Tuesday, March 26, 2002

S4. Studies of Depositional Systems and Sedimentary
Rocks: In Honor of Edward Scudder Belt
(Cosponsored by NE SEPM)

Sheraton Springfield, Mahogony

1:05 PM    Olsen, Paul E.

STRATIGRAPHY AND AGE OF THE EARLY JURASSIC PROTLAND FORMATION OF
CONNECTICUT AND MASSACHUSETTS: A CONTRIBUTION TO THE TIME SCALE OF THE
EARLY JURASSIC
        OLSEN. Paul E., Lamont-Doherty Earth Observatory of Columbia Univ., Rt. 9W, Palisades,
        NY 10964-8000, polsen@ldeo.columbia.edu; KENT, Dennis V., Rutgers Univ., 610 Taylor
        Rd., Piscataway. N.J. 08854-8066; and LETOURNEAU, Peter M., Lamont-Doherty Earth
        Observatory of Columbia Univ., Rt. 9W, Palisades, NY 10964-8000
The stratigraphy of the more than 4 km thick Portland Formation of the Hartford basin has
remained relatively poorly known despite nearly two centuries of study. Within the last three
years, however, we have been able to piece together a fairly complete outline of the stratigraphy
of the lower 2 km of the formation which, together with that of the underlying East Berlin and
Shuttle Meadow formations and coeval strata in the Newark basin, allow an astronomical cal-
ibration of the time scale of the Hettangian Age.
    Cyclical lacustrine strata, similar in to that seen in the East Berlin Formation, characterize the
lower 2 km of the Portland. Most of the hierarchy of climatic precession-related cycles are present
including the 20 ky Van Houten cycle, the ~100 ky short modulating cycle, the 406 ky McLaughlin
cycle, and the ~1.75 my long modulating cycle. Van Houten cycles reflect the climatic precession
cycle of ~20 ky, and are about 20 m thick over much of the Hartford basin, thickening towards the
eastern border fault. Varve, cyclostratigraphic and paleomagnetic correlations show that individual
Van Houten cycles can be traced over most, if not all, of the basin, allowing the scattered outcrops
to be compiled to a common cyclostratigraphic scale. Four full McLaughlin cycles are present in
the lower Portland, with one continuing from the underlying East Berlin Formation; we propose to
recognize these mappable units as members as follows (from the bottom up): "Northampton",
"East Granby", "South Hadley Falls", "Mittinegue", and "Stony Brook" members. Correlation to the
paleomagnetic reversal stratigraphy of the Paris basin marine section suggests that the zones of
reversed polarity in the "Mittinegue" and "Stony Brook" members in the upper part of the lower
Portland are of Sinemurian age. Thus, the Hettangian Age, encompassing in the Hartford basin
the duration of the uppermost New Haven through lower Portland formations, is about 2 million
years long, consistent with estimates from marine cyclostratigraphy. Simple extrapolation of the
accumulation rate into the upper, largely fluvial, Portland (~2 km) suggests that there is an add-
itional 2 million years represented, probably all of Sinemurian age.
 

From: Olsen, P. E., Kent, D. V., and LeTourneau, 2002, Stratigraphy and Age
of the Early Jurassic Portland Formation of Connecticut and Massachusetts:
A Contribution to the Time Scale of the Early Jurassic. Geological Society of
America, Abstracts with Programs, v. 34, no. 2, p. A-61.