Paleogeographic evolution of the central segment of the South Atlantic during Early Cretaceous times: Paleotopographic and geodynamic implications

The geodynamic processes that control the opening of the central segment of the South Atlantic Ocean (between the Walvis Ridge and the Ascension FZ) are debated. In this paper, we discuss the timing of the sedimentary and tectonic evolution of the Early Cretaceous rift by drawing eight paleogeographic and geodynamic maps from the Berriasian to the Middle–Late Aptian, based on a biostratigraphic (ostracodes and pollen) chart recalibrated on absolute ages (chemostratigraphy, interstratified volcanics, Re–Os dating of the organic matter). The central segment of the South Atlantic is composed of two domains, with a two phases evolution of the pre-drift (“rifting”) times: a rift phase characterized by tilted blocks and growth strata, followed by a sag basin. The southern domain includes the Namibe, Santos and Campos Basins. The northern domain extends from the Espirito Santo and North Kwanza Basins, in the south, to the Sergipe–Alagoas and North Gabon Basins to the north. Extension started in the northern domain during the Late Berriasian (Congo–Camamu Basin to the Sergipe–Alagoas–North Gabon Basins) and migrated southward. At that time, the southern domain was not a subsiding domain (emplacement of the Parana–Etendeka Trapp). Extension started in this southern domain during the Early Barremian. The rift phase is shorter in the south (5–6 Ma, Barremian to base Aptian) than in the north (19 to 20 Myr, Upper Berriasian to base Aptian). The sag phase is of Middle to Late Aptian age. In the northern domain, this transition corresponds to a hiatus of Early to Middle Aptian age. From the Late Berriasian to base Aptian, the northern domain evolves from a deep lake with lateral highs to a shallower organic-rich one with no more highs. The lake migrates southward in two steps, until the Valanginian at the border between the northern and southern domains, until the Early Barremian, north of Walvis Ridge

Natural sealed fractures from the Montney-Doig unconventional reservoirs tied to burial and tectonic history of the Western Canada foreland basin

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Fluvial landscape evolution controlled by the sediment deposition coefficient: Estimation from experimental and natural landscapes

International audienceThe evolution of a fluvial landscape is a balance between tectonic uplift, fluvial erosion, and sediment deposition. The erosion term can be expressed according to the stream power model, stating that fluvial incision is proportional to powers of river slope and discharge. The deposition term can be expressed as proportional to the sediment flux divided by a transport length. This length can be defined as the water flux times a scaling factor ζ. This factor exerts a major control on the river dynamics, on the spacing between sedimentary bedforms, or on the overall landscape erosional behavior. Yet, this factor is difficult to measure either in the lab or in the field. Here, we propose a new formulation for the deposition term based on a dimensionless coefficient, G, which can be estimated at the scale of a landscape from the slopes of rivers at the transition between a catchment and its fan. We estimate this deposition coefficient from 29 experimental catchment–alluvial fan systems and 68 natural examples. Based on our data set, we support the idea of Davy and Lague (2009) that G is a relevant parameter to characterize the erosional and transport mode of a fluvial landscape, which can be field calibrated, with a continuum from detachment-limited (G = 0) to transport-limited behavior (G >0.4 from the studied examples)