Facies Analysis and Paleontology of Carbonate Sedimentary Rock in Hagere-Selam, Messobo and Wukro Stratigraphic Sections; Northern Ethiopia, Tigrai: Implication for Depostional Environment Reconstruction and Age Determination.
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Date
2018-05-02
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Addis Ababa University
Abstract
There Is Carbonate Unit Deposited In The Mekelle Outlier During The Upper Jurassic Period As A
Result Of Flooding Of The Area By Paleotethys Ocean Toward The Southeast Direction. The
Mekelle Outlier Is Situated In The Northern Most Part Of Northwestern Plateau (NWP) And The
Study Carbonate Successions Are Aligned Along The Western (Hagere-Selam), Southeastern
(Messsobo) And Northeastern (Wukro Section) Margin Of The Mekelle Outlier. This Study
Focused On Detailed Investigation Of Facies Analysis And Paleontology Of The Upper Jurassic
Carbonate Units In Order To Obtain A Detailed Picture Of Depositional Environment, Age
Determination And Correlation. Three Main Methods Were Implemented In Order To Accomplish
The Stated Research Problem And Objective Of The Present Study. These Are Pre-Fieldwork, A
Detailed Main Fieldwork And Laboratory Analysis (Petrographic Analysis, Micro And Macro
Fossil Description And Systematics And Microfacies Analysis). A Total Of 65 Rocks And 26
Productive Dry Marl Sediment Samples Are Collected From The Study Sections And Examined
Under Petrographic Microscope. Lithostratigraphically, The Carbonate Succession Has A Total
Thickness About 400m, Which Is Characterized By Thin-Thick Bedded Limestone, Mudstone,
Fossiliferous, Coquinoidal, Oolitic And Sandy Limestone With Different Skeletal Components And
Different Sedimentary Structures. Based On A Detailed Field Investigation, Paleontological And
Petrographical Information, 19 Microfacies Type Are Recognized. These Are Grouped Into Four
Microfacies Association Including Tidal Flat (MFT1-3), Lagoon (MFL1-2), Shoal (MFS1-6) And
Open Marine Environment (MFO1-8). Therefore, The Depositional System Of The Carbonate
Succession Represents A Homoclinal Ramp Setting Because Of Thier Wide Lateral And Vertical
Distribution Of Facies. Additionally, The Carbonate Units Of The Study Area Are Affected By
Different Diagenetic Features Including Compaction, Cementation, Dissolusion, Micrtization,
Dolomitization, Neomorphism, And Silicification. The Carbonate Rock Units Are Correlated
Within Different Measured Sections In The Mekelle Outlier And Regionally Correlated With The
Antalo Limestone Of Blue Nile, The Urandab Formation Of Ogaden, The Antalo Limestone Of
Eretria And Other Arabian Platforms Based On Biostratigraphy And Lithostratigraphy.
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Keywords
Stratigraphy, Microfacies Analysis, Age, Paleontology, Depositional Environment, Diagenesis, Mekelle Outlier