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

Kenneth S Edgett,Ranjan Sarkar

doi:10.3390/rs13214296

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.

Highlights

Sedimentary rocks are records of past surface and subsurface environments that capture information about the nature and actions of fluids and the histories of associated tectonic, magmatic, and impact events
The foundational steps in the study of the sedimentary rock record of other worlds are to use images acquired by instruments onboard flyby, orbiting, airborne, ascending, or descending platforms to: 1. Learn to recognize sedimentary rock occurrences; and 2
Most of the tens of thousands of satellite images examined were acquired by the MGS MOC-NA (1.4–12 m/pixel) [50,89], Mars Reconnaissance Orbiter (MRO) CTX (~6 m/pixel [90]), and MRO High Resolution Imaging Science Experiment (HiRISE; 25–60 cm/pixel [91]) cameras

Summary

Introduction

Sedimentary rocks are records of past surface and subsurface (diagenetic) environments that capture information about the nature and actions of fluids and the histories of associated tectonic, magmatic, and impact events. These steps can lead to detailed studies using existing data, e.g., [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32], or to target new data collections, or to develop new spacecraft and instrumentation, to obtain additional observations This contribution is about learning to recognize sedimentary rock occurrences—for Mars—largely using visible wavelength, reflected light images, to identify sub-meter- to decameter-scale sedimentary structures and other signs that a given geological material, exposed at the planet’s surface, is sedimentary rock.

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Conclusion