Post by Dr. Gino Erkeling, Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Germany
The hypothesis of ancient Martian standing bodies of water, which might have occupied the lowlands of the northern hemisphere and which might have existed in local- to regional-scale paleolakes once in Martian history, is one of the most important subjects of ongoing discussion in Mars research (e.g., Parker et al., 1989, 1993; Head et al., 1999; Cabrol and Grin, 1999, 2001; Clifford and Parker, 2001; Kreslavsky and Head, 2002; Carr and Head, 2003; Ghatan and Zimbelman, 2006; Di Achille and Hynek, 2010; Mouginot et al., 2012). The case for large standing bodies of liquid water, including lakes, seas and oceans, is attributed to a complex hydrologic cycle that may have once existed on Mars in the Noachian (>3.7 Ga) and perhaps also in the Hesperian (>3.1 Ga).
The existence of oceans, seas or lakes is supported by a large variety of morphologic landforms, including ridges, wave-cut platforms and coastal cliffs (e.g., Parker et al., 1993; Head et al., 1999; Webb, 2004; Ghatan and Zimbelman, 2006; Erkeling et al, 2012) and associated delta deposits (e.g., Hauber et al., 2009; Di Achille and Hynek, 2010). Some of these morphologies appear along two global “paleoshorelines” that represent the two most continuous contacts on Mars and possibly reflect different water levels, i.e., the Arabia “shoreline” and the Deuteronilus “shoreline” (e.g., Parker et al., 1989, 1993; Head et al., 1999; Clifford and Parker, 2001; Carr and Head, 2003; Ghatan and Zimbelman, 2006).
A series of morphologic landforms indicative of fluvial and lacustrine environments in the Libya Montes and seas in Isidis Planitia have been identified at three different elevation levels along the boundary between southern Isidis Planitia and the Libya Montes highlands (Image 1 a). In particular, (1) local occurrences of valleys and associated alluvial fans, a delta and an open-basin paleolake between -2500 and -2800 meters (Image 1b), (2) a series of possible coastal cliffs of the Arabia shoreline at -3600 and -3700 meters (Image 1c), and (3) the Deuteronilus shoreline contact as an onlap morphology, i.e. the Isidis interior plains are superposed onto the Isidis exterior plains (Image 1d).
The geologic setting and chronostratigraphic sequence, that indicate Late Noachian landforms at the Libya / Isidis contact, Hesperian landforms at the Arabia shoreline and Early Amazonian landforms at the Deuteronilus contact, are consistent with the proposed Hesperian climate change from warm and wet to cold and dry conditions.