Depositional and burial history controls on the diagenetic evolution of interbedded sandstone and shale: application to the Ordovician Khabour formation, Iraq
1 - Al-Juboury, Ali I., 2 - McCann, Tom, 3 - Jones, Brian G., 3 - Hutton, Adrian C., 4 - Al-Hadidy, Aboosh
1 - Research Center for
Dams & Water Resources, Mosul University, 58001, Iraq E-mail: allaljubory@yahoo.com
2 - Steinmann Institute
for Geology, Bonn University, Nussallee 8, D-53115 Bonn, Germany
3 - School of Earth and Environmental Sciences, University of
Wollongong, NSW 2522, Australia
4 - Geology Department, Northern Oil Company, P.O. Box 1, Kirkuk, Iraq
Petrographic
(optical, scanning, and backscattered electron microscopy), mineralogical
(X-ray diffraction) compositional analysis of interbedded sandstones and shales
from the Or- dovician-age Khabour Formation of western Iraq were investigated
in order to determine the diagenetic evolution of these units. The Khabour
sandstones are generally quartzarenites with subordinate sublitharenites and
subfeldsarenites which were deposited in a range of shelf environments
(offshore shelf through tidal-storm regressive middle shelf to near-shore inner
shelf). Several diagenetic events have affected the Khabour sandstones
including compaction, cementation, replacement, dissolution and alteration.
Early diagenetic events were closely related to the composition of
depositional water (especially in terms of oxygen and sulphate content), Fe and
organic content of the sediments, rate of sedimentation, and proximity to the
shoreline. Shales interbedded with the sandstones contain evidence of
authigenic illite, chlorite, kaolinite and mixed-layer illite-smectite. The
later diagenetic events within the Khabour Formation were related to the burial
history of the sandstone and shale succession as it was deposited on the
slowly-subsiding shelf. Typical features include quartz overgrowths, the development
of authigenic kaolinite, chlorite and illite, albitization, as well as
Fe-dolomite and titanium and ferruginous cementation that resulted in decreased
permeability by reducing pore-throat openings in the studied sandstones.
Keywords: Burial diagenesis, Depositional control, Siliciclastic rocks,
Ordovician