Abstract In northwestern Argentina (NWA), particularly at ∼27° S, the best known Neogene depocenters are intermountain tectonic valleys located in the Sierras Pampeanas geological province. Conversely, basins located to the east from the Aconquija and Ambato ranges, toward the Chaco-Pampean Plain, have been scarcely studied due to the extensive vegetal coverage. In the last decade, despite some contributions were focused in these areas and reported valuable data concerning tectonic and lithological interpretations, chronostratigraphic data are scarce, even absent so far. Herein we present a sedimentological analysis and an 40Ar/39Ar age of the Dulce River outcrops related to the Neogene Guasayan Range deposits, at the transition between NW Sierras Pampeanas and Chaco-Pampean Plain basin (∼27° S). The study area includes Neogene fossiliferous sediments of the Las Canas Formation; particularly, we focused in a section located between Canada de la Costa and Sotelo localities (Rio Hondo Department, Santiago del Estero Province). The chronostratigraphic study allowed us to assign an early Pliocene age to the studied section of the unit; the first absolute dating obtained for this unit is 3.73 ± 0.07 Ma. The measured stratigraphic logs are ∼540 m thick of relatively well-preserved light to reddish-brown clastic deposits. The paleoenvironmental analysis of partial stratigraphic sections suggests the presence of a braided sandy river with well-developed muddy floodplains. We identified two fossiliferous beds below the dated tuff bed, separated by a tuffaceous-sandstone deposit. The new chronostratigraphic datum indicates that the Guasayan Range began to rise during the late Pliocene. Based on the stratigraphy, absolute age, and geographical location of the studied area, a correlation among the Las Canas Formation, India Muerta Formation (NW Sierras Pampeanas), and the Pozo del Tigre Member, Chaco Formation (Chaco-Pampean Plain) is suggested. This study represents a significant contribution in the context of the scarcely, isolated, and fossiliferous Neogene outcrops of the Tucuman Basin.

中文翻译：

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Dulce 河露头中 Las Cañas 地层的沉积学分析和放射性同位素年龄，Río Hondo, santiago delestero（阿根廷西北部）

摘要在阿根廷西北部 (NWA)，特别是在 27°S 附近，最著名的新第三纪沉积中心是位于 Sierras Pampeanas 地质省的山间构造山谷。相反，位于 Aconquija 和 Ambato 山脉以东，朝向 Chaco-Pampean 平原的盆地，由于植被覆盖广泛，几乎没有被研究过。在过去的十年中，尽管一些贡献集中在这些领域，并报告了有关构造和岩性解释的有价值的数据，但年代地层数据很少，甚至到目前为止还没有。在此，我们介绍了与新近纪瓜萨扬山脉沉积物相关的杜尔塞河露头的沉积学分析和 40Ar/39Ar 年龄，位于 NW Sierras Pampeanas 和 Chaco-Pampean 平原盆地（~27° S）之间的过渡处。研究区包括拉斯卡纳斯组的新近纪含化石沉积物；特别是，我们专注于位于 Canada de la Costa 和 Sotelo 地区（Rio Hondo 省，圣地亚哥德尔埃斯特罗省）之间的部分。年代地层学研究使我们能够将上新世早期分配给该单元的研究部分。该单元获得的第一个绝对年代为 3.73 ± 0.07 Ma。测得的地层测井大约有 540 m 厚，是保存相对完好的浅色至红棕色碎屑沉积物。部分地层剖面的古环境分析表明存在一条辫状沙河和发育良好的泥质漫滩。我们在年代久远的凝灰岩层下方发现了两个含化石的层，被凝灰质砂岩矿床隔开。新的年代地层数据表明瓜萨扬山脉在上新世晚期开始上升。根据研究区的地层、绝对年龄和地理位置，提出了 Las Canas 组、India Muerta 组（NW Sierras Pampeanas）和 Pozo del Tigre 段 Chaco 组（Chaco-Pampean 平原）之间的相关性. 这项研究在 Tucuman 盆地新近纪稀少、孤立和含化石的新近系露头的背景下做出了重大贡献。