The Cambrian source rocks are considered as one of the most important source of marine oil and gas in Tarim Basin.Previous literatures documented various descriptions of their depositional settings

causing confusion in prediction of source rocks

especially those with no sufficient data.Analyses of outcrops

new drilling and seismic data

and assumptions of prototype basin from the Sinian to Cambrian

were used to study the sedimentary environment of the rocks through a perspective of sedimentary texture and hydrocarbon generating organisms to work out constraints over their distribution.The results show that the Cambrian sedimentary framework of Tarim basin can be characterized as “Western Platform and Eastern Basin”.It evolved through a carbonate ramp in the Early Cambrian and a feebly rimmed platform in the Middle-Late Cambrian.The source rocks of the Lower Cambrian were widely distributed in the middle-outer ramp.The Lower Cambrian Xishanbulake Fm source rocks in eastern Tarim Basin and the Lower Cambrian Yuertusi-Xiaoerbulake Formation in western Tarim Basin have the same bio-precursors assemblage which change from benthic algae of to planktonic algae

corresponding to the Early Cambrian progressive-retrogressive sedimentary succession.Regional sedimentary-tectonic evolution background and lithology and bio-precursors reveals that the Cambrian source rocks were developed in the deep shelf environment predominantly

and could be further divided into muddy source rocks and carbonate source rocks.The muddy source rocks were dominated by benthic algal

while the carbonate source rocks were dominated by planktonic algae.In vertical

the muddy source rocks and carbonate source rocks are superimposed on each other.