Study on internal-wave and internal-tide deposits of the third member of the Lower Cambrian Balang Formation at Yangjiaping, Shimen

Abstract：The third member of the lower Cambrian Balang Formation at Yangjiaping, Shimen, Hunan Province consists mainly of dark-gray, gray-green laminated to thinly bedded silt-bearing hydromica mudstones and muddy siltstones intercalated with lenticular and striped siltstones, whose sedimentary environment was a slope environment. Cross laminations are well developed in lenticular and striped siltstones of the middle and upper Parts of the third member, whose laminae are inclined not only bi-directionally up- and down the slope, but also uni-directionally which correspond to up-or down-slope directions. The characteristics indicated that lenticular and striped siltstones should not be contourites or turbidites, but should be formed by alternating up- and down-slope currents produced by internal waves and internal tides. This is the first example of internal-wave and internal-tide deposits found in the Cambrian.