Shaler: insitu analysis of a fluvial sedimentary deposit on Mars

Research areas:
  • Lauren A. Edgar
  • Sanjeev Gupta
  • David M. Rubin
  • Kevin W. Lewis
  • Gary A. Kocurek
  • Ryan B. Anderson
  • James F. Bell
  • Gilles Dromart
  • Kenneth S. Edgett
  • John P. Grotzinger
  • Craig Hardgrove
  • Linda C. Kah
  • Richard Leveille
  • Michael C. Malin
  • Nicolas Mangold
  • Ralph E. Milliken
  • Michelle Minitti
  • Marisa Palucis
  • Melissa Rice
  • Scott K. Rowland
  • Juergen Schieber
  • Kathryn M. Stack
  • Dawn Y. Sumner
  • Roger C. Wiens
  • Rebecca M. E. Williams
  • Amy J. Williams
This paper characterizes the detailed sedimentology of a fluvial
sandbody on Mars for the first time and interprets its depositional
processes and palaeoenvironmental setting. Despite numerous orbital
observations of fluvial landforms on the surface of Mars, ground-based
characterization of the sedimentology of such fluvial deposits has not
previously been possible. Results from the NASA Mars Science Laboratory
Curiosity rover provide an opportunity to reconstruct at fine scale the
sedimentary architecture and palaeomorphology of a fluvial environment
on Mars. This work describes the grain size, texture and sedimentary
facies of the Shaler outcrop, reconstructs the bedding architecture, and
analyses cross-stratification to determine palaeocurrents. On the basis
of bedset geometry and inclination, grain-size distribution and bedform
migration direction, this study concludes that the Shaler outcrop
probably records the accretion of a fluvial barform. The majority of the
outcrop consists of large-scale trough cross-bedding of coarse sand and
granules. Palaeocurrent analyses and bedform reconstruction indicate
that the beds were deposited by bedforms that migrated towards the
north-east, across the surface of a bar that migrated south-east.
Stacked cosets of dune cross-bedding suggest aggradation of multiple
bedforms, which provides evidence for short periods of sustained flow
during Shaler deposition. However, local evidence for aeolian reworking
and the presence of potential desiccation cracks within the outcrop
suggest that fluvial deposition may have been intermittent. The
uppermost strata at Shaler are distinct in terms of texture and
chemistry and are inferred to record deposition from a different
sediment dispersal system with a contrasting provenance. The outcrop as
a whole is a testament to the availability of liquid water on the
surface of Mars in its early history.