Paleocurrent Analysis

By: Jason Choquette

Overview Why is paleocurrent analysis important? Fabric and why it’s useful Internal and external structures

How they are related to each other Liner structures; types and usesPractial study of paleocurrents in western Maine and some implications

Definition Paleocurrent- The study of ancient flow Paleocurrent indicators- oriented sedimentary structures interpreted to have been deposited by ancient flows

Paleocurrent Indicators Include…Cross-beds clast imbrication/fabrictool marks groove casts and molds ripple crest orientation

Paleocurrent Analysis….Provides direct information about the orientation of the sedimentary systems.Yields information about the flow directions of rivers, longshore currents, sediment gravity flows, and paleowindsProvides direction of initial dip or paleoslopeYields clues to the provenance of sediment supply Aids in determining geologic setting to which it was placedProvides info on paleogeography

Three Maine flow Indicators FabricExternal structures Internal structures

FabricsRefers to the spatial orientation of material in which they where deposited.

Includes various material types ranging in size from large cobbles to micro-fabricsFossilsEncompasses other fields lithologies such as carbonate rocks and volcanic deposits Imbricated bedding

Uses of fabric analysis

Largely used to infer current directions in sand and gravels.Reconstruct glacial motionPrimarily used if there is no other flow indicators or to support other data.

www2.umt.edu/.../hendrix/g432/g432_L12.htm

Compton Robert R. Geology in the Field, 1985 p.52

Internal and External Structures e.g cross bedding and ripple marksUsed in unison to map large areasBoth are found in many geologic environments

FluvialLittoral Marine Aeolian

Some Internal Structures

www2.umt.edu/.../hendrix/g432/g432_L12.htm

Some External Structures

www2.umt.edu/.../hendrix/g432/g432_L12.htm

http://www.ualberta.ca/~jwaldron/images/sedCD1024/05.jpg

http://www.depauw.edu/acad/geosciences/tcope/SedStruct/HiRes/LinguloidRipples.jpg

http://www.coloradocollege.edu/dept/GY/pmyrow/Web%20Photos/Solemarks2.jpg

http://www.ulg.ac.be/geolsed/processus/tool.jpg

http://www.studiozoic.com/adventures/2004/pct/wa/IMG_4153.jpg

Paleocurrent Analysis in Practice Combining internal and external structures to develop a…Detailed mapPaleoslopeTectonic history

Potter, 1977

Bradley;Hanson, 2002 p.442

References Lunguloid ripples jpeg from; http://www.depauw.edu/acad/geosciences/tcope/SedStruct/HiRes/LinguloidRipples.jpgRipple marks http://www.studiozoic.com/adventures/2004/pct/wa/IMG_4153.jpgBradley Dwight C., Hanson Lindley S., Paleocurrent analysis of a deformed Devonian foreland basin in the Northern Appalachians, Maine, USA. Sedimentary Geology, 148 (2002) p.425- 447 Potter Paul E., Pettijohn Francis J., Paleocurrents and Basin Analysis, second edition. Springer-Verlag, Berlin Hiedelberg New York, 1977Lewis D.W. Practical Sedimentology, University of Canterbury NZ. 1984. Compton Robert R., Geology in the Field. 1985 p. 52, 162-175 Class handout thingy…