Abstract
Most Lower Cretaceous limestones in the Kopetdag basin are reefal in origin and display a cyclicity of facies related to eustatic changes in sea-level. The best developed reef systems formed during two major highstands, one in the Lower Hauterivian and the other in the Lower Barremian, with smaller reef systems formed during intermediate minor highstands. The second transgression resulted in the formation of typical ‘Urgonian’ deposits with their characteristic fauna of corals, stromatoporoids, chaetetids, algae, rudists and orbitoline foraminifera. The principal facies zones are traced for each reef system. Stratigraphically higher reefs have more complex lithofacies and a more specific ‘Urgonian’ fauna. Two separate types of ‘Urgonian’ deposits are distinguished; an ‘immature’ pre-orbitoline one and a later, more ‘mature’ one with a more extensive fauna.
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