SUBDIVISION, ZONATION AND CORRELATION OF THE DEVONIAN FORMATIONS IN LUNGMENSHAN AREA, NORTHWESTERN SZECHUAN.
S.S.Yoh Department of Geology and Geology and Geography.Peking University
The Lungmenshan area of northwestern Szechuan is well known for itspicturesque landscape and especially for its marvelously developed Devonianformations with abundance of perfectly preserved fossils. It is a very mountainousregion situated on the northwestern border of the Szechuan Red Basin forming aNE-SW range extended for about 100 km. in length and rising to heights over1200 m. above the valley of the River Fou, which and several of its tributariesfrom the northwest dissect through this range resulting in the formation of manybeautiful canyons where excellent exposures of Devonian strata are here and thereclearly observable. The Devonian geology of Lungmenshan area had long been studied by manyprominent geologists such as Y. T. Chao and T. K. Huang in 1929, S. Chu, L.T. Yeh and C. C. Wu in 1938, and T. F. Hou and K. C. Yang in 1939. Amongthem Chu and his collaborators had carried out a series of splendid works andpublished their important results. But so far no detailed subdivision and systematiccollection of fossils from the Devonian formations have ever been attempted. Untilearly in 1953 the Southwestern Petroleum Prospecting Bureau of Chengtu sent twofield parties headed by T. Pao and K. C. Peng respectively to restudy the strati-graphy of this area particularly for the purpose of detailed subdivision, zonationand correlation of the Devonian formations. Meanwhile the writer was engagedto take part in the field work for three weeks. At the end of 1953 ten carefullymeasured columnar sections had been accomplished by Pao and Peng and fossilsfrom more than 180 horizons critically determined by the writer. The Devoniamformations of Lungmenshan area are now subdivided into 3 series, 6 stages and13 fossil zones. It is worthy to note that during our field work we had discoveredthe late Coblenzian beds with Euryspirifer paradoxus fauna which can be compar-able with the upper part of Szipai shale of eastern Kuangsi and also with thePaochiao shale of eastern Yunuan. In addi ion we had found great number ofcalceoloid corals which may be classified into 4 subspecies and represent 4 differ-ent horizons ranging from late Coblenzian up to midde Givetian. Moreover ithappened to discover for the first time some specimens of a new arthrodian fish occurred in the middle Devonian limestone of Kuanwushan near Kiangyou city. Thisnewfish had been determined and named as Kiangyousteus yohii gen. et sp. nov.,by H. T. Liu who had described minutely in a paper "Kiangyousteus, a new Ar-throdian from Szechuan, China" (see Acta Palaeontologia Sinica, Vol. Ⅲ. № 4.pp. 261-274, Pls. I-V. 1955). The ample collection of Devonian corals and brachiopodsfrom the Lungmenshan area are going to be descibed in the near future. Owing to their enormous thickness, their pronounced lateral change of litho-logy and lack of igneous rocks, the Devonian formations of Lungmenshan areawhich unconformably overlie the Silu?ian "Sintan shale" and disconformablyunderlie the Lower Carboniferous Chungchangkow series were deposited in aparageosyncline between the Caledonian folded mountains on the norhtwest andSzechuan platform on the southeast. This parageosyncline can be traced fromChaotienyu near the Szechuan-Shensi border on the northeast and southwestwardlythrough Kiangyou, Kuanhsien, Kintang and Kanting. These Devonian formationsoccupy at present the axial region in a closed syncline which is complicated on the southeastern side near Kianyou by many thrust faults assuming typicalschuppen-structure. The results so far obtained from the biostratigraphical study of the Devonianformations in the Lungmenshan Proper in 1953 may be generalized as in thefollowing table (also refer to Pls. Ⅱ-Ⅲ):Supra-formation: Chungchangkow Series (Lower Carboniferous) Disconformity and hiatusUpper Devonian (D_3): Tangwangchai Series 6) Maopa Limestone (D_3~2): chiefly light grey and whitish grey pure limestones with ooliticstructure in the top part, fossils rare, carrying l fossil zone D_3~2I (Famennian). 360 m.D_3~2I: Zone of Camarotoechia hsikwangshanensisWith Camarotoechia hsikwangshanensis TienHunanospirifer cf. ninghsiangensis Tien5) Shawotze Dolomite (D_3~1): mainly whitish to brownish grey crystalling dolomites interc-alated with rather pure limestones, richly fossiliferous, carrying 2 fossil zones, D_3~1Ⅰ-Ⅱ(Frasnian). 350-550 m.D_3~1 Ⅱ: Zone of Tabulophyllum gorskyi kuanwushanense With Tabulophyllum gorskyi var. kuanwushanense Yoh var. nov. Peneckiella shawotzeensis Yoh sp. nov. Keriophyllum temeniophylloides Wang Syringopora sp.D_3~1Ⅰ: Zone of Sinospirifer sinensis and Cyrtiopsis spiriferoides With Cyrtiopsis spiriferoides Grabau C. shawotzeensis Yoh sp. nov. Sinospirifer sinensis Grabau S. subextensus Grabau Atrypa douillii Mansuy Meristella kutsingensis Grabau Camarotoechia cf. shetienchiaoensis var. beta Tien Athyris chitzechiaoensis Tien Campophyllum crypophylloides Yoh sp. nov. C. paoi Yoh sp. nov. Temeniophyllum ovaliforme var. minor Yoh var. nov.Middle Devonian(D_2): Peshihpu Series 4) Kuanwushan Limestone (D_2~2): mainly blackish impure limestones and dark thick-bedded or massive magnesian limestones, the impure limestones always containing cherty nodu- les, the uppermost part usually capped by blackish earbonaceous shaly limestone, while the bottom part characterized by the cliff-making massive magnesian limestone, very richly fossiliferous with perfect specimens of Bryozoa and brachiopods, carrying 5 fossil zones, D_2~2Ⅰ-Ⅴ(Givetian). D_2~2Ⅴ: Zone of Camarophoria schizoplicata With Camarophoria schizoplicata Grabau Hypothyridina lungtungpeensis Kayser H. Lungtungpeensis var. obesa Grabau Leiorhynchus deprati var. obesus Grabau Atrypa richthofeni KayserD_2~2Ⅴ: Zone of Schizophoria macfarlani With Schizophoria macfarlani Meek S. excellens Grabau S. striatula mut. alpha Grabau S. striatula var. quadrdngularis Grabau Gypidula planisinosa Grabau Atrypa desquamata mut. kansuensis Grabau A. bodini Mansuy Neospongophyllum gracile Yoh sp. nov. Campophyllum szechuanense Yoh sp. nov.D_2~2Ⅲ: Zone of Gypidula mansuyi with Gypidula mansuyi Grabau Hypothyridina lungtungpeensis Kayser Leiorhynchus deprati var. obesus Grabau Camarophoria huotiformis Grabau C. huotiformis var. subcircularis Yoh var. nov. C. uniplicata Yoh sp. nov. C. letiensiformis Grabau C. sutschuansis Loczy Reticularia maureri Holzapfel R. lensiformis Grabau Schizophoria excellens Grabau Meristella kutsingensis Grabau Atrypa bodini Mansuy A. peshiensis Grabau Pugnax lungmenshanensis Yoh Campophyllum oligocystosum Yoh sp. nov. C. unsymmetricum Yoh sp. nov. Grypophyllum tenue Wedekind Keriophyllum ef. conicum Wang Temeniophyllum breviseptatum Yoh sp. nov. T. complicatum Wang Stringophyllum primodiale Wedekind Prismatophyllum hexagonum var. minor Yoh var. nov.D_2~2Ⅱ: Zone of Stringocephalus burtini and Diplochone tungshanense With Stringocephalus burtini Defrance S. obesus var. grandis Grabau S. transversa Grabau Atrypa aspera var. kwangsiensis Grabau A. elongata Yoh sp. nov. A. desquamata mut. hunanensis Grabau A. desquamata mut. kansuensis Grabau A. retricularis Linnaeus Hypothyridina cuboides var. sinensis Grabau Spiriferina tieni Grabau Gypidula peshihpuensis Yoh sp. nov. Diplochone tungshanense Wang Cystiphylloides kwangsiensis Yoh Calceola sndalina var. inflata Yoh var. nov. Wedekindophyllum striatus Wedekind Stringophyllum wedekindi Yoh sp. nov. Pachypora crassa var major Yoh var. nov. Kiangyousteus yohii Liu gen. et sp. nov.D_2~2Ⅰ: Zone of Disphyllum goldfussi With Disphyllum goldfussi Geinitz Prismatophyllum hexagonum Goldfuss Phacellophyllum peshihpuense Yoh sp. nov. Temeniophyllum waltheri Yoh T. poshiense Wang T. complicatum Wang T. breviseptatum Yoh sp. nov. Keriophyllum temeniophylloides Wang Cystiphylloides kwangsiensis Yoh Wedekindophyllum corneolum Wedekind Grypophyllum tenue Wedekind Chaetetes cyclostome Yoh sp. nov. Atrypa aspera kwangsiensis Grabau A. desquamata mut. kansuensis Grabau Schizophoria striatula Schlotheim Conchidium devonicum Yoh sp. nov. C. deronicum var. ellipticum Yoh sp. and var. nov. Plectospirifer undiferus var. tangwangchaiensis Yoh var. nov. 3) Younmapa Formation (D_2~1): mainly graywackes and impure limestones, usually inter- bedded with black carbonaceous shales in the upper part and yellow shales and sandstones in the lower part, thickness very variable from more than 10 m. up to 800m. abounding in corals and brachiopods, carrying 2 fossil zones, D_2~1-Ⅱ (Eifelian).D_2~1Ⅱ: Zone of Leptostrophia mccarthyi and Endophyllum longicystosum With Leptostrophia miccarthyi Grabau Schizophoria striatula var. quadrangularis Grabau Conchidium transversa Yoh sp. nov. Plectospirifer dichoplicata Yoh sp. nov. P. heimi Grabau P. undiferus var. tangwangchaien is Grabau Atrypa desquamata mut. kansuensis Grabau A. deaquamata mut. magna Grabau A. desquamata var. hunanensis Grabau A. gloublaris Yoh sp. nov. Endophyllum longicytosum Yoh sp. nov. E. fungioforme Yoh sp. nov. Microplasma fongi Yoh Nardophyllum articulatum Wedekind Vollbrecht N. cuneiforme Wedekind Wedekindophyllum tabulatum Wedekind Bothriophyllum vollbrechti Yoh sp. nov. Loipophyllum kueichihensise Yoh sp. nov. L. subrundum Yoh sp. nov.D_2~1Ⅰ: Zone of Calceola sanda?ina sandalina With Calceola sandalina var. sandalina (Lam.) Wedekindophyllum pseudostriatum Yoh sp. nov. Prismatophyllum sedgwicki var. pegrangtungense Yoh var. nov. Favosites goldfussi E. et H. F. cylindricus Yoh sp. nov. Emanuella takwanensis Kayser Megastrophia (?) kiangyouensis Yoh sp. nov. Plectospirifer fongi Grabau P. heimi mut. alpha Grabau Spirifer tonkinensis Mansuy S. semicircularis Yoh sp. nov. Douvillina inaequistriata Mansuy Proetus indosinensis Mansuy Disconformity and hiatusLower Devonian (D_1): Pingyipu Series 2) Kanchih Formation (D_1~2): chiefly yellowish green shales interealated with graywackes and numerous lenticular impure limestones, the lenticular limestones and shales being erowded with brachiopods always in lumachelle in association with abundant trilobites, pelecypods but few corals, carrying 2 fossil zones D_1~2Ⅰ-Ⅱ (late Coblenzian). Thickness very variable from more than 10 m. up to 850 m.D_1~2Ⅱ: Zone of Calceola sandalina elongata With Calceola sandalina var. elongata Yoh var. nov. Wedekindophyllum crassicaulum Wedekind W. corneolum Wedekind and Vollbrecht Favosites goldfussi E. et H. Plectospirifer heimi Grabau P. fongi Grabau Spirifer semicircularis Yoh sp. nov. Calymene maloungaensis MansuyD_1~2Ⅰ: Zone of Euryspirifer paradoxus lungmenshanensis With Euryspirifer paradoxus var. lungmenshansis Yoh var. nov. Spirifer tonkinensis Mansuy S. semicircularis Yoh sp. nov. S. speciosus Bronn Plectospirifer dichoplicata Yoh sp. nov. Spiriferina kanchihensis Yoh sp. nov. Athyris pseudoundata Yoh sp. nov. Chonetes prebeja Schnur C. sarinulata Schlotheim Calceola sandalina var. intermediata Yoh var. nov. Cystiphyllum yinpingshanensi Yoh sp. nov. Pterinea pingyipuensis Yob sp. nov. Cyrtoceras devonica Yoh sp. nov. Calymene maloungaensis Mansuy Disconformity and hiatus1) Pingyipu Sandstone (D_1): chiefly quartzitie sandstones with some graywacke and shale intercalations, thickness varying from 180 m. up to 2550 m. but as a rule, that on the NW. wing of the syncline being the most thickest but becoming thinner and thinner towards the SE. wing, from a shale bed in the lower part yielding many moulds of brachiopods, pelecypods, and gastropods usually poorly preserved, carrying only 1 fossil zone D_1~1Ⅰ (Siegnian).D_1~1Ⅰ: Zone of Kochia szechuanensis With Kochia szechuanensis Yoh sp. nov. Subrensselaerlandia of. claypolii Hall Tingella (?) peshihpuensis Yoh sp. nov UnconformitySub-fornation: "Sintan Shale", (Silurian)