Fig. 6. Development of paleo-weathering sequences in Gale crater.

(A) Airfall deposition of sediments with fine laminations and cross-bedding by volcanic and sandstorm events. (B) Anoxic weathering leached Fe and formed Al clays and silica-rich amorphous materials at the top section. (C) Physical weathering promotes erosion, and leaching causes porosity. Later, oxidizing water penetrated depth to form hematite and nontronite. Ca was leached to form veins that cut across layers with high angles in the middle section but low angles in the lower section and lastly occurs as bedding parallel veins and even disseminates in the bedrock around the contact between Sutton island. (D) Deposition of sand dunes of the Siccar Point group above VRR sequence. The mobile elements (e.g., Na and Cl) dissolved in the diagenetic water accumulated around the unconformity can penetrate deeper and occupy the pores and space created by weathering and leaching. It well explains why the sodium chloride mainly occurs in nodules and altered textures in the upper sequence (32). (E) Warm diagenesis around the unconformity promoted K-metasomatism and formation of gray hematite and sulfates (65). PPT, Pettegrove Point.