MEANDERING RIVER FACIES IN THE LOWER PART OF THE 
NEW HAVEN ARKOSE, SOUTH-CENTRAL CONNECTICUT: 
EARLY EVOLUTION OF THE HARTFORD BASIN IN LATE 
TRIASSIC TIME

	McINERNEY, D. P., Dresdner Robin Environmental 	
		Management Inc.,  Jersey City, NJ 07302
	HUBERT, J. F., Dept. of Geosciences, University of 	
		Massachusetts,  Amherst, MA 01003

Fluvial redbeds about 650 m above the base of the 2-km New Haven 
Arkose were studied in two continuous exposures along I-84 in 
Southington and I-691 in Cheshire.  These 150 m of strata 
accumulated in a valley produced by NW-SE extension, early in the 
basin history before formation of the eastern border faults.  The river 
meandered over a low gradient, exiting the subtropical basin to the 
south.  The high plagioclase content of the arkosic sandstones suggest 
that most of the detritus came from west of the valley.  
	Channel sandstones, 50% of the sequence, are mostly 
multistory, each story fining upwards and representing passage of a 
meander bend.  The channel sandstones average 2.3 m, ranging from 
0.6-6.5 m.  Beds of floodbasin reddish brown mudstone, 25% of the 
sequence, average 3.4 m, varying from 0.75-9.6 m.  Reddish brown 
fine sandstone to silty mudstone in beds 0.4-1.1 m in thickness 
accumulated on crevasse splays and levees, forming another 25%.  
Plant roots and Scoyenia burrows are abundant.  Numerous caliche 
paleosols imply semiaridity.  
	Lateral accretion cross-beds (point bars) allow calculation of 
the paleotopography and paleohydrology for two channels.  Data for 
the second channel are in parentheses: width = 11 m (37 m), depth = 
2.0 m (2.7 m), bankfull discharge = 8 cubic m per sec (47 cubic m per 
sec), sinuosity = 2.2 (1.7), meander wave length = 157 m (601 m), 
radius of curvature = 42 m (161 m), and river gradient = 0.0009 
(0.0006). 
	Migration of meanders towards and away from the sections 
generated two types of cycles, each with minor variations.  The cycles 
average 7 m, varying from 2-16 m. Each cycle starts with a channel 
sandstone.  Channel incision commonly ceased on a resistant caliche 
layer.  In type 1, the lower and middle parts of the overlying 
floodbasin sequence are mudstone interbedded with levee and 
crevasse-splay deposits with immature stage 1 caliche paleosols.  The 
upper part of the floodbasin sequence is mudstone with caliche 
horizons of stage 2 or higher.  Stratigraphically upwards, caliche 
paleosols become closer spaced, thicker, and more mature.  A new 
cycle starts with arrival of a channel by river avulsion.  The type 2 
cycle is initially similar to type 1, but then there is a return to 
interbedded mudstones and levee and crevasse-splay deposits with 
immature caliche, reflecting the approach of a meandering channel, 
whose arrival ends the cycle.  Caliche maturity increases as the 
chance of being buried in sediment decreases, so that immature 
caliche occurs on levees, proximal crevasse splays, and proximal 
floodbasin muds, whereas mature caliche forms on distal floodbasin 
muds.  
	Four megacycles, from 21-28 m in thickness, are characterized 
by upward increases in thickness of the channel sandstones, number 
of stories in each channel sandstone, and maximum grain size in each 
channel sandstone.  These megacycles may be due to a climate-
forcing Milankovitch mechanism.

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