The Characteristics Of Sequence Stratigraphy And The Responses To Relative Sea Level Change, Northern Carnarvon Basin, Australia

The strata of late Oligocene to mid Miocene are dominated by carbonate sediment and interbeded clastic sediment in Northern Carnavon Basin, North West of Australia. The character of the strata is progradational clinoform sediment from southeast to northwest. The progradational clinoform sediment is considered as a very good model to investigate the relationship between sedimentary system and relative sea level change.Based on thred dimensional seismic data, well log data, well core data, paleontology and paleobathemetry, we recognized 6 third-order sequence boundaries (5 third order sequences: SQ1-SQ5) and 21 four-order sequence boundaries. We analyzed the the character of each sequence, including inner reflection, geometry and special geological phenomena. Then we generated TWT isopach maps of each sequence and depict the depocenter of each sequence. All sequences exhibit strike-oriented depocenters prograding northwest.We apply seismic attributes extraction techniques to trace the boundaries of different lithology and facies, and also use seismic data and well data to construct the sedimentary facies distribution maps. From southeast to northwest, sediment facies of objective area are divided into carbonate platform ramp face, carbonate platform margin face and shallow sea basin face. Carbonate platform ramp face is divided into inner ramp sub-face, middle ramp sub-face and outer ramp sub-face. Carbonate platform margin face is divided into front of clinoform sub-face and toe of clinoform sub-face.According to the method of making relative sea level change chart from Vail et al. (1977), we chose one seismic profile to build sea level relative chage curve. The chart shows relative sea level is low in SQ2 and the lower part of SQ3, but high in the higher part of SQ3 and SQ4. Then we compare this relative sea level change curve to the paleobathymetry of G7. The trend of these two curves mathced generally well except some parta. The relative sea level change chart can help us to understand the mechanism of developing of geological phenomena on sequence boundaries.During the falling period of relative sea level, small gullies developed during SQ2. We propose that water derived from compaction can cause such features. The mounds grew on SB3 and overlying strata may represent biogenic buildups. Although SQ4 developed during the rising period of relative sea level, this sequence had several short term relative rise and fall cycles. From the chart, we observed that SB4 located in relative sea level fall period. The step-like discontinuity on SB4 stands for a rare example of a buried and preserved sea cliff, generated by wave erosion at ambient sea level. SQ5 was in the period of relative sea level fall and shallow paleobethmetry. We suggest that incisions in SQ5 may indicate two geological effects caused this phenomenon: gravity flow along progradation direction and contour current along strike orientation.