eprintid: 1468955 rev_number: 43 eprint_status: archive userid: 608 dir: disk0/01/46/89/55 datestamp: 2015-06-03 08:46:06 lastmod: 2021-11-07 23:46:45 status_changed: 2015-06-03 08:46:06 type: article metadata_visibility: show item_issues_count: 0 creators_name: Harrison, SK creators_name: Balme, MR creators_name: Hagermann, A creators_name: Murray, JB creators_name: Muller, J-P creators_name: Wilson, A title: A branching, positive relief network in the middle member of the Medusae Fossae Formation, equatorial Mars—Evidence for sapping? ispublished: pub divisions: UCL divisions: B04 divisions: C06 divisions: F63 note: This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. abstract: The Medusae Fossae Formation (MFF) is a geological formation comprising three geological units (members) spread across five principal lobes. It dominates a quarter of the longitudinal extent of the equatorial region of Mars. Positive relief features referred to as ‘sinuous ridges’ (commonly interpreted as inverted paleoflow channel or valley fills) have been observed in the lowest member of the western MFF, but have not been identified within the central and eastern portions of the formation, in the middle and upper members. This paper presents the identification and analysis of a branching, positive relief system which occurs in the central lobe of the MFF in what appears to be an exposure of the middle member. A simple geomorphological map of the system is presented, from which we have adopted the working hypothesis that this is an inverted fill of a branching fluvial channel or valley system. A suite of morphological and topographic evidence supporting this hypothesis is presented, including analysis of the network using a ∼15 m/pixel digital terrain model derived from a Context Imager (CTX) stereo image pair. The evidence supporting this hypothesis includes: (1) the local slope and topography of the upper surface of the network are consistent with a contributory network; (2) the braided, fan-like form at the termination of the branching network is consistent in morphology with it being a depositional fan at the end of a fluvial system; (3) the terminal fan and surrounding deposits show layering and polygonization; and (4) there is strong association between the lower order branches and amphitheater shaped scarps in the depression walls. We evaluate the possible origins of this fluvial system and suggest that seepage sapping is the most probable. Two possible models for the evolution of the network and related features are presented; both require melt of ice within the MFF to form liquid water. We conclude that at least some portions of the Medusae Fossae Formation, if not the entire formation, were once volatile-rich. Finally, we note that our observations do not rule out the case that this network formed before MFF emplacement, and has since been exhumed. However, this conclusion would suggest that much of the surrounding terrain, currently mapped as middle-member MFF, is not in fact MFF material at all. date: 2013-09 official_url: http://dx.doi.org/10.1016/j.pss.2013.06.004 vfaculties: VMPS oa_status: green full_text_type: pub language: eng primo: open primo_central: open_green verified: verified_manual elements_source: crossref elements_id: 1035724 doi: 10.1016/j.pss.2013.06.004 lyricists_name: Muller, Jan-Peter lyricists_id: JPALM41 full_text_status: public publication: Planetary and Space Science volume: 85 pagerange: 142 - 163 issn: 0032-0633 citation: Harrison, SK; Balme, MR; Hagermann, A; Murray, JB; Muller, J-P; Wilson, A; (2013) A branching, positive relief network in the middle member of the Medusae Fossae Formation, equatorial Mars—Evidence for sapping? Planetary and Space Science , 85 142 - 163. 10.1016/j.pss.2013.06.004 <https://doi.org/10.1016/j.pss.2013.06.004>. Green open access document_url: https://discovery.ucl.ac.uk/id/eprint/1468955/1/1-s2.0-S0032063313001451-main.pdf