Muschelkalk
From Wikipedia, the free encyclopedia
Muschelkalk (German for "Mussel chalk") is the term in geology for the middle member of the German Triassic. It consists of a series of calcareous, many and dolomitic beds which lie conformably between the Bunter and Keuper formations.
The name Muschelkalk (Fr., calcaire coquillier; concijylien, formation of D'Orbigny) indicates a characteristic feature in this series, viz, the frequent occurrence of lenticular banks composed of fossil shells, remarkable in the midst of a singularly barren group. In its typical form the Muschelkalk is practically restricted to the German region and its immediate neighborhood; it is found in Thuringia, Harz, Franconia, Hesse, Swabia, and the Saar and Alsace districts. Northward it extends into Silesia, Poland and Heligoland. Representatives are found in the Alps, west and south of the Vosges, in Moravia, near Toulon and Montpellier, in Spain and Sardinia; in Romania, Bosnia, Dalmatia, and beyond this into Asia in the Himalayas, China, Australia, California, and in North Africa (Constantine). From the nature of the deposits, as well as from the impoverished fauna, the Muschelkalk of the type area was probably laid down within a land-locked sea which, in the earlier portion of its existence, had only imperfect communications with the more open waters of the period. The more remote representatives of the formation were of course deposited in diverse conditions, and are only to be correlated through the presence of some of the Muschelkalk fossils.
In the German area the Muschelkalk is from 250-350 ft. thick; it is readily divisible into three groups, of which the upper and lower are pale thin-bedded limestones with greenish-grey mans, the middle group being composed of gypsiferous and saliniferous mans with dolomite. The Lower Muschelkalk consists, from below upwards, of the following rocks, the ochreous Wellen Dolomit, lower Wellen Kalk, upper Wellen Kalk (so called on account of the wavy character of the bedding) with beds of Schaumkalk (a porous cellular limestone), and Oolite and the Orbicularis beds (with Myophoria orbicularis). In the Saar and Alsace districts and north Eifel, these beds take on a sandy aspect, the Muschelsandstein. The Middle Muschelkalk or Anbydnite group, as already indicated, consists mainly of mans and dolomites with beds of anhydrite, gypsum and salt. The salt beds are worked at Hall, Friedrichshall, Heilbronn, Stettin and Erfurt. It is from this division that many of the mineral springs of Thuringia and south Germany obtain their saline contents. The cellular nature of much of the dolomite has given rise to the term Zellendolomit. The Upper Muschelkalk (Hauptmuschelkalk, Friedrichshallkalk of von Alberti) consists of regular beds of shelly limestone alternating with beds of marl. The lower portion or Trochitenkalk is often composed entirely of the fragmentary stems of Encrinus liliiforrnis; higher up come the Nodosus beds with Ceratites cornpressus, C. nodosus, and C. semipartitus in ascending order. In Swabia and Franconia the highest beds are platy dolomites with Tringonodus Sandergensis and the crustacean Bairdia. Stylolites are common in all the Muschelkalk limestones. The Alpine Muschelkalk differs in many respects from that of the type area, and shows a closer relationship with the Triassic Mediterranean Sea.
In addition to the fossils mentioned above, the following are Muschelkalk forms: Terebratulina vulgaris, Spiriferina Mantzeln and S. hirsute, Myophoria vulgaris, Rhynchotites hirundo, Ceratites Munsteri, Ptychites studeri, Balatonites balatonicus, Aspidura scutellate, Daonella Lommeli, and in the Alpine region several rock-forming Algae, Baciryllium, Gyroporella, Diptopora, etc.
[edit] References
- This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.
