Fluvial Sedimentary Processes Research Articles

Fluvial response to environmental conditions during MIS 4-3: a sedimentary record at the Brześnica site, central-western Poland

Fluvial deposits subjected to this study are exposed at the Brześnica site, in the south-western part of the Wielkopolska region in Poland, which was close to the ice-sheet limit during the Last Glacial Maximum (LGM). Sedimentological analyses, including lithofacies descriptions, palaeocurrent measurements, grain size and rounding analyses and heavy mineral compositions indicate that the fluvial deposits at Brześnica were deposited in braided river environment. The following fluvial sedimentary processes were inferred: (1) shallow, rapid flow alternating with waning flow, (2) infilling of erosional channels with fluvial sediments during flood events, (3) changes from supercritical to subcritical flows, and (4) shallow sheet floods. The results of OSL dating indicated sediment deposition ~65.2 ±1.5 ka, i.e. in MIS 4, that was here characterized by cold environmental conditions and a general shift from meandering to braided fluvial sedimentation style. This finding contrasts with accumulation/erosion phases interpreted previously in this region for that time interval; however, it is consistent with recent studies of fluvial systems functioning during MIS 5-2 and of factors responsible for sedimentation style.

High-resolution seismic imaging reveals infill history of a submerged Quaternary fjord system in the subantarctic Auckland Islands, New Zealand

AbstractQuaternary processes and environmental changes are often difficult to assess in remote subantarctic islands due to high surface erosion rates and overprinting of sedimentary products in locations that can be a challenge to access. We present a set of high-resolution, multichannel seismic lines and complementary multibeam bathymetry collected off the eastern (leeward) side of the subantarctic Auckland Islands, about 465 km south of New Zealand's South Island. These data constrain the erosive and depositional history of the island group, and they reveal an extensive system of sediment-filled valleys that extend offshore to depths that exceed glacial low-stand sea level. Although shallow, marine, U-shaped valleys and moraines are imaged, the rugged offshore geomorphology of the paleovalley floors and the stratigraphy of infill sediments suggests that the valley floors were shaped by submarine fluvial erosion, and subsequently filled by lacustrine, fjord, and fluvial sedimentary processes.

On the interest of using the multiple center approach in ESR dating of optically bleached quartz grains: Some examples from the Early Pleistocene terraces of the Alcanadre River (Ebro basin, Spain)

The present work reports the first numerical ages obtained for the two highest fluvial terraces (Qt1 and Qt2) of the Alcanadre River system (Northeastern Spain) representing the earliest remnants of Quaternary morphosedimentary fluvial activity in the Ebro basin. ESR dating method was applied to optically bleached quartz grains and both the Al and Ti centers were measured, in accordance with the Multiple Center approach. The results are overall in good agreement with the existing preliminary chronostratigraphic framework and our interpretation indicate that terraces Qt1 and Qt2 have an ESR age of 1276 ± 104 ka and 817 ± 68 ka, respectively. These data provide some chronological insights on the beginning of the fluvial sedimentary processes in a scenario of incision maintained over Quaternary in the Ebro Basin. These are among the first numerical ages obtained for such high terraces in the Iberian Peninsula.Our results demonstrate the interest of using the Multiple Center approach in ESR dating of quartz, since the two centers provide complementary information, i.e. an independent dose control. The overall apparent consistency between the ESR age estimates and the existing preliminary chronostratigraphic framework may be considered as an empirical evidence that the Ti–Li center may actually work for Early Pleistocene deposits, whereas the Ti–H center shows some clear limitations instead. Finally, these results demonstrate the interest of using ESR method to date Early Pleistocene fluvial terraces that are usually beyond the time range covered by the OSL dating method.

O TRANSPORTE DE DIAMANTES POR SISTEMAS FLUVIAIS A LONGAS DISTÂNCIAS: UMA VISÃO CRÍTICA

Many authors believe in the possibility of diamond transport for hundreds of kilometers by fluvial sedimentary processes. This work attempts to show by the integration of alluvial placer observations, experimental data analysis and case study that diamonds cannot be transported for long distances by tractive processes. The presence of diamond in a large geographical area (hundreds of square kilometers) implies in the necessity of the presence of multiple well distributed sources, including primary (kimberlite and lamproite) or secondary (sedimentary rocks) sources. The coarse facies related to the glaciogenic sediments are the most important sources among the secondary host rocks. The case studies exemplified in this paper show clearly that the wide dispersion of diamonds is mainly explained by the presence of secondary sources with regional distribution.

O Transporte de Diamantes por Sistemas Fluviais a Longas Distâncias: Uma Visão Crítica

Many authors believe in the possibility of diamond transport for hundreds of kilometers by fluvial sedimentary processes. This work attempts to show by the integration of alluvial placer observations, experimental data analysis and case study that diamonds cannot be transported for long distances by tractive processes. The presence of diamond in a large geographical area (hundreds of square kilometers) implies in the necessity of the presence of multiple well distributed sources, including primary (kimberlite and lamproite) or secondary (sedimentary rocks) sources. The coarse facies related to the glaciogenic sediments are the most important sources among the secondary host rocks. The case studies exemplified in this paper show clearly that the wide dispersion of diamonds is mainly explained by the presence of secondary sources with regional distribution.

Spectral Gamma-Ray Logging for Facies Discrimination in Mixed Fluvial-Eolian Successions: A Cautionary Tale

Accurate assessment of downhole natural gamma-ray logs requires a reference database built up from well-exposed outcrops where the recognition and interpretation of lithofacies is unequivocal. Although only a few cases have been published for spectral gamma-ray logs, some of these show there is a strong correlation to depositional environment. We present detailed spectral gamma-ray data, within an interpretative framework of the sedimentology and petrography, for a mixed fluvial-eolian succession in the Cutler Group of southeastern Utah, United States. In this case, these data did not help identify depositional environment. Discrimination of eolian from fluvial deposits is not reliable because there is much overlap between the gamma-ray emissions of each lithofacies, although the eolian sediments tend to have lower values than the fluvial sediments. Interdune deposits cannot be discriminated from flood-plain sediments. The thorium/potassium ratio is approximately constant for all lithofacies, and is of no use as a facies discriminator. The thorium/uranium ratio is less than 7, much lower than might be expected for continental lithofacies from a review of the literature. These results have general application to mixed fluvial-eolian successions because they reflect the typical interactions between eolian and fluvial sedimentary processes, and do not depend especially on the character of the original sediment.

Sequence stratigraphy and lithofacies geometry in an early Namurian coal-bearing succession in central Scotland

Abstract High frequency glacial-eustatic allocycles have been identified in the upper part of the early Pendleian Limestone Coal Formation in the north-central Midland Valley of Scotland. Repeated eustatic oscillations caused extensive lateral migrations of a wide spectrum of depositional environments, ranging from quasi-marine to fluvial. This throws doubt on the assumptions that underlie some existing depositional models of similar late Carboniferous cyclic coal-bearing successions. The study interval can be divided into three facies associations. The distal association was dominantly controlled by glacial-eustatic oscillations, which resulted in a remarkably regular ‘layer cake’ succession with laterally persistent coals. In the more sandy and variable transitional facies association, local episodic fluvial processes tended to obscure the underlying allocycles. Here coals may split and also amalgamate to form thick composite seams. The highly variable proximal association was dominantly controlled by irregular autocyclic fluvial sedimentary processes which largely obscured the background changes in relative sea level. Sequence stratigraphy is easy to apply to the distal facies association, harder to apply to the transitional association and very difficult to apply to the variable proximal association.

Geoarchaeological analysis of an acheulean site at Kalambo Falls, Zambia

AbstractAcheulean sites are commonly recovered from sandy channel contexts, particularly in Africa. These sites frequently contain impressive concentrations of artifacts dominated by typical Acheulean large bifacial artifacts (‘handaxes,’ etc.). Possible influences of fluvial sedimentary processes in Acheulean site formation are explored through consideration of sedimentary context and detailed analysis of relevant artifact assemblage characteristics in part of a major Acheulean ‘Floor’ at Kalambo Falls, Zambia. The Kalambo Falls patterns are analyzed here with regard to influences of behavioral and natural processes in their formation, and are compared to those observed in Acheulean horizons at Montagu Cave, South Africa. Spatial concentration of bifaces and paucity of debitage at many Acheulean sites may be due largely to fluvial disturbance and winnowing, although a hominid preoccupation with large bifacial tools may be a bona fide behavior pattern at some sites. Better control over sedimentary context is necessary to elucidate the range of behaviorally‐produced patterns at Acheulean sites.