Geochemical Analysis and Astronomical Cycles on Cambrian MISS

A set of biolaminite with a thickness of 88 meters, a typical type of Microbially Induced Sedimentary Structures, are developed in the clastic rock strata of the Guojiaba Formation of the Cambrian Stage 3 in southern Shaanxi area. The structure is characterized by alternating light and dark laminated silt-fine sandstones. The light-colored laminae are mainly composed of minerals such as quartz and feldspar, representing normal terrigenous clastic deposition, while the dark laminae are rich in organic matter and microfossils, indicative of typical biogenic sedimentation. Paleosalinity analysis reveals that the B/Ga ratio ranges from 3.87 to 5.69 (with an average of 4.75), and the Sr/Ba ratio varies between 0.29 and 0.42 (with an average of 0.34), both indicating a brackish water (transitional facies) sedimentary environment. High-resolution cyclostratigraphic research on the 88-meter-thick microbial laminite succession, conducted via magnetic susceptibility and XRF sampling at 5-centimeter equal intervals, demonstrates that the sedimentation rate of this stratum is 5.16 cm/kyr, with a total depositional duration of approximately 1705 kyr.