Irati/White Hill shales are lacustrine evaporitic source rocks of the southern Gondwana. What happens in other parts of the world? Is this an isolated event or a global one?
Dear Dr. Davila:
In many regions of the northern hemisphere we see the waning stages of the Variscan/ Hercynian orogeny. A strong crustal extension provoked the formation of intramontane basins with a ridge-and-graben paleogeography and volcanic rocks forming along their boundary faults. In these basins mainly the debris of the rising Variscan orogen got debouched leading to mainly siliciclastic sediments. While the lower Permian has still many characteristics also common to the Upper Carboniferous the younger units saw a turning of the rock color from black into red-brown denoting drier conditions which may correlate based upon the lithofacies with your ephemeral lacustrine sediments.
My research focus was on the lower grey facies rather than the red beds because of their higher potential for U and other metals precipitated as sulfides and due to source rock analysis (Type Quinta Basin).
If you are in need of facies descriptions and environment analyses of these rocks including their HC potential and organic matter (organic chemistry + coal petrography) browse my list of publications on the Researchgate server. I can send you some digital prints on request.
With kind regards H.G. Dill
In the Mughalzhar Hills (Kazakhstan) and southern Ural mountain regions (Russia), Kungurian deposits are primarily terrigenous (formed by erosion), consisting of red beds and lagoonal sediment types. Many different kinds of shallow marginal marine, evaporitic, and nonmarine strata were deposited here as lateral sedimentary facies to one another. Elsewhere, conglomerates, sandstones, and other red beds occur. To the east, thick evaporite sequences of gypsum, halite, and potash form the salt basin of the upper Kama River in Russia. Marine limestones occur in the Russian province of Perm, and reef carbonates occur in the western portions of the Mughalzhar Hills.
Golonka J. 2007. Phanerozoic Paleoenvironment and Paleolithofacies Maps. Late Paleozoic. Mapy paleośrodowiska i paleolitofacje fanerozoiku. Późny paleozoik. Kwartalnik AGH. Geologia, 33(2): 145-209.
https://www.researchgate.net/publication/234000853_Phanerozoic_Paleoenvironment_and_Paleolithofacies_Maps_Late_Paleozoic
@Golonka Jan 2012. Paleozoic paleoenvironment and paleolithofacies maps of Gondwana. AGH University of Science and Technology Press: 1-82.
https://www.researchgate.net/publication/267753451_Paleozoic_paleoenvironment_and_paleolithofacies_maps_of_Gondwana
During the Kungurian, a series of rifted basins were formed at the southwestern margin of the Central Asian orogenic belt (CAOB) (Tang et al., 2021 Gondwana Res. In press). Especially in the northwestern margin of the Junggar Basin, it is characterized by the development of the oldest alkaline lake shale source rock in the world (Tang et al., 2021 JAES Under review). It has similar characteristics with the modern Magadi alkaline lake in a rift basin (Kenya) and the Eocene Green River hyperalkaline lake in a foreland basin (USA) (Pietras and Carroll, 2006; Aswasereelert et al., 2013; Miller and Lizarralde, 2013; Törő and Pratt, 2016; Owen et al., 2019). So far I have completed some geochemical analysis, and a lower weathering index indicates arid climate conditions. Based on the soft-sediment deformation structures in the Lower Permian Fengcheng Formation (~280 Ma) and tectono-stratigraphical evolution, the attributes of the basin are determined (10.1016/j.sedgeo.2020.105719; 10.1016/j.marpetgeo.2020.104730; Tang et al., 2020, 2021). It is generally clarified that under arid climate conditions, the syn-rifting process played an important role in the formation of alkaline lake deposits, but the paleoclimatic background of alkaline lake deposits is still a mystery. Based on the above answers, it seems that there were evaporation characteristics at the same time, perhaps a global event. We can discuss this issue together.
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