Geologic Story of the Interstate Park Area

Home , Glacial River Warren, Platteville Limestone

Jim Miller University of Minnesota Duluth Bedrock Geology Glacial Geology Geologic Timescale Plate Tectonic Theory The Earth’s outer shell (lithosphere) is composed of rigid plates that are moving relative to one another. Convergent Divergent Boundaries Boundaries Divergent Boundaries Continental Rifting Making Ocean Crust “Recent” Continental Rifting The Break-up of Pangea

Permian - 225 Ma Triassic - 200 Ma

Today

Jurassic - 150 Ma Cretaceous - 65 Ma North America (Laurentia) in the Late Precambrian (1,100,000,000 years ago) ______

THE MIDCONTINENT RIFT ______An attempt at continental rifting 1.1 billion years ago Evolution of the Midcontinent Rift

1,109-1,086 Ma

1,090-900 Ma

1,000-900 Ma

Fissure Eruption Massive Basalt

Amygdaloidal Basalt Amygdules – Gas bubble fillings

Chlorite & Zeolite Zeolite

Epidote & Feldspar Thompsonite LAKE SUPERIOR AGATES Gemstone of Minnesota Formation of Lake Superior Agates 1,000,000,000 Years Ago Minnesota becomes the stable interior of the North American Continent

500,000,000 Years Ago Shallow seas begin to periodically flood Minnesota Distribution of the Continents ~500 Million Years Ago Global Variations in Sea Level over the past 500,000,000 years Paleozoic Epicontinental Seas

Transgression of the Paleozoic Seas Advanced Transgression Regression Paleozoic Formations of the Midwest

Twin Interstate Park Cities

Interstate Park Ordovician Rocks of the Mississippi River Bluffs P-Platteville Limestone G-Glenwood Shale S-St. Peter Sandstone

P G-- S

Mound Park P G-- Minnehaha Falls S P G--

Ford Dam and Lock Fossil Hunting in the Twin Cities Lilydale Park (the Brickyard) The Pleistocene Epoch THE ICE AGE 1,800,000,000-10,000 years

Minnesota’s Landscape: The Legacy of the Glaciers Zone of Accumulation

Zone of Ablation

Myrdasjokull Ice Cap, S. Iceland, 1999, C.J. Patterson Continental Glacial Landforms formed during Glacial Retreat

The Land of 10,000 Lakes The Invasion of the Canadian Ice Lobes The Last Retreat Glacial Lake Agazzi

The Mother of All Lakes

Maximum ~10,000 years ago Bemis Moraine The Dam Glacial Brule/ St. Croix River Draining Glacial Glacial River Warren/ Lake Duluth Minnesota River The Spillway Mississippi-Minnesota River Confluence Mississippi R.

Buried Bedrock Valley Minneapolis St. Paul Minnehaha Falls Minnesota R.

Buried Bedrock Valley --Pleasant Lake

-- Lake Vadnais

--Gervais Lake

--Phalen Lake Buried River Channel St. Paul - Today

St. Paul – 12,000 years ago

1-1.5 miles 150-200’

1835

St. Anthony Falls 12,000 Years in the Making

1902

1888

Today Potholes of Interstate Park Evidence of Torrents

Photos courtesy of UW-Eau Claire THE ICE AGE IS IT OVER???