The end-Permian biosphere crisis affected both the plants and animals in the oceans and on land. The fossil record demonstrates that marine animals suffered a mass extinction with an estimated loss of ~90% of its biodiversity over a time interval of 60,000 to 100,000 years. It has been hypothesized that a similar biodiversity loss, based on the fossil plant and vertebrate records, occurred across all continents. Yet, the data on which the terrestrial biodiversity crisis is based has been narrowly restricted to a succession of rocks in the Karoo Basin, South Africa, following an idea first published over 100 years ago. That model has been used to explain the fossil record on other continents. The current project initially focused on a unique number of outcrops in Xinjiang Province, the Uighar Autonomous Region, in western China where the crisis on land is preserved in a succession of rocks in the Bogda Mountains. With the advent of a global pandemic, and restricted access to the area, subsequent studies were refocused on the Karoo Basin where the PI and several colleagues have been working for the past two decades.

The reported absence of a megafloral record in the sediments that accumulated during this critical interval of time has been used to interpret a wholesale collapse of plant communities and a cascading effect throughout the landscape. Our studies in both western China and South Africa have shown that the near absence of a megafloral record, one in which above ground plant parts (leaves, branches, stems, reproductive structures), is the result of a combination of physical and chemical factors that operated during this interval of time. The perceived absence of large plant debris is the result of both preservational factors as well as those of sampling available exposed rock. This is because the vast majority of plant biomass is decayed and recycled on an annual basis, the introduction of aerial plant parts to settings in which they may be preserved is low when compared with leaf litters accumulating on the land surface, and presevation of these in the fossil record requires a unique sets of physical and chemical conditions that are rarely met in nature. In contrast, partially decayed plant material (mesofossils) and the more resistant reproductive structures (spores and pollen = palynomorphs) have a higher probability of surviving into the fossil record. But, these data are often overlooked.

Our studies in western China and the Karoo Basin demonstrate that sufficient biomass and biodiversity existed in these regions during the end-Permian marine crisis. Fragmented plants are the most commonly occurring fossil in the Bogda Mountain successions, are ubiquitous, and signal a robust colonization of the land surface. This interpretation is supported by the spore-and-pollen record where plants considered to have preferred more humid  and seaonally wet conditions fluctuate over time with assemblages of palynomorphs that are interpreted to have favored more seasonally dry conditions. The same palynomorph pattern is documented in the Karoo Basin where it once was thought that the region experience a wholesale extinction and turnover of plants between the latest Permian and earliest Triassic. The spore-and-pollen record once interpreted to represent the recovery flora has been shown to exist before and after the biodiversity crisis, and the loss of particular plants is likely not a sudden event. Our China and South African data, coupled with more recent reports from other continental records, show a pattern of primary producer persistence without a critical loss of plants that would have triggered a mass extinction event on land.

The project supported the engagement of undergraduate Geology students at Colby College, particularly with field work and laboratory studies based in South Africa. Student-led projects were featured a national meetings of the Geological Society of America and resulted in their co-authorship on publication in referreed professional journals. A diverse cohort engaged in this project and include both U.S. and international students. Several students continued their pursuit of an advanced geoscience degree and entered the profession, helping to build the workforce.

Last Modified: 12/29/2023
Modified by: Robert A Gastaldo