Page 119 - Carbonate Facies in Geologic History

106 The Advent of Framebuilders in the Middle Paleozoic

!: 160 Known .h.1f
buildup,
.! 70 Pinnacl.
' , •• fs'

..230 TOlol

Iowa

Miuouri

Fig. IV -6. Middle Silurian buildups of middle western states including barrier reef belt sur-
rounding Michigan basin. After Lowenstam (1950), Sangree (1960) and Mesolella et al. (1974)

Shaver (1974) has related the Silurian buildups of Indiana to a biostratigraphic
framework and pointed out some interesting faunal generalizations, Almost
400 species of reef and interreef organisms are known. These faunas evolved
continuously through the Silurian, increasing in diversity, The reef dwellers (flank
and top and niche environments) became more diverse than the frame-builders;
the non-reef forms show little change. This fact and the increased upward expan-
sion of the reefs show a tendency in time for growth into wave base and expansion
of the Middle Silurian reefs to restrict the circulation significantly. Shaver pointed