Turbidite depositional patterns and flow characteristics, Navy Submarine Fan, California Borderland   总被引：6，自引：0，他引：6  

DAVID J. W. PIPER  WILLIAM R. NORMARK† 《Sedimentology》1983,30(5):681-694

The late Pleistocene and Holocene stratigraphy of Navy Fan is mapped in detail from more than 100 cores. Thirteen ¹⁴C dates of plant detritus and of organic-rich mud beds show that a marked change in sediment supply from sandy to muddy turbidites occurred between 9000 and 12,000 years ago. They also confirm the correlation of several individual depositional units. The sediment dispersal pattern is primarily controlled by basin configuration and fan morphology, particularly the geometry of distributary channels, which show abrupt 60° bends related to the Pleistocene history of lobe progradation. The Holocene turbidity currents are depositing on, and modifying only slightly, a relict Pleistocene morphology. The uppermost turbidite is a thin sand to mud bed on the upper-fan valley levées and on parts of the mid-fan. Most of its sediment volume is in a mud bed on the lower fan and basin plain downslope from a sharp bend in the mid-fan distributary system. Little sediment occurs farther downstream within this distributary system. It appears that most of the turbidity current overtopped the levée at the channel bend, a process referred to as flow stripping. The muddy upper part of the flow continued straight down to the basin plain. The residual more sandy base of the flow in the distributary channel was not thick enough to maintain itself as gradient decreased and the channel opened out on to the mid-fan lobe. Flow stripping may occur in any turbidity current that is thick relative to channel depth and that flows in a channel with sharp bends. Where thick sandy currents are stripped, levée and mid-fan erosion may occur, but the residual current in the channel will lose much of its power and deposit rapidly. In thick muddy currents, progressive overflow of mud will cause less declaration of the residual channelised current. Thus both size and sand-to-mud ratio of turbidity currents feeding a fan are important factors controlling morphologic features and depositional areas on fans. The size-frequency variation for different types of turbidity currents is estimated from the literature and related to the evolution of fan morphology.  相似文献   

Geomorphology of the Ablation Point massif, Alexander Island, Antarctica   总被引：1，自引：0，他引：1  

CHALMERS M. CLAPPERTON  DAVID E. SUGDEN 《Boreas: An International Journal of Quaternary Research》1983,12(2):125-135

A coloured geomorphological map at the approximate scale of 1:50,000 is presented for the Ablation Point massif area. The main gcomorphological features have been described, such as ice and snow cover, glacial landforms and deposits (and chronology), ice marginal lakes, melt pools, gelifluction landforms and patterned ground and valley-slope landforms. The area is thought to be a good analogue for glacial-age maritime northwest Europe.  相似文献   

Lateral fluctuations in pelagic sedimentation during the Pleistocene glaciations     

KURT BOSTRÖM  DAVID E. FISHER 《Boreas: An International Journal of Quaternary Research》1972,1(4):275-288

Boström, K., & Fisher, D. E.: Lateral fluctuations in pelagic sedimentation during the Pleistocene glaciations. Boreas, Vol. 1, pp. 275–288. Oslo, 1st December, 1972.
A total of 308 sediment samples of dated cores from 7 different locations have been analyzed for several major and trace elements. Our results, as well as previously published ones, show that during the Pleistocene the pelagic sediments have high concentrations of Mn, Cu, Co, REE, etc., in deposits of glacial age and low concentrations in corresponding interglacial ones; for hemipelagic sediments the situation is reversed. This shows that the boundary between reducing hemipelagic sediments and well-oxidized pelagic sediments has been migrating laterally back and forth due to climatic variations. Such sediment sequences may be easily confused with deposits where postdepositional migration of Mn and other elements has taken place.  相似文献   

Properties of Synthetic Triclinic KFeSi3O8, Iron-microcline, with some Observations on the Iron-microcline{rightleftharpoons}Iron-sanidine Transition     

WONES  DAVID R.; APPLEMAN  DANIEL E. 《Journal of Petrology》1963,4(1):131-137

Triclinic KFeSi₃O₈, iron-microcline, has been synthesized fromoxide mixes and by complete conversion of monoclinic KFeSi₃O₈,iron-sanidine. Iron-microcline is triclinic, C, a=8?68?0?01?, b=13?10?0?01, c=7?34?0?01, =90? 45'?10', ß=116?03'?10', =86?14'?10'. The optical properties (Na light) are:=1?585?0?002, ß=1?596?0?002, =1?605?0?002, 2V=85?(calc.), Xb, Z c=20??5?. A reversible phase transition betweentriclinic and monoclinic KFeSi₃O₈ occurs at 704??6? C at 2000bars total pressure. Iron-microcline is the low-temperaturepolymorph; no intermediate polymorphs were observed in eitherhydrothermal or dry heating experiments.  相似文献   

TECHNIQUES FOR REMOVING INTERSTITIAL WATER FROM COARSEGRAINED SEDIMENTS FOR CHEMICAL ANALYSES     

DAVID W. SCHOLL 《Sedimentology》1963,2(2):156-163

Three methods, (a)dessication, (b)gas extraction and (c)immiscible-liquid extraction, are described and evaluated for removing interstitial water from coarse-grained sedi- ments for semi-quantitative and quantitative chemical analyses. The dessication method is useful for chlorinity or chlorosity determinations and (with a correction of 5%) gives results probably accurate to within about ± 2O% Extraction of interstitial water with gas of high relative humidity gives results which are correct to within an error of ± l.O% The chlorosity of interstitial water extracted by forcing a high- viscosity epoxy plasticizer (immiscible with water) through the sediment falls within about ± 0.1% of the correct value. The immiscible-extraction method is therefore recommended for work requiring quantitative knowledge of interstitial water chemistry.  相似文献   

Surface textures of turbidite sand grains, Laurentian Fan and Sohm Abyssal Plain     

YING WANG  DAVID J. W. PIPER  GUSTAVS VILKS 《Sedimentology》1982,29(5):727-736

Surface textures of quartz grains have been examined from five samples from the Laurentian Fan and Sohm Abyssal Plain, representing varied transport distances and power of the depositing turbidity current. The grains retain their primary irregular shape derived from glacial erosion, and glacial surface textures are preserved in dish-shaped depressions. These features have been superimposed by a slight rounding of edges and an abundance of collision-induced markings, particularly mechanical V-forms. The most intense current modification of this sort occurs in mid-Wisconsinan or earlier sands that have been transported over 1000 km to the distal Sohm Abyssal Plain by turbidity currents. Collision textures probably develop during grain flow on the steep continental slope: delicate resedimented shelf foraminifera are preserved in the same turbidites and most have been transported exclusively in suspension.  相似文献   

Using palaeoenvironmental DNA to reconstruct past environments: progress and prospects          下载免费PDF全文

NICOLAS J. RAWLENCE  DAVID J. LOWE  JAMIE R. WOOD  JENNIFER M. YOUNG  G. JOCK CHURCHMAN  YU‐TUAN HUANG  ALAN COOPER 《第四纪科学杂志》2014,29(7):610-626

Palaeoenvironmental DNA (PalEnDNA) is defined as ancient DNA (aDNA) originating from disseminated genetic material within palaeoenvironmental samples. Sources of PalEnDNA include marine and lake sediments, peat, loess, till, ice, permafrost, palaeosols, coprolites, preserved gut contents, dental calculus, tephras, and soils as well as deposits in caves/rockshelters and at archaeological sites. PalEnDNA analysis provides a relatively new tool for Quaternary and archaeological sciences and its applications have included palaeoenvironmental and palaeodietary reconstructions, testing hypotheses regarding megafaunal extinctions, human–environment interactions, taxonomic studies, and studies of DNA damage. Because PalEnDNA samples comprise markedly different materials, and represent wide‐ranging depositional and taphonomic contexts, various issues must be addressed to achieve robust, reproducible findings. Such issues include climatic and temporal limitations, the biological origin and state (free versus bound) of PalEnDNA, stratigraphic reliability, sterile sampling, ability to distinguish modern from aDNA signals, DNA damage and PCR amplification, DNA extraction methods, and taxonomic resolution. In this review, we provide a non‐specialist introduction to the use of PalEnDNA for Quaternary and archaeological researchers, assess attributes and limitations of this palaeoenvironmental tool, and discuss future prospects of using PalEnDNA to reconstruct past environments.  相似文献   

Dissolution of Quartz, Albite, and Orthoclase in H2O-Saturated Haplogranitic Melt at 800{degrees}C and 200 MPa: Diffusive Transport Properties of Granitic Melts at Crustal Anatectic Conditions     

ACOSTA-VIGIL  ANTONIO; LONDON  DAVID; MORGAN  GEORGE B.  VI; DEWERS  THOMAS A. 《Journal of Petrology》2006,47(2):231-254

We have conducted experiments on dissolution of quartz, albite,orthoclase, and corundum into H₂O-saturated haplogranite meltat 800°C and 200 MPa over a duration of 120–1488 hwith the aim of ascertaining the diffusive transport propertiesof granitic melts at crustal anatectic temperatures. Cylindersof anhydrous starting glass and a single mineral phase (quartzor feldspar) were juxtaposed along flat and polished surfacesinside gold or platinum capsules with 10 wt % added H₂O. Concentrationprofiles in glass (quenched melt) perpendicular to the mineral–glassinterfaces and comparison with relevant phase diagrams suggestthat melts at the interface are saturated in the dissolvingphases after 384 h, and with longer durations the concentrationprofiles are controlled only by diffusion of components in themelt. The evolution of the concentration profiles with timeindicates that uncoupled diffusion in the melt takes place alongthe following four linearly independent directions in oxidecomposition space: SiO₂, Na₂O, and K₂O axes (Si-, Na-, and K-eigenvectors,respectively), and a direction between the Al₂O₃, Na₂O, andK₂O axes (Al-eigenvector), such that the Al/Na molar ratio isequal to that of the bulk melt and the Al/(Na + K) molar ratiois equal to the equilibrium ASI (= mol. Al₂O₃/[Na₂O + K₂O])of the melt. Experiments in which a glass cylinder was sandwichedbetween two mineral cylinders—quartz and albite, quartzand K-feldspar, or albite and corundum—tested the validityof the inferred directions of uncoupled diffusion and exploredlong-range chemical communication in the melt via chemical potentialgradients. The application of available solutions to the diffusionequations for the experimental quartz and feldspar dissolutiondata provides diffusivities along the directions of the Si-eigenvectorand Al-eigenvector of (2·0–2·8) x 10^–15m²/s and (0·6–2·4) x 10^–14 m²/s, respectively.Minimum diffusivities of alkalis [(3–9) x 10^–11m²/s] are orders of magnitude greater than the tetrahedral componentsof the melt. The information provided here determines the rateat which crustal anatexis can occur when sufficient heat issupplied and diffusion is the only mass transport (mixing) processin the melt. The calculated diffusivities imply that a quartzo-feldspathicsource rock with initial grain size of 2–3 mm undergoinghydrostatic, H₂O-saturated melting at 800°C (infinite heatsupply) could produce 20–30 vol. % of homogeneous meltin less than 1–10 years. Slower diffusion in H₂O-undersaturatedmelts will increase this time frame. KEY WORDS: chemical diffusion; haplogranite; mineral dissolution experiments; crustal anatexis  相似文献