Lateglacial to Holocene relative sea‐level changes in the Stykkishólmur area,northern Snæfellsnes,Iceland          下载免费PDF全文

MARTIN D. BRADER  JEREMY M. LLOYD  MICHAEL J. BENTLEY  ANTHONY J. NEWTON 《第四纪科学杂志》2015,30(5):497-507

Comparatively little research has been undertaken on relative sea‐level (RSL) change in western Iceland. This paper presents the results of diatom, tephrochronological and radiocarbon analyses on six isolation basins and two coastal lowland sediment cores from the Stykkishólmur area, northern Snæfellsnes, western Iceland. The analyses provide a reconstruction of Lateglacial to mid‐Holocene RSL changes in the region. The marine limit is measured to 65–69 m above sea level (asl), with formation being estimated at 13.5 cal ka BP. RSL fall initially occurred rapidly following marine limit formation, until ca. 12.6 cal ka BP, when the rate of RSL fall decreased. RSL fell below present in the Stykkishólmur area during the early Holocene (by ca. 10 cal ka BP). The rates of RSL change noted in the Stykkishólmur area demonstrate lesser ice thicknesses in Snæfellsnes than Vestfirðir during the Younger Dryas, when viewed in the regional context. Consequently, the data provide an insight into patterns of glacio‐isostatic adjustment surrounding Breiðafjörður, a hypothesized major ice stream at the Last Glacial Maximum.  相似文献   

Late Younger Dryas and early Holocene palaeoenvironments in the Skagerrak,eastern North Atlantic: a multiproxy study     

DORTHE RENG ERBS‐HANSEN  KAREN LUISE KNUDSEN  ANTHONY CAVEDO GARY  EYSTEIN JANSEN  RICHARD GYLLENCREUTZ  VINCENT SCAO  KURT LAMBECK 《Boreas: An International Journal of Quaternary Research》2011,40(4):660-680

Erbs‐Hansen, D. R., Knudsen, K. L., Gary, A. C., Jansen, E., Gyllencreutz, R., Scao, V. & Lambeck, K. 2011: Late Younger Dryas and early Holocene palaeoenvironments in the Skagerrak, eastern North Atlantic: a multiproxy study. Boreas, 10.1111/j.1502‐3885.2011.00205.x. ISSN 0300‐9843 A high‐resolution study of palaeoenvironmental changes through the late Younger Dryas and early Holocene in the Skagerrak, the eastern North Atlantic, is based on multiproxy analyses of core MD99‐2286 combined with palaeowater depth modelling for the area. The late Younger Dryas was characterized by a cold ice‐distal benthic foraminiferal fauna. After the transition to the Preboreal (c. 11 650 cal. a BP) this fauna was replaced by a Cassidulina neoteretis‐dominated fauna, indicating the influence of chilled Atlantic Water at the sea floor. Persisting relatively cold bottom‐water conditions until c. 10 300 cal. a BP are presumably a result of an outflow of glacial meltwater from the Baltic area across south‐central Sweden, which led to a strong stratification of the water column at MD99‐2286, as also indicated by C. neoteretis. A short‐term peak in the C/N ratio at c. 10 200 cal. a BP is suggested to indicate input of terrestrial material, which may represent the drainage of an ice‐dammed lake in southern Norway, the Glomma event. After the last drainage route across south‐central Sweden closed, c. 10 300 cal. a BP, the meltwater influence diminished, and the Skagerrak resembled a fjord with a stable inflow of waters from the North Atlantic through the Norwegian Trench and a gradual increase in boreal species. Full interglacial conditions were established at the sea floor from c. 9250 cal. a BP. Subsequent warm stable conditions were interrupted by a short‐term cooling around 8300–8200 cal. a BP, representing the 8.2 ka event.  相似文献   

Petrogenesis of sediments in the absence of chemical weathering: effects of abrasion and sorting on bulk composition and mineralogy   总被引：15，自引：0，他引：15  

H. WAYNE NESBITT  GRANT M. YOUNG 《Sedimentology》1996,43(2):341-358

Comminution in the glaciers that debouch into Guys Bight Basin, followed by selective sorting in the fluvial system, has had little effect on the bulk composition, or on the mineralogy, of the basin sands and muds. Most striking are the feldspar contents, and the feldspar-quartz ratios in sands and muds, both of which remain similar to those of average bedrock. The feldspar contents of sands and muds range from 48 to 52% feldspar whereas average bedrock contains 51·7% feldspar. Feldspar-quartz ratios average 1·58:1 in bedrock and 1·54:1, 1·66:1 and 1·69:1 in the medium to coarse sands, fine sands and muds, respectively, indicating minimal feldspar enrichment in the fine-grained sediments. In the absence of appreciable chemical weathering, extreme abrasion followed by hydraulic sorting has not produced mature sediments such as quartz arenites and clay-mineral-rich muds. There is, however, some chemical differentiation. Preferential accumulation of mafic minerals in fine sands and muds is reflected in bulk compositions by higher abundances of MgO, FeO and TiO₂, and in the mineralogy by enrichment of biotite in the fine grades. Bulk compositional studies focused solely on muds and mudstones will result in an overestimate of the mafic contribution from source rocks. This work shows that bulk compositional studies of sediments and sedimentary rocks should include all available granulometric grades.  相似文献   

A Quartz Syenite Intrusion in the New Jersey Highlands     

YOUNG  DAVIS A. 《Journal of Petrology》1972,13(3):511-528

A Sheel of clinopyroxene quartz syenite, in the PrecambrianHighlands of New Jersey near Berkshire Valley, transects structuraltrends in surrounding gneisses that have been metamorphosedto the hornblende granulite subfacies. The quartz syenite lacksfoliation, lineation, and visible layering. The rock has hypautomorphic-granular texture and is composedchiefly of mesoperthite, quartz, and ferrohedenbergite. Locallyfayalite or hornblende are common. Accessory minerals includeplagioclase and potassium feldspar, zircon, apatite, magnetite,ilmenite, covellite, and pyrite. Contour maps based on modesof thirty-six specimens of quartz syenite indicate progressiveincrease in quartz content and corresponding decrease in maficmineral content from east to west. These modal variations suggestsome degree of gravitational settling of crystals. Althoughthe rock is chemically similar to many Precambrian syenitesin eastern North America, it is distinguished from them by anextremely high Fe/Mg ratio. It is believed that the quartz syenite was intruded as a magmaduring the late stages of folding of the host gneisses. Themagma was highly undersaturated with respect to H₂O during mostof the course of crystallization. Initial H₂O content was probablyfar less than 0.5 weight per cent. Crystallization of most ofthe mass occurred at temperatures well in excess of 800°Cand at load pressures well in excess of 2.5 kilobars. The magmawas probably derived by deep-seated anatexis of Fe-rich, Mg-poorsyenitic gnessies that are now widely exposed in the New JerseyHighlands.  相似文献   

The Petrogenesis of the Kirwan Basalts of Dronning Maud Land, Antarctica   总被引：3，自引：3，他引：0  

HARRIS  CHRIS; MARSH  JULIAN S.; DUNCAN  ANDREW R.; ERLANK  ANTHONY J. 《Journal of Petrology》1990,31(2):341-369

The 420 m thick sequence of Kirwan basalt crops out along thesouthernmost 50 km of the Kirwanveggen Escarpment (74?S, 6?W).There is little variation in major element chemistry of thesebasalts (SiO₂ 49?3–51?6 wt.%; MgO 5?1–6?6 wt.%),but the concentrations of certain incompatible elements (e.g.,Zr) vary by factors of approximately two or more. Most interelementplots show rather poor correlation (r<0?78), but rocks fromopposite ends of the data array can be related by 30% fractionationof plagioclase, clinopyroxene, olivine, and magnetite in theproportions 51:35:11:3. Plagioclase is much more abundant inphenocryst assemblages (85%) and it appears that selective transportof plagioclase to the surface occurred. The range in incompatible element concentrations cannot be explainedby crystal fractionation and is most probably a result of theparent liquids of these basalts being derived by slightly differentdegrees of partial melting of a common source, or alternativelyof open-system (RTF) magma processes. The strontium isotopedata for the freshest rocks (R₀=0?7049–0?7065) may beexplained by 7% contamination by crustal material with an R₀of 0?709 and bulk Sr of800 ppm, but there is little supportingevidence from other trace element variations for this hypothesis.Oxygen isotope determinations on whole-rock-plagioclase pairsshow that alteration has resulted in a 0?5%o shift in (¹⁸O.Alteration also appears to have resulted in a greater spreadof data, particularly for the LIL elements and Sr isotopes.The Sr and Nd isotopic composition of the suite is close tobulk Earth at 172 Ma and this, together with REE and other traceelement data, shows these basalts to be similar in compositionto the more primitive basalts among the Karoo basalt lavas.It is suggested that the Kirwan basalts were derived from asource which was similar to that of the southern Lebombo variantof the Sabie River Basalt Formation of the Karoo Volcanic Province.This part of the Karoo was closest to the Kirwanveggen beforethe break-up of Gondwanaland.  相似文献   

Spherical and columnar, septarian, ¹⁸O-depleted, calcite concretions from Middle–Upper Permian lacustrine siltstones in northern Mozambique: evidence for very early diagenesis and multiple fluids     

VICTOR A. MELEZHIK  ANTHONY E. FALLICK†  RICHARD A. SMITH‡  DANTA M. ROSSE§ 《Sedimentology》2007,54(6):1389-1416

Calcite septarian concretions from the Permian Beaufort Group in the Maniamba Graben (NW Mozambique) allow controls on the composition and nature of diagenetic fluids to be investigated. The concretions formed in lacustrine siltstones, where they occur in spherical (1 to 70 cm in diameter) and columnar (up to 50 cm long) forms within three closely spaced, discrete beds totalling 2·5 m in thickness. Cementation began at an early stage of diagenesis and entrapped non‐compacted burrows and calcified plant roots. The cylindrical concretions overgrew calcified vertical plant roots, which experienced shrinkage cracking after entrapment. Two generations of concretionary body cement and two generations of septarian crack infill are distinguished. The early generation in both cases is a low‐Mn, Mg‐rich calcite, whereas the later generation is a low‐Mg, Mn‐rich calcite. The change in chemistry is broadly consistent with a time (burial)‐related transition from oxic to sub‐oxic/anoxic conditions close to the sediment–water interface. Geochemical features of all types of cement were controlled by the sulphate‐poor environment and by the absence of bacterial sulphate reduction. All types of cement present have δ¹³C ranging between 0‰ and −15‰(Vienna Peedee Belemnite, V‐PDB), and highly variable and highly depleted δ¹⁸O (down to 14‰ Vienna Standard Mean Ocean Water, V‐SMOW). The late generation of cement is most depleted in both ¹³C and ¹⁸O. The geochemical and isotopic patterns are best explained by interaction between surface oxic waters, pore waters and underground, ¹⁸O‐depleted, reducing, ice‐meltwaters accumulated in the underlying coal‐bearing sediments during the Permian deglaciation. The invariant δ¹³C distribution across core‐to‐rim transects for each individual concretion is consistent with rapid lithification and involvement of a limited range of carbon sources derived via oxidation of buried plant material and from dissolved clastic carbonates. Syneresis of the cement during an advanced stage of lithification at early diagenesis is considered to be the cause of development of the septarian cracks. After cracking, the concretions retained a small volume of porosity, allowing infiltration of anoxic, Ba‐bearing fluids, resulting in the formation of barite. The results obtained contribute to a better understanding of diagenetic processes at the shallow burial depths occurring in rift‐bound, lacustrine depositional systems.  相似文献   

Quantifying the Building Blocks of Igneous Rocks: Are Clustered Crystal Frameworks the Foundation?   总被引：6，自引：6，他引：6  

JERRAM  DOUGAL A.; CHEADLE  MICHAEL J.; PHILPOTTS  ANTHONY R. 《Journal of Petrology》2003,44(11):2033-2051

Most phenocryst populations in volcanic rocks, and those preservedin shallow-level igneous intrusions, are clustered (variouslyreferred to as clots, clumps or glomerocrysts). These clustersof crystals are the building blocks that accumulate to formthe high-porosity, touching crystal frameworks from which igneouscumulates form. Examination of touching crystal frameworks inolivine- (komatiite cumulates and experimental charges) andplagioclase-dominant crystal populations (Holyoke flood basalt,Connecticut, USA) reveal complex, high-porosity, clustered crystalarrangements. Olivine touching frameworks in komatiite flowsare interpreted to form in hundreds of days. Plagioclase frameworksare calculated to have formed in less than 17 years for a crystalgrowth rate of 1 x 10^-10 mm/s to less than 3 years for a growthrate of 5 x 10^-10 mm/s based on crystal size distributions.The origin of crystal clusters is likely to involve either (ora combination of) heterogeneous nucleation, remobilization ofcumulate mushes or crystals sticking together during settlingand/or flow. The spatial distribution pattern of clustered crystalframeworks from both natural and experimental examples constrainsfields on spatial packing diagrams that allow the identificationof touching and non-touching crystal populations, and furtherimprove our understanding of crystal packing arrangements andcluster size distributions. KEY WORDS: cumulates; CSD; komatiite; basalt; spatial packing; textural analysis  相似文献   

Magma Storage Region Processes Inferred from Geochemistry of Fe-Ti Oxides in Andesitic Magma, Soufriere Hills Volcano, Montserrat, W.I.     

DEVINE  J. D.; RUTHERFORD  M. J.; NORTON  G. E.; YOUNG  S. R. 《Journal of Petrology》2003,44(8):1375-1400

Analyses of Fe–Ti oxides help constrain models of magmastorage region processes for the Soufrière Hills Volcano,Montserrat (W.I.), and provide clear evidence of the natureof transient heating events in the magma storage region. Toconstrain timescales of magma heating and remobilization, theTiO₂ zoning patterns in a time series of natural titanomagnetiteswere compared with those produced in controlled phase equilibriumexperiments on the andesite. Most samples of andesite eruptedfrom 1995 to 2002 contain titanomagnetite crystals with uniformcore compositions (TiO₂  相似文献   

Factors Controlling Chemistry of Magmatic Spinel: an Empirical Study of Associated Olivine, Cr-spinel and Melt Inclusions from Primitive Rocks   总被引：29，自引：5，他引：29  

KAMENETSKY  VADIM S.; CRAWFORD  ANTHONY J.; MEFFRE  SEBASTIEN 《Journal of Petrology》2001,42(4):655-671

Compositions of  相似文献   

Petrology of Biotite-Cordierite-Garnet Gneiss of the McCullough Range, Nevada II. P-T-aH2O Path and Growth of Cordierite During Late Stages of Low-P Granulite-Grade Metamorphism     

YOUNG  EDWARD D. 《Journal of Petrology》1989,30(1):61-78

Thermodynamic calculations based on addition of mass balanceequations to the Gibbs Method (Spear, 1986) are used to modelthe cordierite-producing reaction in pelitic gneiss from theMcCullough Range, southern Nevada. Calculations which treatthe model paragenesis as a system open to transfer of H₂O areconsistent with textural relations. Results indicate that cordieritegrew by the continuous net-transfer reaction: 0?76 BIO+1?72 SILL+3? 55 QTZ+0?27 PLG+0?005 GRT +0?06Al₂R²⁺_–1Si_–1[BIO]1?02 KSP+0?76 H₂O +0?30 FeMg_–1[CRD]+0?15FeMg_–1[BIO]+0?0005 FeMg_–1[GRT] +0?005 CaNaAl_–1Si_–1[PLG] with decreasing P, decreasing T, and increasing a_H2O The steepretrograde dP/dT path for these low-pressure granulites contrastswith isobaric cooling paths typical of higher pressure granulites,and suggests uplift and erosion were active during Proterozoicgranulite-grade metamorphism in this area.  相似文献