77-4 Sedimentology and Diagenesis of Curiosity’s traverse though the Boxwork-Hosting Altadena Member, Gale Crater, Mars

Session: Boxwork and Fracture Halos: Changes in mineralogy and erosion resistance around fracture features on Earth, Mars, and across the Solar System

Presenting Author:

Christina Seeger

Authors:

Seeger, Christina¹, Siebach, Kirsten Leigh², Mondro, Claire A.³, O’Connell-Cooper, Catherine⁴, Schwenzer, Susanne⁵, Gasda, Patrick⁶, Dietrich, William Eric⁷, Banham, Steven⁸, Caravaca, Gwenael⁹, Scuderi, Louis¹⁰

(1) Earth, Environmental, and Planetary Sciences, Rice University, Houston, TX, USA, (2) Rice University, Houston, TX, , (3) Planetary Science Institute, USA, (4) University of New Brunswick, Fredericton, NB, Canada, (5) The Open University, United Kingdom, (6) Los Alamos National Laboratory, Los Alamos, NM, USA, (7) University of California, Berkeley, CA, USA, (8) Imperial College London, United Kingdom, (9) University of Toulouse, France, (10) University of New Mexico, NM, USA,

Abstract:

From May 2025 through March 2026 (Sols 4534-4844 (Martian days)), the Mars Science Laboratory Curiosity rover traversed through a geologic unit distinct from the surrounding aeolian Chenapau member: the Altadena member of the Mirador formation.  This unit is exposed vertically over ~60 meters on the slopes of Aeolis Mons (informally, Mount Sharp), the sedimentary mound that rises ~5km above the floor of Gale crater. From orbit, the Altadena member hosts a network of decameter-scale raised ridges with ~0.5-2m deep hollows between them, which has been interpreted to be the result of diagenetic fluids flowing through and cementing grains within a fracture network (see Siebach et al., this meeting).

In situ rover observations of the stratigraphy and diagenetic fabrics within this unit—including meter- and millimeter-scale imaging, plus chemistry and mineralogy data—provide key insights into the depositional and subsequent groundwater processes.  We present evidence for primary deposition in a lacustrine environment, based on the observed host rock facies and relationships at stratigraphic contacts. Bedrock throughout the Altadena member is characterized by friable, fine-grained rock (likely mudstone, though grains below the scale of very fine sand are unresolvable with rover instrumentation) with faint mm-scale planar lamination.  These deposits are occasionally punctuated by trough cross-stratified sandstone lenses interpreted to be fluvial or lake margin deposits.  Curiosity also investigated stratigraphic contacts between the Altadena and Chenapau members both at the eastern and southern extent of the unit. Preliminary interpretations of a lateral pinch-out to the east and underlying relationship to the south further support the lake margin interpretation 

Rover observations support orbital formation hypotheses and provide a more complex view of the diagenetic fabrics contributing to the Boxwork terrain.  Ridges are characterized by a blocky laminated mudstone morphology with abundant veins with white fill material.  Sparse mm- to cm- scale nodules near ridge centers increase in abundance towards ridge walls, which slope downwards into hollow floors. Where sparse outcrop is visible amidst sand cover in hollow bottoms, the rock tends to be heavily overprinted with nodules forming a knobby, flakey, or dendritic texture.  This evidence for sustained groundwater interaction, coupled with evidence for surface water during lake deposition, has implications for a water-stable Martian climate higher in the stratigraphy—and therefore later in time—than previously hypothesized.

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