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<p>The Early Cretaceous drift deposits of the Douala Basin (Mungo River Formation) were investigated in order to determine the paleoclimatic conditions, compositional maturity, paleoweathering, and depositional environment, based on field geologic mapping and geochemical analyses. This study aims to evaluate weathering intensity, paleoclimatic conditions, and paleo-redox conditions using geochemical data and their various approaches for black shale samples of the Ediki River, Mungo River Formation, Cameroon. The black shale samples from Ediki River were collected and analyzed geochemically using inductively coupled plasma-mass spectrometry (ICP-MS) to reveal their major, trace, and rare earth element composition. The black shales show variable colors ranging from grey to dark, are fine-grained and highly fossiliferous, and have laminations, bedding, cast, and mold structures. The calculated Plagioclase Index of Alteration (PIA 66.36 to 88.21%), Chemical Index of Alteration (CIA 60.99 to 76.38%), and Chemical Index of Weathering (CIW 87.82 to 93.06%) suggest moderate to intense weathering conditions in the source area of the Early Cretaceous black shales. The Index of Compositional Variability (ICV 0.55 to 1.21; mean 0.87) and K₂O/Na₂O ratio indicate compositionally mature shales. The elemental ratios, such as U/Th, Sr/Ba, V/Ni, and Ni/Co, suggest an oxic depositional environment. The elemental ratios of Th/U and Sr/Ba for black shales indicate a non-marine environment with low-salinity water during sedimentation. The parent rock of the Ediki black shales in the Mungo River Formation is a felsic provenance. The enrichment assessment suggests natural geogenic origins of trace elements in the black shales linked to natural geochemical enrichment, provenance control, and sedimentary processes. This study provides significant findings regarding the reconstruction of the paleoclimatic conditions, paleosalinity, and depositional environment of the Ediki River black shales and the Mungo River Formation during the Early Cretaceous period. This study also redesigns previous knowledge available concerning clastic materials in the Douala basin in relation to paleoweathering, climatic conditions, paleoenvironment, and compositional maturity throughout the Cretaceous period.</p>

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Geochemistry of early cretaceous black shales in Ediki River, Mungo River Formation, NW Douala basin (Cameroon): implications for paleoweathering, paleoclimate and depositional environment

  • 期刊论文

  • 发表日期：

    2026年5月26日

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  • Esue Fidelis Mokake,
  • Florence Njinto Kwankam,
  • Lemnyuy Prosper Yiika,
  • Ligbwah Victor Wotanie,
  • Njoh N. Clevis,
  • Christopher M. Agyingi

摘要

The Early Cretaceous drift deposits of the Douala Basin (Mungo River Formation) were investigated in order to determine the paleoclimatic conditions, compositional maturity, paleoweathering, and depositional environment, based on field geologic mapping and geochemical analyses. This study aims to evaluate weathering intensity, paleoclimatic conditions, and paleo-redox conditions using geochemical data and their various approaches for black shale samples of the Ediki River, Mungo River Formation, Cameroon. The black shale samples from Ediki River were collected and analyzed geochemically using inductively coupled plasma-mass spectrometry (ICP-MS) to reveal their major, trace, and rare earth element composition. The black shales show variable colors ranging from grey to dark, are fine-grained and highly fossiliferous, and have laminations, bedding, cast, and mold structures. The calculated Plagioclase Index of Alteration (PIA 66.36 to 88.21%), Chemical Index of Alteration (CIA 60.99 to 76.38%), and Chemical Index of Weathering (CIW 87.82 to 93.06%) suggest moderate to intense weathering conditions in the source area of the Early Cretaceous black shales. The Index of Compositional Variability (ICV 0.55 to 1.21; mean 0.87) and K₂O/Na₂O ratio indicate compositionally mature shales. The elemental ratios, such as U/Th, Sr/Ba, V/Ni, and Ni/Co, suggest an oxic depositional environment. The elemental ratios of Th/U and Sr/Ba for black shales indicate a non-marine environment with low-salinity water during sedimentation. The parent rock of the Ediki black shales in the Mungo River Formation is a felsic provenance. The enrichment assessment suggests natural geogenic origins of trace elements in the black shales linked to natural geochemical enrichment, provenance control, and sedimentary processes. This study provides significant findings regarding the reconstruction of the paleoclimatic conditions, paleosalinity, and depositional environment of the Ediki River black shales and the Mungo River Formation during the Early Cretaceous period. This study also redesigns previous knowledge available concerning clastic materials in the Douala basin in relation to paleoweathering, climatic conditions, paleoenvironment, and compositional maturity throughout the Cretaceous period.