Albian-Cenomanian Calcareous Nannofossils and Depositional Environment of the Wasia Group, Onshore Kuwait
Kadar, Adi P.*1; Yuossef, Abdul K.1; Starkie, Stephen P.2; Al-Baghli, Maha 1; Packer, Stephen 2
(1) Exploration Group, Kuwait Oil Company, Ahmadi, Kuwait. (2) Millennia SC, Buckinghamshire, United Kingdom.
Biostratigraphic analysis of calcareous nannofossils and depositional environment interpretation based on nannofossil, foraminifera, diatom and palynofloras are performed on part of the Wasia group at 10 wells in Kuwait onshore area. Marker species were recognized, allowing the application of Kuwait calcareous nannofossil zones of Al-Fares (1998), and some of the zones are further subdivided into subzones.
The oldest KN32 Zone identified in Mauddud Formation is Late Albian age. N. fragilis in lower Wara Formation indicates evidence Late Albian Zone KN31. The KN29 Zone subdivided into KN29c, KN29b and KN29a based on the first occurrence (FO) of C. kennedyi and last occurrence (LO) of S. glaber. The Albian-Cenomanian boundary is placed within the KN29c Subzone. Tuba member is Early Cenomanian KN28 Zone. The LO of C. chiasta is identified at upper Ahmadi Shale Member indicates KN29a Subzone. The presence of S. glaber above C. kennedyi indicates evidence of Early Cenomanian KN29a and KN29b Subzones for lower part of Ahmadi shale.
Three subzones of KN28 (Al-Fares, 1998), KN28c, KN28b and KN28a, were redefined based on the LO Z. xenotus, the LO of G. theta and A. albianus respectively. Rumaila Formation is Middle to Early Cenomanian age, within subzones KN28b and KN28c. The average stratigraphic resolution of this zonation scheme is approximately 1 m.y except for KN32b and KN31 that are approximately 2.7 m.y.
Base Mauddud Formation dominated by small planktonic with Orbitolina suggesting Middle Neritic. Top of formation rich in agglutinating foraminifera, ostracods with rare planktonic indicating Inner to Middle Neritic. Microfauna in the Wara Formation comprise low diversity small benthic foraminifera and ostracods. Planktonic foraminifera are absent reflecting shallow inner shelf environment. Fish debris suggests fresh water conditions where palynological data provides confirmation. Nannofossil is very poor. Rich and diverse nannofossils assemblage, however, were found on top and base of formations reflecting open marine conditions. Microfossil in the Tuba member dominated by small benthic foraminifera and ostracods, indicating Middle Neritic but influxes of planktonic foraminifera indicate deeper outer neritic conditions found at the base of the formation. Abundant planktonic foraminifera and nannofossils in the Rumalia Formations suggesting Outer Neritic to Middle Neritic environment.
AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain