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The study area was situated in south of the Jiangnan Slope Belt，western Hunan（Peng 1990，1992）.It is well known as one of the most richly fossiliferous areas in China for the Middle and Late Cambrian trilobite faunas.As Cambrian trilobite faunas have been documented around the world，it has become evident that the faunas in western Hunan provide a correlative possibility for worldwide correlations（Text-figure 9）.As discussed above，18 trilobite zones were proposed for the Middle and Late Cambrian in South China（Peng，1999）.The interval with the Ptychagnostusatavus Zone（late Taijiangian Stage in South China）to the Proagnostus bulbus Zone is considered to be correlatable with the early Changhsian Stage（Middle Cambrian）in North China.The interval from the Liguagnostus reconditus Zone（early Waergangian Stage in South China）to the Leiostegium constrictum-Shenjiawania brevica Zone（late Taoyuanian Stage in South China）are considered equivalent with the Kushanian，Changshanian and Fengshanian Stage（Late Cambrian）in North China.In the study area，the topmost zone is the Eolotagnostus decorus-Kaolishaniella Zone，which is considered correlatable with the late Changshanian Stage（Late Cambrian）in North China（Peng，2000）.
As indicated above，the Aoxi Formation of the Middle Cambrian is largely unfossilifeous dolomite in northwest and western Hunan，but its stratigraphical position suggests that is correlated with the lower Changshanian Stage of North China.
Text-figure9 Correlation chart relation of the Middle and Upper Cambrian in studyarea，W.Zhejiang，N.YangtzePlatform，Xinjiang，Australia and S.Kazakhstan
3.2.1 Correlation between the study area and west Zhejiang
In the study area，Ptychagnostusatavus allows a direct correlation with the P.atavus Zone of the Yangliugang Formation of the Middle Cambrian in West Zhejiang（Text-figure 9）；the Ptagnostus punctuosus Zone in West Hunan includes Pseudophalacroma ovata［=Ps.triangularis］and Triplagnostus longitriangularis，the former（Ps.triangularis）also occurred in West Zhejiang as a zonal fossil.Many important elements of the Goniagnostus nathorsti and L.laevigata Zones of the Wangcunian Stage of West Hunan，such as：Lejopyge laevigata，L.armata，Goniagnostus（A.）spiniger，Hypagnostus parvifrons，Proceratopyge（P.）conifrons，and Fuchouia oratolimba，have also been reported from the L.armata Zone of the Upper Cambrian Yangliugang Formation in West Zhejiang.Both zones are comparable each other.As the Proagnostus bulbus Zone and the Linguagnostus reconditus Zone comprise Cyclagnostus yaogongbuensis，and Bergeronites hunanensis，these elements commonly appear in the L.sinonensis Zone of lower part of the Huayanshi Formation of West Zhejiang.These two zones are correlatable with the G.stolidotus and G.reticlatus zones，which are known as index zonal fossils for global correlation of the boundary between Middle and Upper Cambrian，and occurred in both areas.The first discovery of Erixanium in middle part of the Huaqiao Formation of the study area，suggests the subzone that bears its name in the Agnostus inexpectans-Proceratopyge protractaAssemblage Zone is correlatable with the Erixanium Zone in West Zhejiang.
As the Agnostotes clavata-Irvingella angustilimbata and Corynexochus plumula-Sinoproceratopyge cf.kiangshanensis Zone consists of Pseudaagnostus（P.）communis，Proceratopyge（S.）dubius and P.（S.）kiangshensis，Agnostotes clavata［=Pseudoglyptagnostus clavatus］，suggesting a correlation with the A.clavatus-Sinoprocertopyge kiangshanensis Zone in upper part of the Huayansi Formation in West Zhejiang.It is difficult to correlate with the L.punctatus-Hedinaspis Zone of the Xiyangshan Formation and the post A.clavata-Irvingellaangustilimbata Zone of the Bitiao Formation.The Rhaptagnostus ciliensis-Onchonotellus cf.kuruktagnostus and E.decorus-Kaolishaniella Zones may be generally compared with the lower part of the Lotagnostus punctagnostus Zone in West Zhejiang.The L.punctatus Zone-Hedinaspis regalis Zone of west Zhejiang bears L.punctatus and Ketyna zhejiangensis.These two species appeared also in the L.punctatus-H.regalis Zone in West Hunan.
3.2.2 Correlation between the study area and Northern margin of Yangtze Platform
The North Yangtze Platform region is situated around the borders between Sichuan，Hubei and Shanxi provinces.It was poorly known because of lacking fossils and lithofacies data.Since the early 1990"s，great improvement in the Cambrian biostratigrahy and lithofacies has been carried out by Yang etal.（1991）.According to analysis of lithofacies and biostratigraphy，there exist slope belts.Six trilobite zones were established by Yang et al.（1991）（Text-figure 9）.Peng（2000）revised some of the trilobite species names for these zones.Except for the Xystridura？jielingensis Zone that is non-agnostoid，all other zones are based on agnostoids and correlatable widely.
Notably，the Ptychagnostus atavus and Lejopyge laevigata-Clavagnostus（P.）variatus Zones occurred respectively in the base and top of the Baguamiao Formation of the late Middle Cambrian in North Yangtze Platform.These two zones indicate direct correlation with the P.atavus and L.laevigata Zones in Western Hunan，but the other zones bracketed between these two zones cannot be correlated with the study area on a one by one basis.The Gonignostus nathorsti Zone contains Hypagnostus parvifrons and H.brevifrons.Upward，the Fenghuangella and Shengia zones are difficult to correlate with those of West Hunan.Above the Shengia zone，there are hardly any fossils found in the North Yangtze slope belt probably because of an unsuitable，weakly reducing carbonate setting.
3.2.3 Correlation between the study area and Xinjiang（Kuruktag）
The trilobite faunas from the Kuruktag area of Xinjiang（Xiang et al.，1985）are similar to those of the study area（Text-figure 9），both belong to the Southeast-China Type（Lu et al.1974）.As a zonal fossil of the Middle Cambrian，Ptychagnostusatavus occurs in both areas，and therefore can make direct correlation each other.The Pt.punctusus Zone of the Wangcunian Stage may be compared with the Pt.punctuosus Zone of the Moheishan Group；while the Goniagnostus nothorsti Zone of the Wangcunian Stage contains Pseudophalacromaovale，suggesting a correlation with the Ps.ovale Zone of the Moheish Group in Kuruktag.The L.laevigata Zone bears two important elements（L.laevigataand L.sinensis），indicating a correlation with the top part of the Moheishan Group that contains L.laeviata and L.sinensis.Both the Proagnostus bulbus and Linguagnostus reconditus Zones contain Buttsia（Waergangia）globosa in West Hunan，a species also appeared in the bottom of the Buttsia-Acmarhachis Zone of the Torsuqtagh Group in Kuruktag.In Kururtag of Xingjing，due to the Liostracina Zone yielding G.stolidotus，Liostracina，Bergeronites，Shengia and Pseudagnostus，it can be approximately aligned with the G.stolidotus Zone of West Hunan.The interval from the G.reticulates Zone to E.decorus-Kaolishaniella Zone in the study area does not seem to have any equivalents in the Torsuqtngh Group of Kuruktag.Farther upward，the Lotagnostus hedini and L.astaticus-Hedinaspis regalis Zones in the Torsuqtagh Group may be correlated with the L.punctatus-H.regalis Zone and the P.nasailis-P.hunanensis Zone of the Taoyuanina Stage in West Hunan，interims of the existence of L.punctatus，Hedinaspis and Charchqia in both zones.
3.2.4 Correlation between the study area and Australia（Queensland）
The upper part of the Late Templetionian（Floran）Stage of Queensland in eastern Australia marked by Acidusus atavus（=Pt.atavus）and Euagnostus opimus is correlatable with the Ptychagnostus atavus Zone of west Hunan（Text-figure 9）.In addition，the Pt.punctuosus Zone occurs in both areas，suggesting direct correlation.The Doryagnostus notalibrae and the Goniagnostus nathorsti Zones of the Undillan Stage are correlative with the G.nathorsti Zone of West Hunan.
In Queensland，the L.laevigata Zone consists of Ptychagnostus cassis，Proampyx agra，Holteria arepo，Damesella torosa/Ascionepea janitrix.This zone and the succeeding Erediaspis eretes Zone can be correlated with the L.laevigata-Proagnostus bulbus Zone and the Linguagnostus reconditus Zone in west Hunan.The Cyclagnostus quasivespa Zone of the Mindayalian Stage is correlatable with the interval with the Proagnostus bulbus Zone and the Linguagnostus reconditus Zone of western Hunan.Glyptagnostus stolidotus is common to both Australia and west Hunan，suggesting a direct correlation with each other.The Idamean Stage of Queensland is correlative with lower three zones of the Waergangian in the study area because it is defined by the appearance of Glyptagnostus reticulates（s.s.）and is overlain by Irvingella tropica，a species closely resembling I.angustilimbata.Angnostus inexpectans in the upper part of the G.reticulates Zone in Queensland may indicate that the base of the Agnostus inexpectans-P.（P.）protractaZone correlates with a level within the G.reticculatus Zone of Queensland.The assemblage with Irvingella，Prochuangia，Stigmatoa，Eugonocare，Agnostotes and Protemnites from the I.tropicaZone in Queensland（Shergold，1982）is also known from the Agnostus clavata-I.angastilimbataZone to the E.decorus-Kaolishaniella Zone of the study area.In Queensland，the Wentsuia-Rh.apsis Zone（Shergold，1980）contains Rhptagnostus cf.impressus which is similar to R.ciliensis of the R.ciliensis-O.cf.kuruktagensis Zone in west Hunan，while Onchontellus and Maladiodellaare also known from the W.iota-R.aspsis Zone.Peichiashaniellus secunda-Prochuangia glabellamay be correlated with Eolotagnostus decorus Zone-Kaolishshania Zone in west Hunan.
3.2.5 Correlation between the study area and Kazakhstan（Malyi Karatau）
The Cambrian System in the Malyi Karatau region of Kazakhstan can be recognized as a part of westward extension from the Tianshan Mountains in northwest China，where the Cambrian strata are relatively well exposed（see above）.The Middle and Late Cambrian faunas of southern Kazakhstan are similar to those of western Hunan.Trilobites from the Kyrshabakty and Batyrbai sections in Malyi Karatau（Ergaliev，1980，1983a，1983b；Apollonov and Chugaeva，1983a，1983b）provide a basis for precise correlation of the Kazakh sequences with the study area（Text-figure 9）.
The lower part of the Amginian Stage is characterized by the Peronopsis？ultimus Zone，which is approximately correlated with the O.ovientalis Zone in the study area.Upward the Pt.atavus Zone indicates direct correlation with the Pt.atavus Zone in the upper part of the Amginian.Both the Pt.punctuosus and Goniagnostus nathorsti Zones of the Wangcuaian Stage are also found in the Mayanian Stage of Kazakhastan.In Kazakhastan，the L.armataZone contains Ptychagnostusaculeatus，Goniagnostus longispinus，Linguagnostus tricuspis，L.calvus，Homagnostus pater，Pseudophalacroma，Clavagnostus，Ammagnostus，Grandagnostus，Oidalagnostus，Dorypyge，Fuchouia，Lisania，Corynexochus，Prodamesella，Meringaspis，Buttsia，Damesella and Blackwelderia，among which many are common genera in the Goniagnostus nathorsti Zone of the study area.Upward，the L.laevigata Zone occurs in both areas.The Proagnostus bulus and Linguagnostus reconditus zones were below the G.stolidotus Zone in the study area，and can therefore be approximately correlated with the Kormagnostus simplex Zone of the Ajusockanian Stage based on their stratigraphic position.As both G.stolidotus and G.reconditus zones appear in both areas，they suggest a direct and accurate correlation.The Homagnostus hoiformis Zone can only be approximately equated with the Erixanium cf.E.sentum subzone of the study area due to this subzone bearing H.hoiformis.
An assemblage of A.clavatus with Irvingella has been recorded from the base of the Pseudagnostus curtare Zone in Malyi Karatau（Ergaliev，1980，1983a，1983b）.Additionally，the assemblage and the overlying Ivshinagnostus ivshini Zone in Kazkhstan also contains E.（Pseudeugnocare），Corynexochus plumula，Stigmatoa，Ivshinagnostus，Peratagnostus and Acutatagnostus，suggesting an alignment with the A.clavatus-I.angustilimbata Zone of the study area.The Ps.pseudagnostilobus Zone of the lower part of the Malykaratauian Stage may be compared with the Rh.cliensis-O.cf.kuruktagensis Zone to the E.decorus-Kaolishaniella Zone in the study area.