Abstract

The Atlantic coast of Morocco is extensively veneered by littoral marine-eolian calcarenite. Modified littoral dune ridges mark successive strandline positions occupied during progressive emergence since late Miocene time. Principal strandline deposits are mildly transgressive, recording fluctuations in general sea level. Comparisons with Mediterranean chronology set general limits to local rates of emergence. On some transects, rates may have been uniform during the past 3 m.y. — for example, Casablanca, 0.065 m/1,000 yr, and Rabat, 0.053 m/1,000 yr.

Ages of strandlines derived by interpolation, based on the assumptions of uniform rates of emergence and of uniform heights of sea-level maxima, are in broad and some detailed agreement with ages of O18 minima in deep-sea cores. The degree of correspondence encourages confidence in the initial assumptions.

Moghrebian (Early Pliocene, 4.2 to ? m.y. ago), Fouaratian (late Pliocene, 2.8 to 2.4 m.y. ago), and Messaoudian (Calabrian, 1.8 to 1.1 m.y. ago) stages were sustained intervals of high sea level. Each was transgressive — that is, each was preceded by one of three Pliocene intervals of low sea level, presumably reflecting expanded continental ice sheets. Disconformities within Fouaratian and Messaoudian stages reflect smaller fluctuations of sea level, with a periodicity of about 0.2 m.y.

Quarry exposures in a small area southwest of Casablanca allow distinction of at least nine transgressive “cycles” during the past 1 m.y. The implied period of fluctuation is about half that during the Fouaratian and Messaoudian stages; amplitudes are presumably greater. Strandlines marking sea-level peaks between the first, Maarifian, and the sixth, Anfatian, are now as low as or lower than during the early part of the Anfatian cycle. They indicate that “inter-glacial” sea levels fell short of present sea level during a late Matuyama–early Brunhes interval (0.8 to 0.6 m.y. ago). Correlative features will not ordinarily be recognized on coasts with low rates of emergence.

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