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Louderback found no angular unconformity within the Red Beds nor any break between them and the underlying Hsiangchi Series. The plant remains from the latter are generally believed to be Rhætic and though in some localities they have been determined as possibly Liassic, as Louderback remarks, "this still leaves a remarkable gap not yet recognised by direct observation as a definite disconformable or diastrophic break." was thus led during his field work in Szechuan to the belief that the Red Beds were probably not later than Jurassie. He recalls Chao and Huang's assertion that the fresh water forms of Unio and Cyrena from the limestone layers towards the base of the Red Beds, are indistinguishable from those found in the Yangtze valley at Litu and in the Kueichow region and determined by Frech and Grabau respectively as Wealden. He mentions that the Estheria from about the top of the Ts'ienfuyuen formation (E. middendorfi var. sinensis and E. elliptica var. intermedia) are, in Chi's opinion, Lower Cretaceous forms.1 He states his belief that all the members of the Szechuan Series have been folded together and, finally, he announces his own though not the first discovery of dinosaurian bones near Jung Hsien (29°29′: 104°20′), about one thousand feet above the horizon of the Tzeliuching limestone. This stratigraphic position corresponds to about the middle of the Tshungking Series of Arnold. Heim, the top of the Ts'ienfuyuen Formation of Chao and Huang and the middle of the Tsuliuching Formation of T'an and Lee.
The fragments of large bones and Louderback were examined by C. L. they seemed to Reptilian and Other they seemed
part of a tooth found by Camp who concluded that belong to a huge, carniRemains from the Red vorous dinosaur possibly related to TyrannoBeds. saurus of the Upper Cretaceous of North America. But there is an addendum reading as follows: The Szechuan dinosaur belongs evidently to the Megalosaurida. It is an extremely large, advanced form, but even so it may be Jurassic rather than Cretaceous in age."2
In 1935 various fossil teeth from the Tzuliuching Formation were doubtfully referred to some sauropterygian or crocodilian3 and in 1937 the discovery of numerous fish, crocodilian and dinosaurian bones, including a complete skeleton of the latter, was
1 Bull. Geol. Soc. China, Vol. X, pp. 197-198, .
2 Bull. Dept. Geol. Sci., Univ. California, Vol. XXIII, No. 15, pp. 467-472 . Bull. Geol. Soc. China, Vol. XIV, pp. 67-72, [1935.]
announced by C. C. Young, after special searches made for the purpose with Prof. C. L. Camp.1 When these vertebrate remains have been described, it may be possible to determine the age of the Red Beds more precisely.
Such in summary outline are the Cretaceous-Tertiary Red Beds of Szechuan with which the Permo-Triassic Red Beds of Central Yunnan have been confused, though in all fairness it must be admitted that geologists previously acquainted with the Red Basin of Szechuan and then finding enormous expanses of unfossiliferous red rocks of similar lithological characters, in the course of rapid traverses across its borders, are hardly to be blamed for regarding them at first sight as identical.
But we must turn to the fringes of the Red Basin of Szechuan in which the older formations come to the surface, and to the evidence supplied by the deep bores of the Tseliutsin field to find their real equivalents. Y. T. Chao divided these Triassic rocks into a lower, Feisienkuan Series, of purple or purplish-red shales, with some thin intercalations of shaly limestone in its upper part, and an upper limestone division, the Chialing Limestone.2 The same writer and T. K. Huang, added later, that the shales are widely distributed in southern and south-eastern Szechuan, while the overlying limestone beds contain so many purple and yellowish shaly members in their lower horizons that the line of demarcation between the two subdivisions is entirely arbitrary. The limestone too, occurs in all the marginal ranges of the Red Basin.3
As an example of the extreme difficulty which sometimes occurs in attempts to separate the Red Beds of Triassic and Cretaceous The Trias of Omeis- ages, respectively, the following instance taken han, Arnold Heim. from Arnold Heim's account of the geology (1931). of Omeishan is given. In the neighbourhood of this sacred mountain which lies on the south-western lip of the Red Basin, Triassic rocks are exposed in the Szebaho Gorge.4 Of a total thickness of 850 metres (2,790 feet), the lowest 200-250 metres, overlying the Permian basalt, are made up of purple clay shales and marls with thin layers of hard green sandstone. Above
Triassic Rocks of the
Rim of the Red Basin,
1 Bull. Geol. Soc. China, Vol. XVII, pp. 109-120, .
2 Bull. Geol. Soc. China, Vol. VIII, No. 2, p. 143, .
3 Mem. Geol. Surv. China, Ser. A, No. 9, p. 153, .
Omeishau (11,000 feet) lies about 20 miles, as the crow flies, west-south-west of chiating, shown on Pl. I. It is a place of pilgrimage for followers of Buddhism.
these follow 200-250 metres (656-820 feet) of hard sandstone, carrying thin layers of sandy limestone, regularly intercalated with brilliant purple to violet marls. The section is continued upwards with 250 metres of thickly bedded, fine-grained limestone and completed by 80 metres (262 feet) of grey marls which contain marine pelecypods and ammonites in their upper layers. From a collection of the former T. H. Yin has described Halobia comatoides sp. nov., H. omeishanensis sp. nov. and Posidonomya aff. wengensis Wiss. which are regarded as Ladinian in age.1
On the opposite side of the same fold, nevertheless, where a repetition of the same Triassic sequence might reasonably be expected, a thick series of purple clays, followed by soft sandstones, has been mapped as Cretaceous. Heim points out, however, more than once, that this may be wrong and the beds in question may really belong to the purple Lower Trias. Two visits to the area, in 1929 and 1931, respectively, failed to solve the problem. and it is left open for future study with the words "Are the Red Beds of the Omeishan syncline Triassic ?"2
In 1936, Eberhard Wirth published the results of his investigations in Szechuan during which he examined the Triassic deposits of the whole extent of the Red Basin and its Triassic Red Beds of Szechuan, E. Wirth. borders.3 He states that the Triassic forma(1936). tions have been mistaken repeatedly for the Cretaceous Red Beds, an error which has led to incorrect interpretations of the geological relationships of some localities.
Dr. Wirth also made a detailed study of the Tzeliuching anticline where deep borings have been made for brine and gas, during the last millenium, over an area measuring about 70 sq. kms. (27 sq. miles). Extracts from some of the logs of the deeper wells are given which show that a maximum depth of 1,300 metres has been reached, traversing the whole of the Cretaceous, Jurassic and upper division of the Triassic formations (the Chialing Limestone) and penetrating a portion of the Feisienkuan Series (the lower division of the Trias).
His general conclusions may be summarized as follows:-
1. The formation of the Red Basin as a subsiding region between rising borders took place in the Permo-Trias.
1 Bull. Geol. Soc. China, Vol. XI, No. 3, pp. 247-254, .
2 Geol. Surv. Kwangtung & Kwangsi, Spec. Pub., XIII, p. 49, .
3 Neu. Jahrb. für Min., etc., Bd. 73, Abt. B, pp. 412-446, .
2. The greatest thickness of the Trias (1,100m. 3,608 ft.) lies in the middle of the basin: it decreases rapidly towards the west, lessens and finally disappears towards the east, diminishes very quickly towards the north and is entirely absent in the Tsinglingshan. But towards the south, and this is particularly important in connection with the age of the Red Beds of Yunnan, no reduction in thickness has been established. In other words, the basin was open towards the south and the Trias of Szechuan is continued in the developments of the same formation in Yunnan and Kueichow.*
3. The position of the borders of the basin is marked out by the lithological facies, of which two varieties occur. One of these is characterised by the occurrence of typical Red Beds, of red and violet shales and this red mud sedimentation is confined to the border regions. In the centre of the basin, a calcareous development prevails and red sediments are missing.
4. The Triassic basin of Szechuan stands in the same relationship with the Himalayan geosyncline as the Germanic Trias does with the Alpine one.
The marine fauna described by Wirth from the Feisienkuan Series contains 50 per cent. of forms which are characteristic of the Lower Trias, and its distribution proves that beds of Werfenian age reach up to the base of the Chialing Limestone, that is to say they embrace half of the Trias as it is typically developed in Szechuan. No fossils have been obtained from the lowest 200 metres (656 feet) of the Feiseinkuan Stries and it is therefore still not known whether they really belong to the Trias or, on the contrary, form part of the underlying Lopingian (Permian). Moreover, the exact position of the Chialing Limestone in the Trias, remains undecided.
It should now be apparent that in spite of the wide-spread occurrence of Red Beds of Cretaceous age in the Red Basin of Szechuan, there is abundant evidence of the existence there of similar deposits of Triassic age as well.
*The italics are mine. J. C. B.
The Red Beds of the two provinces, Yunnan and Szechuan both contain extensively worked salt deposits, of great importance in local social economy, and it remains to consider the opinions of various authorities on the age of the latter, in so far as they have a bearing on the age of the Red Beds of Yunnan.
A. W. Grabau, quoting Abendanon, places the reddish-brown claystones and sandstones which contain a thin band of rock salt, met with in borings on the Tzuliutsin anticline, in the Trias. In another place he states that the salt wells of Szechuan apparently tap a Permo-Triassic horizon1.
Age of the Salt Deposits of Szechuan.
H. C. T'an and C. Y. Lee, the authors of the official memoir on the salt industry of Szechuan, admit that the only rock salt horizon, a seam which is but 2-5 metres (61-16 feet) thick, extending over an area of about 64 sq. kms., (24 sq. miles), occurs 270-300 metres (885-984 feet) below the top of the Triassic limestone. They point out, however, that brines are won from Triassic, Jurassic and Cretaceous horizons and advance the hypothesis that the rock salt was derived from the brines of these higher horizons. The salt solutions, they imagine, acquired increased salinity by gradually sinking through successively deeper saliferous layers, until, supersaturated, their content was precipitated in cavities of the Triassic limestone.2
These views are not shared by the majority of their Chinese colleagues. Dr. W H. Wong, Director of the Geological Survey of China, for example, states:-"I for one believe that the salt was originally contained in the Triassic at least."3 Dr. E. Wirth is equally emphatic: The salt in the Trias of Szechuan is certainly primary. There is no possibility of explaining it by later immigration from younger salt-bearing beds."4
We see then that the latest available evidence proves that the Triassic basin of Szechuan was open to the south into Yunnan and Kueichow, and if it is admitted that the meagre rock salt deposits of Szechuan are of Triassic age, it is probable that those of Central Yunnan and perhaps of other parts of the province too, represent similar, if not intensified conditions of deposition operating at much the same time.
1 66 Stratigraphy of China ", Vol. 11, pp. 27 and 42.
2 Bull. Geol. Surv. China, No. 22, p. 76, .
3 Ibid., p. 75, (footnote).
Neu. Jahrbuch für Min, etc., Bd. 75, Abt. B, p. 425, .