. Bulletin of the British Museum (Natural History), Mineralogy. SEDIMENTATION IN NORTHERN CARDIGAN BAY CLAYS 103. FELDSPARS 10 QUARTZ Fig. 36. Cardigan Bay sediments classified according to the basic Pettijohn (1957) scheme. Samples plotted here are based on X-ray data for end-member assignment (cf. Moore, 1963). Note that in this system most of the bay deposits are classified as quartzose sands. scheme is ideally suited for comparing trace element data and other mineralogically related parameters, particularly when sediment terminology alone is reported, and it has been used for classifying o
. Bulletin of the British Museum (Natural History), Mineralogy. SEDIMENTATION IN NORTHERN CARDIGAN BAY CLAYS 103. FELDSPARS 10 QUARTZ Fig. 36. Cardigan Bay sediments classified according to the basic Pettijohn (1957) scheme. Samples plotted here are based on X-ray data for end-member assignment (cf. Moore, 1963). Note that in this system most of the bay deposits are classified as quartzose sands. scheme is ideally suited for comparing trace element data and other mineralogically related parameters, particularly when sediment terminology alone is reported, and it has been used for classifying other Recent, shallow water sediments (Moore, 1963). A descriptive petrographic term, not necessarily an entire classification scheme, which may be used to modify the textural description, is useful, particularly for providing more complete descriptions and for signifying the abundance of lithic grains relative to quartz grains. In keeping with this need, a compositional modifier based on petrographic determinations is suggested. This is based on the ratio of quartz grains to lithic grains. A ratio of 9-0 or greater signifies quartzose ; between 9-0 and 3-0, sub-lithic ; less than 3-0, lithic. In the absence of appreciable quantities of detrital feldspar and clay, this modifier suffices to define the general petrographic/ compositional character of the deposit. Used in conjunction with the textural and sorting terms, it provides a descriptive terminology readily understood by Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original British Museum (Natural History). London : BM(NH)
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