Abstract

Tepee structures, banded aragonite cements, and pisoliths are currently forming in Lake MacLeod, a carbonate-evaporite salina in Western Australia. Although Lake MacLeod is separated from the Indian Ocean by a barrier, it lies 3–4 m below sea level, which promotes the seepage of seawater through the barrier and its discharge from vents and seepage mounds around the margin of the salina. Discharging waters have precipitated and diagenetically altered carbonate sediments within these seepage mounds to form tepee structures of lithified protodolomite overlying cavities that are lined with banded aragonite cement and floored by both cement and pisoliths.

Significant variations in δ18O (5.1‰ PDB) and δ13C (5.5‰ PDB) of the aragonite cements were documented and are thought to record shifts in the isotopic composition of the water brought about by the effects of evaporation, influx of meteoric water, and oxidation of organic water. Carbon-14 dating of cements indicates that cementation began about 3400 B.P. and has proceeded at a rate of about 0.2 to 0.4 mm/100 yr, the highest rate occurring during evaporative episodes.

By analogy with Lake MacLeod and other Australian salinas, peritidal tepee structures and associated diagenetic carbonates in the Permian Capitan Reef complex may owe their origin to speleanlike diagenesis operative in a marine groundwater discharge zone.

First Page Preview

First page PDF preview
You do not currently have access to this article.