Ocean drilling: Digging in
A new ship and a wave of funding will let scientists drill where they have never been able to drill before, from near the North Pole to the rocks lying beneath Earth's crust. Rex Dalton and David Cyranoski report.
14. ANALYSIS OF NATURAL GAMMA-RAY SPECTRA OBTAINED FROM SEDIMENT CORES WITH THE SHIPBOARD SCINTILLATION DETECTOR OF THE OCEAN DRILLING PROGRAM: EXAMPLE FROM LEG 156 1
Natural gamma-ray (NGR) spectrometry allows estimation of the elemental concentrations of K, U, and Th, which can be used to help interpret sediment composition, provenance, and diagenesis. Spectral data obtained with the NGR multichannel device installed on the Ocean Drilling Program’s multisensor track in 1993 are presented here for the first time. The spectra were divided into 16 energy intervals using a minima search algorithm that defined all peaks observed in 79 sample NGR spectra. The intervals were further subdivided into peak area and background area segments using a peak baseline algorithm, which allows optimal assessment of the usefulness of spectral segments to estimate elemental abundance. Linear regression with laboratory (X-ray diffraction, inductively coupled plasma-mass spectrometry, and instrumental neutron activation analyses) data was used to estimate elemental concentrations of K, U, and Th for each spectral segment. Conservative estimation errors for the best estimator spectral segments are 16%, 30%, and 20% for K, U, and Th, respectively. These errors also reflect analytical errors of the reference data, and the true estimation error may be significantly smaller. Our method suggests that the best K e stimates (± 16%) are obtained using the peak area segment between 1335 and 1580 KeV. In our study, which uses 4-hr counting times, the best U and Th estimates are obtained using peak areas between 1695 and 1885 KeV and 550 and 700 KeV, respectively. If low counting times are used for routine core logging, however, regressions using the total counts of the entire spec trum yield more reliable U and Th estimates because of Poisson’s law, with maximum total errors of about 35% and 23%, respectively. Spectral analysis using 2048-channel data has no advantage over 256-channel analyses, even with the extremely high counting times used for our study. The full character of natural gamma-ray spectra, as revealed by scintillation detectors , can be defined and measured in full detail with 16 energy intervals.
Organic geochemical characteristics and depositional setting of Tertiary organic-rich sediments from onshore Penyu Basin, Malaysia
Due to the poor knowledge of the organic facies characteristics of the eastern Chenor Pahang has made it remain an untapped potential in the Penyu Basin. Therefore, detailed geochemical and petrographic characterization of the Tertiary organic facies of the eastern Chenor area of the Penyu Basin was carried out to characterized its organic matter (OM) source input. Towards achieving the goal, this study focuses on determination of organic matters richness, type and origin as related to their paleoenvironmental conditions of the carbonaceous mudstone and shale using organic petrography combined with organic and inorganic geochemistry. The sedimentary succession is characterized by fine to coarse grained sandstone occurring in association with carbonaceous mudstone and shale in a predominantly fining upward sequence within a lacustrine environment. These facies are generally enriched in organic matter as indicated by the TOC results, hydrocarbon yield (S2) and extractible organic matter (EOM), suggesting significant hydrocarbon generation potential for the area.