2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 290-4
Presentation Time: 9:00 AM


PIATEK, Jennifer L.1, TORNABENE, Livio2 and OSINSKI, Gordon R.2, (1)Department of Geological Sciences, Central Connecticut State University, 506 Copernicus Hall, 1615 Stanley St, New Britain, CT 06050, (2)Centre for Planetary Science & Exploration, University of Western Ontario, Department of Earth Sciences, 1151 Richmond Street, London, ON N6A 5B7, Canada

The characteristics of pristine impact crater ejecta are not well understood, but stand as an important baseline for better understanding impact processes. It is generally accepted that on airless bodies, most ejecta blanket material is emplaced radially by ballistic transport. This process, however, does not account for all ejecta facies, such as melt-bearing deposits that occur atop ejecta. On Mars, craters often exhibit "fluidized" or "layered" ejecta (possibly due to interactions with sub-surface volatiles and/or the atmosphere) in addition to ballistic ejecta facies. Varying degrees of post-impact modification further complicates the identification of the characteristics of pristine Martian ejecta.

The youngest craters on a planetary surface are often identified by the presence of easily modified deposits such as crater rays and impact melt deposits, in addition to a lack of overprinting craters and a high depth/diameter ratio. Young Martian craters appear to preserve a thermophysical contrast between crater ejecta and the underlying surface, which can manifest as rays visible in infrared data that are not apparent in visible images due to a lack of albedo contrast. An examination of both visible and infrared datasets, however, suggests that crater age and preservation of ejecta are not necessarily correlated. Decoupling these criteria suggests that Martian crater deposits may fall into four general categories:

  1. "pristine" ejecta / young craters (with preserved rays and/or melt deposits and an ejecta blanket that exhibits a thermophysical contrast with the underlying surface)
  2. "modified" ejecta / young craters (craters that appear young but lack thermophysical contrasts)
  3. "well-preserved" ejecta / older craters (lacking preserved melt deposits but still presenting a thermophysically contrasted ejecta blanket)
  4. "degraded" ejecta / older craters (where both crater and ejecta are visibly modified).

An examination of the typical visible morphology and thermophysical character of craters in each of these classes should serve as a first step to identifying the characteristics associated with pristine ejecta and those affected by later modification.