EOCENE AND OLIGOCENE TITANOTHERES OF MONGOLIA 



905 



Approximate ■position of ten Mongolian formations in the geologic 

 column, as determined to the year 19S4 by the fossiliferous levels 

 only 



[Thick formations or series like the Hsanda Gol and Hung Kureh doubtless occupy 

 a larger part of the column. A query (?) indicates that the level is determined 

 only provisionally] 



(?) Hung Kureh. 

 (?) Pang Kiang.. 



Feet 

 2,000 



600 



Loh 100-1, 000 



(?) Hsanda Gol 3,000 



(?) Houldjln 30 



Ardyn Obo 500 



Shara Murun 500 



Irdin Manha 40-100 



(?) Arshanto 40-100 



(?) 



300 





MIOCENE: LOH FORMATION 



Granger, Berkey, and Morris (October 7, 1924, p. 115) 



Definition. — The Loh formation was first defined as 

 follows : 



The lower Miocene clays of Loh, less than 100 feet thick, 

 resting upon the Hsanda Gol clays, without any obvious 

 physical disconformity. Going southward along their dip 

 (fig. 10), we found that they were succeeded by an undeter- 

 mined thickness, probably as much as 1,000 feet, of sandy 

 clays and sands, in which as yet no fossils have been found. 



Osborn added (November 11, 1924, p. 1): 

 In a thin deposit of olive-colored clays and light-gray 

 sandstone resting on the red-banded beds of the Hsanda Gol 

 formation at Loh, and believed to be of lower Miocene age, 

 were found two highly characteristic fossils: (1) Proboscidean. 

 A fragmentary series of lower mastodont teeth (Am. Mus. 

 19152) which first reveals the presence of an undoubted Serri- 

 dentinus in Mongolia, which we name Serrideniinus mongoli- 

 ensis. Serridentinus probably marks the arrival of a 

 proboscidean related to the M. [Trilophodon] angustidens 

 of the lower Miocene of Europe. * * * (2) Rhinocerotine. 

 The facial portion of a skull (Am. Mus. 19185) containing 

 three grinding teeth and perfectly preserved nasals, which we 

 name Baluchitherium mongoliense. 



Fauna. — The type of Serridentinus (Trilophodon) 

 mongoliensis is a smaller and more primitive trilo- 

 phodont mastodon than its successor Serridentinus 

 productus of the upper Miocene marls (lower part of 

 Santa Fe formation) of New Mexico. Its ancestors 

 are found in Miocene lignitic deposits of western 

 Europe, its descendants in PUocene deposits of Texas 

 and Florida. The type of Baluchitherium mongoliense 

 indicates a hornless rhinoceros little more than half 

 the size of the type of Baluchitherium grangeri of the 

 Hsanda Gol, but with premolar teeth of a more 

 progressive stage. These two fossils from the Loh 

 formation, Serridentinus {Trilophodon) mongoliensis 

 and Baluchitherium mongoliense, confirm the judgment 

 of Granger, Berkey, and Morris as to the probable 

 lower Miocene age of the Loh formation. 



OIIGOCENE: HSANDA GOL FORMATION 



Berkey and Granger (May 25, 1923, p. 8) 



Stratigraphic position and lithologic character. — The 

 fine series of Tertiary deposits called the Hsanda Gol 

 formation, so far as discovered up to 1923, lies uncon- 

 formably upon the unevenly eroded surface of the 

 Ondai Sair formation, of Lower Cretaceous (Coman- 

 che) age. PrevaHingly yellowish conglomerates and 

 pebbly sands, varying greatly in quality, constitute 

 at least 800 feet of the lowermost beds; the middle 

 beds consist of alternating sands, marls, clays, and 

 clayey sands of variegated colors, chiefly red, yellow, 

 and white, with no apparent uniformity of succession; 

 the uppermost beds [fossiliferous] are prevailingly 

 sands and clayey sands, are reddish in color, and 

 include some beds that are fairly well indurated. 



This whole series of beds stretches along the Hsanda 

 Gol, a dry, sandy stream course leading from Mount 

 Uskuk through the Ondai Sair locality southward past 

 Loh to the bottom of the basin of Tsagan Nor, at the 

 foot of Baga Bogdo, a total distance of about 15 miles. 

 Altogether, a thickness of approximately 3,000 feet of 

 the formation has been measured and estimated from 

 measurements, and a large part of it has been inspected 

 in detail. 



The uppermost beds of the formation are fossilifer- 

 ous, the middle beds are largely barren, and no fossils 

 whatever are found in the lowermost beds. In the 

 middle beds a fossil is found here and there, but 

 fossils are numerous in the uppermost beds only. 

 These uppermost beds are judged to be of Miocene 

 [Oligocene] age, but whether the whole thickness of 

 3,000 feet to the underlying Cretaceous is also Miocene 

 [Oligocene] is not known; yet in the absence of any 

 physical break in the whole Hsanda Gol formation, it 

 is regarded as a unit of Miocene [Oligocene] age. 

 Thousands of fossils, chiefly rodents, were collected 

 from the uppermost beds, especially in the vicinity of 

 Loh, 10 miles downstream from Ondai Sair, and near 

 the so-called Grand Gorge, a corresponding erosion 

 exposure 10 miles farther west. 



