Gzhelian Age
Brief Domination of Tree Ferns
The Gzhelian (304–299 Ma) is the last age in the Carboniferous Period, occurring after the Kasimovian age, and before the Asselian age of the Permian Era
Geologic Age
303.7±0.1–298.9±0.2 Ma
Eon / Era / Period / Epoch
What happens during this time?
Biological
Flora
This change resulted in a major turnover in the structure of the Coal Swamps.
The lycopsids which so dominated the Bashkirian and Moscovian ages were practically reduced to one genera Sigillaria.
Ferns replaced the lycopsids in abundance with the latter being reduced to the wettest parts of the swamps.
The dominance of the Marattioid ferns was only temporary as pteridosperms eventually supplanted them
At the very end of the age, the Coal Forests underwent a resurgence, expanding mainly in eastern Asia, notably China; they never recovered fully in Euramerica.
The Chinese Coal Forests continued to flourish well into Permian times.
Fauna
This is the age of the giant flying meganeurid insects, called griffinflies
Meganeura was related to living dragonflies and damselflies, in the group Odonatoptera
They had wingspans ranging from 65 cm (25.6 in) to over 70 cm (28 in)
Meganeura monyi is one of the largest-known flying insect species every recorded in Earth's history
It is suggested that extremely high oxygen levels at this time allowed these insects to get to enormous sizes (Chapelle & Peck 1999)
Other researchers have suggested that a lack of aerial vertebrate predators may have been the cause (Bechly 2004)
Geophysical
The climate continues to become dry, with glaciations and polar ice
This resurgence of the Coal Forests seems to have coincided with a lowering of global temperatures, coinciding with a return of extensive polar ice in southern Gondwana.
This lessening of the greenhouse effect may be due to massive coal deposition extracting much carbon dioxide from the atmosphere.
The Gzhelian was also a time of glaciation with the poles extremely cold (particularly in the south).
The equatorial regions remained wet and warm. This period of glaciation persisted into the Permian.
The Late Paleozoic Ice Age (LPIA), lasted from the Late Devonian to the Late Permian, but during the Late Carboniferous alkalophilic methanogenic archaea produced large quantities of methane that were into the atmosphere (Xia et al. 2023)
This increased and consistent supply of methane, which peaked at around 304 mya, could have had a significant impact on global greenhouse gas levels.
