Dynamic Stratigraphy of the Tahara Formation, Hamada Basin, Western Libya

Hassi, Issam Abdul-Hamed Amsaad (1993) Dynamic Stratigraphy of the Tahara Formation, Hamada Basin, Western Libya. MSc(R) thesis, University of Glasgow.

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Abstract

The Hamada basin is little known with respect to tectonic evolution, depositional history, facies relationships and reservoir characteristics. The descriptive stratigraphy of the Hamada basin is however, mostly well established but the dynamic processes that control such intracratonic seas are far from being understood. Thus the scope of this study was to focus on a process oriented stratigraphy; an approach summarized by Matthews (1974,1984) as Dynamic Stratigraphy, in order to reconstruct the dynamics of one of the several stratigraphic accumulations in the Hamada basin (The Tahara Formation). The sequence stratigraphic approach to dynamic stratigraphy, however, depends on the recognition of a hierarchy of strata! units including: lamina, lamina sets, beds, bedsets, parasequences, parasequence sets and sequences, bounded by chronostratigraphically significant surfaces of erosion, non deposition, or their correlative surfaces. At the lowest level in the above hierarchy individual strata are analyzed as the smallest depositional units and as the basic building elements of sequence stratigraphy. Associations of stratal types are grouped into facies. Nine facies are classified, described and interpreted. Stratification and lithotypes, bio and ichnofabrics allow the reconstruction of depositional dynamics (eg. erosional / depositional processes, mode of transport, substrate changes, and colonisation patterns) over short time spans. Each facies is then given an environmental interpretation partly based on a general understanding of the sequence. At an intermediate level (parasequences), vertical and lateral changes of facies over longer time spans are analysed. Such sequential analysis sheds light on parasequence dynamics (eg. progradation, retrogradation). For instance, it was found that the Tahara Formation consists of 16 siliciclastic shallowing upward parasequences stacked in a parasequence set. Each parasequence consists of an upward - shoaling association of facies suggesting deposition in progressively shallower waters. Each parasequence is marked by an upward increase in grain size, bed thickness, and percentage of sand, and a decrease in bioturbation. This vertical pattern of upward coarsening and thickening suggests parasequence progradation (Van Wagoner, 1990). At a higher level (parasequence set) the vertical stacking pattern of parasequences is analysed over still longer time spans. This stratal hierarchy sheds light on parasequence set dynamics (eg. Progradational, aggradational & retrogradational parasequence sets). It was found that younger parasequences tend to be thicker, more sandy and less bioturbated, consisting of a higher percentage of shallow marine facies than older parasequnces in the set. In addition younger parasequences were found to step farther into the basin suggesting a progradational parasequence set (Van Wagoner, 1990). At still higher levels (sequences) the sequential and geometrical arrangement and packaging of parasquence sets within the whole depositional basin is analysed over still longer time spans. The hierarchy of these cycles and their regional distribution patterns give insights to the basin dynamics. However, only the first three of the above four levels are of our concern, sinse the fourth level exceeds the limits of our formation boundary (parasequence set boundary) and is beyond the scope of the present study. The Tahara Formation is, however, interpreted as a silisiclastic shelf-shoreface sequence deposited in a storm dominated regime. The stratigraphic sequence of the Tahara Formation was also analysed using the technique of the Markov chain. End results were similar to those obtained by the sequence stratigraphic technique.

Item Type: Thesis (MSc(R))
Qualification Level: Masters
Additional Information: Adviser: Brian J Black
Keywords: Geology, Sedimentary geology, North African studies
Date of Award: 1993
Depositing User: Enlighten Team
Unique ID: glathesis:1993-75343
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Dec 2019 09:15
Last Modified: 19 Dec 2019 09:15
URI: http://theses.gla.ac.uk/id/eprint/75343

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