A PRELIMINARY PALAEOCLIMATIC ASSESSMENT AND GEOCHEMICAL WEATHERING CHARACTERISTICS OF ISAN CLAYS SOUTHWESTERN NIGERIA: IMPLICATIONS FOR PALAEOWEATHERING PROXY

S. C. Odewumi

Abstract


Isan clay is located within the Precambrian Basement rocks in southwestern sector of the Nigerian Basement Complex. The present study focuses on a preliminary Palaeoclimatic assessment of Isan clay using chemical weathering indices and geochemical climofunctions. Four (4) clay samples from Isan area were collected from a mining pit and subjected to Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) analysis. Chemical Index of Alteration (CIA) ranges from 85.85 to 90.14, Chemical Index of Weathering (CIW) varies from 93.81 to 96.58 %, Plagioclase Index of Alteration (PIA) ranges from 93.17 to 96.30 and Vogt’s Residual Index (V) varies from 8.25 to 11.34 respectively. The values of CIA and CIW are suggestive of weathering. The plots of CIA, CIW, PIA and V against depth indicate that Isan clays did not progressively increase from the deepest sample to the topmost sample suggesting other processes of alteration such as hydrothermal alteration in addition to weathering because if weathering predominates, CIA, CIW, PIA and V values decrease with depth. Climofunction parameters such as Mean Annual Precipitation (MAP) and Mean Annual Temperature (MAT) were computed. MAP has values varying from 1300.6 to 1340.1 mm/year and the average annual precipitation from 2001 to 2010 in Ekiti State was about 1334 mm. It is suggestive that similar precipitation with the present annual rainfall produced Isan clay. MAT values of Isan clay ranges from 12.11 to 13.29 (°C) and average annual temperature from 2001 to 2010 in Ekiti State was 25.1 (o C). This attests that the climate during clay formation was colder than the present climate conditions.

Keywords: Isan Clay, Weathering, Palaeoclimatic, Indices, Climofunction


Full Text:

PDF

Refbacks

  • There are currently no refbacks.