Depositional Record最新文献

Storm-flood-dominated deltas are sedimentary systems in which a complex interplay of hydrodynamic processes occurs during storms (e.g. tropical cyclones) due to the coeval action of continental and oceanic processes. This paper reports on a superbly exposed, 135.5 m thick stratigraphic succession of the Pleistocene Cholan Formation exposed along the Da'an River, Taiwan. The sedimentary succession comprises alternating mudstone and sandstone, is mostly fine-grained, and exhibits multiple event beds that record deposition during tropical cyclones and post-depositional deformation features produced during earthquakes. Detailed facies analyses reveal that deposition towards the base of the succession occurred in the palaeo-Taiwan Strait in storm-flood-dominated prodelta and delta-front environments passing upwards into delta-plain environments. Tropical cyclone beds are encountered throughout the subaqueous storm-flood delta successions, and are identified by (i) trough cross-stratified sandstone bedsets with erosive bases that contain both mud clasts and mudstone beds, (ii) sandstone with aggrading wave ripples and (iii) hummocky cross-stratified sandstone with rare gutter casts filled with coal fragments and shell remains. Tropical cyclone deposits are either top-down burrowed or capped by massive or laminated mudstone. Seismites are rare and are mainly recognised through soft-sediment deformation of beds; they do not show evidence of slope failure. Compared to storm-flood delta successions described elsewhere, the Cholan Formation shows significantly fewer oscillatory-generated sedimentary structures and gutter casts. This difference is attributed to the Cholan Formation being deposited in and along the margin of a strait characterised by strong shore-parallel currents and relatively small storm waves due to its position between Taiwan and mainland China. This study refines depositional process interpretations of the Cholan Formation, provides criteria for recognising storm-flood delta deposits in tectonically active straits with multiple sediment sources fed by steep drainages and short river catchments, and provides additional criteria for recognising tropical cyclone deposits in shallow-marine settings.

When sea-level rise slowed down in the middle Holocene, fluvial and coastal sediments filled the newly created accommodation, whilst others remained largely unfilled because of limited sediment supply. In view of current and future rapid sea-level rise, the question arises how estuarine systems will adapt and whether the land-level rise may keep up. Besides geological data and conceptual models of large-scale and long-term estuary filling, little is known about the filling process during sea-level rise on the decadal-to-centennial time scale that is relevant for society. This study focusses on how sea-level rise affects the morphological and hydrodynamic development of filling estuaries. To this end, scaled laboratory experiments were conducted in a tilting flume facility that creates bidirectional tidal currents and develops entire estuaries. A net importing estuary with sand, mud and vegetation was formed that was subjected to linear sea-level rise. Findings show less of the imported sand was deposited landward following sea-level rise than in an experiment without sea-level rise. The bay-head delta and the flood-tidal delta retained nearly enough sediment to keep up with sea-level rise, whilst the tidal embayment in between drowned except for the highest vegetated bars. Sea-level rise also reduced vegetation survival and sprouting potential, as prolonged inundation increased mortality, negating the potential eco-engineering effect. This resulted in lower vegetation coverage with sea-level rise than under constant sea level. These findings suggest that sea-level rise may cause natural systems to drown even if nearly sufficient sediment is available to fill the newly created accommodation, particularly in areas further away from the fluvial and marine sediment sources. Finally, depending on the sea-level rise rate, the flood-tidal delta may show back-stepping like fluvial deltas, but in the reverse direction towards the sea.

Reactive transport modelling is increasingly deployed to quantitatively evaluate conceptual models of diagenetic processes. However, construction of models of complex systems involves trade-offs between accuracy and simplification. This tension is explored for models of fault-associated dolomitisation by sea water convection in a syn-rift carbonate platform, evaluating the contribution of incorporating stratigraphic growth and fault propagation. Simulations of the high heat flux southern margin of the Derbyshire Platform (Northern England), with heterogeneous matrix permeability that reflects the evolving stratal architecture and burial compaction focusses dolomitisation in more permeable units at all depths. A permeable platform margin fault zone enhances dolomitisation in a broad area on the upper slope and margin, and to a lesser but significant extent, across the interior as platform top waters are entrained and discharge via the fault. Stepwise simulation of flow and reactions during stratigraphic growth suggests that static models over-predict dolomite abundance in younger sediments and show how regions optimally supplied with reactants and heat to drive dolomite formation migrate vertically and laterally during platform growth. Dolomitisation intensity increases with depth due to greater time for reactions and kinetically favourable temperatures. Adding the fault zone to this model focusses and accelerates flow, giving a more spatially restricted dolostone body and reducing dolomitisation temperature. Changes in fault connectivity with the surface of the evolving platform shift fluid flow pathways and change the rate and temperature of dolomite formation. Results concur with petrographic, isotopic and geochemical observations of the early dolomite on the Derbyshire Platform. This work demonstrates the importance of understanding diagenesis as the product of an evolving set of processes that respond to geological and palaeoenvironmental changes rather than as a sequence of individual diagenetic events. This is particularly critical for reactions, such as dolomitisation by geothermal convection of sea water, which occur over timescales synchronous with platform development.

This work investigates how the surface textures and morphology of pyroxene grains evolve during their source-to-sink history. This study applies to detrital clinopyroxenes concentrated in coastal dune sands of the Gulf of Mexico which were sourced in the Trans Mexican Volcanic Belt then transported and deposited in environments subject to limited chemical weathering. The composition and morphology of the pyroxenes was characterised using single-grain geochemical analysis and surface texture imagery with a novel approach based on the compactness property to assess the shape of minerals. This reveals heterogenous diopside-augite populations, displaying mineral morphologies dominantly controlled by impact breakage along cleavages, little physical abrasion along their edges and with limited evidence for chemical weathering. Mechanical surface textures dominate over mechanical/chemical and chemical surface textures. These mechanical surface textures are preserved primarily as flat cleavage surfaces and rounded edges inherited from fluvial-intertidal and aeolian transport, respectively. Mechanically/chemically induced surface textures are preserved as elongated depressions. Chemical surface textures are sparse and mostly represented by mammillated textures that suggest local dissolution under subaqueous conditions. The scarcity of chemical surface textures is attributed to frequent fragmentation of the clinopyroxenes along cleavages and limited chemical weathering during transport of the observed populations. Clinopyroxene grains in the coastal dune sands primarily retain surface characteristics from fluvial transport. Although the breakage of minerals along cleavages can obscure their original morphology under a weathering-limited erosion regime, this study shows how surface textures and morphology of pyroxene grains is used to determine episodes of transport and deposition close to volcanic environments. The use of the compactness property as a shape descriptor measurement of particles provides an alternative approach to observe how clinopyroxene remains unaltered despite the high energy conditions of the coastal area.

Magnesian Limestone zoned dolomite (red and non-luminescent zones) now partly dedolomitized), calcite (yellow luminescence), blue luminescent albite has non-luminescent overgrowths) Mansfield Quarry, Nottinghamshire. Photo credit: J.A.D. Dickson.

Using lake-sediment cores to document past seismicity requires a comprehensive understanding of possible lateral variations in depositional processes. This study aims to reveal the lateral variations in earthquake-induced event deposits throughout Lake Iznik, a large lake located on the middle strand of the North Anatolian Fault. Based on stratigraphic, sedimentological and geochemical analyses of 14 sediment cores from two subbasins across the lake, five different types of event deposits (T1–T5) were identified and characterised. One event deposit type (T5) is restricted to a delta mouth, characterised by the occurrence of authigenic Fe-Mn carbonates and interpreted to result from flood events. The four other types of event deposits are characterised by their synchronicity between cores and their age consistency with historical earthquakes and are interpreted to be likely generated by earthquakes. The locally prominent 1065 CE historical earthquake that ruptured the sub-lacustrine Iznik Fault produced at least three different types of event deposits. One deposit type (T2) is only observed for this very local earthquake, implying that the type of event deposit might also depend on ground-motion parameters. At the lake scale, the occurrence of various event deposits depends on the flow distance from the source of sediment destabilisations to the coring site.

Unconsolidated artificial ground is an ever-increasing feature on the Earth's surface but it poses various challenges such as pollutant release and ground instability. The process of lithification could be an important factor in changing the properties of artificial ground and ameliorating these challenges. In this study, a lithified deposit of a furnace slag associated with a former iron and steel works in Scotland was analysed to determine the mechanisms and drivers of lithification. Scanning electron microscope analysis showed that Ca leached from around the edges of clasts of slag through reaction of the chemically unstable slag with water from an adjacent water body. Dissolution of Ca (and OH⁻) from the slag caused the water in contact with the slag to become hyperalkaline, facilitating ingassing and hydroxylation of CO₂ from the atmosphere (fingerprinted through carbon isotope analysis). Reaction of the dissolved Ca and CO₂ led to precipitation of calcite. Scanning electron microscope analysis showed the calcite is distributed between slag clasts, forming rims around clasts and cementing clasts together into a solid rock-like mass. Understanding the mechanisms and drivers of lithification in artificial ground will be important, given its widespread nature particularly in urban areas where artificial ground is the substrate of most development.

Sketch diagram illustrating the various hydrodynamic processes occurring in coastal to shelf environments, with numbers referring to articles from this issue.

Mixed siliciclastic and carbonate sediments are common in the stratigraphic record, but fully homogenised mixes are not. Many occurrences of mixed sediment sequences are dominated by end-members with stacking of ‘nearly pure’ lithfacies (e.g. cyclothems containing alternating sandstone, limestone and coal units). The Plio-Pleistocene sediments within south-west Florida provide insights into the occurrence of fully homogenised siliciclastic/carbonate deposits. In all defined environments from lagoon to supratidal to inner tidal to beach to offshore to coral reef, quartz sand coexists with carbonates. Perhaps the key feature that allowed full homogenisation of the sediments within all facies and subfacies was the relatively shallow water (<10 m), which facilitated mixing during low-order eustatic sea-level events and storms. However, four factors contributed to the full homogenisation of the sediment types without termination or inhibition of carbonate organism growth. These factors are (1) the shallow water allowing wave-driven sediment transport (all environments within the wave orbital depth), (2) close proximity and perhaps irregular nature of the depositional environment boundaries, (3) low influx rate of quartz sand via longshore transport, and (4) the lack of significant terrigenous mud transport into the system. Mixing processes at the large-scale included movement of sediments from one depositional environment to another during storms, mixing along facies boundaries, and in situ mixing within autochthonous and parautochthonous mollusc death assemblages. At the smaller scale, mixing occurred by bioturbation and diagenetic dissolution of carbonate skeletal grains during minor high sea-level stands.

When compared to their temperate coastal counterparts, sediments deposited and preserved along arid aeolian to shallow-marine margins remain relatively poorly understood, particularly at the scale of lithofacies units and architectural elements. These systems often record evidence for relative sea-level change within sedimentary basins. This work focusses on the Entrada–Curtis–Summerville formations that crop out in central eastern Utah, USA, and provides a detailed analysis of the aeolian Moab Member of the Curtis Formation (informally known as the Moab Tongue) that was impacted by cycles of marine transgressions and regression in the late Jurassic. This study utilises photogrammetry, sedimentary logging and sequence-stratigraphical analysis techniques. Results indicate that four short-lived transgressive-regressive cycles are preserved within the Moab Member, followed by a broad regressive event recorded at the transition between the Curtis and Summerville formations. These cycles relate to changes in the relative sea level of the Sundance Sea and the deflation and expansion of the neighbouring aeolian dune field. During periods of normal regression, marine sediments displayed evidence of tidal and wave action, whereas the continental domain was characterised by growth of the aeolian system. However, when regression occurred within optimal physiographic conditions such as a restricted, semi-enclosed basin, and at sufficient magnitude to outpace erg expansion, this acted to shut-down bedform development and preservation. A rapid restriction of aeolian sediment availability and the inability of the dune field to recover resulted in the formation of deflationary sandsheets, arid coastal plain strata and contemporaneous shallow-marine deposits that are starved of wind-sourced sediments. This study highlights how a rapidly developing high-magnitude regression can lead to the overall retraction of the erg. Deciphering the evolution and sequence stratigraphical relationships of arid aeolian to shallow marine margins is important in both understanding environmental interactions and improving the characterisation of reservoir rocks deposited in these settings.