HR: 0800h
AN: P31C-0545    [Abstracts]
TI: Gully formation in terrestrial simple craters: Meteor Crater, USA and Lonar Crater, India
AU: * Kumar, P
EM: senthilngri@yahoo.com
AF: National Geophysical Research Institute, Post Bag 724, Hyderabad, IND 500 007,
AU: * Kumar, P
EM: senthilngri@yahoo.com
AF: Brown University, Dept of Geological Sciences, Providence, RI 02912, United States
AU: Head, J W
EM: james_head@brown.edu
AF: Brown University, Dept of Geological Sciences, Providence, RI 02912, United States
AU: Kring, D A
AF: Lunar and Planetary Institute, 3600 Bay Area Blvd, Houston, TX 77058, United States
AB: Geomorphic features such as gullies, valley networks, and channels on Mars have been used as a proxy to understand the climate and landscape evolution of Mars. Terrestrial analogues provide significant insight as to how the various exogenic and endogenic processes might contribute to the evolution of these martian landscapes. We describe here a terrestrial example from Meteor Crater, which shows a spectacular development of gullies throughout the inner wall in response to rainwater precipitation, snow melting and groundwater discharge. As liquid water has been envisaged as one of the important agents of landscape sculpturing, Meteor Crater remains a useful landmark, where planetary geologists can learn some lessons. We also show here how the lithology and structural framework of this crater controls the gully distribution. Like many martian impact craters, it was emplaced in layered sedimentary rocks with an exceptionally well-developed centripetal drainage pattern consisting of individual alcoves, channels and fans. Some of the gullies originate from the rim crest and others from the middle crater wall, where a lithologic transition occurs. Deeply incised alcoves are well-developed on the soft sandstones of the Coconino Formation exposed on the middle crater wall, beneath overlying dolomite. In general, the gully locations are along crater wall radial fractures and faults, which are favorable locales of groundwater flow and discharge; these structural discontinuities are also the locales where the surface runoff from rain precipitation and snow melting can preferentially flow, causing degradation. Like martian craters, channels are well developed on the talus deposits and alluvial fans on the periphery of the crater floor. In addition, lake sediments on the crater floor provide significant evidence of a past pluvial climate, when groundwater seeped from springs on the crater wall. Caves exposed on the lower crater level may point to percolation of surface runoff and selective discharge through fractures on the crater wall. Similar relationships are seen at Lonar Crater, India. Although these hydrological processes continue at Meteor Crater today, conditions at the crater are much more arid than they were soon after impact, reflecting a climatic shift similar in direction to that inferred for Mars.
DE: 5419 Hydrology and fluvial processes
DE: 6022 Impact phenomena (5420, 8136)
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting