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Presentado en la Reunión The Panafrican and Cadomian orogenies in North Africa and Western Europe, 01/07/2021 (Session Oral presentations)

We present an updated time frame for the 30 m thick late Miocene sedimentary Trachilos section from the island of Crete that contains the potentially oldest hominin footprints. The section is characterized by normal magnetic polarity. New and published foraminifera biostratigraphy results suggest an age of the section within the Mediterranean biozone MMi13d, younger than similar to 6.4 Ma. Calcareous nannoplankton data from sediments exposed near Trachilos and belonging to the same sub-basin indicate deposition during calcareous nannofossil biozone CN9bB, between 6.023 and 6.727 Ma. By integrating the magneto- and biostratigraphic data we correlate the Trachilos section with normal polarity Chron C3An.1n, between 6.272 and 6.023 Ma. Using cyclostratigraphic data based on magnetic susceptibility, we constrain the Trachilos footprints age at similar to 6.05 Ma, roughly 0.35 Ma older than previously thought. Some uncertainty remains related to an inaccessible interval of similar to 8 m section and the possibility that the normal polarity might represent the slightly older Chron C3An.2n. Sediment accumulation rate and biostratigraphic arguments, however, stand against these points and favor a deposition during Chron C3An.1n.

The concentrations of long-lived cosmogenic nuclides (¹⁰Be, ²¹Ne, ²⁶Al) in quartz obtained from a very recent (~200 a) river terrace in Namibia are nearly constant throughout a 322 cm long depth-profile. These findings corroborate earlier hypotheses postulating a homogeneous distribution of these nuclides in freshly-deposited river terrace sediments. An averaged nuclide concentration is a crucial and generally assumed prerequisite for the determination of numerical ages of old sediments.

The South Um Mongul prospect is a Cu-Mo-Au porphyry system. It is covered by porphyritic dacite and hornblende gabbro. Both units are intruded by monzogranite, which encloses xenoliths of both units. Using LA-ICP-MS U-Pb zircon method, the dacite is dated at ca. 773 ± 6.9 Ma, while the gabbro and the monzogranite are dated at 603 ± 3.5 and 558 ± 4.6 Ma, respectively. The dacite age is consistent with the mid-Cryogenian subduction-related magmatic stage and the gabbro-monzogranite age is comparable to the Ediacaran post-collisional magmatic stage during the evolution of the Arabian-Nubian Shield. The dacite is akin to high-K I-type granitoids and its primitive mantle-normalized trace element patterns show negative Nb anomalies and enrichment in LILE (large ion lithophile elements), Th and U over HFSE. These geochemical characteristics are similar to those of felsic magma formed in a subduction-related tectonic setting. The high La/Ybcn (7.2–30.9), Nb/Yb (2.63–4.41) and Th/Yb (2.07–3.04) ratios of the dacite are comparable to continental rather than oceanic arc systems. Its low Sm/Yb ratios (1.84–3.13) support the primitive nature of the crust beneath the continental arc and derivation from a garnet-free lower crustal source. The dacite has low Sr/Y ratios (5–9) and its Eu/Eu⁎ ratios range from 0.66 to 0.83. Similar to dacite, the primitive mantle-normalized trace element patterns of the post-collisional suite show a subduction-related geochemical signature. However, the gabbro is characterized by Th/Ta ratios (3.4–14.8), which are comparable with the within-plate tectonic setting. The subduction-related geochemical signature is inherited from long subduction history beneath the Arabian-Nubian Shield. Both the gabbro and monzogranite are characterized by high Ba (404–590 ppm and 936–1590 ppm, respectively) and Sr (611–708 ppm and 624–793 ppm, respectively) contents, which make them analogous to the Caledonian appinite-high Ba-Sr granite assemblage. The formation of these rocks is related to the Ediacaran lithospheric erosion accompanying slab break-off. This process induced asthenospheric upwelling, which led to partial melting of the lithosphere previously metasomatised by subducted sediments involving carbonates impregnated by hydrothermal barite. Melting of this lithosphere led to the formation of the hornblende gabbro. Underplating by the mafic magma led to melting of the lower crust and the formation of high Ba-Sr monzogranite in the area. The high Sm/Yb (2.94–4.19) and Sr/Y (52–74) ratios of the monzogranite may indicate the presence of garnet in the melted amphibolitic lower crust. The higher Sr/Y ratios, lower HFSE (high field strength elements) contents and the absence of pronounced Eu anomalies in monzogranite relative to dacite suggest the productive nature of the post-collisional magma relative to the continental arc magma in this prospect.

Our multi-method MS study (AMS, noble gas MS, LA-(MC)-ICP-MS) aims to constrain the evolution of the western Namibian drainages since the last ca. 40 Ma. Therefore, fluvial sediments of several rivers and their precursors were sampled. In order to obtain precise Surface exposure ages of the various terrace levels, the routinely used cosmogenic nuclides 10Be, 21Ne, 26Al (quartz), and 36Cl (calcite) were applied either on surface samples or on depth-profiles consisting of 3 to 5 samples each. U-Pb small scale isochrone (SSI) ages of calcareous matrices were also used for terrace dating. Sedimentary provenances were revealed by detrital zircon (ZrSiO4) geochronology using U-Th-Pb and Lu-Hf isotope systematics. They indicate varying detrital zircon patterns through time. Our approach facilitates the recognition of changes in the fluvial sediment provenance at certain points in time. Such combined studies have a huge potential for revealing the palaeohydrological history, and to estimate amplitudes and processing Speeds of past events or changing sizes of catchment areas, which is of particular interest for modelling the palaeoclimate and palaeogeography.

The Interstellar Medium (ISM) is continuously fed with new nucleosynthetic products. The solar system moves through the ISM and collects dust particles. Therefore, direct detection of freshly produced radionuclides on Earth, i.e. before decaying, provide insight into recent and nearby nucleosynthetic activities [1,2]. Indeed, a pioneering work at TU Munich [3,4], which applied the ultra-sensitive single atom counting technique of accelerator mass spectrometry (AMS) to an ocean crust-sample, showed an enhanced 60Fe signal possibly of extraterrestrial origin. Within an international collaboration [5-7] we have continued to search for ISM radionuclides incorporated in terrestrial archives. We have analyzed several deep-sea sediments, crusts and nodules for extraterrestrial 60Fe (t1/2=2.6 Myr), 26Al (t1/2=0.7 Myr) and 244Pu (t1/2=81 Myr) [5-8] which are complemented by independent work at TU Munich [9-11]. All the data demonstrate a clear global 60Fe influx that is interpreted as exposure of Earth to recent (≤10 Myr) supernova explosions. Furthermore, the low concentrations measured for 244Pu suggest an unexpectedly low abundance of interstellar 244Pu [5]. This finding signals a rarity of actinide r–process nucleosynthesis which is incompatible with the rate and expected yield of standard core collapse supernovae as the predominant actinide-producing sites. In this talk I will also present additional new results for 60Fe and 244Pu measured with unprecedented sensitivity. These data provide new insights into their concomitant influx and their ISM concentrations over a time period of the last 11 million years. [1] J. Ellis et al., ApJ. 470, 1227 (1996). [2] G. Korschinek et al., Radiocarbon 38, 68 (1996); abstract. [3] K. Knie et al., Phys. Rev. Lett. 83, 18 (1999). [4] K. Knie et al., Phys. Rev. Lett. 93, 171103 (2004). [5] A. Wallner et al., Nature Comm. 6, 5956 (2015). [6] J. Feige et al., EPJ Web of Conf. 63, 3003 (2013). [7] A. Wallner et al., Nature 532, 69 (2016). [8] M. Paul M. et al. Astrophys. J. Lett. 558, L133L135 (2001). [9] C. Wallner et al. New Astron. Rev. 48, 145150 (2004). [10] L. Fimiani et al., Phys. Rev. Lett. 116, 151104 (2016). [11] P. Ludwig et al., PNAS 113, 9232 (2016).

The recent stream network of western Namibia is characterised by numerous non-perennial rivers with relatively small catchment areas, framed by the perennial Kunene and Orange Rivers. Most of them originate in the hinterland of the Great Escarpment. Studies based on terrestrial cosmogenic nuclides (TCN) revealed very low erosion rates of 3-16 m/Ma since the end of the Eocene within the proposed field area, which is consistent with the estimated long-term exhumation rates of 2 to 14 m/Ma derived by fission track studies [1,2]. Rates of ca. 10 m/Ma are also supposed for the escarpment retreat [1,3]. Thus, the relief of this region is inferred to have changed little since the Eocene [4]. Such low erosion provided excellent conditions for the preservation of fluvial sedimentary records derived by older river systems. They occur mostly as terrace conglomerates in higher positions of recent valleys. The river incision into the subjacent rocks was likely caused by recurrent tectonic events along the Etosha-Griqualand-Transvaal axis, which resulted in the uplift of the Great Escarpment [e.g. 5,6]. But the uplift possibly also caused changes of the atmospheric circulation and the hydrologic cycle [7]. Tectonic events and climate changes are supposed to be responsible for several variations in the direction of flow and dimension of the catchment areas, e.g. for the Kunene and Orange Rivers, since Palaeogene times. The present study aims to constrain the evolution of the western Namibian drainages since the Eocene. Therefore, fluvial sediments of the Kunene, Ugab, Swakop, Kuiseb, Tsondab, and Orange Rivers, as well as their precursors were sampled. In order to obtain precise surface exposure ages of the various terrace levels the routinely used TCN 10Be, 21Ne and 26Al from quartz were applied either on surface samples or on depth-profiles consisting of 3 to 5 depth sample spots. Additionally, first results of 36Cl in calcite and U-Pb SSI (small scale isochrones) ages of calcareous matrices from pedogenic calcretes will be presented. The provenance of the sediments was studied by detrital zircon geochronology using U-Th-Pb and Lu-Hf isotope systematics as well as single grain morphometrics. Preliminary results from several river terraces indicate differences in the detrital zircon pattern through time. This combination of methods facilitates the recognition of potential changes in the fluvial sediment provenance of a catchment area at certain points in time with high resolution. Thus, this combined approach has huge potential for revealing the palaeohydrological history. All this information can be used to estimate amplitudes and processing speeds of past events like incision rates, changing sizes of catchment areas or discharge, which is of particular interest for modelling the palaeoclimate and palaeogeography. References: [1] Cockburn HAP, Brown RW, Summerfield MA, Seidl MA (2000) Earth Planet Sci Lett, 179: 429-435 [2] Bierman PR, Caffee M (2001) Am J Sci, 301: 326-358 [3] Matmon A, Bierman P, Enzel Y (2002): Geology, 30: 1135-1138 [4] Fujioka T, Chappell J (2011): Aeolian Res, 3:157-164 [5] Haddon IG, McCarthy TS (2005): J Afr Earth Sci, 43: 316-333 [6] Burke K, Gunnell Y (2008): GSA Memoirs, 201: 1-66 [7] Hay WW (1996): Geol Rundsch, 85: 409-437

Las cuencas de Marsella-Aubagne, que se extienden desde Marsella a Roquevaire, ocupan más del cin¬cuenta por ciento del mapa geológico de Marsella-Aubagne con cerca de un millón de personas viviendo en la región. A pesar de su importancia geológica, aún son poco conocidas. La primera visión sintética fue llevada a cabo en el mapa geológico de 1935. Estudiados por Bonifay, los depósitos cuaternarios fueron incluidos en el mapa geológico de 1969. Sin embargo, las formaciones del Oligoceno no se modificaron hasta que Nury proporcionó una gran cantidad de datos estratigráficos muy detallados. Nuevos estudios han sido llevados a cabo en el marco de la tercera edición del mapa geológico 1:50 000. Estos estudios per¬miten distinguir entre tres cuencas diferentes: la «cuenca de Jarret» en la parte norte, la «cuenca del Prado» en la parte suroeste y la «cuenca de Aubagne» en la parte oriental. Cada una de ellas contiene su propia sucesión estratigráfica que incluye varias formaciones desde el Rupeliense hasta el Chattiense. De manera general, las formaciones del Rupeliense inferior a superior están deformadas tectónicamente, mientras que los depósitos del final del Rupeliense hasta el Chattiense superior sólo presentan una deformación leve. Por lo tanto, se han podido diferenciar dos etapas geodinámicas principales: la primera empieza con régimen distensivo en el Oligoceno inferior y conduce a la apertura de depresiones de dirección NNE-SSO a lo largo de toda la plataforma europea y, la segunda, que comienza con un régimen distensivo NNO-SSE coetáneo con el rifting del Mediterráneo Occidental. El punto clave que separa estas dos fases entre sí es un posible régimen compresivo en el Rupeliense más tardío. Para concluir, esta cuenca se puede utilizar como un archi¬vo natural para los eventos del Oligoceno. Por lo tanto, estas cuencas deben ser consideradas como piezas maestras para las reconstrucciones paleogeográficas y geodinámicas del Oligoceno. The Marseille-Aubagne Basins, which extend from Marseille to Roquevaire, occupy more than fifty per cent of the Marseille-Aubagne geological map, with approximately one million people living in this area. Despite this geological importance they are still poorly known. The first synthetic view was delivered in the 1935 geological map. Studied by Bonifay, the Quaternary deposits have been included in the 1969 geological map. Nevertheless, the Oligocene formations remained unmodified until Nury, who provided a lot of very detailed stratigraphic data. New studies have been carried out in the frame of the third issue of the 1:50,000 geological map. These studies allow us to distinguish between three different basins: the “Jarret basin” in the northern part, the “Prado basin” in the southwestern part and the “Aubagne basin” in the eastern part. Each of them contains its own stratigraphic succession, including several formations from the Rupelian to the Chattian. Globally, the Lower to Upper Rupelian formations are tectonically deformed, whilst deposits from the Latest Rupelian to the Latest Chattian show only slight deformation. Thus, two main geodynamic stages have been distinguished: the first beginning with the Early Oligocene extensive regime leading to the opening of NNE-SSW troughs all over the European platform and, the second, beginning with a NNW-SSE extensive regime coeval with the Western Mediterranean rifting. The key point that separates these two stages from each other is a possible Late Rupelian compressive regime. To sum up, this basin can be considered as a natural archive for the Oligocene events. Therefore, these basins should be considered as master pieces for the Oligocene palaeogeographic and geodynamic reconstructions.

Seven samples of Siluro-Devonian sedimentary rocks from the Cantabrian and Central Iberian zones of the Iberian Variscan belt have been investigated for provenance and contain four main age populations in variable relative proportion: Ediacaran–Cryogenian ( c . 0.55–0.8 Ga), Tonian–Stenian (0.85–1.2 Ga), Palaeoproterozoic ( c . 1.8–2.2 Ga) and Archaean ( c . 2.5–3.3 Ga). Five samples contain very minor Palaeozoic (Cambrian) zircons and six samples contain minor but significant zircons of Middle and Early Mesoproterozoic (Ectasian–Calymmian, 1.6–1.8) age. These data highlight the transition from an arc environment to a stable platform following the opening of the Rheic Ocean. Variations in detrital zircon populations in Middle–Late Devonian times reflect the onset of Variscan convergence between Laurussia and Gondwana. The presence of a high proportion of zircons of Tonian–Stenian age in Devonian sedimentary rocks may be interpreted as (1) the existence of a large Tonian–Stenian arc terrane exposed in the NE African realm (in or around the Arabian–Nubian Shield), (2) the participation, from the Ordovician time, of a more easterly alongshore provenance of Tonian–Stenian zircons, and (3) an increase in the relative proportion of Tonian–Stenian zircons with respect to the Ediacaran–Cryogenian population owing to the drift of the Avalonian–Cadomian ribbon continent, or the progressive burial of Ediacaran–Cryogenian rocks coeval with the denudation of older source rocks from the craton interior. Supplementary material: Tables with the analytical data and the geochronological results are available at http://www.geolsoc.org.uk/SUP18812.

Early Carboniferous turbiditic sedimentary rocks in synorogenic basins located on both sides of the Rheic suture in SW Iberiawere studied for provenance analysis. An enigmatic feature of this suture, which resulted from closure of the Rheic Ocean with the amalgamation of Pangea in the Late Carboniferous, is that there are no recognizable mid- to Late Devonian subduction-related magmatic rocks,which should have been generated during the process of subduction, on either side of it. U–Pb LA–ICP-MS geochronology of detrital zircons from Early Carboniferous turbidites in the vicinity of the Rheic suture in SW Iberia, where it separates the Ossa–Morena Zone (with Gondwana continental basement) to the north from the South Portuguese Zone (with unknown/Meguma? continental basement) to the south, reveals the abundance of mid- to Late Devonian (51–81%) and Early Carboniferous (13–25%) ages. The Cabrela andMértola turbidites of the Ossa–Morena and South Portuguese zones, respectively, are largely devoid of older zircons, differing from the age spectra of detrital zircons in the oldest (Late Devonian) strata in the underlying South Portuguese Zone, which contain abundant Cambrian and Neoproterozoic ages. Mid- to Late Devonian zircons in the Cabrela Formation (age cluster at c. 391 Ma, Eifelian–Givetian transition) and Mértola Formation (age clusters at c. 369 Ma and at c. 387 Ma, Famennian and Givetian respectively) are attributable to a source terrane made up of magmatic rocks with a simple geological history lacking both multiple tectonic events and older continental basement. The terrane capa- ble of sourcing sediments dispersed on both sides of the suture is interpreted to have been completely re- moved by erosion in SW Iberia. Given that closure of the Rheic Ocean required subduction of its oceanic lithosphere and the absence of significant arc magmatism on either side of the Rheic suture, we suggest: 1) the source of the zircons in the SW Iberia basins was a short-lived Rheic ocean magmatic arc, and 2) given the lack of older zircons in the SW Iberia basins, this short-lived arc was probably developed in an intra-oceanic environment.

Neste trabalho são apresentados dados preliminares de geoquímica isotópica Rb-Sr e Sm-Nd em amostras de rochas detríticas das bacias do Ediacariano-Câmbrico Inferior da Zona de Ossa-Morena. As amostras analisadas mostram valores baixos da razão 147Sm/144Nd (0.105-0.119) e negativos de εNd(T) (-3.9 to -12.4), sugerindo uma proveniência típica da crusta continental. Estes resultados obtidos para as rochas do Ediacariano-Câmbrico Inferior da Zona de Ossa-Morena são similares aos registados para rochas correlacionáveis da Zona Saxo-Thuringia (Alemanha). This work presents preliminary Rb-Sr and Sm-Nd isotope geochemistry results from samples of detrital rocks from the Ossa-Morena Zone Ediacaran-Early Cambrian basins. The analysed samples present low 147Sm/144Nd values (0.105-0.119) and negative εNd(T) values (-3.9 to -12.4), which suggest a typical upper continental crust provenance. These results of Ediacaran-Early Cambrian Ossa-Morena Zone rocks are close to those obtained for the Saxo-Thuringian Zone (Germany) correlatives.