SYN-TECTONIC SEDIMENTATION RECORDED BY COUPLED BASIN AND ALLUVIAL FAN FORMATION IN VALLES MARINERIS, MARS (Invited Presentation)

Alluvial fans provide a record for tectonic and climate regimes in extensional basins on Earth. On Mars, alluvial fans mostly occur on surfaces considered Hesperian and Amazonian (< 3.7 Ga) in age, eras regarded as mostly cold and dry, and are typically identified in impact craters, rather than basins which subsided. Here, we used high-resolution orbital HiRISE and CTX datasets to identify and characterize distinct sedimentary fans in Coprates Chasma, Valles Marineris, which may have formed in an actively subsiding basin. The channelized nature of the fan surfaces and presence of embedded impact craters are consistent with alluvial fans which accumulated intermittently. The alluvial fans occur at discrete elevations along the canyon wall, suggesting separation by repeat normal faulting. This configuration indicates that for the first time syn-tectonic sedimentation occurred during basin development, similar to extensional rift systems on Earth, despite their distinct tectonic mechanisms. Coprates Chasma is an underfilled basin, suggesting that basin subsidence was outpacing erosion, and consistent with a climate was arid. The presence of widespread faulted alluvial fans in Valles Marineris suggests the syn-tectonic sedimentation at Coprates Chasma is representative of regional processes. Our results demonstrate that fluvial processes occurred during and may be linked to the opening and modification of Valles Marineris.