Wave Ripples Formed In Ancient, Ice-free Lakes In Gale Crater, Mars
Symmetrical wave ripples identified with NASA’s Curiosity rover in ancient lake deposits at Gale crater provide a key paleoclimate constraint for early Mars: At the time of ripple formation, climate conditions must have supported ice-free liquid water on the surface of Mars.
These features are the most definitive examples of wave ripples on another planet. The ripples occur in two stratigraphic intervals within the orbitally defined Layered Sulfate Unit: a thin but laterally extensive unit at the base of the Amapari member of the Mirador formation, and a sandstone lens within the Contigo member of the Mirador formation.
In both locations, the ripples have an average wavelength of ~4.5 centimeters. Internal laminae and ripple morphology show an architecture common in wave-influenced environments where wind-generated surface gravity waves mobilize bottom sediment in oscillatory flows.
Their presence suggests formation in a shallow-water (<2 meters) setting that was open to the atmosphere, which requires atmospheric conditions that allow stable surface water.
Symmetric ripple marks (A) are observed within the AMB outcrop. Ripple crests are identified with yellow arrows (A) and are aligned near-vertical (white arrow) in successive ripple layers. Internal laminae can be traced continuously through the ripple troughs. In plan view (B), the ripple crests are linear with occasional tuning-fork bifurcation, oriented consistently NW/SE. The AMB ripple unit is laterally extensive, of consistent thickness, and is conformably overlain by a unit of planar laminae [(C): contact is covered here—dotted line is inferred contact]. The AMB ripple unit at the Amapari location is ~15 cm thick and is composed of five resistant beds containing symmetric ripple marks. Image credit: NASA/JPL-Caltech/MSSS.
The Prow is an 18-m-long, lenticular outcrop (A) composed of a lower unit of unidirectional cross-strata and an upper unit of flaser bedding (B) containing symmetric ripple marks [(C and D): ripple crests indicated by yellow arrows]. The vertical accumulation of ripple marks within the flaser bedding creates a complex patter of interwoven cross-lamination [as in (34), figure 8, ex. 9], preserving both symmetric ripple troughs and crests at various locations. High-resolution imaging by the MAHLI taken at 1 cm standoff from the outcrop (E) shows observable sand grains making up the ripple layers, draped by fine-grained material with no observable grains (grain size <180 μm, below the MAHLI limit of resolution). See fig. S4 for location context for (E). Image credit: NASA/JPL-Caltech/MSSS.
Wave ripples formed in ancient, ice-free lakes in Gale crater, Mars, Science Advances via PubMed (open access)
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