TY - JOUR
T1 - Geochemistry of Precambrian sedimentary rocks used to solve stratigraphical problems: An example from the Neoproterozoic Volta basin, Ghana
AU - Kalsbeek, Feiko
AU - Frei, Robert
PY - 2010/1
Y1 - 2010/1
N2 - The Neoproterozoic Volta basin of Ghana (∼115,000 km2; depth up to 5–7 km)
consists of flat-lying sedimentary rocks, mainly sandstones that
unconformably overlie the crystalline basement of the West-African
craton. The stratigraphical column has been subdivided into three main
units, in upward succession the Bombouaka, Oti and Obosum Groups, but
poor exposure has resulted in major disagreements on stratigraphical
correlations and on the areal extents of these units. Geochemical data
(major and trace element concentrations as well as Rb–Sr, Pb and Sm–Nd
isotope data) on siltstones and mudstones, intercalated with the
sandstones from the different units, were used in an attempt to solve
some of these problems. Siltstones and mudstones from the Bombouaka
Group can be unequivocally distinguished from similar rocks from the Oti
and Obosum Groups by higher K2O and Rb, larger Eu anamalies, higher 87Sr/86Sr, and more negative ɛNd
values. Geochemical distinction between samples from the Oti and Obosum
Groups is ambiguous because published geological maps differ with
respect to the relative extents of the Oti and Obosum Groups. Rb–Sr
isotope data, combined with high degrees of correlation between the
concentrations of K and Rb, and Ca and Sr, indicate that mobility of
these elements did not significantly change their concentrations during
surface weathering. The clear geochemical distinction between mudstones
and siltstones from the Bombouaka Group and similar rocks from the Oti
and Obosum Groups is used to solve one of the outstanding controversies
regarding the stratigraphy of the Volta basin.
AB - The Neoproterozoic Volta basin of Ghana (∼115,000 km2; depth up to 5–7 km)
consists of flat-lying sedimentary rocks, mainly sandstones that
unconformably overlie the crystalline basement of the West-African
craton. The stratigraphical column has been subdivided into three main
units, in upward succession the Bombouaka, Oti and Obosum Groups, but
poor exposure has resulted in major disagreements on stratigraphical
correlations and on the areal extents of these units. Geochemical data
(major and trace element concentrations as well as Rb–Sr, Pb and Sm–Nd
isotope data) on siltstones and mudstones, intercalated with the
sandstones from the different units, were used in an attempt to solve
some of these problems. Siltstones and mudstones from the Bombouaka
Group can be unequivocally distinguished from similar rocks from the Oti
and Obosum Groups by higher K2O and Rb, larger Eu anamalies, higher 87Sr/86Sr, and more negative ɛNd
values. Geochemical distinction between samples from the Oti and Obosum
Groups is ambiguous because published geological maps differ with
respect to the relative extents of the Oti and Obosum Groups. Rb–Sr
isotope data, combined with high degrees of correlation between the
concentrations of K and Rb, and Ca and Sr, indicate that mobility of
these elements did not significantly change their concentrations during
surface weathering. The clear geochemical distinction between mudstones
and siltstones from the Bombouaka Group and similar rocks from the Oti
and Obosum Groups is used to solve one of the outstanding controversies
regarding the stratigraphy of the Volta basin.
KW - Geochemistry
KW - Ghana
KW - Precambrian
KW - Sedimentary rocks
KW - Stratigraphy
KW - Volta basin
UR - http://www.scopus.com/inward/record.url?scp=71649094863&partnerID=8YFLogxK
U2 - 10.1016/j.precamres.2009.10.004
DO - 10.1016/j.precamres.2009.10.004
M3 - Article
SN - 0301-9268
VL - 176
SP - 65
EP - 76
JO - Precambrian Research
JF - Precambrian Research
IS - 1-4
ER -