VEIN FORMATION IN NON-MARINE MUDSTONES OF THE 
NEWARK BASIN

	SIMONSON, Bruce M., Geology Dept., Oberlin College, 
Oberlin, OH 44074

Mudstones are the dominant lithology in the non-marine sedimentary 
fill of the Newark basin.  Most of these mudstones were deposited in 
paleoenvironments that were at least intermittently subaerial and 
contained depositional macroporosity in the form of air bubbles 
(vesicles), desiccation cracks and (or) root tubules.  Macropores 
typically disappear from marine mudstones during compaction, but 
those of the Newark mudstones are still there, albeit filled with 
coarsely crystalline authigenic minerals (cements).  The principal 
cement phases (analcime polyhedra, albite laths, blocky K-feldspar 
crystals, dolomite rhombs, and anhedral crystals of calcite, gypsum, 
anhydrite and/or barytocelesite) are organized into three paragenetic 
sequences that occur in successive and mutually exclusive 
stratigraphic zone that are each ca. 5,000' (1.5 km) thick (Simonson 
and Smoot, 1995).  Van Houten (1962) first described the cements 
and interpreted them as syndepositional precipitates from surface to 
near-surface saline lake waters, but 40Ar/39Ar age dates of the 
authigenic K-feldspars indicate closure ca. 20 million years after the 
host mudstones were deposited (Kunk et al., 1995).  Given the well-
constrained stratigraphy, this implies reactive fluids continued were 
circulating at depths of ca. 6,500' (2 km) in the Newark Basin.  
	Veins filled with mineral assemblages similar to those filling 
the depositional macropores are widespread in research cores drilled 
in the Newark basin (Olsen et al., 1996).  The veins range up to at 
least 4 cm in width, are mostly either bedding-parallel or bedding-
normal, and vary in character.  Many veins are fibrous and display 
crack-seal textures indicating incremental opening and filling 
(Ramsey, 1980), whereas others are coarsely crystalline and display 
competitive-growth textures indicative of open void-filling 
precipitation.  Still others are banded, indicating multiple stages of 
filling.  In addition, previously precipitated crystals (e.g., coarse 
euhedra of analcime) were fractured after initial growth, creating 
room for additional mineral precipitation in some veins.  Finally, 
veins in the lower part of the mudstone succession (where the organic-
rich deep lake deposits are thickest and most abundant) contain 
bitumen that was also fractured after emplacement.  
	The existence and diverse character of the veins in the Newark 
mudstones has important implications.  1)  Many features of the veins 
indicate  they represent fractures that were reopened and filled 
repeatedly.  This implies a long and complex history of fluid flow 
extending into late diagenesis.  2) The fact that the cements in the 
veins and the depositional macropores in the host mudstones have 
similar parageneses suggests they were made possible by the late 
diagenetic creation of fracture permeability.  The cause(s) of 
fracturing and the driving force for fluid flow have yet to be 
pinpointed, but will be discussed.  The apparent contradiction between 
large-scale, late-diagenetic fluid flow and the stratabound character of 
the vein fillings has likewise yet to be resolved.  

Kunk, M.J., Simonson, B.M., and Smoot, J.P., 1995, 40Ar/39Ar 
constraints on the age of K-feldspar cementation in non-marine 
sediments of the Newark, Gettysburg, and Culpeper basins: 
Geological Society of America Abstracts with Program, v. 27, n. 
1, p. 62.
Olsen, P.E, Kent, D.V., Cornet, B., Witte, W.K., and Schlische, R.W., 
1996, High resolution stratigraphy of the Newark rift basin 
(early Mesozoic, eastern North America): Geological Society of 
America Bulletin, v. 108, p. 40-77.
Ramsey, J.G., 1980, The crack-seal mechanism of rock deformation:  
Nature, v. 284, p. 135-139.
Simonson, B.M., and Smoot, J.P., 1994, Distribution and origin of 
macropore-filling cements in non-marine mudstones, Early 
Mesozoic Newark Basin, New Jersey And Pennsylvania:  
Geological Society of America Abstracts with Program, v. 26, p. 
A-337.
Van Houten, F.B., 1962, Cyclic sedimentation and the origin of 
analcime-rich Upper Triassic Lockatong Formation, west-central 
New Jersey and adjacent Pennsylvania: American Journal of 
Science, v. 260, p. 561-576.