686
Chapter 13 Diagenesis
a
VADOSE ZONE
LOW
HIGH SED.
BEACH ROCK
GOETHITE
HEMATITE
SEDIMENTATION
RATE (+ ORG. (ARAGONITE,
RATE
MATTER) \
HIGH Mg
_L __________ ~-~AL~~
~
~
~~*:~
- --- ---- ---IZ'
~-:
SIDERITE
I
I
I
I
I
I
I
DIFFUSION
PROCESSES
BACTERIAL
SULFATE REDUCTION
(C02 ISOTOPICALLY
SQMEWHAT LIGHTER)
LMIICFIO~IIAL METHANOGENESIS (FERMENTATION
(ISOTOP. HEAVY C02'
BUT LIGHT CH 4 )
THERMOCATALYTIC
DECARBOXYLATION
--- z __ , "' ":' __ ' I ~AOLINITE
I
"
~- - ..)t _ __ ~
DEEP PHREATIC ZONE
~-~-__
- - --:
(MARINE PORE FLUID , BRINES)
-- ~-- -.... _
I
PHREATIC ZONE
{(METEORIC' WATER i
EARL Y DIAGENESIS OF
MUDDY MARINE SEDIMENTS
I I
I I
I J.
PRODUCTS
CONCENTRATION
_
:
WATER
H2 S, C02 (HC0:3)- - -\- - - - -
.. SEDIMENT
PYRITE (FeS2)
"
CALCITE, DOLOMITE
S04' "
(LOW Fe CARBONATES) - - -----r--CH 4 (+C0 2 )
, , /
.
HIGH Fe CARBONATES
"
?-HC03
(CALCITE, DOLOMITE,
• ..!
ANKERITE, SIDERITE,
i' .
RICH IN C-13)
" ,
Fe -RICH CHLORITE MIN.
C02 ' CH4' OTHER
HYDROCARBONS
SIDERITE
!.Ä
CH 4
11111tlll/
LATE DIAGENESIS
IRON-POOR SED. (CARBONATES) : LlTTLE OR NO AUTHIGENIC CARBONATES
IN ZONES OF SULFATE RED. AND METHANOGENESIS
C FRESH WATER ENVIRONMENTS (POOR IN S04)
WATER
~-- -- ------- --- - - - --;;'DK~l
LlTTLE PYRITE
SEDIMENT
:~0m!t-- ABUNDANT SIDERITE
Fig. 13.23. a Overview of various realms of
diagenesis. b,c Proeesses and produets of early
diagenesis: b in marine sediments with oxygenated
bottom water and slow burial (left column), and with
anoxie bottom water and rapid burial (right column).
C Same as b but for fresh water environments. (Based
on several sourees, e.g., Bj0r1ykke 1983; Curtis
1987). See text for further explanation