Warta Geologi, Vol. 46, No. 2, August 2020, pp. 69–75

Geological interpretation of Spectral Gamma Ray (SGR) of
fine clastic rocks from the Nyalau Formation central Sarawak, Malaysia

Walaa Elnasir Ibrahim*, Ahmed Mohamed Ahmed Salim, Chow Weng
Sum, Eswaran Padmanabhan

Universiti Teknologi PETRONAS, Department of Geoscience,
32610 Seri Iskandar,

Perak Darul Ridzuan, Malaysia

* Corresponding author email address: umshamswalaa@gmail.com

Abstract:
The increasing interest for shale gas exploitation as unconventional resources
is aided by the new technological advancement that has marked the pathway to
explore shale gas for local utilization and national economy in Malaysia. The
Nyalau Formation which is an Oligocene – Middle Miocene in age. This article
attempts to analyze the depositional environment, Gamma Ray, clay mineralogy
and evaluate the relationship between uranium concentration and total organic
carbon (TOC) of the Nyalau Formation comprise of shales and mudstones using
Spectral Gamma Ray (SGR). The results from SGR indicate to compose principally
kaolinite and smectite, XRD analysis and FESEM reveals the presence of illite.
The Th/U ratios vary between 0.57 and 0.85 indicate formation is deposited in a
reduced marine environment. Calculated API reveals the ability of the clay
minerals to absorb uranium and thorium through cation exchange capacity. The
relationship between the cross plot of TOC%/U shows positive correlation.

Keywords:
Nyalau Formation, ctral Gamma-Ray log (SGR), clay minerals, organic matter,
Shale, Mudstone

DOI :
https://doi.org/10.7186/wg462202005

ISSN
0126–5539; e-ISSN 2682-7549