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

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-laminated 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 progressively more restricted from western Morocco to presently exposed basins of eastern North America resulting in progressively more fractionated evaporites in the former and clastic-dominated continental sequences in the latter.