Associations of Fossils, Grain-types, and Chemical Constituents in the Upper Devonian and Lower Carboniferous Limestones of the Bonaparte Gulf Basin, Northwest Australia

Abstract

ABSTRACT Principal co-ordinates analysis of 47 modal and chemical attributes of each of 103 representative specimens of reefal and non-reefal limestones is interpreted as showing that, in order of decreasing amount, the variability is caused by: (1) the distance of the site of deposition from the shore, indicated inversely by the amount of terrigenous detritus; (2) the salinity, indicated by the content oF dolomite and stenohaline organisms; (3) an unknown factor that separates skeletal invertebrates from calcareous algae and micrite grains deposited by algal activity; and (4) another unknown factor that separates skeletal invertebrates and calcareous algae from conodonts, glauconite, and quartz. The most abundant skeletal grains--crinoid ossicles, brachiopods, and bryozoans--occur in impure limestone that lacks dolomite and algae. Algae and micrite grains precipitated by algal activity occur in pure limestone without skeletal invertebrates and with or without dolomite. Mg, Fe, Ba, Mn, and P occur in impure limestone, and Ph in pure limestone. Mn, Fe, and Zn seem to be concentrated in the insoluble residue, and Pb in the acid-soluble fraction. Mg occurs also in pure algal reef limestone. Mg is less and Sr more abundant in crinoids and brachiopods than in the enclosing matrix. Sr is almost restricted to skeletal limestone