Page 115 - Carbonate Facies in Geologic History

102 The Advent of Framebuilders in the Middle Paleozoic

Table IV-I. Growth habits of the Chazyan mound organisms
Encrusting Knobby (binders) Upright (frame-tubular)
(binders-stabilizers of fine sediment)

Bryozoans: Atactotechus
Batostoma,
Cheiloporella
Encrusting stromatoporoids: Pseudostylodictyon Coral Eofletcheria
Cystostroma Coral Billingsaria
Encrusting coral: Lamottia
Billingsaria Billingsaria (rare)
Encrusting sponge: Zittelella
Z ittelella (rare) (most common)
Qamellar form)
Algae: Solenopora
Solenopora
Girvanella-anastomosing,
penetrating tubules
Rothpletzella (tiny
beaded chain algae)
Stromatolites
Sphaerocodium?
beads

The earliest Chazyan mounds are among the smallest and are linear ridges of
micrite with flat or bulbous encrusting bryozoans (of the genus Batostoma). They
are surrounded by washed bioclastic and oolitic packstone-grainstone. Later, in
Chazyan time (Crown Point Formation) when less agitation and less terrigenous
influx existed, many diverse organic assemblages constructed mounds. These also
remained small.
Much faunal diversity occurs: (1) An assemblage of Solenopora? and an en-
crusting stromatoporoid, (2) mounds dominated by the lithistid sponge, Zittelel-
la, (3) masses exclusively with the tabulate coral Billingsaria, and (4) mounds com-
posed of three assemblages, (a) stromatolitic algae and small heads of Soleno-
pora? with scattered abundant orthoconic cephalopods, (b) the encrusting bryo-
zoan Batostoma with the tubular tabulate coral Eojletcheria, and (c) Batostoma
with Solenopora?
Some vertical succession is indicated in small mounds of this age in Quebec.
Here the lowest beds are bioclastic packstones overlain by the encrusting bryo-
zoans in micrite and the encrusting coral Billingsaria occurs gradually higher.
The mounds are capped by the tubular Eojletcheria or other Tabulates. In the
Crown Point beds of Lake Champlain the conical sponge Zittelella is prominent
down the flanks, overlain by bryozoan micrite. The two-meter high mound is
capped by lamellar stromatoporoids. The mounds are cut by channels filled
with calcarenite much like those of the Lower Ordovician and Upper Cambrian
mounds. Growth habits of the varied Middle Ordovician forms are given in
Table IV-I.