Outcrops of Oligocene reef facies strata in the Vicentin area of northeastern Italy are well known because of the extensive collections of fossil reef corals that have been made from them. This paper presents an overview of the paleoecologic distribution of these reef corals and identifies coral communities indicative of different environments, or of different stages in ecologie successions.
One of the largest and best exposed of outcropping Tertiary reefs is the Berici barrier-reef/lagoonal complex of the Castelgomberto Limestone in the Colli Berici and eastern Monte Lessini. The barrier-reef, which now forms much of the southeast face of the Colli Berici, has a core facies which is 150-200 meters thick ×800-900 meters wide and about 8 kilometers long. The lagoonal facies represents most of the Castelgomberto Limestone and extends northwestward back of the barrier-reef for about 30 kilometers. Other buildups of this area include a. patch-reefs and coppices in the shelf-lagoon, b. a basal Oligocene sequence alternating between thickets of branching corals in terrigenous beds and coral head biostromes in carbonates, c. coral carpets and biostromes high in the Castelgomberto Limestone which postdate the Berici Barrier-reef and d. biostromal assemblages adapted to soft mud substrates in marine tuffaceous mudstones which cap the Castelgomberto Limestone.
In the Marósticano area, coral thickets, coppices and thin fringing-reefs formed along the northeastern margin of a large Oligocene volcanic complex. These structures developed in a region dominated by terrigenous clastic sedimentation in some cases adjacent to centers of submarine volcanic eruption.
Variations of three basic coral assemblages are responsible for the wide spectrum of buildups: a. low diversity t4pioneer?? or thicket assemblage; b. high diversity reef-core and flank assemblage; and c. soft mud substrate assemblage. The environmental factors which appear to have been important in determining the areal mix of species, the community diversity and the abundance of the reef corals, are adaptation to water flow, potential to colonize unstable substrates and to survive sedimentation, and species-specific dominance relationships. Interaction of these factors can explain the seraJ succession of pioneer-to-intermediate-to-climax communities observed in many Tertiary reef buildups.
Most of the biomass that existed at any given time when these ancient reefs were living left no trace in the fossil record of these buildups. Particularly important in the ecology of these reefs (by analogy with modern reefs) were the benthic algae, sponges and octocorals. For the most part, each of these groups (except coralline red algae) is unrepresented or greatly underrepresented in the Vicentin reef fossil record. This is because they lacked mineralized skeletal parts or because these skeletons were destroyed before they became part of the sediments during diagenesis. Most of the reef dwelling biota which did leave an extensive fossil record in the buildups actually aggregated a relatively minor part of the reef biovolume, either as standing crop or over a period of time.