Lopingian Permian Niger had a Wildly Seasonal Arid Climate With Water Inundations Like the African Namib Desert and Australian Lake Eyre Basin

Biological and physical evidence for extreme seasonality in central Permian Pangea

Authors:

Looy et al

Abstract:

Climate models indicate increased desertification in the continental interior of Pangea during the Permian, which would have affected the composition of the flora and fauna. We present a multi-proxy paleoenvironmental reconstruction of a terrestrial ecosystem in central Pangea of Lopingian age. The reconstruction is based on biological and physical data from the Moradi Formation, located in the Tim Mersoi Basin, northern Niger. Paleosols and sedimentological evidence indicate that the prevailing climate was semi-arid to very arid with marked intervals of high water availability. Carbon stable isotope data from organic matter and paleosols suggest that both the soil productivity and actual evapotranspiration were very low, corresponding to arid conditions. Histological analysis of pareiasaur bones shows evidence of active metabolism and reveals distinct growth marks. These interruptions of bone formation are indicative of growth rhythms, and are considered as markers for contrasting seasonality or episodic climate events. The macrofossil floras have low diversity and represent gymnosperm-dominated woodlands. Most notable are ovuliferous dwarf shoots of voltzian conifers, and a 25-m long tree trunk with irregularly positioned branch scars. The combined biological and physical evidence suggests that the Moradi Formation was deposited under a generally arid climate with recurring periods of water abundance, allowing for a well-established ground water-dependent ecosystem. With respect to its environment, this system is comparable with modern ecosystems such as the southern African Namib Desert and the Lake Eyre Basin in Australia, which are discussed as modern analogues.

 

Miocene Neogene Karungu, Kenya was a dry and Open Habitat

Paleosols and paleoenvironments of the early Miocene deposits near Karungu, Lake Victoria, Kenya

Authors:

Driese et al

Abstract:

A 50 m thick stratigraphic section at Ngira, near Karungu on the shore of Lake Victoria in western Kenya, documents the early Miocene paleoenvironments of the area. The basal Ngira paleosol is a 7.6 m thick, oxisolic Vertisol that formed during a prolonged period of pedogenesis; it began as a smectite-dominated Vertisol that was later overprinted through polypedogenesis to become a kaolinitic paleosol highly depleted of all base cations, with abundant Fe concentrations and depletions, and complexly variegated color mottle patterns that reflect extensive ferruginization. Paleoenvironmental reconstructions using bulk geochemistry indicate warm and wet conditions during development of the Ngira paleosol that probably supported a tropical seasonal forest on a stable upland surface for 10s to 100s of thousands of years. Following this long-lived stable landscape, rapid subsidence, perhaps associated with slip on a high-angle fault associated with the onset or progression of the Nyanza Rift and/or the development and eruptive history of the nearby Kisingiri volcano, buried the paleosol and formed a nascent lake basin that experienced multiple transgressions and regressions. During one interval of regression, fluvial sandstones and conglomerates were deposited along with fluvio-lacustrine sandstones and claystones that include weakly developed paleosols. These weakly-developed paleosols indicate a relatively dry paleoenvironment with seasonal precipitation, and probably a shrubland/bushland or riparian forest habitat. Important terrestrial and aquatic vertebrate fossils are primarily preserved within fluvial and fluvio-lacustrine deposits, indicating that the terrestrial Karungu fauna lived in a relatively dry and open habitat. This study demonstrates polypedogenesis and inferences regarding onset of abrupt tectonic activity in the early Miocene in equatorial eastern Africa, and emphasizes the contrasts between landscape stability of the Ngira paleosol and the poorly developed soils in the fluvio-lacustrine facies.