A chaotically brecciated limestone is found in the Pingliang formation of the Middle Ordovician in Fuping area

Shaanxi province.It occurs as bedded or sheet strata in

and in sharp contact with

the foliated and thinly tabular limestones.The fragments of it are highly varied in size and chaotically distributed

with the giant being 1?7m or larger.This limestone is lack of stratification and sorting

in which floating boulders and blocks are scattered in the matrix of finer clasts.These features show that it is of deep water carbonate sediments of debris.This limestone is dominantly composed of breccias of inner basin source.These clasts

formed by gravity sliding of consolidated or semiconsolidated sedimentary layers on slope of deep water basin

are transported by gravity and have accumulated on the margin of the basin floor.In the Middle Ordovician

the Fuping area was located on the northern margin of the deep water basin

where the maximum water depth was nearly one thousand metres.After the deposition of the Early Ordovician Majiagou formation

this area was subsided to form a deep water basin on the continental margin

by the tension fracturing of the back-arc basin on the northern side of the Qinling and Qilian Mountains.