Abstract

A study was made of the heavy minerals in strata in the Lucero uplift, with special reference to the pre-Morrison Jurassic rocks. Zircon, garnet, tourmaline, rutile, and several opaque minerals are dominant; epidote, biotite, staurolite, and apatite occur in minor quantities. This limited suite of mostly rounded, stable heavy minerals indicates the rocks are multicycle sediments, in agreement with the conclusions previously obtained with other stratigraphic techniques. The pre-Morrison part of the section, in which relatively abundant magnetite-ilmenite occurs, is distinguishable from the Morrison Formation in which these minerals are virtually absent. Considering the pre-Morrison Jurassic rocks in sequence, the Carmel and lower Entrada formations have a low zircon-garnet and high magnetite-ilmenite content, the upper Entrada has a high zircon-garnet and low magnetite-ilmenite content, and the Summerville and Bluff formations have a high zircon-low garnet and variable magnetite-ilmenite content. Except for the upper Entrada, the differences in distribution of the heavy minerals do not characterize any single pre-Morrison unit. Thus, the heavy minerals are not as useful a stratigraphic tool as if the suite were mineralogically more varied.

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