Research paperPalynology, palynofacies analysis, depositional environments and source rock potential of Lower Cretaceous successions in southern Iraq

- A well-preserved palynomorph assemblage was recovered from the Ratawi and Zubair formations except for the Yamama Formation.
- A monospecific assemblage of Subtilisphaera, constitutes the first record of the Subtilisphaera ecozone in Iraq.
- Integrated results of palynofacies and Rock-Eval pyrolysis reveal the following:
- Samples with high TOC and HI values contain abundant AOM, as is the case of the Yamama Formation.
- Samples with lower TOC and HI values contain terrestrial and inertinite fragments and a dearth of fluorescing AOM.

A diverse and well-preserved non-marine and marine palynomorph assemblage was recovered from the Lower Cretaceous Yamama, Ratawi and Zubair formations in southern Iraq.A distinctive monospecific assemblage of the dinocyst Subtilisphaera in the Ru-19 Well, in addition to its frequent occurrence in other wells in the Zubair Formation, reflects an ecologically stressed, marginal-marine environment. This assemblage constitutes the first record of the Subtilisphaera ecozone in Iraq and Arabian realm and indeed only the second one east of Morocco.The palynofacies composition of the studied rock units has been related to previous organic geochemical analyses. Each rock unit has its own palynofacies characteristics and in general, samples dominated by amorphous kerogen have the highest total organic carbon (TOC) and hydrogen index (HI), as is the case for some samples from the studied Yamama Formation and samples belonging to palynofacies PF2 from the Zubair Formation. Samples that are mostly retrieved from the Zubair Formation, containing abundant phyoclasts, have the lowest TOC and HI values.