The Study Of Sequence Stratigraphy And Sedimentary Characteristics Of Mirador-carbonera Formations In Southern Llanos Basin

The study area of this article is located in southern Llanos Basin and the targetlayers are Mirador-Carbonera formations in Eocene-Miocene. Using research contentsas the starting point and based on sequence stratigraphy, sedimentary petrology,structural geology, seismic stratigraphy etc. theories, combined with drilling, welllogging, core and seismic data, we studied the rock type, depositional environment,sequence stratigraphy of the target layers deeply. We can analyze the sedimentaryenvironment by the type rocks and determine the sequence stratigraphic frameworkby identifying of the sequence boundaries, which can contribute to the studying ofsedimentary facies distribution and depositional environments within the sequencestratigraphic and the control factors of sequence development.The tectonic evolution of the Llanos basin can be divided into five stages,including syngenetic rifting in Triassic-Jurassic, back-arc subsidence in Cretaceous,Western Cordillera hyperplasia (early foreland basin) in Paleocene-early Eocene,foreland basin before the Andean in Middle Eocene-early Miocene and foreland basinin middle Miocene-Andean.Through core observation, mud logging and logging data analysis of three wells,Mirador and Carbonera deposition system of Llanos Basin can identify delta, shelfsedimentary facies, delta can be subdivided into delta plain, delta front and pro-deltaand shelf develops inner-shelf subfacies.Delta plain mainly developes in C1, C3, C5, C7, and the M1segments, whichcan identify distributary channel and distributary channel microfacies, delta frontsub-facies develops in C1, C3, C5, C7and M1segments, including sandy underwater distributary channel and mud-based underwater distributary microfacies, prodeltadeposition sub-facies develops in the C2, C4, C6, C8, and M2segments, which can befurther divided frontal sheet sand and prodelta mud microfacies, continental shelfdevelops in the C2, C4, C6, C8and M2segments, which contains shelf mud and sheetsand microfacies.Though the sequence stratigraphy theory of Vail, combined the sedimentarygeological background of Mirador and Carbonera formations and on the basis ofdetailed study of sequence boundary, five Supersequences (SSQ1-SSQ5) can beidentified in Llanos basin from Mesozoic-now, Mirador-Carbonera belongs to SSQ4in study area which can subdivided into five Sequences (SQ1-SQ5), every third-ordersequences is absence of LST, which develops TST and HST.By contrasting the sedimentary and seismic facies of single or connected wells inthe Llanos Basin, we establishes the seismic facies of sedimentary facies in studyingarea. A total of seven sedimentary facies unit and corresponding11seismic faciesunits can be identified. On the combination of well and seismic, third-order sequencesand systems tracts framework can be established and the deposition plane facies ofeach systems tracts can be worked out. Finally, we can analyze of controlling factorsand evolution mode of sequence development. Tectonic movement and sea-levelfluctuation are the main controlling factors of Mirador-Carbonera formations withinthird-order sequences and its internal systems tract in southern Llanos basin.