Paucity of candidate coastal constructional landforms along proposed shorelines on Mars: Implications for a northern lowlands-filling ocean

• Published in: Icarus (New York, N.Y. 1962) N.Y. 1962), 2006-11, Vol.185 (1), p.171-196
• Main Authors: Ghatan, Gil J., Zimbelman, James R.
• Format: Article
• Language: English
• Subjects: Astronomy; climate; Earth, ocean, space; Exact sciences and technology; Mars; Solar system; surface
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2006.06.007

The case for an ocean having once occupied the northern lowlands of Mars has largely been based indirectly on the debouching of the outflow channels into the lowlands, and directly on erosional features along the margins of the lowlands interpreted to be the result of wave action. Two global shorelines were previously mapped from albedo variation, embayment relationships, and scarps interpreted as coastal cliffs. However, not since the early, Viking-based studies, has there been a focused assessment of the presence or absence of coastal constructional landforms such as barrier ridges and spits, located on or near the mapped “shorelines.” Such constructional landforms are typically found in association with coastal erosional features on Earth, and therefore warrant a detailed search for their presence on Mars. All presently available THEMIS VIS and MOC NA images located on or near either of the two “shorelines,” within the Chryse Planitia/Arabia Terra region (10° to 44° N; 300° to 0° E) and the Isidis Planitia region (0° to 30° N; 70° to 105° E), were examined in search of any features that could reasonably be considered candidate coastal ridges. Additionally, raw MOLA profiles were used in conjunction with a technique developed from Differential Global Positioning System profiles across terrestrial paleo-shorelines, to search for coastal ridges throughout these same regions. Out of 447 THEMIS VIS and 735 MOC NA images examined, only four candidates are observed that are plausibly interpreted as coastal ridges; no candidate coastal ridges are observed in the MOLA profiles. This overwhelming paucity of candidate features suggests one of five possible scenarios in terms of the existence of standing bodies of water within the martian lowlands: (1) No ocean existed up to the level of either of the previously mapped “shorelines”; (2) An ocean existed, however wave action, the primary agent responsible for construction of coastal landforms, was minimal to non-existent; (3) An ocean existed, but sediment input was not significant enough to form coastal deposits; (4) An ocean existed, but readily froze, and over time sublimated; and lastly (5) An ocean existed and coastal landforms were constructed, but in the intervening time since their formation they have nearly all been eroded away.