LAKE-BASIN-TYPE EVOLUTION AND SEQUENCE STRATIGRAPHY APPLIED TO THE STRATA IN AEOLIS MONS, MARS

Foundational principles and defining criteria of both sequence stratigraphy and lake basin type (LBT) analysis are essentially geometric, without reference to mechanism of formation or the value of g. Hence both approaches should be applicable to strata on other planets. The similarity of fractal dimensions of lake-basin area, volume, and mean depth on Earth and Mars provide support for this hypothesis.

The succession of stratal geometries and spectrally determined rock composition on Aeolis Mons seen from orbit suggest a LBT evolution from Fluvial to Overfilled to Balanced filled to Underfilled to Aeolian—a pattern widely seen on Earth. The stratigraphic section described so far from ground-based observations includes a basal fluvial conglomerate (Hottah) overlain by unidirectional-flow-dominated sand-prone fluvial-deltaic deposits and mudstone that accumulated under relatively fresh (neutral pH) waters (Kimberly to Murray Fms)—supporting the Fluvial to Overfilled LBT evolution. Farther up Aeolis Mons the clay+sulfate and sulfate-bearing strata can be interpreted as Balanced filled to Underfilled, and the overlying ‘duststone’ as Aeolian LBT phases. Such a LBT evolution in a closed crater lake (whose overall potential accommodation tends to decreases with time) suggests a complex initial topography with early lake phases occupying only part of the overall crater.

Detailed stratigraphic sections reveal 29 parasequences and 3 depositional sequences that can be interpreted as part of a long-term retrogradational stacking. Parasequences in the Bradbury and Mount Sharp Groups comprise mudstone to sandstone in progradationally stacked bedsets 1.2 to 7.8 m thick.

Based on parasequence stacking patterns and bounding surface character, the Bradbury Group appears to contain one partial depositional sequence (Yellowknife Bay Fm) at base and one complete depositional sequence overlying. The Murray Fm (along with the uppermost sandstone bedset of the Bradbury Group) appears to be most of a third depositional sequence. Maximum flooding surfaces are interpreted to be in the middle of the Kimberly Fm and atop the Chinle outcrop of the Murray Fm.

It appears that sequence stratigraphy and LBT analysis can provide useful context for constructing detailed interpretations of the record of lake processes on Mars.