ISSN:0035-919X    

DOI:10.1080/00359197709519911

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

ISSN:0035-919X    

DOI:10.1080/00359197709519912

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

ISSN:0035-919X    

DOI:10.1080/00359197709519913

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

ISSN:0035-919X    

DOI:10.1080/00359197709519914

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

A geochemical and petrographic examination of onland phosphorites from the south-western Cape is made to elucidate their origin and to compare them with the known offshore occurrences. The investigation shows that some of the massive phosphorites and phosphatic pebbles on land have probably formed as phoscretes in a similar manner as calcretes, whereas some of the pelletal deposits originated by disaggregation of phosphorite rock, which was derived by interstitial precipitation. This mechanism is in contrast to the mode of formation suggested for the offshore phosphatic deposits where replacement of calcium carbonate by calcium phosphate is the major diagenetic process. A model which takes these two modes of formation into account is discussed briefly.

ISSN:0035-919X    

DOI:10.1080/00359197709519915

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

An account, with illustrations, is given of 20 terrestrial plant communities found in the vicinity of Langebaan Lagoon. A map is included which is based on the Braun-Blanquet method of vegetation sampling and data synthesis, and on the photo interpretation of 1:10 000 scale colour aerial photographs. Known rare and endangered plants occurring in the Saldanha—Langebaan area are listed. Recommendations are made for the establishment of a nature reserve which includes the marsh communities around the lagoon and the varied West Coast Strandveld vegetation on the Langebaan Peninsula.

ISSN:0035-919X    

DOI:10.1080/00359197709519916

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Fifteen stations were sampled in Langebaan Lagoon using a diver-operated suction sampler. The macrofauna was analysed using numerical methods, by the rarefaction technique, to define relative species richness and by ash-free dry-weight biomass determinations. Three basic groups were defined which were the channel, island and sandbank groups. The channel and island groups had the greatest biomass and the highest species richness values respectively. In contrast the sandbank group had the lowest biomass values, intermediate species richness values and the highest density of individual animals per m2The availability of food, water current velocity and hence sediment texture, water temperatures and salinity apparently were most important factors in determining the distribution of the macrofauna.

ISSN:0035-919X    

DOI:10.1080/00359197709519917

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Detailed continuous seismic reflection profiling and side-scan sonar surveys were made of the part of Saldanha Bay that lies to the landward of a line connecting Hoedjiespunt and Salamanderpunt (the ‘inner’ bay). Six distinctive subsurface units (Q-units) were recognized in the seismic records. They were correlated with a sequence of lithologically distinctive units encountered in boreholes drilled in the bay. At any instant in time the sea abrades the sea floor above a certain limiting depth and deposits materials below that depth. The incursion of the sea into an area therefore leads both to the removal and deposition of materials. The borehole results and the three-dimensional distribution of the Q-units in the bay indicate that the area has been affected by three abrasional/deposition cycles during the Late Pleistocene. During the earliest transgression the sea rose to a few metres above sea-level. During the second transgression it rose to −20 m. The last transgression took place when the sea rose to its present stand. While the sea stood at lowered levels, calcretes formed subaerially along ‘preferred’ zones in the marine deposits that were present. The main period of calcrete formation in the area was between the earliest and next transgression.

ISSN:0035-919X    

DOI:10.1080/00359197709519918

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Aspects of the biology ofChoromytilus meridionaliswere studied while investigating possibilities for cultivating mussels. Plankton samples were taken regularly, and growth, development and settlement behaviour of the larvae are discussed and correlated with results of a larval rearing experiment. Methods are described for the recording of settlement, and the results indicate annual, seasonal and local fluctuations in intensity of settlement at a number of sites. Reference is made to results obtained in Liideritz Bay. The growth rate of mussels suspended from rafts was determined and indicates considerable variation within the study area. This is discussed and aspects of the annual growth curves are presented. Water temperatures were obtained in Saldanha Bay during 2,75 years by means of a continuous recorder.

ISSN:0035-919X    

DOI:10.1080/00359197709519919

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Sediment distribution in Saldanha Bay is wave controlled and can be related to the energy levels created by the refraction pattern. Four energy zones are distinguished in the inner bay: a centrally exposed zone, two marginal semi-exposed zones, a sheltered zone in the north and a bay/lagoon transitional zone in the south. Sediment is supplied on the abrasion platform of the exposed zone and along the rocky shoreline of the North Channel. These areas display the coarsest sediments. In North Bay medium sands dominate, whereas the South Channel is characterized by very fine sands. Both semi-exposed zones as well as the sheltered zone consist of very fine sand. The bay/lagoon transitional zone is constructed of a tidal delta made of fine sand. Sediment distribution seems to be in equilibrium with the prevailing hydrodynamic regime. In contrast, Langebaan Lagoon is a current controlled regime. Four physiographic units can be separated: tidal channels, subtidal flats and sandbanks, intertidal flats, and salt marshes. These units reflect the major energy levels of the tidal system. Texturally the lagoon divides into two major zones separated roughly by the central channel. East of the channel fine sands dominate, whereas west of the channel medium sands are more frequent. Coarse sediments occur as lag deposits in the northern outflow channels. In contrast to the dominating presence of very fine sand in Saldanha Bay this size fraction is surprisingly deficient in Langebaan Lagoon. There is evidence for a Holocene high stand of the sea between 6 000 and 2 000 y B.P. The modern sediment distribution is the result of the subsequent regression and stabilization of the sea-level about 1 800 y B.P., and is therefore essentially a relict feature.

ISSN:0035-919X    

DOI:10.1080/00359197709519920

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor