ORIGINAL ARTICLE

Onset of significant pelagic carbonate accumulationafter the Carnian Pluvial Event (CPE) in the western Tethys

Nereo Preto • Helmut Willems • Chiara Guaiumi •

Hildegard Westphal

Received: 15 June 2012 / Accepted: 12 October 2012 / Published online: 1 November 2012

� Springer-Verlag Berlin Heidelberg 2012

Abstract Abundant calcispheres occur in Upper Carnian

and Norian hemipelagic limestone successions of the

Southern Apennines and Sicily. They exhibit a variety of

morphologies that were investigated with optical and

scanning electron microscopy (SEM). The most common

morphology is that of a full solid sphere of radiaxial calcite

crystals, 20–22 lm in diameter on average, with or without

a minor hollow in the center. Smaller forms may be clus-

ters of sub-micron crystals, only rarely disposed as to form

a spherical test with a diameter of 10 lm or less. Larger

forms are similar to small forms (clusters or spheres of sub-

micron crystals) with an epitaxial calcite overgrowth. The

taxonomic attribution of these calcispheres is uncertain,

mostly because of their poor preservation, but a compari-

son is possible with some Mesozoic calcispheres attributed

to calcareous dinocysts. The amount of epitaxial over-

growth is variable, but in most cases much larger than the

original sphere. This prevents a significant evaluation of

the contribution of calcispheres to carbonate pelagic sedi-

mentation by point counting in thin-section. However, it

can be shown that calcispheres become abundant only after

a major climatic perturbation dated at the end of the Early

Carnian, known as the Carnian Pluvial Event (CPE). This

event involved a strong and prolonged enhancement of the

hydrological cycle, with consequent supply of excess

hydrogen carbonate to the oceans and increased seawater

alkalinity. Although calcispheres of this type are known at

least from the Middle Triassic, it is only shortly after the

CPE that they become abundant, and the first common

occurrence of calcareous nannoplankton in the western

Tethys is thus Late Carnian in age.

Keywords Calcispheres � Calcareous nannoplankton �Hemipelagic sedimentation � Triassic � Tethys

Introduction

The Late Triassic periplatform carbonates of the western

Tethys yield nannofossils, such as calcispheres and nan-

noliths, which were interpreted as early forms of calcareous

nannoplankton (e.g., Di Nocera and Scandone 1977; Jafar

1983; Janofske 1992; Bellanca et al. 1993, 1995; Preto

et al. 2012). This early nannoplankton can reach rock-

forming abundances: Bellanca et al. (1995) suggest that it

may account for as much as 80 % of the lime mudstone in

the Upper Carnian of Pizzo Mondello (Sicily).

If this is true, the periplatform carbonates of the western

Tethys witness one of the major events in the Phanerozoic

carbon cycle, i.e., the onset of a pelagic carbonate factory.

The initiation of massive carbonate production in the open

ocean was in fact identified as a revolution of ocean

chemistry, i.e., the long-term stabilization of seawater pH

and supersaturation (Ridgwell 2005).

The Mid Mesozoic Revolution of Ridgwell (2005) can be

described as the switch from an ocean in Neritan mode (Zeebe

and Westbroek 2003), i.e., an ocean in which carbonate

precipitation could only occur in shallow seas, to an ocean in

Cretan mode (Zeebe and Westbroek 2003), with calcareous

N. Preto (&) � C. Guaiumi

Department of Geosciences, University of Padova,

Via Gradenigo, 6, 35131 Padua, Italy

e-mail: nereo.preto@unipd.it

N. Preto � H. Westphal

Leibniz Center for Marine Tropical Ecology, Bremen, Germany

H. Willems

Department of Earth Sciences, University of Bremen,

Bremen, Germany

123

Facies (2013) 59:891–914

DOI 10.1007/s10347-012-0338-9

plankton contributing significantly to carbonate precipitation

in the oceans. In today’s ‘‘Cretan’’ oceans, about half of the

carbonate is precipitated by carbonate platforms in shallow

seas, the other half being produced by calcareous plankton

(Ridgwell and Zeebe 2005). On a long time scale, carbonate

precipitation must balance the alkalinity produced by the

hydrolysis of silicates in soils and supplied to the oceans by

runoff. However, before the explosion of calcareous plankton

in the Mesozoic, the area available for carbonate precipitation

(i.e., the carbonate platforms) was much less. Ridgwell’s

(2005) model predicts that because of this reason, ‘‘Neritan’’

oceans before the advent of calcareous plankton must have

had a lower pH, higher dissolved inorganic carbon (DIC), and

higher supersaturation with respect to carbonates (X) than

‘‘Cretan’’ oceans. This also involved higher sensitivity of

seawater physico-chemical parameters (pH, DIC, and X) to

environmental changes in a ‘‘Neritan’’ ocean. The pH of

today’s ‘‘Cretan’’ ocean is instead strongly buffered. It could

be said that the long-term carbon cycle, as we know it today,

began with the advent and spreading of calcareous plankton

in the oceans.

Despite their importance, however, studies on these

carbonate successions, which yield the first abundant nan-

noplankton, are scarce, and some fundamental questions

remain unanswered.

Although a taxonomy of Triassic calcareous nannofossils

exists (e.g., Bralower et al. 1991; Janofske 1992), it is

mostly based on standard preparation techniques for nan-

nofossils (smear slides), and does not include the early

calcispheres found in western Tethyan periplatform car-

bonates. Bellanca et al. (1993, 1995) best illustrated Late

Triassic calcispheres but did not provide any insight on their

taxonomic affinity besides excluding they are not nanno-

conids. Are these early calcareous nannofossils related to

coccolithophorides, or rather to Jurassic and Cretaceous

nannoliths, or—as for many other forms generically iden-

tified as ‘‘calcispheres’’—to dinoflagellates?

A second, more fundamental problem regards the mor-

phology of calcispheres with radial test structure, which are

by far the most abundant in Carnian-Norian lime mud-

stones (Bellanca et al. 1995; Preto et al. 2012). These

calcispheres have a tiny central hollow that is dispropor-

tionately small with respect to the test itself, to the point

that occasionally a calcisphere is just a tight sphere of

calcite and the central hollow is completely occluded. As

such a structure cannot accommodate soft tissue, the

question arises, how much the test of these calcispheres

was modified by burial diagenesis, e.g., by the addition of

inward and outward cement overgrowths on the original

calcisphere wall? Is the figure of 80 % carbonate from

nannofossils, suggested by Bellanca et al. (1995), accurate,

or does it include a significant proportion of diagenetically

precipitated calcite?

A third question is: when and why calcareous nanno-

fossils started to be abundant in periplatform limestones?

Furin et al. (2006) noted that the first occurrence of cal-

careous nannofossils in the Carnian roughly coincides with

the eruption of the Large Igneous Province of Wrangellia,

but did not go any further than highlighting a rough time

similarity between the two events. Gardin et al. (2012)

show that Triassic coccoliths and the common incertae

sedis nannofossil Prinsiosphaera appear much later in the

western Tethys (i.e., in the Late Norian or Rhaetian) than

previously thought.

In order to better characterize the Late Triassic peri-

platform carbonates of the western Tethys and the signifi-

cance of calcareous nannofossils in these carbonate

successions, we endeavored a study of their petrology. The

distribution of calcareous nannofossils has been assessed in

the two best-studied Carnian periplatform successions of

southern Italy, namely Pignola 2 in the Lagonegro Basin

and Pizzo Mondello in the Sicani Basin.

Geological setting

Western Tethyan periplatform carbonates were investi-

gated at two localities, representative of two sub-basins of

the Late Triassic western Tethys Ocean: Pizzo Mondello

(Sicani Basin) in central Sicily and Pignola-Abriola

(Lagonegro Basin) in the southern Apennines (Fig. 1). At

both localities, the succession is represented by decimeter-

scale beds of prevailing lime mudstones and wackestones

100 km

12° 14° 16° 18°

38°

40°

PizzoMondello

Pignola 2

Fig. 1 Geographic location of the studied sections within Italy. The

grid on the map provides geographic coordinates

892 Facies (2013) 59:891–914

123

with thin-shelled bivalves (halobiids) and calcified radi-

olarians, which contain abundant layers and nodules of

chert. Millimeter- to centimeter-scale interlayers of clay or

marlstone occur between limestone beds.

Pizzo Mondello (Sicani Mountains, Sicily) is the best

preserved, thickest ([400 m) and most continuous outcrop

of Upper Triassic periplatform carbonates known in Italy

(Bellanca et al. 1995; Muttoni et al. 2001, 2004). Burial

had a limited impact on this succession, as demonstrated by

a Conodont Alteration Index value of 1 (Mazza et al. 2010,

2012; Rigo et al. 2012a), corresponding to maximum burial

temperatures of less than 80 �C.

The succession of Pizzo Mondello is represented by

hemipelagic limestone-marl alternations where cherty

limestone beds, ca. 10–60 cm thick (occasionally thinner,

or as thick as 1 m), alternate with ca. 1 to 20-cm-thick clay

or marlstone interbeds. The present study concentrates on a

123-m-long section, which includes the proposed GSSP

(Global boundary Stratotype Section and Point) of the

Norian (Muttoni et al. 2004; Nicora et al. 2007) (Fig. 2).

This section spans from within the Tuvalian (Upper Car-

nian) to the middle Lacian (Lower Norian), based on

ammonoid, halobiid, and conodont biostratigraphy (Mazza

et al. 2010, 2012; Balini et al. 2012; Levera 2012).

The Upper Triassic hemipelagic carbonates of the

Lagonegro Basin of the southern Apennines were studied at

the ‘‘Pignola 2’’ stratigraphic section, described in Rigo

et al. (2007), along the road between the villages of Pignola

and Abriola (Potenza, Italy). Most of the succession is

made of typical nodular cherty limestones, but the section

includes a ca. 6-m-thick clay- and radiolaritic horizon that

records the Carnian Pluvial Event (Simms and Ruffell

1989; Preto et al. 2010; Dal Corso et al. 2012) in the

Lagonegro Basin. The Pignola 2 section encompasses a

stratigraphic interval from the upper Julian (Lower Car-

nian) to the Tuvalian (Upper Carnian). This age of the

section has been revised with respect to Rigo et al. (2007)

by Rigo et al. (2012a), in the light of new conodont

determinations and advances in the establishment of the

GSSP of the Norian, and is now known to be older than

Pizzo Mondello. The Color Alteration Index of conodonts

at Pignola (CAI = 1.5–2) is higher than that at Pizzo

Mondello (CAI = 1). Pignola 2 is one of very few strati-

graphic sections that encompass the Carnian Pluvial Event

in a deep-water succession, and the only one where cal-

careous nannofossils were studied so far.

Materials and methods

The lower part of the Pizzo Mondello section (Interval 2 of

Muttoni et al. 2004; Fig. 2) has been revisited and sampled

in detail (Fig. 3): a 123-m-long tract has been logged

PM 1PM 2n

PM 2r

PM 3n

PM 3r

PM 4n

PM 4r

PM 6n

PM 6r

PM 10nPM 10r

PM 11n

PM 12nPM 11r

PM 8n

PM 9n

PM 8r

PM 9r

PM 7n

PM 7r

PM 5C

AR

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NR

H.

PL.

Tuva

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B

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2010

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rom

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., 20

12

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12

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rom

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2012

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04

Th

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ork

50 m

Fig. 2 Stratigraphy of Pizzo Mondello. In the center, the stratigraphic

composite and magnetic reversal stratigraphy of Muttoni et al. (2004) is

provided. On the left, the stratigraphic intervals investigated by this and

other relevant studies cited in the text (see Fig. 3 for a detailed log). The

biostratigraphy and chronostratigraphy (on the right) is a compilation of

published results by Gullo (1996), Mazza et al. (2010) and Preto et al.

(2012). P. Gebbia Portella Gebbia Formation (see Gullo 1996; Preto et al.

2012 for description); L. 1 Lacian 1, RH Rhaetian, PL Pliensbachian

(Lower Jurassic). The Pignola 2 section of the Lagonegro Basin is older

than the base of Pizzo Mondello

Facies (2013) 59:891–914 893

123

894 Facies (2013) 59:891–914

123

bed-by-bed with centimeter precision, and about two

samples per meter have been collected. New logging has

been undertaken because logs available in the literature

(Muttoni et al. 2004; Guaiumi et al. 2007; Mazza et al.

2010) are not detailed enough for our sedimentological and

petrological study.

A total of 236 samples of limestone, marlstone, and

chert have been analyzed in terms of lithofacies. Of these

samples, 100 have been prepared as standard (30 lm thick)

thin-sections and studied with respect to microfacies. The

77 least diagenetically altered samples have been selected

for compositional analysis by means of point counting. For

each thin-section, at least 500 points have been counted,

which is considered to yield statistically significant results

(Van der Plas and Tobi 1965).

Scanning electron microscope (SEM) analyses have

been undertaken on 60 samples from Pizzo Mondello for

the study of nannofabric and crystal size distribution as

well as the morphology of calcispheres. SEM samples have

been cut perpendicular to the bedding and polished with

corundum powder (borcarbid 500 and 800). The surfaces

have been then cleaned in an ultrasonic bath and rinsed

with Millipore water, and then etched with 0.3 % (0.1 N)

hydrochloric acid for 10 to 20 s, dried, and carbon- or gold-

coated. Marlstones were found to contain no discernible

nannofossils (Preto et al. 2012) and were thus not consid-

ered for this SEM study.

A detailed log of the studied succession of the

Lagonegro Basin is available in the literature (Rigo et al.

2007, 2012a; Preto et al. 2009), ad hoc field logging was

thus not necessary.

Approximately 30 standard thin-sections were prepared

from samples of the Pignola 2 section, in the framework of

a former study (Rigo et al. 2007), which were examined for

microfacies, but were not point-counted.

Thirty-two samples from Pignola 2 (Lagonegro Basin)

have been prepared as described for the samples of Pizzo

Mondello, and studied under the SEM.

The preparation method of SEM samples was optimized

via a trial-and-error process. Initially, freshly broken

splinters of limestone were prepared. This was also the

method adopted by Di Nocera and Scandone (1977) and

Bellanca et al. (1993, 1995). However, in samples prepared

this way, crystal boundaries are hardly detected, calci-

spheres are not always visible, and their features are often

masked. Etching (Lasemi and Sandberg 1984; Munnecke

1997) was thus attempted in order to highlight crystal

boundaries, and was found to improve the visibility of the

rock texture (i.e., shape and dimension of crystals consti-

tuting the matrix of mudstones and wackestones), while not

compromising the recognition and description of calci-

spheres (Fig. 4; cf. also Munnecke and Servais 2008).

Sharp crystal terminations are sometimes lost after etching,

but those observed in the few freshly broken samples were

considered enough for a complete description of the cal-

cispheres. The reported concentration of acid and time of

etching (i.e., 0.3 % HCl for 10–20’’) represents the optimal

settings for cemented (tight) lime mudstones according to

our experience: lower concentrations and shorter times

make the recognition of crystal boundaries difficult,

whereas with longer time and higher HCl concentration

sub-micron crystals may dissolve, and the polished sur-

faces of crystals may become completely excavated instead

of remaining partially flat.

Preparations and SEM observations were carried out

contemporaneously in the same sessions for samples of the

two localities, and for samples of the lower and upper part

of the Pignola 2 section. This implies that the differences in

component abundances cannot be ascribed to differences in

the preparation (e.g., stronger or weaker etching).

Results

Field observations

The Upper Triassic periplatform limestones of Pizzo

Mondello in Sicily (Fig. 5a) are completely made of

hemipelagic cherty limestone-marl alternations but the

succession exhibits lithological variations. Muttoni et al.

(2004) noticed that chert is absent in the upper half of the

section above the Alaunian (Middle Norian), and that clay

interlayers are more abundant and thicker at the base of the

section.

The present study concentrates on a 123-m-long section

logged within the lower interval, cropping out at ‘‘La

Cava’’ (Fig. 3), which contains the proposed Carnian/No-

rian boundary (Muttoni et al. 2004; Nicora et al. 2007).

Lithological changes are present also within this part of the

section, especially in terms of proportion of fine silicic-

lastics (clay) and chert nodules and layers, in terms of bed

thickness and in terms of bed joints being plane, undulating

or nodular. Three facies associations are recognized

(Guaiumi et al. 2007), which were also reported in Mazza

et al. (2010) at different stratigraphic positions. We here

maintain the original definition of Guaiumi et al. (2007)

with minor adjustments (Fig. 3). The lower part of the

studied interval, from the base up to meter 33 (Fig. 3),

Fig. 3 Litholog of the studied interval at Pizzo Mondello. Numbers

refer to FNP samples, in part also reported by Mazza et al. (2010).

Some of the samples from Muttoni et al. (2001, 2004) are also

reported (prefix PM). Metric scale may be offset, and the boundaries

between facies associations have been cross-checked in the field and

thin-sections and have been corrected with respect to previous

publications (Guaiumi et al. 2007; Nicora et al. 2007; Mazza et al.

2010)

b

Facies (2013) 59:891–914 895

123

Fig. 3 continued

896 Facies (2013) 59:891–914

123

Fig. 4 Comparison between

freshly broken and prepared

(polished and etched) samples.

a Sample from the Lagonegro

Basin (pi 114, Upper Carnian),

etched and subsequently broken

with tongs, in order to assess the

improvement of texture

recognition with etching

preparation. Calcispheres in the

freshly broken part (1) are much

less visible than those

highlighted by etching (2).

b Polished and etched sample

from the Sicani Basin (FNP 124,

Upper Carnian-Lower Norian).

Some calcispheres are

highlighted with arrows. c Same

sample as b, but freshly broken.

Calcispheres (some highlighted

by arrows) are not always

clearly visible in this sample,

which is however one of the

best preserved of our collection

Facies (2013) 59:891–914 897

123

898 Facies (2013) 59:891–914

123

features non-nodular gray limestones with conspicuous

dark clay interlayers and scattered black chert nodules

(Fig. 5c, e). This interval is identified as facies association

A. From meter 33 to meter 74.5, limestone layers are more

nodular, chert is more abundant and pale brown colored,

and clay interlayers are thinner (facies association B).

According to Mazza et al. (2010), the Carnian/Norian

boundary should fall within this interval (Fig. 3). From

meters 74.5 to 92, limestone beds become gradually thinner

and more plane-bedded, while clay layers get thicker and

chert nodules more abundant. This interval represents a

transition from facies association B to C. In the short

interval between approximately 89 and 92 m, chert occurs

in horizons rather than nodules, and concentrations of the

thin-shelled bivalve Halobia (coquinas) are common: this

is the facies association C. Thin-shelled bivalves are typi-

cally silicified in this short interval. Higher up, facies

association B and then A are again found, and the studied

section ends at meter 123 corresponding to the base of a

submarine slump breccia (cf. Muttoni et al. 2004).

In facies associations A and B, chert nodules are typi-

cally concentrated in horizons within the limestone beds, or

adjacent to clay—marlstone interlayers. Occasionally,

large nodules occupy two successive limestone layers, and

thus cross a marlstone interlayer (Fig. 5c, d). In these

instances, ghosts of the original stratification of the marl-

stone layer are preserved in the chert nodule, the stratifi-

cation being marked by concentrations of fossils, most

commonly thin-shelled bivalves. Bedding planes and fossil

concentrations bend at the contact between marlstone and

chert (Fig. 5c–f), and allow to estimate a compaction of

marlstone layers by a factor of more than 5 after the

emplacement of chert (Fig. 5f). At the same time, lami-

nation or fossil concentrations in limestone beds do not

appear to be deflected when they are recognized also in

chert nodules, implying that no compaction occurred in

limestones after the emplacement of chert. An initial

compaction of marls before the emplacement of chert

nodules cannot be excluded.

Concentrations of flattened thin-shelled bivalves ori-

ented parallel to bedding are observed at various positions

throughout the succession but always within or besides

marlstone interbeds. When thin-shelled bivalves occur in

limestone beds, instead, they usually preserve their shape

(in particular, they preserve the original convexity of

valves) and are randomly oriented. One exception to this

rule is facies association C. In this short interval, bivalve

coquinas are common in limestones, and shells are flat-

tened, fractured, and occasionally silicified (see also

Levera 2012). This different disposition of thin-shelled

bivalves between most limestones and those of facies

association C is better observed in thin-sections.

The cherty limestones of Pignola 2 (Lagonegro Basin)

are nearly identical to those of Pizzo Mondello (Fig. 5g, h),

the main differences being the thinner layering, locally

more nodular, and the somehow darker color. Cherty

limestones of Pignola 2 are more nodular especially in the

Tuvalian (Upper Carnian) interval (Fig. 5h), above the

green-clay radiolaritic horizon (Fig. 5g). This feature was

interpreted as representing reduced net sedimentation rates

of carbonate during a slow rebound of the Carbonate

Compensation Depth (Rigo et al. 2007). Darker color may

be explained by a minor, ca. 0.2 % content of organic

matter that was thermally degraded during burial. Organic

matter became dark with heating and hued the limestones.

Graded beds of limestone breccia, grainstone and

packstone, with slightly to deeply erosive base and occa-

sionally a laminated upper part, are present at Pignola 2

and scattered throughout the Upper Triassic cherty lime-

stones of the Lagonegro Basin. These beds are readily

interpreted as calciturbidites, which are derived from

adjacent carbonate platforms and slopes. This is proved by

the presence of shallow-water bioclasts.

Microfacies

Microfacies of cherty limestones are rather monotonous

and do not vary significantly with facies associations at

Pizzo Mondello. The microfacies of typical cherty lime-

stones of the Lagonegro Basin are virtually indistinguish-

able from those of the Sicani Basin, at least with optical

microscopy.

Under the optical microscope, nearly all samples are

identified as wackestones (Fig. 6a–c). Crystals in the

limestone matrix are often too small to be resolved even at

the highest magnification. Under the SEM, the fine car-

bonate fraction appears to consist of a mixture of true

micrite crystals (\4 lm) and microsparite (5–15 lm or

larger) (Fig. 7). Micrite crystals are characterized by the

absence of pits (see Lasemi and Sandberg 1993), while

larger microspar crystals are conspicuously pitted at Pizzo

Mondello (see Lasemi and Sandberg 1984, 1993;

Fig. 5 Upper Triassic periplatform cherty limestones of the Sicani

and Lagonegro Basins in the field. a Lower part of the stratigraphic

section at ‘‘La Cava’’, Pizzo Mondello (Sicani Basin, central Sicily).

b Close-up of slightly nodular cherty limestones (upper part of facies

association A, Pizzo Mondello, at *30 m of Fig. 3). c Black chert

nodules cross-cutting a marly interlayer, Pizzo Mondello, at *17 m

of Fig. 3. d Line drawing of c, where the deflection of marly layers is

highlighted. e Black chert nodule, cross-cutting a marly interlayer,

showing internal lamination. Pizzo Mondello, at *22 m of Fig. 3.

f Close-up of e, where bedding planes are highlighted by dotted lines.

Note that the marlstone was differentially compacted to less than one-

fifth of its original thickness after the emplacement of chert. g Slightly

nodular and cherty limestones of the lower Pignola 2 section (Lower

Carnian). The dotted line marks the base of the green-clay radiolaritic

horizon. h Strongly nodular and cherty limestones of the upper

Pignola 2 section (Upper Carnian)

b

Facies (2013) 59:891–914 899

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900 Facies (2013) 59:891–914

123

Munnecke et al. 1997) (Fig. 7a–d). Upper Carnian samples

from Pignola 2 exhibit similar size distributions, but mi-

crospar crystals are less commonly pitted (Fig. 7e, f). It is

worth noting that pits are visible also in the few samples

that were not etched during preparation, although without

highlighting by etching, they are hardly spotted. This

ensures that at least some of the pits are not an artifact of

our preparation technique (i.e., of etching).

Dolomite occurs as isolated or, less commonly, as

clustered euhedral rhomboids, some tens of microns long,

randomly distributed within the limestone (Figs. 6d, 7a–d).

Such dolomite precipitated in a very early diagenetic stage

and retains a normal marine isotopic signature (Bellanca

et al. 1995). Isolated rhomboids of dolomite few tens of

microns long are also present at Pignola 2 (Fig. 7e).

Non-carbonate grains are virtually absent. Principal

grains recognized in thin-sections are thin-shelled bivalves

(attributed to Halobia spp.; see Levera 2012) (Figs. 6a, b,

7e), calcified radiolarians (Figs. 6a–c; 7a, b), and small

‘‘calcispheres’’ (Figs. 6e–j, 7). Halobiid bivalves are con-

sidered to have a bi-mineralic shell, with an inner arago-

nitic layer and an outer calcitic layer (McRoberts 2011). In

all our samples, only the outer layer is preserved. Fora-

minifers (hyaline and agglutinated), ammonoids, and other

recrystallized and fragmented mollusk shells are also

present but are much scarcer.

Calcispheres appear under the petrographic microscope

as slightly irregular rounded calcitic grains, few tens of

microns in diameter, with radial extinction pattern

(Fig. 6e–l). In some cases, calcispheres appear void, with

the central cavity either empty or filled by opaque minerals

(?pyr) (Fig. 6e, g, j). Calcispheres with a clearly open

central cavity are most common in samples of facies

associations B/C and C at Pizzo Mondello, or in the portion

of Pignola 2 immediately above the green clay-radiolaritic

horizon.

The Lower Carnian samples of Pignola 2 are different in

that they nearly completely lack any calcispheres. These

samples are essentially made up of fine (\10 lm) micro-

spar (Fig. 7e). No other calcareous nannofossils, and

specifically none of the known upper Triassic species (see

review in Gardin et al. 2012), were found associated with

these calcispheres.

Structure of calcispheres

Calcispheres were characterized morphologically via SEM,

and exhibit a variety of morphologies. This variability is, in

our view, determined by different degrees of diagenetic

alteration, as we shall discuss later. For this reason, we do

not formalize morphotypes to rationalize the variety of

forms that are observed.

The simplest type of calcisphere is made of elongated

crystals (hereafter called ‘‘rays’’), some tens of microns

long, disposed radially around a center. Rays usually

leave a small (few microns) hollow in the center of the

calcisphere, but sometimes infill completely the central

cavity (Fig. 8a, b). The external termination of rays may

either be rhombohedral (Fig. 8c, g), or may adapt to the

surrounding crystals or grains (Figs. 8a, b, 9c, d). More

rarely, rays may join with crystals that are obviously not

part of a calcisphere, as for the blocky cement that sub-

stitutes radiolarian moulds (Fig. 8d). The internal termi-

nation of rays, when preserved, is also rhombohedral

(Figs. 8e, 9f). Rays are made of pitted calcite, with pits

greatly highlighted by etching (Fig. 8d, g, i, k) but already

visible on freshly broken samples (Fig. 8f). These calci-

spheres were recognized at Pizzo Mondello also by Bel-

lanca et al. (1993), and in other Tethyan Triassic

hemipelagic carbonates by Di Nocera and Scandone

(1977).

A second group of calcispheres includes, along with

rays, small rhombohedral crystals of less than one micron

in the central cavity. Such small crystals are randomly

arranged (Figs. 8c, g–i, 9b–e) and often engulfed by rays

(Fig. 8h, i; 9e, f). Rays may be variably long, and in some

cases as short as a few microns (Figs. 8d, i, 9b, e, f).

A third group can be described, but could hardly be

classified as calcispheres. It consists of clusters, less than

10 lm in diameter, of randomly arranged small rhombo-

hedral crystals, similar to those found in the nucleus of

some proper calcispheres (Figs. 8g, j, 9a, b, f).

Finally, calcispheres made of small rhombohedral

crystals, arranged to form a small sphere of up to 10 lm

(Figs. 8k, l, 9h), were rarely observed. A few calcispheres

with similar morphology were also illustrated from Pizzo

Mondello by Bellanca et al. (1993).

The diameter of calcispheres varies between less than

10 lm and more than 40 lm with an average of 20–22 lm,

based on a representative sample of 664 calcispheres

measured on SEM images (Fig. 10). Larger diameters are

only attained by forms with rays.

Fig. 6 Microfacies and components of Upper Carnian-Lower Norian

limestones at Pizzo Mondello (Sicani Basin) in thin-sections.

Calcispheres are present in (a–c), but are not visible at this scale.

a Wackestone with calcified radiolarians (r) and thin-shelled bivalves

(b). Sample FNP 141 from 82.2 m. b Wackestone-packstone with

calcified radiolarians (r) and thin-shelled bivalves, concentrated by

mechanical compaction. Sample FNP 156 from 91.8 m. c Wackestone

with abundant calcified radiolarians; part of a chert nodule is visible

in the upper part. Sample FNP 166 from 97.8 m, cross-polarized light.

d Sparse, isolated, relatively large dolomite rhombs (d); dolomite

crystals do not usually achieve these dimensions. Sample FNP 174

from 105.5 m. e–j Examples of calcispheres, some highlighted (c).

e FNP 11, at 14.0 m; f FNP 28, at 20.2 m; g FNP 86, at 49.0 m;

h FNP 127, at 74.9 m; i FNP 130, at 76.7 m; j FNP 142, at 82.8 m

b

Facies (2013) 59:891–914 901

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Fig. 7 SEM pictures of microfacies and components of Upper

Triassic periplatform limestones of the western Tethys. Backscattered

electron images (BEI) in a and c highlight components with different

chemical composition, while secondary electron images (SEI) better

represent morphology. Insoluble minerals pop out as a result of

etching. All samples are polished and etched. a, b Sample FNP 21

from 17.5 m, Pizzo Mondello section (Sicani Basin), contains moulds

of calcified radiolarians (r), few calcispheres (c), sparse dolomite

crystals (d), and sparse, large irregular crystals of pitted microsparite

(M). c, d Sample FNP 126 from 73.9 m, Pizzo Mondello section

(Sicani Basin), with abundant calcispheres (c) in a micritic matrix

(m). Few dolomite (d) and microspar (M) crystals also occur. A bright

element in the center of the frame (p) is a cluster of pyrite crystals. In

the inlet: a clear example of a pitted microspar crystal, sample FNP 83

from 47.4 m of the Pizzo Mondello section. e Sample pi 21 from

2.5 m, Pignola 2 section (Lagonegro Basin), shows dolomite crystals

(d) and the calcitic shell of a thin-shelled bivalve (b) in a microspar

matrix. Calcispheres are virtually absent, as for all samples below the

green clay- and radiolaritic horizon. f Sample pi 117 from 15.4 m,

Pignola 2 section (Lagonegro Basin), contains abundant calcispheres

(c), the matrix still being mostly made of microspar

902 Facies (2013) 59:891–914

123

Stratigraphic distribution of calcispheres

Abundance of calcispheres throughout the study sections

was assessed qualitatively with visual estimation on SEM

images taken with a 2,000- and 3,000-fold magnification.

This estimation was carried out especially on samples from

the Pignola 2 stratigraphic section, which is representative

of the Carnian succession of the Lagonegro Basin, because

it is the only locality so far known that encompasses the

Lower Carnian–Upper Carnian transition in a deep-water

setting in Italy. Calcispheres were considered ‘‘rare’’ when

they only occur in a minority of the observed frames,

‘‘common’’ if present in nearly all fields, ‘‘abundant’’ when

all fields include more than one calcisphere. The volume of

carbonate from calcispheres could not be estimated on

SEM images, because in most cases the original test of the

calcisphere is no more visible, and only the diagenetic

epitaxial overgrowth can be seen.

Calcispheres form a significant component in most

samples analyzed with SEM, but were found to be nearly

absent in the Lower Carnian portion of Pignola 2, below

the green-clay radiolaritic horizon. Calcispheres are

already present in the lowest Upper Carnian sample of

Pignola 2 and become abundant a few centimeters above.

At Pizzo Mondello, they are abundant virtually throughout

the section. The distribution of calcispheres based on

qualitative evaluation of SEM images is reported in Fig. 11

for the Pignola 2 section.

Similar calcispheres were occasionally observed also in

deep-water carbonate sediments of Early Carnian or older

age. Besides the lower (Early Carnian) part of the Pignola 2

section, they occur in the Middle Triassic Livinallongo

Formation of the Dolomites (Preto et al. 2005, 2009) and in

the uppermost Ladinian–lowermost Carnian Stuores section

(Fig. 9g), which is the stratotype of the Carnian stage

(Broglio Loriga et al. 1999; Mietto et al. 2007, 2012).

Calcispheres were also identified in a few wackestones of

the Milieres section (Dal Corso et al. 2012, and observations

by NP), few meters above the isotopic excursion that marks

the Carnian Pluvial Event (CPE). In none of these cases,

however, calcispheres are abundant (rock-forming) com-

ponents of limestones. Finally, calcispheres were found also

in Silurian limestones of Gotland, but never reach rock-

forming abundances (Munnecke and Servais 2008).

Calcisphere abundance was also assessed with standard

point counting on a subsample of 77 thin-sections from

Pizzo Mondello, chosen among those that are less dolom-

itized or silicified. This approach, however, has limitations.

A first limitation is that point-counting of small grains such

as calcispheres, with dimensions in the order of that of the

thickness of the thin-section, is biased, because the centroid

of calcispheres may lay on different plains within the thin-

section. The thickness of the thin-section thus does not

approximate a plain, and as a consequence the abundance

of small objects is overestimated. For spheres, this bias can

be corrected. In the ideal case of a thin-section without

thickness, the result of point counting of small spheres

distributed isotropically in the rock volume would

straightforwardly yield the proportion of volume occupied

by the spheres. In a thin-section with a discrete thickness,

spheres located on different plains are all counted

(Fig. 12a), so the occurrence of a sphere under the crucible

is more probable. This equals to the counting of a

‘‘equivalent solid’’ constituted by the sphere plus a cylinder

with the diameter of the sphere, and the height coinciding

with the thickness of the thin-section (Fig. 12a). The vol-

ume of this solid is larger than that of the sphere, being

V ¼ 4=3ð Þpr3 þ pr2h

where V is the volume of the equivalent solid, r is the

radius of the calcisphere and h is the thickness of the thin-

section. The first term of the expression is the volume of

the sphere with radius r, the second term (cylinder) falls to

zero for a ideal thin-section without thickness. The bias in

point-counting of small spheres can be calculated on the

base of this expression (Fig. 12b), provided that the aver-

age radius of spheres is known. The Carnian–Norian cal-

cispheres of our study can be conveniently modeled as

spheres with average diameter of 20–22 lm (Fig. 10), thus

the proposed correction can be applied. Note that the bias

for 20-lm spheres in a standard (30 lm) thin-section is

huge; the proportion of such spheres being overestimated

by some 450 %. A strong bias should be expected each

time the proportion of small objects, with diameters up to

90 lm (Fig. 12), is evaluated via standard point-counting.

A second limitation is that diagenetic (epitaxial) over-

growth of calcite on calcispheres that occurred in variable

proportions during diagenesis cannot, most of the times, be

evaluated. Furthermore, calcispheres without an epitaxial

growth of rays are typically smaller than 10 lm and

commonly consist of disordered sub-micron crystals—

these better preserved nannofossils are invisible on a

standard thin-section. This limitation cannot be overcome

in our view. The results of point-counting are given in

Tables 1 and 2, but should not be considered reliable. The

diagenetic impact on the shape and dimension of calcip-

heres is discussed in the Sect. ‘‘Diagenetic alteration of

calcareous nannofossils’’.

Discussion

Evidences of differential diagenesis

The periplatform cherty limestones of the Lagonegro Basin

and Sicily fall in the range of limestone-marl alternations

Facies (2013) 59:891–914 903

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904 Facies (2013) 59:891–914

123

(e.g., Einsele and Ricken 1991; Westphal 2006), but in

addition they include chert. The formation of limestone-

marl alternations is a complex process that involves ara-

gonite dissolution and local reprecipitation in the form of

microcrystalline calcite (microspar) (Munnecke et al. 1997,

2001; Westphal 2006) in the marine burial diagenetic

environment (Melim et al. 1995). Aragonite is preferen-

tially dissolved at specific horizons that at the end of the

process become marly interlayers, and reprecipitates as

microspar in adjacent beds. As a consequence, marly in-

terlayers are heavily compacted, while limestone beds

remain essentially uncompacted (differential compaction).

This is the case also for the Upper Triassic cherty

limestones of the Lagonegro and Sicani basins. Differential

compaction is particularly obvious at Pizzo Mondello (Si-

cani Basin), where early formation of chert nodules froze

the process in the act: marly interlayers expand to more

than five times their present thickness when intersected by

chert (Fig. 5c–f).

Differential compaction requires that a significant por-

tion of aragonite is present in the original carbonate sedi-

ment. The source of aragonite in periplatform settings is

normally considered to be carbonate mud exported from

surrounding carbonate platforms (Munnecke et al. 1997;

Westphal and Munnecke 2003; Westphal 2006). Alterna-

tively, the aragonite necessary for the lithification of

limestones by microspar might be provided by the disso-

lution of mollusk shells (Cherns and Wright 2000; Wright

et al. 2003; Wheeley et al. 2008). Both sources were

probably available in the Lagonegro and Sicani basins.

The proximity of carbonate platforms to the Lagonegro

Basin is testified by numerous calciturbidite beds, yielding

shallow-water bioclasts, intercalated within the cherty

limestones at virtually all stratigraphic levels (e.g., Scan-

done 1967; Bazzucchi et al. 2005; Rigo et al. 2007, 2012a).

Carbonate mud could have been produced, on top of nearby

platforms, by green algae, or by the precipitation of ara-

gonite mud in the water column. This latter process has

been proposed by Riding (2006) as an explanation for some

of the anomalously abundant lime mudstones before the

Cenozoic.

Part of the aragonite, however, must derive from the

dissolution of mollusk shells. The thin-shelled bivalve

Halobia, which is considered to have a bi-mineralic shell

(see discussion in McRoberts 2011), is common throughout

both studied sections, but the aragonitic layer of the shell is

never preserved with its original mineralogy. We suggest

that it was dissolved in the marine burial environment, and

provided a significant proportion of the carbonate that

precipitated as microspar cement within limestone beds.

Many aragonitic shells of cephalopods, and perhaps of

other aragonitic mollusks, may have undergone the same

fate, as has been demonstrated for the similar Middle

Triassic facies of the Livinallongo Formation of the Dol-

omites (Preto et al. 2005).

Diagenetic alteration of calcareous nannofossils

Calcispheres are heavily modified by diagenesis, as rays

are not part of the original test of calcispheres but are rather

an epitaxial overgrowth, which often completely engulfed

the primary calcisphere. This is indicated by several fea-

tures of rays (Figs. 8, 9). Their rhombohedral terminations,

both inward and outward, indicate that rays are crystals

grown in an open space. When the external terminations of

Fig. 8 Morphological variability of Carnian-Norian calcispheres of

the western Tethys (see also Fig. 9). a Calcisphere with central cavity

occluded. Arrow points to a radial crystal that has grown adapting to

surrounding grains and crystals. Sample pi 137, polished and etched.

Upper Carnian, from 19 m of the Pignola 2 section. b Calcispheres

with central cavity partially or totally occluded. Arrow points to radial

crystal that has grown adapting to surrounding grains and crystals.

Sample pi 115, polished and etched. Upper Carnian, from 15.2 m of

the Pignola 2 section. c Calcisphere with open central cavity. Arrow

points to the rhombohedral termination of one of the rays, while other

rays adapt to the surrounding grains. Rays are pitted and sub-micron

crystals are visible in the central cavity, some engulfed by rays (cf.

f and h). Sample FNP 124, raw splinter. Upper Carnian–Lower

Norian, from 72.3 m of the Pizzo Mondello section. d Calcispheres

with rays. Rays may be some tens of microns long, clearly pitted and

accounting for most of the calcisphere (arrow 1) or may also be much

shorter (arrow 2). Other clusters of sub-micron crystals in the frame

may also be calcareous nannofossils. Arrow 1 points to rays that

merge with calcite substituting an adjacent radiolarian mould. Sample

FNP 145, polished and etched. Upper Carnian–Lower Norian, from

85 m of the Pizzo Mondello section. e Calcisphere with rays with

inward rhombohedral termination. Sample FNP 124, raw splinter.

Upper Carnian–Lower Norian, from 124 m of the Pizzo Mondello

section. f Close-up of pitted rays of a calcisphere (cf. c). Sample FNP

124, raw splinter. Upper Carnian–Lower Norian, from 72.3 m of the

Pizzo Mondello section. g Calcispere with short rays (2), occasionally

with outward rhombohedral termination (1), and clusters of sub-

micron crystals attributed to calcareous nannoplankton. Note that in

calcisphere 2, rays are pitted and engulf sub-micron crystals of the

inner cavity. Sample FNP 143, polished and etched. Upper Carnian–

Lower Norian, from 83.5 m of the Pizzo Mondello section. h Sub-

micron crystals in the central cavity of a calcisphere, engulfed by rays

with rhombohedral termination (cf. c). Sample FNP 124, raw splinter.

Upper Carnian–Lower Norian, from 72.3 m of the Pizzo Mondello

section. i Calcisphere with short (\5 lm) rays and few sub-micron

crystals in the central cavity. Sample FNP 161, polished and etched.

Upper Carnian–Lower Norian, from 94.4 m of the Pizzo Mondello

section. j Nearly spherical cluster, few microns in diameter, of sub-

micron rhombohedral crystals here interpreted as a calcareous

nannofossil. Compare with nuclei of calcispheres (c, d, g–i) and

similar clusters in g. Sample FNP 161, polished and etched. Upper

Carnian–Lower Norian, from 94.4 m of the Pizzo Mondello section.

k Calcispheres with various morphologies. A calcisphere consisting

of a spherical test of sub-micron rhombohedral crystals is visible in

the center (1), while the calcisphere on the upper left has well-

developed rays (2). Sample FNP 83, polished and etched. Upper

Carnian–Lower Norian, from 47.5 m of the Pizzo Mondello section.

l Calcispheres with sub-micron crystals producing a spherical test

(arrows). Sample FNP 149, polished and etched. Upper Carnian–

Lower Norian, from 88.2 m of the Pizzo Mondello section

b

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906 Facies (2013) 59:891–914

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rays instead adapt to surrounding grains, it implies rays

grew in a limited space during burial. This second case is

far more common than that of rhombohedral terminations,

suggesting that rays formed in the sediment after deposi-

tion, rather than around the test of the calcisphere in the

water column.

Rays are pitted, and this can be explained by the

incorporation of metastable grains (e.g., particles of ara-

gonite mud) that dissolved later during burial (e.g., Mun-

necke et al. 1997; Westphal 2006). Pits on rays also suggest

that they formed during burial within the sediment, rather

than being part of the original calcisphere.

When sub-micron crystals are visible in the central

cavity, they are partly engulfed by rays (e.g., Figs. 8h, 9c,

d). This implies that rays formed after the sub-micron

crystals, and partially grew inward toward the center of the

calcisphere. Completion of the inward growth of rays may

occlude the central cavity completely and hide the sub-

micron crystals of the original calcisphere test.

If rays are interpreted as a diagenetic overgrowth formed

during burial, than the morphological variability of calci-

spheres can be explained with various degrees of diage-

netic alteration (overgrowth). Calcispheres with rays are

overgrown, and their diameter depends on how much

alkalinity was available for the precipitation of calcite as

rays, and on how much free space was available in the

sediment around the original calcisphere test. The rare

calcispheres without rays, 10 lm or less in diameter, are

those that were not overgrown and the clusters of sub-

micron crystals are interpreted as non-overgrown and col-

lapsed calcispheres. A possible diagenetic evolution of

calcispheres is proposed in Fig. 13.

Why rays formed, it is unclear. We hypothesize that rays

around calcispheres may be viewed as a type of carbonate

concretion, formed contextually to the degradation of soft

tissues of the calcisphere cell, during early burial. In such a

diagenetic environment, degradation of organic matter may

occur under anoxic conditions mostly by bacterial sulphate

reduction, which releases bicarbonate (HCO3-) and

hydrogen sulfide (H2S) as by-products. Bicarbonate con-

tributes alkalinity to the pore water surrounding the calci-

sphere and promotes precipitation of calcite, while

hydrogen sulfide may combine with iron to form the pyrite

that we occasionally observed at the nucleus of

calcispheres.

The diagenetic alteration of calcispheres, in the form of

epitaxial formation of rays, is irregular and pervasive to the

point that the contribution of calcipsheres to the carbonate

sediment budget cannot be quantified. Calcite overgrowths

around the original calcisphere tests are extremely irregu-

lar. In many cases, rays constitute most of the calcisphere

(Figs. 8a–f, 9c, d, g) but in other cases rays are minimally

developed or absent. The full range of variability in over-

growth can be observed within the same sample (Fig. 9a).

It is thus impossible to evaluate what proportion of car-

bonate in a calcisphere belongs to the overgrowth with

respect to the original test. Furthermore, the sub-micron

crystals that constitute the original test are in most cases

not visible (Figs. 8a, b, d, e, 9g), either because they were

obliterated by diagenesis or because they are completely

engulfed by rays. In these cases, it is impossible to evaluate

how much carbonate was contributed to the sediment by

the nannofossil.

Calcispheres may be calcareous dinocysts

The calcispheres of Pizzo Mondello were initially com-

pared with Cretaceous nannoconids, but their affinity with

Cretaceous nannoliths was readily excluded (Bellanca et al.

1993). Another straightforward comparison could be with a

common Triassic spherical ‘‘nannolith’’, i.e., Prinsiosph-

aera. However, The inner part of Prinsiosphaera is made

up of piles of calcitic, micron-scale plates that are resistant

to diagenetic alteration, as discussed by Bralower et al.

(1991) and Gardin et al. (2012) and confirmed by our

observations (Preto et al. 2012). Calcispheres of the type

described here and Prinsiosphaera were found together in a

few samples from a younger series in the Lagonegro Basin.

Fig. 9 Morphological variability of Carnian-Norian calcispheres of

the western Tethys (see also Fig. 8). a Calcisphere, the rays of which

are minimally developed (1), and one with well-developed rays with

compromise boundaries with the surrounding sediment (2). The

development of rays thus is variable within each sample. Sample pi

114, polished and etched. Upper Carnian, from 15.1 m of the Pignola

2 section. b Four calcispheres (arrows), mostly consisting of irregular

aggregates of sub-micron crystals. Only one calcisphere (1) shows

minimally developed rays. Sample FNP 161, polished and etched.

Lower Norian, from 94.3 m of the Pizzo Mondello section. c, d Two

calcispheres with well-developed rays. The calcispheres were so close

that rays of one calcisphere grew against those of the other resulting

in the development of compromise boundaries (arrow in c). Sample

FNP 124, raw splinter. Upper Carnian–Lower Norian, from 124 m of

the Pizzo Mondello section. e Three calcispheres with short rays. As

in c and d, calcispheres were close enough that rays developed

reciprocal compromise boundaries. Sample FNP 124, polished and

etched. Upper Carnian–Lower Norian, m 124 of the Pizzo Mondello

section. f Calcisphere consisting of a cluster of sub-micron crystals,

with only minimally developed rays (1). Some rhombohedrons of

calcite which engulf sub-micron crystals (2) are interpreted as the

initial stage of ray growth. Sample FNP 124, raw splinter. Upper

Carnian–Lower Norian, m 124 of the Pizzo Mondello section.

g Calcisphere from the Stuores Wiesen section, lowermost Carnian,

Central Dolomites, northern Italy. Rare calcispheres similar to those

of the Lagonegro and Sicani basins have been reported from the

Middle and Upper Triassic of the Dolomites (cf. Preto et al. 2009).

h Nearly spherical aggregate of sub-micron crystals, interpreted as a

pristine calcisphere. Clusters of sub-micro crystals (as in a, b, and

f) may be interpreted as calcispheres like this one that collapsed

before burial, or later under lithostatic pressure. Sample FNP 124, raw

splinter. Upper Carnian–Lower Norian, m 124 of the Pizzo Mondello

section

b

Facies (2013) 59:891–914 907

123

In these samples, Prinsiosphaera retains all typical char-

acters of the genus while the associated calcispheres are

affected by the strong diagenetic alteration described in this

paper. Thus we exclude that these calcispheres are taxo-

nomically related to Prinsiosphaera.

The taxonomic attribution of Late Triassic calcispheres

from western Tethys is severely hampered by diagenetic

alteration. The large majority of calcispheres do not show

any parts of the original test, that was supposedly made of

sub-micron crystals, and in those that do, the calcisphere is

apparently collapsed. Spherical hollow tests made of sub-

micron crystals were only rarely observed (Figs. 8k, l, 9h).

For those best preserved calcispheres, a comparison may be

possible with other Mesozoic calcispheres that were

doubtfully attributed to calcareous dinocysts (Keupp 1978).

Similarities exist also with Silurian incertae sedis ‘‘nann-

ospheres’’ (Munnecke and Servais 2008).

More specifically, these Late Triassic calcispheres may

be close to some simple-walled calcispheres of the

‘‘Pithonella’’ group (Bolli 1974), and specifically to those

characterized by orientation of crystals perpendicular to the

test wall and lacking a paratabulation. Some forms of this

group are spherical and exhibit a single-layered wall of

crystals with distal rhombohedral termination (e.g., Pitho-

nella loeblichi in Bolli 1974; Keupp 1981; Pithonella

megalithica in Keupp 1981). Silurian specimens in Mun-

necke and Servais (2008) were also compared with these

Mesozoic calcispheres. Our specimens, as well as those

from the Silurian, do not show an aperture.

Also comparable to Late Triassic calcispheres of the

western Tethys are simply-walled forms made of cobble-

stone-arranged sub-micron rhombohedral crystals

described from the Jurassic of Germany by Keupp (1977,

1978). Calcispheres of this type, with a diameter of 10 lm

or less, were found in the Upper Jurassic Solnhofen litho-

graphic limestones (Keupp 1977, pls. 25, 26) and are most

similar to our specimens. The cobblestone wall structure

was illustrated by Keupp (1978) for Pithonella tithonica of

the Upper Jurassic of western Germany: this species has

been interpreted as a calcareous dinocyst.

Similarities with calcispheres of the ‘‘Pithonella’’ group

can also be drawn in terms of typical diagenetic alteration.

According to Bolli (1980), it is sometimes difficult to

determine whether recrystallization or replacement of the

original wall structure has taken place in these calcispheres.

However, it could be argued that a typical modification is

the epitaxial overgrowth of calcite crystals with rhombo-

hedral terminations. Keupp (1981) illustrates a continuum

of morphologies from Pithonella loeblichi, with small

crystals, to Pithonella megalithica, a distinctive form with

few very large rhombohedrons forming the wall. This could

be interpreted as an increasing influence of diagenetic

overgrowth of calcite on an originally thin wall. Also the

well formed, often isolated rhombohedral crystals forming

the inner layer of calcispheres such as Pithonella cf. spha-

erica (Bolli 1978, pl. 5, figs. 9-12) may be interpreted as

inward syntaxial overgrowths. Keupp (1992) illustrates a

specimen of Obliquipithonella loeblichii (a later synonym

of Pithonella loeblichi), in which the distal portion of the

wall is overgrown by a mosaic of calcite crystals with

rhombohedral termination. Similarly to the rays of Late

Triassic calcispheres of the western Tethys illustrated in this

paper, the overgrowth of Obliquipithonella loeblichii adapts

to grains of the surrounding sediment.

The main difference between Late Triassic and younger

calcispheres are probably the dimensions: Triassic calci-

spheres without overgrowth are 10 lm or less in diameter,

while Cretaceous calcispheres of the ‘‘Pithonella’’ group

may attain dimensions of over 100 lm. However, the

simple forms illustrated by Keupp (1977) also range in

diameter around 10 lm.

Summarizing, the Late Triassic calcispheres of southern

Italy are comparable only with Mesozoic calcispheres of the

‘‘Pithonella’’ group, usually attributed to dinoflagellates.

The morphology of our Late Triassic specimens is, how-

ever, not defined enough to allow firm taxonomic attribu-

tion. In particular, the impossibility to observe apertures and

the unusually small dimensions still prevent a satisfactory

comparison with Mesozoic calcareous dinocysts.

Calcareous nannoplankton becomes abundant

after the CPE

Calcispheres are abundant throughout the studied Upper

Carnian to Norian interval at Pizzo Mondello (cf. Bellanca

10 15 20 25 30 35 40 450

10

20

30

40

50

60

70

Diameter (τ m)

Freq

uenc

y

N = 66430 bins

μ

Fig. 10 Distribution of the diameters for 664 calcispheres from the

Upper Carnian to Lower Norian of Pizzo Mondello (Sicani Basin).

Small diameters below 10 lm are those of calcispheres without or

with minimally developed rays

908 Facies (2013) 59:891–914

123

et al. 1993, 1995; Guaiumi et al. 2007) and in the Upper

Carnian portion of Pignola 2, above the green-clay radi-

olaritic horizon that is the expression of the CPE in the

Lagonegro Basin (Rigo et al. 2007). Below the green-clay

radiolaritic horizon, in contrast, calcispheres are virtually

absent. This is in agreement with observations in hemi-

pelagic successions of the Dolomites where calcispheres

were only occasionally found (e.g., Fig. 9g and Preto et al.

2009).

Whether these calcareous nannofossils were produced

by dinoflagellates or by any other organisms, it appears that

they started to be a significant component of carbonate

sediments only after the CPE.

In order to evaluate the flux of carbonate sediment

contributed by calcispheres, sedimentation rates should be

known. Furthermore, a quantitative estimation of the

volume of calcispheres should be performed. We have

shown that this quantitative estimation is at present not

possible. An estimation of the sedimentation rate exists

for Pizzo Mondello (Muttoni et al. 2004) which is based

on the magnetostratigraphic correlation with the Astro-

nomically Tuned Polarity Scale of the Newark Basin.

Depending on the preferred correlation, the net sedimen-

tation rates are estimated to vary between 14 and 43 m/

Myr. Muttoni et al. (2004) favored a correlation that

implies a net sedimentation rate of 20–30 m/Myr. Calci-

spheres are abundant in many of the samples from Pizzo

Mondello, and the estimated net sedimentation rates are

typical for hemipelagic carbonate deep-water depositional

systems. Thus, although carbonate fluxes could not be

calculated, it can be at least excluded that high calci-

sphere abundances are determined by condensed

sedimentation.

Furin et al. (2006) suggested that the biotic radiation that

is observed after the CPE could have been a response to an

extinction that liberated ecological niches. The recent

Fig. 11 Distribution of calcispheres in the Pignola 2 section,

estimated from SEM images. Conodonts from Rigo et al. (2007),

amended as in Rigo et al. (2012a); palynomorphs from Rigo et al.

(2007); radiometric dates (TIMS U/Pb on zircons) from Furin et al.

(2006). Absent: calcispheres were not observed (e.g., sample pi 56

from m 8.2, below); rare: calcispheres only occur in rare frames

(about three calcispheres on a surface of ca. 0.5 9 0.5 cm); common:

calcispheres usually observed in each frame; abundant: many

calcispheres are observed in each frame (e.g., sample pi 110 from

14.3 m, above)

Facies (2013) 59:891–914 909

123

discovery of a significant shift of carbon isotopes coeval to

the CPE (Dal Corso et al. 2012) gave further strength to the

idea that this episode of climate change is related to the

eruption of a Large Igneous Province (Furin et al. 2006).

This would place the CPE among those events that were

caused by exceptional volcanic emissions, such as the end-

Permian, Triassic/Jurassic, and perhaps the Cretaceous/

Paleogene mass extinctions, as well as many Jurassic and

Cretaceous Oceanic Anoxic Events (Wignall 2001).

The main effect of the CPE on sedimentary systems was

a crisis of carbonate systems, that is clearly seen in shal-

low-water settings (Preto and Hinnov 2003; Keim et al.

2006) and is reflected in deep-water settings as reduced

carbonate accumulation rates (Rigo et al. 2007; Lukeneder

et al. 2012). Associated to this, a strong supply of silicic-

lastics is observed throughout the western Tethys and in the

Germanic Basin (Simms and Ruffell 1989, 1990; Kozur

and Bachmann 2010; Preto et al. 2010), explained by Dal

Corso et al. (2012) with an acceleration of the hydrological

cycle. Siliciclastic supply occurred in multiple phases

(Hornung et al. 2007; Breda et al. 2009; Roghi et al. 2010),

suggesting that the enhancement of the hydrological cycle

hypothesized by Dal Corso et al. (2012) was a prolonged

phenomenon, or at least occurred in many episodes within

the Early to Late Carnian transition. A ca. 1.5 % shift in

the oxygen isotope composition of biogenic apatite may

suggest a global warming episode (Hornung et al. 2007;

Rigo and Joachimski 2010; Rigo et al. 2012b). This sce-

nario is similar, although probably on a lesser scale, to that

of the end-Permian mass extinction and subsequent Early

Triassic ‘‘delayed recovery’’. During and after the end-

Permian event (P/T), the nearly complete demise of

5 10 15 20 25 30 35 40 45 5010

15

20

25

35

40

45Volume bias

(%, in excess)

Thickness of thin-section (μ

μ

m)

Rad

ius

of th

e sp

here

(m

)

Ultrathin-section,Erba and Tremolada, 2004

Standardthin-section

1010

2525

25

50

50

5010

0

100

100

200

200

200

500

View on a microscope

Ideal case (no thickness)

Ultrathin-section

Standard thin-section

Equivalent solid

View on a microscope

30 μ m

8 m

a b

μ

Fig. 12 Illustration of bias in point-counting of small objects

(spheres in this case) and its correction. a Bias in counting spheres

with a radius of 30 lm, for a ideal thin-section of no thickness, for a

ultra-thin-section of 8 lm (Erba and Tremolada 2004), and for a

standard thin-section of 30 lm. A sphere is seen with its full

diameter, under the microscope, when its centroid is within the

thickness of the thin-section. In the ideal case of a thin-section with

no thickness, the case of a great circle lying on the plane of the thin-

section is a degenerate one. In this case, the point-counting of small

spheres yields a accurate estimate of the proportion of rock volume

they occupy. Point-counting spheres in a thin-section with some

thickness (i.e., any real thin-section) is equivalent to point-counting

‘‘equivalent solids’’ (on the right) in an ideal thin-section with no

thickness. This implies that the volume of small spheres is overes-

timated. b Bias, as a function of the thickness of the thin-section and

of the radius of the spheres. Given a standard thin-section and spheres

with a diameter of 60 lm, (the case illustrated in a), the volume

occupied by spheres is overestimated by more than twice (150 %).

Spheres with smaller diameter (as in the case of this study) imply a

much larger bias

Table 1 Relative abundances (in %) of components in carbonate facies of Pizzo Mondello

Matrix Calcispheres T.S. Bivalves Radiolarians Forams Ammonites Undeterm. N (mean)

F.A. A 46.38 13.39 7.48 25.70 0.18 0.02 5.98 672

F.A. B 40.53 16.00 6.83 29.51 0.22 0.05 6.86 676

F.A. B/C, C 34.57 28.96 6.85 24.35 0.17 0.02 5.08 675

All section* 43.41 18.32 6.98 25.27 0.19 0.03 5.81 672

These figures are obtained as an average of thin-section point-counts, weighted for the number of points counted in each thin-section. The

averages relative to the whole section (last row, *) include some thin-sections from outside of the measured interval, above the breccia level,

attributed to facies association A. Last column gives the average number of points counted in each thin-section per each of the intervals

910 Facies (2013) 59:891–914

123

skeletal carbonate producers (Payne and Clapham 2012)

along with the accelerated supply of bicarbonate from

enhanced chemical weathering on continents (Algeo and

Twitchett 2010) led carbonate species to accumulate in

seawater, eventually promoting the microbial and abiotic

precipitation of carbonate (e.g., Baud et al. 2007).

Enhanced hydrological cycle and microbial-abiotic car-

bonate precipitation (so-called anachronistic facies)

occurred repeatedly during the Early Triassic (Pruss et al.

2006; Baud et al. 2007).

Similarly, at the onset of the CPE an accelerated supply

of bicarbonate from rivers, coupled with the compromised

capability of shallow-water carbonate systems to seques-

trate the carbon in excess by precipitating calcium car-

bonate (Simms and Ruffell 1989; Keim et al. 2006; Preto

and Hinnov 2003; Preto et al. 2010), may have temporarily

increased seawater alkalinity and supersaturation with

respect to carbonate minerals. This could have facilitated

precipitation of carbonate from pelagic organisms in the

open ocean, and may have triggered a significant

calcification of nannoplankton for the first time. Whatever

organisms were responsible for the production of the cal-

cispheres found in periplatform limestones of the western

Tethys, they seem to have retained the ability to produce

carbonate tests or cysts for tens of millions of years,

throughout the rest of the Late Triassic, and probably

beyond.

Conclusions

In this work, we studied the petrology of Upper Triassic

periplatform fine carbonates at two selected stratigraphic

sections of the western Tethys, located in separated sub-

basins, which bear the oldest record of abundant calcareous

nannofossils. These nannofossils can be described as cal-

cispheres, usually smaller than 10 lm and composed by

rhombohedral sub-micron elements, similar to some

Mesozoic calcispheres interpreted as calcareous dinocysts.

Calcispheres are almost invariably affected by a strong

Table 2 Relative abundances (in %) of components in carbonate facies of Pizzo Mondello, after correction for the volume of calcispheres (for a

average diameter of 20 lm and thin-section thickness of 30 lm, see Fig. 12)

Matrix Calcispheres T.S. Bivalves Radiolarians Forams Ammon. Undeterm. N, mean

F.A. A 52.31 2.43 8.44 28.98 0.20 0.02 6.74 672

F.A. B 46.85 2.91 7.89 34.11 0.25 0.06 7.93 676

F.A. B/C, C 46.10 5.27 9.13 32.47 0.23 0.03 6.77 675

All section * 51.38 3.33 8.26 29.91 0.22 0.04 6.88 672

Correction implies a significant (550 %) reduction of the volume of calcispheres; the residual volume was distributed proportionally between

other components. Results of point-counting before correction are given in Table 1

a b c d

Fig. 13 Model of the diagenetic alteration of calcispheres and

generation of the different morphologies observed in the Carnian to

Lower Norian samples of this study. a hollow sphere made of sub-

micron crystals, rarely observed and usually less than 10 lm in

diameter (e.g., Fig. 8k, l). b Collapsed calcisphere with no overgrowth

(e.g., Fig. 8j). c Calcispheres with remnants of the original sub-micron

crystals, and diagenetic epitaxial overgrowth (e.g., Figs. 8g–i, 9c, d).

d Calcispheres without the original sub-micron crystals (e.g., Fig. 8a,

e). Original sub-micron crystals are represented in gray, while

diagenetic overgrowth is represented in white

Facies (2013) 59:891–914 911

123

diagenetic overprint, consisting of an epitaxial overgrowth

of calcite that commonly masks completely the original

structure of the calcisphere test.

Because of this diagenetic overprint, the contribution of

calcispheres to carbonate sedimentation in this periplat-

form environment cannot be confidently quantified. It is

possible, however, to date the first common occurrence of

calcareous nannoplankton to the base of the Upper Carnian

in the Lagonegro Basin. The expansion of calcareous

nannoplankton thus immediately follows the CPE, the

expression of which in the periplatform environments was

a temporary halt of carbonate accumulation. We suggest

that increased chemical weathering on continents, along

with a transient diminished sequestration of carbonate

species due to a crisis of carbonate platforms, induced a

rise of alkalinity in the open ocean which triggered the

precipitation of carbonate by pelagic organisms.

Acknowledgments Evelyn Kustatscher, Manuel Rigo, Elisabetta

Erba, and an anonymous referee read, and commented on, this

manuscript at various stages of its development. Pietro Di Stefano

introduced us to the Pizzo Mondello section. Petra Witte helped with

scanning electron microscopy. Manuel Rigo was of great help in the

selection of samples. Leonardo Tauro and Sebastian Flotow collab-

orated with preparation of samples for SEM and thin-sections. Axel

Munnecke is thanked for digging out some old literature that would

have been otherwise impossible to find. Finally, Christopher McRo-

berts provided insightful help on the shell structure of halobiid

bivalves. This research was funded by the Alexander von Humboldt

Foundation.

References

Algeo TJ, Twitchett RJ (2010) Anomalous Early Triassic sediment

fluxes due to elevated weathering and their biological conse-

quences. Geology 38:1023–1026

Balini M, Krystyn L, Levera M, Tripodo A (2012) Late Carnian-Early

Norian ammonoids from the GSSP candidate section Pizzo

Mondello (Sicani Mountains, Sicily). Riv Ital Paleont Stratigr

118:47–84

Baud A, Richoz S, Pruss S (2007) The lower Triassic anachronistic

carbonate facies in space and time. Global Planet Change 55:81–89

Bazzucchi P, Bertinelli A, Ciarapica G, Marcucci M, Passeri L, Rigo

M, Roghi G (2005) The Late Triassic–Jurassic stratigraphic

succession of Pignola (Lagonegro-Molise Basin, Southern

Apennines, Italy. Boll Soc Geol Ital 124:143–153

Bellanca A, Di Stefano E, Di Stefano P, Erba E, Neri R, Pirini

Radrizzani C (1993) Ritrovamento di ‘‘Calcisfere’’ e nannofos-

sili calcarei in terreni carnici della Sicilia. Paleopelagos 3:91–96

Bellanca A, Di Stefano P, Neri R (1995) Sedimentology and isotope

geochemistry of Carnian deep-water marl/limestone deposits

from the Sicani Mountains, Sicily: environmental implications

and evidence from planktonic source of lime mud. Palaeogeogr

Palaeoclimat Palaeoecol 114:111–129

Bolli HM (1974) Jurassic and Cretaceous Calcisphaerulidae from DSDP

leg 27, Eastern Indian Ocean. Initial Rep Deep Sea 27:83–91

Bolli HM (1978) Cretaceous and Paleogene Calcisphaerulidae from

DSDP Leg 40, Southeastern Atlantic. Initial Rep Deep Sea

40:819–838

Bolli HM (1980) Calcisphaerulidae and Calpionellidae from the

Upper Jurassic and Lower Cretaceous of DSDP Hole 416A,

Moroccan Basin. Initial Rep Deep Sea 50:525–543

Bralower TJ, Bown PR, Siesser WG (1991) Significance of Upper

Triassic nannofossils from the Southern Hemisphere (ODP Leg 122,

Wombat Plateau, N.W. Australia). Mar Micropaleont 17:119–154

Breda A, Preto N, Roghi G, Furin S, Meneguolo R, Ragazzi E, Fedele

P, Gianolla P (2009) The Carnian Pluvial Event in the Tofane

area (Cortina d’Ampezzo, Dolomites, Italy). GeoAlp 6:80–115

Broglio Loriga C, Cirilli S, De Zanche V, di Bari D, Gianolla P, Laghi

MF, Lowrie W, Manfrin S, Mastandrea A, Mietto P, Muttoni C,

Neri C, Posenato C, Rechichi MC, Rettori R, Roghi G (1999)

The Prati di Stuores/Stuores Wiesen Section (Dolomites, Italy): a

candidate Global Stratotype Section and Point for the base of the

Carnian stage. Riv Ital Paleont Stratigr 105:37–78

Cherns L, Wright VP (2000) Missing molluscs as evidence of large-

scale, early skeletal aragonite dissolution in a Silurian sea.

Geology 28:791–794

Dal Corso J, Mietto P, Newton R, Pancost R, Preto N, Roghi G,

Wignall P (2012) Discovery of a major negative d13C spike in

the Carnian (Late Triassic) linked to the eruption of Wrangellia

flood basalts. Geology 40:79–82

Di Nocera S, Scandone P (1977) Triassic nannoplankton limestones

of deep basin origin in the central Mediterranean region.

Palaeogeogr Palaeoclimat Palaeoecol 21:101–111

Einsele G, Ricken W (1991) Limestone–marl alternations–an over-

view. In: Einsele G, Ricken W, Seilacher A (eds) Cycles and

events in stratigraphy. Springer, Berlin, pp 23–47

Erba E, Tremolada F (2004) Nannofossil carbonate fluxes during the

Early Cretaceous: phytoplankton response to nitrification epi-

sodes, atmospheric CO2, and anoxia. Paleoceanography

19:PA1008 1–18

Furin S, Preto N, Rigo M, Roghi G, Gianolla P, Crowley JL, Bowring

SA (2006) A high-precision U/Pb zircon age from the Triassic of

Italy—implication for the Carnian origin of calcareous nanno-

plankton and dinosaurs. Geology 34:1009–1012

Gardin S, Krystyn L, Richoz S, Bartolini A, Galbrun B (2012) Where

and when the earliest coccolithophores? Lethaia 45:507–523

Guaiumi C, Nicora A, Preto N, Rigo M, Balini M, Di Stefano P, Gullo

M, Levera M, Mazza M, Muttoni G (2007) New biostratigraphic

data around the Carnian/Norian boundary from the Pizzo

Mondello Section, Sicani Mountains, Sicily. In: Lucas SG,

Spielmann JA (eds) The global Triassic. New Mex Mus Nat Hist

Sci Bull 41:40–42

Gullo M (1996) Conodont biostratigraphy of uppermost Triassic

deep-water calcilutites from Pizzo Mondello (Sicani Mountains):

evidence for Rhaetian pelagites in Sicily. Palaeogeogr Palaeo-

climatol Palaeoecol 126:309–323

Hornung T, Brandner R, Krystyn L, Joachimski M, Keim L (2007)

Multistratigraphic constraints on the NW Tethyan ‘‘Carnian

crisis’’. In: Lucas SG, Spielmann JA (eds) The global Triassic.

New Mex Mus Nat Hist Sci Bull 41:59–67

Jafar SA (1983) Significance of Late Triassic calcareous nannoplank-

ton from Austria and Southern Germany. N Jb Geol Palaont Abh

166:218–259

Janofske D (1992) Calcareous nannofossils of the Alpine Upper

Triassic. In: Hamrsmid B, Young JR, Nannoplankton Res

1:87–109

Keim L, Spotl C, Brandner R (2006) The aftermath of the Carnian

carbonate platform demise: a basinal perspective (Dolomites,

Southern Alps). Sedimentology 53:361–386

Keupp H (1977) Ultrafazies und Genese der Solnhofener Plat-

tenkalke. Abh Naturhist Ges Nurnberg 37:1–128

Keupp H (1978) Calcisphaeren des Untertithon der Sudlichen

Frankenalb und die systematische Stellung von Pithonella

Lorenz 1901. N Jrb Geol Palaont Mh 1978:87–98

912 Facies (2013) 59:891–914

123

Keupp H (1981) Die kalkigen Dinoflagellates-Zysten der borealen

Unter-Kreide (Unter-Hauterivian bis Unter-Albium). Facies

5:1–190

Keupp H (1992) Calcareous dinoflagellate cysts from the Lower

Cretaceous of hole 761C, Wombat Plateau, eastern Indian

Ocean. Proc Ocean Drill Progr Sci Results 122:497–509

Kozur HW, Bachmann GH (2010) The middle Carnian wet

intermezzo of the Stuttgart Formation (Schilfsandstein), Ger-

manic Basin. Palaeogeogr Palaeoclimat Palaeoecol 290:107–119

Lasemi Z, Sandberg PA (1984) Transformation of aragonite-domi-

nated lime muds to microcrystalline limestones. Geology

12:420–423

Lasemi Z, Sandberg PA (1993) Microfabric and composition clues to

dominant mud mineralogy of micrite precursors. In: Rezak R,

Lavoie DL (eds) Carbonate microfabrics. Springer, New York,

pp 173–185

Levera M (2012) The halobiids from the Norian GSSP candidate

section of Pizzo Mondello (western Sicily, Italy): systematics

and correlations. Riv Ital Paleont Stratigr 118:3–45

Lukeneder S, Lukeneder A, Harzhauser M, Islamoglu Y, Krystyn L,

Lein R (2012) A delayed carbonate factory breakdown during

the Tethyan-wide Carnian Pluvial Episode along the Cimmerian

terranes (Taurus, Turkey). Facies 58:279–296

Mazza M, Furin S, Spotl C, Rigo M (2010) Generic turnovers of

Carnian/Norian conodonts: climatic control or competition?

Palaeogeogr Palaeoclimatol Palaeoecol 290:120–137

Mazza M, Rigo M, Gullo M (2012) Taxonomy and biostratigraphic

record Upper Triassic conodonts of the Pizzo Mondello section

(Western Sicily, Italy), GSSP candidate for the base of the

Norian. Riv Ital Paleont Stratigr 118:85–130

McRoberts CA (2011) Late Triassic Bivalvia (chiefly Halobiidae and

Monotidae) from the Pardonet Formation Willisston Lake area,

northeastern British Columbia, Canada. J Paleont 85:613–664

Melim LA, Swart PK, Maliva RG (1995) Meteoric-like fabrics

forming in marine waters: implications for the use of petrogra-

phy to identify diagenetic environments. Geology 23:755–758

Mietto P, Andreetta R, Broglio Loriga C, Buratti N, Cirilli S, De

Zanche V, Furin S, Gianolla P, Manfrin S, Muttoni G, Neri C,

Nicora A, Posenato R, Preto N, Rigo M, Roghi G, Spotl C (2007)

A candidate of the global boundary stratotype section and point

for the base of the Carnian Stage (Upper Triassic): GSSP at the

base of the canadensis Subzone (FAD of Daxatina) in the Prati di

Stuores/Stuores Wiesen section (Southern Alps, NE Italy).

Albertiana 36:78–97

Mietto P, Manfrin S, Preto N, Rigo M, Roghi G, Gianolla P, Posenato

R, Muttoni G, Nicora A, Buratti N, Cirilli S, Spotl C (2012) The

global boundary stratotype section and point (GSSP) of the

Carnian stage (Late Triassic) at Prati di Stuores/Stuores Wiesen

section (Southern Alps, NE Italy). Episodes 35:414–430

Munnecke A (1997) Bildung mikritischer Kalke im Silur auf Gotland.

Cour Forschungsinst Senckenberg 198:1–71

Munnecke A, Servais T (2008) Palaeozoic calcareous plankton:

evidence from the Silurian of Gotland. Lethaia 41:185–194

Munnecke A, Westphal H, Reijmer JJG, Samtleben C (1997)

Microspar development during early marine burial diagenesis:

a comparison of Pliocene carbonates from the Bahamas with

Silurian limestones from Gotland (Sweden). Sedimentology

44:977–990

Munnecke A, Westphal H, Elrick M, Reijmer JJG (2001) The

mineralogical composition of precursor sediments of calcareous

rhythmites: a new approach. Int J Earth Sci 90:795–812

Muttoni G, Kent DV, Di Stefano P, Gullo M, Nicora A, Tait J, Lowrie

W (2001) Magnetostratigraphy and biostratigraphy of the

Carnian/Norian boundary interval from the Pizzo Mondello

section (Sicani Mountains, Sicily). Palaeogeogr Palaeoclimatol

Palaeoecol 166:383–399

Muttoni G, Kent DV, Olsen PE, Di Stefano P, Lowrie W, Bernasconi

SM, Hernandez FM (2004) Tethyan magnetostratigraphy from

Pizzo Mondello (Sicily) and correlation to the Late Triassic

Newark astrochronological polarity time scale. GSA Bull

116:1034–1058

Nicora A, Balini M, Bellanca A, Bertinelli A, Bowring SA, Di

Stefano P, Dumitrica P, Guaiumi C, Gullo M, Hungerbuehler A,

Levera M, Mazza M, McRoberts CA, Muttoni G, Preto N, Rigo

M (2007) The Carnian/Norian boundary interval at Pizzo

Mondello (Sicani Mountains, Sicily) and its bearing for the

definition of the GSSP of the Norian stage. Albertiana

36:102–129

Payne JL, Clapham ME (2012) End-Permian mass extinction in the

oceans: an ancient analog for the twenty-first century? Annu Rev

Earth Planet Sci 40:89–111

Preto N, Hinnov LA (2003) Unravelling the origin of shallow-water

cyclothems in the Upper Triassic Durrenstein Fm. (Dolomites,

Italy). J Sediment Res 73:774–789

Preto N, Spotl C, Gianolla P, Mietto P, Riva A, Manfrin S (2005)

Aragonite dissolution, sedimentation rates and carbon isotopes in

deep-water hemipelagites (Livinallongo Formation, Middle

Triassic, northern Italy). Sediment Geol 181:173–194

Preto N, Spotl C, Guaiumi C (2009) Evaluation of bulk carbonate

d13C data from Triassic hemipelagites and the initial composi-

tion of carbonate mud. Sedimentology 56:1329–1345

Preto N, Kustatscher E, Wignall PB (2010) Triassic climates—state of

the art and perspectives. Palaeogeogr Palaeoclimatol Palaeoecol

290:1–10

Preto N, Rigo M, Agnini C, Bertinelli A, Guaiumi C, Borello S,

Westphal H (2012) Triassic and Jurassic calcareous nannofossils

of the Pizzo Mondello section: a SEM study. Riv Ital Paleont

Stratigr 118:131–141

Pruss SB, Bottjer DJ, Corsetti FA, Baud A (2006) A global marine

sedimentary response to the end-Permian mass extinction:

examples from southern Turkey and the western United States.

Earth-Sci Rev 78:193–206

Ridgwell A (2005) A mid Mesozoic revolution in the regulation of

ocean chemistry. Mar Geol 217:339–357

Ridgwell A, Zeebe RE (2005) The role of the global carbonate cycle

in the regulation and evolution of the Earth system. Earth Planet

Sci Lett 234:299–315

Riding R (2006) Cyanobacterial calcification, carbon dioxide con-

centrating mechanisms, and Proterozoic-Cambrian changes in

atmospheric composition. Geobiology 4:299–316

Rigo M, Joachimski M (2010) Palaeoecology of Late Triassic

conodonts: constraints from oxygen isotopes in biogenic apatite.

Acta Palaeont Polon 55:471–478

Rigo M, Preto N, Roghi G, Tateo F, Mietto P (2007) A CCD rise in

the Carnian (Upper Triassic) of western Tethys, deep-water

equivalent of the Carnian Pluvial Event. Palaeogeogr Palaeocli-

matol Palaeoecol 246:188–205

Rigo M, Preto N, Franceschi M, Guaiumi C (2012a) Stratigraphy of

the Carnian -Norian Calcari con Selce formation in the

Lagonegro Basin, Southern Apennines. Riv Ital Paleont Stratigr

118:143–154

Rigo M, Trotter J, Preto N, Williams I (2012b) Isotopic evidence of

Late Triassic monsoonal upwelling in the northwestern Tethys.

Geology 40:515–518

Roghi G, Gianolla P, Minarelli L, Pilati C, Preto N (2010) Palynological

correlation of Carnian humid sub-events throughout western

Tethys. Palaeogeogr Palaeoclimatol Palaeoecol 290:89–106

Scandone P (1967) Studi di geologia lucana: nota illustrativa della

carta dei terreni della serie calcareo-silico-marnosa. Boll Soc Nat

Napoli 76:1–175

Simms MJ, Ruffell AH (1989) Synchroneity of climatic change and

extinctions in the Late Triassic. Geology 17:265–268

Facies (2013) 59:891–914 913

123

Simms MJ, Ruffell AH (1990) Climatic and biotic change in the Late

Triassic. J Geol Soc Lond 147:321–327

Van der Plas L, Tobi AC (1965) A chart for judging the reliability of

point counting results. Am J Sci 263:87–90

Westphal H (2006) Limestone-marl alternations as environmental

archives and the role of early diagenesis: a critical review. Int J

Earth Sci 95:947–961

Westphal H, Munnecke A (2003) Limestone–marl alternations—a

warm-water phenomenon? Geology 31:263–266

Wheeley JR, Cherns L, Wright VP (2008) Provenance of microcrys-

talline carbonate cement in limestone-marl alternations (LMA):

aragonite mud or molluscs? J Geol Soc Lond 165:395–403

Wignall PB (2001) Large igneous provinces and mass extinctions.

Earth-Sci Rev 53:1–33

Wright VP, Cherns L, Hodges P (2003) Missing molluscs: field

testing taphonomic loss in the Mesozoic through early large-

scale aragonite dissolution. Geology 31:211–214

Zeebe RE, Westbroek P (2003) A simple model for the CaCO3

saturation state of the ocean: the ‘‘Strangelove’’, the ‘‘Neritan’’,

and the ‘‘Cretan’’ Ocean. Geochem Geophys Geosys 4 (1104):26

914 Facies (2013) 59:891–914

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