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Flat Landing Brook Formation facts for kids

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Flat Landing Brook Formation
Stratigraphic range: Darriwilian, 466–465Ma
Type Geological formation
Unit of Tetagouche Group
Sub-units Reids Brook Member, Forthy Mile Brook Member, Roger Brook Member, Moody Brook Member
Underlies Little River Formation
Overlies Nepisiguit Falls Formation
Thickness Unknown
Primary Rhyolite flows, hyaloclastics, breccias, hyalotuffs
Other Shale, greywacke, siltstone, iron formation, tholeiitic basalt, alkali basalt
Region  New Brunswick
Country  Canada
Type section
Named for Flat Landing Brook
Named by R.W. Sullivan, 1990; C.R. van Staal et al., 1990

The Flat Landing Brook Formation is a geological formation in Gloucester County of northern New Brunswick, Canada. It consists mostly of volcanic rocks that were deposited 466 to 465 million years ago during the Darriwilian stage of the Middle Ordovician epoch.


Rhyolite flows, breccias and hyaloclastics are the primary rocks comprising the Flat Landing Brook Formation. Locally abundant rocks include tholeiitic to transitional mafic fragmental rocks and massive flows, as well as felsic tuffs, tholeiitic pillow basalts and minor porphyritic felsic flows. Siltstone, greywacke, iron formation, ferromanganiferous shale and chert represent minor rocks.


Relationship to other units

The Flat Landing Brook Formation is the middle member of the Tetagouche Group. Exposures between Route 490 and the headwaters of Flat Landing Brook are the type locality. It is conformably overlain by massive pillowed alkali basalt of the Little River Formation and conformably underlain by crystal tuff as well as quartz-feldspar augen schist of the Nepisiguit Falls Formation. The contact of the Flat Landing Brook and Little River formations is exposed in the Brunswick Mines area and near California Lake whereas the contact of the Flat Landing Brook and Nepisiguit Falls formations is exposed along The Narrows of the Nepisiguit River.


Four named subdivisions comprise the Flat Landing Brook Formation:

Formation Age Lithology Reference
Reids Brook Member Middle Ordovician Rhyolite flows, hyaloclastites, breccias
Forty Mile Brook Member Middle Ordovician Tholeiitic pillow basalt
Roger Brook Member Middle Ordovician Tuff and minor porphyritic felsic flows
Moody Brook Member Middle Ordovician Tholeiitic to transitional mafic fragmental rocks and massive flows


With an estimated original volume of approximately 12,000 km3 (2,900 cu mi), the Flat Landing Brook Formation incorporates the eruptive products of a supervolcano similar in size and eruption rates to the Taupo and Yellowstone calderas. It may also represent the largest supervolcanic eruption of the Paleozoic era. Most of the volcanic rocks were laid down during a timespan of possibly less than two million years. A region of coarse co-ignimbritic breccias in the Flat Landing Brook Formation (Grants Lake pyroclastics) is interpreted to represent the infill of a large caldera with a radius of about 80 km (50 mi). The only rocks that do not seem to be related to the caldera are scattered dikes and small effusive flows of the Taylor Brook rhyolites, the latter of which probably issued from parasitic vents on the outer margins of the caldera.

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