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Anabranching rivers evolve in various geomorphic settings and various river planforms are present within these multichannel systems. In some cases, anabranches develop meandering patterns. Such river courses existed in Europe prior to intensive hydro-technical works carried out during the last 250 years. Proglacial stream valleys, inherited from the last glaciation, provided a suitable environment for the development of anabranching rivers (wide valleys floors with abundant sand deposits). The main objective of the present study is to reconstruct the formation of an anabranching river planform characterized by meandering anabranches. Based on geophysical and geological data obtained from field research and a reconstruction of palaeodischarges, a model of the evolution of an anabranching river formed in a sandy floodplain is proposed. It is demonstrated that such a river system evolves from a meandering to an anabranching planform in periods of high flows that contribute to the formation of crevasse splays. The splay channels evolve then into new meandering flow paths that form 'second-order' crevasses, avulsions and cutoffs. The efficiency of the flow is maintained by the formation of cutoffs and avulsions preventing the development of high sinuosity channels and redirecting the flow to newly formed channels during maximum flow events. A comparison with other anabranching systems revealed that increased discharges and sediment loads are capable of forming anabranching planforms both in dryland and temperate climate zones. The sediment type available for transport, often inherited from older sedimentary environments, is an important variable determining whether the channel planform is anabranching, with actively migrating channels, or anastomosing, with stable, straight or sinuous branches. [ABSTRACT FROM AUTHOR]

Charcoal morphometry is increasingly employed in the analysis of Quaternary sediments, but has not been applied in studies of earlier sediments. We present findings relating to charcoal morphometry and morphotypes in a Toarcian sequence, which contains a preponderance of highly elongate forms, and morphometric values well outside expected ranges. SEM imaging reveals elongate particles of two distinct kinds. One originates in conifer xylem, and may be associated with formation at high levels of heating. It is proposed that the other may derive from tree ferns, or from plants with similar growth forms. Our results show the importance of recognizing the wide morphological variation that exists in sedimentary charcoal. Failing to do so may result in serious errors in its identification, interpretation and quantification. [ABSTRACT FROM AUTHOR]

The Aínsa Basin of northern Spain contains a deep-marine succession comprising up to 24 sandstone bodies separated by thick marl-rich units. A detailed analysis of nine outcrops (>900 m of sediment profiles) from the Morillo Formation of the San Vicente Group, from the upper part of the basin succession, has enabled a reappraisal of the unit. Within the Morillo Formation, sediment transport was to the NW, and a range of environments are recognized including channels, lobes and pelagic deposits. The overlying Coscojuela Formation, which partly cuts into the Morillo Formation, shows W-directed palaeocurrents in its proximal reaches, with flows being deflected to the N along an adjacent slope. Destabilization of the adjacent carbonate platform resulted in a significant input of carbonate material into the flow. The final phases of sedimentation within the Aínsa Basin were more complex than previously suspected, probably as a result of a combination of factors, including tectonic activity, resulting in basin narrowing due to anticlinal growth, as well as encroachment and/or destabilization of the adjacent regional carbonate platforms. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Glacier thermal regime is shown to have a significant influence on the formation of ice-marginal moraines. Annual moraines at the margin of Midtdalsbreen are asymmetrical and contain sorted fine sediment and diamicton layers dipping gently up-glacier. The sorted fine sediments include sands and gravels that were initially deposited fluvially directly in front of the glacier. Clast-form data indicate that the diamictons have a mixed subglacial and fluvial origin. Winter cold is able to penetrate through the thin (<10 m) ice margin and freeze these sediments to the glacier sole. During winter, sediment becomes elevated along the wedge-shaped advancing glacier snout before melting out and being deposited as asymmetrical ridges. These annual moraines have a limited preservation potential of ∼40 years, and this is reflected in the evolution of landforms across the glacier foreland. Despite changing climatic conditions since the Little Ice Age and particularly within the last 10 years when frontal retreat has significantly speeded up, glacier dynamics have remained relatively constant with moraines deposited via basal freeze-on, which requires stable glacier geometry. While the annual moraines on the eastern side of Midtdalsbreen indicate a slow steady retreat, the western foreland contains contrasting ice-stagnation topography, highlighting the importance of local forcing factors such as shielding, aspect and debris cover in addition to changing climate. This study indicates that, even in temperate glacial environments, restricted or localised areas of cold-based ice can have a significant impact on the geomorphic imprint of the glacier system and may actually be more widespread within both modern and ancient glacial environments than previously thought. [ABSTRACT FROM AUTHOR]

The tectonics of the Virgin Islands Basin are controlled by the plate boundary between the Puerto Rico-Virgin Islands Microplate and the stable part of the Caribbean Plate. Several contradicting theories about the formation and development of this basin have previously been proposed. As part of the Danish Galathea 3 expedition, extensive marine geological investigations of the basin were carried out in March 2007 including sediment coring and acquisition of multi-beam and two-dimensional seismic data. This paper represents a summary of the key observations from the multi-beam and the seismic data set. The interpretation of these observations leads to the proposition of a tectonic model for the Virgin Islands Basin. The model consists of N-S to NW- SE directed extension combined with E-W trending sinistral strike-slip and the new structural evidence from the Virgin Islands Basin is entirely consistent with the most recently published GPS data. [ABSTRACT FROM AUTHOR]

Two sand wedge structures and their host sediments, from Jonzac in SW France, were successfully dated using Optically Stimulated Luminescence ( OSL) measurements on both small aliquots and single grains of quartz from the 180-212 μm size fraction. One of the sand wedges clearly contains primary infilling. However, grain-size analysis and field observations do not clearly indicate whether the other feature represents a primary sand wedge or a composite sand wedge with primary and secondary infilling. OSL results and the geological setting justify using the Central Age Model ( CAM) for the calculation of age estimates. Grain-size analysis and detailed investigations of OSL results revealed the contamination of one sand wedge sample with host sediment. However, age calculation using the Finite Mixture Model ( FMM) provided what is considered to be a reliable age estimate for the contaminated sample. The age estimates for all samples correspond to Marine Isotope Stage ( MIS) 3. While fine-grained sediments were deposited in the middle of MIS 3 ( c. 43-55 ka), the sand wedges unexpectedly correspond to the end of this period ( c. 33 ka) or the onset of MIS 2 ( c. 27 ka). The sand wedges were probably formed during intense but short cold periods, possibly correlated with a Heinrich event ( H2 and/or H3). The results help us to assess how effective luminescence dating is on sand wedges and the limitations involved in correlating sand wedge ages with Heinrich events, and contribute to the debate on the timing of cryogenic formation processes and the permafrost distribution in SW France. [ABSTRACT FROM AUTHOR]

From thinly laminated marlstones of the Hessel-tal Formation, representing the Late Cenomanian Oceanic Anoxic Event (OAE) 2, at Lengerich in the Teutoburger Wald (Westfalen, north-west Germany), 17 sediment-com-pacted baculitid ammonites with carbonised and partially phosphatised soft parts are recorded. Some preserve remains of the buccal mass, including jaws (occasionally articulated) and radulae, as well as of the cephalic cartilage, such as eye capsules. Such have not yet been recorded previously for the order Ammonoidea. In addition, originally unmineralised parts found preserved in these specimens include extensive portions of the digestive tract, the siphonal tube, false colour patterns (megastriae), as well as traces of what would appear to be the oviduct. At the same levels, patches with numerous isolated horny upper and rarer lower jaws as well as radulae occur; these may represent regurgitates or faeces of larger predators. The cephalopod remains described were deposited in an epicontinental setting, possibly at palaeodepths between 200 and 600 m. In this particular Late Cretaceous fossil Lagerstätte, upper jaws and anaptychi of ammonites rank among the commonest fossils. [ABSTRACT FROM AUTHOR]

The generation and composition of carbonate sediment within tropical carbonate settings is controlled by the skeletal production of CaCO3 in conjunction with physical, biological and chemical processes which act to break down and disperse skeletal remains. Using the results of detailed tumbling barrel experiments, this paper discusses the role the physical durability of common constituents of reef sediment plays in the composition of coral reef deposits. The durability of the skeletal remains of six reef sediment constituents was determined experimentally using tumbling barrels. Results indicate that constituent durability varies considerably amongst common reef sediment constituents. Calcareous algae Halimeda was the least durable constituent tested, followed by larger benthic foraminifera Baculogypsina sphaerulata and Marginopora vertebralis and the pelecypod Fragum fragum. Two species of branching coral ( Acropora sarmentosa and Acropora nasuta) were found to be the most resistant to physical destruction. These findings provide increased power to interpret reef and island deposits and the potential role skeletal durability plays in the retention of constituent skeletons within coral reef associated sedimentary systems. [ABSTRACT FROM AUTHOR]

Peat and gyttja (organic lake sediment) are important indicators for past environmental conditions; they form in areas where the supply of clastic sediment is insufficient to fill the accommodation space. Previous studies of delta sediments, however, have focused mainly on clastic deposits, whereas organics have received only minimal attention. Identification of organic facies can be of value for understanding delta formation as it provides insight into, for example, palaeoenvironmental conditions and compaction susceptibility of these layers. Currently, however, field characteristics of organics are not well-documented for the full range of facies present in delta plains. In this study, a field method - a classification key - for identifying organic facies in delta plains was developed based on concisely described organic facies in selected cores from the Rhine-Meuse delta, The Netherlands. This method was tested on archived borehole descriptions of the diachronous basal peat layer in the distal Holocene Rhine-Meuse delta; this was done by means of a semi-automated procedure to select and classify samples from a database. The resulting data set was used for mapping organic facies in the basal peat layer by means of indicator kriging and inverse distance weighting. The resulting facies distribution map shows consistent and geologically meaningful patterns, which were interpreted in terms of hydrological regimes. The formation of the basal peat layer, which marks the onset of Holocene aggradation, has been controlled by marine-dominated, fluvial-dominated and seepage-dominated environments. Before 9000 cal yr bp, marine processes influenced the initial stage of organic accumulation in the western part of The Netherlands. After 9000 cal yr bp, on the flanks of topographical higher regions, seepage-dominated mesotrophic organic facies characterized the onset of accumulation. Simultaneously, nutrient-rich organic facies could develop in the Rhine-Meuse valley: gyttja formed in the sediment-limited Meuse realm, whereas reed peat accumulated in the Rhine realm, indicating lower water depths and thus a higher elevated surface level. It is concluded that the classification key for identifying organic facies is a strong tool to better recognize peat and gyttja types on the basis of macroscopic field characteristics. Application of the key on archived boreholes also proved to be feasible. Identification of organic facies and determination of their spatial distribution at delta scale, as is shown in this study, contributes to understanding delta evolution. [ABSTRACT FROM AUTHOR]

Stratigraphic and sedimentological analyses of the Quaternary tufa and associated deposits in the Piedra and Mesa river valleys allowed a number of stages of their sedimentary evolution to be characterized, and a depositional sedimentary model for this north-central sector of the Iberian Range (Spain) to be established. The proposed sedimentary facies model may explain tufa arrangements in other medium to high gradient, stepped, fluvial tufa systems with narrow transverse profiles occurring in temperate, semi-arid areas, in both recent and past scenarios. There are several tufa deposits within the Piedra and Mesa river valleys that, over a maximum thickness of about 90 m, record one or more stages of tufa deposition produced following the fluvial incision of the bedrock or previous tufa deposits. Each depositional stage begins with coarse detrital sedimentation. Six fundamental, vertical sequences of tufa facies with small amounts of detrital material reveal the sedimentary processes that occurred in different fluvial environments: channel areas with: (i) free-flowing water; (ii) barrages and/or cascades; and (iii) dammed water and palustrine floodplains. The proposed sedimentary model involves narrow, stepped, fluvial valleys in which tufa cascades were common. Alternating intervals of bryophyte and stromatolite facies commonly formed at some cascades. Many of these represented barrage-cascade structures that consisted of phytoclast rudstones, thick phytoherms of mosses and associated stromatolites, and curtain-shaped phytoherms of stems. Upstream of these structures, dammed areas with bioclastic sands and silts developed and palustrine vegetation grew. The channel stretches between barrages and/or cascades were loci for extensive stromatolite growth in fast flowing water. The palustrine floodplain was home to pools and drainage channels. The model also explains the growth of some barrages in the River Piedra that surpassed the height of the divide, with the diffluence of the main channel into a secondary course forming other tufa deposits in the area. The distribution and abundance of certain types of tufa facies in fluvial basins may be an indicator of differences in their gradients. The facies studied in this work suggest that the gradient of the ancient River Piedra was steeper than that of the ancient River Mesa. Assuming similar scenarios for climate and hydrology, the depositional settings mentioned above and their dimensions would have been determined mainly by the gradient and width of the associated river valleys. This sedimentary model may also be useful for inferring variations in other river basin slopes, as well as accounting for the presence of tufas in areas that normally have no permanent water input. [ABSTRACT FROM AUTHOR]

Incised valleys are canyon-like features that initially form near the highstand shoreline and evolve over geological time as rivers erode into coastal plains and continental shelves to maintain equilibrium-gradient profiles in response to sea-level fall. Most of these valleys flood during sea-level rise to form estuaries. Incised-valley morphology strongly controls the rate of creation of sediment accommodation, valley-fill facies architecture and the preservation potential of coastal lithosomes on continental shelves, and affects coastal physical processes. Nonetheless, little is known about what dictates incised-valley size and shape and whether these metrics can be used to explain principal formation processes. The main control on alluvial channel morphology over human time scales is discharge; this is based on numerous empirical studies and is well-constrained because all variables are easily measured at this short time scale. Knowledge of long-term river evolution over a complete glacio-eustatic cycle, on the contrary, remains largely conceptual, experimental and based on individual systems because variables that are thought to drive morphological change are not easily quantified. In spite of this difficulty, existing models of incised-valley formation at the coast suggest that valley evolution is driven largely by downstream forcing mechanisms, highlighting sea-level and shelf gradient/morphology as the dominant controls on valley incision. Although valleys are cut by rivers, whose channels are a direct reflection of discharge, little empirical data exist in coastal areas to address the degree to which valley evolution is governed by upstream controls. The late Quaternary is the best time period to examine because it provides the most complete sedimentary record and many variables, including sea-level, tectonics, substrate lithology and drainage network characteristics, are accurately constrained. Here, 38 late Quaternary valleys along the coast of two different passive continental margins are compared, which suggests that valley shape and size are governed primarily by upstream, intrinsic controls such as discharge. Valley width, depth and cross-sectional area are found to be predictable at the highstand shoreline and are scaled with the size of their drainage basin, which has important implications for estimating sediment discharge to continental shelves and deep water environments during periods of low sea-level. [ABSTRACT FROM AUTHOR]

The Honggang member of the early Paleogene Buxin Formation is the main source rock in the Sanshui Basin, characterized by organic-rich black shales with the cyclic recurrence of organic-poor sediments. The geochemical characteristics of the Honggang member have been documented to determine the organic matter types and depositional environments in this paper. The organic matter of the black shales mainly consists of a mixture of land plant-derived and phytoplankton-derived organic matter. Total organic carbon content (TOC)-sulfur-iron (Fe) relationships suggest that the organic-rich black shales were deposited under dysoxic-to-euxinic water conditions. The time that iron minerals remained in contact with H2S in anoxic waters possibly influenced the formation of syngenetic pyrite, and organic carbon controlled the formation of diagenetic pyrite. Organic-poor intervals usually show pyrite sulfur enrichment and higher degree of pyritization values relative to low organic carbon contents. This resulted from HS− diffusing downward from overlying organic-rich sediments and formed Fe sulfides through reactions with sufficient Fe. Trace elements generally exhibit low concentrations and little TOC dependence, suggesting some degree of depletion in these elements in the early Paleogene sediments of the Sanshui Basin. This probably resulted from cyclic recurrences of oxic benthic conditions, which promoted the remobilization of trace elements and caused the low concentration of trace elements. [ABSTRACT FROM AUTHOR]

The Marnoso Arenacea Formation provides the most extensive correlation of individual flow deposits (beds) yet documented in an ancient turbidite system. These correlations provide unusually detailed constraints on bed shape, which is used to deduce flow evolution and assess the validity of numerical and laboratory models. Bed volumes have an approximately log-normal frequency distribution; a small number of flows dominated sediment supply to this non-channelized basin plain. Turbidite sandstone within small-volume (<0·7 km3) beds thins downflow in an approximately exponential fashion. This shape is a property of spatially depletive flows, and has been reproduced by previous mathematical models and laboratory experiments. Sandstone intervals in larger-volume (0·7–7 km3) beds have a broad thickness maximum in their proximal part. Grain-size trends within this broad thickness maximum indicate spatially near-uniform flow for distances of ∼30 km, although the flow was temporally unsteady. Previous mathematical models and laboratory experiments have not reproduced this type of deposit shape. This may be because models fail to simulate the way in which near bed sediment concentration tends towards a constant value (saturates) in powerful flows. Alternatively, the discrepancy may be the result of relatively high ratios of flow thickness and sediment settling velocity in submarine flows, together with very gradual changes in sea-floor gradient. Intra-bed erosion, temporally varying discharge, and reworking of suspension fallout as bedload could also help to explain the discrepancy in deposit shape. Most large-volume beds contain an internal erosion surface underlain by inversely graded sandstone, recording waxing and waning flow. It has been inferred previously that these characteristics are diagnostic of turbidites generated by hyperpycnal flood discharge. These turbidites are too voluminous to have been formed by hyperpycnal flows, unless such flows are capable of eroding cubic kilometres of sea-floor sediment. It is more likely that these flows originated from submarine slope failure. Two beds comprise multiple sandstone intervals separated only by turbidite mudstone. These features suggest that the submarine slope failures occurred as either a waxing and waning event, or in a number of stages. [ABSTRACT FROM AUTHOR]

Analysis of accommodation space variation during deposition of the Cretaceous Qingshankou Formation in the Songliao Basin, NE China, indicates that accommodation space changed both through time and across the basin as a seesaw movement. The mid-upper Qingshankou Formation is divided into three units. In each unit, changes of accommodation space differ in the southern and northern part of the basin. Increasing accommodation in the southern part is accompanied by a decrease in the northern part, and vice versa. Between the northern and southern basin, there was a neutral belt that is like a fulcrum, called the transformation belt here, where the accommodation did not change to any significant degree. We call this response ‘accommodation transformation’, whose characteristics are defined by tectonic subsidence analysis, palaeontological and sedimentary analyses. The accommodation increasing belt, decreasing belt, transformation belt and accommodation transformation boundary together constitute the accommodation transformation system. The recognition of accommodation transformation in the Songliao Basin provides a new insight into sequence stratigraphy and might be widely applicable. [ABSTRACT FROM AUTHOR]

Discusses the influence of glacial conditions on sedimentation in the Smalfjord Formation of northern Norway. Absence of evidence for coeval tectonism; Suggestion that there is no transition at the top of the Smalfjord Formation from deep-water and shallow-water environments; Subglacial tectonism and banded diamictite at Tarmfjord; Varangerfjord ice-scoured palaeovalley.

Discusses the influence of glacial conditions on sedimentation in the Smalfjord Formation of northern Norway. Suggestion that the striations should not be used as evidence for direct glacial influence on sedimentation of the overlying deposits; Argument that the occurrence of Neoproterozoic diamictites in widely separated regions in Norway cannot be used to support a glacial origin for the Smalfjord Formation.

Discusses the influence of glacial conditions on sedimentation in the Smalfjord Formation of northern Norway. Failure of direct sedimentological observations and comparisons to deliver unequivocal conclusions when deteremining whether diamictites are glacial or non-glacial; Suggestion that localized facies analysis must be harnessed together with other geological data on all scales.

The complex development of the northern Crotone Basin, a forearc basin of the Calabrian Arc (Southern Italy), has been documented by sedimentological, stratigraphic and structural analyses. This Mediterranean-type fault bounded basin consists of small depocentres commonly characterized by a mix of facies that grades from continental to shallow marine. The lower Pliocene infill of the Crotone Basin consists of offshore marls (Cavalieri Marl) that grade upwards into a shallow-marine to continental succession up to 850 m thick (Zinga Formation). The succession is subdivided into three main stratal units: Zinga 1, Zinga 2, Zinga 3 bounded by major unconformities. The Zinga 1 stratal unit grades from the Cavalieri Marl to deltaic and shoreface deposits, the latter organized into several stacked progradational wedges that show spectacular thickness changes and progressive unconformities related to salt-cored NE-trending growth folds and listric normal faults. The Zinga 2 stratal unit records a progressive and moderate deepening of the area, marked by fluvial sedimentation at the base, followed by lagoonal deposits and by a stacking of mixed bioclastic and siliciclastic shoreface units, organized into metre-scale high-frequency cycles. Deposition was controlled by NE-trending synsedimentary normal faults that dissected the basin into a series of half-grabens. Hangingwall stratigraphic expansion was compensated by footwall condensed sedimentation. The extensional tectonic regime continued during sedimentation of the Zinga 3 stratal unit. Deposition confined within structural lows during a generalized transgressive phase led to local enhancement of tidal flows and development of sand-wave trains. The tectonic setting testifies the generalized structural domain of a forearc region. The angular unconformity at the top of the Zinga 3 stratal unit is regional, and marks the activation of a large-scale tectonic phase linked to strike-slip movements. [ABSTRACT FROM AUTHOR]

There are few descriptions of pre-Quaternary tufa or travertine, yet these deposits have important climatic, hydrological and tectonic implications. In the Badlands of South Dakota, the Late Eocene Chadron Formation contains a variety of tufa (fluvial, lacustrine, paludal and perched springline types), travertine and calcrete (pedogenic and non-pedogenic types). In fluvial channels, tufas and tufa barrages (oncolites, tufa lithoclast conglomerates and phytoherms) are transitional to travertines (pseudostromatolitic boundstone gravels and small pinnacle resurgences with rimstone edges and pools). Lacustrine tufas formed in small ponds adjacent to other types of tufas and are similar to the ‘low-energy, bench-margin facies’ types observed in modern, groundwater-fed, temperate-zone hardwater lakes. Paludal tufas are laterally discontinuous sheets of pisoid-intraclast wackestone that fill palaeotopography. Distal perched springline tufas are mounds of numerous sloping tufa sheets. Concretions and rhizoliths associated with palaeosols are recognized as pedogenic calcretes, whereas non-pedogenic calcretes are variably cemented, vertically oriented conduits for palaeogroundwater discharge that are located in fault zones. These deposits resulted from palaeogroundwater discharge along faults during the Late Eocene. Coeval unroofing of the Black Hills uplift created a regional groundwater flow system through karsted Palaeozoic limestones exposed in the Black Hills. The Chadron Formation is an avulsion-dominated, siliciclastic unit, yet important bodies of carbonate accumulated in it as a result of groundwater processes. [ABSTRACT FROM AUTHOR]

Two contrasting marine sedimentary facies, the Haida Formation of sandy and argillaceous sediments and the conformably overlying Honna Formation of gravelly sediments were formed within different types of tectonic basins during mid- to Late Cretaceous time. The sediments of both formations were derived from the east. Sandstones from the two formations show characteristics of mature magmatic arc provenance and are classified as lithic and feldspathic arenites. However, the Honna sandstones are more feldspathic and less quartzose than the Haida sandstones. The Honna sandstones have many volcanic rock fragments (VRF) but the Haida sandstones do not. Feldspars of the VRF-rich Honna sandstones, however, do not seem to have been derived from the breakdown of volcanic rocks. The observed petrographic differences between the two formations can be ascribed to a process in which the volcanic cover and the basement rock denudation took place simultaneously in the source area during deposition of the Honna Formation. [ABSTRACT FROM AUTHOR]