Paleogene Sedimentary Basin Development in the Bolivian Altiplano and Implications for Initial Mountain Building in the Central Andes

9908003Brian K.Horton位于安第斯山脉中部的高原含有长达10千米的第三系沉积岩，可以说是收缩造山带中心的沉积盆地的典型例子。尽管关于高原表面的历史有许多假说，特别是关于地表抬升的时间和机制(S)，但还没有对暴露的第三纪沉积岩进行系统的分析，这些岩石最终包含了最完整的地表过程记录。该项目旨在评估阿尔蒂普诺中北部的古近纪序列，以了解该地区早-中第三纪的构造-沉积演化，并详细评估当地地层几何形状(包括增厚趋势、相转变和不整合)和区域对比，这将有助于综合安第斯山脉中部的构造-沉积发展。该项目将评估有关高原古近纪盆地发展的四种假说。首先，它是一个单一的综合前陆盆地，向西接受来自早期褶皱冲断带的沉积。其次，它由许多次盆地组成，可能与走滑变形有关，从局部源区接收沉积物。第三，它是一个裂谷系统，东西两侧都有沉积物来源。或者第四，它代表了一个封闭的地形盆地中的沉积物的简单堆积(或“圈闭”)。这些假设可以根据沉积物的年龄、沉积物扩散模式、沉积物源区的位置和组成以及沉降史来区分-这些未知的历史将由地层学、沉积学和40Ar/39Ar地质年代学研究确定。这项研究将限制高原早-中第三纪的历史，从而改进旨在理解高原隆升的模拟工作，并将为山脉带核心的沉积盆地的起源提供一个概念基础(可能还有新的假设)。

9908003Brian K. HortonThe Altiplano plateau of the central Andes contains up to 10 km of Tertiary sedimentary rocks and is arguably the type example of a sedimentary basin in the center of a contractional orogenic belt. Despite numerous hypotheses regarding the history of the Altiplano's surface, particularly the timing and mechanism(s) of surface uplift, there has been no systematic analysis of the exposed Tertiary sedimentary rocks which ultimately contain the most complete record of surface processes. This project aims to evaluate the Paleogene succession of the north-central Altiplano in order to provide an understanding of the early-middle Tertiary tectonic-sedimentary evolution of the region and a detailed assessment of local stratigraphic geometries (including thickening trends, facies transitions, and unconfonnities) and regional correlations that will aid syntheses of the tectonic-sedimentary development of the central Andes. The project will evaluate four hypotheses regarding Paleogene basin development in the Altiplano. First, that it was a single integrated foreland basin receiving sediment from an early fold-thrust belt to the west. Second, that it was composed of a number of sub-basins, probably related to strike-slip deformation, that received sediment from localized source areas. Third, that it was a rift system flanked by sediment sources to the east and west. Or fourth, that it represents simple ponding (or "trapping") of sediment in a closed topographic basin. The hypotheses are distinguishable on the basis of the age of the deposits, sediment dispersal patterns, location and composition of sediment source areas, and subsidence histories-unknowns that will be determined by stratigraphic, sedimentologic, and 4OAr/39Ar geochronologic research. This study will place constraints on the early-middle Tertiary history of the plateau, thus improving modeling efforts aimed at understanding Altiplano uplift, and would provide a conceptual basis (and possibly new hypotheses) for the origin of sedimentary basins in the cores of mountain belts.