Three competing factors for late Quaternary fluvial incision in the Moyobamba piggyback basin, located in the northeastern Peruvian Subandes, were investigated, namely base-level change as a result of basin opening, changes in the ratio sediment load:discharge (Q_s: Q_w) controlled by orbital and suborbital climate cyclicity, and thrust-related tectonic uplift. To assess the relative importance of these factors, the fluvial terrace staircases of five rivers were studied in terms of their sedimentology, stratigraphy and geomorphology. A new dataset of eight Optically Stimulated Luminescence (OSL) and four ¹⁴C ages shows that the final phase of endorheic alluvial fan aggradation lasted until 18.0 ± 1.4 ka, after which basin-wide incision occurred. Incision at the basin outlet as a result of adaptation to the new base level is decoupled from the observed incision in the middle and upper parts of the basin. There, incision is the result of a northwestward increase in uplift related to movements of the Cerro Blanco thrust at the western border of the Moyobamba basin. Incision was continuous from 18 ± 1.4 ka until 10.3 ± 0.7 ka without terrace formation, but between 10.3 ± 0.7 ka and 5.5 ± 0.4 ka up to four terrace levels were formed. Deposition of fluvial terrace sediments may have occurred during short periods characterised by a more intense South American Summer Monsoon (SASM) controlled by suborbital climate cyclicity, but a more precise age control is needed to confirm this theory. Precession-controlled, increased Holocene aridification between 10.3 ± 0.7 ka and 5.5 ± 0.4 ka may have resulted in a decrease in the ratio Q_s: Q_w leading to a five-fold increase in fluvial incision rates of up to 6.0 mm a⁻¹ and flattening of terrace profile gradients with rates of up to 2.6 mm a⁻¹. After 5.5 ± 0.4 ka, rates dropped again. Over longer timescales, movement of the Cerro Blanco thrust caused basin-wide uplift and fluvial incision at a more constant pace. During the past ~20 ka, incision increases from the southwest basin border towards the northwestern basin border with corresponding uplift rates increasing from ${0.2}_{-0.2}^{+0.3}$ mm a⁻¹ to ${2.1}_{-0.2}^{+0.2}$ mm a⁻¹; and with shortening rates increasing northwestward from ${0.2}_{-0.2}^{+0.4}$ mm a⁻¹ to ${2.8}_{-0.2}^{+0.3}$ mm a⁻¹. The highest, presented uplift rates are in agreement with independently published data for our study area. Our data shows that over longer timescales of ~20 ka, incision rates can be used as proxies for tectonic uplift, but over shorter timescales incision rates may be seriously affected by climate change and cannot be used to infer uplift rates.

It is further suggested that continuous uplift and erosion of the Cerro Blanco thrust system, and subsequent sedimentation in the basin, in combination with increased precipitation during Heinrich events 1 and 2 and the Last Glacial Maximum (LGM), led to basin overflow. Simultaneously, river capture through headward erosion, guided by strike-slip faulting, may have led to the definitive opening up of the Moyobamba basin. To our knowledge, this is the first time that late Quaternary basin opening has been demonstrated for the South American Andes and one of the few, known cases worldwide.

研究了位于秘鲁Subandes东北部的Moyobamba背basin盆地晚期第四纪河流切口的三个竞争因素，即盆地开放导致的基准面变化，沉积物荷重与流量之比的变化（Q _s：Q _w）由轨道和亚轨道的气候周期性以及与推力有关的构造隆升控制。为了评估这些因素的相对重要性，从沉积学，地层学和地貌学的角度研究了五条河流的河流阶地阶梯。一个新的数据集，其中包含八个光学刺激发光（OSL）和四个¹⁴年龄表明，内流性冲积扇积聚的最后阶段一直持续到18.0±1.4 ka，此后才发生全盆切口。由于适应了新的基准高度，盆地出口处的切口与盆地中部和上部观察到的切口脱钩。那里的切口是与Moyobamba盆地西部边界的Cerro Blanco逆冲运动有关的隆起向西北增加的结果。切口从18±1.4 ka一直持续到10.3±0.7 ka，没有阶地形成，但是在10.3±0.7 ka和5.5±0.4 ka之间形成了多达四个阶地层。河流阶地沉积物的沉积可能发生在短期内，其特征是南亚夏季风（SASM）更为强烈，受亚轨道气候周期控制，但是需要更精确的年龄控制来证实这一理论。由进动控制，全新世的干旱化程度在10.3±0.7 ka和5.5±0.4 ka之间可能会导致比率降低Q_小号：Q _{w ^}导致了河流的切割率增加五倍至6.0毫米^-1和最多率露台轮廓渐变的扁平化至2.6毫米^-1。在5.5±0.4 ka之后，速率再次下降。在更长的时间范围内，Cerro Blanco推力的运动使盆地范围内的隆起和河流切口以更恒定的速度移动。在过去约20 ka的时间里，切口从西南盆地边界向西北盆地边界增加，相应的上升速率从${0.2}_{-0.2}^{+0.3}$mm a ^-1至${2.1}_{-0.2}^{+0.2}$毫米a ^-1 ; 并且随着缩短率从${0.2}_{-0.2}^{+0.4}$mm a ^-1至${2.8}_{-0.2}^{+0.3}$mm a ^-1。提出的最高抬升率与我们研究区域的独立发布数据一致。我们的数据表明，在〜20 ka的较长时间尺度上，切开率可以用作构造隆升的代理，但是在较短的时间尺度上，切口率可能会受到气候变化的严重影响，不能用于推断隆升率。

进一步表明，塞罗布兰科逆冲系统的持续隆升和侵蚀，以及随后在盆地的沉积，再加上海因里希事件1和2和最后冰川期（LGM）期间的降水增加，导致盆地溢出。同时，在走滑断层的引导下，通过向前侵蚀引起的河流捕获可能导致了Moyobamba盆地的最终开放。据我们所知，这是首次向南美安第斯山脉展示第四纪盆地晚期开放，这是世界上为数不多的已知案例之一。