Characteristics of  Lithology and Lithofacies  of Kalagang Volcanic Rocks in Malang Depression, Santanghu Basin

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Abstract:  Comparison and classification of volcanic rocks are the premise and foundation of  their lithology research, lithofacies and variation. According to log data, seismic data and pollen analysis, we found that the Kalagang volcanic rocks of Malang depression in Santanghu Basin were thick in the north  and  east, thin in the south  and westareas. The pollen assemblage showed that Gymnosperm pollen had a clear advantage in fern spores and comprised of Genus Cordaitina(Samoilovichi) Hart,Genus Florinites Sehof, WilSonet Bentall, Genus Protohaploxypinus(Samoilovichi) Hart, Genus Striatoabieites(Sedova) Hartpollen. The content of Genus Cordaitina(Samoilovichi) Hart was up to 25.3~54.3%. Compared the log response of Kalagang volcanic rocks and Sedimentary rocks, there performed low natural gamma, low acoustic time, low compensation neutrons, high density and high resistance. The natural gamma value of Kalagang volcanic rocks was lower than Harjiawu Formation, while the resistance was higher. The lithology was mainly maficneutral basalt and andesite, and minor of the tuff, tuffite, volcanic breccia, and so on. Kalagang volcanic rocks of Malang depression can be divided into outbreak phase, overflow phase and volcanic sediment facies. The volcanic activity mainly occurred as a relatively quiet overflow phase, followed by strong eruption phase, and locally developed volcanic sediment facies.