Geology Reference
In-Depth Information
20 Adding Some Samples
by
Axel Munnecke
Due to the work by Erik Flügel, who passed away far too early in 2004, microfacies investigations of carbonate
rocks have a long tradition in our institute in Erlangen (Germany). He stimulated several generations of geologists
in the field of carbonate sedimentology, and it is a great honor for me to provide a small additional chapter to the
present topic. The chapter presents examples from a variety of depositional environments and ages. The thin
sections have been prepared for the international microfacies courses held in Erlangen regularly since 1974. The
chapter has two goals. On one side, thin sections have been chosen which complement the previous chapters,
and provide some additional information, on the other, this chapter is intended as some sort of self-test. Before
reading the figure captions you might try to study the pictures and build your own interpretation.
After reading the topic many of the features visible in the following pictures are 'old friends', but some are
new documenting that carbonate microfacies analysis is a fascinating, living scientific field, and each thin section
tells its own story.
Fig. 20.1.
The cold-water origin of this modern carbonate sediment (with some siliciclastic SI and carbonate rock fragments
CR) is dominated by various types of herbivorous gastropods from the
Fucus-Ascophyllum
belt (common intertidal brown
seaweed species - SW). Remnants of other epifaunal organisms (e.g. balanids - B, serpulids - S) are also typical for this
environment. The rock fragments have been derived from the rocky shore. The black, mostly porous components represent
remnants of the brown seaweed, which in diagenetically mature carbonate rocks are not preserved. Please note that carbonate
deposits from sublittoral kelp forests (
Laminaria
) have a different appearance. These large seaweed plants use phenolic
compounds as chemical defense against herbivores, and as a result, sediments from these environments usually lack herbivorous
gastropods. Thin section of a recent beach deposit near Galway, Ireland.
B - Balanids, CR - Carbonate rock fragment, SC - Light-gray siliciclastic component, SP- Serpulids, SW - Seaweed
