Abstract:

The development characteristics and origin of leopard limestone in the third member of Majiagou Formation in Ordovician of north-western Henan Province were studied by using methods of outcrop observation and thin section analysis. The results show that the ‘leopard’ can be divided into five types of biological burrows according to their morphological characteristics and ichnology, i.e.Psilonichnus, Chnodrites, Thalassinoides, Helminthopsis and Planolites. The emergence of different types of biological burrow was mainly restricted by sedimentary environment. The burrow fillings can be divided into two types according to their different dolomitization degrees: (1)micritic dolomite fillings, mainly exist in Psilonichnus and Chnodrites; (2)powder-fine crystal dolomite fillings, mainly exist in Thalassinoides, Helminthopsis and Planolites. The process of dolomitization can be divided three stages,i.e. the preparation stage before dolomitization, the formation stage of dolomites and the adjustment stage of dolomites,and the different dolomitization statuses of burrow fillings are formed in this process.

Key words: Henan Province, Majiagou Formation, leopard limestone, biological burrow, dolomization