The Mesopotamian Sedimentology researches..

Sedimentological Study of  Nahr Umr Formation (Southern Iraq)

 Ali Mansour Mohamed Masour

Abstract

   One hundred and eighty core samples were  collected from the sand stone of Nahr Umr Formation in Luhais-2,3, and 13, NorthRumiala -64, southRumaila-72, and Suba-2 oil wells. Heave minerals analysis, surface feature study, some sedimentary structures and grain size analysis of the samples were carried out.

   Sandstone of Nahr Umr Formation consist primarily of  Quartz( including only microcrystalline; 85.67%) with very small amount of feldspar(only K-feldspar;1.59%) and heavy minerals 0.3% while the rock fragments are absent. The binding material including cement (silica, carbonate, and anhydrite) form about 12.71% of the total bulk sample. The heavy minerals assemblages including ; opaque mineral , tourmaline, amphibole, zircon, rutile, pyroxene, staurolite, biotite, epidote, and corundum. From the mineralogical classification and relating the heaver minerals to their possible source rocks, Nahr Umr sandstone are classified as quartz arenite which formed after long distance of transportation from the source area whose rocks  include a variety of igneous, sedimentary, and metamorphic. These sandstone are in mature stage.

   Grain size analysis were carried out by sieving 182 samples, the analysis shows that sandstone of the Nahr Umar Formation are on the average moderately well srorted to well sorted and fine to medium grained, subangular to subrounded, mesokurtic to leptokurtic, near symmetrical to fine skewed.

   The depositional environment deduced from lithology, grain size analysis and some sedimentary structures is suggested to mixed environment (including delta, river, and shallow marine) due to the transgression and regression of the sea.

   Several diagenetic processes were observed to have affected the sandstone of Nahr Umr Formation including cementation, compaction, recrystallization, replacement, authigenesis, and differential solutions. Cementation thought to be the most active. Three type of minerals were recognized to form the mineral cement (silica, calcite, and anhydrite) among which silica is the most common. The cementing material is considered to of epigenetic origin and are believed to be derived from source outside these sandstone rocks.

M.Sc. Thesis submitted by Ali Mansour Mohamed Masour, Dept. Geology, College of Science, Baghdad University, 1982. 162P.

Supervized by DR. Ali Jawad Ali, and Dr. Qasim Hassan Al-Habib