AAU-ETD :: Browsing by Author "Atnafu, Balemwal (PhD)"

Browsing by Author "Atnafu, Balemwal (PhD)"

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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.
(Addis Ababa University, 2018-05-02) Girmay, Werede; Atnafu, Balemwal (PhD)
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.
Facies and Microfossil Analysis of Jurassic Carbonate Unit In Lemi Area (Jema Section) Northern Shewa; Central Ethiopia.
(Addis Ababa University, 2018-05-30) Gecho, Geremu; Atnafu, Balemwal (PhD)
A thick Jurassic carbonate succession of about 157m thickness was studied in Jema section, the Blue Nile basin; of the Northwestern Ethiopian Plateau. This study was mainly aimed on exploring the stratigraphy, paleontology, facies analysis, biostratigraphy and determination of the depositional environments of carbonate unit of the Jema section. Based on the petrographic study of 18 representative carbonate rock samples and 8 marl samples; the compositional and textural analysis of rocks were studied and grouped into six (6) microfacies associations and about 22 foraminiferal and 7 ostracodals species are identified; which characterizes for intertidal zone, shoal restricted marine and shelf facies to open circulation environments. The presences of micritic, bioclastic wackestone and peloidal grainstone microfacies in the Jema section indicate shoal to shelf facies deposits. The Pelsparite and algal stromatolite mudstone are indicators of carbonate intertidal to shoal deposits of shallow marine setting. Based on the presence of index fossils such as Kurnubia cf. morrisi, Alveosepta jaccardi and Kurnubia palastiniensis with their associations of Conicokurnubia orbitoliniformis, Valvulina lugeoni, and Nautiloculina oolithica; the age of carbonate succession was determined to an age from Callovian to Oxfordian. Paleontological study of the section in Abay basin shows the carbonate unit is rich in micro fossils and less in macro fossils that supply additional data for stratigraphic and Paleoenvironmental interpretations; particularly of foraminifers and ostracods explored. Among the macrofossils few groups of bivalves, gastropods brachiopods and echinoids are also identified. The carbonate deposits of the logged section are correlated with chronostratigrphically equivalent and lithostratigrphically similar basins in North western and Southeastern plateau of the country regionally and with the previously logged sections in the Bilu Nile Basin locally.
Facies and Paleoenvironment of the Carbonate Unit in the Mertule Mariam Section: East Gojjam, Central Ethiopia
(Addis Ababa University, 2020-09-23) Mulugeta, Mahider; Atnafu, Balemwal (PhD)
A detailed study on the facies and paleoenvironment of the 330m thick carbonate unit of the Mertule Mariam section has been conducted. Field work and laboratory analysis were implemented inorder to accomplish the main objectives of this study. A total of 34 rocks and 17 dry marl samples are collected from the study area and have been examined under petrographic and binocular microscopes respectively. Lithostratigraphically, the carbonate unit of the section is characterized by bedded and bioturbated limestone, fossiliferous limestone, mudstone, oolitic limestone and marl unit. Based on field investigations and based on paleontological and petrographical studies, 11 microfacies types have been recognized and are grouped into four microfacies associations related to paleoenvironments of tidal flats, lagoon, high energy shoal and open marine. Consequently, the carbonate units of the study area represent a shallow marine setting depositional system. Based on paleontological studies various macro and micro fossis are identified including foraminifera and ostracod microfossils; and Bivalve, Brachiopod and gastropod. Additionally algal fossils also recognized The age of the carbonate unit is indicated as Callovian to early Kimmerdigian due to the presence of the following index fossils: pfenderina sp., Kurnubia palastiniensis and Alveosepta jaccardi. The present carbonate unit is correlated with different measured sections in the Blue Nile basin and regionally with the Antalo limestone of the Mekele basin and Urandab Formation of the Ogaden basin depending on biostratigraphy and lithostratigraphy.
The Geology and Geochemical Characterization of Tercha Coal, Southwestern Ethiopia: Indication for Energy Value
(Addis Ababa University, 2018-05-04) Mengistie, Takele; Atnafu, Balemwal (PhD)
Energy is critical input for different purposes. Present study deals with characterizing the energy of Tercha coal and its use. In countries, like Ethiopia, which imports almost all of their energy source, hydrocarbon, further analysis of known deposits and investigation of new area, like this, should forward in detail to decrease exchange rates, expand energy related accessibilities, factories, agricultural sector and others. The coal, in which this research conducted, is found in Southwestern Ethiopia, Dawro Zone, Tercha town approximately 550 Km distant from Addis Ababa. The geology of the area comprises two rock groups of Oligocene age; Igneous (trachyte, welded ignimbrite and volcanic glass units) and Sedimentary (mudstone, shale and coal units) rocks. NW and SE part of the study area is covered by volcanic rock while the sedimentary units are exposed along NE and SW part. The units are formed in two different swamps or lagoons. Different stratigraphic sections recorded in SW part of the study area are correlated litho-stratigraphically. The main objective of this research is characterization of the physical and chemical properties of the coal in the perspective of its energy value for different economic scopes. The methods involved to achieve the objectives are desk studies about the area, fieldwork for mapping and sampling, laboratory analysis (Proximate, Ultimate, CV and TOC). Four stratigraphic sections and Geological map (1:10,000) have been developed. The coal thickness in S1 and S2 stratigraphic sections, are very thin and dominated by clastic materials. The integrated analysis results confirmed that the coal which is found NE of the study area, is higher than other studied coal, in its rank (High Volatile B bituminous coal), best energy (steel-grade I) and, vitrinite and liptinite in maceral type in addition to that of it has considerable thickness. The coal which is found south of the study area, is subbituminous – bituminous in rank and Washery Grade IV in its energy value. Seam 1 and seam 4 are lowest in grade, rank and its energy value. From all studied samples, in general, the coal found southern and NE part of the study area have better quality for different economic purposes like; steam, coking, power generation, fertilizer production, in cement industry and chemical production.
Hydrocarbon Source Rock Potential Evaluation of Bokh Shale of Calub Area In the Ogaden Basin, Southeastern Ethiopia
(Addis Ababa University, 2018-05-03) Geremew, Geleta; Atnafu, Balemwal (PhD)
The Ogaden Basin is situated in the Southeastern part of Ethiopia. It is the largest sedimentary basin with thick successions and has got an attention for petroleum exploration since the mid of twentieth century. Bokh shale is one of the source rocks in this basin and it is the most targeted formation as it is considered to be a source for Hilala and Calub gas deposit. The previous petroleum exploration and development activities were focused on the regional geology, basin evolution, as well as biostratigraphy of the basin but a little is done about the hydrocarbon potential. Therefore, this study iss proposed to determine the hydrocarbon potential of the source rock and to establish the depositional environment and to infer the provenance of Bokh shale. In this study a total of 12 core samples of Bokh shale from Calub 2, 3 and 5 were selected. The organic geochemical of six samples were analyzed using Rock-Eval pyrolysis analytical method. The results were used to determine organic richness and hydrocarbon generation potential, and kerogen type. The organic petrography of the two samples were studied, the results then applied to establish thermal maturity of the Bokh shale. The major, minor and trace elements of four samples were investigated using X-ray fluorescence (XRF) techniques. The results were used to infer the depositional environment and provenance of the source rock. From the analyzed samples the average total organic content (TOC) of the Bokh shale obtained is 0.521 wt% and ranges from 0.5 to 0.56 wt%. The pyrolysis result indicated S1 ranging from 0.02 to 0.23 mgHC/g rock with an average of 0.076 mgHC/g rock and that of S2 is from 0.05 to 0.27 mgHC/g rock with an average of 0.116 mgHC/g rock. The average generation potential of the source rock is 0.192 mgHC/g rock. The vitrinite reflectance of Calub 3 exhibits 1.79 Ro (random reflectance) whereas Calub 5 indicates 1.3 Ro. The overall organic richness and kerogen type of Bokh shale signify fair carbon quantity and poor gas generation potential. The studied sample shows kerogen type IV, i.e. it is dominated by inertinite macerals that generate little or no hydrocarbons upon further maturation. The examined vitrinite reflectance of samples suggest late maturate (Calub 5) to over-mature (Calub 3) organic matter in the Bokh shale. The V to Ni ratio of Calub 3 indicates it was formed of mixed marine and terrestrial organic matter while the Calub 5 was formed of marine organic matter. The examination of ratio of V to V+Ni suggests both samples were deposited under sub-oxic environmental condition. The Zr/Cr, La/Sc, and La/Co ratio indicates both samples were sourced from felsic preexisting rock.
Microfacies Analysis of Mesozoic Carbonate Units of Dire Dawa Area, South Eastern Ethiopia
(Addis Ababa University, 2014-05-05) Fufa, Geramu; Atnafu, Balemwal (PhD)
The lithostratigraphy and microfacies analysis of three selected stratigraphic sections were studied using field data and about thirty four thin sections analysis. These were used to understand the depositional environments, diagenetic settings and age of the carbonate succession (the Antalo Limestone Formation) of the Dire Dawa area, in South Eastern Ethiopia. The field observations, microfacies analysis, and biostratigraphic examinations on the carbonate successions of the area, which sandwiched between lower and Upper Sandstone units, reveal that: these carbonate units have about (~306 m) thickness , have been deposited during Bathonian-Kimmeridgian time; and can be sub-divided into three sub-units, according to their facies contents and stratigraphic positions. These, from older to younger are: (1) The lower sub-unit (Bathonian-Callovian) which is (~119m) thick and consists of mixed siliciclastic - carbonates units of tidalflat-lagoon deposits; and peloidal and ooilitic grainstone facies of carbonate shoal/barrier deposits of the shallow marine setting, (2)The middle sub-unit(Oxfordian-lower Kimmeridgian) is about (~84m ) thick , conformably overlies the lower sub-unit , consists of the foreshoal facies of thick, allochemical rich wackestone-grainstone limestones, mainly dominated by reworked intraclastic grains and rare amounts of patches of colonial organisms, and (3) The upper sub-unit (Kimmeridgian) is about (~103m) thick, overlies the middle sub-unit conformably and topped unconformably by the Upper Sandstone. It consist of low energy deposits of fine grained dark micritic limestones with some cherts and clastic shale interbedded at its lower; and some colonial and carbonate buildup organism bearing layers at its upper part. The overall microfacies and facies successions throughout the unit shows a carbonate ramp depositional setting , under which various submarine depositional environments ranging from shoreline carbonate deposits( including low energy tidalflat and lagoon) and high energy platform margin carbonate sand bodies) of inner ramp , foreshoal deposits of midramp to the offshore deposits(basin margins and open sea) of outer ramp, successively from bottom to top. The diagenetic sequence of these carbonate units, when ordered form early to late stage, comprises the following: micritization, dissolution, early marine cementation, meteoric calcite cementation, mechanical and chemical compaction, fractures; stylolitization, dolomitization, silicification and burial cementation. These processes have taken place with varying intensities and occurrence throughout the area. Lastly deposition and facies patterns throughout this unit are related to already established paleogeoraphic changes particularly involving the transgression of the sea on the horn of Africa. These deposits are also correlated with some of equivalent deposits in major Ethiopian sedimentary basins and with the Sana a basin of Yemen.
Paleoenvironmental Reconstruction of the Adigrat Sandstone Formation Around Dire Dawa Area, Southeast Ethiopia
(Addis Ababa University, 2014-06-06) Adefris, Damenu; Atnafu, Balemwal (PhD)
The Adigrat Sandstone Formation of southeastern Ethiopia was not previously studied independently from the other Mesozoic sedimentary units. Its environment of deposition has been inferred as braided stream from regional studies with limited data. The present research work has tried to study this unit in more detail to reconstruct paleoenvironment (depositional processes and environments) that led for the formation of this sandstone unit. The data used in this study are mainly field data such as lithology, color, sedimentary structures, textures, composition and trace fossils together with petrographic analysis of thin-sections. Using these field data and laboratory results thirteen facies types have been identified and interpreted. These facies types are: poorly sorted massive pebbly sandstone facies, poorly sorted medium grained massive sandstone, trough cross-bedded fine sandstone facies, greenish color massive mudstone facies, brownish yellow shale-dolomite-gypsum unit, herringbone cross-stratified fine sandstone facies, hummocky cross-stratified fine sandstone, slightly bioturbated normal graded sandstone, intensively bioturbated fine-medium grained sandstone, horizontally laminated fine grained sandstone, massive and well sorted quartz rich sandstone, calcareous sandstone and sandy limestone. From these, related facies types have been grouped together by which four facies associations are established and interpreted in terms of depositional environments. These are: meandering stream, shore zone clastic, lagoonal-tidal flat and shallow marine mixed carbonate & clastic facies associations from bottom to top respectively. The depositional environment and the subsequent sediment accumulation for the Adigrat Sandstone Unit of southeastern Ethiopia could have a close relationship with the Late Triassic-Early Jurassic paleogeography of Eastern Africa and to the sea level fluctuation related to the Gondwana breakup. Based on datings on the Adigrat Sandstone in more northern locations of Ethiopia and by considering the age of the top part of the presently studied unit, the sea level fluctuation responsible could be that of Norian-Callovian time. Accordingly, southeast facing and gradually subsiding marginal environment is the probable depositional site for this unit.
Petroleum Source Rocks Analysis Based on Geochemical Data a Case Study in the Melut Oilfields South Sudan
(Addis Ababa University, 2021-10-20) Tap, Chuol; Atnafu, Balemwal (PhD)
The Melut Basin is an important petroliferous rift basin in Africa, and a large number of structural hydrocarbon accumulations have been discovered in it. In this paper, Rock-Eval 6 instrument was used as the main apparatus to achieve the objectives of this study. The general objective of this study is to characterize the petroleum source rock in the Melut Basin based on geochemical data. Geochemical parameters obtained from rock-eval 6 analysis was presented. The samples have been evaluated using geochemical analysis. Following the temperature program and taking into account all measurement and assumptions, S1, S2, S3, TOM, TOC, HI, OI, PP, and Tmax has been measured and calculated in this study. Other parameters include organic carbon content and source rock maturity are evaluated with various factors including quantity and quality of organic matter, petroleum potential, type of organic matter and thermal maturation were considered. For all the selected settings, 5 samples were collected from the Galhak formation, 4 from Al Gagyer and 4 from Melut formations. From all the selected samples, sample TNP011 have shown a considerable richness in total organic matter (TOC), which is 3.24wt.% indicating a very good rate for petroleum potential. The maturation possibility of these sequences is ranging between 423-436℃ as indicated by the Tmax values. Most of the above have shown immature, early and post maturities. For post, maturity samples are mentioned for sample TPW012 as its value equals 448℃. The lowest Tmax value equals 423℃ for sample AMF013 which show an immature level. The criterion for determining kerogen type (quality) is usually depending on the value of the hydrogen index. The overall results show that the source rock quality range from fair to very good hydrocarbon potential stage, with kerogen confined, is encompassed into Type II that has the capability of generating oil and limited gas. Location-1 and location-2 samples have shown poor pair quantity of source rocks. Mostly, gas can be produced in these locations which correspond to type III kerogen. Type III kerogen is known for producing gas. The quality of kerogen in this study is ranging from kerogen type II, III and IV. Type IV kerogen cannot produce oil or gas. Oil and gas are produced from type II and Type III respectively. In this thesis work, the geochemical results have shown that S1 values are lower than S2 values in each source rock sample, which might be interpreted as hydrocarbons migrated out of the investigated source rocks into the traps system.
Petrology, Petrography and Stratigraphical Study of the Evaporite-Carbonate Rocks in the Korrahie Formation (Korrahie Locality), Ogaden Basin, Southeastern Ethiopia
(Addis Ababa University, 2020-06-06) Mohamed, Mowlid; Atnafu, Balemwal (PhD)
This thesis utilizes petrology, petrography and stratigraphical techniques to study the evaporite-carbonate rocks in Korrahie Formation, Ogaden Basin, southeastern Ethiopia, at Korrahie locality. Apart from detailed field observations and lithofacies descriptions as well as graphic logging made on the various outcrops in the studied section at Korrahie locality. A total of 29 representative samples composed of evaporite and carbonate rocks were described and analyzed in detail under petrographic microscope. The results obtained from these outcrop lithofacies and petrographic investigations permitted the interpretation of depositional paleoenvironment. Accordingly, the deposition of this sequence took place under three types of setting namely: shallow subtidal, intertidal and supratidal sabkha. The evaporite (gypsum) rocks were deposited on the intertidal and supratidal zones, mainly under subaerial conditions, and locally under subaqueous conditions along the tidal flats. Microfacies analysis of the carbonate rocks allowed the detection of six microfacies types that are associated with a shallowing upward pattern, and characterizes shallow subtidal through beach barrier/tidal bar to intertidal-supratidal setting. The presence of the bioturbated peliodal-bioclastic wackstone/packstone indicates a shallow subtidal setting and the overlying ooid-bioclastic grainstone represents a relatively high energy environment on the island beach barrier. Passing up on the section we have an interlaminated micrite-packstone which represents back barrier/wash-over setting, and in turn the overlaid by dark grey dolomudstone of upper restricted lagoon to lower intertidal. Laterally changing into microbial laminated boundstones indicates intertidal to supratidal environments along with non laminated and non fossilliferous micritic limestones on the sabkha. The lithological logs of this sequence indicate shoaling up stacked meter scale cycles where the lower part of each cycle is carbonate and the upper part is evaporite with thin layers of marl, shale and dolomite. Microscopic investigation shows that the gypsum in the outcropped part of Korrahie Formation is generally of secondary origin that formed from rehydration of precursor anhydrite during the evaporite return to the cooler and low salinity phreatic zone due to exhumation and uplift. Accordingly much of the gypsum textures observed under the microscope are secondary with minor anhydrite relics, and based on their fabrics four microfacies types of secondary gypsum were recognized which are: porphyroblastic gypsum, granoblastic gypsum, alabastrine gypsum and fibrous satin spar and selenitic gypsum.
Petrology, Petrography and Stratigraphical Study of the Evaporite-Carbonate Rocks in the Korrahie Formation (Korrahie Locality), Ogaden Basin, Southeastern Ethiopia
(Addis Ababa University, 6/6/2020) Mohamed, Mowlid; Atnafu, Balemwal (PhD)
This thesis utilizes petrology, petrography and stratigraphical techniques to study the evaporite-carbonate rocks in Korrahie Formation, Ogaden Basin, southeastern Ethiopia, at Korrahie locality. Apart from detailed field observations and lithofacies descriptions as well as graphic logging made on the various outcrops in the studied section at Korrahie locality. A total of 29 representative samples composed of evaporite and carbonate rocks were described and analyzed in detail under petrographic microscope. The results obtained from these outcrop lithofacies and petrographic investigations permitted the interpretation of depositional paleoenvironment. Accordingly, the deposition of this sequence took place under three types of setting namely: shallow subtidal, intertidal and supratidal sabkha. The evaporite (gypsum) rocks were deposited on the intertidal and supratidal zones, mainly under subaerial conditions, and locally under subaqueous conditions along the tidal flats. Microfacies analysis of the carbonate rocks allowed the detection of six microfacies types that are associated with a shallowing upward pattern, and characterizes shallow subtidal through beach barrier/tidal bar to intertidal-supratidal setting. The presence of the bioturbated peliodal-bioclastic wackstone/packstone indicates a shallow subtidal setting and the overlying ooid-bioclastic grainstone represents a relatively high energy environment on the island beach barrier. Passing up on the section we have an interlaminated micrite-packstone which represents back barrier/wash-over setting, and in turn the overlaid by dark grey dolomudstone of upper restricted lagoon to lower intertidal. Laterally changing into microbial laminated boundstones indicates intertidal to supratidal environments along with non laminated and non fossilliferous micritic limestones on the sabkha. The lithological logs of this sequence indicate shoaling up stacked meter scale cycles where the lower part of each cycle is carbonate and the upper part is evaporite with thin layers of marl, shale and dolomite. Microscopic investigation shows that the gypsum in the outcropped part of Korrahie Formation is generally of secondary origin that formed from rehydration of precursor anhydrite during the evaporite return to the cooler and low salinity phreatic zone due to exhumation and uplift. Accordingly much of the gypsum textures observed under the microscope are secondary with minor anhydrite relics, and based on their fabrics four microfacies types of secondary gypsum were recognized which are: porphyroblastic gypsum, granoblastic gypsum, alabastrine gypsum and fibrous satin spar and selenitic gypsum.
Sedimentological and Geochemical Analysis of Sediments in the Excavated Rock Shelter at Fincha Habera Section, Bale Mountain, Southeastern Ethiopia: Implications on Provenance (Source) and Depositional History
(Addis Ababa University, 2019-01-04) Hadush, Trhas; Atnafu, Balemwal (PhD)
This study is about the provenance and depositional history of clastic sediments deposited in a rock shelter at the Bale Mountains, Southeastern Ethiopia. The sediment section has been excavated for archaeological study. Sedimentological and geochemical characteristics of the sediments in the Fincha Habera section, at the excavated rock shelter site have been investigated. A total of 22 sediment samples have been collected and analyzed, and the analysis results are used to determine the provenance (source) and depositional history of the sediments. The grain size analyses of the unconsolidated sediments show that the sediments range from fine to coarse (silt to silty sand) with mean particle size ranging from 11.97 to 140 μm, poorly to very poorly sorted, with standard deviation of most samples ranging from 1.829 to 5.12 μm; very fine skewed to very coarse skewed with skewness ranging from -0.378 to 0.396 μm, and platykurtic to very leptokurtic with kurtosis ranging from 0.709 to 1.537μm. The relationship between the mean grain size and sorting suggests that sedimentation took place in high energy, open fluvial depositional environments. The integrated data from the field (lithofacies associations), sedimentological analysis (grain size and magnetic susceptibility measurement), and geochemical analysis (elemental and mineralogical compositions) of the sediments has been used as a combined proxy for provenance determination. Accordingly, the integrated data suggest that the materials/sediments that are deposited in the rock shelter have a mixture of three sources: geogenic (either as endogenic or exogenic), biogenic or human induced (anthropogenic) origins. The grain size analysis (sorting), the log ratio of major elements (low log (SiO2/Al2O3) value), the less mobile major elements (Al2O3 and TiO2) ratio, and the mineralogical composition (i.e., predominantly of plagioclase feldspars, particularly anorthite and albite) suggests that the geogenic materials are texturally as well as chemically immature and derived predominantly from mafic source rocks. The magnetic susceptibility of the sediments is indicative of either the anthropogenic sources of some layers in the section, or significant accumulation of organic matter, as the combustion/heating of the sediments by anthropogenic activities or occurrence of sizable quantity of organic matter such as ash and charcoal deposits, respectively, can affect the magnetic susceptibility value. Furthermore, the magnetic susceptibility value of the sediments can be correlated with the Ca and P concentrations (indicators of biogenic materials).
Sedimentological and Petrographic Analysis of Adigrat Sandstone in Yejube Section Central North Western Ethiopia Implication for Paleoenvironment
(Addis Ababa University, 2021-09-14) Kasa, Natinael; Atnafu, Balemwal (PhD)
This thesis is about the interpretation of the depositional environment of Adigrat sandstone from the neglected section of yejube in the Blue Nile sedimentary basin in central northwestern Ethiopia after following a detailed field investigation supported by petrographic and grain size analysis. The data obtained mainly field data that includes color, texture, sedimentary structure, the lateral and vertical continuity of lithology that were investigated. Additionally, the stratigraphic log of the section and geological mapping is conducted. Petrographic and grain size analysis was performed on 27 representative samples. A petrographic analysis result indicates that the studied sandstone is classified mainly as quartz arenite from the modal analysis following point counting of framework grain. The analysis indicating that the sandstone unit is both compositionally and texturally matured. Grain size analysis generally indicates that the sediment consisting of more than one provenance and sediment is deposited not in a restricted environment rather it is deposited in a mixed environment of a fluvial and marine process. Based on the field investigation supported by laboratory result nine lithofacies type has been identified, these are namely Fine-grained Trough cross-laminated sandstone, Medium grained mud crack developed sandstone Facies, Planar cross-bedded medium-grained sandstone facies from lower sub section, Medium grained herringbone cross stratified sandstone facies from the middle part of the section and Well sorted thinly bedded sandstone, Fine-grained hummocky cross stratified sandstone, Fine-grained well-sorted tool marked sandstone, Moderately sorted horizontal bedded sandstone facies, Medium to Coarse grain Bioturbated sandstone facies from lower sub- section. These identified lithofacies type has to be grouped into three facies association to interpret its depositional environment. These facies assemblages are the Meandering river deposit, tidal flats, and continental shelf deposit. The facies stacking pattern indicates that the retrogradational effect of Transgresion process deposits this Formation.
Stratigraphic, Petrographic and Geochemical Characteristics of the Gohatsion Formation in the Blue Nile Basin, Central Ethiopia: Implications for Paleoenviroment Reconstruction
(Addis Ababa University, 2018-06-02) Getachew, Samuel; Atnafu, Balemwal (PhD)
This thesis investigates the stratigraphic, petrographic and geochemical characteristics of the Gohatsion Formation in the Blue Nile Basin, central Ethiopia. In addition to detailed geological mapping and stratigraphic logging in the field, petrographic, mineralogical and major/trace element chemical analysis was performed on 27 samples by means of XRD, ICP-MS/AES analysis. The Formation consists cyclic intercalation of fine siliciclastic and evaporite beds and has been classified into 3 informal members namely, the Upper Mudrock Member, Gypsum Member and the Lower Mudrock Member. Four lithostratigraphic sections were constructed at the Gohatsion-Dejen, Mugher and Jemma localities. Lithofacies at an outcrop and petrographic scale indicates the presence of complex geological history. The Lower and Upper Mudrock Members were formed under tidal influenced environments such as intertidal, supratidal, lagoonal, back-barrier mudflats and tide dominated estuary. The Gypsum Member shows both subaqueous and subaerial facies formed under holomictic brine flux with both continental and marine influences. Geochemistry of mudrock samples showed lower compositional maturity and low weathering index (CIA and PIA values) which is indicative of first cycle deposition. Trace element analysis showed that the provenance composition for such rocks are felsic to intermediate metamorphic to plutonic rocks formed under an active continental arc setting. Diagenetic evolution of sandstone and dolomitic packstone rocks seem to be influenced by meteoric and late stage diagenetic processes whereas the gypsum recorded much of telogenetic processes.
Systematics and Paleoenvironment of Quaternary Corals and Ostracods In Dallol Carbonates, North Afar
(Addis Ababa University, 2017-11-12) Hailu, Addis; Atnafu, Balemwal (PhD)
There are reef structures developed in Dallol during the Quaternary Period as a result of flooding of the area by the Red Sea at least two times. Dallol area is situated in the northern most part of the Eastern African Rift system. The studied coral outcrops are aligned along the northwestern margin of the Afar rift. This research focused on the investigation of systematics of corals and associated fossils of mollusca, echinoidea, ostracoda and foraminifera together with the reconstruction of past environmental conditions. Different scientific methods were followed in order to achieve the objectives of the study. These are detailed insitu morphological descriptions; field observations and measurements; laboratory preparations and microscopic examinations; comparison of the described specimens with type specimens; and paleoecological calculations using PAST-3 software. Total of 164 fossil and 9 sediment samples are collected from the field and examined. The Dallol corals are classified into 12 Families, 29 Genera and 60 Species. The most common species include massive Porites, Porite lobata, Goniastrea pectinata, Goniastrea retiformis, Goniastrea stelligera, Echinopora hirsutissima, Echinopora gemmacea, Echinopora sp., Caulastrea furcata, Caulastrea tumida, Pavona venosa, Stylopora wellsi. Bivalvia classified into 9 Genera and 12 Species which are dominated by Tridacna maxima, Tridacna crocia, Arca boucardi and Crossastrea sp.; gastropoda classified into 6 Genera and 7 Species dominantly Cerithideopsilla cingulata, Canarium mutabile and Rhinoclavis sordidula; and echinoidea classified into 6 Genera and 8 Species dominantly Clypeaster humilis, Echinometra mathaei and Phyllacanthus imperialis. Ostracoda grouped into 15 Genera and 27 Species most of them are monospecific and dominantly Cyprideis torosa, Cyprideis longespina, Xestoleberis rotunda, Xestoleberis depressa, Leptocythere castanea, Loxoconcha carinata, Pontoparta salina, Keijia demissa and Cytherella sp. are recognized. Most of them are euhaline ostracoda species. Foramenifera grouped in to 9 Genera and 13 Species with dominant species Trocohamina sp., Quinqueloculina oblonga, Quinqueloculina lamarckiana, Quinqueloculina sagamensis, Elphideum crispum, Amphistegina lenssonii and Ammonia tepida. From paleoecological analysis of coral species 36% of total identified species are rare, 40% moderately abundant and 23% abundant. Shannon-Wiener index indicates that the older (MIS7) coral species are more diverse than the younger (MIS5) coral species. Paleoenvironmental interpretations are made from biofacies associations and paleoecological results. These are shallow open marine environments of two different phases with small sub – environments of shallow lagoon, brackish protected environment and lacustrine environment.

Browsing by Author "Atnafu, Balemwal (PhD)"

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