EVOLVING PALEOGEOGRAPHIC INTERPRETATIONS OF THE 
HARTFORD AND DEERFIELD RIFT BASINS (NEWARK 
SUPERGROUP): AN HISTORIC OVERVIEW

	McDONALD, Nicholas G., Dept. of Earth and Environmental 
		Sciences, Wesleyan University, Middletown, CT  06459
	LeTOURNEAU, Peter M., Lamont-Doherty Earth Observatory 
		of Columbia University, Palisades, NY  10964

In the earliest comprehensive consideration of the depositional 
environments of the strata in the various Newark basins, Rogers 
(1840) advocated that the sediments were laid down with their present 
oblique dip by currents in an extensive "noble" river, which arose in 
the mountains of North Carolina and flowed northeastward, eventually 
draining into an oceanic estuary near New York City.  A similar 
scenario was envisioned for the Connecticut Valley Mesozoic rocks by 
Mather (1843) and others, except that oceanic currents rather than 
fluvial processes were invoked as the depositional agents.  At the turn 
of the century, championed by Russell (1892) and Emerson (1898), 
"Bay of Fundy" analogs for the Connecticut Valley deposits were in 
vogue: the sediments presumably accumulating in shallow, broad, 
tide-swept estuaries, in which expansive mudflats were subaerially 
exposed at low water intervals.  
	Davis (1898), after nearly 20 years of structural and 
physiographic investigations in central Connecticut, hypothesized 
sedimentation occurring in an elongate, downwarped trough, bowl-
shaped in cross-section, with no oceanic connections.  He postulated 
that streams supplied detritus to the slowly sagging basin from both 
margins, and that sediments accumulated in near-horizontal layers.  In 
his model, lacustrine conditions, characterized by fossiliferous black 
shales, intermittently prevailed in the central  regions of the trough.  
	Barrell (1915) was a visionary in recognizing that the faults 
which bound the eastern edge of the Hartford basin were 
syndepositionally active, and exerted a controlling influence on basin 
geometry.  He theorized deposition in a wedge-shaped trough, 
subsiding on the eastern edge, with nearly all of the detritus being 
supplied from highlands adjacent to the eastern boundary faults.  
Paleoslopes on the basin floor, he suggested, were near horizontal or 
gently inclined to the west, and he maintained that the basin once 
extended well beyond its present western limit, perhaps even as far as 
to be syndepositionally confluent with the Newark basin of New 
Jersey.  Barrell's model was clearly influenced by the "broad terrane" 
hypothesis of Russell (1879), who advocated that the stratigraphically-
similar Hartford and Newark basins are erosional (half graben) 
remnants of a once contiguous full graben, postdepositionally isolated 
by basement arching in western Connecticut.  Barrell's conclusions 
and broad terrane principles were endorsed by most subsequent 
researchers, including Longwell, Wheeler and Krynine, and received 
more recent support from Sanders (1974) and the early studies of 
Hubert and his co-workers.
	Challenges to broad terrane doctrines in the Hartford basin, 
however, were boldly advanced by Klein (1968, 1969), whose 
sedimentological data revealed a western provenance and east-dipping 
paleoslopes for some deposits in the region, thus rendering persistent 
connections with the Newark basin unlikely.  Hubert et al. (1978) 
however, advocated a modified broad terrane model like that of 
Krynine (1950) which connected the Hartford Basin with the 
Pomperaug Basin of western Connecticut based on localized 
southwest paleocurrent trends in the upper Triassic strata, assumed 
westerly paleoslopes on Jurassic lake floors, and the "likely" extension 
of an East Berlin Formation perennial lake to the Pomperaug Basin.  
	Studies of the Jurassic strata of the Hartford basin by 
LeTourneau (1985), LeTourneau and McDonald, (1985); McDonald 
and LeTourneau (1988, 1990) using paleocurrents, sediment 
provenance, facies analysis, stratal geometry, modeled configuration 
of the hinged and faulted basin margins, and basalt flow directions 
(Ellefsen and Rydel, 1985), proposed an asymmetrically subsiding 
basin that was deepest adjacent to the eastern border faults.  In this 
isolated basin model, east-dipping paleoslopes prevail on the broad, 
western, hinged-margin side of the basin, and small, steep drainages 
flow west from the narrow eastern footwall margin into the adjacent 
depocenter.  Hettangian-age fossiliferous black shale units which 
invariably thicken toward the basin margin rather than toward basin 
center provide a demonstrative argument for basin isolation.  Hubert, 
et al. (1992), armed with additional petrographic data indicating the 
prevalence of western (hinged-margin) sediment sources, rejected the 
earlier "modified-broad terrane" positions of Hubert et al. (1978) and 
Weddle and Hubert (1983) and supported the isolated half graben 
model advocated by LeTourneau and McDonald.  McHone (1996), 
however, resurrects the possibility of basin interconnections during the 
Triassic, and provides compelling evidence for a broad terrane Jurassic 
flood basalt province which may have extended over much of 
northeastern North America. 
	The isolated basin model presented above is supported by recent 
work on the structural geology of modern and ancient continental rift 
basins.  Models based on sedimentary facies analysis suggest a 
tectonic framework common to extended terranes (Kusznir and Egan, 
1989; Kusznir et al. 1995; Rosendahl et al., 1986; Rosendahl, 1987; 
Schlische and Anders, 1996; Scholtz and Rosendahl, 1990).  
Asymmetric half graben are the most common form of rift basins.  
Due to differential isostatic loading, the footwall of the master border 
fault system undergoes profound uplift during extension, resulting in 
small, steep catchments on the faulted margin.  The basin depocenter 
is skewed toward the faulted margin.  The broad area of the hinged or 
platform margin dips shallowly toward the faulted margin and 
contains major inflowing rivers.  Most basin-filling sediment is 
derived from hanging wall and axial sediment sources; footwall 
sources are only of local importance.  Pre-rift drainages may be 
captured or breach the footwall (Johnson, Wells and Scholtz, 1995; 
Smoot 1995).   Half-graben may be linked perpendicular to the main 
extension direction, as seen in the modern East African rift basins, the 
Newark-Gettysburg-Culpeper basin complex, and the Hartford-
Deerfield complex.  Studies of the varied structural and depositional 
histories of modern rift basins may ultimately prove the fallibility of 
simplistic models for the paleogeography of the Newark basins.