A fungal proliferation near the probable Oligocene/Miocene boundary, Nukhul Formation, Gulf of Suez, Egypt

Haytham El Atfy,Rainer Brocke,Dieter Uhl

doi:10.1144/jmpaleo2013-004

Abstract

Abstract. Moderately to well-preserved palynomorph assemblages were recorded from thirty samples of the Nukhul Formation (GH 404-2A Well), southern Gulf of Suez, Egypt. The taxa are dominated by highly diverse fungi, freshwater algae (e.g. Botryococcus, Pediastrum) beside a sparse record of spores and pollen. Marine palynomorphs, such as dinoflagellate cysts (dinocysts), are very rare. The stratigraphy and age of the Nukhul Formation is highly debated due to lack of diagnostic fossils (e.g. foraminifera, nannoplankton). It has been referred mostly to the Early Miocene; however, some recent publications interpret it as being of latest Oligocene–Early Miocene age. A prominent fungal proliferation composed of diverse and moderately well-preserved fungal spores, fungal fragments, fructifications and hyphae is recorded. This fungi-rich interval occurs mainly from 11370 to 11430 ft in the GH 404-2A Well. Such an observation has not been noted previously within the Nukhul Formation or its stratigraphic equivalents in Egypt. This putative ‘eco-event’ is probably associated with the well-known eustatic sea-level fall in the latest Chattian to early Aquitanian or at the Oligocene/Miocene boundary (OMB). It also seems possible that it may represent a more local event related to the rifting of the Gulf of Suez during this period. The high diversity of fossil fungi is interpreted herein as an indication of an episodic prevalence of humid climate at the end of a regressive phase, as also indicated by a lithological change near the top of the Shoab Ali Member of the Nukhul Formation. In addition, the co-occurrence of freshwater algae, mainly Botryococcus and Pediastrum, together with some aquatic fungal genera, such as Involutisporonites, Paragrantisporites, Quilonia, Striadiporites and Reduviasporonites, suggests the temporary existence of shallow, pond- or lake-like aquatic habitats, possibly related to tectonic activity.

Highlights

Tectonic subsidence and sedimentation were slow during the initial phase of rifting, which was related to the separation of the African and Arabian plates from the latest Oligocene to the Early Miocene (c. 24–15.5 Ma)
As we are dealing with cuttings, the occurrence and ranges of microfossils within the profile may be partially inconsistent in terms of small-scale stratigraphic accuracy
The microscopic examination clearly shows that the reported fungal assemblages did not result from a contaminating effect of sample storage as all samples were preserved in a similar way; fungal proliferation has been witnessed exclusively in a definite interval (Fig. 2)

Summary

Introduction

There has been growing interest recently in fungal palynomorphs of different ages and areas all over the world (e.g. Lange & Smith, 1971; Sherwood-Pike & Gray, 1985; Jarzen & Elsik, 1986; Ediger & Alişan, 1989; Kumar, 1990; Srivastava & Binda, 1991; Takahashi, 1991; Eshet et al, 1995; Visscher et al, 1996; Kalgutkar, 1997; Parsons & Norris, 1999; Steiner et al, 2003; Vajda & McLoughlin, 2004; Kalgutkar & Braman, 2008; Kar et al, 2010; Krings et al, 2010, van Geel et al, 2011; Vajda, 2012). No detailed palynological studies on fossil fungi have so far been carried out from Egyptian sediments or other North African and Arabian areas. Such fungal palynomorphs have been noted sporadically from the Tertiary and Cretaceous of this area Geological Setting The Gulf of Suez is approximately 300 km long with an average width of 70 km and forms the northern extension of the Red Sea, covering an area of about 25 000 km at an average water depth of 55–100 m (Schlumberger, 1984; Young et al, 2000). The Gulf of Suez is the main oil-producing province in Egypt, with oil being produced from Palaeozoic, Mesozoic and Cenozoic rocks

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