The Paleoenvironment of the Meyer Desert Formation, Transantarctic Mountains

迈耶沙漠组生长在横贯南极山脉中部多明尼安山脉的奥利弗布拉夫斯地区，南纬85度，距南极约500公里。该地点位于靠近极地高原边缘的比尔德莫尔冰川上。极地沙漠气候太冷太干，不适合高等生命的生存。该奖项支持对将从含有木材的粉砂岩以及1995年发现的泥炭和泥质沉积物中提取的化石进行研究。在早期的研究中发现的化石包括：南方山毛榉的花粉、木材和叶子，4种维管植物的种子，苔藓的茎和叶子，一种不会飞的甲虫的腿部分，介形虫的瓣，腹足类和双壳类动物的壳，以及一颗鱼的牙齿。木本维管植物在其原始生长位置的垫层表明化石组合是原位的，而不是运输到现场的。这些化石所代表的各种生物生活在南纬85度，当时南极冰盖还较小。地层学证据表明，当时的环境包括一个冰川边缘附近有植被覆盖的冰碛湖。有一个问题是现场的温度有多高。对Nothofagus化石的研究表明，在植物生长的极限处存在着恶劣的气候。然而，这种解释与化石所代表的生物多样性不一致。此外，湖中鱼类的出现表明它并没有冻结到底部。南美洲南部的麦哲伦沼地的年平均气温比今天的奥利弗布拉夫斯地区至少高出23摄氏度，这可能是古环境的一个类似物。从生物地理上看，这些生物似乎与南美洲南部有着更密切的进化联系。根据1995年在该地点收集的250公斤沉积物，将进行一系列古生物学和地球化学研究，以确定气候的温暖程度。这些生物是什么时候在比尔德莫尔山谷生活的，这个问题很重要，因为它关系到冰盖的稳定性。沉积物年龄的最佳估计是上新世，基于海洋硅藻的迁移。这意味着南极冰原的现有结构是一个相对较新的特征，在第四纪期间形成。来自南极洲和南大洋的其他证据表明，极地冰盖要古老得多，而干谷地区的地貌自中新世以来没有太大变化。上新世以全球海平面上升和北极气候变暖而闻名。这种变暖是否导致了南极冰盖在上新世期间的大规模崩解，还是它们保持了稳定？考虑到我们目前对全球变暖的担忧，回答这个问题尤为重要。迈耶沙漠组的上新世时代对这个问题至关重要，它的原位陆生生物化石表明环境要温暖得多。年龄需要确认，并将开展一系列探索项目，试图利用陆生生物化石的生物地层学，腹足类和双壳类贝壳的氨基酸分析，以及种子内生长的晶体的氩/氩分析来确定沉积物的年代。这些化石对于检验有关南半球生物地理学的假设非常重要。这些假说试图解释南美洲、澳大拉西亚、亚南极群岛和南极洲之间相关生物的分布，但由于缺乏新近纪陆生化石资料，直到现在它们还无法得到检验。

OPP 9615252 Ashworth Abstract The Meyer Desert Formation crops out in the Oliver Bluffs region of the Dominion Range in the central Transantarctic Mountains, latitude 85 degrees South, about 500 km from the South Pole. The site is on the Beardmore Glacier near the margin of the Polar Plateau. The polar desert climate is too cold and too dry to support higher forms of life. This award support studies of fossils that will be extracted from siltstones containing wood, and from peat and marl deposits discovered in 1995. Fossils discovered in earlier studies include: pollen, wood, and leaves of Nothofagus (southern beech), seeds of 4 species of vascular plants, stems and leaves of mosses, leg parts of a flightless beetle, valves of ostracodes, shells of gastropods and bivalves, and a fish tooth. A cushion of a woody vascular plant in its original growth position demonstrates that the fossil assemblage is in situ and not transported to the site. The diverse organisms represented by the fossils lived at latitude 85 degrees South during a time when the Antarctic ice sheets were smaller. Stratigraphic evidence suggests an environment that included a lake with vegetation-covered moraines, near a glacier margin. There is a question of how warm temperatures were at the site. Studies of the Nothofagus fossils suggest a harsh climate at the limits of plant growth. That interpretation, however, does not agree with the diversity of organisms represented by fossils. Also, the occurrence of fish in the lake indicates that it did not freeze to the bottom. The Magellanic Moorland of southern South America, with a mean annual temperature of at least 23 degrees Celsius higher than the Oliver Bluffs location today, is a possible analog for the paleoenvironment. Biogeographically, the organisms also seem to have closer evolutionary links with southern South America. Based on 250 kg of sediments collected at the site in 1995, a series of paleontological and geochemical s tudies will be undertaken to determine how warm the climate was. The question of when these organisms inhabited the Beardmore Valley is very important to answer because of the question of stability of the ice sheets. The best estimate for the age of the sediments is Pliocene based on transported marine diatoms. This implies that the existing configuration of the Antarctic ice sheets is a relatively recent feature, developing during the Quaternary. Other evidence from Antarctica and the Southern Ocean suggests that the polar ice sheets are much older and that the landscapes of the Dry Valleys region have not changed much since the Miocene. The Pliocene is known for its globally high sea levels and warmer climates in the Arctic. Did this warming cause a major disintegration of the Antarctic ice sheets during the Pliocene or did they remain stable? This question is especially important to answer in regard to our present concerns about global warming. The Pliocene age that has been assigned to the Meyer Desert Formation, with its in situ fossils of terrestrial organisms indicating much warmer conditions, is critical to this question. The age needs to be confirmed and a series of exploratory projects will be undertaken to attempt to date the deposits using the biostratigraphy of the fossils of terrestrial organisms, amino acid analysis of the gastropod and bivalve shells, and argon/argon analysis of crystals growing inside the seeds. The fossils are very important to test hypotheses about Southern Hemisphere biogeography. These hypotheses have attempted to explain the distribution of related organisms between South America, Australasia, the Subantarctic Islands, and Antarctica but until now they have been untestable because of an absence of Neogene terrestrial fossil data.