Sedimentary facies of the Silurian tide-dominated paleo-estuary of the Tazhong area in the Tarim Basin

摘要

As the relative sea-level rose,a paleo-estuary was formed by the marine inundation of the braided river incised valley during the period of the lower sub-member of the upper member of the Kalpingtage.formation of the Silurian in the Tarim Basin,west China.Sandstone-mudstone rhythmite, tidal structures and bimodal cross-bedding are common in these deposits,indicating that tides played a significant role in generating the sedimentary structures and the estuary type was tide-dominated.Five depositional facies were grouped:tidal river,sandy and muddy subtidal flat,tidal flat,tidal bar,tidal channel on the basis of lithology,electric properties,rhythmicity,sedimentary structure,fossil and the contact relationship.The sediment distribution showing first fining seaward and subsequent coarsening seaward from head to mouth,implies the two sediment sources in the paleo-estuary.The paleo-estuary of the Tarim Basin is very different from other representative estuaries.The most important distinction is that there are two adjacent estuaries joined by tidal flat onshore and by sandy and muddy subtidal flat in the sea at the same time,while the others only have one.So the Tazhong paleo-estuary shows a good architecture model for the tide-dominated estuary.