Factors controlling the mineralogical and chemical distributions in Safra member (Upper Maastrichtian)‎, Western Desert, Iraq

Abstract EN

Safra Member (Upper Maastrichtian) represents the upper part of Digma Formation, which outcrops to the west of Ga’ara depression.

It consists of dolostone alternating with claystone, marl and thin beds of phosphorites ; limestone occupies the upper part of the rocks.

Factor analysis shows that the mineralogical distribution is represented by four groups ; the first is dolomite ; the second is montmorillonite and fine grained quartz ; the third is palygorskite, sepiolite and apatite and the last is calcite.

There are two main factors that control the distribution of elements ; the first is the offshore environment factor represented by precipitated calcite and the detrital fraction; montmorillonite and fine-grained quartz.

The second factor is represented by the effect of brackish water (schizohaline) nearshore environment, which is enriched with Mg, and caused the complete dolomitization of calcite, and the transformation of the outer part of montmorillonite to palygorskite.

Some palygorskite grains adsorbed dissolved silica, which has resulted from the dissolution of fine-grained quartz or from amorphous silica and transformed to sepiolite.

Apatite has formed due to decreasing in Mg/Ca ratio.

In addition to the less effective third factor which is represented by the presence of X-ray amorphous phosphates (collophane) as teeth and fish bones.