Sequence Stratigraphy And Marine Source Rocks Of Cambrian And Ordovician, Helan Aulacogen

The paper is part results of"The Research on Hydrocarbon of NorthChina Platform and Two Rift Systems". The results come from detail measurements, descriptions and analysis on lots of outcrops and painstakingly work indoor. Based on the research of sedimentology and sequence stratigraphy, the lithology, depositional environment and sequence stratigraphy features are concluded. In addition, the marine carbonate source rocks of Helan Aulacogen were preliminary assessment.The main deposition of Cambrian (ε) and Ordovician (O) in Helan Aulacogen is marine carbonates; The second is argillaceous rocks and glutenite rocks. And the stratigraphy ofε-O1-2 can be divided into 2 super sequences, 11-second order sequences and 48 third order sequences.The sedimentary facies ofεin Helan Aulacogen are as follows: tidal flat, offshore fords, restricted platform, open platform, plateau boundary shallows, plateau foreslope, et al. Restricted platform, open platform, neritic continental shelf, abyssal fan and biohermal facies are mainly facies of Ordovician. The sedimentary facies pattern of Eopaleozoic from land to sea can be regard as: land-transition area-ristrict platform-open platform- plateau foreslope-continental shelf.Carbonate source rocks organic matter ofε-O in Helan Aulacogen belong to IIA model or I. The value of Rock Eval Tmax mainly over 460℃which mean that organic matter evolution attain high or post mature period. The thermal evolution of Lower Ordovicion source rocks mainly fall in high mature, some in over mature. Except Pingliang area source rocks of Middle Ordovician attains maturity period, others are all accomplish high or over mature period. Most of them are relatively bad source rocks, but source rocks of several areas as Zhuozishan, Xiangshan, Pingliang and Tonghcuan have high organic content that can be regard as preferable source rocks.Preferable source rocks mostly locate at the middle-lower part or bottom of the sequence, transgression system or condense stratigraphy, which is controlled by the seal level fast ascend. Source rocks deposition has osculated links to sedimentaryenvironment, restrict platform, bight of open platform and deep-water facies are the better area for the development of good source rocks.