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From
Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
AAPG Annual Convention, Calgary, Alberta, Canada, June 19–22, 2005 Geomorphology of the Mars Northeast Holden Delta Abstract: Mars' NE Holden Delta contains six separate depositional
lobes that appear to have prograded ~17 km from their apex. Crosscutting
distributary relationships and compensated lobe deposition are visible
in images from the Mars Global Surveyor Orbiter Camera. Sinuosity, radius
of channel curvature, meander-bend width, and channel-width parameters
are examined for several lobe systems. Channel sinuosities of 1.2–1.8
define low- to moderate-sinuosity channel systems typical of subaerial
systems transporting bed- or mixed-grain-size loads. Some convergence
between age and sinuosity occurs; however, some younger systems show specific
reaches of increased sinuosity associated with abutment against resistant,
older-lobe beds. This effect of older deposits on channel morphology suggests
that these older lobes were fairly well indurated before deposition of
the youngest progradational lobes. 86% of distributaries in Mars deltas
are 100–240m wide. This number compares with 62% and 44% in Atchafalaya
and Wax Lake Deltas of Louisiana, respectively, although the Mars delta
is ~14 times larger than these deltas. Such small distributaries may indicate
lower average, shorter duration flows or coarser sediment volumes in Mars
distributaries than those typical of Gulf Coast systems. However, the
volume of material in the Mars deposit suggests long periods of active
sediment deposition. Likewise, sinuosity indices, meander-bend migration,
and ridge-and-swale point-bar topography development all suggest periods
of stable discharge on the delta surface. Future comparative research
in the architectural morphometrics of alluvial fans versus deltas will
help differentiate these features and bear significantly on scientific
communities' understanding of fluid behavior and distribution on other
planets. |