(Cd, Ag, Zn, Sb, Mo, V, Cu, etc.) relative to normal shales, Lower Toarcian black shales from SW. Germany or TOC-rich sediments from recent upwelling areas.
A co~,'ibutlon
TRACE METAL ACCUMULATION IN BLACK SHALES FROM THE CENOMANIAN/TURONIAN BOUNDARY EVENT
BRUMSACK,
Hans-J~rgen
to Project
um~gl~]
O k O BAL B t0 EVENTS
*)
Abstract: B l a c k s h a l e s f r o m the C e n o m a n i a n / T u r o n i a n Boundary Event show a r e m a r k a b l e e n r i c h m e n t in t r a c e m e t a l s (Cd, Ag, Zn, Sb, Mo, V, Cu, etc.) r e l a t i v e to n o r m a l s h a l e s , L o w e r T o a r c i a n b l a c k s h a l e s f r o m SW G e r m a n y or T O C - r i c h s e d i m e n t s f r o m r e c e n t u p w e l l i n g a r e a s . If t h e s e e n r i c h m e n t s are a u t h i g e n i c in o r i g i n , t r a c e m e t a l s m a y s e r v e as i n d i c a t o r s for the p a l e o e n v i r o n m e n t a l c o n d i t i o n s d u r i n g d e p o s i t i o n of b l a c k s h a l e s . Low s e d i m e n t a c c u m u l a t i o n r a t e s , a c o m p a r a b l y l o w o r g a n i c p r i m a ry p r o d u c t i v i t y and e n h a n c e d p r e s e r v a t i o n of T O C d u e to a n a e r o b i c c o n d i t i o n s in the w a t e r c o l u m n t h e n are i n d i c a t e d for the C e n o m a n i a n / T u r o n i a n time interval. 7 `°°.
~
,oAEh-'~
+
L.+L
'~+"
"
°'
A8
~r
Islands_ / A 2
/ / Ahaggar 4, Mountain5
Ca.pe Verde Is,
o +;
A •
,.%,
AREAS WHERE THE ~ _ ~ IS PRONOUNCEDAND LARGELYOUTCROPPING SMALLAREASOR SINGLEOUTCROPSAND / OR ONLY F£W DATA AVAILABLE
367 DSD~/ODP- SITES G GIBRALTAR le.
Figure I. Important E v e n t (CTBE) .
outcrops
I
Fuerteventura (Canary Islands) (not clearly proven) 2 Tarfaya Basin (SW Morocco) 3 Agadir Basin (SW Morocco) 4 Rif Mountains (N Morocco) (Gibraltar Arch Area) 5 Penibetic (S Spain) 6&7 Tell Atlas (N Algeria) 8 9 10 11
Bahloul Formation (Tunisian Atlas) Umbrian Apennines (Central Italy) Euganean Hills (Northern Italy) Casamance Area
*) G e o c h e m i s c h e s F.R.G.
Institut,
of
I;0",
the C e n o m a n i a n / T u r o n i a n
Boundary
: Slope to Basin Plain Deposits : Coastal Basin : Coastal Basin to Outer Shelf Area : Slope to Basin Plain Deposits : Intramarginal High : Slope to Basin Plain Deposits (comparable with Rif) : Shelf Sea (? with local depressions) : Intramarginal Basin : Trough margin
Universitit
GSttingen,
D-3400
G6ttingen,
Lecture Notes in Earth Sciences, 'vbl. 8 Global Bio-Events. Edited by O. Walliser © Springer-Verlag Berlin Heidelberg 1986
338
0 2 (mlll)
Cd (ppb)
° 'i 0
F i g u r e 2. in d i f f e r e n t B = stagnant
The
3
60
event
(see Fig.
in the
pattern
I) and
et al. this
Boundary
black
and m a c r o f o s s i l
investigation
Gibraltar
Arch
area
367
(DSDP
41),
besides
Table
I).
drill
hole
stable ganic Gulf
Leg
recent
Samples
from both
CTBE
a remarkable
(Ag,
Cd,
(U, V)
or b o t h oozes,
elements,
TOC-rich
black
areas
occurring
in r e g i o n s
with
hydrogen
Sea
(see Fig. due
of
sulfide 2).
in time,
(Thurow
and
sediments and
1986,
(Mo)
or are
(see
Table
2).
are
less
though
TOC
and
their
m a y be f o r m e d
of
primary
present
oxygen
the h i g h
rate
content sediment
anoxic
shales
S contents
plankton
rate
production
rates.
Here
subsurface
waters
is i m p o r t a n t .
Reliable,
the
tool
preservation
to d i s t i n g u i s h
'oceanographically
consistent'
Black the
waters,
water and
basins
(oxy-
rapid
TOC e v e n u n d e r
low p r i m a r y
provide
the
enters
intermediate
oxygen-free may
presently anoxic
like
TOC
comparably
metals
environmental
in s u r f a c e
accumulate
and
are c o m p a r a b l e .
like
column,
or-
in t h e s e
two d i f f e r e n t
accumulation
basins
form
Toarcian
environment
of the
of
(see
with
The
SW
and D S D P
which
and r e s t r i c t e d ,
of
Gulf
associated
enriched
in the w a t e r
an u p w e l l i n g
on l a n d
production,
upwelling,
production
to this,
under
the
from
from
elements
of e l e m e n t s
strongly
on l a n d
shales
shales
from
14 m i n o r
outcrops
enrichment
black
black
completely
vironments.
the d e p o s i -
in the f a u n a l
outcrops
20 T O C - r i c h
in c o n t r a s t ,
being
diminished
zone),
In c o n t r a s t
Trace
oceanoTethys
& Kuhnt
from
Toarcian
5 major
etc.)
intense
In c a s e
and
Lower
of h i g h b i o l o g i c a l
to the h i g h
the r e s u l t i n g gen minimum
even
shales
settings:
sediment
0,1
a distinct
change
samples
settings,
show
Cu,
shale
upwelling
for
367,
of C a l i f o r n i a
burial.
analyzed
25
sulfides
particular
associations
(Morocco)
diatomaceous
have been
matter
marks
as in the w e s t e r n
and a d i s t i n c t
20 b l a c k
the
and
6 0
1978).
Site
Germany
(CTBE)
as w e l l
by its c o n s t a n c y
shales,
from
California
Event
Ocean
is c h a r a c t e r i z e d
of m i c r o -
For
3
Atlantic
t i o n of b i o s i l i c e o u s
Wiedmann
0.!
Cd (ppb)
I d e a l i z e d o x y g e n ( h y d r o g e n s u l p h i d e ) and c a d m i u m p r o f i l e s paleoenvironmental s e t t i n g s : A = o x y g e n - m i n i m u m zone, basin.
Cenomanian/Turonian
graphic
0 2 (m|/l)
of T O C
between
both
analytical
in
en-
data
339
rd ~H
(1) o
0 0 t~
.~
n, 0 U 40 C~
0 X~ +~
m p~
#
0
~O O~
0 o
-H
4J
0
•
0
.
,
.
tl
.
~
o
,
,
~
.
°
°
°
~
~
° , ° , ~
~ro 0
~ 0 ~
@
rq © 4~ @
E o
o
q4 r-q
0
rq
4d~4~ddJ
~d
o
~
¢
@
r~ rd
4~4~4
C~
.r4 0 ~d 0
•
o
°
.
.
•
o . °
.
o
.
.
"0
,
.r-I +~ ~)
0 0 o o 0 0
¢q E~ 0
~44S~d4Jgg4~g4
JgJg4
II
d
0 cq ~
0
~
0
~
~
0
~
~ 0 ~ 0 ~
~
°
~
~
~
°
,
O
°
°
O
~
~
°
,
O
,
~
°
,
~
h
f~
rd
E~ rJ 0 4J q4 0 0 0-,4 4J rd 0
~ 0
0
E 0 O-H o
L-~ '-0
,-t
~ 0
0
~
+~
~
0
-,4 (D E E Z~"O U @
~ 0 ~ 0 ~ ~
~4J
~
~ II
r~ U
rT}
>
1
%
•
+,~ ~-d ,.~ ,1) @ ,.d
0 E~
0 4J 0
840
for a large number of trace metals generated during techniques
the past
and a v o i d i n g c o n t a m i n a t i o n d u r i n g
concentration
profiles
like phosphate,
of many e l e m e n t s
nitrate
take by organisms, processes within elements,
or silica,
In s e a w a t e r
resulting
(see Fig.
should not a c c u m u l a t e
the
f o l l o w those of n u t r i e n t s
with s u r f a c e m i n i m a due
the oxic water c o l u m n
like Cd,
3).
to the up-
from r e g e n e r a t i o n
Therefore
labile
in s e d i m e n t s d e p o s i t e d
they are a l r e a d y r e m i n e r a l i z e d
at
in the upper
column.
In areas
of high p r i m a r y
the s e d i m e n t c h e m i s t r y taking
nutrients
and a s s o c i a t e d
tration
levels
Brumsack
finally buried
(see c o m p i l a t i o n
only a r e l a t i v e l y in the u n d e r l y i n g
sediments,
conditions
high
levels,
CTBE black
shales,
trace metal are never
V, Cu,
and Ni,
investigations sulfide
basins.
found
comparable
and to a lesser d e g r e e of Cu,
enrichments
an anoxic water
column
for
The a b s o l u t e metal
enrichment
the s e d i m e n t
relative
to
'average shale' of Mo,
periods
Sediment
are much higher
particulates composition
Sb,
1985)
Zn.
Recent
several
showed
(see also Fig.
sediments.
a
2) and
The a b i l i t y of
trace metals may there-
r e c o r d by i n c r e a s e d metal c o n t e n t s .
of Cd and Ag in CTBE black
by more than a factor of 100,
Zn,
of c o m p l e t e accumulation
tion of TOC very high.
element/TOC
and
in
to
a c c u m u l a t i o n rate.
the e n r i c h m e n t indicates
Cd,
then should be i n v e r s e l y c o r r e l a t e d
The e x t r e m e l y high e n r i c h m e n t
oceans.
(Jacobs et al.
accumulating
in the g e o l o g i c a l
Ag,
Sea are e n r i c h e d
and Cd at the o x y g e n / h y d r o g e n
in the u n d e r l y i n g
fore be d o c u m e n t e d
in many
sediments.
about the trace metal
s o l u b i l i t y d e c r e a s e of these e l e m e n t s
corresponding
to those found
in Co,
Zn,
in is
oceanographic
in T O C - r i c h u p w e l l i n g
i n t e r f a c e of an anoxic fjord
dramatic
high c o n c e n -
even in the d e p t h range of
S e d i m e n t s from the Black
on the b e h a v i o u r
Even though
of p l a n k t o n d a t a
Under p r e s e n t day
r e l a t i v e l y few d a t a exist
of s t a g n a n t
and r e g e n e r a t i o n
]986).
small f r a c t i o n of these e l e m e n t s
margins.
Unfortunately,
(Brumsack
trace metals may reach c o m p a r a b l y plankton
400 to 800 m at c o n t i n e n t a l
content
like the Gulf of California,
the p l a n k t o n c h e m i s t r y
place in the water c o l u m n
in m a r i n e
1986),
productivity,
reflects
processes
Mo,
sampling.
closely
and d e e p water e n r i c h m e n t s
g r e a t e r water d e p t h b e c a u s e water
in the marine e n v i r o n m e n t have been
5 to 10 years by a p p l y i n g new a n a l y t i c a l
V, and Cu by f a c t o r s
of these s e d i m e n t s
shales
preserva-
ratios of CTBE b l a c k
shales
sediments,
e x c e e d those f o u n d in o r g a n i c - r i c h
trap e x p e r i m e n t s
of T o a r c i a n black
as
(Table 2)
s t a g n a t i o n for the C e n o m a n i a n / T u r o n i a n rates must have been very low,
The m e t a l / a l u m i n u m
from s e d i m e n t
as well
of 10 to 100
than those r e p o r t e d for recent u p w e l l i n g
ratios
shales
from
(Table
3).
SW G e r m a n y
The c h e m i c a l
and r e c e n t
Gulf of
341
enrichment factor
)I00
