Fluid Inclusion Studies
Fluid inclusions can be found in virtually all crystals. They range in size from less than 1 μm to a few centimeters, although inclusions larger than 1 mm are uncommon. Most contain a solution which represents a sample of the original waters from which the crystal formed, plus a gas or solid phase which may have separated during cooling.
Careful petrographic study (commonly using heating or freezing stages) can determine the composition and original temperature of the fluids involved in crystal formation. This can provide useful information on the timing and conditions of cementation or mineralization, although care must be taken to determine the exact time relations of the fluid inclusions and the host mineral.
The top photo shows two phase (fluid and liquid) inclusions from the fluorite-zinc district of Illinois (0.40 mm).
The middle photo illustrates a three phase (solid, liquid, and gas) inclusion in a quartz geode from Iowa (10 μm).
The bottom photo shows a two phase immiscible mixture of oil and water within a fluorite crystal from the same locality as the top photo. The colorless fluid is a strong brine; yellow fluid is oil; gas bubbles are methane associated with oil. All photos by Edwin Roedder.
Figures & Tables
A Color Illustrated Guide To Constituents, Textures, Cements, and Porosities of Sandstones and Associated Rocks
This book is designed as a companion volume to AAPG Memoir 27. As with its predecessor volume, the purpose of this book is to provide identified illustrations of important grains, textures, cements, and porosity types for geologists who may not be specialists in the petrography of sandstones and associated sedimentary rocks.
Sandstone petrography is of particular interest to the explorationist for several reasons. First, it can provide valuable information on the detailed composition of sedimentary rocks. From this, one can often draw conclusions about the lithology, climate, and tectonic history of the source area, as well as predicting the response of such units to a variety of subsurface diagenetic environments. Second, one can acquire significant data on the grain size, sorting, and rounding of sedimentary grains. For Iithified sediments this may be the only way to obtain such data, which may be useful in determinations of the transport mechanisms and depositional environment of the sediment. Third, information may be obtained on the postdepositional alteration history of sedimentary rocks. This may include data on compaction, cementation, leaching, fracturing, porosity types, and other factors. These are essential for a proper understanding of reservoir rocks and, commonly, petrography provides the only technique forgathering accurate data on such diagenetic factors.
This book is intended as an introduction for exploration geologists or students and is by no meansa complete textbook or treatise. However, it does include a wide variety of color photographs of terrigenous clastic grains, cements, and textures of sandstones and common accessory rock types. Although most of the illustrations are of features seen with the petrographic microscope, some scanning electron micrographs are included. The illustrations were made from samples having as wide a range of lithologies, geologic ages, and localities as possible to insure a fairly representative presentation. In addition, the photographs were generally selected to show the most common grain and textural types encountered by the geologist and to present typical, rather than spectacular, examples of most features. Thus, the book shouId have applicability to any sandstone petrographic study.
This volume focuses on the descriptive aspects of petrography and includes no text other than figure captions. Bibliographies are provided in each section of the book. For more detailed descriptive and interpretive information, the references listed in both the general and specific bibliographies should be consulted.
The major emphasis of th is book is on the fou... major fabric elements of sandstones: framework grains; detrital fine-grained matrix; cements; and pore space.