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181.
182.
Abstract. Living, symbiont-bearing, larger foraminiferids restricted to the photic zone incorporate mechanisms blocking solar radiation and water current transportation. They can be divided in two groups according to their wall structure: 1, Families with opaque test walls, reducing light penetration: Peneroplids inhabit shallow-water environments from the intertidal ( Peneroplis in large numbers) down to 40 m ( Dendritina , preferring sandy substrates). Soritids are restricted to subtidal environments with less water turbulence and range from the reef moat down to 60 m. Amphisorus and Marginopora are common down to 30 m, whereas Parasorites is restricted to deeper parts of the reef slope. Alveolinella can be found in the upper 40 m of the reef slope. 2. Families with hyaline test walls, adjusted for light penetration: amphisteginids inhabit the whole photic zone, demonstrating a correlation of test flattening with increasing depth. Calcarinids cling with their spines to firm substrates such as algal thalli or macroids. Baculogypsina is restricted to high energetic regions on the reef flat. Calcarina inhabits similar environments, extending its distribution range within fore reefs down to 80 m. Baculogypsinoides is a dominant calcarinid genus from 30 to 70 m depth. Within nummulitids, Heterostegina prefers hard substrates on the reef slope, while Assilina (= Operculina ) is frequent in deeper parts and is independent of substrates. Sandy bottoms from 30 to 60 m are inhabited by the last living representative of the genus Nummulites, N. venosus . The giant foraminifer Cycloclypeus , with test sizes up to 7 cm, is restricted to fore reef areas below 50 m down to the base of the photic zone. 相似文献
183.
Abstract. The sponge fauna of three neighbouring submarine caves of the Island of Majorca (Balcaric Islands) is studied along a light gradient; 45 species have been recorded and systematic data are given for those showing morphological, pigmentary, or spicule differences. Adaptation to darkness and precarious trophic conditions is also discussed. 相似文献
184.
L. I. Gonzalez de Vallejo R. Capote L. Cabrera J. M. Insua J. Acosta 《Marine Geophysical Researches》2003,24(1-2):149-160
A series of clastic dikes and tubular vents were identified in southern Tenerife (Canary Islands). These features are the result of seismic liquefaction of a Holocene sand deposit, as the consequence of a high intensity paleoearthquake. The peak ground acceleration (pga) and magnitude of the paleoearthquake generating these liquefaction features were estimated by back calculation analysis. A representative value of 0.30 ± 0.05 g was obtained for the pga. From this, an earthquake intensity of IX was estimated for the liquefaction site. Magnitude bound methods and energy based approaches were used to determine the magnitude of the paleoearthquake, providing a moment magnitude M = 6.8. The zone in which the liquefaction structures are found has undergone tectonic uplift and is affected by two faults. One of these faults was responsible for displacing Holocene materials. Dating of the uplifted sand formation indicates an age of 10,081 ± 933 years, the liquefaction features ranging from this age to 3490 ± 473 years BP. This paleoearthquake was of much greater magnitude than those known historically. Faults with neotectonic activity are significant features that should be borne in mind when assessing the seismic hazards of the Canary Islands, presently considered as low and mainly of volcanic origin. 相似文献
185.
根据1990年春季至1991年冬季采自南日岛海域浮游动物样本,初步鉴定出98种浮游动物和12类浮游幼虫。桡足类种类和数量均占优势。精致真刺水蚤、中华哲水蚤、肥胖箭虫、中华假磷虾和短尾类氵蚤状幼虫为优势种。本文报道了浮游动物总生物量,总个体数和种类数的季节分布及平面分布,讨论其分布与环境的关系。 相似文献
186.
187.
J. Acosta E. Uchupi D. Smith A. Muñoz P. Herranz C. Palomo P. Llanes M. Ballesteros 《Marine Geophysical Researches》2003,24(1-2):59-90
The meso-scale (km) morphology of the well-studied volcanic rift zones on the Island of Hawaii is compared to the morphology of the lesser known rift zones of La Palma and El Hierro, Canary Islands. We find that there are both differences and similarities in their morphologic characteristics. In general, the rift zones on La Palma and El Hierro are shorter (a few tens of km in length) than those on Hawaii (ranging up to >100 km in length), perhaps reflecting both magma supply and composition. Many of the rift zones on Hawaii have well defined axial zones, both on-and offshore. In contrast, the rift zones on La Palma and El Hierro display various geometries ranging from linear ridges having smooth to irregular crests to structures with a broad fan-like morphology in plan view. The pronounced fanning may be a reflection of: 1) the stress field within the rift being insufficient to trap dikes within a narrow region, 2) dike injection and volcanism shifting laterally through time, 3) volcanoes building nearly one atop of another in the Canary Islands, superimposing the stress field of one structure on the other and thus yielding a more complex distribution of gravitational stresses, and 4) low rate of magma supply producing low magma pressures and thus randomly oriented dike injections. Irregularities and curvature along the axes of the rifts on La Palma and El Hierro may be a reflection of differences in the rate of magma production. Unlike the volcanoes on the Island of Hawaii there may be insufficient volumes of lavas erupted on La Palma and El Hierro to smooth out irregularities. The superposition of rifts from different volcanoes may also add to topographic irregularities in the Canary Islands, especially if eruption rates are low. 相似文献
188.
189.
Theresearchontheremotesensing'sinformationtreemodeloftheNanshacoralisletsandreef'sspatialstructure¥LiuBaoyin;WangYanfengandHa... 相似文献
190.
南沙群岛永暑礁钻井珊瑚礁和珊瑚碎屑的磁学分析 总被引:1,自引:0,他引:1
通过南沙群岛永暑礁南永1、2井珊瑚礁和南永3井潟湖珊瑚碎屑的磁性测试与研究发现,它们的磁化率以负值(χ<0)为主,具抗磁性特性,但有稳定的剩余磁化强度,又具有铁磁性特性,即具有抗磁性与铁磁性共存的磁学性质。珊瑚礁和珊瑚碎屑的磁性主要来源于珊瑚骨骼及死亡后古生物和富铁细菌等壳体中变价的铁离子,这些变价铁离子在不同年代、不同环境下组成新的铁氧体,具有似单畴(PSD)的磁性特征。这个磁性不但在井深103m和254m处记录了布容/松山和松山/高斯地球磁场极性转换界限(年龄分别为0.78MaB.P.和2.58MaB.P.),而且记录了布容正极性期和松山反极性期内的琵琶湖I、II、贾拉米洛、奥都维、留尼汪Ⅰ、II地球磁场漂移,并提供了磁化率的变化可能与气候冷暖变换有关的信息。当χ<0时表示冷期,当χ>0时表示暖期。 相似文献