River incision in upland areas is controlled by prevailing climatic and tectonic regimes, which are increasingly well described, and the nature of the bedrock lithology, which is still poorly constrained. Here, we calculated downstream variations in stream power and bedrock strength for six rivers crossing a normal fault in western Turkey, to derive new constraints on bedrock erodibility as function of rock type. These rivers were selected because they exhibit knick zones representing a transient response to an increase in throw rate, driven by fault linkage. Field measures of rock mass strength showed that the metamorphic units (gneisses and schists) in the catchments are ∼2 times harder than the sedimentary lithologies. Stream power increases downstream in all rivers, reaching a maxima upstream of the fault within the metamorphic bedrock but declining markedly where softer sedimentary rocks are encountered. We demonstrate a positive correlation between throw rate and stream power in the metamorphic rocks, characteristic of rivers obeying a detachment-limited model of erosion. We estimated bedrock erodibility in the metamorphic rocks as kb = 2.2–6.3 × 10−14 m s2 kg−1; in contrast, bedrock erodibility values were 5–30 times larger in the sedimentary units, with kb = 1.2–15 × 10−13 m s2 kg−1. However, in the sedimentary units, stream power does not scale predictably with fault throw rate, and we evaluated the extent to which the friable nature of the outcropping clastic bedrock alters the long-term erosional dynamics of the rivers. This study places new constraints on bedrock erodibilities upstream of active faults and demonstrates that the strength and characteristics of underlying bedrock exert a fundamental influence on river behavior.

中文翻译：

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量化岩性和抛率对基岩河切口的竞争影响

高地地区的河流切口受盛行气候和构造制度的控制，这些制度越来越得到很好的描述，而基岩岩性的性质仍然没有很好的约束。在这里，我们计算了穿越土耳其西部正断层的 6 条河流的河流动力和基岩强度的下游变化，以推导出对作为岩石类型函数的基岩可蚀性的新限制。之所以选择这些河流，是因为它们表现出代表对由断层连接驱动的抛出率增加的瞬态响应的缺陷区。岩体强度的现场测量表明，流域中的变质单元（片麻岩和片岩）比沉积岩性坚硬约 2 倍。所有河流下游的溪流功率增加，在变质基岩内达到断层上游的最大值，但在遇到较软的沉积岩时明显下降。我们证明了变质岩中的抛掷速率和河流功率之间存在正相关，这是河流遵循分离限制侵蚀模型的特征。我们估计变质岩的基岩可蚀性为 kb = 2.2–6.3 × 10−14 m s2 kg−1；相比之下，沉积单元的基岩可蚀性值大 5-30 倍，kb = 1.2-15 × 10-13 m s2 kg-1。然而，在沉积单元中，河流动力不会随着断层抛出率而按可预测的方式缩放，我们评估了露头碎屑基岩的易碎性质在多大程度上改变了河流的长期侵蚀动力学。