Comprehensive geophysical surveys including magnetotelluric, seismic, and aerial gravity–magnetic surveys are essential for understanding the history of Antarctic tectonics. The ice sheet and uppermost structure derived from those geophysical methods are relatively low resolution. Although ice-penetrating radar can provide high-resolution reflectivity images of the ice sheet, it cannot provide constraints on subice physical properties, which are important for geological understanding of the Antarctic continent. To obtain high-resolution images of the ice sheet and uppermost crustal structure beneath the Larsemann Hills, Prydz Bay, East Antarctica, we conduct an ambient noise seismic experiment with 100 short-period seismometers spaced at 0.2 km intervals. Continuous seismic waveforms are recorded for one month at a 2 ms sampling rate. Empirical Green’s functions are extracted by cross correlating the seismic waveform of one station with that of another station, and dispersion curves are extracted using a new phase-shift method. A high-resolution shear-velocity model is derived by inverting the dispersion curves. Furthermore, body waves are enhanced using a set of processing techniques commonly used in seismic exploration. The stacked body-wave image clearly shows a geological structure similar to that revealed by the shear-wave velocity model. This study, which is the first of its kind in Antarctica, possibly reveals a near-vertical intrusive rock covered by an ice sheet with a horizontal extent of 4 km. Our results help to improve the understanding of the subice environment and geological evolution in the Larsemann Hills, Prydz Bay, East Antarctica.

The Cambrian strata in the North China Platform are fully exposed. A wide variety of carbonate oncoids with different shapes occur in the Xuzhuang and Zhangxia formations (Miaolingian Series) from six Cambrian sections in the study area. A comprehensive study involving outcrop description, microscopic observation, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and carbon and oxygen isotope analysis is conducted to determine the facies, morphology, internal structure, and geochemical properties of the oncoids. The oncoids are divided into six types based on their morphology and internal structure. Microscopic and ultrastructural observations reveal typical microbial fossils (Girvanella) and microbially-related sediments (framboidal pyrite), indicating the biogenicity of the oncoids. Additionally, the XRD and carbon and oxygen isotope analysis results suggest that the formational environments of these oncoids are different due to terrestrial influences. Statistical data on the oncoids from the six sections show that there are obvious differences in the types of oncoids and the proportions of different varieties in each section. The spatial differences in the oncoid morphologies are associated with different palaeogeographic settings. The rough oncoid growth patterns developed in nearshore environments were influenced by terrigenous debris and steep terrain, whereas the delicate oncoid growth patterns developed in offshore environments were less affected by terrestrial factors and were featured by more stable depositional processes related to microbial mats.

In order to study the sedimentological response of the first episode of “cyanobacteria calcification event” in Phanerozoic, we studied the microbialites from Furongian Series in Qijiayu section, Hebei Province, which is located in the central part of the North China Platform. Cambrian Furongian Series is made up of three third-order depositional sequences, Depositional Sequence 1 (DS₁) in Changshan Formation and DS₂and DS₃in Fengshan Formation. Two beds of massive limestone of a shallow ramp facies developed in Changshan Formation and the first third-order sequence of Fengshan Formation. Both of them contains many dome-shaped carbonate structures that formed as a result of forced regression. These structures can be described as leiolitic bioherms, with a morphology like string of beads. In the current study, microorganisms such asEpiphyton,GirvanellaandRenalcisare reported from the leiolitic bioherms. This provides not only documentation for the model of cyanobacteria calcification, but also describes the genesis of leiolitic bioherms by microbial processes inside cyanobacteria dominated microbial mats. Moreover, the diverse emergence of the calcified microorganisms represents the fossil evidence of calcified microorganisms’ blooms in Cambrian Furongian and offers a reference for studying the complex microbial processes in such old carbonate depositions.