Geology Reference
In-Depth Information
MICROFACIES ANALYSIS
This topic consists of three major parts. This first part 'Microfacies Analysis'‚ deals with the methods of micro-
facies studies (Chap. 3), qualitative and quantitative microfacies data (Chap. 4, 5 and 6), diagenetic criteria
(Chap. 7), limestone classification (Chap. 8) and biological controls on the formation of carbonate rocks (Chap. 9
and 10).
3 Methods
A highly recommended description of field meth-
ods is given by Tucker (1982). The methods used in
the study of litho- and biofacies of sedimentary rocks
are the subject of several textbooks (Leeder 1982; Lewis
1984; Pettijohn et al. 1987; Miall 1990; Chamley 1990;
Blatt 1992, Friedman et al. 1992, Lewis and McConchie
1993; Boggs 1995; Reading 1996; Leeder 1999; Miall
2000; Einsele 2000).
This chapter summarizes field work studies, sampling
strategies and laboratoy methods relevant to microfa-
cies analysis. A precise field record of geological and
paleontological data as well as sampling strategies that
consider the vertical and lateral variations in these data
are vital for the success of microfacies studies. Labo-
ratory methods study microscopic features and miner-
alogical and geochemical data.
3.1 Field Work and Sampling
3.1.1.1 Lithology, Texture and Rock Colors
Lithology:
Sedimentary rocks are classified into silici-
clastic rocks (claystone/mudstone, siltstone and sand-
stone), conglomerates and breccias, carbonate rocks
(limestone, dolomite), mixed siliciclastic-carbonates
(marl, argillaceous and sandy limestones), evaporites
(gypsum, anhydrite, salt), siliceous sedimentary rocks
(cherts), phosphorites and organic-rich rocks.
Carbonate rocks make up 20 to 25 percent of all
sedimentary rocks in the geological record and are clas-
sified into limestones and dolomites (dolostones); see
Fig. 3.1. Limestones consist of more than 50% CaCO
3
.
They comprise limestones and dolomitic limestones.
Dolomites are composed of more than 50% CaMg(CO
3
)
2
and are subdivided into calcitic dolomites (50-90% do-
lomite) and dolomites. Although detailed differentia-
tion of carbonate rocks is best performed in the labora-
tory, field distinctions can also be made, using dilute
10% hydrochloric acid (limestone will fizz strongly,
dolomite will show little or no reaction). Alizarin-red-S
Many criteria that are important in facies interpreta-
tion can not be recognized sufficiently in small-scale
microfacies. Paleoenvironmental interpretations de-
rived from microfacies should be controlled by litho-
logical criteria and sedimentary structures evaluated
by the high information potential provided by fossils
and biogenic structures.
Microfacies sampling requires an understanding of
the meaning of bedding and the depositional charac-
ters reflected by sedimentary structures.
3.1.1 Field Observations
Field work forms the basis for studying sedimentary
deposits. Criteria that can be studied in outcrops and
cores in facies analyses are: lithology, texture, rock
color, bedding, sedimentary structures and diagenetic
features, and fossils and biogenic structures.
