Friday, August 27, 2010

Fossil Pollen Reveals Florissant's Ice Age Environment

Out of the mists of prehistory—through fossil pollen and spores—comes an unprecedented glimpse into Florissant’s past. Experts used cutting-edge science to examine pollen and spores buried with a fossil mammoth to better understand the Ice Age world of Florissant.

Entrance to the Florissant Fossil Beds, Colorado
The Florissant mammoth lived and died more than 50,000 years ago, during the last Ice Age. Its bones were fossilized safely in the ground until a student intern found it in 1994. During careful excavation of the mammoth, all of the fossil material was collected and bagged—including soil, gravel, and sediment samples. A molar tooth and part of the mammoth’s jaw were the main fossils recovered. Scientists used these to identify the mammoth as a Columbian mammoth.

A lab recently analyzed a sample from the sediment layer just below the mammoth. The lab determined that the sedimentary layer is a limestone containing fine sandy and silty quartz grains.

New pollen evidence from the mammoth site at the Florissant Fossil Beds reveals environmental conditions during one of the warm, interglacial periods of Teller County's Ice Age.  Above is a fossil pine pollen. The abundance of pine pollen, along with the rock moss, indicates a dry climate at Florissant.  Photomicrogrpah is by D. Jarzen.
The lab first prepared the limestone for processing to recover pollen and spore grains. Solutions of corrosive chemicals such as potassium hydroxide, hydrochloric acid, and hydrogen fluoride removed the organic and mineral particles in the sample. The pollen, because it is composed of some of the most chemically resistant organic compounds in nature, survived this harsh chemical processing.

Next, lab workers made microscope slides from the residual pollen and carefully examined them. When viewed with a microscope, pollen grains from different plants have distinctive appearances that can identify the plant species they came from. The pollen and spores were identified and counted.
The lab work identified an amazing assemblage of Ice Age vegetation at Florissant, making it possible to reconstruct much of the local environment based on these tiny fossils. A major surprise was finding hickory (Carya) and oak (Quercus)—both hardwoods—in the Rocky Mountains from a lab sample that was at least 50,000 years old. From microscopic examination of the hardwood pollen it appears that they grew locally during the Ice Age. There is no reason to think they are reworked from sediments redeposited from earlier times.

Image of a hickory (Carya) pollen grain.  Pollen grains are incredibly resistant and are difficult to destroy by physical or chemical processes.  The plentiful and hardy nature of pollen makes it a source of data about past climates in specific places. Photomicrograph by D. Jarzen.
The pollen and spore assemblage is a tiny time capsule from Florissant’s Ice Age and reveals that Florissant had a dry climate during this interglacial period—indicated by the abundance of pine pollen and rock moss (Selaginella). The landscape was relatively open and covered with vegetation. Scattered stands of pine, along with some hardwoods growing near streams, dotted the landscape. Groundcover included asters, daisies, sunflowers (Compositae), and sagebrush. Most important was the rock moss, which grows on rocks and thrives on direct sunlight. Rock moss is a key indicator of a dry climate.

Image of an aster pollen grain.  Image of an aster pollen grain. Because most plant species have distinctive pollen shapes, botanists can identify from which plant the pollen came, allowing scientists to determine the plants found in a certain place at a given time. Photo by D. Jarzen.
Florissant’s fossil mammoth and associated material continues to yield scientific information. The current pollen study is important because in the continental United States there is little information on interglacial floras. The Florissant pollen adds significantly to our understanding of North American interglacial floras.
The Florissant mammoth and its associated pollen has not only unlocked some of the secrets of Florissant’s Ice Age, but has earned an enduring place in the paleontological record.

Note: Steven Veatch is the principal investigator working on the Florissant pollen project. His team incldes David Jazen of the University of Florida, Estella Leopold of the University of Washington, and Herbert Meyer, park paleontologist (Florissant Fossil Beds Natinal Monument).

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