divlsion of pro-Caledonian granites; 2: The existence of Varisian granites and their position in the age-division;3, The upper and lower limits of Indosinian Cyele and the distribution patterns of granites belonging to the cycle; and 4. The sub-division of Yenshanian granites.     

Comparing the Upper Triassic Deep-sea Flysch of theShannan Terrane with the Coeval Shallow Shelf Sediments ofthe Tethys Himalaya,Southern Tibet

The provenance and paleogeography of the Upper Triassic deep-sea flysch Langjiexue Group(LG) of the Shannan Terrane in the northeastern Himalaya orogen, south of Yarlung Zangbo, have been disputed in recent years since its affinity to the Tethys Himalaya was suspected during the early 2000 s. Based on the earlier discoveries of the Upper Permian–Triassic basalts and mafic dykes from the LG and of coeval detrital zircons from the Qulonggongba Formation(QF) in shallow shelf sediments of the Tethys Himalaya, the previous viewpoints on the basin and tectonics of the LG have been recently rejected. We compared the two units of the Upper Triassic, and our results reveal a number of differences,discrepancies, and inconsistencies in the debate, raising crucial questions on the postulation and provenance model of the remote Gondwanide Orogen for the LG. It is suggested that more observations and evidence are needed to further improve the paleogeographic understanding and relationship of the two units.     

Ocean Chemistry Revealed by Mineralogical and Geochemical Evidence at the Permian–Triassic Mass Extinction, Offshore the Persian Gulf, Iran

The Upper Permian Dalan Formation and the Lower Triassic Kangan Formation in the Persian Gulf area are mainly composed of shallow marine facies limestone and dolomite. Two subsurface-cored intervals were investigated in order to understand the original mineralogy and paleoceanic conditions. The decreasing trend of Sr concentration in these deposits shows that aragonite was precipitated during the Late Permian and then gradually changed to calcite toward the Permian–Triassic boundary (PTB). The dissolution rate of aragonite decreased from 60 m below the PTB toward the boundary, with the only exception at 10 m below the Permian-Triassic Boundary (PTB) due to the Permian–Triassic unconformity in this region. The increasing trend of Mg/Ca ratio in a global scale at the end-Permian time shows that the interpreted variation of mineralogy does not result from the change of this ratio. The increasing pCO2 and decreasing pH are considered to be the main controlling factors. The increase of Ca2+ at the end-Permian time due to the input of meteoric waters is too little to fully compensate this effect. A local maximum of the Si content just at the PTB confirms the input of runoff waters.     

前寒武摩天岭岩体同位素地质年龄讨论

Six zircon smaples were collected from the Motianling massif. According to the characteristics of zircons, they were divided into three types and that of type Ⅲ were separated for isotopic age determination. Through calculation and graphical analysis of the isotopic data on each zircon sample, true zircon ages were obtained:2860 m.y. for type Ⅰ, 760 m.y. for type Ⅱ and 510-580 m.y. for type Ⅲ, It is evident from geological environments of the Motianling massif, in conjunction with the characteristics of the zircons, that the first type formed earlier than the massif, the second one was contemperary with the massif, thus representing the age of the latter,and the third came into being due to metamorphism to which the massif had been subjected after its formation. From the above facts it is reasonable to believe that the Motianling massif is formed by granitization during the Xuefeng movement fromthe Sibao Group and the Banchi Group in the studied area. Later, it once again suffered metamorphism during the Caledonian movement and thus giving rise to the massif we observed at present.     

广西花岗岩时代讨论

Distributed in Guangxi Province are granites of the Szipao, the Hsuehfengian and the other three periods. Hereynian and Indosinian granites are treated in this paper as produets of a single eycle because the Permian granitism in Guangxi is thought to be eontinuity of the late Paleozoic magmatism. Although the Darongshan granite is found to have intruded into the upper Permian, but it yields an age of 231--289 m.y. This discrepaney may be due to, among other things, an inappropriate age division between the Permian and Triassic periods as set in the International Geochronological Table, and to a strong contamination.     

Evolution of isotopic composition and deuterium excess of brines in the Sichuan Basin, China

The isotopic composition and parameters for deuterium excess of brines, which were sampled in the Si-chuan Basin, show obvious regularities of distribution. The brine isotopic composition shows distinct two systems of marine and terrestrial deposits, with the Middle Triassic strata as the boundary. Brine hydrogen isotopic composition of marine deposits is lower while oxygen isotopic composition is higher than that of the SMOW, respectively, indicating that the brines were derived from seawater with different evaporating degrees at different times. From the Sinian strata, up to the Cambrian, Permian Maokou Formation and the Triassic Jialingjiang Formation, the δD values of brines tend to become relatively positive with the strata becoming younger. Brines of terrestrial deposits are considered to have been derived from precipitation and their isotopic composition is close to the globe meteoric water line (GMWL). Brines of transitional deposits between marine and terrestrial ones (the Upper Triassic Xujiahe Formation) have δD and δ18O values falling between the two end members of marine deposit brines and precipitation, indicating that the brines are a mixture of precipitation and vaporing seawater. Water samples from the brine-bearing strata of different ages show various deuterium excesses (d) with an evident decreasing trend as the age of strata gets older and older. Brine-bearing strata of the Triassic Leikoupo-Jialingjiang Formation, the Permian Maokou Formation, the Cambrian and Sinian strata are all carbonate rocks which have experienced intensive water/rock reaction and the deuterium excess essentially changes with time. All brine-bearing-strata surrounding the basin or faults, as well as those brine wells exploited for resources, have been obviously influenced by the precipitation supply. Therefore, the deuterium excesses of their brines have increased to different extents, depending on the amount of involvement of meteoric water. The variation and distribution of d values of the brines from different Triassic strata are related to the embedded depth of the strata. The deuterium excesses of brines become lower with increasing burial depth of the strata.     

华南某花岗岩型铀矿床成矿机理的铀铅同位素体系研究

The uranium deposit studied in this paper occurs in a Precambrian (Xuefengian)granite batholith. The emplacement age of the granite is 760 m.y. The average content of uranium in the granite is 7 ppm, but the yield of leachsd U is higher With an average of about 33.8%. The granitic rocks, contain; Some uraninite. Uranium mineralization mainly takes the form of siliceous veins With an age of 47 m.y. K-feldspar. present in the granite and pyrite associated with pitchblende were massspectrometrically analyzed for Pb isotopic compositious, characterized by anomalous lead. A reasonably linear array can be seen on the ^207Pb/^206Pb--^205Pb/^204Pb plot, implying a genetic connection between the rock and the ore, and a derivation of rock-forming materials from. a uranium-rich source. According to the continuous-growth model for anomalous lead, evolution, two isochrons give the. ages-of about 764 m.y. and 708 m.y.for ore-forming materials, close to the emplacement age of .the granite batholith. This indicates that the ore-forming materials came from the granite batholith. Eight granite samples collected from the mining .area were analyzed, but no uranium-lead ages could be worked out because of the pregressive destruction of the closed U-Pb isotopic system since granite emplacement, which resulted in the loss of uranium(78%). It can be imagined that in the period of continental weathering the surface water would infiltrate downwards, leaching out large amounts of uranium from the granitic rocks to form infiltration solution. The solution was heated at great depth and then found its way upwards, on which it dissolved constantly U from the rocks to form the uranium deposit.     

The Discovery of a Crinoid Community in the LateTriassic Zhuganpo Formation of Guizhou Provinceand Its Geological Significance

Recently a rich and well-preserved crinoid community including Traumatocrinus and Encrinus has been found in the Late Triassic Zhuganpo Formation in Guanling and Xingyi, Guizhou province, China. Among the fossils Traumatocrinus is the richest, and most of it occurs as clusters, with each cluster containing 3-42 crinoid branches. Study of the stem and calyx of Traumatocrinus shows that the number of stem-joints (columnals) is equal to the total stem length × K (5.85 per cmx stem-diameter). There are about 376 first- and second-order columnals on the whole stem. This number seems to coincide with the number of days in a year at that time. According to the present study of the palaeoecological environment of the crinoid community, it is considered that the reproduction and preservation of the crinoid community were controlled by the Late Triassic regression and the restricted bay of an interior sea behind the S-shaped shoal zone.