Abstract

Sufficient data on Mesozoic and Tertiary deposits in the offshore area of Nova Scotia and Morocco are now available to further substantiate the concepts of sea floor spreading.

The basement of each area comprises Paleozoic rocks deformed during the Hercynian orogeny. The earliest Mesozoic rocks are salt and evaporitic sequences of Late Triassic and earliest Jurassic age. These are overlain by Early Jurassic shelf clastics and carbonates. In Morocco, the Middle and Upper Jurassic grades from clastics in the east to an oolitic limestone bank and marine shales to the west. This distribution is similar to that in Nova Scotia where clastics occur west of the Abenaki carbonate which grades to and interfingers eastward with marine shales. On both sides of the Atlantic the Jurassic succession is overlain by delta-like clastics, the youngest of which are Late Cretaceous in age. Additional similarities in the Mesozoic rocks of these two areas are indicated from geochemical data which include information on clay mineral assemblages, trace elements, and organic carbon.

Following a common Mesozoic history, the first important difference between these two areas is manifest by the widespread presence of the Wyandot Chalk in the western North Atlantic. Equivalents are not present in Morocco. Mesozoic and Tertiary rocks in Morocco were folded in the Early and Late Tertiary whereas equivalent formations were tectonically unaffected in Nova Scotia. These observations can be accounted for by adopting the concept of sea-floor spreading.

Salt was deposited in narrow restricted embayments during the early stages of rifting. As rifting progressed, more open marine conditions prevailed allowing deposition of shelf-type sediments. Oceanic depths between the continents were initiated at the beginning of the Middle Jurassic. As spreading progressed and the land masses became more distant from each other, the Mesozoic sections on each side of the Atlantic increasingly became different. From Late Cretaceous time onward the margins were sufficiently distant from each other that different histories resulted.

Triassic-Jurassic salt diapirs are present in each area. These structural features are the main targets for hydrocarbon exploration at this early stage of knowledge. Because of encouragement on Sable Island it is suggested that the Lower Cretaceous of Morocco — Rio de Oro should be given more attention by exploration geologists. Conversely, because of good oil shows in the Upper Jurassic carbonate bank of Morocco, the outer edge of the Abenaki bank of Nova Scotia may be the most favourable and rewarding formation for exploration.