Abstract:

      Molar Tooth (MT), is a special sedimentary phenomenon and only developed in carbonates in Precambrian. It has been
found in many areas of the world. Abundant MTs with complicated morphology were found in the Neoproterozoic carbonate rocks of Dalian, Liaoning Province, China. The MT from Dalian was divided into autochthonous MT and allochthonous MT, according to its morphology. The autochthonous MT was further divided into four subtypes containing ribbons, bars, worms, spots and the allochthonous MT consists of fragments only. The MTs from Dalian were mainly developed in a shallow subtidal to intertidal zone. Based on the analysis of different types of MT and their distribution in a micro-sedimentary environment zone, a special relationship between morphology and micro-sedimentary environment was found. MT1-1 and MT1-2 types mainly occur in a lagoon; MT1-3 and MT4 are the principal types in the middle of a tidal zone; MT2 and MT3 dominate the middle to upper pare of a tidal zone, while MT5 type appears in a shallow subtidal zone (around base of storm waves) or lower of an intertidal zone.Therefore we infer that wide and long MT ribbons were probably easily produced in a low-energy environment without substance from land, but a high energy environment with plenty of land-substances is favorable for short and small MT. It is concluded that hydrodynamic force and land-substances can influence the morphology of MT. Besides, considerable land-substances can inhibit the formation of micro-spars or reduce the sizes of MT.

Key words: Molar Tooth, sedimentary environment, Neoproterozoic, Dalian