中文摘要：

通过野外露头实测、手标本观察、光薄片观察、X光衍射分析、电子扫描等方法,对鄂尔多斯盆地东北部延安组第Ⅱ成因地层单元中的叠锥各方面的特征进行了系统研究。结果表明,叠锥整体呈结核状产出于暗色泥质岩中,泥质岩中发现丰富的20μm左右的炭化微生物化石,反映相对还原的沉积成岩环境。叠锥内部常可分为3层,中层为块状灰岩,上、下层由大小不等的、同轴或错落叠置的直圆锥组成。叠锥内部主要为纤维状方解石呈锥形套叠,纵切面上可见明显的＂V＂字型或＂W＂字型纹层,横切面上可见大小不等的同心圆状构造。上、下层位叠锥的锥顶均朝上,反映出类似叠层石的生长特征。综合分析认为,叠锥可能是由微生物和沉积作用联合作用形成的一种特殊的生物沉积构造;并推断出鄂尔多斯盆地东北部延安组第Ⅱ成因地层单元中的叠锥发育于由河流向湖泊过渡的浅水、沉积速率较低的环境中。

英文摘要：

Cone-in-cones are among the most spectacular and enigmatic geological features. They are shaped like caliche nodule,globular-ellipsoidal,and mainly composed of carbonate. They are so termed as they are formed by six of straight cones which are coaxial or scattered overlay. To fully understand the depositional feature of cone-in-cones and dicuss the problems of genetic model and situational meaning of cone-in-cones,a systematic research is made on the cone-in-cones developed in the second genetic stratigraphic unit of Yan＇an Formation in the northeast of Ordos Basin by means of outcrop observation,hand specimen observation,polished thin section observation,X ray diffraction analysis,electronic scanning etc. The results show that cone-in-cones develop in mudstone with tuberculosis-like output,where there are plenty of planktonic microfossils with a diameter more or less than 20 μm. This illustrated a comparatively reductive depositional and diagenetic environment. The internal nodules always can be divided into three tiers. The upper and the lower are formed by sixes of straight cones which are coaxial or scattered overlay. The internal cones are mainly fibrous calcite and cone-shaped nest,but also contain a considerable number of clay filling. On the longitudinal section of the upper and lower cone surface ＂V＂ shaped or ＂W＂-shaped laminaecan be clearly seen,showing the concentric circles of varying sizes structure in cross section. Both the cone top of the upper and the lower block is upward,reflecting their growth characteristics similar to those of the stromatolite. A synthessized analysis of the information on alls asepects suggests that the cone-in-cones structure should be a special kind of biostructure formed by the microbial action joined with sedimentation. It is thus inferred that cone-in-cones of the second genetic stratigraphic unit of Yan＇an Formation in the northeast of Ordos Basin should develop in the transitional environment from the river to the lake,where the water was shallow and th