HR: 0800h
AN: T41A-1276    [Abstracts]
TI: Qimen Tagh Uplift Constrained From Tectonostratigraphy of Southwest Qaidam Basin, Northern Tibet Plateau, China.
AU: * Hertz, M
EM: mhertz@indiana.edu
AF: Indiana University Dept. of Geological Sciences, 1001 East 10th St., Bloomington, IN 47405-1405 United States
AU: Ritts, B
EM: britts@indiana.edu
AF: Indiana University Dept. of Geological Sciences, 1001 East 10th St., Bloomington, IN 47405-1405 United States
AU: Bovet, P
EM: pbovet@indiana.edu
AF: Indiana University Dept. of Geological Sciences, 1001 East 10th St., Bloomington, IN 47405-1405 United States
AU: Kent-Corson, M
EM: malkc@stanford.edu
AF: Stanford University Geological and Environmental Sciences Dept., Braun Hall (Geo Corner) #118 450 Serra Mall, Building 320 Stanford, CA, Stanford, CA 94305 United States
AB: The initiation of Qimantagh uplift is an important tectonic event in the evolution of the northern Tibet plateau. The Qimantagh bounds the SW edge of Qaidam basin, and is the northern extent of the east Kunlun Mountains. Cenozoic sedimentary rocks located in SW Qaidam basin have recorded tectonic activity from this adjacent uplift. The tectonostratigraphy of Qaidam basin suggests that Qimantagh uplift began in early Miocene. A section of Oligocene - Miocene sedimentary rocks located on the SW edge of Qaidam basin near Lao Mangnai was studied. Its total thickness is 2166 m and is subdivided into two units. The Oligocene-Miocene? unit is 1246 m thick. It consists of laterally-continuous red and green intervals interbedded on a 5 - 10 m scale. The green intervals are composed of green to grey marl, siltstone and fine sandstone, and contain oscillation ripples, small-scale hummocky cross-stratification and ostracods. The red intervals are composed of red massive mudstone, siltstone and plane-bedded or ripple cross-stratified fine to medium mud-chip bearing sandstone. Paleocurrent indicators show a wide spread of generally north-directed flow, with strong north-directed flow near the top. This unit coarsens upward over the upper 247 m, with systematically more abundant and coarser red intervals toward the top. These red intervals contain coarse sand and m-scale packages of boulder-bearing pebble to cobble conglomerate. Clast composition consists of granite, marble, limestone, meta-volcanic, meta-sediment, and mylonite. The overlying Miocene unit is 920 m thick. It is composed of massive boulder-bearing pebble to cobble conglomerate. Clast composition is similar to that of the underlying transitional package. Paleocurrent in the Miocene conglomerate was north-directed. The fine-grained Oligocene-Miocene? represents a marginal lacustrine environment, with no evidence for nearby coarse sediment sources or steep depositional gradients, in spite of proximity to the present Qimantagh front. An increase in depositional energy is indicated by coarsening upward into the massive Miocene conglomerate. Clast composition and paleocurrent indicators suggest a Qimantagh provenance. Thus, the increase in depositional energy indicates that proximal thrusting had propagated in SW Qaidam basin - northern Qimantagh by Miocene, replacing earlier, finer-grained distal or tectonically quiescent deposits.
DE: 8169 Sedimentary basin processes
SC: Tectonophysics [T]
MN: Fall Meeting 2005