Struktury nagromadzeń graptolitów na powierzchniach warstwowania

Abstract

STRUCTURES OF GRAPTOLITE AMASSMENTS ON THE STRATIFICATION PLANES

The author shortly presents stl1udmres of graptolite amassments and proposes the names for the structures investigated as follows.

C ha o t i c s t r u c t u r e. This structure is formed in the case when bottom currents are missing in sedimentary basin. P a r a I I e I s t r u c t u r e (Fig. 4e) has been observed in the middle part of the Mielnickie beds in bore hole Gołdap IG-I, and described by many authors. The Mielnickie beds are, in the Polish Lowland area, referred to the lower Ludlovian (E. Tomczykowa, H. Tomczyk, 1961). The parallel structure arises as a result of activity of feeble bottom currents. F e a t h e r s t r u c t u r e (Fig. 4d). Graptolite fragments occurring in current channel are arranged obliquely to its edges. Ends of rhabdosomes occurring in a closer distance to the axial part of a channel reflect direction of current. Arrangement of graptolites in the feather structure lends support to the view of H. Klachn (fide O.M.B. Bulman, 1957), who in 1930 suggested existence of gravity center by graptolites near the end of a rhabdosome. The feather structure was observed by the author in the Siedleckie beds in bore hole Lębork IG-I at a depth amounting 2755 m. The Siedleckie beds are related in the Polish Lowland area to the middle Ludlovian (E. Tomczykowa, H. Tomczyk, 1961). N e t  s t r u c t u r e (Fig. 4a) originates as a result of activity of gas rubbles occurring on the surface of sediment (L. Stermer, 1938, PI. Figs. 1, 2). R i n g  s t r u c t u r e (Fig. 4b) is formed by eddy currents (L. Størmer, 1938, Fig. 1). S t r e a k  s t r u c t u r e (Fig. 4C). Graptolites assemble in furrows filled with sediment, separating crests of ripple marks and arrange obliquely or transversally to the latter (J. Weigelt, 1930, Fig. 2). This structure is connected with currents forming ripple marks.

Structures of .graptolite amassments are valuable index of bottom water dynamics in sedimentary basin. Thus, using fades nomenclatures introduced by R. C. Moore (1949) we may determine these structures as an interesting e[element of physiofacial analysis.