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首页> 外文期刊>Icarus: International Journal of Solar System Studies >An analysis of open-basin lake deposits on Mars: Evidence for the nature of associated lacustrine deposits and post-lacustrine modification processes
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An analysis of open-basin lake deposits on Mars: Evidence for the nature of associated lacustrine deposits and post-lacustrine modification processes

机译：火星上的流域湖泊沉积物分析：相关湖相沉积物的性质和湖相后修饰过程的证据

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摘要

A large number of candidate open-basin lakes (low-lying regions with both inlet valleys and an outlet valley) have been identified and mapped on Mars and are fed by valley network systems that were active near the Noachian-Hesperian boundary. The nature of processes that modified the open-basin lake interiors subsequent to lacustrine activity, and how frequently sedimentary deposits related to lacustrine activity remain exposed, has not been extensively examined. An analysis of 226 open-basin lakes was undertaken to identify evidence for: (1) exposed deposits of possible lacustrine origin and (2) post-lacustrine-activity processes that may have modified or resurfaced open-basin lakes. Spectroscopic data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument were analyzed over identified exposed open-basin lake deposits to assess the mineralogy of these deposits. Particular attention was paid to the possible detection of any component of aqueous alteration minerals (e.g. phyllosilicates, hydrated silica, zeolites) or evaporites (e.g. carbonates, sulfates, chlorides) associated with these exposed deposits. The aim of this paper is to act as a broad survey and cataloguing of the types of lacustrine and post-lacustrine deposits that are present within these 226 paleolake basins. Results of the morphologic classification indicate that 79 open-basin lakes (~35% of the population) contain exposed deposits of possible lacustrine origin, identified on the basis of fan/delta deposits, layered deposits and/or exposed floor material of apparent lacustrine origin. Additionally, all 226 open-basin lakes examined appear to have been at least partially resurfaced subsequent to their formation by several processes, including volcanism, glacial and periglacial activity, impact cratering and aeolian activity. Results from the analysis of CRISM data show that only 10 (~29% of the 34 deposits with CRISM coverage) of the exposed open-basin lake deposits contain positively identified aqueous alteration minerals, with one deposit also containing evaporites. The identified hydrated and evaporite minerals include Fe/Mg-smectite, kaolinite, hydrated silica and carbonate, with Fe/Mg-smectite the most commonly identified mineral. These results indicate that hydrated and evaporite minerals are not as commonly associated with lacustrine deposits on Mars as they are on Earth. This suggests. in situ alteration and mineral precipitation, a common source of such minerals in terrestrial lakes, was not a major process occurring in these paleo-lacustrine systems, and that the observed minerals are likely to be present as transported material within the lacustrine deposits. The lack of widespread. in situ alteration also suggests that either the water chemistry in these paleolake systems was not conducive to aqueous alteration and mineral precipitation, or that the open-basin lake systems were relatively short-lived.
机译：在火星上已经发现并绘制了大量候选的流域湖（低谷地区，都有入口谷和出口谷），并由活跃在Noachian-Hesperian边界附近的谷网络系统提供营养。在湖水活动之后改变开阔湖泊内部的过程的性质，以及与湖水活动有关的沉积物保持暴露的频率，尚未得到广泛研究。对226个开放盆地湖泊进行了分析，以确定以下方面的证据：（1）可能是湖相来源的裸露沉积物;（2）可能改变或重现了开放盆地湖泊的湖后活动过程。在确定的裸露开放盆地湖沉积物上分析了紧凑型火星侦察成像光谱仪（CRISM）的光谱数据，以评估这些沉积物的矿物学。特别注意可能检测与这些裸露的沉积物相关的含水蚀变矿物（例如页硅酸盐，水合二氧化硅，沸石）或蒸发物（例如碳酸盐，硫酸盐，氯化物）的任何成分。本文的目的是对这226个古湖盆地中存在的湖相和湖相后沉积物类型进行广泛的调查和分类。形态分类的结果表明，有79个开放流域湖泊（约占人口的35％）含有可能是湖相的裸露沉积物，这些沉积物是根据扇形/三角洲沉积，分层沉积和/或明显的湖相成因的裸露地面物质确定的。此外，所检查的所有226个流域湖泊似乎在形成之后至少经过部分过程被重新浮出水面，这些过程包括火山作用，冰川和冰缘活动，撞击坑和风积活动。 CRISM数据分析的结果表明，裸露的开阔湖泊沉积物中只有10个（占CRISM覆盖的34个沉积物中的约29％）含有被明确识别的含水蚀变矿物，其中一个沉积物中也含有蒸发岩。鉴定出的水合和蒸发矿物包括铁/镁蒙脱石，高岭石，水合二氧化硅和碳酸盐，其中铁/镁蒙脱石是最常用的矿物。这些结果表明，水合矿物质和蒸发矿物质与火星上湖相沉积的联系不像地球上那样普遍。这表明。原位改变和矿物沉淀是陆地湖泊中此类矿物的常见来源，并不是这些古湖相系统中发生的主要过程，而且所观察到的矿物很可能以传输物质的形式存在于湖相沉积物中。缺乏普遍性。原位改变也表明，这些古湖系统中的水化学不利于水相改变和矿物沉淀，或者开阔湖泊系统的寿命相对较短。

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