Resumen de Late Cretaceous paleoenvironment of the Calabar Flank sediments (Southeastern Nigeria) based on planktonic foraminifera
Planktonic foraminiferal morphological studies and inferred isotopic paleotemperature estimations indicate that the two Late Cretaceous (Cenomanian-Turonian and Senonian) marine transgressions onto the Calabar Flank, southeastern Nigeria, involved warm shallow seas.
Important morphologic categories represented in the Cenomanian-Turonian strata (belonging largely to the Odukpani Formation) are hedbergellid (dominant), globigerinelloid and single-keeled globotruncanid. These indicate a maximum paleodepth of less than 50m. for the invading sea. Similarly, rugoglobigerine (dominant), globigerinelloid and single-keeled globotruncanid forms indicate a slightly greater paleodepth (deeper than 50m. but shallower than 100m.) for the Senonian sea. The fact that no deep water morphologic categories (rotaliporid and clavate) were encountered, among other evidences, strongly supports this conclusion.
The occurrence of Hedbergella delrioensis and H. planispira in the planktonic foraminiferal assemblage indicates a maximum temperature of less than 30°C for the Cenomanian-Turonian sea. Sedimentation of the Senonian Nkporo Shale occurred in a sea with a maximum temperature of about 32°C as indicated by the association of Heterohelix globulosa, Rugoglobigerina rugosa and Globigerinelloides sp.
The considerable agreement between the results of this study and previous ones based on other methods is remarkable. It apparently strongly indicates the utility and applicability of planktonic foraminiferal morphology and inferred paleotemperature estimations as reliable tools in paleoenvironmental reconstructions.
