by Lionel Jackson Monday, July 2, 2018
Pollen grains thought to have once been trapped in rock from the Late Triassic Chinle Formation (left) and the Pennsylvanian to lower Permian Supai Group (right) in the Grand Canyon area of northern Arizona were found in the former delta complex of the Paleo-Bell River beneath the Labrador Sea, roughly 5,000 kilometers from their former outcrops. Credit: left: Finetooth, CC BY-SA 3.0; right: Luca Galuzzi, CC BT-SA 2.5.
Pollen makes an ideal fossil. Pollen grains — each only a few tens of microns in diameter — are produced in astronomical quantities by plants and record information about the ecosystem from which they came, thus providing a way to reconstruct past environments. Additionally, pollen is composed of a highly stable organic substance, sporopollenin, which resists decay as well as the high heat and pressure associated with deep burial, lithification and tectonism. It is so resistant, in fact, that it can be eroded from rock and recycled into younger sediments, a process recognized in the 1980s by V. Eileen Williams of the University of British Columbia in her studies of Paleo-Bell River sediments deposited in the Labrador Sea.
In a 2013 paper in GSA Today, James Sears of the University of Montana reviewed Williams' findings and noted that among the recycled palynomorphs was an assemblage common in the Chinle Formation and the Supai Group in the Grand Canyon area. This fit well with Sears' reconstruction of the drainage history of the Grand Canyon area and supported a connection to the Paleo-Bell River system. Sears postulated that this connection was eventually blocked about 16 million years ago by volcanic eruptions from the Yellowstone Hot Spot track as it migrated eastward, as well as diversion farther south due to faulting in the Colorado Plateau region. If his hypothesized connection is correct, then during the first half of its history, the Paleo-Bell River Basin would have been substantially larger than Robert Bell had even imagined.
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