Abstract
It has been proposed that ~3.4 billion years ago an ocean fed by enormous catastrophic floods covered most of the Martian northern lowlands. However, a persistent problem with this hypothesis is the lack of definitive paleoshoreline features. Here, based on geomorphic and thermal image mapping in the circum-Chryse and northwestern Arabia Terra regions of the northern plains, in combination with numerical analyses, we show evidence for two enormous tsunami events possibly triggered by bolide impacts, resulting in craters ~30 km in diameter and occurring perhaps a few million years apart. The tsunamis produced widespread littoral landforms, including run-up water-ice-rich and bouldery lobes, which extended tens to hundreds of kilometers over gently sloping plains and boundary cratered highlands, as well as backwash channels where wave retreat occurred on highland-boundary surfaces. The ice-rich lobes formed in association with the younger tsunami, showing that their emplacement took place following a transition into a colder global climatic regime that occurred after the older tsunami event. We conclude that, on early Mars, tsunamis played a major role in generating and resurfacing coastal terrains.
Highlights
In THEMIS night-time infrared images, the upper reaches of the older deposit that were emplaced along Arabia and Tempe Terrae (member lHl1 (Fig. 1A)) appear thermally bright[15] and abruptly transition upland-ward into thermally dark[15] surfaces (e.g., Figs 2A,B and 3B)
The lobes of member lHl1 include boulders several meters in diameter (Figs 2C and 3E, Fig. S3D), and those of member lHl2 appear to be mostly composed of water-ice[6,12,13,14]
We propose that the two unit Late Hesperian lowland unit (lHl) members represent deposits emplaced by highly energetic, sediment-rich tsunami waves that originated from a Late Hesperian paleo-ocean
Summary
® Mapping in this investigation was performed using Esri’s ArcGIS 10.3 software Embayment and overlapping relationships leading to the recognition of the outer margins of members lHl1 and lHl2 involved an integrated analysis of (1) thermal infrared image data (i.e., Mars Odyssey Thermal Emission Imaging System (THEMIS) night-time and day-time infrared image mosaics (100 m per pixel)), (2) visible image data (i.e., Mars Reconnaissance Orbiter Context Camera (CTX, (5.15–5.91 m/pixel)) images, and (3) Mars Global Surveyor Mars Orbital Laser Altimeter (MOLA, ~460 m/pixel horizontal and ~1 m vertical resolution) digital elevation models. Contacts are buried underneath ejecta blanket materials or are locally resurfaced; we mapped these sections as uncertain contacts (Fig. 2A)
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