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Journal of Sedimentary Research (SEPM)

Abstract


Journal of Sedimentary Petrology
Vol. 33 (1963)No. 1. (March), Pages 14-22

Laminites: A Structure of Flysch-Type Sediments

Augustin Lombard

ABSTRACT

The concept of turbidity currents has been widely recognized and has been used to explain the formation of intricately bedded sequences in orogenic deposits such as the flysch. Turbidities are the result of this mechanism, forming thick and regular beds, with graded bedding and sole marks. The concept of turbidity currents has been broadened in order to explain several types of bedding. The author describes herein a style of stratification frequently observed in natural sequences complementary to typical turbidites; these beds are herein termed laminites. The lithologic composition is the same as the turbidites but the grains are finer, beds are thinner and lack many of the characteristics of the turbidites. Laminites of first order (lam. I) form simple layers (monostratas) alt rnating with shales. One may succeed the other in thick sequences. Laminites of the second order (lam. II) show thin bedding laminations throughout the whole sequence or form the top of the turbidites. Laminites I and II can be closely related, as for example in sequences of thin beds of flysch.

Turbidites and laminites may be considered as two extreme members of a series of gradual changes in the depositional character of flysch sequences. Whereas the concept of laminites is essentially descriptive, a tentative explanation is proposed, although the author is well aware of its hypothetical character. One of its weak aspects is the lack of experimental data. It is founded mainly on Gilbert's papers. The physical agents involved are the same as for the turbidites: mobile slope, gravity sliding, and fluidity of the sediments. However, in the laminite-forming process the clastic fine-grained sediments are transported not only by gravity but also by the water in a mixed process of bottom traction and gravity.

Ph. H. Kuenen's studies on turbidites (1950, 1952, 1953a and b, 1959) have stimulated field studies in recent years and have resulted in the recognition of many turbidite sequences in various flysch series of the Swiss Alps (also Kuenen and Carozzi, 1953). In addition to the true turbidites, there seems to be a wide group of beds which do not fit the strict definition of turbidites. Flysch troughs may have one or both types of sediments. Laminites II are a phenomenon of local bedding, integrated with the development of laminites I, which are more general and belong to active phases of sedimentation. (Lombard, 1956, p. 276).


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