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Unique chronostratigraphic marker in depositional fan stratigraphy on Mars: Evidence for ca. 1.25 Ma gully activity and surficial meltwater origin

¹ Department of Geological Sciences, Brown University, 324 Brook Street, Box 1846, Providence, Rhode Island 02906, USA

View larger version (89K): [in this window] [in a new window]   Figure 1. Eastern Promethei Terra crater wall gully system. Tiered alcoves contribute to eastern and western channels feeding the depositional fan complex. Distinct lobes provide evidence for multiple episodes of gully activity (HiRISE: PSP_002293_1450).

View larger version (155K): [in this window] [in a new window]   Figure 2. Sketch map of gully system depositional fan. The depositional fan is composed of six visible lobes. Lobe 1 is oldest visible lobe and retains dense population of secondary craters. Superposing uncratered lobes (2–4) postdate emplacement of secondary craters and require episodes of more recent gully activity (HiRISE: PSP_002293_1450).

View larger version (94K): [in this window] [in a new window]   Figure 3. Eastern Promethei Terra (35°25'S, 130°25'E). A: THEMIS (Thermal Emission Imaging System) nighttime thermal infrared images show a pattern of fresh rays emanating from the ~7-km-diameter inner crater. The crater containing fan deposits (Figs. 1 and 2) is highlighted with white arrow. B: Crater counts displayed on incremental size-frequency plot of smooth near-rim deposits of the inner crater yield a crater retention age of ca. 1.25 Ma, placing formation of this crater in a period of obliquity-controlled mantle accumulation and modification. C: Mars obliquity variations (Laskar et al., 2002) over the past 3 Ma, with periods of mantle accumulation and modification (dark gray) and desiccation and degradation (light gray) indicated. Low-amplitude line between 22° and 24° is the obliquity range of Earth (after Head et al., 2003).