The meso-scale coarse-grained packets, by definition (see Section
4 .9 .2 .1 ), are individual architectural elements which in the Nalneset section, are oblique to the overall section palaeocurrent trend and have an overall sheet-like nature. (For this study, the meso-scale fine-grained packets are essentially treated as the 'background' deposition, punctuated by metronomic pulses of coarse-grained sedimentation, discussed
below). These sheets can be considered as third-order Sheet (SH)
elements using the architectural element scheme proposed by Pickering et al. (1995). The lowermost eight meso-scale coarse-grained packets form relatively simple parallel-sided units of relatively few
amalgamated sand-rich beds. Some of these packets (Nos. 2 and 8; see Enclosure 4.11) pass out laterally or undergo lateral facies changes and hence could be considered to form 'lenses', though in no examples are both terminations observed.
Meso-scale coarse-grained packet no 9, as has been noted
previously, marks the change in depositional style of the system. It has an overall sheet-like nature, but is notably non-parallel-sided, formed by a series of coalescing or amalgamated small-scale sheet- and lens-like packets. Following deposition of packet 9, subsequent meso-scale coarse grained packet geometry is apparently broadly sheet-like, and, as has been shown on Enclosure 4.11, these sheets are assumed to extend across the entire 3.5 km-long Nalneset section. It is possible that the lateral thickness variations of these packets means that some of them have elongate 'cigar' shapes or possess a repeated 'pinch-and-swell'
appearance but these packets are generally insufficiently exposed to be specific. In detail, some of the more well-exposed examples show
overall amalgamation and compensation of thickness in relation to other meso-scale coarse-grained packets (Enclosure 4.4), but exposure is lacking elsewhere.
4.13 P A C K E T S: A SUMMARY
A summary table of the primary sedimentary, geometrical and architectural characteristics of both the fine-grained and coarse-grained meso-scale packets is presented in Figure 4.32. These details have been summarised in a schematic, generic sketch showing the key important factors of sheet-like, sedimentary packet deposition in the Nalneset section of the Kongsfjord Formation (Figure 4.33).
4.14 GAMMA RAY SPECTROSCOPY
4.14.1 Introduction
A pilot study was undertaken to investigate the gamma ray signature of the Nalneset section sediments. This was unfortunately of only very limited success due to equipment malfunction in adverse weather conditions. However some results were obtained and a brief appraisal of these is presented below.
4.14.2 M ethodology
For a full description of the principles of gamma-ray
spectrometry the reader is referred to Davies (1993) where there is an extensive discussion on the theory of radioactive decay and interaction of gamma radiation with natural materials. Insufficient field time was
available to obtain full spectrographic profiles, so a 'total count' was obtained only. Following the guidelines described in Davies (1993) a large body of surface water was used to obtain the background rate: 17 c.p.s. was obtained from the Barents Sea in August 1993.
Of the 30 logs described for the Nalneset section, only two were sampled before the equipment malfunctioned, and as stated above, these were sampled for total count only. Short profiles from some of the more detailed enclosures were also run (see Enclosures 4.5, 4.7 and 4.9), but again, these are of total count only. The data is presented in an unconverted form, apart from subtraction of the background count. A vertical sample spacing of 50 cm was taken, except for those profiles used on Enclosures 4.5, 4.7 and 4.9 where sample spacing was 20 cm.
The attitude of the detector with respect to outcrop geometry has a vital effect upon results as it is important to maintain an internally consistent dataset (Davies 1993). Most consistent results are obtained by placing the detector normal to the rock surface wherever possible. This proved to be particularly difficult to maintain with the very angular attitude to outcrops at the Nalneset section, and the possible variances caused by these problems should be accounted for when interpreting the data.
4.14.3 Results
Results of the two simple profiles are shown in Figures 4.34 and 4.35. Total count values vary between 10 c.p.s. up to 120 c.p.s. For Log
11, the gamma ray profile was assigned to a simplistic lithological scheme, without reference to the original sedimentological profile. As shown on Figure 4.34, the match between the proposed Ethology and the actual sedimentary profile is good, but much further work needs to be carried out before extensive lateral correlation of sections based on gamma ray profiles can be successfully completed (and this of course will be hindered by the extensive lateral variation of meso-scale coarse grained packets described above).
Total count profiles essentially pick out the concentrations of the three radioactive elements (i.e. potassium, thorium and uranium which comprise the total count) present within alumino-silicate minerals, or in arenites with large concentrations of potassium-rich minerals (e.g. K-
feldspar in immature greywackes). As described in Section 4.6, the sandstones of the Kongsfjord Formation are essentially sub-arkosic, and the presence of abundant potassium-feldspar has been noted. This would certainly affect the gamma ray signature of these sediments in addition to the numerous mud-rich intervals. Indeed, it is noticeable that some of the very thinnest shales did not register upon the gamma ray profile (see Enclosures 4.5, 4.7 and 4.9), but it is important to remember the
problems of outcrop / detector geometry experienced at Nalneset.
4.14.4 Sum mary
Apart from the identification of shales and a simplistic lithological interpretation for Log 11, little real information was obtained from this study, partially as a result of the lack of full spectrographic analyses, and more importantly as a result of equipment malfunction. The Nalneset section remains an ideal section for the interwell-scale examination of the lateral variation in a sandy deep-marine turbidite formation using one of the most common downhole tools. All three sections described in this thesis (Nalneset, Veines and Hamningberg) would benefit from a full spectrographic analysis to conceivably identify section-wide lithostratigraphic markers.
4 . 1 5 THE UPPER MACRO-SCALE SA N D /G R A N U L EST O N E-R IC H