Origins and genesis of loess deposits in central Spain, as indicated by heavy mineral compositions and grain‐size variability
Origins and genesis of loess deposits in central Spain, as indicated by heavy mineral compositions and grain‐size variability
复制标题
DOI：
10.1111/sed.12539
复制
发表时间：
2018-12
期刊：
影响因子：
3.5
通讯作者：
D. Wolf;K. Ryborz;T. Kolb;Ruben Calvo Zapata;J. Sanchez Vizcaino;L. Zöller;D. Faust
中科院分区：
文献类型：
--
作者：
D. Wolf;K. Ryborz;T. Kolb;Ruben Calvo Zapata;J. Sanchez Vizcaino;L. Zöller;D. Faust
黄土沉积物的形成在很大程度上取决于可充气粉尘大小物质的可用性。确定粉尘产生的来源区域和机制对于适当地描述相关的古环境条件至关重要。迄今为止，对地中海地区黄土沉积的研究还很少，关于其产尘机制的资料也很少。在这种情况下，西班牙中部塔古斯盆地上游的黄土沉积的起源尚不清楚。这项研究的主要目的是找出这些黄土沉积是否主要是由山脉作用和河流粉碎形成的，或者它们是否起源于马德里盆地中心第三系泥灰岩的风化作用。进一步的关切是将确定的来源地区与黄土形成机制和伴随的环境背景联系起来。综合使用重矿物和粒度数据，结合地层特征和地貌位置信息，可以确定不同的局部黄土来源。研究表明，在过去的35年中，塔古斯黄土沉积物的主要部分来自河流洪泛区，而伊比利亚山脉的山区被确定为各自洪泛区沉积物的重要来源。根据重矿物组成和定年结果，发现在Heinrich Stadial 3期间，来自伊比利亚山脉的沉积物供应强烈增加，表明在海洋同位素阶段3晚期，环境从最初的温暖转向寒冷。此外，我们还发现，粒径模式清楚地表明Heinrich Stadial 3、Heinrich Stadial 2和Heinrich Stadial 1期间的最大风力强度。这些结果表明，在地中海的这一部分，尘埃大小的颗粒的形成过程与温带和大陆地区的许多其他地方相似，而与炎热和干燥环境有关的风化过程只是次要的。
The formation of loess deposits strongly depends on the availability of deflatable dust‐sized material. Identification of source areas and mechanisms of dust production is essential for an appropriate characterization of related palaeoenvironmental conditions. So far, little research has been done on loess deposits in the Mediterranean region and information about mechanisms of dust production is very rare. In this context, it is not clear from where the loess deposits from the upper Tagus Basin in central Spain originated. The main objective of this study was to find out whether these loess deposits were formed primarily by mountain processes and fluvial comminution, or whether they have their origin in the weathering of Tertiary marls in the centre of the Madrid Basin. A further concern was to link the determined source areas with loess formation mechanisms and concomitant environmental contexts. Following a comprehensive approach using heavy minerals and grain‐size data, together with information on stratigraphic features and geomorphic positions, different local loess sources could be identified. This study shows that during the last 35 kyr a major proportion of the Tagus loess deposits was deflated from river floodplains, while the mountain region of the Iberian Range was identified as a significant source of respective floodplain sediments. Based on heavy mineral compositions and dating results, it was found that during Heinrich Stadial 3, sediment supply from the Iberian Range strongly increased, suggesting an environmental shift from initially warmer towards colder temperatures in late Marine Isotope Stage 3. Furthermore, it was found that grain‐size patterns clearly indicate maximum wind strengths during Heinrich Stadial 3, followed by Heinrich Stadial 2 and Heinrich Stadial 1. These results demonstrate that the formation of dust‐sized particles in this part of the Mediterranean operated similar to many other places in temperate and continental regions, and that weathering processes linked to hot and dry environments were only of minor importance.