Geological and Stratigraphic Relationships between Slump Deposits and
Stacked Delta Deposits in the Melas Chasma Rift Margin, Valles Marineris
Abstract
In order to assess the sedimentological and stratigraphic history of the
Melas Chasma rift basin, Mars, and investigate the possibility of past
bodies of water, we have mapped Hesperian stacked sedimentary deposits
containing what appear to be 102 m scale topsets,
clinoforms, toesets and olistoliths located on the immediate hangingwall
of a normal fault, and correlated these with folded and slumped units on
the basin floor. The vertical extent of clinoforms suggest deposition in
bodies of water that were tens to hundreds of metres deep associated
with gravity-driven mass-movement of sediment to the basin floor. We
correlated the basin margin deposits with basin-floor deposits by
mapping unconformities, which define four depositional sequences. Using
the principles of sequence stratigraphy in rifts, developed for
terrestrial analogues in the Gulf of Corinth, Greece, we infer the
history of the Melas Chasma deposits. Results suggest that
water-high-stand delta deposits became stacked across unconformities in
a basin undergoing active hangingwall subsidence. Assuming slip-rates on
the basin-bounding normal fault similar to that found on other
terrestrial and Martian faults, we infer timescales of
~1.25 to 15 million years for the sedimentation and
water body. We discuss our findings in terms of a possible connection to
the putative paleo-ocean on the Martian northern hemisphere.