Jurassic Radiolarite Pulses, from the Dorsale Calcaire (Internal Rif, Morrocco): A Clue for Correlating and Interpreting the Tethyan Radiolarites

Horstemeyer, M., & El Kadiri, H. (2009). Jurassic Radiolarite Pulses, from the Dorsale Calcaire (Internal Rif, Morrocco): A Clue for Correlating and Interpreting the Tethyan Radiolarites. Stratigraphy. Micropaleontology Press. 6(4), 137-156.

The Jurassic radiolarian-bearing sequences from the Rifian Dorsale Calcaire are both lithostratigraphically and biostratigraphically significant. Their stratigraphic base proved to be diachronous and allows them to be divided into seven main litho- and biofacies intervals, herein referred to as “radiolarite pulses” (RP. 1-7). Each RP can be defined as corresponding to the first radiolarite deposition onto pelagic carbonate strata and/or paleokarst surfaces. At the regional scale, the well-marked radiolarite diachronism between the external Dorsale and the internal Dorsale units is explained herein by the fact that the only late Jurassic pulses (or even the sole seventh pulse) reached the Internal Dorsale area. In the case these pulses stack in a single stratigraphic sequence, they exhibit contrasting color and lithofacies and are generally separated by erosional surfaces, chaotic breccias and/or synsedimentary normal faults. Taxonomic analyses reveal that the majority of the first species occurrences coincide with the stratigraphic base of each radiolarite pulse. Thus, the main taxonomic turnovers and mass extinctions could have occurred penecontemporaneously with the stratigraphical gap that separate two given RPs. On the whole, the lithological and tectonic signatures and the biostratigraphic record allow the triggering mechanisms of these radiolarite pulses to be primarily assigned to tectonic-mediated paleoenvironmental and/or eustatic changes, and to roughly correlate a radiolarite pulse with a third-order tectono-eustatic sequence. These mechanisms also provide a correlation tool that can be applied to the rest of the Tethyan and Pacific Jurassic radiolarites.