Effects of igneous intrusions on thermal maturity of carbonaceous fluvial sediments: A case study of the Early Cretaceous Strzelecki Group in west Gippsland, Victoria, Australia

This study has investigated the effect of small igneous intrusions on Early Cretaceous carbonaceous fluvial sediments of the Gippsland Basin of south-eastern Australia, based on outcrops in the onshore western part of the basin. Vitrinite reflectance measurements, quantitative mineral phases and cla...

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Bibliographic Details
Published in:International journal of coal geology 2015-11, Vol.152, p.68-77
Main Authors: Aghaei, Hamed, Gurba, Lila W., Ward, Colin R., Hall, Mike, Mahmud, Syed Amir
Format: Article
Language:English
Subjects:
Australia
Carbonaceous sediments
Gippsland Basin
Harmers Haven
Igneous intrusion
Strzelecki Group
Vitrinite reflectance
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Summary:This study has investigated the effect of small igneous intrusions on Early Cretaceous carbonaceous fluvial sediments of the Gippsland Basin of south-eastern Australia, based on outcrops in the onshore western part of the basin. Vitrinite reflectance measurements, quantitative mineral phases and clay mineralogy were carried out on twenty two samples of organic-rich mudstone up to 25m east and west of a 1m wide dyke. Samples of the dyke allowed classification as an alkali-basalt, based on its optical characteristics, and major- and trace-element properties. Background vitrinite reflectance of 0.75%–0.80% [Rmax] in the sediments is elevated up to 6.67% [Rmax] close to the dyke margin, with slightly different patterns on each side of the intrusion. Analysis of seven selected organic-rich mudstone samples shows that they all have very similar XRD patterns, with the main minerals in all cases being quartz, feldspar (mainly plagioclase), chlorite, illite and interstratified illite/smectite. These observations suggest that the thermal maturity of the organic matter in the sediments was locally elevated by heating due to emplacement of the dyke, but no significant changes were observed in host-rock mineralogy that could be related to the heat generated by the dyke and the associated vitrinite reflectance variations. •Twenty two organic-rich mudstone samples were collected on both sides of a dyke.•The thermal maturity of the sediments was due to the emplacement of the intrusive.•No significant trends in mineralogy were observed that can be related to the dyke.
ISSN:0166-5162
1872-7840
DOI:10.1016/j.coal.2015.10.002