Alan McGugan

Ikaite, CaCO3̇6H2O, precursor of the thinolites in the Quaternary tufas and tufa mounds of the Lahontan and Mono Lake Basins, western United States

The thinolites in the Quaternary tufas and tufa mounds of the Lahontan and Mono Lake basins of the western United States are identified as being pseudomorphous after crystals of the mineral ikaite, CaCO36H2O. Ikaite is a metastable mineral in the sedimentary realm. It crystallizes from solution at temperatures close to zero Celsius but rapidly decomposes at warmer temperatures and becomes pseudomorphed in calcite by in situ redistribution of the calcium and carbonate ions. The likely implication is that the thinolites record ice-cold episodes during deposition of the tufas.

OCCURRENCE AND PERSISTENCE OF THIN SHELF DEPOSITS OF UNIFORM LITHOLOGY: REPLY

In the Permian of western Canada lithologic units of 100 feet or less in thickness cover areas up to 180,000 square miles. These have a high persistence factor ( P ), where P = areal extent of unit/thickness of unit. Other occurrences of thin persistent formations are noted, and it is concluded that they are condensed diachronous shelf deposits of a transgressing sea.

Foraminiferal characterization of the Morrowan/Atokan (lower Middle Pennsylvanian) boundary: Discussion and reply

No Abstract Available. The article discussed appeared in the Bulletin , v. 97, p. 346–353.