The Palaeogomorphic Features Of The Silurian System In The Northern Tarim Basin And Its Control On Sedimentary System

Northern Tarim uplift is a first grade tectonic belt located at the north of Tarim basin.Under the influence of the late Jialidong structure uplift activity,the paleogeomorphology of Silurian system constantly changed and gradually transformed from an microlong slope zone in early stage to a large slope zone,and the topographic gradient continued to increase.Through rebuilding the paleogeography of the Silurian system and reproducing the process of paleotopography evolution,this paper aims to enhance the study the control of paleotopography upon the sequence and sedimentary system.Based on multiple related therories including sedimentology,sequence stratigraphy,geomorphology and seismic geomorphology,this paper makes use of the core data,logging data and seismic data,combines the calculation of single well denudation and earthquake virtual extrapolation method to complete the qualitative and quantitative calculation of the denudation of key sequence interfaces in study area and determines the range of original boundary.At the same time,this paper uses logging data and formation reclamation method to complete compaction correction and paleo-thickness recovery.Combining the erosion thickness restoration and compaction thickness restoration,this paper recontructs the paleogeomorphology of the main sedimentary period of Silurian system,analyzes and elaborates the characteristics and evolution process of paleotopography.On the basis of above research findings,this paper explores the control of paleogeomorphology on the development of sedimentary system.Through the study of the paleogeomorphology of the Silurian system and its control on the sedimentary system,this paper obtains following understanding: during the early sedimentary period of Silurian system in study area,the depth of Tarim basin is between 270-1620 m,and the paleogeomorphology is mainly composed of a low amplitude uplift slope and a sag area.Then,affected by the equilibrium uplift activity of late Caledonian,the gradient of paleogeomorphology continued to increase.At the late Silurian sedimentary period,depth of the basin was 1-2.2km,and the southeastern study area was a sag.The slope shrank to the northwest with narrowing range.The original sedimentary boundary of Silurian system was 3-15 km away from the north of its current denudation line.The original sedimentary range was wide in the west,while it was relatively smaller in the middle and east area.The denudation thickness is between 500-2000 m,and the denudation thickness in the northeastern part is largest with the maximum depth of 1789 m.The average compaction rate obtained after compaction correction is 43%,and the compaction rate in the western area is relatively larger with the biggest compaction of 678 m.The paleo-geomorphology pattern with constantly increasing topography gradient and slope controls the developmental characteristics of sequences and sediments of the whole Silurian system: the sequence is aepicontinental sea shallow slope type sequence,and it is composed of TST and HST without LST;the main sedimentary system is tidal flat(or shore shore)-continental shelf facies.