LAUSR

Abstract Shallow marine benthic microbial carbonate sediments declined episodically during the Phanerozoic. They were relatively abundant during the Cambrian/mid-Ordovician, late Devonian/Mississippian, mid-Permian/mid-late Triassic, and to a lesser degree in the late Jurassic/early Cretaceous. They were least abundant when invertebrate, especially reef, diversity was relatively high in the mid-Ordovician/late Devonian, early-mid Permian, late Triassic, mid-late Jurassic, and early Cretaceous to present-day. These intervals of microbial carbonate abundance and invertebrate diversity generally alternate transitionally with one-another; but ‘lows’ and periods of overlap also occur. ‘Lows’, when benthic microbial carbonate abundance and invertebrate diversity both declined, are apparent during the Pennsylvanian and early-mid Jurassic. Overlaps, when microbial carbonates and invertebrates were both relatively common, occur in the early Cambrian and late Jurassic. Overall, these patterns broadly support suggestions that microbial carbonate abundance declined as calcified invertebrates increased. To further explore these relationships, we compared microbial carbonate abundance and invertebrate diversity with estimates of changes in sea-surface temperature and marine dissolved oxygen for the past 490 Myr. This analysis suggests that invertebrate diversity varied directly with oxygen availability. Invertebrate diversity was low when dissolved oxygen was low in the early Ordovician, late Devonian, early Triassic, and early-mid Jurassic. It appears that, by reducing invertebrate diversity, low oxygen levels favored microbial carbonates. At the same time, low oxygen levels likely stimulated anaerobic metabolisms favoring carbonate precipitation. This study suggests that dissolved oxygen was a major control on secular patterns of marine microbial carbonate abundance during the Phanerozoic, together with marine temperature and carbonate saturation state.