Downloaded from http://sp.lyellcollection.org/ at Pennsylvania State University on May 12, 2016
Unconformities in the Cenozoic of the North-East Atlantic
I. Pearson & D. Graham Jenkins
Unconformities in the North-East Atlantic and Norwegian Greenland Sea have been
examined from 60 DSDP boreholes, and correlated to a single biostratigraphic time-scale of
the Cenozoic. The unconformities can be divided into two types: (a) widespread events with
equivalent episodes outside this study area, and (b) locally restricted events.
Unconformities equivalent to those recognized by Vail & Hardenbol (1979) and Keller &
Barron (1983) are present in the late Pliocene, Miocene, mid-Oligocene and late to midEocene. Hiatuses corresponding to other unconformities noted by Vail & Hardenbol are
difficult to recognize, being encompassed within large local unconformities.
Hiatuses have been formed either by (a) a change in bottom water activity or (b) tectonic
events, diapirism and slope instability. Recognition of these types through a series of filters
allows greater accuracy in defining circulatory events.
Since the recognition of an early Eocene to
Cretaceous unconformity during DSDP Leg 1
(Ewing & Worzel 1969), the identification of
hiatuses in the deep sea sedimentary record has
assumed increasing importance for the explanation of changes in bottom water circulation and
oceanographic events.
Several authors have produced papers dealing
with the Cenozoic record of hiatuses (Rona 1973;
Berggren & Hollister 1974; Vail et al. 1977, 1980;
Moore et al. 1978; Hardenbol et al. 1981;
Tucholke 1981; Keller & Barron 1983; Miller &
Tucholke 1983) and there are numerous references
to unconformities in Initial Reports of the Deep
Sea Drilling Project (e.g. Poag et al., in press).
Correlation of hiatuses between different
DSDP Legs is complicated by the constant
revision of the magnetic time-scale, and associated revisions of the ages of biostratigraphic
zones.
The present work reviews the ages of unconformities in the NE Atlantic during the Cenozoic
(Fig. 1), recalibrating them to the most recent
time-scale ofBerggren et al. (1984a, b). Due to the
importance of hiatuses in the reconstruction of
oceanographic events and palaeocirculation, this
paper attempts to recognize and gradually
exclude, through a series of filters, those hiatuses
caused by non-circulation events, such as tectonics and slope instability.
Unconformities
Primary data have been extracted from (1) the site,
biostratigraphy and synthesis chapters of DSDP
volumes 12, 13, 14, 38, 47, 48, 49 and 50, (2) from
the initial core descriptions of Legs 80 and 81, (3)
from data provided by shipboard workers, Legs
81 and 94, and (4) from other published literature
(Perch-Nielson 1971; Backman 1978, 1979; Berggren 1978; Berggren & Aubert 1976; Berggren &
Schnitker 1983; Miller & Tucholke 1983).
An unconformity is defined as being a gap in
the sedimentary record. As stated by Vail et al.
(1980) 'all rocks below the unconformity are
older than the rocks above it'. The age of the
sediments immediately below an unconformity is
controlled by the amount of erosion into previously deposited sediments. The time interval
during which the unconformity was formed is
determined at a locality where the hiatus time gap
is at a minimum. This constraint may not represent the actual period of unconformity production, due to the inability to define the interaction
between non-deposition, solution and erosion at
a particular place. Hence an unconformity can
only be reliably dated by its upper boundary, the
age at which sediment deposition recommenced.
Several mechanisms have been proposed to
account for deep-sea unconformities. These
mechanisms produce two classes of unconformity. Members of the first class are caused by
changes in circulation, which include changes in
the relative intensity of bottom water circulation
giving rise to non-deposition and/or erosion;
other oceanographic changes, including variations in the CCD, bring about solution of previously deposited sedirnents. In this study no
distinction has been made between these mechanisms.
The second class of unconformity, whose differentiation has sometimes been overlooked in
circulation studies, is caused by tectonic events,
diapirism or slope instability.
Methods
To determine which hiatuses for each NE Atlan-
From SUMMERHAYES,C.P. & SHACKLETON,N.J. (eds), 1986, North Atlantic' Palaeoceanography, Geological
Society Special Publication No. 21, pp. 79-86.
79
Downloaded from http://sp.lyellcollection.org/ at Pennsylvania State University on May 12, 2016
I. Pearson and D.G. Jenkins
80
30°W
20
I
10
0
I
10
I
70ON
e350
/
-"
e33
4o.
34/
~
~
60 _
e
e336
e114
. ~
115" 116..117
50
l
~fl~
• oo,
I
('~
-
400~39~
4o.
:o,
40
136
- • e544 7
,,e 416ee (70 -
418eJ$
30
F1o. 1. Location map of sites used in this study.
tic site were probably produced by circulation
effects, a series of screening filters was employed
to remove successively various types of noncirculatory hiatuses.
To consider the correlation of hiatuses between
sites it is first necessary to have confidence in the
dating of the hiatus intervals at each individual
site. The methods used to recalibrate the data
from each site, and the criteria used are discussed
further in Pearson et al. (in press). This recalibration acted as the first filter, removing those sites
with a poor coring record, poor biostratigraphic
control or a complete sedimentary record (Table
1).
Filter 2 removed those hiatuses assigned to be
of tectonic origin by the DSDP Initial Report
volumes (Table 2). A further study of the relevant
seismic reflection profile for each site acted as
filter 3, and removed probably tectonically
formed hiatuses showing evidence of an angular
unconformity between overlying and underlying
sediments (Table 3). Finally, filter 4 involved the
examination of the probable palaeogeographic
setting of each hiatus in order to identify areas
Downloaded from http://sp.lyellcollection.org/ at Pennsylvania State University on May 12, 2016
Unconformities in the Cenozoic of the north-east Atlantic
TABLE 1. Filter 1: sites removed due to poor
coring, poor biostratigraphic control or having no hiatuses
TABLE 3. Filter 3. hiatuses removed due to
evidence of an angular unconformity on seismic reflection profiles
Site
Filter control
Site
Hiatuses removed
114
115
120
341
344
347
348
350
399
410
41!
412
413
414
558
606
607
609
610
611
551
339
Poor coring record
No hiatuses
Poor coring in Tertiary sediments
Large slump section
Poor biostratigraphy. No hiatuses.
Poor coring record
No hiatuses
Poor coring record. Poor biostratigraphy.
No hiatuses
No hiatuses
Mid Ocean Ridge Crest
Pleistocene only
Pleistocene only
Pleistocene only
No hiatuses
No hiatuses
No hiatuses
No hiatuses
No hiatuses
No hiatuses
Poor coring record in Tertiary
Poor biostratigraphy
398
415
416
544
545
548
Middle Eocene
Early Eocene to Middle Eocene
Early Palaeocene
All
All
All
TABLE 2. Filter 2: hiatuses removed where
D S D P Initial Report volumes state they are
o f tectonic origin
Site
Hiatuses removed
349
549
550
608
118
Upper Oligocene to Middle Miocene
Middle Eocene and older
Palaeocene
All
All
All
All
All
All
Early Oligocene
119
546
547
340
346
where slope instability was likely to have been the
causal factor (Table 4).
NE Atlantic unconformities
The area under investigation has been divided
into three regions.
(a) Norwegian-Greenland Sea and IcelandFaroe Ridge.
8I
TABLE 4. Filter 4." hiatuses removed where
sediment instability on slopes was likely to
have been the causal factor in their formation
Site
Hiatuses removed
337
401
549
550
402
All
Early Pliocene to Upper Oligocene
Recent to Early Oligocene
Recent to Palaeocene
All
(b) Rockall-Goban Spur and Biscay.
(c) Portuguese and N W African margin and the
Kings Trough.
When examining the diagrams produced by the
removal of all non-circulatory hiatuses (Figs 2, 3
and 4), the immediate impression is of nonuniformity of hiatus upper boundaries. This is the
result of a large number of very long hiatus
intervals, some of which were probably caused by
a series of erosional events. It is therefore necessary to make the assumption that the hiatus upper
boundary was present at a site with a long hiatus
when the presence of the equivalent boundary is
detectable in adjacent sites. For example the midOligocene hiatus in the Rockall area at 30 Ma can
be seen in Sites 403, 552 and 406 and its presence
is assumed in holes 553, 404 and 555 where a
younger hiatus has eroded to below the 30 Ma
level (Fig. 3).
Norwegian-Greenland Sea and
Iceland-Faroes Ridge (Fig. 2)
After the removal of Sites 337 and 340 and the
mid-Miocene and early Oligocene hiatuses from
Sites 349 and 346 by the filtering process (TaMes 2
and 4) only one laterally extensive hiatus can be
attributed to circulation effects. This commences
Downloaded from http://sp.lyellcollection.org/ at Pennsylvania State University on May 12, 2016
I. Pearson and D.G. Jenkins
82
(/)
~._1
'<
::::3(/) (DIE
wO
<0
oz
..Jz
<<
oz
0
0-~
z'<
<t~
.~0
nu.
ICELANDFAROE
RIDGE
m
NORWEGIAN
m
12-"'
z
_
CO CO [.O
O~
(D
COCO0')
CO
CO
AB
NH
--7
--
" I" "
L- ~o 16
7
CO
CO
........I['....
QL at 19 2 2
d L ~ -.
_
.
4 - ~_ E _i-2. 19'
17
11
-
8-
SEA
12
--6
--5
--4
--3
LU M _6_ ~.~
16-~ o _ 5
20-
8
3
6
E 2
5
--2
--PH
2£
A
A
--
Base
of coring
Basalt
basement
FIG. 2. Hiatuses (heavy vertical lines) present in the Norwegian-Greenland Sea and Iceland-Faroe Ridge
area that are probably due to circulatory effects. Light horizontal lines = probable correlated events.
A=major unconformities after Vail & Hardenbol (1979). B=Miocene unconformities after Keller & Barron
(1983).
in the late Pliocene at c.2.5 Ma in all the
Norwegian Sea sites (Fig. 2). Downcutting of this
hiatus varies between sites but the hiatus is
probably constrained between 2.5 Ma and 6 Ma
at Site 338. In addition three localized hiatuses
occur in Site 343 at 12 Ma and 44 Ma and at Site
342 at 18 Ma. The two youngest hiatuses may
have been obliterated by erosion in 342, 345 and
in 348.
The late Pliocene hiatus at site 352 on the
Iceland-Faroes Ridge can probably be correlated
with late Pliocene hiatus sedimentation recommencing at 2 Ma in the Norwegian Sea. At site
336, sedimentation recommenced earlier, at 4
Downloaded from http://sp.lyellcollection.org/ at Pennsylvania State University on May 12, 2016
Unconformities in the Cenozoic of the north-east Atlantic
83
O3
0(~
LuO
ROCKALL
--
GOBAN
SPUR
~ .,,.~
OZ Z<
oz
'~'(0
LOLO
LOLt)
03
0
"d"
"~" (~I t,,O
~. LO 0
LI') "~"
t tL®
0 ]Quat119 ~
4
If)
0
'~"
~
I.(3
LO
(.0 P",
~r-'- ~',,-- .,--
0
LO
~
BISCAY
MARGIN
0
0
~"
~:)
'Il
E
AB
--
i
'1
...[..
i
NH
--7
--6
--5
--4
--3
--2
I
I
24-I I INP-I~4-
/NI-M 7
321+1E
"+t' ...I...i...
"•'1 •''
40- I I+I';I-'-+_
+'+I,,+,I
561 l - ~
•.
/k
/k
5----
I
--PH
--t
A
- - Base of coring
Basalt basement
FIG. 3. Hiatuses (heavy vertical lines) present in the Rockall, Goban Spur and Biscay Margin areas that are
probably due to circulatory effects. See Fig. 2 for key.
Ma, probably reflecting localized variability in
the current speed of N A D W flowing over the
ridge. It is therefore suggested that the erosional
capability was greatest near to Iceland, at least
during the period 4 Ma to 2 Ma.
Rockall-Goban Spur and Biscay (Fig. 3)
The filtering process removed Sites 116 and 117
(Table 2) and Pliocene to Oligocene hiatuses at
Sites 549 and 401. In addition, early Eocene to
Palaeocene hiatuses were removed at Sites 549
and 550. There is a good correlation of upper
hiatus boundary ages between the Rockall area
and the Goban Spur from the middle Miocene
(Fig. 3), suggesting a uniformity of palaeoceanographic events affecting these two areas.
Sites 405 and 555 have a hiatus in the late
Pliocene at 2-2.5 Ma which correlates with
hiatuses in the Norwegian Sea area. The position
of these holes between the Rockall and Hatton
banks suggest that this trough was one of the
main passages for the southward flow of N A D W
during this period. The late to middle Miocene
has several concordant upper hiatus boundaries.
Three distinct surfaces occur between the period
8-12 Ma, although local conditions appear to
have influenced their distribution. These surfaces
correlate well with previously detected hiatuses
NH5 and N H 4 (Keller & Barron 1983), and one
at 9.8 Ma (Vail & Hardenbol 1979). A major
correlatable surface found in all sites in Rockall
and the Goban Spur except at Site 406, occurs at
15 Ma, and is equivalent to Keller & Barron's
NH2.
The middle Oligocene hiatus at 30 Ma detailed
Downloaded from http://sp.lyellcollection.org/ at Pennsylvania State University on May 12, 2016
I. Pearson and D.G. J e n k i n s
84
O0
~ o5
o~~'~
uJO O N
<0
oz z<
NW AFRICAN
MARGIN
(JDO
<<
OZ
0 Quat119
~
LO r..D 00
AB
I
NH
--7
--5
--4
--3
. .i.iiliilil
-2
1 6 _ _~
1
20-
~
24-
--PH
36- 18ti
~
40- 15
44- ,,
5256-
1~68°
64~.~~
I
Fl~. 4. Hiatuses (heavy vertical lines) present in the NW African Margin area that are probably due to
circulation effects. See Fig. 2 for key.
by Poag et al. (in press) can be traced through all
the Rockall and Goban Spur sites except Site 554.
It correlates to Vail's mid-Oligocene sea-level fall,
which is though to be of glacial origin (Keller &
Barron 1983).
Rockall sites show three correlatable surfaces
during the Eocene that are only partially detectable outside this area. The well documented late
Eocene hiatus, c.40 Ma, can be traced in every
Rockall site and those on the Biscay Margin, but
is conspicuously absent from the Goban Spur.
Two middle Eocene hiatus intervals are also seen
in the Rockall area at 45 Ma and 49 Ma. These
three Eocene surfaces can be detected on seismic
records (Masson & Kidd, in press). The late
Eocene hiatus has been ascribed to a circulation
event on a global scale (Vail & Hardenbol 1979),
although in this study area the hiatus is of dual
origin, being a circulation effect in the Rockall
area but caused by tectonic activity associated
Downloaded from http://sp.lyellcollection.org/ at Pennsylvania State University on May 12, 2016
Unconformities in the Cenozoic of the north-east Atlantic
with the Pyrennean event in the south (Pearson et
al., in press).
Sites from the Goban Spur and Biscay Margin
show two small hiatus producing events in the
Palaeocene at 60 Ma and 65 Ma.
Portuguese and NW African Margins and
Kings Trough (Fig. 4)
The late Eocene to late Oligocene hiatus at site
608 was removed by filter 2, being tectonic in
origin. This also applied to a long hiatus commencing in the early Miocene at Site 415 and two
smaller hiatuses in the middle Eocene of Site 398
and the Palaeocene of Site 416/370.
A middle Miocene hiatus at site 398 correlates
with Keller & Barron's NH5 and equivalent
hiatuses in the Rockall and Goban Spur area
(Fig. 4).
A hiatus at 23 Ma at Sites 135, 136, 544, 545
and 547 is equivalent to PH (Keller & Barron
1983) and Vait's 22.5 Ma hiatus (Vail & Hardenbol 1979), and can possibly also be recognized in
Sites 550 and 118. This appears to be a major
event on the N W African margin. The middle
Oligocene hiatus recognized in Rockall and the
Goban Spur is also present at Site 416/370 and is
probably also present at those sites with an early
Miocene hiatus.
Conclusions
Inter-regional unconformities are rare. Three
possible exceptions are (1) the late Pliocene
85
unconformity at 2.5 Ma, in the Norwegian Sea,
Rockall and Goban Spur areas, (2) an early
Miocene unconformity at 23 Ma in areas south of
the Goban Spur, and (3) a middle Oligocene
unconformity at 30 Ma in areas from Rockall
southwards. However, these events are not represented at every site in the regions where they
occur. This, together with the difficulty of detecting Vail's unconformities associated with sealevel changes, suggests that local circulation
effects (cf. Hollister & McCave 1984) have a
greater effect on Cenozoic stratigraphic
sequences recovered from cores in the NE Atlantic than do supposedly 'global' eustatic events.
The major difficulty in accurately correlating
unconformities lies in detecting the presence of
individual unconformities within long hiatuses.
Future work should follow the example of Vail et
al. (1980), and concentrate on the rigorous investigation of seismic profiles in the areas around
each drill site to determine the lateral stratigraphic relationships of beds that coalesce onto
each unconformity surface.
ACKNOWLEDGEMENTS: The authors thank Dr
R.B. Kidd for performing the filter analysis of
data and for helpful suggestions. Also many
thanks go to Professor B.M. Funnell and Dr C.
Summerhayes for useful comments and suggestions during the review process. Thanks also to
Carol Whale for typing the manuscript and to
John Taylor and Helen Boxall for the cartography. This work was performed while D.G. Jenkins was in receipt of an N E R C research grant.
References
BACKMAN,J. 1978. Miocene-Pliocene nannofossils and
sedimentation rates in the Hatton-Rockatl Basin.
N.E. Atlantic Ocean. Stock. Contrib. Geol. XXXVI
(1), 1-91.
1979. Pliocene biostratigraphy of DSDP sites 111
and 116 from the North Atlantic Ocean and the age
of northern hemisphere glaciation. Stock. Contrib.
Geol. XXXII (3), 115 37.
BERGGREN,W.A. 1978. Recent advances in Cenozoic
planktonic foraminiferal biostratigraphy, biochronology and biogeography, Atlantic Ocean. Micropaleontology 24, 337-70.
--•
HOLLISTER, C.D. 1974. Paleogeography, paleobiology and the history of circulation in the Atlantic
Ocean. Soc. econ. Paleont. Miner. Spec. Publ. 20,
126-86.
--&
AUBERT,J. 1976. Late Paleogene (Late Eocene
and Oligocene) benthonic foraminiferal biostratigraphy and paleobathymetry of Rockall Bank and
Hatton-Rockall Bank. Micropaleontology 22, 30726.
- - & SCHNITKER, D. 1983. Cenozoic marine environ-
ments in the North Atlantic and Norwegian-Greenland Sea. In: BOTT,M.H.P., SAXOV,S., TALWANt,M.
& TmEDE, J. (eds), Structure and Development of the
Greenland-Scotland Ridge. NATO Conference Series. Plenum Press, New York.
, KENT, D.V. & FLYNN, J. 1984a. Jurassic to
Paleogene: Part 2. Paleogene geochronology and
chronostratigraphy. In: Snelling, N.J. (ed.), The
Chronology of the Geological Record. Mem. Geol.
Soc. Lond. 10, 141-95 Blackwell Scientific Publications, Oxford.
- - , KENT, D.V. & VAN COUVER1NG,J.A. 1984b. The
Neogene: Part 2. Neogene geochronologyand chronostratigraphy. In: Snelling, N.J. (ed.), The Chronology of the Geological Record. Mem. Geol. Soc.
Lond. 10, 211 60. Blackwell Scientific Publications,
Oxford.
EWING,M. & WORZEL,J.L. 1969. Init. Rept. DSDP, 1.
US Govt. Print. Off., Washington, DC.
HARDENBOL,J., VAIE, P.R. & FERRER, J. 1981. Interpreting paleoenvironments, subsidence history, and
sea level changes of passive margins from seismic
Downloaded from http://sp.lyellcollection.org/ at Pennsylvania State University on May 12, 2016
86
I. Pearson and D.G. Jenkins
and biostratigraphy. Oceanol. Acta, Colloq, C3,
Geology of Continental Margins, 3344.
HOLLISTER,C.D. & MCCAVE, I.N. 1984. Sedimentation
under deep-sea storms. Nature 309, 220 5.
KELLER, G. & BARRON, J.A. 1983. Paleoceanographic
implications of Miocene deep-sea hiatuses. Geol.
Soc. Am. Bull. 84, 590-613.
MASSON, D.G. & KIDD, R.B., in press. Revised Tertiary
seismic stratigraphy of the southern Rockall
Trough. Inic Repts. DSDP. 81. US Govt. Print.
Off., Washington, D.C.
MILLER, K.G. & TUCHOLKE,B.E. 1983. Development of
Cenozoic abyssal circulation south of the Greenland
Scotland Ridge. In: BOTT, M.H.P., SAXOV, S.,
TALWANI, M. & THIEDE, J. (eds), Structure and
Development of the Greenland-Scotland Ridge.
NATO Conference Series. Plenum Press, New
York.
MOORE, T.C., VAN ANDEL, T.J.H., SANCETTA, C.
PISIAS, N.G. 1978. Cenozoic hiatuses in pelagic
sediments. Micropaleontology 24, 113-38.
PEARSON, I., KIDD, R.B., BIART, B. & JENKINS, D.G., in
press. Cenozoic unconformities of the North-East
Atlantic: formational processes with reference to
DSDP/IPOD Leg 94. Init. Repts DSDP, 94.
PERCH-NIELSEN, K. 1971. Einige neve Coccolithen aus
dem Paleozan der Bucht von Biskaya. Bull. Geol.
Soc. Denmark 20, 347 61.
POAG, C.W., REYNOLDS, L.A., MAZZULO, J.M. &
KEIGWIN, L.D. jr., in press. Foraminiferal, Lithic
and Isotopic changes across four major unconformities at DSDP-IPOD site 548, Goban Spur. Init.
Repts DSDP 80. US Govt. Print. Off., Washington,
DC.
RONA, P.A. 1973. Worldwide unconformities in marine
sediments related to eustatic changes of sea-level.
Nature Phys. Sci. 244, 25-6.
TUCHOLKE, B.E. 1981. Geological significance of seismic reflection in the deep western North Atlantic.
In: Warme, J.E., Douglas, R.G. & Winterer, E.L.
(eds), The Deep Sea Drilling Project: A Decade of
Progress. Soc. econ. Paleo. Miner. Spec. Publ. 32,
23-38.
VAIL, P.R. & MITCHUM, R.M. jr. et al. 1977. Seismic
stratigraphy and global changes of sea level. In."
Payton, C.E. (ed), Seismic Stratigraphy--Applications to Hydrocarbon Exploration. Am. Ass.
Petrol. Geol. Mere. 26, 49-205.
& HARDENBOL,J. 1979. Sea-level changes during
the Tertiary. Oceanus 22, 71-9.
--,
MITCHUM, R.M. jr, SHIPLEY, T.H. & BUEELER,
R.T. 1980. Unconformities of the North Atlantic.
Trans. R. Soc. Lond. A 294, 137-55.
-
-
I. PEARSON d~. D. GRAHAM JENKINS, Department of Earth Sciences, The Open University,
Walton Hall, Milton Keynes MK7 6AA.