Orbital Control of Shallow Water Late Paleoproterozoic Iron Formation Deposition Along Opposing Margins of North China Craton

Two thin, shallow water, dominantly hematite-rich iron formation (IF) deposits flank the northern and southern margins of North China craton at ca. 1.64 Ga, the Chuanlinggou and the Yunmengshan, respectively. Current age control suggests they are broadly similar in age, although unable to resolve whether or not they are coincident. We conducted high-resolution magnetic susceptibility-based cyclostratigraphy on both units and, despite their slightly different thicknesses, provide differential sedimentation rates that indicate a similar ~400 k.y. duration of deposition for both IFs, suggesting IF deposition was controlled over the duration of one long eccentricity ~405 k.y. cycle. Furthermore, the Milankovitch signals both suggest a consistent orbital phasing with a node, or low, in the 405 k.y. metronome, as evidenced in reduced frequency/amplitude modulation of both the eccentricity and processional signals of both IFs. Thus, whether the two IFs are coeval or not, their consistent orbital duration and phasing implies unique orbital control of IF deposition on either side of the craton during the “last gasp” of such IFs during the late Paleoproterozoic.