遗迹相在边缘海相分析中的应用

THE APPLICATION OF ICHNOFACIES TO THE ANALYSIS OF MARGINAL MARINE FACIES

本质上 ,边缘海相储层是由一系列复杂排列的岩相所组成 ,代表几种亚环境结合部位的特征。在边缘海环境中 ,对应于相对海平面变化 ,关键的层序界面之上可被淡水、半咸水和纯海水 (沉积 )所覆盖。因此 ,在对这样的储层进行勘探和开发时 ,区分淡水、半咸水和纯海水沉积就显得格外重要。而遗迹化石组合有助于区分这些环境。总的来说 ,半咸水遗迹化石组合有如下特征 :①低分异度 ;②贫乏的海相组合 ,而不是海相和非海相的混合 ;③由机会物种形成的简单构造组成 ;④遗迹组合常以某个遗迹属为主 ;⑤形态微小 ;

Marginal marine reservoirs, by their very nature, consist of a complex array of facies reflecting the juxtaposition of several sub environments. The superimposition of freshwater, brackish and fully marine settings across key sequence stratigraphic surfaces is a common response to changes in relative sea level in the marginal marine realm. Consequently, distinguishing between freshwater, brackish and fully marine deposits is of paramount importance in the exploration and exploitation of such reservoirs. Trace fossil assemblages can be used to assist in the differentiation of these settings. In general, brackish water trace fossil suites are characterized by: ① low diversity; ② an impoverished marine suite, rather than a mixture of marine and non marine traces; ③ simple structures constructed by tropic generalists; ④ suites that are commonly dominated by a single ichnogenus; ⑤ diminutive forms; and ⑥ vertical and horizontal ichnofossils that are common to both the Skolithos and Cruziana ichnofacies. The purpose of this paper is: ① to document the distribution and types of trace fossils associated with marginal marine deposits; ② to summarize the biological and ichnological characteristics of brackish water environments; and ③ to propose distinct brackish water ichnofossil assemblages.