Soumia Chahidi’s research while affiliated with University of Hassan II Casablanca and other places

This paper relates to two marly outcrop sections of the South Rifian Ridges central unit (Moulay Idriss Zerhoun area), dated by Upper Domerian-Lower Toarcian ammonites. The Upper Domerian marls from the SKM outcrop section (Souk of Moulay Idriss Zerhoun) have yielded palynofacies very rich in lignitic particles (needle-like phytoclasts), Tasmanites (unicellular green algae), spores and pollen grains. The marine microfossils, especially dinoflagellate cysts and acritarchs, are not present. These latter marine organisms are predominant in the Lower Toarcian palynofacies samples collected from the FA (Feddane Amar) outcrop section, in association with a significant amount of lignitic particles. This striking difference in the palynological content between the palynofacies of the Upper Domerian and the Lower Toarcian indicates an important change in the marine paleoenvironment in the South Rifian Ridge domain. Therefore, the anoxic period during the Upper Domerian is marked by the abundance of spores and pollen grains and the absence of marine microfossils, except for the Tasmanites; it is followed by a normal salinity-marine period, characterized by abundant marine-related palynomorphs, in the Early Toarcian. This paleoenvironmental change may be related with the Middle Liassic carbonate platform dislocation of the South Rifian Ridge domain and probably to the global marine transgression, occurring at the base of Toarcian, known all over the world.

This paper relates to two marly outcrop sections of the South Rifian Ridges central unit (Moulay Idriss Zerhoun area), dated by Upper Domerian-Lower Toarcian ammonites. The Upper Domerian marls from the SKM outcrop section (Souk of Moulay Idriss Zerhoun) have yielded palynofacies very rich in lignitic particles (needle-like phytoclasts), Tasmanites (unicellular green algae), spores and pollen grains. The marine microfossils, especially dinoflagellate cysts and acritarchs, are not present. These latter marine organisms are predominant in the Lower Toarcian palynofacies samples collected from the FA (Feddane Amar) outcrop section, in association with a significant amount of lignitic particles. This striking difference in the palynological content between the palynofacies of the Upper Domerian and the Lower Toarcian indicates an important change in the marine paleoenvironment in the South Rifian Ridge domain. Therefore, the anoxic period during the Upper Domerian is marked by the abundance of spores and pollen grains and the absence of marine microfossils, except for the Tasmanites; it is followed by a normal salinity-marine period, characterized by abundant marine-related palynomorphs, in the Early Toarcian. This paleoenvironmental change may be related with the Middle Liassic carbonate platform dislocation of the South Rifian Ridge domain and probably to the global marine transgression, occurring at the base of Toarcian, known all over the world.

A biostratigraphic study of dinoflagellate cysts of the Upper Jurassic series from the eastern External Rif Chain, has been achieved for the first time on four outcrop sections : the DM section (Douar Marticha), the TB section (the Tarhchenna “Sof”), the KSD section (the Kef Mallou “Sof”) and the Y section (Douar Lamriene) among which three sections (TB, KSD and Y) are well-dated by ammonites and calpionellids fauna. The DM and TB sections are complementary in terms of stratigraphy and correspond respectively to the upper part of the “Ferrysch” Formation, a thick shaly–silty and sandy sequence assigned to the Callovian-Oxfordian stages and to the El Gouzat limestones Formation (Kimmeridgian - Lower Tithonian age) and to the Tarhchenna marly limestones Formation (Upper Tithonian age) from the EL Gouzat area (Mesorif). The KSD and Y sections are also complementary and correspond to the Kimmeridgian-Lower Tithonian Msila limestones Formation and to the overlying marly limestones Massif Formation of Upper Tithonian age, outcropping in the Msila region (Internal Prerif). These four sections have shown many dinocysts rich levels, which had allowed characterizing the Middle? and Upper Oxfordian substages in the DM section. In the other sections, the dinoflagellate cyst assemblages are nearly similar to those of the Kimmeridgian–Tithonian of many sections from the Boreal, Sub-boreal and North tethyan realms, particularily from England, Russia and South-East France basin. The results of the present work confirm once again, the important value of dinoflagellate cysts, for age dating of ammonites-lacking Mesozoic sedimentary sequences and for biostratigraphic correlations.