Biological Signals in Carbonate Platforms in Sequence Stratigraphy: Examples from the Cretaceous of Pacific Guyots, Europe and Azerbaijan

ARNAUD-VANNEAU, ANNIE M.

The changes in benthic foraminifera assemblages are one of the most sensitive biological signals in carbonate platforms. They are the best indicators of sea level change and are induced by a combination of various ecological factors including light, salinity, oxygenation, detrital input, physical disturbance and nature of sea-floor substrate.

We can distinguish several specific assemblages in early and late lowstand, transgressive and highstand systems tracts and the assemblages are now established for Cretaceous carbonate platforms.

1. Lowstand systems tracts of carbonate platforms deposited above fair weather wave base are characterized by the abundance of conical tests and thick test foraminifera.

2. Transgressive systems tracts can be characterized by the abundance of agglutinated and arenaceous foraminifera tests when the transgression is associated with detrital input. Transgressive systems tract are the moment when opportunistic species (like Orbitolina, Choffatella, Dictyopsella,...) invaded the inner platform and became dominant. It is also the time of well developed sea grasses and algae.

3. The maximum flooding surface can be characterized by a few percentage of deeper water species of foraminifera (from 5 to 10%) and the presence of rare planktonic foraminifera.

4. Highstand systems tracts are characterized by species living in water devoid of detrital input and abundant Miliolids.

It seems that assemblages of transgressive systems tracts indicate cooler water than assemblages of highstand systems tracts. 

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.