Environmental changes at the Frasnian–Famennian boundary in Central Morocco (Northern Gondwana): integrated rock-magnetic and geochemical studies

Abstract

Rock magnetic (magnetic susceptibility and hysteresis parameters) and geochemical analyses (major and trace elements) were carried out on whole rock samples of two Frasnian–Famennian boundary sections, Anajdam and Bou-Ounebdou in the Central Morocco (Western Meseta). During the Frasnian, the decreasing trend of the magnetic susceptibility signal, mainly carried by low-coercivity magnetite grains, indicates a gradual reduction of detrital influx. This decrease in detrital input parallels a Frasnian long-term sea-level rise. In the Late Frasnian Kellwasser Horizons, that are classically considered to represent highstand deposits, the magnetic signal exhibits the lowest intensities in connection with maximum diamagnetic contribution of the carbonate fraction. With respect to geochemical data, the two black carbonate-rich Kellwasser Horizons are characterized by noticeable positive anomalies of bottom-water dysoxic proxies and of marine primary productivity markers. Our data thus suggest that in Central Morocco, the Late Frasnian marine environments were marked by a relatively important biogenic productivity favouring the onset of oxygen-depleted conditions during periods of maximum transgression on the continental platforms.

Characterization of Hydrocarbon Bearing Jardepahar Porcellanite Formation, Vindhyan Basin

“…The higher concentration of Zn in the middle unit indicates high organic matter ux and reducing conditions (Tribovillard et al, 2006). A higher Si/Al ratio in the middle unit re ects the clastic in ux with high to moderate energy condition (Riquier et al, 2007). It also supports the concept of high biological productivity in the middle unit as compared to the upper and lower units.…”

Pattern and Timing of the Late Devonian Biotic Crises in Western Canada: Insights from Carbon Isotopes and Astronomical Calibration of Magnetic Susceptibility Data

“…While the LKE and UKE are first and foremost biotic crises (McGhee 1988, Bambach et al 2004, Stigall 2012, assembling detailed species richness data from many sections would be labor intensive. Wide varieties of geochemical data are available across the F-F interval, including elemental data that serve as proxies for detrital input, productivity, and redox conditions (Over et al 1997;Riquier et al 2006Riquier et al , 2007Whalen and Day 2008;Boyer et al 2011;Whalen et al 2015). However, many of these proxies vary with depositional setting, hampering their use as global markers (Algeo and Rowe 2012).…”

Diagenetic versus detrital origin of the magnetic susceptibility variations in some carbonate Frasnian–Famennian boundary sections from Northern Africa and Western Europe: implications for paleoenvironmental reconstructions

“…For two of the studied sections (the Beringhauser Tunnel section in the Rhenish Massif and the Anadjam section in the Moroccan Meseta), we investigated a possible secondary alteration of the magnetic signal, using (1) representative clay mineral assemblages and calibrated illite crystallinity measurements (XRD analyses), (2) major and trace element geochemistry (ICP-AES and ICP-MS analyses) and (3) scanning electron microscopic observations and probe analyses. The detailed measurement protocol of these complementary analyses can be found in Riquier et al (2006Riquier et al ( , 2007. The identification of clay minerals was made according to the position of the (001) series of basal reflections on X-ray diffractograms (Brindley and Brown 1980) and following the protocol defined by Bout-Roumazeilles et al (1999).…”

“…In recent years, a growing number of studies have focused on the use of the magnetic susceptibility (MS) signal as a marker of stratigraphic cycles and paleoenvironmental changes in Paleozoic carbonate rocks (Ellwood et al 1999;Crick et al 2002;Averbuch et al 2005;Hladil et al 2005;Da Silva and Boulvain 2006;Riquier et al 2007;Mabille and Boulvain 2007;Whalen and Day 2008). In these studies, variations in MS have been largely shown to relate to sedimentary facies evolution (Ellwood et al 1999; da Silva and Boulvain 2006;Whalen and Day 2008) and possibly to correlate over long distances within an individual basin or even on the margins of different oceanic realms Ellwood et al 2001).…”