川中-川南地区上三叠统滨浅湖沉积中的遗迹化石

川中-川南地区上三叠统滨浅湖沉积中产有丰富的动物遗迹化石,识别为3大类6属8种,包括Sko-lithos linearis,S.verticalis,Ophiomorpha nodosa,Planolites beverleyensis,P.montanus,Palaeophycus tubularis,Taenidiumsatanassi和Cochlichnus anguineus,另外,逃逸构造也很发育。这些遗迹化石主要是无脊椎动物的居住迹、进食迹和觅食迹,大多为全浮痕和上浮痕保存。根据遗迹化石的组合特征及其沉积环境,可识别出3个遗迹组合:1)Skolithos linearis遗迹组合,主要由长的垂直或高角度倾斜的悬食居住潜穴构成,反映高能的砂质滨湖环境;2)Cochlichnus-Planolites遗迹组合,主要由进食迹和牧食迹组成,形成于低能的滨湖沼泽环境;3)Skolithos-Planol-ites遗迹组合,以居住潜穴和进食潜穴为主,遗迹化石的丰度较高,代表潮湿气候条件下的浅湖环境。根据生物扰动的分布及扰动强度,浅湖中可识别出两类扰动类型,即1)砂泥边界扰动,扰动主要发育于砂泥交界处,代表了浅湖下部环境;2)薄砂层扰动,扰动主要发育于薄砂层中,主要出现于浅湖中下部沉积中。

ICHNOCOENOSIS OF SHORE-SHALLOW LACUSTRINE UPPER TRIASSIC IN CENTRAL AND SOUTH SICHUAN PROVINCE

The shore-shallow lacustrine sediments of Upper Triassic in Central and South Sichuan Basin is enriched with ichnocoenosis, which consists of at least 6 ichnogenera, 8 ichnospecies, namely, Skolithos linearis, S.verticalis, Ophiomorpha nodosa, Planolites beverleyensis, P. montanus, Palaeophycus tubularis, Taenidium satanassi and Cochlichnus anguineus. The ichnocoenosis represents Domichnia, Fodinichnia and Pascichnia of invertebrates, and is preserved in full relief and epirelief. In addition, escape structure is also abundant. Based on the composition and distribution characteristics of these trace fossils and their country rock features, three types of ichnocoenosis under different sedimentary environments have been recognized as follows:1) Skolithos linearis ichnocoenosis,which mainly consists of dwelling burrows,generates in high-energy shore lacustrine sedimentary environment;2) Cochlichnus-Planolites ichnocoenosis, which mainly consists of pascichnia and fodichnia, forms in lower-energy zone of shore-lake swamp;3) Skolithos-Planolites assemblage,which is characterized by dwelling burrows and feeding burrows, and presents itself in shallow lacustrine sediments under moist climate. Based on analysis of bioturbation index, two types of bioturbation assemblages in shallow lacustrine deposits are identified as follows: 1) bioturbation near boundary between sandstone and mudstone, which occurs mainly in sediments of lower shallow lake; 2) bioturbation in thin-bedded sandstones, which develops mainly in sediments of middle to lower shallow lake.