Search results for: ichnofossils

Authors: Waleed Sulaiman Shingaly

Abstract:

The Ordivician-Khabour Formation from the Northern Thrust Zone of Iraqi-Kurdistan comprises between 500 and 800 m of alternating predominantly greenish-grey sandstones, siltstones and shales. The succession has revealed an abundant ichnofossils characterized by 11 ichnogenus, namely: Helminthopsis, Gordia, Cruziana, Rusophycus, Monomorphichnus, Rhizocorallium, Thalassinoide, Planolite, Paleophycus, Deplocraterion and Skolithose. Ethologically these ichnogenera display dwelling and feeding activities of the infaunal organisms. This association of ichnofossils contains elements of the Skolithose and Cruziana ichnofacies. The presence of Skolithos ichnofacies indicates sandy shifting substrate and high energy conditions in foreshore zone while the Cruziana ichnofacies indicate unconsolidated, poorly sorted soft substrate and low energy condition in the shore face/offshore zone. These ichnogenera indicate shoreface-offshore zone of shallow-marine environment for the deposition of the rocks of the Khabour Formation.

Keywords: Ichnofossils, shoreface-offshore zone, Khabour Formation, Iraq

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Authors: Otosigbo Gloria Ogochukwu, Ehinola Olugbenga Ajayi, Gingras Murray K.

Abstract:

The ichnofossil assemblages of Cretaceous Abeokuta Group from Southeastern Dahomey have not been documented in the literature. This can be traced to deficit of outcrops from the onshore, and also scarce cores from the offshore wells. Ichnofossils and sediment are inseparable and significant in effective interpretation of depositional settings. The ichnology of the tide-dominated estuary to wave-dominated shoreface of offshore Abeokuta Group revealed a brackish water types. The bioturbation is mostly controlled by tidal sedimentation and the vertical succession through the cores within the tide-dominated estuary exhibits regular heterogeneous bioturbations. These are alternations of bioturbated and non-bioturbated units or highly bioturbated and scarce bioturbated alternations. The bioturbations within the wave -dominated shoreface is low to moderate at the lower units but scarce at the upper shoreface. Abeokuta Group sediment are mostly massive sandstone alternations with mud-rich heterolithic facies, sand-rich heterolithic and inclined heterolithic stratifications and shaly fine grained sandstone beds. The ichnofossils observed in Abeokuta Group are basically simple structured, stressed and of low diversity which belong to soft ground, loose ground and firm (substrate controlled) suites. Eleven ichnogenera were identified such as; Asterosoma, Chondrites, Ophiomorpha, Palaeophycus, Planolites, Phycosiphon Rhizocorallium, Rosselia, Skolithos, Teichichnus and Thalassinoides. These were grouped into four recurring ichnofacies of Cruziana, Skolithos Skolithos-Cruziana and Glossifungites ichnofacies. The ichnofossils are significant in distinguishing the upper estuarine embayment boundary from shoreface complex by the paucity of suspension feeding structures in delta front and predominance of suspension feeding structures in the shoreface. Also, the firm substrate suite identifies the flooding surface/transgressive surface, and the regressive surface of marine erosion within the intertidal flats and shoreface respectively.

Keywords: estuary, tide, ichnofossils, ichnogenera, ichnofacies, skolithos, cruziana, glossifungites

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Authors: Aswan Aswan

Abstract:

Ichnofossils were examined based on two wells cores of Jurassic sediment from Bintuni Basin, West Papua, Indonesia. The cores are the Jurassic interval and known as the potential reservoir interval in this area. Representative of 18 ichnogenera was recorded including forms assigned to Arenicolites, Asterosoma, Bergaueria, Chondrites, cryptic bioturbation, Glossifungites, Lockeia, Ophiomorpha, Palaeophycus, Phycosiphon, Planolites, Rhizocorallium, Rosselia, root structure, Skolithos, Teichicnus, Thalassinoides, and Zoophycos. The two cores represent a depositional system that is dominated by tidal flat, shallow marine shelf continuum possibly crossed by estuaries or tidal shoals channels. From the first core identified two deepening cycles. The shallow one is a shallow marine with tidal influence while the deeper one attached to the shelf. Shallow interval usually indicates by appearances of Ophiomorpha and Glossifungites while the deeper shallow marine interval signs by the abundance of Phycosiphon. The second core reveals eight deepening cycles.

Keywords: ichnofossil, Jurassic, sediment, reservoir, Bintuni, Indonesia, West Papua

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