Geomorphology of the Mars Northeast Holden Delta

Lesli Wood
The University of Texas at Austin, Austin, TX

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.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005