| Autor: |
N'nanga, Alexandrine, Ngueutchoua, Gabriel, Ekomane, Emile, Tematio, Paul |
| Zdroj: |
Arabian Journal of Geosciences; Sep2021, Vol. 14 Issue 17, p1-17, 17p |
| Abstrakt: |
Eutrophication of lakes reinforced by climate changes constitutes a serious threat for tropical and equatorial African lakes. The Lake Fonjak ecosystem steady development was studied from the lake paleoproductivity records deciphered with the geochemistry and textural analysis. The C-values above 0.8 and the Ga/Rb ratio greater than 0.25 suggest humid conditions in the Adamawa plateau during the Holocene. Three sequences of the grain size distribution correspond to three episodes of rainfall intensity upward variations from moderate to stormy. The consistent high biogenic Ba and positive BSi values point toward continuous good primary productivity in the lake during the Holocene. However, the ash deposit from the volcanic activity in the Adamawa plateau, as well as extreme rainfall events coupled to strong wind during the phase II, may have increased this primary productivity around 4400, 3600, and 1250 cal year BP respectively. The REEs fractionation evidenced by the La n/Yb n ratio suggests fast-sedimentary rate that slow down from lower to upper units, with rapid burial. The Cr content between 205 and 1368 ppm and the important Ni and Cu enrichments indicated that the original OM flux in the Lake Fonjak was relatively important but partially lost after deposition. From the Cd × Mn below 0.04 and the Cd/Mo ratio of 0.1, the lake setting was successively changing from the restricted setting to upwelling of nutrient conditions. This was probably due to paleoclimate changes marked by rainfall slowdown and strong wind events respectively during the sub-phase 2 and the phase II. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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