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MARTINA HÄTTESTRAND ANN‐MARIE ROBERTSSON 《Boreas: An International Journal of Quaternary Research》2010,39(2):296-311
Hättestrand, M. & Robertsson, A.‐M. 2010: Weichselian interstadials at Riipiharju, northern Sweden – interpretation of vegetation and climate from fossil and modern pollen records. Boreas, 10.1111/j.1502‐3885.2009.00129.x. ISSN 0300‐9483. The most complete records of Weichselian ice‐free conditions in northern Sweden have been retrieved from kettleholes in the Riipiharju esker. In an earlier study, the Riipiharju I core was described as containing two Weichselian interstadials and Riipiharju was chosen as type site for the second Weichselian interstadial in northern Sweden. Here, we present a palynological investigation of two new sediment cores (Riipiharju II and III) retrieved from Riipiharju. Together, the new cores comprise a late cold part of the first Weichselian interstadial recorded in northeastern Sweden (Tärendö I, earlier correlated with Peräpohjola in Finland) as well as a long sequence of the second Weichselian interstadial (Tärendö II, earlier named Tärendö). The results indicate that the climate during deposition of the Tärendö II sequence was more variable than earlier suggested. According to the present interpretation it was relatively warm in the early part of Tärendö II; thereafter a long cold phase persisted, and finally the climate was warmer again in the late part of Tärendö II. The warm phases are characterized by Betula‐dominant pollen assemblages, while the cold phase is characterized by high percentages of Artemisia and Gramineae pollen. Since there is still no firm chronology established of the interstadials in northeastern Sweden, two possible correlations are discussed; either Tärendö I and II are correlated with Brörup (MIS 5c) and Odderade (MIS 5a), or, perhaps more likely, they are correlated with Odderade and early Middle Weichselian (MIS 3) time. 相似文献
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Coagulation and transport of sediments in the Gironde Estuary 总被引：3，自引：0，他引：3
The distribution of suspended particle size and concentration were measured along the Gironde Estuary, France, from the river seaward to the ocean. The suspended particle size and volume concentration were measured using in situ holography and onboard optical techniques utilizing special procedures in order to avoid floc breakage. Sediments discharged by the rivers coagulate upon encountering the very low salinities (0.2‰ of the upper estuary (confirmed with laboratory experiments), and are then transported and deposited by currents in the remainder of the estuary. This coagulation, coupled with estuarine circulation, produces a turbidity maximum which is offset between the surface and bottom waters. The floc size maximum is oceanward of the turbidity maximum and is, likewise, offset along the estuary by about 30 km. The estuary can be subdivided into the following zones: (1) coagulation; (2) hydrodynamic, landward of the null point; and (3) hydrodynamic, seaward of the null point. Initial coagulation appears to be completed in coagulation zone (1), and particles are transported and settled (with very little floc breakage and recoagulation) in zones (2) and (3) only. The floc settling velocities, coupled with estuarine circulation, control the concentration and size distributions of flocs in the water column, and eventually control the deposition of sediments. 相似文献
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McBRIDE J. S.; LAMBERT D. D.; NICHOLLS I. A.; PRICE R. C. 《Journal of Petrology》2001,42(6):1197-1218
Basalts from the Quaternary Newer Volcanics Province in southeasternAustralia have a large diversity in their chemical and Nd, Srand Os isotopic compositions. Plains series olivine tholeiitesand Cones series nepheline hawaiites have distinctive isotopiccompositions and are clearly not related to each other by asimple genetic process. The Cones series nepheline hawaiiteshave trace element abundances and Nd ( 相似文献
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Penelope J. WOZNIAKIEWICZ Hope A. ISHII Anton T. KEARSLEY Mark J. BURCHELL John P. BRADLEY Mark C. PRICE Nick TESLICH Martin R. LEE Mike J. COLE 《Meteoritics & planetary science》2012,47(4):708-728
Abstract– The grains returned by NASA’s Stardust mission from comet 81P/Wild 2 represent a valuable sample set that is significantly advancing our understanding of small solar system bodies. However, the grains were captured via impact at ～6.1 km s?1 and have experienced pressures and temperatures that caused alteration. To ensure correct interpretations of comet 81P/Wild 2 mineralogy, and therefore preaccretional or parent body processes, an understanding of the effects of capture is required. Using a two‐stage light‐gas gun, we recreated Stardust encounter conditions and generated a series of impact analogs for a range of minerals of cometary relevance into flight spare Al foils. Through analyses of both preimpact projectiles and postimpact analogs by transmission electron microscopy, we explore the impact processes occurring during capture and distinguish between those materials inherent to the impactor and those that are the product of capture. We review existing and present additional data on olivine, diopside, pyrrhotite, and pentlandite. We find that surviving crystalline material is observed in most single grain impactor residues. However, none is found in that of a relatively monodisperse aggregate. A variety of impact‐generated components are observed in all samples. Al incorporation into melt‐derived phases allows differentiation between melt and shock‐induced phases. In single grain impactor residues, impact‐generated phases largely retain original (nonvolatile) major element ratios. We conclude that both surviving and impact‐generated phases in residues of single grain impactors provide valuable information regarding the mineralogy of the impacting grain whilst further studies are required to fully understand aggregate impacts and the role of subgrain interactions during impact. 相似文献
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Abstract The data-based mechanistic (DBM) modelling methodology is applied to the study of reservoir sedimentation. A lumped-parameter, discrete-time model has been developed which directly relates rainfall to suspended sediment load (SSL) at the reservoir outflow from the two years of measured data at Wyresdale Park Reservoir (Lancashire, UK). This nonlinear DBM model comprises two components: a rainfall to SSL model and a second model, relating the SSL at the reservoir inflow to the SSL at the reservoir spillway. Using a daily measured rainfall series as the input, this model is used to reconstruct daily deposition rates between 1911 and 1996. This synthetic sediment accretion sequence is compared with the variations in sand content within sediment cores collected from the reservoir floor. These profiles show good general agreement, reflecting the importance of low reoccurrence, high magnitude events. This preliminary study highlights the potential of this DBM approach, which could be readily applied to other sites. 相似文献
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Primitive Magma From the Jericho Pipe, N.W.T., Canada: Constraints on Primary Kimberlite Melt Chemistry 总被引：12，自引：7，他引：5
We report the first estimates of primary kimberlite melt compositionfrom the Slave craton, based on samples of aphanitic kimberlitefrom the Jericho kimberlite pipe, N.W.T., Canada. Three samplesderive from the margins of dykes where kimberlite chilled againstwall rock (JD51, JD69 and JD82) and are shown to be texturallyconsistent with crystallization from a melt. Samples JD69 andJD82 have geochemical characteristics of primitive melts: theyhave high MgO (20–25 wt %), high mg-numbers (86–88),and high Cr (1300–1900 ppm) and Ni (800–1400 ppm)contents. They also have high contents of CO2 (10–17 wt%). Relative to bulk macrocrystal kimberlite, they have lowermg-numbers and lower MgO but are enriched in incompatible elements(e.g. Zr, Nb and Y), because the bulk kimberlite compositionsare strongly controlled by accumulation of mantle olivine andother macrocrysts. The compositions of aphanitic kimberlitefrom Jericho are similar to melts produced experimentally bypartial melting of a carbonate-bearing garnet lherzolite. Onthe basis of these experimental data, we show that the primarymagmas from the Jericho kimberlite could represent 0·7–0·9%melting of a carbonated lherzolitic mantle source at pressuresand temperatures found in the uppermost asthenosphere to theSlave craton. The measured CO2 contents for samples JD69 andJD82 are only slightly lower than the CO2 contents of the correspondingexperimental melts; this suggests that the earliest hypabyssalphase of the Jericho kimberlite retained most of its originalvolatile content. As such these samples provide a minimum CO2content for the primary kimberlite magmas from the Slave craton. KEY WORDS: kimberlite; melt; primitive; primary magma; Slave craton 相似文献
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Abstract Bangladesh, with its small but rich agricultural land (total area 9 million ha) and large population (80 million) is faced with an acute food crisis. The economy of Bangladesh is dependent mainly upon agriculture which, in turn, is dependent upon rainfall. An increase in crop acreage and productivity during the pre-monsoon season, March to May, offers a partial solution to the problem. The water available from the rainfall of this season could be utilized through proper planning for better agricultural uses. The present study is an attempt at an inventory of such pre-monsoon rainfall, both monthly and seasonally, and its variability over time and space. The technique employed is that of trend surface mapping. 相似文献
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RAPHAËL BOURILLOT EMMANUELLE VENNIN JEAN‐MARIE ROUCHY CHRISTOPHE DURLET VINCENT ROMMEVAUX CHRISTOPHE KOLODKA FREDERIC KNAP 《Sedimentology》2010,57(2):477-512
The Sorbas Member is a late Messinian complex sedimentary system that formed immediately following deposition of the Messinian evaporites in the Sorbas Basin (South‐east Spain). This work describes the sequence architecture and facies organization of a continuous kilometre long, alluvial fan to open platform transect near the village of Cariatiz in the north‐east of the basin. The post‐evaporitic Cariatiz platform was a mixed carbonate‐siliciclastic system composed of four intermediate‐frequency, fifth‐order depositional sequences (Depositional Sequences 1 to 4) arranged in an overall prograding trend. The intense fracturing and brecciation of these deposits is attributed to the deformation and dissolution of an evaporite body measuring several tens of metres in thickness. The four sequences display significant spatial–temporal variability in both architecture and facies distribution, with two main phases: (i) Depositional Sequences 1 and 2 are ooid and oobioclastic dominated, and show normal marine faunas; and (ii) Depositional Sequences 3 and 4 show a higher siliciclastic contribution and are microbialite dominated. These important changes are interpreted as modifications of the primary controlling factors. Following an initial 70 m drowning, possibly linked to increased oceanic input, Depositional Sequences 1 to 3 were controlled mainly by eustatic variations and inherited topography; their progradation destabilized the evaporite body near the end of the Depositional Sequence 2 period. During the second phase, Depositional Sequences 3 and 4 recorded a progressive restriction of the Sorbas Basin related to a 30 to 40 m fall in water level that was driven mainly by regional factors. These regional factors were dissolution and gravity‐induced deformation of the evaporites and correlative evaporative fluid circulation associated with the contrasted arid/humid regional climate that, respectively, controlled sequence geometry and fluctuating water salinity which caused a microbialite bloom. 相似文献
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ILFRYN PRICE 《Sedimentology》1977,24(4):529-546
The Othris Mountains of eastern Greece contain a calcareous continental margin/ocean basin sequence exposed in a stack of Cretaceous thrust sheets. Upper Triassic to Lower Cretaceous shelf, submarine fan and basinal successions overlie shallow marine units of Lower Triassic and Permian age. In off-shelf sequences the older sediments are separated from the younger by a horizon of alkaline ‘early-rifting’ basalts. Ophiolites overthrust the marginal sequence. Pre-rifting sediments are represented by a varied suite of limestones and clastics resting on metamorphic basement and include distinctive, green lithic arenites. In the thrust sheet immediately over the para-autochthonous shelf sequence, pre-rifting sediments are separated from the rift basalts by an intermittent horizon of calcareous sandstones and conglomerates reworked from uplifted basement and older sediments. Textural and petrographic immaturity suggests that these are probably deposits derived from fault scarps, produced in an early phase of rifting. Above the basalts in the same sheet is a suite of calciclastic sediment-gravity-flow deposits, apparently sedimented on a submarine fan. Progressive downslope modification of calcirudites suggests deposition from evolving, high concentration flows. Massive calcarenite facies (? grain flows) are unusually abundant; a possible reflection of a shallow palaeo-shelf break since provenance and palaeocurrent evidence proves the clastic carbonates to have been derived from a calcareous shelf. In addition to limestone lithoclasts the calcirudites, but not the massive calcarenites, contain fragments of pre-rifting lithologies including the distinctive arenites. Since the shelf sequence in Othris is totally nondetrital these clasts imply derivation of coarse sediment from an off-shelf position; probably the walls of a submarine canyon. This may have occurred either by direct erosion of wall rock, or by reworking of material from an older clastic sequence. In the latter case the inferred fault-scarp deposits are a likely source. 相似文献