白暨豚种群数量及资源保护

为了了解长江中白鱀豚的分布状况及种群数量,从1978年至1983年1月止,先后9次在长江中、下游(宜昌至南通)的干流进行了白鱀豚的生态考察,并到汉江和鄱阳湖、洞庭湖等水域查访有无白鱀豚活动的情况,依据考察所得资料,对长江白鱀豚群体的数量作了初步剖析。 通过考察,到1983年初为止,中游最上是在湖北枝城,约距长江口1,613公里的江段和下游最下是江苏太仓浏河口距长江口24公里的江段都有白鱀豚的活动。白鱀豚种群约156头,20个群体,分布在长江中、下游的17个江段里,在安庆一黑砂洲南水道约170公里及嘉鱼—王

Paleomagnetic properties of igneous rocks from several DSDP and ODP sites, western Pacific

Oceanic basalts and other related igneous rocks are considered excellent recorders of the Earth's paleomagnetic field. Consequently, basalt core paleomagnetic data are valuable for the constraints they provide on plate tectonic motions, especially for oceanic plates such as the Pacific. Unfortunately, few Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) boreholes have been cored very deeply into the ocean crust. The result is that there are only a few sites at which a large enough number of basalt flows have been cored to properly average secular variation (e.g., Kono, 1980, doi:10.2973/dsdp.proc.55.135.1980; Cox and Gordon, 1984, doi:10.1029/RG022i001p00047). Furthermore, there are a number of sites where basaltic core samples were retrieved but the cores were not measured. Often this occurs because leg scientists had more important sections to work on, or the section was ignored because it was too short to record enough time to average secular variation and obtain a reliable paleolatitude. Even though it may not be possible to determine a precise paleolatitude from such short sections, measurements from a small number of flows are important because they can be combined with other coeval paleomagnetic data from the same plate to calculate a paleomagnetic pole (Gordon and Cox, 1980, doi:10.1111/j.1365-246X.1980.tb02642.x; Cox and Gordon, 1984, doi:10.1029/RG022i001p00047). For this reason, I obtained samples for paleomagnetic measurements from eight Pacific sites (169, 170, 171, 581, 597, 800, 803, and 865), most of which have not been previously measured for paleomagnetism.