Geochemical Evidence for Large‐Scale Drainage Reorganization in Northwest Africa During the Cretaceous

Abstract

West African drainage reorganization during Cretaceous opening of the Atlantic Ocean is deciphered here from geochemical provenance studies of Central Atlantic sediments. Changes in the geochemical signature of marine sediments are reflected in major and trace element concentrations and strontium‐neodymium radiogenic isotopic compositions of Cretaceous sedimentary rocks from eight Deep Sea Drilling Project (DSDP) sites and one exploration well. Homogeneous major and trace element compositions over time indicate sources with average upper (continental) crust signatures. However, detailed information on the ages of these sources is revealed by neodymium isotopes (expressed as ɛNd). The ɛNd(0) values from the DSDP sites show a three‐step decrease during the Late Cretaceous: (1) the Albian‐Middle Cenomanian ɛNd(0) values are heterogeneous (–5.5 to −14.9) reflecting the existence of at least three subdrainage basins with distinct sedimentary sources (Hercynian/Paleozoic, Precambrian, and mixed Precambrian/Paleozoic); (2) during the Late Cenomanian‐Turonian interval, ɛNd(0) values become homogeneous in the deepwater basin (–10.3 to −12.4), showing a negative shift of 2 epsilon units interpreted as an increasing contribution of Precambrian inputs; (3) this negative shift continues in the Campanian‐Maastrichtian (ɛNd(0) = −15), indicating that Precambrian sources became dominant. These provenance changes are hypothesized to be related to the opening of the South and Equatorial Atlantic Ocean, coincident with tectonic uplift of the continental margin triggered by Africa‐Europe convergence. Finally, the difference between ɛNd(0)values of Cretaceous sediments from the Senegal continental shelf and from the deepwater basins suggests that ocean currents prevented detrital material from the Mauritanides reaching deepwater areas.

Cretaceous continental margin evolution revealed using quantitative seismic geomorphology, offshore northwest Africa

“…Canyons and associated erosion at this stratigraphic level extend beyond the limit of the study area (Figure 1), as indicated to the north (Martin et al, 2010) and south Mourlot, Roddaz, et al, 2018). Mounded interfluves are preserved, with the largest having a maximum area of ca.…”

“…This regional, extra-basinal, siliciclasticprone source of sediment and drainage is postulated to vary laterally and may have also exerted a control over the location and health of the carbonate factories and accumulation of the platform along this mixed-system margin. , Mourlot, Roddaz, et al (2018) show multiple entry points for similar-aged deltaic systems (see their Figure 9b), introducing a regional source of sediment from rivers draining the onshore Senegal Basin and hinterland of northwest Africa. This sediment is likely to be very different in composition to locally derived material associated with the erosion and collapse of the margin.…”

“…Covault, 2011;Galloway, 1998). However, these are present further north and south of the study area where there is higher siliciclastic sediment supply Mourlot, Roddaz, et al, 2018). The basinal deposits form a strike-discontinuous apron that are interpreted to nearly all originate from point sourced canyon systems interpreted upslope (Playton et al, 2010).…”

Low‐temperature thermochronology as a control on vertical movements for semi‐quantitative source‐to‐sink analysis: A case study for the Permian to Neogene of Morocco and surroundings

“…Sediment provenance analysis conducted in Morocco and surroundings are scarce. Five recent works investigated the provenance with detrital zircon U-Pb (Azdimousa et al, 2019;Domènech et al, 2018;Marzoli et al, 2017;Pratt et al, 2015;Perez et al, 2019); one study used traced elements and radiogenic Nd-Sr isotopes (Ali et al, 2014), one using neodymium isotopes and major/trace elements from DSDP wells (Mourlot et al, 2018), and one produced detrital LTT ages (Sehrt, 2014). Several studies have also documented palaeocurrent directions in fluvial systems (e.g.…”

“…Pratt et al (2015) collected Albian sediments deposited in the Rif basin, and traced the provenance to two sources: the Meseta and another unknown area. Finally, Mourlot et al, (2018) undertook a largescale provenance study targeting Albian to Maastrichtian sediments from DSDP wells (from north to south offshore Morocco sites 370, 416, 415 and 369 were sampled) along the NW African coast. They used the major and trace element concentrations from these marine sediments, as well as Nd isotopes, to constrain continental crust signatures.…”