Masters Theses

Date of Award

3-1985

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Paul A. Delcourt

Committee Members

Hazel R. Delcourt, Thomas Broadhead, Kenneth Walker

Abstract

A 6.2 meter core of lacustrine sediment from Jackson Pond, Larue County, Kentucky represents the first continuous sequence from Kentucky permitting the vegetational reconstruction for the full-glacial through late-Holocene intervals. Jackson Pond is a spring-fed pond situated within a karst-collapse basin underlain by Ste. Genevieve and St. Louis limestone of Mississippian age. The site is located at 37°27'N, 85°30'W, 190 km south of the full-glacial limit of the Laurentide Ice Sheet. Six sediment samples submitted for radiocarbon analysis provide an absolute chronology for the site for the last 20,460 years.

From 20,460 yr B.P. to 20,330 yr B.P. the forest community consisted of a jack pine (Pinus banksiana) dominated boreal forest with a spruce (Picea) subdominant. The remainder of the full-glacial interval, from 20,330 yr B.P. to 16,800 yr B.P., is marked by a co-dominance of jack pine and spruce, and a limited population of the temperate species oak (Quercus), black ash (Fraxinus nigra), elm (Ulmus), sugar maple (Acer saccharum), and hornbeam (Ostrya/Carpinus). A spruce dominated open woodland represents the late-glacial interval, with pine remaining a subdominant. The late glacial is marked by a number of rapid biotic changes in which oak, spruce, and black ash have a co-dominance of the arboreal taxa. The early Holocene, from 10,040 yr B.P. to 7300 yr B.P., is characterized by a mesic northern hardwood-conifer open woodland with spruce, elm, hornbeam, oak, basswood (Tilia), beech (Fagus grandifolia), and hemlock (Tsuga). The remainder of the Holocene is represented by an open oak savannah. Near the pond a suite of warm temperate arboreal taxa, sweetgum (Liquidammbar styraciflua), blackgum (Nyssa), and red maple (Acer rubrum) are established along with a swamp shrubbery of buttonbush (Cephalanthus occidentalis), blackberry (Rubus), and virginia willow (Itea virginica).

Full-glacial climatic extremes reduced temperate taxa to near elimination, with only a few cold-hardy species able to maintain sparse populations 190 km from the maximum ice front. Late-glacial climatic amelioration is marked by a decline in boreal taxa density, but without any significant replacement by deciduous taxa. During the Holocene an open oak savannah predominated, producing the "Barrens" observed by early Euro-American settlers. Distributions of plant taxa are suggested to be dependent upon the environmental parameters established by major air mass systems. The changing positions of the Maritime Tropical, Pacific, and Arctic Air Masses determined the nature of vegetation around Jackson Pond.

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