The end of moai quarrying and its effect on Lake Rano Raraku, Easter Island

We reconstruct aspects of the history of Easter Island over the last 4-5 centuries based on the study of a core from Rano Raraku Lake, situated in the crater that contains the quarry of the island's giant statues or moai. We use microfossils of plants and animals to identify five zones. The last three of these are separated by waves of immigration from South America and from the subantarctic. We argue that the first or South American wave, dated to the second half of the 14th century, may represent a visit by South American Indians. Magnetic information, pollen, diatoms, chrysophyte stomatocysts and fossil plant pigments reveal a synchronism between the South American contact and the cessation of moai quarrying. We therefore suggest that Amerindians contributed to the cultural collapse of the island. The second or subantarctic wave may reflect an early European visit to the island, possibly by Cpt. James Cook in 1774, or by Jacob Roggeveen in 1722.     

广东省海岛资源开发与相关产业选择

本文对广东海岛优势资源及开发条件进行综合评价，依据产业的科学性提出建立以港口为中心的交通运输业，以基础工业为主体的港口工业，以及海洋水产业、海洋生物工程和旅游业。     

VOLCANIC ACTIVITY IN TAIWAN

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Climatic influences on streamflow and sediment flux into Lake C2, northern Ellesmere Island, Canada

Streamflow, suspended sediment transport and meteorological variables at two elevations were measured through the 1990–1992 field seasons at Lake C2, Northern Ellesmere Island, as part of the Taconite Inlet Lakes Project. The objectives were to determine the extent to which suspended sediment flux responded to climatic variability, and to ascertain which meteorological variable was most strongly associated with daily discharge and sediment load. This study provided a partial test of our hypothesis that the annually-laminated sediments of Lake C2 contain a paleoclimate signal. Streamflow to the lake was almost exclusively the result of snowmelt, in response to inputs of atmospheric energy as measured by air temperature at the median watershed elevation (520 m). Sea-level air temperature, global solar and net all-wave irradiance were less clearly associated with discharge. Fluctuations of discharge and suspended sediment concentration were nearly synchronous, and non-linearly related. Daily sediment discharge was therefore linked by streamflow, with a time lag, to the energy available for snowmelt. Mean daily air temperature and cumulative degree-days above 0 °C, at 520 m elevation, were successfully used to predict the daily and seasonal discharge of runoff and sediment to the lake.This is the third in a series of papers published in this issue on the Taconite Inlet Lakes Project. These papers were collected by Dr R. S. Bradley.     

Structure and geological evolution of the island of Ponza, Italy: inferences from geological and gravimetric data

A geological and a geophysical survey have been carried out at Ponza Island, Tyrrhenian sea, Italy. Geological and structural data allowed to identify three main tectonic systems: NW-SE, NE-SW and E-W trending. The first one is related to a pre-volcanic tectonic event, probably linked to the Pliocene extensional activity of the Tyrrhenian evolution; the other two systems affected the volcanic units in two different stages of the Lower Pleistocene, the earlier one after the rhyolitic hyaloclastic formation (HF) emplacement and the later one after the emplacement of older trachytic pyroclastic deposits (Lower Pyroclastic Units—LPU). The latter event was followed by the emersion of the whole Ponza area, as testified by a marked erosional surface and marine terrace deposits cropping out at the top of LPU. The Upper Pyroclastic Units (UPU) represent the younger trachytic activity of the island (1.3 Myr) and do not show evidence of tectonic activity.The NW-SE-trending tectonic system probably assisted the rhyolitic magma rise, while the NE-SW- and E-W-trending systems mainly assisted the trachytic magma rise, responsible for the explosive and effusive activity in the southern area and for the hydrothermal fluids that caused alteration processes in the northern area.A 161-station gravimetric survey was carried out on the island and surrounding islets. The geological data and the gravimetric survey have been used to propose a 2.5 D model in which rhyolitic hyaloclastic deposits (ρ = 1.7 g cm⁻³) overlay an articulated Meso-Cenozoic sedimentary substratum (ρ = 2.6 g cm⁻³) laying at a depth to 300 m below sea level. Both formations are crossed by rhyolitic dykes (ρ = 2.4 g cm⁻³) which mark feeder fractures. In the M. Guardia area, where a maximum is present, this model accounts for the presence of a horst of the rigid basement, a shallow trachytic lava flow and its feeder (ρ = 2.8 g cm⁻³).     

Concentrations of atmospheric constituents observed at Alert,Canada, in relation to air trajectories and synoptic systems

A meteorological analysis is presented for environmental data set obtained from the Canadian Arctic haze study, which is part of AGASP-II. Results of the study indicated that atmospheric carbon dioxide (CO₂), methane (CH₄), sulphate (SO₄ ⁼), ozone (O₃) and other air pollutants observed at Alert, N.W.T. underwent periodical fluctuations. It was found that high concentrations of these atmospheric constituents were associated with a deep (1430–2074 m) inversion and with a major anticyclone. In contrast, relatively low values of these constituents were associated with a cyclonic disturbance near Alert. High concentrations of these constituents occurred with air trajectories coming from the N-W direction, while low values occurred with S trajectories. In addition, examinations of satellite imagery with other meteorological data suggested that volcanic inputs of ash and gases from Augustine Island, Alaska were negligible for the observed high values of these constituents at the ground level at Alert.     

从栅格数据直接建立拓扑关系的算法研究

本文提出了从栅格数据直接建立拓扑关系的思想,用跟踪过程中容易获得的拓扑信息来优化拓扑生成的算法模型,借以提高拓扑生成的效率。本文还提出用连通性区域填充的方法处理各种任意复杂岛的思想。     

海南岛兰洋地区石炭系孢子的发现及其意义

笔者等在海南岛兰洋地区发现了丰富的石炭系孢子,计３８属６４种。其中,产于青天峡组上部的孢子组合,与Ｇ．Ｃｌａｙｔｏｎ等人所建立的“ＰＵ“带相当,属韦宪期早期。产于石岭组下部的孢子组合,则具有韦宪期中晚期的色彩。这些孢子的发现,为该区石炭系的划分与对比提供了重要依据,同时也有助于探讨海南岛大地构造的某些问题。作者依据孢子组合及其伴生的植物化石,对石炭纪广东大陆与海南岛分属两个地体的看法提出了质疑,而     

Late proterozoic island arc volcanics from Gebeit,Red Sea Hills,north-east Sudan

The area of Gebeit Mine in the northern Red Sea Hills, Sudan, is built up of voluminous volcanic rocks and minor volcaniclastic and clastic sequences. According to their chemical and modal compositions the Gebeit volcanics can be devided into four groups: (a) cpx-physic basalts with clinopyroxene and plagioclase as the dominant phenocrysts and minor opaques; (b) hbl-physic basalts with hornblende, clinopyroxene, plagioclase and subordinate magnetite including one rare dacite; (c) pl-phyric andesites with plagioclase phenocrysts in a matrix that is rich in magnetite; and (d) aphyric basalts. The compositional variation within the distinct volcanic groups can only partly be explained by fractional crystallization, and more than one magma source reservoir is required.Mineral and whole rock Sm/Nd data for the cpx-physic and hbl-physic basalts yield an isochron age of 832 ± 26 Ma (Nd_T = 6.74 ± 0.19, MSWD = 0.12) which is interpreted as the age of eruption. The Nd_t values for the aphyric basalts and pl-physic andesites range from 6.7 to 8.3, indicating the involvement of different depleted magma sources. The Nd and Sr isotopic data rule out any significant influence of older continental crust in the formation of the Gebeit volcanics and indicate an intraoceanic origin. This implies that the Gebeit terrane is a segment of juvenile crust that originated in a subduction-related environment and supports the arc accretion model for the Arabian-Nubian Shield.     

MULTI-OBJECTIVE PROGRAMMING MODEL OF TROPICAL CROPS IN HAINAN ISLAND

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