1999 Fiscal Year Final Research Report Summary
Paleoceanography of the East Tethys
| Project/Area Number |
10041114
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (A).
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Stratigraphy/Paleontology
|
|---|
| Research Institution | NIIGATA UNIVERSITY |
|---|
Principal Investigator |
MATSUOKA atsushi Faculty of Science, NIIGATA UNIVERSITY Associate Prof., 理学部, 助教授 (00183947)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
KOBAYASHI Kenta Graduate School, NIIGATA UNIVERSITY Assistant, 大学院・自然科学研究科, 助手 (30283005)
|
|---|
| Project Period (FY) |
1998 – 1999
|
| Keywords | Tibet / Tethys / chert / ophiolite / radiolaria / Mesozoic |
|---|
| Research Abstract |
Sedimentological and micropaleontological analyses on siliceous sediments distributed in and around the Yarlung Zangpo Suture Zone, southern Tibet, reveal that these siliceous sediments represent a pelagic environment and yield radiolarian fossils ranging Middle Triassic to Early Cretaceous in age. The Middle Triassic age is older than the previously accepted timing (Late Triassic - Jurassic) of the Gondwana - Lhasa Block break-up. The Xialu Chert, one of our primary target, is dated as Middle Jurassic to Early Cretaceous, recording more than 50 m.y. pelagic sedimentation. The accretionary event of the Xialu Chert took place in middle Cretaceous time.
Structural analysis on the Xialu Chert makes it clear that the siliceous sediments record pre-collisional strike-slip deformation due probably to accretionary processes. The mode of occurrence and petrological-geochemical analyses of basaltic rocks intercalated with siliceous sediments show that these are intrusive (sills) and have features of oceanic island origin.
Siliceous sediments are distribeted in rather narrow areas of southern Tibet at present. They have originally been accumulated in different oceanic settings which were far from each other. Paleobiogeographic analysis of radiolaria can clarify a relative position of the sedimentary basins. The latest Jurassic radiolarian assemblage in the Xialu Chert is similar to that in the same-aged northern middle lattitude in faunal composition.
|
