SEDIMENTARY ROCKS

Source, Slope and Sink



SOURCE Area : the composition of the source 
area exerts a great influence on the nature of 
the sedimentary rock(s) that can form -- 


CLIMATE and PLATE SETTING.


	granite could alter to form clays (from the 
	feldspars) leaving quartz

	basalt, would alter rapidly to form clays 	 
	plus various iron-rich compounds

SLOPE refers to those processes which move 
solid material at the surface of the Earth



		Wind


		Water


		Ice




In addition to carrying solid particles, water 
can carry ions in solution.  Clays do not have 
the same composition as the materials from 
which they were produced.  Some ions are 
carried away in solution.

The SINK refers to a place of accumulation 
of previously transported material


	Granites in central Texas are weathered 
	chemically and physically.  The quartz is 
	transported by the river systems and some 
	eventually end up being deposited along 
	the Texas beaches.



	Will characteristics of the beach 
	environment be imposed on these grains?  
	Can a geologist infer the SINK from the 
	properties of a sedimentary rock?



Diagenesis and Lithification


Loose grains are called sediment






Sediment can be converted to sedimentary 
rock if the particles are either cemented 
together or compacted during burial.



As sediment is buried, changes in 
composition and texture may take place and 
sedimentary processes merge with 
metamorphc

Classification of Sedimentary Rocks



Clastic - particles carried from the source to 
the sink by slope processes .... grains do not 
interpenetrate



Chemical - ions in solution are łforced˛ to 
react to precipitate solid material.  If you leave 
a glass of water outside it will evaporate 
leaving a white film of calcium carbonate....an 
interpenetrating texture

Clastic Sedimentary Rocks
n About 75% of the Earth's continental crust is 
covered by sedimentary rocks



Sedimentary rocks form a thin covering 




About 85% of the sedimentary rocks consist 
of grains that were transported as solids



Grains between 2mm and 1/16mm in 
diameter are called SAND sized.  

Coarse Clastics



Conglomerates & Breccias > 2mm



Sandstones consist of framework grains plus 
matrix (finer in size)



Quartz Arenite - framework grains are Quartz



Arkose - framework grains are Feldspar



Litharentite - framework grains are rock 
fragments



Grains between 1/16mm and 1/256mm are 
called SILT


Grains less than 1/256 mm are called CLAY


SAND, SILT and CLAY are SIZE terms.  A 
sandstone is a sedimentary rock made up of 
SAND sized grains.


SANDSTONES account for about 20% of the 
Earthąs sedimentary rocks


CLAY and SILT sized grains are dominated 
by clay minerals

All clay minerals have a good cleavage.
If the cleavage planes are lined up parallel to 
each other the rock is said to be FISSILE - A 
SHALE is a fine grained clastic rock with 
fissility.



If the cleavage planes are not oriented in 
parallel, the rock is said to be non-fissile.  A 
MUDSTONE is a fine grained clastic rock 
without fissility.



SHALES and MUDSTONES are the most 
abundant sedimentary rocks - ~60%.





Chemical Sedimentary Rocks


~15% of the sedimentary rocks are chemical - 
original transport was as ions in solution.


Carbonates - limestones and dolomites - 
calcium carbonate precipitated or extracted 
from solution(s)...shells....animal dies and shell 
transported and eventually deposited.



Evaporite Sequences - Carbonates, Sulfates 
and Salts



Mineralogical Maturity



Given time, minerals, with the singular 
exception of quartz, will react to form clays.



The more quartz in a coarse sedimentary 
rock the higher the mineralogic maturity.



A feldspar-rich sandstone (Arkose) is 
immature - not enough time for the feldspar 
to form clays


Shales and mudstones are mineralogically 
mature - clay minerals



Textural Maturity



Texturally Mature Coarse Clastics are WELL 
SORTED (particles are all about the same 
size)



The quartz grains in these rocks tend to be 
rounded.



The more persistent the energy level, the 
greater the textural maturity

Other Properties of Sedimentary Rocks



Porosity - the percentage of open space - 
remember the generalizations about packing 
spheres



The poorer the sorting, the lower the porosity



Permeability - a measure of the łinter  
connectnedness of the pores - permeable 
units will transmit fluids
Sedimentary Structures
n Parallel Beds 



Cross Beds



Graded Beds



Ripple Marks


"Sinks"	


In broad terms environments of deposition 
can be viewed as Continental, Transitional 
(beaches and shorelines) and Marine



In Continental settings the supply of sediment 
may be high but the łpreservation potential˛ 
is usually low --too many things can happen 
before the sediment is lithified.






Transitional - supply of sediment may be 
high (at the mouth of a river) and 
preservation potential is usually high.



Marine - preservation potential is high but 
the supply of sediment may be low.








Much of the sedimentary section on Earth 
accumulated in the Transition Zone - deltas, 
barrier islands, beaches, etc.








Geologists study modern sediments to try and 
see what imprint the environment of 
deposition leaves on the sediment and 
resulting sedimentary rock.


Evaporite Basins



Climate



Structure



Evaporate 1 liter of marine water



		50% gone : carbonate : 2.8 g/cc


		80% gone : sulfate : 2.4 g/cc


		90% gone : salt : 2.1 g/cc


		Repeat

Sedimentary Facies



Focus on grain size - related to proximity to



source area



Sea Level Rises : encroachment of marine 
environment onto continental area (or, land 
subsides) : TRANSGRESSION



Sea Level Falls : encroachment of continental 
environment onto marine area (or land rises) 
: REGRESSION