海南省南好地区南好组地质特征及时代

Geological characteristics and age of Nanhao Formation in Nanhao Area,Hainan Province

南好组是晚古生代海进序列底部的一个岩石地层单位。层型剖面所反映的岩石组合特征为石英细砂岩、砂岩与绢云板岩、粉砂质板岩不等厚互层,底部为含砾不等粒砂岩,产腕足类、腹足类、海百合化石。厚度>156 m,未见顶,与下伏早志留世足赛岭组呈角度不整合接触。选层型剖面第2层上部粉砂质板岩中产腕足类(Ⅲ31)Fusella sp.,Leptagonia sp.,Chonetipustula sp.,剖面中尚含腕足类Eochiristites sp.,地质时代为早石炭世岩关期。第2层下部粉砂岩中产腕足类(Ⅲ17)Tenticospirifer cf.supervilis,Ptychomaletoechia sp.,Fusella sp.及海百合茎。前二者时代为晚泥盆世锡矿山期。而Fusella及海百合化石时代应为早石炭世,具有共生特点。此外在同为南好地区的锌山剖面及东部相邻的万宁县峰膏岭剖面均未发现泥盆纪化石,因此将南好组划下石炭统。近来有人在选层型剖面第2层采获志留纪化石,认为选层型剖面属志留纪而非石炭纪,南好组与下伏地层也非不整合接触,主张南好组应废弃。笔者认为所谓选层型剖面第2层采获的志留纪化石实际上是采自南好组下伏的志留纪地层中,南好组不存在废弃问题。

The Nanhao Formation is a rock-stratigraphic unit at the bottom of Neopaleozoic transgressive sequence. The rock association characteristics of the lectostratotype section is alternating beds of quartz fine sandstone, sandstone, sericite slate and silty slate with different thicknesses, whose bottom is pebbled inequigranular sandstone with Brachiopoda, Gastropod and crinoidal fossils. The Nanhao Formation is in angular unconformity contact with the underlying Lower Silurian Zusailing Formation, with the thickness over 156 m, and the top is unobserved. The top of the second bed of the lectostratotype section is silty slate, having Fusella sp., Leptagonia sp. and Chonetipustula sp. ofBrachiopoda （Ⅲ31）, and the section also contains Eochiristites sp. of Brachiopoda in Lower Carboniferous Yanguan stage. As for the bottom of the second bed, there are siltstones with Tenticospirifer cf. supervilis, Ptychomaletoechia sp., Fusella sp. of Brachiopoda （ Ⅲ 17） and crinoidal caudex. The first two, belonging to Upper Devonian Xikuangshan stage, are associated with the last two which are of Lower Carboniferous period. Since there is no Devonian fossil in either the Xinshan section or the east adjacent Fenggaohng section in Nanhao area, the Nanhao Formation is classified as Carboniferous period. Recently, some researchers collected Silurian fossils in the second bed of the lectostratotype section, and they thus hold that the lectostratotype section belongs to Silurian instead of Carboniferous, that the Nanhao Formation is not in angular unconformity contact with the underlying Strata, and that the Nanhao Formation should be abandoned. The authors here point out that the Silurian fossils in the second bed of the lectostratot-ype section are actually collected from the Silurian Strata that underlie the Nanhao Formation, and hence the Nanhao Formation should not be abandoned.