Page 153 - Carbonate Facies in Geologic History

140 The Advent of Framebuilders in the Middle Paleozoic

o
Micrile mound wilh bryozoan and / or algae and
spong ... Surrounded by shale; usually symmetrical.

b
Palch reef wilh stromaloporoid cop; lIank beds of crinoid debri •.
Thi. may develop inla a cample" of multiple cor .. and flank bed •.
Windward and leeward .ide. may be discernible. Shapes may be
elongale and bodies Irend parallel 10 depth conlours.

Massive irregular '5'
J
c =- ~ rs' '5''''''- Tobulat. and
5 ~.... ... __ S"'S\ Colonial corals
~ t<;' '. 'S' S' S\ --s--;: -N"
rc;-
(C;
~ ---.;~...:::::::::-::
s
~ relief bonk •• • 'ramatoporoid rim •. Size may Yory from
low
giant bonks 100·. of km' 10 circular 01011. 1·2 km in diomeler.
No .'rang windward -leeward differentialion.
Fig. IV -27. Three common types of Middle Paleozoic shelf buildups

Summary

Tectonic Settings of Middle Paleozoic Carbonate Buildups

These accumulations exist in a wide variety of forms and tectonic settings. The
growth potential, particularly of the Devonian biota, while not capable of with-
standing the strongest surf, was vigorous and could keep up with considerable
subsidence.
Practically all these carbonate accumulations built to wave base but not nec-
essarily to sea-surface. The tectonic classification in Chapter XII includes many
examples of Middle Paleozoic buildups and illustrates their wide variety of tec-
tonic settings. They are found as basinal micritic mounds and organic framework
pinnacle reefs ranging in size from 1 square km to major offshore banks. The
coral-stromatoporoid assemblage also existed in the Variscan geosyncline in Eu-
rope. More commonly the biota formed large banks and platforms bordering
large basins in all parts of the world. Such include linear shelf margins and areas
of isolated banks trending parallel to and along the external borders of platforms.