Triassic Reworking of Palaeozoic Palynomorphs and Acritarchs: Observations on The Origin of The Beduh Shale and the Basal Part of Geli Khana Formation, Zagros Mountains, Northern Iraq.

Abstract

An increase of argillaceous influx in the Lower Triassic has been observed worldwide; this event could be correlated to the ‘Campili’ event described from the Southern Alps, the Karavanka Mountains as well as the Northern Calcareous Alps. In Northern Iraq, the lower Triassic Beduh Formation is represented by red shales and marls. Based on similarities in paleofacies, this formation could be an equivalent of the Campili member of the Alpine Werfen Formation. Two populations of palynomorphs with different styles of preservation were found in one of the samples. One group had poor preservation, distorted by mineral growth, and includes very questionable miospores. A second group contained marine acritarchs (e.g Dictyotidium tenuiornatum) with moderate preservation and maturity suggesting that these are of different stratigraphic origin. Basal member ‘E’ of the Geli Khana Formation, overlying the Beduh Formation, comprises shales with intercalations of thin bedded limestones. This basal limestone unit can correlate to basal peritidal carbonates of the Alpine Werfen Formation. In a sample from the basal part of the Geli Khana Formation, assemblages of acritarchs, including the Ordovician or younger genus Diexallophasis, and Ordovician - Devonian chitinozoan fragments were recovered. During the Ordovician, a shallow subsiding shelf environment was predominant, acting as a depositional area for the Ordovician Khabour Formation. The unconformity between the Devonian Pirispiki Formation and the Khabour Formation can be related to the Caledonian Orogeny. The red beds of the Pirispiki Formation correlate directly to those in Turkey, as well as the Old Red Sandstones. This stage represents deposition in a subsiding basin, beginning with the continental deposits of the Pirispiki Formation and the Kaista Formation. The Ora Formation is associated with the global Devonain/Carboniferous mass extinction (‘Hangenberg Event’). The acritarchs recovered in a sample from the basal Geli Khana Formation are derived from Palaeozoic (Ordovician – Devonian) sediments. The limited data do not allow a definitive interpretation of their origin, but according to the recent knowledge, their origin could be (1) either the Khabour Formation, (2) the Kaista Formation, (3) or evidence of eroded sediments not previously described from the area. Possible reworking, of uncertain origin, is also identified in a sample from the base of the Beduh Formation.

AAPG Datapages/Search and Discovery Article #90194 © 2014 International Conference & Exhibition, Istanbul, Turkey, September 14-17, 2014