The Jurassic climate change in the northwest Gondwana (External Rif, Morocco): Evidence from geochemistry and implication for paleoclimate evolution

Abstract

The present work deals with Jurassic deposits belonging to the External Rif chain. It is well known that the Jurassic time was a crucial period in the earth's history as witness of significant climate changes. This work aims to provide a preliminary reconstruction of the regional Jurassic paleoclimate of the northwest Gondwana hinterland and its global paleogeographic context. We used diverse geochemical proxies to unravel paleoclimate of the Jurassic sediments accumulated in the Atlantic and Tethysian hyperextended passive margins bordering the northwest Gondwana. We reconstituted their paleo-humidity, paleo-precipitation, paleo-weathering, paleo-productivity, paleo-floral landscape distribution in the Gondwanaland, the paleo-redox, paleo-oxygenation and paleosalinity of the bordering oceanic sinks. The obtained results indicate that the early Jurassic climate was cool with low rainfall and productivity, while the middle Jurassic was characterized by a semi-moist warm climate with high chemical weathering and subsequent seaward terrigenous supply. The Uppermost Jurassic climate was warm, semi-moist to moist with a return to an arid cold climate marked by high rainfall amount which yielded more terrigenous material to the bordering Tethysian and Atlantic hyperextended passive margins around the northwest Gondwana hinterland. The result of this research reveals, among others, the control of the first-order geodynamic processes on the Jurassic mid-latitude climate change, such as plate tectonics reorganization, oceanic seafloor spreading, and subsequent volcanic activity. The latter may triggered a climate shift from early Jurassic dry “cool” to middle-late Jurassic wet warm “greenhouse” climate conditions around the northwest Gondwanaland. Besides, the Jurassic climate change may have been also controlled by successive mega-monsoons that occurred through the Inter-Tropical Convergence Zone (ICZ) over margins and oceanic realms bordering the northwest Gondwanaland.