Transition from alluvial to fluvial systems in the Guadalentín Depression (SE Spain) during the Holocene: Lorca Fan versus Guadalentín River
Transition from alluvial to fluvial systems in the Guadalentín Depression (SE Spain) during the Holocene: Lorca Fan versus Guadalentín River
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全新世期间瓜达伦丁凹陷（西班牙东南部）从冲积系统向河流系统的转变：洛尔卡范与瓜达伦丁河
DOI：
10.1016/j.geomorph.2007.10.023
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发表时间：
2008
期刊：
影响因子：
3.9
通讯作者：
C. Zazo
中科院分区：
文献类型：
--
作者：
P. Silva;T. Bardají;M. Calmel;J. Goy;C. Zazo
洛尔卡冲积扇（西班牙东南部）是半干旱地区从冲积到河流沉积环境过渡的一个很好的例子。扇体是一个以砂-粉砂质成分为主的大型缓坡冲积扇。目前，瓜达伦汀河将其整个长度切开，该河曾是主要的扇水道，仍然作为一个负责历史性大洪水事件的激流拉姆布拉型水道运作。在扇尖、扇中和扇尾位置分析了三种不同的露头，同时考虑到在主扇沟内在当前深泓以上+8-9 m、+5-6 m、+3-4 m和+1-2 m处发育的不同嵌入阶地。现有的放射性碳数据和考古遗迹中收集的风扇沉积物和嵌入阶地，使建设一个初步的假设，从史前到历史时期的扇形体的渐进切口。近端扇沉积发生在全新世早期，约7900-7700 cal. yr。BP，并持续到新石器时代晚期到Calcolithic时期（~ 5500-4200 cal. yr。当扇面稳定时，河道切割产生了第一扇头沟。随后的扇槽充填导致了上部阶地（+ 8-9 m）的发展，该阶地与洛尔卡下游23 km处的沼泽环境合并，在青铜时代晚期和后罗马时代为远端扇叶提供了养分。第二阶地水平（+5-6 m）是自罗马时代发展起来的约5 m厚的切填幕，其年代约为1700 - 950 cal. yr。BP.上阶地的几何形状和测高，以及在中到远扇位置的河流纵剖面中出现的不同台阶，强烈表明古代扇槽的切割受到交叉点头切发展的帮助（意义[Harvey，A.M.，1978.西班牙东南部的冲积扇。Catena 5，177-211.]）在近中扇的位置，但在远端沼泽环境的邻近流域盆地施加溯源侵蚀。因此，洛尔卡扇证实了大型扇在从纯冲积环境过渡到河流环境的过程中的行为，以及在历史时期受动态基准面影响的区域排水网络的最终初期整合。
The Lorca alluvial fan (SE Spain) constitutes an excellent example of transition from alluvial to fluvial sedimentary environments in a semiarid region. The fan body represents a large gently-sloping alluvial fan of mainly sandy–silty composition. It is presently dissected throughout its length by the Guadalentín River, which worked as the main fan channel and still operates as a torrential rambla-type channel responsible for historic large flood events. Three different outcrops are analysed at fan-apex, mid-fan and distal-fan locations, taking also into account the different inset terrace levels developed within the main fan trench at + 8–9 m, + 5–6 m, + 3–4 m and + 1–2 m above the present thalweg. Available radiocarbon data and archeological remains collected in fan sediments and inset terraces enable the construction of a preliminary hypothesis about the progressive incision of the fan body from pre-historical to historical times. Proximal fan aggradation took place during the Early Holocene before ~ 7900–7700 cal. yr. BP and continued until the Late Neolithic to Calcolithic Period (~ 5500–4200 cal. yr. BP) when the fan surface stabilised, and channel incision generated a first fanhead trench. Subsequent infilling of the fan trench led to the development of the upper terrace level (+ 8–9 m) which merged with the palustrine environments 23 km downstream of Lorca, feeding distal fan lobes during Late Bronze Age and Post-Roman times. The second terrace level (+ 5–6 m) is a cut & fill episode of about 5 m thickness developed from Roman times, and dated to ~ 1700 to 950 cal. yr. BP. The geometry and altimetry of the upper terrace level, together with the occurrence of different steps in the longitudinal profile of the river at mid to distal fan locations, strongly suggest that the incision of the ancient fan channel was assisted by intersection point headcut development (sensu [Harvey, A.M., 1978. Dissected alluvial fans in southeast Spain. Catena 5, 177–211.]) at proximal-mid fan locations, but by headward erosion exerted by neighbouring drainage basins at distal palustrine environments. Therefore, the Lorca fan exemplifies the behaviour of large-sized fans in its transition from pure alluvial environments to fluvial ones, and its eventual incipient integration into a regional drainage network subject to a dynamic base-level during the historic period.