ABSTRACT

Upper Jurassic Norphlet sandstone of the northern Gulf coast is predominantly subarkose, with some arkose in the eastern area and sublitharenite and quartzarenite in the western area. Despite great depths of burial and despite feldspar and rock fragment constituents, diagenesis has not appreciably altered the composition of Norphlet sandstone. Therefore, reconstruction of original composition of Norphlet sandstone presented little difficulty.

Variation in detrital modes of the Norphlet suggests compositionally distinct source terranes. Samples from Florida, Alabama, and Mississippi reflect the influence of metamorphic and plutonic rocks of the Appalachian Piedmont province and paleohighs, such as the Wiggins Arch, and of Triassic-Jurassic volcanic rocks. Sandstones in east Texas, northern Louisiana, and southern Arkansas were derived from sedimentary and metasedimentary rocks of the Ouachita System. Arbuckle Mountains and the Llano Uplift may have supplied trace amounts of quartzofeldspathic and volcanic rock fragments to the extreme western part of the study area.

Norphlet sandstones represent a mixture of collision-orogen-derived sediment from the Appalachian/Ouachita system and continental-block-derived sediments from paleohighs and uplifts within the Gulf basin. However, Norphlet sandstones plot in the "craton-interior" and "transitional-continental" fields on Q-F-L and Qm-F-Lt tectonic-provenance diagrams because of: (1) mineralogically mature source rocks, (2) elimination of unstable grains by weathering, abrasion and sorting during deposition, and/or (3) sediment mixing from different source terranes.