Stratigraphy and origin of New Forest brickearths,England

The thin, loamy brickearth deposits overlying the flinty terrace gravels of the New Forest are divided into older and younger members. The Lower (older) Brickearth includes sediments thought to be mainly loess, with some aeolian sand and possible river floodloam (overbank sediment). These share the common feature of palaeo-argillic soil horizons in their upper layers. Two separate phases of pre-Holocene temperate pedogenesis often can be distinguished in the palaeo-argillic horizons. The Lower Brickearth is the most extensive pre-Devensian loess in Britain. The Upper (younger) Brickearth consists mainly of Late Devensian (Oxygen Isotope Stage 2) loess, but its lower layers also contain fine sand derived mainly from local Tertiary strata. Both brickearths occur on all the terrace surfaces of the New Forest and indicate that the terraces date from Oxygen Isotope Stage 6 or earlier.     

Estuarine, barrier-island to strand-plain sequence and related ravinement surface developed during the last interglacial in the Paleo-Tokyo Bay, Japan

Recognition of sequence boundaries and transgressive surfaces (i.e. ravinement surfaces, RS) is now known to be of great importance in stratigraphy. The sedimentary features of deposits immediately above a transgressive surface are well exposed in the Upper Pleistocene Kioroshi Formation of the Kanto Plain in central Japan. The formation comprises mainly coastal and shallow-marine deposits (estuarine, barrier-island and the strand-plain systems) which accumulated along a wavedominated coast in the Late Pleistocene, i.e., the last interglacial to last glacial period. The Kioroshi Formation is bounded above and below by sequence boundaries that formed in the lowstand periods correlative to the glacial periods of oxygen isotope stages 4 and 6, respectively. A significant transgressive surface that was formed by landward migration of barrier islands during the transgressive interval, the ravinement surface (RS), is found within the deposits of the upper shelf environment.

This ravinement surface is characterized by the exotic nature of the overlying sediment veneer (pebbles, shells and scattered mud clasts) which is poorly sorted. The RS shows a very flattened erosional surface in the shore-parallel sense, and the gradient of the surface in shore-normal sense is calculated as 0.0021, where the syndepositional tectonic movement is revised. The RS commonly cuts through the lower sequence boundary. However, in the places where the river or tidal channel valleys incised, the valley-filling sediment shows a deepening-upward sequence recognized as a transgressive systems tract and the RS can be clearly distinguished from the lower sequence boundary.     

Intra- and extra-caldera volcaniclastic facies and geomorphic characteristics of a frequently active mafic island–arc volcano, Ambrym Island, Vanuatu

Ambrym is one of the most voluminous active volcanoes in the Melanesian arc. It consists of a 35 by 50 km island elongated east–west, parallel with an active fissure zone. The central part of Ambrym, about 800 m above sea level, contains a 12 kilometre-wide caldera, with two active intra-caldera cone-complexes, Marum and Benbow. These frequently erupting complexes provide large volumes of tephra (lapilli and ash) to fill the surrounding caldera and create an exceptionally large devegetated plateau “ash plain”, as well as sediment-choked fluvial systems leading outward from the summit caldera. Deposits from fall, subordinate base surge and small-volume pyroclastic (scoria) flows dominate the volcaniclastic sequences in near vent regions. Frequent and high-intensity rainfall results in rapid erosion of freshly deposited tephra, forming small-scale debris flow- and modified grain flow-dominated deposits. Box-shaped channel systems are initially deep and narrow on the upper flanks of the composite cones and are filled bank-to-bank with lapilli-dominated debris flow deposits. These units spill out into larger channel systems forming debris aprons of thousands of overlapping and anastomosing long, narrow lobes of poorly sorted lapilli-dominated deposits. These deposits are typically remobilised by hyperconcentrated flows, debris-rich stream flows and rare debris flows that pass down increasingly shallower and broader box-shaped valleys. Lenses and lags of fines and primary fall deposits occur interbedded between the dominantly tabular hyperconcentrated flow deposits of these reaches. Aeolian sedimentation forms elongated sand dunes flanking the western rim of the ash-plain. Outside the caldera, initially steep-sided immature box-canyons are formed again, conveying dominantly hyperconcentrated flow deposits. These gradually pass into broad channels on lesser gradients in coastal areas and terminate at the coast in the form of prograding fans of ash-dominated deposits. The extra-caldera deposits are typically better sorted and contain other bedding features characteristic of more dilute fluvial flows and transitional hyperconcentrated flows. These outer flank volcaniclastics fill valleys to modify restricted portions of the dominantly constructional landscape (lava flows, and satellite cones) of Ambrym. Apparent maturity of the volcanic system has resulted in the subsidence of the present summit caldera at a similar rate to its infill by volcaniclastic deposits.     

A preliminary report on the Stanton Harcourt Channel Deposits (Oxfordshire,England): geological context,vertebrate remains and palaeolithic stone artefacts

A summary is given of the geological, faunal and archaeological information obtained during excavations in the Stanton Harcourt Channel Deposits from 1990 to 1995. The channel deposits underlie the ‘cold-climate’ Stanton Harcourt Gravel Member of the Summertown– Radley Terrace Formation. The Channel sediments are attributed to Oxygen Isotope Stage 7, when the Thames was undergoing down-dip migration and eroding the Weymouth Member of the Oxford Clay (Upper Jurassic), the contemporary Jurassic (Corallian) escarpment being near to Stanton Harcourt at that time. Abundant large vertebrate remains have been recovered, mainly from the base of the Channel deposits, where a cobble and boulder bed rests on thin silt or sand horizons or in scour hollows in the clay bedrock. Smaller bones occur throughout the deposits, which are mainly poorly sorted gravels, but especially at erosive horizons. Several palaeolithic artefacts have been found in the same contexts; many of the bones and some of the artefacts appear not to have been transported far. Although the artefacts cannot be linked directly with the bones, a study of them adds to our knowledge of the Middle Pleistocene human settlement of the Upper Thames Valley. It is of interest that mammoth is abundant as part of the interglacial faunal assemblage, and the significance of this is discussed. The environment clearly included substantial areas of open grassland, although there was also some forest in the vicinity. Evidence appears to be accumulating for important faunal and floral differences between particular interglacial events during the British Middle and Late Pleistocene.     

Three‐dimensional architecture and hydrostratigraphy of cross‐cutting buried valleys using airborne electromagnetics,glaciated Central Lowlands,Nebraska, USA

Buried valleys are characteristic features of glaciated landscapes, and their deposits host important aquifers worldwide. Understanding the stratigraphic architecture of these deposits is essential for protecting groundwater and interpreting sedimentary processes in subglacial and ice‐marginal environments. The relationships between depositional architecture, topography and hydrostratigraphy in dissected, pre‐Illinoian till sheets is poorly understood. Boreholes alone are inadequate to characterize the complex geology of buried valleys, but airborne electromagnetic surveys have proven useful for this purpose. A key question is whether the sedimentary architecture of buried valleys can be interpreted from airborne electromagnetic profiles. This study employs airborne electromagnetic resistivity profiles to interpret the three‐dimensional sedimentary architecture of cross‐cutting buried valleys in a ca 400 km² area along the western margin of Laurentide glaciation in North America. A progenitor bedrock valley is succeeded by at least five generations of tunnel valleys that become progressively younger northward. Tunnel‐valley infills are highly variable, reflecting under‐filled and over‐filled conditions. Under‐filled tunnel valleys are expressed on the modern landscape and contain fine sediments that act as hydraulic barriers. Over‐filled tunnel valleys are not recognized in the modern landscape, but where they are present they form hydraulic windows between deep aquifer units and the land surface. The interpretation of tunnel‐valley genesis herein provides evidence of the relationships between depositional processes and glacial landforms in a dissected, pre‐Illinoian till sheet, and contributes to the understanding of the complex physical hydrology of glacial aquifers in general.     

Aeolian granule ripple deposits, Namibia

Granule ripples are a common feature of most dunefields, yet they have seldom been recognized in ancient deposits. Although granule ripples are common in erosional settings, such as windward slopes of dunes, or scour surfaces in interdunes, they nevertheless migrate laterally and leave distinctive deposits that can be recognized in ancient rocks. These deposits have characteristics of ‘type B’sand sheet deposits, including: ‘poured-in’texture; curving ripple trough; tangential, coarse-grained foresets; irregular silty layers; well-sorted coarse and fine layers (either horizontal or within foresets); and fine layers in ripple troughs. Wind tunnel experiments suggest that under low-velocity wind conditions, granule ripples grow to a significant degree as parasites dependent on saltation of fine sand grains whose impact moves the larger grains of the granule ripple. Although the depositional surface of granule ripples is commonly coated with a layer of coarse grains, this is in most places only a few grains thick. Underlying deposits commonly have a poorly sorted, or ‘poured-in’texture. This texture results from an admixture of fine grains that fall among the spaces between the larger grains during deposition.     

The subaerial origin of mantle depositsZur subaerischen entstehung der decksedimenteL'origine subaérienne des formations de couverture

The authors deal with the problems of the origin of mantle formations consisting of loams and sandy loams that occur on the surface of Central and Eastern Europe. The loams are usually considered periglacial deposits; however, the authors have developed a new theory on the origin of these formations. In their opinion loams developed as a result of deposition of atmospheric dust. The new theory is supported by measurements of dust fall mainly on glaciers in the Caucasus and in Central Asia. The measurements correspond favorably with the absolute age of humus in the soils of the Russkaya ravnina (Lowland). Recently, dust fall has increased owing to activities by man. The increase disturbs the equilibrium in the subaerial lithogenesis — soil development system and therefore more attention should be given to this phenomenon.     

Glaciomarine facies within subglacial tunnel valleys: the sedimentary record of glacioisostatic downwarping in the Irish Sea Basin

Coastal exposures of Late Pleistocene sediments deposited after 19 000 yr BP near Dublin, Ireland, provide a window into the infill of a subglacially-cut tunnel valley. Exposures close to the steeply dipping bedrock wall of the valley show boulder gravels within multi-storey U-shaped channels cut and filled by subglacial meltwaters driven by a high hydrostatic head. Gravels are truncated by poorly sorted ice-proximal glaciomarine sediments that record the pumping of large volumes of subglacial debris along the tunnel valley to a tidewater ice sheet margin. The sedimentary succession is dominated by sediment gravity flow facies comprising interbedded diamict and massive, poorly sorted gravel facies interpreted as subaqueous debris flow deposits. Gravel beds show local inverse and normal coarse-tail graded facies recording the restricted development of turbulent flow. Sediment gravity flow deposits fill broad (<2 km) shallow (10 m) and overlapping channels. Penetrative deformation structures (e.g. dykes) are common at the base of channels. The same subglacially-eroded topography and glaciomarine infill stratigraphy can be identified on high resolution seismic profiles across nearly 600 km² of the western Irish Sea. Tunnel valleys are argued to have been exposed to glaciomarine processes by the rapid retreat of a calving tidewater ice sheet margin in response to marine flooding caused by glacio-isostatic downwarping below the last British Ice Sheet. The facies associations described in this paper comprise an event stratigraphy that may be found on other glaciated continental shelves.     

辽宁、吉林、黑龙江地区流水成因的砂金矿

该区具有重要工业意义的砂金矿床,几乎皆是流水成因的。研究其矿质来源、含金地质体的风化剥蚀作用、砂金矿在河谷中的搬运方式和距离、砂金矿的成矿作用及矿床特征,不但可以扩大砂金矿的找矿前景,还能为在砂金矿分布区寻找岩金矿提供依据。     

内蒙古虎拉林地区砂金与岩金的关系

虎拉林地区砂、岩金矿的空间位置关系十分密切。在虎拉林河上中下游及虎拉林岩金矿分别采取样品，结果表明虎拉林河砂金粒度大，分选较差，磨圆度差；砂金形态总体上以粒状为主；溶蚀系数均值小于1。微量元素含量特征表明砂金的主要物质来源是近源，与岩金矿关系密切且具有继承性。虎拉林岩金矿床的矿石中自然金颗粒粗大，矿体的上部遭到剥蚀，虎拉林河砂金主要来源于虎拉林岩金矿床，砂金可作为岩金的找矿标志。自然金化学-结晶温度图表明砂金的原生Au源为中低温热液矿床。     

Large,prehistoric clay slides revealed in road excavations in Buvika,mid-Norway

Several excavated sections along new roads in Buvika, mid-Norway, display records of large, prehistoric clay slides. Slightly undulating but otherwise intact laminated clay, with minor amounts of unsorted or sorted coarser-grained debris, appears in the sections. Folding, shearing and internal slide surfaces have also been recorded, and the deposits are interpreted as slide debris. Slide-scar morphologies are diffuse or absent for most of these deposits, and the inferred slide mechanism is translation and rotation of blocks on a thin layer of remoulded quick clay. One section cuts through a slide block inside a classic, morphologically well-defined quick-clay slide scar. Varying results from ¹⁴C-datings of organic material in the deposits give only maximum ages of the slide events. The style of sliding reflected in several sections differs from slide events in the area known from historical records. These younger slide events seem to be characterised by collapse and remoulding of thicker quick-clay layers. The present study of slide deposits gives information on processes and deformation history of the slides. It is suggested that the gradual formation of quick clay has an important impact on long-term landscape degradation and on the character of the present day landscape. There may be far more signs of slide activity in Norwegian valleys than solely indicated by slide scars and also in the relatively high-lying parts of the valley fill, such as interfluve areas.     

Paleoenvironment and stratigraphy during the last glacial in the Belgian-Dutch border region

The Weichselian deposits of the flat Dutch-Belgian coversand area are characterized by highly varying facies types. The geomorphological location and the role of water during the deposition and the transportation of the original eolian sediments may fully explain the texture and sedimentary structures of the lithostratigraphic units. Directly deposited eolian loams and sands on the dry interfluves contrast with the same, but reworked, sediments in wet valleys and depressions. The formation of periglacial phenomena is also dependent on the geomorphologic, lithologic, and hydrologic conditions. The occurrence of peaty beds is restricted to wet environments without precise climatic significance. The Pleniglacial sequence is subdivided into early and late Pleniglacial stades, both characterized by (partial) permafrost conditions, interrupted by a middle Pleniglacial interstadial complex with clearly milder conditions.     

Distinguishing base-surge deposits and volcaniclastic fluviatile sediments: an ancient example from the Lower Devonian Snowy River Volcanics, south-eastern Australia

A 500‐m‐long road cutting in the Lower Devonian Snowy River Volcanics (SRV), eastern Victoria, Australia, exposes phreatomagmatic units and volcaniclastic sediments. Based on bed geometry, sorting and sedimentary structures, it was possible to distinguish base‐surge deposits from ephemeral fluvial deposits in this relatively well‐exposed ancient succession. Where the base‐surge deposits infill irregular topography, bed sets mantle the pre‐existing surface but thicken into topographic lows. In contrast, where the fluvial deposits infill topographic depressions, beds onlap laterally against channel walls. In addition, curvi‐planar slide surfaces within the base‐surge deposits generated by inter‐eruptive slumping indicate rapid emplacement as a constructional tuff rampart (? maar). The base‐surge deposits are always poorly sorted and commonly contain accretionary lapilli, reflecting their deposition from turbulent, low‐particle‐concentration, steam‐rich pyroclastic currents. In contrast, the fluvial deposits are relatively well‐sorted, reflecting hydraulic sorting and winnowing during tractional transport and deposition. There are significant differences in the types of sedimentary structures present. (1) Bedding in the base‐surge deposits is entirely tabular, and beds can be traced laterally to the limits of the outcrop. In contrast, the fluvial deposits have abundant internal scour surfaces that result in beds/bedding intervals lensing out laterally over intervals of the order of 5–10 m. (2) Cross‐beds with relatively high‐angle foresets are restricted to the fluvial deposits. (3) Laterally persistent tabular beds that contain abundant, densely packed accretionary lapilli are restricted to the base‐surge deposits. In summary, although base‐surge deposits and ephemeral fluvial deposits can appear superficially similar, it is possible to apply facies models carefully to distinguish between them, even in ancient successions.     

Controls on sedimentation in distal margin palaeovalleys in the Early Tertiary Alpine foreland basin, south-eastern France

The influence of palaeodrainage characteristics, palaeogeography and tectonic setting are rarely considered as controls on stratigraphic organization in palaeovalley or incised valley systems. This study is an examination of the influence of source region vs. downstream base level controls on the sedimentary architecture of a set of bedrock-confined palaeovalleys developed along the distal margin of the Alpine foreland basin in south-eastern France. Three distinct facies associations are observed within the palaeovalley fills. Fluvial facies association A is mainly dominated by poorly sorted, highly disorganized, clast-to-matrix-supported cobble-to-boulder conglomerates that are interpreted as streamflood deposits. Facies association B comprises mainly yellow siltstones and is interpreted as recording deposition in an estuarine basin environment. Estuarine marine facies association C comprises interstratified estuarine siltstones and clean, well-sorted washover sandstones. The sedimentary characteristics of the valley fill successions are related to the proximity of depositional sites to sediment source areas. Palaeovalleys located proximal to structurally controlled basement palaeohighs are entirely dominated by coarse fluvial streamflood deposits. In contrast, distal palaeovalley segments, which are located several kilometres downstream, contain successions showing upward transition from coarse fluvial facies into estuarine central basin fines, and finally into estuarine-marginal marine facies. Facies distributions suggest that the fluvial deposits form wedge-shaped, downstream-thinning sediment bodies, whereas the estuarine deposits form an upstream-thinning wedge. The vertical stacking of fluvial to estuarine to marginal marine depositional environments records the fluvial aggradation and subsequent transgression of relatively small bedrock-confined river valleys, which drained a rugged, upland terrain. Facies geometries suggest that a fluvial sediment wedge initially prograded downvalley, in response to high bed load sediment yields. Subsequently, palaeovalleys became drowned during the passage of a marine transgression, with the establishment of estuarine conditions. Initial fluvial aggradation and subsequent marine flooding of the palaeovalleys is a consequence of the interaction of high local rates of sediment supply and relative sea-level rise driven by flexural subsidence of the basin.     

Examining the geometry,age and genesis of buried Quaternary valley systems in the Midland Valley of Scotland,UK

Buried palaeo‐valley systems have been identified widely beneath lowland parts of the UK including eastern England, central England, south Wales and the North Sea. In the Midland Valley of Scotland palaeo‐valleys have been identified yet the age and genesis of these enigmatic features remain poorly understood. This study utilizes a digital data set of over 100 000 boreholes that penetrate the full thickness of deposits in the Midland Valley of Scotland. It identified 18 buried palaeo‐valleys, which range from 4 to 36 km in length and 24 to 162 m in depth. Geometric analysis has revealed four distinct valley morphologies, which were formed by different subglacial and subaerial processes. Some palaeo‐valleys cross‐cut each other with the deepest features aligning east–west. These east–west features align with the reconstructed ice‐flow direction under maximum conditions of the Main Late Devensian glaciation. The shallower features appear more aligned to ice‐flow direction during ice‐sheet retreat, and were therefore probably incised under more restricted ice‐sheet configurations. The bedrock lithology influences and enhances the position and depth of palaeo‐valleys in this lowland glacial terrain. Faults have juxtaposed Palaeozoic sedimentary and igneous rocks and the deepest palaeo‐valleys occur immediately down‐ice of knick‐points in the more resistant igneous bedrock. The features are regularly reused and the fills are dominated by glacial fluvial and glacial marine deposits. This suggests that the majority of infilling of the features happened during deglaciation and may be unrelated to the processes that cut them.     

Karst bauxite deposits in the Zagros Mountain Belt,Iran

More than 190 occurrences of bauxitic–lateritic deposits were investigated in seven areas within the Zagros Simply Folded Mountain Belt in southwestern of Iran. The bauxitic horizons are situated in eroded major NW–SE trending anticlines and occur in karst cavities near or at the boundary between the Sarvak and Ilam Formations. Uplift in the Cenomanian–Turanian period had exposed the Sarvak limestone to karst weathering and, during a period of unconformity, layers of ferruginous–argillaceous limestone debris developed and accumulated on its surface. The ferruginous–argillaceous debris was partly converted to bauxite. Folding and faulting in Oligocene–Miocene time, with ensuing erosion, exposed the bauxitic horizons on the limbs and cores of anticlines. The karst bauxite deposits are probably of authigenic origin, as evidenced by their lithologic associations, textural and mineralogy.     

中国西部天山高山带冷生土壤及相关土壤的地貌发生学

The soil landscape relationship was investigated in the Upper Urumqi River Basin of the Tienshan Mountain Range, Xinjiang, China. Cryosols occurred in glaciated valleys and north-facing toeslopes at elevations above 3 000 m. Most cryosols developed in moraine are Aquiturbels. The microrelief is dominated by earth hummocks, thus the surface organic layers are either discontinuous or broken due to frost action. The Bg horizons are either gleyed or mottled and frost-churned organic matter is common in the lower Bg horizons. Stratified horizons and buried organic or A horizons are also common on gentle sloping or undulating moraines indicating the effects of gelifluction. Reticular structures formed in the lower active layers due to ice lens formation and freeze-thaw cycles. The active layer thickness ranges from 140～200 cm. The organic cryosols (Hemistels) occur in depressions and north-facing toeslopes with an active layer thickness ranging from 90～110 cm. Soils formed on south-facing slopes have a mollic epipedon 20～25 cm thick and a strong brown cambic horizon and are classified as Haplocryolls. The distribution of cryosols is smaller as compared with the extent of permafrost due to the depth requirement of permafrost in cryosol classification. However, the existence of permafrost at greater depth cannot be ignored in land use interpretations.     

Paleozoic glaciation in NE Africa: field and remote sensing-based evidence from the South Eastern Desert of Egypt

ABSTRACT

Exhumed Paleozoic glacial deposits and landforms of the North Gondwana are reported here for the first time from the South Eastern Desert (SED) of Egypt. Using field observations and remote sensing datasets (Advanced Land Observing Satellite [ALOS], Phased Array L-band Synthetic Aperture Radar [PALSAR] radar, multispectral Landsat TM datasets, and digital elevation models [DEMs]), we mapped the distribution of Paleozoic glacial features (i.e. deposits and landforms) in the SED. Two main glaciogenic facies were identified in three locations in the SED: (1) massive, poorly sorted, matrix supported, boulder-rich diamictites in Wadi El-Naam and Korbiai, and (2) moderately-sorted, occasionally bedded outwash deposits in Betan area. Inspection of radar, DEMs, and Landsat Operational Land Imager (OLI) images revealed previously unrecognized ENE-WSW trending glacial megalineations (MLs) over the peneplained Neoproterozoic basement rocks in the central sections of the SED, whose trends align along their projected extension with those of glacial features (tunnel valleys and striation trends) reported from Saudi Arabia. The glaciogenic features in the SED are believed to be largely eroded during the uplift associated with the Red Sea opening, except for those preserved as basal units beneath the Nubia Sandstone Formation or as remnant isolated deposits within paleo-depressions within the basement complex. The apparent spatial correlation of the SED glacial features with well-defined Late Ordovician deposits in North Africa and in Saudi Arabia, and the reported thermochronometric analyses and fossil records are consistent with a Late Ordovician age for the SED glaciogenic features and support models that call on the continuation of the Late Ordovician (Hirnantian) ice sheet from the Sahara into Arabia through the SED of Egypt.     

Hypotheses of the brown loam formation in the Primorye region (Russian Far East): Hindsight and the new view

This paper addresses the hypotheses of the formation of the brown loams widely spread in the zone with hummocky relief within the intermontane Razdol’noe-Khanka Depression. These hypotheses were proposed in the 1970s–1980s. The accumulation of information on the loess formation in southern East Siberia, as well as obtaining new analytical data on the microtextural, mineralogy, and major and trace-element composition of the brown loams, and the comparative analysis of these deposits provided for the formulation of a more substantiated view concerning the place of the brown loams in the group of loess-type rocks.     

Mesozoic carbonate rudites, megabreccias and associated deposits from central Greece

In the Kokkinovrakhos Formation of central Greece, poorly sorted, grain supported, lithoclastic carbonate rudites, megabreccias and olistoliths are associated with accumulations of fine-grained laminated carbonates. The laminae frequently exhibit grading and are interpreted as turbidity current deposits. The coarser grained rudites and megabreccias were also redeposited but were probably transported downslope by sliding and rolling, i.e. they are rock-fall deposits. Olistoliths were emplaced into deeper water by sliding. The fine-grained sediments of the laminated facies appear to have accumulated in pockets on an uneven sea floor during episodes of minimal rock fall activity. The sedimentary association is similar to that described from some modern fore-reef environments and is possibly characteristic of accumulations of sediment on, or near to, steep slopes adjacent to carbonate platforms, when episodes of tectonic activity lead to the shearing off and transport downslope of masses of well-cemented shallow marine carbonates.