海陆过渡区交织水动力沉积:以厄瓜多尔奥连特盆地为例OA

The transitional zone between land and sea is an area where rivers,waves and tides act together,and the interwoven hydrodynamic forces shape the sand body morphology and palaeogeographic pattern.This paper takes the Main-Mi member and LU sub-member of the oil and gas-rich Napo Formation in the Oriente Basin of Ecuador as an example.By using core,logging and mud logging data,the sequence framework is established.Provenance was constrained using heavy-mineral assemblages and detrital zircon U-Pb geochronology,while pre-depositional palaeogeomorphology was restored using residual-thickness and imprint methods.The study shows that the Napo Formation can be divided into one second-order sequence and five third-order sequences.The Main-Mi member and LU sub-member are both in the lowstand systems tract of their respective third-order sequences.The provenance mainly comes from the eastern and southeastern Amazon Craton,and the palaeogeomorphology is generally a single inclined slope with the east high and the west low.The LU sub-member is an intertidal delta system controlled by rivers and tides as a whole,with a delta plain in the east and a delta front in the west.The Main-Mi member has evolved into a mixed system of east tidal delta,west wave-controlled shallow marine shelf and coastal current interwoven transformation.The Napo Formation records the evolution process from the river-tide inter-control to the river-wave-tide ternary mixed system,indicating that under the constraints of tectonic subsidence and provenance conditions,the interwoven hydrodynamic forces are the key factors controlling the distribution of sand bodies and palaeogeographic patterns in the transitional zone between land and sea in the foreland basin.This has reference significance for the palaeogeographic restoration of similar transitional zones between land and sea in foreland basins.