SUNY Stony Brook
June 27, 2002
The Hartford Basin is one of the many rift basins
along the east coast of North America that formed during the early stages of
rifting of Pangea during the Triassic and Jurassic. The rifting of Pangea
eventually led to the formation of the Atlantic Ocean. The Hartford Basin
contains a thick sequence of stream and lake sediments and basaltic sills and
lava flows all of which are well exposed. We will have lunch at Dinosaur State
Park in Rocky Hill Connecticut where you will see five hundred dinosaur tracks
enclosed within the Exhibit Center's geodesic dome.
You may wish to visit some of these sites that give geological information pertinent to the Hartford Basin
Wesleyan College Virtual field trip through part of the Mesozoic Hartford Basin
Wesleyan College field trip to the Dinosaur State Park
Wesleyan College photos of pillow basalt at Stop 4
Colby College Field Trip to the Hartford Basin of Connecticut
Hunter College Newark Basin and Connecticut River Basin
Geologic Sketch Map of Connecticut
Early Mesozoic Paleontology in the Connecticut River Valley
Massive Ancient Fish Kills
breakup of Pangea Animation showing the motions of the continents during the last 200 million years.
Calcite Cements in a Fluvial Cycle, Hartford Basin, Connecticut
Flood basalt provinces of the Pangean Atlantic Rift: Regional extent and environmental significance by J. Gregory McHone and J.H. Puffer
Age of dinosaurs bracketed by asteroid or comet impacts
580 ky duration of the Early Jurassic flood basalt event in eastern North America estimated using Milankovitch cyclostratigraphy
International Workshop for a Climatic, Biotic, and Tectonic, Pole-to-Pole Coring Transect of Triassic-Jurassic Pangea
Extensional Tectonics Working Group /Triassic-Jurassic Working Group at Rutgers
Stop 1. Off exit 10 on Interstate 91 on Route
40 going toward Mt. Carmel and Hamden. We will examine a large exposure of an
alluvial plain sequence of sandstone and conglomerate interbedded with
floodplain mudstones and well-developed caliche profiles in the New Haven Arkose.
is a braided stream (alluvial plain) sequence of pale red, channel sandstone and
conglomerate interbedded with a small fraction (14%) of flood plain mudstone in
the New Haven Arkose. Caliche, soil calcite, commonly found in the B soil
horizon in semi-arid climates is found at the tops of mudstone sequences as well
as in some of the channel sediments. The braided streams were draining to the
southwest. The rivers were ephemeral, with large fluctuations in
water discharge associated with flash floods. There was a high gradient and the
streams carried a coarse bedload of sand and gravel. The flood plains were
exposed for periods long enough for soil horizons to develop before the next
channel would erode the sandy mud down to the caliche layer and then deposit
channel sands and gravels . Note that the caliche occurs as independent nodules,
around roots and occasionally as more massive units.
Stop 2. Dinosaur State Park at Rocky Hill,
Connecticut. At the Dinosaur Park please note in the
displays the environments of the setting of the Hartford Basin. In the
background of the large display you can see the mountains to the east with the
alluvial fans forming in front. The mountains are east of the border fault and
in the eroding basement. The alluvial fans are the settings for the Portland
Arkose at Stop 5. The streams and lakes are the setting for the East Berlin Formation. In
front of the building there is an outcrop showing a perennial lake sequence.
Stop 3. Northeast side of Highway 9 just
before exit 22 in Berlin Township. We will see a sequence typical of a perennial
lake setting in the East Berlin Formation. A typical sequence consists of pyritic black shale that
accumulated in a deep, anaerobic part of an alkaline lake. These beds sometimes
contain fossil fish remains. The gray mudstone on either side of the black shale
formed in shallow water and commonly has ripple marks, mud cracks and dinosaur
footprints. Sandstone is commonly found near the top and bottom of the cycles
and is indicative of shallow water near the shore. It is thought that the lakes
essentially covered the rift valley and periodically increased and decreased in
size perhaps due to Milankovitch
forcing (Olsen and Kent, 1996). Based on the pollen the climate was
humid with annual wet and dry seasons typical of the tropics.
Stop. 4. East side of Route 5 south of Hawthorne Inn (2387 Wilbur Cross Parkway, Berlin). We will see a sequence of vesicular pillow basalts. The pillows often have sediment or shattered volcanic debris between them. Pillow basalt forms under water. The pillows are actually tubes through which the lava flowed. The outer rim cools very rapidly and the lava flows through the center continually breaking through the cooled front. Most two-dimensional slices through a tube produce a pillow shape.
Stop 5. Intersection of Routes 17 and 77 south of Durham Center. At this location we are close to the eastern border of the Hartford Basin where there is coarse sandy conglomerates of the Portland Arkose. This sequence formed in an alluvial fan along the Eastern Border Fault. At this stop the Eastern Border Fault is only 0.6 kilometers to the southeast. Boulders up to 60 cm in diameter are found here. Sedimentation was episodic characterized by flash floods after heavy rains. The conglomerate would be transported and deposited during the peak of flow and the interbedded lenses of sandstone were deposited during the waning stages of flow. The absence of mud suggests that debris or mudflows were not a factor in the formation of these deposits.
Stop 6. 0.25 miles west of exit 59
off the Wilbur Cross Parkway is an outcrop of conglomerate of the New Haven Arkose unconformably overlying the Paleozoic Maltby Lakes
metavolcanic rocks on the western margin of the Hartford Basin.
This guide is dominantly derived from Hubert et al, 1978.
J.F. Huber, A.A. Reed, W.L. Dowdall, J.M. Christ, 1978, Guide to the Redbeds of Central Connecticut: 1978 Field Trip, Eastern Section of SEPM.
Olsen, P. E. and Kent, D. V. 1996. Milankovitch climate forcing in the tropics of
Pangea during the Late Triassic. In Palaeogeography, Palaeoclimatology, and Palaeoecology 122: 1-26.
Click on images to get large photo.
|Stop 1 New Haven Arkose
Outcrop of lighter color channel gravel and sand with darker red mud layers
Possibly caliche developed around roots.
|Gravelly arkosic channel sand
overlying dense array of caliche nodules developed
in mud overbank deposit
|Stop 2 Dinosaur State Museum
Diorama looking toward east showing setting at time of deposition of East Berlin Formation. Mountains in background are along Eastern Border Fault.
Another diorama looking toward east at time of deposition of East Berlin Fm.
|Stop 2 Dinosaur tracks||Stop 3 East Berlin Fm.
Typical perennial lake cycle.
Deformation in black shale
Fossil wood in black shale
|Stop 4 Pillow Basalt||Stop 5
Sand layer within conglomerate Portland Arkose
|Stop 6 Unconformity
Thin layer of basal conglomerate of Portland Arkose overlying metavolcanic rocks of the Maltby Lakes Fm.