摘要:
松辽盆地是我国白垩系分布最广、厚度最大、发育最全的陆相沉积盆地.孢粉分析发现桫椤孢在松辽盆地白垩系中比较常见.但由于桫椤孢与桫椤科或者蚌壳蕨科具有亲缘关系.桫椤孢在地层中的发现不能明确表明桫椤科植物的存在.这种状况影响了我们对松辽盆地古环境和古气候的精确分析.白垩纪桫椤科矿化茎干化石在黑龙江省齐齐哈尔市克山县的发现为解决桫椤科植物在松辽盆地存在与否的难题提供了重要证据.该化石为桫椤科树蕨植物的茎干片段,包括髓、网状中柱、皮层.分体中柱的横截面呈U、W或S形,外围具有厚壁组织鞘,分休中柱末端朝向髓部或者皮层.髓和皮层由薄壁组织组成,其中分布有许多维管束和根.创伤组织在髓中常见.当前化石是我国第一个桫椤科茎干化石记录.它的发现表明白垩纪时期松辽盆地北部曾经分布着现今多生长于热带、亚热带的桫椤科树蕨祖先类群.结合与其伴生的一些登普斯基树蕨、本内苏铁茎干等化石证据,可能指示当时气候为热带或者亚热带.
关键词:
-
桫椤科
/
-
树蕨
/
-
茎干
/
-
解剖结构
/
-
桫椤孢
/
-
白垩系
/
-
黑龙江
Abstract:
Songliao Basin is one of the largest,thickest and best preserved Cretaceous continental sedimentary basins in China.Palynological studies show that Cyathidites spores are common in the Cretaceous strata in the basin.As Cyatheaceae and Dicksoniaceae are spread in common by means of Cyathidites spores,the discovery of the Cyathidites spores is still considered to be an ambiguous evidence for the existence of Cyatheaceae plants,which hinders further precise analysis of paleoenvironment and paleoclimate in the basin.A series of Cretaceous Cyatheaceae stem fossils,found from Keshan County,Qiqihar City,Heilongjiang Province,provide solid evidence for the presence of Cyatheaceae tree fern in the Songliao Basin.The studied fossils are permineralized stem fragments of Cyatheaceae tree fern,and each piece consists of pith,dictyostele and cortex.Each meristele is S-,U-or W-shaped in transverse section,enclosed by a sclerenchyma sheath.Margins of the meristeles of the main dictyostelic ring curve deeply toward cortex or pith at the distal end of each leaf gap.Pith and cortex are parenchymatous,in which medullary bundles and roots are abundant.Wound tissues often occur in pith.This specimen is the first fossil record of Cyatheaceae trunk found in China,which suggests that ancestor taxa of the extant Cyatheaceae tree fern now living in tropical or subtropical region used to grow near Keshan County in northern Songliao Basin in Cretaceous.The present fossils and their associated petrified fossils of Tempskya and Bennettitales,may indicate that the paleoclimate there might have been tropical or subtropical.
下载: