Chronology of deposition and alteration in the Mawrth Vallis region, Mars

Research areas:
Year:
2012
Authors:
Journal:
PLANETARY AND SPACE SCIENCE
Volume:
72
Number:
1, SI
Pages:
31-43
Month:
November
ISSN:
0032-0633
Abstract:
The Mawrth Vallis area displays some of the largest phyllosilicate-rich
outcrops of Mars, on Noachian highlands. The Mawrth Vallis region is
located just at the dichotomy boundary between the Noachian highlands
and the younger, northern lowlands. A large, thick, layered clay-rich
unit is present throughout the inter-crater plateaus. Clay-rich layers
have also been identified in parts of the Mawrth Vallis and Oyama crater
floors. The age of the alteration and its relationships with other
processes such as fluvial activity is fundamental for estimating the
timing of aqueous activity and habitability in this region, and on Mars.
We have investigated the relative stratigraphy and ages of the regional
plateau, of key surfaces of the inter-crater plateau, of Oyama crater's
floor and of Chryse Planitia deposits in Mawrth Vallis' mouth to
constrain the age of the clay unit and its alteration. According to the
cratering model results, the main layered unit may have started forming
prior to similar to 4.0 Ga ago, was largely deposited by similar to 3.9
Ga ago, and suffered erosion and redeposition up to similar to 3.8 Ga
ago, as indicated by the latest age of the deposits on the floor of
Oyama crater. Surface aqueous alteration stopped no later than 3.7-3.6
Ga ago, corresponding to the age of the dark, non-altered material
capping the region, and of the dark deposits in Mawrth Vallis' mouth.
This work provides useful boundaries for constraining the time period of
surface or shallow sub-surface water activity in this region. This
preserved window into early phases of aqueous activity on Mars gives us
a unique opportunity to study an aqueous environment of exobiological
interest in the early solar system. (C) 2012 Elsevier Ltd. All rights
reserved.