Discover Maine USA and Explore the Geodiversity and Fossils of Acadia National Park
- Wayne Munday
- Mar 28
- 3 min read
Acadia National Park is a 47,000 acre woodland located along the Atlantic Coast of the United States of America and stands out as the only national park on the eastern seaboard with a coastline shaped by Pleistocene continental glaciers. The park’s landscape showcases a dynamic interplay of tectonic forces, glaciation, and ongoing coastal erosion. Mount Desert Island, the park’s largest landmass, features Cadillac Mountain the highest peak on the U.S. Atlantic coast. Acadia National Park belongs to the New England Physiographic Province, sharing geological characteristics with a broader north eastern region. The park’s geological history and landforms tell a a story of coastal and glacial forces as well as both a terrestrial and marine fossil record.
Nestled along the rugged coast of the US State of Maine is Acadia National Park a breath taking destination offering visitors a perfect blend of natural beauty, outdoor adventure, and rich history. The main entrance is near Bar Harbor and as the only national park in the north eastern United States it boasts stunning landscapes including Cadillac Mountain the highest peak on the U.S. Atlantic coast as well as over 240Km miles of hiking trails or drive or cycle the 43Km Park Loop Road starting at Hulls Cove Visitor Centre to take in the forests, lakes and mountains.
The Fossils of Acadia National Park
The fossiliferous Presumpscot Formation of the Acadia National Park is a glaciomarine deposit and marks a period of submersion in coastal Maine following the last glacial retreat. The formation is also known as Presumpscot Clay or Leda Clay and was deposited between 15,000 - 11,000 years ago and remains the only named Quaternary unit in the region.
Composed primarily of silt and clay it was formed as seawater deposited sediments while glacial retreat and isostatic loading depressed the land by up to 100 - 120 meters below sea level. Subsequent post-glacial rebound exposed the nearshore to 60 meters below the present level before global sea-level rise reshaped the coastline into its current state.
The Presumpscot Formation has produced a diverse and predominantly marine fossil record, providing insight into the region’s paleoenvironment. Plant remains include pollen, spores and wood such as White spruce (Picea glauca) and Balsam Poplar (Populus balsamifera) that dominate the plant macrofossil assemblage. Invertebrate fossils range from foraminifera and sponge spicules to bryozoans, bivalves, gastropods and Spirorbis a shell-dwelling polychaete worm. Arthropods, including beetles, ants, barnacles, and decapod crustaceans are also present alongside ostracods and ophiuroids or brittle stars.
Vertebrate discoveries include fish and rare large mammals such as walruses and whales as well as a single mammoth specimen. Atlantic Walrus remains have been recorded at Andrews Island, Addison Point, and Gardiner though not all necessarily originate from the Presumpscot Formation. Mammoth bones were uncovered in Scarborough, 140Km southwest of Isle au Haut.
The Geodiversity of Arcadia National Park
Acadia National Park bedrock consists of a combination of metamorphic, igneous, and sedimentary formations that tell a story if significant tectonic deformation and volcanic activity. The Cadillac Mountain intrusive complex, Schoodic Peninsula granite, and the Cranberry Island volcanic series illustrate these dynamic geological events. Additionally, features such as pink granite, diabase dykes and joint sets or groups of parallel or sub-parallel joints fractures in the rock that share similar orientations, spacing, and physical properties contribute to the park’s geological diversity.
Acadia’s coastline is primarily composed of rocky cliffs, with limited sand accumulation due to rising sea levels. The few sandy beaches, like Sand Beach, contain sand primarily composed of calcium carbonate shell fragments. Powerful Atlantic surf and extreme weather events, such as nor’easters a large-scale extratropical cyclone in the western North Atlantic Ocean continuously shapes and modifies the coastal landscape, forming cliffs, sea caves, and wave-cut platforms.
The park’s ridges and valleys are remnants of extensive glaciation. Glacial processes sculpted landforms such as U-shaped valleys, roches moutonnées, striations and erratic's. Meltwater streams deposited sediment, forming glacial till, moraines, and outwash deltas. As glaciers receded, crustal rebound and sea level changes further altered the park’s topography.
Acadia’s surficial deposits reflect past glacial activity and sea level fluctuations. The maximum glacial extent 21,000 years ago caused significant sea level drop, followed by isostatic rebound, which elevated landforms previously submerged. Rising sea levels subsequently reshaped the coastline, submerging former landmasses and creating the current island-dominated landscape.
Acadia National Park contains sea caves formed through wave erosion. Some caves evolve into sea arches when further eroded. Additionally, older inland caves represent remnants of past higher sea levels. All cave resources in the park are federally protected under conservation laws.