PETROLOGY, GEOCHEMISTRY, AND NA METASOMATISM OF TRIASSIC-JURASSIC NONMARINE CLASTIC SEDIMENTS IN THE NEWARK, HARTFORD, AND DEERFIELD RIFT BASINS, NORTHEASTERN USA

Many sandstones and associated siltstones and shales of the Triassic-J urassic Newark Supergroup in the Newark, Hartford, and Deerfield rift basins are immature feldspathic alluvial and lacustrine closed-basin d eposits. They were derived from felsic igneous and metamorphic contine ntal blocks on the flanks of their depositional basins. The provenance was dominantly calc-alkaline basement rocks similar to the Sierra Nev ada of California. The physical and chemical environments of erosion a nd deposition were probably similar to those in moist Pleistocene-Holo cene alluvial basins and playas in the Great Basin of California and N evada. New petrographic and geochemical data for 113 samples indicate that albite-rich sandstones and shales of the Stockton, Lockatong, and Passaic Formations in the Newark Basin and in the Portland and East B erlin Formations of the Hartford Basin and analcime-rich shales (up to 52% normative analcime) of the Lockatong Formation have unusually hig h Na2O contents (4-7%). Textural evidence indicates both sodium replac ement in feldspars and formation of authigenic albite and analcime in these rocks. By comparison with modern sediments derived from similar provenance, using mixing models, it is estimated that up to 4% Na2O wa s diagenetically added to the detrital clastics. Trace metals (Co, Cr, Cu, Ni, Zn) abundances were apparently enhanced by deposition from br ines in the Lockatong Formation. Analcime deposition occurred in shale s with (Al2O3 + Na2O)/SiO2 > 0.46; this ratio is found only in sedimen ts to which Na has been added from salts/brines. Source rocks and the weathering products derived from them may be considered as a closed sy stem in which sodium was retained partly in solids, as feldspar, and p art went into solution during weathering. The dilute solution migrated into the depositional basin where evaporation yielded concentrated br ine during semi-arid to arid climate in the drier parts of similar to 21,000-yr Milankovitch cycles. Reaction of brine during diagenesis at near surface and/or shallow depths (< 2 km) with Ca-plagioclase, K-fel dspar, and layer silicates at estimated temperatures < 50 degrees C to similar to 100 degrees C and pH 7-9 + yielded thermodynamically stabl e authigenic albite and analcime in the sodium-metasomatised elastic s ediments, Low activity of K+ precluded development of authigenic K-fel dspar. However, K+ from solution incorporated into muds and slits as s mectites were transformed to illite. Some Lockatong beds contain anoma lously high P2O5, Ce. La, Y, Th, and U in authigenic apatite or monazi te, suggestive of mobilization of these elements in diagenesis.