--> ABSTRACT: Paleogeographic Implications of New Fossil Finds in the Altun Mountains, Xinjiang Province, NW China, by A. D. Hanson, W. Berry, R. A. Fortey, and E. Serpagli; #91021 (2010)

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Paleogeographic Implications of New Fossil Finds in the Altun Mountains, Xinjiang Province, NW China

HANSON, ANDREW D., WILLIAM BERRY,  RICHARD A. FORTEY, and ENRICO SERPAGLI

Detailed examination of recently discovered and previously undescribed marine fossils from a Lower Middle Ordovician outcrop northwest of Xorkoli in the Altun Mountains, Xinjiang Province, NW China, help to constrain Ordovician paleogeographic relationships. The fossils are found within a >240 m thick section of green muds tone, blue-grey silty limestone, grey calcareous silts tone , thick-bedded limestone, and thick-bedded stromatoporoid-bearing limestone.

The upper two fetid, thick-bedded limestone units contain Llanvirnian aged conodonts and scattered scolecodonts; whereas the underlying calcareous siltstone has abundant graptolites, trilobites, and occasional orthoconic nautiloids (most likely the genus Michelinoceras, or, less likely, the genus Orthoceras) that are also Llanvirnian age. Graptolites are tentatively identified as glyptograptids which most resemble Undulograptus sinodentatus and are among the oldest known biserial graptolites in the world. Trilobite fauna include at least three very different taxa that include a species of Basilicus, one of the olenid Triarthrus, and a third closely allied to Endymionia. Both trilobite and graptolite species indicate an outer shelf setting. The graptolite and conodont fauna indicate that the area was at mid to high paleolatitudes with coolwater.

Similar aged Ordovician graptolite faunas from the adjacent (present-day geography) Qilian Mountains are tropical are very clearly unrelated to these new Altun fauna. Graptolites reported here are dissimilar to those reported in the Chinese literature from the northern Tarim basin and are most similar to those of the same age reported in the Yangtze (South China) craton. The few conodonts recovered belong to the South China Province and are, in general, similar to those of the Atlantic Faunal Province. These relationships suggest that the Altun Mountains were adjacent to South China, possibly marginally related to Tarim, and entirely unrelated to the Qilian Mountains geographically during the early Middle Ordovician.

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.