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far as the Burmese border to the west of Raheng, which lies about the same latitude as Thaton in Lower Burma.1
E. Lower Burma.
The Red Sandstone
G. de P. Cotter, in 1921, found that the Red Beds of NorthWestern Siam cross the valley of the Thaungyin River into the eastern parts of the Amherst district of Lower Series of Eastern Burma. They lie east of the crystalline rocks of the Dawna Range and are separated from the underlying Kamawkala Limestone by an unconformity. This limestone yielded a badly preserved fauna, the investigation of which by various specialists led the late Prof. J. W. Gregory to the following conclusions:-" Only the Upper Trias and not more than the Carnian and the Norian, are represented in the collection. So far as the evidence goes it suggests that the Lower and Middle Trias were not present in this area". He compared these conditions with those in parts of Northern Yunnan traversed by himself, where the Upper Trias contains corals and brachiopods and the Lower Trias is continental.3
Cotter states that the typical and most predominant rock of the Red Beds is a pink or brick-red to purple sandstone, of fine to medium grain and often pebbly. Associated with it are clays, varying in colour from grey to cherry-red, bands of conglomerate and sandstones of a buff tint. These clays sometimes contain thin layers of argillaceous limestone, about 1 to 3 inches thick, which show traces of fossils in certain localities. These are unfortunately unidentifiable with the exception of an Astarte, "not unlike some of the Jurassic species". Both sandstones and clays frequently exhibit steep or even vertical dips. The presence of red sandstone boulders, as well as limestone, in what appears to be a basal conglomerate resting on the Kamawkala Limestone is puzzling and the derivation of its sandstone is unknown. For the time being, it and other conglomerates are grouped with the red sandstone, with the suggestion that they may be of later date or at least form high horizons in the Red Sandstones. Cotter regarded these Red Beds as of probable Jurassic age and added the following remarks on the problem of their correlation :-" Enough has been said to show the
1 Personal Communication.
2 Rec. Geol. Surv. Ind., Vol. LV, Pt. 1, pp. 273-313, (1924).
3 Rec. Geol. Surv. Ind., Vol. LXIII, Pt. 1, pp. 155-167, (1930).
probability that these Red Sandstones are to be correlated broadly with those of the Northern Shan States, Kalaw, and of Siam and Tongking. May we add also with those of Mergui? There is no fossil evidence for this last correlation which although very possible is at present quite unproved ".1
The Red Beds of the Mergui Coast and its innermost islands, stretching north-north-west and south-south-east for a distance of 43 miles in a straight line from Canister Bank The Red Sandstones to Mergui Island, in a series of isolated exposures, mainly but not entirely separated from the mainland by sea or mangrove swamp, were described by the late Rao Bahadur Sethu Rama Rau.2 He divided them in descending order as follows:
of the Mergui Coast.
IV. Purple sandstones, shales and conglomerates.
III. Fine-grained, pinkish sandstones and shales with patches of white clay.
II. Calcareous sandstones.
I. Conglomerates and grits.
The conglomerates and grits are confined to Pataw and Patit Islands near Mergui itself. The lateral variation in the nature of the sediments, and the fact that they contain fresh felspar and pebbles of quartz and slate which have not been carried far, led to the conclusion that the rocks had been derived from the disintegration of the local granite and slates. Near Mergui they rest on the denuded edges of the argillites of the series with the same name, and, here as elsewhere, they are gently folded with angles of dip not exceeding 20°. Regarding their age Sethu Rama Rau wrote as follows:-" Although direct fossil evidence was not obtained in the Mergui district, the author thinks that the Red Sandstone Series of this district forms a link in the chain of outcrops extending from the Northern Shan States to Tongking and Siam, and may probably be of the same age, viz., Jurassic."
The red sandstones are known to contain silicified wood in places, particularly in the quarries of Patit Island, and in this respect they bring to mind the sandy Red Beds of the Bas Laos which are believed to be of Rhætic-Liassic age.3 Until the Mergui occurrences, however,
1 Op. cit., p. 283.
2 Mem. Geol. Surv. Ind., Vol. LV, Pt. 1, pp. 18-19, (1930).
3 Bull. Serv, géol. Indo-Chine, Vol, XX, Fasc. 2, pp. 96-97, (1933).
have received specialised palæobotanical investigation, it is unwise to speculate on their age or relationships.
IV. PALAEOGEOGRAPHY OF THE YUNNANESE REGION IN PERMO-TRIASSIC TIMES.
The highest undoubted Permian rocks underlying the Red Beds of Central Yunnan contain the Neoschwagerina craticulifera fauna and are thus of Yangsinian age. Whatever The divergence of opinion may exist about its exact Transgression. position in the Permian System as a whole, unanimity prevails that it is a transgressive formation, often unconformable on older beds. At the end of the preceding epoch, the Chuanshanian, or Uralian, in the usually accepted meaning of the term, of Huang, renamed the Mapingian and elevated to the Lower Permian by Grabau, the sea had almost completely withdrawn from the southern Chinese basin, though not perhaps from the whole of Indo-China or the Shan States. Its readvance was slow, for the basal beds of the Yangsinian, here and there, contain sandstones and shales with thin coal seams. It is possible that the examples which I described from Siyang (Lat. 25° 6' Long. 103° 9') in Eastern Yunnan, as Moscovian, really belong to the Chihsia Series of the Lower Yangsinian, because of the occurrence in the vicinity of Michelinia siyangensis Reed, one of its characteristic fossils.1 The coral fauna is remarkable and one distinguishing genus, Tetrapora, has not been found outside China, with the probable exception of the Southern Shan States, though several of the others, in many cases specifically identical, have been described recently from SouthWestern Iran by Prof. J. A. Douglas.2
The Yangsinian transgression reached its maximum in Chihsia times and extended over practically the whole of South China, though not across certain islands in the south-east and about the HunanSzechuan-Kueichow borders. Northwards it stretched to the foothills of the Tsinlingshan, considerably beyond the limits of its Carboniferous and Permian predecessors.
The recession of the Yangsinian sea appears to have been a slow process and while regions covered in the east and perhaps in the
1 Rec. Geol. Surv. Ind., Vol. XLIV, p. 103, (1914).
2 Pal. Ind., N. S., Vol. XXII, No. 6, pp. 14-27, (1936).
far west were laid bare, active deposition still proceeded in central and south-western China generally, particularly in Szechuan, Western Kueichow and the greater part of Yunnan, resulting in the formation of the thick Maokou Limestones which are conformable with the underlying Chihsia Limestone. The former carry the highly developed fusulinid fauna with Neoschwagerina, Doliolina, Verbeekina and Sumatrina. The known western limits of this fauna. in Yunnan lie in the Mekong basin, where it was recognised by von Loczy and by Gregory in the north and by myself in the far south.
Overlying these Yangsinian Limestones is the Lopingian Series and in South-Eastern China the two are disconformable; in the middle Yangtze Valley, on the other hand, no disconformity has been reported, but in the region of more immediate concern here, followed by vast followed by vast thicknesses of
the Yangsinian Limestones are volcanic rocks of subærial origin. Thus we are led to deduce a complete withdrawal of the sea from parts of Yunnan and Southern Szechuan and from a smaller portion of Western Kueichow, where the eruptive rocks extend, followed by uplift and long-continued denudation preceding these outbursts. This is the impression remaining in my mind after several traverses across the affected regions in Yunnan and Szechuan, but some observers, particularly Arnold Heim, advocate a submarine origin for the basic rocks. On the edges of the vast area covered by the flows, as for example in the Mekong and Salween (?) valleys in the west and in western Kueichow in the east, this may possibly be the case, but not elsewhere. Chinese writers give the thickness of the volcanic rocks as approximately 500 to 1,000 feet in Eastern Yunnan, 2,500 feet in Northern Yunnan and 4,000 feet near the great bend of the Yangtze. In the north-west it diminishes again to about 500 to 800 feet.
The Lopingian Regression and the Yunnanese Basic Rocks.
Lying above the basic rocks in North-Eastern Yunnan, about the Yunnan-Kueichow borders and in some parts of Western Kueichow, or directly on the Yangsinian Limestones further east still, are the Lopingian sandstones, shales and coal seams with the Gigantopteris nicotinafolia flora (the Liupakou Series). Minor bands of cherty limestone sometimes occur in, amongst, or above the coal measures, carrying the Loping fauna with Lyttonia and Oldhamia. Grabau and Ting have pointed out
The Lopingian Liupakou Series and the
how the marine intercalations of the Lopingian disappear about Long. 106°E, where the series becomes entirely continental, while further west still, about 103° 30′E, the coal measures themselves and their characteristic flora abruptly finish.1 (See Pl. I.) As is indicated earlier in this paper this is about the line where the basic rocks are overlain directly by the Red Beds. East of this narrow zone of some 21° of longitude, the land was subjected to shallow, intermittent flooding by the sea. Grabau and Ting explain the absence of the Gigantopteris flora in Central and Western Yunnan by its inability to cross the great basaltic highlands which then occupied these regions, an explanation which is unacceptable to the palæobotanist Prof. B. Sahni.2
A remarkable feature of the Lopingian sea is that although it carried the typical Indo-Pacific Lyttonia fauna and brought the Shan-Chinese area into communication with the Himalayan geosyncline, perhaps by means of a waterway passing through Western Yunnan, Western Szechuan and Eastern Tibet, on the one hand and with Indo-China and Malayasia on the other, it was at the same time, shallow, fluctuating and inconstant. Thus Giganopteris nicotinafolia and its associated plants came to flourish on the tidal flats and coastal swamps around large islands, themselves liable to innundation and submergence from time to time. The involved shore lines of such transient lands washed by a sea which nowhere appears to have attained a great depth and which was constantly receiving clastic detritus in abnormal quantities, in a period and in a region distinguished alike by their general instability, are peculiarly difficult to determine, though Huang has ventured to outline three principal coastal plains over which the Gigantopteris flora was spread.3
Character of the
Turning now to Indo-China, the French geologists maintain that the sea level oscillated constantly throughout the duration of the Anthracolithic period, but only two main Permian Transgression transgressions are at present recognised. The in French Indo-China. first, of short duration, following an earlier complete emergence of the land, commenced in the Upper Moscovian and was soon followed by a regressive pulsation, so that by Middle Uralian times, outside the Laotian geosyncline on the western side
Rept. Internat. Geol. Congress, Washington, 1933, Vol. 1, p. 669.
2 Journ. Ind. Bot. Soc., Vol. XV, No. 5, p. 326, (1936).
3 Mem. Geol. Surv. China, Ser. A, No. 10, Pl. VI, (1932).