Paleoenvironmental implication of marine bioturbated horizons in the majzir formation, Western Yemen

الملخص EN

Several thin variegated and/or bioturbated horizons of fine siliciclastic sediments occur in the lower part of the Majzir Formation (Paleocene– L.

Eocene) of Western Yemen.

Field examination and laboratory analysis of sediments from these horizons at localities around the Sana’a and Rad’a areas show that they represent four different marine or equivalent facies These facies are: shoreface Thalassinoides sandstone, shoreface mottled sandstone, foreshore vertically burrowed sandstone, and variegated paleosole of the coastal plain.

These horizons are considered to represent a facies tract of short-lived marine incursions of different magnitude which interrupt the fluvially dominated sandstone sequence of the Majzir Formation.

Each facies represents a different environment within a single marine flooding, which typically consists of a lower thick, transgressive part of fossiliferous and fine-grained sandstone.

The upper regressive unit is relatively thin and intensively bioturbated sandstone.

The bioturbated horizons contain trace fossils of Thalassinoides and Skolithos groups.

Regional correlation of these horizons with eastward equivalents shows that these marine floodings are related to the Early Paleocene Tethyan transgression.

Key Words: Paleogene sediments, Paleoecology of marine horizon, Western Yemen, Majzir Formation, Paleogeography of Arabia-