Abstract

The normal Triassic arkoses of Connecticut and Massachusetts contain moderate amounts of secondary feldspar and very little secondary quartz. Locally calcite or the zeolite laumontite is important. Secondary albite is more abundant than secondary potash feldspar and forms overgrowths on detrital microcline, orthoclase, and plagioclase. Calcite and laumontite occur as pore fillings and replacements of feldspar. Growths formed after considerable compaction but before pressure solution ceased.

Microcrystalline secondary albite is abundant in the arkoses near intrusives. The albite filled pores and partly replaced mica, garnet, and potash feldspar. Secondary chlorite, epidote, sericite, laumontite, and calcite are common in some contact zones. With increasing distance from the intrusives, the microcrystalline albite becomes coarser and decreases in amount, whereas enlargements on detrital grains become more common.

Large amounts of cryptocrystalline quartz, potash feldspar, and sericite were deposited in the sediments along the border fault in western Connecticut. In some faulted arkoses in the Triassic basin, small to moderate amounts of sericite, chlorite, quartz, barite, albite, and calcite were deposited. Sediments near the eastern border fault have undergone considerable pressure solution, but the amount of cement is not abnormally high.

Most of the cement in the normal arkoses is believed to be of igneous origin because it is chemically similar to the material introduced along igneous contacts. The widespread distribution of cement in areas where exposed igneous bodies are absent suggests that some of the introduced material emanated from the diabase reservoirs at depth. The more siliceous solutions that rose along faults may have been derived from the diabase reservoirs during a different stage of differentiation or they may have emanated from other bodies. The present study indicates that a magmatic source for cement should not be ruled out even though effects of hydrothermal activity may be absent.

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