The Elements of economic geology

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Monograph

Identifikator:: 1773832379

URN:: urn:nbn:de:zbw-retromon-172798

Document type:: Monograph

Author:: Gregory, John W. http://d-nb.info/gnd/11683014X

Title:: The Elements of economic geology

Place of publication:: London

Publisher:: Methuen

Year of publication:: 1928

Scope:: XIV, 312 S.; graph. Darst.

Digitisation:: 2021

Collection:: Economics Books

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Document type:: Monograph

Structure type:: Chapter

Title:: Part III. Earthy minerals

Collection:: Economics Books

THE SALT DEPOSITS 200 pre-Cambrian to Lower Carboniferous rocks, sank beneath the sea and was covered by beds laid down in the Upper Carbonifer- ous and Permian Sea. The earlier beds were ordinary marine deposits, which were followed by red shales and a dolomitic limestone (the Zechstein); their stunted fossils show that the connection between the sea of Central Germany and the outer ocean had been closed, so that the water had changed in composition, and the less adaptable animals and plants had perished. As the water evaporated salts were precipitated ; the series began at Stassfurt, in the centre of the basin, with a thick deposit of rock-salt interbedded with layers of anhydrite (CaSO,). These minerals occur in such regular alternation as to suggest precipitation by the annual change from winter to summer. The lower series of rock-salt and gypsum was succeeded by a bed containing potash and magnesium salts, so that the sea-water and the bittern were both evaporated. These very soluble salts were then covered with a layer of clay; the sea again submerged the area; a fresh layer of limestone was deposited, and was followed by a thick bed of anhydrite and a younger series of interbedded rock-salt and anhydrite. Above this series occurs a wide- spread sheet of massive rock-salt due to the redeposition of salt dissolved out of the underlying beds. Then followed another invasion of the sea, which deposited another layer of Zechstein and prevented the deposition of a second layer of potash salts. This upper limestone was covered by the red sandstones of the Bunter or Lower Trias, which were deposited under desert conditions on land. In other parts of the German salt basin the sequence of events was different. Thus towards the valley of the Werra River (Fig. 54 A) the primary rock-salt was not deposited, but a secondary rock-salt was formed, doubtless of material dissolved from the older beds, and the evaporation of occa- sional brine pools deposited patches of potash salts. Then followed two further layers of Zechstein and a widespread thick sheet of Bunter sandstone. The South Harz (C) and the Hanover district (B) show an intermediate condition, with the lower secondary rock-salt of the Werra basin in- tercalated between two great primary salt deposits as at Stassfurt (D). Iv

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