| PDF: | |
| Time: | 1997 |
| Journal: | The editorial board for sedimentary facies and palaeogeography |
| Volumn: | 17 |
| Issue: | 1 |
| Pages: | 22-27 |
| Type: | Other |
| Author: | Wanzhu Liu,Pujun Wang |
Abstract: | The argillaceous dolomite concretions occur mainly in the intercalations of the greyish green silty mudstones,shales and ostracod beds in the Nenjiang Formatin of the Cretaceous Songliao continental basin. Their isotopic compositions are:δ13C (PDB)=1. 105±2.4; δ18O(PDB) = - 5. 174±3. 5 ;87Sr/86Sr = 0. 7078 ± 0. 0005. Generally speaking, these dolomite concretions do not cut the adjacent beddings,and internally have horizontal laminations. It is inferred that the concretions were formed in the shallow-water stage during the rapid fluctuation of lake leve l,and are assigned to sedimentary and early diagenetic concretions. The authors interprete the dolomite as having a mixed sea water-fresh water origin, and the ellipsoidal shape of the concretions as the result of uninterrupted compaction from the overlying muddy sediments during syngenetic cementation of the carbonate sediments. |