RACE METAL ANOMALIES IN SOILS AND SEDIMENTS OF THE MOANDA-BANANA COASTAL AREA (CONGO COASTAL BASIN): RELATIVE ROLES OF ANTHROPOGENIC PROCESSES AND DEEP GEOGENIC CONTROLS

This study investigates the controls governing the spatial distribution of trace metals (TMs) in soils and coastal sediments of the Moanda-Banana sector within the Congo Coastal Basin. The objective is to discriminate the relative roles of near-surface sedimentary processes and deeper geogenic influences in the development of metal anomalies within an active Atlantic margin context. Eighteen samples were collected along an ~8 km coastal transect during the 2025 dry season and analyzed using ICP-MS and AMA-254. The geochemical dataset was evaluated through enrichment and contamination indices (EF, Igeo, CF, DC and PLI), ecological risk factors (Eri and RI), multivariate statistics, and residual Bouguer gravity data.
Physico-chemical parameters show strong spatial contrasts between the estuarine domain of Moanda and the sandy environments of Banana. Fine estuarine sediments display high water contents (up to 76.9%) and total organic matter reaching 28.9%, whereas Banana soils are predominantly sandy (>80%). The highest metal concentrations occur at station M0S2, where Zn, Pb and Cu reach 412.6, 196.7 and 84.2 mg·kg⁻¹, respectively, indicating localized enrichment in fine-grained deposits. Zinc frequently exceeds the SQG guideline (123 mg·kg⁻¹) and locally approaches the PEL threshold (315 mg·kg⁻¹), while Pb surpasses the PEL value (91 mg·kg⁻¹) at stations M0S2 and M0S3.
At the regional scale, geochemical indices indicate predominantly low-to-moderate contamination despite localized enrichments, particularly for Pb and Zn. Principal Component Analysis explains 88.91% of total variance (F1=74.73%; F2=14.19%) and reveals a coherent Cu-Zn-Pb association mainly controlled by surficial sedimentary conditions. The overall ecological risk remains limited, although Hg and Cd represent the main local contributors. Residual Bouguer anomalies (- 0.69 to +1.97 mGal) indicate basement heterogeneity and show partial spatial correspondence with surface geochemical patterns. This spatial relationship is compatible with a possible halokinetic structural influence but does not demonstrate direct deep metal transfer. Overall, trace metal distribution in the Moanda-Banana coastal zone is dominantly controlled by surficial sedimentary processes, while deep geogenic influences remain secondary and locally plausible.