1) Explain the tectonic evolution of the following types of sedimentary basins
Tectonics has to do with the evolution of the earth crust with respect to time (Wikipedia)
i) Median sedimentary basin: The stress generated from wrench faulting which occurs within a region of subsidence coupled with subcrustal erosion, and the subsiquent introduction of oceanic material leads to the formation of a median basin. A median basins is therefore described basins situated between the collision (Subduction) zone of two cratonic plates, that is they are found between the fore arc and the volcanic arc. According to H.D Klemme, they are the rifts of the median zone formed by wrench movements and foundering creating…show more content… Levin) areas on the earth crust having hotspots are likely present due to the presence of a thermal plume beneath it, so also is the formation of aulacogen likely to be dependent on the presence of a thermal plume, the heat generated beneath the continental plate causes a triple joint plate tectonic rift in a case where one of continental rift is brought a halt unlike the other two arms which continue to experience rifting and later on stop, the failed arm of the continental rift is known as an aulacogen. There is a sequence in which this occurs, firstly there is swell in the continental plates due to thermal plumes , then comes the rift which splits up the continental plates into three, and the collision which stops the spreading of one of the arms of the split continental plate (leading to the formation of mountains) thereby causing an aulacogen to be formed F(ig 1) . Aulacogen are very good source of hydrocarbon because the embody large amount of Mesozoic and Cenozoic marine and non-marine…show more content… They are usually bounded by an impervious rock following the process of formation and migration and help in subsequent accumulation and storage of hydrocarbon. There are two major types of petroleum traps they are :
a) Structural traps
b) Stratigraphic traps
In the Aulacogen sedimentary basins the major hydrocarbon trapping system is the Structural trapping mechanism due to the presence of faults. there are also rare cases of unconformities in Aulacogen sedimentary basins.
In the median sedimentary basin the trap is most times a block uplift over which Structural- Stratigraphic accumulations occur, we can therefore say we have a combination of both trapping mechanism
ii) Source rock: they are rocks that help in the generation of hydrocarbons. In the bot the median and the Aulacogen sedimentary basin the sediments are majorly Clastic sediments, for the median sedimentary basin we have sandstone while in the Aulocogen sedimentary basin we have shale as the source
