Laval B, Cady S L, Pollack J C, McKay C P, Bird J S, Grotzinger J P, Ford D C, Bohm H R
School of Engineering Science, Simon Fraser University, Burnaby, British Columbia, Canada.
Nature. 2000 Oct 5;407(6804):626-9. doi: 10.1038/35036579.
Microbialites are organosedimentary structures that can be constructed by a variety of metabolically distinct taxa. Consequently, microbialite structures abound in the fossil record, although the exact nature of the biogeochemical processes that produced them is often unknown. One such class of ancient calcareous structures, Epiphyton and Girvanella, appear in great abundance during the Early Cambrian. Together with Archeocyathids, stromatolites and thrombolites, they formed major Cambrian reef belts. To a large extent, Middle to Late Cambrian reefs are similar to Precambrian reefs, with the exception that the latter, including terminal Proterozoic reefs, do not contain Epiphyton or Girvanella. Here we report the discovery in Pavilion Lake, British Columbia, Canada, of a distinctive assemblage of freshwater calcite microbialites, some of which display microstructures similar to the fabrics displayed by Epiphyton and Girvanella. The morphologies of the modern microbialites vary with depth, and dendritic microstructures of the deep water (> 30 m) mounds indicate that they may be modern analogues for the ancient calcareous structures. These microbialites thus provide an opportunity to study the biogeochemical interactions that produce fabrics similar to those of some enigmatic Early Cambrian reef structures.
微生物岩是一种有机沉积结构，可由多种代谢方式不同的生物分类群构建而成。因此，微生物岩结构在化石记录中大量存在，尽管形成它们的生物地球化学过程的确切性质通常并不清楚。其中一类古老的钙质结构，即附生藻类和丝状蓝细菌，在寒武纪早期大量出现。它们与古杯动物、叠层石和凝块石一起，构成了寒武纪主要的礁带。在很大程度上，寒武纪中期到晚期的礁体与前寒武纪礁体相似，只是后者（包括新元古代末期的礁体）不包含附生藻类或丝状蓝细菌。在此，我们报告在加拿大不列颠哥伦比亚省的帕夫柳恩湖发现了一种独特的淡水方解石微生物岩组合，其中一些微生物岩的微观结构与附生藻类和丝状蓝细菌所呈现的结构相似。现代微生物岩的形态随深度变化，深水（> 30米）丘体的树枝状微观结构表明它们可能是古代钙质结构的现代类似物。因此，这些微生物岩为研究生物地球化学相互作用提供了一个机会，这种相互作用产生的结构类似于一些神秘的寒武纪早期礁体结构。
