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111.
Morphology and facies architecture of a falling sea level strandplain, Umiujaq, Hudson Bay, Canada 总被引:1,自引:0,他引:1
Coastal strandplain deposits near Umiujaq, eastern Hudson Bay, Canada, were formed under falling relative sea level conditions resulting from postglacial isostatic uplift. Ground-probing radar profiles across the strandplain reveal a lower progradational unit (LPU) discordantly overlain by an upper progradational unit (UPU), which were correlated with stratigraphic sections exposed in incised valley walls. The discordance is a wave erosion surface (WES) that separates fine shoreface sands of the LPU from coarse-sand and gravel of the UPU. Major basal downlap surfaces can be traced updip into marine terraces and define downstepping wedges. The downstepping is interpreted as representing ‘autocyclic’ morphological reconfiguration rather than a response to changes in the rate of sea level fall. The internal architecture is strongly dependent on the accommodation and thus on antecedent topography. A conceptual model for strandplain deposition under falling sea level incorporates a bipartite shallowing-upward sandy succession when sufficient accommodation is available. Where accommodation space is limited, a sharp-based bar-and-beach sandbody directly overlies muddy deeper water deposits and the WES resembles a regressive surface of erosion. 相似文献
112.
HENRIK VOSGERAU SVEND FUNDER MICHAEL KELLY KAREN LUISE KNUDSEN CHRISTIAN KRONBORG HANNE BIRGIT MADSEN HANS PETTEK SEJRUP 《Boreas: An International Journal of Quaternary Research》1994,23(4):398-411
Coastal cliffs and stream cut sections at Langelandselv on Jameson Land show a 22 m thick sedimentary succession reflecting the development of shallow marine and fluvial environments during the last interglaciation. The shallow marine sediments were deposited in upper shoreface, back-barrier, and delta environments during a rise in the relative sea level from 0 to 18 m. The interglacial succession ends with glaciotectonically dislocated fluvial sand, and is capped by alternating beds of lodgement till and fluvial sand, deposited during the Early Weichselian. The age is determined by palacoceanographic correlation of molluse and foraminifer faunas with isotopic substage 5e in the deep sea record, supported by luminescencs and U/Th dates and amino acid analysis. 相似文献
113.
114.
ANDREAS PAUL JOHN J. G. REIJMER JÖRN FÜRSTENAU HANNO KINKEL CHRISTIAN BETZLER 《Sedimentology》2012,59(5):1640-1658
A piston core from the Maldives carbonate platform was investigated for carbonate mineralogy, grain‐size distributions, calcium carbonate content and organic carbon. The sedimentary record was linked to Late Pleistocene sea‐level variations, using an age model based on oxygen isotopes obtained from planktonic foramanifera, nannofossil biostratigraphy and 14C age determinations. The correlation between the sedimentary record and Late Pleistocene sea‐level showed that variations in aragonite and mud during the past 150 000 years were clearly related to flooding and sea floor exposure of the main lagoons of the atolls of the Maldives carbonate platform. Platform flooding events were characterized by strongly increased deposition of aragonite and mud within the Inner Sea of the Maldives. Exposure events, in contrast, can be recognized by rapid decreases in the values of both proxy records. The results show that sediments on the Maldives carbonate platform contain a continuous record of Pleistocene sea‐level variations. These sediments may, therefore, contribute to a better understanding of regional and even global sea‐level changes, and yield new insights into the interplay between ocean currents and carbonate platform morphology. 相似文献
115.
SOHINI?GANGULYEmail author JYOTISANKAR?RAY CHRISTIAN?KOEBERL THEODOROS?NTAFLOS MOUSUMI?BANERJEE 《Journal of Earth System Science》2012,121(1):91-108
Several basaltic lava flows have been identified in the study area in and around Linga, in the Eastern Deccan Volcanic Province
(EDVP) on the basis of distinctly developed structural zones defined by primary volcanic structures such as columnar joints
and vesicles. These basaltic lava flows are spatially distributed in four different sectors, viz., (i) Bargona–Gadarwara (BG)
sector (ii) Shikarpur–Linga (SL) sector (iii) Arjunvari–Survir Hill (AS) sector and (iv) Kukrachiman–Morand Hill (KM) sector.
A three-tier classification scheme has been adopted for the characterization and classification of individual lava flows.
Each lava flow consists of a Lower Colonnade Zone (LCZ) overlain by the Entablature Zone (EZ) and Upper Colonnade Zone (UCZ).
The LCZ and UCZ grade into a distinct/indistinct Lower Vesicular Zone (LVZ) and Upper Vesicular Zone (UVZ), respectively.
The LCZ and UCZ of the flows are characterized by columnar joints while the EZ is marked by multi-directional hackly jointing.
The geometry of different joint patterns corresponds to different styles of cooling during solidification of lava flows. Detailed
petrographic studies of the investigated lava flows reveal inequigranular phenocrystal basalts characterized by development
of phenocrystal phases including plagioclase, clinopyroxene and olivine, whereas groundmass composition is marked by tiny
plagioclase, clinopyroxene, opaque mineral and glass. Electron microprobe analyses indicate that the olivine has a wide range
∼Fo22 to Fo66 revealing a wide spectrum of compositional variation. Pyroxene compositions are distinctly designated as Quad pyroxenes.
Phenocrystal pyroxenes are mostly diopsidic, while the groundmass pyroxenes mainly correspond to augite with a minor pigeonite
component. Pyroxene phenocrysts are characterized by a prominent Ti-enrichment. Phenocrystal plagioclase grains are calcic
(An52.7–An72.9), whereas groundmass plagioclase are relatively sodic (An39.2–An61.6). Groundmass opaque minerals are characteristically found to be Ti–magnetite/ilmenite/pyrophanite. Pyroxene thermometry reveals
a temperature span of 850°C to 1280°C for the studied lavas while olivine–clinopyroxene thermometry yields a temperature range
from 1040°–1160°C. The variation of temperature for the lava flows is ascribed to their normal cooling history after eruption. 相似文献