Gerhard Schellmann

A revised morpho- and chronostratigraphy of the Late and Middle Pleistocene coral reef terraces on Southern Barbados (West Indies)

The Barbados coral reef terraces are one of the few type localities worldwide that provide insights into interglacial sea level change during the Late and Middle Pleistocene. Several sea level estimates have been established since the late 1960s and each has contributed to the “Barbados Model” of sea level change. This paper presents new morpho- and chonostratigraphic data from the Barbados coral reef terraces developed over the last 12 years. The work is based on significant advances in Electron Spin Resonance (ESR)-dating of fossil coral, air photo interpretation, and a greatly improved geomorphic map of preserved fossil beach formations and reef terraces above present sea level. The need for a revision of past published morpho- and chronostratigraphies is best demonstrated on the southern part of the island. The morpho- and chronostratigraphic sequence in this region is both more complex and diverse than has been assumed so far. The revised morphostratigraphy presented here includes a differentiation of coral reef terraces, wave-cut platforms and other erosive features, such as notches and cliffs. Our study of these geomorphic features, combined with new numeric dating results (ESR, U/Th), enable a revised estimate of the spatial and temporal variation in tectonic uplift rate within south Barbados. These new rates are an essential requirement for more precise glacio-eustatic sea level reconstructions during the Late and Middle Pleistocene from this region.

ESR dating stratigraphically well-constrained marine terraces along the Patagonian Atlantic coast (Argentina)

Abstract ESR dating of marine mollusc shells is an important tool in coastal geomorphology as well as in palaeosea-level and other research. Some severe problems, however, remain as far as the accuracy of the dating results are concerned. Case studies of Patagonian Middle and Younger Quaternary marine terraces help to illustrate the potential of an improved ESR dating technique. It can be demonstrated that a discrimination of Holocene, Last Interglacial, Penultimate Interglacial and “older” samples is possible. A chronostratigraphic separation of the well-known Last Interglacial substages 5a, 5c, and 5e is still missing, partly due to the misleading accuracy of ESR dating results. Consequently, it cannot be decided yet whether the morphologically well-conserved Last and Penultimate Interglacial age substages result from a relative sea-level fall (glacioeustatic and/or decreasing wind intensities) during the one and the same interglacial highstand shortly after the 5e or 7 transgression maximum or whether they were deposited during the much younger sea-level sub-highstands, e.g. 5c, 5a or 7c, or 7a.

Electron spin resonance (ESR) techniques applied to mollusc shells from South America (Chile, Argentina) and implications for palaeo sea-level curve

ESR dating of marine mollusc shells gives no evidence for a so-called Mid-Wisconsin sea-level high stand in Argentina and Chile. The idea of this high stand around 30,000–40,000 BP is still alive, especially in Argentina, but the evidence for it is, in our opinion and that of others, solely based on the misinterpretation of 14C dates. All ESR ages from southern South America belong either to the Holocene or the Last Interglacial or older Interglacial periods. Apart from the regional aspect, this paper deals with some methodological problems in ESR dating. Estimates have been improved by using only mollusc shells that are still closed and in living position and by introducing a plateau screening test for the determination of the accumulated dose (AD). The estimate of the environmental dose has been refined by analysing the infill sediments in the shells for their U, Th and K contents, separately from the embedding matrix. Special interest has been paid to the debated problem of early or continuous U uptake; the U contents of recent Holocene molluscs support the early uptake model. A probable solution to the problem of age overestimation of Holocene shells is also presented. Present-day shells are shown to possess frequently a fully developed signal and to give AD of 2–4, in one case up to 9 Gy. If the Holocene AD values of 14C-dated shells are corrected by subtracting these “recent”, and spurious, values, the resulting age estimates are more consistent with radiocarbon ages.

ESR Dating of Coral Reef Terraces on Curacao (Netherlands Antilles) with Estimates of Younger Pleistocene Sea Level Elevations

Abstract A sequence of at least three Late and Middle Pleistocene coral reef terraces (Lower Terrace, Middle Terrace I and II), which are uplifted up to 45 m a.s.l., is conserved on Curaçao. The less uplifted Lower terrace (elevation 6 to 12 m above sea level) consists of two different coral reef formations: the Hato unit and the underlying Cortalein unit. The discontinuity between these two superimposed units is typically marked by a strong difference in the degree of weathering. Samples of coral in growth position were collected from the Lower Terrace (Hato and Cortalein unit) and the Middle Terrace I. ESR ages indicate a Last Interglacial age of the Hato unit of about 122 ky BP, and a correlation with the Last Interglacial sea level maximum (stage 5e). The ESR age of the underlying Cortalein unit is about 216 ky BP (stage 7). Palaeo sea level calculations imply a correlation with the youngest of three Penultimate coral reef terraces located on the island of Barbados, which was uplifted more strongly than the island of Curaçao. No equivalents of older Penultimate Interglacial coral reefs and of the Interglacial stage 9 were found. Middle Terrace I could be at least as old as stage 11 (approx. 400 ky BP), however, it could also be more than 500 ky old.

Progress in ESR dating of Pleistocene corals — a new approach for DE determination☆

Abstract ESR dating has been widely applied for dating of corals of the age up to 500,000 to 600,000 years ago. Many studies have yielded promising results but the accurate determination of the equivalent dose ( D E ) remains a major limitation. Inflexion points in the dose–response curve are shown to hinder correct fitting and limit the reliability of D E values. Here, we present a new approach to obtain more reliable D E values.

Uplift History along the Clermont Nose Traverse on the West Coast of Barbados during the Last 500,000 Years— Implications for Paleo-Sea Level Reconstructions

Abstract Barbados is one of the few localities in the world with uplifted fossil coral reef tracts that provide detailed insights into interglacial sea level change during the Late and Middle Pleistocene. Since the late 1960s, several sea level reconstructions have been established, each contributing to the “Barbados Model” of sea level change. Considering the global importance of paleo–sea level research in Barbados, it is important to note that substantial issues are still unresolved regarding the results obtained thus far. In this paper, we deal with one of the major problems of paleo–sea level reconstruction on Barbados—the assumption of constant uplift—which we test along the Clermont Nose traverse on the southern part of the west coast of Barbados. We demonstrate that uplift along this transect was not, in fact, constant over the last 500,000 years. The data from Clermont Nose strongly support the argument that anticlinal warped areas might have complex tectonic histories and are therefore not necessarily suitable for Pleistocene sea level reconstructions.

Soil development over millennial timescales - a comparison of soil chronosequences of different climates and lithologies

This paper reports soil development over time in different climates, on time-scales ranging from a few thousand to several hundred thousand years. Changes in soil properties over time, underlying soil-forming processes and their rates are presented. The paper is based on six soil chronosequences, i.e. sequences of soils of different age that are supposed to have developed under the similar conditions with regard to climate, vegetation and other living organisms, relief and parent material. The six soil chronosequences are from humid-temperate, Mediterranean and semi-arid climates. They are compared with regard to soil thickness increase, changes in soil pH, formation of pedogenic iron oxides (expressed as Fed/Fet ratios), clay formation, dust influx (both reflected in clay/silt ratios), and silicate weathering and leaching of base cations(expressed as (Ca+Mg+K+Na)/Al molar ratios) over time. This comparison reveals that the increase of solum thickness with time can be best described by logarithmic equations in all three types of climates. Fed/Fet ratios (proportion of pedogeniciron Fed compared to total iron Fet) reflects the transformation of iron in primary minerals into pedogeniciron. This ratio usually increases with time, except for regions, where the influx of dust (having low Fed/Fet ratios) prevails over the process of pedogeniciron oxide formation, which is the case in the Patagonian chronosequences. Dust influx has also a substantial influence on the time courses of clay/silt ratios and on element indices of silicate weathering. Using the example of a 730 kasoil chronosequence from southern Italy, the fact that soils of long chronosequences inevitably experienced major environmental changes is demonstrated, and, consequentially a modified definition of requirements for soil chronosequences is suggested. Moreover, pedogenic thresholds, feedback systems and progressive versus regressive processes identified in the soil chronosequences are discussed.

Application of Remote Sensing Technologies to Map the Structural Geology of Central Region of Kenya

Advancements of digital image processes (DIP) and availability of multispectral and hyperspectral remote sensing data have greatly benefited mineral investigation, structure geology mapping, fault pattern, and landslide studies: site-specific landslide assessment and landslide quantification. The main objective of this research was to map the geology of the central region of Kenya using remote-sensing techniques to aid rainfall-induced landslide quantification. The study area is prone to landslides geological hazards and, therefore, it was necessary to investigate geological characteristics in terms of structural pattern, faults, and river channels in a highly rugged mountainous terrain. The methodology included application of PCA, band rationing, intensity hue saturation (IHS) transformation, ICA, false color composites (FCC), filtering applications, and thresholding, and performing knowledge-based classification on Landsat ETM + imagery. PCA factor loading facilitated the choice of bands with the most geological information for band rationing and FCC combination. Band ratios (3/2, 5/1, 5/4, and 7/3) had enhanced contrast on geological features and were the input variables in a knowledge-based geological classification. This was compared to a knowledge-based classification using PCs 2, 5, and IC1, where the band ratio classification performed better at representing geology and matched FCC [IC1, PC5, saturation band of IHS (5,7,3)]. Fault and lineament extraction was achieved by filtering and thresholding of pan-band8 and ratio 5/1 and overlaid on the geology map. However, the best visualization of lineaments and geology was in the FCC [IC1, PC5, saturation band of IHS (5,7,3)], where volcanic extrusions, igneous, sedimentary rocks (eolian and organic), and fluvial deposits were well discriminated.

Potential and limits of combining studies of coarse- and fine-grained sediments for the coastal event history of a Caribbean carbonate environment

Abstract The coastal deposits of Bonaire, Leeward Antilles, are among the most studied archives for extreme-wave events (EWEs) in the Caribbean. Here we present more than 400 electron spin resonance (ESR) and radiocarbon data on coarse-clast deposits from Bonaire’s eastern and western coasts. The chronological data are compared to the occurrence and age of fine-grained extreme-wave deposits detected in lagoons and floodplains. Both approaches are aimed at the identification of EWEs, the differentiation between extraordinary storms and tsunamis, improving reconstructions of the coastal evolution, and establishing a geochronological framework for the events. Although the combination of different methods and archives contributes to a better understanding of the interplay of coastal and archive-related processes, insufficient separation, superimposition or burying of coarse-clast deposits and restricted dating accuracy limit the use of both fine-grained and coarse-clast geoarchives to unravel decadal- to centennial-scale events. At several locations, distinct landforms are attributed to different coastal flooding events interpreted to be of tsunamigenic origin. Coastal landforms on the western coast have significantly been influenced by (sub)-recent hurricanes, indicating that formation of the coarse-clast deposits on the eastern coast is likely to be related to past events of higher energy. Supplementary material: The entire dataset of ESR and 14C dating results used in this paper is available at http://www.geolsoc.org.uk/SUP18637.