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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 49 (1965)

Issue: 3. (March)

First Page: 361

Last Page: 361

Title: Origin of Sodium-Rich Triassic Lacustrine Deposits, New Jersey and Pennsylvania: ABSTRACT

Author(s): F. B. Van Houten

Article Type: Meeting abstract


Successive Stockton arkose, Lockatong argillite, and Brunswick mudstone, nonmarine basin deposits, contain abundant sodium derived from Na-feldspar-rich source rocks that lay to the east.

Lockatong lacustrine deposits (3,750 feet thick), in cycles averaging 15 feet thick, accumulated at a rate of about 0.2 mm. a year. Detrital cycles consist mainly of mudstone containing abundant Na-feldspar, illite (and muscovite) and chlorite, and calcite, but very little quartz or K-feldspar. They are composed of abundant Na2O (4.0%), K2O (5.2%), and MgO (3.8%), and only about 49 per cent SiO2. They accumulated in an open lake with estimated low salinity, Eh 0 to -2.5, and pH 7 to 8.

Chemical cycles consist mainly of colloidal-chemical mudstone containing abundant analcime, Na-feldspar, dolomite and calcite, and illite and chlorite; quartz is absent and K-feldspar is very rare. The rock is composed of K2O (3.3%), abundant MgO (4.0%), very abundant Na2O (6.4%), and only 49 per cent SiO2. Cr, V, Ni, and Co approach or exceed concentrations in marine mud. These cycles accumulated when the lake was closed; gray deposits in an environment of estimated moderate salinity, Eh -1 to -3, and pH 7.5 to 8.5, and grayish-red deposits in an environment of somewhat higher salinity, Eh -0.5 to 1.5, and pH 7.0-8.5.

Lockatong detrital and chemical cycles shared a common physical (lacustrine) environment. But detrital cycles and fine-grained Stockton fluvial facies shared a rather similar geochemical environment, as did chemical cycles and lowermost Brunswick mudflat facies.

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Copyright 1997 American Association of Petroleum Geologists