26AL /10BE BURIAL DATING AND MAGNETOSTRATIGRAPHY WITHIN SEDIMENTARY BASINS: FIELD EXAMPLES OF ACTIVE DEFORMATION IN THE WESTERN TARIM BASIN, NW CHINA

Sedimentary basins adjacent to growing orogens record key information about the deformational and erosional history of the orogen. However, dating sedimentary basin fills often presents a challenge when other means of age control, such as tephrochronology, biostratigraphic markers, or magnetostratigraphy, are unavailable or ambiguous. ²⁶Al /¹⁰Be cosmogenic burial dating provides a means to assign an age to commonly coarse grained, Plio-Pleistocene detrital strata that are typically difficult to date with more traditional methods. In this study, we present eight new ²⁶Al/¹⁰Be cosmogenic burial ages from Plio-Pleistocene conglomerates from the Pamir and Tian Shan foreland basin in the western Tarim Basin in NW China.

The Pamir and Tian Shan orogens formed as a result of the Indo-Eurasian collision. These two orogens are impinging on each other and gradually deforming and closing the western Tarim Basin. To determine the onset of deformation of individual structures, samples were strategically collected from growth strata and from sedimentary units beneath active faults. Where feasible, we combine our burial ages with magnetostratigraphic sections to place further constraints on the deposition of the basins and the deformation of nearby structures. Furthermore, modeling of the effect of post-burial nuclide production on the burial age reveals production during sediment burial within the basin has a negligible effect on the burial age at sediment accumulation rates >50 m/Myr, whereas production due to Late Quaternary incision and reduced depth shielding has a more significant effect depending on the timing of incision and the amount of reduced shielding. In our study, we found post-burial production during sediment burial in basins to be negliglble due to rapid (400-1000 m/Myr) sediment accumulation rates, yet post-burial production from recent incision may have perturbed our burial ages by as much as 60%. Finally, our new burial ages, in conjunction with previously published magnetostratigraphic sections, document the late Neogene growth of both the Pamir and Tian Shan orogens, and they delineate both eastward propagation of deformation and basinward growth of both mountain belts.