Early Jurassic eolian dune field, Pomperaug basin, Connecticut and related synrift deposits: Stratigraphic framework and paleoclimatic context

Abstract

The discovery of an extensive eolian sandstone in the Pomperaug basin, Connecticut is noteworthy because it is the most significant occurrence of eolian rocks in the continental rifts of the Newark Supergroup south of the Fundy basin, Canada. Climate-sensitive rocks provide important constraints for the influence of supercontinent landmass configurations on models of early Mesozoic Pangaean climate. The sedimentary structures and textures in the Pomperaug basin sandstone compare favorably with modern and ancient eolian sands. The eolian sandstone is traceable for at least 5 km and occupies a stratigraphic interval that is dominated by arid facies in the Pomperaug and Hartford basins, indicating that the eolian deposit is indicative of regional climate. The eolian sands were stabilized by a return to more humid conditions and subsequently buried beneath a thick, basin-wide basalt flow, preserving the dune field. Also described are related synrift eolian sandstones from the Hartford (Connecticut, USA), Fundy (Nova Scotia, Canada), and Argana (Morocco) basins. Using revised paleolatitude models for the Pangaean rifts, the distribution of eolian sandstones suggests that the Norian–Hettangian world had zonal climate belts with modified latitudinal gradients.

Full text

Early Jurassic eolian dune field, Pomperaug basin,
Connecticut and related synrift deposits:
Stratigraphic framework and paleoclimatic context
Peter M. LeTourneau
a,
*, Phillip Huber
b
a
Lamont–Doherty Earth Observatory of Columbia University, Palisades, NY 10964, United States
b
Minnesota State University, Department of Education, K-12 Programs, Mankato, MN 56001, United States
Received 18 August 2005; received in revised form 28 November 2005; accepted 2 December 2005
Abstract
The discovery of an extensive eolian sandstone in the Pomperaug basin, Connecticut is noteworthy because it is the most
significant occurrence of eolian rocks in the continental rifts of the Newark Supergroup south of the Fundy basin, Canada. Climate-
sensitive rocks provide important constraints for the influence of supercontinent landmass configurations on models of early
Mesozoic Pangaean climate. The sedimentary structures and textures in the Pomperaug basin sandstone compare favorably with
modern and ancient eolian sands. The eolian sandstone is traceable for at least 5 km and occupies a stratigraphic interval that is
dominated by arid facies in the Pomperaug and Hartford basins, indicating that the eolian deposit is indicative of regional climate.
The eolian sands were stabilized by a return to more humid conditions and subsequently buried beneath a thick, basin-wide basalt
flow, preserving the dune field. Also described are related synrift eolian sandstones from the Hartford (Connecticut, USA), Fundy
(Nova Scotia, Canada), and Argana (Morocco) basins. Using revised paleolatitude models for the Pangaean rifts, the distribution of
eolian sandstones suggests that the Norian–Hettangian world had zonal climate belts with modified latitudinal gradients.
D2005 Elsevier B.V. All rights reserved.
Keywords: Eolian; Sandstone; Paleoclimate; Pomperaug rift basin; Newark Supergroup; Portland brownstone
1. Introduction
This paper describes a basin-wide eolian dune field
in Early Jurassic continental rocks of the Pomperaug
basin, Connecticut and documents associated, recently
recognized, eolian deposits in related Rhaetian–Hettan-
gian synrift strata in the Hartford basin. The Pomperaug
and Hartford basins are part of the early Mesozoic
Pangaean breakup rift system, known in North America
as the Newark Supergroup (Fig. 1). Affiliated rifts,
including the Argana basin, Morocco, discussed in
this paper, are part of this circum-North Atlantic rift
province. The Pomperaug basin dune field comprises
the most extensive eolian sandstone in the Newark
Supergroup found south of the Fundy basin (Hubert
and Mertz, 1980, 1984; LeTourneau and Huber, 1997;
Smoot, 1991a,b; Olsen, 1997), at less than about 258
paleolatitude (Kent and Olsen, 2000a; Olsen and Kent,
2000; Olsen et al., 2000; Kent and Tauxe, 2005). Eolian
deposits are important paleoclimate indicators and,
along with coals and evaporites, have been widely
0037-0738/$ - see front matter D2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.sedgeo.2005.12.005
* Corresponding author.
E-mail address: Letour@LDEO.Columbia.edu
(P.M. LeTourneau).
Sedimentary Geology 187 (2006) 63 – 81
www.elsevier.com/locate/sedgeo

used to constrain Pangaean climate models (e.g., Hay et
al., 1982; Chandler et al., 1992; Parrish, 1993; Hallam,
1994a,b; Wilson et al., 1994). Our identification of this
basin-wide eolian dune field is important because it
revises the distribution pattern of climate-sensitive
rocks in the Newark rifts.
Eolian sandstones are, in general, uncommon within
the Newark Supergroup rift basins (Fig. 2) but are com-
mon in Late Triassic and Early Jurassic age rocks of the
Fundy basin, Canada, deposited at paleolatitudes rang-
ing from about 178N (Carnian, Triassic) to about 258N
(Hettangian, Jurassic) (Hubert and Mertz, 1980, 1984;
Nadon and Middleton, 1985; Olsen, 1997; Smoot,
1991a; Olsen, 1997; Kent and Olsen, 2000a; Olsen and
Kent, 2000; Kent and Tauxe, 2005). In the Hartford
basin, eolian sandstones have been recognized in the
Late Triassic New Haven Arkose (Smoot, 1991a) and
the Early Jurassic bbrownstonesQand bLongmeadow
sandstone faciesQof the Portland Formation (LeTour-
neau, 2001), both deposited at approximately 228N
(Kent and Olsen, 2000a; Olsen and Kent, 2000;
Olsen et al., 2000; Kent and Tauxe, 2005). The
Argana basin, Morocco, a North African affiliate of
the Newark rifts, also contains noteworthy Norian age
eolian strata of wide areal extent deposited at an
approximate paleolatitude of 158N, including the
Tadrart Sandstone Member of the Bigoudine Forma-
tion (Tixeront, 1973; Olsen, 1997, Hofman et al.,
2000; Olsen et al., 2000).
Paleoclimate reconstructions of the Late Triassic and
Early Jurassic rely, in part, on identification of climate-
dependent facies, including coals, evaporites, and eo-
lian beds (e.g. Hay et al., 1982; Hallam, 1985, 1994a,b;
Sellwood and Price, 1994; Wilson et al., 1994). Placing
climate-sensitive strata in their paleogeographic and
stratigraphic settings is necessary for constructing mod-
els of Pangaean climates, such as zonal (e.g., Kent and
Olsen, 2000a; Olsen and Kent, 2000; Kent and Tauxe,
2005); modified zonal (e.g., Wilson et al., 1994), or
non-zonal (e.g., Manspeizer, 1982; Parrish, 1993) at-
mospheric circulation hypotheses. It is particularly im-
Fig. 1. Location of the Newark Supergroup rifts and the Pomperaug basin.
Fig. 2. Paleolatitudinal distribution of eolian sandstone in the circum-
North Atlantic Pangean rift system.
P.M. LeTourneau, P. Huber / Sedimentary Geology 187 (2006) 63–8164

portant to constrain facies-dependent climate interpreta-
tions with high-resolution stratigraphy to discriminate
paleogeographic, paleotopographic (Manspeizer, 1982),
and paleolatitudinal (Ziegler et al., 1982) patterns from
stratigraphic patterns produced by periodic climate var-
iability (Olsen, 1986; Kent and Olsen, 2000a,b; Olsen
and Kent, 2000). Mis-registration of climate-sensitive
facies by as little as 20 ky in chronostratigraphic space
(sensu Kent and Olsen, 2000b) may lead to flawed
interpretations of regional paleoclimatic and paleogeo-
graphic trends.
2. The Pomperaug basin
2.1. Setting
The Pomperaug basin is part of the suite of rifts
located along the central Atlantic margin (CAM) in
North America, North Africa, and western Europe
that formed during the incipient breakup of Pangaea
in the Late Triassic and Early Jurassic (Manspeizer,
1988; Olsen, 1997; LeTourneau and Olsen, 2003).
The CAM rifts include onshore exposed basins, and
onshore and offshore basins buried by Late Jurassic and
younger passive margin deposits (Benson, 1992)
(Fig. 1). The Pangaean-breakup rifts of eastern North
America are the best known of the Triassic–Jurassic age
CAM basins and they contain the rocks of the Newark
Supergroup (Olsen, 1997), including continental fluvial
and lacustrine sedimentary rocks and, in some cases,
extensive tholeiitic basalt flows and dikes. Collectively,
the Newark rifts contain the geologic record of more
than 30 million years of Late Triassic through Early
Jurassic earth history and span more than 208of paleo-
latitude from paleoequatorial to low mid-latitude
regions (Olsen, 1997). Therefore the Newark rifts pro-
vide ideal opportunities to study the Pangaean paleo-
climate record as a function of both paleolatitude and
astronomically forced climate cycles through an exten-
sive period of geologic time (Olsen, 1986, 1997; Olsen
and Kent, 2000; LeTourneau, 2003).
2.2. Note on stratigraphy and age of the Pomperaug
basin
The Pomperaug basin is a small (~12 by ~4 km),
Late Triassic to Early Jurassic age rift located about 20
km west of the Hartford basin and roughly centered
near Southbury, Connecticut (Davis, 1888; Hobbs,
1901; Rodgers, 1985)(Fig. 1). The stratigraphy of the
Pomperaug basin has been described by Davis (1888),
Hovey (1890),Hobbs (1901),Scott (1974), and Rod-
gers (1985). Work by Davis (1888) and Hobbs (1901),
and data from an early oil exploration well (Hovey,
1890), clearly reveals the presence of two basin-wide
basalt flow units intercalated with fluvial and lacustrine
strata, then believed to be of Late Triassic age.
Both Davis (1888) and Hobbs (1901) show, how-
ever, that the Pomperaug basin is structurally complex
with several generations of post-depositional faulting.
Some of the complexity in the basin structure is almost
certainly due to the presence of inversion structures
formed under post-extensional compression, similar to
that recently defined for other rifts in the Newark
Supergroup (Withjack et al., 1998; LeTourneau,
2003; Burton et al., 2005). This structural complexity,
coupled with discontinuous exposures, has contributed
to varied interpretations of basin stratigraphy. For ex-
ample, although early workers (Davis, 1888; Hovey,
1890; Hobbs, 1901) document two separate basalt flow
units, Krynine (1950),Scott (1974),Rodgers (1985),
and more recently Philpotts (1998) suggest the pres-
ence of three basalt flow units based mainly on com-
parison with the neighboring Hartford basin. On-going
work by the U.S. Geological Survey in the Pomperaug
basin (Burton et al., 2005) also suggests the possibility
of a third basalt flow, but, to date, the macroscopic and
geochemical characteristics of the unit remain ambig-
uous. It is just as likely that the unit is in a faulted
block of the Orenaug, or main, basalt. Advocates of
the bbroad-terraneQhypothesis cited the Pomperaug
basin as evidence of the former connection of the
Hartford and Newark basins (Russell, 1892; Hobbs,
1901; Barrell, 1915; Longwell, 1922). Influenced by
the broad-terrane hypothesis, Krynine (1950) believed
that the Pomperaug rift was merely an eroded boutlierQ
of the large neighboring Hartford Basin and he sug-
gested that the stratigraphy of the two basins was the
same. Modern interpretations of the Pomperaug stra-
tigraphy by Scott (1974) and Rodgers (1985) adopted
the Hartford basin terminology and considered the
basin an boutlierQfollowing Krynine’s (1950) hypoth-
esis. It is interesting to note that of the writers who
proposed stratigraphic schemes for the Pomperaug
only Davis (1888),Hobbs (1901), and Scott (1974)
actually conducted extensive field research in the
basin. Scott (1974) was obviously led astray by the
complex structure and glacial till cover when he pro-
posed up to five or more intercalated sedimentary and
basalt units within the lowest flow. Because the basalt
flows provide important stratigraphic markers that are
traceable throughout the basin, work to determine the
distribution and character of the flows and their rela-
tionship to three intercalated sedimentary formations of
P.M. LeTourneau, P. Huber / Sedimentary Geology 187 (2006) 63–81 65

Late Triassic and Early Jurassic age is continuing
(Burton et al., 2005).
We advocate the hypothesis that the Pomperaug
basin was an isolated basin (Davis, 1888; Huber and
McDonald, 1992; Burton et al., 2005) based on sedi-
mentological evidence, especially paleocurrents and
clast provenance that clearly show eastern and western
source areas. Our reinterpretation of the Pomperaug
stratigraphy is in general agreement with the early
interpretations of Davis (1888) and Hobbs (1901) and
the relatively unambiguous stratigraphy from explor-
atory oil well data reported by Hovey (1890). None of
the previous workers in the Pomperaug basin formal-
ized the stratigraphic nomenclature, either by the stan-
dards of their day (e.g., Davis, 1888; Hobbs, 1901)orin
accordance with modern criteria, and there are no de-
scribed type sections or reference sections for lithostra-
tigraphic units.
Rodgers (1985) applied the stratigraphy of the near-
by Hartford basin to the Pomperaug. However, Rodgers
(1985) did not realize that most of the Hartford basin
rock units he extended into the Pomperaug basin them-
selves lacked valid defined stratotypes, and that the
Pomperaug rocks are composed of lithosome associa-
tions that are, by and large, distinct from their Hartford
basin chronostratigraphic equivalents.
We have revised the stratigraphic nomenclature of
the Pomperaug basin based on our stratigraphic and
sedimentologic investigations (Burton et al., 2005),
but until our work meets the publication criteria of
the North American Commission on Stratigraphic No-
menclature (NACSN, 1983), the lithostratigraphic units
named here should be considered informal, but accu-
rate, descriptions of basin stratigraphy. Note, however,
that the U.S. Geological Survey has adopted our strati-
graphic nomenclature for Pomperaug basin strata and
basalts (Burton et al., 2005; in prep.). We do not refer to
the earliest stratigraphic nomenclature of Davis (1888)
or Hobbs (1901) because their terminology is antiquat-
ed, cumbersome, and confusing (e.g., banterior shale,Q
bposterior basalt,Qbamygdaloid,Qetc.). Nor do we refer
to the earlier stratigraphic units of Rodgers (1985) or
Scott (1974) because their interpretations are clearly in
error as shown by simple field relationships and super-
position of strata (Burton et al., 2005), and use of the
incorrect stratigraphic scheme would serve only to
further obfuscate the geologic relationships in the Pom-
peraug basin.
In our revised stratigraphy (Fig. 3) the coarse fluvial
South Britain Formation (~250 m) of Late Triassic and
Early Jurassic age forms the base of the Pomperaug
basin section. The Triassic–Jurassic boundary is located
in the uppermost portion of the South Britain Forma-
tion. The South Britain Formation is overlain by Early
Jurassic strata (Huber and McDonald, 1992; Lucas and
Huber, 1993) in the following vertical succession: the
East Hill Basalt (10 m); the fluvial, eolian, and lacus-
trine Cass Formation (40 m); the Orenaug Basalt, 80 m;
and the fluvial and lacustrine White Oaks Formation
(30+ m). A possible third basalt unit is not shown in
Fig. 3 because, at the time of this writing, its identity
remains ambiguous. The eolian sandstone described in
this paper comprises the upper several meters of the
Cass Formation.
3. Eolian sandstones of the Pomperaug basin
3.1. Location and occurrence
The eolian sandstone is exposed in two quarries
about 5 km apart near the towns of Southbury and
Woodbury, Connecticut. In addition, talus and float
blocks of eolian sandstone are abundant at the correla-
tive stratigraphic interval of the Cass formation in
several areas of the basin including Platt Farm Park
near South Britain, and exposures along South Brook
located about 1 km south of the northern (Woodbury)
quarry (Fig. 4). The eolian sandstone rests on fluvial
Fig. 3. Stratigraphic section of the Pomperaug basin.
P.M. LeTourneau, P. Huber / Sedimentary Geology 187 (2006) 63–8166

conglomerate, sandstone, and siltstone and is overlain
by the upper lava flow—the Orenaug basalt (Fig. 3).
The base of the section containing the eolian sandstone
consists of poorly sorted fluvial conglomerate contain-
ing clasts of high-grade metamorphic rocks, plutonic
igneous rocks, and dolomitic marble. The coarse fluvial
rocks are overlain by weakly bedded, red-brown, silt-
stone with deep root traces, in turn overlain by an
extensive horizon of pedogenic carbonate nodules and
calcareous rhizoconcretions found directly beneath the
eolian sandstone (Fig. 5).
The eolian sandstone ranges from light tan to light
yellow-brown and has secondary light to dark brown
limonite and green malachite mineralization along
coarse-grained, porous laminae. Individual eolian beds
about 0.5- to 1-m thick combine to form a sandstone
unit up to 3-m thick. Low-angle, planar to undulatory
surfaces form the contacts between the beds, and cross-
bedding ranges from low- to high-angle as a function of
apparent dip of the foresets and variable foreset inclina-
tions (Fig. 6). The eolian beds are overlain by a 5- to
10-cm bed of well-sorted shallow lacustrine sandstone
with planar lamination and oscillatory ripple cross-lam-
ination (Fig. 7).
The section described above is capped by the 80-m
thick Orenaug basalt that provides basin-wide stratigraph-
ic control for correlation of exposures of the eolian sand-
stone. The eolian beds, including the undulatory surface
Fig. 4. Simplified geologic map of the Pomperaug basin.
Fig. 5. Caliche paleosol and calcified roots traces in unit underlying eolian sandstone.
Fig. 6. (A) Eolian dune showing multiple truncation surfaces from
dune migration and reactivation of slip faces. (B) Tracings of cross-
bedding and surfaces.
P.M. LeTourneau, P. Huber / Sedimentary Geology 187 (2006) 63–81 67

of the dune field, were apparently preserved by the over-
lying basin-wide basalt flow. Similar preservation of eo-
lian sandstones by extensive lava flows has been
described for Precambrian rocks in South Greenland
(Clemmensen, 1988), and for Cretaceous deposits in
Namibia (Mountjoy et al., 1999) and in Brazil (Scherer,
2000). Portions of the lower contact of the Orenaug lava
flow contain vesicular pillow structures (Fig. 7) indicat-
ing that, in places, the flow encountered surface water.
These observations support the sedimentological evi-
dence that in some areas (inter-dune) the upper few
centimeters of the eolian deposit were briefly reworked
under sub-aqueous conditions, as discussed below.
3.2. Sedimentary structures
Diagnostic sedimentary structures observed in eolian
sandstones of the Upper Cass Formation of the Pom-
peraug basin compare favorably with features observed
in modern and ancient eolian sand deposits. Recogni-
tion of the inverse-graded strata formed by subcritically
climbing high-index ripples and grainflow and grainfall
cross-stratification is key to the identification of eolian
sand deposits (Hunter, 1981; Kocurek and Dott, 1981;
Fryberger and Schenk, 1988).
3.2.1. Pinstripe lamination
The Pomperaug basin eolian sandstone contains lat-
erally continuous, inverse-graded horizontal and low-
angle inclined laminae that repeat vertically to form a
distinctive bpin-stripeQappearance (Figs. 7, 8). Al-
though relatively scarce, isolated high-index ripples
are also observed as millimeter-scale lenses within
inverse- and normal-graded laminae in the Pomperaug
basin sandstone. Inverse-graded pin-stripe lamination
results from grain sorting in migrating high-index
Fig. 7. Upper contact of the eolian sandstone. Bed immediately overlying the dune foresets is lacustrine re-worked eolian sand with planar
lamination and oscillatory ripples in upper surface (not visible in this view). Topmost unit is basalt with pillow structures.
Fig. 8. Block of eolian sandstone showing diagnostic features. Gfa, grainfall layer; gfl, grainflow (mass flow) layer.
P.M. LeTourneau, P. Huber / Sedimentary Geology 187 (2006) 63–8168

wind ripples, where finer grains are deposited in ripple
troughs and coarser grains are deposited on the ripple
crests and upper lee slopes (Hunter, 1977a; Fryberger
and Schenk, 1988; Kocurek and Dott, 1981, Schenk,
1990). Fryberger and Schenk (1988) demonstrated the
origin of inverse-graded lamination by wind ripples in
laboratory experiments and field studies of modern and
ancient eolian dunes.
3.2.2. Grainfall deposits
Other distinctive eolian features of the Pomperaug
basin beds are well-sorted, non-graded cross-laminae
that form sheet-like asymmetric wedges that thicken
abruptly toward foreset toes and thin gradually toward
the upper slipface (Figs. 8, 9). These fine-to-medium-
grained layers interfinger with coarse-grained, wedge-
shaped, cross-strata (described below), and truncate
against basal, low-angle and horizontal surfaces com-
prised of wind ripple laminae. These clinoform-shape
layers are interpreted as grainfall deposits that form by
direct fall-out of sand in the zone of airflow separation
in the leeward side of dunes (Hunter, 1977a, 1981;
Fryberger and Schenk, 1988; Kocurek and Dott,
1981; Schenk, 1990). The interfingering of grainfall
layers with grainflow and wind ripple laminae suggests
that the upper Cass Formation dunes were relatively
small, meter-scale bedforms (Kocurek and Dott, 1981;
Kocurek, 1996).
3.2.3. Grainflow deposits
The eolian origin of the sandstone is also indicated
by layers of medium to coarse sand that interfinger with
grainfall and wind ripple laminae (Figs. 8, 9). These
distinct sedimentary structures variably referred to as
grainflow (Kocurek and Dott, 1981; Kocurek, 1996),
sandflow (Hunter, 1977a), or avalanche (McKee, 1979;
Schenk, 1990) cross-beds. The Cass Formation grain-
flow cross-beds are massive (non-graded) to inverse-
graded and form asymmetrical clinoforms that thin
abruptly toward the lower slipface, and taper gradually
toward the upper slipface (Figs. 8, 9). Strike-parallel
views of the Pomperaug grainflow layers reveal narrow
(decimeter-scale), thin (centimeter-scale) coarse-
grained lenses with rounded tops and flat bottoms.
The grainflow layers recognized in the Pomperaug
basin sandstones are similar in geometry and grain
size to grainflow tongues observed in small modern
eolian dunes (Hunter, 1977a; Kocurek and Dott, 1981).
3.3. Bedding
The meter-scale cross-bedding in the sandstone
ranges from low- to high-angle with a maximum dip
of approximately 308(tilt corrected) (Figs. 6, 7). Cross-
stratification is predominantly wedge-planar and sets
taper to low-angle tangential contacts at the lower
bounding surfaces. Internally, the laminae comprising
the cross-stratification have varied textures ranging
from inverse-graded to normal-graded to massive
(non-graded) in wind ripple, grainfall, and grainflow
laminae. Contacts between cross-laminae range from
parallel and continuous to irregular and discontinuous
to lenticular. Most of the eolian beds observed in the
Pomperaug basin contain dune-form cross-stratification
bounded by low-angle planar to undulating surfaces.
Low-angle inclined planar stratification is less com-
mon, which suggests that the Pomperaug eolian envi-
ronment was dominated by dunes rather than low-angle
sand sheets or extensive interdune areas (Ahlbrandt and
Fryberger, 1981).
Migration of dunes and repetitive aggradation and
erosion of dune flanks modify depositional bedding
patterns and commonly create a hierarchy of bounding
surfaces that reflect the interplay between sand depo-
sition and erosion on several temporal and spatial
scales (Brookfield, 1977; Fryberger, 1990a,b;
Kocurek, 1986, 1988, 1996). The sandstone beds in
the Pomperaug basin contain a hierarchy of bounding
surfaces separating compound cross-bed sets. Second-
order surfaces (sensu Fryberger, 1990b) created by
dune migration form prominent surfaces truncate the
Fig. 9. Blocks of eolian sandstone showing diagnostic features. Gfa,
grainfall layer; gfl, grainflow (mass flow) layer.
P.M. LeTourneau, P. Huber / Sedimentary Geology 187 (2006) 63–81 69

eolian cross-beds at low angles (Fig. 6), and the third-
order reactivation surfaces form angular discordances
between cross-beds (Fig. 8) as a result of local re-
working and reactivation of dune slip faces (Fryberger,
1990a; Fryberger et al., 1979; Kocurek, 1996). The
upper part of the eolian sandstone bed is in places
truncated by the overlying basalt flow and locally by a
thin layer of eolian sand reworked by shallow lacus-
trine processes.
3.4. Texture
The Pomperaug basin sandstone consists of moder-
ately well-sorted, fine to coarse sand. The layers pos-
sess a bimodal segregation of medium and coarse sand
in distinct layers and lenses, but highly sorted contin-
uous and discontinuous laminae are common as a result
of sub-aerial grain sorting processes (Fryberger and
Schenk, 1988). Sand grains range from sub-rounded
to well-rounded and consist of mostly of quartz with
subordinate quantities of feldspar and lithic fragments;
mica flakes are notably absent. Laboratory measure-
ments of porosity and liquid and gas permeability
support high porosities observed in hand sample. Po-
rosities range from 14% to 21%, and gas and liquid
permeabilities (in millidarcies, mD) reach values as
high as 395 and 368 mD, respectively. In addition,
certain beds or layers observed in outcrop contain
prominent malachite grain coatings and pore fillings.
The malachite is the result of secondary hydrothermal
mineralization that preferentially penetrated high poros-
ity eolian sandstones and fractures in sedimentary and
igneous rocks in the Pomperaug basin. The high poros-
ity and permeability of the eolian sandstone, coupled
with the fact that it is capped by a thick, less permeable,
basalt flow unit, suggest that it has a very good poten-
tial to be a significant aquifer.
Although textural characteristics are not entirely
reliable indicators of eolian sand (Ahlbrandt, 1979),
modern dune sands are commonly well-sorted with
well-rounded individual grains (Ahlbrandt and Fryber-
ger, 1982). In addition, the general absence of mica in
the Pomperaug sandstone beds, in contrast with the
highly micaceous siltstones and arkosic sandstones
that form most of the basin section, suggests that
mica flakes were effectively winnowed during subaerial
transport.
3.5. Paleocurrents
Measurements of dune-scale cross stratification in-
dicate a mean sand transport azimuth direction of 0168
(north–northeast) (Fig. 10). Dispersion of foreset dip
directions is low, perhaps due to the relatively small
number of measurements (n= 28) obtained from five
cross-bed sets, or a fairly well organized set of
straight- to slightly sinuous-crested dunes. Limited
three-dimensional exposures revealed mainly trans-
verse dune forms with straight crested to broadly
barchanoid or sinuous dune morphologies. The paleo-
current directions indicate that sand was transported
north and east, roughly parallel to the long axis of the
rift (Fig. 4).
3.6. Interpretation
The sedimentary structures and features described
above compare favorably to those observed in modern
dune sands and in ancient sandstones interpreted as
eolian deposits. In particular, the presence of repetitive
inverse-graded pinstripe laminae with interbedded
grainfall and grainflow laminae are considered diagnos-
tic of eolian sedimentation (Hunter, 1977a, 1981;
Kocurek and Dott, 1981; Fryberger and Schenk,
1988; Kocurek, 1996). Other more ambiguous sedi-
mentary features support an eolian interpretation when
found with the above-mentioned fabrics include good
sorting, high primary porosity and permeability, types
of hierarchical bounding surfaces, meter-scale cross-
bedding, and slump sheets (e.g., Hunter, 1977a,b,
1981; Fryberger et al., 1979; McKee, 1979; Kocurek
and Dott, 1981; Schenk, 1990).
Based on the thickness of the cross-bed sets and the
minimum 5 km lateral extent of the eolian sandstone,
the Pomperaug eolian beds evidently formed a thin field
Fig. 10. Paleocurrent direction derived from eolian foresets.
P.M. LeTourneau, P. Huber / Sedimentary Geology 187 (2006) 63–8170

of small dunes with amplitudes up to several meters.
The grainfall and grainflow wedges at the foreset toes,
coupled with the scale of some of the sedimentary
structures (Fig. 9), suggest that the dunes were small
(G. Kocurek, pers. comm.) in comparison to those
found in coeval rifts such as the Fundy and Argana
basins (see below). A modern analogy for the Pomper-
aug dune field may be the dune field at Stovepipe Wells
in Death Valley, California (Fig. 11E, F), where a
relatively thin layer of eolian sand overlies playa-lake
beds and the height of the dunes averages about 2–3 m,
reaching a maximum of about 7–10 m.
Fig. 11. Eolian sandstone from the Portland brownstone quarry, Portland Formation, Portland, Connecticut and modern dune field and coppice
dunes, Stovepipe Wells, Death Valley, California. (A) Outcrop (left) and cut slab (right) of Portland brownstone showing inverse-graded wind ripple
laminae (selected examples shown in brackets) and normal-graded layers. (B) Eolian dune foresets with inverse-graded wind ripple laminae and
grainfall and grainflow toesets. (C) Coppice dune (bracketed), view is sub-parallel to flow direction. (D) Cross-cutting sets of inverse-graded wind
ripple laminae. Thick striations on surface are chisel marks on surface of worked quarry block. (E) Coppice dune (arrow), Stovepipe Wells, Death
Valley, California. Numerous coppice dunes are shown at top right. (F) View south and west across Stovepipe Wells dune field, Death Valley,
California. Average thickness of eolian sand overlying carbonate and saline playa beds, and alluvial fan deposits (background) is about 3 m with
largest dunes reaching about 10 m. (G) Cartoon of coppice dunes and their internal structure (inset).
P.M. LeTourneau, P. Huber / Sedimentary Geology 187 (2006) 63–81 71

3.7. Preservation of the Pomperaug eolian dune field
Our observations lead us to conclude that the Pom-
peraug eolian dune field was ultimately preserved by
the overlying basin-wide Orenaug basalt flow (Fig. 7).
As the lava flow filled the Pomperaug rift surface
waters were displaced and the upper several centi-
meters of the eolian deposit were reworked by shallow
and temporary lake waters. The presence of ponded
water in the brief interval between dune deposition and
preservation by the lava flow is also indicated by well-
developed, oscillatory ripples at the top of the Cass
Formation and pervasive vesicular pillow structures at
the base of the overlying Orenaug basalt at all local-
ities where the eolian sandstone–basalt contact is ob-
served. The source of the displaced surface water in
the hypothesized arid to semi-arid interval was likely a
playa lake ponded near the footwall margin of the rift,
or perhaps from fluvial watersheds and channels
whose drainage was disrupted by the westward ad-
vance of the Orenaug Basalt from source areas located
more than 20 km away in, and near, the Hartford
basin. Regardless, the occurrence of extensive dune
fields and playa lakes within a single depositional
basin is common in many modern arid to semi-arid
extensional valleys, including those of the U.S. basin
and range province.
An alternative hypothesis for the preservation of the
dune field that cannot be entirely discounted requires a
return to humid climatic conditions that stabilized the
eolian sand by raising the regional water table (e.g.,
Stokes, 1968; Clemmensen and Dam, 1993; Crabaugh
and Kocurek, 1993; Kocurek and Havholm, 1993;
Benan and Kocurek, 2000) and submerging the dunes
beneath shallow lacustrine waters. This hypothesis is
appealing, but the lack of fluvial deposits and the
apparently slight reworking of the upper layers of eo-
lian sand would require a very rapid rise in lake level.
The short-term astronomically forced climate cycles are
approximately 21 ky long with the transition from
maximum wet to maximum dry conditions taking
about 10 ky which we feel would have likely caused
greater reworking or destruction of the eolian sand
layers. Based on our analysis of the foreset structures,
the Pomperaug dunes were in the meter-scale range,
although some amalgamated dunes may have reached
up to 3–5 m, and therefore the relatively thin dune field
may have been particularly susceptible to reworking
under a more humid climatic regime. However, the
original thickness of the eolian deposits, and the
amount of possible erosion are unknown. Furthermore,
the occurrence of the lava flow nearly coincident with
the shallow lacustrine conditions seems to us unrealis-
tically fortuitous.
4. Discussion
4.1. Eolian sandstones in related Pangean rift basins
Eolian sandstones occur in Newark Supergroup rift
strata in the Fundy and Hartford basins, and the Argana
(Morocco) rift basin. In the Hartford basin, LeTourneau
(2002) recognized eolian sandstones in the Hettangian
Portland Formation at the Portland bbrownstoneQquar-
ry, Portland, Connecticut, as well as in samples of the
Portland Formation from dimension stone quarries at
Longmeadow, Massachusetts.
The strata of the Portland brownstone quarry are of
both fluvial and eolian origin (Fig. 11). The eolian
strata (LeTourneau, 2002) include: sand sheet deposits
dominated by inverse-graded wind ripple laminae
(pinstripe lamination) (Fig. 11A); small-scale dune
forms with pinstripe laminae and grainfall and grain-
flow toesets (Fig. 11B, D); and unusual bcoppiceQ
dunes deposited around clumps of vegetation (Fig.
11C, E, G).
The porosity and permeability of the Portland eolian
sandstones are lower than either the Pomperaug or
Longmeadow eolian sandstones. Porosity of the Port-
land brownstone measured about 10% and gas and
liquid permeability measured 5 and 7 mD, respectively
(LeTourneau and Olsen, unpublished data). The Long-
meadow samples have 21% porosity-comparable to the
porosity of the Pomperaug samples, and permeabilities
of 78 mD (gas) and 73 mD (liquid) (LeTourneau and
Olsen, unpublished data).
We identify here for the first time eolian sandstones
in outcrop and quarry blocks at the Newgate Prison
State Park, Granby, Connecticut (Fig. 12). Due to an
unconformity which cuts out the Talcott basalt, an
important stratigraphic marker, it is uncertain if the
Newgate eolian beds are part of the Rhaetian upper
New Haven Formation or Hettangian lower Shuttle
Meadow Formation. We believe that the beds are in
the Rhaetian part of the upper New Haven Formation
and may be lateral equivalents of the thin eolian sand
sheets described by Smoot (1991a) (see below).
The Newgate eolian sandstone is formed mainly of
sand sheet beds containing pinstripe laminae (Fig. 12,
top) and isolated high index ripples. Other eolian fea-
tures including reactivation surfaces that cross-cut low-
angle, inverse-graded, dune foresets (Fig. 12, middle),
and grainfall and grainflow toesets (Fig. 12, bottom) are
observed at the Newgate site. Interestingly, the New-
P.M. LeTourneau, P. Huber / Sedimentary Geology 187 (2006) 63–8172

gate sandstones were mined during the American Co-
lonial Period for copper, which occurs as malachite
pore fillings, similar to, but in higher concentrations
than the malachite pore fillings observed in the Pom-
peraug eolian sandstone. The porosity of a sample
obtained from an outcrop near Newgate (we were not
allowed to sample the historic stone walls containing
some of the best eolian beds) was about 10% and the
permeability was negligible (LeTourneau and Olsen,
unpublished data), perhaps as a result of the copper
and silicate mineralization. In the Newgate Prison and
Pomperaug mineralizations the copper-bearing hydro-
thermal fluids preferentially flowed through the high
porosity eolian sandstones.
Smoot (1991a) described an eolian sand sheet from
the upper part of the Late Triassic New Haven Forma-
tion in the Hartford basin, Connecticut (Fig. 13). This
deposit, located in road cuts on I-691 in Meriden,
Connecticut, is 1–2 m thick and consists mainly of
low-angle inclined planar stratification with pinstripe
laminae and a small dune about 1m high. The well-
sorted medium to fine sandstone did not contain visible
mica, which is abundant and characteristic of the fluvial
beds that enclose the eolian sand sheet (Smoot, 1991a).
Hubert and Mertz (1980, 1984) and Nadon and
Middleton (1985) described eolian sandstones, the
Red Head beds, of the Fundy basin associated with
alluvial-fan and fluvial deposits. Hubert and Mertz
(1980, 1984) identified diagnostic eolian features in-
cluding; a hierarchy of bounding surfaces; sedimentary
structures including grainflow, grainfall, and wind-rip-
ple pinstripe laminae; large scale cross-strata; bimodal
Fig. 12. Eolian sandstone, Newgate Prison State Park, Granby, Connecticut (Late Triassic New Haven Formation, Hartford basin). All photos are
quarry blocks from copper mine and adjacent quarry. (top) Inverse-graded wind ripple laminae. (middle) Cross-cutting sets of inverse-graded wind
ripple laminae and small dune foresets. Arrows mark reactivation surfaces. (bottom) Foresets of small dune showing grainfall (upper arrow) and
grainflow laminae (upper arrow). Lower arrow at bounding surface.
P.M. LeTourneau, P. Huber / Sedimentary Geology 187 (2006) 63–81 73

grain size distribution; and presence of ventifacts. The
Red Head dunes are much larger than the dunes ob-
served in the Pomperaug basin, and the entire eolian
sequence there is measured in dekameters compared to
1–3 m for the Pomperaug. Paleocurrent directions
obtained from cross-beds indicates sand transport to-
ward the west–southwest by easterly to northeasterly
paleowinds in the Fundy basin. Nadon and Middleton
(1985) recognized similar eolian features and sand
transport directions in the Fundy basin, but also ob-
served features interpreted as wet interdune deposits,
including mud drapes and burrowed horizons.
An eolian sandstone (Fig. 14) approximately 20 m
thick and at least 50 km in lateral extent occurs in the
Tadrart Sandstone Member of the Bigoudine Formation,
Late Triassic (Unit t6 of Tixeront, 1973), in the Argana
basin, Morocco (see also Hofman et al., 2000; Olsen et
al., 2000, Et-Touhami and Olsen, 2003). The Argana
eolian sandstone contains high and low angle tabular,
wedge-planar, and trough cross strata in well-sorted
sandstone and characteristically shows a bimodal grain
size distribution between adjacent wind-ripple laminae.
Typical eolian features such as high-index ripples ori-
ented perpendicular to the dip of the dune slipface in
exhumed straight-crested dunes were also observed.
Porosity and permeability of the Tadrat eolian sandstone
are low, 7% and b1 mD (LeTourneau and Olsen, un-
published data), respectively, due in large part to sec-
ondary mineralization of a high porosity sandstone.
Of the eolian sandstones discussed here, those found
in the Fundy and Argana basins are the most extensive
and contain large-scale dune forms (Fig. 14). Recon-
structions of Late Triassic Pangaea show that the Nor-
ian-age eolian beds were deposited when the Fundy and
Argana rifts were located at paleolatitudes of approxi-
mately 178and 158, respectively (Kent and Olsen,
2000a,b; Kent and Tauxe, 2005). The extensive eolian
sandstones found in the Fundy and Argana rifts are
likely indicative of arid to semi-arid, regional, if not
hemispheric, paleoclimates at sub-tropical paleolati-
tudes (Olsen et al., 2000). Examination of Pangaean
rifts from southerly paleolatitudes reveals that eolian
sandstones become progressively scarce with only three
distinct occurrences noted in the Hartford basin, one in
the Pomperaug basins, and one in the Newark basin. No
eolian occurrences of any age have been noted in the
Fig. 13. Eolian dune deposits, upper New Haven Formation, Meriden, Connecticut. First described by Smoot (1991a,b) this outcrop shows large
scale dune foresets with grainfall and grainflow foresets, and inverse-graded wind ripple laminae (pinstripe laminae). Scale bar is 1 m.
Fig. 14. Eolian dunes of the lower Bigoudine formation, Late Triassic,
Argana basin, Morocco. (top) Meter-scale dune foresets enclosed in
second-order bounding surfaces. Photo: Paul E. Olsen, Columbia
University (bottom). View of the Bigoudine dune field north of
Argana, Morocco. Photo: Mohammed Et-Touhami, LGVBS, Univer-
site’ Mohamed Premier, Oujda, Morocco.
P.M. LeTourneau, P. Huber / Sedimentary Geology 187 (2006) 63–8174

Newark rifts at paleolatitudes less than ~158by previ-
ous workers (Olsen, 1997; Smoot, 1991a,b; Smoot and
Olsen, 1994; LeTourneau, 2003; Kent and Tauxe,
2005).
4.2. Paleoclimate considerations
The Late Triassic and Early Jurassic Pangaean world
apparently represent an important end-member state
with a maximum of continental aggregation and a
global climate dominated by a strong land–sea contrast
(Chandler et al., 1992; Parrish, 1993). In the Late
Triassic and Early Jurassic the Pangaean landmass
spanned from about 858Nto908S(Ziegler et al.,
1982) and was arranged nearly symmetrically about
the equator (Chandler et al., 1992). Furthermore, during
the Late Triassic and Early Jurassic the polar latitudes
of Pangaean were likely ice-free (Frakes and Francis,
1988) and atmospheric CO
2
may have approached four
times present values (Berner, 1990, 1991). In concert
with elevated global temperatures, the presence of a
large Pangaean landmass may have promoted a strong-
ly seasonal bmegamonsoonQclimate dominated by a
persistent summer low pressure system over the vast
continental interior (Kutzbach and Gallimore, 1989;
Parrish, 1993). Parrish (1993) further suggests that
the monsoonal climate would have completely dis-
rupted zonal climate belts in the Late Triassic and
Early Jurassic.
The modern moisture balance model (MMBM) of
Crowley and North (1991) allows predictions about
the depositional environments expected at various
latitudes (and paleolatitudes) (Fig. 15). If paleolati-
tudes of climate-sensitive rocks are known with some
certainty, their plotted position on the MMBM should
show rough agreement with expected facies. Further-
more, the MMBM suggests a possible range of re-
sponse to astronomical climate forcing (Fig. 16).
Depositional environments in basins located at lati-
tudes near the humid or arid maxima should show
little variability because only extreme astronomical
forcing could cause the necessary deviation from the
mean expected precipitation (Zones 1 and 3, Fig. 16).
Sediment deposited at latitudes located near the zero-
crossing points of the MMBM should show a high
degree of variability because astronomical forcing will
cause periodic alternations between bhumidQand
baridQmodes (Zone 2, Fig. 16). Lastly, the validity
of the zonal climate belts predicted by the MMBM
are testable over geologic time by comparing data
from ancient sedimentary deposits with the range of
expected facies.
The Fundy basin is located within the arid zone
maximum predicted by the MMBM and indeed it
does contain abundant evidence of arid to semi-arid
depositional environments, with few excursions into
wetter paleoclimates in the Early Jurassic (Hubert and
Mertz, 1980, 1984; Nadon and Middleton, 1985; de
Fig. 15. Modern moisture balance model of Crowley and North (1991) showing latitudinal distribution of climate belts. Location of basins discussed
in text shown for reference.
P.M. LeTourneau, P. Huber / Sedimentary Geology 187 (2006) 63–81 75

Wet and Hubert, 1989; Olsen, 1997; Smoot, 1991a;
Tanner, 2003). Most of the Fundy basin stratigraphic
section is dominated by eolian and fluvial-reworked
eolian sand, while organic-rich, deep-water lacustrine
are absent and shallow lake or palustrine beds are
scarce (Tanner and Hubert, 1992; Olsen, 1997). Appar-
ently, the Fundy basin was located favorably within the
central part of the evaporation-dominated envelope of
the MMBM and only rarely did orbitally forced climat-
ic fluctuations cause a shift into precipitation-dominat-
ed paleoclimates (Fig. 16). As North America
continued to drift north in the Early Jurassic, the
Fundy basin drifted away from the arid maxima and
closer to the zero-crossing point on the MMBM, allow-
ing a greater range of depositional climates due to
astronomical forcing, and indeed the Early Jurassic
rocks show evidence of increased precipitation (de
Wet and Hubert, 1989; Olsen, 1997; Tanner, 2003).
The Argana basin, Morocco, located a little south of
the Fundy basin in the Late Triassic, is also dominated
by arid and semi-arid facies, but does include a few
perennial lacustrine beds (Olsen, 1997; Olsen et al.,
2003).
In contrast, the bsouthernQNewark rifts, including
Carnian-age rocks of the Richmond and Taylorsville
basins in Virginia (Fig. 1), are dominated by organic-
rich lacustrine and palustrine deposits, including coal
beds and seams, and fluvial sequences, deposited near
the paleoequator. Plotting those basins on the MMBM
shows that they were located within a precipitation-
dominated envelope of the model and only rarely
could astronomically forced climatic fluctuations
cause a shift into evaporation-dominated paleoclimates
(Kent and Olsen, 2000a; LeTourneau, 2003; Olsen and
Kent, 2000; Olsen et al., 2000). As the Taylorsville
basin drifted north away from the paleoequator and
toward the northern edge of the humid paleoequatorial
zone its rocks show a broader range of climate-sensitive
facies and a shift from lacustrine, deltaic, and coal
deposits to intercalated and alternating shallow lacus-
trine and fluvial deposits with well-developed carbon-
ate paleosols.
Basins located at paleolatitudes sensitive to small
fluctuations in the E–P balance should show wide
paleoenvironmental variations in deposition, ranging
from deep lake organic-rich black shale (lacustrine
and palustrine), to perennial and ephemeral streams
and rivers, to eolian deposits. The Newark, Hartford,
and Pomperaug basins do show a wide range of
depositional environments but the Pomperaug and
Hartford basins are located near the modern arid max-
imum (Fig. 15). If the MMBM holds in the Late
Triassic and Early Jurassic, those basins should con-
tain a record of mainly arid depositional environments.
While arid indicators such as caliche paleosols
(Hubert, 1978), halite crystal molds (Parnell, 1983),
and eolian sandstones (Smoot, 1991a) may be found in
certain stratigraphic intervals, organic-rich deep lake
shales (Olsen, 1986, 1997) and perennial fluvial
deposits (Hubert et al., 1978) are common and occur
Fig. 16. Our model of sensitivity of basin environments based on position within climate belts. Sediments deposited in basins located near edges of
climate belts have greater sensitivity to orbitally forced variability and show alternations of humid and arid facies. Basins located toward central
portions of climate belts are less sensitive and tend to contain either predominately arid or predominately humid facies.
P.M. LeTourneau, P. Huber / Sedimentary Geology 187 (2006) 63–8176

with cyclic regularity within the basin section (Olsen,
1984).
Comparison of the paleolatitudinal distribution of
eolian sandstones in the Newark rift with the MMBM
of Crowley and North (1991) shows that the deposits
formed within the central part of the evaporation-dom-
inated climate zone, ranging from about 158Nto258N
during the Norian–Hettangian. What is surprising, how-
ever, is that there are no eolian deposits recognized at
lower paleolatitudes within the Newark rifts, closer to
the 118N zero-crossing of Crowley and North’s (1991)
moisture balance model.
There are, however, sedimentary indicators of arid
conditions at lower paleolatitudes. Abundant, well-de-
veloped Norian-age carbonate paleosols that formed
between 98and 118N are found in the Leedstown
Formation of the Taylorsville basin, Virginia (LeTour-
neau, 2003), and Coffey and Textoris (2003) describe
Norian carbonate paleosols formed about 3–58N from
the Durham sub-basin of the Deep River basin, North
Carolina. There is also evidence of Norian-age evapo-
rite mineral formation at 10–128N in the Newark basin
(Olsen, 1997; Olsen and Kent, 2000; Kent and Tauxe,
2005).
The MMBM of Crowley and North (1991) (Fig. 15)
indicates that precipitation exceeds evaporation below
118N latitude and evaporation exceeds precipitation in
the sub-tropical zone from about 118to 35 8N latitude.
The Pangaean rift eolian sandstones of the Newark
Supergroup are at paleolatitudes within descending
air-mass (btrade windQ) zones based on modern atmo-
spheric circulation patterns (e.g., Glennie, 1987;
Kocurek, 1996), supporting the hypothesis (contra Par-
rish, 1993) that zonal circulation patterns prevailed
during the Late Triassic and Early Jurassic on Pangaea
(Kent and Olsen, 2000b; Kent and Tauxe, 2005). Al-
though zonal paleoclimate patterns may have prevailed,
they were likely modified from modern patterns. Fur-
thermore, the paleogeographic patterns of Newark eo-
lian sandstones and their correspondence with the
modern negative moisture balance zone argue against
the hypothesis that orography strongly controlled cli-
mate in the Pangaean breakup rifts (Manspeizer, 1982).
The Pomperaug basin eolian sand beds overlie a
well-developed caliche paleosol indicative of arid to
semi-arid conditions (Fig. 5). Pedogenic carbonates
form optimally in strongly seasonal climates with
mean annual precipitation estimated as less than
1000 mm by Blodgett (1988) and less than 760 mm
by Royer (1999). Correlation of the eolian unit over a
minimum extent of 5 km shows that the Pomperaug
basin eolian sandstone is a nearly basin-wide deposit
that formed during an arid to semi-arid interval, rather
than a local deposit of wind-blown sand. This hypoth-
esis is supported by the regional correlation of the
Pomperaug eolian sandstone with an arid interval in
the Hartford (LeTourneau, 2002) and the Newark
basins (Olsen and Kent, 1996; Olsen et al., 1996).
Thus, the Pomperaug eolian sandstone formed at
paleolatitudes where evaporation exceeded precipita-
tion in an arid to semi-arid climatic interval that
promoted the development of eolian dunes. The
Cass Formation (Fig. 3) also contains organic-rich
lacustrine beds with abundant fossil fish, indicating
that the climate within the Pomperaug rift alternated
between arid to semi-arid and humid intervals similar
to periodic paleoclimate patterns observed throughout
the Newark Supergroup (e.g., Olsen, 1986; Olsen,
1997). The association of humid depositional facies
alternating with arid facies in the Pomperaug, Hart-
ford, and Newark basins suggests that the latitudinal
distribution of climate zones defined by the modern
moisture balance model of Crowley and North (1991)
may, in fact, have differed in the Late Triassic and
Early Jurassic.
The wide range of alternating humid to arid deposi-
tional environments in the Pomperaug, Hartford and
Newark basins suggest that the zonal climate belts
delineated by the MMBM were modified in the Late
Triassic and Early Jurassic (Fig. 17). Accommodation
Fig. 17. Possible configuration of early Mesozoic low latitude, north-
ern hemisphere climate belts based on distribution of Pangaean rift
eolian sandstones. Note that the transition between zones is attenuated
and the arid zone is shifted south in comparison to modern zones.
P.M. LeTourneau, P. Huber / Sedimentary Geology 187 (2006) 63–81 77

of both low latitude carbonate paleosols in the Taylors-
ville and Deep River basins and alternating humid and
arid conditions in the Pomperaug, Hartford, and New-
ark basins (Zone 2, Fig. 16) is accomplished by atten-
uating the gradient between the equatorial humid and
sub-tropical zones and by shifting the sub-tropical arid
belt southward (Fig. 17).
The next challenge in assessing early Mesozoic
paleoclimates of the Pangaean rift system is to apply
quantitative methods, using known precipitation values
for climate sensitive rocks and compare those values
with calculated precipitation variability expected from
orbital forcing, to further constrain and define the dis-
tribution of atmospheric patterns in the supercontinent-
dominated Late Triassic and Early Jurassic.
5. Conclusions
The laterally extensive eolian sandstones in the
Early Jurassic (Hettangian) Pomperaug and Hartford
rift basins are evidence for paleolatitudinal distribution
of arid to semi-arid environments. Previously, large
scale eolian deposits were recognized in Norian–Het-
tangian strata in the Fundy basin, Canada, Norian rocks
of the Argana basin, Morocco, and a few limited
occurrences in Rhaetian–Hettangian rocks of the New-
ark and Hartford basins. The Pomperaug basin sand-
stone is one of the most southerly Early Jurassic eolian
deposits within the Newark Supergroup rifts, providing
a constraint for the distribution of climate-sensitive
rocks in the early Mesozoic. In the Pomperaug basin,
eolian sedimentation was favored by paleolatitudinal
position and deposition during an arid to semi-arid
climatic interval. Furthermore, the paleogeographic dis-
tribution of eolian sandstone and other arid facies sug-
gest that although the climate zones predicted by the
modern moisture balance model of Crowley and North
(1991) are recognizable in the early Mesozoic, the
zones were likely modified.
Acknowledgments
The authors thank John Hubert, Gary Kocurek, and
Paul Olsen for their careful reviews and constructive
comments. Ken Faroni, O and G Industries, Torrington,
Connecticut is thanked for access to basalt quarries in
the Pomperaug basin. Paul E. Olsen, Columbia Univer-
sity and Mohammed Et-Touhami, LGVBS, Universite’
Mohamed Premier, Oujda, Morocco graciously provid-
ed photos for Fig. 14. Porosity and permeability mea-
surements were made by Core Laboratories, Houston,
Texas.
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