摘要:

SUMMARYZircons have been studied in the sedimentary rocks of the Sparagmite Group (Eocambrian) and their metamorphic associates from the Trondheim area and the adjacent regions in Norway and Sweden. The majority of zircon population (typeB) has been formed in the sediments by authigenesis. Another authigenic associate is rutile. The authigenic zircons have irregular, round and ellipsoidal habits. In metamorphic rocks the same grains show a greater tendency of euhedrism, forming drum‐like crystals with acute (331) pyramids and short prisms. Authigenic zircons are usually clear and transparent but some grains may show cloudy appearance. A few other grains (typeA) with different habit and many inclusions appear to be of detritai nature.Dissolution of a metamictized zircon population in the source rock is possible in many ways. An important possibility is the dissolution of zircons in alkaline solution. Carbonated lime‐rich waters or other acidic solutions could be equally effective. Zirconates, so formed, are transported to the basin of deposition as colloidal particles or as ionic complexes. The authigenic process is visualized as a deposition of the zirconates by adsorption or by precipitation as zirconium hydroxide, possibly due to change in the Eh and pH in the environment. The hydrated oxide subsequently reacts with silica to form metastable hydrozircon. In course of time hydrozircon dehydrates and becomes a normal zircon.Numerous growths have been noted and are classified genetically into (l) late authigenic growths, and (2) growths syngenetic with metamorphism. The shape of the host grain usually controls the final shape of the overgrown grain.There is some effect of metamorphism on the morphology of the authigenic zircons. In view of the characters of the newly generated zircons, the use of shape, size, zoning and such other parameters of zircons in petrogenetic problems, has to be retested to ensure its reliability.Rather than being a mineral of igneous derivation only, zircon is from three parentages: igneous, authigenic and metamorphic. It is argued that the persistence of the authigenic zircons should be greatest because of very low concentration of radioactive eleme

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1966.tb01568.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

SUMMARYCareful sampling of the constituent laminae of cross‐stratified units and their subsequent mechanical analyses have revealed a rhythmic pattern of size differentiation. The cross‐strata have been analysed in terms of our existing knowledge of the mechanics of layering in granular sediments. The concept of “elementary rhythm‐unit” has been introduced and the genesis of a cross‐stratified unit has been reviewed in terms of the growth and interplay of the elementary

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1966.tb01569.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

摘要:

Book reviewed in this article:Geochemistry of Sediments E. T. Degens.Identification of Mineral Grains. M. P. Jonesand M. G. Fleming.

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1966.tb01570.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY

ISSN:0037-0746    

DOI:10.1111/j.1365-3091.1966.tb01571.x

出版商:Blackwell Publishing Ltd    

年代:1966

数据来源: WILEY