排序方式： 共有3条查询结果，搜索用时 0 毫秒
1
1.
Zazo C. Dabrio C.J. Borja F. Goy J.L. Lezine A.M. Lario J. Polo M.D. Hoyos M. Boersma J.R. 《Geologie en Mijnbouw》1998,77(3-4):209-224
The stratigraphic relationships, genesis and chronology, including radiocarbon dating, of the Quaternary sandy deposits forming the El Asperillo cliffs (Huelva) were studied with special emphasis on the influence of neotectonic activity, sea-level changes and climate upon the evolution of the coastal zone. The E-W trending normal fault of Torre del Loro separates two tectonic blocks. The oldest deposits occur in the upthrown block. They are Early to Middle Pleistocene fluviatile deposits, probably Late Pleistocene shallow-marine deposits along an E-W trending shoreline, and Late Pleistocene and Holocene aeolian sands deposited under prevailing southerly winds. Three Pleistocene and Holocene aeolian units accumulated in the downthrown block. Of these, Unit 1, is separated from the overlying Unit 2 by a supersurface that represents the end of the Last Interglacial. Accumulation of Unit 2 took place during the Last Glacial under more arid conditions than Unit 1. The supersurface separating Units 2 and 3 was formed between the Last Glacial maximum at 18 000 14C yr BP and ca. 14 000 14C yr BP, the latter age corresponding to an acceleration of the rise of sea level. Unit 3 records wet conditions. The supersurface separating Units 3 and 4 fossilised the fault and the two fault blocks. Units 4 (deposited before the 4th millennium BC), 5 (> 2700 14C yr BP to 16th century) and 6 (16th century to present) record relatively arid conditions. Prevailing wind directions changed with time from W (Units 2–4) to WSW (Unit 5) and SW (Unit 6). 相似文献
2.
Pollen analyses off Senegal: Evolution of the coastal palaeoenvironment during the last deglaciation
Pollen and dinoflagellate cysts from marine sediments in core A180-48 (15°19′N, 18°06′W; 2450 m water depth; 530 cm length) are used to reconstruct palaeoenvironmental conditions of nearshore tropical west Africa during the last deglaciation. High concentrations and influxes of pollen and dinoflagellate cysts between 11 000 and 10 000 yr BP are interpreted as reflecting an increase in continental trade-wind circulation and related coastal upwelling at 15°N latitude. The sea-surface temperature difference between glacial and interglacial times was not as strong as previously suggested. Together with local (fresh) ground-water input, this smaller temperature difference may explain the persistence of the Rhizophora mangrove and Guinean gallery forests near the shore until their massive extension during the early Holocene humid maximum around 9500 yr BP. Pollen data from the core are compared with data from Rosilda N110-Z, from the continental shelf at the same latitude. 相似文献
3.
Pollen data from core KW31 recovered off the mouth of the Niger River (3°31′1N–05°341E; 1181 m water depth) provide an exceptional record of vegetation changes in the West African lowlands between 40,000 and 3500 cal yr B.P. The highly diverse microflora testify for the permanency of rain and secondary forests in the Niger river catchment, at least as gallery formations along rivers, during the last glacial period when dry conditions occurred in relation to enhanced trade-wind circulation. The direct consequence of the post-glacial warming and the correlative increase in monsoon fluxes over West Africa was the increase in forest diversity and the expansion of rain and secondary forests on the nearby continent. Comparison between KW31 pollen record and continental pollen data from 5°S to 25°N allows the evaluation of migration rates of tropical forest populations throughout North West Africa at the beginning of the Holocene and the vegetation response to the shift toward aridity recorded widely at the end of the African Humid Period around 4000 cal yr B.P. 相似文献
1