. These sedimentary formations provide valuable insights into the region’s geological history, depositional environments, and hydrocarbon potential. Ekenkpon Shale: 1. Description: • The Ekenkpon Shale is part of the sedimentary sequence in the Calabar Flank of southeastern Nigeria. • It consists mainly of dark grey to black shales with occasional intercalations of sandymud and mudstone. 1. Geochemical Characteristics: • Geochemical analyses reveal the following features: • Trace Elements: Enriched in phosphorus (P), manganese (Mn), barium (Ba), strontium (Sr), vanadium (V), cerium (Ce), zirconium (Zr), rubidium (Rb), and chromium (Cr). • Depleted Elements: Relatively depleted in antimony (Sb), germanium (Ge), bismuth (Bi), silver (Ag), tellurium (Te), indium (In), and mercury (Hg). 1. Rare Earth Elements (REE): • The REE composition of the Ekenkpon Shale shows a slight enrichment in light rareearth elements (LREE) and middle rare-earth elements (MREE), with a depleted heavy rare-earth element (HREE) pattern. • The Ce/Ce* ratio ranges from 0.67 to 1.40, indicating variable redox conditions during deposition. 1. Redox Conditions: • The Mn content and U/Mo ratio suggest a poor oxygen-transitional environment during Ekenkpon Shale deposition. • The V/Mo and V/(V+Ni) ratios indicate anoxic to suboxic conditions. 1. Organic Matter Source: • The organic matter in the Ekenkpon Shale is both terrigenous and marine in origin, as indicated by the V/Ni ratio. Nkporo Shale: 1. Description: • The Nkporo Shale is another significant shale unit in the Calabar Flank. • It consists of dark grey to black shales, micritic limestones, and oolitic ironstone. 1. Trace Elements: • The Nkporo Shale is enriched in phosphorus (P), manganese (Mn), strontium (Sr), barium (Ba), zinc (Zn), cerium (Ce), rubidium (Rb), and zirconium (Zr). • It is depleted in tantalum (Ta), germanium (Ge), antimony (Sb), bismuth (Bi), cadmium (Cd), silver (Ag), tellurium (Te), and indium (In). ___________________________________________________________________________________________________________ ___________________________ Geology of Ekenkpon and Nkporo Shales: The Ekenkpon and Nkporo shales are Cretaceous formations located within the Calabar Flank in Southeastern Nigeria. They have been studied for their geochemical properties, which provide insights into their provenance, transportation history, and depositional environment12. The shales are primarily composed of major oxides like SiO2, Al2O3, and Fe2O3, with the Ekenkpon Shale showing a higher degree of weathering than the Nkporo Shale as indicated by their Index of Chemical Variation (ICV)1. History: These shales have a rich geological history tied to the Cretaceous period. Their composition reveals a story of sediments sourced from felsic rocks and deposited in environments ranging from oxic, continental to transitional marine settings. This is supported by the presence of elements like Sr, Th, and U, which suggest a felsic granodiorite source with some input from volcanic provenance1. Geological Differences and Similarities: Both shales exhibit similarities in their source rock characteristics, with a felsic origin and signs of moderate to high weathering. However, they differ in their degree of metal enrichment and the specific trace elements present. The Nkporo Shale is enriched with elements like P, Mn, Sr, Ba, Zn, Ce, Rb, Zr, V, Cr, and Ni, while the Ekenkpon Shale shows enrichment in P, Mn, Ba, Sr, V, Ce, Zr, Rb, Cr, Zn, and Ni2. The rare earth element (REE) patterns also differ, with the Nkporo Shale showing a slightly flat pattern, while the Ekenkpon Shale shows slight enrichment in light and middle REEs but depletion in heavy REEs2. Key Points: The shales are indicative of a passive to active continental margin tectonics. They have a history of deposition in anoxic to suboxic conditions. The organic matter in the Nkporo shale is terrigenous, while the Ekenkpon shales contain both terrigenous and marine organic matter. ___________________________________________________________________________________________________________ _______ Continuing with the exploration of the Ekenkpon and Nkporo shales, let’s delve deeper into their geological significance and the sedimentary settings in which they are found. Sedimentary Settings in Africa: The sedimentary basins in Africa, including the setting for the Ekenkpon and Nkporo shales, have developed primarily in an extensional tectonic regime, although some have experienced compressional or transpressional modifications. The geometry and evolution of these basins are often influenced by the underlying basement structureHYPERLINK "https://www.osti.gov/biblio/5787109"1. In the case of the Central African Copperbelt, for example, the sediment-hosted stratiform copper provinces were formed in cratonic or hinterland extensional sedimentary basinsHYPERLINK "https://pubs.geoscienceworld.org/segweb/books/book/1385/chapter/107056968/The-CentralAfrican-CopperbeltDiverse"2. Geological Significance of Ekenkpon and Nkporo Shales: The Ekenkpon and Nkporo shales are significant for several reasons: • They serve as source rocks in hydrocarbon-producing sedimentary basins, containing organic matter (kerogen) that determines the type of hydrocarbon producedHYPERLINK "https://link.springer.com/article/10.1007/s11631-020-00434-2"3. • Their geochemistry provides insights into the provenance, transportation history, and depositional environment of the sedimentsHYPERLINK "https://www.ajol.info/index.php/gjgs/article/view/168066"4. • The Index of Chemical Variation (ICV) suggests varying degrees of weathering, with the Ekenkpon Shale showing a higher degree of weathering than the Nkporo ShaleHYPERLINK "https://www.ajol.info/index.php/gjgs/article/view/168066"4. • The presence of elements like Sr, Th, and U indicates a felsic granodiorite source with some volcanic input, reflecting the tectonic setting and sedimentary processes at play during their formationHYPERLINK "https://www.ajol.info/index.php/gjgs/article/view/168066"4. Key Geological Differences and Similarities: • Both shales show enrichment in trace elements like P, Mn, Sr, Ba, Zn, Ce, Rb, Zr, V, Cr, and Ni, but with different degrees and patterns of enrichmentHYPERLINK "https://link.springer.com/article/10.1007/s11631-020-00434-2"3. • The REE patterns differ between the two, with the Nkporo Shale showing a slightly flat pattern, while the Ekenkpon Shale shows slight enrichment in light and middle REEs but depletion in heavy REEsHYPERLINK "https://link.springer.com/article/10.1007/s11631020-00434-2"3. • The V/Ni ratio suggests that the organic matter in the Nkporo shale is terrigenous, while the Ekenkpon shales contain both terrigenous and marine organic matterHYPERLINK "https://link.springer.com/article/10.1007/s11631-020-00434-2"3. _____________________________________________________________________________________ _____________________ Certainly! Let’s dive deeper into the geological details of the Ekenkpon and Nkporo shales within the Calabar Flank in Southeastern Nigeria. Ekenkpon Shale: 1. Geochemical Composition: • • The Ekenkpon Shale is characterized by the dominance of major oxides: • SiO2: 44.50% - 54.83% • Al2O3: 19.20% - 20.20% • Fe2O3: 5.64% - 7.30% These oxides constitute the bulk of the Ekenkpon ShaleHYPERLINK "https://www.ajol.info/index.php/gjgs/article/view/168066"1. 1. Trace Elements: • Enriched in trace elements such as: • • Depleted in elements like: • • P > Mn > Ba > Sr > V > Ce > Zr > Rb > Cr > Zn > Ni Sb > Ge > Bi > Ag > Ce > Te > In > Hg The enrichment and depletion patterns provide insights into the provenance and depositional environmentHYPERLINK "https://www.ajol.info/index.php/gjgs/article/view/168066"1. 1. Rare Earth Elements (REE): • The REE patterns in the Ekenkpon Shale show: • Slight enrichment in light rare-earth elements (LREE) and middle rare-earth elements (MREE). • Depletion in heavy rare earth elements (HREE). • Ce/Ce* ranges from 0.67 to 1.40HYPERLINK "https://www.ajol.info/index.php/gjgs/article/view/168066"1. 1. Tectonic Setting and Environment: • The Ekenkpon Shale was deposited in an anoxic to suboxic environment. • The organic matter in the Ekenkpon Shale has a mixed origin, including both terrigenous and marine components. • The shale formation is associated with passive to active continental margin tectonicsHYPERLINK "https://www.ajol.info/index.php/gjgs/article/view/168066"1. Nkporo Shale: 1. Geochemical Composition: • • The Nkporo Shale is characterized by major oxides: • SiO2: 45.27% - 46.45% • Al2O3: 22.27% - 23.57% • Fe2O3: 8.30% - 9.04% These oxides constitute the bulk of the Nkporo ShaleHYPERLINK "https://www.ajol.info/index.php/gjgs/article/view/168066"1. 1. Trace Elements: • Enriched in trace elements such as: • • Depleted in elements like: • • P > Mn > Sr > Ba > Zn > Ce > Rb > Zr > V > Cr > Ni Ta > Ge > Sb > Bi > Cd > Ag > Te > In > Hg The enrichment and depletion patterns provide insights into the provenance and depositional environmentHYPERLINK "https://www.ajol.info/index.php/gjgs/article/view/168066"1. 1. Rare Earth Elements (REE): • The REE patterns in the Nkporo Shale show: • Slightly flat LREE, MREE, and HREE enrichment. • Ce/Ce* ranges from 0.95 to 1.09HYPERLINK "https://www.ajol.info/index.php/gjgs/article/view/168066"1. 1. Tectonic Setting and Environment: • The Nkporo Shale was also deposited in an anoxic to suboxic environment. • The organic matter in the Nkporo Shale is terrigenous in origin. • The area is associated with passive to active continental margin tectonicsHYPERLINK "https://www.ajol.info/index.php/gjgs/article/view/168066"1. In summary, both shales have distinct geochemical signatures, reflecting their different origins and depositional environments. The Ekenkpon Shale contains mixed organic matter, while the Nkporo Shale has a terrigenous source. These insights contribute to our understanding of the geological history of the Calabar FlankHYPERLINK "https://www.ajol.info/index.php/gjgs/article/view/168066"1.
