Upper Jurassic Bedded Limestones and Early Diagenetic Dolomitized Limestones in the Light of Mineralogical, Geochemical and Sedimentological Studies; Kraków Area, Poland

Marcin Krajewski,Piotr Olchowy

doi:10.3390/min11050462

Abstract

This paper describes and analyzes the Upper Jurassic (Lower Kimmeridgian) succession exposed in the Zakrzówek Horst, located in the Kraków area. Three distinguished facies types FT 1-FT 3 comprise several limestone varieties: sponge-microbial, pelitic-bioclastic, and partly dolomitized detrital-bioclastic. Their sedimentary environments varied from relatively deeper, attaining storm-wave base, to more shallower, probably close to normal-wave base. Characteristic features of limestones are changes in contents of CaCO3 and insoluble residuum as well as porosity values in vertical transitional zones between facies types. The investigated facies types differ in sediment porosity dependent on development of limestones and its susceptibility to mechanical compaction during the early diagenesis. The studied limestones show high CaCO3 contents and minor insoluble residuum contents comprising quartz, chalcedony and clay minerals. No distinct variability occurs in contents of magnesium, silica, alumina and iron accumulated in clay minerals, iron oxides and oxyhydroxides, as well as in the amounts of amorphous silica. Early diagenetic dolomites, which occur locally within the limestones, were unrelated to fracture systems as possible pathways responsible for transfer of solutions rich in Mg2+ ions. The possible source of Mg2+ ions might have been the pore solutions, which migrated from compacted basinal bedded facies towards reef facies or the grain-supported bedded facies developed in the adjacent areas. Microscopic studies revealed dedolomitization at the surfaces and in the inner parts of dolomite crystals. In many cases, dolomite crystals were replaced by calcite forming pseudomorphs.

Highlights

The most characteristic features of the Kraków area (Southern Poland) are isolated hills built of the Upper Jurassic (Oxfordian-Lower Kimmeridgian) white rocks, which represent bedded and massive reefal facies deposited onto the Mesozoic northern shelf of the Tethys Ocean [1,2]
Kimmeridgian sediments are dominated by thick-bedded facies with cherts (Figure 2A), which can be observed in numerous quarries in the Kraków area
Detailed research of Upper Jurassic deposits was carried out in several quarries of the Zakrzówek Horst, which is located in Kraków urban area

Summary

Introduction

The most characteristic features of the Kraków area (Southern Poland) are isolated hills built of the Upper Jurassic (Oxfordian-Lower Kimmeridgian) white rocks, which represent bedded and massive reefal facies deposited onto the Mesozoic northern shelf of the Tethys Ocean [1,2]. In Europe, exposures of these rocks form an extended belt, which stretches from Portugal to the Caucasus Mts. In the Kraków area (Figure 1), research of the Upper Jurassic deposits has been focused mainly on sedimentological analysis of the massive facies, which comprises various types of Oxfordian reefs [2,3,4,5]. In the southern and central Poland, Upper Jurassic bedded facies provide mineral raw materials appreciated by various industry branches and architecture. When categorized by the age of carbonate deposits in Poland, Upper Jurassic limestones constitute nearly 60% of the resources [6]

Methods

Discussion

Conclusion