Spectral gamma-ray measurements - a key for sequence stratigraphy in black shales: example Posidonia Shale (Lias ɛ, Toarcian, SW-Germany)

ABSTRACTTwelve specimens of early Toarcian Mecoptera and Diptera from the vicinity of Wolfsburg were investigated for the present study. The material was found during house building activities in the 1980s at the locality Große Kley in Mörse, an urban district of the city of Wolfsburg, Lower Saxony, Germany. The specimens were found in calcareous nodules of the Harpoceras falciferum Zone that occur within the Liassic black shales (Posidonia shale). Six specimens of Mecoptera, five belonging to the family Orthophlebiidae and one belonging to the Bittacidae, and six representatives of the following Diptera families were identified: Ptychopteridae, Limoniidae, Anisopodidae and the superfamily Mycetophiloidea. The fossil fauna of Wolfsburg is similar to that of other early Toarcian sites in Germany, described by Handlirsch (1906, 1939), Bode (1905, 1953) and Ansorge (1996) from Braunschweig, Dobbertin and Grimmen. Two new species are described, Mesorhyphusulrichi sp. nov. (Anisopodidae) and Archipleciomima germanica sp. nov. (Mycetophiloidea).

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Spectral gamma ray characterization of high resolution sequence stratigraphy: examples from Upper Carboniferous fluvio-deltaic systems, County Clare, Ireland

Geological Society London Special Publications ◽

10.1144/gsl.sp.1996.104.01.03 ◽

1996 ◽

Vol 104 (1) ◽

pp. 25-35 ◽

Cited By ~ 19

Author(s):

S. J. Davies ◽

T. Elliott

Keyword(s):

High Resolution ◽

Sequence Stratigraphy ◽

Gamma Ray ◽

Upper Carboniferous ◽

High Resolution Sequence Stratigraphy

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A high-resolution, multiproxy stratigraphic analysis of the Devonian–Carboniferous boundary sections in the Moravian Karst (Czech Republic) and a correlation with the Carnic Alps (Austria)

Geological Magazine ◽

10.1017/s0016756812001057 ◽

2013 ◽

Vol 151 (2) ◽

pp. 201-215 ◽

Cited By ~ 36

Author(s):

TOMÁŠ KUMPAN ◽

ONDŘEJ BÁBEK ◽

JIŘÍ KALVODA ◽

JIŘÍ FRÝDA ◽

TOMÁŠ MATYS GRYGAR

Keyword(s):

Czech Republic ◽

Gamma Ray ◽

Sensu Stricto ◽

Black Shales ◽

Element Geochemistry ◽

Carnic Alps ◽

Sea Level Fluctuations ◽

Stratigraphic Analysis ◽

Carbon Isotope Excursion ◽

Moravian Karst

AbstractA multidisciplinary correlation of the Devonian–Carboniferous (D–C) boundary sections from the Moravian Karst (Czech Republic) and the Carnic Alps (Austria), based on conodont and foraminifer biostratigraphy, microfacies analysis, field gamma-ray spectroscopy (GRS), carbon isotopes and element geochemistry, is presented in this paper. The study is focused on the interval from the MiddlePalmatolepis gracilis expansaZone (Late Famennian) to theSiphonodella sandbergiZone (Early Tournaisian). In Lesní lom (Moravian Karst), a positive δ13C excursion in theBisphatodus costatus–Protognathodus kockeliInterregnum from a distinct laminated carbonate horizon is correlated with a carbon isotope excursion from the Grüne Schneid section of the Carnic Alps and is interpreted as the equivalent of the Hangenberg black shales and a local expression of the global Hangenberg Eventsensu stricto. Higher up at both sections, a significant increase in the terrigenous input, which is inferred from the GRS signal and elevated concentrations of terrigenous elements (Si, Ti, Zr, Rb, Al, etc.), provides another correlation tieline and is interpreted as the equivalent of the Hangenberg sandstone. Both horizons are discussed in terms of relative sea-level fluctuations and palaeoceanographic changes. Recent studies show that conodont biostratigraphy is facing serious problems associated with the taxonomy of the first siphonodellids, their dependence on facies and discontinuous occurrences of protognathodids at the D–C boundary. Therefore, the correlative potential of geochemical and petrophysical signatures is high and offers an alternative for the refining of the problematic biostratigraphic division of the D–C boundary.

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Identification of early Llandovery (Silurian) anoxic palaeo-depressions at the western margin of the Murzuq Basin (southwest Libya), based on gamma-ray spectrometry in surface exposures

GeoArabia ◽

10.2113/geoarabia1103101 ◽

2006 ◽

Vol 11 (3) ◽

pp. 101-118 ◽

Cited By ~ 1

Author(s):

Nuri Fello ◽

Sebastian Lüning ◽

Petr Štorch ◽

Jonathan Redfern

Keyword(s):

Black Shale ◽

Gamma Ray ◽

Regional Distribution ◽

Uranium Content ◽

Organic Content ◽

Black Shales ◽

Gamma Ray Spectrometry ◽

Hydrocarbon Source Rock ◽

Western Margin ◽

Anoxic Event

ABSTRACT Following the melting of the Gondwanan icecap and the resulting postglacial sea-level rise, organic-rich shales were deposited in shelfal palaeo-depressions across North Africa and Arabia during the latest Ordovician to earliest Silurian. The unit is absent on palaeohighs that were flooded only later when the anoxic event had already ended. The regional distribution of the Silurian black shale is now well-known for the subsurface of the central parts of the Murzuq Basin, in Libya, where many exploration wells have been drilled and where the shale represents the main hydrocarbon source rock. On well logs, the Silurian black shale is easily recognisable due to increased uranium concentrations and, therefore, elevated gamma-ray values. The uranium in the shales “precipitated” under oxygen-reduced conditions and generally a linear relationship between uranium and organic content is developed. The distribution of the Silurian organic-rich shales in the outcrop belts surrounding the Murzuq Basin has been long unknown because Saharan surface weathering has commonly destroyed the organic matter and black colour of the shales, making it complicated to identify the previously organic-rich unit in the field. In an attempt to distinguish (previously) organic-rich from organically lean shales at outcrop, seven sections that straddle the Ordovician-Silurian boundary were measured by portable gamma-ray spectrometer along the outcrops of the western margin of the Murzuq Basin. It was found that the uranium content of the shales remained largely unaltered by the weathering processes and could therefore be used as a valid proxy parameter to distinguish between pre-weathering organically rich and lean shales. It is now possible to identify and map-out the thickness and approximate organic richness of the black shale using measurement of uranium radiation. Five of the newly measured sections are characterised by uranium-enriched intervals, representing areas of earliest Silurian palaeo-depressions. Major uranium peaks are absent in the spectral gamma-ray curves of two other sections, which are interpreted to mark earliest Silurian palaeo-highs. The new data on the distribution of Silurian black shales from the outcrop belt was integrated with subsurface data from the Murzuq Basin. The resulting map of the distribution of black shales may help with predictions of the occurrence of this unit in less well-explored areas of the basin. Graptolite biostratigraphic data suggests that the anoxic event centred on the middle Rhuddanian, with more oxygenated conditions and onset of deposition of organically leaner shales having commenced sometime during the late Rhuddanian. The presence of anoxic palaeo-depressions during the earliest Silurian within the Ghat outcrop belt indicates that the Tihemboka High at the western margin of the Murzuq Basin could not have been a positive structure during this time.

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Identification of Clay Mineral Content Using Spectral Gamma Ray on Y1 Well in Karawang Area, West Java, Indonesia.

Journal of Geoscience Engineering Environment and Technology ◽

10.25299/jgeet.2020.5.3.4504 ◽

2020 ◽

Vol 5 (3) ◽

pp. 153-160

Author(s):

Rahmat Catur Wibowo ◽

Alia Puja Pertiwi ◽

Suci Kurniati

Keyword(s):

Source Rock ◽

Mineral Content ◽

Gamma Ray ◽

Clay Content ◽

Black Shales ◽

Reducing Conditions ◽

Natural Gamma ◽

Redox Indicator ◽

U Value ◽

Low K

Northwest Java Basin (NWJB) is one of the proven hydrocarbon basins in Indonesia. The scope of this paper will focus onthe shales and sandstone interval within Y1 well in Karawang area, NWJB, Indonesia.A cored interval from Y1 well was chosen for an investigation of the clay minerology for the gamma-ray activity and with the purpose of determining how the Spectral Natural Gamma (SNG) log could be used as an indicator of source rock and reservoir quality. The Th/U as a redox indicator is used to assert that the shales are of anoxic conditions of shallow marine environments. Despite the relatively high insoluble Th values (60-74.15) ppm, the presence of U in substantial amounts, which only occurs in reducing conditions where it is preserved as a lower insoluble valence (U4+) explains for the low Th/U values ranging between (5.8-7.1) ppm/ppm. The overall Th/U value of the evaluated shales remain less than 25, where Th/U <25 is suggestive of marine sediments, whereas Th/U <4 is indicative of marine black shales of reducing conditions. Although no linear relationship was found between clay content and K, Th, or U, the K content characteristic three discrete reservoir characteristic (RC). The RC-I has predicted a matrix-supported texture with the highest K signal, illite and illitised kaolinite are roughly equal in importance as source of K. The RC-II has predicted a grain-supported texture with intermediate K content. K-feldspar, mica and illite as the main sources. The RC-III has predicted have a low K content with grain-supported texture and most of the K is hosted in feldspar. Overall, the laboratory measurements appear to be applicable to the log data, and, using SEM or XRD, the detail facies subdivision can be extended throughout the source rock and reservoir section based on the SNG log.

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