Possibilities and limitations of ESR dating applied to Pliocene and Pleistocene units of western central mainland Portugal

Summary: This work aims to give a short description of the applicability of ESR method for dating Pliocene and Pleistocene units of western central mainland Portugal ranging between 2.5 and 0.2 Ma. The vast culminant unit of the sedimentary infill only was previously dated, at the base, in one site. The dating of the topmost deposits of this unit will allow to date the transition from the stage of sedimentary infilling to that of fluvial incision and to understand the controls of this. Only the lower coastal terraces are dated to <ca. 300 ka provided by OSL methods. The ESR dating will support stratigraphic correlations and estimate the local uplift rates and the identification of the main active tectonic structures in central western mainland Portugal

Geomorphic markers of Quaternary tectonics in Westernmost Iberia: insights from the Lower Mondego River terraces (central Portugal)

The Lower Mondego Valley (LMV), located in the Western Iberian passive margin which is under compressive tectonic reactivation since ca. 80 Ma, is used for deciphering long-term landscape evolution during the Quaternary and the control played by active tectonics, eustasy and climate. The elaboration of a detailed geomorphological map allowed the establishment of the spatial and temporal distribution of the different geomorphological units and morphogenetic systems operating in the LMV. The culminant unit of the Mondego Cenozoic Basin (allostratigraphic unit UBS13, recording an Atlantic fan-delta and adjacent shallow marine siliciclastic environments) and terrace levels (river and marine) are used as geomorphic markers to quantify fluvial development and tectonic activity. The main stages of evolution are a transition of endorheic to exorheic (Atlantic base level) drainage in the Mondego Cenozoic Basin, ca. 3.7 Ma ago, followed by onset of the fluvial incision stage (valley entrenchment) by ca. 1.8 Ma. Electron spin resonance (ESR) dating is used to improve the chronological framework for the terrace staircases of the LMV and to decipher the response of the river to the regional uplift and other longterm controls (resistance of the substratum to erosion, eustasy and climate). Six river terrace levels (T1, the older, to T6, the younger), inset in the UBS13 and previous to the modern alluvial plain, were characterized and correlated with marine terraces represented at Cape Mondego, near the river mouth. The fluctuating eustatic and climate controls are superimposed on a long-term crustal uplift. The data show marked compartmentalization of fluvial system behaviour with changes in incision rates (acting as a proxy of uplift rates) from east to west, creating distinctly different sectors. Differential uplift is inferred between the valley sides and between the four main reaches in which the LMV is subdivided by major faults. Differential uplift is mainly related to regional fault sets trending N-S to NNW-SSE, NNE-SSW, ENE-WSW, and E-W to WNW-ESE. Using as geomorphic references the topmost deposits of the UBS13 unit and river terraces located above the alluvial plain, average long term incision rates were estimated ranging from 0.03 to 0.16 m/ka, dependin

A escadaria de terraços marinhos de Peniche (Portugal centro-oeste)-estratégias para a datação

Summary:The Peniche staircase of marine terraces (central-west Portugal) dating strategies At the rocky coast of Peniche Peninsula, a staircase of six wave-cut surfaces and associated sedimentary deposits was identified. The strategies for the absolute dating of the several records of the Pliocene and Pleistocene marine incursions is here presented. The three lower marine terraces could be dated by optically stimulated luminescence, by using the proto-col pIRIR (k-feldspar as the dosimeter). The three upper terraces and the culminant marine unit could be dated by electron spin resonance. The limited thickness of the deposits does not allow the use of Cosmogenic (TNC) dating. The uppermost deposits of some of the marine terraces contain vertebrate bones and travertines, which could also be used for U-series dating (13) (PDF) A escadaria de terraços marinhos de Peniche (Portugal centro-oeste)-estratégias para a datação. Available from: https://www.researchgate.net/publication/327582780_A_escadaria_de_terracos_marinhos_de_Peniche_Portugal_centro-oeste-estrategias_para_a_datacao [accessed Feb 15 2019]

Plio-Quaternary coastal uplift along the western Iberian margin: insights from dated marine terraces (Peniche, central Portugal)

This study provides a detailed geomorphological study of the Peniche Peninsula, located in westernmost Iberia, a resistant rocky limestone headland subjected to high energy Atlantic Ocean coastal processes. We have used field mapping, surveying, sedimentary facies analysis, geochronology (electron spin resonance [ESR]; U-Series), but also identification of fossils and lithic artefacts, in order to: 1) reconstruct styles and timing of paleoenvironmental changes, 2) correlate to Marine Isotope Stages (MIS), and 3) quantify coastal uplift rates during the Quaternary. The marine terrace deposits, comprising calcite cemented conglomerates and siliciclastic sandstones, sometimes capped by travertines, were studied in detail along the SW sector of the peninsula, at the Furninha Cave site. The mapping (1/10,000 scale) and dating results obtained allow to identify several marine levels and to correlate them to MIS’s: 1) a culminant wave-cut platform at 29-33 m (above mean sea level) (Pm), with a probable age of 3.7 Ma; 2) a wave-cut platform at 24-28 m (Tm1), dated as 883±120 ka, probably correlated with high sea level conditions spanning ca.1000-790 ka (MIS25-19); 3) a wave-cut platform at 19-21 m (Tm2), with a beach conglomerate and sandstone, dated as 707±32 ka and correlated to 790-680 ka (MIS17); 4) a wave-cut platform at 14-16 m (Tm3), with a beach conglomerate and sandstone, and capping travertine, probably recording aggradation during 620-460 ka (MIS15-13) (ESR: 598±160, 563±63, 490±44 ka; U-series: >620 ka); 5) a wave-cut platform at 11-13 m (Tm4), with beach conglomerate and sandstone followed by travertine, dated as 315±48 ka, probably recording 430-275 ka (MIS11-9); 6) a wave-cut platform at 6-9 m (Tm5), with beach conglomerate, sandstone and travertine, dated as 288±53 ka, probably spanning 290-180 ka (MIS7); 7) a wave-cut platform at 4.0 m (Tm6), probably spanning 125-85 ka (MIS5); 8) aeolian sand units, respectively, of Late Pleistocene and Holocene age; 9) modern beach sediments, ranging from sands to boulders. A long term Plio-Quaternary corrected uplift rate of 0.004-0.006 m/ka is obtained using the Pm level as a key geomorphic marker (eustatic level = +10-20 m). In contrast, for the last ~1 Ma the inset Pleistocene marine terrace levels (Tm1-Tm6) indicate apparent short-term uplift rates between 0.02 and 0.05 m/ka (means of 0.03 to 0.04 m/ka) and corrected short-term uplift rates between -0.05 and 0.05 m/ka (means of -0.02 to 0.05 m/ka). This study demonstrates that the Quaternary compressive reactivation of the Western Iberian Margin has determined coastal low to moderate uplift rates; active tectonics play an important role in the geomorphic expression and distribution of Pleistocene marine terraces, recording vertical ground motions (uplift/subsidence) superimposed onto global sea-level oscillations

Electron spin resonance dating of the culminant allostratigraphic unit of the Mondego and Lower Tejo Cenozoic basins (W Iberia), which predates fluvial incision into the basin-fill sediments

The Cenozoic basins of western Iberia have a culminant allostratigraphic unit (designated UBS13), which records the beginning of Atlantic drainage and predates the fluvial incision that led to the development of the present drainage networks. However, the available numerical dating is quite limited and mainly restricted to the lower-level terrace deposits. Therefore, this study uses for the first time the electron spin resonance (ESR) method to date this culminant unit in the Mondego and Lower Tejo Cenozoic basins of Portugal. The depositional age of this unit is supposed to lie between ~3.7 Ma (basal deposits) and ~1.8 Ma (uppermost deposits). The Al-centre provided reliable ESR data, but the dates obtained by using the TiLi centre clearly underestimate the burial ages. With reference to the existing independent dating of the Vale Farpado site (3.7–3.6 Ma) at the lowermost basal level of the UBS13 deposits, the ESR (Al-centre) ages of 3.0 to 2.3 Ma obtained for the UBS13 basal and middle deposits give reliable estimates of the burial age. The ESR ages (Al-centre) obtained for the UBS13 uppermost deposits indicate a probable age of ~1.8 Ma. Thus, these results are of international significance, in that they constitutes the first numerical ages obtained for the uppermost levels of the Cenozoic basin-fills of western Iberia, which predate the fluvial incision that took place in response to lower Quaternary base levels

Vallée de la Dives : étude des terrasses à Morteaux-Couliboeuf (L’Herbage Vieille), Le Mesnil-Mauger (Écajeul) et Biéville-Quétiéville (Quétiéville)

Dans le cadre des projets soutenus par le PCR « les premiers Hommes en Normandie », de nouvelles recherches de terrain portant sur l’étude géomorphologique et sédimentaire de vallées fluviatiles pléistocènes de la Dives ont été engagées, afin de préciser les contextes environnementaux et de tenter de mettre en évidence d’éventuelles occupations humaines. Le fleuve Dives s’inscrit dans le contexte de bordure du système Manche-Atlantique qui a laissé des replats recouverts de nappes alluviales ..

Les nappes alluviales pléistocènes de la vallée moyenne du Cher (Région Centre, France) : contexte morphosédimentaire, chronologie ESR et Préhistoire. Premiers résultats

L’inventaire des nappes alluviales fossiles conservées dans la vallée moyenne du Cher, l’un des principaux affluents de la Loire en rive gauche, a été entrepris depuis 2003. Une fois repérées, les formations alluviales ont été sondées mécaniquement jusqu’au substratum, étudiées stratigraphiquement et échantillonnées pour analyses géochronologiques par la méthode de la résonance électronique de spin (ESR) appliquée aux quartz fluviatiles optiquement blanchis.Deux secteurs ont été définis dans la moyenne vallée du Cher, de part et d’autre de Vierzon, et appelés respectivement secteurs « Berry » et « Sologne ».Dans le secteur « Berry », la vallée a une orientation N 160o et suit de grands accidents tectoniques qui mettent au contact les formations calcaires du Jurassique et les dépôts calcaires lacustres tertiaires. Dans ce secteur, l’incision totale de la vallée est de 50 m et neuf formations alluviales étagées ont été inventoriées. Elles sont généralement conservées sur la rive gauche de la vallée actuelle, dans des systèmes karstiques et sur des blocs basculés ou abaissés. Trois de ces formations ont été particulièrement étudiées et datées.Dans le secteur « Sologne », la vallée suit un axe synclinal orienté est-ouest. Elle traverse les formations crétacées, puis les sables burdigaliens, et son incision passe d’amont en aval de 35 m à 20 m seulement. Dans ce secteur, quatre ou cinq nappes alluviales ont été individualisées selon les sous-secteurs. Pour les plus hautes d’entre elles, les différences d’altitudes relatives sont très faibles, ce qui complique l’étude. Par ailleurs, les nappes moyennes sont mal conservées.La datation des nappes de la vallée moyenne du Cher par ESR est en cours. Les premiers résultats indiquent que la mise en place de la vallée du Cher a débuté dès le Pléistocène inférieur. Les industries du Très-Ancien Paléolithique du site de Lunery (Cher), dont la situation a pu être précisée par des fouilles, sont ainsi datées de 1,1 Ma, en accord avec les données biochronologiques obtenues sur le site voisin de Rosières, et confirment la présence de l’Homme dès cette époque dans le bassin de la Loire moyenne. Par ailleurs, les âges obtenus sur les nappes moyennes, s’ils sont confirmés, indiqueraient que les industries à bifaces étaient déjà présentes dans cette zone et très développées il y a 700 ka.Since 2003, field surveys in the Middle Cher River Valley, a left tributary of the Loire River, have allowed the inventory of the Pleistocene alluvial formations. Most of them have been mechanically bored as far as the substratum, stratigraphically studied and sampled for Electronic Spin Resonance (ESR) geochronological analyses.Two different sectors, called respectively “Berry” and “Sologne”, have been defined upstream and downstream of Vierzon.In the “Berry” Sector, the river flow N. 160o along a major tectonic accident which cuts Jurassic limestones and Tertiary lacustrine calcareous deposits. The incision of the valley is about 50 m and nine Pleistocene alluvial formations have been recognized on the left side of the modern valley only. The deposits are often preserved in karstic systems or on tilted down blocks.In the “Sologne” Sector, the river flows along an east-west syncline through the Cretaceous chalky and clayeous formations and the Burdigalian sands. In this sector, the incision, about 35 m upstream, reduces to 20 m downstream and four or five alluvial formations have been studied. Differences between the relative altitudes of the highest terraces are very small. The middle sheets are rarely preserved and the lower formations spread out the two kilometres wide alluvial plain.The dating of the different sheets by the ESR method applied to optically bleached fluvial quartz is in progress. First results indicate that the present Cher Valley began its incision during the Lower Pleistocene, in spite of a low incision referred to the other main tributary valleys of the Middle Loire Basin.The Early Lower Palaeolithic artifacts founded by excavations in the alluvial deposits of the Lunery site (Cher) have been dated about 1.1Ma and confirm other evidences of such ancient human settlement of the Middle Loire Basin. The ESR ages obtained for the middle formations, if they will be confirmed, indicate that Acheulian handaxes industries were present and developed in this area since 700 ka

Marine terrace staircases of western Iberia: uplift rate patterns from rocky limestone coasts of central Portugal (Cape Espichel and Raso)

The Western Iberian passive margin is under compressive tectonic reactivation resulting in spatial and temporal variations in surface uplift. This uplift can be quantified in coastal settings using staircases of wave-cut platforms developed onto rocky headlands. This study focuses on two marine terrace staircases of central Portugal: Cape Raso (west of Lisbon) and Cape Espichel (western Arrábida mountain chain). Geomorphic and stratigraphic analyses identified four marine terraces above sea level at Cape Raso area and twelve at Cape Espichel. ESR and pIRIR dating were used to develop a chronological framework for the staircases, from which uplift rates were calculated. Using the interaction between the global mean sea-level elevations in the Quaternary and the local uplift rate (Roberts et al., 2013) the marine terraces were correlated with Marine Isotope Stages (MIS). At Cape Raso, Tm1 (+38 m) corresponds to MIS 17 (712-676 ka), Tm2 (+34 m) corresponds to the MIS 15 (621-563 ka) and was reworked during the MIS 11 (399-408 ka), Tm3 (+ 22 m) correlates with MIS 13 (533-478 ka) and was reworked during the highstand of MIS 9 (330-316 ka) and Tm4 (+9 m) correlates with MIS 7 (243 -191 ka). At Cape Espichel, a correlation was found between the relative sea-level elevations of the eight lowest terraces with several MISs (MIS 5 until MIS 17). The correlation becomes unclear for terraces older than MIS 17, translating into an apparent decrease in uplift rate towards older times. Either in Cape Raso or Espichel, the terrace staircases do not correlate in all cases with sea level high stands sequentially. For instance, the palaeoshoreline elevation of MIS 11 is higher than the palaeoshoreline of MIS 13. This suggests that marine terraces have been formed by superposition of multiple sea-level fluctuations in a long-term uplift context, but with an uplift rate low enough to allow the reworking of older shorelines during subsequent MISs. At Cape Raso, the dating of Tm2 correlated with MIS 15 allows for an estimation of an uplift rate of ~0.07 m/ka for this coast, seemingly decreasing over the last ~125 ka. At Cape Espichel, the chronological framework of Tm5 and Tm6 allows associations with MIS 15 and MIS 11, respectively.The estimated mean uplift rate from MIS 5e to MIS 17 was ~0.14m/ka. For times older than MIS 17 (up to ca. 3.7 Ma) the uplift rate was lower than during the last ~125 ka (~0.04 m/ka). The present elevations of the late Zanclean wave-cut platform, represented by the Raso Cape Platform (~100 m) and the Cape Espichel (up to ~220 m) platforms, further express the differential uplift between the study areas for the last ~3.7 Ma. References: Roberts, G.P., Meschis, M., Houghton, S., Underwood, C., Briant R.M., 2013. The implications of revised Quaternary paleo-shoreline chronologies for the rates of active extension and uplift in the upper plate of subduction zones. Quaternary Science Reviews 78, 169-187