Geochemo-Petro-Sedimentologic Studies of Upper Cretaceous Lokoja Sandstone: Implication for Paleoenvironment and Paleogeographic Reconstruction

Abstract

Analyzing sections of the Lokoja Sandstone in Nigeria's southern Bida Basin involved 
sedimentary facies, petrographic, textural, morphometric, and geochemical 
assessments to understand its paleoenvironments, tectonic setting, weathering 
history, source area, and compositional maturity. Sedimentary facies analysis 
identified fifteen lithofacies, organized into four associations (FA-1 to FA-4) based 
on linkages and structures. Skolithos-Cruziana ichnofacies presence indicated 
shallow, moderate to high-energy water environment. Petrographic analysis 
showed varying compositions among lithofacies, mainly quartz, microcline, and 
weathered feldspar. Textural analysis suggested high-energy fluviol-marine 
deposition, supporting a braided stream to nearshore marine system with rounded 
pebbles indicative of long-distance transport. Geochemical data revealed moderate 
SiO2 (77.82%) and Al2O3 (9.53%), elevated K2O (1.62%) and Na2O (1.56%), and low 
Fe2O3, MnO, TiO2, and P2O5. The majority of the sandstones were quartz-arenite, 
with smaller amounts of sublitharenite and subarkose. Ba, Rb, Ta, La/Co, Th/Co, 
La/Th and Eu/Eu* trace element proxies suggested a felsic rock-dominated 
protolith. A passive margin depositional basin was suggested by discriminant plots 
of the tectonic context. Conditions were moderate to very humid to semi-arid, 
according to paleo-weathering studies. A-CN-K diagram, CIA (73.48), CIW (84.14), 
PIA (81.82) and A-CN-K mean values indicated low to moderate compositional 
immaturity and chemical weathering. The study concluded that Lokoja Sandstones 
are immature, originating from faulted granitic blocks at the basin's edge.