South China, the northern part of the Australasian strewn field (AASF) of tektites and microtektites is located at the uprange of the hypothesized source crater that is still unconfirmed. Magnetic properties of impact glasses are an important indicator of their source materials and thermal history. Extensive magnetic investigations have been performed on various AASF tektites sampled from both the Indochina Peninsula and further south, but such information remains sparse for those sampled from South China. Here, we present a detailed rock magnetism study for both Muong Nong‐type and splash‐form AASF tektites from South China, showing that all the tektites have rather weak remanent magnetization, but ferromagnetic information can be extracted from their dominating paramagnetic signal. Signals caused by superparamagnetic particles are elusive, but those of single domain magnetite are detected in the splash‐form tektites, and signals of pseudo‐single domain magnetite are discovered in the Muong Nong‐type tektites. Each morphological type of tektites from a same geographic area exhibits large dispersions in their magnetic properties. Across the entire AASF, the Muong Nong‐type tektites from South China exhibit the lowest average magnetic susceptibility, and the splash‐form tektites exhibit the smallest average natural remanent magnetization and ratio of equivalent magnetization. The observed heterogeneous magnetic properties are mainly caused by the different contents and sizes of magnetic particles, which can be explained by the different shock level and/or cooling history of the tektite melts. Micro‐sized immiscible Fe‐S spherules in the Muong Nong‐type tektites from South China were likely originated from the pre‐impact target.

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The Daggyai geyserites serve as hosts for cesium deposits; however, their origin, whether by chemical deposition or biological formation, is a topic of debate. To decipher the origin of geyserites, the petrographic features of the geyserite samples were examined. The geyserites exhibited columnar laminated, planar laminated and spicular morphologies. Furthermore, they contained morphological and confocal microscopic evidence of the coccoid, bacilliform and filamentous microbes that formed them. Minor calcite and quartz crystals were found locally in the columnar laminated and spicular geyserites. Cyanobacteria tentatively assigned to the genus Calothrix dominated in the planar and columnar laminated geyserites, but were rare in the spicular geyserites. The results demonstrated that the microbes contributed to the Daggyai geyserite formation.

Natural magnetite nanoparticles (NPs) are important iron oxides in the surficial Earth system, and widely used as a paleoenvironmental indicator (e.g.,