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Sedimentation patterns around three classes of bathymetric high in the Persian Gulf vary according to regional setting and diameter of the high. Around basin-center highs, the sedimentation patterns are concentric but become progressively asymmetric toward the coast (coastal highs) due to accretion of bioclastic sand on windward sides. Where the diameter of the high exceeds 5 km, downwind tails of bioclastic sand enclose muddy lagoonal-type sediments. Highs submerged below 10 m favor active submarine lithification on their crests, while emergent highs favor beach-rock lithification without dolomitization.
The Persian Gulf bathymetric high model can be directly applied to the Middle Ordovician carbonate rocks of southwestern Ontario and can be used to explain the complex biofacies and lithofacies relations, as well as the location of Ordovician hardgrounds. Both Persian Gulf and Ontario Ordovician hardgrounds occur predominantly on bioclastic and intraclastic sands, deposited in shoaling areas around the islands or highs where rates of deposition are low, especially on accretion tails. Both hardground occurrences exhibit certain faunal similarities, for example, encrusting bryozoans, sponges (stromatoporoids), abundant browsing gastropods (associated with algal mats); similar large branching burrow tunnels are present at omission surfaces in both examples. However, the abundance of pelm tozoan echinoderms and the absence of encrusting corals and bivalves in the Ordovician of southwestern Ontario contrast with recent hardground faunas.
A preliminary justification of the Ordovician-Persian Gulf comparison is presented in terms of general lithofacies and biofacies comparisons and location of hardgrounds. Unfortunately the study is handicapped by poor exposure and lack of precise stratigraphic control; a program of shallow drilling is needed to test some of the inferred sediment distributions around Ordovician submarine highs.
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