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21.
Graeme Whittington Rodger E. Connell G. Russell Coope Kevin J. Edwards Adrian M. Hall Peter D. Hulme Jack Jarvis 《第四纪科学杂志》1998,13(4):309-324
Pre-Late Devensian organic deposits in the Buchan area of northeast Scotland were investigated for their geomorphological and palaeoecological (pollen, plant macrofossils, coleoptera) properties. Close ecological agreement exists between fossil indicators and allows the inference that the environment in the vicinity of the deposits was a dwarf shrub tundra of the type met today in high latitude areas of Scandinavia and arctic Russia. The latest in a series of radiocarbon dates from the site produced determinations beyond the limits of the method, although the geomorphological and fossil evidence appears to point to an interstadial date within Oxygen Isotope Stages 5a or 5c. The site has special significance for arguments concerning the much-debated concept of ‘Moraineless Buchan’; indeed, evidence is presented which supports the concept of extensive ice sheet glaciation during the Late Devensian for this crucial geographical area. If Buchan is to be seen as a further casualty amongst other disputed ice-free enclaves, then a return to earlier models of extensive ice sheet glaciation in the Late Devensian of Scotland would seem to be necessary. © 1998 John Wiley & Sons, Ltd. 相似文献
22.
James G. Brophy Carla S. Whittington Young-Rok Park 《Contributions to Mineralogy and Petrology》1999,135(2-3):277-290
Several high alumina basalts from the Aleutian volcanic centers of Cold Bay and Kanaga Island contain large (up to 1.5 cm
diameter) megacrysts of sector-zoned augite. The megacrysts are invariably euhedral with well developed {001}, {010} and {111}
forms. All crystals display concentric bands that are rich in mineral and glass inclusions. The sector zonation typically
occurs as well developed (010), (100), (111) and (110) sectors which grew at different rates. A comparison of the width of
synchronous growth bands indicates that following relative growth rates: (111) ≫ (100) ∼ (110) > (010). Compositionally, SiO2 and MgO abundances decrease, and TiO2, Al2O3, FeO and Na2O abundances increase in the different sectors in the order (111), (100) ∼ (110), (010). This order is identical to that deduced
for the relative growth rates, implying that growth rate clearly had a role in the development of the sector zonation. Calculated
pre-eruption H2O contents of the basalts range from 1 to 3 wt% but actual (measured) post-eruption H2O contents range from 0.01 to 0.3 wt%. Deteurium isotopic values are heavily depleted and range from −110 to −141‰ . Together
these indicate significant vapor (H2O) exsolution prior to eruption. Maximum H2O abundances in primitive glass inclusions, thought to be most representative of the host liquid reservoir at the time of
melt entrapment, systematically decrease from the core to the rim of one augite megacryst studied in detail. We conclude that
the presence of sector-zoned augite is due to augite supersaturation and rapid crystallization brought about by magma decompression
and volatile (H2O) exsolution. The calculated pre-eruption H2O contents of 1–3 wt% limit vapor exsolution and basalt crystallization to depths of less than 3 and more likely 1.5 km. Very
rapid crystallization at very shallow depths makes it unlikely that the time scales between initial crystallization and final
eruption are sufficient to permit appreciable amounts of fractional crystallization. Given that high alumina basalt fractionation
is the dominant process for generating more evolved andesite, dacite and rhyolite magmas of the calc-alkaline suite, the inability
of parental high alumina basalt to yield such derivative magmas in the low pressure environment places the likely site of
fractionation in the high pressure environment, at or near the base of the crust.
Received: 1 December 1997 / Accepted: 23 December 1998 相似文献
23.
M. W. Pedersen A. Kokkalis H. Bardarson S. Bonanomi W. J. Boonstra W. E. Butler F. K. Diekert N. Fouzai M. Holma R. E. Holt K. Ø. Kvile E. Nieminen K. M. Ottosen A. Richter L. A. Rogers G. Romagnoni M. Snickars A. Törnroos B. Weigel J. D. Whittington P. Woods J. Yletyinen A. S. A. Ferreira 《Climatic change》2016,134(1-2):147-161
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25.
T. S. Switzer B. L. Winner N. M. Dunham J. A. Whittington M. Thomas 《Estuaries and Coasts》2006,29(6):1011-1018
We examined nekton community-level responses to Hurricanes Frances and Jeanne, which made landfall 20 d apart in the St. Lucie
estuary in southeastern Florida in 2004. The passage of these storms contributed to large freshwater discharges that exceeded
150 m3 s−1, as well as estuary-wide reductions in salinity and near-hypoxic conditions in the North Fork of the estuary that persisted
for several months. Although such environmental variations are not uncommon, seasonal patterns of community structure were
disturbed throughout much of the estuary, likely in response to uncharacteristically-rapid reductions in salinity. Immediately
following the hurricanes, abundances of several freshwater and oligohaline taxa (i.e., blue crabCallinectes sapidus, shadDorosoma spp., and ladyfishElops saurus) increased markedly in the inner estuary, while abundances of several other fishes (i.e., striped mulletMugil cephalus, white mulletM. curema, lookdownSelene vomer, pigfishOrthopristis chrysoptera, and pinfishLagodon rhomboides) declined. Nekton communities recovered quickly, and by spring, community structure throughout much of the estuary was indistinguishable
from pre-hurricane conditions. Although nekton communities were resilient to hurricane-related disturbances, projected increases
in Atlantic hurricane activity and associated freshwater discharges over the coming decades may test the resilience of estuarine
communities in Florida. 相似文献