天津蓟县中元古界高于庄组“球形臼齿状构造”新解——1400 Ma以前球形或似球形实体宏观藻类化石的细胞显微结构

天津蓟县剖面高于庄组,组成一个复杂而特别的叠层石—非叠层石碳酸盐岩沉积序列,其中,第三段构成一个特征迥异的非叠层石碳酸盐岩沉积序列。在该非叠层石序列上部的均一石灰岩(隐晶质泥晶灰岩)中普遍发育大小不等的带状臼齿状构造,与臼齿状构造共同产出的是一些数毫米乃至厘米级的球形体或似球形体。这些球形体或似球形体,曾经被解释为球形臼齿状构造,也被解释为灰岩结核、燧石结核或凝灰岩结核。岩石薄片的显微镜观察表明,这些球形体或似球形体的内部,显示出较为明显但又较为原始的多细胞组织,如分生组织和类似于薄壁组织的成熟组织,其中一些成熟细胞还保留着较为明显的细胞显微结构,表明这些球形体或似球形体的内部结构明显不同于臼齿状构造的特殊填充物——等粒状微亮晶方解石。因此,这些球形体或似球形体应该归为丘尔藻或拟丘尔藻之类的宏观藻类化石,而不是球形臼齿状构造。尽管前人在前寒武纪地层之中描述了若干宏观藻类化石,但多以碳质压型的形式保存在泥岩之类的细粒沉积之中。发现于天津蓟县剖面高于庄组灰岩中的实体球形或似球形宏观藻类化石,以其较老的地质年代(大于1400Ma)、较为明显而又原始的多细胞组织和一些成熟细胞的可能细胞显微结构,表明该球形实体化石具明显的多细胞真核生物属性。这些初步研究和发现为探讨真核生物的起源演变、揭示宏观藻类化石的生物学属性提供了罕见的实际材料,因而具有重要的意义。

New Interpretation of Spheroidal Molar-Tooth Structures from Mesoproterozoic Gaoyuzhuang Formation at the Jixian Section in Tianjin:Possibly Cellular Microstructure of the Spheroidal or the Sub-spheroidal Three-Dimensional Fossils of Megascopic Algae befo

The Mesoproterozoic Gaoyuzhuang Formation at the Jixian section in Tianjin makes up a stromatolitic and non-stromatolitic carbonate succession,in which the third member is a particular sedimentary succession of the non-stromatolitic carbonate.Various ribbon-shaped molar-tooth structures are developed in the leionite limestones(aphanitic limestones) of the upper part of the succession of the non-stromatolitic carbonate,and lots of spherical or sub-spherical bodies with the sizes from several millimeters to more than one centimeter are frequently paragenetic with the molar-tooth structures.These spherical or sub-spherical bodies can be interpreted as the spherical molar-tooth structure,the lime concretion,the chert concretion,or the tuff concretion.Preliminary observation under the common microscope shows that there is a differentiation of primitive multicellular tissues within these spherical or sub-spherical bodies,i.e.the possible meristem in the central part and the possible mature tissue like the parenchyma.And some possible mature cells indicate the obvious microstructure.These features of the microstructures of the spherical or sub-spherical bodies show the strong difference from the molar-tooth structure filling with the special substance,i.e.the calcite microspar.Thus,these spherical or sub-spherical bodies should be grouped into the fossils of megascopic algae such as the Chuaia or the Parachuaria but not the spherical molar-tooth structure.Furthermore,most fossils of megascopic algae that had been found and described are mainly preserved as the fashion of carbonaceous compressions in fine deposits such as mudstones or shales,but fossils of megascopic algae in the leiolite limestones of the third member of the Gaoyuzhuang Formation at the Jixian section are characterized by three-dimensional fossils.Other features such as the older geological time that is more than 1,400 Ma,the obvious but primitive differentiation of the multicellular tissue and the possibly cellular microstructure,endow these fossils of megascopic algae with the biologically eukaryote attributes,which provides an unusual material and is meaningful for the further research on the evolution and origin of the eucargote.