Early Triassic calcimicrobial mounds and biostromes of the Nanpanjiang basin, south China

Abstract

Stanley’s model (1988) proposed that a Permiantype reef fauna survived the Early Triassic reefless period in yet undiscovered refuges in the ancestral Pacific ocean and then reappeared as the builders of Middle Triassic reefs. Flugel (1994), in contrast, suggested that the Middle Triassic reefbuilding fauna are not holdovers from the Permian, but bear only a superficial resemblance to Permian fossils. Recent publications reflect a consensus that the Early Triassic lacked reefs and reef mounds although some authors acknowledged the possibility that reef-like structures may have existed in poorly explored areas such as south China and Russia (Senowbari-Daryan et al., 1993; Flugel, 1994). It is shown herein that Calcimicrobial framework mounds and biostromes existed in the Early Triassic in the Nanpanjiang basin of south China. Organic framework in this paper refers to a three dimensional, biologically-constructed network of calcified fossils that forms a rigid mass and supports an interconnected network of internal cavities that were open during accumulation. Although the calcimicrobial frameworks discussed herein are much smaller than frameworks of modern metazoan reefs, the term framestone is more appropriate for these fabrics than other reef-rock terms such as bindstone or bafflestone (Embry and Klovan, 1971). These calcimicrobial mounds and biostromes are important as the first organic framestones documented from the Early Triassic.