Jurassic Brachiopod in Blue Nile Basin Msc Thesis by Bikila Argeta 2020

UNIVERSITY OF GONDAR

COLLEGE OF NATURAL AND COMPUTATIONAL SCIENCES DEPARTMENT OF GEOLOGY MSC PROGRAM IN PALEONTOLOGY & PALEOENVIRONMENT

MSC Thesis Entitled Jurassic Brachiopods from Dejen-Gohatsion Section, Blue Nile Basin, Central Ethiopia By Bikila Argeta Ayele Adviser: Dr. Dawit Lebenie

A thesis submitted to Geology Department University of Gondar in the partial fulfillment of the requirements for the degree of Master of Science in Paleontology and Paleoenvironment.

September 2020 Gondar, Ethiopia UNIVERSITY OF GONDAR

COLLEGE OF NATURAL AND COMPUTATIONAL SCIENCES

DEPARTMENT OF GEOLOGY

MSC PROGRAM IN PALEONTOLOGY & PALEOENVIRONMENT

MSC Thesis Entitled Jurassic Brachiopods from Dejen-Gohatsion Section, Blue Nile Basin, Central Ethiopia BY BIKILA ARGETA ADVISORY DAWIT LEBENIE (PhD)

APPROVED BY

Examiner

Name Signature ______Advisor Name Signature ______Co- advisor Name Signature ______Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

ABSTRACT A Jurassic Brachiopod fauna from Blue Nile basin from Dejen to Gohatsion was represented by two articulated class Ryhnchellida and Terebratulida. The class comprises of five species viz., Dhagnirynchia sp, Somalirhynchia sp, Cymatorhynchia sp, Monsardithyris sp, Cererithyris sp, the material studied herein was collected from three sections. The species seem to be geographically restricted within the Jurassic Ethiopian Province. The study presents morphological description of Jurassic brachiopod fauna from the Blue Nile basin of central Ethiopia. This taxonomically study aid in establishing the history of brachiopod species and their evolution within the Blue Nile basin. The data compiled as a result of these studies enable us to interpret the biogeographic history of the Blue Nile basin, as well as gain insight into the structure and palaeoecology of its marine communities. It also contributes to define faunal- and province-realm boundaries with greater accuracy. From the compiled data Correlation of the brachiopod fauna of the area with those of Mekelle and Dire Dawa regions is similar. So the description of brachiopods from the Antalo Limestone in Blue Nile basin of central Ethiopia presents this fauna is largely of Oxfordian age and lived in shallow sub tidal environments. In combining the new data with fossil occurrence data from the Paleobiology Database the conducted taxonomic analyses to assess biogeographic patterns and the delineation of the Ethiopian Province for the Callovian to Kimmeridgian stages. Results suggest that an Ethiopian Province is indeed evident for our focal groups, but this is more confined than traditionally assumed. The so defined Ethiopian Province includes Tunisia, the Levant, Arabia and much of East Africa, but excludes Tanzania and India. The special status of India and Tanzania is perhaps due to latitudinal gradients in faunal composition.

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

ACKNOWLEDGEMENTS First of all, and for being a wonderful guide for me, I would like to express my special appreciation and thanks to my advisor Dr. Dawit Lebenie. I would like to thank him for his unlimited helps, critical constructive comments, guidance‘s, conceptual motivations, readiness for help at any time asked throughout the work and always positive thinking made him the most facilitator and contributor individual for completion of this work and suggestions. His advice on both researches as well as on my career has been priceless and words cannot express how grateful. I am also deeply grateful thanks to my oldest Brother Amsalu Zeleke and mom Mareme Wabulcho for their endless pray and help for me was what sustained me thus far and Mr. Liknew Mengesete, for his a lot of helps to me during my thesis work in laboratory. Lastly, I have thanks to University of Gondar Department of Geology for being sponsor of my studies and for allowing me to use laboratories and various field instruments for my thesis works.

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

Table of Contents ABSTRACT ...... I ACKNOWLEDGEMENTS ...... II CHAPTER ONE ...... 1 1. INTRODUCTIONS ...... 1 1.1 Background ...... 1 1.2. Geographic Setting of the Area ...... 2 1.2.1. Location and Accessibility ...... 2 1.2.2. Physiographic and Drainage...... 4 1.2.3. Climatic Condition and Vegetation ...... 4 1.2.4. Population and Settlement ...... 5 1.3 previous works ...... 6 1.4 Significance of the study ...... 7 1.5 Statement of problem ...... 7 1.6. Objectives...... 8 1.6.1 General objective ...... 8 1.6.2 Specific objective ...... 8 1.7 Methodology and Materials ...... 8 1.7.1 Methodology ...... 8 1.7.1.1 Phase I (Pre-Fieldwork) ...... 8 1.7.2 Materials ...... 9 1.8 Limitation of the study ...... 9 CHAPTERTWO ...... 10 2. LITERATURE REVIEW ...... 10 2.1. Regional Geology ...... 10 2.2 General Stratigraphic Succession of Northwestern Ethiopia Plateau ...... 11 2.2.1 The Precambrian Basement rocks ...... 12 2.2.2. Pre-Adigrat ...... 12 2.2.3 Adigrat Sandstone ...... 13 2.2.4 Gohatsion Formation ...... 13 2.2 4 Antalo Limestone Formation ...... 14 2.2 6 Mugher Mudstone ...... 14

III

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

2.2.7 The Debre Libanose Sandstone...... 15 2.2.8 The Tertiary Trap Series ...... 15 2.3 Jurassic brachiopod fossil study of Sedimentary Basins ...... 17 CHAPTER THREE ...... 20 3. Lithostratigraphy of the study area (Dejen - Gohatsion) ...... 20 3.1 Lower Sandstone Unit ...... 20 3.2 Red Sandstone Unit...... 21 3.3 White Sandstone ...... 21 3.4 Glauconitic sandy mudstone unit ...... 22 3.5 Gypsum unit ...... 23 3.6 Lower Marl Unit ...... 23 3.7 Lower Limestone Unit ...... 24 3.8 Upper Marl Unit ...... 25 3.9 Upper limestone unit ...... 26 3.10 Basalt Unit ...... 26 CHAPTER FOUR ...... 27 4 PALEONTOLOGICAL STUDIES OF BRACHIOPODS ...... 27 4.1 INTRODUCTION ...... 27 4 .2 Geologic History ...... 28 4.3 Description of Brachiopod Species ...... 29 4.3.1 Systematic Paleontology ...... 29 CHAPTER FIVE ...... 36 5 Discussion, conclusion and Recommendation ...... 36 5.1 Discussion ...... 36 5.2 Conclusions ...... 38 5.3 Recommendation ...... 39 REFERENCES ...... 41 List of fossil plates ...... 45 Plate 1 Dhagnirynchia sp ...... 45 Plate 2, Somalirhynchia sp ...... 46 Plate 3 Cymatorhynchia sp ...... 47 Plate 4 Monsardithyris sp ...... 48

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

Plate 5 Cererithyris sp ...... 49 APENNDEX...... 50

Table of Figures Figure 1shows A) location map of study area and B) shows sample locality map ...... 3 Figure 2shows 3D view of topography and drainage pattern of study area modified from (Yoseph Endalamaw 2010) ...... 4 Figure 3climatic condition of Blue Nile Basin (www.climate.org) ...... 5 Figure 4shows Mesozoic sediments and basins of Ethiopia (Source: Ethiopian Institute of Geological Survey, by Mengesha Tefera et al., 1996) ...... 11 Figure 5 the geological map ...... 16 Figure 6 lower sandstone unit with drop inclusions ...... 20 Figure 7 Red sandstone unit ...... 21 Figure 8White sandstone units with cross bedding structure ...... 22 Figure 9 Glauconitic mudstone unit ...... 22 Figure 10 Gypsum units with fault ...... 23 Figure 11lower marl unit with Brachiopod fossils ...... 24 Figure 12Lower limestone unit ...... 25 Figure 13upper marl unit with tempestite ...... 25 Figure 14 upper limestone unit...... 26 Figure 15 columnar basal unit ...... 26

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

CHAPTER ONE

1. INTRODUCTIONS 1.1 Background Sedimentary basins are regions of large depression due to prolonged crustal subsidence, in which sediments are accumulated (Philip and John, 2005). Excluding the thin Quaternary and unconsolidated sediments, which are deposited in the main Ethiopian rift valley, sedimentary regions of Ethiopia covers a major part of the country and mainly exposed in five distinct basins they are the Ogaden Basin, the Blue Nile Basin, the Gambela Basin, the Mekele outlier and the Southern Rift Basins (Ethiopian Ministry of Mines, (2011). The development of most of these basins is related to the extensional tectonic events that have taken place since the Late Paleozoic time (Merla et al., 1979).

From sedimentary rocks Carbonate rocks, are characterized by containing important and varied textures, sedimentary structures and fossils that yield important information about ancient marine environments, paleoecological conditions and the evolution of life forms, particularly marine organisms, through time.

According to Geni et al The Blue Nile Basin is located in the North Western Ethiopia plateau, was formed due to rifting during the Mesozoic era (250Ma – 66Ma) with the breakup of Gondwana. Between the Triassic and early Jurassic about 300m of fluvial sediments were deposited by river and stream. During the Jurassic (200Ma – 115Ma) the basin was twice covered by an arm of the Indian ocean for extended periods, creating a lower limestone sediment 450m thick. In the late Jurassic and early cretaceous periods the basin rose and the 280m upper sandstone sediments, both alluvial and fluvial, were deposited in total about 1.4km of sediment was deposited over the basement rock in this period. Late the Afar mantle plume caused volcanic eruption in the early and late Oligocene (34.23Ma), depositing volcanic rocks between 500m and 200m thick with further eruptions in the quaternary depositing another zoom of rock. These layers have been exposed were the Blue Nile River has cut through the strata creating 1600m Gorge where the rock of different periods can be studied.

In general, the Early Jurassic saw the separation of India from Africa and the emergence of the Indian Ocean. With increasing subsidence of the Blue Nile Basin, a shallow marine embayment

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020 was formed that extended northwestwards from the Indian Ocean and thus, submerged the newly formed NW–trending basin. This Early Jurassic initial marine transgression marked the deposition of the glauconitic sandy mudstone followed by continued basin deepening and the deposition of Early–Middle Jurassic marine sediments. Cyclic flooding and drying of the basin turned it into an evaporate basin for most of the Middle Jurassic, and thereafter, was followed by a second phase of marine transgression during the Middle–Late Jurassic. In the Mesozoic sedimentation history of Ethiopia Most limestone are ultimately biogenic in origin and understanding of biological and palaeobiological factors is essential in knowing their formation. The remains of animals or plants preserved as a fossil in carbonate rock are used for the interpretation of depositional environment, the geological record dating, and correlation of strata. The Brachiopod fossils are preserved in carbonate rocks of Blue Nile basin so systematic study of this fossils in Blue Nile basin from Dejen to Gohatsion area, their stratigraphic column and paleontology provide the recognition of periods in the history of the earth in terms of geological record, paleoenvironmental changes.

1.2. Geographic Setting of the Area 1.2.1. Location and Accessibility The study area is located in the Blue Nile gorge of central Ethiopia. It is around 180 km north of the capital, Addis Ababa. It lays in UTM zone 37 with a Geographical extent of 1105467m to 1124549m Northing and 398989m to 422888 m Easting. Gohatsion and Dejen are two small towns located just outside the gorge in the south and in the north side of the gorge respectively. Figure 1 clearly shows the location of the study area. The study area can be reached easily using the asphalt road that goes from Addis Ababa to the northern part of the country. The road passes through the gorge crossing the two small towns in the north and south edge of the valley. Since the topography is very rugged it is impossible to drive away from the road in both sides. But in some places it can be accessed on foot to the vicinity of the road. Total coverage of the Blue Nile basin is approximately 42 km2 and study is undertaken on two locally selected stratigraphic section in Dejen and Gohatsion section.

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

Figure 1shows A) location map of study area and B) shows sample locality map

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

1.2.2. Physiographic and Drainage The geographical feature in the study area consists of ridge on Gypsum, flat lands on Gypsum, cliff forming mountains on Upper Sandstone, Limestone, Gypsum and Basalt. These all are formed due to tectonic and erosion activities. The main river in the study area is Abay River and there are tributaries that flow to the main river. These tributaries are: Mekentuta, Ada Wedeb and Kurar rivers. The flow direction of the main river is from NE to SW and the tributaries flow from NW to SE along the Dejen side and from SE to NW along Gohatsion side. General flow arrangement of tributaries show dendritic pattern.

Figure 2shows 3D view of topography and drainage pattern of study area modified from (Yoseph Endalamaw 2010) 1.2.3. Climatic Condition and Vegetation The monthly average rainfall of the area is presented in figure. The rainfall in Dejen station (monthly average from 2006 – 2012) shows higher values in all months compared to the Filiklik station (Monthly average from 2006 – 2012). The later station is found lower in altitude

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020 compared to the former. This indicates that the rainfall pattern shows a decreasing trend from the two opposite highlands towards the valley bottom. According to the data from these stations, the main rainy season is from June to September. During this season heavy intermittent rains, lasting from a few minutes to several hours are common. The other months of the year are relatively dry. According to the Meteorological map of Ethiopia, 2006, the study area receives annual rainfall in the range of 1400 – 2000 mm. The average minimum and maximum temperature in the study area is around 15 and 22respectively (Ayalew, 1999). But the temperature in the gorge rises up to 420 during the day insome months (Gezahegn and Dessie 1994). The natural vegetation cover of the study area is different from place to place (sparsely distributed in the Gohatsion side and densely distributed near Dejen side areas). In the study area grown trees are: Weyra, Kitkita, Wanza and Girare in their local name and other areas are not covered by vegetation and it is not suitable for crop cultivation due to geographical land forms.

Figure 3climatic condition of Blue Nile Basin (www.climate.org) 1.2.4. Population and Settlement The population density in the study area is very low. The closest big town to the study area is Dejen the two largest ethnic groups in the area were the Oromo and Amhara. Amhara people at the Dejen side (North) and Oromo peoples near Gohatsion side (south).

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

1.3 previous works Concerning the present thesis work no research has been well done on the specific study area especially in terms of Jurassic brachiopods. But a number of other reports have been done in geological work at regional wise, in central north western part of Ethiopia by different authors. The Blue Nile basin been investigated by several researchers; from those, Kernkel (1926), Stefanini (1933), Merla, G., and Minucci, E. (1938), Jepsen and Athearn (1961 a, b), Meral(1973) and Mohr (1962 and 1974) has been carried out a concise account of Geological work prior to 1975. Kovaiac, J. (1975), Getaneh Assefa (1987 and 1991), Zanettinet. al (1973, 1974, 1976 and 1978), Peccerillo and Bekele Megerssa (1992), Russo et al. (1994), Serawit and Tamrat (1999, 1996 and 1995), Tamrat and Tibebe (1997), BalemwalAtnafu (2003) Wolela Ahmed (1997 and 2004), were made a valuable contributions to understanding the geology of the area. Systematic paleontology of Jurassic brachiopods in Ethiopian faunal province has also studied by many researchers among the authors;- Weir (1925, 1929) and Muir-Wood (1935, 1936) described the brachiopod fauna from Somalia; Weir (1929) from Kenya, Cooper (1983, 1989) from Saudi Arabia, and Feldman (1986, 1987), Feldman et al. (1991, 2012a), and Hegab (1989, 1992) from Sinai; Feldman et al. (2001) and Krawczynski and Wilson (2011) from Israel, and Feldman et al. (2012b) from Jordan. A more detailed stratigraphical summary of the Jurassic strata in Somalia (formerly British Somaliland) can be found in Weir (1929) and Muir-Wood (1935). Cooper (1989) described brachiopods from Saudi Arabia that were collected from 1125.6m of Jurassic strata. These strata are comprised of seven formations, for a more detailed description of these formations see Cooper (1989) and Sharief (et al., 1991). Overall correlation of the faunas among these regions on a larger scale is, with exceptions, still lacking. This paper is dealing with fossil finds from Blue Nile basin of central Ethiopia and their correlation with various regions within the Ethiopian Province and within theytan faunal realm. The paleontology of Blue Nile basin also studied specifically by many authors but it is not focused on brachiopod study. Ficcarelli (1968) Studied marine fossils of the Blue Nile section, Beauchamp and Lemoigne (1974, 1975) Reconstructed the palaeogeography and subsidence of the central Ethiopian sedimentary basins in the Jurassic period and also Studied palaeofloral dating of volcanics on the Ethiopian PlateauKalb and Oswald (1974) Studied the Canuti and Radrizzani (1975) Described microfacies of the limestone in the Blue Nile Basin Beauchamp

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

(1977) Determined the age of palaeoflora of the Ethiopian Plateau volcanic rocks. Kalb and Oswald (1974) studied Mesozoic invertebrate fossils of Ethiopia Wood et al. (1997) Presented the first palynostratigraphic dates for Mesozoic faunas, Kesiling (2011) studied Marine benthic invertebrates from the Upper Jurassic of northern Ethiopia and their biogeographic affinities. Systematic paleontology of Jurassic brachiopod faunas are also studied by different auther in different Ethiopian faunal province but the selected area is not figured in detail.

1.4 Significance of the study This taxonomically study will aid in establishing the history of brachiopod species and their evolution within the Blue Nile basin. The data compiled as a result of these studies will enable us to interpret the biogeographic history of the Blue Nile basin, as well as gain insight into the structure and palaeoecology of its marine communities. Furthermore, the study attempts to determine the position of the brachiopod fauna in the Indo-African Faunal Realm, and its possible relation with the Tethyan Realm, within the Ethiopian Province. It also contributes to define faunal and province realm boundaries with greater accuracy.

1.5 Statement of problem Brachiopod fossils are poorly known from the Ethiopian Jurassic sedimentary rocks mostly from the Blue Nile, Mekelle and Dire Dawa regions (Blanford, 1870; Douvillé, 1886; Merla and Minucci, 1938; Wells, 1943; Arkell, 1956; Jaboli, 1959; ZuffardiComerci, 1959; Ficcarelli, 1968; Jordan, 1971). In the Blue Nile basin of central Ethiopia, previous studies have focused on sedimentology, stratigraphy, and geochemistry (Beyth, 1972; Bosellini et al., 1995, 1997; Martire et al., 1998; Worash and Valera, 2002).

However taxonomic study of invertebrates helps to interpret the biogeographic history of the basin, as well as the palaeoecology of its marine communities, systematic paleontological study on marine invertebrates in the basin is poorly known. This paper attempts to present morphological description of Jurassic brachiopod fauna from the Blue Nile basin of central Ethiopia.

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

1.6. Objectives

1.6.1 General objective The main objective of this research is taxonomic study of Jurassic brachiopod fauna in Dejen – Gohatsion area from the Blue Nile basin of central Ethiopia.

1.6.2 Specific objective The specific objectives of this research are as follows:

 Conducting morphological description of Jurassic brachiopods in study area  Description of stratigraphic succession of Blue Nile basin.  Interpretation of the depositional environment of study area  Reconstruction of the palaeoecology of brachiopod communities in the basin  Correlate of the brachiopod fauna of the area with those of Mekelle and Dire Dawa regions  Determining the brachiopod fauna in the Indo-African Faunal Realm, and its possible relation with the Tethyan Realm within the Ethiopian Province

1.7 Methodology and Materials

1.7.1 Methodology To successfully accomplish this thesis, different methodology will have been applied. In order to reduce difficulty during the work and achieve objectives three phases of methodology will be applied. These are: - phase I (pre-field) or preparation, Phase II (during-field) or main field work and phase III (post-field). Each method was followed by its own detailed activities.

1.7.1.1 Phase I (Pre-Fieldwork) Before the main fieldwork, office preparation has been undertaken. These includes review of previous work and available base maps, previous geological map in order to have an overview about the geology of the study area and their surrounding region, collecting of secondary data geological map, preparation of working plan and scheduling the various research activities, finalization of the methodology to be adopted for the proposed study and preparation for the fieldwork (equipment, base map, transport and personal preparation).

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

1.7.1.2 Phase II (Field data collection) Field trip would be carried for one month from December 05/04/2012 to January 05/052012 during the field work collection of lithology and fossil samples were done. Each rock unit and their stratigraphic relationship to other rock units were identified, description of all the lithological variation in color, textures, sedimentary structures, mineral composition and macrofossils based on fossil association.

360 brachiopod fossil samples were collected. Sample selection will be done aiming at having complete succession of units. Photographs will also take at each layer to document fossil associations. Collections of fossil will be conducted in the selected stratigraphical section. The fossil that needs to be collected in the field are brachiopod fossil and have already been removed from the rock those can be easily collected and some fossils remain embedded in the rock. This fossils are collected in three locality namely Gelegele, Dembeza and Filiklik area. The sample codes are SG1, SG2, SG3, SG4, SD1, SD2 and SF1, SF2, SF3, SF4 are for somaliranchia sp in three localities for instance (SG1 somaliranchia species in Gelegele area), CG1, CG2, CG3, CG4 CG5, CG6, CD1, CD2, CD3, CD4 and CF1, CF2, CF3, CF4 for Cymatorychia species (CG1Cymatorychiaspecies in Gelegele area) and DG1 ,DG2 ,DD1 ,DF1 and DF2 for Daghanirhynchia species ( DG1 Daghanirhynchia species in Gelgele area).

1.7.1.3 Phase III (Post Fieldwork) During this phase the collected samples were washed in the laboratory and selected for descriptions. To reduce difficulty during systematic study 38 good samples are selected and coded.

1.7.2 Materials Instruments which are necessary for data collection and laboratory analysis to accomplish this research study. Field instruments that will be used to perform field work are camera, geological hammer, dilute 50% H2O2, GPS, sample bag, plastic sample bag, marker, pen, note book, meter stick and Dejen -Gohatsion topographic map.

1.8 Limitation of the study The principal limitation of this study is shortage of brachiopod species from many additional sections due to accessibility problems. Most of the limestone outcrops located in the Blue Nile

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

Canyon, which is very ragged and steep to access on foot. Lack of representative sections that are distributed throughout the basin highly affect the reliability of the data, with regard to determining the paleoecological conditions under which they existed during the Jurassic. Moreover, lack of laboratory equipment’s, such as Scanning Electron Microscope (SEM), for the analysis of shell microstructures and shortage of instruments for preparation of serial section hinders the proper identification brachiopod species.

CHAPTERTWO

2. LITERATURE REVIEW

2.1. Regional Geology Geology of Ethiopia is characterized by the occurrence of a very wide variety of rocks, differing in their age, origin and evolution. The rocks in the country classified into three broad categories; Tertiary and Quaternary volcanic rocks which occupy large parts of the country along the rift valley and plateau, continental and marine of late Paleozoic to Mesozoic sedimentary rocks and Precambrian basement complexes (Tefera et al. (1996). The East African region has been affected by two major phases of rifting. The first phase was the widespread rifting in Karoo times (Late Carboniferous to Early Jurassic) which stretches from Ethiopia to South Africa corresponds to the initiation of the break-up of Gondwanaland in that further subsidence took place. This subsidence combined with sea-level fluctuation produce cyclic patterns of shallow- marine carbonates, shales, evaporites and minor clastic deposits. The second rifting relates to the formation of the East African rift system from Cenozoic to Recent (Bosellini, 1989).

According to Beyth (1972a; 1972b), Sedimentary regions of Ethiopia cover a significant portion of the country. They classify into five distinct basins, namely: The Ogaden, Abay, Gambela, Southern rift and Mekele basin. Paleozoic and Mesozoic sedimentary successions of Ethiopia are unconfarmably overly Precambrian basements. Most of sedimentary succession of the country is part of the vast sedimentary succession of East Africa which was deposited during the Mesozoic transgression. But also there are some late Paleozoic to early Mesozoic sedimentary rocks mainly sandstones and minor tillite, shale, siltstone and conglomerate present in some parts of the country. The Mesozoic succession of Ethiopia is present in the Mekele outlier, Blue Nile Basin

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020 and Southeastern Ethiopia with adjacent in the Ogaden Basin (Kazmin, 1973; Merla et al., 1979; Bosellini et al., 2001; Beyth 1972a; 1972b; Getaneh Assefa; 1991; Russo et al., 1994).

Figure 4shows Mesozoic sediments and basins of Ethiopia (Source: Ethiopian Institute of Geological Survey, by Mengesha Tefera et al., 1996) 2.2 General Stratigraphic Succession of Northwestern Ethiopia Plateau Different studies have confirmed that stratigraphically wide rock units were present in Southeastern and Northwestern Ethiopia which ranges from older Precambrian up to recent. From those, Blanford, 1869; Kazmin 1973; Merla et al., 1979; Bosellini et al., 2001; Mengesha Tefera et al., 1996; AbiyyuHunegnaw et al., 1998; Balemwal Atnafu (2003); Asfawossen Asrat 2015; G/yohannes Habtezeghi, 1984; Workineh Haro, 2010; Russo, et al. (1994); Gilamechael Kidanemariam et al.,(2009) Turi et al. (1980) ; Gani et al. (2008) and Wondafrash et al. (1993), Dawit and Bussert, (2009); Dawit, (2010) are given some contribution to describe the stratigraphy of Blue Nile basin.

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

As it is stated by Wolela Ahmed (2007), the Blue Nile basin part of Northwestern Ethiopian Plateau contains thick Mesozoic sedimentary section and this thick Mesozoic deposit is underlain by Neoproterozoic basement rocks and overlain by early–late Oligocene volcanic rocks. Rabbenet al., (1979), Beicip (1985) and Balemwal Atnafu (2012) also elaborately discuss the stratigraphy and history of sedimentation in the Abay basin.

Based on this study and the data reported by Mohr (1963), Assefa (1991) and Russo et al. (1994), the complete succession in the Blue Nile Basin consists of a crystalline basement (precamberia) rocks, Paleozoic sediments (pre-Adigrat sandstone), Adigrat Sandstone, Gohatsion Formation, Antalo Limestone, Mugher Mudstone, Debrelibanose and Tertiary Volcanic rock in ascending order . Its lithological description is as follows:-

2.2.1 The Precambrian Basement rocks

The Precambrian rocks are mainly exposed in all parts of the country. The age of the basement rocks is consider to be Neoproterozoic, ranging from 850 to 550 ma as documented from U-Pb and Rb-Sr geochronology studies (Ayaew et al.,)

2.2.2. Pre-Adigrat

This Unit has been considered to be continental sediment deposited in the Upper Carboniferous to lower Mesozoic age interval consisting of sandstone, silts and shales filling channel (Kazimin, 1975). There are three unconformity bounded silicaclastic sedimentary rocks, which are named informally as Pre-Adigrat I, II and III from bottom to top (Dawit and Bussert, 2009; Dawit, 2010).

The Pre-Adigrat I, Which is 50 Meter thick deposited in a North-south trending channels incised into the underlying crystalline basement rocks (Dawit, 2009). The age and stratigraphic position of this unit is still ambiguous with a range of Upper Carboniferous-Lower Mesozoic (Kazmin, 1975; Russo et a., 1994) and Ordovician-Silurian (Mesfin 1989).

The Pre-Adigrat II, 400m thick in Fincha valley of central Ethiopia, unconformably overlies either the Precambrian basement or Pre-Adigrat I (Dawit, 2009). Unlike the Pre-Adigrat I, these sediments are widespread in the Blue Nile Basin and are not limited to north-south trending channels.

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

The Pre-Adigrat III, ~100-350m thick, latest carboniferous to early Permian (the basal part) and middle Triassic (at the top) age from Palynological study by Dawit (2010), comprises three successive cycles of stacked, multi-story sheet sandstone bodies that are capped by overbank fines and crevasse splay deposits which are deposited in alluvial plains and/or lacustrine-deltaic environment (Dawit, 2010).

2.2.3 Adigrat Sandstone

This Unit unconformably overlies the Karoo sediments, consisting of sub horizontal layers of fine-grained sandstone that are intercalated with reddish shale’s and siltstones in its lower part (Russo et al., 1994) or Pre-Adigrat III of Dawit (2010). It’s thickness, stratigraphic position and depositional environment in the Blue Nile Basin has been controversial. Fluvial and/or lacustrine-deltaic depositional environment are anticipated by (Krenkel, 1925; Beyth, 1972a, 1972b; Beauchamp, 1977; Garland, 1980; Bosellini, 1998, 1997 in Dawit, 2010) and Russo et al., 1994) while transgressive shallow marine deposition environment was hypothesized by Dainelli (1943 in Dawit, 2009). Dawit and Bussert (2009) and Dawit (2010) have identified two unconformity bounded stratigraphic Units within the Adigrat sandstone succession, which they named it as Unit I and II with thickness ranges from 100-200m. Unit I, late Triassic (Late carnian-Early Rhaetian), represents the lower stratigraphic unit. This Unit consists of transgressive tide-dominated estuarine and prograding storm-dominated shore face deposits. Unit II, late liassic (Early Toarcian) age, represents the upper stratigraphic unit with barrier/inlet-spit origin in the Blue Basin.

2.2.4 Gohatsion Formation

The Gohatsion formation is 450m thick (Russo etal., 1994), formally define by Getaneh (1981) after its type section at Gohatsion town vicinity in central Ethiopia.

According to Getaneh (1981), four informal members are identified, from bottom to top; mudstone member, lower claystone member, gypsum member and upper claystone member.

Russo et a.,(1994) described alternating dolostone 50-80cm and shale beds 10-20cm at the lower part of this formation while it has been reported to have a glauconitic sandy mudstone suggesting shallow marine influenced environment at the same part (Gani et a.,2008). This unit is thought to characterize the first marine transgression in the Blue Nile Basin (Russo et al., 1994 and Gani et

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020 al., 2008). The middle part of the formation is characterized by thick beds of gypsum with cyclic intercalation of shale, dolostone, marlstone and fine grain sandstone (Getaneh, 1981; Russo et al., 2008). The upper part of this formation consists of variegated color clays and siltstones with coarsening upward beds (Russo et al., 1994).

The age of Gohatsion formation was given as Early-Middle Jurassic (Toarcian to Bathonian) (Getaneh, 1981). Supratidal, intertidal, lagoonal and subtidal environments of deposition are indicated from lithofacies analysis Getaneh (1981) while peritidal environment with associated lagoonal and pond water bodies are indicated from gastropods (Corbiculinaelucinids, arcomytilus, protocerithium) and small bivalves (Russo et al.1994).

2.2 4 Antalo Limestone Formation

The Antalo limestone,420m thick (Russo et al., 1994 and Atnafu, 2003) is of Middle-Late Jurassic age based on the callovian to kimmeridgian benthic foraminifers and macro faunas(Canuti and Radrizzani 1975 in Gani et al., 2008; atnafu,1991, 2003and Russo et al., 1994) is superimposed on the Gohatsion formation conformably. This name was originally given to the limestone unit in Northern Ethiopia (Banford, 1870 in Dawit and Bussert, 2009).

In its lower part ,this formation reaches 180m thick and characterized by scarcely fossiliferous and burrowed mudstone that grade upwards in to an oolitic limestone’s that contain corals, stromatoporoids , bivalves, gastropods, foraminifers and ostracods, and then into fossiliferous limestone interbededded with very thin marl beds.

The fossiliferous interbeds of marly limestone, marl and silty limestone characterize the middle part of Antalo limestone, which is 200m thick (Russo et a., 1994). Nanogyrafourtai, Nanogyra sinuate associated with ammonites (Lithacoceras sp. And subplanitesspathi) are common fossils in the marl beds. According to Russo et al (1994) and Atnafu (2003), a shelf to open Marin environment of deposition was inferred from ammonite fauna, in association with brachiopods and other in faunal siphon feeders for the part of the Antalo limestone.

2.2 6 Mugher Mudstone

This unit was previously known as the Upper Gypsum ‖ (Aubry 1886, Merla et al. 1979). The succession is 15 m in the Gohatsion area but thickens eastwards to reach up to 320 m in the Jema river valley. In its type locality, it is 260 m thick and conformably overlies the Antalo Limestone.

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Based on Assefa (1991) and Russo et al. (1994) it is subdivided the unit into two parts. The lower part (15 m thick) is composed of alternating beds of nodular and vein-filling gypsum, dolomites, and shale, for which Getehan Assefa (1991) assign as supratidal and lagoonal environment. The rest of the succession (240 m thick) is characterized by interbedded sand- silt and mudstones with local occurrences of lignite layers and scattered plant fragments. This siliciclastic succession was interpreted by Assefa (1991) to represent deposits of a meandering river system. Regarding the stratigraphic position of the Mugher Mudstone, Assefa (1991) assumed a broad interval of post-Kimmeridgian to pre-Middle Eocene age.

2.2.7 The Debre Libanose Sandstone

The Unit, 280m thick is conformably superimposed on the Mugar Mudstone Unit and unconformable overlies by the Tertiary flood Basalts. Based on the lithostratigraphic position, an upper age limit of late Eocene was given to the Debre Libanose (Getaneh, 1991). However, Wolela (2009) assigned the age of this unit to be 120-94 Ma years (Barremian to cenomanian) from the Apatite Fission Track Analysis (AFTA).

2.2.8 The Tertiary Trap Series

The tertiary trap series uncoformably overlies the Antalo Limestone Unit at GohastionDejen section, Blue Nile gorge. These volcanic rocks are dated to be 26.9-29.4 Ma years based on 40Ar/39Ar age dating and magnetostratigraphy (~Oligocene) and locally exceeding 2000m thick (Hofmann et al. 1997)

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

A. Geological map of the Blue Nile canyon (modified after Kazmin 1973). B. A schematic cross section across the Blue Nile Basin (not to scale). C. The stratigraphy of central Ethiopia.

Figure 5 the geological map

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2.3 Jurassic brachiopod fossil study of Sedimentary Basins Jurassic brachiopods are important not only in stratigraphic and paleontological studies, or for their abundance and diversity in the marine sediments, but also for their widespread distribution and rapid evolution and their ecological adaptation to different environments.

Concerning the present thesis work no research has been well done on the specific study area especially in terms of Jurassic paleontology of brachiopods. But a number of other reports have been done in geological work at regional wise, in central north western part of Ethiopia by different authors. The study area has been investigated by several researchers has been carried out a concise account of Geological work prior to 1975. And were made a valuable contributions to understanding the geology of the area. Among the researchers which have been done on regional wise on brachiopod species are discussed below.

The basic systematic of the Jurassic brachiopods was laid out by Buckman (1918). As a result of the limitation in techniques, equipment, and knowledge at that time, Buckman's system is far from satisfactory in the view of present knowledge. Most of his genera were established without knowledge of internal characters, and many of them were not defined clearly on any consistent feature, so that much confusion has resulted. Buckman did, of course, contribute a great deal to the systematic, and his monograph is still used as one of the most important standard books on the Brachiopod. In later years, tremendous work was done on the Jurassic Rhynchonellids, and great advances were achieved in studies of their taxonomy, paleoecology, biostratigraphy, and paleobiogeography as well as in some facets of their evolution. Comprehensive study of Jurassic brachiopods reveals that species or generic names vary from country to country, or even from area to area. These problems in taxonomy, in turn, produce new difficulties and confusion in the studies of biostratigraphy, paleobiogeography, and evolution. Therefore, as the basis of paleontology and its related subjects, taxonomic study should still be emphasized and the study of interiors, which is of great importance in the classification, should receive especially close attention.. Most genera have been based on their type-species by aid of either silicified specimens or serial sections. The interior characters of those forms are relatively clear. This paper, therefore, concentrates mainly upon the Middle Jurassic ones (the majority of Jurassic brachiopod) that have not previously been studied sufficiently. It focuses on internal structures and resultant taxonomic revisions. Some Early and Late Jurassic genera had to be studied in

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020 order to trace trends in evolution. With the rapid accumulation of data resulting from the expansion in areas and subjects studied, ever more new taxa have been created. We judge that this is an opportune time to revise and synthesize the classification before too many homonyms, synonyms, and confused classifications result from insufficient study, while recognizing that much remains to be done.

Rocks of Jurassic age are present in all of the east-central Africa basins in Somalia, Kenya, and Ethiopia. These rocks represent a primarily marine carbonate and fine clastic facies deposited on the western shelf of the Somali Basin, which may be a southern arm of the Mesozoic Tethyan Middle East Arabian Basin. This facies reaches a western zero edge that runs approximately north-south in central Ethiopia. Thickness is approximately 1,000 to 4,000 m (3,000 to 13,000 ft) in Somalia, eastern Ethiopia, and eastern Kenya but is less than 300 m (1,000 ft) on the Nogal uplift and in the vicinity of the Bur Acaba uplift.

The basal Jurassic unit (Adigrat Sandstone), ranging from less than 25 m (80 ft) to more than 100 m (325 ft.) thick, represents the initial deposits of the widespread Tethyan marine transgression of the east African and Arabian shelf. This unit is probably latest Triassic and Early Jurassic age in the coastal basins of Somalia and is younger to the northwest, becoming uppermost Jurassic in age near its western limits in central Ethiopia where it grades upward into sandstone beds of Early Cretaceous age. To the south, in the Mandera-Lugh Basin and Lamu embayment, the Adigrat probably merges into the upper part of the Karroo facies or the Mansa Guda Formation. In the shelf area, the Adigrat grades upward into the Hamanlei Formation (Antalo Limestone of northern Ethiopia), primarily a Tethyan marine shelf carbonate facies of Middle and Upper Jurassic age). The Hamanlei is composed of fossiliferous limestone, some gray shale, and minor amounts of siltstone or fine sandstone. Oolitic and coralline limestone beds are present in southern Somalia and parts of Ethiopia, and anhydrite is interbedded with dolomite and limestone in northern Somalia. The carbonates become Shailer and are interbedded with dark gray marine shale in the Somali embayment and the Mandera-Lugh Basins and Lamu embayment. The Hamanlei Formation ranges in thickness from less than 300 m (1,000 ft) to more than 2,000 m (6,500 ft) in Somalia and eastern Ethiopia and thins and becomes sandier to the west toward the depositional limit in Ethiopia.

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

According to Asfawossen Asrat (2015) more than 100,000 sq. km of carbonate rocks are exposed in Ethiopia and these are widely exposed in the Mekele, in the Blue Nile basin and in the Ogaden Basin (including the Bale and Western Harrarghe areas). Jurassic limestones in Ethiopia have various names according to its type locality throughout the country, example: Antalo Limestone Formation (in Abay, Mekele and Dire Dawa area), Hammanlei Formation, Urandab and Gabredarre Formation (in Ogaden basin and Harrar) (Kazmin, 1973; Blanford, 1869; Beyth 1972a;1972b; Bosellini et al,1997; Getaneh Assefa 1991; Russo et al, 1994).

The age and stratigraphy of carbonate rocks of Blue Nile basin is conducted by some authors. These are: - Based on the work of Russo et al. (1994) and Balemwal Atnafu (2003), the carbonate succession of Blue Nile basin which is 420 m thick, described by, conformably overlies the Gohatsion Formation and can be subdivided into three parts. The lower part (180 m thick) is composed of burrowed mudstones that grade upwards into oolitic and coquinoid limestone’s with or without intercalated marl beds, and then into massive limestone with scattered patches of corals, nerineids and stromatoporoids, for which a shallow water environment was inferred.

The middle part (200 m thick) consists of highly fossiliferous interbedding of marly limestones and marls. The presence of ammonite fauna (e.g., Lithacoceras sp. and Subplanitesspathi), in association with brachiopods (e.g. Terebratulapelagica and Nanogyra) and other infaunal siphone feeders (Anisocardia, Venilicardia and Somalirhynchia somalica and Zeilllerialatifrons) suggests a shelf to open marine environment (Russo et al. 1994, Belmwal Atnafu 2003). The upper part (50 m thick) comprises planar laminated oolitic and reefal limestones, which was interpreted to indicate the return of shallow water conditions.

However the Blue Nile rocks are not detail studied in terms of invertebrates (mainly Jurassic brachiopods analysis) of the rocks. Therefore, in this paper, the study will presents on paleontology of Jurassic brachiopods.

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

CHAPTER THREE 3. Lithostratigraphy of the study area (Dejen - Gohatsion) The study area (Dejen-Gohatsion) has lithological units that are mapped during fossil sample collection and which are deposited in the following order as going from oldest unit to youngest. These are Lower Sandstone, Upper Sandstone (white and red sandstone), glauconitic mudstone, Gypsum, lower limestone, lower marl, upper limestone, upper marl, upper limestone and youngest basalt unit. Through the field observation the Lithostratigraphy of the area, were described and measured.

3.1 Lower Sandstone Unit This is the oldest of all units in study area which is exposed by river cutting and overlain by red sandstone unit with approximate thickness of 30 – 40 meter. This unit is characterized by fine to medium grain size, greenish white color. Structurally this unit ranges from massive with some exotic drop inclusion (sandstone and volcanic basalt) to cross bedded and ripple laminated with fragile nature. This unit is formed by glacial process which is revealed by the existence of drop inclusions. It is dominated by feldspar minerals which give this rock low strength and light color.

Figure 6 lower sandstone unit with drop inclusions

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3.2 Red Sandstone Unit This unit is underlain by lower sandstone and overlaid by white sandstone and exposed by road cutting with approximately 110 meter thick .It has grains which are angular to sub angular rounded, fine to coarse grained and poorly sorted. It is dominantly composed of quartz cemented by hematite (Fe2O3) which gives the rock reddish brown color. This unit is formed, by storm (hummocky) and post storm (bioturbated in fair water condition) processes in low tectonic stability environment. This alternative storming and post storm results an intercalation of hummocky and bioturbated sandstone. There is fining upward from storm to post-storm and coarsening upward from post-storm to storm. There is also conglomerate, which is called storm lag.

Figure 7 Red sandstone unit 3.3 White Sandstone White sandstone unit is found next to red sandstone and followed by glauconitic unit with thickness of approximately 90 meter. Compositionally it is similar to red sandstone but the white sandstone is silica cemented quartz arenite. Since quartz dominates; this unit is resulted from high reworking activity of water from distant. It is characterized by coarse grained, poorly sorted, whitish grey color. This unit is formed in low tectonic stability and high energy environment. Structurally this unit is characterized by planar tabular cross bedding.

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Figure 8White sandstone units with cross bedding structure 3.4 Glauconitic sandy mudstone unit The Glauconitic unit belongs to the Gohatsion Formation which is underlain by white sandstone and overlaid by the gypsum unit and has an approximate thickness of about 30-35 meters. Since, it composed of lenticular shaped sand materials and glauconitic shale/mudstone, this intercalation of glauconite and calcareous sand is called lenticular bedded glauconitic mudstone. This unit is resulted from the digenesis of biotite in the marine environment. The glauconitic shale has greenish colordue to the presence of glauconitemineral.

Figure 9 Glauconitic mudstone unit

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

3.5 Gypsum unit The gypsum unit belongs to the Gohatsion formation, which is underlain by glauconitic unit and overlaid by the limestone formation with approximate thickness about 400 meters and mostly exposed by quarry cut. It has colors ranging from whitish grey to somewhat dark on the algal mat. This unit is formed by evaporation of saline water in the arid environment where rate of evaporation exceeds rate of precipitation. There is an intercalation of chikenwire gypsum and dolomite with evaporitic mudstone and chikenwire, algal mat, satin spar gypsum;. Some of the structures in this unit include elephant skin structure, faults, and joints.

Figure 10 Gypsum units with fault 3.6 Lower Marl Unit This unit belongs to the Antalo limestone formation which is underlain by gypsum unit and overlaid by the lower cliff forming limestone unit and exposed by road cut with approximate thickness of about 80 meter. It is an intercalation of micritic limestone and marl and has yellowish grey color. It composed of autochthonous or sessile organism fossils which include brachiopods, bivalves and gastropods. This unit has fragile nature and easily susceptible to erosion since it is less compacted and unconsolidated. This unit is formed at low energy deeper shelf environment.

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

Figure 11lower marl unit with Brachiopod fossils 3.7 Lower Limestone Unit Lower lime stone unit is lower cliff forming limestone which is underlain by lower marl and overlaid by upper marl unit and exposed by road cut and hill side with approximate thickness about 80 meter. It is formed at high energy relatively shallow shelf environment and characterized by intraclasts and some fossil fragments; the limestone contains lithoclastic carbonate grain cemented by micrite with massive bed structure.

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

Figure 12Lower limestone unit 3.8 Upper Marl Unit The upper marl is underlain by lower limestone and overlaid by the upper limestone with approximate thickness 150 -180 meters and exposed by road cut. Most of the time this unit forms gentle slope. This unit characterized by the intercalation of brownish marl and whitish grey fosilferous and micritic limestone, this intercalation indicates sea level fluctuation and change in the energy of the depositional agent. There is highly fossiliferous bed called tempestite resulted from water waves/tides which make it aligned within the marl.

Figure 13upper marl unit with tempestite

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

3.9 Upper limestone unit This unit is the youngest of the limestone formation, which forms cliff and exposed by road and hill side exposure with approximate thickness about 60-70 meter. The wavy bedded micritic limestone contains oolitic carbonate grain cemented by sprite and some micrites and named as oosprite and packstone to grainstone by Folk and Dunham classification respectively. This unit formed under high energetic shallow shelf environment and characterized by whitish grey fresh color.

Figure 14 upper limestone unit 3.10 Basalt Unit This is the youngest unit in the study area. It is an igneous rock exposed on both Dejen and Gohatsion sides and forms cliff topography. It has dark fresh color and dark brown to brown weathered color. This unit is uncomformab1ly overlaid on the sedimentary successions with dominant columnar joints.

Figure 15 columnar basal unit

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

CHAPTER FOUR

4 PALEONTOLOGICAL STUDIES OF BRACHIOPODS 4.1 INTRODUCTION Phylum Brachiopoda have certain specific features like a shell or test made of two unequal valves still extant in them. Within this shell, the soft parts of their body are sheathed. The larger one is explained to be the ventral valve, while the dorsal valve is the smaller one. The Umbo or the tapering beak is present towards or the posterior end of any valve. The Umbo on the ventral valve is usually more prominent and obvious. The class Inarticulata from which the Brachiopods hail; the two valves are clasped together by means of the muscles whereas in the class Articulata, the two valves clutched together at their posterior ends. A pair of teeth emerged on the ventral valve (close to the Umbo) in such type of Brachiopods and these could fit into the two sockets which were near the beak of the dorsal valve. The hinge line or the cardinal margin where the teeth and sockets evolve is the posterior margin of the two valves. In few Brachiopods, between the Umbo and the hinge line, a triangular portion is present. This portion is called as the hinge area or cardinal area and this is flat or a bit concave in appearance. The hinge area is more obvious and pronounced in the ventral valve, though it is existent in either of the two valves. An opening normally occurs on the ventral valve at the apex of the umbo or inside the hinge area. The accurate location on the shells of different genera is referred to as the pedicle or the peduncle foramen and the pedicle is seen with a variety of sizes and shapes. The pedicle opening is doled out by either of the valves in some Brachiopods. This subset exists however in most of the cases on the ventral valve exclusively. The pedicle opening in some cases is somewhat triangular in shape and occurs below the umbo of the ventral valve. This type of opening is known as delthyrium. By means of two plates, the delthyrium is somewhat closed and together constitute what is known as deltidium. In these cases, the pedicle openings come into being, either in between the deltidial plates or at the apex of the umbo of the ventral valve. The delthyrium is completely or intermittently shut by mode of a single plate forming the pseudodeltidium. The muscle of the animal help in the opening and closure of two valves represent the shell of the Brachiopod. Usually on the inner side of the valves the imprint or indentations are left. A frame work made of calcium carbonate is existent inside the shell of a few kinds of Brachiopods. The

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020 so called brachial skeleton is affixed to posterior end of the dorsal valve. It is found that brachial skeleton is bestowed got in almost all the articulate Brachiopods and missing in inarticulate types. The shells are found to be of various sizes between wide limits. The larger ones are about 12 inches in width; whereas a few of these are just a fraction of an inch in length and width. Speaking about the shape, biconvex, Plano-convex, concavo convex, Brachiopods shell varieties are present. The upper ribs radiating away from the umbo in all directions, but it is noticed that however concentric ribs are existent surrounding the umbo region on either of the valves. There is a drastic difference seen in the beautification and adornment of the hinge area, usually from the rest of the shell. The Brachiopod shell is organized, well planned, and set up in the manner of three dissimilar, well defined layers and the material which they are generally made of is calcareous and chitinous. The two inner layers are calcareous in composition and are preserved in the fossil form while the outer most chitinous layer is not ordinally preserved. Brachiopod fossils are generally seen to be having a punctuated shell. Mostly, the Brachiopods have an equilateral shell with an absolute, exemplary, and flawless bilateral symmetry, displayed by the individual valve. Narrating in other words, if ashell is accommodated and adjusted in a proper manner i.e. with its ventral valve situated below the dorsal and its beak placed in a posterior position, the shell can be divided into two identically positioned halves by a vertical plane, which runs through the beaks and also the middle region of the anterior margin of the shell.

4 .2 Geologic History

A long geologic history has been observed in Brachiopods. The most primitive forms of the Brachiopods are supposed to live in Pre-Cambrian Sea. So far, no clear fossil record has been put across in support of the view, but within the Lower-Cambrian age certain remains of Brachiopods are found. Though a few early articulates have been discovered which hail mostly from the class Inarticulata. Some Brachiopods like Lingulella, Kutorgina, Obolella, etc. hail from the Lower-Cambrian age. Both the Inarticulates and the Articulates developed to certain degree of the Cambrian. The Brachiopods became high in number in the Ordovician period and Articulates were vitally important. The zenith of their development was reached by the Brachiopods in the course of Ordovician, Silurian and Devonian periods. The Brachiopods become less important since the Devonian and there were only thirteen super families’ survivors,

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020 out of the nineteen super-families which emerged out during the Silurian period and they could continue to exist. Some of the commonest of Brachiopods of the Lower-Paleozoic were - Lingulella, Kutorgina, Obolella, Leptaena, Strophomena, Rafinesquina, etc. A reference can be made from the Upper- Paleozoic forms, of Athyris, Atrypa, Spirifer, Syringothyris, Products, Stringocephalus, etc. The Carboniferous and Permian age rocks are distinct and characterized by two predominant super families i.e. Productacea and Spiriferacea. Most of the super families vanished during the end of Palaeozoic era and among them only nine continued till the Triassic period. A new super family made its appearance when Jurassic period began, whereas three of these super-families ceased during the Mesozoic era. In the Mesozoic era Terebratula and Rhynchonella are the two very important Brachiopods. There were some other Brachiopods like Lingula, Discina, Crania, Terebratella, Terebratulinaetc. Between the Permian and the Triassic the number of Brachiopods decreased rapidly. This drastic draw is known as Permo- Triassic mass extinction. In this largest extinction, nearly 90 percent of species of Brachiopods died. The Brachiopods were flourished during the Paleozoic era and afterwards they have never regained their abundance. They are reported as index fossils. As the Mesozoic was near to its end, the Brachiopods lost their importance. Sometimes only the Brachiopods are seen within the rocks of Tertiary age. The members of only six of the super families existed during the Tertiary era and they have continued to survive even up to the present day.

4.3 Description of Brachiopod Species 4.3.1 Systematic Paleontology The Brachiopod fauna of Blue Nile basin from Dejen to Gohatsion was represented by two articulated group’s class Ryhnchellida and Terbatullida. The class comprises of six species viz., Dhagnirynchia sp, Somalirhynchia sp, Cymatoryhynchia sp, Amydroptycus sp, Monardityris sp, Cererityries sp, Colpotoria sp and Septaliphoria sp which have been described by Kiessling (2011). During the course of present investigation, the collected well preserved Brachiopod specimens are belongs to Dhagnirynchia sp, Somalirhynchia sp, Cymatoryhynchia sp, Monardityris, Cererityries, species. All the specimens will be coded during the field. The classification adopted by Moore (1965) in his “Treatise on invertebrate paleontology part- H” has been followed in the present work.

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

Daghanirhynchia Sp. (Plate 1 A)

Systematic paleontology Phylum Brachiopoda Duméril, 1806 Subphylum Rhynchonelliformea Williams et al. 1996 Class Rhynchonellata Williams et al. 1996 Order Rhynchonellida Kuhn, 1949 Family Tetrarhynchiidae Ager, 1965 Subfamily Tetrarhynchiinae Ager, 1965 Genus Daghanirhynchia Muir-Wood, p. 82-83, 1935 Daghanirhynchia sp (plate 1 A) Type species Daghanirhynchia daghaniensis Muir Wood, 1935: 82; by original designation Materials 5 individuals 2 from Gelgele area, 1 from Ddembeza area and 2 from Filkik with sample code DG1 ,DG2 ,DD1 ,DF1 and DF2 Dimensions; DG1 Length (L) - 16 mm Width (W) - 18 mm Thickness (T) - 9 mm Description: The genus Daghanirhynchia is characterized by Dorsi- biconvex shell outline. Wider (13-18 mm) than length (12-16 mm) with maximum thickness (7 to 9 mm) In smaller specimens, width is greater than length but comparatively in larger specimens length is more or less equal to its width. Maximum width of the test is at the middle. Gently arched to rectimarginate anterior commissure, no fold recognizable on the dorsal valve, short acute beak, numerous fine costae, sometimes irregularly branched. Brachial valve convexity is greater than pedicle valve and anterior commissure area is slightly flattened giving a resupinate shape in section. Pedicle valve is slightly depressed in the middle portion near the commissure, producing a furrow in the central region of the commissural line, flanked by two concomitant bulged portions in the side. Fine ridges radiating from the beak are present in both the valves. These ridges of both the valves give the anterior commissural line, a denticulate pattern with a ‘W’

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020 shaped out line. Both the beaks are curved but P-valve beak is to some extent erect. Prominent pedicle opening is present in the P-valve. Remarks: Daghanirhynchia consists of several species; most of them are identified by internal morphology. Externally my material resembles mostly D. daghaniensis Muir-Wood. Locality: Filiklik, Gelegele and Dembeza areas of Blue Nile Basin. Horizoan: Top most layer of marly limestone beds.

Somalirhynchia Sp. (plat 2 B) Systematic paleontology Phylum Brachiopoda Duméril, 1806 Subphylum Rhynchonelliformea Williams et al. 1996 Class Rhynchonellata Williams et al. 1996 Order Rhynchonellida Kuhn, 1949 Family Tetrarhynchiidae Ager, 1965 Subfamily Tetrarhynchiinae Ager, 1965 Genus Somalirhynchia Weir, 1935

Somalirhynchia Africana Weir (plate 2 B)

Type species Somalirhynchia Africana Weir by original designation

*1925 Somalirhynchia Africana sp. nova. Weir: 80, pl. 12, Figs. 20–30. v. 1935 Somalirhynchia Africana Muir-Wood: 94, text-figs 7–8, pl. 10, Fig. 7-a. v. 2001 Somalirhynchia Africana Feldman et al: 641, text-figs3, pl. 1, Figs. 7–15. Materials: 10 samples 4 from Gelgele, 2 from Dembeza and 4 from Filkilik area with sample code of SG1,SG2,SG3,SG4 ,SD1,SD2 and SF1,SF2,SF3,SF4. Dimensions: SG1 Length (L) - 25 mm Width (W) - 27 mm Thickness (T) - 19 mm Description: Shell is large, roundly subtrigonal to subpentagonal in shell outline sub medially widest and thickest, moderately tumid, rather coarsely ribbed with 30-35 ribs on the dorsal valve. Maximum width of test and also both of the valves are at the middle. Lateral commissure

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020 deflected ventrally; anterior commissure strongly uniplicate. Dorsal valve evenly convex; fold distinct, broad and moderately raised over slopes, with rounded top Costae numerous, coarse and subangular, on each valve numbering 26-34, with 5-8 on fold and 4-7 in sulcus, growth lines fine, visible on whole shell. Beak is strong and massive, beak ridges subangular to obtuse well defined and slightly concave with fine transverse lines. Remarks: This genus is similar to Daghanirhynchia both externally and internally; some young forms of Somalirhynchia Africana could hardly be separated from the species of the latter. These two genera are separable mainly in chronology rather than morphology (Shio and Grant). Nevertheless, Somalirhynchia generally is much larger and broader than Daghanirhynchia, and usually has more developed and clearly defined interareas. Locality: Dembeza, Filkilik and Gelgele area of Blue Nile basin. Horizon: mostly from Filiklik area and few specimens from the two sections Age and Distribution: Oxfordian to Kimmeridgian; North and East Africa, Ethiopia, Middle East, and Europe Cymatorhynchia Sp. Zieten, 1830 (plate 3 C)

Cymatorhynchia Sp. Zieten, 1830 (plate 3 C)

Type species Cymatorhynchia quadriplicata (Zieten, 1830) 1918 Cymatorhynchia quadriplicata (Zieten); Buckman 1918: 53–54 1966 Cymatorhynchia quadriplicata (Zieten); Almeras 1966: 70–97 Materials 14 individuals 6 from Gelgele area, 4 from Ddembeza area and 4 from Filkik with sample code CG1,CG2,CG3,CG4 CG5,CG6 CD1, CD2,CD3,CD4 and CF1,CF2,CF3,CF4. Dimensions; CG2

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Length (L) - 24 mm Width (W) - 23 mm Thickness (T) - 18 mm Description: Shells are medium to large, subpentagonal to subquadrate in outline, moderately dorsi biconvex, and maximum width near mid length. Anterior commissure is uniplicate. Ventral beak short, suberect to erect, deltidial plates disjunct to conjunct; costae subangular to sharp numbering about 16–17; growth lines barely visible near anterior commissure. Ventral valve moderately to strongly convex posteriorly but less convex anteriorly; a broad, shallow sulcus originates just past one−third of valve length bearing 3–4 strong subangular costae, 5–6 costae on ventral flank; foramen round, small to medium sized. Dorsal valve more globose posteriorly, flattened toward anterior commissure; moderately convex in lateral view; a broad, low fold originates just posterior to mid length bearing 4 costae with 6 costae on dorsal flank. REMARKS: Cymatorhynchia is important in the early Middle Jurassic of the Tethyan Realm. Most of its species were recorded from the Middle to Upper Bajocian, except Cymatorhynchia cymatophorina Buckman, the type-species, which was reported from the Aalenian and is far less known than Cymatorhynchia quadriplicata (Zieten). The genus is externally similar to Kutchirhynchia Buckman, which Ager (1965a) thought might be synonymous with this genus. Generally, Cymatorhynchia has stronger and fewer costae, a less tumid dorsal umbo, and a stronger beak. Internally, Cymatorhynchia has a less massive septum and slightly incurved crura. There is little doubt that these two genera are closely related, and possibly Cymatorhynchia had led to the Kutchirhynchia-Daghanirhynchia-Somalirhynchia group that constituted a main lineage of the subfamily Tetrarhynchiinae in the Bathonian to Oxfordian on the south shore of Tethys. Age and Distribution: Aalenian to Upper Bajocian; Europe, Africa, Arabia, India, Burma, China, and Tibet. Locality: Filiklik, Gelegele and Dembeza areas of Blue Nile Basin. Horizon: Marly limestone beds.

Monsardithyris Sp (plate 4 D) Phylum Brachiopoda Duméril, 1806

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Subphylum Rhynchonelliformea Williams et al. 1996 Class Rhynchonellata Williams et al. 1996 Order Terebratulida Waagen, 1883 Suborder Terebratulidina Waagen, 1883 Superfamily Loboidothyridoidea Makridin, 1964 Family Lissajousithyrididae Cooper, 1983 Subfamily Lissajousithyridinae Cooper, 1983 Genus Monsardithyris Alméras, 1971 Type species: Terebratula ventricosa Hartmann Monsardithyris Sp (plate 4. D) Material: 3 individuals from 1 from Gelgele, 1 from Dembeza and 1 from Filiklik with sample code of MG1, MD1 and MF1. Dimensions; MF1 Length (L) - 20 mm Width (W) - 18 mm Thickness (T) - 14 mm Description: Shells subcircular in outline or elongated. Surface is smooth. Anterior margin gently rectimarginate to uniplicate but sulcus and fold is not recognizable on shell surface. Growth lines are gently visible at anterior margin. Beak is short with large foramen. Remarks: The specimens are rather small in comparison to other Monsardithyris Taxa. This may explain the faint development of sulcus and fold, which are more clearly developed in larger forms. Therefore, we interpret our material as young adult forms. Age and Distribution: Jurassic in age Europe, Africa, Arabia, India, Burma, China, and Tibet. Locality: Filiklik, Gelegele and Dembeza areas of Blue Nile Basin. Horizon: Marly limestone beds.

Cererithyris sp (plate 5 E) Phylum Brachiopoda Duméril, 1806 Subphylum Rhynchonelliformea Williams et al. 1996 Class Rhynchonellata Williams et al. 1996 Order Terebratulida Waagen, 1883

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Family Loboidothyrididae Makridin Genus Cererithyris Buckman 1918 Cererithyris sp. (plate 5 E) Type species: Terebratula intermedia J. Sowerby Material: 4 individuals 2 from Filiklik, 1 from Dembeza and 1 from Gelgele with sample code of CrD1, CrG1 and CrF1, CF2. Dimensions; CrG1 Length (L) - 14 mm Width (W) - 13 mm Thickness (T) - 11 mm Description: Shells elongate and quite globular, biconvex in longitudinal section. Beak is low with large foramen. Anterior is margin sulciplicate. Very weak sulucus with broad but low median costa which starts shortly anterior of hinge line. Remarks: Taxa of Cererithyris are characterized by a strong intraspecific variability. At this stage of research it is impossible to identify the material to species level. Age and Distribution: Aalenian to Upper Bajocian; Europe, Africa, Arabia, India, Burma, China, and Tibet. Locality: Filiklik, Gelegele and Dembeza areas of Blue Nile Basin. Horizon: Marly limestone beds.

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CHAPTER FIVE

5 Discussion, conclusion and Recommendation 5.1 Discussion The Jurassic Brachiopod fossil fauna was found in different regions of the world. A large number of invertebrate fossils were explored including the Brachiopods from Blue Nile basin. Their occurrence was scanty. Their rare availability might be due to the hard limestone in which the fossils were embedded.

Brachiopods were most abundant in the Paleozoic period. They possessed phosphatic or calcitic shells. Due to stable nature of calcite, the Brachiopod shells were preserved. Both Rhynchonellids and Terbatulids Brachiopods were first noticed by Kiessling (2011) from Northern Ethiopia. They found only single species in certainty Somaliranchia Africana. They explored four endemic genus of Rhynchonellida family, the Dhagnirynchia Sp Cymatoranchia Sp, Amydroptycus sp and somaliranchia sp from the Blue Nile basin. They were found in marly Limestone. The anterior margin of Dhagnirynchia has fine ribbing while it is coarse in Kiessling. So from the samples Rhynchonellida species have the degree of coarseness indicates that the coarseness is developed from a smooth one. The ventral valve is shallower than the dorsal one. Daghanirhynchia The genus is characterized by having a subpentagonal shell boundary. The plane anterior commissure of shell is slightly curved. On the dorsal valve no fold is recognized. They possessed short acute beak with abundant fine costae, which are sometimes branched and arranged irregularly. With a broad similarity in external morphological characters of this genus found in Lower Jurassic – Upper Jurassic period, it is somewhat tentatively referred as genus Daghanirhynchia Serial sectioning of the specimens would be needed to determine, if the specimens represent a new genus. The Blue Nile specimens compare favourably with Cooper’s (1989) shells in that they are large and widely triangular with maximum width anterior to mid length. Muir Wood’s (1935) description of the genus includes the presence of fine radial striae as a feature of the genus. Cooper (1989) did not observe these features on his shells from Saudi Arabia and found none on

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020 the specimens in the USNM collections from the type locality of D. daghaniensis Muir Wood, 1935 (USNM 75665, 75666). Cymatorhynchia The shells differ from Cymatorhynchia Singularris (USNM 303631) of Cooper (1989) in possessing less costa, a more inflated dorsal valve and less tumid ventral posterior. Buckman’s (1918: pl. 17: 15a, c) C. cymatophorina is wider and has finer and more numerous costae (about26 on the dorsal valve). Cymatorhynchia quadriplicata var. inflata Alméras (USNM 319165) has a more subcircular outline, more inflated dorsal valve, finer and denser ribs as well as a less developed fold and sulcus as noted by Shi and Grant (1993). They also noted that the Tethyan form varies considerably in morphology and were split into seven variants by Alméras (1966). Five of the variants (except for C. quadriplicata var. densecosta and C. quadriplicata var. inflata) have the same basic characteristics namely, less tumid dorsal than ventral valve, slightly depressed shell, subpentagonal outline, and few but strong ribs. Shi and Grant therefore regard them as a single variable species: C. quadriplicata (Zieten, 1830). They suggest combining the varieties C. quadriplicata denecosta and C. quadriplicata var. inflate into a single species: Cymatorhynchia denecosta Alméras, 1966. Alméras and Elmi (1996) describe a specimen of C. quadriplicata var. inflate from Toulon, France, that is larger (USNM 541691: L, 30.3; W, 29.4 [est.]; T, 24.8), much more gibbous and has finer and more numerous costae (about 26). C. quadriplicata var. inflate from Württemberg, Germany, has similar dimensions (USNM 541692: L, 30.1; W, 33.0; T, 24.4) but the costae are less numerous (20) and sturdier. Somalirhynchia This genus is similar to Daghanirhynchia both externally and internally; some young forms of Somalirhynchia Africana could hardly be separated from the species of the latter. These two genera are separable mainly in chronology rather than morphology. Nevertheless, Somalirhynchia generally is much larger and broader than Daghanirhynchia, and usually has more developed and clearly defined interareas. Monsardithyris The specimens are rather small in comparison to other Monsardithyris Taxa. This may explain the faint development of sulcus and fold, which are more clearly developed in larger forms. Therefore, we interpret our material as young adult forms. Cererithyris

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Taxa of Cererithyris are characterized by a strong intraspecific variability. At this stage of research it is impossible to identify the material to species level.

5.2 Conclusions According to Kiessling et al. (2011) the Jurassic Ethiopian Province includes Tunisia, the Levant, Arabia and much of East Africa, but excludes Tanzania and India. They consider that the special status of India and Tanzania is possibly due to latitudinal gradients in faunal composition. In this paper we believe that the Ethiopian Province consists of today’s Arabian Peninsula, Jordan, the Sinai Peninsula and other neighboring basins, the Horn of Africa, parts of the eastern Mediterranean coast, and northeastern Africa. During the Middle Jurassic it was part of the southern Tethys with a characteristic faunal content. Strata of the Ethiopian Province were studied intensely during petroleum exploration after the First World War; however, primary attention was paid to structural geology and sedimentology. Italian and British geologists made large fossil collections that were described piecemeal by paleontologists (e.g. Weir 1925, 1929; Hudson, 1958; Jaboli, 1959; Ficcarelli, 1968). Special attention was paid to the ammonite and foraminiferal faunas because of their stratigraphical value. Referring to the brachiopod faunal assemblages, Weir (1925, 1929) and Muir-Wood (1935, 1936) described the brachiopod fauna from Somalia; Weir (1929) from Kenya, Cooper (1983, 1989) from Saudi Arabia, and Feldman (1986, 1987), Feldman et al. (1991, 2012a), and Hegab (1989, 1992) from Sinai; Feldman et al. (2001) and Krawczynski and Wilson (2011) from Israel, and Feldman et al. (2012b) from Jordan. A more detailed stratigraphical summary of the Jurassic strata in Somalia (formerly British Somaliland) can be found in Weir (1929) and Muir-Wood (1935). Cooper (1989) described brachiopods from Saudi Arabia that were collected from 1125.6m of Jurassic strata. Overall correlation of the faunas among these regions on a larger scale is, with few exceptions, still lacking. This paper is dealing with systematic paleontology of Jurassic brachiopods and their correlation with various regions within the Ethiopian Province. However, its first species were described by Weir (1925) and subsequently Cooper (1989) described additional species. Cooper (1989) and Shi and Grant (1993) discussed the inclusion of taxa assigned to other genera into brachiopod. The Brachiopod species occurs in the Sinai Peninsula at Gebel Engabashi (Feldman, et al., 2012a) and Saudi Arabia (Cooper, 1989) however this distribution is a bit puzzling since it is apparently missing from correlative strata in the Negev.

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020

The Jurassic Brachiopod fossil fauna was found in different regions of the world. A large number of invertebrate fossils were explored including the Brachiopods from Blue Nile basin.

Paleontological data from the Blue Nile basin of central Ethiopia allow evaluating the significance of an Ethiopian Province in the late Jurassic. The Jurassic Ethiopian Province was originally defined for ammonites (Uhlig, 1911; Arkell, 1956) and belemnites (Stevens, 1963) but has also been noted for bivalves (Hallam, 1977; Liu et al., 1998) and brachiopods (Agerand Sun, 1988; Feldman et al., 2001), whereas little is known about Brachiopods provinciality in the Jurassic. The distinctive character and spatial extent of the Ethiopian province has been discussed repeatedly, even for ammonites (Hillebrandt et al., 1992; Enay andCariou, 1997).

The analyses, based on recorded brachiopod fauna data from the Paleo DB, confirm that a distinct African province was indeed evident in Callovian–Kimmeridgian times incorporating a vast region from Tunisia in the north to Madagascar in the south. Ethiopia, situated approximately in the center of this province, deserves being eponymous of this province.

The spatial extent of the Ethiopian Province was perhaps smaller than usually assumed, at least for brachiopods and bivalves. India and Tanzania should probably not be included in the Ethiopian Province. These countries exhibit similar faunal associations but plot far from other countries of the Ethiopian Province.

Oceanographic clines, linked to latitudinal temperature gradients are responsible for the distinct character of India and Tanzania, which were situated at approximately 30_S in the Late Jurassic. Interestingly, a distinct South Gondwana Province was suggested based on ostracods to comprise Tanzania, India and Madagascar (Mette, 2004) and Enay and Cariou (1997).

So this thesis work on the Jurassic brachiopod species of Dejen to Gohatsion of Blue Nile basin central Ethiopia are Dhagnirynchia sp, Somaliranchia sp, Cymatoranchia sp are classified under class of Rhynchonellida and Monsardithyris Sp, Cererithyris sp are classified under class of Terebratulida.

5.3 Recommendation Knowledge of Brachiopod morphology, life history, ecology, biogeography, and the like is far too general, and makes it dangerously possible to over generalize to the entire phylum on the basis of information from a small number of species. Establishing the nature and degree of

Jurassic Brachiopod in Blue Nile Basin Msc thesis by Bikila Argeta 2020 variation among extant species is critical to be able to generate and test informed hypotheses about extinct species.

This thesis needs to develop a deeper and more detailed understanding of the relationship between morphology, development, and genetics, as well as genomics and proteomics. How do brachiopod morphological features develop, what are the developmental genetics regulating the expression of morphology, and how do they relate to the phylogenetic patterns of morphological characters that can generate? It is vitally important that can reach a better understanding of the processes governing morphology in such a paleontologically important group in which well over 95% of species are extinct.

The paper needs to more paleontologists work on questions of brachiopod evolution. Very fortunately, more and more intelligent, creative, and enthusiastic younger scientists over the past decade have become intrigued by brachiopods and the fascinating interdisciplinary questions our current knowledge of their evolution raises. The study sincerely hopes this trend continues; our future knowledge of brachiopod evolution requires their diligence and their scientific passion. In general the present Brachiopod fauna offers an important contribution to our knowledge of the group in Blue Nile basin of central Ethiopia.

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List of fossil plates

Plate 1 Dhagnirynchia sp All fossils are from the Jurassic of Blue Nile basin. All figures in scale of 19 mm size.

A1) Dorsal view, A2) Ventral view, A3) Posterior view, A4) Anterior view, A5) Lateral view

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Plate 2, Somalirhynchia sp B1) Dorsal view, B2) Ventral view, B3) Posterior view, B4) Anterior view, B5) Lateral view

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Plate 3 Cymatorhynchia sp C1) Dorsal view, C2) Ventral view, C3) Posterior view, C4) Anterior view, C5) Lateral view

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Plate 4 Monsardithyris sp D1) Dorsal view, D2) Ventral view, D3) Posterior view, D4) Anterior view, D5) Lateral view

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Plate 5 Cererithyris sp E1) Dorsal view, E2) Ventral view, E3) Posterior view, E4) Anterior view, E5) Lateral view

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APENNDEX List of measurements

Table 1 Measurement (in mm) of Dhagnirynchia sp Weir 1935

Specimen Length Width Thickness DG1 18 14 9 DG2 16.4 13.2 8 DD1 16 12 9 DF1 18 13 9 DF2 17 14.2 7

Table 2 Measurement (in mm) of Somaliranchia sp

Specimen Length Width Thickness SG1 25 27 19 SG2 25.5 26 18.7 SD3 26 24 19.2 SD4 25.5 25.4 19 SG1 27 24.2 17 SG2 25 26 29 SF1 22 27 19.5 SF2 25.8 25.3 19 SF3 26 24 18 SF4 25 23 19.5

Table 3 Measurement (in mm) of Cymatorhynchia Sp. Zieten, 1830

Specimen Length Width Thickness CG1 24 23 18 CG2 23 23 18.2 CG3 25 22.8 18 CG4 23.5 23.1 17.9 CG5 24.5 23.7 16.8 CG6 24 22.5 17 CD1 23.4 22.8 18.3 CD2 24.3 23 16.7 CD3 24.7 23 18 CD4 23.4 23.6 17.6 CF1 24.4 23.2 18

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CF2 24.7 23.9 17.8 CF3 24 22 18 CF4 23 22.7 17.5

Table 4 Measurement (in mm) of Monsardithyris Sp, Alméras, 1971

Specimen Length Width Thickness MG1 20 18.3 14.5 MD1 20 18 14 MF1 19 17 13.5

Table 5 Measurement (in mm) of Cererithyris Sp. Buckman 1918

Specimen Length Width Thickness CrG1 14 13 11.5 CrD1 14 12.6 11 CrF1 13.5 13 11.5 CrF2 14 12.9 11.6