Early Jurassic normal faulting in a carbonate extensional basin: characterization of tectonically driven platform drowning (High Atlas rift, Morocco)

Abstract

This paper describes a tectonostratigraphic model of the synrift evolution of the Early Jurassic High Atlas rift of Morocco. The model is constrained by mapping of a set of inverted extensional blocks, by facies analysis of carbonate platform and turbiditic to hemipelagic synrift deposits, and by high-resolution (n 3 100 ka) biostratigraphy of the Early Jurassic succession. The chronostratigraphic packages of the High Atlas of Rich vary significantly in thickness, facies and architecture from one tectonic block to another. Our study shows how synrift strain varied in space and time over a long time interval (14 Ma) around the High Atlas rift. Initially, in Sinemurian time, the High Atlas rift was affected by low-strain normal faulting that controlled the growth of an extensive, low-gradient carbonate platform, except in the northern domain (towards the rift axis), where hemipelagic deposition related to high-rate faulting prevailed. Subsequently, in Carixian-Domerian time, a rapid increase in accommodation space and block subsidence caused by highstrain normal faulting brought about localized drowning of the carbonate platform and the development of calciturbidites and of starved deposits towards the rift axis. During this interval, high-strain, upper-crustal normal faulting migrated rapidly (over a period of 5 Ma) towards the rift periphery.

Sequence development in an isolated carbonate platform (Lower Jurassic, Djebel Bou Dahar, High Atlas, Morocco): influence of tectonics, eustacy and carbonate production

“…Tectonic rotation of the smaller fault blocks (commonly >2° as recorded by dip measurements in strata from Sequences I, II and III) only led to a smooth (<2°) rotation of the entire DBD block towards the south (Tables S4 to S6). This scenario, here considered as the most probable one, is in accordance with most of the geological observations presented here and fits with the model proposed by Lachkar et al. (2009).…”

“…1A). A broad carbonate system nucleated along the southern margin of the basin, which evolved during the Lotharingian and Pliensbachian into narrower carbonate platforms as a consequence of the tectonic development of the rift basin (Warme, 1988; Crevello, 1991; Wilmsen & Neuweiler, 2008; Lachkar et al. , 2009).…”

“…This effect might be a result of accelerated hanging wall subsidence along the JBFF (see Fig. 1C and D for location) and progressive deactivation of numerous minor normal faults that compartmentalized the DBD block during deposition of Sequence III; this coincided with the onset of the rift climax phase in the High Atlas Basin (Lachkar et al. , 2009).…”

A mechanism for brief glacial episodes in the Mesozoic greenhouse

“…The δ 18 O values are converted into temperature using the equation of Anderson and Arthur [1981] and a δ 18 O seawater of −1‰ SMOW. Periods of platform carbonate production crises have been represented by yellow to brown horizontal bars [ Dromart et al , 1996; Föllmi et al , 1994, 2006; Lachkar et al , 2009; Morettini et al , 2002; Quesada et al , 2005; Rousseau et al , 2005; Ruiz‐Ortiz et al , 2004; van Buchem et al , 2002; Weissert et al , 1998]. Note that the proposed reconstructions of the carbonate crisis are tentative and clearly not definitive.…”

Stratigraphic Unconformities: Review of the Concept and Examples from the Middle-Upper Paleozoic

“…Non-actualistic mud-mound carbonate factory can likely produce thick carbonate buildups in dimmed or aphotic settings and at elevated nutrient levels (M-factories; [31,77]). Drowning unconformities are usually produced in settings of tectonic subsidence, e.g., in extensional rifted basins [78] or foreland basins [79][80][81]. It remains unclear to what extent high-amplitude eustatic rise of sea level, without aid of other factors, is capable of shutting off carbonate platforms.…”