Sedimentary stratigraphy of Lake Chalco (Central Mexico) during its formative stages
Sedimentary stratigraphy of Lake Chalco (Central Mexico) during its formative stages
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DOI：
10.1007/s00531-020-01964-z
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发表时间：
2021-01
影响因子：
2.3
通讯作者：
Rodrigo Martínez-Abarca;B. Ortega‐Guerrero;S. Lozano-García;M. Caballero;B. Valero-Garcés;D. McGee;E. Brown;M. Stockhecke;Alastair G. E. Hodgetts
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作者：
Rodrigo Martínez-Abarca;B. Ortega‐Guerrero;S. Lozano-García;M. Caballero;B. Valero-Garcés;D. McGee;E. Brown;M. Stockhecke;Alastair G. E. Hodgetts
Chalco湖位于墨西哥盆地南部，一直是研究晚第四纪气候变率的主题。2016年，国际大陆科学钻探计划“MexiDrill项目”从Chalco湖恢复了520米的沉积物记录。磁化率测量显示，在343至285 m深度之间，沉积物物理性质发生了实质性变化，表明沉积物组成的变化与沉积环境的波动有关。我们针对343-285 m区间的沉积物进行了高分辨率相分析，建立了Chalco湖地层模型。根据沉积物组成、质地、矿物学和微形态特征，我们确定了3种相组合：(1)碎屑相，由层状粉砂、块状砂、层状粉砂、碎屑支撑砾石和基质支撑砾石组成；(2)生物成因相，包括硅藻泥相和双壳藻相；(3)火山碎屑相，以碎屑支撑浮石矿床为代表。根据沉积物特征的变化，我们认为Chalco湖的形成经历了四个阶段。第一阶段为冲积三角洲环境，碎屑和超浓流是主要的输沙介质。第二类以河流三角洲环境中的湍流为特征，与洪泛平原相关的层流交替发生。第三阶段是盆地的河湖过渡时期，形成了先前确定的古chalco - i湖，这是对潮湿条件的反应。在第四阶段，形成了一个深富营养化湖泊（古chalco - ii），其起源似乎与区域火山作用有关。我们的工作年龄-深度模型表明该湖的建立时间约为400±46 ka。本文介绍了Chalco湖由冲积沉积向湖相沉积过渡的唯一记录。我们的结果使我们能够确定(1)湖泊是如何形成的，它的发展阶段是什么，(2)一次主要的火山事件是如何改变和改造湖泊沉积的，以及(3)在湖泊形成期间，哪种气候条件占主导地位。首次将Chalco湖相沉积的开始年龄限定在400 ka左右。这使我们能够在一段时间内扩大我们对气候的认识，因为没有来自热带北美的陆地记录的信息。
Lake Chalco lies south of the Basin of Mexico and has been the subject of studies related to Late Quaternary climate variability. In 2016, the International Continental Scientific Drilling Program “MexiDrill Project” recovered a 520-m sediment record from Lake Chalco. Magnetic susceptibility measurements revealed substantial changes in sediment physical properties between 343 and 285 m depth, suggesting changes in composition associated with fluctuations in the depositional environment. We targeted sediments in the 343–285 m interval for high-resolution facies analysis, to develop a model of Lake Chalco formation. We identified three facies associations, using sediment composition, texture, mineralogy and micro-morphological characteristics: (1) detrital facies, consisting of laminated silt, massive sand, stratified silty sand, clast-supported gravel and matrix-supported gravel; (2) biogenic facies, which include diatom ooze and bivalve coquina; and (3) volcaniclastic facies, represented by clast-supported pumice deposits. We propose that formation of Lake Chalco occurred in four stages, which we identified by changes in sediment characteristics. The first stage was an alluvial delta environment, in which debris and hyper-concentrated flows were the main sediment transport agents. The second was characterized by turbulent flows in a fluvial deltaic environment, which alternated with laminar flows associated with floodplains. The third stage was a time of fluvio-lacustrine transition in the basin, with formation of the previously identified Paleo-Chalco-I Lake, in response to wet conditions. During the fourth stage, a deep eutrophic lake formed (Paleo-Chalco-II), with an origin that appears to have been related to regional volcanism. Our working age-depth model indicates establishment of the lake at ca. 400 ± 46 ka. This paper presents the only available record of the transition from alluvial to lacustrine sedimentation of Lake Chalco. Our results allow us to establish (1) how the lake was formed and what the phases of its development were, (2) how a major volcanic event altered and transformed the lacustrine sedimentation, and (3) which climatic conditions dominated during the lake formation. The age for the onset of the lacustrine sedimentation in Chalco is for the first time constrained to around 400 ka. This enables to expand our knowledge of the climate for a time for which there is no information from terrestrial records of tropical North America.