The mineralogy, geochemistry and sedimentation of the shark tooth shale member, Bahrain

Abstract EN

The Shark Tooth Shale (STS) is of Middle Lutetian age and consists of ocher or green fissile shale, marl, carbonate mudstone and subordinate phosphate, stacked in a multi cyclic rhythm.

Each cycle consists, from bottom to top of phosphates-shale-marl-carbonate mudstone.

The top of each cycle is usually a bioturbated hardground.

The mineralogy consists of carbonate fluorapatite, palygorskite, dolomite, calcite and quartz, with less amount of glauconite, halite and gypsum.

The phosphates are granular, composed of phosphoclasts mainly bioclasts including fish bones, shark teeth and coprolites.

The chemical composition is dominated by SiO2, CaO and MgO with variable amounts of P2O5 (1.0 – 13.5%).

The purified concentrates of phosphate coprolites and bones show 34 – 35% P2O5, about 52.5% CaO, 3.7% F and 6.6 – 7.2% L.O.I (CO2 and H2O+ ).

The STS was deposited on a shelf controlled locally by the Bahrain Anticline or Dome.

The sedimentation took place in several sharp transgressive episodes; each was concluded by temporary shallowing and emergences.

The phosphate are mainly related to the early stages of transgression; the shale-rich sediments were laid down at the maximum transgression under subtidal anoxic conditions and the carbonate mud were deposited and simultaneously dolomitized in the tidal mud flats at shallowing stage and were later emerged and bioturbated.

The phosphate showings of the STS are correlatable, as a phosphogenic event, and geological setting with other Tythian deposits (of the same age i.e.

Lutetian) in Saudi Arabia, Qatar, Jordon, Iraq, and probably other same age deposits in North Africa.