Blue Nile Incision on the Ethiopian Plateau: Pulsed Plateau Growth, Pliocene Uplift, and Hominin Evolution

The 1.6-km-deep Gorge of the Nile, a rival of the Grand Canyon, resulted from the deep incision of the Blue Nile drainage into the uplifted Ethiopian Plateau. Understanding the incision history of the plateau is crucial to unraveling the Cenozoic tectonoclimatic evolution of the region, particularly because the region has long been used as a natural laboratory to understand the geodynamics of continental rifting and the evolution of hominins. We undertake a quantitative geomorphologic approach integrating field, geographic information system (GIS), and digital elevation model (DEM) data to analyze incision (volume, long-term rates, and spatiotemporal variability) and river longitudinal profiles of the Blue Nile drainage. Previously published isotopic ages of the Cenozoic volcanic rocks are used to constrain long-term incision rates through geologic time. Our data argue that (1) the Blue Nile drainage has removed at least 93,200 km3 of rocks from the northwestern Ethiopian Plateau since ca. 29 Ma (early Oligocene) through a three-phase (ca. 29-10 Ma, ca. 10-6 Ma, and ca. 6 Ma to present) incision, where long-term incision rates increased rapidly and episodically in the late Miocene (ca. 10 Ma and ca. 6 Ma); (2) being out-of-phase with the past climatic events and in-phase with the main volcanic episodes of the region, this episodic increase of incision rate is suggestive of episodic growth of the plateau; (3) of the ~2-km rock uplift of the plateau since ca. 30 Ma, 0.3 km was due to isostatic uplift related to erosional unloading, and the rest was due to other tectonic activities; (4) the extremely rapid long-term incision rate increase, thus a rapid uplift of the plateau, ca. 6 Ma might be related to lithospheric foundering, caused by ponded plume material beneath the Ethiopian Plateau and aided by huge tectonic stresses related to the Messinian salinity crisis of the Mediterranean Sea. These events could have caused the plateau to rise \u3e1 km within a few m.y. in the early Pliocene. This uplift history of the Ethiopian Plateau can shed critical light on the geodynamics of the Afar mantle plume and the evolution of the East African hominins via climate change

Predictable patterns in stacking and distribution of channelized fluvial sand bodies linked to channel mobility and avulsion processes

ACKNOWLEDGMENTS Funding from the American Chemical Society Petroleum Research Fund (ACS PRF 50310-DNI8), the University of New Orleans (Louisiana, USA), and a Marie Skłodowska-Curie grant (no. 707404) is thankfully acknowledged. We thank Martin Gibling, Mike Blum, and Jeffrey Nittrouer for constructive and critical reviews.Peer reviewedPublisher PD

Submarine channel and lobe hidden inside mass-transport deposits in the northern Gulf of Mexico

Despite numerous subsurface studies of mass-transport deposits (MTDs) using seismic data, internal characters of MTDs at the seismic scale are still not well understood, largely because of the limitation of seismic resolution. This study investigates Miocene-Pliocene MTDs in an understudied, hydrocarbon-rich region of the northern Gulf of Mexico. With the help of quantitative seismic geomorphology techniques, we utilized a high-quality 3D seismic dataset. We document sinuous channel and lobe features hidden within individual MTDs. This provides evidence for considering a seismically-defined MTD unit as amalgamated deposits of multiple events with different flow types (e.g., turbidity currents and cohesive flows), rather than an en masse deposit of a singular event. Additionally, we document an unshielded erosional remnant, which is generated by the bifurcation of a megascour marking the base of an MTD unit. Remnant strata are interpreted as sandy sediment waves. Channel, lobe, and erosional remnant features examined in this study demonstrate the presence of reservoir-prone facies encased within MTD units, forming stratigraphic traps. This research enhances our understanding of the intermingling nature of MTDs and other typical deep-water deposits, and the reservoir potential of MTDs and associated strata

Stratigraphic and Structural Evolution of the Blue Nile Basin, Northwestern Ethiopian Plateau

The Blue Nile Basin, situated in the Northwestern Ethiopian Plateau, contains ~1400 m thick Mesozoic sedimentary section underlain by Neoproterozoic basement rocks and overlain by Early-Late Oligocene and Quaternary volcanic rocks. This study outlines the stratigraphic and structural evolution of the Blue Nile Basin based on field and remote sensing studies along the Gorge of the Nile. The Blue Nile Basin has evolved in three main phases: (1) pre-sedimentation phase, include pre-rift peneplanation of the Neoproterozoic basement rocks, possibly during Palaeozoic time; (2) sedimentation phase from Triassic to Early Cretaceous, including: (a) Triassic-Early Jurassic fluvial sedimentation (Lower Sandstone, ~300 m thick); (b) Early Jurassic marine transgression (glauconitic sandy mudstone, ~30 m thick); (c) Early-Middle Jurassic deepening of the basin (Lower Limestone, ~450 m thick); (d) desiccation of the basin and deposition of Early-Middle Jurassic gypsum; (e) Middle-Late Jurassic marine transgression (Upper Limestone, ~400 m thick); (f) Late Jurassic-Early Cretaceous basin-uplift and marine regression (alluvial/fluvial Upper Sandstone, ~280 m thick); (3) the post-sedimentation phase, including Early-Late Oligocene eruption of 500-2000 m thick Lower volcanic rocks, related to the Afar Mantle Plume and emplacement of ~300 m thick Quaternary Upper volcanic rocks. The Mesozoic to Cenozoic units were deposited during extension attributed to Triassic-Cretaceous NE-SW-directed extension related to the Mesozoic rifting of Gondwana. The Blue Nile Basin was formed as a NW-trending rift, within which much of the Mesozoic clastic and marine sediments were deposited. This was followed by Late Miocene NW-SE-directed extension related to the Main Ethiopian Rift that formed NE-trending faults, affecting Lower volcanic rocks and the upper part of the Mesozoic section. The region was subsequently affected by Quaternary E-W and NNE-SSW-directed extensions related to oblique opening of the Main Ethiopian Rift and development of E-trending transverse faults, as well as NE-SW-directed extension in southern Afar (related to northeastward separation of the Arabian Plate from the African Plate) and E-W-directed extensions in western Afar (related to the stepping of the Red Sea axis into Afar). These Quaternary stress regimes resulted in the development of N-, ESE- and NW-trending extensional structures within the Blue Nile Basin