| Putumayo Basin lies in south-western Colombia and lies to the west edge in the north part of South America, controlled by the collision between the Pacific Plate and the west edge of the South American plate. It is a Meso-Cenozoic back-arc foreland basin in Andean arc foreland basin group. Arc foreland basins are exploration hotspot in Colombia and even in South America. Previous studies focused on geochemistry, regional tectonic evolution and accumulation conditions of Putumayo basin, but study of gravity and magnetic field characteristics and geological significance in basin is few. Gravity and magnetic structure with high-resolution capability in the horizontal direction and be able to provide information of the deep crustal structure, can also calculate the sedimentary cover, which plays an economic and effective role in the formation and evolution of the study of sedimentary basin. In order to explore the characteristics the distribution of hydrocarbon source rocks of the study area, on the basis of previous studies and the basic theories of petroleum geology, collated and summarized data of source rocks, reservoir,cap rock and geological conditions of the study area, then collected, collated and digested the geological data, gravity and magnetic field data and drilling data in Putumayo Basin, re-digitized the gravity and magnetic data, got the Bouguer gravity anomalies and the△T magnetic anomaly map, and the production and interpretation of the various conversion parameters maps with profound knowledge. Found that the main hydrocarbon source rocks is the Cretaceous marine shale of Villeta formation, reservoir is lower Cretaceous sandstone of Caballos formation and upper Cretaceous sandstone of Villeta formation, seals are mainly local and intraformational shales. Gravity anomaly contour line is in NNE, NE direction macroscopically.The gravity field values inside the basin are manifested by a high-low alternating feature, magnetic anomalies in the study area is developed. Considered that the structural trend in basin is in NE direction. Gravity field shows three gravity lows and two gravity highs from east to west of basin, the high and low of gravity value is developed, primarily reflecting good correspondence sedimentary caprock development characteristics of the formation and the base burial condition Cretaceous developed in Western depression and Central Depression, the thickness is0.5km-0.8km. Distribution of magnetic bodies have good corresponding relationship with metamorphic basement, igneous rocks and Paleozoic strata. |
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