四川盆地南部赤水地区下三叠统嘉陵江组遗迹化石及其沉积环境

在赤水地区嘉陵江组中共发现遗迹化石4个属8个种,其中有3个未定种,即Palaeophycus tubularis(管状古藻迹),Palaeophycus curvatus(弯曲古藻迹),Palaeophycusisp.A(古藻迹未定种A),Palaeophycus isp.B(古藻迹未定种B),Planolites octichnus(八曲漫游迹),Helminithopsis abeli(阿伯尔拟蠕形迹),Helminithopsis isp(似蠕虫迹未定种),Phycodes pedum(足状拟藻迹)。这些遗迹化石主要为无脊椎动物的觅食迹和进食迹,其中多数为下浮雕保存,其次为上浮雕保存,少数为全浮雕保存。根据遗迹相组合特征,结合沉积相分析,可划分出两个遗迹组合:Palaeophycus遗迹组合,代表的是水体较浅、受短期海平面变化影响较大的灰岩坪沉积环境;Planolites-Helminithopsis遗迹组合,代表的是与Palaeophycus遗迹组合相比水体较深、能量较低的开阔海台地的台内洼地环境。

Ichnofossils and Sedimentary Environment of Lower Triassic Jialingjiang Formation in Chishui Area, Southern Part of Sichuan Basin

Some Lower Triassic ichnofossils are first discovered in Chishui area, the southern part of Sichuan Basin. These fossils are attributed to 4 ichnogeneras and 8 ichnospecies, including 3 ichnospecies indeterminated, in Jial- ingjiang Formation, namely Palaeophycus tubularis, Palaeophycus curvatus,Palaeophycus isp.A, Palaeophycus isp.B, Planolites octichnus,Helminithopsis abeli, Helminithopsis isp and Phycodes pedum. All of these ichno- fossils chiefly are invertebrate fodinichnia and agrichnia, in which the majority is preserved as hyporelief, the next as epirelief and the minority as full relief. According to the characteristics of ichnofacies assemblages, com- bined with the analysis of sedimentary facies,these fossils can be divided into two ichnoassemblags: (1)Palaeo- phycus ichnoassemblage,representing the depositional environment of limestone flat during shallow water effected by short term change of sea level. (2)Planolites—Helminithopsis ichnoassemblage, representing the depositional environment of innerdepression within open sea platform with lower energy during deeper water than that of the Palaeophycus ichnoassemblage.