BioBlitz

The Cayuga Basin

Geology of the Cayuga Basin

Deltas form where a river enters the ocean, or, where a creek enters a large lake such as Cayuga Lake. The waterfront at Taughannock Park is formed by a modern delta where Taughannock Creek enters the lake. The same is true on Cayuga Lake’s east shore where Salmon Creek forms Myers Point. The creeks carry sediment eroded from the landscapes they pass through, and when the muddy current arrives at the less turbulent lakefront the sediment is deposited. These deposits build out into the lake to form Myers Point and Taughannock Point.

In the geologic past deltas mark the positions of ancient lakes. While it seems obvious to point out in a modern environment that deltas lie at-or-near sea level (or lake level), this fact is less evident when considering paleo-deltas. Yet just as modern Cayuga Lake features a delta at the mouth of each creek that enters the lake, ancient Cayuga Lake did as well. At the height of the last ice age 20,000 years ago Ithaca and the Cornell Campus were buried under a continental ice sheet more than a mile thick. As the climate warmed and the ice melted, the meltwater was impounded behind piles of sediment deposited by the retreating glacier. The oldest of these glacial lakes – Lake Newfield – was at an elevation of 1200 feet above sea level. Creeks carried sediment into the lake, forming deltas that mark the position of the ancient shoreline. The meltwater eventually eroded through the sediment dam, causing the lake level to drop until it stabilized at a new, lower, elevation. In the Cayuga Basin this processes repeated itself several times, leaving behind a series of deltas high above modern Cayuga Lake. Deltas left high and dry on the shores of lakes that no longer exist are called hanging deltas. The Cornell campus is built on a series of hanging deltas created by Fall Creek as it responded to the retreating lake levels of ancient Cayuga Lake. The Ag Quad, Arts Quad, and West Campus are each built on successively lower shores of the disappearing glacial lake.

Farther back in time deltas were also important in central New York. In the Devonian Period (360-416 million years ago) what we now call the Finger Lakes region lay beneath the ocean. The tectonic collision of North America with continental micro-fragments from Europe created the Acadian mountain range, located to the east of modern Ithaca. Erosion of sediment from the Acadian Mountains formed a series of deltas along the western margin of the range. These deltas, together, are called the Catskill Delta complex. While the delta surface lay at sea level, extensive sedimentary deposits continued offshore into deeper water. The bedrock of the Cayuga Basin is formed of ancient delta deposits; sandstone and shale from the submarine portion of the Catskill Delta. 

Later, in the Permian Period (252-299 million years ago), the African continent collided with North America, creating the modern Appalachian Mountains. This event uplifted and fractured the Devonian sedimentary rocks. The fractures are remarkably straight and planar, forming parallel sets of joints that are important controls on the geometry of the modern landscape. The Cayuga Lake shorelines follow the joints, as do the courses of the region’s rivers and creeks.

Ecology of the Cayuga Basin

The landscape around Ithaca was shaped by ancient tectonic forces and then modified much more recently by the repeated advance and retreat of glacial ice. One effect of glacial scouring was to completely remove the living organisms that had once inhabited the Cayuga Basin. The current ecosystems date from the last retreat of glacial ice around 12,000 years ago. Boreal forest species were the first colonizers, particularly conifers such as fir and spruce. The rapidly warming climate created conditions more suitable for the mixed hardwoods that still grow in the region today.

The glacial debris that blankets the local hills contains abundant limestone, picked up from bedrock outcrops north of Tompkins County and carried south by the advancing ice. As soils began to form on top of the glacial deposits their composition was profoundly influenced by the presence of limestone debris. Limestone raises the pH of both soil and surface waters, creating a unique substrate for the organisms that eventually colonized the Cayuga Basin.

Soil and topography work together with climate to create the conditions that support varied communities of organisms. The Cayuga Basin straddles an ecotone – a transition from one ecosystem type to another. The northern end of Cayuga Lake sits within the Eastern Great Lakes Lowlands. Historically this was a hardwood forest dominated by beech and sugar maple with smaller amounts of white oak, basswood, elm, and white ash. Although forests once entirely covered the Lowlands, only scattered patched remain today following clearing for agriculture. The southern end of Cayuga Lake is part of the Northern Allegheny Plateau. Historically, the natural vegetation was primarily Appalachian oak forest dominated by white oak and red oak, with some northern hardwood forest at higher elevations. The glaciated landscape – especially the steep U-shaped valleys of the Finger Lakes and the tributary valleys that feed them – creates an array of microhabitats within these larger ecosystems that support highly diverse biological communities.