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New palynological evidence for the age of the Beda Formation, Sirte Basin, Libya

Arun Kumar

Plain Language Abstract

The Beda Formation is an oil and gas rich sequence of sedimentary rocks that occurs in the Sirte Basin of Libya. Further oil exploration in this basin requires a definite age and a new definition of this formation. Barr and Weegar (1972) defined this formation and assigned a Middle Paleocene (Montian) age to this formation based on foraminifera, a group of microfossils. But they did not list the age diagnostic Montian foraminifera upon which this age was assigned. Thus, it is not possible to reevaluate the foraminiferal assemblage and age of this formation is questionable. Palynological (study of microfossils of plant affinities) research was carried out with the objective to reevaluate the age of the Beda Formation. The results of the present research suggest that either the studied samples do not belong to the Beda Formation, or the age of the Beda Formation is younger than originally suggested by Barr and Weegar (1972); it ranges from Middle Paleocene to Early-Middle Eocene. An extensive study of this formation using diverse groups of microfossils could conclusively define the age of the Beda Formation.

Resumen en Español

Nueva evidencia palinológica para la edad de la Formación Beda, Cuenca de Sirte, Libia

La Formación Beda representa la secuencia subsuperficial de las calizas intercaladas con dolomías subordinadas, que son los principales reservorios de hidrocarburos en la parte occidental de la cuenca de Sirte en Libia. La edad Paleoceno Medio (Montiense) ha sido asignada a esta formación de acuerdo a su asociación de foraminíferos, pero la lista de los foraminíferos diagnósticos para atribuir una edad no se ha podido encontrar en la bibliografía publicada, por lo que la edad de esta formación es puesta en duda. En esta cuenca también se presentan potentes calizas y arcillas calcáreas del Paleoceno-Eoceno Temprano a Medio. Se realizó un estudio palinológico de 32 muestras de testigos de la Formación Beda provenientes de cuatro sondeos diferentes; no obstante, sólo cuatro muestras del Testigo # 1 (6854'-6884') en el Sondeo # X43 proporcionaron asociaciones de palinomorfos pero con poca diversidad. Los granos de polen y las esporas indican una edad Paleógeno. Sin embargo, las asociaciones de quistes de dinoflagelados proporcionan varias formas estratigráficamente significativas que indican una edad Eoceno Temprano-Medio.
Los resultados del presente estudio sugieren que las muestras estudiadas no pertenecen a la Formación Beda o la edad de la Formación Beda va desde el Paleoceno Medio hasta el Eoceno Medio-Temprano. Se sugiere un extenso estudio de un gran número de muestras de testigo de varias secciones de sondeos para generar nuevos datos micropaleontológicos y palinológicos que puedan definir de manera concluyente la edad de la Formación Beda.

Palabras clave: Formación Beda; Cuenca de Sirte; Libia; Quistes de dinoflagelados; Palinología del Paleoceno-Eoceno; Foraminifera; Palinología

Traducción: Enrique Peñalver (Sociedad Española de Paleontología)

Résumé en Français

text

Translator: Antoine Souron

Deutsche Zusammenfassung

Neue palynologische Nachweise zum Alter der Beda Formation, Sirte Becken, Libyen

Die Beda Formation repräsentiert die Untergrund-Sequenz von zwischengelagerten Kalksteinen mit subordinatem Dolomitgestein, die eine wichtige Kohlenwasserstoff-Lagerstätte im westlichen Sirte Becken in Libyen darstellt. Anhand von Foraminiferen wurde für diese Formation ein mittelpaläozänes Alter (Montium) festgelegt, jedoch wurde in der publizierten Literatur keine Liste dieser altersbestimmenden Foraminiferen gefunden und so ist das Alter der Formation fragwürdig. Mächtige frühpaläozäne bis mitteleozäne Kalke und kalzitische Tone treten ebenfalls im Becken auf. Es wurde eine palynologische Untersuchung von 32 Bohrkernproben aus der Beda Formation aus vier verschiedenen Bohrungen durchgeführt, jedoch erbrachten nur vier Proben aus Bohrkern # 1 (6854'-6884') der Bohrung # X43 eine zwar geringe Vielfalt aber akzeptable Assemblage von Palynomorphen. Die Pollenkörner und Sporen weisen auf ein paläozänes Alter hin. Die Dinoflagellatenzysten-Assemblagen zeigen einige stratigraphisch signifikante Formen, die auf ein früh-mitteleozänes Alter hinweisen. Die Ergebnisse der vorliegenden Studie legen nahe, dass die untersuchten Proben entweder nicht aus der Beda Formation stammen oder das Alter der Beda Formation vom mittleren Paläozän bis zum frühen-mittleren Eozän reicht. Es wird vorgeschlagen, eine große Anzahl von Bohrkernen aus verschiedenen Bohrungen zu untersuchen, um neue mikropaläontologische und palynologische Daten zu gewinnen, die das Alter der Beda Formation abschließend festlegen.

Schlüsselwörter: Beda Formation; Sirte Becken Libyen; Dinoflagellatenzysten; paläozäne-eozäne Palynologie; Foraminifera; Palynologie

Translator: Eva Gebauer

Arabic

Translator: Ashraf M.T. Elewa

 

 

authorArun Kumar. Department of Earth Sciences, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada. This email address is being protected from spambots. You need JavaScript enabled to view it.

 I am a retired Research Scientist and Professor from the Research Institute, King Fahd University of Petroleum Exploration (KFUPM), Dhahran in Saudi Arabia. In 2014-2015, I worked as a Senior Palynologist with the Sirte Oil Company of Libya. At present I am associated with the Department of Earth Science, Carleton University, Ottawa, Canada.

I completed my first Ph.D. degree in Stratigraphic Palynology in 1976 at Michigan State University, USA and a second one in 1999 in Environmental Micropaleontology from Carleton University, Ottawa, Canada. Earlier I did my B.Sc. and M.Sc. degrees in Geology from Lucknow University, India. I was a Nuffield Foundation research fellow at Sheffield University in 1980-81 and a Matsumae Foundation research fellow at Nagasaki University in 1989. During the past forty years I taught at several universities and worked with oil companies as a geologist and biostratigrapher in different parts of the world.

My areas of research interest include palynology and biostratigraphy in basin exploration and benthic foraminifers and thecamoebians as proxies for environmental, oceanographic and climate change during the past 15,000 years. I have published in these fields of science and during the past few years I also published in the field of natural hazards of the Arabian Peninsula.

 

FIGURE 1. Structural elements of the Sirt Basin, Libya showing locations of major oil and gas fields. Location X indicates wells X13, X23, and X43 in the Hagfa Trough and location Y indicates well Y47 on the Beda Platform. (modified after Burwood et al. 2003, NARG Website).

figure1

FIGURE 2. Dinoflagellate cysts. 2.1. cf. Cyclonephelium sp. (6854’ 8”, slide 1: 97.2 x 23). Size: 41x31 µm. 2.2. Canningia sp. (6854’ 8”, slide 2: 95 x 37.7). Size: 28x17 µm. 2.3. Spiniferites ramosus group (6854’ 8”, slide 2: 95 x 37.7). Cyst diameter 19 µm; and process length 3-4.5 µm. 2.4. Batiacasphaera compta (6871’ 4”, Slide 1: 91.5x33.4). Cyst diameter 32x27 µm. 2.5. Homotryblium floripes (6871, slide 1: 95.9x32.1) Cyst diameter 38µm; and process length 12-15 µm. 2.6. Spiniferites ramosus group (6863, slide 2: 97.8 x 33). Cyst diameter 27 µm; and process length 5 µm. 2.7. Polysphaeridium subtile (6863, slide 2: 104.8 x 38). Cyst diameter 13 µm; process length 2-3 µm. 2.8. Operculodinium centrocarpum (6863, slide 1: 100 x 38.8). Cyst diameter 28x24µm; and process length 4-5 µm. 2.9. Fibrocysta cf. bipolaris (6871’ 4”, slide 1: 96.5x30.5). Cyst diameter 42x34 µm; process length 12-18 µm. 2.10. Homotryblium floripes (6871’ 4”, slide 1: 94.7x28.2). Cyst diameter 42x31 µm; process length 12-15 µm.

figure2

FIGURE 3. Dinoflagellate cysts, acritarchs and foraminiferal remains. 3.1. Homotryblium floripes (6871’ 4”, slide 1: 96.5x30.5). Cyst diameter 32 µm; process length 11-14 µm. 3.2. Adnatosphaeridium multispinosum (6872’ 2”, slide 1: 101.9x36). Cyst diameter 22 µm; process length 8-10 µm. 3.3. Homotryblium floripes (6871’ 4”, slide 2: 103.5x35.7). Cyst diameter 40 µm; process length 11-13 µm. 3.4. Homotryblium floripes (6872’ 2”, slide 1: 96.8x38). Cyst diameter 42 µm; process length 13-15 µm. 3.5. Tityrosphaeridium cantharellus (6872’ 2”, slide 1: 97.8x28.7). Cyst diameter 36 µm; process length 11x14 µm. 3.6. Apteodinium australiense (6872’ 2”, slide 2: 108x39.6). Cyst diameter 22x16 µm. 3.7. Leiosphaeridia sp. (6872’ 2”, slide 1: 98.2x24.6). Cyst diameter 21x14 µm. 3.8. cf. Pterospermella sp. (6872’ 2”, slide 1: 98x24). Cyst diameter 25x21.5 µm. 3.9. Batiacasphaera cf. sphaerica Stover, 1977 (6872’ 2”, slide 2: 104.5x31.5). Cyst diameter 22x16 µm. 3.10. Foraminiferal lning (6863, slide 1: 94.2 x 28). Size: 40 µm. 3.11. Micrhystridium sp. (6863, slide 2: 103.4 x 30). Cyst diameter 15 µm; and process length 3-4 µm. 3.12. Micrhystridium sp. (6863, Slide 2: 103.2 x 32.3). diam. 7 µm; proc. 2-3 µm.

figure3

FIGURE 4. Pollen grains and fungal remains. 4.1. Arecipites indicus (6854’ 8”, Slide 2: 95 x 33.5). Size: 14 x 6 µm. 4.2. Proxapertites cursus (6863’, Slide 1: 98.4 x 32.4). Size: 14 µm. 4.3. Retitricolpites sp. (6863’, Slide 1: 101 x 27). Size: 8 µm. 4.4. Palmaepollenites sp. (6863’, Slide 1: 107.4 x 35.8). Size: 23x11 µm. 4.5. Proxapertites operculatus (6863’, Slide 2: 105.2 x 39). Size: 15x8 µm. 4.6. Tricolpites microreticulatus (6863’, Slide 2: 105.5 x 34.5). Size: 8 µm. 4.7. Tricolporopollenites sp. (6863’, Slide 2: 94x31.5). Size: 16x 12 µm. 4.8. Arecipites indicus (6863’, Slide 2: 93.8x39.2). Size: 19x 11 µm. 4.9. Palmidites sp. (6863’, Slide 2: 95.7x31.2). Size: 16x 8 µm. 4.10. Palmidites sp. (6863’, Slide 2: 92x37.6). Size: 18x12 µm. 4.11. Retibrevitricolpites sp. (6863’, Slide 2: 92.4x25). Size: 10 µm. 4.12. Brevitricolpites sp. (6863’, Slide 2: 104.4x33.5). Size: 10 µm. 4.13. Neocouperipollis sp. (6863’, Slide 2: 91.5x29.6). Size: 16 µm. 4.14. Trisyncoloporopollenites sp. (6863’, Slide 2: 90x23.2). Size: 12 µm. 4.15. Fungal spore (6863, slide 1: 99.6 x 33). Size: 30 µm. 4.16. Fungal remain (6863, slide 2: 105.6 x 30.3). Size: 23x8 µm.

figure4

 

TABLE 1. List of samples studied from various cores belonging to wells X43, Y47, X13, and X23.

DEPTH LITHOLOGY PALYNOMORPH YIELD
Well # X43: Core # 1 Beda Formation (6854’-6884’)
6854’ 8” Shale Fair
6863’ 0” Mudstone Good
6871’ 4” Mudstone Poor
6872’ 2” Mudstone Good
6880’ 6” Limestone Barren
Well # Y47: Core # 1 Beda Formation (5965’-5995’)
5965’ 0” Mudstone Barren
5970’ 6” Mudstone Barren
5972’ 6” Argillaceous wackestone Barren
5991’ 4” Grainstone with rootlet Barren
Well # Y47: Core # 2 Beda Formation (5995’-6025’)
6004’ 0” Grainstone Barren
6017’ 6” Grainstone Barren
6022’ 4” Grainstone Barren
Well # X13: Core # 1 Beda Formation (6885’-6929’)
6886’ Claystone (grey-brown) Barren
6895’ Claystone (grey-brown) Barren
6897’ Claystone (grey-brown) Barren
6904’ Grey Shale Barren
6905’ Grey Shale Barren
6923’ Claystone (grey-brown) Barren
6928’ Claystone (grey-brown) Barren
Well # X23: Core # 2 Beda Formation (7151’-7197’)
7152’ Claystone Barren
7157’ Claystone Barren
7163’ Claystone Barren
7165’ Claystone Barren
7169’ Claystone Barren
7174’ Claystone Barren
7177’ Claystone Barren
7183’ Claystone Barren
7186’ Claystone Barren
7189’ Claystone Barren
7193’ Claystone Barren
7194’ Claystone Barren
7196’ Claystone Barren

TABLE 2. List of palynomorphs.

A. Dinoflagellate Cysts
1. Adnatosphaeridium multispinosum Williams and Downie, 1966
2. Apteodinium australiense (Deflandre and Cookson, 1955) Williams, 1978
3. Apteodinium sp.
4. Batiacasphaera compta Drugg, 1970
5. Batiacasphaera cf. sphaerica Stover, 1977
6. Batiacasphaera sp.
7. Canningia sp.
8. Cordosphaeridium sp.
9. Cyclonephelium sp.
10. Fibrocysta cf. bipolaris (Cookson and Eisenack, 1965) Stover and Evitt, 1978
11. Homotryblium floripes (Deflandre and Cookson, 1955) Stover, 1975
12. Hystrichosphaeropsis sp.
13. Operculodinium centrocarpum (Deflandre and Cookson, 1955) Matsuoka et al. 1997
14. Polysphaeridium subtile Davey and Williams, 1966
15. Spiniferites ramosus group (Ehrenberg, 1838) Mantell, 1854
16. Tityrosphaeridium cantharellus (Brosius, 1963) Sarjeant, 1981
B. Acritarchs
1. Leiosphaeridia spp.
2. Micrhystridium spp.
3. Pterospermella spp.
C. Pollen Grains
1. Arecipites indicus Venkatachala and Rawat, 1972
2. Brevitricolpites sp.
3. Neocouperipollis sp.
4. Palmaepollenites spp.
5. Palmidites sp.
6. Proxapertites operculatus van der Hammen, 1956
7. Proxapertites cursus van Hoeken-Klinkenberg 1966
8. Retibrevitricolpites sp.
9. Retitricolpites sp.
10. Spinizonocolpites sp.
11. Tricolpites microreticulatus Venkatachala, 1973
12. Tricolpites spp.
13. Tricolporopollenites sp.
14. Trisyncoloporopollenites sp.
D. Spores
1. Laevigatosporites sp.
2. Polypodiaceoisporites sp.
E. Miscellaneous palynomorphs
1. Foraminieral linings
2. Fungal spores
3. Fungal remains

TABLE 3. Distribution of palynomorphs in four samples of core #1 in well X43.

Palynomorphs Core # 1: Sample Depth (Feet)
6854’ 8” 6863’ 0” 6871’ 4” 6872’ 2”
Dinoflagellate Cysts    
Adnatosphaeridium multispinosum       P
Apteodinium australiense       P
Apteodinium sp.       P
Batiacasphaera compta     P  
Batiacasphaera cf. sphaerica P      
Batiacasphaera spp. P P    
Canningia spp. P      
Tityrosphaeridium cantharellus       C
Cordosphaeridium spp.        
Cyclonephelium spp. P      
Fibrocysta cf. bipolaris     P  
Homotryblium floripes     C C
Hystrichosphaeropsis sp.       P
Operculodinium centrocarpum   P    
Polysphaeridium subtile   P    
Spiniferites ramosus Group P P   P
Acritarchs    
Leiosphaeridia spp. P     C
Micrhystridium spp   P    
Pollen Grains    
Arecipites indicus P P    
Brevitricolpites sp   P    
Palmaepollenites spp.   P   P
Palmidites sp.   P    
Proxapertites operculatus   P    
Proxapertites sp.   P    
Spinizonocolpites sp.   P    
Tricolpites microreticulatus   P    
Tricolpites spp.   P    
Tricolporopollenites sp.   P   P
Spores    
Laevigatosporites sp. P P    
Polypodiaceoisporites sp. P      
Miscellaneous palynomorphs    
Foraminieral linings   P    
Fungal spores   P    
Fungal bodies   P