Ecological succession from corals to coralline algae in Eocene patch reefs, northern Spain.

Abstract

Middle Eocene sedimentation on the southeastern margin of the Catalan Basin (northeast Spain) is characterized by alluvial fan and deltaic sedimentation. Northwards these clastic sediments pass into a carbonate ramp, with nummulitid mounds in shallower areas. Coralgal reefs develop in an arcuate band on preexisting delta lobes. The small patch reefs are constructed by an intergrowth of corals (Caulastrea, Porites, Astreopora and Acropora) and coralline algae. The coralline algae overgrow the corals with up to 30 cm densely superposed crusts of Mesophyllum, Archaeolithothamnium and Lithoporella. Some crusts are built laterally around coral heads and others are eroded and redeposited. Abundant previous submarine cements are now present in the form of calcite micrite and spar botryoids. The association of corallines within the crusts is typical of relatively deep tropical waters, which contrasts with the shallow marine corals and surrounding fan delta and beach sediments. The coralline crusts are thought to represent a shallow shaded flora growing over and between corals, in relatively turbid waters. -Authors