Sedimentology

Journal: Sedimentology

Abbreviation

Sedimentol

Publisher

Wiley

ISSN

0037-0746
1365-3091

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Publications 1 - 10 of 12

Nature and significance of Late Pleistocene to Holocene thick evaporite deposits of the Danakil Depression, Afar, Ethiopia
Rime, Valentin; Negga, Haileyesus; Fentimen, Robin; et al. (2025)
Sedimentology
Large evaporite deposits, reaching several hundreds of metres of thickness, occur in many basins of our planet but remain poorly understood due to the absence of modern analogues. The origin of ancient evaporites and their highly variable sedimentation rates are often debated and ambiguous. The Danakil rift basin in northern Afar (Ethiopia) features several hundreds of metres of evaporites with deposition still continuing today and, as such, represents a unique modern analogue for older thick evaporite deposits. This study focuses on the multi-proxy analysis of a 625 m long core from the central part of the basin. The core record, dominated by halite (ca 60%) with subordinate clastic sediments (ca 35%) and potash minerals (ca 5%) reveals, for the first time, the Late Pleistocene to Recent geological and environmental history of the basin. Sediments experienced restricted marine conditions after the last Late Pleistocene marine incursion in the basin, followed by a hypersaline stage leading to the near-desiccation of the basin with the deposition of thick halite and potash deposits. Subsequent recycling of marginal halite deposits by meteoric waters in lacustrine and salt pan environments significantly increased the evaporite thickness in the subsiding central part of the basin. These findings have implications for the understanding of older thick evaporite deposits that formed in similar depositional settings. They show that several hundred of metres of evaporite can form in less than 128 kyr by evaporation of meteoric and seawater following a single marine flooding of the basin.
Holocene sea-level changes and the influence of storms on beach ridge formation in the Lower Gulf of Thailand
Leknettip, Smith; Chawchai, Sakonvan; Bissen, Raphael; et al. (2025)
Sedimentology
Beach ridges are depositional landforms that provide information related to coastal evolution, storm activity and sea-level variations. However, beach ridges are sometimes modified by aeolian processes, storm washover and/or human activity. Therefore, systematic investigations are required to use beach ridges as an archive of palaeoenvironmental conditions and sea-level changes. In this study, a multidisciplinary approach involving ground-penetrating radar, sedimentological analysis and optically stimulated luminescence as well as radiocarbon dating was used to reconstruct sedimentary processes and past sea-level changes that formed beach ridges in the coastal zone of Nakhon Si Thammarat province, Lower Gulf of Thailand. Ground-penetrating radar data reveal evidence of beach progradation coupled with the presence of beach scarps and washover deposits. This implies that the formation of the beach ridges occurred under swash processes on the beachface and was later punctuated by erosion during storm surges, leading to the deposition of washover sediments. During a storm, elevated seawater transported moderately to poorly sorted medium-to-coarse sand onto a higher position along the beach profile, resulting in an elevation of the beach ridge of up to 4.6 m above mean sea-level. In addition, aeolian processes contributed to vertical accretion by depositing well-sorted fine sand on the surface of the beach ridges. The dating results indicate that the formation of the beach ridges occurred approximately between 8.6 ka and 6.1 ka and can be attributed to an upper sea-level limit of 1.8 to 2.3 m above present-day mean sea level. Both allogenic (e.g. sea-level and climate variability) and autogenic (e.g. sediment supply and wave action) factors play crucial roles in the formation and evolution of beach ridges. Therefore, the multidisciplinary approach of this study enhances the understanding of these composite depositional processes and improves palaeoenvironmental reconstructions derived from beach ridges.
Modelling Ediacaran metazoan–microbial reef growth
Curtis, Andrew; Wood, Rachel; Bowyer, Frederick; et al. (2021)
Sedimentology
Throughout the Phanerozoic, sessile metazoans grew in close association with various microbial carbonates to form reefs. The first metazoans with calcareous hard‐parts appeared in the terminal Ediacaran, ca 550 million years ago, and these also commonly grew associated with microbial mats, thrombolites and stromatolites, to form the oldest known metazoan–microbial reefs. These hard‐parts also formed the first skeletal (bioclastic) carbonate sediments, which increased to dominate shallow marine carbonate sedimentary production during the Phanerozoic. Here the growth dynamics and sedimentary interactions between Ediacaran microbial–metazoan reefs and their bioclastic products are described based on reef complexes from the Nama Group, Namibia (ca 547 Ma), and the first three‐dimensional numerical models are constructed to parametrize these dynamics. These reefs are observed to form large domal mounds and columns neighbouring locally high rates of bioclastic sediment accumulation, and commonly evolve to flat‐topped surfaces overlain by sediment. This model is parsimonious, embodying a single dynamic rule: metazoans attach to microbialite mounds which grow radially into free space shedding bioclasts in proportion to metazoan production. Models evolve mounds into columns due to spatial competition, and produce an oscillating interplay between mound expansion and smothering that results in an inter‐fingering of microbialite mound and detrital sediment. This dynamic is shown to be non‐linear in the proportion of bioclastic sediment produced. Smothering by bioclastic sediment is also demonstrated to both reduce the rate (by volume) of subsequent mound growth, and to overwhelm the growing mat surfaces of stromatolites: after a threshold is reached in the rate of bioclastic sediment deposition, sediment terminates all stromatolite growth. These models show that the general characteristics of field observations can be explained by a single dynamic rule, and that reef‐sourced bioclasts may make an important local contribution to Ediacaran to Cambrian microbial–metazoan reef dynamics – a contribution that remains important throughout the Phanerozoic.
Depositional system and palaeoclimatic interpretations of Middle to Late Pleistocene travertines: Kocabaş, Denizli, south-west Turkey
Toker, Ezher; Kayseri-Özer, Mine S.; Özkul, Mehmet; et al. (2015)
Sedimentology
Pyroclastic dune bedforms: macroscale structures and lateral variations. Examples from the 2006 pyroclastic currents at Tungurahua (Ecuador)
Douillet, Guilhem A.; Bernard, Benjamin; Bouysson, Mélanie; et al. (2019)
Sedimentology
Pyroclastic currents are catastrophic flows of gas and particles triggered by explosive volcanic eruptions. For much of their dynamics, they behave as particulate density currents and share similarities with turbidity currents. Pyroclastic currents occasionally deposit dune bedforms with peculiar lamination patterns, from what is thought to represent the dilute low concentration and fluid‐turbulence supported end member of the pyroclastic currents. This article presents a high resolution dataset of sediment plates (lacquer peels) with several closely spaced lateral profiles representing sections through single pyroclastic bedforms from the August 2006 eruption of Tungurahua (Ecuador). Most of the sedimentary features contain backset bedding and preferential stoss‐face deposition. From the ripple scale (a few centimetres) to the largest dune bedform scale (several metres in length), similar patterns of erosive‐based backset beds are evidenced. Recurrent trains of sub‐vertical truncations on the stoss side of structures reshape and steepen the bedforms. In contrast, sporadic coarse‐grained lenses and lensoidal layers flatten bedforms by filling troughs. The coarsest (clasts up to 10 cm), least sorted and massive structures still exhibit lineation patterns that follow the general backset bedding trend. The stratal architecture exhibits strong lateral variations within tens of centimetres, with very local truncations both in flow‐perpendicular and flow‐parallel directions. This study infers that the sedimentary patterns of bedforms result from four formation mechanisms: (i) differential draping; (ii) slope‐influenced saltation; (iii) truncative bursts; and (iv) granular‐based events. Whereas most of the literature makes a straightforward link between backset bedding and Froude‐supercritical flows, this interpretation is reconsidered here. Indeed, features that would be diagnostic of subcritical dunes, antidunes and ‘chute and pools’ can be found on the same horizon and in a single bedform, only laterally separated by short distances (tens of centimetres). These data stress the influence of the pulsating and highly turbulent nature of the currents and the possible role of coherent flow structures such as Görtler vortices. Backset bedding is interpreted here as a consequence of a very high sedimentation environment of weak and waning currents that interact with the pre‐existing morphology. Quantification of near‐bed flow velocities is made via comparison with wind tunnel experiments. It is estimated that shear velocities of ca 0·30 m.s−1 (equivalent to pure wind velocity of 6 to 8 m.s−1 at 10 cm above the bed) could emplace the constructive bedsets, whereas the truncative phases would result from bursts with impacting wind velocities of at least 30 to 40 m.s−1.
The sediment budget and dynamics of a delta-canyon-lobe system over the Anthropocene timescale: The Rhone River delta, Lake Geneva (Switzerland/France)
Silva, Tiago A.; Girardclos, Stéphanie; Stutenbecker, Laura; et al. (2019)
Sedimentology
Human‐initiated autocyclic delta failures
Gastineau, Renaldo; Girardclos, Stéphanie; Kremer, Katrina; et al. (2025)
Sedimentology
River regulations have resulted in changes in the hydrology and particle budgets of fluvial systems. Since the 19th century, many rivers have been significantly modified to control flood hazards, to gain land from swamp areas for agricultural purposes, and to stabilize river-levels and lake-levels to facilitate navigation. These dramatic changes of the river courses have impacted the sediment budgets and grain-size dissemination along them as well as the sediment distribution at the delta mouths in the downstream lakes, which could lead to slope instabilities. Deposits of such catastrophic lacustrine mass movements caused by delta collapses have been, for instance, observed in Lake Brienz (Switzerland), where relatively thick (0.5 to 1.3 m) and voluminous (>1 million m3) megaturbidites are stacked in the deep basin witnessing these processes. This study uses sediment cores and seismic data to reconstruct the megaturbidites' history in Lake Brienz. Data reveal that mass-movement deposits, originating from the Aare Delta, one of the two main inflows, have mean ages of 1853, 1905, 1942 and 1996 ce and that they were unprecedented in, at least, half a millennium. The fact that the numbers of floods and earthquakes have not changed radically over this time period implies that human impact is the most likely explanation for these failure events. Therefore, the recurrent delta collapses are attributed to the focused sediment accumulation at the front of the channelized inflow in the proximal delta region, caused by the modification of the Aare River through its straightening and channelization during the late 19th century. These findings indicate that river regulation can affect delta sedimentation, leading to autocyclic delta collapses. Those collapses, in turn, can potentially generate tsunami waves, representing an additional natural hazard for shoreline communities.
Fingerprint of tropical climate variability and sea level in sediments of the Cariaco Basin during the last glacial period
Deplazes, Gaudenz; Meckler, Anna N.; Peterson, Larry C.; et al. (2019)
Sedimentology
Sedimentary evolution and lake level fluctuations of Urmia Lake (north-west Iran) over the past 50 000 years; insights from Artemia faecal pellet records
Sari, Selma; Mohammadi, Ali; Schwamborn, Georg; et al. (2024)
Sedimentology
A 25 m long sediment core from hypersaline Urmia Lake (north-west Iran) was studied for the Late Quaternary depositional history and palaeoclimate variations using the abundance and compositional characteristics of Artemia faecal pellets. Sediment analysis is supported by scanning electron microscopy - energy dispersive X-ray spectroscopy, organic and inorganic carbon content measurements, and stable isotopes (delta C-13 and delta O-18) from faecal pellet carbonates. The imprecise chronology of the core back to 50 kyr bp is supported by ten radiocarbon ages from faecal pellets and bulk sediments. The palaeoenvironmental record is subdivided into four periods: (i) During much of Marine Isotope Stage 3, a period of lake level lowering is characterized by a decreasing amount of faecal pellets, and an increasing amount of coated grains, sulphate minerals and reworked shell fragments. (ii) During late Marine Isotope Stage 3 and early Marine Isotope Stage 2 a lake level lowstand and a lake floor exposure is interpreted based on the relatively low abundance of pellets, which are multicoloured and appear together with volcanic lithics and rounded sulphate minerals. (iii) During late Marine Isotope Stage 2 the record is devoid of pellets but dominated by large sulphate crystals suggesting a prolonged low lake level. (iv) During Marine Isotope Stage 1 a relative lake level highstand is rapidly established with sediments that are highly abundant in fresh pellets. The modern lake level lowstand is represented by a salt crust. The delta C-13 and delta O-18 records measured from faecal pellet carbonates suggest a link with the precipitation versus evaporation balance in the lake over time. From bottom to top the linear trend towards more negative delta values illustrates the increasing amount of precipitation arriving at the lake from the Late Pleistocene to the Holocene. Two prominent isotope minima during the Late Pleistocene and one prominent minimum in the early Holocene mark relative high lake levels, which can also be linked to Lake Van in Turkey.
Microstratigraphy and palaeoenvironmental implications of a Late Quaternary high-altitude lacustrine record in the subtropical Andes
Guerra, Lucia; Martini, Mateo A.; Vogel, Hendrik; et al. (2022)
Sedimentology
High-mountain lake records in semiarid foreland settings, such as the central Andes of North-western Argentina, are highly restricted and often deprived of well-preserved microstratigraphic information to analyze palaeoenvironmental changes and their causes, particularly for periods prior to the Last Glacial Maximum. Laguna La Salada Grande (23°S/65°W, 4063 metres above sea-level) is a closed shallow lake located at Cordillera Oriental, North-western Argentina with a unique depositional record, including geomorphic and stratigraphic evidence of palaeoenvironmental changes since the Late Pleistocene. In order to understand the depositional dynamics of this mountain lacustrine system at different timescales, limnogeological multiproxy analyses together with a radiocarbon and 210Pb-based chronology were applied on massive and laminated sediments from La Salada Grande. Laminated deposits were further analyzed using novel sub-centimetric mineralogical, textural and geochemical automated methods (including a combination of micro-X-ray fluorescence and quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN®). Thick laminated microfacies at the beginning of the sequence record a deep and organic matter productive palaeolake prior to ca 34 ka (1 ka = 1000 years before 1950), that changed into a highly fluctuating shallower-palaeolake with frequent detrital influxes after ca 34 ka. Microstratigraphy of the coarser-grained detrital laminae between 31 ka and 25 ka reveals irregular and probably sub-centennial high-energy discharge events, pointing to convective atmospheric activity as the main trigger. After ca 21 ka the lake evolved to deeper water-level conditions resulting in fine-grained deposits with limited delivery of coarse-grained sediments, followed by an abrupt lake level drop and incision. The multi-millennial palaeoenvironmental reconstruction of La Salada Grande, and its correlation with other palaeoclimate records, shows a close link between the lacustrine depositional processes and palaeoclimate changes associated with the South American summer monsoon dynamics. This multifocal research in such an understudied environment provides key knowledge about lacustrine functioning and discharge events−climate interactions of mountain lakes of semi-arid climates.

Publications 1 - 10 of 12

Journal: Sedimentology

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