The Sedimentary Rock Record of Mars: Distribution, Origins, and Global Stratigraphy
The Sedimentary Rock Record of Mars: Distribution, Origins, and Global Stratigraphy
复制标题
火星沉积岩记录：分布、起源和全球地层学
DOI：
10.2110/pec.12.102.0001
复制
发表时间：
2012
影响因子：
--
通讯作者：
R. Milliken
中科院分区：
文献类型：
--
作者：
J. Grotzinger;R. Milliken
过去十年的火星探索产生了一系列发现，为火星上存在沉积岩提供了令人信服的证据。以前，火星主要被认为是一个火山行星，其主要的表面过程是熔岩和火山碎屑沉积物的喷发，尽管早期的研究确实认识到了山谷网络，巨大的外流通道，以及向火星北方平原输送沉积物质的必要性。相比之下，我们对火星的新看法显示了水和表面之间相互作用的丰富历史，以及水和风成过程对沉积物的风化，运输和沉积。令人惊讶的是，层状岩石的厚堆积物可以追溯到诺亚时代，其中最古老的可能形成于40亿年前，使这些岩石比地球上保存的任何沉积岩都要古老得多。一些沉积岩是在当地形成和沉积的，而另一些则是以巨大的岩片的形式积累起来的，可以在数百公里或更远的地方进行对比。局部沉积物形成于冲积扇、三角洲、湖底扇和湖泊环境中，此外，还可能形成于洪水造成的峡谷和山谷中。这些以前的沉积物表明更渐进的侵蚀和沉积作用，甚至可能涉及流星降水，它们为早期火星上的大气条件的概念提供了支持。与此相反，快速侵蚀和沉积可能发生在大型区域流出通道内，这些通道被认为是地下水爆发造成的。区域广泛的沉积矿床有不太明显的起源，但水合硫酸盐矿物的存在表明，这些矿床中的一些可能已经形成为湖相辉长岩，特别是在水手谷网络的开放和封闭的盆地。其他可能涉及风成改造以前沉积的硫酸盐，或者可能是水（地下水）改变以前沉积的玄武岩沉积物。另一种主要类型的区域性广泛沉积存款出现米级分层与高度韵律组织。这些沉积物出现在火星Arabia Terra地区的几个地方，也在Gale Crater的5公里厚的地层剖面顶部观察到。相对较薄的岩层具有显著的横向连续性，它们分布在广泛定义的高点和低点，以及缺乏强烈的光谱吸收特征，表明这些岩石可能是尘埃石，由火星大气中沉降的细颗粒的弱岩化作用形成。火星上最古老的沉积物可能主要是堆积的、撞击产生的碎片片层，与月球上看到的类似，可能包括
The last decade of Mars exploration produced a series of discoveries that provide compelling evidence for the existence of sedimentary rocks on Mars. Previously, Mars was regarded principally as a volcanic planet, the dominant surface processes of which were eruption of lavas and pyroclastic deposits, although early studies did recognize valley networks, enormous outflow channels, and the required transport of sedimentary materials to the northern plains of Mars. In contrast, our new view of Mars shows a rich history of interactions between water and the surface, with weathering, transport, and deposition of sediments by water as well as eolian processes. Surprisingly thick accumulations of stratified rocks extend back into the Noachian Era—the oldest of which were likely formed over 4 billion years ago, making these rocks much older than any sedimentary rocks preserved on Earth. Some sedimentary rocks were formed and deposited locally, whereas others accumulated as vast sheets that can be correlated for hundreds of kilometers or farther. Local deposits were formed in alluvial fan, deltaic, sublacustrine fan, and lacustrine environments in addition to deposits that fill canyons and valleys possibly carved during catastrophic floods. These former deposits indicate more gradual erosion and sedimentation, perhaps even involving meteoric precipitation, and they provide support for the notion of clement conditions on early Mars. In contrast, rapid erosion and sedimentation may have occurred within large, regional outflow channels thought to have resulted from outbursts of groundwater. Regionally extensive sedimentary deposits have less obvious origins, but the presence of hydrated sulfate minerals indicates that some of these deposits may have formed as lacustrine evaporites, particularly in the Valles Marineris network of open and closed basins. Others may have involved eolian reworking of previously deposited sulfates, or perhaps aqueous (groundwater) alteration of previously deposited basaltic sediments. Another major type of regionally extensive sedimentary deposit occurs as meter-scale stratification with highly rhythmic organization. These deposits occur in several places in the Arabia Terra region of Mars and are also observed at the top of a 5-km-thick stratigraphic section in Gale Crater. The significant lateral continuity of relatively thin beds, their distribution over broadly defined highs as well as lows, and the lack of strong spectral absorption features indicate that these rocks may be duststones, formed by weak lithification of fine particles that settled from the Martian atmosphere. The most ancient sedimentary deposits on Mars may be dominated by stacked, impact-generated debris sheets, similar to those seen on the Moon, and may include