Geodiversity Atlas—Heartland I&M Network Index

Geology and Stratigraphy of the Heartland I&M Network Index

The Heartland Inventory & Monitoring Network (HTLN) consists of 15 national park units distributed across midwestern America in parts of Arkansas, Indiana, Iowa, Kansas, Nebraska, Ohio, Minnesota, and Missouri. These park units include Arkansas Post National Memorial (ARPO), Buffalo National River (BUFF), Cuyahoga Valley National Park (CUVA), Effigy Mounds National Monument (EFMO), George Washington Carver National Monument (GWCA), Herbert Hoover National Historic Site (HEHO), Homestead National Historical Park (HOME), Hopewell Culture National Historical Park (HOCU), Hot Springs National Park (HOSP), Lincoln Boyhood National Memorial (LIBO), Ozark National Scenic Riverways (OZAR), Pea Ridge National Military Park (PERI), Pipestone National Monument (PIPE), Tallgrass Prairie National Preserve (TAPR), and Wilsons Creek National Battlefield (WICR). In addition, although not officially considered part of the HTLN, Fort Scott National Historic Site (FOSC) is included in this report. The parks that comprise the network protect a combined 95,901 hectares (236,978 acres) and feature prehistoric earthworks, battleground sites of the American Revolution and Civil War, free-flowing rivers, geothermal hot springs, and more. Park units of the HTLN range in size from 38,159 hectares (94,293 acres) in BUFF to approximately 7 hectares (17 acres) at FOSC.

The geologic history of the HTLN area goes back to the Precambrian nearly 2 Ga (Giga-annum, billion years ago) and involves several major collisional events that slowly constructed the proto-North American continent (Laurentia) and assembled the configuration of the American Midwest (see Geologic Time Scale). The Proterozoic Penokean Orogeny occurred approximately ~1.88 Ga and resulted in the accretion of crustal material (terranes) to Laurentia that represent portions of modern-day Iowa, Michigan, Minnesota, Missouri, and Wisconsin (Schulz and Cannon 2007). The Central Plains Orogeny that occurred ~1.8 to 1.63 Ga incorporated additional terranes that would become parts of Kansas and Nebraska (Sims and Peterman 1986). Approximately 1.4 Ga to 0.99 Ga marks a period of volcanic activity, rift basin development, and rift basin infilling across the North American continent (Hunt et al. 2008).

The predominant bedrock underlying the park units of HTLN consists of Paleozoic sedimentary rocks featuring a thick sequence of carbonate rocks. Limestones and dolostones that are widespread throughout the network were originally deposited in warm, shallow marine settings and are responsible for the diverse karst landscapes that exist in BUFF and OZAR. The Paleozoic stratigraphy of the Midwest records numerous depositional changes resulting from global sea level fluctuations, domal uplifts, and orogenic events including the collisional episodes that produced the Appalachian–Ouachita Mountains (Thomas et al. 2021). Uplift and erosion of the newly formed mountains provided immense amounts of sedimentary material that was eventually deposited in a variety of marine, coastal, and terrestrial settings.

The rock record of the Cenozoic Era in the midwestern United States tells the story of numerous glacial advances and erosion. The northern portions of the United States, including Indiana, Iowa, Minnesota, and Ohio, were once covered by massive continental glaciers, although minor glaciated periods also occurred in parts of Kansas, Missouri, and Nebraska. During periods of glacial retreat, large amounts of glacial meltwater flowed southward and deposited vast amounts of till that blanketed older underlying strata. Glacially derived sands and gravels that were eroded and transported by the ancestral Mississippi and Ohio Rivers were deposited along the Mississippi Embayment in Missouri and Arkansas to form the western and eastern lowlands in Arkansas (Hunt et al. 2008). Throughout the Holocene, the Midwest has continued to experience erosion, as dynamic fluvial systems continue to incise through strata to produce terrace deposits and alluvium (unconsolidated clay, silt, sand, and gravel).

A Brief Geologic History

A few examples of events and Network resources in each geologic time period are highlighted below, from youngest to oldest.

• See also, Geologic Time Scale - Geology (U.S. National Park Service)

Geology & Soils—Heartland Network Parks

Type Sections—Heartland Network Index

The geologic history above is excerpted from a report titled, "National Park Service geologic type section inventory: Heartland Inventory & Monitoring Network". Type sections are essential reference locations for the geoscientists who study geologic history and paleontology. A summary of the type sections in each park can be found at the links below.

• Arkansas Post National Memorial, Arkansas (no designated stratotypes identified)

• Buffalo National River, Arkansas (contains two identified stratotypes)

• Cuyahoga Valley National Park, Ohio (contains one identified stratotype)

• Effigy Mounds National Monument, Iowa (no designated stratotypes identified)

• Fort Scott National Historic Site (no designated stratotypes identified)

• George Washington Carver National Monument, Missouri (no designated stratotypes identified)

• Herbert Hoover National Historic Site, Iowa (no designated stratotypes identified)

• Homestead National Monument of America, Nebraska (no designated stratotypes identified)

• Hopewell Culture National Historical Park, Ohio (no designated stratotypes identified)

• Hot Springs National Park, Arkansas (contains two identified stratotypes)

• Lincoln Boyhood National Memorial, Indiana (no designated stratotypes identified)

• Ozark National Scenic Riverways, Missouri (contains one identified stratotype)

• Pea Ridge National Military Park, Arkansas (no designated stratotypes identified)

• Pipestone National Monument, Minnesota (no designated stratotypes identified)

• Tallgrass Prairie National Preserve, Kansas (no designated stratotypes identified)

• Wilson's Creek National Battlefield, Missouri (no designated stratotypes identified)

The full Network report is available in digital format from:

• DataStore - National Park Service geologic type section inventory: Heartland Inventory & Monitoring Network (nps.gov)

Please cite this publication as:

• Henderson TC, Santucci VL, Connors T, Tweet JS. 2022. National Park Service geologic type section inventory: Heartland Inventory & Monitoring Network. Natural Resource Report. NPS/HTLN/NRR—2022/2455. National Park Service. Fort Collins, Colorado.

NPS Stratotype Inventory

Fossil Resources—Heartland Network

Between 2002 and 2011, network-based paleontological resource inventories were completed for all the 32 I&M networks, and six of the earliest were completely updated between 2012 and 2016. The report linked below summarizes the paleontological resources of all park units in the Paleontological resource inventory and monitoring— Heartland Network Inventory & Monitoring Network (HTLN). The report provides geologic background and paleontological resource data for each park to support management operations, planning, and science-based decision making as required by NPS management policies and the Paleontological Resources Preservation Act (2009).

The full report is available in digital format from

• DataStore - Paleontological resource inventory and monitoring— Heartland Network (nps.gov)

Please cite this publication as:

• Hunt, R., J. P. Kenworthy, and V. L. Santucci. 2008. Paleontological resource inventory and monitoring— Heartland Network. Natural Resource Technical Report NPS/NRPC/NRTR—2008/132. National Park Service, Fort Collins, Colorado.

Related Links

• Heartland Inventory & Monitoring Network
• NPS Geodiversity Atlas
• NPS—Geologic Resources Inventory

Geodiversity Atlas pages—by Inventory & Monitoring Network

Geodiversity Atlas pages—by State, U.S. Commonwealth, and Territories