Erosion rates in the source region of an ancient sediment routing system: comparison of depositional volumes with thermochronometric estimates

Calculation of the total depositional volume of an ancient source-to-sink system, combined with estimates of the area of catchments
acting as source regions using provenance methods, is used to evaluate average catchment erosion rates on a million year time
scale. These rates are compared with values derived from thermochronological methods. Using the mid- to late Eocene (33.9–41.6 Ma)
Escanilla palaeo-sediment routing system from the south–central Pyrenean orogenic wedge-top zone as an example, c. 3500 ± 300 km3 of solid particulate sediment was derived from two catchments in the south–central Pyrenees over a 7.7 myr period, equivalent
to a mean erosion rate of c. 0.15–0.18 mm a−1. Average exhumation rates in contributing catchments over the same time interval are estimated at 0.2–0.3 mm a−1 based on apatite fission-track analysis of pebbles in proximal conglomerates, and 0.23–0.34 mm a−1 from fission-track analysis of detrital apatites sampling a wider range of grain size. Sediment supply progressively increased
during the mid- to late Eocene time period, at least in part driven by catchment expansion deep into the Pyrenean Axial Zone
at c. 39 Ma. The consistency of the rates of catchment-averaged erosion calculated from different methods builds confidence that
source areas have been connected to depositional sinks correctly.

通过计算古代源至汇系统中的总沉积体积，并结合使用源岩方法对作为源区的流域面积进行估算，评估百万年尺度上的平均流域侵蚀速率。这些速率与热年代学方法得出的值进行对比。以中新世至晚中新世（约33.9至41.6百万年前）的Escanilla古沉积物路由系统为例，位于南-中央比利牛斯造山楔顶部区域，约3500±300立方千米的固体颗粒沉积物源自比利牛斯山脉南-中央地区的两个流域，在7.7百万年的期间内，相当于平均侵蚀速率为约0.15至0.18毫米每年。在同一时间间隔内，根据邻近的砾岩中的磷灰石裂变轨迹分析，贡献流域的平均抬升速率估计为0.2至0.3毫米每年，而从更广泛粒度范围的碎屑磷灰石裂变轨迹分析中，估计为0.23至0.34毫米每年。在中新世至晚中新世期间，沉积物供给量逐渐增加，至少部分是由约39百万年前深入比利牛斯轴部区域的流域扩张所驱动。从不同方法计算出的流域平均侵蚀速率的一致性，增强了正确连接源区与沉积汇的信心。