川东黔北奥伦阶碳酸盐岩岩相和相组及其沉积环境分析

ANALYSIS OF LITHOFACIES, LITHOFACIES ASSOCIATIONS AND SEDIMENTARY ENVIRONMENTS OF OLENIKIAN CARBONATE ROCKS IN EASTERN SICHUAN AND NORTHERN GUIZHOU

本文以结构分类为基础,将工作区的碳酸盐岩归纳为20种岩相,同时对比分析了每种岩相的基本沉积条件。根据岩相的相邻和共生关系,建立了7个岩相组合,并解释了各个相组的沉积环境和各岩相的微环境。根据相组在剖面上的分布特征,讨论了环境的时空演化。认为纵向上存在着两套向上变浅的旋回;横向上在大环境格局类似前提下,存在着个别环境差异。

Olenikian carbonate rocks in Eastern Sichuan and Northern Guizhou were deposited on the Upper Yangtze Platform. On the basis of Dunham's (1962) textural classification and consulting the types of grain and sedimentary structure, the carbonate rocks can be divided into twenty kinds of lithoracles, such as five kinds of grainstones (G_1—G_5 ), three packstones (P_1—P_3), three wackestones (W_1—W_3), six mudstones (M_1—M_6) and two boundstones (B_1—B_2) and a secondary carbonate rock—salt-solution breccia(S). Owing to the ease in dissolution, evaporites have been replaced in terrane by a kind of secondary carbonate rock(salt-solution breccia). These lithofacies represent respectively different sedimentary conditions, such as sedimentary energy, the way of energy action (wave, tidal or storm wave), and water depth or salinity of medium. Seven kinds of lithofacies associations have been established according to neighbouring and paragenetic relationship of lithofacies. Each association corresponds a designated sedimentary environment. These lithofacies associations are M_3-P_2-W_1-M_1, G_2-G_1-M_1-P_1-W_1, W_2-M_2-P_3-M_4, G_3-G_1-M_2-W_1-M_5, M_2-B_1-M_4-M_5-W_3, G_4-G_5-W_3-M_5 and M_5-B_2-M_6-S. Sedimentary environment evolution curves have been made according to the distribution feature of lithofacies associations in profiles. It can be seen from the curves that the evolution of environments shows vertically two upwardly-shallowing cycles. Evolution order of environments in first cycle is open shallow sea-subtidal-low energy inter-supratidal flat→supratidal sebkha→salted lagoon, and that in second cycle is subtidal→moderate energy intertidal→high energy intertidal→high energy salty intertidal→supratidal sebkha→salted lagoon. Environment evolution indicates that horizontally the total environment pattern is of consistency, but there are also differences among concrete environments in different places.