J.L. Goy

U-series measurements in tyrrhenian deposits from mallorca — Further evidence for two last-interglacial high sea levels in the Balearic Islands

The Campo de Tiro type-section for the Tyrrhenian ecostratigraphic beds of the Balearic Islands shows four indurated littoral conglomerates and beach-rocks, unconformably superimposed. The lower two units (1 and 2) are separated by a thin layer of reddish continental silts; both contain a typical Eutyrrhenian fauna, whereas a Neotyrrhenian fauna characterizes the overlying units 3 and 4. ThU measurements by thermal ionisation mass spectrometry on mollusk shells from these deposits yielded ages of ∼135 ka (unit 1), ∼117 ka (units 2 and 3), and a scatter of ages around ∼100 ka (unit 4). The stratigraphic relationships and ThU data indicate (i) that uranium was uptaken by mollusks shells (but Arca sp.) each time during a relatively short early diagenetic interval before cementation ensured a ‘fair’ closure of the radioactive system, (ii) two high sea stands characterized the Last Interglacial (Isotopic Substage 5e) of the Balearic Islands area, (iii) the duration of this episode was ∼17 ka, and (iv) the change in faunal assemblages and disconformity observed between units 2 and 3 are due to fluctuations in sea level and surface water conditions which occurred during the second high sea level episode of the Last Interglacial.

Landscape response to strike-slip faulting linked to collisional settings: quaternary tectonics and basin formation in the Eastern Betics, southeastern Spain

Abstract Neotectonic behaviour of the Eastern Betics (southeastern Spain) has been controlled by the presence of a large, left-lateral shear zone. This is an intraplate transcurrent zone, probably decoupled by a mid-crustal detachment horizon. The morphological expression of this crustal structure is a sigmoidal corridor in which the main Quaternary basins are located. Three types of morphostructural domains can be distinguished in the sigmoidal corridor: the central segment, and the northern and southern terminal splays. The central segment is characterized by wrench tectonics, whilst the southern and northern terminal splays are controlled by transtensional and transpressional tectonics, respectively. The Quaternary morphostructural pattern is only the more recent picture of the tectonic processes that have controlled the late orogenic evolution of the Eastern Betics: the indentation of the Aguilas arc, accompanied by thin-skinned thrusting and tectonic escape in its easternmost sector; and extensional collapse, accompanied by thin-skinned stretching, in its westernmost sector.

Global and regional factors controlling changes of coastlines in Southern Iberia (Spain) during the holocene

The interaction between global (glacio-eustatic sea-level rise) and regional factors (oceanographic and tectonic) has controlled the evolution of coastline during the Holocene in Southem Iberia. At ca. 10,000 14C years BP a deceleration of relative sea-level rise took place both in the Atlantic and Mediterranean littorals, with a maximum transgression at 6450 14C years BP. In subsiding areas (present tidal flats) estuaries illustrate a clear marine influence recorded both in sediments and the fauna while in uplifting areas prograding spit-bar systems developed. Two phases of major progradation are distinguished in these systems: the first one between 6450 and 3000 14C years BP, with a sedimentary gap at ca. 4000 14C years BP; and the second one from 2750 14C years BP up to present, with an intervening gap between 1200 and 1050 14C years BP. These progradation phases develop during stillstands followed by relative sea-level fall, while the sedimentary gaps represent relative high sea level. In the Mediterranean areas, with a higher uplift rate, marine terraces almost coeval to those gaps occur. The most pronounced modifications in littoral dynamics occurred at between 3000 and 2750 14C years BP represented by changes in the direction of longshore drift and prevailing winds and in the predominance of progradation over aggradation processes. At ca. 1000 14C years BP the estuaries record a greater fluvial than marine influence, and at 500 years ago an extraordinary increase in coastal progradation took place in all littoral zones. The European Medieval Warm period is characterized, at least during its initial phase, by low pressure climate conditions, while during the Little Ice Age anticyclonic conditions gave rise to a strong coastal progradation.

Coastal deformation and sea-level changes in the northern Chile subduction area (23°S) during the last 330 ky

Abstract The Nazca-South American plate boundary is a subduction zone where a relatively complex pattern of vertical deformation can be inferred from the study of emerged marine terraces. Along the coasts of southern Peru and northern Chile, the vertical distribution of remnants of Pleistocene terraces suggests that a crustal, large scale uplift motion is combined with more regional/local tectonic processes. In northern Chile, the area of Hornitos (23°S) offers a remarkable sequence of well-defined marine terraces that may be dated through U-series and aminostratigraphic studies on mollusc shells. The unusual preservation of the landforms and of the shell material, which enabled the age determination of the deposits, is largely due to the lengthy history of extreme aridity in this area. The exceptional record of late Middle Pleistocene to Late Pleistocene high seastands is also favoured by the slight warping of two distinct fault blocks that have enhanced the morphostratigraphic relationships between the distinct coastal units. Detailed geomorphological, sedimentological and chronostratigraphic studies of the Hornitos area led to the identification, with reasonable confidence, of the depositional remnants of sea-level maxima coeval with the Oxygen Isotope Substages 5c, 5e, 7 (probably two episodes) and the isotope stage 9 (series of beach ridges). The coastal plain, at the foot of the major Coastal Escarpment of northern Chile, appears to have been uplifted at a mean rate of 240 mm/ky in the course of the last 330 ky. From the elevation of the older terraces and late Pliocene shorelines, it can be inferred that these steady vertical motions were much more rapid than during the Early Pleistocene.

Particle size characterisation of Holocene back-barrier sequences from North Atlantic coasts (SW Spain and SE England)

Abstract In this paper, we present the results of bivariate plots of grain size parameters (mean against sorting) in the reconstruction of Holocene environmental change in coastal environments where barrier formation has had an important control on sedimentation. Sites on the North Atlantic coast with differing histories of climate, sediment flux, sea-level change and barrier integrity are investigated to determine the general efficacy of this bivariate parameter model in distinguishing between open- and closed-basin conditions, and in reviewing the significance of aperiodic high-energy geomorphic events in controlling late stage back-barrier sedimentation.

Pampa del Palo : an anomalous composite marine terrace on the uprising coast of Southern Peru

Abstract Quaternary sediments along the southern Peruvian coast occur as staircase terraces of coastal and shallow-marine deposits in response to continuous uplift related to the active boundary between the Nazca and South-American plates. However, near ILO (in the same coastal stretch) the emergent Pampa del Palo terrace consists of a relatively-thick, vertical stack of shallow-marine, coastal and lagoonal deposits that indicate a rather different geodynamic behaviour. Coastal deposits are correlatable with the successive marine highstands of isotopic stages 7 (?) and 5 (substages 5e and 5c). Combining aerial photo-interpretation, geomorphological mapping, sedimentological analysis, chronostratigraphical data, and structural observations, the Pampa del Palo feature is interpreted as a faulted block that moved independently of the remaining southern Peruvian coast and, for some time between the end of Middle Pleistocene (before ca. 220 ka) and the early Late Pleistocene (ca. 120 ka), it rose more slowly or was even down-faulted relative to the rest of the southern Peruvian margin. The independent block movements ceased after substage 5e, when the Pampa del Palo “terrace” was incorporated into the regional uplift of the area. Since ca. 100 ka, measured uplift rates in the Ilo area amounted up to 160 mm 10 3 y when the area has been affected by a few active, NE-SE trending faults only.

QUATERNARY SHORELINES IN SOUTHERN PERU: A RECORD OF GLOBAL SEA-LEVEL FLUCTUATIONS AND TECTONIC UPLIFT IN CHALA BAY

Abstract The coastal area bordering the bay of Chala (14°50′S., 74°15′W.), southern Peru, contains one of the most complete sequences of Quaternary shorelines in South America. Remnants of about 27 high seastands have been preserved between present mean sea-level and +275 m. Most remnants consist of staircased marine terraces and associated deposits which are partly covered by alluvial fan and colluvial units deposited during intervening periods of lower sea-levels. No geochronological data are yet available; a tentative chronostratigraphy of the terrace sequence is based on the geometric and stratigraphic relationships between successive landforms, and deposits. We group most marine terraces into 15 ‘major morphostratigraphic units’ (MMUs). Some of these major units seem to correlate with interglaciations, for example Isotopic Stage 5, or with interstadials (Stage 3). Higher in the Chala sequence, major morphostratigraphic units mapped during field and air-photo studies may represent only parts of Middle Pleistocene interglaciations. We infer that shorelines located at +68, +121, +168, and +184 (or +200) m correlate with the highest seastands of Isotopic Stages 5, 7, 9, and 11, respectively. The proposed chronostratigraphy suggests an average uplift rate of ca. 460 mm/kyr for the Chala Bay area during the last 500 ka. This rate is slightly higher than in the surrounding coastal areas (ca. 270–350 mm/kyr), but significantly lower than rates in the area where the Nazca Ridge is being subducted below the South American Plate (maximum rate ca. 740 mm/kyr). Deformed shorelines evidence several fault displacements within the Chala basin, but such deformation does not seriously disort the record of former sea-levels in the basin. The Chala terrace sequence is the first reliable record of Middle and Late Quaternary sea-level fluctuations described from Peru.

Multi-isotopic age assessment of dirty speleothem calcite: an example from Altamira Cave, Spain

The dating of dirty speleothem calcite of Late Pleistocene or Holocene age can be problematic. This is notably the case with the 14 C method, due to uncertainties in the initial 14 C activity of the cave CO2, and withth e 230 Th– 234 U method, due to either low U contents in the authigenic calcite, and/or to the presence of heterogeneous detrital particles containing high concentrations of U and Thseries isotopes frequently out of secular equilibrium. In this study of a B60 cm-thick flowstone sealing archaeological remains of the Magdalenian period in the Altamira Cave (NW Spain), we used a combination of isotopic approaches and analytical techniques to confront dating methods and finally tried to validate chronological interpretations based on stable isotope paleoclimate constraints. U-series data indicate the presence of a relatively important and heterogeneous detrital fraction resulting in 232 Th/ 230 Th mass ratios generally too high (0.1–0.25 � 10 6 ) to allow precise TIMS measurements. MC-ICP-MS measurements provided more reliable results and allowed the calculation of 230 Th– 234 U isochron ages of 11.870.8 ka in the upper part of the flowstone, and of B22 ka, in the lower part of it. In view of the calibrated 14 C ages of these layers (B13 and B15 ka BP, respectively), the isochron age of the lower unit of the flowstone seems erroneous, suggesting the presence of an isotopically heterogeneous contaminating fraction in this layer. 226 Ra/ 230 Thratio measurements indicate near secular equilibrium conditions. Seriate stable isotope measurements indicate calcite precipitation in isotopic equilibrium with ambient waters. They suggest that flowstone deposition ended at the very onset of the Younger Dryas. This transition seems to have occurred here at 11.870.8 (72s) ka (based on Th/U isochron), and 10.770.08 (71s) uncalibrated 14 C kiloyears. The 14 C activity for the cave CO2 seems to have been near that of atmospheric CO2 during the precipitation interval. It is concluded that the 14 C data provide here relatively reliable ages, in spite of the fact that they partly fall into a period characterized by 14 C-plateau effects, but that other isotopic data revealed essential in validating them.

Towards a Plio-Pleistocene chronostratigraphy in Eastern Betic Basins (SE Spain)

AbstractThe evolution of Neogene and Quaternary littoral basins in the Eastern Betic Cordillera is largely related to tectonic activity along the Eastern Betic sinistral shear zone.Detailed mapping of sedimentary units in these basins, together with sedimentological and paleomagnetic analysis lead to the proposal of a new chronostratigraphie framework for Pliocene and Quaternary deposits.This chronostratigraphie setting rejects the synchronous character of the “Pliocene Unite” previously referred to as: “P.I” (grey-blue marls), “P.H” (yellow calcarenites), and “Р.Ш” (variegated silts and clays). Instead, tectonics would have controlled the paleogeographic evolution of the Eastern Betic realms, causing the lithofacies to occur repeated in space and time. The Plio-Pleistocene boundary in these basins is not accompanied by changes in geodynamic behaviour or climatic conditions. According to the paleomagnetic data, these changes occurred at different times during the Pleistocene in the different studied basins.

Geomorphology applied to landscape analysis for planning and management of natural spaces. Case study: Las Batuecas-S. de Francia and Quilamas natural parks, (Salamanca, Spain)

Geomorphology is fundamental to landscape analysis, as it represents the main parameter that determines the land spatial configuration and facilitates reliefs classification. The goal of this article is the elaboration of thematic maps that enable the determination of different landscape units and elaboration of quality and vulnerability synthetic maps for landscape fragility assessment prior to planning human activities. For two natural spaces, the final synthetic maps were created with direct (visual-perceptual features) and indirect (cartographic models and 3D simulations) methods from thematic maps with GIS technique. This enabled the creation of intrinsic and extrinsic landscape quality maps showing sectors needing most preservation, as well as intrinsic and extrinsic landscape fragility maps (environment response capacity or vulnerability towards human actions). The resulting map shows absorption capacity for areas of maximum and/or minimum human intervention. Sectors of high absorption capacity (minimum need for preservation) are found where the incidence of human intervention is minimum: escarpment bottoms, fitted rivers, sinuous high lands with thick vegetation coverage and valley interiors, or those areas with high landscape quality, low fragility and high absorption capacity, whose average values are found across lower hillsides of some valleys, and sectors with low absorption capacity (areas needing most preservation) found mainly in the inner parts of natural spaces: peaks and upper hillsides, synclines flanks and scattered areas. For the integral analysis of landscape, a mapping methodology has been set. It comprises a valid criterion for rational and sustainable planning, management and protection of natural spaces.