![]() ![]() As the platform continuously increased, ocean trough gradually disappeared in Feixianguan Period. The reef or oolitic reservoir belongs to hidden lithologic trap, and the sedimentary evolution process and palaeogeomorphology settings of open sea platform-ocean trough sedimentary facies belt formed in the Late Permian in Sichuan basin are very complicated. 129–144.According to previous geological achievements, the development of the reef or oolitic reservoir is closely related to sedimentary facies. American Association of Petroleum Geologists Memoir, pp. (Ed.), Interregional Unconformities and Hydrocarbon accumulation, vol. Vail, P.R., Hardenbol, J., Todd, R.G., 1984, J urassic unconformities, ChronoStratigraphy and sea-level changes from seismic stratigraphy and BioStratigraphy. (Eds.), Sea Level Changes––An Integrated Approach, vol. In: Wilgus, C.K., Hastings, B.S., Kendall, C.G.St.C., Posamentier, H.W., Ross, C.A., Van Wagoner, J.C. Loutit, T.S., Hardenbol, J., Vail, P.R., Baum, G.R., 1988, Condensed sections: the key to age-dating and correlation of continental margin sequences. In conclusion condensed sections and sequences, their condensed pelagic fauna and high gamma ray signal form common time markers for sequence stratigraphic analysis and are equated with maximum flooding surfaces. High gamma signals in well logs are often associated with condensed sections the radioactive elements that cause this signal were sequestered by the organic matter (often cyanobacteria and phytoplankton) that accumulated preferentially as the clastic input from the basin margin decreased. Sometimes the transgressive surface marking the base of the trangressive systems tract is immediately overlain by a condensed section that is in turn capped by the mfs. This is because commonly the upper layer of the transgressive systems tract forms a condensed section which is associated with the mfs where it is overlain by the downlapping highstand systems tract. The condensed sections are often used as markers during sequence stratigraphic analysis. Initially the condensed sections are seen to accumulate in more distal slope and basinal settings, but as the shoreline backsteps landward during the sea level rise of a transgression so the condensed sections may gradually expand in their coverage to include not only the basin but all of the slope and part of the shelf as well ( T.S. Examples of condensed pelagic fauna used in this way include graptolites, conodonts, goniatites, ammonites and foraminifera. These condensed layers of fauna are often used as paleomarkers of time. Because the clastic sedimentation rates are starved of the sediment from the continental margin, the skeletal remains of pelagic fauna preferentially accumulate to form condensed layers of fauna. A thin marine stratigraphic interval characterized by very slow depositional rates (<1-10 mm/yr) ( Vail et al., 1984).Ī condensed section often consists of hemipelagic and pelagic sediments, starved of indigenous materials, and deposited on the middle to outer shelf, slope, and basin floor during a period of maximum relative sea-level rise and maximum transgression of the shoreline. ![]()
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