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首页> 外文期刊>Sedimentology: Journal of the International Association of Sedimentologists >Sedimentological and palaeohydrological characterization of Late Pleistocene and Holocene tufa mound palaeolakes using trenching methods in the Spanish Pyrenees
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Sedimentological and palaeohydrological characterization of Late Pleistocene and Holocene tufa mound palaeolakes using trenching methods in the Spanish Pyrenees

机译：在西班牙比利牛斯山脉使用挖沟方法对晚更新世和全新世的图法丘古湖区进行沉积学和古水文表征

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摘要

Lakes developed in the inner depressions of tufa mounds are rare geomorphic features and still poorly understood. Sedimentation in this unusual type of endorheic lake with a very restricted catchment area is highly sensitive to environmental and hydrological changes. The Isona tufa mound complex, north-eastern Iberian Peninsula, is associated with the discharge zone of a confined artesian aquifer and comprises 11 tufa mounds consisting of an annular rimstone enclosing a central depression filled with lake deposits. Data gathered from trenches excavated in four palaeolakes located within three different morphostratigraphic units permitted a precise analysis of the geometrical characteristics and stratigraphic relationships of the deposits and provided a sedimentation model for the Late Quaternary infilling of the spring-fed lakes. The work illustrates that trenches allow a precise characterization of the stratigraphic arrangements, lateral facies changes and deformation structures, which are not apparent in studies relying solely on borehole records, and facilitate sampling for dating and geochemical analyses. The five sedimentary facies described represent different evolutionary stages of the lakes, including: (i) carbonate-rich palustrine deposits probably related to periods with strong hydrological seasonality; (ii) massive highly bioturbated organic ooze; (iii) banded organic carbonate-rich facies associated with an increase in the regional effective moisture; (iv) fine-grained quartz-rich aeolian/slope-wash sediments; and (v) colluvial facies deposited following the desiccation of the lakes located at higher altitudes. Geochemical and sedimentological analyses of the lacustrine sequences provided information on the palaeohydrological evolution of the Isona tufa mound complex and the palaeoenvironmental conditions of the area over the last 28ka. Radiometric dating suggests that deposition occurred simultaneously at ca 22ka in palaeolakes situated at different elevations. A drop in the piezometric level prompted by the opening of springs at lower altitudes probably caused the deactivation of the upper springs and the desiccation of the lakes. Arid conditions prevailed in the area during the Late Glacial and the early Holocene (280 to 85ka bp). More humid conditions recorded from 85 to 42ka and again since 17ka are in accordance with palaeoenvironmental reconstructions available in the Western Mediterranean since the Last Glacial Maximum.
机译：在石灰岩丘的内部凹陷中发育的湖泊是罕见的地貌特征，仍然知之甚少。在这种异常的内陆湖泊中，其集水区非常有限，其沉积对环境和水文变化高度敏感。伊萨尼亚半岛东北部的伊索纳（Isona）石灰土丘群与承压自流含水层的排放区相连，包括11个石灰土丘，由环形的轮辋组成，其包围着充满湖泊沉积物的中央凹陷。从位于三个不同形态地层单元中的四个古湖中开挖的沟槽收集的数据可以对沉积物的几何特征和地层关系进行精确分析，并为春季湖的第四纪晚期充填提供了沉积模型。这项工作表明，沟槽可以精确地描述地层排列，侧相变化和变形结构，这在仅依靠钻孔记录的研究中是不明显的，并且可以方便地进行测年和地球化学分析。所描述的五个沉积相代表了湖泊的不同演化阶段，包括：（i）富含碳酸盐的古沉积物，可能与水文季节性强的时期有关; （ii）大量高度生物扰动的有机渗出物; （iii）与区域有效水分增加有关的带状富含有机碳酸盐的相; （iv）细粒富含石英的风沙/斜坡冲刷沉积物; （v）海拔较高的湖泊干燥后沉积的河床相。湖相序列的地球化学和沉积学分析提供了有关伊索纳（Isona）图法土丘复合体的古水文演化以及过去28ka时期该地区古环境条件的信息。放射性测年表明，沉积同时发生在不同海拔的古湖约22ka处。较低高度的弹簧打开导致测压仪高度下降，可能导致上部弹簧的失活和湖泊的干燥。冰川期晚期和全新世早期（280至85ka bp），该地区普遍存在干旱条件。从最后一次冰河期以来，西地中海地区的古环境重建符合从85ka到42ka以及自17ka以来的更多潮湿条件。

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