Biostratigraphic and aminostratigraphic constraints on the age of the Middle Pleistocene glacial succession in north Norfolk,UK

Considerable debate surrounds the age of the Middle Pleistocene glacial succession in East Anglia following some recent stratigraphical reinterpretations. Resolution of the stratigraphy here is important since it not only concerns the glacial history of the region but also has a bearing on our understanding of the earliest human occupation of north‐western Europe. The orthodox consensus that all the tills were emplaced during the Anglian (Marine Isotope Stage (MIS) 12) has recently been challenged by a view assigning each major till to a different glacial stage, before, during and after MIS 12. Between Trimingham and Sidestrand on the north Norfolk coast, datable organic sediments occur immediately below and above the glacial succession. The oldest glacial deposit (Happisburgh Till) directly overlies the ‘Sidestrand Unio‐bed’, here defined as the Sidestrand Hall Member of the Cromer Forest‐bed Formation. Dating of these sediments therefore has a bearing on the maximum age of the glacial sequence. This paper reviews the palaeobotany and describes the faunal assemblages recovered from the Sidestrand Unio‐bed, which accumulated in a fluvial environment in a fully temperate climate with regional deciduous woodland. There are indications from the ostracods for weakly brackish conditions. Significant differences are apparent between the Sidestrand assemblages and those from West Runton, the type site of the Cromerian Stage. These differences do not result from contrasting facies or taphonomy but reflect warmer palaeotemperatures at Sidestrand and a much younger age. This conclusion is suggested by the higher proportion of thermophiles at Sidestrand and the occurrence of a water vole with unrooted molars (Arvicola) rather than its ancestor Mimomys savini with rooted molars. Amino acid racemisation data also indicate that Sidestrand is significantly younger than West Runton. These data further highlight the stratigraphical complexity of the ‘Cromerian Complex’ and support the conventional view that the Happisburgh Till was emplaced during the Anglian rather than the recently advanced view that it dates from MIS 16. Moreover, new evidence from the Trimingham lake bed (Sidestrand Cliff Formation) above the youngest glacial outwash sediments (Briton's Lane Formation) indicates that they also accumulated during a Middle Pleistocene interglacial – probably MIS 11. All of this evidence is consistent with a short chronology placing the glacial deposits within MIS 12, rather than invoking multiple episodes of glaciation envisaged in the ‘new glacial stratigraphy’ during MIS 16, 12, 10 and 6. Copyright © 2009 John Wiley & Sons, Ltd.     

Coastal processes and cliff recession between Gabicce and Pesaro (northern Adriatic Sea): a case history

Cliff recession on the high rocky coast between Gabicce and Pesaro Adriatic sea causes a wide range of mass movement processes on the whole slope, affecting both the bedrock and the overburden. The outcropping late Miocene rock formations are represented by marls, marly limestones, dark laminated mudstones and bedded sandstones and marls. Mass movements are common because of stratification and discontinuities in the rocks that, together with the presence of groundwater and weathering processes, reduce the overall strength of the slopes. A model for the evolution of this coastal area is proposed, which involves cyclic basal erosion, followed by mass movement that favours debris accumulation at the base of the cliff. The longshore currents have to then remove the material before a new cycle can begin.     

The potential of Pléiades images with high angle of incidence for reconstructing the coastal cliff face in Normandy (France)

To monitor chalk cliff face along the Normandy coast (NW France) which is prone to erosion, we tested the potential of cliff face 3D reconstruction using pairs of images with high angle of incidence at different dates from the agile Pléiades satellites. The verticality aspect of the cliff face brings difficulties in the 3D reconstruction process. Furthermore, the studied area is challenging mainly because the cliff face is north-oriented (shadow). Pléiades images were acquired over several days (multi-date stereoscopic method) with requested incidence angles until 40°. 3D reconstructions of the cliff face were compared using two software: ASP® and ERDAS IMAGINE®. Our results are twofold. Firstly, despite ASP® provides denser point clouds than ERDAS IMAGINE® (an average of 1.60 points/m² from 40° incidence angle stereoscopic pairs on the whole cliff face of Varengeville-sur-Mer against 0.77 points/m² respectively), ERDAS IMAGINE® provides more reliable point clouds than ASP® (precision assessment on the Varengeville-sur-Mer cliff face of 0.31 m ± 2.53 and 0.39 m ± 4.24 respectively), with a better spatial distribution over the cliff face and a better representation of the cliff face shape. Secondly, the quality of 3D reconstructions depends mostly on the amount of noise from raw images and on the shadow intensity on the cliff face (radiometric quality of images).     

Cliff retreat and talus development at the caldera wall of Mount St. Helens: Computer simulation using a mathematical model

To simulate the landform evolution at the caldera wall of Mount St. Helens, USA, a mathematical model for talus development was applied to model the topographic change during the 11years from the volcanic eruption, i.e., from formation of the cliff. Simulated results show that the topographic change is predicted to be large for about 10years after the eruption and to decline thereafter. If snow accumulation in the talus slope deposits is negligible, the talus top will not reach the cliff top within 300years after the eruption. Talus growth in Mount St. Helens was much faster than that in the Chichibu Basin, Japan. This may indicate the low strength and/or high weathering rate of the rockwall of Mount St. Helens, resulting in rapid production of debris and rapid retreat of the cliff.     

丹霞地貌发育几个重要问题的定量测算

论述了用河流阶地冲积层相当于古河流平水期水面的样品年龄及该采样点至今日河流平水期水面的相对高度求得地壳上升速度,再由地壳上升速度及丹霞地貌的相对高度求得地貌年龄,由地貌年龄及陡崖谷地上缘的宽度求得岩壁后退速度,由地貌年龄及被蚀去的地貌体积求得侵蚀速度,这是地貌学由定性描述向定量研究的一次尝试.     

A composite fall-slippage model for cliff recession in the sedimentary coastal cliffs

A composite fall-slippage model is proposed in this study for the Tertiary sedimentary coastal cliffs of Varkala in the western coastal tract of Peninsular India which are retreating landwards due to the combination of several factors. The fall model in the present study accounts both spring seepage and wave action, resulting in undercutting and this fall affects only the topmost laterite and the just below sandstone in the cliff. Slippage in this area affects all the litho-units and hence the geologic characteristics of all the litho-units are considered for developing the slippage model. This mathematically derived model can be used in other cliffs exhibiting the same morphology as well as the one controlled by the same influencing factors. This model differs from other models in incorporating multi-lithounits as well as multi-notches. Varkala cliffs form a part of the aspiring geopark in the Global Geopark Network and hence a study on the cliff recession is a pressing requirement.     

Stress–strain history from the geological evolution of the Orvieto and Radicofani cliff slopes (Italy)

The study proposes geological evolution models for the cliff slopes of the two Italian towns of Orvieto (Umbria) and Radicofani (Tuscany). The models were validated by the use of a stress–strain numerical modelling, implemented by the finite-difference code FLAC 5.0. The numerical modelling was approached in a sequential way, by assuming specific stiffness values related to the evolutionary stages. For this purpose, unconventional laboratory tests were performed aiming at reproducing the stress path related to the geological evolution model, using standard equipment for CID triaxial testing. The geological evolution models infer that deformation in both cases is driven by stress reduction. At the Orvieto plateau, stress reduction is induced by stress relief involving a tuff plate; in the case of Radicofani, stress reduction is due to stress release in consequence of lateral erosion of clay. Numerical simulations refine the lithotechnical zoning of the two investigated slopes, introducing a stress–strain criterion in addition to the conventional geological and geomechanical ones.     

Cliff retreat and sea bed morphology under monochromatic wave forcing: Experimental study

Wave flume experiments have been performed to investigate a sandy cliff recession under monochromatic wave forcing. We varied the wave climate through the wave energy flux F and the surf similarity parameter ξ. The various processes of the cliff erosion cycle are depicted. The sea bed evolution mostly depends on the surf similarity parameter ξ. Steep planar (ξ > 0.7), gentle planar (0.5 < ξ < 0.7) and bared (ξ < 0.5) profiles are observed. We observed different bar dynamics, including steady and unsteady self-sustained oscillating states. Then we analyze the role of the eroded material on the cliff recession rate. We show that the cliff recession rate increases with the wave energy flux. Moreover, for a given wave energy flux, it is larger for a gentle planar profile than for a bared profile. However it is similar for both a bared profile and a steep planar profile. The cliff recession rate is not a monotonic function of the cliff height as the type of bottom profile influences the wave energy at the cliff.