干旱区生态环境知识资源中心

Sedimentary records in northern Tianshan are in response to the uplift of the Tianshan Mountain from the late Cenozoic. Eocene-Oligocene Anjihaihe formation mainly deposite gray or dark gray lacustrine mudstone with flat bedding; Late Oligocene Shawan formation are overlain purple meander sandstone, siltstone and interbedded conglomerate are dominant; the lower of Early Miocene Taxihe formation consist of gray or brownish siltstone and mudstone frequently coexist; the upper are brownish or gray-yellowish sandstone with interbedded siltstone; Late Miocene-Early Pliocene Dushanzi formation are composed of braided-fluvial accumulation of dark gray conglomerate or associated with brownish or gray-yellowish sandstone; Late Pliocene-Early Pleistocene Xiyu formation consist of a large amount of alluvial fan pebble to boulder conglomerate. Stable carbon and oxygen isotopic data show: average VC values from Eocene-Oligocene, through Late Oligocene, lower of Early Miocene, upper of Early Miocene, Late Miocene-Early Pliocene to Late Pliocene-Early Pleistocene are similar to-3. 9 parts per thousand, similar to-8. 1 parts per thousand,similar to- 5. 9 parts per thousand, similar to- 8. 5 parts per thousand, similar to- 6. 0 parts per thousand respectively, while average delta O-18 values are similar to - 5. 0 parts per thousand, similar to - 11.0 parts per thousand, similar to- 7. 7 parts per thousand, similar to- 10. 3 parts per thousand, similar to - 10. 4 parts per thousand respectively. Stable isotopic changes and sedimentary records indicate paleoenvironmental changes: warm-wet during Eocene-Oligocene, and and cold during Late Oligocene, semi-humid and semi-warm during lower of Early Miocene, and and cold during upper of Early Miocene, and and cold during Late Miocene-Early Pliocene, arid and semi-warm during Late Pliocene to Pleistocene. Combined with paleomagnetic data in this area, stable isotopic results, sedimentary records and global climate change, five paleoenvironmental changes have developed in northern Tianshan since the late Cenozoic: climate conversion during late of Qligocene, climate break at Early Miocene( similar to 24Ma), climate conversion during early of Miocene(24 similar to 19Ma), C-4 rapidly expand at Late Miocene( similar to 7Ma) and climate intensely vibrate at Late Pliocene to Early Pleistocene ( similar to 3. 17Ma).