A model for the development of phosphatic and calcareous lithofacies in the Middle Cambrian Thorntonia Limestone, northeast Georgina Basin, Australia

Abstract

Chemical sediments of the Thorntonia Limestone were deposited during a major, gradually transgressive, but rapidly regressive sea level cycle that spanned the Ordian Stage of the early Middle Cambrian. In the northeastern parts of the Georgina Basin the Cambrian sea invaded an irregular landscape and proceeded to drown basement rocks with a series of small scale transgressive pulses, represented by repeating sets of three generalized shallowing‐upward cycles. Sediments deposited within the cycles are represented by seven lithofacies within two mineralogical suites of rocks. One, a mixed mineralogy suite (Suite A), contains: (1) the mud dominant, peloid and bioclast lithofacies, (2) a coated peloid, phosphate pavement lithofacies, and (3) the skeletal particle dominant lithofacies. The other, a calcareous mineralogy suite (Suite B), comprises: (1) the peloid and oncolite grainstone dominant lithofacies, (2) the peloid boundstone dominant lithofacies, (3) the thin bedded and fenestrate mudstone lithofacies,...