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Presque Isle Geology Field Trip Guide
Dr. Chunzeng Wang, UMPI Geology Program
Stop 1: A road-cut by Parsons Road (about 3 miles from the mall) Silurian (~430 Ma) Spragueville Formation bioturbation limestone
(1) The Spragueville Formation comprises a sequence of thinly interbedded and interlaminated medium-gray silty mudstone and light-gray silty limestone or calcareous siltstone. The limestone is fine-grained chemical limestone. With diluted hydrochloric acid, you can tell it is limestone. Existence of limestone indicates an offshore marine depositional environment during Silurian time (about 430 million years ago). (2) The Spragueville Formation is typically characterized by distinctive bioturbation features, burrows and other trace fossils. (Note: Bioturbation refers to disruption of sediments by feeding and burrowing organisms. Trace fossils are evidence of the organism's behavior that is indirect evidence of life. Trace fossils include burrows, track marks/foot prints, fossilized feces, and fossil remains of roots). (3) Graptolites, brachiopods, trilobites, and conodonts are some of the fossils found in the formation. These were marine invertebrates that became extinct many millions years ago. You will learn more about fossils in Historic Geology. (4) Layers of rocks at this stop dip/face toward west. This site is part of the east limb of the Chapman syncline.
(Ma = million years ago)
Stop 2: Donald Maynard Quarry by Parsons Road (about 4.5 miles from the mall) A Devonian (~385 Ma) felsic pluton/intrusion
(1) The Devonian igneous pluton is light-gray in color and of felsic composition. It is coarse-grained and contains mostly plagioclase feldspar and few orthoclase (i.e. potassium feldspar). Quartz accounts for about 20%-35% of the rock. So, more specifically, it is a tonalite (sort of granite). The character of containing few or no potassium feldspar makes it different from regular granite. Ferromagnesian minerals (always dark colored) identified include hornblende and biotite. (2) Small-scale faults. Most of them are reverse faults, suggesting a compressional tectonic force. (3) Another character notified here is that the igneous rock is badly fractured. The fractures may be filled up by water, serving as groundwater aquifer (named as fractured-rock aquifer).
Stop 3: Victor Winslow and Sons Quarry by Griffin Ridge Road Upper Devonian Mapleton (~360 Ma) Formation sandstone and conglomerate
(1) Exposed in the quarry is the very well-known Mapleton Formation that deposited in late Devonian time (about 360 million years ago). It is the youngest sedimentary rock formation in northern Maine. This formation only exists around this hill. Rocks of the formation include non-metamorphosed thin-to-think layered red sandstone and conglomerate. (2) Rocks of the Mapleton Formation are tilted and form the open Mapleton Syncline. (3) Ripple marks and mud-cracks indicate shallow water depositional environment. (4) The Mapleton Formation is a post-Acadian inter-mountainous basin sequence. Redbeds indicate oxidization and continental/land depositional environment. (5) The Mapleton Formation is also geologically famous for its content of plant fossils within the green sandstone and siltstone beds. The plant fossils are of Psilophyton. A piece of rock with very-well-preserved Psilophyton was collected by a well-known geologist many years ago and now is displayed in the Smithsonian National Museum of History, Washington D. C. These rocks are green in color because they were not oxidized when deposited. Non-oxidization environment well facilitated preservation of plant fossils. (6) Any other species of fossils? Well, you have already learned that there were also fish living in Devonian time. (You will earn a grade of A+ for the course if you find a fish fossil at the quarry. )
Stop 4: Intersection of Griffin Ridge Road and Mapleton Road (Watch traffic!) Upper Devonian (~360 Ma) Mapleton Formation conglomerate
(1) North side of Mapleton Road on the top of the ridge is a nice road-cut with layers of conglomerate of Mapleton Formation exposed. (2) Beds dip toward west, indicating this site is located on the east limb of the Mapleton syncline.
Stop 5: Edmunds Hill quarry off Carvell Road Lower Devonian (~395 Ma) Chapman sandstone and andesite
(1) Rocks exposed at the quarry are Lower Devonian Chapman sandstone and andesite. These rocks were slightly metamorphosed during the Acadian orogeny (about 380 million years ago) and are older than the non-metamorphosed redbeds of the Mapleton Formation. Rock layers at the quarry are near vertical and dip toward the east, indicating strong rock deformation. The quarry lies in the west limb of the Chapman syncline. (2) On the right side of the quarry are nearly vertical medium-thick beds of Chapman sandstone. The sandstone contains fossils of brachiopods and bivalves. Also presented includes primary sedimentary features of ripple marks near the top of the quarry wall. The Chapman sandstone deposited in a near-shore shallow-water environment, indicating a sea-level-rising event (or a transgressive event) in Early Devonian time (about 395 million years ago). (3) Excellent spheroidal weathering is observed in the Chapman sandstone. (4) On the left side of the quarry are the layers of andesite which is intermediate volcanic/extrusive igneous rock. It has either a porphyritic or fine-grained texture, indicating a rapid magma cooling rate. Presence of andesite also suggests extensive volcanic eruptions in an Andean-type plate subduction tectonic environment, during Early Devonian Period (395 million years ago) in the Presque Isle area.
Stop 6: A road-cut on Mapleton Road (1.5 miles east from downtown Mapleton) Silurian Spragueville Formation on the west limb of Chapman syncline
(1) Silurian Spragueville Formation crops out at this location. Same as seen at Stop 1, it is a sequence of thinly interbedded and interlaminated medium-gray silty pelites (mudstone) and light-gray silty limestones or calcareous siltstones, and is characterized by distinctive bioturbation features, burrows and other trace fossils. (2) Notice that the rock layers dip toward east because this site lies in the west limb of the Chapman syncline.
Acknowledgements: The Presque Isle regional map is adopted from "Bedrock Geologic Map of the Mars Hill Quadrangle and Vicinity, Aroostook County, Maine" by Louis Pavlides, 1978, USGS. Professor Bill Forbes has provided great help in field trip preparation and is very much thanked.
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