Research On The Sequence Stratigraphy And Lithofacies Paleogeography Of The Early Paleozoic In Erdos Basin

Based on the investigation of massive field sections and analysis of huge well-log and seismic data, coupled with observation of slices, identification of fossils and previous study, we have conducted integrated research on the sedimentary facies, sequence stratigraphy and lithofacies paleogeography of the early Paleozoic in Erdos basin. This work was partially supported by the program"Research on the Sequence Stratigraphy and Sedimentary facies of the early Paleozoic in Erdos Basin"from Petro China.Carbonate sediments dominated the early Paleozoic in Erdos basin, according to their character, we can distinguish more than 10 sedimentary facies, which are coastal facies, supratidal, intertidal, subtidal, restricted platform, lagoon, open platform, oolitic beach, platform margin slope, bioherm, slump, shallow-water shelf and deep-water basin.28 sequences can be recognized during this interval in Erdos basin, 10 from Cambrian with an average age 3.8 Ma, 18 from Ordovician with an average age 1.9 Ma. 2 Mesosequences were divided at the boundary of Liangjiashan Fm. and Majiagou Fm, the early Paleozoic was composed of 1 complete Megasequece.The Paleozoic succession in Erdos basin can be correlated between western, southern and eastern margin during the Cambrian period due to the similar sea-level change. Coastal clastic facies dominated the early Cambrian. With the sea-level rise in middle Cambrian, it turned to supratidal facies with interbedded sandstone and mudstone in Maozhuang Fm, intertidal-subtidal facies with muddy limestone in Xuzhuang Fm and extended carbonate platform in Zhangxia Fm; Further transgression made the late Cambrian oolitic beach. Whereas, the sedimentary environment became different between east and west since the Ordovician began because of the isolation of Zhongyang block. During the Majiagou period, middle Ordovician, the eastern part of Erdos basin belonged to restricted platform with strong evaporation and three obvious sea-level cycles. however in the western part, sea-level continued to rise with extensive shallow water sediments almost all over the basin. During the late Ordovician, Tectonic movement led to uplift in the east side and strong subside in the west with thick turbidite deposits.We proposed the design and application of a spatial database while using sequence as unit for lithofacies paleogeogrpahy research. Quantificational paleogeography research has been done through the following steps: firstly quantified the strata records with natural layer unit, then extract the secondary information such as sequence thickness, terrigenous detrital content, penecontemporaneous dolostone content, average color, the number of parasequence, the thick rate of lower and upper unit in a parasequence, finally use isoline map for spatial correlation and overlay Analysis. It is proved a viable scientific research method and can be widely used. 28 sequence lithofacies paleogeography map have been drawn through this method.