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Comment on a paper by Schito et al. (2017) “Thermal evolution of Paleozoic successions of the Holy Cross Mountains (Poland)”
Accepted Manuscript Comment on a paper by Schito et al. (2017) “Thermal evolution of Paleozoic successions of the Holy Cross Mountains (Poland)” Marek Narkiewicz PII:
S0264-8172(17)30062-4
DOI:
10.1016/j.marpetgeo.2017.02.016
Reference:
JMPG 2823
To appear in:
Marine and Petroleum Geology
Received Date: 14 January 2017 Accepted Date: 13 February 2017
Please cite this article as: Narkiewicz, M., Comment on a paper by Schito et al. (2017) “Thermal evolution of Paleozoic successions of the Holy Cross Mountains (Poland)”, Marine and Petroleum Geology (2017), doi: 10.1016/j.marpetgeo.2017.02.016. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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ACCEPTED MANUSCRIPT Discussion
Comment on a paper by Schito et al. (2017) “Thermal evolution of Paleozoic successions
Marek Narkiewicza a
Polish Geological Institute-NRI, 00-975 Warszawa, Poland
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e-mail: [email protected]
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of the Holy Cross Mountains (Poland)”
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Abstract
The paper by Schito et al. (2017) contains many misquotations of the regional literature on the Holy Cross Mountains, that may confuse the reader. Present comment suggests more appropriate references related to the stratigraphic, tectonic and palaeothermal aspects of the
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commented paper. The burial-thermal history as interpreted by Schito et al. is based on doubtful, poorly documented or even unsubstantiated thermal maturity and stratigraphical data, ignoring important regional evidence, such as Caledonian (sub-Devonian) unconformity
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and Permian thermal anomaly. The 1-D modelling study performed by Schito et al. (2017) did not consider published alternative concepts of the temporal and spatial heat flow patterns. The
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resulting models, assuming uniformly low heat flow between the Ordovician and the earliest Cretaceous, are inconsistent with independent regional data pointing to the hotter Variscan (Carboniferous-Permian) thermal regime.
Keywords: burial-thermal history, Early Palaeozoic, Holy Cross Mountains, Variscan heat flow
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ACCEPTED MANUSCRIPT 1. Introduction
Holy Cross Mountains (HCMts) located in S-Central Poland are commonly referred to as the unique window into the sub-Permian basement of Central Europe (Dadlez et al., 1994;
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Dadlez, 2001). In particular, they expose a complete stratigraphic succession recording
complex Early Palaeozoic processes in a belt adjoining the East European Craton margin,
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commonly labelled as the Trans-European Suture Zone (Berthelsen, 1993).
In their recent study Schito et al. (2017) investigated thermal maturity patterns of
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predominantly Lower Palaeozoic shaly strata from the HCMts using several independent methods: clay mineralogy, Rock Eval pyrolysis, vitrinite/organoclast reflectance, and for a few selected samples, Raman spectroscopy of kerogen and Palynomorph Darkness Index. These results supplement the existing database on a thermal maturity of sedimentary rocks in
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the HCMts area, and generally confirm earlier observations by Belka (1990), Szczepanik (1997), Narkiewicz (2002), Narkiewicz and Malec (2005), Malec et al. (2010) and others. Moreover, Schito et al. (2017) used their maturity data to constrain 1-D modeling of a burial-
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thermal development in two distinct palaeotectonic domains of the HCMts separated by the
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Holy Cross Fault – northern (Łysogóry) and southern (Kielce) regions.
The following comment will refer to two interconnected regional aspects of the study: (1) published regional data pertinent to the burial-thermal history of the HCMts, and (2) burialthermal modeling results, in particular the question of temporal changes and lateral gradients of a regional heat flow (HF) during the Phanerozoic.
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ACCEPTED MANUSCRIPT 2. Regional data
The discussed paper refers to regional data from many published sources. Nevertheless, the quotations are in a large part misleading for the reader as in fact cited papers do not contain
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the respective information. Only selected, most striking examples of such misquotation are given below together with the indication of more adequate sources advisable for the reader.
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Contrary to the quotation in the “Introduction” (Ch. 1 in Schito et al., 2017) the papers by Belka (1990), Marynowski et al. (2001), Poprawa et al. (2005), Narkiewicz and Narkiewicz
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(2010) do not deal with the Lower Silurian „maturation and timing of hydrocarbon generation of Lower Silurian potential source rocks” – in fact these papers are devoted to Devonian and younger rocks of the HCMts. It would be advisable to quote papers by e.g. Malec et al. (2010)
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and Smolarek et al. (2014) instead.
Dadlez (2001) and Kutek (2001) did not pursue the “kinematic evolution” of the Holy Cross Fault (as quoted in the “Geological setting” - Ch. 2). This issue is discussed by several other
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authors, more recently by Lamarche et al. (2002) and Konon (2007) who also cite earlier publications. It is not clear why the information on “Interlayered organic matter rich black
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shales” in Pragian-Emsian is quoted from Marynowski et al. (2001), advisable reference would be Malec (2005). Narkiewicz and Narkiewicz (2010) did not describe “middle and Upper Devonian carbonates” – their paper is concerned with selected aspects of a part of the Eifelian succession (advisable: Szulczewski, 1995, Belka and Narkiewicz, 2008). Gągała (2015) could not detect “an Early Caledonian deformation in the Lower and Middle Cambrian rocks in the Kielce block” as he investigated late Caledonian (Late Silurian-earliest Devonian) deformations in the Łysogóry Region. Contrary to Schito et al. (2017) quotation, Lamarche et
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ACCEPTED MANUSCRIPT al. (1999) and Konon (2007) also did not discuss the Cambrian tectonics, in fact they described and interpreted Variscan and Alpine deformations (advisable: Gągała, 2005).
“Polish Rift Basin” (Kutek, 2001, but not Kutek and Głazek, 1972, Lamarche et al., 1999,
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Mizerski 2004) is a misleading term (no true rifting occurred), the widely accepted concept of a polyphase Permian-Mesozoic Polish Basin (Dadlez et al., 1995) is more adequate. Konon (2004) and Kozłowski (2008) did not describe Permian-Mesozoic succession in the HCMts –
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the first paper is concerned with extensional tectonic structures in the Devonian rocks, while
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the second one with the Silurian stratigraphy (advisable: Kutek and Głazek, 1972).
Tectonic framework of the Permian-Mesozoic depositional development of HCMts has not been studied by Lamarche et al. (1999) and Konon (2004) (advisable: Dadlez et al., 1995; Hakenberg and Świdrowska, 1997). Dadlez et al. (1994) did not pursue the issue of the late
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Cretaceous/early Paleogene inversion (see also Ch. 5.6 of Schito et al., 2017, the same refers to Mizerski, 2004). Gągała (2015) or Kozłowski (2008) cannot be used as primary or even general source of information on the Cambrian to Devonian-Carboniferous stratigraphy (cf.
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fig. 3 and Ch. 6.2 in the discussed paper) as both contributions have more specific scopes – the late Caledonian tectonics and Upper Silurian stratigraphy, respectively. Narkiewicz (2002)
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cannot be used as source of information or assumptions on the HF evolution from Cambrian to recent (Ch. 3.2.6 in Schito et al., 2017) as no such data are given in that paper. Moreover, Belka (1990) is not responsible for the vitrinite reflectance data from the Łysogóry Region (Ch. 4). On the other hand, several determinations for this region were provided by Marynowski (1999) – the source not quoted by Schito et al. (2017).
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ACCEPTED MANUSCRIPT Gągała (2015) is inappropriately cited in Ch. 5.6 as a source of information on the Pridolian sedimentation (advisable: Kozłowski, 2008). Paper by Szulczewski et al. (1996) is hardly an adequate reference on the Lower-Middle Devonian deposition as it is devoted to the late Frasnian to Early Carboniferous sedimentation in a specific aerally limited setting of a
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drowned carbonate platform. Neither Kutek and Głazek (1972) nor Narkiewicz and
Narkiewicz (2010) “suggest that thermal maturity of the Paleozoic successions could have been acquired during the Late Paleozoic” (Schito et al., 2017, Ch. 6.2) – these papers are
3. Burial and thermal modelling
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3.1. Modeling constraints
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Marynowski, 1999; Narkiewicz et al., 2010).
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concerned with other, unrelated topics (more adequate quotations are: Belka, 1990;
The authors of the discussed paper claim that their reconstructed geological evolution of the
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area “allows a robust calibration against organic and inorganic thermal indicators”. The confusing misquotations related to the regional geological data (partly listed above) cast some
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doubt on such statement. The confusion further rises when looking in a more detail at the input data for the 1-D modeling performed by Schito et al. (2017).
Two models by Schito et al. (separately for the Łysogóry and Kielce regions) are not tied to any particular section, thus their “pseudowells” have no constrained regional location. It is unclear how the stratigraphic-lithologic columns for both models have been constructed (Ch. 3.2.6). The authors cite papers by Kozłowski (2008), Gągała (2015) and Trela (2007) in
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ACCEPTED MANUSCRIPT which overview of parts of the Early Palaeozoic succession is given, and refer in a general
way to various well sections dispersed throughout the study area (Schito et al., 2017, fig. 2b). It is nowhere stated, however, which sections and why were used for the modelling, which raises questions about the validity of the stratigraphic data. For example, assuming 250 m of
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Ordovician developed as a shale in the Kielce Region (Ch. 5.6) is an oversimplification (to say the least). Ordovician is composed not only of “clayey and silty deposits” (as stated in Ch. 2) but includes also sandstone-conglomeratic complexes (Arenigian) and condensed
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carbonates (mostly Middle Ordovician) (Trela, 2006). According to the discussed paper the Upper Silurian of the Kielce Region is represented by sandstones and conglomerates while in
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fact it is composed of mostly shaly succession with greywacke intercalations. It is not true that in the Kielce Region “the carbonate platform drowning occurred in the beginning of the Givetian and led to the deposition of 700 m thick black shales during the Upper Devonian” (compare Szulczewski et al., 1996). In view of the above incorrect statements it is not
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surprising that fig. 3 of Schito et al. (2017) showing synthetic stratigraphic columns for both regions of the HCMts contains many errors (e.g. graptolitic shales in the Upper Devonian).
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Unfortunately, Schito et al. (2017) nowhere explain how did they reconstruct the missing strata (both thickness and lithology), including those removed by the Variscan erosion and the
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late Cretaceous-early Paleogene unroofing. The latter is estimated in the commented paper as 3500 m (Kielce) and 4300 (Łysogóry) with erosion starting 70 My ago, but the ground for such numbers is unclear. Certainly they cannot be based on the paper by Dadlez et al. (1994) quoted in this context, because the paper discusses the Palaeozoic and not Meso-Cenozoic tectonics of Poland.
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ACCEPTED MANUSCRIPT “Two main events of burial” and “two exhumation events” are concluded for the studied
Ordovician to Recent burial history (see also figs. 11a and 12a in Schito et al., 2017) in which Early Palaeozoic-Carboniferous is regarded as a single “burial event”. No erosion of the Silurian (Kielce Region) has been assumed (fig. 12a) in spite of a published evidence of the
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late Caledonian angular unconformity between the Silurian and overlying Lower Devonian, and related erosional and nondepositional gap of ca. 10 Ma (e.g. Dadlez et al., 1994). Also, the late Silurian magmatism (Bardo diabase – Nawrocki et al., 2013) is not even mentioned.
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It may be parenthetically added that the occurrence of the late Caledonian unconformity and associated erosional gap is possible also in the Łysogóry Region (e.g. Kozłowski, 2008;
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Gągała 2015) – the variant that should be at least taken into account when modelling the burial-thermal history.
The two-stage HF evolution assumed in the discussed paper (35 mW/m2 from 490 Ma to 130
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Ma, then gradual increase to 45 mW/m2 until recent) is not backed by any data or substantiated assumptions. Narkiewicz (2002) is quoted in this context (Ch. 3.2.6) but that
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paper does not include such information (see above).
The authors state that their thermal model of the Łysogóry Region is consistent with maturity
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data from the Lower Jurassic. The latter data are derived, however, from the unnamed localities tens of kilometres to the north of the Palaeozoic outcrops and thus incompatible with the latter. It has been documented e.g. by Głazek and Kutek (1972) that the PermianMesozoic strata markedly thin away from the Paleozoic core of the HCMts.
Finally, the vitrinite reflectance data used by Schito et al. (2017; tab. 4) for callibration of their burial-thermal models are partly questionable. For 10 samples out of 28, the reflectance
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data are based on less than 10 measurements which is considerably below the acceptance limit (Barker and Pawlewicz, 1993), thus excluding most of the Devonian data.
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3.2. Question of elevated Variscan heat flow
One of the conclusions from the 1-D modeling performed by Schito et al. (2017) is the twostage Ordovician to recent HF evolution, lacking any Carboniferous-Permian thermal events.
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This conclusion contradicts several earlier results (e.g. Belka, 1990, Marynowski, 1999,
Narkiewicz et al. 2010). Such conclusion deserves a separate discussion as it has further
metallogeny and petroleum generation.
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consequences for both basic regional geology and mineral resources, including questions of
Two arguments are given by Schito et al. (2017) to disprove the end-Palaeozoic heat flow
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increase:
1) the thermal maturity curve fits Silurian palaeothermal indicators from the Kielce block (fig. 11c) only with a HF value of 35 mW/m2 during the Carboniferous, much lower than the
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present-day one (about 45 mW/m2), when using present-day thicknesses of Paleozoic and Mesozoic successions;
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2) the thermal maturity curve fits Devonian and Silurian data (fig. 11c) only with a burial of about 4000 m during the Mesozoic rather than with an increase of HF in the Łysogóry block at the end of Paleozoic.
First, the above-raised objections as to the stratigraphic constraints on burial-thermal history cast serious doubt on the validity of the modelling results of Schito et al. (2017). Second, it can be noted that the respective curves (figs. 11c and 12c) show a rather poor fit with the
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ACCEPTED MANUSCRIPT maturity data points for the assumed two-stage HF evolution. Lastly, and most importantly,
no alternative simulations are discussed by Schito et al. (2017) although at least two published alternatives are available (Poprawa et al., 2005; Narkiewicz et al., 2010). The first-quoted authors assume constant Devonian to recent HF, while in the second paper several burial-
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thermal scenarios are simulated and the elevated Variscan HF is accepted as highly probable.
The elevated (and laterally variable) Variscan (Late Carboniferous-?early Permian) HF was
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interpreted already by Belka (1990) based on the conodont CAI pattern in the Devonian-
Carboniferous and Triassic. The crucial observation was the presence of elevated and laterally
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variable CAI values in the range 1-3.5 showing SSW-NNE oriented gradient, contrasting with uniformly low CAI 1 values in the closely juxtaposed Triassic sediments. The highest values were observed along the WNW-ESE trending Holy Cross Fault – the major, deeply-rooted tectonic discontinuity. This pattern has been later confirmed and refined by Narkiewicz and
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Malec (2005) and Marynowski et al. (2002; see also Narkiewicz et al., 2010).
Marynowski et al. (2002) found measurable differences in maturity levels of the Upper
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Permian sediments between both regions of the HCMts., based on vitrinite reflectance and biomarker indices. The southern region shows low values, comparable to the Triassic rocks,
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while in the north they are significantly higher, close to those in the Nieświń IG 1 borehole, ca. 30 km to the north of the HCMts. (Grotek, 1998). The difference cannot be accounted for solely by contrasting burial depths, thus implying existence of a positive thermal anomaly north of the Holy Cross Fault before the Triassic. More generally speaking, the maturity distribution in the pre-Triassic versus younger rocks point to a decisive role of the elevated late Paleozoic HF for the present thermal maturity patterns in the sub-Permian rocks.
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The question of the Mid-Palaeozoic to Cenozoic thermal and burial evolution of the HCMts. has been investigated by means of 1-D modelling by Narkiewicz et al. (2010). The study was based on two wells located in the SW (Kowala 1) and NE (Janczyce I) part of the Kielce Region (see Narkiewicz et al., 2010, for the location). A relatively complete, cored Devonian
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sections in both wells have been supplemented by stratigraphical data on the Carboniferous from the nearby outcrops. The Permian-Mesozoic cover (eroded during the
Cretaceous/Paleogene uplift) has been restored using two alternative datasets from Kutek and
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Głazek (1972) and Dadlez et al. (1998), respectively. The burial-thermal models have been callibrated using Devonian vitrinite reflectance values either directly determined or calculated
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from biomarker indices (Marynowski, 1998, Ph.D. Thesis). Several HF evolutionary scenarios have been simulated with various assumptions regarding eroded Carboniferous thicknesses.
It appeared that the variant of a thinner Permian-Mesozoic cover (Dadlez et al., 1998),
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implying lower magnitude of the Late Cretaceous-Paleogene inversion, allows more realistic assumptions regarding heat flow distribution through time. The alternative scenario, assuming deeper burial, generally lower heat flow and smaller Carboniferous thickness was regarded as
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less probable. The accepted variant of the Permian-Mesozoic burial history implies that the total post-Carboniferous burial in the study area was on the order of 2000-2500 metres (Fig.
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1). The respective Upper Cretaceous thickness could have been 400 to 500 m whereas the Late Cretaceous-Paleogene inversion most likely started already in the Santonian (ca. 85 Ma). Consequently, the preferred magnitude of total inversion was on the order of 2500 m.
The modeling results are consistent with the assumption of a constant HF from the Devonian to recent. However, the modelled HF shows also a very good fit with the empirical data if elevated Carboniferous-Early Permian HF up to 80 mWm-2 is assumed, particularly in the
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ACCEPTED MANUSCRIPT Janczyce I located close to the HCF (Fig. 1). The elongated zone of increased thermal
maturity in the Devonian, stretching directly south of the HCF may be partly accounted for by Carboniferous siliciclastics thicker by ca. 500 m in comparison to previous estimates.
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The presence of the elevated Variscan HF is consistent with several lines of independent
regional evidence (Fig. 1; Narkiewicz et al., 2010; Smolarek et al., 2014). The latter include: (1) hydrothermal sulphide mineralization ascribed to the Variscan (pre-Permian) metallogenic
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stage (Rubinowski, 1971); (2) low-hydrothermal calcite mineralization and associated
hydrothermal karst dated paleomagnetically as Permian (Lewandowski, 1999); (3) pervasive
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burial dolomitization associated with circulation of hot mineralized fluids during the Carboniferous (Narkiewicz, 2009), (4) Early Permian thermochemical remagnetization related to cooling of a regional fluid circulation system (Grabowski et al., 2006). Narkiewicz et al. (2010) concluded that the Variscan thermal anomaly, particularly well-pronounced along the
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crustal discontinuities such as the Holy Cross Fault (Narkiewicz et al., 2011), is a satisfactory explanation of both vertical and lateral maturity patterns and other regional data quoted
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above.
It should be noted that in the case of the thermal modeling of the Lower Palaeozoic strata the
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above HF history interpreted by Narkiewicz et al. (2010) is superimposed on the maturity pattern attained during the earlier Caledonian cycle (Cambrian to Late Silurian-earliest Devonian). Narkiewicz (2002) argued, based on a tentative comparison of the Devonian versus Lower Paleozoic thermal maturity patterns, that the present difference in their levels in the Lower Palaeozoic strata between both regions of the HCMts. is at least partly inherited from pre-Devonian times. This was regarded, together with a contrasting subsidence history of the Kielce versus Łysogóry regions, as the evidence of paleogeographic separation of both
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regions being independent terranes during the Early Palaeozoic. Although new data cast some doubt on such interpretation (Kozłowski et al., 2014; Smolarek et al., 2014), the question of the possible elevated Caledonian HF remains open. In this context the presence of the latest Silurian-earliest Devonian (ca. 424-416 Ma; Nawrocki et al., 2013) mafic magmatism in the
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HCMts. is particularly important.
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4. Conclusions
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Although Schito et al. (2017) provide new maturity data for the Lower Palaeozoic shaly successions of the HCMts, their 1-D burial-thermal modeling of the Ordovician to recent evolution of the area is poorly supported by partly misquoted and/or irrelevant regional
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stratigraphical and tectonic data.
The authors did not take into account the late Caledonian uplift and erosion, documented at least for the Northern (Kielce) Region of the HCMts. They also neglected published maturity
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data for the Permian-Triassic (Marynowski et al., 2002). Their reconstructed missing sections, particularly for the end Cretaceous-early Paleogene inversion and unroofing, lack support
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from any previous or new data/interpretations.
Consequently, the two-stage model of the HF evolution proposed by Schito et al. (2017) is poorly substantiated. Moreover, it has not been confronted with earlier published models based on 1-D burial-thermal modelling, assuming constant Devonian-recent HF (Poprawa et al., 2005) or elevated Variscan (late Palaeozoic) HF (Narkiewicz et al., 2010). The latter model is corraborated by various regional data pointing to elevated thermal regime during the
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ACCEPTED MANUSCRIPT Carboniferous-Permian, including hydrothermal mineralization and karst, as well as burial dolomitization by hot fluids, and thermochemical remagnetization of the Devonian strata.
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Acknowledgments
Funding of the present work was provided by the Polish Geological Institute-NRI statutory
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funds (project no. 62.9701.1401.00.1). I thank Leszek Marynowski (Silesian University) for
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his helpful comments and suggestions to the earlier version of the manuscript.
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Narkiewicz, K., Malec, J. 2005. New conodont CAI database. Przegląd Geol. 53, 33-37. Narkiewicz, M., 2002. Ordovician through earliest Devonian development of the Holy Cross Mts.(Poland): constraints from subsidence analysis and thermal maturity data. Geol. Q. 46 (3), 255-266.
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ACCEPTED MANUSCRIPT Narkiewicz, M., 2009. Late burial dolomitization of the Devonian carbonates and a
tectonothermal evolution of the Holy Cross Mts area (Central Poland). Mineralogia – Special Papers, 35, 51-59. Narkiewicz, M., Resak, M., Littke, R., Marynowski, L., 2010. New constraints on the Middle
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Palaeozoic to Cenozoic burial and thermal history of the Holy Cross Mts. (Central Poland): results of numerical modelling. Geol. Acta 8 (2), 189-205.
Narkiewicz, M., Grad, M., Guterch, A., Janik, T., 2011, Crustal seismic velocity structure of
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southern Poland: preserved memory of a pre-Devonian terrane accretion at the East European Platform margin. Geol. Magazine 148(2), 191-210.
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Nawrocki, J., Salwa, S., Pańczyk, M., 2013. New 40Ar-39Ar age constrains for magmatic and hydrothermal activity in the Holy Cross Mts.(southern Poland). Geol. Q. 57 (3), 551560.
Poprawa, P., Żywiecki, M., Grotek, I., 2005. Burial and thermal history of the Holy Cross
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Mts. area - preliminary results of maturity modelling. Polskie Towarzystwo Mineralogiczne, 26, 251-254.
Rubinowski, Z., 1971. The non-ferrous metal ores of the Góry Świętokrzyskie and their
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metallogenic position. Biul. Inst. Geol. 247, 1-166. Schito, A., Corrado, S., Trolese, M., Aldega, L., Caricchi, C., Cirilli, S., Grigo, D., Guedes,
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A., Romano, C., Spina, A., and Valentim, B., 2017. Assessment of thermal evolution of Paleozoic successions of the Holy Cross Mountains (Poland). Marine and Petroleum Geology, 80, 112-132.
Smolarek, J., Marynowski, L., Spunda, K., Trela, W., 2014. Vitrinite equivalent reflectance of Silurian black shales from the Holy Cross Mountains, Poland. Mineralogia, 45 (1-2), 79-96.
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Szczepanik, Z., 1997. Preliminary results of thermal alteration investigations of the Cambrian acritarchs in the Holy Cross Mts. Geol. Q. 41 (3), 257-264. Szulczewski, M., 1995. Depositional evolution of the Holy Cross Mts. (Poland) in the Devonian and Carboniferous – a review. Geol. Q. 39, 471-488.
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Szulczewski, M., Belka, Z., Skompski, S., 1996. The drowning of a carbonate platform: an example from the Devonian-Carboniferous of the southwestern Holy Cross Mountains, Poland. Sediment. Geol. 106 (1), 21-49.
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Trela, W., 2006. Lithostratigraphy of the Ordovician in the Holy Cross Mountains. Przegląd Geol. 54 (7), 622-631.
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Trela, W., 2007. Upper Ordovician mudrock facies and trace fossils in the northern Holy Cross Mountains, Poland, and their relation to oxygen-and sea-level dynamics.
Figure caption
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Palaeogeogr. Palaeoclimatol. Palaeoecol. 246(2), 488-501.
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Fig. 1 – Burial-thermal history of the Kielce Region modelled in the Janczyce I well-section (after Narkiewicz et al., 2010, modified and supplemented); (a) measured (triangles) versus
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calculated (curves) vitrinite reflectance for two selected variants of the heat flow development through time shown in (b), assuming the Permian-Mesozoic stratigraphy restored after Dadlez et al. (1998), thick Lower Carboniferous and significant Variscan erosion; (b) two modelled variants of the temporal HF pattern; (c) burial graph with temperature distribution through time (in oC) according to the variant b (elevated Variscan HF), showing stages of subsidence/uplift development (bottom part), and duration of geological processes attributable to the elevated Variscan HF (upper part).
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ACCEPTED MANUSCRIPT Comment on Schito et al. (2017) Highlights:
The misquotations in the commented paper are indicated and more adequate references are suggested
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The 1-D modelling results are critically commented and published alternative heat flow evolution is briefly presented
S0264-8172(17)30062-4
DOI:
10.1016/j.marpetgeo.2017.02.016
Reference:
JMPG 2823
To appear in:
Marine and Petroleum Geology
Received Date: 14 January 2017 Accepted Date: 13 February 2017
Please cite this article as: Narkiewicz, M., Comment on a paper by Schito et al. (2017) “Thermal evolution of Paleozoic successions of the Holy Cross Mountains (Poland)”, Marine and Petroleum Geology (2017), doi: 10.1016/j.marpetgeo.2017.02.016. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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ACCEPTED MANUSCRIPT Discussion
Comment on a paper by Schito et al. (2017) “Thermal evolution of Paleozoic successions
Marek Narkiewicza a
Polish Geological Institute-NRI, 00-975 Warszawa, Poland
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e-mail: [email protected]
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of the Holy Cross Mountains (Poland)”
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Abstract
The paper by Schito et al. (2017) contains many misquotations of the regional literature on the Holy Cross Mountains, that may confuse the reader. Present comment suggests more appropriate references related to the stratigraphic, tectonic and palaeothermal aspects of the
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commented paper. The burial-thermal history as interpreted by Schito et al. is based on doubtful, poorly documented or even unsubstantiated thermal maturity and stratigraphical data, ignoring important regional evidence, such as Caledonian (sub-Devonian) unconformity
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and Permian thermal anomaly. The 1-D modelling study performed by Schito et al. (2017) did not consider published alternative concepts of the temporal and spatial heat flow patterns. The
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resulting models, assuming uniformly low heat flow between the Ordovician and the earliest Cretaceous, are inconsistent with independent regional data pointing to the hotter Variscan (Carboniferous-Permian) thermal regime.
Keywords: burial-thermal history, Early Palaeozoic, Holy Cross Mountains, Variscan heat flow
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ACCEPTED MANUSCRIPT 1. Introduction
Holy Cross Mountains (HCMts) located in S-Central Poland are commonly referred to as the unique window into the sub-Permian basement of Central Europe (Dadlez et al., 1994;
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Dadlez, 2001). In particular, they expose a complete stratigraphic succession recording
complex Early Palaeozoic processes in a belt adjoining the East European Craton margin,
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commonly labelled as the Trans-European Suture Zone (Berthelsen, 1993).
In their recent study Schito et al. (2017) investigated thermal maturity patterns of
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predominantly Lower Palaeozoic shaly strata from the HCMts using several independent methods: clay mineralogy, Rock Eval pyrolysis, vitrinite/organoclast reflectance, and for a few selected samples, Raman spectroscopy of kerogen and Palynomorph Darkness Index. These results supplement the existing database on a thermal maturity of sedimentary rocks in
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the HCMts area, and generally confirm earlier observations by Belka (1990), Szczepanik (1997), Narkiewicz (2002), Narkiewicz and Malec (2005), Malec et al. (2010) and others. Moreover, Schito et al. (2017) used their maturity data to constrain 1-D modeling of a burial-
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thermal development in two distinct palaeotectonic domains of the HCMts separated by the
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Holy Cross Fault – northern (Łysogóry) and southern (Kielce) regions.
The following comment will refer to two interconnected regional aspects of the study: (1) published regional data pertinent to the burial-thermal history of the HCMts, and (2) burialthermal modeling results, in particular the question of temporal changes and lateral gradients of a regional heat flow (HF) during the Phanerozoic.
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ACCEPTED MANUSCRIPT 2. Regional data
The discussed paper refers to regional data from many published sources. Nevertheless, the quotations are in a large part misleading for the reader as in fact cited papers do not contain
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the respective information. Only selected, most striking examples of such misquotation are given below together with the indication of more adequate sources advisable for the reader.
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Contrary to the quotation in the “Introduction” (Ch. 1 in Schito et al., 2017) the papers by Belka (1990), Marynowski et al. (2001), Poprawa et al. (2005), Narkiewicz and Narkiewicz
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(2010) do not deal with the Lower Silurian „maturation and timing of hydrocarbon generation of Lower Silurian potential source rocks” – in fact these papers are devoted to Devonian and younger rocks of the HCMts. It would be advisable to quote papers by e.g. Malec et al. (2010)
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and Smolarek et al. (2014) instead.
Dadlez (2001) and Kutek (2001) did not pursue the “kinematic evolution” of the Holy Cross Fault (as quoted in the “Geological setting” - Ch. 2). This issue is discussed by several other
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authors, more recently by Lamarche et al. (2002) and Konon (2007) who also cite earlier publications. It is not clear why the information on “Interlayered organic matter rich black
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shales” in Pragian-Emsian is quoted from Marynowski et al. (2001), advisable reference would be Malec (2005). Narkiewicz and Narkiewicz (2010) did not describe “middle and Upper Devonian carbonates” – their paper is concerned with selected aspects of a part of the Eifelian succession (advisable: Szulczewski, 1995, Belka and Narkiewicz, 2008). Gągała (2015) could not detect “an Early Caledonian deformation in the Lower and Middle Cambrian rocks in the Kielce block” as he investigated late Caledonian (Late Silurian-earliest Devonian) deformations in the Łysogóry Region. Contrary to Schito et al. (2017) quotation, Lamarche et
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ACCEPTED MANUSCRIPT al. (1999) and Konon (2007) also did not discuss the Cambrian tectonics, in fact they described and interpreted Variscan and Alpine deformations (advisable: Gągała, 2005).
“Polish Rift Basin” (Kutek, 2001, but not Kutek and Głazek, 1972, Lamarche et al., 1999,
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Mizerski 2004) is a misleading term (no true rifting occurred), the widely accepted concept of a polyphase Permian-Mesozoic Polish Basin (Dadlez et al., 1995) is more adequate. Konon (2004) and Kozłowski (2008) did not describe Permian-Mesozoic succession in the HCMts –
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the first paper is concerned with extensional tectonic structures in the Devonian rocks, while
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the second one with the Silurian stratigraphy (advisable: Kutek and Głazek, 1972).
Tectonic framework of the Permian-Mesozoic depositional development of HCMts has not been studied by Lamarche et al. (1999) and Konon (2004) (advisable: Dadlez et al., 1995; Hakenberg and Świdrowska, 1997). Dadlez et al. (1994) did not pursue the issue of the late
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Cretaceous/early Paleogene inversion (see also Ch. 5.6 of Schito et al., 2017, the same refers to Mizerski, 2004). Gągała (2015) or Kozłowski (2008) cannot be used as primary or even general source of information on the Cambrian to Devonian-Carboniferous stratigraphy (cf.
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fig. 3 and Ch. 6.2 in the discussed paper) as both contributions have more specific scopes – the late Caledonian tectonics and Upper Silurian stratigraphy, respectively. Narkiewicz (2002)
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cannot be used as source of information or assumptions on the HF evolution from Cambrian to recent (Ch. 3.2.6 in Schito et al., 2017) as no such data are given in that paper. Moreover, Belka (1990) is not responsible for the vitrinite reflectance data from the Łysogóry Region (Ch. 4). On the other hand, several determinations for this region were provided by Marynowski (1999) – the source not quoted by Schito et al. (2017).
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ACCEPTED MANUSCRIPT Gągała (2015) is inappropriately cited in Ch. 5.6 as a source of information on the Pridolian sedimentation (advisable: Kozłowski, 2008). Paper by Szulczewski et al. (1996) is hardly an adequate reference on the Lower-Middle Devonian deposition as it is devoted to the late Frasnian to Early Carboniferous sedimentation in a specific aerally limited setting of a
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drowned carbonate platform. Neither Kutek and Głazek (1972) nor Narkiewicz and
Narkiewicz (2010) “suggest that thermal maturity of the Paleozoic successions could have been acquired during the Late Paleozoic” (Schito et al., 2017, Ch. 6.2) – these papers are
3. Burial and thermal modelling
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3.1. Modeling constraints
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Marynowski, 1999; Narkiewicz et al., 2010).
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concerned with other, unrelated topics (more adequate quotations are: Belka, 1990;
The authors of the discussed paper claim that their reconstructed geological evolution of the
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area “allows a robust calibration against organic and inorganic thermal indicators”. The confusing misquotations related to the regional geological data (partly listed above) cast some
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doubt on such statement. The confusion further rises when looking in a more detail at the input data for the 1-D modeling performed by Schito et al. (2017).
Two models by Schito et al. (separately for the Łysogóry and Kielce regions) are not tied to any particular section, thus their “pseudowells” have no constrained regional location. It is unclear how the stratigraphic-lithologic columns for both models have been constructed (Ch. 3.2.6). The authors cite papers by Kozłowski (2008), Gągała (2015) and Trela (2007) in
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ACCEPTED MANUSCRIPT which overview of parts of the Early Palaeozoic succession is given, and refer in a general
way to various well sections dispersed throughout the study area (Schito et al., 2017, fig. 2b). It is nowhere stated, however, which sections and why were used for the modelling, which raises questions about the validity of the stratigraphic data. For example, assuming 250 m of
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Ordovician developed as a shale in the Kielce Region (Ch. 5.6) is an oversimplification (to say the least). Ordovician is composed not only of “clayey and silty deposits” (as stated in Ch. 2) but includes also sandstone-conglomeratic complexes (Arenigian) and condensed
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carbonates (mostly Middle Ordovician) (Trela, 2006). According to the discussed paper the Upper Silurian of the Kielce Region is represented by sandstones and conglomerates while in
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fact it is composed of mostly shaly succession with greywacke intercalations. It is not true that in the Kielce Region “the carbonate platform drowning occurred in the beginning of the Givetian and led to the deposition of 700 m thick black shales during the Upper Devonian” (compare Szulczewski et al., 1996). In view of the above incorrect statements it is not
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surprising that fig. 3 of Schito et al. (2017) showing synthetic stratigraphic columns for both regions of the HCMts contains many errors (e.g. graptolitic shales in the Upper Devonian).
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Unfortunately, Schito et al. (2017) nowhere explain how did they reconstruct the missing strata (both thickness and lithology), including those removed by the Variscan erosion and the
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late Cretaceous-early Paleogene unroofing. The latter is estimated in the commented paper as 3500 m (Kielce) and 4300 (Łysogóry) with erosion starting 70 My ago, but the ground for such numbers is unclear. Certainly they cannot be based on the paper by Dadlez et al. (1994) quoted in this context, because the paper discusses the Palaeozoic and not Meso-Cenozoic tectonics of Poland.
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ACCEPTED MANUSCRIPT “Two main events of burial” and “two exhumation events” are concluded for the studied
Ordovician to Recent burial history (see also figs. 11a and 12a in Schito et al., 2017) in which Early Palaeozoic-Carboniferous is regarded as a single “burial event”. No erosion of the Silurian (Kielce Region) has been assumed (fig. 12a) in spite of a published evidence of the
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late Caledonian angular unconformity between the Silurian and overlying Lower Devonian, and related erosional and nondepositional gap of ca. 10 Ma (e.g. Dadlez et al., 1994). Also, the late Silurian magmatism (Bardo diabase – Nawrocki et al., 2013) is not even mentioned.
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It may be parenthetically added that the occurrence of the late Caledonian unconformity and associated erosional gap is possible also in the Łysogóry Region (e.g. Kozłowski, 2008;
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Gągała 2015) – the variant that should be at least taken into account when modelling the burial-thermal history.
The two-stage HF evolution assumed in the discussed paper (35 mW/m2 from 490 Ma to 130
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Ma, then gradual increase to 45 mW/m2 until recent) is not backed by any data or substantiated assumptions. Narkiewicz (2002) is quoted in this context (Ch. 3.2.6) but that
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paper does not include such information (see above).
The authors state that their thermal model of the Łysogóry Region is consistent with maturity
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data from the Lower Jurassic. The latter data are derived, however, from the unnamed localities tens of kilometres to the north of the Palaeozoic outcrops and thus incompatible with the latter. It has been documented e.g. by Głazek and Kutek (1972) that the PermianMesozoic strata markedly thin away from the Paleozoic core of the HCMts.
Finally, the vitrinite reflectance data used by Schito et al. (2017; tab. 4) for callibration of their burial-thermal models are partly questionable. For 10 samples out of 28, the reflectance
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data are based on less than 10 measurements which is considerably below the acceptance limit (Barker and Pawlewicz, 1993), thus excluding most of the Devonian data.
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3.2. Question of elevated Variscan heat flow
One of the conclusions from the 1-D modeling performed by Schito et al. (2017) is the twostage Ordovician to recent HF evolution, lacking any Carboniferous-Permian thermal events.
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This conclusion contradicts several earlier results (e.g. Belka, 1990, Marynowski, 1999,
Narkiewicz et al. 2010). Such conclusion deserves a separate discussion as it has further
metallogeny and petroleum generation.
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consequences for both basic regional geology and mineral resources, including questions of
Two arguments are given by Schito et al. (2017) to disprove the end-Palaeozoic heat flow
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increase:
1) the thermal maturity curve fits Silurian palaeothermal indicators from the Kielce block (fig. 11c) only with a HF value of 35 mW/m2 during the Carboniferous, much lower than the
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present-day one (about 45 mW/m2), when using present-day thicknesses of Paleozoic and Mesozoic successions;
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2) the thermal maturity curve fits Devonian and Silurian data (fig. 11c) only with a burial of about 4000 m during the Mesozoic rather than with an increase of HF in the Łysogóry block at the end of Paleozoic.
First, the above-raised objections as to the stratigraphic constraints on burial-thermal history cast serious doubt on the validity of the modelling results of Schito et al. (2017). Second, it can be noted that the respective curves (figs. 11c and 12c) show a rather poor fit with the
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ACCEPTED MANUSCRIPT maturity data points for the assumed two-stage HF evolution. Lastly, and most importantly,
no alternative simulations are discussed by Schito et al. (2017) although at least two published alternatives are available (Poprawa et al., 2005; Narkiewicz et al., 2010). The first-quoted authors assume constant Devonian to recent HF, while in the second paper several burial-
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thermal scenarios are simulated and the elevated Variscan HF is accepted as highly probable.
The elevated (and laterally variable) Variscan (Late Carboniferous-?early Permian) HF was
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interpreted already by Belka (1990) based on the conodont CAI pattern in the Devonian-
Carboniferous and Triassic. The crucial observation was the presence of elevated and laterally
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variable CAI values in the range 1-3.5 showing SSW-NNE oriented gradient, contrasting with uniformly low CAI 1 values in the closely juxtaposed Triassic sediments. The highest values were observed along the WNW-ESE trending Holy Cross Fault – the major, deeply-rooted tectonic discontinuity. This pattern has been later confirmed and refined by Narkiewicz and
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Malec (2005) and Marynowski et al. (2002; see also Narkiewicz et al., 2010).
Marynowski et al. (2002) found measurable differences in maturity levels of the Upper
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Permian sediments between both regions of the HCMts., based on vitrinite reflectance and biomarker indices. The southern region shows low values, comparable to the Triassic rocks,
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while in the north they are significantly higher, close to those in the Nieświń IG 1 borehole, ca. 30 km to the north of the HCMts. (Grotek, 1998). The difference cannot be accounted for solely by contrasting burial depths, thus implying existence of a positive thermal anomaly north of the Holy Cross Fault before the Triassic. More generally speaking, the maturity distribution in the pre-Triassic versus younger rocks point to a decisive role of the elevated late Paleozoic HF for the present thermal maturity patterns in the sub-Permian rocks.
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The question of the Mid-Palaeozoic to Cenozoic thermal and burial evolution of the HCMts. has been investigated by means of 1-D modelling by Narkiewicz et al. (2010). The study was based on two wells located in the SW (Kowala 1) and NE (Janczyce I) part of the Kielce Region (see Narkiewicz et al., 2010, for the location). A relatively complete, cored Devonian
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sections in both wells have been supplemented by stratigraphical data on the Carboniferous from the nearby outcrops. The Permian-Mesozoic cover (eroded during the
Cretaceous/Paleogene uplift) has been restored using two alternative datasets from Kutek and
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Głazek (1972) and Dadlez et al. (1998), respectively. The burial-thermal models have been callibrated using Devonian vitrinite reflectance values either directly determined or calculated
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from biomarker indices (Marynowski, 1998, Ph.D. Thesis). Several HF evolutionary scenarios have been simulated with various assumptions regarding eroded Carboniferous thicknesses.
It appeared that the variant of a thinner Permian-Mesozoic cover (Dadlez et al., 1998),
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implying lower magnitude of the Late Cretaceous-Paleogene inversion, allows more realistic assumptions regarding heat flow distribution through time. The alternative scenario, assuming deeper burial, generally lower heat flow and smaller Carboniferous thickness was regarded as
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less probable. The accepted variant of the Permian-Mesozoic burial history implies that the total post-Carboniferous burial in the study area was on the order of 2000-2500 metres (Fig.
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1). The respective Upper Cretaceous thickness could have been 400 to 500 m whereas the Late Cretaceous-Paleogene inversion most likely started already in the Santonian (ca. 85 Ma). Consequently, the preferred magnitude of total inversion was on the order of 2500 m.
The modeling results are consistent with the assumption of a constant HF from the Devonian to recent. However, the modelled HF shows also a very good fit with the empirical data if elevated Carboniferous-Early Permian HF up to 80 mWm-2 is assumed, particularly in the
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ACCEPTED MANUSCRIPT Janczyce I located close to the HCF (Fig. 1). The elongated zone of increased thermal
maturity in the Devonian, stretching directly south of the HCF may be partly accounted for by Carboniferous siliciclastics thicker by ca. 500 m in comparison to previous estimates.
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The presence of the elevated Variscan HF is consistent with several lines of independent
regional evidence (Fig. 1; Narkiewicz et al., 2010; Smolarek et al., 2014). The latter include: (1) hydrothermal sulphide mineralization ascribed to the Variscan (pre-Permian) metallogenic
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stage (Rubinowski, 1971); (2) low-hydrothermal calcite mineralization and associated
hydrothermal karst dated paleomagnetically as Permian (Lewandowski, 1999); (3) pervasive
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burial dolomitization associated with circulation of hot mineralized fluids during the Carboniferous (Narkiewicz, 2009), (4) Early Permian thermochemical remagnetization related to cooling of a regional fluid circulation system (Grabowski et al., 2006). Narkiewicz et al. (2010) concluded that the Variscan thermal anomaly, particularly well-pronounced along the
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crustal discontinuities such as the Holy Cross Fault (Narkiewicz et al., 2011), is a satisfactory explanation of both vertical and lateral maturity patterns and other regional data quoted
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above.
It should be noted that in the case of the thermal modeling of the Lower Palaeozoic strata the
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above HF history interpreted by Narkiewicz et al. (2010) is superimposed on the maturity pattern attained during the earlier Caledonian cycle (Cambrian to Late Silurian-earliest Devonian). Narkiewicz (2002) argued, based on a tentative comparison of the Devonian versus Lower Paleozoic thermal maturity patterns, that the present difference in their levels in the Lower Palaeozoic strata between both regions of the HCMts. is at least partly inherited from pre-Devonian times. This was regarded, together with a contrasting subsidence history of the Kielce versus Łysogóry regions, as the evidence of paleogeographic separation of both
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regions being independent terranes during the Early Palaeozoic. Although new data cast some doubt on such interpretation (Kozłowski et al., 2014; Smolarek et al., 2014), the question of the possible elevated Caledonian HF remains open. In this context the presence of the latest Silurian-earliest Devonian (ca. 424-416 Ma; Nawrocki et al., 2013) mafic magmatism in the
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HCMts. is particularly important.
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4. Conclusions
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Although Schito et al. (2017) provide new maturity data for the Lower Palaeozoic shaly successions of the HCMts, their 1-D burial-thermal modeling of the Ordovician to recent evolution of the area is poorly supported by partly misquoted and/or irrelevant regional
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stratigraphical and tectonic data.
The authors did not take into account the late Caledonian uplift and erosion, documented at least for the Northern (Kielce) Region of the HCMts. They also neglected published maturity
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data for the Permian-Triassic (Marynowski et al., 2002). Their reconstructed missing sections, particularly for the end Cretaceous-early Paleogene inversion and unroofing, lack support
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from any previous or new data/interpretations.
Consequently, the two-stage model of the HF evolution proposed by Schito et al. (2017) is poorly substantiated. Moreover, it has not been confronted with earlier published models based on 1-D burial-thermal modelling, assuming constant Devonian-recent HF (Poprawa et al., 2005) or elevated Variscan (late Palaeozoic) HF (Narkiewicz et al., 2010). The latter model is corraborated by various regional data pointing to elevated thermal regime during the
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Acknowledgments
Funding of the present work was provided by the Polish Geological Institute-NRI statutory
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funds (project no. 62.9701.1401.00.1). I thank Leszek Marynowski (Silesian University) for
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his helpful comments and suggestions to the earlier version of the manuscript.
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Figure caption
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Fig. 1 – Burial-thermal history of the Kielce Region modelled in the Janczyce I well-section (after Narkiewicz et al., 2010, modified and supplemented); (a) measured (triangles) versus
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calculated (curves) vitrinite reflectance for two selected variants of the heat flow development through time shown in (b), assuming the Permian-Mesozoic stratigraphy restored after Dadlez et al. (1998), thick Lower Carboniferous and significant Variscan erosion; (b) two modelled variants of the temporal HF pattern; (c) burial graph with temperature distribution through time (in oC) according to the variant b (elevated Variscan HF), showing stages of subsidence/uplift development (bottom part), and duration of geological processes attributable to the elevated Variscan HF (upper part).
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ACCEPTED MANUSCRIPT Comment on Schito et al. (2017) Highlights:
The misquotations in the commented paper are indicated and more adequate references are suggested
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The 1-D modelling results are critically commented and published alternative heat flow evolution is briefly presented