Title: Middlesex/punctata Event in the Rhenish Basin (Padberg section, Sauerland, Germany) –
Geochemical clues to the early-middle Frasnian perturbation of global carbon cycle
Author: Agnieszka Pisarzowska, R. Thomas Becker, Z. Sarah Aboussalam, Marek Szczerba, Katarzyna
Sobień, Barbara Kremer, Grzegorz Racki i in.
Citation style: Pisarzowska Agnieszka, Becker R. Thomas, Aboussalam Z. Sarah, Szczerba Marek,
Sobień Katarzyna, Kremer Barbara, Racki Grzegorz i in. (2020). Middlesex/punctata Event in the
Rhenish Basin (Padberg section, Sauerland, Germany) – Geochemical clues to the early-middle Frasnian
perturbation of global carbon cycle. “Global and Planetary Change (Vol. 191 (2020), Art. No. 103211),
doi 10.1016/j.gloplacha.2020.103211
Global and Planetary Change 191 (2020) 103211
Contents lists available at ScienceDirect
Global and Planetary Change
journal homepage: www.elsevier.com/locate/gloplacha
Research article
Middlesex/punctata Event in the Rhenish Basin (Padberg section, Sauerland,
Germany) – Geochemical clues to the early-middle Frasnian perturbation of
global carbon cycle
T
Agnieszka Pisarzowskaa, , R. Thomas Beckerb, Z. Sarah Aboussalamb, Marek Szczerbac,
Katarzyna Sobieńd, Barbara Kremere, Krzysztof Owockie, Grzegorz Rackia
⁎
a
Institute of Earth Sciences, University of Silesia in Katowice, Będzińska 60, 41-200 Sosnowiec, Poland
Institut für Geologie und Paläontologie, Westfälische Wilhelms-Universität, Corrensstrasse 24, 48149 Münster, Germany
Institute of Geological Sciences, Polish Academy of Sciences, Kraków Research Centre, Senacka 1, 31-002 Kraków, Poland
d
Polish Geological Institute - National Research Institute, Rakowiecka 4, 00-975 Warszawa, Poland
e
Institute of Paleobiology, Polish Academy of Sciences, Twarda 51/55, 00-818 Warszawa, Poland
b
c
A R T I C LE I N FO
A B S T R A C T
Keywords:
Early–middle Frasnian
Rhenish Massif
Padberg Formation
Carbon isotope stratigraphy
Middlesex/punctata Event
Trace metal geochemistry
A positive carbon stable isotope excursion of about 3‰ is documented in the topmost lower Frasnian at Padberg,
eastern Rhenish Massif, as a muted record of the worldwide early−middle Frasnian isotopic perturbation
(punctata Event; up to 6–8‰ shift in both δ13Ccarb and δ13Corg elsewhere), comparable with the Appalachian
δ13C curve. This German isotopic signature occurs in a 12 m thick calciturbidite succession and correlates well
with the three-step chemostratigraphic pattern known from the Holy Cross Mountains, Poland. It is especially
clear in the δ13Corg shifts, whilst δ13Ccarb (and elemental geochemical) proxies are partly biased by post-sedimentary alterations. The New York State, Polish, Nevada and Padberg conodont successions place the onset of
the major positive δ13C excursion slightly beneath the early–middle Frasnian boundary, with Ancyrodella nodosa
(previously Ad. gigas form 1) as the main conodont guide species, and coincident with the Middlesex transgression and spread of cold, nutrient-rich, poorly oxygenated water masses. In the light of geochemical proxies,
enhanced primary production and oxygen deficiency occurred evidently in the Rhenish Basin during the punctata
Event. Moderate Hg enrichments in the early Middlesex/punctata Event interval suggest a volcanic signature.
However, conclusive data from other regions are required to differentiate between effects of the regionally wellknown synsedimenary magmatism and of a possible global volcanic trigger for the biogeochemical perturbation.
1. Introduction
The Devonian Period is characterized by a series of global biotic
changes in marine and terrestrial ecosystems of different magnitude
(e.g. Walliser, 1996; House, 2002; McGhee, 2013). The last overview by
Becker et al. (2016) introduced a distinction between 1st to 4th order
global events. The chemostratigraphic record of many Devonian global
events (e.g. Taghanic, Frasnian-Famennian, Hangenberg) is marked by
comprehensive isotopic evidence of worldwide biogeochemical perturbations (e.g. Buggisch and Joachimski, 2006; Becker et al., 2012).
However, significant geochemical anomalies are not only associated
with documented 1st or 2nd order global events (Racki, 2005). In
particular, unexpectedly large temporal changes in δ13C values (above
7‰) were discovered by Yans et al. (2007) in the early–middle Frasnian
(E–MF) transition in the Ardennes of Belgium, supported by refined,
⁎
four-step shift patterns from the Holy Cross Mountains (Pisarzowska
and Racki, 2012; see also Racki et al., 2004; Pisarzowska et al., 2006;
Baliński et al., 2016). Correlative carbon isotope excursions have also
been reported from South China (Ma et al., 2008), the western USA
(Morrow et al., 2009), the Appalachian Basin of the eastern USA (Lash,
2019), the Western Canada Sedimentary Basin (Śliwiński et al., 2011),
northeast Alberta, Canada (Holmden et al., 2006), southwest Siberia
(Izokh et al., 2015), and, likely, from Moravia, Czech Republic (see
Geršl and Hladil, 2004) and the Russian Platform (Zhuravlev et al.,
2006). However, in terms of background δ13C levels, particular spike
magnitudes, and especially the exact timing of the δ13C shifts in the
conodont zonal scheme, a significant paleogeographic variation among
the isotope profiles across the E–MF transition records the multifaceted
interplay between various regional and global factors (Śliwiński et al.,
2011; Pisarzowska and Racki, 2012).
Corresponding author.
E-mail address: agnieszka.pisarzowska@us.edu.pl (A. Pisarzowska).
https://doi.org/10.1016/j.gloplacha.2020.103211
Received 10 February 2020; Received in revised form 23 April 2020; Accepted 24 April 2020
Available online 04 May 2020
0921-8181/ © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/BY/4.0/).
Global and Planetary Change 191 (2020) 103211
A. Pisarzowska, et al.
The extended δ13C excursion interval coincided with the global
Timan, Middlesex and the Lower Rhinestreet events (sensu House and
Kirchgasser, 1993; House et al., 2000; House, 2002; Racki et al., 2008;
Becker et al., 2016), and all four-step changes in the global carbon cycle
were collectively called E–MF perturbation by (Racki et al. 2008;
Pisarzowska and Racki, 2012). Following a recent refinement of conodont data (Klapper and Kirchgasser, 2016), the major positive δ13C
shift of as much as 6–7‰, begins near the end of the early Frasnian
Palmatolepis transitans or MN 4 Zone (Lash, 2019), at the level of the
sedimentologically defined Middlesex Event. Similarly to Lash (2019),
we retain the commonly used term of Yans et al. (2007), the punctata
Event, for the most characteristic, extended plateau in δ13C values,
which is still largely in the middle Frasnian Palmatolepis punctata Zone.
In continental Europe, well-dated and continuous Frasnian successions of Germany could fill a paleoregional gap in the well-proven
geochemical signatures of the E–MF isotopic perturbation in the Holy
Cross Mountains and Ardennes. Based on precise results of conodont
biostratigraphy, this contribution focuses on high-resolution information on δ13C time series (the organic and inorganic reservoirs), combined with elemental geochemical signatures, across the early-middle
Frasnian transition in a Rhenish reference section at Padberg near Adorf
(eastern Sauerland, Fig. 1). The δ13C record reveals some unique
characteristics, biased in part by diagenetic processes. Nevertheless, the
integrated isotope and elemental signatures conclusively provide an
insight into the complex causes of the prolonged biogeochemical perturbation, in the context of both regional and supra-regional controls,
such as tectonic and volcanic activities, sea-level variation, and climate
evolution. Furthermore, recent more precise biostratigraphic data allows for a critical review of the conodont datings and carbon isotope
chemostratigraphy in all regions with a published record of the early–middle Frasnian isotopic perturbation.
The comprehensive discussion of conodont biostratigraphic questions, paired with microfacies, rock magnetic and mineralogic information on the Padberg succession, significantly affected by postsedimendary alterations such as hematitisation/limonitisation
processes, will be presented by the authors in a related contribution.
of the middle Frasnian (Stritzke, 1989).
3. Lithologic succession and facies
The Padberg Quarry exposes from north to south ca. 250 m individual beds with a total thickness of ca. 32 m. During fieldwork in
2014 and 2016, only the upper, ca. 12 m thick succession was sampled,
and subdivided into 144 layers (Fig. 2). Three lithologic sets are distinguished, with a silty shale-enriched middle portion (set B), separating two turbiditic limestone-dominated units (sets A and C):
A - Dark-grey, thin- to medium bedded, bioclastic limestones, separated irregularly by fossil-poor, platy to thickly fissile, shaly intervals
up to 0.6 m thick (mudstones in. petrological terms, because dominated
by quartz and 2 M1 muscovite).
B - Two non-fossiliferous, dark grey to black, silty shale units,
maximally 0.5 m thick, separated by micritic and marly limestones
(total thickness 1.1 m; beds 119–125). A uniquely, slightly ash-looking
horizon, 2 cm thick, occurs in the uppermost part (bed 124ash).
C - Typically medium- to -thick-bedded, grey, bioclastic limestones
(total thickness 3.2 m; beds 126–144), with subordinate shaly intercalations.
Although there are no significant successional changes of mineralogy in the profile, some stratigraphic trends are visible: (i) increase of
hematite content relatively to goethite in the upper part of the section
(set B and C; this yellowish and reddish interval was marked as the
altered zone); (ii) small increase of kaolinite content in the upper part
(set B and C); (iii) transition from more illite-smectite in the lower part
to more muscovite in the upper one.
The Padberg succession includes a typical Frasnian fore-reef talus,
which is possibly associated with a calcareous ooze input from backreef areas, induced by episodic heavy storm action, as inferred from
ecologically mixed bioclastic accumulations. It was originated from the
southern margin of the Brilon Reef, where extensive subtidal crinoidalgal forests must have grown. On the other hand, laminated lithofacies
of set B are interpreted as a depositional record of pelagic rain pulses
from blooming plankton in the near-surface zone.
2. Regional setting and facies aspects
4. Samples and methods
The studied succession is exposed in an abandoned quarry in the
northeastern Rhenish Massif (eastern Sauerland) on the eastern slope of
the Padberg, ca. 500 m SE of the small village with the same name, and
ca. 1.75 km S of Bredelar. The coordinates on the topographic and
geological sheets Madfeld, 1:25000 (GK 4518 Madfeld) are x = 34
84,500, y = 56 96,250 (50°23′52″ N, 08°46′17″ E; Fig. 1).
In Middle-Late Devonian times, the area was part of the extensive
outer shelf of southern Laurussia (Eder et al., 1977). In terms of the
regionally complex tectonics, the near vertical to slightly overturned (at
the southern quarry wall) beds belong to the northeastern margin of the
first order Ostsauerland Anticline and to the second order Padberg
Anticline. In its core lie Givetian volcanic rocks, the so-called Hauptgrünstein (diabase). Intrusive basaltic lavas and volcaniclastics were
mined in the near-by Selecta Quarry at the southern flank of the Padberg. They belong to a submarine eruption centre and seamount, the
Padberg volcano (Sunkel, 1990). The directly overlying sediments
consist of Givetian-Frasnian dark-grey, fossil-rich turbiditic limestones,
the Padberg Limestone (Paeckelmann and Kühne, 1936), and intercalated, dark-grey, poorly fossiliferous shale (Flinz shale). Both are
characteristic for the Padberg Formation (Ribbert et al., 2006), with the
Padberg Quarry as its type section. The Brilon Reef grew contemporaneously with the volcanic activity to the North and its debris
formed the Padberg Formation (Stritzke, 1989, 1990). The nearest
outcrop of the reef margin occurs ca. 5 km to the NW. The calciturbiditic sequence is locally followed by pelagic, micritic cephalopod
limestone with abundant goniatites (Burgberg Formation). This reflects
the expansion of condensed pelagic seamount facies in the higher part
The main subject of the multidisciplinary analyses were 126 samples taken during fieldwork in 2014 and 2016 by the Polish group. The
numbering of samples (marked by Pd) corresponds to the successive
numbers of layers. The conodont stratigraphy is based on 14 samples
taken independently by R.T. Becker (marked by P).
The mineralogy of 31 samples was determined by XRD analysis of
randomly oriented powder specimens using a Thermo ARL X'tra diffractometer at the Institute of Geological Sciences PAS in Kraków,
Poland. XRD analyses of clay-mineral (< 2 μm) fractions were performed for samples Pd: 104, 124, and 124top. Thirty-eight samples
were powdered and geochemically analysed at the Bureau Veritas Acme
Labs Canada Ltd. Major, minor and rare elements were analysed using
inductively coupled plasma atomic emission spectrometry (ICP-AES)
and inductively coupled plasma mass spectrometry (ICP-MS) methods.
The reliability of the analytical results was examined based on the
analyses of several international standard reference materials and on
duplicate measures of several samples. The precision and accuracy of
the results were better than ± 0.05% (mostly ± 0.01%) for the major
elements and commonly better than ± 1 ppm for the trace elements.
The isotope compositions of carbonate were determined for 44
samples. Powdered bulk-rock samples were analysed for δ13C and δ18O
using a Kiel IV Carbonate Device connected to a Finnigan Delta Plus
isotope ratio mass spectrometer in a Dual Inlet system at the Institute of
Geological Sciences PAS in Warsaw, Poland. Samples reacted with
purified H3PO4 at 70 °C. A calibration to international standards (NBS
18, NBS 19 and IAEA-CO-9) was made per every ten samples. Isotope
ratios are reported as δ13Ccarb and δ18O values and expressed relative to
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A. Pisarzowska, et al.
Fig. 1. Location of the Rhenish Massif in (A) the late Devonian Laurussia–peri-Gondwana contact (after Blakey, 2011) and Padberg Quarry in (B–C) Germany on
geological sheet 4518 Madfeld (northeastern Sauerland, Ribbert et al., 2006, updated). Abbreviations: de-vT = early/middle Givetian “Tentaculite Beds”,
dvV = “Hauptgrünstein” (middle Givetian metabasalts and pyroclastics), dv-fR = hematitic iron ore, dv-fP = Padberg Formation (middle Givetian to early middle
Frasnian), df-fA, k = Burgberg Formation (“Adorf Limestone”, middle Frasnian to early Famennian), dfaN = “Nehden Beds” outside the Brilon Reef (early Famennian), dfaH = Hemberg Formation (middle/early upper Famennian), dfaD-W = “Dasberg and Wocklum Beds” in basinal facies (late/latest Famennian),
d–c = Hangenberg Formation (topmost Famennian – early Tournaisian), cd2, alk = Kahlenberg and Hardt Formations (Lower Alum Shale and “Kieselschiefer”,
middle Tournaisian to early Viséan), cd2, ki = Hillershausen Formation (“Kieselkalk”, ca. middle Viséan), cd3, kt = Bromberg Formation (“kieselige Übergangsschichten”, late Viséan), cnB = Bredelar Formation (late Viséan to Serpukhovian), L, ta = Quaternary terraces.
of carbonate in a few samples. For these samples, the procedure was
repeated three times using a Sonic Ultrasonic Processor to disintegrate
aggregates in which carbonate grains are probably coated by clay-minerals or organic matter. This procedure was ineffective for ten samples
(Supplementary Data 1, SD 1).
the Vienna Pee Dee Belemnite (V-PDB) standard. The measurement
precision (1σ) is better than 0.05‰ for δ13C and 0.15‰ for δ18O, respectively.
Organic matter for analyses was recovered from micritic partings
(wackestones) and shales in 42 samples. Powdered samples reacted
with 10% HCl for 8 h at 60 °C in a water bath. Following dissolution,
the residues were repeatedly rinsed with deionized water.
Mineralogical analyses of the acidized residue revealed trace amounts
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A. Pisarzowska, et al.
Fig. 2. Lithologic succession of the Frasnian carbonate strata at Padberg Quarry and field photos of different lithologies (taken by K. Owocki). Note thin to medium
bedding of calciturbidites, alternating with platy-fissile mudstone (shales) partings in set A (photos A–D), contrasting with more shaly (photo E) and thicker limestone
layering (photo F) of overlying sets (B and C, respectively).
Kirchgasser, 2016).
Sample P 123 yielded the most important fauna. The distinctive
Ancyrodella nodosa enters, which has been revised by Klapper and
Kirchgasser (2016). This is the same species as Ad. gigas form 1 sensu
Klapper (1989). It can be strictly separated from the true Ad. gigas (=
form 3 sensu Klapper, 1989). Ad. nodosa commences globally high in
the transitans Zone (Klapper and Kirchgasser, 2016) and is used here to
define the nodosa Zone, re-naming the gigas Zone of Vandelaer et al.
(1989). An important first occurrence of A. nodosa lies at the base of the
Middlesex Shale in New York State (Over et al., 2003), which marks the
hypoxic Middlesex Event sensu House and Kirchgasser (1993). It
slightly pre-dates the appearance of Pa. punctata in the overlying basal
Cashaqua Shale. The entry of Ad. nodosa (=Ad. gigas M1) approximates
the base of Pa. punctata and markes the onset of the punctata Event in
the C-isotope record (Event III of the E–MF isotopic perturbation) of
various authors (see Racki and Bultynck, 1993, and Chapter 6.2.1). The
term Middlesex Event can be used alternatively.
There are common Pa. transitans in sample P 137 but no Pa. punctata. This suggests that the basal punctata Zone (MN 5 Zone) has not yet
been reached in the sampled succession. Graphic correlation (Klapper,
1997; Klapper and Kirchgasser, 2016) of the continuing association of
5. Conodont dating and correlations
The section is characterized by very abundant conodont assemblages, commonly with several hundred specimens in one normal-sized
(2–3 kg) sample. For the early-middle Frasnian we apply the Montagne
Noire zonation of Klapper (1989), with updates in Ji and Ziegler
(1993), Klapper (1997), Aboussalam and Becker (2007), Bardashev and
Bardasheva (2012), and Klapper and Kirchgasser (2016). In order to
prevent any misunderstandings, we prefer to name all biozones after
their index species but give the MN numbering in addition (Fig. 3).
However, early-middle Frasnian zonations are further complicated by
biofacies influences, which may result in the episodic or local absence
or strongly fluctuating abundances of index taxa.
The lowest samples provided faunas typical for the Ancyrodella rotundiloba rotundiloba (Sub)Zone (upper MN Zone 2, basal Frasnian,
Klapper, 1997). Due to the complete absence of Palmatolepis rugosa, it is
not possible to fix locally the base of the MN Zone 3. Because of the
entry of Ad. pramosica, we place bed 13 at the base of the pramosica
Zone, which base is correlated with the upper MN 3 Zone. An important
newcomer in the same bed 21 is Ad. alata, which appears elsewhere in
the upper part of the rugosa Zone (higher MN Zone 3, Klapper and
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A. Pisarzowska, et al.
Fig. 3. Lower-middle Frasnian conodont zonations, showing the entry of index species of Ancyrodella, Mesotaxis, Zieglerina, Palmatolepis, and other genera, and of
the stratigraphic range of the studied succession at Padberg (right column). Abbreviations: Ad. = Ancyrodella, Ag. = Ancyrognathus, M. = Mesotaxis,
Pa. = Palmatolepis, Pad. – Padberg, Po. = Polygnathus, Z. = Zieglerina, chron. – chronostratigraphy.
Ad. nodosa and Ad. pramosica in sample P 137 supports this view.
However, Pisarzowska et al. (2006) recorded from Śluchowice, sample
37, a direct pramosica-punctata co-occurrence at the base of the punctata
Zone (MN 5 Zone), and therefore the middle Frasnian zone is doubtfully
shown in the topmost Padberg succession in Fig. 2.
7. Evolution of sedimentary conditions
7.1. Input of terrigenous material, paleoproductivity and redox conditions
Abrupt changes in mineral and element assemblages of the two
distinct types of rocks at Padberg indicate changes in depositional
conditions and variable detrital sedimentation in a basin with an episodic influx of proximal to distal calcareous turbidites, particularly
during the pramosica Zone and the base of the nodosa Zone (set B). The
increase of Al vs. Ti contents in sets B and C, in conjunction with a
highly matured mineralogical composition increased content of kaolinite and hematite(SD 2) in comparison to set A, suggests changes of the
weathering regime, from an arid/cooler to a more humid/warmer climate setting (Kiipli et al., 2012) or to the input of more strongly
weathered material (e.g. Kołtonik et al., 2018) in the pramosica/nodosa
zonal boundary interval. Retallack and Huang (2011) calculated atmospheric CO2 level (based on pedotype paleosols) for this interval. In
the opinion of these authors, the deposition of the Middlesex Shale took
place at times of a transient greenhouse climatic spike (warm and wet)
related to a large increase in atmospheric CO2.
There is a significant increase in the TOC content and in the TOC/P
(Corg/P) ratio in set C. This increase precedes elevated Mo, Sb and U
concentrations, but is corresponding to low values of Th/U ratio (< 1
for limestone and < 3 for shale), which are traceable for dysoxic
bottom-water conditions (Fig. 4). The higher values of the Corg/P ratio
correspond to higher TOC values (generally above 1%) and are indicative for an increase of productivity (Algeo and Ignall, 2007). Simultaneous increase of Corg/P ratio and decrease of Th/U ratio are
characteristic for a higher productivity and periodically oxygen restricted conditions. The lowest Th/U ratio during the nodosa Zone are
correlated with higher concentrations of Mo, Sb and U (Fig. 4). What is
unusual in the present case, As enrichments exceed these of Mo, and Sb,
which are also relatively high (Fig. 5). Uranium is relatively less enriched than As, Sb and Mo and the maximum UEF values precede the
anomalous AsEF, MoEF, and SbEF values. Such specific trace metal enrichments have been reported from active and ancient mud volcano
6. Elemental geochemistry
The Padberg section includes alternating limestones and shales, and
this lithological differentiation is evidenced by enrichment/depletion
patterns in Supplementary Data 1. For the purpose of more convenient
interpretations, we use Al-normalization (element/Al) and enrichment
factors (XEF = X/Alsample/X/Alstandard, Tribovillard et al., 2012; SD 1).
Small differences in the chemical composition between upper and
lower parts of the succession are visible. SiO2, TiO2, K2O and Al2O3
contents of the carbonate samples have higher values in the lower and
middle (samples Pd 1 to Pd 126) and the topmost (Pd 142 to Pd 144)
parts of the sections, and lower CaO contents in opposite to most parts
of set C (Pd 128 to Pd 141). FeO and MnO have higher values in set B
and in the lowest part of set C. Additionally, the MnO content is distinctly lower in the lower part of the section (set A and lowest part of set
B; Pd 1 to Pd 119) in comparison to middle and upper parts (sets B and
C). The Corg/P ratios range from 0.8 to 69.0 with the highest values in
set A and lower part of set C, and with the lowest values in set B. The
measured Th/U ratios for most carbonate-rich samples of the pramosica
and bottom and top parts of nodosa zones show values > 1. Lower Th/U
ratios (< 1), occur in the middle part of set C (from Pd 128 to Pd
140 M). The shale samples from sets A and B reached Th/U ratio < 3,
and only shale samples from set B show values > 3. The Th/U ratio
shows a good correlation with Mo/Al (Spearman correlation
R = −0.74). Strong enrichments of Mo, As, Sb and U are observed in
the upper part of set C.
The detailed results of trace elements of limestone and shale samples from Padberg are tabulated in the Supplement Data 1.
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A. Pisarzowska, et al.
Fig. 4. Composite plot of the Frasnian Padberg section (see Figs. 2 and 6) showing organic carbon and Al-normalized inorganic proxy data. Shaded area represents
the fluid migration front zone.
volcanisms occurred in the middle Givetian (e.g. Sunkel, 1990), followed by subordinate volcaniclastic eruptions and hydrothermal exhalations, especially of hematite-rich brines that were siliceous at the
exhalation centres and that mixed with micrite laterally. The regional
volcanism (volcaniclastic deposition) and hydrothermalism lasted locally into the early and lower part of the middle Frasnian (Bottke, 1965;
Sunkel, 1990; Stritzke, 1990; Nesbor et al., 1993; Aboussalam, 2003;
Ribbert et al., 2006), but in the case of carbonatic iron ores it is commonly difficult to distinguish the primary hydrothermal influx from
common secondary, metasomatic mobilisations of Fe-rich fluids.
As noted above, the thick Padberg volcanites predate and underlie
the Padberg Formation. In the eastern Sauerland, close to Padberg,
massive siliceous or carbonatic hematite ore bodies that were exploited
in extensive mines formed in the Givetian and early Frasnian by submarine hydrothermal exhalation (Lahn-Dill ore type; Nesbor et al.,
1993), in times of decreased basaltic volcanism or at the end of volcanic
activities (e.g. Bottke, 1965). However, at the famous Martenberg, a
few km to the SSE of Padberg, the regionally youngest volcaniclastics
systems (see summary in Tribovillard et al., 2013), because As and Sb
abundance in seawater is very low and only a specific mechanism fosters the transfer of these elements from seawater to sediment. Simultaneous significant enrichment in Mo, As and Sb and positive correlation with Fe2O3 suggest scavenging them by the Fe-particles and
trapping in authigenic minerals (Burdige, 2006).
Cd/Mo ratios are differentiated between hydrographically restricted
basins (< 0.1) and upwelling settings (> 0.1; Sweere et al., 2016). Cd/
Mo ratios are variable through sets A and B (from 0.05 to 0.50; Fig. 4)
and suggest the fluctuation from a slightly more to a less oxygen-deficient basin. In the middle part of set C (Pd 136 and Pd 137), the values
significantly increase (4.0) and show high values to the top (~1.0).
7.2. Hydrothermal and volcanic activity
Submarine hydrothermal and volcanic activity is well documented
in the Rhenish Massif during the Givetian – early Frasnian (Von Raumer
et al., 2017). In the eastern Sauerland, the main episode of basaltic
Fig. 5. Enrichment factors of key minor elements at the Frasnian Padberg succession (see Figs. 2 and 6).
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suggests that bottom- and pore-water conditions influenced insignificantly the measured δ13Corg values.
Consequently, the determined δ13Ccarb and δ13Corg values in sets A
and C reflect largely the approximate primary marine values.
Significant changes of the geochemical signature took only place at the
silty shale unit (upper part of set B) forming the fluid migration front
zone (Fig. 6; samples Pd 123 – Pd 125; compare Buggisch and
Joachimski, 2006), where CaCO3 was partialy removed, while organic
matter and pyrite were probably oxidized.
The Padberg succession reveals Frasnian background δ13Ccarb values
(~1‰, see Pisarzowska and Racki, 2012) throughout sets A and B
(Fig. 6, SD 1). A negative δ13Ccarb shift, corresponding to Event II sensu
Pisarzowska et al. (2006), with peak value of −7.9‰ in sample Pd 125,
precedes a distinctive positive δ13Ccarb excursion. This Event III (sensu
Pisarzowska et al., 2006) or the main punctata Event (sensu Yans et al.,
2007), with values of about 3‰, occurs in the basal set C, above the
pramosica-nodosa conodont zonal boundary (correlative with the transitans-punctata zonal boundary sensu Racki and Bultynck, 1993;
Pisarzowska et al., 2006). A gradually decreasing shift to a value of
−0.5‰ (Fig. 6), followed by a return to values around 1‰, occur in
the upper part of set C.
The δ13Corg record shows a similar pattern as δ13Ccarb (Fig. 6). The
δ13Corg values obtained across set A (pramosica Zone) lie around
−27.5‰. In the upper portion of set A, δ13Corg attains values around
−25.3‰ in two samples (probably the Inception Event I of Pisarzowska
et al., 2006), followed by a shift to −28‰ (?Event II) in set B. The
Padberg section reveals a positive δ13Corg excursion (Event III) up to
3‰ at the base of the nodosa Zone. In the upper part of the section,
δ13Corg values decrease slightly to −26.5‰, which is higher than in the
long interval (most of the pramosica Zone, set A) before the isotopic
perturbation (Fig. 6).
The oxygen isotopes (δ18Ocarb, Fig. 6) present values in the
range − 6.9‰ to −10.3‰ (average − 8.8‰) in set A. The δ18O values
increase up to −3.9‰ (average − 5.1‰) in the upper part of set B and
in the basal set C (sample Pd 126). In set C, oxygen isotopes return to
values of around −8.7‰.
and iron ores accumulated around the early–middle Frasnian transition
(Ziegler, 1958; Aboussalam, 2003). Episodic influx of fine volcanic ash
could have some contribution to a higher illite-smectite content relatively to muscovite in the lower part of the studied profile (SD 2).
Mercury concentrations, a worldwide tracer for volcanic (Pyle and
Mather, 2003), and submarine hydrothermal paroxysms (Higueras
et al., 2013), are higher in most of investigated carbonate samples than
in average marine carbonates (Hg > 0.04 ppm; Fig. 4). Two shale
samples (Pd 122 and Pd 135) show also a higher Hg content in comparison to the post-Archean Australian shale (Hg > 0.6 ppm). A positive Hg anomaly occurs in set B, while, higher enrichments in Hg is
recorded from the middle part of set C (Pd 133 to Pd 140B), with an
average HgEF of 15 (Fig. 5).
Recent studies documented that the Kola alkaline magmatism (Wu
et al., 2013) and the first phase of magmatic activity of the Vilyui paleorift (eastern Siberia, Polyansky et al., 2017; Tomshin et al., 2018)
were initiated at ca. 380 Ma, i.e. during the transitans-punctata time
interval (see timescale in Becker et al., 2012). Recently, increased Hg
concentration was documented for the late Frasnian Kellwasser Crisis
(Racki et al., 2018; Racki, 2020). On the other hand, there is recognized
hydrothermalism at the early-middle Frasnian transition of the eastern
Sauerland (e.g. Bottke, 1965). The record of the volcanic and especially
submarine hydrothermal activity in the studied section is unclear due to
secondary (post-diagenetic) processes. Therefore, further research has
to search for trace element signals in other regions and to clarify
whether the hydrothermal deposits of the eastern Sauerland may carry
also synsedimentary Hg enrichments.
8. Carbon isotope chemostratigraphy
8.1. Diagenetic alterations
The existence of small amounts of ankerite/dolomite (SD 2), a mineral commonly considered as secondary mineral (forming cements),
can indicate that the succession underwent some degree of diagenesis.
Cementation with ankeritic/dolomitic minerals is one of the first steps
of diagenesis, and sample Pd 125 contains up to 2% of ankerite/dolomite, indicating similar origin of hematite/goethite in this sample.
Hematite (more abundant in the upper part of the section) and goethite
(more abundant in the lower part of the section) are the main secondary
iron minerals (Fig. 6, SD 2). Variations of the ratio of goethite to hematite up section can be explained by gradual changes of oxidation
conditions, or by post-sedimentary oxidation of primary pyrite
(Mahoney et al., 2019) in the upper part (sets B and C). The second
explanation is more favourable as the hematite-ankerite/dolomitebearing mineralization (doillite sensu Nieć and Pawlikowski, 2019),
occurring in the upper part of set B and most of set C (Fig. 6) likely
reflects a local migration of oxidizing, Mn- and 18O-enriched fluids
along fractures and faults (e.g. Nieć and Pawlikowski, 2019). Diagenetic fluids in carbonate rocks generally contain comparatively insignificant amounts of secondary carbon; therefore, δ13C values have a
higher preservation potential than oxygen isotopes (Banner and
Hanson, 1990). The primary carbon isotopic composition may be altered in case that the stabilization occurs in system open for 12C-enriched CO2 derived from the remineralisation of organic carbon (Allen
and Matthews, 1982; Joachimski, 1994). The input of 13C-depleted CO2
should shift the carbon isotope composition to lower values. In the
studied section, the dolomite/ankerite mineralization is a trace component (≤1%) and, therefore it had no significant effect on the isotope
signature (compare Holser, 1997; Buggisch et al., 2003).
Many authors demonstrated that diagenesis under oxygenated
conditions can enrich organic matter in 13C (e.g. Sackett and
Thompson, 1963; Fruedenthal et al., 2001; Marynowski et al., 2017).
The conodont alteration index values (ca. 4) indicate that thermal
maturation affected the Padberg section uniformly. Furthermore, the
lack of covariance of TOC and δ13Corg in the studied section (R = 0.11)
8.2. Timing of the early–middle Frasnian biogeochemical perturbation in
Laurussian sections
The three C-isotopic events (I–III) are part of the long-lasting, fourstep early to middle Frasnian E–MF isotopic perturbation (see Yans
et al., 2007; Racki et al., 2008), recorded by both the organic and inorganic carbon reservoirs (Pisarzowska et al., 2006; Pisarzowska and
Racki, 2012). The revision of the conodont zonal scheme enables a
comparison with E–MF δ13C curves described from other regions, which
are known to be variable at intra- and inter-regional scales
(Pisarzowska and Racki, 2012; Lash, 2019).
The term punctata Event, introduced by Yans et al. (2007), has been
widely used for the sequence of isotopic shifts described above, since it
was assumed that these occurred within the Palmatolepis punctata Zone
(MN Zone 5). However, recent biostratigraphic data and increasing
precision, especially an improved correlation of parallel ancyrodellid
and palmatolepid evolution (Fig. 3), gives a refined time scale for the
sequence of E–MF events.
In the Dyminy reef complex succession of the Holy Cross Mountains,
Poland, the first appearance datum (FAD) of Pa. punctata is only accidentally recorded due to a common delayed entry, partly as late as
jointly with the next higher zonal marker Pa. hassi. The pelagic guide
species is even absent in particular sections (Racki and Bultynck, 1993;
Pisarzowska et al., 2006; Vierek and Racki, 2011). The comparison of
the conodont sequence with the detailed δ13C curves (Fig. 6), provide
good evidence for differentiated local FADs. The chemo-stratigraphically tuned most reliable FAD for Pa. punctata is recognized at
Kostomłoty-Mogiłki, where the index species enters in the lower part of
the major broad C-isotope excursion (‘plateau’), the guide character of
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A. Pisarzowska, et al.
Fig. 6. Lithology, conodont biostratigraphy, mineralogical composition (MC), total organic carbon (TOC), and stable carbon isotope geochemistry for the earlymiddle Frasnian succession at Padberg (Frasnian background values after Pisarzowska and Racki, 2012), against the regional and global events (see Fig. 7).
eastern North America (Lash, 2019, Fig. 4).
The critical ancyrodellid zonal boundary is well recognizable at
Padberg, with the base of the re-named Ad. nodosa Zone below sample P
123 (middle set B). The abundance of Pa. transitans and absence of Pa.
punctata in sample P 137 (middle set C) indicates that the transitanspunctata zonal boundary has not yet been reached at that level. Since
Pa. punctata is known to display facies-controlled late entries in some
sections (e.g. in the Holy Cross Mountains), the base of the punctata
Zone is questionably assumed for the topmost part of set C (Fig. 2). The
crucial Event III starts at least 4 m below, at the Ad. pramosica – Ad.
nodosa zonal boundary (sample P 123; Figs. 6–7). Therefore, guided by
the worldwide chemostratigraphical pattern, only the top early Frasnian part of the muted δ13C plateau occurs evidently in the Padberg
section (Figs. 6–7). Event IV of Pisarzowska et al. (2006) is predicted to
lie several meters above, in the covered middle Frasnian interval of the
Padberg succession. A corresponding but neglected earlier Rhenish record comes also from the Brilon Reef area, from the upper slope of the
small atoll on top of the Grottenberg Volcanoe exposed in the Beringhauser Tunnel section (see review of the section by Hartenfels et al.,
2016). Buggisch and Joachimski (2006, p. 69) documented a sharp
positive δ13C spike > 4.5‰ (Fig. 7) (but associated with many diagenetically overprinted δ13C measurements probably connected with the
secondary fluid migration) from the proximal reefal debris at the top of
the lower cliff, which they assigned to the “Upper falsiovalis Zone”
(compare sections and facies analyses in Clausen and Ziegler, 1989;
Clausen et al., 1991, and Errenst, 1993). However, Stritzke (1989, loc.
3, Niederhof section = Beringhauser Tunnel) reported the oldest Ad.
E–MF perturbation (=Event III in Pisarzowska et al., 2006, Fig. 10), in
relatively deeper-shelf (off-reef) marly facies. In the similar facies of the
nearby Radlin area (Baliński et al., 2016), Pa. punctata enters after the
maximum positive peak of this δ13C excursion (in sample PR I/6 – fig. 5
therein).
Conversely to dispersal/immigration pattern of palmatolepids
during the Middlesex and Rhinestreet sea-level rises (cf. “invasion of
pelagic species”; Racki and Bultynck, 1993, Fig. 6), the phylogenetic
succession of Ancyrodella species across the E–MF boundary is comprehensively documented in Polish sections (Pisarzowska et al., 2006)
and elsewhere (see below). The onset of the global punctata Event was
approximated with the base of the Pa. punctata Zone using of the FAD of
Ad. gigas form 1 as an alternative zonal marker (e.g. Racki and
Bultynck, 1993; Morrow et al., 2009; Izokh et al., 2015). In the Appalachian Basin, the base of the middle Frasnian has previously been
approximated with the base of the Middlesex Formation and with the
Middlesex transgressive-anoxic Event (House and Kirchgasser, 1993;
House, 2002). However, Over et al. (2003) showed that Pa. punctata
enters just above the Middlesex Shale, in the lower Cashaqua Shale,
whilst the Middlesex Shale is characterized by the FAD of Ad. gigas form
1, which was subsequently synonymized with Ad. nodosa (Klapper and
Kirchgasser, 2016). As shown in the graphic correlation chart of
Klapper (1997), the FAD of Ad. nodosa (=gigas form 1) is in the top part
of the Pa. transitans Zone (MN 4 Zone). The major δ13C excursion (Event
III) falls in the level of Ad. nodosa, which is well established in several
Polish sections (Pisarzowska et al., 2006: entry of Ad. gigas form 1). It
continues well above the entry of Pa. punctata both in Poland and in
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A. Pisarzowska, et al.
Fig. 7. Records of the early-middle Frasnian punctata/Middlesex Event from reef foreslope and hemipelagic settings: (1) present study, (2) Buggisch and Joachimski,
2006, (3) Pisarzowska and Racki (2012), (4) Morrow et al. (2009), (5) Śliwiński et al., 2011, (6) Lash (2019), (7) Becker and Aboussalam (2013), (8) Izokh et al.
(2015), (9) Ma et al. (2008), (10) Hillbun (2015), plotted against global biotic and eustatic events. Frasnian paleogeographic reconstruction after Blakey (2016). Sealevel curve compiled after Pisarzowska et al. (2006, fig. 18) and da Silva et al. (2010, fig. 8). Conodont zonation based on the Ancyrodella index species (1) revised in
these studies and (2) proposed by Racki and Bultynck (1993). Al – position of Alamo impact after Morrow et al. (2009), MS - position of the microtektite-like
spherules described by Lash (2019). TA – tectonic activation,VE – volcanic eruption, T – Timan Event, M – Middlesex Event.
1989).
At the margin of the Miette Carbonate Platform of western Alberta
(North America), marked isotopic excursions, both of δ13Ccarb and
δ13Corg, have been found in two sections (AB and K) in the transgressive
systems tract (TST) and maximum flooding interval at the base of the
lower Perdrix Formation (lower Sequence 5, Śliwiński et al., 2011).
gigas (=nodosa) from the same interval, which provides a good correlation with the Padberg and Polish isotope Event III.
For the Ardennes, there is no precise correlation of the isotopic
curve based on brachiopod shells of Yans et al. (2007) with the conodont ranges in the same general succession. However, the pramosica
and nodosa Zones are regionally well recognizable (Vandelaer et al.,
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Global and Planetary Change 191 (2020) 103211
A. Pisarzowska, et al.
Klapper and Lane (1989) showed that a fauna with Pa. transitans and
Ad. gigas form 1 may occur regionally in the basal Perdrix bed, followed
slightly higher by faunas with Pa. punctata and Po. timanicus (local Zone
2 = MN Zone 5). This suggests a precise correlation of the Perdrix base
with the Middlesex Transgression. Palmatolepis punctata enters in Section K well above the base of the Perdrix, below a second maximum of
δ13Corg and a maximum of δ13Ccarb in Section AB.
In the Great Basin of Nevada, the E–MF perturbation was recognized
in close association with the Alamo Impact Event (Alamo Breccia
Member of the Guilmette Formation, Morrow et al., 2009). Playfordia
primitiva, which enters at Padberg in the ca. middle part of the pramosica Zone, occurs just below the Alamo Breccia Member (Warme and
Sandberg, 1995). In this interval, as well as in the first impact-related
debris (Unit D), isotopic values are negative. Much more negative values (ca. -3‰), Event II, are recorded from the lower half of their Unit
C. Event III, with local δ13Ccarb values of only ca. 3‰, but with an
amplitude of the isotopic shift of 6‰, begins in the upper part of Unit C,
which is characterized by a peculiar, shallow-water pandorinellid biofacies, which cannot be correlated internationally. Since the region is
lacking Pa. punctata, the punctata Zone was instead recognized by the
occurrence of Ad. gigas (=nodosa) in the immediately overlying main
impact breccia (Unit B, Warme and Sandberg, 1995), which partly has
positive δ13Ccarb values. Therefore, the overall succession of marker
conodonts and isotopic excursions is well correlated with the Polish and
Padberg record (Fig. 7; Morrow et al., 2009; Izokh et al., Fig. 4). The
deepening episode recognized by Morrow et al. (2009) at the early M.
johnsoni level could easily correlate with the transgressive/eustatic
Timan Event (House et al., 2000; Becker et al., 2012, 2016). The subsequent Middlesex Event occurred perhaps near the base of the Alamo
Breccia Member (T-R cyles in Morrow et al., 2009, Fig. 3; see Fig. 7).
8.4. High-resolution chemostratigraphic pattern
As reviewed above, a strict similarity of our Padberg results with the
chemostratigraphic pattern of the Holy Cross Mountains, especially in
the δ13Corg time series, is noteworthy. The minor positive δ13C excursion near the top of the pramosica Zone (upper part of MN Zone 4, Event
I of the E–MF perturbation) is hardly perceptible in the studied section
and saved only in δ13Corg (Fig. 6). The amplitude of the negative δ13C
anomaly recorded at Padberg is the highest among the previously observed (Event II) in Poland (Holy Cross Mountains, Pisarzowska and
Racki, 2012), western USA (Nevada; Morrow et al., 2009), China
(Dongcun; Ma et al., 2008), and Siberia (Izokh et al., 2015). Lash
(2019) suggests that the sharp negative excursion terminating the
Middlesex/punctata Event of western New York might have been connected with the Alamo (or other still unrecognized) impact-induced
destabilization of sea-floor methane hydrates. Recent studies, e.g. on
the negative carbon isotopic excursions associated with mass excursions
show that massive volcanism (Gutjahr et al., 2017) and thermogenic
gas release (Schobben et al., 2019) have a far greater potential to release large amounts of isotopically light carbon into the atmosphere and
hydrosphere. On the other hand, however, the negative excursion in the
German section uniquely corresponds in fact to the fluid migration front
zone (characterized by a clay- and Fe-enrichment and de‑carbonated
samples; Fig. 6), where diagenetic fluids probably significantly changed
the isotopic signature.
The global major δ13C positive excursion (Event III) of the E–MF
isotopic perturbation known worldwide (see above) is well manifested
in the Padberg section (Figs. 6–7). The isotope signal (about 3‰) at
Padberg is relatively muted, when compared with the 6–8‰ shift in the
Holy Cross Mountains and Ardennes, but it is comparable with the
Appalachian signature (Fig. 7). Correlations of facies and isotopic records from Eastern Laurussia reef foreslope sections show striking similarities (Pisarzowska et al., 2006; Pisarzowska and Racki, 2012;
Fig. 7). The Frasnian Padberg Limestone was deposited on the lower
slope of a volcanic seamount south of the steep marginal slope of the
Brilon Reef. In relation to the reef margin, the Padberg facies pattern is
more distal than the reefal slope setting documented for the middle
Wietrznia Beds in the Holy Cross Mountains (Szulczewski, 1971; Vierek,
2007; Vierek and Racki, 2011; see also Baliński et al., 2016). The two
δ13C curves derived from the foreslope succession in the Rhenish Massif
show the same chemostratigraphical pattern as on the reef foreslope of
Laurussian and Chinese settings (see Fig. 7) The similarity between the
δ13C records confirms an isotopic uniformity of the dissolved inorganic
carbon (DIC) of water masses within the distant carbonate shelves.
8.3. Timing of the early-middle Frasnian isotopic perturbation in Siberian,
Chinese and Gondwanan sections
The E–MF C-isotope pattern is very different in the Rudny Altai
Mountains of southern Siberia, a shelf region that faced a different
oceanic system. Unusually high δ13Ccarb values > 5‰ characterize the
rugosa Zone (MN Zone 3; Fig. 7), followed by a two-stepped decrease to
lower positive values towards the rugosa/nodosa Zone boundary (recognizable in Izokh et al., 2015, by the onset of Ad. gigas). This interval
may partly correlate with Event II, followed by a rapid return to values
of up to 5.3‰, the probable major Event III equivalent.
In the Yangsuo Basin of Guangxi Province, South China, two E–MF
sections described by Ma et al. (2008) provided detailed carbon isotope
curves, which, unfortunately, have no bed-by-bed correlation with the
conodont record. At Dongcun, δ13Ccarb values are unusually negative
through most of the early Frasnian. Event II and the initial sharp positive rise of Event III slightly predate the entry of Pa. punctata. Ancyrodella gigas/nodosa is locally delayed. At Longmen, records of Pa.
transitans and Pa. punctata are separated by a gap in the section and of
the conodont record. There is no correlation with the earlier published
conodont succession of Wang (1994). Event II and the locally rather
gradual rise towards δ13Ccarb values > 2‰ predate the first Pa.
punctata, as everywhere.
Preliminary data from the northern margin of stable cratonic
Gondwana (southeastern Morocco, Becker and Aboussalam, 2013;
Fig. 7) yielded constantly lower δ13Ccarb values (< 2‰) in a very organic-rich styliolinite facies corresponding to the Timan/Middlesex
Event Intervals (pramosica to lower punctata Zones). Carbon isotope
data from Western Australia (Caning Basin, Hillbun, 2015) documented
positive δ13Ccarb excursion with an amplitude of 2‰ in the middle
Frasnian (within MN Zones 5–10; Fig. 7). The excursion was interpreted
by the author as the punctata Event and related to a major sea-level rise
(the Waggon Pass event) at the 5–6 MN zones boundary.
9. Implications for regional vs. global biogeochemical
perturbation
The δ13C positive excursion of about 3‰ near the early–middle
Frasnian boundary is documented for the first time in detail for a
German section. It provides not only an additional confirmation for the
global nature of the E–MF perturbation in carbon cycling, but also has
regional implications thanks to our multidisciplinary approach.
In the context of transgressive–regressive cyclicity, the Timan (base
of depophase IIb4 in Becker et al., 2012) and Middlesex (base of depophase IIc) sea-level rises (compare Johnson et al., 1985; House, 2002;
Pisarzowska and Racki, 2012) are poorly identifiable in the Padberg
fore-reef/turbidite succession, in terms of the limestone microfacies and
conodont biofacies. Only few data, such as more frequent micritic
lithologies and the entry of pelagic palmatolepids, may suggest a
deeper-water setting of exposed upper Padberg limestones. An episode
of reduced carbonate supply, associated with the Timan transgressive
pulse in the Holy Cross Mountains (Pisarzowska et al., 2006), may be
presumed for the mudstone-enriched set B but was probably not a relevant factor in the overall paleogeography of the Brilon Reef area (see
Stritzke, 1990).
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A. Pisarzowska, et al.
initial phase (set B) of the biogeochemical perturbation. Calciturbiditic
re-inputs recorded in the uppermost part of the Padberg section, on one
hand could have diluted organic mater and on the other ventilated the
sea-bottom, and re-oxidized the sediment-water interface and underlying sediments (Caillaud et al., 2020; compare Rakociński et al., 2016;
Broda et al., 2019).
Lack or trace amounts of pyrite in the studied section probably results from its oxidation into hematite during migration of diagenetic
solutions. Similar processes of hydrothermal oxidation were proposed
in the Holy Cross Mountains (Kowala section) in the middle Frasnian
limestones and shales (Marynowski et al., 2008). The processes of the
secondary fluid migration, taking place after the lithification of the
sediments, caused also partial organic matter oxidation and disguised a
record of climatic perturbation observed in the Holy Cross Mountains
(i.e., cooling trend – Pisarzowska and Racki, 2012; Baliński et al.,
2016). On the other hand, CO2-greenhouse spikes connected with
transient external perturbations to the atmosphere are confirmed,
among others, by the presence of large cladoxylopsid trees in New York
during the Middlesex Event (Retallack and Huang, 2011). According to
the authors, the reason for such abrupt climatic changes may have been
massive volcanic eruptions and/or meteorite impacts. Thus, the climatic context of Middlesex/punctata Even (i.e. cooling in marine settings vs. continental warming) may be seen as uncertain, but, perhaps,
explainable by the low resolution of marine oxygen isotope signature in
biogenic apatites (see further discussion in Racki, 2020).
Moderate Hg enrichments in set C of Padberg need a confirmation
from other regions in order to separate just regional and more widespread (terrestrial and/or submarine) signatures of volcanisms, and its
possible general participation in the global perturbation. The same
approval awaits a supposed role of extraterrestrial factors (e.g. of the
contemporaneous Alamo Impact; see discussion in Yans et al., 2007 and
Hladil et al., 2009), recently revived by Lash (2019) because of the
finding of microtektite-like spherules (see also Sim et al., 2015).
However, the microspherule horizon reported by Lash (2019) and
Hladil et al. (2009) comes from the middle part of the punctata δ13C
plateau (Fig. 7), which negates the suggested correlation with the base
of the Middlesex Event.
In the crucial interval referred herein to as the terminal early
Frasnian (=basal Middle Frasnian in Pisarzowska et al., 2006), encompassing the upper set B and lower set C, there is local evidence for
an increased input of terrigenous material. Whilst there was continuing
synsedimentary tectonic activity in the eastern Rhenish Massif associated with the final volcanic phase, which also triggered recurrent
turbidites, there is no evidence for significant Eovariscan uplift in the
region and in the critical time interval that could have led to increased
regional erosion and detrital influxes. Such block faulting events occurred only very locally in the Rhenish Massif in the Givetian (e.g.
Salamon and Königshof, 2010), Frasnian-Famennian boundary (Becker
et al., 2018), and middle Famennian (e.g. Clausen, 1972). The tectonic
events are marked by significant synsedimentary reworking and by the
shedding of coarse conglomerates, breccias, debris flows, and olistolites
over short distances. In terms of block faulting and uplift, the early−middle Frasnian was a calm period in the Rhenish Massif. There
were no clastic wedges in the outer shelf facies realm; only the reef
complexes and volcanic seamounts acted as sources for shedding carbonates (Krebs, 1979). Therefore, eustasy was rather a dominating
factor for the fluctuating basinward transport of siciliclastics, which
were derived from the distal Old Red Continent shelf in the north.
The adopted geochemical proxies permit to postulate that during
the higher parts of the early Frasnian (MN Zones 3/4, pramosica Zone),
the eastern Sauerland sea was a relatively restricted epicontinental
basin (reefs and numerous volcanic seamounts formed barriers on the
outer shelf), with mostly low oxygen conditions on the seafloor. The
oxygen-restricted conditions resulted likely from limited renewal of
deep-water in the basin but they were interrupted by the episodes of
benthic re-oxygenation associated with episodic heavy storm calcareous
turbiditic inputs.
The presence of oxygen-restricted conditions occurring around the
early−middle Frasnian boundary and during the punctata Zone was
described from the Laurussia shelf basin deposits of Poland
(Marynowski et al., 2008; Pisarzowska et al., 2014), Timan–Pechora
region (Bushnev et al., 2016), Western Canada (Śliwiński et al., 2011;
Kabanov, 2018), and Western New York State (Sageman et al., 2003;
Blood and Lash, 2018). Early Frasnian oxygen deficiency and high
productivity, leading to the mass accumulation of dacryoconarids, occurred also widely on the North African craton of Gondwana, for example in southern Morocco (part of the “Lower Kellwasser” unit of
Wendt and Belka, 1991; Upper Styliolinite of Aboussalam and Becker,
2007; Becker and Aboussalam, 2013) basin as well as in southern Algeria and Libya (Lüning et al., 2003, 2004; Mahboubi et al., 2019).
Development of anoxic and high productivity conditions is closely related to global E–MF transgression (cycle IIc of Johnson et al., 1985;
Middlesex Event, Pisarzowska et al., 2006). At Padberg, the relationships cannot be reliably documented because of extensive post-depositional alterations in the key succession level (set B). However,
elevated concentrations of micronutrients, such as Cd and P, and concurrent TOC increases correspond to transgressive pulses near the early−middle Frasnian boundary. The sea-level changes are correlated
with the accumulation of redox sensitive trace elements and the positive inorganic and organic carbon isotope excursion, well recognizable
in set C (Figs. 4–6). The input of deep, cold, nutrient-rich water masses
during the sea-level rise would have first stimulated primary productivity in the surface waters and stimulated expanded more oxygendeficient conditions in the nodosa Zone (top transitans Zone) and assumed punctata Zone, i.e., during the Middlesex/punctata Event (compare with model of Pisarzowska and Racki, 2012; Śliwiński et al., 2012;
Crasquin and Horne, 2018). Pyritized spheromorphs observed in the
Padberg limestones undoubtedly suggests a reducing sedimentary environment with available iron and sulfur. Additionaly, the absence of
benthic fauna indicates not particularly favourable conditions for
bottom colonization. Interestingly, laminated depositional fabrics, interpreted as a consequence of pelagic rain from plankton blooms from
the near-surface zone (Kremer, 2011), are recognized only in the weak
10. Conclusions and final remarks
A stable carbon isotope positive excursion of about 3‰ is documented in the basal nodosa Zone (topmost Palmatolepis transitans Zone,
top MN Zone 4) at Padberg, Rhenish Massif, as a muted record of the
worldwide early−middle Frasnian isotopic perturbation. Only the
lower part of the δ13C “plateau” occurs in the Padberg section (as
shown by the uncertain conodont datings). The German signature is
overall correlative with the chemostratigraphic pattern (Events I–III)
from the Holy Cross Mountains. The stratigraphic level of Event IV of
Pisarzowska et al. (2006), which terminated the longer-lasting positive
δ13C excursion, is certainly not exposed at Padberg.
Based on the conodont data from Padberg, in comparison with data
from the Holy Cross Mountains and New York State, the isotopic Event
III (punctata Event) occurred near the boundary between the pramosica
and nodosa Zones of the ancyrodellid succession, or near the top of the
transitans Zone (top MN Zone 4). Palmatolepis punctata enters slightly
later, within the long-lasting positive δ13C excursion interval. A critical
review of the conodont datings and carbon isotope chemostratigraphy
in all regions with a published record of the punctata Event suggests that
the same timing of δ13C events is also true for all regions of western
North America, Siberia, and South China.
In eastern North America, chemostratigraphical Event III is directly
correlated with the transgressive and hypoxic Middlesex Event, which
defines the base of the global depophase IIc sensu Johnson et al. (1985).
Corresponding correlations of Event III and transgression are also evident in western Canada (e.g. Christina Member of Waterways Formation, lower Hay River Formation), in Nevada (transgression at the base
11
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A. Pisarzowska, et al.
of the Alamo Breccia Member), in the Holy Cross Mountains, and
possibly in the Rhenish Massif. The main Alamo Impact breccia contains the Event III episode, starting in Unit C of Warme and Sandberg
(1995), and the first, possibly locally delayed (due to a unique “pandorinellid" biofacies interval in Unit C), Ad. nodosa in Unit B. Therefore,
possible long-term relationships between the isotopic event and the
regional impact destruction of a carbonate platform, as a potential
source of CO2 and CO (Kawaragi et al., 2009; Artemieva et al., 2017),
have to be re-considered (Fig. 7).
The δ13Ccarb pattern and elemental geochemical proxies are partly
biased by post-sedimentary alterations in Padberg succession.
Neverheless, enrichments in specific elements (e.g. Hg, As, Sb) observed
in Padberg section indicate volcanic activity and/or hydrothermal exhalations during the early-middle Frasnian isotopic perturbation. A
rather uncertain volcanic signal is surprising in the context of current
data on the timing of Devonian large igneous provinces (LIPs, especially
from Siberia; see summary in Ernst et al., 2020 and Racki, 2020). A
possible volcanic trigger needs a comprehensive verification for all
early and middle Frasnian anoxic events, likely corresponding to CO2/
greenhouse spikes (Retallack and Huang, 2011) and/or negative δ13C
shifts (Schobben et al., 2019).
Analogous to other Laurussian shelf settings, intensified sea water
exchange between the epeiric sea and the open waters during transgressive pulse coupled with an increase in nutrient supply to the basin
probably enhanced primary production and the development of more
oxygen-restricted conditions (see discussion in Sim et al., 2015), as
evident in the Rhenish Basin during the punctata/Middlesex Event.
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Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
Krzysztof Broda, Michał Rakociński and Michał Zatoń are acknowledged for their extensive help in field works in 2014 and 2016.
We thank Dorota Bakowska, Zuzanna Ciesielska, Beata Gebus-Czupyt
and Magdalena Radzikowska for their laboratory works. At Münster,
Davina Mathijssen processed and picked the conodont samples, Traudel
Fährenkemper assisted with the drawing of Figs. 1 and 3. The paper was
greatly improved following suggestions by David Bond, an anonymous
reviewer, and by guest editor Paul Wignall. This study was supported
by the National Science Centre in Poland research grant 2013/08/A/
ST10/00717 for G. Racki.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.gloplacha.2020.103211.
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