Hydrology and Sedimentology of a Series of Dam-Breach Paleolakes at Idaeus Fossae, Mars

Abstract:

We report on the identification and geological study of a nearly 300-km-long valley system located westward of Idaeus Fossae, in Tempe Terra, Mars. The valley apparently originates from a subsided area surrounding the ejecta of a relatively fresh crater and after about 25 km from its source area enters a series of dam-breach paleolakes. The lake chain consists of six open basins (with associated fan-shaped sedimentary deposits) and covers an area of about 2500 sq. km over a E-W stretch of about 100 km. The latter lakes are interconnected and were likely coeval and drain eastward into a main 20-km-diameter crater-lake forming a complex and multilobate deltaic deposit whose front lies at about 1800-1820 m below the martian datum. The deltaic deposit is about 8-km-long and morphologically resembles the Jezero delta, showing a well-developed distributary pattern with evidence of channel switching on the delta plain. The floor of the crater-lake is not incised by the main valley, however a breach area is present along the eastern crater rim and consists of two spillover channels at about the same elevation of the crater inlet (-1820 m). These latter channels connect the crater lake to the eastward portion of the valley continuing towards Idaeus Fossae with a more than 180-km-long complex pattern of anabranching channels . We used high-resolution imagery and topography (HRSC, and CTX and HiRISE stereo pairs) to derive a geological-geomorphological map of the area and to understand its evolution. The extension and morphology of the observed fluvio-lacustrine features suggest relatively long-term (>10³ yrs) formation timescales as also supported by the presence of the main fan delta in the central open basin. The overall water source for the 300-km-long fluvial system is unclear, though the occurrence of many rampart craters and the relationships between their ejecta and the channels suggest that subsurface volatiles might have also played an important role.