Troisème Réunion du Groupe Marocain du Permien et du Trias, Casablanca, 18-20 Avril 2002


OLSEN Paul E.1, KENT Dennis V. 1,2, ET-TOUHAMI Mohammed1,3, FOWELL Sarah J. 4, and

1Lamont Doherty Earth Observatory, Palisades, NY 10964, USA

2Dept. of Geological Sciences, Rutgers University, Piscataway, NJ 08854, USA
3LGVBS, Faculté des Sciences, Université Mohamed Premier, Oujda 60 000
4Dept. of Geology and Geophysics, University of Alaska Fairbanks, Fairbanks, AK 99775, USA

        Predominately continental strata of the Argana basin are divided into four at least partially
unconformity bounded tectonostratigraphic sequences (TSI to TSIV), each with a characteristic set of
acies and its own style of lacustrine to evaporite cyclicity. The oldest tectonostratigraphic sequence
(TS-I) consists of the Ikakern Formation (T1 and T2 of Tixeront, 1973) which is Permian in age. It is
predominantly fluvial, although locally (e.g. near Timesgadouine), laterally continuous carbonate beds
mark out a prominent cyclicity the specific nature of which is poorly known but under investigation. In
Canada the Honeycomb Point Formation of New Brunswick and the Cap aux Meules Formation of the
Magdalen basin (Gulf of St. Lawrence) appear to broadly correlate with the Ikakern, based on our
preliminary magnetostratigraphic in conjunction with published data from the Cap aux Meules
Formation. The duration of time of deposition of the Ikakern is presently unknown.
        The Ikakern Formation is separated from the overlying TS II by a locally strong angular
unconformity; this sequence is comprised of the lacustrine, deltaic, and fluvial Timesgadouine
Formation (T3-T5 of Tixeront, 1973). At least the middle part of the formation (lower T5) is strikingly
cyclical with a strong hierarchical pattern with well developed ~20, 100, 400, and 1750 ky lake-level
cycles. This is strongly reminiscent of the marginal lacustrine strata of the Triassic Lockatong
Formation of the Newark rift basin (Eastern United States), consistent with its paleolatitude. Based on
accumulation rates derived from preliminary Fourier analysis of the lower T5 section, and  extrapolated
to the entire section, the preserved portion of the Timesgadouine Formation was deposited over about
7 million years. Based on vertebrate biostratigraphy, the Timesgadouine Formation correlates with the
Stockton Formation of the Newark basin; the newly recovered magnetostratigraphy allows a more
detailed correlation. Adding the 7 my from the Timesgadouine Formation to the younger
astronomically-calibrated portion of the Newark basin section yields a date of 232 Ma for the oldest
Timesgadouine Formation.
        Overlying the Timesgadouine Formation is the Bigoudine Formation (T6-T8 of Tixeront), which is
separated from the former by an at least local gentle angular unconformity; the Bigoudine makes up
TS-III and the base of TS-IV. Nearly the entire formation is cyclical, but the mode of cyclicity changes
up section. The lowest Bigoudine (T6) consists of a basal conglomerate and fluvial sandstone overlain
by laterally-persistent cycles of red mudstone and eolian sandstones. Locally there is some bedded
halite, although its relationship to the cyclicity is unknown. Conformably overlying T6, T7 has very well
developed cyclicity resembling that of the middle and upper Passaic Formation of the Newark Basin;
some cycles have well-developed black lacustrine shales. There is a significant eolian-playa sand-
patch component to the drier phases of the cycles, which becomes progressively more important
upward. T8 conformably overlies T7 and, except for its uppermost few meters, continues the cyclical
pattern of T7, although with only one well-developed black shale.
        Interestingly, from north (Timesgadouine) to south (Argana), this black shale changes color. The
transition can be seen in ravines just northeast of Argana; the color changes without an obvious
change in facies. The Bigoudine consists otherwise almost entirely of sand-patch cycles, with large
variations in the amounts of red shale. The uppermost few meters of T8 have a well-developed
cyclicity with very thin black and gray shales. This portion contains the Triassic-Jurassic boundary,
based on palynology, and represents the lower part of the succeeding TS-IV. Preliminary
magnetostratigraphy of the lower half of the Bigoudine allows the accumulation rates of the formation
to be determined by correlation with the astronomically-tuned Newark basin time scale. Based on this
correlation, there are significant accumulation rate changes through the formation. However, when the
accumulation rate is adjusted to that seen in the Newark basin, Fourier analysis indicates the
pervasive presence of well developed ~20, 100, 400, and 1750 ky lake-level cycles that correlate
remarkably well to the Passaic Formation. The correlation is fully supported by the available
palynology from the Bigoudine, and indicates that the deposition of the Bigoudine began at about 218
Ma and ended at about 201 Ma, with the conformable outpouring of the Argana Basalt.
        Resting conformably on the Argana Basalt is the Amescroud Formation (uppermost part of  T8 of
Tixeront, 1973). The basal part of this formation consists of at least one black shale and carbonate
cycle, followed by a mostly red-cyclical sequence; it appears to have been deposited under
significantly wetter conditions than most of the underlying Bigoudine Formation. Based solely on
cyclostratigraphic correlation, the outcropping Amescroud spans only about 450 ky of the early

From: Essamoud, R. and Ekamel, F. (eds.), 2002, Troisème Réunion du Groupe Marocain du
Permien et du Trias, Casablanca, 18-20 Avril 2002, Résumés, p. 29-30.