Recognition of Sedimentary Rock Occurrences in Satellite and Aerial Images of Other Worlds—Insights from Mars

Abstract

Sedimentary rocks provide records of past surface and subsurface processes and environments. The first step in the study of the sedimentary rock record of another world is to learn to recognize their occurrences in images from instruments aboard orbiting, flyby, or aerial platforms. For two decades, Mars has been known to have sedimentary rocks; however, planet-wide identification is incomplete. Global coverage at 0.25–6 m/pixel, and observations from the Curiosity rover in Gale crater, expand the ability to recognize Martian sedimentary rocks. No longer limited to cases that are light-toned, lightly cratered, and stratified—or mimic original depositional setting (e.g., lithified deltas)—Martian sedimentary rocks include dark-toned examples, as well as rocks that are erosion-resistant enough to retain small craters as well as do lava flows. Breakdown of conglomerates, breccias, and even some mudstones, can produce a pebbly regolith that imparts a “smooth” appearance in satellite and aerial images. Context is important; sedimentary rocks remain challenging to distinguish from primary igneous rocks in some cases. Detection of ultramafic, mafic, or andesitic compositions do not dictate that a rock is igneous, and clast genesis should be considered separately from the depositional record. Mars likely has much more sedimentary rock than previously recognized.

Rivers and Lakes in Western Arabia Terra: The Fluvial Catchment of the ExoMars 2022 rover landing site

“…However, a volcanic interpretation is not necessarily appropriate (e.g. ; Edgett, 2005;Edgett and Sarkar, 2021) and in this case is inconsistent with the distribution and variety of contexts seen for Irregular Dark Depressions seen in the Oxia Basin catchment: none of the 109 examples within the study area show evidence for volcanic architecture that might be expected from Amazonian volcanism (Brož et al, 2017).…”

“…We propose that these dark deposits, when located in crater floors and associated with the channel network, represent allochthonous mafic volcaniclastic/aeolian materials (Edgett and Sarkar, 2021) that have been cemented by high stand of groundwater activity (Andrews-Hanna et al, 2007;Schmidt et al, 2021). The deposits accumulated in topographic lows associated with the ancient low-relief/wide flat floored channel network, which could have provided hydrological corridors within the regional groundwater flow (Andrews-Hanna et al, 2010, 2007, or mafic enrichment in a desert pavement-like process (Irwin III et al, 2018;Rogers et al, 2018).…”

Rivers and Lakes in Western Arabia Terra: The Fluvial Catchment of the ExoMars 2022 Rover Landing Site

“…However, a volcanic interpretation is not necessarily appropriate (e.g. ; Edgett, 2005; Edgett & Sarkar, 2021) and in this case is inconsistent with the distribution and variety of contexts seen for IDD seen in the Oxia Basin catchment: none of the 109 examples within the study area show evidence for volcanic architecture that might be expected from Amazonian volcanism (Brož et al., 2017).…”

“…We propose that these dark deposits, when located in crater floors and associated with the channel network, represent allochthonous mafic volcaniclastic/aeolian materials (Edgett & Sarkar, 2021) that have been cemented by highstand of groundwater activity (Andrews‐Hanna et al., 2007; Schmidt et al., 2021). The deposits accumulated in topographic lows associated with the ancient low‐relief/wide flat floored channel network, which could have provided hydrological corridors within the regional groundwater flow (Andrews‐Hanna et al., 2007, 2010), or mafic enrichment in a desert pavement‐like process (Irwin et al., 2018; Rogers et al., 2018).…”

The Circum‐Isidis Capping Unit: An Extensive Regional Ashfall Deposit Exposed in Jezero Crater

“…Additionally, the Capping Unit is a coherent layer of rock that exclusively superposes and thinly drapes (with thicknesses not exceeding 10 of meters) the Noachian Basement and Olivine-Rich Units (Kremer et al, 2019;Mustard et al, 2009), precluding an origin as an igneous intrusion. Although the Capping Unit is darktoned, mafic, and crater-retaining, these characteristics in a rock formation do not exclude a clastic origin as discussed in Edgett and Sarkar (2021). Work thus far has been ambiguous regarding whether the Capping Unit is a lava derived from Syrtis Major or vents (Bishop et al, 2013;Bramble et al, 2017;Tornabene et al, 2008), a product of impact condensates (Cannon et al, 2017), an aeolian erg deposit, or a volcanic ashfall (Bramble et al, 2017;Cannon et al, 2017;Edwards & Ehlmann, 2015).…”