Application of U–Pb detrital zircon geochronology to drill cuttings for age control in hydrocarbon exploration wells: A case study from the Rukwa Rift Basin, Tanzania

Abstract

Precise dating and correlation of drilled wells through continental successions is challenging for hydrocarbon exploration, especially where preservation and recovery of age-diagnostic fossils is poor. As a complement or alternative to biostratigraphic dating we demonstrate the effectiveness of U-Pb geochronology via laser ablation-inductively coupled plasma-mass spectrometry on detrital zircon from well cuttings. In basins with syndepositional volcanic input, the youngest zircons in a stratigraphic interval can refine and serve as a proxy for the age of deposition. We demonstrate the reliability of this technique when applied to hydrocarbon exploration wells by analyzing drill cuttings through a continental interval of the Galula-1 well in the Rukwa Rift Basin, East African rift system, Tanzania, which previously yielded conflicting biostratigraphy results. The lower third of the well section reveals a late Miocene to Pliocene up-hole younging trend in the youngest detrital zircon populations, which matches new radioisotopic ages on volcanic tuffs from a correlative outcrop section. This is followed by an interval with recycled young zircons, followed by a zircon-free interval, interpreted to correspond to changes in magma composition of the nearby Rungwe volcanic province. This study provides the first radioisotopic age constraints for the Lake Beds in the Rukwa rift

Drainage reorganization and Laramide tectonics in north‐central New Mexico and downstream effects in the Gulf of Mexico

“…Detrital zircon geochronology can be used to establish the maximum depositional age (MDA) of sedimentary rocks (Dickinson & Geherls, ). This method produces MDAs closest to the depositional age of the rocks when there is proximal and contemporaneous volcanism within the catchment (Coutts, Matthew, & Hubbard, ; Hilbert‐Wolf et al, ).…”

“…(a) The absolute youngest age possible is the youngest single grain (YSG, Dickinson & Gehrels, ). (b) The weighted mean of the three youngest grains (WM), can provide a more statistically robust approach but lacks a robust cut‐off criterion for older ages (Dickinson & Gehrels, ; Hilbert‐Wolf et al, ). (c) Youngest 1σ grain cluster (YC1σ) calculates MDA by identifying the youngest cluster of grains with overlapping 1σ uncertainty ( n ≥ 2) and determining their weighted mean (Dickinson & Gehrels, ).…”

Kinematics of Active Deformation in the Malawi Rift and Rungwe Volcanic Province, Africa

“…There are few constraints on the timing of basin initiation. U‐Pb dating of detrital zircons in the post‐Karroo sequences of the Rukwa rift indicates the existence of a lake basin by 8.7 Ma (Hilbert‐Wolf et al, ). Extrapolation of modern depositional rates from drill core data to decompacted sedimentary sequences leads to an estimate of ~7 Ma (McCartney & Scholz, ; Scholz & Lyons, ), and structural and stratigraphic patterns onshore indicate that the present‐day fault architecture developed after about 8 Ma (e.g., Ebinger et al, ; Fontijn et al, ).…”

Thermochemical Modification of the Upper Mantle Beneath the Northern Malawi Rift Constrained From Shear Velocity Imaging

“…Magmatism in the Rungwe volcanic province initiated by 19 Ma (Mesko et al, 2016;Mesko, 2019) and possibly as early as 25 Ma (Roberts et al, 2012). The age of rift basins in the Western Rift are poorly known, but the ages of Rungwe volcanism suggest that volcanism may have preceded the estimated onset of faulting along the Livingstone border fault bounding the North basin at ~8.6 Ma (Ebinger et al, 1989) and to renewed subsidence in the Rukwa rift at 8.7 Ma (Hilbert-Wolf et al, 2017). Active magma reservoirs are thought to be present beneath parts of the RVP (Fontijn et al, 2012).…”