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Hydrogeochemical Processes and Fades in Confining Units of the Atlantic Coastal Plain in New Jersey
Author(s) -
Pucci Amleto A.
Publication year - 1998
Publication title -
groundwater
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.84
H-Index - 94
eISSN - 1745-6584
pISSN - 0017-467X
DOI - 10.1111/j.1745-6584.1998.tb02838.x
Subject(s) - coastal plain , pore water pressure , geology , groundwater , facies , aquifer , borehole , silt , carbonate , mineralogy , hydrology (agriculture) , geochemistry , geomorphology , chemistry , geotechnical engineering , paleontology , organic chemistry , structural basin
Pore water solutes and sediments in the New Jersey Coastal Plain were studied to assess processes that control pore water chemistry in confining units and interactions with aquifer water chemistry. Solute chemistry and variations with depth are reported for 19 samples collected from a continuously cored borehole in the lower Miocene Kirkwood Formation at Atlantic City, New Jersey. In 14 pore water samples collected from the Lower Confining Unit overlying the Atlantic City 800‐foot Sand, and from the silt interbeds in the Upper Part of the Atlantic City 800‐foot Sand, linear regressions showed especially high correlations (R 2 0.89) between concentrations of Mg and Ca; between concentrations of Na and the sum of Ca and Mg; between concentrations of SO 4 and the sum of Ca and Mg; and between concentrations of Na and SO 4 . There were three distinct water quality types: Ca‐SO 4 , Ca‐Na‐SO 4 ‐Cl‐HCO 3 , and Na‐SO 4 ‐HCO 3 ‐Cl. Each water type generally is within distinct intervals (tens of meters), or hydrogeochemical facies, in the core. The first two facies were found only in the units overlying the Atlantic City 800‐foot Sand; the third type was found only in samples from the underlying composite confining unit. Significant variation of pore water solute concentrations was indicated on a scale smaller than the sampling interval (about 3.5 m). Two principal components explained 82.5% of the total variation in pore water chemistry. The processes which control the variation in water quality include (1) chemical processes such as shell dissolution, incongruent carbonate dissolution, and clay transformations; (2) a hypothesized physical‐chemical mechanism of differential migration of sulfate accompanied by divalent cations; and (3) fresh water flushing of, and mixing with, residual sea water at paleoflow rates. Cation‐exchange reactions do not appear to be an important process in these sediments.