| 川西北地区早志留世风暴岩及其环境与古生态意义 |
| |
| 引用本文： | 张廷山,侯方浩.川西北地区早志留世风暴岩及其环境与古生态意义[J].沉积学报,1993,11(2):55-74. |
| |
| 作者姓名： | 张廷山 侯方浩 |
| |
| 作者单位： | 西南石油学院, 南充 |
| |
| 摘 要： | 研究区为扬子地块西北缘的一套巨厚页岩、泥岩层,间夹生物礁、生物丘及透镜状和不规则层状风暴生屑灰岩。根据风暴岩的地层分布及岩石学特征,作者将三类不同层位的风暴岩划分为A,B,C,D,E五类:A、B型为近源风暴岩,C、D及E型为远源风暴岩。从A型到E型反映出风暴能量逐渐减弱,水体加深的趋势。由于生物碎屑层形成在泥质陆架上,使生境的底质性质发生变化,造成底栖生物群落从适于泥底生活的内栖生物群落通过埋藏反馈作用转变为表栖固着生物群落,形成众多的礁及丘。一般A型风暴岩是本区礁的基底;B型因其沉积位置较A型深且规模小,仅在少数地方可见其上发育丘1C型风暴岩之上可见生物层;而D、E型不适于表栖固着生物发育,其上均为泥页岩所覆盖。
|
| 关 键 词： | 风暴岩 生物礁发育 古生态 川西北地区 早志留世 |
| 收稿时间： | 1991-07-11 |
Tempestites and the Environmental Paleoecological Significance of Early Silurian,Nvv Sichuan Area |
| |
| Institution: | SW Petroleum Institute, China |
| |
| Abstract: | Several Early Silurian storm-wave genesis of bioclastic limestone beds which deposited on the muddy shelf have been recognized from NW Sichuan area. The Early Silurian deposited at the NW margin of the S-China Paleo-plate tectonically and it has the very thick sequence of shale,silty shale,muddy shale and silty sandstone with some reefs, bioherms and stratigraphically discontinuous lenticular and irregular bioclastic limestone beds. The fossils (trilobites, pelmatozoas, brachiopods and some small solitary rugose corals) which are dispersed in surrounding siliclclastic deposites,are the source of the bioclasts for tempestites. The bioclasts result from storm wave-caused winnowing effects and they are lag concentrates. It is one of the very important characteristics of the shallow muddy shelves. Detailed petrographic and stratigraphic analysis reveals 5 distinct tempestite (bioclastic limestone beds) patterns which located at 3 stratigraphic levels, according to 5 different stratigraphic sections. Pattern A:Thick lenticular or irregular bioclastic limestone beds (1-3m thick) with erosion at the bottom. Generally, the beds show three gradding subdivisions from bottom to top (at the Middle-Upper Ningqinag Formation). Pattern B:The small lenticular bisclastic limestone beds with l-20cm thick and 10-50cm long. The petrography of this pattern is similar to the third subdivision of the Pattern A (at the Upper Ningqiang For-mation). Pattern C:The lenticular or irregular bioclastic limestone beds with erosion at the mastem. The lower parts of the beds are mud-teariag bioclaslic limestone and gradually cosfer to the bioclastic grains upwardly. The eds are 5-15cm thick and locate at the gjianwan Formation. Patterm D:The small enticular limestone beds with 2-6cm thick and over 10cm lung, which can be divided into 4 petrographic subdivisions vertically. The first containing thin-shell brachiopod and ostracoda shells.is lag concentrates .the second is rizental lamunar zone,the third is the hummocky cross laminar stratification zone and the woverh is parullet laminar zone(at the Cuijiagou Formation). Pattern E: It is very similar to the Pattern D on the size, the distribution and from the second to the fourth subdivisions of Pattern D petrographically. Because the storm wave is different on energy .frequency and the span of the storm pro cess.several different types of tempestite deposited in this area. The petrographic and paleoe-cologic analysis reveals that the Pattern A and B are proximal and Pattern C.D.E .are distal. Form Pattern A to E,the petrographic characteristics show that the storm energy became weaker and the depth of water increase gradully. The storm wave accumulation of bioclasts can directly influence the structure and dynamics of nature of the sea floor and can change the physical characteristics of benthis habitats. Along with the bioclast accumulations in abundance,the soft muddy sea floor would be transformed into a coarser,firmer and topographically more complex benthic habitat. Many coarser substratum-like and firmer substratum-like epi-organisms,such as encrusting organisns,can settle and develop on it and form the biological hardgrounds. Many reefs and bioherms developed on the biological hardground through the process of taphonomic feedback. Usually, reefs developed on Pattern A tem-pestite.a firm bioherms can be seen on Pattern B,biostrome on Pattern C and Pattern D,E are covered by shale,because the depth of water increased gradually. |
| |
| Keywords: | |
| 本文献已被 CNKI 维普 等数据库收录！ |
| 点击此处可从《沉积学报》浏览原始摘要信息 |
| 点击此处可从《沉积学报》下载免费的PDF全文 |
|
