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The Features Of Tertiary Sequence Stratigraphy And Their Controlling Factors In The Hong-Shi Area Of Qaidam Basin

Posted on:2004-01-04Degree:DoctorType:Dissertation
Country:ChinaCandidate:J MuFull Text:PDF
GTID:1100360092996469Subject:Mineral prospecting and exploration
Abstract/Summary:PDF Full Text Request
On the basis of a comprehensive study of the outcrop, core, well log and seismic data, taking the high resolution sequence stratigraphic theory as a direction, the Tertiary sequence stratigraphic system was firstly established in Hong-Shi area in Qaidam basin, which consists of 42sequences, 12 supersequences, 3 supersequence sets and 1 megasequence.Depended on the stacking patterns of 8 typical types of short-term cycles from outcrop and 5 types of those from well logs, 10 types of sequences (middle-term cycles) developed in different sedimentary backgrounds have been recognized. Through analysis of key-seismic-profiles, it can be divided into 4 seismic sequences from Lulehe Formation to Upper Ganchaigou Formation, which probably equal to supersequences. In the same time, seismic stratigraphic framework was also established. Fromconnecting-well profiles that reflect filling characteristic of basin, combining with comprehensive analysis of seismic stratigraphic framework, the sequence stratigraphic framework of Tertiary was established in Hong-shi area and the distribution of sedimentary systems in time and space was deeply discussed. The controlling factors of Tertiary sequences in Hong-shi area are tectonic, climate and their combinations. The tectonic movement controls different types of sequences by controlling subsidence of basement and sediment supply rate. The climate controls different types of sequences by affecting therelations between rainfall and evaporation. Results of study show that there are 7 types of sedimentary facies developed in the Hong-shi area, include alluvial fan facies, subaqueous alluvial fan facies, fluvial facies, delta facies, fan-delta facies, lacustrine facies, and lake-floor fan facies. Besides, the sedimentary facies of Upper Ganchaigou and Lower Ganchaigou Formation were also mapped in supersequences which are the main target strata for exploration. The high resolution sequence stratigraphic framework showed the genetic relationship between the distributions of sedimentary facies and their tectonic settings. The near-source sedimentary systems such as subaqueous alluvial fan and lake-floor fan are often deposed in rise-hemicycles in the steep slope background in the north, the coarse lithology of fan-delta prograded from north to south in fall-hemicycles, and the braided stream facies areformed in the rise-hemicycles in gentle slope background in the south, braided stream facies prograded from sorth to north in the fall-hemicycles,but the lacustrine facies and salt lake facies developed in the middle part of the area. Furthermore, the prospected area for oil exploration was predicted. The good reservoir facies are braided stream and braided delta in Alaer area, fan-delta in Arhati area and lake-floor fan in Shizigou-Ganchaigou area. All of these areas are the main targets for oil exploration,It has discovered that there is an important unconformity between Upper Youshashan and Lower Youshashan Formation of Tertiary, on which there are a large amount of erosion and long time of depositional hiatues. It is much more clear compared with that between Youshashan and Ganchaigou Formation of Tertiary, which was consided as the most important one. The further study shows that the sandstones at the bottom of the Lower Ganchaigou Formation, which is a trlithostratigraphic unit, were deposited in different stages of base level cycle, and they are not chronostratigraphic unit. So, to identify different sequences, especially high order sequences in analysis of terrestrial stratigraphic sequences, the sequence distribution feature must be fully consided. This view has practical significance for recognizing forming, evolution and filling history of Qaidam baisn correctly, and has both theorical and practical meaning for directing further oil exploration.
Keywords/Search Tags:sequence stratigraphy, sedimentary facies, controlling factors, Tertiary, Hong-shi area, Qaidam basin
PDF Full Text Request
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