1. Conglomerates San Onofre Breccia, Laguna Beach
geology.about.com/.../lagunaconglom.htm
San Onofre Breccia, Laguna Beach

2. Introduction Rocks mostly of > 2mm clasts (gravel)
Also called rudites
Common, not abundant
Important for tectonics, provenance, depositional environments, economics
Grains = mostly rk fragments
May contain matrix--clay or sand
matrix is finer material which infills the spaces between grains

3. Example of Matrix Matrix is not cement
It is deposited with rest of sediment
Miocene San Onofre Breccia, Aliso Beach County Park,

4. Study mostly in field--hand sample not truly representative of outcrop
Need to see large scale variations in composition & textures

5. Definition Varies Folk - 30% gravel; less = gravelly mud/sand
Gilbert - 50% gravel
< 50% = conglomeratic ss/mudstone
Also called pebbly ss/mudstone
Gilbert uses this term at <25%
Is pebbly correct term?
Confusion led to term “diamictite”
Poorly sorted, large particles in mud matrix
So, have conglomerates with/without matrix
Definition

6. Diamictite
Boulder of diamictite of the Precambrian Mineral Fork Formation. It is lithified glacial till. Along the Elephant Head Trail, Antelope Island, Utah. Scale bar on notebook is 10 cm. Taken 2002.

7. Conglomerates Defined Using Fabric
Clast-supported (framework supported)
Matrix supported-diamictite
memoirs.gsapubs.org/content/198/105/F7.large.jpg

8. Breccias
Angular, gravel-sized particles
sublimereddit.aesptux.com

9. Origin of Breccias Sedimentary--mass flows--triggering mechanism
Non-sedimentary--tectonic (faults, folds); volcanic
When is rk a breccia?--is any fragmented rk a breccia
Miocene San Onofre Breccia, Aliso Beach County Park,

10. Intraformational Conglomerate/Breccia
Intraformational= redeposited fragments. of weakly consolidated beds
Thin, short term events e.g. landslides
Rounded to angular fragments. common in shales & l.s.

11. Epiclastic (extraformational) Conglomerates
Generated outside basin thru breakdown of older rks
Framework clasts
Oligomictic (e.g. qtz, arenite-stable fragments.)
Polymictic (many dif types of fragments)
Polymictic conglomerate. w/-unstable clasts-shale, L.S., basalt -Petromict conglomerate

12. Epiclastic Conglomerate Continues
Recycling leads to oligmictic conglomerate, but depends on source of rock (qtzite, qtz arenite, chert etc.)
Composition may reflect sorting
shale breaks down, metaqtzite= coarser durable clasts
volcanic –bigger clasts survive; finer clasts may not survive transport

13. Matrix Supported, Polymictic Conglomerate, New Zealand

14. Oligomictic Breccia, New Zealand

15. Matrix of Epiclastic Conglomerate
Clay & sand-size material
May have qtz, calcite, hematite, clay cement

16. Conglomerate Textures
Matrix content & fabric support
High energy transport process=gravels w/little sand
Glaciers=matrix supported=diamictites
Typically, 2 size modes gravel and mud to sand

17. 1998 Debris flow deposits in Chalone Creek, Pinnnacles National Monument, San Benito County, California
USGS

18. Debris flow deposits partly cover a road in Stevens Creek Canyon (Santa Clara County). The debris flow occurred during a storm in late January 2003

19. Structures Massive—lacks internal stratification
Crude to good planar horizontal or inclined stratification
Tabular & trough x-beds , less common than S.S
May have normal & inverse grading

20. Fluvial Conglomerate, France
Conglomerates and sandstones representing bars deposited in the channel of a braided river. Note the lenticular bed geometry and crude stratification. The northward dip (to the left) is a result of folding during Pyrenean earth movements.

21. Crudely stratified Conglomerate/breccia,Protestant Cathedral, Ireland Note alignment of the clasts

22. Classification Lack adequate system Classify Clast Stability
use informal names--qtzite cong (comp.); fluvial conglomerate (dep env.); pebble conglomerate. (clast size
probably because cong. not easily class; don’t have 3 principle clast types
Classify Clast Stability
ultra stable clasts (>90) = qtzose cong/diamictite---multicycle
meta/unstable clasts (> 90)= petromict conglomerate/diamictite; First cycle

23. Classification Continued
Classify Clast Lithology
clast stability class--little info of comp
meta-clast, ig-clast, sed clast, polymict conglomerate
tells about provenance
also used for diamictite

24. Classification Continued
Clast Size
cobble-rich qtzose rudite;boulder-rich petromict diamictite

25. Qtzose Conglomerate Metaqtzite, vein qtz, chert--sed, meta, ig rk
least stable lithology destroyed by weathering, erosion, transportation
vein quartz=erosion of ig/meta rk
implies intense weathering or vigorous transport
mostly fluvial
magicmomma.smugmug.com/.../1/ _A6f9J
Massanutten Formation ,Silurian, Virginia

26. Petromict Conglomerate
have metastable clast, various source rks
plutonic not as common--maybe due to weather.
first cycle
can be extensive
imply rapid erosion, elevated highlands
limited transport--fluvial to deep marine

27. Depositional Environments
textures & structures related to environmental conditions
reconstruct ancient environments
genetic class. desirable but difficult
fluvial, glacial, marine gravel
process-related sheetflood, streamflow, wave-worked--this is favored

28. Genetic Classification Paleocene-Eocene Submarine Fan Conglomerate & Turbidites, German Rancho Fm, Salt Point, San Francisco

29. Conglomerate Textures
Shape and orientation
Gravel rounded in short distances
Therefore, fluvial conglomerate. may have rounded gravel in angular sand

30. Pebble Imbrication
geolojay.com

31. Conglomerate Textures
Preferred orientation to elongate clasts
Transverse to flow, imbricated
Pebble Imbrication,Quaternary Aluvial Fan Deposit, Spain

32. More Imbrication, Truckee River Nevada
(c) 2006 Andrew Alden

33. Form (sphericity) related to parent rock-
fissile/schistose fabric=tabular, massive rocks more equant