Decoding the Late Palaeozoic glaciated landscape of Namibia: A photogrammetric journey

The geometry of unconformities carved by deep time ice sheets is often obscured and restricted by discontinuous exposure, or outcrop conditions that do not readily permit the examination of glacial unconformities (for example, steeply dipping strata). Here, we present new uncrewed aerial vehicle (UAV) data from selected outcrops across northern, central and southern Namibia to shed further light on the nature of the basal Dwyka Group unconformity. This includes the onlap relationship of basal diamictites onto the Gomatum palaeo-fjord system in northern Namibia, highly complex mapped ice flow orientations elsewhere in the northern Kaokoveld, previously undiscovered grooves along the Fish River area, and a set of subglacial grooves along the border with South Africa along the Orange River. In the latter two cases, photogrammetric methods integrating orthophotos and digital elevation models reveal the presence of subglacial grooves. Furthermore, subglacial grooves often show different orientations to striations and fabrics measured in overlying diamictites, raising fresh questions about the nature of small-scale flow variations beneath Late Palaeozoic ice sheets

Was climatic cooling during the earliest Carboniferous driven by expansion of seed plants?

The expansion of land plants is considered to have played a key role in triggering the Late Paleozoic Ice Age (LPIA), but evidence linking climatic events to terrestrial floral changes is limited. Here, we generated bulk carbonate δ13C, conodont δ18O and 87Sr/86Sr profiles from the lowermost Carboniferous of South China and Vietnam in order to investigate their relationship to contemporaneous land plant evolution. Climatic cooling in the mid-Tournaisian coincided with large perturbations to the global carbon cycle and continental weathering regimes as well as with a major diversification episode among seed plants. These relationships are consistent with terrestrial floral changes triggering intensified weathering of basalts (i.e., lower 87Sr/86Sr), enhanced marine productivity (i.e., higher δ13Ccarb), and reduced atmospheric pCO2 and attendant global cooling (i.e., higher conodont δ18O). The results of our study suggest that expansion of terrestrial floras was a key driver of Early Carboniferous climate change

Multiphase Phanerozoic Subsidence and Uplift History Recorded in the Congo Basin: A Complex Successor Basin

International audienceThe Congo Basin of central Africa is a large iconic Phanerozoic sedimentary basin whose origin and tectonic evolution are poorly understood, mostly because of a lack of modern stratigraphic data, reflecting a long hiatus in field investigations during the past five decades. It is usually assumed that the Congo Basin experienced a long and continuous history of slow subsidence since the late Precambrian (e.g. 2–4 m/Ma), linked to steady-state mantle processes. Here, we used revised sedimentological and stratigraphic data of the four historic deep boreholes drilled in the center of the basin to calculate a new first-order model for its subsidence and uplift history. Because the sedimentary sequences of this basin are largely terrestrial, we apply a new backstripping method especially designed for continental domain. The results reveal two main episodes of subsidence: initially rapid subsidence during the Carboniferous-Triassic (10–20 m/Ma), and then slower subsidence during the Jurassic-Cretaceous (5–10 m/Ma), punctuated by several uplifts at 160–180 Ma (e.g. ‘Karoo’), 120–140 Ma (e.g. ‘Paraná-Etendeka’), and again in the Cenozoic, ca. 30–50 Ma (e.g. ‘Ethiopian’). This complex, multiphase subsidence and uplift history of the Congo Basin can be linked to evolving far-field geodynamic processes that first led the formation of Pangea (large-scale compression) during the late Paleozoic, and then to its break-up associated with successive outpourings of Large Igneous Provinces (or hotspot plumes) and the opening of the Indian and South Atlantic Oceans around Africa