济源盆地谭庄组(T_(2-3))上段湖相沉积及遗迹化石特征

Lacustrine Deposits and Associated Trace Fossils in the Upper Part of the Tanzhuang Formation (T_(2-3)), Jiyuan Basin, Henan Province

济源市西南郊出露有中—上三叠统谭庄组,代表了济源中生代盆地充填的一部分。在湖相剖面中识别出六种岩相组成的两类相序,相序 1呈叠置的向上变粗的序列,由下到上由富有机质页岩 (相E,类型Ⅰ ),纹层粉砂岩 (相A)和水流波痕层理砂岩(相B)组成,记录了在温暖潮湿条件下常年性开放湖泊中小型河口坝三角洲的进积作用;相序 2缺少明显的垂直序列,由互层状细粒碳酸盐岩和粉砂岩(相C),变形层理和波浪改造砂岩 (相D),富有机质页岩(相E,类型Ⅱ)和粘土岩组成,虽然也代表了常年性开放浅水湖泊体系,但反映出很强的季节性气候控制特征。湖相剖面的相C中发育丰富的Skolithoslinearis组合,也反映出底层受季节性气候控制。文章深入探讨了该组上段浅湖沉积的环境演替及气候对沉积作用的控制作用,在湖泊演化过程中,很可能出现过几次水体分层。根据晚三叠世时期的古地理重建,推测谭庄组上段湖相沉积反映出的强烈季节性可以用潘加亚巨型季风影响的设想模式解释。

The Middle to Upper Triassic Tanzhuang Formation, being well cropped out near Jiyuan City, Henan Province, represents a part of the infill of the early Mesozoic Jiyuan-Yima Basin. The upper part of this stratigraphic unit records deposition within prevailing shallow lake conditions. Six sedimentary facies clustered into two facies assemblages were recognized in the lacustrine section. Facies assemblage 1 consists of the stacked coarsening-upward sequences composed, from base to top, of organic-rich shale (facies E, type Ⅰ), laminated siltstones (facies A) and current-rippled laminated sandstones (facies B). Units of assemblages 1 record progradation of small mouth-bar deltas within a perennial open lacustrine system under temperate and humid conditions. Facies assemblage 2 lacks a clear vertical progradition pattern and consists of interbedded fine-grained carbonates and siltstones (facies C); deformed and wave-reworked sandstones (facies D); organic-rich shales (facies E, type Ⅱ) and clayey mudstones (facies F). The assemblage also represents a perennial, hydrologically open, shallow lacustrine system, but characterized by strong seasonal climatic control. The Skolithos linearis monospecific assemblage mainly occurred abundantly in facies C suggests the substrates controlled by seasonal climate. Water stratification probably occurred in several periods of the lake history. Pangaean megamonsoonal influence is envisaged to explain the strong seasonality imprint evidenced toward the upper part of the Tanzhuang lacustrine column.