Tuesday, March 26, 2002

T3. Rift Basins of the Northeast (Cosponsored with
NE SEPM)

Sheraton Springfield, Mahogony

9:05 PM   Olsen, Paul E.

COMPARISON OF THE CONTINENTAL SYN-BASALT (CAMP) EARLIEST JURASSIC AGE
STRATA OF EASTERN NORTH AMERICAN RIFT BASINS WITH COEVAL CONTINENTAL TO
MARINE STRAT OF MOROCCO.
        OLSEN. Paul E., Lamont-Doherty Earth Observatory of Columbia Univ., Rt. 9W, Palisades,
        NY 10964-8000, polsen@ldeo.columbia.edu; KENT, ET-TOUHAMI Mohammed, LGVBS,
        Départment des Sciences de la Terre, Université Mohammed Premier; Oujda, Oujda, 60
        000, Morocco; and PUFFER, John, Department of GeologicalSciences, Rutgers Univ.
        185 University Avenue, Boyden 407, Newark, NJ 07102
In eastern North America, sedimentary interbeds and overlying strata of the basalts of the
CAMP are comprised of cyclical lacustrine strata. Two of the Van Houten-type cycles above the
oldest basalt flow (HTQ type) in these basins can by traced throughout not only eastern North
America, but also into and throughout Morocco, overlying the oldest CAMP basalt there in some
cases in fully marine strata.
    The eastern North American contingent of these two cycles are limestone-rich and contain a
stereotyped assemblage of non-marine fish and invertebrates. The deepest water deposits of
these cycles were deposited during the wet phases of climate cycles, and tend to be very finely
laminated or microlaminated, preserving whole fish; the dry phases of the cycles tend to be clastic
dominated (except in Nova Scotia, where limestone is also present). In central Morocco similar
sequences occur, but often with a directly overlying lava flow sequence of similar composition
(HTQ). In these cases, laminated, often black limestones still characterize the humid phases of the
cycles, but bedded evaporites dominate the dry phases of the cycles. A similar stratigraphy of two
HTQ flow sequences with two sedimentary cycles is also present in eastern Morocco; however,
the entire interbed is limestone-dominated. Based on homotaxiality we believe that the dry phases
of the cycles are represented by bedded to massive limestones and the wetter phases by finely
laminated black limestones. No determinable animal fossils have been found in the finely-laminat-
ed units, but abundant and diverse serpulid-bearing bivalves are present in the more massive
beds. Although the bivalves have not yet been systematically studied, we propose that these are
consistent with a marine environment, possible part of the pre-Planorbis zone.
    We hypothesize that the laminated units throughout represent the influx of abundant fresh
water during wet phases of climatic cycles. In contrast the dry phases of the cycles in eastern
Morocco were dominated by the influx of marine water from the Tethys. Basins were progres-
sively more restricted from  western Morocco to presently exposed basins of eastern North
America resulting in progressively more fractionated evaporites in the former and clastic-domi-
nated continental sequences in the latter.
 

From: Olsen, P. E..  Et-Touhami, M., and Puffer, J., 2002, Comparison of the
continental syn-basalt (CAMP) Earliest Jurassic age strata of Eastern North
American rift basins with coeval continental to marine strata of Morocco.
Geological Society of America, Abstracts with Programs, v. 34, no. 2, p. A-31.