Kryteria podziału lito stratygraficznego triasowej serii dolomitowej na obszarze śląsko-krakowskim

Abstract

Utwory litofacji dolomitowej przedstawiono na tle wapiennych litofacji występujących na obszarach otaczających. Przedstawiono cechy litologiczne utworów dolomitowych, zarówno wczesnodiagenetycznych, jak i przeobrażonych (kruszconośnych), które mogą być pomocne w rozdzieleniu całej serii na dwie jednostki stratygraficzne: warstwy górażdżańskie i warstwy terebratulowe i karchowickie.CRITERIA OF UTHOSTRATIGRAPIDC SUBDIVISION OF TRIASSIC DOLOMITE LITHOFACIES OF THE CRACOW·SILESIAN AREADolomite Iithofacies, to which zinc and lead deposits are related, is presented on the background of surrounding limestone lithofacies (fig. 1). The limestone lithofacies is subdivided into two groups:1. Lithofacies with predominance of limestones, which may be further subdivided into three stratigraphic links (Górażdże, Terebratula and Karchowice Beds) characterized by a high variability in lithology and presence of guide fauna.2. Limestone lithofacies which at present cannot be subdivided into three stratigraphic links because of uniform development and impoverishment in fauna. The paper presents the results of detailed analysis of dolomite lithofacies corresponding to the Górażdże, Terebratula and Karchowice Beds. The lack of guide fauna precludes its biostratigraphic subdivision. Advanced post-diagenetic alterations make it possible to treat the whole series of ore-bearing dolomites, although numerous sedimentary features enable further subdivision of these rocks into the Górażdże Beds and joint link of Terebratula and Karchowice Beds. The facies analysis of primary deposits showed that rocks of this Iithofacies originated in tidal flat and the whole sedimentary area was at that time elevated in relation to the neighbouring ones. The tidal flat was the site of deposition of shallow-water limestones and dolomites. The number of dolomite intercalations increases towards the top of the section and in the Karchowice Beds they are more numerous that limestone ones or they form a continuous series. Original features of the whole dolomite Iithofacies appear markedly similar to those of reef series with Zn - Pb deposits, known from several parts of the world. Figure 2A presents simplified section of original layers.Dolomite Iithofacies is strongly alterated in the Silesian - Cracow area Some early-diagenetic dolomites were subjected to recrystallization, and limestones - to almost complete dolomitic metasomatism (Fig. 2B). Two varieties of dolomite Iithofacies may be differentiated at present: early-diagenetic dolomites . and altered, ore-.bearing ones. The latter may be further subdivided into three types, differing in the mode of origin and type of parent rocks subjected to alteration: 1 - metasomatic, post-limestone, 2 - recrystallized, post-early-diagenenetic dolomites, and 3 - those infilling free space ·in altered rocks. The types (1) and (2) usually display features resembling sedimentary features of their parent rocks. This makes it possible to use the method of Iithostratigraphic correlation. These features include:1. Silica and clay content remain unaffected by alterating processes. Clay horizons and envelopes occurring in limestones from the top part of the Gogolin Beds represent excellent marker horizon. The other marked horizons between Gogolin and Górażdże Beds are: numerous thin intercalations of early-diagenetic dolomites and mottled rock formed of limestone debris and clay, marly and calcareous or dolomitic cement. Despite of the further metasomatic alterations, that latter rock displays its original macroscopic appearance (Table I, fig. 3).2. Original crumpled, breccia and conglomeratic nature of the Górażdże Beds is not much changed deposite of recrystallization and metasomatism (Table II, fig. 5).3. Fauna moulds and skeletons are macroscopically visible in rock and only their shape is obliterated. It is even possible to identify some species when alterating processes are less advanced.4. Siliceous nodules typical of the Górażdże and Terebratula Beds remain at place, undergoing some diagenetic changes only.5. Erosional surfaces, surfaces of the hard ground type, non-crystalized various borings and impregnations of earthy pyrite are preserved in early-diagenetic dolomites of the Górażdże Beds.6. Conglomeratic layer resembling basal conglomerates known from some areas may be traced in several places at the top of the Górażdże Beds.The thin layers of grained or spotted dolomites are found at the top of the Karchowice Beds (Table II, fig. 6). These rocks originated due to emergence of sea floor and. they were usually not much affected by subsequent alterations.