THE STRATIGRAPHY AND STRUCTURE OF THE BURIED 
LATE TRIASSIC TAYLORSVILLE BASIN, VIRGINIA AND 
MARYLAND: RESULTS OF RECENT SUBSURFACE 
INVESTIGATIONS

	LeTOURNEAU, Peter M., OLSEN, Paul E., and KENT, 	
		Dennis V. Lamont-Doherty Earth Observatory of 	
		Columbia University Palisades, NY  10964-8000

The Triassic-Jurassic rift basins of the eastern North American form a 
broad zone of linked or isolated half-graben that stretch from Georgia 
to the Canadian Maritimes including:  onshore, exposed basins; 
onshore basins buried beneath coastal plain deposits; and offshore 
basins.  The exposed basins of the Newark Supergroup (sensu stricto) 
are well-known and studies of these have contributed to our 
understanding of the tectonics, structure, stratigraphy, and igneous 
activity of continental rifts, as well as the  depositional environments, 
paleogeography and paleontology of the Late Triassic and Early 
Jurassic.  However, the onshore and offshore buried basins have only 
been recognized by geophysical surveys and limited drilling (water 
well or geotechnical) since the mid-1970's, and until recently few rock 
samples had been obtained from the buried basins.  
	The buried Taylorsville Basin (TVB) located beneath coastal 
plain deposits in Virginia and Maryland was the target of petroleum 
exploration from about 1985 to 1992 (Benson, 1992).  Six 5,500 ft. 
(~1,700 m) stratigraphic test wells produced continuous cores totaling 
over 21,000 ft. (~6,100 m) and three deep, 8,000 - 10,000 ft. (~2,100 - 
3,000 m), test wells produced chips (mud log) and limited short cores 
and sidewall cores.  In addition, over 80 mi. (~123 km.) of seismic 
reflection profiles were obtained across the NE-SW oriented basin.  
This ongoing study has evaluated about 12,000 ft. (3,750 m) of core 
from three wells (Payne, Butler, Bowie-Fogg), 7,500 ft. (~2,340 m) of 
cuttings from one deep well (Wilkins) that encountered basement, and 
available seismic profiles.  In addition, paleomagnetic analysis of over 
700 samples from the Payne, Butler and Bowie-Fogg wells was 
performed to evaluate the paleomagnetic polarity stratigraphy.
	The buried TVB is believed to be the subsurface extension of 
the exposed Taylorsville Basin centered near Ashland, VA (Benson, 
1992; Weems, 1980).  While the exposed TVB is one of the smallest 
of the Newark basins (circa 19 by 11 km ;140 sq. km), the TVB ranks 
as one of the largest at 150 by 50 km or about 4,500 sq. km (Benson, 
1992).  This relationship is important because the previously studied 
exposed portion of the TVB may not be representative of the basin as 
a whole, particularly because the exposed portion is in a structurally 
complex area near the southern terminus of the basin.
	The TVB contains approximately 15,000 ft  (~4,690 m) of 
fluvial and lacustrine strata, including conglomerate, sandstone, 
siltstone and shale, ranging from red-brown to black in color.  The 
overall stratigraphy of the basin consists of a 1,000 - 2,000 ft. (~312 - 
625 m) lower fluvial-lacustrine sequence (I), separated by an 
unconformity from a thicker, 13,000 - 14,000 ft. (~4060 - 4375 m) 
upper fluvial-lacustrine sequence (II) .  
	Sequence I forms the base of the rift fill and occupies smaller, 
faulted basins separated from the overlying sequence II by a basin-
wide unconformity.  The strata of I consist of gray to black lacustrine 
siltstone and shale and red-brown fluvial sandstone and siltstone.    
Sequence II consists of two assemblages: IIA) gray fluvial-deltaic-
lacustrine sandstone, siltstone and shale; IIB) red-brown fluvial 
channel and floodplain sandstone and siltstone.  IIA  is characterized 
by laminated, fossiliferous black shale and gray sandstone and 
siltstone.  Finer portions of IIB include pedogenic carbonates, root 
casts, invertebrate burrows, desiccation cracks, and soil fabrics, while 
coarser portions have climbing ripple cross-lamination, basal scour 
surfaces, intraformational conglomerate, planar to tangential cross 
strata and planar, horizontal lamination.  The two assemblages are 
indicative of relatively "wet" (IIA) and "dry" (IIB) depositional 
sequences.  The boreholes also encountered diabase dikes and the 
seismic profiles show subvertical dike swarms, although these appear 
to occupy a small portion of the basin fill.
	The seismic reflection profiles and the borehole dipmeter data 
indicate that TVB strata dip both toward and away from the master, 
western border fault.  The axes of these broad, post-depositional folds 
are oriented along the long axis of the basin and may be a result of 
NW-SE oriented post-rift compression.  One seismic profile that 
spans the width of the basin shows a secondary set of faults 
paralleling the east-dipping western border fault that  likely define a 
footwall rider block.  The base of the rift basin consists of smaller 
half-graben presumably the result of distributed extension during 
early rifting.  Later rifting was accommodated by the master western 
border fault system.  A basin-wide unconformity formed during the 
transition from early to later phases of rifting.  During the later phase 
of rifting sequence (II) strata filled the broad half-graben.
	This new data from the buried basin suggests that the exposed 
TVB represents a portion of the lower basin fill (sequence I).  
Additionally, based on lithostratigraphy and paleomagnetic reversal 
stratigraphy (Olsen et al., 1996) sequence IIA correlates to the 
Lockatong Formation and IIB correlates to the Passaic Formation of 
the upper Triassic portion of the Newark Basin.