THE STRATIGRAPHY OF THE LIANGSHAN AREA, SOUTH SHENSI, WITH DISCUSSIONS OF ITS GEOLOGICAL HISTORY

The stratigraphy of the Liangshan Area may be summarized as follows: 1. Archaean Complex. The pre-Sinian forms the foundation of the Tapashan Platform whichis composed of granite, diorite with numerous small quartz veins. In the Liangshan Area someplaces are found where diorite dikes cut across granite ones. Occasionally diorite may be seen asxenoliths of granite. So the former is older than the latter. The age of these intrusive rocks iscollectively Archaean. 2. Sinian. The Sinian consists of arkosic sandstone and siliceous limestone. They repeat threetimes in this Area. Strange bodies attributed to Collenia occur at two horizons. The to?al thi-ckness of this system is 450 m. It lies unconformably upon the Archaean Complex. 3. Cambrian. The Cambrian consists of shale, sandy shale, marl and limestone. These rocksform a complete cycle of sedimentation. This formation, over 350m. thick, contains Eoredlichia,Redlichia, Parabadiella. Liangshanella, Hanchungella, Nanchengella, Hanchiangella. Shensiella, Wu-chiapingella, Obolus, Obolella and Hyolithes. It is therefore not impossible that the exact age ofthis formation is the early part of the Lower Cambrian. In some places of the Liangshan Area thereis a bed of oolitic limestone (which overlies conglomeratic sandstone) with abundant Archaeocya-thids, forming the topmost of the formation. This is the result of the deepening of sea. In theLiangshan Area the Sinian is overlain by the Cambrian and there is an angular unconformity be-tween the two. 4. Ordovician. The rocks above the Cambrian belong to the Ordovician which represents acomplete cycle of sedimentation. The lower division of this formation consists of shale and marl,with a layer of conglomerate at the base. This division yields a fauna such as Ningkianolithus,Didymograptus and Sinocystis, and its exact age corresponds to Arenigian-Llanvirnian. Theupper division of this formation mainly consists of limestones. The lowest greyish limestone in thisupper division contains Glyptograptus teretisculus and is equivalent to the Llandeilian. It soongives way to a purple thin-beded argillaceous limestone. Sinoceras and Staurocephalus, abound inthis formation. Higher up, the limestone becomes grey and dense in which occurs Phylacops. Theage of the purple thin-beded argillaceous limestone and grey dense thin-beded limestone is Cara-docian-Ashgillian. The Ordovician is 100m. thick. It rests disconformably on the Lower Cam-brian. 5. Silurian. It is mainly composed of shales which overlie the Ordovician with apparent con-formity. Trilobits and graptolites occur in these shales and represent the Lower Silurian. The totalthickness of this series is estimated at from 200 to 350 m. In the Lower Silurian the writer hasestablished nine zones by means of the index fossils mentioned above. Although there is no discordancebetween the Silurian and the Ordovician, biostratigraphical facts leave little doubt as to the changeof deposition. It is evident that sea-floor of the Liangshan Area was gently lifted in post-Ordoviciantime. 6. Permo-Carboniferous (Liangshan Coal Series). On the Lower Silurian Shale of which thethickness varied in different localities, rests unconformably the Liangshan Coal Series of some 20m,containing abundant marine fossils of Permo-Carboniferous age. This series consists of white, greyand brown shale with a coal seam of no workable value. There exists no trace of Devonian in thisArea. These facts clearly signifies that an intense erosion of long duration took place in post-Siluriantime. We do not know precisely whether this is the result of one period of erosion or two. 7. Permian. In the Liangshan Area the Permian is mainly represented by pure, grey and fine-textured limestone which forms the precipitous cliffs. The Permian attains a thickness of 470 m,which may be divided into three parts. The lower part, 200 m thick, is corresponding to the Yang-sing Limestone; and the upper part, 270 m thick, is named by Professor Lu as the WuchiapingLimestone. The middle part between the two series is a bed of shale, only 2m thick, which isequivalent to the Loping Coal Series. 8. Triassic. It may be divided into three parts: the lower, consisting of red and yellow limes-tone, 80 m thick; the middle, about 100m thick, adark purple shale which contains Claria clarai, C.wangi and C. gresbachi; and the upper, 120m thick, essentially consisting of greyish white limes-tone. The lower and middle belong to the Lower Triassic, and the upper is supposed to be Middleto Upper Triassic. The Triassic overlies the Permian disconformably. 9. Early Tertiary. It may be divided into two parts: the lower a coarse conglomerate of whichthe fragments are derived from Permian or Triassic limestone; and the upper, loosely cementedsands and gravels of which the materials are of many kinds. The Early Tertiary lies unconformablyabove various older strata. 10. Late Tertiary. Gravels of angular fragments of limestone. 11. Quaternary. Red soil and yellow greyish sands.