Preliminary study on the taphonomy of brachiopod shell concentrations from the Cambrian Jindingshan Formation in Xifeng, Guizhou
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Abstract:
Brachiopods are key components of the Cambrian marine benthic ecosystems. Through the efficient filter-feeding and attachment functions, they contributed to the stabilization of the benthic environments. Brachiopod shell concentrations played a significant role in shaping the ecological tiering and community structures during the Cambrian explosion. Numerous brachiopod shell concentrations have been discovered from the middle part of the Jindingshan Formation (Cambrian Stage 4) in Xifeng, Guizhou Province, China. Comprehensive investigations reveal that these brachiopod shell concentrations predominantly exhibit two distinct burial types: (1) The concentrations are mainly composed of a single species, Westonia sp., with shells preserved in black; and (2) The concentrations are dominated by Westonia sp., but with grayish-white shells, co-occurring with a few specimens of Eoobolusmalongensis, trilobites, chancelloriids, and hyoliths. The shells in both types of concentrations are oriented nearly parallel to the bedding plane. The shell sizes vary considerably, and no obvious preferred orientation is observed. Examination of polished, longitudinal surfaces of rock slabs and thin sections reveals only faint horizontal bedding, with no evidence of strong hydrodynamic forces or traces of bioturbation. These observations suggest that the brachiopod communities were buried in situ in a relatively stable environment, without significant disturbance from currents or transportation Energy-dispersive spectroscopy (EDS) analyses show that the brachiopod shells from this area are enriched in iron-aluminum silicates. During burial, mineral replacement occurred: Pyrite in the shell resulted from early diagensis was altered, and iron-aluminum-rich silicates were subsequently deposited as secondary minerals, playing an important role in diagenesis. These findings not only provide new insights into the brachiopod assemblages of the Jindingshan Formation but also offer crucial evidence for reconstructing the paleoenvironmental conditions and sedimentary events during the Cambrian explosion.
