Geochemical characterization of Cretaceous sandstones from the Southern Benue Trough, Nigeria

Abstract

Geochemical studies of sandstones from the three lithostratigraphic successions in the southern Benue Trough of Nigeria were undertaken for a geochemical characterization of the sandstones, and to assess their stratigraphic and source evolution.Major and trace elements data were obtained from outcrop sandstone samples. The SiO 2 /Al 2 O 3 , Fe 2 O 3 /K 2 O ratios and CaO contents have been used to characterize the Cretaceous sandstones into Al-rich and high and low Fe 2 O 3 /K 2 O ratio sandstones. Results indicate that there are geochemical features that display stratigraphic trends across the succession from the Asu River Group, Eze-Aku Group to the proto-Niger Delta succession which may imply a discontinuous evolution from different source terrains of Precambrian and Mesozoic ages that supplied the sediments. The Asu River Group sandstones have lower SiO 2 , Al 2 O 3 , Fe 2 O 3 and higher MgO; the Eze-Aku sandstones have higher TiO 2 , CaO, alkalis and lower MgO while the proto-Niger Delta sandstones have higher SiO 2 , Al 2 O 3 , Fe 2 O 3 and lower alkalis and CaO. These discontinuities signify the influence of tectonic impulses that affected the southern Benue Trough during the Cretaceous time. Changes in ratios of TiO 2 /Al 2 O 3 , Fe 2 O 3 , Cr and Zr suggest an increasingly mafic contribution to the depositional basin with time. The chemical index of alteration increases with time, possibly suggesting that a more intense weathering regime in the hinterland developed with time.

Determination of Aquifer Position Using Electric Geophysical Method

“…The albian ARG is the oldest sedimentary rocks in the study area and they directly overlie the Precambrian basement; They are basically non-marine to marginal marine in character and predominantly cover the eastern part of the study area. The sediments within the ARG consist of impervious shales, limestone with some sandstone intercalation and ammonites (NGSA, 2006;Odigi & Amajor, 2009). The EAG comprises of thick flaggy impervious calcareous and non-calcareous shales, sandy shally limestone and calcareous sandstone (NGSA, 2006;Odigi & Amajor, 2009).…”

“…The sediments within the ARG consist of impervious shales, limestone with some sandstone intercalation and ammonites (NGSA, 2006;Odigi & Amajor, 2009). The EAG comprises of thick flaggy impervious calcareous and non-calcareous shales, sandy shally limestone and calcareous sandstone (NGSA, 2006;Odigi & Amajor, 2009). The EAG is overlain by the post santonian NASF which occupy most of the western parts of the study area.…”

“…The EAG is overlain by the post santonian NASF which occupy most of the western parts of the study area. Sandstone, mudstone and shale are the major lithologic units in the formation (NGSA, 2006;Odigi & Amajor, 2009). The shales are often carbonaceous and pyritic which is suggestive of sediments that were deposited in a poorly oxygenated shallow water environment with restricted air circulation (Peters et al, 1987).…”

Geochemistry of source rocks in the Es3 and Es4 members in the Shahejie Formation of the Western Depression, Liaohe Oilfield, China

“…Organic matter is the material basis for hydrocarbon generation, so the abundance and distribution of organic matter are the most basic indices for evaluating source rocks (Sharaf, 2003;Liu Luofu and Jin Zhijun, 2005;Zhu Guangyou et al, 2005;Li Zhoubo et al, 2007;Odigi and Amajor, 2009). TOC values were utilized to evaluate organic matter contents, and 642 field samples were analyzed while data from 334 wells were processed by using the technology of transforming logging data into TOC (Yue Bingshun et al, 2005;Zhang Han and Zhu Guangyou, 2007;Zhang Zhengying et al, 2004).…”

Geochemical characteristics and geological significance of the Neoproterozoic carbonates from northern Anhui Province, China

“…La-Th-Sc and Th-Sc-Zr/10 diagrams designed by Bhatia and Crook (1986) for shales were used in some literature for discrimination of tectonic background of mudstone and sandstones (Odigi and Amajor, 2009). However, they can not be used directly for tectonic background discrimination of carbonates.…”