Intramontane basin opening and erosive unloading: A 10Be-supported model for the Usia drainage basin, southern Pyrenees.

山内盆地是许多山脉的共同特征。这些地形凹陷在山系的同生和后生演化过程中起到了沉积圈闭的作用。因此，研究山地内盆地的沉积档案和形态发育提供了(1)对山脉侵蚀-沉积过程的重要洞察，(2)有助于评估它们对变化的环境条件的敏感性。拟议的研究项目旨在揭示山内流域的盆地开放和挖掘过程。以USIA集水区(比利牛斯山南部)为例，特别关注严重后期侵蚀阶段的原因和后果。USIA盆地是始新世AINSA凹陷(西班牙阿拉贡)的一个子盆地，AINSA凹陷是夹在比利牛山南部逆冲板块之间的一个大型背靠式盆地。该盆地充填了始新世海相沉积物和固结的同造山碎屑和砾岩。申请人在USIA盆地进行了一项未发表的初步研究，该盆地在通过AINSA凹陷时被排向辛卡主要河谷。现场观察显示，山谷梯田和残余侵蚀表面系统被沟壑和峡谷深深解剖。USIA出口峡谷深深地切入洛斯莫利诺斯逆冲前锋，代表了一个与USIA流域基准面和开放历史相关的戏剧性景观特征。在盆地内，冲积阶地序列经历了一系列强烈的晚期侵蚀事件。初步观察和阶地暴露测年表明，该盆地的年龄出乎意料地年轻(18，2+1，3/-2，8ka)，并在最近的盆地挖掘中表现出非凡的规模。这些项目的目标是澄清(I)USIA流域的开放机制，(Ii)后期侵蚀和阶地沉积阶段的时机和控制，以及(Iii)评估构造和气候参数(例如水文)对山地内沉积物通量的相对影响。我们将结合实地调查和宇宙核素暴露测年，应用最先进的数字地形分析。预期结果涉及(I)USIA流域的侵蚀模型和(Ii)高度可侵蚀集水区的短期和长期侵蚀率。两者都将为今后对中纬度山脉山地内盆地系统的研究提供可靠的参考数据集。

Intramontane basins are common features of many mountain ranges. These topographic depressions function as sediment traps during the syn- and postorogenic evolution of a mountain chain. Hence, studying the sedimentary archives and morphogenetic development of intramontane basins provides (i) crucial insights into erosion-sedimentation processes in mountain ranges, and (ii) conduces to assess their sensitivity to changing environmental conditions. The proposed research project is aimed at unravelling the processes of basin opening and excavation of intramontane drainage basins. Using the example of the Usia catchment (southern Pyrenees), a particular focus is set on the causes and consequences of severe late-stage erosion phases. The Usia basin is a sub-basin of the Eocene Ainsa depression (Aragon, Spain) - a large piggyback basin sandwiched between south-Pyrenean thrust sheets. The basin is filled with Eocene marine sediments and consolidated synorogenic debris and conglomerates.An unpublished pilot study was carried out by the applicant in the Usia basin which is drained towards the Cinca main river valley at its passage through the Ainsa depression. Field observations revealed systems of valley terraces and residual erosion surfaces that are deeply dissected by gullies and canyons. The Usia outlet canyon is deeply cut into the Los Molinos thrust front and represents a dramatic landscape feature that is relevant to the base level and opening history of the Usia drainage basin. Within the basin, alluvial terrace successions witness a series of intense late stage erosion episodes. Preliminary observations and terrace exposure dating point to an unexpected young age (18,2 +1,3/-2,8 ka) and exceptional magnitude of recent basin excavation. The projects objectives are to clarify (i) the opening mechanisms for the Usia drainage basin, (ii) the timing and controls of late stage erosion and terrace aggradation phases, and (iii) to assess the relative impacts of tectonic and climatic (e.g. hydrological) parameters on intramontane sediment fluxes. We will apply state of the art digital terrain analysis in combination with field surveys and cosmogenic nuclide exposure dating. The expected outcomes concern (i) an erosion model for the Usia drainage basin and (ii) short- and long-term erosion rates for an highly erodible catchment. Both will provide a solid reference data set for future studies on intramontane basin systems in mid-latitude mountain ranges.