Turbidites

Turbidites and Submarine Fans By Jesse Powers

Outline Turbidites Description Environment • Submarine Fans Lithology • Bouma Sequence Structures • Graded Beds • Cross Beds • Convoluted Laminations • Channel Scours

Case Study: Bald Mt

Turbidites • Defined as the deposit of a turbidity current • Typically associated with Deep ocean environments •Each Couplet is the result of a single shot-lived event

http://www.maine.gov/doc/nrimc/mgs/explore/bedrock/sites/mar01-3.htm

http://www.enres.nl/Images/turbidites.jpg

• Couplets are composed of two rocktypes: Arenites (sandstone) and lutites (mudstones) • Tops are easily determined within turbidite facies

Depositional Environment

http://www.mie.utoronto.ca/labs/lcdlab/biopic/fig/57.11.jpg

Submarine Fans • Similar to alluvial fans, submarine fans are gravity feed debris flows down the continental slope • Stretch for hundreds of miles out into the abyssal  plane and can contain hundreds of cubic ft. of sediment • Consist of olistholiths, olistostromes, and trubidites

http://instruct.uwo.ca/earth-sci/200a-001/07turbidity.jpg

Congo River Congo, Africa

http://www.aquatic.uoguelph.ca/oceans/AtlanticOceanWeb/Images/grand_banks.jpg http://eur.i1.yimg.com/eur.yimg.com/ng/mo/allocine_films/20060405/01/3345713940.jpg

Magdalena River Columbia, South America

http://www.poledakar.org/IMG/gif/africa_congo.gif 

Bouma Sequence A E

Muds (pelagic and hemipelagic) D

Laminated Silts Cross Beds (lower flow regime)

C B

Laminated sands (upper flow regime) A

Graded beds (upper flow regime) Sole Marks (flutes and grooves)

http://csmres.jmu.edu/geollab/fichter/SedRx/subfan.html

Graded Bedding •A fining upward within a individual layer or couplet

http://www.winona.edu/geology/MRW/mrwimages/gradedbedding.jpg

Cross Laminations

Convoluted Laminations

Channel Scours

http://web.uct.ac.za/depts/geolsci/dlr/laingsburg/lng21.JPG

Rip-up clasts

Bald Mt.

Devonian ~400ma

NW

SE Silurian ~440ma

• Bald Mt. part of Day Mt. formation, a sub-group of the Seboomook formation • Couplets have been metamorphosed into  metagreywackes and  garnet- staurolite- schists

• Later deformation of the strata lead to  present structures

• Variety of bed thicknesses along the Mt. possibly suggest different depositional depths? Or thinning due to metamorphism?