ABSTRACT

Thompsons Lake reef, a small reef complex within the Edgecliff Member of the Onondaga Formation (Devonian, New York), displays a progressive pattern of faunal and lithologic succession. A crinoidal calcarenite represents the establishment of a substrate-stabilizing community. It is abruptly overlain by an irregularly bedded Acinophyllum-bearing calcisiltite, marking the colonization by reef-inhabiting organisms. Perturbations in the environment are evidenced by alternating thin interstratified beds of these lithologies. These are overlain by a blanket of rugosan detritus which marks the final stabilization stage. Establishment of domal tabulate coral heads (both underlying and flanking the reef's inner core) initiated reef development.

The reef proper is marked by distinct lateral zonation. As domal tabulates achieved relief above the substrate, they acted as sediment baffles, trapping crinoidal sands and creating current shadows where silt- and clay-sized grains were deposited. Rugose corals flourished in these quieter waters. Apparently, buildup into the surf zone destroyed the zonation: the reef is capped by a deposit of sheet tabulates in a detritus of crinoidal sands and reef talus.

Reef geometry and facies distribution reflect the prevailing current directions and energies. However, local alteration of these conditions by reef-forming organisms is the key to the development of this patch reef community.

The pattern of development of Thompsons Lake reef is compared to currently existing models for the succession of reef communities. The Walker and Alberstadt (1975) model, while applicable, is found to be too general to yield much additional information on the nature of the reef. The Hoffman and Narkiewicz (1977) model for Paleozoic reefs does not show good correlation with the Thompsons Lake reef. It is suggested that a model dealing specifically with patch reef communities throughout the Phanerozoic record is required.