FLUVIAL AND LACUSTRINE PROCESSES IN MERIDIANI PLANUM AND THE ORIGIN OF THE

Introduction: The prime MER landing site in Meridiani Planum is located on layered materials, including hematite, whose origin as lacustrine or aeolian sediments, or volcanic materials is uncertain. Our detailed mapping of the region provides important constraints on the history of the region. Our mapping of the location of fluvial and lacustrine land forms in the region relative to the layered deposits provides new evidence of a long history of erosion and deposition as has long been noted [1]. In addition, our detailed mapping of the southern boundary of the hematite deposit strongly supports an association between longlived fluvial channels and lacustrine basins and the strongest hematite signatures. This evidence supports an origin of the hematite deposits by interaction with water under ambient conditions in contrast to suggestions of hydrothermal processes due to volcanic or impact crater processes. An important part of the story is the evidence for the localization of the layered deposits due to topographic control induce by the presence of a large early basin we have identified that extends to the north-east of the landing site. Distribution of current channel networks, drainages, and basins Channel systems leading to the southern boundary of the hematite-rich surface deposit can be observed originating from a large highlands region that extends south-eastwards from the hematite regions for hundreds of kilometers (Fig. 1, inset). These channels appear to terminate near the boundary with the hematite deposit. Based on the Viking data, Edgett and Parker [1] identified this boundary as the edge of an ocean or large body of water. However, careful examination of the high resolution MOC images and the MOLA topography clearly shows that these highly visible channels flowed into a system of paleo-lakes and channels that currently appear to drain westward into the unnamed 150 km diameter crater, and further east towards Iani Chaos. A possible extension of the drainage area to the south of Schiaparelli basin includes Evros Vallis. Because the topography is so flat in the area between the two drainages, the topographic gradient cannot be easily determined, and may have varied in direction at different times in the past. The total area of the drainage region is impressive, 580,000 km 2 , about the size of the state of Texas. The area for the northwestern portion of the drainage area closest to the hematite area is 200,000 km 2 , about the size of Kansas. The area for the Evros Vallis portion is 380,000 km 2 . There is also a large system of highland valleys (not mapped in this study) that fed into the lowland region east of the hematite area. If flooded, this lowland would currently drain to the north.