The park's rock formations, made famous by
Robert Stevens and
Harold Williams, include
oceanic crust and
mantle rock exposed by the
obduction process of
plate tectonics, as well as
sedimentary rock formed during the
Ordovician,
Precambrian granite and
Palaeozoic igneous rocks. The
Global Boundary Stratotype Section and Point (GSSP) of the
Tremadocian stage and the all Ordovician system is defined in the Green Point section within this park. The park is located in the
Great Northern Peninsula of Western Newfoundland. This peninsula is referred to as the Humber Zone, a
Miogeocline, the
Highlands of which contain the largest external
basement massif of the
Grenville Orogeny in the
Appalachian Orogen. This
Precambrian basement is known as the Long Range
Inlier, Long Range Complex or Basement
Gneiss Complex, consisting of
quartz–
feldspar gneisses and
granites that are up to 1550
Ma in age. Mt. Gros Morne and Mt. Big Level lie within this Inlier. The western boundary of this inlier (along
Western Brook Pond, St. Pauls Inlet, and south of Portl Creek Pond) consists of
Devonian and
Ordovician thrust faults, where crystalline rocks thrust over
Cambrian–Ordovician
carbonate rocks and the Lower
Paleozoic Humber Arm
Allochthon. The
Rocky Harbour mélange is a Lower–Middle
Ordovician collection of
greywacke,
quartzite,
dolomite shale,
chert, limestone blocks within a black, green, and red scaly shale
matrix, which occurs along the shore from West Brook Pond to Humber Arm (Bay of Islands). The south portion of the park, Table Mtn. (Tablelands) and North Arm Mtn., consists of Upper Cambrian and Lower Ordovician
ophiolites known as the Bay of Islands Complex, Little Post Complex, and Old Man Cove
Formation. Finally, a
Pleistocene ice cap flowed radially across the island, developing
fjords such as
Bonne Bay.
Tablelands The Tablelands, found between the towns of Trout River and
Woody Point in south west of Gros Morne National Park, look more like a barren
desert than traditional Newfoundland. This is due to the
ultramafic rocks –varieties of
peridotite and
serpentinite – which make up the Tablelands. They are thought to originate in the Earth's mantle and were forced up from the depths during a plate collision several hundred million years ago. Ultramafic rocks lack some of the usual nutrients required to sustain most plant life and have a toxic quality, hence their barren appearance. Ultramafic rocks are also high in iron, which accounts for its brownish colour (rusted colour). Underneath the weathered surface zone, the unweathered rock is a dark green colour. == Soils ==