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Abouessa A.,University of Strasbourg | Abouessa A.,Libyan Petroleum Institute LPI | Duringer P.,University of Strasbourg | Schuster M.,University of Strasbourg | Pelletier J.,Total S.A.
Journal of African Earth Sciences | Year: 2015

The majority of decapod crustaceans are defined as marine organisms. Crayfish are one of the relatively few known exceptions. They are freshwater-environment adapted decapods that build characteristically large, simple and branched cylindrical morphotype traces in fluvial plains. Their burrows bear lots of special features that make them different from other burrows. Consequently, the identification of true crayfish burrows in the sedimentary record is crucial for the interpretation of depositional environment. The studied interval (45 m thick, exposed in the Dur At Talah escarpment southern Sirt Basin; Fig. 1) represents a case-study which is previously believed to be purely tidal. In this interval, the identification of the crayfish burrows provides a reliable tool for distinguishing terrestrial environments.The crayfish burrows of Dur At Talah are characterized by dimensional, morphological, and especially behavioral aspects that combined, cannot be ascribed to another burrow makers. Essential criteria used to attribute these burrows to the crayfish include: Their length (the depth of penetration into the sediments), their regularly circular cross-sectional area, the presence of mid-way enlargement chamber along the burrow vertical axis, as well as the subtle preservation of the burrow chimney. More importantly, these morphological features allow the recognition of some of the crayfish diagnostic behavioral habits. Most significant of these is the one deduced from the interaction of the burrow with the seasonal fluctuation of the paleo groundwater level. Supplementary indications that restrict the studied burrows to terrestrial organism include their occurrences within pedogenically altered strata that bear evident features of prolonged emersion. Of these features, mud cracks and burrows that are filled with continental fossil are the clearest. Few horizons with termite fungus comb are also distinguishable. Although other burrows of the classically known thalassinoide morphotypes are common in the studied outcrop, this article focuses essentially on the relatively (several orders of magnitude) larger cylindrical morphotypes. This study is based on comparing the field data concerning the studied burrows with those morphometrically similar modern and ancient documented cases. © 2015 Elsevier Ltd.


Abouessa A.,Libyan Petroleum Institute LPI | Duringer P.,University of Strasbourg | Schuster M.,University of Strasbourg | Pelletier J.,Total S.A. | Rubino J.-L.,Total S.A.
Journal of African Earth Sciences | Year: 2014

The Dur At Talah escarpment (150. m thick and 150. km long) is exposed at the southern side of the Sirt Basin, central Libya. This outcrop exposes an Upper Eocene succession, composed by highly bioturbated fine grained sandstones to claystones at the base (New Idam Unit; 80-100. m thick), overlain by medium grained to microconglomeratic sandstones at the top (Sarir Unit; 60. m thick). The latter is split into two subunits of nearly equal thickness: the lower Sarir subunit, composed of medium to coarse cross-bedded sandstones; and the upper Sarir subunit, composed of very coarse to microconglomeratic sandstones.The whole succession evolves from shallow marine estuarine (the New Idam Unit) to fluvial deposits (the upper Sarir subunit). The sandstone of the lower Sarir subunit, which is the focus of this article, is previously misinterpreted as being deposited in a purely fluvial environment. However, close observations revealed that the depositional environment is largely tide-influenced. It is notably marked by conspicuous subaqueous dune cross-stratifications that bear a variety of discrete, multi-scale, sedimentary structures evidencing their deposition in tidal rather than fluvial setting. Mud drapes, tidal bundles, and perpendicularly draining and oppositely climbing ripples are largely developed. Among these structures, the most diagnostic are of millimetric to centimetric scale.As a prime aim of this article, all these sedimentary structures are described, interpreted, and discussed for the first time from this outcrop. Their style of association and the quality of their preservation provide an outstanding ancient example of tide-dominated siliciclastic systems. Such structures are rarely found together in one outcrop as they are in Dur At Talah, and they provide a significant indicators in identifying ancient bedforms of tidal origin. Evidences of subtidal and intertidal depositional environments are afforded by these structures. Criteria indicative of semidiurnal regime of the tide are also presented. These criteria are especially well-preserved in the bundled foresets of the spring tides, the neap tide record is also distinguishable but it provides no discernible structures. Moreover, sedimentary features that can be used to infer a macrotidal range during the depositional time are also afforded by a combination of these structures. Above all, this study also concludes that one of the most reliable sedimentary structures for recognizing the tidal bedforms are the ripple-scale (centimetric) sedimentary structures. These are preserved inside and at the base of the cross-sets. © 2014 Elsevier Ltd.


Elhoud A.,Sinai | Jewilli F.,Libyan Petroleum Institute LPI | Abouswa K.,Libyan Petroleum Institute LPI | Rageai O.,Libyan Petroleum Institute LPI
Materials Performance | Year: 2012

A sudden leak in a 6-in (152-mm) gas line designed to carry dry gas occurred after being in service for one year. The failure took place on the bottom of the pipe from internal corrosion. Visual and metallographic observations confirmed that the pipe split was due to an internal circumferential crack, which then turned in a longitudinal direction. Severe corrosion was noticed on the internal pipe surface. Laboratory analysis confirmed that the pipe failed from the presence of condensate within the pipe.

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