DISCUSSION ON THE SEQUENCE STRATIGRAPHY AND SEA-LEVEL CHANGES OF THE KAILI FORMATION AT BALANG, TAIJIANG, GUIZHOU

The Kaili Formation at Balang Village, with the Kaili biota as one of the Burgess shale-type biotas, has been intensively studied in many respects, but little has been reported about sequence stratigraphy. In the Kaili Formation at Balang, the sedimentary rhythms are evidently composed of carbonate mudstone to marlite, or carbonate mudstone to siltstone, or carbonate mudstone to limestone. The Kaili Formation contains mainly shelf systems tract, transgressive systems tract, condensed section and early highstand system tract. In the early depositionary period of the Kaili Formation, the water in the Taijiang area was comparatively shallow, and there were few life-forms. When the sea-level rose, the kind and number of living things began to increase and then constituted the Taijiang biota. When the sea-level reached the top-level, the Taijiang area was in the environment of deeper water, and a large number of floating and swimming organisms, such as medusiform animals Pararotadiscus and bivalve arthropods Tuzoia and trilobites Pagetia, Oryctocephalus, were living here and constituted the beginning of the Kaili biota. Then, the floating organisms gradually decreased when the sea-level was descending. In the later depositionary period of the Kaili Formation, the sea-level was continuously descending so that the water in the Taijiang area gradually shoaled again, and there were few fossils. In the Balang section, the bottom of the condensed section is just consistent with the boundary of the Late-Middle Cambrian. The Early Cambrian trilobites, such as Redlichia, Protoryctocephalus, Bathynotus and others, disappear below the condense section, and the trilobites of Middle Cambrian age, such as Oryctocephalus, Xingrenaspis and others began to appear in the condensed section.