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首页> 外文期刊>Stratigraphy >Pre-neogene non-marine diatom biochronology with new data from the late eocene florissant formation of Colorado, USA
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Pre-neogene non-marine diatom biochronology with new data from the late eocene florissant formation of Colorado, USA

机译：前新生代非海洋硅藻生物年代学，来自美国科罗拉多州始新世晚期佛罗里达植物形成的新数据

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Studies of the non-marine diatom assemblages from Eocene deposits in North America extend the fossil record of a number of extant freshwater diatom lineages. These and other accounts show that the earliest documented appearances of non-marine diatoms consisted of 7 genera from late Cretaceous deposits, followed by 36 more from the Eocene, and 4 additional genera from Oligocene to early Miocene localities. A total of 47 diatom genera, 45 of which are extant, therefore, are known from pre-Neogene (>23.8 Ma) non-marine deposits. The chronological extension of these first-occurrences of genera has implications for terrestrial diatom biostratigraphy, paleoclimate, and diatom phylogenetic studies. An overview of the pre-Neogene non-marine diatom biochronology from published records and original work provides the geologic and geographic context for the more current findings. Two geologic range charts synthesize the data from the pre-Neogene non-marine (fresh and brackish water) diatom floras from the 9 published localities, supplemented by additional findings from a recent floristics study of the Florissant site in Colorado. These charts allow easy comparison of the timing, floral composition, and taxon-richness at the genus level and higher for the 9 sites. Among the pre-Neogene sites discussed here are early and middle Eocene deposits in Canada and middle Eocene deposits in Idaho andWyoming that provide evidence of an early pulse in the post-Cretaceous radiation of freshwater diatoms. The survey of the fossil diatoms from lake sediments of the Florissant Formation in Colorado showed that this deposit contains the most diverse (genus-rich) early freshwater diatom flora on record. This late Eocene flora suggests a later pulse in freshwater diatom radiation during pre-Neogene time that contributed to the rich taxonomic diversity of today. The Florissant fossil diatom investigations yield a total of 33 freshwater diatom genera. This number exceeds by 20 genera any other single known non-marine diatom-bearing Eocene and older deposit. The Florissant diatom flora consists of taxa with decidedly modern affinities, has superior diversity (taxon-richness), and yields the first-reported occurrence in the geologic record of 14 freshwater genera. From the 9 featured pre-Neogene sites, genera of centric, araphid, biraphid, and monoraphid morphologic groups are represented. While the findings of these studies are not inconsistent with the previously predicted timing of the first appearance of the major morphological diatom groups, the actual known fossil record post-dates the presumed timing of such morphological differentiation. Although the first occurrences in these deposits must be treated as apparent first occurrences due to the innate incompleteness of the fossil record, such findings confirm that species of many of the modern non-marine diatom genera had evolved prior to the end of the Eocene. It is anticipated that this synthesis of the pre-Neogene non-marine diatom floras will provide necessary paleontological evidence for interpreting the true geologic ranges of several diatom lineages. This work could facilitate future application of diatoms in biostratigraphic studies of fossil lake beds in hydrologic and climate change studies and in hydrocarbon exploration. Perhaps such data will generate insights to diatom phylogenetics that may lead to a greater understanding of their evolutionary histories. Further research could potentially relate changes in diatom forms to global events that might include climate shifts.
机译：对北美始新世矿床的非海洋硅藻组合的研究扩展了许多现存淡水硅藻谱系的化石记录。这些和其他说明表明，最早记录的非海洋硅藻的出现包括白垩纪晚期沉积物中的7属，其次是始新世以来的36属，以及渐新世到中新世早期的另外4属。从新近纪前（> 23.8 Ma）的非海洋沉积物中已知总共有47个硅藻属，其中现存的是45个。这些属的按时间顺序扩展对陆生硅藻生物地层学，古气候和硅藻系统发育研究具有影响。从已出版的记录和原始工作中获得的新近纪前非海洋硅藻生物年代学概述为最新发现提供了地质和地理背景。两张地质测距图综合了来自9个已发布地区的新近纪前非海洋（淡水和微咸水）硅藻植物区系的数据，并补充了科罗拉多州Florissant遗址的最新植物学研究结果。通过这些图表，可以轻松比较属类及更高级别的9个位点的时间，花组成和类群丰富度。这里讨论的新近纪前站点是加拿大的始新世中期和中新世沉积以及爱达荷州和怀俄明州的始新世中期沉积，这提供了白垩纪后淡水硅藻辐射的早期脉动的证据。对科罗拉多州弗洛里森特组湖沉积物中的硅藻化石进行的调查显示，该矿床包含有记录以来种类最多（属丰富）的早期淡水硅藻群落。始新世晚期的植物群表明，在新近纪之前的时间里，淡水硅藻的辐射出现了较晚的脉冲，这导致了当今丰富的生物分类学多样性。弗洛里森化石硅藻的研究共产生了33个淡水硅藻属。这个数字比任何其他已知的非海洋硅藻始新世和较老的沉积物都多20属。 Florissant硅藻菌群由具有明显现代亲和力的生物分类组成，具有优越的多样性（丰富的生物分类），并在14个淡水属的地质记录中首次报道了这种生物。从9个特征性的新近代前位点中，代表了中枢，阿拉菲特，双头怪和单头怪形态群的属。虽然这些研究的结果与主要的形态硅藻群首次出现的时间并不相符，但实际已知的化石记录将这种形态分化的时间推后。尽管由于化石记录的先天不完全性，这些沉积物中的首次出现必须被视为明显的首次出现，但这些发现证实，许多现代非海洋硅藻属的物种在始新世末期就已经进化了。可以预期，新近纪前非海洋硅藻植物区系的这种合成将为解释若干硅藻谱系的真实地质范围提供必要的古生物学证据。这项工作可以促进硅藻在水文和气候变化研究以及油气勘探中化石湖床生物地层学研究中的未来应用。也许这样的数据将对硅藻的系统发育产生深刻的见解，从而可能导致对它们的进化历史的更多了解。进一步的研究可能会将硅藻形式的变化与可能包括气候变化的全球事件联系起来。

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