Study of Sequence Stratigraphy in Mesozoic Southeast Tarim Foreland Basin

ZHOU Qi; WANG Jian guo; DU Hong lie

Tarim basin is a large,complex and multicycle basin, and has a complex geologic evolution history.Nevertheless,little is known about the geology of the Southeast Tarim basin.With the development of oil, people pay more attention to Mesozoic stratum exposed on basin margin.There develop Jurassic terrestrial coal measure strata and Cretaceous red beds.The present paper aims at analysing Jurassic system by use of sequence stratigraphy to study Mesozoic stratum distribution,contrast,sedimentary character,and to build up pattern of sequence stratigraphy.Using unconformity as main mark of different sequences,it shows Jurassic makes up a second order sequence,which represents a structural subsidence uplift process.Inside Jurassic,lacustrine invasion onlap and basinmargin exposure truncation can differentiate the third order sequence,which represents a relative water invasion water regression process. Sequence I subface is a regional erosion unconformity.It because of appearance on piedmont thrust belt on field outcrop is fault contact and bottom development incomplete.The sequence consists of alluvial fan facies or braided river facies with positive cycle.Its storage condition is good.Sequence 2 subface is lacustrine invasion onlap surface land alluvial fan facies is replaced by delta facies.Delta plain consist of braided river sequence with positive cycle.Delta front and lacustrine facies consist of prograding sequence with counter cycle.The sequence have good storage condition.Its upper part is a coal measure strata and it has fairly good oil source rock.Sequence 3 subface is lacustrine invasion onlap surface.The sequence consists of delta facies with counter cycle and rhythmic unit of lacustrine facies.At this moment lacustrine invasion is the largest.It takes shape of condensed section of deep lake facies.That is good oil source bed and overlying formation.Sequence 4 subface is basin margin truncation surface.That consists of river facies with positive cycle.At this moment,the lake is with small scope,climate change arid and hot.Sequence 5 subface is basin margin truncation surface.Its top surface is regional unconformity,which consists of alluvial fan facies with positive cycle in arid climate.It can become good reservoir that develops secondary dissolved porosity. Jurassic in southeast Tarim basin distributes extensively with a great thickness.It has good hydrocarbon, potential,and is also major hydrocarbon bearing sequence.In Sequence 3,condensed section of deep lake and semi deep lake is the most favorable oil source rock.Moreover,it is a regional overlying formation.Sequence 1 and 2 one of the most profitable exploration horizons since sequcence 5 and lower Cretaccous Kezileqiapu Formation is reservoir,and lacustrine shale and gypsum layer in Kezileqiapu Formation is its caprock.

Qinhuangdao Branch of Petroleum Geology Institute, Qinhuangdao Hebei 066004

Received Date: 1999-05-19

Rev Recd Date: 1999-07-21

Publish Date: 2000-08-10

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Abstract: Tarim basin is a large,complex and multicycle basin, and has a complex geologic evolution history.Nevertheless,little is known about the geology of the Southeast Tarim basin.With the development of oil, people pay more attention to Mesozoic stratum exposed on basin margin.There develop Jurassic terrestrial coal measure strata and Cretaceous red beds.The present paper aims at analysing Jurassic system by use of sequence stratigraphy to study Mesozoic stratum distribution,contrast,sedimentary character,and to build up pattern of sequence stratigraphy.Using unconformity as main mark of different sequences,it shows Jurassic makes up a second order sequence,which represents a structural subsidence uplift process.Inside Jurassic,lacustrine invasion onlap and basinmargin exposure truncation can differentiate the third order sequence,which represents a relative water invasion water regression process. Sequence I subface is a regional erosion unconformity.It because of appearance on piedmont thrust belt on field outcrop is fault contact and bottom development incomplete.The sequence consists of alluvial fan facies or braided river facies with positive cycle.Its storage condition is good.Sequence 2 subface is lacustrine invasion onlap surface land alluvial fan facies is replaced by delta facies.Delta plain consist of braided river sequence with positive cycle.Delta front and lacustrine facies consist of prograding sequence with counter cycle.The sequence have good storage condition.Its upper part is a coal measure strata and it has fairly good oil source rock.Sequence 3 subface is lacustrine invasion onlap surface.The sequence consists of delta facies with counter cycle and rhythmic unit of lacustrine facies.At this moment lacustrine invasion is the largest.It takes shape of condensed section of deep lake facies.That is good oil source bed and overlying formation.Sequence 4 subface is basin margin truncation surface.That consists of river facies with positive cycle.At this moment,the lake is with small scope,climate change arid and hot.Sequence 5 subface is basin margin truncation surface.Its top surface is regional unconformity,which consists of alluvial fan facies with positive cycle in arid climate.It can become good reservoir that develops secondary dissolved porosity. Jurassic in southeast Tarim basin distributes extensively with a great thickness.It has good hydrocarbon, potential,and is also major hydrocarbon bearing sequence.In Sequence 3,condensed section of deep lake and semi deep lake is the most favorable oil source rock.Moreover,it is a regional overlying formation.Sequence 1 and 2 one of the most profitable exploration horizons since sequcence 5 and lower Cretaccous Kezileqiapu Formation is reservoir,and lacustrine shale and gypsum layer in Kezileqiapu Formation is its caprock.

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Reference (11)

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Study of Sequence Stratigraphy in Mesozoic Southeast Tarim Foreland Basin

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