www.geologicacarpathica.sk
GEOLOGICA CARPATHICA, JUNE 2010, 61, 3, 193—200 doi: 10.2478/v10096-010-0010-7
Climatic cycles recorded in the Middle Eocene hemipelagites
from a Dinaric foreland basin of Istria (Croatia)
BORNA LUŽAR-OBERITER
1
, PETER A. HOCHULI
2
, LJUBOMIR BABIĆ
1
, BOSILJKA GLUMAC
3
and
DARKO TIBLJAŠ
4
1
Institute of Geology and Paleontology, Faculty of Science, University of Zagreb, Horvatovac 102a, 10000 Zagreb, Croatia;
bluzar@geol.pmf.hr
2
Paläontologisches Institut, Universität Zürich, Karl Schmid-Strasse 4, CH-8006 Zürich, Switzerland
3
Department of Geosciences, Smith College, Northampton, Massachusetts 01063, USA
4
Institute of Mineralogy and Petrology, Faculty of Science, University of Zagreb, Horvatovac 95, 10000 Zagreb, Croatia
(Manuscript received July 20, 2009; accepted in revised form March 11, 2010)
Abstract: Middle Eocene hemipelagic marls from the Pazin-Trieste Basin, a foreland basin of the Croatian Dinarides,
display repetitive alternations of two types of marls with different resistance to weathering. This study focuses on the
chemical composition, stable isotopes, and palynomorph content of these marls in order to better understand the nature of
their cyclic deposition and to identify possible paleoenvironmental drivers responsible for their formation. The less resis-
tant marls (LRM) have consistently lower carbonate content, lower
δ
18
O and
δ
13
C values, and more abundant dinoflagel-
late cysts than the more resistant marls (MRM). We interpret these differences between the two marl types to be a result of
climatic variations, likely related to Milankovitch oscillations. Periods with wetter climate, associated with increased
continental runoff, detrital and nutrient influx produced the LRM. Higher nutrient supply sparked higher dinoflagellate
productivity during these times, while reduced salinity and stratification of the water column may have hampered the
productivity of calcareous nannoplankton and/or planktonic foraminifera. In contrast, the MRM formed during dryer
periods which favoured higher carbonate accumulation rates. This study provides new information about the sedimentary
record of short-scale climate variations reflected in wet-dry cycles during an overall warm, greenhouse Earth.
Key words: Eocene, Dinarides, Croatia, climate, cycles, hemipelagites.
Introduction
Deep-sea pelagic and hemipelagic strata are perhaps the best
recorders of cyclic climatic changes due to their largely un-
interrupted depositional history with little or no local influ-
ences. These deposits commonly display small-scale
alternations in lithology, which are usually interpreted as a
product of cyclic climatic changes driven by orbital forcing
(e.g. de Boer & Smith 1994; and references cited therein).
Climatically driven changes in atmospheric and oceano-
graphic conditions affect the productivity of organisms, in-
flux of terrigenous material, as well as ocean circulation and
oxygen concentrations. Consequently, small-scale sedimen-
tary cycles of similar appearance can have variable origins as
cycles of productivity, dissolution, dilution by terrigenous
input, or redox cycles (Einsele 1982). Although any of these
mechanisms can by itself produce cyclic lithological alterna-
tions, in a natural environment, it is often reasonable to as-
sume that a complex interplay of these mechanisms is
responsible. In some cases diagenesis is interpreted as gener-
ator of rhythmic bedding by causing carbonate redistribu-
tion. However, it is generally considered unlikely that
diagenesis is capable of creating rhythms from initially ho-
mogeneous sediment by self-organization alone, but instead
only enhances an already existing cyclic pattern (Einsele
1982; Böhm et al. 2003). An array of different analytical
methods are commonly used to identify and distinguish be-
tween the possible causes of cyclic alternations, including
Fig. 1. Study area. A – Location of the study area (framed) within
the Mediterranean region. B – Stratigraphic position of the investi-
gated Globigerina Marls unit. C – Simplified geological map of
the study area. Small stars mark the locations of outcrops of Globi-
gerina Marls showing cyclicity. The large star is the location of the
studied outcrop.
194
LUŽAR-OBERITER, HOCHULI, BABIĆ, GLUMAC and TIBLJAŠ
major and trace element geochemistry, stable isotopes, mi-
cro- and nannofossil records, and time series analysis
(Schwarzacher 2000).
Although the most profound expression of orbital forcing
on climate is the occurrence of ice ages (Hays et al. 1976),
many examples of pre-Pleistocene cyclic successions
demonstrate that orbital forcing may influence the sedimen-
tary record in an ice-free greenhouse world (de Boer &
Smith 1994). Orbitally driven cyclicity has been widely
studied in pelagic and hemipelagic successions of different
settings: oceanic domains, intermontane basins, grabens, and
epicontinental settings (de Boer & Smith 1994; D’Argenio et
al. 2004; and references cited therein). Here we describe
small-scale cycles formed in a specific paleogeographic lo-
cation and stage of peripheral foreland basin evolution. The
cycles occur in the Middle Eocene hemipelagites from the
Pazin-Trieste Basin on the Istrian peninsula of the coastal
Croatian Dinarides (Fig. 1A—C; Lužar-Oberiter et al. 2004).
Variations in chemical composition, stable isotopes, and pa-
lynomorph content have been investigated. These offer new
insights into the nature of the cycles and the driving mecha-
nisms responsible for their formation. They provide a new
understanding of how climate influenced sedimentation in
the foreland basin of the Dinaric region of Croatia during the
Middle Eocene greenhouse climate.
Geological setting
The sedimentary cyclicity that this study focuses on is
characteristic of hemipelagic marls which make up a litho-
stratigraphic unit named Globigerina Marls by Schubert
(1905). This unit occupies a specific position in the sedimen-
tary and tectonic evolution of the Pazin-Trieste Basin, an
Eocene Dinaric foreland basin (Fig. 2A). The NW—SE elon-
gated basin evolved on top of Mesozoic carbonates, which
were first emerged and karstified, and subsequently overlain
by a brackish to marine limestone succession of Early to
Middle Eocene age (Fig. 1B; Schubert 1905; Muldini-
Mamužić 1965; Drobne 1977). This succession is further
overlain by the Upper Lutetian to Upper Eocene Globigerina
Marls unit and flysch deposits (Muldini-Mamužić 1965;
Kraseninnikov et al. 1968; Piccoli & Proto-Decima 1969).
The Globigerina Marls unit of the Pazin-Trieste Basin is re-
garded as the middle member of the underfilled foreland
trinity of Sinclair (1997), which follows the formation of a
forebulge, and consists of ramp limestones, hemipelagites,
and flysch (Fig. 2B; Živković & Babić 2003). The develop-
ment of this tripartite succession was related to the subsid-
ence of the foreland towards the SW in response to the load
imposed by the propagating Dinaric tectonic structures from
the NE. The onset of hemipelagic deposition marks the time
when carbonate production could not keep pace with subsid-
ence, while the sedimentation of the overlying flysch started
when the area came under the influence of the orogen and re-
ceived detritus from the orogen to the NE and from the car-
bonate foreland to the SW (Babić & Zupanič 1996). The
abundance of planktonic foraminifera in the Globigerina
Marls unit suggests deposition at depths of about 1000 m
Fig. 2. Reconstruction of the Pazin-Trieste (PT) Basin. A – Paleo-
geographic map of the Adriatic region during the Lutetian showing
the position of the PT Basin (after Tarlao et al. 2005). B – Cross-
section through the basin showing its location in front of the ad-
vancing Dinaric orogen and the structural and depositional setting
of the cyclic Globigerina Marls unit.
(Gohrbandt 1962; Juračić 1979; Živković & Babić 2003).
The Globigerina Marls unit is a 40 to 60 meter thick monoto-
nous succession of grey marls, homogeneous in appearance,
exposed along the margins of the basin. Thin turbiditic lay-
ers are very rare, but become more common up-section at the
transition to flysch. Subtle cyclicity is observable at many
localities, but it is commonly obscured in tectonically dis-
turbed areas and only well preserved in smaller segments of
individual outcrops of the Globigerina Marls unit. Our de-
tailed study was conducted in an outcrop located in the
southern part of the basin (Figs. 1C, 3), where the strata dis-
play horizontal bedding and negligible tectonic disturbance.
This part of the succession corresponds to the middle part of
the unit, and has been assigned to the lower part of the
planktonic foraminiferal Zone P12 of Berggren et al. (1995)
(Živković & Babić 2003) which corresponds to Zone E10 of
Berggren & Pearson (2005).
The studied cycles consist of two types of marls identified
on weathered surfaces of certain outcrops: marls more resis-
tant to weathering (MRM – sample numbers U) slightly
protrude from the outcrop surface compared to less resistant
marl (LRM – sample numbers L) intervals in between them
(Fig. 3A). Transitions between the two marl types are always
gradual. The subtle nature of the cyclicity does not allow vi-
sual identification in all outcrops of the Globigerina Marls
unit. In the studied outcrop the average thickness of individ-
ual MRM—LRM couplets is approximately 35 cm, without
much variation laterally and vertically.
195
CLIMATIC CYCLES RECORDED IN THE MIDDLE EOCENE HEMIPELAGITES (CROATIA)
taminants. After reacting with 100% H
3
PO
4
at
70 °C for 5 minutes they were analysed using
an on-line automated carbonate preparation
system (Kiell III) linked to a Finnigan-MAT
DeltaXL+ ratio mass spectrometer. Standard
isobaric and phosphoric acid fractionation cor-
rections were applied to all results, and analyt-
ical precision was monitored through daily
analysis of a variety of carbonate standards.
For palynological analysis cleaned, crushed
and weighed samples (15 g) were treated with
HCl and HF following standard preparation
techniques (e.g. Traverse 2007). All samples
were productive and were studied for their
content of particulate organic matter and pa-
lynomorph types (e.g. phytoclasts, dinoflagel-
late cysts, acritarchs, and spore-pollen). A
minimum of 250 particles were determined
and counted per sample.
Results
Both the LRM and MRM consist of calcite,
quartz, muscovite/illite, kaolinite and smec-
tite. Only calcite and quartz show well defined
peaks on the X-ray spectra. Observation under
the scanning electron microscope showed no
apparent difference between the two marl
types. In all samples most of the carbonate is
present as nannoplankton and foraminiferal re-
mains, which are generally well preserved.
Minute barite crystals occur mostly as scat-
tered individual crystals and occasionally in
small aggregates.
CaCO
3
content varies from 46.70 to
63.46 %, with samples from the LRM layers
containing on average about 11 % less CaCO
3
compared to the MRM (Fig. 4). Measured bulk
carbonate
δ
18
O values vary between —1.18 ‰
and —2.69 ‰. The MRM consistently have
Fig. 3. Field photographs of the Globigerina Marls deposits of the Pazin Basin in
Istria, Croatia. A – View of the studied outcrop with the clearly visible alterna-
tions of marls with slightly different resistance to weathering. B – Close up view
of a segment of the studied outcrop during sampling. Positions of samples were
marked prior to the removal of the weathered surface material.
Methods
Sampling points were chosen where the MRM and LRM
could be most clearly differentiated in the outcrop. The posi-
tion of each sample was marked before removing the weath-
ered surface cover since the differentiation between the two
marl types proved to be difficult after cleaning the rock sur-
face (Fig. 3B). Several intervals in the studied section were
omitted due to insufficient quality of the exposure (see Fig. 4).
Element concentrations were determined by ICP-MS.
CaCO
3
contents were measured by complexometrical titra-
tion. XRD analyses on unoriented whole-rock mounts and
scanning electron microscope imaging were used to identify
the mineral constituents and refine the petrography of the
marls. Organic carbon (C
org
) was determined by combustion
of dry, carbonate free samples on a LECO IR 212 instrument.
For stable isotope analysis whole-rock powdered samples
were roasted at 380 °C for one hour to remove volatile con-
higher
δ
18
O values, averaging 0.86 ‰ above those of LRM
(Fig. 4). The measured
δ
13
C values range between 0.69 and
0.91 ‰, and are higher in the MRM than in the adjacent
LRM (Fig. 4). Both
δ
18
O and
δ
13
C values correlate positive-
ly with CaCO
3
content (r
2
= 0.91 and r
2
= 0.71, respectively;
Fig. 5). SiO
2
, Al
2
O
3
, TiO
2
and K
2
O concentrations are high-
er in the LRM relative to the MRM. Al
2
O
3
concentrations are
positively correlated with concentrations of TiO
2
, K
2
O, and
SiO
2
, whereas concentrations of Al
2
O
3
and CaO correlate
negatively. C
org
values are low for all the studied samples
(0.10—0.15 %), and are slightly higher in the LRM (Fig. 4).
The preservation of palynomorphs is fairly good to excel-
lent. Individual grains exhibit no obvious signs of post-depo-
sitional degradation. Thermally unaltered conditions of the
organic matter are indicated by the virtually unchanged co-
lour of the palynomorphs (thermal alteration index < 2). In
most samples the assemblages of particulate organic matter
(POM) are strongly dominated by translucent phytoclasts,
196
LUŽAR-OBERITER, HOCHULI, BABIĆ, GLUMAC and TIBLJAŠ
including woody particles, and cuticles of terrestrial origin as
well as membranes of undetermined origin. The second most
abundant element is a particular type of acritarch (Acritarch
A), which is characterized by a dense cover of long hair-like
processes. Dinoflagellate cysts are also very common, repre-
senting the third most important POM constituent. All other
groups including inertinite, opaque phytoclasts and the
palynomorph groups such as acritarchs, bisaccate pollen and
other spore-pollen grains, are present, but are quantitatively
of minor importance. Among the various categories of
palynomorphs, only dinoflagellate cysts seem to show a
clear cyclic distribution. They are more common in the LRM
(L samples in Fig. 4) than in the MRM.
Among the observed palynomorphs, dinoflagellate cysts
are not only the most abundant component, but also show a
relatively high diversity (see Appendix). The assemblages
show a rather homogeneous composition throughout the
studied interval. Compared to other coeval assemblages,
some of the typical species of this stratigraphic interval (e.g.
Aerosphaeridium diktyoplokus and marker species of the
Wetzeliella group), have not been found in the studied sam-
ples. Pollen grains and spores are relatively rare. The spore-
Fig. 5.
Scatter
plots
showing the relationship
between carbonate con-
tent and stable isotopes.
A positive correlation is
evident in both dia-
grams. Circles – LRM;
triangles – MRM.
Fig. 4. Vertical variations in measured parameters within the studied section of the Globigerina Marls unit. Note the consistent differences
in carbonate content, stable isotopes, dinoflagellate abundance, and C
org
between the alternating less resistant (LRM; samples L) and more
resistant (MRM; samples U) marls. The sampling gap is due to poor outcrop conditions.
197
CLIMATIC CYCLES RECORDED IN THE MIDDLE EOCENE HEMIPELAGITES (CROATIA)
pollen assemblages are dominated by bisaccate pollen
grains. Among the relatively rare angiosperm pollen, a few
grains of Echimonocolpites (Nipa) were observed.
Discussion
Our geochemical and palynological data (Fig. 4) follow a
cyclic pattern of deposition which corresponds to the vertical
changes in the degree of weathering observed on the studied
outcrop (Fig. 3). The parameters we have measured are gener-
ally considered to be good proxies for past environmental con-
ditions (e.g. Pross & Schmeidl 2002; Mader et al. 2004;
Sagasti 2005), which suggests that the deposition of the stud-
ied marls was influenced by cyclic changes in oceanographic
conditions of the Eocene seaway which flanked the early
Dinarides (Fig. 2).
Although commonly used as indicators of oceanographic
conditions such as temperature, salinity and productivity,
oxygen and carbon stable isotopes can be subject to serious
diagenetic alterations, often causing difficulties in differenti-
ating between a diagenetic and environmental signal (Mitchell
et al. 1997). In the data from the studied marls, the correlation
between CaCO
3
,
δ
18
O and
δ
13
C (Fig. 5) is suggestive of a pos-
sible diagenetic imprint. However, if diagenetic carbonate re-
organization was the cause of the approximately 11%
difference in CaCO
3
between LRM and MRM, one would ex-
pect MRM to display more negative
δ
18
O values due to higher
amounts of secondary carbonate cement (Thierstein & Roth
1991; Frank et al. 1999; Westphal 2006). The subtle and
consistent differences in isotope values (Fig. 4), the overall
good preservation of microfossils (Živković & Babić 2003;
Živković & Glumac 2007) and the lack of a significant
amount of secondary carbonate in the studied marls suggest
the absence of notable diagenetic overprint. High clay content
of both studied marl types would have prevented serious verti-
cal circulation of porewater, creating a relatively closed diage-
netic system. This contrasts with limestone—marl systems
where carbonate ooze intervals, due to higher permeability
and a greater number of carbonate growth centers, take on a
larger amount of diagenetic carbonate (Mitchell et al. 1997;
Frank et al. 1999). Although some postdepositional alteration
of isotope values in both marl types cannot be ruled out, it is
not probable that the observed relative differences in isotope
values between LRM and MRM are purely a product of
carbonate reorganization. Instead, it is probable that these dif-
ferences reflect changes in oceanographic conditions.
We suggest that the deposition of the investigated marls was
influenced by changes between wetter and dryer periods
(Mader et al. 2004; Sagasti 2005). The positive correlation be-
tween
δ
18
O and
δ
13
C values suggests that variations in conti-
nental runoff, which can affect both isotopes, played a role in
the formation of the observed cycles (Mader et al. 2004). Dur-
ing wetter periods, greater input from continental runoff led to
an increased input of lighter isotopes, river fed nutrients and/
or detrital siliciclastic material resulting in the formation of
LRM (Fig. 6). The abundance of Braarudosphaera in the
nannoplankton assemblages from the base of the Globigerina
Marls unit has been suggested as an indicator of freshwater
influx to the Pazin-Trieste Basin (Pavlovec & Pavšić 1986),
and abundant vegetation rafted dropstones found in the basal
parts of the Globigerina Marls point to the existence of deltaic
systems located along the NE margin of the basin (Tarlao et
al. 2005). The higher concentrations of Al
2
O
3
, TiO
2
, SiO
2
and
K
2
O in the LRM samples, as well as their negative correlation
with CaO, possibly reflect an increased siliciclastic terrige-
nous input for the LRM compared to the MRM. The sediment
source area was the emerging Dinaric orogen to the NE, which
later became an even more active source area for flysch depos-
its. However, dilution by changing terrigenous supply of detri-
tus probably had a minor role in producing the marl cycles, as
one would expect a larger thickness of LRM intervals (Einsele
1982). The higher abundance of dinoflagellate cysts in the
LRM (Fig. 4) can be interpreted as a response to the increased
influx of nutrients related to enhanced runoff. As no corre-
sponding variation is observed in the distribution of POM of
terrestrial origin, the similar trend in the C
org
and dinoflagel-
late cyst abundance suggests that the differences in the abun-
dance of dinoflagellate cysts between the LRM and MRM are
related to changes in dinoflagellate productivity rather than
changing input of terrestrial organic matter. At the same time
overall productivity of calcareous nannoplankton and/or
planktonic foraminifera was reduced as indicated by lower
CaCO
3
concentrations and
δ
13
C values (Fig. 4). The cause of
this may have been unfavourable oceanographic conditions
due to a decrease in surface water salinity and possible stratifi-
cation of the water column. In contrast to periods of wetter cli-
mate, during deposition of MRM the climate was less humid
resulting in reduced continental runoff and possibly increased
evaporation as suggested by higher
δ
18
O values. The waters of
the Pazin Basin at these times experienced less stratification
and conditions more suitable for calcareous nannoplankton
and/or planktonic foraminifera which resulted in higher car-
bonate accumulation rates (Fig. 6). Changing paleoceano-
graphic conditions have been reported from the same section
of the Globigerina Marls unit by Živković & Glumac (2007),
based on assemblages of small benthic foraminifera. Although
they used much broader sampling intervals, these authors did
Fig. 6. Climatic and environmental conditions responsible for the
origin of cyclicity in the Globigerina Marls unit of the Pazin-Trieste
Basin during the Middle Eocene. See text for explanation.
198
LUŽAR-OBERITER, HOCHULI, BABIĆ, GLUMAC and TIBLJAŠ
identify episodes of higher refractory organic matter flux and/
or lowered oxygen concentrations in the bottom waters during
overall mesotrophic conditions.
During the Eocene, the region of Istria was situated in mid
latitudes and experienced overall warm subtropical climate
conditions (Pavlovec & Pavšić 1986; Živković & Babić 2003;
Tarlao et al. 2005). The occurrence in the studied marls of
Echimonocolpites, which is attributed to the mangrove palm
genus Nypa, is typical of the Middle Eocene assemblages and
is considered a good indicator of the optimum climatic condi-
tions during the Eocene. Assuming similar climatic conditions
for the fossil representatives of the genus as for the extant spe-
cies, surface water temperatures would have been above 20 °C
(Fechner 1988; Akkiraz et al. 2006).
In their modelling of Eocene greenhouse climate, Sloan &
Huber (2001) showed that ocean-related climate processes re-
sponded significantly to variations in orbital forcing on a pre-
cessional scale (~ 21 ka), enough to produce rhythmic
sedimentation in many regions of the world (e.g. D’Argenio et
al. 1998; Burgess et al. 2008; Machlus et al. 2008). Cyclic
changes in ocean surface moisture and continental runoff
amounts were particularly pronounced in low latitudes. These
changes were related to periods of higher and lower insolation
and seasonality, which affected the intensity of monsoonal cir-
culation in the atmosphere and associated precipitation pat-
terns (Prell & Kutzbach 1992). The results of our study
suggest that such Milankovitch-scale changes probably also
had an influence on the mid latitude area of the Dinarides and
caused shifts between wetter and dryer climatic periods during
the Middle Eocene greenhouse climate. These climate chang-
es are reflected in fluctuating amounts of biogenic and detrital
material being supplied to the sediments of the Pazin-Trieste
foreland basin (Fig. 6). This study illustrates how subtle
small-scale depositional cycles, not always apparent and com-
monly obscured in the field, can become evident when exam-
ined in detail for their geochemistry and fossil content, and are
able to provide unique insights into climatic oscillations. Such
integrative data derived from sedimentary records are valuable
and necessary inputs for various climate modelling efforts and
for our ability to evaluate and predict complex temperature
and precipitation patterns in an overall warm, ice-free world.
Conclusions
The regular alternations between less and more resistant
marls observed in the Middle Eocene hemipelagic Globigeri-
na Marls unit probably resulted from cyclic climatic changes
between wetter and dryer periods affecting the mid-latitude
Pazin-Trieste foreland basin of the Croatian Dinaric region.
Our data suggest that periods of wetter climate, associated
with increased continental runoff supplied by rivers draining
the Dinarides along the NE margin of the basin, and ensuing
higher detrital and nutrient influx, produced the LRM. An in-
creased nutrient supply due to higher runoff may have been
the cause for increased dinoflagellate productivity, but the re-
duced salinity as well as possible stratification of the water
column reduced the overall productivity of calcareous nanno-
plankton and/or planktonic foraminifera. As a result, the LRM
exhibit lower
δ
18
O and
δ
13
C values, lower CaCO
3
, higher con-
centrations of SiO
2
, Al
2
O
3
, TiO
2
, K
2
O and C
org
, and higher
abundance of dinoflagellate cysts compared to the MRM,
which formed during periods of dryer climate. The dryer pe-
riods were in turn characterized by less runoff, higher salini-
ty of surface waters and less stratification of the water
column which favoured higher carbonate accumulation rates.
This multifaceted study of depositional cycles in the
Globigerina Marls unit of the Pazin-Trieste Basin provides
important new data towards our understanding of short-scale
climate variations reflected in wet-dry cycles, which were
likely related to Milankovitch oscillations during the Eocene
greenhouse Earth.
Acknowledgments: This work was funded by the Croatian
Ministry of Science, Education and Sports project 119-
1191155-1159 “Evolutionary Changes of the Dinarides from
Subduction to Modern Adriatic Beaches”. We sincerely thank
Robert Koščal for helping prepare the figures. Stable isotope
analyses were performed at the Stable Isotope Laboratory of
Prof. Stephen Burns at the University of Massachusetts at
Amherst, USA. Element concentrations were determined by
ICP-MS at Actlab Laboratories, Canada.
References
Akkiraz M.S., Akgün F., Örçen S., Bruch A.A. & Mosbrugger V.
2006: Stratigraphic and palaeoenvironmental significance of
Bartonian-Priabonian (Middle—Late Eocene) microfossils from
the Basçesme Formation, Denizli Province, Western Anatolia.
Turkish J. Earth Sci. 15, 155—180.
Babić Lj. & Zupanič J. 1996: Coastal Dinaric flysch belt: paleotrans-
port for the Pazin Basin, and the role of a foreland uplift (lstria,
Croatia). Natura Croatica 5, 317—327.
Berggren W.A. & Pearson P.N. 2005: A revised tropical to subtrop-
ical Paleogene planktonic foraminiferal zonation. J. Foram.
Res. 35, 279—298.
Berggren W.A., Kent D.V., Swisher C.C. III & Aubry M.-P. 1995: A
revised Cenozoic geochronology and chronostratigraphy. In:
Berggren W.A., Kent D.V., Aubry M.-P. & Hardenbol J. (Eds.):
Geochronology, time scales, and global stratigraphic correlation.
SEPM Spec. Publ., Tulsa 54, 129—212.
Böhm F., Westphal H. & Bornholdt S. 2003: Required but disguised:
environmental signals in limestone-marl alternations. Palaeo-
geogr. Palaeoclimatol. Palaeoecol. 189, 161—178.
Burgess C.E., Pearson P.N., Lear H.L., Morgans H.E.G., Handley L.,
Pancost R.D. & Schouten S. 2008: Middle Eocene climate cy-
clicity in the southern Pacific: Implications for global ice vol-
ume. Geology 36, 651—654.
D’Argenio B., Fischer A.G., Richter G.M., Longo G., Pelosi N., Mo-
lisso F. & Duarte Morais M.L. 1998: Orbital cyclicity in the
Eocene of Angola: visual and image-time-series analysis com-
pared. Earth Planet. Sci. Lett. 160, 147—161.
D’Argenio B., Fischer A.G., Premoli Silva I., Weissert H. & Ferreri
V. (Eds.) 2004: Cyclostratigraphy: Approaches and case histo-
ries. SEPM Spec. Publ. 81, 1—311.
de Boer P.L. & Smith D.G. (Eds.) 1994: Orbital forcing and cyclic
sequences. IAS Spec. Publ., Blackwell, Oxford, 19, 1—559.
Drobne K. 1977: Alvéolines Paléog
e
nes de la Slovénie et de l’lstrie.
Schweiz. Palaeont. Abh. 99, 1—174.
Einsele G. 1982: Limestone-marl cycles (periodites): Diagnosis, sig-
nificance, causes – a review. In: Einsele G. & Seilacher A.
è
199
CLIMATIC CYCLES RECORDED IN THE MIDDLE EOCENE HEMIPELAGITES (CROATIA)
(Eds.): Cyclic and event stratification. Springer, Berlin, 8—53.
Fechner G.G. 1988: Selected palynomorphs from the Lower to Mid-
dle Eocene of the South Atlas Border Zone (Morocco) and
their environmental significance. Palaeogeogr. Palaeoclima-
tol. Palaeoecol. 65, 73—79.
Frank T.D., Arthur M.A. & Dean W.E. 1999: Diagenesis of Lower
Cretaceous pelagic carbonates, North Atlantic: paleoceano-
graphic signals obscured. J. Foram. Res. 29/4, 340—351.
Gohrbandt K. 1962: Vorläufige Mitteilungen über ökologische Un-
tersuchungen an Kleinforaminiferen aus dem Flyschbereich von
Istrien. Verh. Geol. Bundesanst. 1962/2, 228—235.
Hays J.D., Imbrie J. & Shackleton N.J. 1976: Variations in the Earth’s
Orbit: Pacemaker of the ice ages. Science 194, 1121—1132.
Juračić M. 1979: Depth of sedimentation of “Marl with crabs” esti-
mated from the ratio between planktonic and benthic foramin-
ifera. Geol. Vjes. 31, 61—67 (in Croatian, English summary).
Kraseninnikov V.A., Muldini-Mamuzic S. & Dzodzo-Tomic R.
1968: Signification des foraminif
è
res planctoniques pour la divi-
sion du Paléog
e
ne de la Yougoslavie et comparaison avec les au-
tres régions examinées. Geol. Vjes. 21, 117—145.
Lužar-Oberiter B., Babić Lj., Glumac B., Zupanič J. & Tibljaš D. 2004:
Cycles in Middle Eocene marls of Istria (Croatia). 23. IAS Meet-
ing of Sedimentologists, Coimbra, Portugal. Abstracts Book (Pena
dos Reis R., Callapez P. & Dinis P. (Eds.)), Coimbra, 1—178.
Machlus M.L., Olsen P.E., Christie-Blick N. & Hemming S.R. 2008:
Spectral analysis of the lower Eocene Wilkins Peak Member,
Green River Formation, Wyoming: Support for Milankovitch
cyclicity. Earth Planet. Sci. Lett. 268, 64—75.
Mader D., Cleaveland L., Bice D.M., Montanari A. & Koeberl C.
2004: High-resolution cyclostratigraphic analysis of multiple
climate proxies from a short Langhian pelagic succession in the
C
o
nero Riviera, Ancona (Italy). Palaeogeogr. Palaeoclimatol.
Palaeoecol. 211, 325—344.
Mitchell S.F., Ball J.D., Crowley S.F., Marshall J.D., Paul C.R.C.,
Veltkamp C.J. & Samir A. 1997: Isotope data from Cretaceous
chalks and foraminifera: Environmental or diagenetic signals?
Geology 25/8, 691—694.
Muldini-Mamužić S. 1965: The microfauna of limestones and of the
clastic development in the Paleogene of central Istria. Geol.
Vjes. 18, 281—289 (in Croatian, English summary).
Pavlovec R. & Pavšić J. 1986: Biostratigraphy of beds with crabs in
Istria. Geologija 28/29, 55—68 (in Slovenian, English summary).
Piccoli G. & Proto Decima F. 1969: Ricerche biostratigrafiche sui
depositi flyschoidi della regione Adriatica settentrionale e orien-
tale. Mem. 1
st
. Geol. Miner. Univ., Padova, 27, 1—21.
Prell W.L. & Kutzbach J.E. 1992: Sensitivity of the Indian monsoon
to forcing parameters and implications for its evolution. Nature
360, 647—652.
Pross J. & Schmiedl G. 2002: Early Oligocene dinoflagellate cysts
from the Upper Rhine Graben (SW Germany): paleoenviron-
mental and paleoclimatic implications. Mar. Micropaleontology
45, 1—24.
Sagasti G. 2005: Hemipelagic record of orbitally-induced dilution cy-
cles in Lower Cretaceous sediments of the Neuquén Basin. In:
Veiga G.D., Spalletti L.A., Howell J.A. & Schwarz E. (Eds.):
The Neuquén Basin, Argentina: A case study in sequence
stratigraphy and basin dynamics. Geol. Soc. London, Spec. Publ.
252, 231—250.
Schubert R.J. 1905: Zur Stratigraphic des istrisch-norddalmatinis-
chen Mitteleocäns. Jb. Geol. Reichsanst. 55, 153—188.
Schwarzacher W. 2000: Repetitions and cycles in stratigraphy. Earth
Sci. Rev. 50, 51—75.
Sinclair H.D. 1997: Tectonostratigraphic model for underfilled pe-
ripheral foreland basins: An Alpine perspective. Geol. Soc.
Amer. Bull. 109, 324—346.
Sloan L.C. & Huber M. 2001: Eocene oceanic responses to orbital forc-
ing on precessional time scales. Paleoceanography 16, 101—111.
Tarlao A., Tunis G. & Venturini S. 2005: Dropstones, pseudoplank-
tonic forms and deep-water decapod crustaceans within a Lu-
tetian condensed succession of central Istria (Croatia): relation
to palaeoenvironmental evolution and palaeogeography. Palaeo-
geogr. Palaeoclimatol. Palaeoecol. 218, 325—345.
Thiersten H.R. & Roth P.H. 1991: Stable isotopic and carbonate cy-
clicity in Lower Cretaceous deep-sea sediments: Dominance of
diagenetic effects. Mar. Geol. 97, 1—34.
Traverse A. 2007: Paleopalynology, 2
nd
edition. Springer, Berlin,
1—814.
Westphal H. 2006: Limestone-marl alternations as environmental ar-
chives and the role of early diagenesis: a critical review. Int. J.
Earth Sci. 95, 947—961.
Živković S. & Babić Lj. 2003: Paleoceanographic implications of
smaller benthic and planktonic foraminifera from the Eocene
Pazin Basin (Coastal Dinarides, Croatia). Facies 49, 49—60.
Živković S. & Glumac B. 2007: Paleoenvironmental reconstruction
of the Middle Eocene Trieste-Pazin basin (Croatia) from benthic
foraminiferal assemblages. Micropaleontology 53/4, 285—310.
è
ò
è
è
200
LUŽAR-OBERITER, HOCHULI, BABIĆ, GLUMAC and TIBLJAŠ
Dinoflagellate cysts
:
Achilleodinium biformoides (Eisenack) – Eaton 1976
Achomosphaera alcicornu (Eisenack) – Davey & Williams
1966
Achomosphaera spp.
Caligodinium amiculum – Drugg 1970
Cerebrocysta spp.
Cordosphaeridium inodes (Klimpp) – Eisenack 1963
Cribroperidinium sp.
Dapsilidinium pastielsii (Davey & Williams) – Bujak et al.
1980
Deflandrea phosphoritica – Eisenack 1938
Diphyes colligerum (Deflandre & Cookson) – Cookson
1965
Distatodinium craterum – Eaton 1976
Distatodinium ellipticum (Cookson) – Eaton 1976
Enneadoysta arcuata (Eaton) – Stover & Williams 1995
Glaphyrocysta sp.
Heteraulacacysta leptalea – Eaton 1976
Histiocysta spp.
Homotryblium plectilum – Drugg & Loeblich Jr. 1967
Homotryblium tenuispinosum – Davey & Williams 1966
Hystrichokolpoma cinctum – Klumpp 1953
Hystrichokolpoma rigaudiae – Deflandre & Cookson 1955
Hystrichostrogylon membraniphorum – Agelopoulos 1964
Hystrichostrogylon spp.
Impagidinium spp.
Lejeunecysta spp.
Lentinia serrata Bujak – Bujak et al. 1980
Lingulodinium machaerophorum (Deflandre & Cookson) –
Wall 1967
Melitasphaeridium pseudorecurvatum (Morgenroth) Bujak
– Bujak et al. 1980
Operculodinium microtriainum (Klumpp) – Islam 1983
Operculodinium spp.
Phthanoperidinium echinatum – Eaton 1976
Rottnestia borussica (Eisenack) – Cookson & Eisenack 1961
Samlandia chlamydophora – Eisenack 1954
Spiniferella cornuta (Gerlach) – Stover & Hardenbol 1994
Spiniferites ramosus (Ehrenberg) – Mantell 1854
Spiniferites spp.
Thalassiphora pelagica (Eisenack) – Eisenack & Gocht 1960
Wetzeliella aff. spinulosa – Wilson 1988
Acritarchs
:
Comasphaeridium sp.
Acritarch sp. A (hairy) “Kalyptocysta exoleta” Stover
Spore-pollen
:
Bisaccate pollen (common, partly reworked)
Cicatricosisporites dorogensis – Potonié & Gelletich 1933
(consistent)
Classopollis spp. (rare, reworked)
Echimonocolpites spp. (Nypa, rare)
Podocarpidites spp.
Polypodiaceoisporites spp.
Trilites multivallatus (Pflug) – Krutzsch 1959
Appendix
List of identified palynomorphs in the samples of the hemipelagic Globigerina Marls