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1.
Timothy Pietsch Justine Kemp Colin Pardoe Rainer Grün Jon Olley Rachel Wood 《第四纪科学杂志》2019,34(8):662-673
Kiacatoo Man, a large, rugged Aboriginal adult buried in the Lachlan riverine plains of southeastern Australia, was discovered in 2011. Laser‐ablation uranium series analysis on bone yielded a minimum age for the burial of 27.4 ± 0.4 ka (2σ). Single‐grain, optically stimulated luminescence ages on quartz sediment in which the grave had been dug gave a weighted mean age of 26.4 ± 1.5 ka (1σ). Luminescence samples from the grave infill and from sediment beneath the grave exhibit overdispersed dose distributions consistent with bioturbation or other disturbance, which has obscured the burial signal. The overlap between the minimum (U‐series) and maximum (luminescence) ages places the burial between 27.0 and 29.4 ka (2σ). Luminescence ages obtained from the channel belt of between 28 ± 2 and 25 ± 3 ka indicate that fluvial sedimentation was occurring before the Last Glacial Maximum, which is consistent with the broader geomorphic setting. Together, these results are internally and regionally consistent, and indicate that Kiacatoo Man was one of the more ancient individuals so far identified in Australia. His remains are important to our understanding of patterns of biological variation and other processes that have shaped people in the Murray‐Darling Basin through time. Copyright © 2019 John Wiley & Sons, Ltd. 相似文献
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Aurora C. Elmore Robert C. Thunell Richard Styles David Black Richard W. Murray Nahysa Martinez Yrene Astor 《Journal of South American Earth Sciences》2009,27(2-3):197-210
The varved sediments that accumulate in the Cariaco Basin provide a detailed archive of the region’s climatic history, including a record of the quantity of fluvial and wind-transported material. In this study, we examine the sedimentological characteristics (clay mineralogy and grain size) of both surface sediments and sinking lithogenic material collected from sediment trap samples over a three-year period from 1997 to 2000. Data from biweekly sediment trap samples show a tri-modal particle size distribution, with prominent peaks at 2, 22 and 80 μm, indicating sediment contributions from both eolian and fluvial sources. The clay mineralogy of the water column samples collected from 1997 to 1999 also shows distinctive characteristics of eolian and fluvial material. An examination of surface sediment samples from the Cariaco Basin indicates that the Unare River is the main source of riverine sediments to the eastern sub-basin. By combining these sedimentological proxies, we estimate that ～10% of the terrigenous material delivered to the Cariaco Basin is eolian, while ～90% is fluvial. This represents an annual dust accumulation rate of ～0.59 mg/cm2/yr. Since aerosols are closely linked to climate variability, the ability to quantify paleo-dust fluxes using sedimentological characteristics will be a useful tool for future paleoclimate studies looking at sub-Saharan aridity and latitudinal migration of the Intertropical Convergence Zone. 相似文献
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The Mesoproterozoic Lower Tombador Formation is formed of shallow braided fluvial, unconfined to poorly-channelized ephemeral sheetfloods, sand-rich floodplain, tide-dominated estuarine, and shallow marine sediments. Lowstand braided fluvial deposits are characterized by a high degree of channel amalgamation interbedded with ephemeral, intermediate sheetflood sandstones. Sand-rich floodplain sediments consist of intervals formed by distal sheetflood deposits interbedded with thin layers of eolian sandstones. Tide-dominated estuarine successions are formed of tide-influenced sand-bed braided fluvial, tidal channel, tidal sand flat and tidal bars. Shallow marine intervals are composed of heterolithic strata and tidal sand bars. Seismic scale cliffs photomosaics calibrated with vertical sections indicate high lateral continuity of sheet-like depositional geometry for fluvial–estuarine successions. These geometric characteristics associated with no evidence of incised-valley features nor significant fluvial scouring suggest that the Lower Tombador Formation registers deposition of unincised fluvial and tide-dominated systems. Such a scenario is a natural response of the interplay between sedimentation and fluctuations of relative sea level on the gentle margins of a sag basin. This case study indicates that fluvial–estuarine successions exhibit the same facies distributions, irrespective of being related to unincised or incised-valley systems. Moreover, this case study can serve as a starting point to better understand the patterns of sedimentation for Precambrian basins formed in similar tectonic settings. 相似文献
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Michael Houmark-Nielsen 《Sedimentary Geology》1983,36(1):51-63
Four major sedimentary facies are present in coarse-grained, ice-marginal deposits from central East Jylland, Denmark. Facies A and B are matrix-supported gravels deposited by subaerial sediment gravity flows as mudflows (facies A) and debris flows (facies B). Facies C consists of clast-supported, water-laid gravels and facies D are cross-bedded sand and granules. The facies can be grouped into three facies associations related to the supraglacial and proglacial environments: (1) the flow-till association is made up of alternating beds of remobilized glacial mixton (facies A) and well-sorted cross-bedded sand (facies D); (2) the outwash apron association resembles the sediments of alluvial fans in containing coarse-grained debris-flow deposits (facies B), water-laid gravel deposited by sheet floods (facies C) and cross-bedded sand and granules (facies D) from braided distributaries; (3) the valley sandur association comprises water-laid gravel (facies C) interpreted as sheet bars and longitudinal bars interbedded with cross-bedded sand and granules (facies D) deposited in channels between bars in a braided environment.The general coarsening-upward trend of the sedimentary sequences caused by the transition of bars and channel-dominated facies to debris-flow-dominated facies indicate an increasing proximality of the outwash deposits, picturing the advance and still stand of a large continental lowland ice-sheet. The depositional properties suggest that sedimentation was caused by melting along a relatively steep, active glacier margin as a first step towards the final vanishing of the Late Weichselian icesheet (the East Jylland ice) covering eastern Denmark. 相似文献
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Twenty thin sections were studied from Cactus Hill, a ca. 20 ka stratified sand dune site in Virginia, USA, with a Clovis and hypothesized pre‐Clovis component. The high‐resolution soil micromorphology investigation focused on testing the integrity of Clovis and pre‐Clovis stratigraphy from one location where there is a high density of artifacts. Site formation processes were dominated by eolian (dune) sand formation. There was also ephemeral topsoil development and associated occupation, along with their penecontemporaneous disturbance and dispersal by scavenging animals (assumed) and localized down‐working by small invertebrate mesofauna (as evidenced by aggregates of fine phytolith‐rich humic soil and fine soil‐coated charcoal fragments). Partial erosion of these occupation soils (deflation?) was followed by successive sand burial. Post‐depositional processes affecting these sand‐buried occupations involved only small‐scale bioturbation and overprinting of clay lamellae, suggesting site stratigraphy has been stable for a long time. Soil micromorphological analysis has defined a difference between occupational units (pre‐Clovis and Clovis) and sterile units found between these units as well as above and below. In summary, according to this analysis, the site appears intact with only minor disturbances affecting the long‐term integrity of the stratigraphy. © 2008 Wiley Periodicals, Inc. 相似文献
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Joshua Griffiths Richard H. Worden Luke J. Wooldridge James E. P. Utley Robert A. Duller Rhiannon L. Edge 《Sedimentology》2019,66(6):2011-2047
The spatial distribution of clay minerals in sandstones, which may both enhance or degrade reservoir quality, is poorly understood. To address this, clay mineral distribution patterns and host‐sediment properties (grain size, sorting, clay fraction abundance and bioturbation intensity) have, for the first time, been determined and mapped at an unprecedentedly high‐resolution in a modern estuarine setting (Ravenglass Estuary, UK). Results show that the estuary sediment is dominated by illite with subordinate chlorite and kaolinite, although the rivers supply sediment with less illite and significantly more chlorite than found in the estuary. Fluvial‐supplied sediment has been locally diluted by sediment derived from glaciogenic drift deposits on the margins of the estuary. Detailed clay mineral maps and statistical analyses reveal that the estuary has a heterogeneous distribution of illite, chlorite and kaolinite. Chlorite is relatively most abundant on the northern foreshore and backshore and is concentrated in coarse‐grained inner estuary dunes and tidal bars. Illite is relatively most abundant (as well as being most crystalline and most Fe–Mg‐rich) in fine‐grained inner estuary and central basin mud and mixed flats. Kaolinite has the highest abundance in fluvial sediment and is relatively homogenous in tidally‐influenced environments. Clay mineral distribution patterns in the Ravenglass Estuary have been strongly influenced by sediment supply (residence time) and subsequently modified by hydrodynamic processes. There is no relationship between macro‐faunal bioturbation intensity and the abundance of chlorite, illite or kaolinite. Based on this modern‐analogue study, outer estuarine sediments are likely to be heavily quartz cemented in deeply‐buried (burial temperatures exceeding 80 to 100°C) sandstone reservoirs due to a paucity of clay grade material (<0·5%) to form complete grain coats. In contrast, chlorite‐enriched tidal bars and dunes in the inner estuary, with their well‐developed detrital clay coats, are likely to have quartz cement inhibiting authigenic clay coats in deeply‐buried sandstones. 相似文献
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Paulo S.G. Paim 《Sedimentary Geology》2007,202(4):776-795
The upper portion of the Pedra Pintada Alloformation includes about 100 m of mostly eolian deposits. This paper emphasizes the vertical succession and lateral association of sedimentary facies, based on analysis of outcrop data and aerial photographs, as well as the hierarchy and origin of bounding surfaces. It aims to propose a high-resolution stratigraphic and depositional model that may be useful to exploitation of eolian reservoirs. The succession has been preserved due to basin subsidence, and is described in terms of four facies associations that constitute three dominantly eolian units. These units are sharply bounded by major flooding surfaces (super surfaces) that, in turn, are overlain by 1 to 2 m thick, dominantly water-laid facies (lacustrine, fluvial, deltaic and eolian). Both their internal organization and boundaries were controlled by changes in the base level rise rate. The basal Eolian Unit is composed of crescentic eolian dunes and damp interdune deposits ascribed to a wet eolian system. On the other hand, eolian units II and III, also characterized by crescentic eolian dunes (simple and compound) deposits, were related to dry eolian systems, since they comprise dry (eventually wet) interdune facies. Eolian Unit III is truncated by basinwide unconformity, which is then overlain by the ephemeral fluvial deposits (Varzinha Alloformation). This second type of super surface is related to climate-induced wind erosion (deflation) down to the water table level (regional Stokes surface) followed by fluvial incision linked to tectonic activity. 相似文献
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David J. Went 《Sedimentology》2013,60(4):1036-1058
Quartzites are especially characteristic of Proterozoic and Cambro‐Ordovician shallow marine strata, whereas equivalent age fluvial deposits are commonly arkosic. The absence of land vegetation in the pre‐Silurian influenced weathering processes and styles of fluvial deposition. It may also have had an impact on shallow marine sedimentation. Two field studies from the English Channel region are presented to investigate the processes leading to quartzite formation. On Alderney, nearshore marine and fluvial facies occur interbedded on a metre scale and are interpreted to represent deposition on the lower reaches of an alluvial plain, and in beach and upper shoreface environments. The marine and fluvial sandstones display marked differences in textural and mineralogical maturity, pointing to a process of sediment maturation by the destruction of feldspar and labile grains at the shoreline. At Erquy, fully mature, marine quartzites occur bounded above and below by alluvial deposits via sharp or erosional surfaces, and are interpreted to represent high energy, storm and tidally influenced lower shoreface and inner shelf deposits. A model for quartzite development is proposed where, under a cool climate, frequent storms in un‐vegetated, tectonically rejuvenated uplands provided an abundance of arkosic sand to fluvial basins and clastic shorelines. The model proposes that the marine basins were subject to high wave energies, frequent storm events and tidal currents. These were conditions conducive to transforming arkosic sand to quartz‐rich sand by the attrition of feldspar at the shoreline and in the shallow marine environment. On sediment burial, further feldspar destruction occurred during diagenesis. The proposed model highlights the potential for a step change in sediment maturity to occur at the shoreline in early Palaeozoic depositional systems tracts. 相似文献
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M. L. PORTER 《Sedimentology》1987,34(4):661-680
The Lower Jurassic Aztec Sandstone is an aeolian-deposited quartzose sandstone that represents the western margin of the southerly-migrating Navajo-Nugget sand sea (or erg). Vertical and lateral facies relations suggest that the erg margin encroached upon volcanic highlands, alluvial fan, wadi and sabkha environments. In southern Nevada, 700 m thick facies successions record the arrival of the Aztec sand sea. Initial erg sedimentation in the Valley of Fire consists of lenticular or tongue-shaped aeolian sand bodies interstratified with fluvially-deposited coarse sandstone and mudstone. Above, evaporite-rich fine sandstone and mudstone are overlain by thick, cross-stratified aeolian sandstone that shows an upsection increase in set thickness. The lithofacies succession represents aeolian sand sheets and small dunes that migrated over a siliciclastic sabkha traversed by ephemeral wadis. These deposits were ultimately buried by large dunes and draas of the erg. In the Spring Mountains, a similar facies succession also contains thin, lenticular volcaniclastic conglomerate and sandstone. These sediments represent the distal margin of an alluvial fan complex sourced from the west. Thin aeolian sequences are interbedded with volcanic flow rocks, ash-flow tuffs, debris flows, and fluvial deposits in the Mojave Desert of southern California. These aeolian strata represent erg migration up the eastern flanks of a magmatic arc. The westward diminution of aeolian-deposited units may reflect incomplete erg migration, thin accumulation of aeolian sediment succeptible to erosion, and stratigraphic dilution by arc-derived sediment. A two-part division of the Aztec erg is suggested by lithofacies associations, the size and geometry of aeolian cross-strata, and sediment dispersal data. The leading or downwind margin of the erg, here termed the fore-erg, is represented by a 10–100 m thick succession of isolated pods, lenses, and tongues of aeolian-deposited sediment encased in fluvial and sabkha deposits. Continued sand-sea migration brought large dunes and draas of the erg interior into the study area; these 150–500 m thick central-erg sediments buried the fore-erg deposits. The trailing, upwind margin of the erg is represented by back-erg deposits in northern Utah and Wyoming. 相似文献
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Vance T. Holliday Bruce B. Huckell Robert H. Weber Marcus J. Hamilton William T. Reitze James H. Mayer 《Geoarchaeology》2009,24(3):348-370
The Mockingbird Gap site is one of the largest Clovis sites in the western United States, yet it remains poorly known after it was tested in 1966–1968. Surface collecting and mapping of the site revealed a dense accumulation of Clovis lithic debris stretching along Chupadera Draw, which drains into the Jornada del Muerto basin. We conducted archaeological testing and geoarchaeological coring to assess the stratigraphic integrity of the site and gain clues to the paleoenvironmental conditions during the Clovis occupation. The 1966–1968 excavations were in stratified Holocene eolian sand and thus that assemblage was from a disturbed content. An intact Clovis occupation was found elsewhere in the site, embedded in the upper few centimeters of a well‐developed buried Bt horizon formed in eolian sand, representing the regional Clovis landscape. Coring in Chupadera Draw revealed ∼11 m of fill spanning the past ∼11,000 14C years. The stratified deposits provide evidence of flowing and standing water on the floor of the draw during Clovis times, a likely inducement to settlement. © 2009 Wiley Periodicals, Inc. 相似文献
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Reconstructing the pattern and depth of flow onshore in a palaeotsunami from associated deposits 总被引：1，自引：0，他引：1
The widespread sheets of fine particulate sediment frequently deposited by tsunami constitute valuable evidence from which to reconstruct tsunami inundation. This is illustrated with evidence from three sites near Montrose, in eastern Scotland, U.K., where a horizon of mainly sand, laid down during the Holocene Storegga Slide palaeotsunami of circa 8000 BP is examined. The horizon is remarkably consistent in its distribution, morphology, stratigraphy, and particle size characteristics. These properties allow inferences to be made on the nature of tsunami flow onshore and run-up. It is suggested that estimates can be made of the possible depth of water involved from the characteristics of the sediment, and thus of the extent of inundation involved in the tsunami at these sites. 相似文献
16.
《Russian Geology and Geophysics》2014,55(5-6):610-618
An integrated lithofacies analysis of the Middle-Upper Bathonian petroleum horizon J2 in the northeastern part of the latitudinal Ob’ region was carried out. The new data were used to supplement and refine the available data. The recognized lithofacies and their associations clearly mark off the boundaries of reconstructed sedimentation conditions. A petrographical study of the silt-sandy rocks of the horizon was carried out with a detailed calculation of their grain size and petrographic compositions. Grain size coefficients were analyzed with the use of genetic, dynamic, and dynamogenetic diagrams. The new data permitted a considerable refinement of the reconstructed sedimentation conditions of the horizon. It has been found that the transgressive change of sedimentation conditions is reflected in regular changes in some characteristics of the studied sediments: a decrease in the total number and thickness of coal interbeds, an increase in the degree of sediment bioturbation, a change of ichnofossils, and an increase in the amount of pyrite. More detailed paleogeographical schemes have been constructed for the formation of the lower (continental), middle (transitional), and upper (littoral marine) parts of the horizon. They provide a better understanding of the regularities of development of the Middle-Late Bathonian sedimentary basin in the study area. 相似文献
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The question of a primary versus diagenetic origin for the limestone-shale rhythms of the Blue Lias has been addressed through a study of pyrite abundance and isotopic composition. Pyrite is relatively abundant and isotopically light in the central portions of the bioturbated limestones as compared to adjacent, less calcareous, sediment. The abundance of pyrite shows that the limestones were a focus for prolonged sulphate reduction and pyrite formation. The isotopic data indicate that bioturbation oxidized some pyrite to produce isotopically light sulphate, part of which was subsequently reduced back to pyrite before preservation by burial. Acidity generated by pyrite oxidation was buffered in the limestones by carbonate dissolution, hence supersaturation of sulphides could be maintained. By contrast, in adjacent less calcareous sediments, carbonate dissolution was unable to buffer acidity and bioturbational oxidation of pyrite formed iron-rich pore solutions. Continued sulphate reduction in the limestones acted as a sink for iron from the adjacent sediments and, with burial below the zone of bioturbation, the alkalinity so generated caused cementation of the limestones. Diagenetic cementation would be enhanced during an hiatus in sedimentation, an event which might be related to a Milankovitch forcing mechanism, but which would not be recorded in bioturbated, less calcareous sediment, thus leaving an imperfect record. Only cyclicity in pre-diagenetic sedimentation patterns may be safely related to a Milankovitch forcing mechanism as proposed by Weedon. 相似文献
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Todd A. Surovell Nicole M. Waguespack James H. Mayer Marcel Kornfeld George C. Frison 《Geoarchaeology》2005,20(6):627-649
Shallowly buried archaeological sites are particularly susceptible to surface and subsurface disturbance processes. Yet, because cultural deposition often operates on short time scales relative to geologic deposition, vertical artifact distributions can be used to clarify questions of site formation. In particular, patterns in artifact distributions that cannot be explained by occupation histories must be explained by natural processes that have affected sites. Buried only 10–50 cm beneath the ground surface for 10,450 14C yr, the Folsom component at Barger Gulch Locality B (Middle Park, Colorado) exhibits many signs of post‐depositional disturbance. Through examination of variation in the vertical distribution of the artifact assemblage, we are able to establish that only a Folsom component is present. Using vertical artifact distributions, stratigraphy, and radiocarbon dating, we are able to reconstruct the series of events that have impacted the site. The Folsom occupation (˜10,450 14C yr B.P.) was likely initially buried in a late‐Pleistocene eolian silt loam. Erosion brought the artifacts to rest on a deflation surface at some time prior to 9400 14C yr B.P. A mollic epipedon formed in sediments that accumulated between 9400 and 7000 14C yr B.P. Some time after 5200 14C yr B.P., this soil was partially truncated, and artifacts that had previously dispersed upward created a secondary lag at its upper contact. This surface was buried again and artifact dispersal continued. © 2005 Wiley Periodicals, Inc. 相似文献
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Cactus Hill is located in the Virginia Coastal Plain on a terrace above the Nottoway River. The site has a record of occupation that spans the Holocene and also offers evidence of humans late in the Pleistocene before Clovis time. Soil investigations identified several deposit types, and demonstrated that multisequal eolian sands forming the site's primary core are arrayed in spatially and temporally discrete horizons. Resting atop an ancient paleosol, the earliest sand stratum (19,540 ± 70 14C yr B.P.) is marked by a conspicuous but culturally sterile buried surface horizon. Eolian sand above this surface supports another sequum in which Clovis and underlying “Blade” artifacts are associated with a fainter surface horizon and pronounced subsoil lamellae. Early Archaic and successively younger artifacts occur above the Clovis level in a more weakly developed uppermost sequum. This soil and cultural stratigraphy, together with considerations of regional topography, demonstrate that the landscape has evolved incrementally since about the last glacial maximum. © 2004 Wiley Periodicals, Inc. 相似文献
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The Ouémé River estuary is located on the seasonally humid tropical coast of Benin, west Africa. A striking feature of this microtidal estuary is the presence of a large sand barrier bounding a 120 km2 circular central basin, Lake Nokoué, that is being infilled by heterogeneous fluvial deposits supplied by a relatively large catchment (50 000 km2). Borehole cores from the lower estuary show basal Pleistocene lowstand alluvial sediments overlain by Holocene transgressive–highstand lagoonal mud and by transgressive to probably early highstand tidal inlet and flood‐tidal delta sand deposited in association with non‐preserved transgressive sand barriers. The change in estuary‐mouth sedimentation from a transgressive barrier‐inlet system to a regressive highstand barrier reflects regional modifications in marine sand supply and in the cross‐barrier tidal flux associated with barrier‐inlet systems. As barrier formation west of the Ouémé River led to an increasingly rectilinear shoreline, the longshore drift cell matured, ensuring voluminous eastward transport of sand from the Volta Delta in Ghana, the major purveyor of sand, to the Ouémé embayment, 200 km east. Concomitantly, the number of tidal inlets, and the tidal flux associated with a hitherto interlinked lagoonal system on this coast, diminished. Complete sealing of Lake Nokoué has produced a large, permanently closed estuary, where tidal intrusion is assured through the interconnected coastal lagoon via an inlet located 60 km east. Since 1885, tides have entered the estuary directly through an artificial outlet cut across the sand barrier. Although precluding the seaward loss of fluvial sediments, permanent estuary‐mouth closure has especially deprived the highstand estuary of marine sand, a potentially important component in estuarine infill on wave‐dominated coasts. In spite of a significant fluvial sediment supply, estuarine infill has been moderate, because of the size of the central basin. Estuarine closure has resulted in two co‐existing highstand sediment suites, with limited admixture, the marine‐derived, estuary‐mouth barrier and upland‐derived back‐barrier sediments. This situation differs from that of mature barrier estuaries characterized by active fluvial‐marine sediment mixing and facies interfingering. 相似文献