Sedimentology

doi: 10.1111/sed.12896pmid: N/A

Pantopoulos, George; Manica, Rafael; McArthur, Adam D.; Kuchle, Juliano; Felletti, Fabrizio

doi: 10.1111/sed.12960pmid: N/A

Fractionation of particles in deep‐water sediment gravity flows is an important factor in the resulting deposit and for discriminating sedimentary environments, but remains poorly understood. Quantitative characterization of particle shape was performed for more than ten‐thousand particles of experimental gravity flow experiments (both of cohesive and non‐cohesive nature) made using coal and kaolin particles. Eleven particle shape parameters were calculated and their distribution and trends within the experimental basin were evaluated. Results indicate the existence of non‐normal distributions and observable correlations between particle shape parameters. Shape parameters such as circularity and roundness are dominant controls on shape variation. Strong correlations exist between mean shape parameters and along‐flow distance from the source for particles in non‐cohesive flow experiments. Important differences were observed between shape parameter distributions of particles sampled at different areas within the experimental basin, which can be grouped based on their depositional setting (proximal or distal) using multivariate statistical analysis, especially for the non‐cohesive flow experiments. A tendency for more elongated and irregularly‐shaped particles at the more distal and marginal areas of the studied experimental basin was observed and validated by previous field studies in real‐world deep‐marine deposits. Besides, fractionation of particles is less‐pronounced in cohesive flows compared with non‐cohesive ones suggesting the soundness of discrimination of depositional settings based solely on particle shape characteristics is strongly dependent on parent flow characteristics. Yet, results highlight the potential of particle shape analysis in revealing spatial particle shape trends due to hydrodynamic fractionation and discriminating different depositional settings within submarine fans. This methodology may be applied to seafloor and subsurface samples to help identify the flow process and depositional environment.

Luo, Lianchao; Wen, Huaguo; Brogi, Andrea; Capezzuoli, Enrico; Pérez, Andrea Martin

doi: 10.1111/sed.12961pmid: N/A

Travertine mounds are common spring‐constructed landforms with highly variable geometries, but factors controlling their development have not yet been fully understood. To investigate processes linked with their lateral and vertical growth, this study investigated travertine mounds at Heinitang (China) and compared them with typical mounds around the world. Calcium concentration variation modelling and height evaluation of travertine mounds were also performed. The lateral extent of travertine mounds was found to be mainly controlled by Ca2+ and HCO3‐ concentrations and water discharge: relatively small metre‐scale mounds, like those from Heinitang, are largely the products of Ca2+‐deficiency (<150 mg L−1, commonly <100 mg L−1) or HCO3‐‐deficiency (<500 mg L−1) springs with low discharges (<0.1 L s−1), whereas springs with higher Ca2+ and HCO3‐ concentrations and discharges give rise to the formation of wider mounds. Additional factors affecting mound lateral development include infiltration, evaporation, micro‐organisms, water cooling, CO2 degassing and flow paths. Height of travertine mounds cannot be simply considered to represent the piezometric surface, because the vertical growth of travertine mounds is also influenced by the water table change triggered by tectonic pulses and climate fluctuations, and the closing of conduits induced by self‐sealing. The extinction of travertine mounds at Heinitang is, for example, probably caused by the water table lowering triggered by earthquakes or climate drying after 4 kyr bp. These findings offer new inputs for the better understanding of factors controlling travertine mound development and might assist in the reconstruction of fluid properties, hydrodynamics, tectonics and climate fluctuations in fossil geothermal systems with travertine mounds.

Zhao, Zhongwei; Mitchell, Neil C.; Quartau, Rui; Moreira, Sandra; Rusu, Liliana; Melo, Carlos S.; Ávila, Sérgio P.; Das, Diya; Afonso, Pedro; Pombo, Joaquim; Duarte, João; Rodrigues, Aurora; McArthur, Adam

De Gelder, Gino; Doan, Mai Linh; Beck, Christian; Carlut, Julie; Seibert, Chloé; Feuillet, Nathalie; Carter, Gareth D. O.; Pechlivanidou, Sofia; Gawthorpe, Robert L.; McArthur, Adam

doi: 10.1111/sed.12964pmid: N/A

A major challenge in subaqueous palaeoseismology is to understand the relationship between an earthquake/tsunami and a sedimentary event deposit recorded in drillcores. Expedition 381 of the International Ocean Discovery Program was dedicated to understanding the development of the Corinth Rift, Greece. Its drilled cores provide a potentially important resource to better understand depositional mechanisms of sedimentary event deposits within changing open marine to (semi‐)isolated environments. To achieve this, U‐channels and spatula samples were analysed from the topmost part (0–65 m below seafloor maximum depth) of holes M0078B and M0079A (ca 0–25 ka), using high‐resolution X‐ray microtomography in combination with grain‐size, magnetic and X‐ray fluorescence measurements. Structures and grain fabric are resolved down to 10 μm in voxel size, characterizing the geometry of the basal surface of ‘turbidite+homogenite’ sedimentary event deposits, and the internal base‐upward evolution at high‐resolution scale. This analysis suggests that these types of deposits are more complex than previously proposed, especially at the transition between the basal coarse turbidite sub‐unit and the fine‐grained homogenite upper sub‐unit, as well as within the homogenite. Combined with the other observations and parameters, X‐ray microtomography results are consistent with the interpretation of the Corinth ‘turbidite+homogenite’ deposits as having predominantly originated from seismic and/or aseismic slope failures followed by tsunami/seiche effects, despite subtle differences according to depositional environment.

Holz Boffo, Carolina; Bayer da Silva, Daniel; Manica, Rafael; de Oliveira Borges, Ana Luiza; Roessler Viana, Adriano; Baas, Jaco

doi: 10.1111/sed.12966pmid: N/A

A laboratory tank experiment tested whether a subsurface flow from a confined aquifer causes slope instability and leads to the formation of pathways for sediment transfer from shallow to deep water when the subsurface flow discharges through the face of a subaqueous slope. A sandy slope with multilayer stratigraphy was built inside the tank, and a confined aquifer was simulated within the stratigraphy. To induce groundwater flow out of the face of the slope, water was injected in the proximal zone of the confined aquifer at progressive increased discharge. Sediment movement on the slope occurred by rolling of particles, fluidized flow, grain flow and slides. The fluctuation of phreatic pressure in the confined aquifer was measured by a set of piezometers, from which the hydraulic gradient generated by the water flow moving towards the slope was determined. This study determined that the mass movements started when the imposed injected flow rate was greater than the hydraulic conductivity capacity of the simulated aquifer, using the flow capacity calculated from the Darcy equation for porous media. The various physical parameters used in the experiment were found to scale well to natural prototypes. Moreover, the patterns of erosion and deposition in the physical simulation resembled natural features observed in seismic‐geomorphology maps and modern deep‐sea physiography. Therefore, water sapping by a confined aquifer flow is a potential mechanism for slope erosion and instability and for the formation of pathways connecting shallow‐water and deep‐water environments.

Wang, Jie; Dai, Zhijun; Fagherazzi, Sergio; Long, Chuqi; Ghinassi, Massimiliano

doi: 10.1111/sed.12970pmid: N/A

Sediments in deltaic tidal flats regulate physical and chemical processes. Grain‐size distribution plays an important role in determining sediment dynamics and substrate properties. However, it is challenging to quantify large‐scale depositional environments in intertidal flats, due to time‐consuming grain‐size analyses and sparse sedimentary information extracted from scattered sediment samples. In this study, a novel terrestrial laser scanner (TLS) based method was developed to characterize the substrate of an intertidal flat. Surface sediment samples in the Nanhui flats in the Yangtze Delta, China, and the corresponding waveform amplitudes of TLS echoes at fixed sampling sites were collected for a total of 22 months. A negative logarithmic relationship was found between the sediment sand fraction, average grain size, D50, and corrected waveform amplitude of TLS echo in different hydro‐meteorological conditions. The mean of average grain size of five sediment sampling sites along a transect was 58.78 μm when measured by traditional grain‐size analysis, and 49.48 μm when calculated with the proposed logarithmic equation. The mean error at each site was up to 21.77%. The mean error for the sand and silt fraction at each location was as high as 27.28% and 21.75%, respectively. The spatial distribution pattern of TLS‐based average grain size in the entire study area was consistent with the measured pattern with a Root Mean Square Error of 13.83 μm. These errors could be caused by the accuracy of the TLS waveform amplitude correction and by limits of the method in recognizing different substrates. The effects produced by the presence of microphytobenthos (for example, cyanobacterial mats or diatom biofilms) or bedforms have not been investigated and may have affected the results. The TLS‐based grain‐size measurements can rapidly and effectively discriminate sediment characteristics, thus avoiding traditional time‐consuming measurements. It is expected that the TLS‐based method proposed here will have wide applications in shoreline studies, especially in inaccessible tidal flats.

Ingalls, Miquela; Fetrow, Anne C.; Snell, Kathryn E.; Frantz, Carie M.; Trower, Elizabeth J.; Rogerson, Mike

doi: 10.1111/sed.12967pmid: N/A

Stromatolites have often served as a diagnostic carbonate facies for deep‐time palaeoclimatic and geobiological studies because they may form under favourable environmental conditions for microbially mediated carbonate production. ‘Giant’ (<5 m) stromatolites occur in the Laney Member of the Eocene Green River Formation in the Vermillion Creek section of the Sand Wash Basin (north‐west Colorado, USA). Giant stromatolite growth was hypothesized to have been promoted by both availability of large substrates as nucleation sites and physicochemical factors, including increased calcium carbonate mineral saturation states due to the generally warmer Eocene climate and a dynamic period in Lake Gosiute’s hydrological balance. Depositional horizons of giant stromatolites were observed at two distinct stratigraphic levels, which demonstrated that the formation of the giant morphotype was not a unique occurrence, and provided an opportunity to examine both onset and cessation of stromatolite development. Coincident increases in carbonate clumped isotope‐derived temperatures, the carbon and oxygen isotopic compositions of lake water (δ18Ow), carbonate mineral saturation states (Ω) estimated by ooid size, and salinity estimated by ostracod assemblages demonstrated that formation of giant stromatolites was facilitated by lake level drawdown. Decreased lake levels: (i) promoted carbonate precipitation; and (ii) positioned benthic microbial communities within the photic zone. Field and petrographic analyses revealed that the giants preserved micritic laminations, ‘trapped and bound’ grains, and aragonite fans, interpreted as reflecting contributions from both microbially mediated and abiotic carbonate mineral precipitation. Field and microscopic sedimentological and stable isotope data indicated that giant stromatolite growth ceased as a result of subaerial exposure of mounds during lake level lows. Although microbial mediation of carbonate chemistry was seemingly important for initiation of stromatolite growth, this work demonstrated that stromatolite macromorphology was dominantly controlled by availability of large substrates, lake level and resultant solute chemistry, i.e. increased Ω.

Marini, Mattia; Patacci, Marco; Felletti, Fabrizio; Decarlis, Alessandro; McCaffrey, William; Valdez, Victoria

doi: 10.1111/sed.12968pmid: N/A

Basal interaction beneath frontally‐emergent mass‐transport deposits has been widely documented in seismic data, but its effect on deposit heterogeneity not convincingly calibrated at outcrop. Several blocky mass‐transport deposits occur as part of the Late Eocene Ventimiglia Flysch of north‐west Italy, comprising slope‐derived marlstones, representing the original slide, and turbidite material, entrained after erosion of substrate sediments; this study reports on the best exposed. Correlation of twenty‐nine sedimentary logs tied to the hosting turbidite stratigraphy allows thickness and facies changes to be tracked over an area of ca 40 km2, spanning the erosionally confined to emergent transition. A basal erosion >55 m deep and several kilometres wide confines a marlstone megabreccia containing megaclasts of up to 1 km across, interpreted as the product of a submarine slide originated from a sector collapse of the western basinal slope. Approaching the downstream limit of this erosional confinement the marlstone megabreccia is replaced by highly deformed turbidites that, more distally, are in turn superseded by a debrite composed dominantly of turbidite material. Structural and textural characteristics suggest that the distally‐extending debrite was deposited by a forerunner debris flow formed as substrate sediments liquefied ahead of the advancing slide, whereas the deformed turbidites were accumulated at slide margins shortly before it came to a halt. Farther downstream, the debrite is a few metres thick and sits onto the undisturbed basin floor, indicating that the mass flow became emergent distally, and was sufficiently mobile (with an estimated runout in excess of a few tens of kilometres) to redistribute the material evacuated from the basal erosion (>0.5 km3). The mass‐transport deposit terminates upward into a graded marlstone conglomerate deposited by a late‐stage multiphase flow. This study provides a rare insight into facies variation in a frontally‐emergent mass‐transport deposit, showing how basal interaction with poorly consolidated substrates can result in erosional confinement and significant transformation of the parental flow.

Tentori, Daniel; Mancini, Marco; Milli, Salvatore; Stigliano, Francesco; Tancredi, Simone; Moscatelli, Massimiliano; Sheldon, Nathan

doi: 10.1111/sed.12969pmid: N/A

This study reports a high‐resolution micromorphological characterization of floodplain deposits to investigate the relationships among compositional, textural and geotechnical data, and integrate soil micromorphology with sequence stratigraphy. Compositional and textural characterization of facies associations and soil features are calibrated against geotechnical parameters. The latter, obtained from cone penetration and pocket penetrometer tests from a borehole advanced 60 m into the Tiber channel belt and floodplain, show that depositional features and post‐depositional modifications are intrinsically associated with cone penetration test parameters: cone resistance; sleeve friction; and friction ratio. Petrographic and micromorphological features document pedogenetic modifications across stratigraphic markers evidenced by faunal and plant activity, accumulation of peat, and typified by precipitation of heavy metals, iron oxides and secondary carbonates. All of these features developed in correspondence with alluvial flooding surfaces that are correlated with non‐marine and marine flooding surfaces recognized in the transgressive and highstand coastal and lagoonal deposits of the Tiber Depositional Sequence. These observations may serve as a model to reconstruct the sequence‐stratigraphic evolution of ancient relict soils. Nevertheless, additional criteria (for example, their stratigraphic position and correlative surfaces) are necessary to adequately interpret the genesis of such low‐rank stratigraphic surfaces. This work demonstrates that a combination between sedimentological and stratigraphic observations and soil micromorphology can be critical to supplement field observations and determine the relative effect of pedogenic and depositional processes on the organization, composition and texture, and geotechnical properties of floodplain in urban areas.