Effects of Postdepositional Subaerial Weathering and Intrastratal Solution on Paleoclimatic and Paleotectonic Interpretation: ABSTRACT

Abstract

In the nonlithified Cretaceous and Tertiary sediments of eastern and southeastern United States, two different, readily recognizable mineral assemblages are nearly ubiquitous. One, termed a suite, generally contains the following minerals: (1) epidote, garnet, staurolite, zircon, kyanite, hornblende, sillimanite, tourmaline, rutile, and monazite among the heavy nonopaque minerals; (2) quartz, muscovite, and feldspar among the light minerals; and (3) the clay minerals montmorillonite and kaolinite. The other mineral suite contains an impoverished or assemblage: (1) the heavy, nonopaque minerals zircon, tourmaline, staurolite, kyanite, rutile, sillimanite, and monazite; (2) the light minerals quartz and muscovite; and (3) the clay mineral kaolinite. The full assemblage is characteristic of sediments of distinctly marine origin, whereas the limited suite commonly is associated with sediments interpreted as originating in a fluvial or littoral environment. Analysis of outcropping sediments demonstrates that, upward in a section, a full assemblage may change to a limited assemblage where the strata are porous, permeable, and stand topographically high. Fluvial or littoral sands in outcrop or in the shallow subsurface contain limited assemblages, whereas their downdip marine equivalents contain a full suite. These two distinctly different mineral suites are not necessarily the result of changes in provenance, source-area climate, or tectonic stability. Instead, they should be attributed in large part to postdepositional subaerial weathering and intrastratal solution. Reevaluation of mineral analyses of Cretaceous and Tertiary sediments in the eastern and southeastern United States to include consideration of postdepositional subaerial weathering End_Page 783------------------------------ and intrastratal solution will require revision of some previous interpretations of their provenance and of some prior reconstructions of the paleoclimate and paleotectonics. End_of_Article - Last_Page 784------------