Lycopsid forests in the early Late Devonian paleoequatorial zone of Svalbard
Lycopsid forests in the early Late Devonian paleoequatorial zone of Svalbard
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DOI：
10.1130/g37000.1
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发表时间：
2015-12-01
期刊：
影响因子：
5.8
通讯作者：
Marshall, John E. A.
中科院分区：
文献类型：
--
作者：
Berry, Christopher M.;Marshall, John E. A.
中晚泥盆世早期的过渡，从小型植物的第一个森林是一个关键的插曲在terrestrialization。目前在这种“过渡森林”中确认的两个主要植物类群是pseudosporochnaleans（小型至中型树木，形态上与现存的蕨类植物和棕榈树相似）和archaeopteridaleans（树干木质，树枝多叶，可能与现存的针叶树有关）。在这里，我们报告了一种新的类型的“过渡”在原地泥盆纪森林的基础上从Planteklofta组，穆宁达伦，斯瓦尔巴特群岛石松化石。以前被认为是最晚的泥盆纪（最晚的法门期，360 Ma），他们的年龄，根据孢粉学，是早期弗拉斯（约。380 Ma）。原地树的代表是树形石松类的内部铸型，具有球茎状基部和小的带状根，出现在密集的林分中，间隔约为15-20厘米，在这里被鉴定为Protolepidodendropsis pulchra Hoeg。这种植物也作为压缩化石出现在吉韦阶晚期-弗拉斯阶早期的米默达伦亚群的大部分地区。石松类植物生长在一个局部的、快速沉降的、短命的盆地的潮湿土壤中。重要的是，这种新类型的中晚泥盆世早期森林是古赤道，因此热带。与其他当代和更高纬度的森林相比，这种高树木密度的热带植被可能促进了土壤的快速风化，从而增加了二氧化碳的减少。
The Middle to early Late Devonian transition from diminutive plants to the first forests is a key episode in terrestrialization. The two major plant groups currently recognized in such "transitional forests" are pseudosporochnaleans (small to medium trees showing some morphological similarity to living tree ferns and palms) and archaeopteridaleans (trees with woody trunks and leafy branches probably related to living conifers). Here we report a new type of "transitional" in-situ Devonian forest based on lycopsid fossils from the Planteklofta Formation, Munindalen, Svalbard. Previously regarded as very latest Devonian (latest Famennian, 360 Ma), their age, based on palynology, is early Frasnian (ca. 380 Ma). In-situ trees are represented by internal casts of arborescent lycopsids with cormose bases and small ribbon-like roots occurring in dense stands spaced similar to 15-20 cm apart, here identified as Protolepidodendropsis pulchra Hoeg. This plant also occurs as compression fossils throughout most of the late Givetian-early Frasnian Mimerdalen Subgroup. The lycopsids grew in wet soils in a localized, rapidly subsiding, short-lived basin. Importantly, this new type of Middle to early Late Devonian forest is paleoequatorial and hence tropical. This high-tree-density tropical vegetation may have promoted rapid weathering of soils, and hence enhanced carbon dioxide drawdown, when compared with other contemporary and more high-latitude forests.