The Deposits of Oolitic Shoal Facies and Algal Flat Facies—Dissect of the Zhangxia Formation of the Middle Cambrian, Western Shandong Province

Key words: 
• oolitic shoal /
• algal flat /
• Middle Cambrian /
• Shandong province

Abstract: The characteristics of sedimentology and petrology of the Middle Cambrian in western Shandong province show that: (1)The oolitic sediments developed at various places and stratum of no rth China are almost the allo- genic sediments, but no t the o riginal ”shoal”. They had been influenced by the changes of sea level and w ater current, so that the ooids was transported in a sho rt or long distance.In the study area, the oolitic limestone are not formed at the same time, it is time-transgressive(diachronons).In general, the horizon of oolitic limestone elevated gradually from SE to NW.That is the magnafacies, not the parvafacies.(2) The different texture of ooids occurred in the same oolitic limestone bed or thin band may be caused by the mixing of ooids form differ- ent places, termed the ”sedimentary mixing”, or ow ing to the ooids affected by the different diagensis after de- posit, termed the ”diagenetic mixing”. (3) Following the ooid deposit, the algal sediment composited of Epi- phyton developed.They occurred at the tidal flat, that is the algal flat.The algal sediments interbeded w ith the ooid sediments occurred off and between algal flats, as a result of frequent changes of sea level and tidal current.(4) The ooids (m ainly brick and radial texture) of the Zhangxia Formation lower member basically formed under the condition of stronger and medium active environment, the ooids (mainly arc texture) of the upper member basically fromed under the weaker active environments.(5)Before the Zhangxia Fo rmation up- per member and the Upper Cambrian Gushan Fo rmation, the obvious depositonal break caused by the sea level falling had happened.(6)Summarizing the sedimentary environment can be induce out the distribution situa- tion of sedimentary facies form near land to open sea. They are in turn: tidal(algal)flat facies near shore(ooid) sand sheet(or ridge)facies restricted water field(or lagoon)facies tida(ooid) bar facies open sea facies.