Flat Landing Brook Formation

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.[2]

Flat Landing Brook Formation
Stratigraphic range: Darriwilian,
TypeGeological formation
Unit ofTetagouche Group[1]
Sub-unitsReids Brook Member, Forty Mile Brook Member, Roger Brook Member, Moody Brook Member[2]
UnderliesLittle River Formation[1]
OverliesNepisiguit Falls Formation[1]
ThicknessUnknown[2]
Lithology
PrimaryRhyolite flows, hyaloclastics, breccias, hyalotuffs[1]
OtherShale, greywacke, siltstone, iron formation, tholeiitic basalt, alkali basalt[1]
Location
Region New Brunswick
Country Canada
Type section
Named forFlat Landing Brook[2]
Named byR.W. Sullivan, 1990; C.R. van Staal et al., 1990[2]

Lithology

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.[2] Siltstone, greywacke, iron formation, ferromanganiferous shale and chert represent minor rocks.[1][2]

Stratigraphy

Relationship to other units

The Flat Landing Brook Formation is the middle member of the Tetagouche Group.[1] Exposures between Route 490 and the headwaters of Flat Landing Brook are the type locality.[2] 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.[1] 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.[2]

Subdivisions

The Flat Landing Brook Formation contains four named subdivisions:

MemberAgeLithologyReference
Reids Brook MemberMiddle OrdovicianRhyolite flows, hyaloclastites, breccias [2]
Forty Mile Brook MemberMiddle OrdovicianTholeiitic pillow basalt [2]
Roger Brook MemberMiddle OrdovicianTuff and minor porphyritic felsic flows [2]
Moody Brook MemberMiddle OrdovicianTholeiitic to transitional mafic fragmental rocks and massive flows [2]

Volcanology

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 Taupō and Yellowstone calderas.[3][4] It may also represent the largest supervolcanic eruption of the Paleozoic era.[3] Most of the volcanic rocks were laid down during a timespan of possibly less than two million years.[4] 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).[3][5] 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.[3]

See also

References
  1. Tetagouche Group – Unit Descriptions
  2. Flat Landing Brook Formation
  3. Wills, Alexander Oakley (2014). "Chemostratigraphy and hydrothermal alteration of the Flat Landing Brook Formation, Brunswick Belt, Bathurst Mining Camp". University of New Brunswick.
  4. "A mid-Darriwilian super volcano in northern New Brunswick, rapid climate change and the start of the great Ordovician biodiversification event" (PDF). Archived from the original (PDF) on 13 December 2019.
  5. The petrological variations of the Ordovician felsic volcanic rocks of the Tetagouche Group, New Brunswick

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