广西上泥盆统肾形藻泥丘的沉积模式和成岩模式

SEDIMENTARY AND DIAGENETIC MODEL OF RENA-LCIS MUDMOUND OF UPPER DEVONIAN IN GUANGXI

本文从沉积学角度研究肾形藻泥丘的形成、发育及其成岩作用,对肾形藻及其有关藻类给予了初步的形态分类,指出广西含肾形藻的地层分布于贵塘组至融县组,并阐述了肾形藻地层的古地理概况;根据肾形藻的含量不同将(含)肾形藻碳酸盐岩进行了成因分类,对其岩石学特征进行了讨论。本文还探讨和分析了肾形藻、肾形藻泥丘的分布规律和环境意义,并深入系统地研究和建立了肾形藻泥丘的沉积模式和成岩模式,将广西上泥盆统肾形藻泥丘的发育过程分为4个时期,其结构分为3个亚相;并详细阐述了肾形藻泥丘成岩过程的8个阶段。指出肾形藻泥丘可能是寻找油、气的目的层。

The author investigated and studied the Renalcis-bearing strata from more than ten section in Guilin, Liujing in Guangxi province, and Ionnd abundant Renalcis and well-preserved Renalcis Mudmound in Rongxian. For mation of Upper Devonian. A thorough research about several aspects of these material is given in this paper.1. The Classification of Renalcis: Six basic types of Renalcis and related Algae in Devonian of Guangxi can be distinguished: (1) Branching structure,(2) Branching structure with septa. (3) Grape cluster-like mass structuce. (4) Chamber structure. (5) Cyst-like structure, (6) Transitional association structure.2. The earliest occurrence ot Devonian Renalcis fossils in Guangxi is in Guitang Formation, and it developed in Donggangling Formation,Guilin,For ination and Rongxian .Formation. The evolutionary process ol their litho Paleogeography is: continental marginal elastics littoral depositional period of carbonate platform from later Em ian to Givetion; in later Givetian, especially the transgression and fault trough movements in the base of ocean basin in Fransian became so strong that the carbonate platforms were dis integrated completely and became into a Paleogeographic form ol which alt ernated between trenches and platforms and two different depositional facies in late Devonian of Guangxi. Becanse of Famennian regression, the benthon extincted and algae took up their place, that time was a flourishing period of Renalcis growing (fig. 1).3. The classification of Renalcis-bearing carbonate: rock and their petro logic characteristics.(1) Classification of Renalcis-bearing carbonate rock (genetic classifica tion).A: Micro-Renalcis-bearing micrite (the content of Renalcis is 5-10%: B: Renalcis-bearing micrite (Renalcis content 10-25%); C: Renalcis micrite (Renalcis content 25-50%;D: Micritic Renalcis framestone (Renalcis content more than 50%). (2) Petroiogic characteristics of Renalcis-bearing carbonate rock. A: Intraclastic limestone: three types can be distinguished, by the strength of their forming energy. (a) sparry (micritic) pebbly itraclastic limestone, (b) sparry intraclastic calcarenite or micritic intraclastic calcarenite, (c) intraclastic biomicrite.B: Bioclastic limestone: (a) Renalcis-clastic limestone, (b) stratapora-clastic limestone (c) calcisphere-bearing micrite. Three types can be distinguished by whether calcisphere with micrite envelope or not: the calcisph-eres with irregular micrite envelope and the calcispheres without micrite envelope.C: Framestone: (a) Stratapora framestone, (b) Renalcis framestone.4. The Distribution and Environmental significance of Renalcis and Renalcis Mudmound.According to the paleogeographic distribution of Renalcis and Renalcis Mudmound, the following several kinds of environment can be recognized: (1) the back of platform marginal bank;(2) the storm deposits of platform margin; (3) platform marginal reef; (4) platform tidal flat; (5) the upper part of platform marginal slope; (6) the lower part of platform marginal slope. To sum up, the growing and developing rules of Devonian Renalcis in Guangxi are following: (a) the most Renalcis developed in platform margin and platform marginal slope deposits; (b) sporadic distributed Renalcis grew generally between pebbJes and intraclasts. Also the remains of Renalcis growth can be seen in the storm deposits. (c) Renalcis be often broken in the back of platform marginal bank because the movement of arenaceous bank or oolitic bank and the periodic changes of energy; (d) in the environment of platform marginal reef, Renalcis usually grew in the depression of reefs and between frame-builders on the style of attached to low evolutionary organism; (e) the slope of platform margin is the best environment of Renalcis Mudmound developed and preserved.5. The Sedimentary model of Renalcis Mudmound.The developing process of Upper Devonian Renalcis Mudmound in Guangxi can be analyzed into four periods: the foundational period of Renalcis Mudmound growing; the growing period; flourishing period and dying out period. Three subf