Curiosity’s Investigation of the Distinctive “Boxwork” Interval in Gale Crater, Mars

Session: Geomorphology and Surface Processes Across the Solar System

Presenting Author:

Kirsten Siebach

Authors:

Siebach, Kirsten Leigh¹, Seeger, Christina², Mondro, Claire A.³, Schwenzer, Susanne⁴, O'Connell-Cooper, Catherine⁵, Gasda, Patrick⁶, Thompson, Lucy Margaret⁷, Caravaca, Gwénaël⁸, Scuderi, Louis A.⁹, Yen, Albert S¹⁰

(1) Rice University, Earth, Environmental and Planetary Sciences, Houston, TX, USA, (2) California Institute of Technology, Pasadena, CA, USA, (3) California Institute of Technology, Pasadena, CA, USA, (4) The Open University, Milton Keynes, United Kingdom, (5) University of New Brunswick, New Brunswick, Canada, (6) Los Alamos National Laboratory, Los Alamos, NM, USA, (7) University of New Brunswick, New Brunswick, USA, (8) Université de Toulouse, Toulouse, France, (9) University of New Mexico, Corrales, NM, USA, (10) NASA, Jet Propulsion Laboratory, Pasadena, CA, USA,

Abstract:

The Mars Science Laboratory Curiosity rover is currently investigating a distinctive stratigraphic interval with meter-scale intersecting ridges in a boxwork pattern that is expressed at nearly the same elevation across 14 km of stratigraphy with about 100 m vertical relief. The orbital expression of the boxwork is striking, with ridges that extend up to ~5 meters across and 10-20-meter diameter hollows between ridges that are often filled with sediment. In the uppermost portions of the interval, where the boxwork are best defined, dark lines can be seen in the centers of the resistant ridges. This has led to the interpretation that these boxwork ridges were strengthened by groundwater alteration or fluid-deposited cements. The boxwork is hypothesized to have formed through: (1) deposition, (2) lithification, (3) fracturing of the host rock, which may be contemporaneous with (4) fluid flow through the fractures under sufficient pressure to cause the fluid to percolate into ~2-3 meters of rock on either side, creating a cementation or alteration zone around the fracture, and (5) preferential eolian erosion of weaker zones in the rock.

Curiosity’s traverse up Mount Sharp in Gale crater approached the easternmost edge of the mapped boxwork interval and crossed the contact from the Layered Sulfate unit (LSu) on sol 4534 (5/7/2025). The boxwork-containing rock has distinct texture and chemistry from the LSu: the bedrock is friable, weakly-laminated, fine-grained mudstone with relatively more Si and Al and less Mg and S. CheMin XRD at “Altadena” found phyllosilicates, which were largely absent from the surrounding LSu. The boxwork-containing interval may represent an unconformity-bound facies with the contact with LSu marking the vertical and potentially horizontal bounds. Further observations have shown that the boxwork-containing rock includes intervals of cross-bedded (likely fluvial) sandstone and some highly diagenetically overprinted nodular regions, which may or may not be associated with ridges. Ridges within the lower boxwork interval investigated to date are heavily fractured and shallow, without significant chemical differences, but images looking ahead to the upper portion of the boxwork interval show better definition. We plan to drill in the endmember ridge-forming material and a nearby hollow representing bedrock unaffected by the ridge-strengthening event to understand the fluid alteration interpreted to have generated the discrepancies in erosion-resistance within this interval.