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Geological Society, London, Special Publications
doi: 10.1144/SP363.17
p381-394. 2012, v.363;Geological Society, London, Special Publications
Piotr Krzywiec
within the Polish basin: An overview
Mesozoic and Cenozoic evolution of salt structures
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Mesozoic and Cenozoic evolution of salt structures within
the Polish basin: An overview
PIOTR KRZYWIEC
Polish Geological Institute, ul. Rakowiecka 4, 00-975 Warsaw, Poland
(email: piotr.krzywiec@pgi.gov.pl)
Abstract: The Permian–Cretaceous Polish Basin belonged to the system of epicontinental
depositional basins of Western and central Europe and was filled with several kilometres of silici-
clastics, carbonates, and also thick Zechstein (approximately Upper Permian) evaporites. Its axial
part (the so-called Mid-Polish Trough) characterized by the thickest Permo-Mesozoic sedimentary
cover, developed above the Teisseyre –Tornquist Zone, lithospheric-scale boundary separating the
East European Craton and the Palaeozoic Platform. The Polish Basin was inverted in Late Cretac-
eous–Paleocene times. A synthesis of studies based on seismic reflection data allowed some
general rules regarding salt tectonics of the Polish Basin to be formulated. Two general classes
of structures genetically related to the presence of the Zechstein evaporites have been described:
peripheral structures located within NE and SW flanks of the Polish Basin, outside its axial part
and structures located within its axial part. The first class of structures includes grabens
bounded by listric faults detached above salt or salt pillows that developed where Zechstein eva-
porites were of relatively smaller thickness and where sub-Zechstein fault tectonics played a rela-
tively smaller role. The second class of structures includes more mature salt structures such as salt
pillows and salt diapirs and is related to the more axial part of the basin, characterized by relatively
thicker Zechstein evaporites and by more intense basement tectonics. First salt movements (salt
pillowing) took place in the Early Triassic that in certain cases was followed by the Late Triassic
salt diapirism and extrusion. In Jurassic– Early Cretaceous times, no significant growth of salt
structures took place. Most of the salt diapirs have been finally shaped by the Late Cretaceous
inversion tectonics. Some salt diapirs also underwent Cenozoic reactivation, associated with loca-
lized Oligocene or Miocene subsidence that in some cases was followed by younger (Pliocene–
Quaternary) inversion and uplift.
The presence of a relatively thick salt layer within
intracontinental sedimentary basins at the base of
synextensional sedimentary series causes signifi-
cant, often basin-scale, mechanical decoupling
from the pre-salt ‘basement’; as a consequence, it
directly influences the structural style of extension
as well as inversion-related deformation of the
supra-salt cover. The flanks of extensional sedimen-
tary basins that contain a thick basal ductile salt
layer and display a well-developed axial subsidence
centre delineated by major fault zones are often
characterized by an array of various peripheral
structures detached above the salt layer. Depending
on various parameters such as original salt thick-
ness, amount and rate of basement faulting,
thickness of supra-salt cover, etc. such peripheral
structures develop in response to thin-skinned
extension and/or to salt flow (Vendeville &
Jackson 1992a,b) and might include blocks
rotated above listric faults detached above salt, salt
pillows or even salt diapirs (e.g. Stewart 1999;
Withjack & Callaway 2000; Dooley et al. 2005).
During tectonically driven subsidence of intraconti-
nental basins salt structures might also form within
more axial parts of the basins, above or in close
proximity to major basement fault zones, respon-
sible for subsidence of the basin (e.g. Koyi &
Petersen 1993; Koyi et al. 1993).
A simplified geometry of a sedimentary basin
developed above a relatively thick ductile salt layer
at its base is shown schematically in Figure 1. In
this model, based on results of analogue modelling
(Withjack & Callaway 2000), subsidence of the
axial part of the basin was related to thick-skinned
supra-salt normal faulting. This part of the basin
is characterized by the thickest synextensional
sedimentary cover, with the maximum thickness
centred above the down-faulted subsalt basement
block. Due to the basin-scale decoupling effect of
the salt layer, peripheral salt-related structures
(grabens) developed within both flanks of this basin.
During basin inversion, the presence of a thick
salt layer causes stress partitioning between the
subsalt basement (thick-skinned inversion tectonics)
and the supra-salt sedimentary succession (thin-
skinned or cover-inversion tectonics). Salt-related
peripheral extensional structures detached above
the salt layer or more mature salt structures
(salt pillows, salt diapirs) tend to focus inversion-
related deformation because they form local zones
From:Alsop, G. I., Archer, S. G., Hartley, A. J., Grant,N.T.&Hodgkinson, R. (eds) 2012. Salt Tectonics, Sediments
and Prospectivity. Geological Society, London, Special Publications, 363, 381– 394. http:// dx.doi.org/10.1144/SP363.17
#The Geological Society of London 2012. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics
by guest on February 13, 2012http://sp.lyellcollection.org/Downloaded from
of weakness within the supra-salt sedimentary
cover, more prone to tectonic deformations triggered
by regional compressional stresses (e.g. Nalpas
et al. 1995).
Polish basin: geological background
The Polish Basin formed part of the of Permian –
Mesozoic system of epicontinental basins of
Western and Central Europe, the so-called Central
European Basin System (Fig. 2; Ziegler 1990;
Scheck-Wenderoth et al. 2008; Pharaoh et al.
2010). Its axial part, the so-called Mid-Polish
Trough, was located along the NW– SE trending
Teisseyre– Tornquist Zone that is one of the most fun-
damental lithospheric boundaries in Europe, separ-
ating the East European Craton and the Palaeozoic
Platform (see Scheck-Wenderoth et al. 2008;
Guterch et al. 2010; Pharaoh et al. 2010 for a recent
summary and extensive list of relevant references).
For the central and NW segments of the Polish
Basin there is a general lack of reliable seismic
information on its internal structure (apart from
very few exceptions) at the sub-Zechstein levels, be-
cause Zechstein evaporites very effectively screen
seismic energy. Only indirect information can be
used to infer modes of basement tectonic activities
responsible for its subsidence and inversion. A new
model for sub-Zechstein basement tectonics was
recently developed using regional geophysical (grav-
ity, magnetic, seismic) and geological data (Krzy-
wiec 2006a,b; Krzywiec et al. 2006). It shows a
complex array of NW – SE and WNW– ESE striking
fault zones (Figs 3 – 5) that played an important role
during the Mesozoic subsidence and subsequent
inversion and uplift within the axial part of the
Polish Basin that is the Mid-Polish Trough. These
Fig. 1. Schematic model of a sedimentary basin with thick salt layer at the base of its infill, developed during
thick-skinned extension (after Withjack & Callaway 2000, modified and supplemented; cf. Krzywiec 2006b).
Fig. 2. Zechstein palaeogeographic map of the Southern Permian Basin (Ziegler 1990). Red rectangle: area shown
on Figures 4 and 5, red lines 1 and 2: regional geo-seismic transects shown on Figure 6. Pink: evaporites; blue:
carbonates; yellow and orange: siliciclastics, see Ziegler (1990) for further explanations. The Permian Basin in Poland
with its axial part (the Mid-Polish Trough) was aligned along the Teisseyre– Tornquist Zone (grey area), the major
crustal-scale boundary separating the East European Craton and the West European Platform.
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inferred sub-Zechstein fault zones are also shown on
the regional seismic profiles in Figure 6.
During the Permian stage of its evolution, the
Polish Basin formed the eastern part of the Southern
Permian Basin (Kiersnowski et al. 1995; van
Wees et al. 2000, fig. 2). It experienced long-term
thermal subsidence, commencing in the Permian
and lasting until the Late Cretaceous. This subsi-
dence was punctuated by three major pulses of
extension-related accelerated tectonic subsidence:
during Zechstein to Scythian times, in the Oxfordian
to Kimmeridgian and in the early Cenomanian
(Dadlez et al. 1995; Stephenson et al. 2003). The
Mid-Polish Trough was filled with several kilometres
of Permian– Mesozoic sediments (Dadlez et al.
1998), including a thick (up to c. 1.6 km; Wagner
1998) Zechstein evaporites (Fig. 3). The presence of
the Zechstein salt led to the development of a
complex system of salt structures in the central and
northwestern segments of the Mid-Polish Trough
(Fig. 4). Salt movements were initiated during the
Early Triassic, significantly modifying subsidence
patterns locally (e.g. Sokołowski 1966; Marek &
Znosko 1972a,b; Krzywiec 2004, 2006a).
The Polish Basin was inverted during the Late
Cretaceous–Palaeogene. InversionofthePolishBasin
was multiphase; it commenced in Late Turonian
and lasted until Maastrichtian–post-Maastrichtian
Fig. 3. Reconstructed palaeothickness of the Zechstein evaporites in the eastern part of the Southern Permian
Basin (based on Wagner 1998). PZ1, PZ2, PZ3, PZ4: extent of the Werra, Stassfurt, Leine and Allen +Ohre
cyclothems, respectively (cf. Słowakiewicz et al. 2009). Grey hatched lines: inferred major basement fault zones
responsible for subsidence and inversion of the Mid-Polish Trough (cf. Krzywiec et al. 2006, Scheck-Wenderoth et al.
2008), grey area: devoid of the Zechstein cover; black rectangle: area shown on Figures 4 and 5, black lines: location of
seismic profiles shown on Figures 7 – 15. Thickest Zechstein evaporates delineate axial part of the basin that is the
Mid-Polish Trough.
SALT STRUCTURE EVOLUTION WITHIN THE POLISH BASIN 383
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times. It was associated with substantial uplift
and erosion of the axial part of the Polish Basin
i.e. the Mid-Polish Trough which presently forms
a regional antiform structure referred to as the Mid-
Polish Swell (Fig. 6), outlined by the Cenozoic
subcrop of the Lower Cretaceous and older rocks
(Fig. 5).
A more detailed discussion on various aspects of
subsidence and inversion in different segments of
the Polish Basin and the Mid-Polish Trough (as
well as extensive reference lists of rich older litera-
ture) is given by Marek & Pajchlowa (1997), Krzy-
wiec (2002, 2006b), Mazur et al. (2005), Krzywiec
et al. (2006, 2009), Resak et al. (2008), Scheck-
Wenderoth et al. (2008), Narkiewicz et al. (2010)
and Pharaoh et al. (2010).
The goal of this paper is to summarize the results
of the last several years’ of studies on salt tectonics
in the Mid-Polish Trough carried out using seismic
reflection data, and to overview basin-scale variabil-
ity of structural styles of salt-related and salt struc-
tures (pillows, diapirs) as well as timing of their
tectonic activity.
Salt tectonics within the polish basin:
basin-scale variations in structural style
and timing of activity
NE flank of the Mid-Polish Trough
The NE edge zone of the Polish Basin is character-
ized by relatively thin Zechstein evaporites, of the
order 200–600 m (Fig. 3). In this area, outside the
axial part of the Polish Basin (i.e. outside of the Mid-
Polish Trough), a system of peripheral salt-related
structures (grabens) therefore formed. Development
of such structures has been discussed above using
the model depicted in Figure 1. Faults bounding
these grabens were mostly detached above the Zech-
stein salt; only in the northwestern-most segment of
the Mid-Polish Trough are they characterized to
some degree by hard linkage with deeper faults
reaching the sub-Zechstein basement (Krzywiec
2006b).
A first example of such a peripheral salt-related
structure is shown in Figure 7 (Krzywiec 2006b).
This structure consists of several rotated blocks
Fig. 4. Salt structures within the Mid-Polish Trough: yellow: salt pillows; pink: partly pierced salt diapirs; orange: fully
pierced salt diapirs; blue: non-salt anticlines (after Dadlez & Marek 1998; Lokhorst 1998, modified and simplified).
Grey hatched lines: inferred major basement fault zones responsible for subsidence and inversion of the Mid-Polish
Trough (after Krzywiec et al. 2006, Krzywiec 2006a,b), red lines: location of seismic profiles shown on Figures 7 – 15.
Patterned area: inverted axial part of the basin (i.e. the Mid-Polish Swell, cf. Fig. 6) outlined by the sub-Cenozoic
sub-crops of the Lower Cretaceous or older rocks (after Dadlez et al. 2000, simplified). Peripheral salt or salt-related
structures are those structures located outside of this area, both to the NE as well to the SW.
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Fig. 5. Geological map of Poland without Cenozoic cover (Dadlez et al. 2000); black lines: location of seismic
profiles shown on Figures 7– 15. Green colours (K
1
,K
2
,Ka
2
2t, Kc +t, Ka
2
+c, Kt, Kcn +s, Kk, Km): Cretaceous;
blue colours (J
1
,J
2
,J
3
): Jurassic; pink colours (Tp, Tm, Tk): Triassic; orange (Pz): Zechstein (for more details see
Dadlez et al. 2000). Pomeranian Swell and Kuiavian Swell: two segments of the Mid-Polish Swell located above the
Teisseyre–Tornquist Zone (cf. Fig. 6).
Fig. 6. Regional seismic transects across the NW (1) and central (2) segments of the Polish Basin (based on
Krzywiec 2006b, modified). These transects illustrate main segments (parts) of this sedimentary basin: its axial part,
characterized by the thickest Permo-Mesozoic sedimentary cover (the so-called Mid-Polish Trough) and by the largest
amount of the inversion-related uplift that created the Mid-Polish Swell, and its peripheral parts, characterized by
thinner Permo-Mesozoic cover and smaller amount of uplift and inversion. Black hatched lines: inferred basement zones
responsible for subsidence and subsequent inversion of the Mid-Polish Trough (cf. Krzywiec 2006b; Krzywiec et al.
2006; Scheck-Wenderoth et al. 2008). For location see Figure 1. Vertical scale in TWT sec.
SALT STRUCTURE EVOLUTION WITHIN THE POLISH BASIN 385
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bounded by listric faults detached above the Zech-
stein evaporites, located approximately between
wells Bielica-1 and Miastko-3 (Fig. 7). Within
these blocks, a significant local increase of the Jur-
assic thickness could be observed, reflecting loca-
lized subsidence controlled by faults detached
above the Zechstein evaporites. The next phase of
tectonic activity of this structure was associated
with the Late Cretaceous inversion of the Mid-
Polish Trough. Prominent intra-Upper Cretaceous
angular unconformity reflects reverse thin-skinned
faulting and associated folding, all caused by a
first pulse (Late Turonian– Early Coniacian; cf.
Krzywiec 2006bfor further details) of inversion tec-
tonics of the Mid-Polish Trough.
The next seismic example of a salt-related
peripheral structure is shown in Figure 8. This
seismic profile very clearly documents multi-stage
inversion history within the NE flank of the Pomer-
anian segment of the Mid-Polish Swell. Peripheral
structure, located in the central part of this seismic
profile, evolved as half-graben bounded by listric
normal faults detached above the Zechstein evapor-
ites in the Triassic and Jurassic times, as evidenced
by localized thickening of synkinematic strata.
A very complex history of several stages of sedi-
mentation, uplift and erosion can be inferred for
the Late Cretaceous period of development of this
structure. Several prominent localized uncon-
formities developed within the Upper Cretaceous
succession point to the progressive Turonian(?)–
Maastrichtian inversion-related compressional reac-
tivation of major listric faults, folding, uplift and
erosion (cf. Krzywiec 2006bfor further details).
Inversion tectonics seems to have had a thin-skinned
character caused by the presence of ductile eva-
porates. Only locally folding of the Zechstein –
Mesozoic cover (vicinity of Stobno-1 well) seems
to be related to localized uplift of the sub-Zechstein
basement. The final phase of the inversion tectonics
in this segment of the Polish Basin took place
in the latest Late Cretaceous (Maastrichtian) or
Fig. 7. Seismic example of the peripheral structure located along the NE boundary of the Mid-Polish Trough developed
above the Zechstein evaporites (from Krzywiec 2006b, modified). This seismic line is located at the NE end of
regional seismic transect (1) shown on Figure 6. Green dotted lines highlight intra-Upper Cretaceous architecture
related to the first phase of the basin inversion associated with compressional reactivation of peripheral salt-related
structure. For location see Figures 3 – 5. Vertical scale in TWT sec.
Fig. 8. Seismic example of the peripheral structure located along the NE boundary of the Mid-Polish Trough
developed above the Zechstein evaporites (from Krzywiec 2006b, modified). Green dotted lines highlight intra-Upper
Cretaceous architecture formed by inversion-related compressional reactivation of peripheral salt-related structure.
For location see Figures 3–5. Vertical scale in TWT sec.
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post-Maastrichtian times, as evidenced by an angu-
lar unconformity between the Upper Cretaceous and
the Cenozoic deposits.
A last example of a peripheral salt-related struc-
ture located along the NE edge of inverted Mid-
Polish Trough (i.e. Mid-Polish Swell) and drilled
by well Bodzano
´w GN-2 is depicted in Figure 9.
Across this structure, thinning of the Triassic suc-
cession is observed. This suggests a first Triassic
stage of growth of this structure as a salt pillow.
Jurassic succession maintains constant thickness
across this structure, indicating a lack of any signifi-
cant salt movements. Uppermost Cretaceous cover
is characterized by an angular unconformity related
to the compressional reactivation and uplift of this
structure, caused by the inversion tectonics within
flank of this segment of the Mid-Polish Trough.
The entire Upper Cretaceous sequence was mildly
folded, resulting in the development of a top-
Maastrichtian erosional unconformity that was
transgressed by Palaeogene flat-laying series (cf.
Krzywiec 2006bfor further details).
Similar peripheral salt-related structures detach-
ed above the Zechstein salt are also known from
the SW edge zone of the Mid-Polish Trough. They
form linear zones of asymmetrical half-grabens,
roughly located between the cities of Poznan
´and
Kalisz (Fig. 5), initiated in the Triassic and inverted
in the Late Cretaceous (Kwolek 2000). These
grabens are at least partly aligned along a NW– SE
trending strike-slip fault zone rooted in the deeper
(sub-Zechstein) basement.
SW flank of the Mid-Polish Trough
The SW flank of the Mid-Polish Trough is charac-
terized by significantly thicker Zechstein evaporites,
of the order 1000–1500 m (Fig. 3). Such a high
Fig. 9. Seismic example of the peripheral structure located along the NE boundary of the Mid-Polish Trough
developed above the Zechstein evaporites (from Krzywiec 2006b, modified). This seismic line is located at the
NE end of regional seismic transect (2) shown on Figure 6. Green dotted lines highlight intra-Upper Cretaceous
architecture formed by inversion-related compressional reactivation of peripheral salt-related structure. For location
see Figures 3 –5. Vertical scale in TWT sec.
Fig. 10. Golenio
´w salt diapir (from Krzywiec 2009, modified). Dotted green lines: Upper Cretaceous syntectonic
deposits related to inversion-induced growth of salt structures. For location see Figures 3– 5. Vertical scale in TWT sec.
SALT STRUCTURE EVOLUTION WITHIN THE POLISH BASIN 387
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thickness of ductile evaporites led to the develop-
ment of mature salt structures such as salt diapirs
and salt pillows. Their development was triggered
by regional tectonics stresses (extensional during
early basin development and compressional during
basin inversion).
The Golenio
´w salt diapir (Fig. 10) has a clearly
asymmetric shape; its SW wall was interpreted as
controlled by a steep reverse fault (Krzywiec
2009). In the Triassic and Jurassic, first salt move-
ments might have occurred in this area as evidenced
by a local thinning of syntectonic strata present
above this salt structure. This stage could be inter-
preted as salt pillowing along the SW flank of the
Mid-Polish Trough, outside its axial most subsiding
part. The Golenio
´w diapir was finally shaped during
the Late Cretaceous – Palaeogene inversion of the
Mid-Polish Trough. It might have been connected
to two partly related tectonic processes. The first
of these was regional compression, which may
have caused the diapir to grow and move towards
the surface. The present-day shape of this salt struc-
ture (especially its asymmetry) might also have
been caused to some degree by extension and
SW-directed listric faulting above the Rokita salt
pillow, triggered by localized basement uplift
within the axial part of the basin, below this salt
pillow (Fig. 10). Extension within the uplifted area
might have been partly compensated by com-
pression within the basin’s SW flank where the
Golenio
´w salt diapir is located, similar (although
at a much smaller scale) to upslope extension and
downslope compression along continental margins
(e.g. Rowan et al. 2004).
Some structures in the NW part of the basin
developed solely in the Late Cretaceous during
inversion of the Mid-Polish Trough. An example
of such a structure is shown in Figure 11. Both
salt pillows shown on this seismic profile are co-
vered by Triassic, Jurassic and lower part of the Cre-
taceous deposits of rather uniform thickness. Only
the uppermost part of the Upper Cretaceous succes-
sion (approximately Maastrichtian; cf. Krzywiec
2006b; Fig. 5) is characterized by a reduced thick-
ness above Chabowo salt pillows. Such a deposi-
tional architecture points to the formation of this
salt pillow solely during the Late Cretaceous, that
is, during the inversion of the Polish Basin, without
any significant salt movements during earlier basin
extension and subsidence.
The next seismic example (Fig. 12) comes from
the area adjacent to the most axial part of the basin
characterized by thicker Zechstein evaporites, of
order 1400 – 1500 m (Fig. 3).
The relatively thick salt in this part of the basin
gave rise to the development of a large and
complex system of salt structures called Dzwo-
nowo–Człopa salt diapirs (cf. Krzywiec 2006b).
Along this seismic profile, the Triassic cover is
characterized by a very gradual thickness increase
towards the NE (towards the basin centre). Triassic
only attains larger thicknesses locally, between
these two salt diapirs, and this could have been
caused by first localized salt movements in this
area. Salt overhangs (wings) were interpreted
within the Upper Triassic succession, although this
interpretation is partly tentative due to the variable
quality of the seismic imaging. The problem of the
formation of salt overhangs in the Late Triassic is
analysed in more detail below, using the Kłodawa
salt diapir as a proxy. Jurassic succession seems to
maintain gradual and gentle thickness changes
Fig. 11. Chabowo and Marianowo salt pillows. Dotted green lines: Upper Cretaceous syntectonic deposits related to
inversion-induced growth of these salt pillows. For location see Figures 3 – 5. Vertical scale in TWT sec.
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across this structure, testifying to a lack of any sig-
nificant salt movements. On the contrary, the
depositional architecture of the Upper Cretaceous
complex above the Dzwonowo– Człopa salt
diapirs, characterized by the presence of angular
unconformities and localized thickness reductions,
clearly points to an important Late Cretaceous
compressional reactivation of this salt structure
(Krzywiec 2006b). The growth of these salt struc-
tures was multistage and continued at least until
the Campanian, as Campanian sediments are the
oldest Upper Cretaceous sediments preserved in
this area (Fig. 5). The possibility that growth of
the Dzwonowo–Człopa salt structure continued
at least until the Maastrichtian, but might have
been completely removed due to later erosion
synkinematic Maastrichtian sediments, cannot be
excluded.Campanian sediments are presently uncon-
formably covered by the post-kinematic flat-lying
Cenozoic strata.
The Damasławek salt diapir (Fig. 13a, b) is
located within the SW flank of the central (Kuia-
vian) Mid-Polish Trough, where the Zechstein eva-
porites (including salt) have retained a relatively
large thickness of the order 1400 – 1500 m (Fig. 3).
This salt diapir is characterized by a steep walls; it
almost pierces the surface and its caprock is
covered by very thin remnants of the Upper Cretac-
eous cover and Cenozoic (Miocene – Pliocene –
Quaternary) succession (Krzywiec et al. 2000;
Krzywiec 2009; Fig. 13b). Significant lateral thick-
ness changes of Jurassic succession across this salt
structure and in its vicinity (Fig. 13a) suggest Juras-
sic growth of an early salt structure (pillow?), most
probably located above a basement fault zone.
Upper Cretaceous thickness changes in the immedi-
ate vicinity of this salt diapir are visible only on a
shallow high-resolution seismic profile (Fig. 13b),
as the regional seismic profile is of inferior quality
at shallower depth levels. However, localized thick-
ness reduction of the Upper Cretaceous succession
towards the crest of the Janowiec salt pillow
located to the SW of the Damasławek salt diapir
(Fig. 13a) suggest a Late Cretaceous growth of
salt structures in this part of the basin. A shallow
high-resolution seismic profile imaged the structure
of the Cenozoic cover deposited above this salt
diapir with great accuracy. Miocene siliciclastics
together with several brown coal seams (confirmed
by several shallow wells drilled in this area) are
characterized by a locally increased thickness
above the Damasławek salt diapir, caused by normal
faulting above the salt diapir that triggered localized
Miocene subsidence (Krzywiec et al. 2000; Jaro-
sin
´ski et al. 2009; Krzywiec 2009). Miocene depos-
its are covered by a relatively thin Pliocene–
Quaternary succession. The entire Cenozoic cover
is presently uplifted above the Damasławek salt
diapir and is locally dissected by a steep reverse
fault reaching almost to the surface. Along this
fault the base Pliocene – Quaternary is uplifted.
This geometry directly points to yet another, very
young (Quaternary) phase of growth of the
Damasławek salt diapir.
Axial part of the Mid-Polish Trough
The Lubien
´salt diapir (Fig. 14) provides an example
of different Cenozoic tectonic reactivation of salt
diapirs from the central (Kuiavian) part of the Mid-
Polish Trough. Similarly to the Damasławek salt
diapir, this salt diapir pierced relatively close to
the surface and is characterized by very steep
walls. In this part of the inverted Mid-Polish
Trough, the entire Upper Cretaceous cover and
partly also the Jurassic cover were removed by
deep erosion related to the inversion of the Mid-
Polish Trough and formation of the Mid-Polish
Fig. 12. Dzwonowo– Człopa salt diapirs and Trzcianka salt pillow (from Krzywiec 2006b, modified). Purple dotted
lines: Triassic reflectors unconformably overlying salt extrucsions (wings); green dotted lines highlight intra-Upper
Cretaceous architecture related to the inversion of the Mid-Polish Trough and inversion-related compressional
reactivation of these salt diapirs. For location see Figures 3–5.Vertical scale in TWT sec.
SALT STRUCTURE EVOLUTION WITHIN THE POLISH BASIN 389
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Swell (cf. Fig. 6). A significant but local unconfor-
mity within the Upper Triassic sedimentary cover
is observed in the immediate vicinity of this salt
diapir (Fig. 14a). It documents the Triassic growth
of a salt pillow followed by erosion of the crest of
a salt-cored anticline and subsequent unconform-
able sedimentation of the uppermost Triassic and
Jurassic succession. The preserved Jurassic cover
is not characterized by any thickness changes
across this salt structure, documenting the lack of
any important tectonic activity in this area. At a
much later stage, most probably in the Late Cretac-
eous, this salt diapir pierced the surface (similarly to
the Damasławek diapir described above) due to the
regional compressional stress regime responsible
for the inversion of the Mid-Polish Trough. Such
timing, although being in agreement with overall
tectonic characteristics of the Kuiavian segment
of the Mid-Polish Trough (cf. Krzywiec 2004), is
purely conjectural due to the lack of preserved
Upper Cretaceous cover that might have recorded
the last stages of growth of this salt diapir. Recently
acquired shallow high-resolution seismic data above
this salt diapir (Kasin
´ski et al. 2009) also precisely
imaged its Cenozoic cover. Directly above Lubien
´
salt diapir, the Oligocene deposits are locally
present (i.e. missing on its flanks). Deposition of
these sediments was controlled by faults developed
above the salt diapir. This geometry resembles
deposition of the Miocene strata above the Damasła-
wek salt diapir (Fig. 13b). However, the younger
(Neogene–Quaternary) cover above the Lubien
´
salt diapir is generally flat-lying, and is not showing
any important uplift related to younger stages of
growth of this salt diapir. This suggests a lack of
any recent tectonic activity of this salt structure, con-
trary to the Damasławek salt diapir which seems to
have been recently active.
The Kłodawa salt diapir (Fig. 15) is the largest
salt structure present within the Mid-Polish
Trough, located in the central (Kuiavian) segment
of the Mid-Polish Trough (cf. Figs 4 & 5). It is
characterized by the very asymmetric thicknesses
of the Triassic– Jurassic cover (Krzywiec 2004;
Fig. 13. Damasławek salt diapir (from Krzywiec 2009, modified). For location see Figures 3– 5. Vertical scale in TWT
sec. (a) Regional seismic profile. Purple and blue dotted lines: syntectonic Triassic and Jurassic deposits respectively;
green dotted lines: Upper Cretaceous syntectonic deposits related to inversion-related growth of the Janowiec salt
pillow. (b) Shallow high-resolution seismic profile. Green dotted lines: Upper Cretaceous syntectonic deposits related to
inversion-related growth of the Damasławek salt diapir; orange dotted lines: Miocene brown coal seams.
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Fig. 14. Lubien
´salt diapir (from Krzywiec 2009, modified). For location see Figures 3–5. Vertical scale in TWT
sec. (a) Regional seismic profile. Purple dotted lines: intra-Triassic architecture highlighting consecutive stages
of tectonic activity of the Lubien
´salt structure (growth of salt pillow followed by erosion of salt-cored anticline and
unconformable sedimentation of the uppermost Triassic and Jurassic succession). Blue dotted lines: intra Jurassic
horizons (top of Lower and Middle Jurassic). (b) Shallow high-resolution seismic profile.
Fig. 15. Kłodawa salt diapir (from Krzywiec 2009, modified). Purple dotted lines: syntectonic Triassic deposits
and unconformities; green dotted lines: Upper Cretaceous syntectonic deposits related to inversion of central
(Kuiavian) segment of the Mid-Polish Trough (cf. Krzywiec 2004, 2009). For location see Figures 3 –5. Vertical scale in
TWT sec.
SALT STRUCTURE EVOLUTION WITHIN THE POLISH BASIN 391
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Scheck-Wenderoth et al. 2008; Pharaoh et al. 2010,
figs 6 & 15). The NE side of the Kłodawa salt diapir
is characterized by significantly thicker Triassic and
Jurassic deposits than its SW side; the NE side of
this salt diapir is also characterized by the most sig-
nificant Late Cretaceous inversion and uplift con-
trolled by the inferred basement fault zone, which
also controlled growth of the Kłodawa salt structure
(Krzywiec 2004). Analysis of seismic data cali-
brated by several deep wells point to three main
stages of the Triassic evolution of this structure
(Krzywiec 2004).
A salt pillow formed above a basement exten-
sional fault zone during the Early – Middle Triassic,
which is documented by thinning of the Lower–
Middle Triassic deposits towards the present-day
Kłodawa diapir (Fig. 15; Burliga 1996). Enhanced
basement faulting in the Late Triassic also caused
faulting of the salt pillow’s overburden; this led
to salt extrusion on the floor of the basin and the
formation of a large, asymmetric salt overhang
(i.e. submarine salt glacier). This salt overhang
has been consecutively unconformably covered
(onlapped) by youngest Triassic and Jurassic depos-
its. Because of the large vertical thickness of this
overhang, available seismic data was able to
image an angular unconformity between the post-
extrusion Triassic cover and the salt overhang.
It can be hypothesized that a similar mechanism
might have been responsible for the formation of
other salt overhangs for other salt structures such
as Dzwonowo– Człopa salt diapir (see above;
Fig. 12) or Mogilno salt diapir (Krzywiec 2009).
In these salt diapirs, the thickness of the salt over-
hang is smaller than in the Kłodawa salt diapir
and angular unconformity is less clearly visible.
The same model of formation of salt overhangs
(wings) was recently adapted in order to explain
very similar salt overhangs in salt structures from
the North German Basin (Kukla et al. 2008).
Due to substantial uplift of its axial part, the
entire Cretaceous cover (including possible
synkinematic Upper Cretaceous deposits related to
inversion tectonics) was eroded NE of the
Kłodawa salt diapir during inversion of the
Kuiavian segment of the mid-Polish Trough (cf.
Figs 5, 6 & 15). However, the Upper Cretaceous
cover (up to Maastrichtian) is preserved in the
close vicinity of the Kłodawa diapir (Fig. 15). It is
thinning towards this diapir and, at the same time,
towards the basin inversion axis. Such depositional
architecture provides evidence of a Late Cretaceous
onset of the inversion tectonics and another related
phase of the Kłodawa salt diapir growth (cf.
Leszczyn
´ski 2000). During this phase of tectonic
activity, the salt overhang that was formed in the
Late Triassic was also squeezed and its Jurassic
cover folded (Fig. 15).
Conclusions
A basin-scale analysis of seismic data describing
various salt-related and salt structures allowed
some conclusions regarding regional aspects of salt
tectonics within the Polish Basin to be formulated.
The NE flank of the Mid-Polish Trough is
characterized by relatively thin (200– 600 m) Zech-
stein evaporites. In this part of the basin a system
of peripheral structures developed within the supra-
salt (Triassic– Cretaceous) cover. These structures
were active as mostly asymmetric grabens bounded
by listric faults detached above the salt. They
were initiated in the Triassic and finally shaped by
the Late Cretaceous inversion of the Mid-Polish
Trough. Their compressional reactivation, caused by
the inversion of the Mid-Polish Trough, usually
encompassed several stages and resulted in substan-
tial uplift and folding of their axial parts, associated
with the localized erosion of their crests. Peripheral
salt-related structures located within the NE flank of
the Mid-Polish Trough do not show signs of any sig-
nificant post-inversion (i.e. Cenozoic) reactivation.
The SW flank of the Mid-Polish Trough, as
well as its axial part, is characterized by thicker
(1200–1600 m) Zechstein evaporites. These areas
are associated with the development of the more
mature salt structures such as salt pillows and salt
diapirs. Salt diapirs have usually formed above or
in the near vicinity of inferred basement fault
zones, that may have controlled basin subsidence,
and its subsequent inversion. Some salt structures
show an early stage of salt pillowing (Early–
Middle Triassic) followed by diapirism (Late
Triassics).
Within the central part of the Mid-Polish Trough,
characterized by the thickest salt and by the most
active basement faulting, Late Triassic diapirism
led to extrusion of salt on the basin floor and for-
mation of large salt overhang that was subsequently
covered by the uppermost Triassic and younger
sediments (Kłodawa salt diapir).
Similar processes might be invoked in order to
explain the formation of smaller-scale salt over-
hangs interpreted in other salt diapirs, for example
Dzwonowo–Człopa salt diapir system. Most of
the salt diapirs have been finally shaped by the
Late Cretaceous inversion tectonics; they were com-
pressionally squeezed towards the surface. This last
stage of growth of the salt diapirs often strongly
influenced surrounding depositional systems, creat-
ing localized thickness variations and unconformi-
ties within the Upper Cretaceous cover.
Some salt pillows located within the SE flank
of the Mid-Polish Trough (e.g. Chabowo salt
pillow) seem to have been formed solely during
the Late Cretaceous inversion due to lateral salt
flow triggered by a regional compressional stresses,
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without any earlier (Triassic – Jurassic) significant
salt movements during basin subsidence.
Shallow high-resolution seismic data proved that
some salt diapirs underwent substantial Cenozoic
reactivation, although the modes of such reactiva-
tion might have been different. Cenozoic reactiva-
tion documented by seismic data encompassed
localized subsidence in the Oligocene (Lubien
´
diapir) or Miocene (Damasławek diapir). In the
case of some diapirs, this was not followed by any
younger tectonic movements within and above the
diapir (Lubien
´diapir). For other diapirs (e.g.
Damasławek diapir), this localized subsidence stage
was followed by younger (Pliocene– Quaternary)
inversion and uplift.
CalEnergy Polska, Apache Poland and PGNiG S.A. kindly
provided access to some of the seismic data used in this
paper. S. Burliga and an anonymous reviewer are
thanked for their remarks and suggestions that helped to
shape this paper. I however remain fully responsible for
my ideas and conclusions, especially those not fully
shared by the first reviewer.
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