Abstract
The Upper Jurassic sediments from the Kraków-Częstochowa Upland developed as carbonates, mostly limestones, which represent the microbial-sponge megafacies that were typical of the northern margin of the Tethys Ocean. Outcrops of these rocks are scattered along an extended belt ranging from Portugal to the Caucasus Mts. One of the common features of the bedded limestones belonging to this megafacies is the local occurrence of chert concretions.The siliceous rocks embedded within the Upper Jurassic sequences from the southern part of the Kraków-Częstochowa Upland originated from a broad spectrum of limestone silicification processes and are represented by chert concretions, bedded cherts and epigenetic siliceous rocks. These rocks served as raw materials in the production of stone tools from the Middle Palaeolithic onwards. These tools have been studied extensively by archaeologists.This paper presents the identification of the above mentioned types of siliceous rocks used in the manufacture of tools based upon (i) microscopic observations of thin sections which reveal the primary microfacies of limestones subjected to silicification, and (ii) X-ray diffraction analyses, including the determination of the crystallinity index of SiO2. Unfortunately, the available research methods do not permit the identification of the varieties of chert concretions to an extent that would permit them to be even roughly connected with particular outcrops or, at least, with particular regions of the occurrence of siliceous raw materials on a Pan-European scale. Macroscopic criteria have recently been adopted in archaeological classifications aimed at determining the origin of stone tools and drawing conclusions as to the source outcrops or regions. However, regrettably, these have proven groundless from the geological point of view.
Highlights
The Upper Jurassic sediments from the southern part of the KrakówCzęstochowa Upland (KCU) (Fig. 1) are home to a variety of siliceous rocks
The siliceous rocks described below occur mostly within the Upper Jurassic normal facies (=bedded facies), sediments belonging to the socalled microbial megafacies (Gwinner, 1971), which occupies an extended area in Europe, from Portugal through Spain, France, Germany, Poland, Romania, Crimea and reaching as far as the Caucasus Mts
The fractures typical of chert concretions hosted in limestones from large fault zones are filled with carbonate sediments which are partly silicified with cryptocrystalline SiO2
Summary
The Upper Jurassic sediments from the southern part of the KrakówCzęstochowa Upland (KCU) (Fig. 1) are home to a variety of siliceous rocks. This characterization is closely related to the development of the primary depositional structures of their limestone hosts. The methodology includes macroscopic and microscopic descriptions, microfacial analysis and X-ray diffraction patterns This attempt enabled the authors to relate the types of siliceous rocks distinguished to particular stratigraphic intervals of the Upper Jurassic succession from the southern KCU. The research results obtained with these methods enabled us to delineate different types of silication, but for valuable stone tool collections it is necessary to develop non-destructive methods of analysis. Both the detailed results and the interpretation of the geochemical. Only the data which is crucial to the argumentation are included
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