Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC, 20560, USA.
Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, 33149, USA.
Sci Rep. 2022 Jul 28;12(1):12902. doi: 10.1038/s41598-022-16651-z.
Microbialites and peloids are commonly associated throughout the geologic record. Proterozoic carbonate megafacies are composed predominantly of micritic and peloidal limestones often interbedded with stromatolitic textures. The association is also common throughout carbonate ramps and platforms during the Phanerozoic. Recent investigations reveal that Hamelin Pool, located in Shark Bay, Western Australia, is a microbial carbonate factory that provides a modern analog for the microbialite-micritic sediment facies associations that are so prevalent in the geologic record. Hamelin Pool contains the largest known living marine stromatolite system in the world. Although best known for the constructive microbial processes that lead to formation of these stromatolites, our comprehensive mapping has revealed that erosion and degradation of weakly lithified microbial mats in Hamelin Pool leads to the extensive production and accumulation of sand-sized micritic grains. Over 40 km of upper intertidal shoreline in the pool contain unlithified to weakly lithified microbial pustular sheet mats, which erode to release irregular peloidal grains. In addition, over 20 km of gelatinous microbial mats, with thin brittle layers of micrite, colonize subtidal pavements. When these gelatinous mats erode, the micritic layers break down to form platey, micritic intraclasts with irregular boundaries. Together, the irregular micritic grains from pustular sheet mats and gelatinous pavement mats make up nearly 26% of the total sediment in the pool, plausibly producing ~ 24,000 metric tons of microbial sediment per year. As such, Hamelin Pool can be seen as a microbial carbonate factory, with construction by lithifying microbial mats forming microbialites, and erosion and degradation of weakly lithified microbial mats resulting in extensive production of sand-sized micritic sediments. Insight from these modern examples may have direct applicability for recognition of sedimentary deposits of microbial origin in the geologic record.
微生物岩和泥粒通常在地质记录中共同出现。元古宙碳酸盐巨相主要由泥晶质和泥粒石灰岩组成，常与层状叠层石纹理交错。这种组合在古生代碳酸盐缓坡和台地中也很常见。最近的研究表明，位于西澳大利亚鲨鱼湾的哈密尔顿池是一个微生物碳酸盐工厂，为地质记录中普遍存在的微生物岩-泥晶质沉积相组合提供了现代类比。哈密尔顿池拥有世界上已知最大的活体海洋叠层石系统。尽管以导致这些叠层石形成的建设性微生物过程而闻名，但我们的综合测绘揭示，哈密尔顿池中弱石化微生物席的侵蚀和降解导致大量砂级泥晶颗粒的广泛产生和积累。在池中超过 40 公里的上潮间带岸线包含未石化到弱石化的微生物疱状席状微生物席，它们侵蚀后释放出不规则的泥粒。此外，超过 20 公里的凝胶状微生物席，带有薄而脆的泥微晶层，殖民于亚潮坪。当这些凝胶状席状微生物侵蚀时，泥微晶层分解形成不规则边界的片状、泥晶内碎屑。疱状席状微生物席和凝胶状铺砌微生物席的不规则泥晶颗粒加起来占池总沉积物的近 26%，每年可能产生约 24000 公吨微生物沉积物。因此，哈密尔顿池可以被视为一个微生物碳酸盐工厂，通过使微生物席石化来建造微生物岩，以及通过侵蚀和降解弱石化的微生物席来大量产生砂级泥晶质沉积物。这些现代实例的启示可能对识别地质记录中微生物成因的沉积矿床具有直接的应用价值。
