Rock Strata Inclination: Insights into the Paleo-Coastal Marine Environment at the Zhurong Landing Zone

Evidence from instruments in Mars orbit and from the Zhurong rover suggests that oceans may have existed in the northern plains of Mars. Sedimentary stratification is a key indicator for verifying the historical presence of oceans on the Martian surface. However, there is still disagreement about the formation mechanism of sedimentary stratification at the Zhurong rover landing site. In this study, three-dimensional point clouds are generated from images taken by the Zhurong rover's navigation stereo camera. These point clouds are used to perform quantitative measurements and statistical analyses of the cross-bedding angles in sediments in rocks, and these angles are then compared with sedimentary bedding angles from various terrestrial environments to infer the dynamic sedimentary processes in the Zhurong landing area. The dip angles of the rocks at the Zhurong landing site on Mars range from 18.5° to 51.5°, with a median of 33.4°. The dip angles of the rocks in Gale Crater range from 14.7° to 41.7°, with a median of 31.5°. On Earth, the dip angles of strata in humid regions range from 7.4° to 38.4°, with a median of 27°, whereas in arid regions, the dip angles of strata range from 7.6° to 38°, with a median of 22.6°. These dip ranges indicate that the cross-bedding angles of sedimentary rocks on the Martian surface are similar to those of coastal aeolian cross-bedding on Earth, which indicate that their formation mechanism was comparable to the formation mechanism of coastal dunes. The sedimentary rocks at the Zhurong landing site were concluded to have formed in a nearshore marine depositional environment. This study represents the first statistical analysis of critical information on cross-bedding in Martian surface rocks compared with that in similar terrestrial environments, providing evidence from a sedimentary dynamics perspective for the depositional evolution of the Martian Utopia Planitia and indicating the historical presence of an ancient ocean in this region.