The origin and timing of fluvial activity at Eberswalde crater, Mars

Research areas:
The fan deposit in Eberswalde crater has been interpreted as strong
evidence for sustained liquid water on early Mars with a paleolake
formed during the Noachian period (>3.7 Gy). This location became a key
region for understanding the Mars paleo-environment. Eberswalde crater
is located 50 km north of the rim of the 150 km diameter crater Holden.
Stratigraphic relationships and chronology obtained using recent Mars
Express High Resolution Stereo Camera and Mars Reconnaissance Orbiter
Context Camera images show that Eberswalde fluvial activity crosscuts
Holden ejecta and thus postdates Holden crater, whose formation age is
estimated from crater counts as Late Hesperian (similar to 3.5 Gy,
depending on models). Fluvial modeling shows that short term activity
(over several years to hundreds of years) involving dense flows (with
sediment:water ratio between 0.01 and 0.3) may be as good an explanation
of the fluvial landforms as dilute flow over longer durations. Modeling
of the thermal effect of the Holden impact in the Eberswalde watershed
is used to evaluate its potential role in aqueous activity. The relative
timing of the Holden impact and Eberswalde's fan is a constraint for
future studies about the origin of these landforms. Holden ejecta form a
weak and porous substrate, which may be easy to erode by fluvial
incision. In a cold climate scenario, impact heating could have produced
runoff by melting snow or ground ice. Any attempt to model fluvial
activity at Eberswalde should take into account that it may have formed
as late as in the Late Hesperian, after the great majority of valley
network formation and aqueous mineralization on Mars. This suggests that
hypotheses for fan formation at Eberswalde by transient and/or localized
processes (i.e. impact, volcanism, unusual orbital forcing) should be
considered on a par with globally warmer climate. (C) 2012 Elsevier Inc.
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