During the late Miocene, the development of topography of the eastern margin of the Puna Plateau of the Central Andes, was related to the onset of the eastward migration and foreland fragmentation. The Guanaco and Piquete formations (late Miocene-early Pleistocene, Jujuy Subgroup) represent a thick succession of the adjacent foreland. These units outcrop in the Río Chico (=Xibi Xibi) locality (Jujuy in north-west Argentina), a transition zone between the Eastern Cordillera (EC) and the Subandean Ranges (SR). We combine a detailed stratigraphic section, paleocurrent measurements, provenance and facies analyses, as well as a new absolute age near to the top of the Guanaco Formation (5.7 ± 0.8 Ma), and new data on the Neogene environmental changes in this region to characterize these units in the context of the regional tectono-sedimentary evolution. Our analyses suggest a progradation of an alluvial-fan system over a braided-fluvial system, linked to an increase in relief due to rapid shortening pulses and associated to the regional climatic changes in this part of the Central Andes. In the studied area, the earliest uplift of the eastern margin of the Puna Plateau and other areas of the EC generated higher topographic relief to the north and north-west, which increased the relevance of local sources and caused the deflection of paleo-rivers toward the south. The limit between the Guanaco and Piquete formations was reinterpreted to be located 1000 m higher in the stratigraphic section compared to previous proposals, in agreement with the age of the newly dated tuff. Our analysis improves the temporal and spatial characteristics of tectonic processes in the southern Central Andes and provides a framework for the study of landscape as well as biotic, and environmental changes during the late Miocene within the context of the eastward migration of the orogenic front and coeval foreland evolution in the Central Andes.

中新世晚期，中安第斯普纳高原东缘地形的发展，与东移的开始和前陆破碎化有关。Guanaco 和 Piquete 地层（晚中新世-早更新世，胡胡伊亚群）代表了相邻前陆的厚层序列。这些单元在 Río Chico（=西比西比）地区（阿根廷西北部的胡胡伊）出露，这是东科迪勒拉 (EC) 和苏班德山脉 (SR) 之间的过渡带。我们结合了详细的地层剖面、古水流测量、物源和相分析，以及靠近 Guanaco 组顶部的新绝对年龄 (5.7 ± 0.8 Ma)，以及该地区新近纪环境变化的新数据，以表征这些单元在区域构造沉积演化的背景下。我们的分析表明冲积扇系统在辫状河流系统上的前移与由于快速缩短的脉冲而导致的地势增加有关，并且与中部安第斯山脉的这一部分的区域气候变化有关。在研究区，普纳高原东缘和欧共体其他地区最早的隆升产生了向北和西北部更高的地形起伏，增加了当地源的相关性，导致古河流向南方。与之前的提议相比，Guanaco 和 Piquete 地层之间的界限被重新解释为位于地层部分高 1000 m，与新约会的凝灰岩的年龄一致。