Microfacies Analysis and its Implications for Depositional Environment of Margala Hill Limestone from Khaira Gali Road Section, North Eastern Hazara, Pakistan
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Abstract:
Stratigraphic section of Margala Hill Limestone exposed in the Khaira Gali road section of the Hazara Basin, northwestern Himalayas has been measured, logged and sampled. The 96m thick section of Margala Hill limestone mainly consists of medium to thick bedded nodular limestone with intercalations of shale. This high resolution petrographic study of the formation has been done with an integrated approach of sedimentology, paleoecology and biostratigraphy and it mainly shows wackstone to packstone carbonate texture with different assemblages of Larger Benthonic Foraminifera e.g. (Assilina spinosa, Nummulites globulus, Ranikothalia sindensis, Nummulites mamillatus, Assilina subspinosa, Nummulites atacicus, Assilina granulosa, Operculina patalensis, Assilina laminosa, Ranikothalia nuttalli, Lockhartia conditi, Ranikothalia sahni, Lockhartia tipperi, Discocyclina dispansa, Discocyclina ranikotensis and Quinqueloculina), Bivalves and green algae. Five types of microfacies have been interpreted on the basis of carbonate texture and skeletal grains observed in thin sections. These microfacies include Rotaliids-milliolids mud-wackstone, Algal- bioclastic packstosne, Nummulitic wack-packstone, Assilinids wack-packstone and Discocyclina- Ranikothalia wack-packstone microfacies. The presence of these assemblages draws the conclusion that the deposition was occurred in closing Neo-Tethys on an inner to middle shelf environment at the northern extremity of the Indian Plate. Based on age diagnostic Foraminiferal assemblages, Ypresian, Early Eocene age has been designated to the Margala Hill Limestone.Keywords:
Wackestone
Section (typography)
Baltica
Carbonate platform
The Devonian succession between the Guadiana and Guadalquivir valleys in the Obejo-
Valsequillo Domain comprises more than 600 m of shale and sandstone with some interbedded limestone
and marl. The most complete reefal sequences of the region are exposed in the Guadamez-2
section, which is located on the western bank of the Guadamez River, near Zalamea de la Serena. It
consists mainly of shale and calcareous shale in its lower part and shaly, skeletal and reefal limestone
in its upper part. Conodont and brachiopod data indicate that this section spans the interval from
the Lochkovian to at least the upper Emsian. Eight microfacies types have been identified in the
calcareous facies: A, brachiopod-echinoderm wackestone/packstone; B1, echinoderm grainstone;
B2, echinoderm-bryozoan grainstone/packstone; C, echinoderm packstone; D, tabulate coral
rudstone; E, brachiopod wackestone/packstone; F, brachiopod grainstone/packstone; and G,
stromatoporoid and tabulate coral boundstone/rudstone. Microfacies A, B1, C, E and F represent
a sequence of environments from middle platform (A) to tidal flat (F), including shoals (B1) and
shallow platform facies. Microfacies B2, D and G represent the development of patch-reefs super -
imposed on the shoals.
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The Kohat Formation from the Shekhan Nala was sampled and measured for detailed stratigraphical and micropalentological studies to determine the age and environment of the formation. The Kohat Formation contains abundant varieties of larger foraminifera belonging to the genera Nummulites, Assilina and Alveolina. On the basis of larger foraminifera Middle Eocene age of the formation has been confirmed The microfacies studies identified the bioclastic wackestone, bioclastic packstone and bioclastic grainstone where the bioclasts are larger foraminiferal species, Nummulites beaumonti, Nummulites mamillatus, Assilina exponens and Alveolina elliptica. The Kohat Formation on the basis of larger foraminifera and micro facies analysis draws attention to the fact that it was deposited in shallow marine environments. The Kohat Formation has been identified into four lithofacies, which are from base to top, TS-l:- Calcareous shale interbedded with fossiliferous limestone. TS 2:- Nummulitic shale and limestone. TS-3:-Highly fossiliferous limestone. TS-4: Massive nodular limestone.
Wackestone
Grainstone
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A limestone unit is exposed in Batu Luang exhibited well preserved larger benthic foraminifera. This limestone is in-situ and no sign of transported block due to its clear interbed with the argillaceous sediment in the sequence of the measured section. The argillaceous sediment in the surrounding area was mapped by previous researcher as a turbidite sedimentary sequence of the Setap Shale Formation. The aims of this study are to determine the age of the larger benthic foraminifera and the paleoenvironment of the limestone. Three samples of limestone were collected and thirty thin sections samples were prepared and analysed. A total of eleven species of larger benthic foraminifera were identified. One assemblage of larger benthic foraminifera can be recognised, namely Lepidocyclina (N.) verbeeki assemblage. This foraminifera assemblage is an indicative of Te5 or early Lower Miocene (Aquitanian) age. Two microfacies were characterised namely; 1) Coral-coralline algae boundstone microfacies (MF1) representing the reef flat environment and 2) Foraminifera packstone microfacies (MF2) which was related to the shallow open marine carbonate environment. The microfacies analysis and the outcrops observation show that the limestone unit at Batu Luang was a small reef deposited in shallow marine of carbonate environment. The limestone of Batu Luang could be the remnant bioherm that was developed during Te5 or early Lower Miocene (Aquitanian), associated with shoreline environment which negate the previous study.
Peninsula
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Wackestone
Sequence (biology)
Sequence Stratigraphy
Stratigraphic unit
Grainstone
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Microfacies analysis of the carbonate rocks of Ukhrul were conducted to understand the sedimentological features, microfacies associations and depositional environment of the flyschoidal sediments deposited within Upper Disang Group. These rocks composed mainly of microcrystalline calcite matrix, sparry calcite cement, skeleton grains and shell fragments. Three microfacies were identified as mudstone, wackestone and packstone. Based on the energy index classification, these limestones can be categorized into subtype II1 of type II those were deposited in an intermittently agitated environment. Foraminifera of Upper Cretaceous to Eocene age have been identified in the present study. The recognized microfacies of the present study have been compared and correlated with the standard microfacies association (SMA), and in all probability they falls in Facies Zone 8. The detail microfacies analysis show that the studied limestones were deposited in a shallow marine shelf condition with restricted to moderately agitated water within an interior platform basin during the Maastrichtian – Eocene time.
Key words: Microfacies, shallow water Carbonate, restricted environment.
Carbonate platform
Micrite
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Wackestone
Carbonate platform
Pelagic sediment
Outcrop
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A surface section of Harur Formation of Early Carboniferous (Tournaisian) in Nazdur area, northeast of Zakho town, Northern Iraqi Kurdistan, was selected for this study. Lithologically, Harur Formation consists of thin to medium bedded, black organic limestone, dolomitic limestone, with black micaceous shale mainly in lower and upper parts. The petrographic study has shown that these limestones consist of micrite and sparit e groundmass. The skeletal grains included shallow water brachiopods, bryozoans, corals, and e chinoderms, in addition to ostracods, while non-skeletal grains included peloids only. Four different microfacies were distinguished ; Boundstone, Grainstone, Lime Packstone, and Lime Wackestone. Each of these had been further subdivided. Using lithologic and paleontologic criteria, the depositional environment of Harur For mation is concluded to be shallow marine environment, mostly reef and reef flanks.
Tournaisian
Wackestone
Micrite
Grainstone
Lithology
Ditch
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Wackestone
Cenomanian
Carbonate platform
Biozone
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Cyclostratigraphy
Paleogene
Section (typography)
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