Diagenesis of limestone and Dolomitization and the effects of phreatic water

ABSTRACT

Diagenesis is the hardening of loose sediment into sedimentary rocks, these are  types of rock formed after the deposition, compaction and cementation of sedimentary material produced by either the weathering and erosion of the Earth’s surface, biological organisms (shells) or chemical precipitation (ooids). Because limestone is often formed from shells and bones, it possess a light color like white, tan, or grey. The color of the limestone depends on the other sediments in the mixture besides the mineral calcite, which is white; impurities such as sand, clay, and organic material are also present in limestone and affect the color.

There are a few ways to recognize limestone. Firstly limestones are rocks that when crushed or scratched with a sharp object, it becomes a white powder except in cases where it contains a lot of organic matter then it gives a dark grey color. When limestone comes in contact with an acid like vinegar or hydrochloric acid (HCI), the stone will produce effervescence and deteriorate and then neutralize the acid. Limestone has quite a history A long time ago, limestone was used to build the pyramids in Egypt. And Romans would mix limestone with volcanic ash to form a type of concrete for building strutures in Rome. The diagenesis of limestone and dolomites takes place in the vados and the meteoric zone which is connected to the water table where the sediments are more porous and permeable due to increase in temperature and pressure in depth.

CHAPTER ONE

GENERAL INTRODUCTION

1.1    Introduction

Limestone is a common type of carbonate sedimentary rock. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCo₃).

Limestone is forms when these minerals precipitate out of water containing dissolved calcium. This can take place through both biological and non-biological processes, though biological processes have likely been more important for the last 540 million years (Boggs, et al 2006). Limestone often contains fossils, and these provide scientists with information on ancient environments and on the evolution of life.(Blatt, et al 2013) About 20% to 25% of sedimentary rock is carbonate rock, and most of this is limestone. The remaining carbonate rock is mostly dolomite,or a closely related rock, which contains a high percentage of the mineral dolomite, (Ca Mg(CO3).

Magnesium limestone is an obsolete and poorly-defined term used variously for dolomite, for limestone containing significant dolomite (dolomitic limestone), or for any other limestone containing a significant percentage of magnesium.(Jackson Julia A, 1997). Most limestone was formed in shallow marine environments, such as continental shelves or platforms, though smaller amounts were formed in many other environments. Much dolomite is secondary dolomite formed by chemical alteration of limestone. Limestone is exposed over large regions of the Earth’s surface, and because limestone is slightly soluble in rainwater, these exposures often are eroded to become karst landscapes. Most cave systems are found in limestone bedrock. Limestone has numerous uses: as a building material, an essential component of concrete (Portland cement), as aggregate for the base of roads, as white pigment or filler in products such as toothpaste or paints, as a chemical feed-stock for the production of lime, as a soil conditioner, and as a popular decorative addition to rock gardens. Most importantly, Limestone formations contain about 30% of the world’s petroleum reservoirs.

Further reading; Geology project topics with Materials