Guantou Fm

Its base marked by dark purple moderately thick-bedded sandy conglomerate is distinguished from the underlying Lower Cretaceous Jiuliping Fm consisting of light gray massive rhyolitic porphyry. It often overlaps unconformably the Jiuliping Fm and Xishantou Fm. In a few basins it lies unconformably on the underlying Chawan Fm and Gaowu Fm and locally overlaps the Shouchang Fm or older strata.

Its top is conformably bounded by the Upper Cretaceous Chaochuan Fm consisting of purple red moderately thick-bedded gravel-bearing tuffaceous medium- and coarse-grained feldspar lithic sandstone.

The formation occurs throughout Zhejiang Province and is extremely developed in the southeastern part of the province. It varies considerably both in lithology and thickness in Wuyi-Zhuji. It is mainly represented by gray green and yellow green microclastic sediments with red beds and occasionally with volcanic rocks, with more volcanic partings in the northeastern part than in the southwestern part. It generally ranges from 300 to 600 m in thickness, 41.4 m at minimum in the Hushan basin, 831.3 m at maximum in the Ningbo basin. In the Wencheng-Zhenhai area, the formation increases remarkably in the amount of volcanic rocks, intercalated with rhyolite, andesite, olivine basalt and moderately acidic pyroclastic rocks in the Wencheng basin; andesite is predominant in the Kunyang basin, with sedimentary rocks occurring as partings. In the Putuoshunmu basin, the Guantou Formation is not exposed completely, generally ranging from 130 to 600 m in thickness in the area, 2300 m at maximum in the Ningxi basin, only 28.6 m near Licha at the southeast extremity, 109.3 m in Sanjianshan in the northeastern part.