Middle-Lower Triassic in eastern part of North China is fragmentarily distributed in small areas;however

they have similar lithologies

fades and rhythmic characteristics

indicating a depositional setting of a large basin.It can be observed in a wide area that the grain size of sandstone is fining

shale content is increasing

and sediment is thickening apparently from NW to SE

indicating that sedimentary features in Early-Middle Triassic were similar with that in late Late Permian(Shiqianfeng age).Middle-Lower Triassic has inherited not only the Late Permian palaeogeodynamic setting of“convergence in the north and divergence in the south”

but also the palaeogeographie flamework of high in the northwest and low in the southeast.All these show that Hercynian movement would have lasted till Middle Triassic.Several methods including vitrinite reflectance(R

o

)

interval transit time and apatite fission track

are used to reconstruct the sedimentary thickness of Middle-Lower Triassic

and to plot the isopach map of the prototype basin.The sedimentary-subsidence center is located in Linqing-Dongpu-Taikang and Huainan-Huaibei areas

where the Middle-Lower Triassic is as thick as 2000～2600m.At the end of Meddle Triassic

the burial depth of the top of Majiagou Formation in Lower Paleozoic would have reached 3080～3690m

the palaeogeotemperature would be 112.4～130.7℃

and the R

o

would be 0.85%～1.10%.The Lower Paleozoic source rocks

mainly consisting of marine organic matters

would have passed the peak oil generation stage

with 80% of the organic matters have been converted into oil

thus the hydrocarbon generation potential in later stage would be very low.While the Upper Paleozoic source rocks

mainly consisting of coal formation

were still in the early stage of hydrocarbon generation with relatively good hydrocarbon generating potential

because the peak hydrocarbon generation of humic coal would lag behind the Type Ⅰ-Ⅱ

1

kerogens.