Hello,

If shale formation itself forms "source rock = reservoir" of the play, particular eutrophic or dysoxic benthic foraminiferal assemblages be found, and they can be biostratigraphic markers … depend on the field.

Well, if you're talking about gas/oil plays in the Devonian-Mississippian black shales, not much.  Conodonts form the biostratigraphic framework for them.

Thanks Satoshi and Larry, the shale samples are of Lower Turonian age.

Dear Oladotun,

in Late Cretaceous source rocks you may expect foraminifer taphocoenoses affected by eutropy as mentioned Satoshi. In case of planktonic foraminifera it means blooms of surface-water opportunistic  Hedbergellids and low-oxygen-tolerant heterohelicids. Plankton will prevail over low-diversity benthos composed of taxa tolent to low-oxic environment (see literature)

Thanks Miroslav, I have a challenge here. One of my samples is silica rich  (low clay content) with 3wt.% TOC; with no planktics but abundant benthics. pore space morphology looking good within mesopore.

What can cause the absence of planktics in organic rich and siliceous sample?

Olatodun,

you may consider low salinity of surface waters connected with water stratification. There are also other factors unfriendly to foraminifer plankton like proximity of land or isolation in lagoons. Plankton usually require open-marine setting. Benthic foraminifera community may help with paleoenvironment.

See:

Waśkowska A., Golonka J., Machowski G., Pstrucha E. 2018. Potential source rocks in the Ropianka Formation of the Magura Nappe (Outer Carpathians, Poland) – geochemical and foraminiferal case study. Geology, Geophysics & Environment, 44 (1), 49–68.