In a PICL: The sedimentary deposits and facies of perennially ice‐covered lakes
In a PICL: The sedimentary deposits and facies of perennially ice‐covered lakes
复制标题
DOI：
10.1111/sed.12522
复制
发表时间：
2018-10
期刊：
影响因子：
3.5
通讯作者：
F. Rivera‐Hernández;D. Sumner;T. Mackey;I. Hawes;D. Andersen
中科院分区：
文献类型：
--
作者：
F. Rivera‐Hernández;D. Sumner;T. Mackey;I. Hawes;D. Andersen
常年冰雪覆盖的湖泊与开放水域湖泊的相貌可能明显不同，因为沉积物被输送到冰上并在那里积聚，而沙粒优先融化并沉积在湖底。为了表征这些湖泊的相，我们利用湖底观测、水下视频和图像以及沉积物岩心描述了来自五个南极常年冰雪覆盖的湖泊的沉积物。其中一个湖泊的主要成分是层状微生物垫和泥浆（来自毗邻的冰川），还有浸染的沙子和稀有的砾石。其他四个湖泊主要由层状微生物垫和中等至中等分选的中等到非常粗的沙子以及稀疏的颗粒和卵石组成；它们含有少量的间隙或层状泥（来自溪流和毗邻的冰川）。沙子分布或集中在土丘和 1 m 至 10 m 以上长的细长山脊中。土丘的直径从厘米到米不等。形状为圆锥形、细长形或圆形；且彼此隔离或沉积在彼此附近或之上。土丘中的沙层具有正常级配、反级配或无级配。根据泥砂相对比例和砂沉积类型，将常年冰封湖泊划分为九个泥砂混合相。虽然常年被冰覆盖的湖泊相与其他受冰影响的湖泊和冰海相重叠，但它们的特点是缺乏比颗粒粗的颗粒、沙粒尺寸范围狭窄以及沙丘的反级配。这些相可用于推断冰盖随时间的变化，并识别岩石记录中常年被冰覆盖的湖泊。地球和火星上预计会存在古老的常年冰雪覆盖的湖泊，它们的特征将为过去的气候条件和宜居性提供新的见解。
Perennially ice‐covered lakes can have significantly different facies than open‐water lakes because sediment is transported onto the ice, where it accumulates, and sand grains preferentially melt through to be deposited on the lake floor. To characterize the facies in these lakes, sedimentary deposits from five Antarctic perennially ice‐covered lakes were described using lake‐bottom observations, underwater video and images, and sediment cores. One lake was dominated by laminated microbial mats and mud (derived from an abutting glacier), with disseminated sand and rare gravel. The other four lakes were dominated by laminated microbial mats and moderately well to moderately sorted medium to very coarse sand with sparse granules and pebbles; they contained minor interstitial or laminated mud (derived from streams and abutting glaciers). The sand was disseminated or localized in mounds and 1 m to more than 10 m long elongate ridges. Mounds were centimetres to metres in diameter; conical, elongate or round in shape; and isolated or deposited near or on top of one another. Sand layers in the mounds had normal, inverse, or no grading. Nine mixed mud and sand facies were defined for perennially ice‐covered lakes based on the relative proportion of mud to sand and the style of sand deposition. While perennially ice‐covered lake facies overlap with other ice‐influenced lakes and glaciomarine facies, they are characterized by a paucity of grains coarser than granules, a narrow range in sand grain sizes, and inverse grading in the sand mounds. These facies can be used to infer changes in ice cover through time and to identify perennially ice‐covered lakes in the rock record. Ancient perennially ice‐covered lakes are expected on Earth and Mars, and their characterization will provide new insights into past climatic conditions and habitability.