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Equatorial East Africa experienced significant variations in paleoclimatic and paleoceanographic conditions during the Holocene. These environmental changes influenced sedimentation patterns on the continental shelf. To date, however, little is known about the sediment source, its transport to, and deposition on, the Tanzanian shelf. This paper presents a new high-resolution Holocene sedimentary record off northeast Tanzania (equatorial East Africa) and provides insights into how sedimentation patterns responded to climatic and oceanographic changes during the Holocene. Based on grain-size distribution patterns and mineral assemblages, three types of shelf sediments were identified: Type I (fine-grained terrigenous sediment) is dominated by clay minerals that originated from continental weathering; Type II (coarse-grained terrigenous sediment) is mainly composed of feldspar and quartz, derived from reworking of pre-existing deposits; and Type III (biogenic marine sediment), with low- and high-magnesium calcite, was produced by marine carbonate-secreting organisms. The high input of Type I sediment during the early Holocene (10–8 cal kyr BP) was caused by river mouth bypassing. This supply-dominated regime was controlled by intense river discharge and subsequent resuspension of mud in shelf settings, responding to the humid climate in the hinterland and sea-level rise with low rate off Tanzania. The first occurrence of Type II sediments was around 8 cal kyr BP and dominated when sedimentation rates lowered. This accommodation-dominated regime was caused by shoreface bypassing due to an arid climate and sea-level highstand. Type III sediments increased significantly from the early to late Holocene, resulting from the weakening dilution effect of the terrigenous component. The sedimentation pattern on the Tanzanian shelf shifted from allochthonous to autochthonous sedimentation constrained by climatic changes and relative sea-level fluctuations at the end of the early Holocene. Our results also suggest that, with respect to sea-level rise, high sedimentation rate on the continental shelf could be caused by high terrigenous sediment input as a result of a dynamic interplay between the shelf topography and humid climatic conditions inland.

Dryland alluvial successions across interior South Africa are a focus of pedosedimentary research because they provide insights into past hydrogeomorphic changes and improve our understanding of allogenic and autogenic controls on fluvial system behaviour. This paper focuses on an alluvial succession preserved within the Wilgerbosch River, on the Great Escarpment, South Africa. The pedosedimentary architecture of a calcretized palaeosol formed within an abandoned MIS 3 (51–39 ka) floodplain was investigated using grain size, micromorphological, XRD and mineral magnetic analyses. The primary controls on pedogenesis are inferred and the impacts of their products on subsequent landscape development outlined. The biologically-dominated calcrete micromorphology is consistent with the rhizogenic calcrete variety, which together with XRD, grain size and soil magnetic data provides evidence for a palustrine palaeowetland system. Palustrine wetland systems have been documented across interior South Africa, but the formation of rhizogenic calcretes in association with these systems has, to our knowledge, not been reported previously. We interpret these palaeowetlands to have resulted from basin-wide hydrogeomorphic adjustments, rather than localised discontinuous channel and floodout processes. Magnetic enhancement of the soil column overlying the calcrete compared to the overlying floodplain deposits is indicative of moister climate conditions at ~51 ka relative to ~39 ka. We hypothesise that the longevity of geomorphic quiescence, coupled with relatively moist climate conditions in early MIS 3 resulted in enhanced soil CaCO3 accumulation. The resultant cementation of this abandoned floodplain deposit accounts for an alluvial record that is dominated by older rather than younger (e.g. Holocene) deposits, despite the narrow valley context (

Intertidal coralline red algal build-ups (Lithophyllum byssoides rims or ridges) are considered precise sea level markers and mostly used for Holocene sea level history. Several well-preserved patches of relict red algal ridges crop out along the north-west Sardinian coast (Mediterranean Sea, Italy) and have great potential in reconstructing the late Pleistocene sea level history of the western Mediterranean. The aim of this paper is to determine the sedimentary characteristics of the relict Lithophyllum byssoides build-ups cropping out along the Sardinian NW coast and to demonstrate how these can be used as past sea-level indicators. To establish a chronological framework for these deposits, luminescence dating (both quartz OSL and K-feldspar pIRIR290) has been applied and allows for the Lithophyllum byssoides ridge formation to be assigned to Marine Isotopic Stage (MIS) 5e (132–112 ka). The studied relict ridges confirmed that MIS 5e sea-level was at least at 4 m above present, well matching the widely accepted last interglacial global sea-level curves. Hence, fossil Lithophyllum byssoides ridges can be used as stratigraphic and chronologic indicators of late Pleistocene sea-level. Moreover, the study has underlined that Lithophyllum byssoides may grow: (1) in sheltered places along high cliffy coasts forming bench-like structures, and (2) in high-energy environments on wave cut platforms around fallen blocks or potholes, first as isolated mounds and then merging to form reef-like structures.

Few Lateglacial (15,200–11,500 Cal BP) fluvial deposits are known from southern England, UK. This paper outlines a sedimentological investigation of a Lateglacial site near the village of Roxton in the middle reach of the River Great Ouse. Below the Holocene argillaceous alluvium, several large gravelly lithofacies units representing long-term fluvial processes are recognised based on their lower bounding surfaces and sedimentary features. In line with palaeontological evidence and radiocarbon dating, detailed facies analysis indicates that the river changed from a braided to a wandering/meandering regime in response to the warming-induced reduction in nival peak discharge and increase in vegetation cover consisting of birch woodland and grassland during the Lateglacial Interstadial (15,200–12,700 Cal BP). This was followed by a change back to a braided river in response to climatic deterioration during the Younger Dryas Chronozone (12,700–11,500 Cal BP). The interstadial floodplain consisted of both overbank fines and channel lateral or point-bar sands and gravels. The two suites of contemporaneous sediments in the geological succession may be easily mis-interpreted as independent climato-stratigraphical units due to their cross-cutting relationship and marked difference in facies assemblage. Lateral channel movement in such a system also implied that the floodplain underwent constant erosion, resulting in underdeveloped overbank sequences, insufficient to withstand post-depositional removal by erosion. This probably accounts for the rare preservation of fine-textured overbank deposits of the Lateglacial Interstadial in southern England.

The purpose of this paper is to present a complete stratigraphic framework for the modern Simeto River delta (eastern Sicily, Italy) by the description of its geomorphology and sedimentology, which allow an analysis of its recent evolution. The Simeto River delta represents an asymmetric wave-influenced delta which developed during the Holocene by prograding into the Catania Gulf. This delta represents a good example of a Mediterranean-type system, characterized by a micro-tidal regime and moderate wave energy; the peculiar distribution of sedimentary facies both in the subaerial and in the subaqueous sectors is interpreted as the response of the system to the intimate interaction of geological and, in recent times, anthropogenic coastal activity. The integration of a large amount of historical data allows the definition of prograding and retrograding pattern within the delta and the cyclical shifting of the river mouth over the last two centuries. A hypothetical model is proposed to explain this phenomenon, and it is suggested that this may be a characteristic of several Mediterranean-type deltas. Progradation of the delta ended during the early–middle XIX Century after which it began to retreat. The retreat of the coastline accelerated after the 1950s when owing to the construction of embankments on the delta plain and, since 1970s, increasing diversion of water resources in the upper part of the Simeto River drainage basin, the sediment input of the river to the Ionian Sea sharply decreased. This caused a dramatic change of the deltaic morphology and significant coastal land loss. The morphological and sedimentary features of the Simeto River fully reflect the processes of its adaptation to the persistence of coastal human activity within an active geological setting.

The geomorphological evolution of the Holocene wave-dominated barrier estuary at Burrill Lake on the New South Wales coast, Australia, has been investigated using a combination of seismic stratigraphy and lithostratigraphic analysis of vibracores collected from the back-barrier estuarine environment. A combination of radiocarbon and aspartic acid racemisation-derived ages obtained on Holocene fossil molluscs, and the thermoluminescent signal in remnant the Last Interglacial barrier provides the chronological framework for this investigation. Results from this paper show that the barrier estuary occupies a relatively narrow (

The Song Hong (Red River) delta, located on the western coast of the Gulf of Bac Bo (Tonkin) in the South China Sea, formed as a result of the Song Hong sediment discharge throughout the Holocene. The river's sedimentary basin upstream from the delta plain is not large. The delta plain comprises emerged tidal/mangrove flats formed during the sea-level highstand at + 2–3 m (6–4 cal. kyr BP) and a beach-ridge strandplain, with straight-to-lobate beach ridges, on the landward and seaward sides of the delta plain, respectively. The delta affords us the opportunity to examine river-mouth morphodynamics comprehensively in relation to sediment discharge and sea-level changes. In this paper, we describe the Holocene evolution of the Song Hong delta system and the river-mouth morphodynamics on the basis of seven sediment cores, each 30–70 m long, taken from the delta plain during 1999–2001 and 101 radiocarbon dates obtained from the core sediments. Sediments from the seven cores, consisting of incised-valley fills since the last glacial maximum, can be divided, in ascending order, into fluvial sediments composed of gravelly sand and mottled clay, tide-influenced estuarine sediments containing shell and wood fragments, and deltaic sediments composed of tide-influenced sand and mud deposits, in which the contents of sand and wood fragments increase upward. By applying sequence stratigraphic concepts, a transgressive surface can be identified at the gravelly sand-mottled clay boundary, and the maximum flooding surface can be identified at the estuarine–deltaic sediments boundary. The lowstand systems tract, transgressive systems tract, and highstand systems tract record ∼15, 15–9, and 9–0 cal. kyr BP, respectively. During the past 9 kyr, the majority of the sediment discharged by the Song Hong accumulated in the incised valley and enhanced progradation at the river mouth. The river mouth prograded from the bay head toward the gulf, and its morphology changed from funnel-shaped (9–6 cal. kyr BP) to straight (6–2 cal. kyr BP) and finally to lobate (2–0 cal. kyr BP). The morphological change from a funnel-shaped to straight coast is interpreted to have been closely related to a hydrologic regime shift from a tide-dominated bay-head setting to a wave-influenced open-coast setting. The cessation of the sea-level rise at 6 cal. kyr BP may have played only a small role in the change of river-mouth morphology because the progradation rate decelerated from 22 to 4 m/yr, instead of accelerating at that time. The river-mouth morphodynamic change from straight to lobate was largely caused by an increase in the Song Hong sediment discharge from 17–27 (9–2 cal. kyr BP) to 49 million t/yr (2–0 cal. kyr BP) as a result of anthropogenic deforestation along the upper reaches of the Song Hong.

This paper presents an interpretation of 3.5 kHz reflection seismic data together with information from lower frequency seismic data and sediment cores from Flathead Lake in northwestern Montana. Flathead Lake is located at the margin of the Cordilleran Ice Sheet during the last glacial maximum and is the repository for about 160 m of syn- and post-glacial sediment. Six seismic stratigraphic units (A–F) are identified in Flathead Lake above the acoustic basement reflector. The deepest unit is interpreted to be late Pleistocene glacial till (unit A) overlain by well-layered glaciolacustrine sediments (unit B). Overlying seismic reflectors (unit C) include slump deposits, turbidites fed by meltwater surges associated with retreat of the Flathead glacial lobe, and homogeneous silty mud. Preliminary age models suggest that the transition from glacial rhythmites (unit B) to more homogenous lake sediments (unit C) occurred approximately between 14,500 and 13,180 cal.y.b.p. Parallel high amplitude reflectors of the oldest Holocene unit (unit D) drape Pleistocene stratigraphy. Sediment core analyses suggest that these fine sediments were deposited below wave base by suspension settle out in a lake similar to today's. The Mt. Mazama tephra (7630 ± 80 cal.y.b.p.) is interpreted as the top reflector of unit D. Onlap geometries between units D and E imply a significant drop in lake level before deposition of unit E. Sedimentation of unit E was confined to several sub-basins that were separated by bedrock highs. Lake level rose gradually during deposition of unit E to form the well-developed basal onlap geometry. Parallel high amplitude reflectors of the youngest Holocene sediments (unit F) drape all of the older stratigraphy and bedrock highs across the lake basin, suggesting a late Holocene lake highstand.

It is generally accepted that recycling of sandstone generates relatively more mature sand than its parent sandstone. Such maturity is accomplished mainly through chemical weathering as the chemically unstable minerals are eliminated. Because chemical weathering is ubiquitous on the Earth's surface, maturity due to recycling is expected in most geological settings. However, contrary to one's expectation, second-cycle Holocene sand, exclusively derived from sandy facies of the first-cycle Pennsylvanian–Permian Cutler Formation, is actually less mature than its first-cycle parent near Gateway, Colorado. Both the Cutler sandstone and Holocene sand were the products of similar geological processes that controlled their respective composition. In spite of such similarities, a significant difference in composition is observed. We propose that the unexpected immaturity in second-cycle Holocene sand may be due to mechanical disintegration of coarse-grained feldspar and feldspar-rich rock fragments into relatively smaller fractions. Results presented in this paper are the first quantitative estimation of recycling of parent sandstone into daughter sand, and the first observed reverse maturity trend in second-cycle sand. These unexpected results suggest the need for further research to quantitatively understand the recycling process.

The Volga delta differs from all other major deltas in the world by its extremely gentle onshore and offshore gradient (similar to 5 cm/km) and by being affected by the rapid sea-level changes of the Caspian Sea, at rates up to a hundred times the global sea-level rise. This paper reports (1) the morphological and facies development of part of the lower delta during the last full sea-level cycle between 1929 and 1995, as monitored using remote sensing and field mapping, and (2) the Holocene development of the delta from outcrop data and augered transects. During a sea-level fall of 3 m between 1929 and 1977, rapid progradation of levees, composed of fine sand, took place along over 800 distributary channels along the delta front. Smaller distributaries became filled with clay and organics. During the 3-m sea-level rise from 1977 to 1995, aggradation occurred, leading to deposition of silt and clay on the levees and minor filling of the flood basins. Sedimentation rates as established with Cs-137 dating are up to 2-5 cm/year. Total thickness of Holocene deposits in the lower delta plain is 4-10 m. A coarsening-upwards sequence in the Damchik sandpit shows freshening-upwards mollusc assemblages dated around 1000 BP, and has been attributed to the Derbent regression at that time. Four transects with a total of 79 augerings down to 7 m depth show rapid lateral facies changes of: (a) lagoonal clays deposited in the palaeo relief between the dunes, (b) channel sands, (c) levee sands and silts, (d) laminated overbank and interdistributary bay deposits, (e) mouthbar deposits and (f) prodelta clays. Holocene depositional patterns are unrelated to the present drainage network, though the spatial variability is similar to that of the present highly segmented network. Seven C-14 datings give a range of 6000-800 BP, and several phases of progradation seem to be present, but the lateral variability is too large and the age data too limited to make a solid correlation with known Holocene sea-level fluctuations. The Volga delta differs essentially from the classic river-dominated Mississippi delta because the offshore gradient is so gentle that no marine reworking takes place at the outlets, and the friction-controlled bifurcation continues basinward until a very fine maze of distributary outlets is produced. The Volga Holocene sequences more resemble those of the Atchafalaya and Saskatchewan lacustrine deltas. However, they differ from them in not being subsystems of a larger delta but the main depositional facies of the delta as a whole. Moreover, the recent Volga delta development shows that progradation is related to forced regression, not to avulsion triggered by base-level rise and/or subsidence. Thus, the Volga delta provides an excellent example of the impact of high-frequency sea-level changes on a ramp margin-type fluvio-deltaic system. (C) 2002 Elsevier Science B.V. All rights reserved.

Interglacial fluvial sediment sequences are common in lowland Britain where their palaeontology has been considerably studied but their sedimentology is poorly known. By contrast, Holocene (Flandrian) sequences have yielded important insights into river, and thus, environmental evolution. This paper examines the nature of the interglacial fluvial sedimentary record in southern Britain, showing similarities and differences in the sedimentary record. A four-phase pattern of fluvial behaviour through an interglacial cycle is presented. The utility of using Holocene sequences as analogues for previous interglacial sedimentation is discussed and an attempt is made to explain the proposed four-phase pattern in terms of predictable fluvial responses to an interglacial climate cycle. Finally, the implications of the pattern for alluvial unit preservation and the stratigraphical interpretation of Pleistocene temperate events from river sediments are highlighted. It is shown that British lowland rivers normally adopt three major behavioural modes in the Pleistocene: braided or wandering gravel-dominated mode, fine-sediment-dominated stable meandering to anastomosing mode, and incision or non-depositional mode.

The Changjiang (Yangtze) River, China, has formed a large tide-dominated delta on the western coast of the East China Sea. This paper presents the architecture and Holocene evolution of the delta, based on analyses of three borehole samples taken from the present delta plain. The deltaic sediments are 25–30 m thick and composed largely of subaqueous deposits, which can be divided into three facies: prodelta, delta front and delta plain, in ascending order. Tide-influenced sedimentary structures such as sand–mud couplets and bi-directional crosslaminations characterize the delta plain and delta front deposits. An upward-coarsening facies succession from prodelta to delta front is overlain by an upward-fining facies succession from the uppermost delta front to the delta plain. The deposits at the boundary between delta plain and delta front are composed of well-sorted, coarse deposits because it is in the zone of highest energy. The depth from the top of the intertidal facies of the delta plain to this boundary is almost the same, 9–11 m, among the three cores. Sediment accumulation rates are highest in the delta front facies (ca. 10 m/kyr maximum) and decrease toward both delta plain and prodelta facies (ca. 1 m/kyr). The evolution of the Changjiang delta, which began in a bay approximately 8 kyr bp , can be divided into two stages by its stacking pattern: aggradational and progradational. The aggradational system developed during the slow rise of sea level from 8 to 6 kyr bp , and the progradational system developed after sea level reached or approached its present position. The evolution of distributary channels and related river-mouth sand bars was an important process of delta migration or progradation.

This paper describes the styles and sedimentation patterns of Holocene avulsions of the Saskatchewan River at the Cumberland Marshes predating the most recent (1870's) avulsion. Holocene avulsions involved two major styles: (1) progradation of lacustrine deltas and splay complexes, and (2) local reoccupation or appropriation of preavulsive channels. Most avulsions were progradational and occurred in floodplain lakes occupying floodbasin areas between elevated alluvial ridges. The two most recent avulsions (Old Channel and 1870's) diverted mainly into inundated peatland. Progradational avulsions were accompanied by deposition of avulsion-belt sediments associated with multiple channel networks. The characteristics of avulsion-belt deposits include: (1) sediments dominated by poorly sorted silt and very fine sand, (2) lateral continuity in transverse and longitudinal directions with subhorizontal upper and lower boundaries, (3) predominantly nonerosional contacts with underlying sediments, (4) coarsening-upward successions, (5) consistent radiocarbon dates for the tops of preavulsive substrates, and (6) occurrence beneath levee and overbank deposits of the associated major channel belt, indicating that avulsion-belt deposition occurs prior to the development of a new master channel. The width of ancient avulsion belts reaches 18 km, with typical thicknesses of 2–3 m. Avulsion belt deposition accompanied by many small channels was followed by flow reversion to a few larger channels and, eventually, to one single channel, accompanied by deposition of levee and channel deposits. Reoccupational avulsions were not accompanied by deposition of widespread avulsion-belt sediments and led mainly to the modification of pre-existing channel belts. The sedimentation patterns of Holocene avulsions of the Saskatchewan River reveal that avulsion-belt sediments represent major components of the floodplain deposits, supporting the model developed from observations of the 1870's avulsion.

The characteristics of ice-contact glaciomarine systems are reviewed, based on a range of Weichselian and Holocene examples from the fjordal basins in Norway and Svalbard. These depositional systems occur as large morphological ridges, “end-moraines” (including “push-moraines”), which are coarse grained and show large-scale foreset bedding. The paper addresses some of the major problems with regard to the recognition, classification and stratigraphic analysis of these systems. The ice-proximal glaciomarine systems are classified here into three categories: (1) ice-contact submarine fans, (2) ice-contact deltas and (3) glaciofluvial deltas. This classification integrates morphological and sedimentological criteria, and renders these glaciomarine systems not only easier to recognize in the stratigraphic record but also possible to compare with common, non-glacial deltaic systems. The emphasis is on the criteria for the recognition of the ice-contact glaciomarine systems (i.e., ice-contact fans and ice-contact deltas) and their discrimination from common Gilbert-type deltas and fan deltas. The review further focuses on ice-contact glaciomarine systems as highly sensitive recorders of glacier dynamics and climatic fluctuations. It is shown that both the periods of ice-front “stability” and changes in the ice-front position, as well as the magnitude and rate of those changes, are all recorded in the ice-contact depositional system. The sedimentary record further reflects glacio-isostatic sea-level changes and local palaeogeography. A new conceptual model is suggested, which places these ice-contact glaciomarine systems in a dynamic stratigraphic context. The model integrates sedimentary facies and their depositional architecture in an allostratigraphic framework, and is meant to be a guide for the analysis of the sedimentary record of ice-contact systems.

Sebkra el Melah, located in southern Tunisia, exhibits an example of subrecent evaporitic sedimentation (beginning 4000 years B.C.). Notwithstanding the sebkra's small dimensions (150 km2 in surficial extent and a maximum thickness of 30 m), its sedimentary features present a general interest for the interpretation of larger fossil basins because of (1) the presence of a dense network of boreholes; (2) the diversity of the deposits occurring, (3) the lack of diagenesis of the sediments. The knowledge of the sedimentary pan, the analysis of successive deposits (marine detrital limestones, euxinic beds, magnesian carbonates, gypsum, polyhalite, halite), the analysis of their arrangement (longitudinal, or antero-posterior; concentric pattern) and of their diachronism, allow of precising the determinism of evaporitic facies: importance of the shape of the basin, of aridity and of eustatic movements. From this analysis, some mechanisms of saline deposition, can be inferred, such as deposition of salts under some 10 m of water. Both the descriptive and the interpretative parts of this paper give the opportunity of comparison with the fossil record in larger evaporitic basins.

This publication forms the introduction to a series of papers that will be presented in the near future. They will all deal with the “sloef” (also called Almere deposits), a Holocene lagoonal silt that has been deposited in the former Zuiderzee (The Netherlands). The silt formed between about 375 and 2000 years ago and shows a typical grain-size distribution. The percentage of particles from 0 to 2 μm is abnormally low, whereas the percentage of particles from 2 to 50 μm is high. Over large areas the “sloef” contains abundant sedimentary structures, among which metasedimentary faults and flow structures are frequently present.