K- bentonites from the boundary of Ordovician and Silurian, due to extensive distribution and multi- layers, is an ideal objective to study stratigraphic chronology, correlation of event stratigraphy, biological mass extinction and icehouse event, and structural setting of provenance. This study carried out zircon U- Pb dating for bentonites from Late Ordovician Wufeng Formation and Earlier Silurian Longmaxi Formation near boundary of Chongqing and Hubei province in the eastern section of South Dabashan. Two ages of 459. 9±6. 0Ma and 447. 9±2. 9Ma are obtained for K- bentonites from dark mudstone in the Liziping profile and about 450. 9±1. 6Ma obtained K- bentonites from from dark silicalite in Yanzi profile, and they indirectly constrain the sedimentary age of the strata. Lithogeochemical characteristics reveal that SiO2 contents of K- bentonites from the YZ profile are between 53. 61% and 56. 34%, which indicates intermediate magma, but those from the LZP profile are about 35. 56%～43. 81%, its low values perhaps relate to high Fe content and high LOI; their K2O contents vary from 5. 61% to 5. 47% and K2O＞Na2O, which imply these bentonites belong to K- bentonite. REE contents of K- bentonites from YZ and LZP profiles vary greatly. The former has ΣREE of about 46. 48～73. 70×10 -6 with an average value of 63. 08×10 -6 , and the latter hasΣREE of between 113. 34×10 -6 and 356. 98×10 -6 with an average value of 164. 08×10 -6 . Both LREE/HREE and LaN/YbN ratios demonstrate less notable differentiation between LREE and HREE, and slightly LREE enrichment. Both K- bentonites show Eu negative anormalies, distinct differentiation of trace elements such as Ba, U, Nb and Ti. The former with obvious depletion of Nb, Ta and Ti indicates characteristic of typical island- arc basalt while the latter shows trace element feature of intraplate basalt. The recovery results of the protolith indicate that primary magmas of LZP K- bentonites derived from peralkaline trachyte andesite and YZ K- bentonites are high K and sub- alkaline rhyolite, indicating that two K- bentonites should belong to different magmatic rocks with different period and deferent sources. The discrimation diagrams of tectonic settings demonstrate that LZP sample falls mainly to intraplate granite and YZ sample falls into volcanic- arc or syn- collision granite. Combined with the geological background of the Dabashan region, authors can conclude that K- bentonites with ages of ～459. 9Ma and ～450. 9Ma may be related to northward subduction of Qinling palaeo- oceanic crust and theirs volcanic tuffs may originate from volcanic- arc eruption along the northern margin of Qinling palaeo- ocean basin, while K- bentonites of ～447. 9 Ma may be related to intraplate extension and the volcanic ash derived primarily from intraplate volcanic eruption.