共查询到20条相似文献，搜索用时 31 毫秒
1.
Inferring the mass fraction of floc-deposited mud: application to fine-grained turbidites 总被引：1，自引：0，他引：1
K. J. Curran P. S. Hill T. M. Schell T. G. Milligan† D. J. W. Piper‡ 《Sedimentology》2004,51(5):927-944
Fine sediment deposition in the ocean is complicated by the cohesive nature of muds and their tendency to flocculate. The result is disaggregated inorganic grain size (DIGS) distributions of bottom sediment that are influenced by single‐grain and floc deposition. This study outlines a parametric model that characterizes bottom sediment DIGS distributions. Modelled parameters are then used to infer depositional conditions that account for the regional variation in the grain sizes deposited by turbidity currents on the Laurentian Fan–Sohm Abyssal Plain, offshore south‐eastern Canada. Results indicate that, on the channellized Laurentian Fan, the mass fraction of floc‐deposited mud increases only slightly downslope. The small evolution in this fraction arises because sediment concentration and turbulent energy are associated in turbidity currents. On the Sohm Abyssal Plain, however, the mass fraction of floc‐deposited mud decreases, probably as a result of lower sediment concentration at this source‐distal site. Estimates of the mass fraction of mud deposited as flocs suggest that floc deposition is the dominant mode by which sediment is lost from suspension, although single‐grain deposition contributes more to the depositional flux in proximal areas where high energy breaks flocs and in distal areas where low sediment concentration limits floc formation. It is concluded that, throughout the dispersal system, changes in the fraction of flocculated mud deposited from turbidity currents reflect changes in sediment concentration and energy downslope. 相似文献
2.
Six closely spaced sediment cores taken below the carbonate compensation depth penetrated fine silty muds and entered sandy sediment at 10–12 m below the seafloor. Foraminiferal assemblages and δ8O analyses on planktonic foraminifera indicated that the surface muds down to 2 m are Holocene and derived from local promontories above the CCD. Below these sediments are about 6 m of clays deposited during the late Wisconsin. These are unfossiliferous and have a possible northern source suggested by the higher chlorite content. Sandy sediments below 9 m in the cores contain well preserved benthic foraminifera from the Scotian Shelf. Glacial δ18O values on planktonic tests indicate the sandy sediments are most likely of latest Wisconsin age. Thus during the recent interglacial, the sand fraction of the southern Sohm Abyssal Plain sediments is mostly locally derived, but during glacial periods the sediments have a distant northern source containing quartz sand that was initially deposited on the Scotian Shelf 1,500 km to the north. 相似文献
3.
Determination of turbidity current erosional characteristics from reworked coccolith assemblages, Canary Basin, north-east Atlantic 总被引：1，自引：0，他引：1
P. P. E. WEAVER 《Sedimentology》1994,41(5):1025-1038
Turbidites contain mixtures of sediments of various ages. These sediments can include both material that was eroded to form the initial turbidity current plus additions derived from erosion of the sea floor during transport. It has been possible to interpret the age range of sediments incorporated into individual turbidites from the Madeira Abyssal Plain by examining the proportions of microfossil (coccolith) species that they contain. The pelagic record of coccoliths is well known for the Quaternary period and shows a succession of dominant species or acmes each lasting a few tens of thousand years. Hence, erosion of sediment representing more than a few tens of thousand years will produce coccolith mixtures not seen in the pelagic record, but dependent upon the age range of the sediments that were eroded. This age range can be estimated by comparison with synthetic ratios of coccolith species created by combining ratios of species from successively older layers in the pelagic record. These can then be compared with the ratios found in individual turbidites until a match is found. The results show age ranges of 54–500 kyr for the sediment mixture in seven turbidites from the Madeira Abyssal Plain. Since the volumes of these turbidites are also known, and accumulation rates in their source areas can be estimated, it is possible to determine both the thickness and the area of the eroded sediment mass that generated the turbidity current. Minimum depths of erosion on the north-west African continental margin vary from 8 to 50 m and minimum areas eroded from 1600 to 5800 km2. None of the turbidites examined contains a significant excess of surface sediment, suggesting that, once formed, the turbidity currents that transported them were virtually non-erosional, and that they travelled several hundred kilometres in this state. 相似文献
4.
Turbidite depositional architecture across three interconnected deep-water basins on the north-west African margin 总被引：1，自引：0，他引：1
Russell B. Wynn Philip P. E. Weaver Douglas G. Masson Dorrik A. V. Stow 《Sedimentology》2002,49(4):669-695
ABSTRACT The Moroccan Turbidite System (MTS) on the north‐west African margin extends 1500 km from the head of the Agadir Canyon to the Madeira Abyssal Plain, making it one of the longest turbidite systems in the world. The MTS consists of three interconnected deep‐water basins, the Seine Abyssal Plain (SAP), the Agadir Basin and the Madeira Abyssal Plain (MAP), connected by a network of distributary channels. Excellent core control has enabled individual turbidites to be correlated between all three basins, giving a detailed insight into the turbidite depositional architecture of a system with multiple source areas and complex morphology. Large‐volume (> 100 km3) turbidites, sourced from the Morocco Shelf, show a relatively simple architecture in the Madeira and Seine Abyssal Plains. Sandy bases form distinct lobes or wedges that thin rapidly away from the basin margin and are overlain by ponded basin‐wide muds. However, in the Agadir Basin, the turbidite fill is more complex owing to a combination of multiple source areas and large variations in turbidite volume. A single, very large turbidity current (200–300 km3 of sediment) deposited most of its sandy load within the Agadir Basin, but still had sufficient energy to carry most of the mud fraction 500 km further downslope to the MAP. Large turbidity currents (100–150 km3 of sediment) deposit most of their sand and mud fraction within the Agadir Basin, but also transport some of their load westwards to the MAP. Small turbidity currents (< 35 km3 of sediment) are wholly confined within the Agadir Basin, and their deposits pinch out on the basin floor. Turbidity currents flowing beyond the Agadir Basin pass through a large distributary channel system. Individual turbidites correlated across this channel system show major variations in the mineralogy of the sand fraction, whereas the geochemistry and micropalaeontology of the mud fraction remain very similar. This is interpreted as evidence for separation of the flow, with a sand‐rich, erosive, basal layer confined within the channel system, overlain by an unconfined layer of suspended mud. Large‐volume turbidites within the MTS were deposited at oxygen isotope stage boundaries, during periods of rapid sea‐level change and do not appear to be specifically connected to sea‐level lowstands or highstands. This contrasts with the classic fan model, which suggests that most turbidites are deposited during lowstands of sea level. In addition, the three largest turbidites on the MAP were deposited during the largest fluctuations in sea level, suggesting a link between the volume of sediment input and the magnitude of sea‐level change. 相似文献
5.
C. J. A. SOUTENDAM 《Sedimentology》1967,8(4):281-290
For the study of the surface textures of quartz sand grains the normal microscope was used, besides the sofar generally applied electron microscope, and a new method was developed for using incident illumination. Grains from a desert sand and a river sand were studied, the former grains displayed textures not described yet by previous authors, the latter grains possessed a variety of textures, some of which have been found with beach sand grains, others with glacial sand grains by previous investigators. 相似文献
6.
7.
We present the first multi-channel seismic reflection data ever collected from the Eurasian Basin of the Arctic Ocean. The 200 km data set was acquired by a 20 channel sonobuoy array deployed at U.S. ice drift station FRAM-IV and operated for 34 days about 370 km north of Svalbard in April–May 1982. Cross array drift and ice floe rotation which may constitute the most serious obstacle to the advantage of multi-channel data acquisition did only occur to a minor degree during the experiment and render most of the data set suitable for processing using common mid-point binning.A 0.7–1.4 s (two-way traveltime) thick sedimentary section has been deposited over oceanic crust of mid-Oligocene age below the Barents Abyssal Plain. In the deepest part, sediments are infilling topographic lows which indicate predominantly turbidite deposition. Erosional truncations are only locally present in the central part of the section. Conformable bedforms deposited over gentle basement highs indicate a relatively stable bottom current regime since mid-Oligocene time. Thus the establishment of a deep water connection between the Arctic Ocean and lower latitude water masses appear to have had only minor effect on Eurasian Basin bottom current circulation.Extensive submarine slide scars on the north slope of Yermak Plateau show that mass waste have been a sediment source to the Barents Abyssal Plain. 相似文献
8.
9.
Side-scan sonar, seismic and core data are used to identify mega-flutes, transverse and ‘V’ shaped bedforms in turbidites around the Valencia channel mouth, north-west Mediterranean. Long-range side-scan sonar data reveal a broad, curved, asymmetric, channel, that widens and terminates downfan. The western channel bank near the channel mouth has been partly eroded by turbidity currents that spilled out of the channel. Transverse bedforms on the east of the channel floor are interpreted as antidunes and, if this interpretation is correct, they indicate that the flow was probably supercritical at least locally within the channel. Trains of mega-flutes, are incised into coarse-grained sediments of the channel floor near the channel mouth. The association of mega-flutes and antidunes is thought to be diagnostic of channel–lobe transitions on deep-sea fans. The mega-flutes pass downfan into an area of streaks that diverge at up to 45° and indicates flow expansion from the channel mouth. About 75 km downfan from the channel mouth, deep-towed side-scan data record transverse bedforms (interpreted as antidunes) passing downfan into an area covered by ‘V’ shaped bedforms with upflow pointing apices (named chevrons here). The chevrons are commonly c. 200 m from limb to limb and c. 2 m in amplitude with flow-parallel wavelengths of c. 400 m. We propose that chevrons were formed by a strong, probably supercritical (or near critical) turbidity current spreading from the channel mouth and flowing towards the Balearic Abyssal Plain. Thinning of the turbidity current, resulting from flow spreading would allow the Froude number to remain high up to 100 km from the channel mouth and could explain the observed reduction in antidune wavelength. 相似文献
10.
Mats O. Molén 《Sedimentology》2014,61(7):2020-2041
Interpretation of quartz sand grain surface microtextures with scanning electron microscopy has been riddled with inconsistencies, invalid assumptions and much subjectivity. Therefore, a novel classification for analysing grain surface microtextures is presented based on the origin of complete grain surfaces. This novel method has solved most of the earlier problems of interpretation of surface microtextures, and it is easy to use and to quickly find evident genetic interpretations of diamicts. The data are plotted graphically in ‘2‐History Diagrams’ or ‘3‐History Diagrams’ for quick visual inspection and statistical evaluation. Source rocks and Quaternary glacial deposits from Scandinavia and Southern Ontario, representing different ice‐substrate dynamics, are analysed to define surface microtextures from typical glacigenic grains, bedrock and fluvially transported grains. Typical glacially crushed grains display large‐scale fractures and abrasion. Shield bedrock grains display large or small‐scale fractures and solution/precipitation microtextures. Fluvially transported grains exhibit abrasion and solution/precipitation microtextures. 相似文献
11.
The surface textures of fine sand particles from the Deep Sea Drilling Project Leg 39 have been studied via scanning electron microscopy. A large portion of the coarsest fraction of these grains from deep sea cores were formerly fragments of larger sand-sized grains that had been mechanically broken. Surface textures characteristic of previous aeolian and subaqueous environments were preserved in fragments broken from the original larger grain surfaces, thus making palaeo-environmental reconstruction possible. Previously, characteristic mechanical markings had not been observed on deep sea sands; the momentum of grain to grain collisions with respect to fine sands is generally insufficient to initiate mechanical breakage. 相似文献
12.
Shale depositional processes: Example from the Paleozoic Barnett Shale, Fort Worth Basin, Texas, USA
A long held geologic paradigm is that mudrocks and shales are basically the product of ‘hemipelagic rain’ of silt- and/or clay-sized, detrital, biogenic and particulate organic particles onto the ocean floor over long intervals of time. However, recently published experimental and field-based studies have revealed a plethora of micro-sedimentary features that indicate these common fine-grained rocks also could have been transported and/or reworked by unidirectional currents. In this paper, we add to this growing body of knowledge by describing such features from the Paleozoic Barnett Shale in the Fort Worth Basin, Texas, U.S.A. which suggests transport and deposition was from hyperpycnal, turbidity, storm and/or contour currents, in addition to hemipelagic rain. On the basis of a variety of sedimentary textures and structures, six main sedimentary facies have been defined from four 0.3 meter intervals in a 68m (223 ft) long Barnett Shale core: massive mudstone, rhythmic mudstone, ripple and low-angle laminated mudstone, graded mudstone, clay-rich facies, and spicule-rich facies. Current-induced features of these facies include mm- to cmscale cross- and parallel-laminations, scour surfaces, clastic/biogenic particle alignment, and normal- and inverse-size grading. A spectrum of vertical facies transitions and bed types indicate deposition from waxing-waning flows rather than from steady ‘rain’ of particles to the sea floor. Detrital sponge spicule-rich facies suggests transport to the marine environment as hypopycnal or hyperpycnal flows and reversal in buoyancy by transformation from concentrated to dilute flows; alternatively the spicules could have originated by submarine slumping in front of contemporaneous shallow marine sponge reefs, and then transported basinward as turbidity current flows. The occurrence of dispersed biogenic/organic remains and inversely size graded mudstones also support a hyperpycnal and/or turbidity flow origin for a significant part of the strata. These processes and facies reported in this paper are probably present in other organic-rich shales. 相似文献
13.
D. G. F. Long 《Geological Journal》1991,26(4):279-293
The presence of a dispersed clast fraction in strata near the base of the Cosquer Formation in west Brittany, does not support a glacial origin for this unit. The upper 25 to 30 m of the underlying Kermeur Formation consists of a prograding sequence of very fine to fine sandstones deposited in a mid to distal current swept shelf setting. This sequence shows signs of slope instability, as do the supposed ‘glacial strata’ which overlie it. The upper two thirds of the Cosquer Formation contain spectacular slump-breccias. Smaller clasts within the laminated mudrocks at the base of the formation are associated with thin graded and non-graded sandstone laminae. They show no evidence of active penetration into underlying laminae other than can be explained by compaction. Larger clasts are confined to thicker massive beds, or disrupted units with marked internal contorted lamination. This, along with the abundance of slump features within the sequence suggests lateral emplacement by sediment gravity flows in a distal shelf-slope setting. Surface textures of sand grains within the formation are related to rock disaggregation along fractures developed during post-depositional deformation and are not related to glacial processes. Distinctive mineralogically immature, poorly-sorted aggregate sediment pellets, which have been considered as positive proof of glaciation, are not present. 相似文献
14.
北京潭柘寺地区第四纪冰川遗迹的宏观和微观特征 总被引：2，自引：1，他引：1
以北京西山潭柘寺地区第四纪冰川遗迹的宏观特征研究为基础,对管坨岭冰期和赵家台冰期的古冰川沉积进行了石英颗粒表面结构形貌组合特征的分析。结果表明,管坨岭冰期的管坨岭冰碛层和大富庄冰碛层,以及赵家台冰期的太平庄冰碛层中的石英颗粒表面结构,以冰川成因的形貌组合占优势,而赵家台冰期鲁家滩冰水沉积中的石英颗粒表面结构,则以冰川和流水共有成因的形貌占优势。所以,据冰川遗迹的宏观和微观特征,可以肯定该区分别在早更新世和中更新世曾发育过两次古冰川作用。 相似文献
15.
Surface textures of quartz sand grains from several glacial environments at the Feegletscher, Switzerland examined by means of scanning electron microscopy are described. The difference between supraglacial and subglacial material is very slight. At the moment the interpretation of these textures must be done with care until the full statistical relation to environments can be ascertained. This does not necessarily invalidate earlier investigations although it does mean that glacial and extraglacial environments in the vicinity of glaciers are apparently not distinguishable. Examination of surface precipitation features suggests a sequence of events which can be used to help discriminate between different ages of deposits in an area. A similarity between some of the surface debris from moraine samples and those seen in loess and quickclay deposits is also suggested. 相似文献
16.
17.
Middle and late Pleistocene glaciations in the Campo Felice Basin (central Apennines, Italy) 总被引：1，自引：0，他引：1
The present paper refers to research conducted in the tectonic-karst depression of Campo Felice in the central Apennines (Italy), in which glacial, alluvial and lacustrine sediments have been preserved. Stratigraphic interpretations of sediments underlying the Campo Felice Plain are based on evidence obtained from nine continuous-core boreholes. The boreholes reach a depth of 120 m and provide evidence of five sedimentation cycles separated by erosion surfaces. Each cycle is interpreted as an initial response to a mainly warm stage, characterized by low-energy alluvial and colluvial deposition, pedogenesis, and limited episodes of marsh formation. In turn, a mainly cold stage follows during which a lake formed, and glaciers developed and expanded, leading to deposition of glacial and fluvioglacial deposits. The chronological framework is established by eleven accelerator mass spectrometer 14C ages and three 39Ar-40Ar ages on leucites from interbedded tephra layers. These age determinations indicate five glacial advances that respectively occurred during marine oxygen isotope stages 2, 3-4, 6, 10 and 14. 相似文献
18.
Units of remarkably pure Archaean quartz arenite occur in the northwestern part of the Superior Province and in the northern terrane of the Western Churchill Province (Rae Province) of the Canadian Shield. In the Superior Province, silica-cemented quartz arenites of Archaean age are well preserved in several greenstone belts. The example from the Keeyask Lake sedimentary assemblage displays tabular–planar and trough cross-beds, ripple marks, reactivation surfaces and pebble lag deposits. In spite of penetrative deformation and greenschist-grade metamorphism, primary textures are extremely well preserved, showing framework grains to be very well rounded and sorted. The succession of Keeyask Lake quartz-arenite beds is overlain by siltstones containing small-scale stratiform, domal and columnar stromatolites. A shallow-marine environment of deposition is inferred. Detrital heavy minerals include pyrite, magnetite, zircon, tourmaline, apatite, sphene and topaz. In the northern part of the Western Churchill Province (Rae Province), Archaean quartz arenites occur in northeasterly trending belts where intense structural deformation has in most places obscured or obliterated primary textures and structures. This has led to speculation that some of these units are metachert or recrystallized vein quartz, but local preservation of primary textures and structures provides clear evidence of epiclastic origin. In the example described herein, quartz arenites of the Woodburn Lake Group display sparse occurrences of trough and tabular–planar cross-beds, channels, ripple marks and pebble lag deposits. Probable environments of deposition for these quartz arenites include fluvial systems and shallow-marine shelf settings. The occurrence of unequivocal quartz-arenite clasts in beds of intercalated conglomerate provides direct evidence of at least two episodes of accumulation of almost pure quartz sand. Thin sections and polished slabs reveal frameworks of clastic quartz grains with little to no matrix (now mainly muscovite), and rare detrital grains of accessory heavy minerals, predominantly zircon and opaque iron oxides. Pyrite and other sulphides have been introduced along fractures, but some intergranular sulphide grains may be of detrital origin. The principal source for the quartz arenites in both areas must have been quartz-rich granitoid rocks. Conditions of intense chemical weathering are indicated. The widespread occurrence of extremely mature quartz arenites throughout Archaean terranes of the Canadian Shield, and in other shields of the world, are suggestive of crustal stability during early Earth history. The association of quartz arenites and ultramafic rocks, uncharacteristic of younger terranes, is now recognized in many Archaean greenstone belts of the Canadian Shield. 相似文献
19.
The occurrence of a millennial‐scale bipolar climate seesaw has been documented in detail for the last glacial period and Termination. There is, however, debate whether it occurs during interglacials and if it does what influence it could have on future climate. We present here new evidence from a North East Atlantic Ocean deep‐sea core which supports the hypothesis for a Holocene bipolar climate seesaw. BENGAL Site 13078#16, from the Porcupine Abyssal Plain, is 4844 m deep and situated at the North Atlantic Deep Water and Antarctic Bottom Water (AABW) interface. Planktic foraminiferal fragment accumulation rate data at this site is an indicator of coarse carbonate dissolution, which is highly sensitive to the incursion of under‐saturated AABW. Five dissolution peaks have been identified, which seem to occur approximately 500 a after each of the North Atlantic 'Bond' ice rafting pulses, suggesting a subsequent subtle shallowing of AABW. This indicates a possible lagged climatic link between North East Atlantic surface water conditions and AABW production in the Southern Ocean during the Holocene. This provides the first tentative evidence that there was a Holocene bipolar climate seesaw and that the deep ocean was involved. This study also suggests that extremely sensitive locations need to be sought as the Holocene bipolar climate seesaw seems to be very subtle compared with its glacial counterparts. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
20.
石英颗粒表面结构类型以及它们和形成环境间的对应关系,国外已有初步总结[1,2,3]。对石英颗粒表面结构应用于历史环境分析,有着不同的意见[4-6]。多数研究者认为,对于松散的或未固结的沉积物(主要为第四纪的)中的石英颗粒表面结构,具有显著的环境分析意义,而对于地质年代久远、早已半固结或固结成岩的则看法不一,有的则予以否定。因为,地质年代愈老,成岩作用(包括浅变质作用)影响也就愈大。但也有些情况表明[7,8],虽已固结成岩,其物源区的搬运、沉积过程中产生的机械结构,仍然部分或大部分被保存下来,仍可以指示其环境。 相似文献