West
Yunnan was attributed to the Shan-Thai Terrane or to the Sibumasu Terrane by
some geologists (Burrett et al., 1 990;Fortey and Cocks, 1998). Alternatively
by other geolo-gists it has been divided into eastern and western parts along
the Lanchangjiang Fault:assigned respectively to the Indo-China and Sibumasu
terranes. Ordovician strata are exposed intermittently in eastern West Yunnan, the
Lower to Middle Ordovician rock sequence being particularly well exposed in
Xiangyang village near Dali, where it is represented in ascending order by the
Haidong, Hsiangyang, and Tongchang formations. The Haidong Formation reaches
more than 384 min thickness, of massive to thick-bedded fine sandstone and quartzite.
It is unfossiliferous but the correlative context shows it to be basal
Tremadocian to Middle Arenigian in age. The fauna is rich in brachiopods, especially
Ectenoglossa daliensis sp.nov., Monor-this intercalase sp.nov., and
Nocturnellia oriental is sp.nov., and in bivalves such as Fasciculodonta
impressa Fan et al. and Yunnanoredonia laevis Fan et al. A strophomenoid fauna
occurs only at the base of this interval, yielding abundant Murinella
xiangyangensis sp.nov.and a few other brachiopods, such as Tritoechiasp.and
Fenxiangellasp.