The c Formation, which outcrops between the b and d Formation of the Late Ordovician Tanjianshan Group and appears as tectonic slice, is mainly made up of slightly metamorphous grey purple -amaranth conglomerate、pebbly sandstone、feldspathic quartz sandstone and siltstone. For a long time, it has been a part of the Tanjianshan Group with the a, b and d Formation. 69 detrital zircons from aubergine pebbly sandstone of the c Formation are analysed firstly by using LA-ICPMS technique in this study. The measured 206Pb/238U (<1000 Ma) and 207Pb/206Pb (>1000 Ma) ages range from 429 to 2636 Ma，forming a significant peak at ca 431 Ma. subordinate age peaks are present at ca 456 Ma, ca 908 Ma and ca 1847 Ma. The minimum peak age of 431Ma imply that the deposition age of the c Formation should be later 431 Ma and not belongs to Late Ordovician. All the studied detrital zircons, which include metamorphic and magmatic zircons and show mostly euhedral to subhedral crystals, indicate that these magmatic and metamorphic rocks are the most likely sources for the detrital sediments of the c Formation by short-distance transport from the neighboring Xitieshan source region. The magmatic and metamorphic barcode revealed by the detrital zircon age patterns is largely coincident with the pre-Mesozoic tectonic-magmatic-metamorphic events, especially the Caledonian-aged Orogeny occured in the Xitieshan region of the north margin of Qaidam basin. Detrital zircons of 857~937Ma and 1610~1992Ma imply that a Precambrian old age stratum served as a provenance area.