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Petroleum source rock characteristics of the Mesozoic units, Mekelle Basin, northern Ethiopia

Damenu Adefris

Damenu Adefris

  • Department of Geology, Debre Berhan UniversityDebre Berhan, Ethiopia
  • Petroleum Geosciences Program, Pan African University, Life and Earth Sciences Institute (including Health and Agriculture), University of IbadanIbadan, Nigeria
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Adefris, Damenu
, 
M.E. Nton

M.E. Nton

Department of Geology, University of IbadanIbadan, Nigeria
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Nton, M.E.
, 
O.A. Boboye

O.A. Boboye

Department of Geology, University of IbadanIbadan, Nigeria
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Boboye, O.A.
 und 
Balemwal Atnafu

Balemwal Atnafu

School of Earth Sciences, Addis Ababa UniversityAddis Ababa, Ethiopia
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Atnafu, Balemwal
  
04. Sept. 2023
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Artikel-Kategorie: Original Scientific Article
Online veröffentlicht: 04. Sept. 2023
Seitenbereich: 1 - 13
Eingereicht: 11. März 2022
Akzeptiert: 28. März 2022
DOI: https://doi.org/10.2478/rmzmag-2021-0019
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© 2022 Damenu Adefris et al., published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Figure 1

(a) Map showing Gondwana breakup (after [18]); (b) Mesozoic rift basins of the Horn of Africa including Ethiopia (after [21]).
(a) Map showing Gondwana breakup (after [18]); (b) Mesozoic rift basins of the Horn of Africa including Ethiopia (after [21]).

Figure 2

Geological map of the Mekelle Basin with sampling locations (after [42]). The inset map is a simplified geological map of Ethiopia (after [43]).
Geological map of the Mekelle Basin with sampling locations (after [42]). The inset map is a simplified geological map of Ethiopia (after [43]).

Figure 3

Lithologic logs showing the locations of samples collected for source rock characterization.
Lithologic logs showing the locations of samples collected for source rock characterization.

Figure 4

Outcrop photographs showing black shale layers and limestone beds within the Antalo Limestone at the central part of the Mekelle Basin. (a) thickly bedded black fine-grained limestone (Mesobo section, sample MS-1); (b) black shale within black micritic limestone beds (sample MS-7); (c) 16 m thick stream-side cliff exposure comprising limestone and shale beds (samples EY-2 to EY-5) around Mekelle town (Endayesus section); (d) Black shale along stream at the bottom of Endayesus section (sample EY-1).
Outcrop photographs showing black shale layers and limestone beds within the Antalo Limestone at the central part of the Mekelle Basin. (a) thickly bedded black fine-grained limestone (Mesobo section, sample MS-1); (b) black shale within black micritic limestone beds (sample MS-7); (c) 16 m thick stream-side cliff exposure comprising limestone and shale beds (samples EY-2 to EY-5) around Mekelle town (Endayesus section); (d) Black shale along stream at the bottom of Endayesus section (sample EY-1).

Figure 5

Outcrop photographs showing black shale layers within the Adigrat Sandstone and Agula Shale, at the central part of the Mekelle Basin. (a) lower part of Antalo Limestone conformably overlies the upper part of Adigrat Sandstone at Giba River section; (b) about 5–10 cm thick oil shale beds (sample GV-1) from the upper part of Adigrat Sandstone; (c) Some part of the Agula Shale at Chelekot section (samples; CH-1, CH-2).
Outcrop photographs showing black shale layers within the Adigrat Sandstone and Agula Shale, at the central part of the Mekelle Basin. (a) lower part of Antalo Limestone conformably overlies the upper part of Adigrat Sandstone at Giba River section; (b) about 5–10 cm thick oil shale beds (sample GV-1) from the upper part of Adigrat Sandstone; (c) Some part of the Agula Shale at Chelekot section (samples; CH-1, CH-2).

Figure 6

(a) Oxygen index (OI) and hydrogen index (HI) cross plot for the recognition of kerogen types (after [57]); (b) Kerogen type based on TOC versus pyrolysis yield (S2) cross-plot, showing very poor quality organic matter for hydrocarbon generation (after [47]).
(a) Oxygen index (OI) and hydrogen index (HI) cross plot for the recognition of kerogen types (after [57]); (b) Kerogen type based on TOC versus pyrolysis yield (S2) cross-plot, showing very poor quality organic matter for hydrocarbon generation (after [47]).

Figure 7

(a) Rock-Eval Tmax versus hydrogen index (HI) plot showing the thermal maturity level of the organic matter (after [57]); (b) TOC versus (S1 + S2) cross-plot, indicating poor hydrocarbon generating potential (after [47]).
(a) Rock-Eval Tmax versus hydrogen index (HI) plot showing the thermal maturity level of the organic matter (after [57]); (b) TOC versus (S1 + S2) cross-plot, indicating poor hydrocarbon generating potential (after [47]).

Rock-Eval pyrolysis data of the analyzed samples_

Sample no. Sample type TOC (wt.%) S1 S2 S3 Tmax HI OI PI PP
CH-1 limestone 0.18 0.00 0.00 0.17 327 0 94 -- 0.00
CH-2 shale 0.40 0.01 0.00 0.25 524 0 62 1.00 0.01
EY-1 shale 0.25 0.00 0.00 0.26 498 0 106 -- 0.00
EY-2 shale 0.77 0.01 0.01 0.20 485 1.3 26 0.50 0.02
EY-3 shale 0.20 0.00 0.01 0.98 495 5 488 0.00 0.01
EY-4 limestone 0.21 0.02 0.07 0.64 475 34 309 0.22 0.09
EY-5 shale 0.23 0.00 0.00 0.26 496 0 111 -- 0.00
MS-1 limestone 0.11 0.00 0.00 0.30 -- 0 275 -- 0.00
MS-2 shale 0.50 0.00 0.02 0.39 493 4 78 0.00 0.02
MS-3 shale 0.41 0.00 0.01 0.51 505 2.44 125 0.00 0.01
MS-4 limestone 0.10 0.00 0.00 0.28 484 0 294 -- 0.00
MS-5 limestone 0.22 0.00 0.00 0.26 484 0 119 -- 0.00
MS-6 shale 0.20 0.00 0.00 0.39 491 0 194 -- 0.00
MS-7 shale 0.92 0.02 0.02 1.10 519 2 119 0.50 0.04
GV-1 shale 0.42 0.00 0.00 0.35 527 0 83 -- 0.00

Outcrop samples collected for organic geochemical analyses_

Sample no. Sampling location Sample type Formation
CH-1 13°25’36’’, 39°23’39’’, 1912 m asl. limestone Agula Shale
CH-2 shale Antalo Limestone
EY-1 13°29’26’’, 39°29’07’’, 2113 m asl. shale  
EY-2 shale
EY-3 shale
EY-4 limestone
EY-5 shale
MS-1 13°33’23’’, 39°30’36’’, 2094 m asl. limestone  
MS-2 shale
MS-3 shale
MS-4 limestone
MS-5 limestone
MS-6 shale
MS-7 shale
GV-1 13°37’55’’, 39°24’51’’, 1818 m asl. shale Adigrat Sandstone
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