Biostratygrafia famenu z otworu wiertniczego Kowala 1 na podstawie konodontów

Abstract

W otworze Kowala 1 usytuowanym na północnym skrzydle synkliny bolechowickiej, pod utworami czwartorzędu i najniższego karbonu przewiercono osady famenu reprezentowane przez 6 kompleksów litostratygraficznych o łącznej miąższości około 200 m. W osadach tych udokumentowano dolny podpoziom triangularis oraz poziomy crepida, marginifera, trachytera, expansa i praesulcata. Na podstawie konodontów ustalono wąski interwał, w obrębie którego winna być przeprowadzona granica pomiędzy franem a famenem. Z uwagi na to, że część próbek litologicznych nie zawierała konodontów lub napotkano tylko gatunki o szerokim zasięgu stratygraficznym, precyzyjne określenie granic pomiędzy poszczególnymi poziomami było na ogól niemożliwe. Famennian biostratigraphy of the Kowala 1 borehole on the basis of conodonts Biostratigraphy is given of the Famennian sediments from the Kowala 1 borehole located in the northern limb of the Bolechowice syncline in the southwestern part of the Holy Cross Mts, Central Poland. The Famennian sediments embracing 6 lithologic complexes over 200 meters thick occur under, the lowermost Carboniferous and lie on the Frasnian rocks (A. Romanek, M. Rup, 1990). Aside of conodonts also macro- and microfauna and pollen have been encountered in the Famennian sediments (E. Turnau, 1990; Z. Żakowa, K. Radlicz, 1990). On the basis of analysis of conodont ranges of Palmatolepis and Bispathodus genera equivalents of the Lower triangularis Subzone and crepida, marginifera, trachytera, expansa and praesulcata zones have been found. There are no data about the rhomboidea and postera zones. With help of conodonts also the interval has been determined within which the Frasnian-Famennian boundary was tentatively determined at depth of 239,4 m (Fig. 1). Precise definition of depths at which the limits between the particular conodont zones should be put was impossible as a rule as a part of the studied lithologic samples did not contain conodonts or the species found represent taxons of broad stratigraphic ranges. Occurrence of all determined conodonts is given on Table 1 and that of the selected index taxons on Fig. 1. In the complex of marls, limestones and nodular sediments (depth 197.7-238.3) and in the top part of the complex of detrital limestone distinguished below the triangularis and crepida zones have been documented. The sediments of the Lower triangularis Subzones have been distinguished at depth of 236.7 - 239.4 m on the basis of concurrence of Palmatolepis subperlobata Branson et Mehl, P. gigas Miller et Youngquits and P. coronata Miller. A conodont assemblage typical for the crepida Zone has been stated at depth of 197.7-234.2 m although the index taxon P. crepida Sannemann has not been found. The correlation has been based on occurrence of Palmatolepis quadrantinodosalobata Sannemann, P. minuta wolskae Szulczewski and P. tenuipunctata Sannemann. It was impossible to distinguish the counterpart of the rhomboidea Zone in the Kowala 1 borehole. The sediments at depth of 76.4-95.8 m have been correlated with the marginifera Zone. Those are marls with limestone nodules (upper part of the complex). The marginifera Zone is documented by: Palmatolepis glabra lepta Ziegler et Huddle and P. glabra pectinata Ziegler. The sediments occurring at depth of 83.9 - 95.8 m represent most probably the Lower marginifera Subzone. This statement is based on occurrence of Palmatolepis stoppeli Ziegler et Sandberg and P. glabra lepta Ziegler et Huddle. Occurrence of Scaphignathus velifer velifer Helms and P. rugosa trachytera Ziegler accompanied by P. glabra lepta Ziegler et Huddle has been noted at depth of 42. 7-55.4 m. This is sufficient to state that the top part of the complex of marls and limestone nodules (48.1- 55.4 m) as well as the lowermost part of the marly complex with claystone and limestone interbeds (42.7 -48.1 m) should be correlated with the trachytera Zone. There are no data to distinguish the lower and upper parts of this zone nor basis for documentation of counterparts of the postera Zone. Appearing at depth of 22.1 m Pseudopolygnathus brevipennatus Ziegler and slightly higher up - at 17.6 m and higher Bispathodus aculeatus aculeatus (Branson et Mehl) point to the expansa Zone. Starting from depth of 14.9 m Bispathodus ultimus (Bischofl) sensu Ziegler et Sandberg has been found which shows that the nodular limestones from that depth and higher up cannot be older than the upper part of the expansa Zone. A conodont assemblage occurring at depth of 10.7 -14.9 m contains species that are typical for both the upper expansa and praesulcata zones. There are no taxons, however, to precise the boundary between these zones. The occurrence of Pseudopolygnathus marburgensis trigonicus Ziegler at depth of 10.7- 10.9 m suggests that those sediments are not younger that the Lower praesuicata Subzone. The Devonian Carboniferous boundary cannot be established in the Kowala 1 borehole on the basis of conodonts. This boundary has been established at depth of 10.1 m on the basis of analysis of stratigraphic ranges of bivalves, ostracods and trilobites characteristic for the Carboniferous as well as the pollen zones occurring above that depth (H. Żakowa et al., 1985; E. Turnau, 1985).