| The provenance and sedimentary system is the fundament of oil and gas exploration. In this paper, on the basis of core observation and rocks section, combined with drilling geological data, well logging and analysis of test results, and regional geological understanding, provenance and characteristics of sedimentary system of the Xuejiahe Formaiton in southern Sichuan Basin has been carried on the detailed study, depositional model is established and Xujiahe Formation 1st Member—6th Member sandstone thickness isoline figure, distribution map of sedimentary facies and other related mapsordrawings.Through the rock section analysis, heavy mineral analysis, combined with the regional components characteristics, Xujiahe Formation considered to be in a multi-provenance area, sedimentary process is controlled by South of Longmen Mountain, Kangdian ancient land, Xufeng Palaeouplift and Central Guizhou Palaeouplift, Longmen Mountain in a tectonic active period of the Late Triassic, magmatic deris and metamorphic deris are provided by the provenance, heavy minerals mainly are zircon, rutile and taltalite; mudstone deris and siltstone deris are provided by Kangdian ancient land and Xufeng Palaeouplift as the older-strata, of which Xufeng Palaeouplift strata is complex, except for ancient strata formed before Silurian, there are also distribute metamorphic strata, providing metamorphic rock deris for the study area, heavy minerals mainly are zoisite and garnet; the Central Guizhou Palaeouplift is a carbonate platform uplift at the Duyun Movement, host rock type is carbonate. The main provenance system is different in the different periods, during the 2nd Member period, the western of study area was affected by the Kangdian ancient land and the Longmen Mountain, the southern was affected by the Xufeng Palaeouplift; supply capacity of Longmen Mountain became stronger during the 4th Member, the affected area of Kangdian ancient land became smaller which make influence of the Qiangzhong Palaeouplift in south appeared; the 6th Member same to the 4th Member, as the center of sedimentary of Longmen Mountain migrated to the southeast, meanwhile, Xufeng Palaeouplift continued provide materials for the study area.From the view of sedimentary types, tidal bedding development in the calcareous siltstone during the 1st Member, reflecting the early period of Xujiahe Formation(1st Member- 3rd Member) Southern Sichuan Basin connected to the sea, mainly developed tidal-flat sediments and marine braided river delta sediments. After the 4th Member into the terrestrial sedimentary facies, mainly were lacustrine dalta. Analysis from the tectonic characteristics, because uplift of the organic belts around the basin, especially the differentiation uplift of the Longmen Mountain and Kangdian ancient land fade away in southwest, the 1st Member to the 6th Member, marine sedimentary facies – transitional sedimentary facies- terrestrial sedimentary facies were developed in the basin. Southern Sichuan Basin affected by its main control material source, the distribution of sedimentary facies belt basically characterized by provenance from the edge to the middle area of the study area, sedimentary facies was also a regular change, developed from the source region: alluvial fan — river(alluvial plains)—delta(shallow lake) model. The study area mainly developed delta facies. Because Kangdian ancient land, Central Guizhou Palaeouplift and Xuefeng Palaeouplift were located in the south margin of the basin, and continued to provide material for the southern basin, formed banded distribution of delta plain—alluvial plain subphase from the southwest to the southeast(north) in the study area.The evolution of tectonic activity around basin is the key factor control the distribution of sedimentary facies, and change of sedimentary basin could be reversed by change of distribution of sedimentary facies, on the influence of transgression and regression in the Late Triassic, sedimentary facies of 1st Member to 6th Member were barrier coast face- marine dalta- lacustrine- lacustrine dalta, showing provenance area was uplift by Indo-china Movement, move forward intermittently, during the 2nd Indo-china Movement, overall uplift of Longmen Mountain with seawater receded from the west, which make the Sichuan Basin became the inland basin. |
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