The Deposits of Oolitic Shoal Facies and Algal Flat Facies—Dissect of the Zhangxia Formation of the Middle Cambrian, Western Shandong Province
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摘要: 鲁西地区中寒武统张夏组岩石的各种沉积特征表明：①华北地区普遍发育的鲕粒沉积在许多地点和层位是受海平面和水流条件变化影响的异地沉积物，而并非原始的“滩”。不同地点的鲕粒沉积具穿时性，一般由东和南向西和北层位逐步抬高，而并非同一时间的产物，即它们属同性相，而非同时相；②在鲕层中不同结构的鲕粒在一起，是由于沉积过程中不同地方的鲕粒相混合造成的，可称“沉积混合”，有的是在沉积稳定后受差异成岩作用的影响而造成的，可称“成岩混合”；③鲕粒沉积之后普遍为一套藻沉积，基本组分是Eiphyton，它处于潮坪环境，即藻坪。其中潮渠和干裂较发育。藻沉积的类型有藻斑块，藻丘、叠层石，个别地点发育藻礁；④由于海平面和潮流条件的频繁变化，使藻坪外或藻坪间的鲕粒沉积与藻坪沉积相互交替；⑤张夏组上、下段中鲕粒的形成环境不同，前者主要是较弱扰动条件下的产物，后者主要是较强和中等扰动条件下的产物；⑥综合沉积环境分析归纳出主要沉积相带的基本展布状况，由近陆向外海依次是：潮坪相—受局限水域（或泻湖）相—潮汐坝相—开阔浅海相。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.
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Key words:
- oolitic shoal /
- algal flat /
- Middle Cambrian /
- Shandong province
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