an unusual brachiopod assemblage in a late jurassic ......iuliana laza˘r • cristina e. panaiotu...

ORIGINAL ARTICLE

An unusual brachiopod assemblage in a Late Jurassic(Kimmeridgian) stromatactis mud-mound of the EasternCarpathians (Haghimas Mountains), Romania

Iuliana Lazar • Cristina E. Panaiotu •

Dan Grigore • Michael R. Sandy • Jorn Peckmann

Received: 21 August 2010 / Accepted: 28 December 2010

� Springer-Verlag 2011

Abstract An unusual fossil assemblage dominated by

superabundant rhynchonellid brachiopods in a stromatactis

mud-mound is recorded from the Haghimas Mountains

(Eastern Carpathians), Romania. The mound mainly con-

sists of bioclastic wackestones to packstones with a very

rich macrofauna including crinoids, sponges, juvenile

ammonites, and echinoids. The brachiopods represent a

low-diversity but high-abundance association, dominated

by the rhynchonellids Lacunosella and Septaliphoria. The

taphonomical features of the fossil assemblage indicate an

autochthonous fauna, with successive generations of bra-

chiopods in life position and complete well-preserved

individuals in different growth stage alongside an acces-

sory population of crinoids and sponges. Brachiopod-

brachiopod endosymbiotic life strategy is documented for

the first time from a post-Paleozoic brachiopod assem-

blage. The mound reveals abundant stromatactis, filled by

radiaxial fibrous or drusy calcite cement and internal

polymud sediments. This is the first Late Jurassic (Kim-

meridgian) stromatactis mud-mound identified in the

Eastern Carpathians.

Keywords Brachiopoda � Stromatactis � Mud-mounds �Late Jurassic � Carpathians � Romania

Introduction

The Haghimas Mountains (Eastern Carpathians) are well

known in the geological literature for geological sections

with some of the richest faunal assemblages at the

Kimmeridgian-Tithonian stage boundary. Neumayr (1873)

provided the first detailed ammonite zonation and defined

the ‘‘Acanticum Beds’’ formation from the Ghilcos

Mountains and Arkell (1956) recognized that this forma-

tion is one of the most complete successions of ammonites

of the Kimmeridgian interval. The stratigraphy of the

Mesozoic from the Haghimas Mountains was first studied

by Herbich (1878). His pioneering research was followed

by many other papers on the ammonite fauna, stratigraphy,

and geotectonic evolution of this area (Jekelius 1915;

Sandulescu 1967, 1968, 1969; Preda 1969, 1973; Grasu

1971; Grigore 2002).

The present paper describes an unusual Upper Jurassic

succession (Kimmeridgian–Tithonian) from the Haghimas

Mountains, previously mentioned in the literature for the

remarkable abundance of rhynchonellid brachiopods

(Herbich 1878; Bancila 1941; Grasu 1964; Pelin 1965;

Preda 1973). Several species of Lacunosella have been

described from this section by Grasu (1964), Pelin (1965)

I. Lazar (&)

Department of Geology and Palaeontology,

Faculty of Geology and Geophysics, University of Bucharest,

1 N. Balcescu Bd, 010041 Bucharest, Romania

e-mail: [email protected]

C. E. Panaiotu

Department of Mineralogy, Faculty of Geology and Geophysics,

University of Bucharest, 1 N. Balcescu Bd,

010041 Bucharest, Romania

D. Grigore

Geological Institute of Romania, Caransebes 1st.,

Bucharest 012721, Romania

M. R. Sandy

Department of Geology, University of Dayton,

300 College Park, Dayton, OH 45469-2364, USA

J. Peckmann

Department of Geodynamics and Sedimentology,

Center for Earth Sciences, University of Vienna,

1090 Vienna, Austria

123

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DOI 10.1007/s10347-010-0261-x

and Preda (1973). In view of the demonstrated variability

of the external characters shown by approximately 1,200

brachiopod specimens that have been studied so far, a

revision of the existing species is necessary. The detailed

taxonomy of these brachiopods will be presented in a

further paper. For the time being, we refer to the rhynch-

onellids as Lacunosella arolica (Oppel), Lacunosella

sparsicosta (Quenstedt), and Septaliphoria moravica

(Uhlig). Early reports on some of the results presented here

were given by Lazar et al. (2009a, b). Sandy (2010)

speculated that this locality could be a hydrocarbon-seep

deposit based on the low-diversity mass occurrence of

rhynchonellid brachiopods within a restricted stratigraphic

horizon. However, the results herein including isotopic

analyses support the mud-mound interpretation.

Mesozoic stromatactis mud-mounds and especially

Jurassic ones are uncommon. Neuweiler et al. (2001)

suggested that this circumstance is related to the different

taphonomy of Mesozoic and Paleozoic sponge mud-

mounds. The most widely accepted definition of stroma-

tactis is that of Bourque and Boulvain (1993), who

described stromatactis as a ‘‘spar network, whose elements

have flat to undulate smooth lower surfaces and digitate

upper surfaces, made up principally of isopachous crusts of

centripetal cement and embedded in finely crystalline

limestone’’. After the first description of stromatactis mud-

mounds by Dupont (1881), who suggested that stromatactis

structures were confined to Paleozoic mud-mounds, it is

now widely accepted that such structures can also be found

in Mesozoic successions. However, the origin of stroma-

tactis is still under discussion. Stromatactis was recently

suggested to result from calcification of siliceous sponge

and organic matter diagenesis (Neuweiler et al. 2001,

2007), dissociation of CO2-gas hydrate (Krause 2001), or

even from sedimentation of polydisperse, polymodal, and

irregularly shaped grains resulting from a viscous turbidity

flow (Hladil 2005). Sedimentary fabrics similar to

stromatactis have also been recognized in methane-seep

limestones (Peckmann et al. 2002).

This is the first study concerning the general taphonomic

features of an unusual brachiopod assemblage in a mud-

mound limestone from the Haghimas Mountains, Eastern

Carpathians, Romania, with a detailed description of the

microfacies and geochemistry (carbon and oxygen stable

isotopes).

Geological settings and studied sections

The Eastern Carpathians are built up of a succession of

nappes and thrust sheets with a complicated geotectonic

structure within the Alpine Carpathian Folded Belt. The

Haghimas Mountains represent a huge syncline structure in

which Sandulescu (1975, 1984, 1994) distinguished three

superposed Alpine tectonic units, in ascending order:

the Sub-Bucovinian Nappe, the Bucovinian Nappe, and the

Haghimas Nappe. The studied section belongs to the

Haghimas Nappe. According to Sandulescu (1975, 1984),

this nappe has no crystalline formations. It is made up of

Upper Jurassic–Lower Cretaceous carbonate deposits with

sporadic pre-Kimmeridgian ophiolites in the lower part of

the Mesozoic sequence. The Haghimas Nappe belongs to

the Transylvanian Nappe System (Fig. 1a), which origi-

nated from the Transylvanian Domain, an inferred exten-

sion of the western Tethys (Sandulescu 1988; Sandulescu

and Visarion 2000). The Transylvanian Domain was most

probably a true oceanic spreading domain, based on the

occurrence of ophiolites.

The studied succession outcrops on the upper part of the

Fagul Oltului Valley (Figs. 1b, 2a). This valley is the main

tributary of the Olt River, one of the larger rivers in

Romania. The Fagul Oltului Valley is situated on the wes-

tern flank of the Haghimas Mountains, northward from

Hagmimasul Mare (Great Haghimas) Peak. The valley is

narrow and deep with steep slopes (Fig. 2b, c) and the

outcrops are situated on the upper part of the valley: N

46�4204700; E 25�4705000; 1,416 m altitude. The western

slope is named Piatra Rosie (‘‘red rock’’) referring to the red

color of the Kimmeridgian–Tithonian limestones. The

sequence is described by correlation of the outcrops from the

two slopes. The slight difference in the thickness of the beds

on the two slopes of the valley is due to tectonics. The beds

of the Kimmeridgian–Tithonian interval are well stratified

(Fig. 2d), the general strike and dip is 120�/20� NE.

The first part of the observed succession is between 2.5

and 5.5 m thick and is represented by reddish fine-grained

stromatactis-bearing limestone (Fig. 3a–c). This succession

contains 12–80-cm-thick beds very rich in crinoids and

densely packed rhynchonellid brachiopods belonging

mainly to the genus Lacunosella (Fig. 3a–c). The next level

is represented by 3.5 m (the observed thickness) of yel-

lowish to pink intraclastic granular limestone containing

5–20-cm-thick beds, without evident macrofauna (Fig. 3a).

The stratigraphic age of the thick level with Lacunosella

can be determined by the following biostratigraphic

observations. The interval between samples FO1A1 to

FO1F2 (Fig. 3a, b) contains numerous, very well preserved

Saccocoma ossicles, associated with Crescentiella mor-

ronensis (Crescenti), ‘‘Trocholina’’ cf. conica (Schlum-

berger), ‘‘Trocholina’’ palestiniensis Henson, and numerous

epistominid Foraminifera. In the geological literature con-

cerning the stratigraphy of the Upper Jurassic deposits from

the Romanian Carpathians (e.g., Sandulescu 1967, 1969;

Patrulius 1969; Dragastan 1975, 1980; Bucur 1997), this

type of lithofacies was named ‘‘Saccocoma facies’’ and

is considered to be representative of the Kimmeridgian.

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123

We found one poorly preserved ammonite specimen of

Sowerbyceras cf. loryi (Munier and Chalmas) (Fig. 4),

which is characteristic for the Kimmeridgian. This speci-

men was extracted from the Lacunosella bed FO2B2.

Patrulius (1969, pp. 65–67) mentioned a similar facies

from the Bucegi Mountains (SE Carpathians): red limestone

with Lacunosella and the ammonoid taxa Ataxioceras aff.

homalinum Schneid, Sowerbyceras loryi (Munier and

Chalmas), Metahaploceras aff. subnereus (Wegele), which

are indicators for the Lower Kimmeridgian age of this

facies. From a red stratified limestone from the Fagul

Oltului Sect. 2.5 m above the level with ‘‘Rhynchonella’’

lacunosa Herbich (1878) recorded the ammonites Oppelia

cf. compsa (=Taramelliceras compsum (Oppel)) and Peri-

sphinctes ulmensis (=Lithacoceras ulmense (Oppel)), taxa

corresponding to the uppermost Kimmeridgian, Bekeri

Zone. The ammonites mentioned by Herbich (1878, p. 132)

have been found in the interval corresponding to the sample

FO1H (‘‘fine stratified limestone (‘‘rothen Schichten’’)

oriented with the direction parallel with the edge of the

mountain slope’’). Bancila (1941, pp. 75–76) retraced

Herbich’s route along the Fagul Oltului Valley and con-

firmed Herbich’s description. Grasu (1964) described

Lacunosella sparsicosta (Quenstedt), Glossothyris (= Nu-

cleata) nucleata (Schlotheim) and Terebratulina sp. from

the basal part of the Kimmeridgian deposits, which outcrop

along the Fagul Oltului Valley. Pelin (1965) considered that

the beds rich in Lacunosella from Fagul Oltului Valley

represent ‘‘the red level of the Portlandian’’, like an inter-

calation within the white–grey limestones of the ‘‘Port-

landian’’ interval.

In thin-sections, we recognized numerous juvenile

phylloceratids. Based on Sarti (1993, 2003), who studied

the stratigraphy, ontogeny, and taphocoenosis aspects of the

cosmopolitan Sowerbyceras, we consider that these speci-

mens are probably juveniles of Sowerbyceras cf. silenum

(Fontannes), which would indicate an Early Kimmeridgian

age. Moreover, the Saccocoma facies is considered typical

for the Kimmeridgian–Lower Tithonian interval in the

Carpato-Balkanic realm and others Tethyan areas (e.g.,

Michalik et al. 1993; Misik et al. 1994 for Slovakia; Keupp

and Matyszkiewicz 1997; Matyszkiewicz 1997; Rehakova

and Wierzbowski 2005 for Poland–Pieniny Klippen Belt;

Lakova et al. 2007 for Bulgaria; Biskaborn 2009 for Ger-

many). Considering all of these aspects, the lower part of

the succession with abundant rhynchonellid brachiopods

belongs most probably to the Lower Kimmeridgian.

The sample FO1H (Fig. 3a, b) contains Salpingoporella

pygmaea (Gumbel) and in the superjacent sample FO4

Calpionella alpina Lorenz was identified. The upper part of

the studied sequence (FO4–FO10) belongs to the Upper

Tithonian–Berriasian interval, as indicated by the presence

of Calpionella alpina Lorenz in sample FO4. This calpi-

onellid is associated with numerous benthonic microor-

ganisms: Bramkampella arabica Redmond, Rajkaella

bartheli (Bernier), and Clypeina/Actinoporella sp. The next

Fig. 1 Location of the studied section: a Position of the Haghimas

Mountains within the Eastern Carpathians, based on the geotectonic

map of Romania (Sandulescu 1984). b Location of the Fagul Oltului

Valley on the geological outline map of the Haghimas Mountains

(based on Sandulescu et al. 1975)

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Fig. 2 a The entrance on the Fagul Oltului Valley. b, c The

uppermost part of the Fagul Oltului Valley with steep slopes and large

outcrops of the Tithonian—Berriasian deposits. d Outcrop FO2

showing the clear bedding of the Kimmeridgian red bioclastic

limestones, wackestones to packstones very rich in rhynchonellid

brachiopods

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succession (FO5–FO10) (Fig. 3a) contains Bramkampella

arabica Redmond, Clypeina/Actinoporella sp., Acicularia

sp., Mayncina sp., Andersenolina alpina (Leupold), and

Mohlerina basiliensis (Mohler), a specific association for

Upper Tithonian-Berriasian interval. The deposits situated

below the basal part of the studied sequence have not yet

been identified by us. However, Pelin (1965) stated that in

the sectors Fagul Oltului Valley and Piatra Rosie Cliff, the

Callovian–Oxfordian interval is represented by radiolarites

and jaspers, which are superimposed by Kimmeridgian and

‘‘sometimes by Portlandian’’ limestones. The same strati-

graphic succession for the Middle-Upper Jurassic is pre-

sented for the Haghimas Mountains by Barbulescu and

Dragastan (1972).

Fig. 3 Lithostratigraphic sections of the studied outcrops and samples: a Synthetic lithostratigraphic log on the Fagul Oltului Valley. b The

outcrop FO1 on the right slope of the valley. c The outcrop FO2 on the left slope of the valley

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Materials and methods

Rock samples and brachiopods were collected from the

Fagul Oltului Valley. Detailed sample locations are indi-

cated in Fig. 3a, c. Besides sampling, the field study also

included measurement of the stratigraphic profile and

macroscopic examination of lithologic textures and struc-

tures. Rock samples were prepared for both petrographic

and isotopic analyses. About 50 thin-sections and polished

slabs were studied petrographically by polarized light

microscopy, UV fluorescence microscopy, and by cold

cathodoluminescence microscopy (CITL). Many slabs

were stained by alizarin and potassium ferricyanide to

reveal zonation of the cements filling the stromatactis

cavities. Carbon and oxygen stable isotopes were analyzed

at the Center for Marine Environmental Science (Univer-

sity of Bremen). Samples were taken from polished slabs

with a handheld micro-drill. Sample powders were reacted

with 100% phosphoric acid at 75�C, and the evolved CO2

gas was analyzed with a Finnigan MAT 251 mass spec-

trometer. The d13C and d18O values are corrected accord-

ing to the NBS19 standard and reported in per mill (%)

relative to the V-PDB (Vienna-PeeDee Belemnite) stan-

dard (standard deviation smaller than 0.04%).

Results and discussion

Sequence of lithofacies

In the studied outcrops several lithofacies can be distin-

guished, the first three lithofacies represent the mud-mound

while the latter ones are covering the mound:

• reddish stromatactis-bearing fine-grained limestones

with brachiopods and other invertebrate fauna

(FO1A0 to FO1G; FO2A1 to FO2B10) (Fig. 3a–c);

• yellowish intraclastic granular limestone = bio-intra-

clastic grainstone (FO1H) reddish fine-grained lime-

stone with thin shell bivalves = bioclastic wackestone

with Bositra sp. (FO3);

• yellowish fine-grained limestone with small gastropods

and algae = bioclastic packstone (FO4 to FO5);

• yellowish sandstone with small gastropods (FO6);

• yellowish limestone with large nerineids = bioturbated

wackestone with large gastropods and dasycladal algae

like Salpingoporella pygmea (Guembel), Clypeina/

Actinoporella sp. (FO7 to FO9);

• whitish coarse-grained limestone = rudstone with coral

reef fragments and calcite cement (FO10).

In this paper, we focus on the stromatactis-bearing

limestones. They are bioclastic limestones, wackestones to

packstones, often having a micropeloidal matrix or a

complex polymud fabric (in the sense of Lees and Miller

1995). Skeletal particles change in frequency across this

unit, but they are dominated by crinoids, echinoid plates

and spines, sponges (as fragments of lithistid sponges

(Fig. 5c) or isolated calcified spicules from hexactinellid

sponges (Fig. 5d), brachiopods and ‘‘Tubiphytes’’ (e.g.,

Crescentiella morronensis (Crescenti), Fig. 5b; as defined

by Senowbari-Daryan et al. 2008). At some levels, pelagic

crinoid debris is abundant (Fig. 5f). Less-abundant fossils

include agglutinated and hyaline foraminifers (Fig. 5e),

juvenile ammonites (Fig. 5d), bryozoans and worm tubes.

Most of the brachiopod and echinoderm shell fragments are

marginally micritized and some borings filled with micrite

have been observed. Thick microbial and bryozoan in-

crustations on large skeletal fragments are common

(Fig. 5e). All these features suggest a low sedimentation

rate, intense microbial activity, and in some cases, slight

reworking. Besides carbonate particles, few quartz and

muscovite grains occur at certain levels.

The entire unit (FO1A0–FO1H; FO2A1-FO2D) is thick-

bedded, has no internal organization other than the levels

with more abundant stromatactis, and with abundant bra-

chiopods. We interpreted this unit as a transitional phase

from a microbial to a biodetrital mud-mound (cf. Bosence

Fig. 4 Sowerbyceras cf. loryi (Munier and Chalmas) lateral and

frontal view (cross section), specimen extracted from Lacunosella bed

FO2B2

Fig. 5 Petrography of the mud-mound rocks: a Lacunosella shells in

life position. Note the internal cavities completely or partially filled

with geopetal mud and calcite cement. b Typical example of

Crescentiella morronensis (FO1B). c Calcified sponge spicules and

fragments of calcified lithistid sponge (FO2B10). d Calcified hexac-

tinellid sponge and an encrusted juvenile ammonite (FO1B). e Bra-

chiopod shell encrusted by bryozoans (FO2B3). f Well-preserved

Saccocoma crinoid (FO2B10). g Filamentous bivalve facies (FO3).

h Bioclastic grainstone facies covering the mud-mound (FO1H)

c

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and Bridges 1995), the latter being composed of stacked

biostromes. Each individual biostrome is limited vertically

by a bedding surface where intraclasts and more reworking

of the sediment are apparent. However, the entire unit

seems to be condensed due to low sedimentation rates and

minor reworking. Taking into account the small diameter

of the ‘‘Tubiphytes’’ tests along with the well-preserved

pieces of fragile pelagic crinoids Saccocoma (Fig. 5f) and

many juvenile ammonites, the depositional setting of the

mud-mounds is interpreted as a deep ramp, below wave-

base (cf. Schmid 1996; Hess 2002; Brodacki 2006). The

primary lateral extent of the mud-mound cannot be asses-

sed, as flank deposits have not yet been found, mainly due

to the severe tectonic fragmentation of the study region and

to the outcrop conditions.

The covering units—yellowish intraclastic grainstone

(Fig. 5h) and the reddish fine-grained limestone with fila-

mentous bivalves (possible Bositra sp., Fig. 5g)—show a

first episode of intense reworking followed by a deepening

trend. These two lithofacies drape the mud-mound and

represent a transition to the superjacent shallow-water units

dominated by gastropods (Nerinea sp.) and algae within

the general regressive trend, which is characteristic for the

evolution of the Jurassic carbonate platforms from the

Eastern and Southern Carpathians during the Oxfordian–

Tithonian interval.

Mud-mound biota

The biota of the mud-mound in order of declining abun-

dance are brachiopods, crinoids, sponges, annelids,

Foraminifera, echinoids, ammonites, and extremely rare

fragments of bivalves and gastropods.

Brachiopods: The richest brachiopod horizon is 1.63 m

thick and is packed with rhynchonellid brachiopods

(Fig. 6a) dominated by Lacunosella (80–90%) and Sep-

taliphoria (10–20%), occurring within red crinoidal lime-

stone (Saccocoma facies). Other brachiopods such as

Terebratulina sp. are represented by a few specimens.

From a rock sample of 4.74 kg, 79 adults specimens and 24

juvenile specimens have been collected, most of them

belonging to the genus Lacunosella. The dimensions of the

specimens are between 38.15–28.44 mm in length,

33.99–28.54 mm in width, and 24.80–20.10 mm thickness

for adult specimens and 26.66–8.45 mm in length,

28.50–9.00 mm in width, and 16.75–4.40 mm in thickness

for juveniles. The total volume of the rock occupied by the

brachiopod shells is estimated to be 72–85%, which reveals

a high density of individuals within the population.

The degree of preservation is remarkable. Based on field

and laboratory observations, tens-of-thousands of speci-

mens are very well preserved with original shell, articu-

lated, and the shells are neither decorticated nor eroded

(Fig. 6b–f). All rhynchonellids have cyrtomatodont (inter-

locking) hinges, which prevented disarticulation. Of the

specimens, 90% are filled with micrite and 10% are par-

tially filled with micrite and later cement resulting in

geopetal structures (Fig. 6b–f), confirming that specimens

have not been transported. The infilling micrite occurs as

very thin laminae parallel to bedding (Fig. 6e), but

numerous specimens contain infilling of bioclastic matrix.

Details of the internal morphology such as the attachment

surface of the dorsal muscles and the mantle canal patterns

are very well preserved in almost all individuals. The great

majority of individuals is orientated with the umbo pre-

dominantly downwards and with the anterior commissure

generally orientated upwards (Fig. 6c, d). The brachiopods

show no evidence of deformation by compaction, reflecting

early cementation of the host lithology. However, the

brachiopod shells show small deformations like small

depressions, which appear to be concentrated in the ante-

rior half of the shells (Fig. 7a–c, f). These deformations

may result from compression of the brachiopod shell from

the umbones of other specimens, resulting from the

crowding of the brachiopods in clusters.

A wide-range of shell sizes is preserved, indicating

successive generations/biocoenoses. Numerous adults or

ephebic specimens have complete juvenile brachiopods

within them (Fig. 7d–g). This was observed during the

preparation of the fossils, when complete specimens were

accidentally broken. Both juveniles and adult hosts show

articulated shells, with valves closed, revealing that bra-

chiopod larvae settled and developed within the adult

brachiopods. The fact that the juveniles are all found close

to the anterior commissure, indicates that juveniles may

have lived inside a living adult ‘‘host’’ brachiopod.

Brachiopod-brachiopod symbiosis is rare and is mainly

epibiotic, however Schemm-Gregory and Sutton (2010)

reported the first record of brachiopod-brachiopod endo-

parasitism (from the Devonian, involving a strophomenid

within a spiriferid). Our observations on the studied pop-

ulation of Lacunosella, support an endosymbiotic life

strategy for these Jurassic brachiopods. This is the first

record of brachiopod endoparasitism in the post-Paleozoic

and also the first record from an extant Order of brachio-

pods indicating that it is a phenomenon that could be

expected to occur in some living brachiopods. Perhaps the

flourishing brachiopods and limited substrate availability

for attachment in the mud-mound environment led to this

endosymbiotic relationship. It seems likely that this is a

purely fortuitous association and one tolerated, at least for

a time, by both brachiopods. Presumably the settler was

never able to attain true adult dimensions.

A few specimens of Lacunosella show evidence of shell

damage, like indentations or punctures. In one specimen,

an indentation like a ‘bowl-shaped’ depression and two

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symmetrical small and deep, puncture-like concavities near

the anterior commissure of the dorsal valve have been

observed (Fig. 8). Similarly, the ventral valve shows two

other small and deep punctures near the anterior commis-

sure. Such types of damage possibly result from compac-

tion of the host sediment, but a biological origin from

predation cannot be excluded. Six teeth of Sphaerodus, a

durophagous pycnodontidae fish, have been found in the

same levels with brachiopods with shell damage. Notably,

the Sphaerodus teeth fit perfectly in the ‘bowl-shaped’

depression of one specimen of Lacunosella. Boreholes

were identified in both dorsal and ventral valves near the

lateral commissure. All recognized boreholes were circular

with sharp edges and ranged in size from 0.5 to 1.2 mm.

One specimen of Lacunosella shows numerous micro-

scopic ‘spiral-tube carbonate structures’ up to approxi-

mately 1 mm in diameter that perforate the shell

perpendicularly (Fig. 9). These structures are probably

parasitic in origin.

Crinoids: The limestone contains a large amount of

crinoid debris, preserved mostly as columnals and pluri-

columnals. The columnals vary between 1 and 5 mm in

Fig. 6 a, b Autochthonous brachiopod fauna in nest-like accumulations: thousands of specimens are very well preserved in original life position.

b, c, e Specimens filled with micritic matrix or partially filled with matrix and geopetal infills. c, d, f Specimens well preserved with original shell

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diameter. Columnals are circular, oval, or pentagonal in

cross section (Fig. 10a). Numerous very well preserved

Saccocoma brachials have been identified in thin section

(Figs. 5f, 10b, d).

Echinoids: A few complete specimens from the family

Cidaridae have been extracted, but their overall frequency

is higher. Large specimens (around 2–3 cm in diameter) of

cidarids have been observed in outcrops, but are difficult to

extract completely from rock samples. Numerous spine

fragments were identified macroscopically and in thin

sections. Irregular echinoids are also present, being repre-

sented by small representatives (1.0–1.3 cm in diameter) of

the family Collyritidae.

Sponges: The relative abundance of sponges is very

difficult to assess because of the lack of macroscopic evi-

dence. However, in thin sections, the most abundant faunal

elements are sponges represented by numerous calcified

spherical rhaxa, monaxone spicules, irregular spicules of

lithistid sponges, large fragments from the skeletons of

lithistid sponges (Fig. 10c), and very abundant fragmentary

skeletons of siliceous sponges (Fig. 10d).

Annelid fossils are represented by agglutinating worms

Terebella lapilloides Munster and serpulid worms

(Cycloserpula Parsch and Dorsoserpula Parsch) associated

with peloidal crusts and sponge skeletons. Terebella lapil-

loides Munster (Fig. 10e, f) is quite common in the sponge

mud-mounds (Hammes 1995). In cross section, this worm

has tubes up to 1 mm in diameter, a very fine agglutinated

wall up to 0.1 mm thick and the tube interior is filled with

geopetal calcite, peloids, and micritic sediments (Fig. 10e)

or micritic internal sediments and peloids (Fig. 10f).

Ammonites: Representatives of this group belong to the

families Perisphinctidae, Oppelidae, and Phylloceratidae.

Numerous juveniles have been identified in thin sections

and a few small adults, showing a moderate degree of

preservation.

Fig. 7 a–f Small circular deformations (white arrow) of the brachio-

pods shells and internal moulds caused by crowding of the living

brachiopods in clusters. d Deformation (black arrow) in the

brachiopod shell seen from the interior part of the shell. e, g–i Ephebic

specimens, which have complete juveniles (black dashed oval lines)

within the interior of the closed, unbroken original shells

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123

Other representatives of the macrofauna are extremely

rare fragments of bivalves and gastropods. Microfossils are

represented by Foraminifera, radiolarians, a few possible

ostracods, and putative benthic microbial communities

forming microbial fabrics (in the sense of Oloriz et al.

2006). The foraminiferal fauna was investigated in thin

sections and is represented in the studied mud-mound facies

by Crescentiella morronensis (Crescenti), ‘‘Trocholina’’ gr.

Fig. 8 Possible traces of predation on Lacunosella: a Anterior view

of the ventral valve (notice two deep and sharp concavities near the

anterior commissure, arrows). b Dorsal valve of the same specimen is

broken and other two sharp and circular concavities near the anterior

commissure (arrows). c Anterior view of the dorsal valve (notice the

large ‘bowl-shaped’ depression). d Spherodus tooth with scratches on

the surface, which fits perfectly into the large deformation of the

dorsal valve

Fig. 9 Possible parasitic structures that perforate the shell of Lacunosella

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123

Fig. 10 a Micritic crinoidal limestone—notice the marginal bioero-

sion of the crinoids ossicles (FO1C). b Well-preserved Saccocomaossicles embedded in putative mineralized bacterial mats, Cresce-centiella morronensis (Crescenti), skeleton of a lithistid sponge

(FO1F2). c Skeleton of a lithistid sponge in the stromatactis-bearing

micritic crinoidal limestone (FO1A0). d Macerated skeleton of a

hexactinellid sponge encrusted by peloidal crusts (p); skeletal

elements are partly collapsed and filled with internal sediments (1);

notice putative Fe-rich biofilm (2) (FO1G). e Terebella lapilloidesMunster associated with peloidal crusts (p) (FO1B). f Terebellalapilloides Munster (FO2A1)

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123

conica (Schlumberger)/palastiniensis Henson, Ammobacu-

lites sp. and by numerous epistominid Foraminifera. The

encrusting rotaliid Bullopora sp. is also present.

Stromatactis and other early diagenetic features

Early induration of mud-mounds is probably partially

caused by the syn-vivo to early post-mortem calcification

of siliceous sponges (Neuweiler et al. 2007), giving way to

a patchy sediment lithification, which in conjunction with

aragonite and skeletal opal dissolution, decay of organic

tissues, sediment shrinkage and collapse creates the

stromatactis voids in the early phases of diagenesis.

Besides brachiopods, the most apparent feature of the

studied mud-mound unit is stromatactis, showing the typ-

ical flat bottom and undulating ceiling. Many stromatactis

are completely filled with different generations of cement

(true stromatactis, Figs. 11a, 12a, b), others have incipient

marine cementation followed by internal sediment infilling

(inhibited stromatactis with geopetal mud) and few of them

are only filled with internal sediment (aborted stromatactis;

sensu Neuweiler et al. 2001). The true stromatactis domi-

nate and are largest in size (centimeter range with maxima

at around 12 cm in width and 4 cm in height) (Fig. 12a, b),

while the inhibited and aborted varieties are less abundant

and smaller. True stromatactis are partly filled either by

inclusion-rich radiaxial fibrous calcite (RFC, Fig. 11b) or

drusy calcite, both are non-luminescent under CL. These

early marine cements are followed by later inclusion-free

blocky cement, displaying bright as well as dull lumines-

cence. In inhibited stromatactis, early intrusion of the

muddy sediment into cavities prior to the precipitation of

the drusy cement created normal and reverse grading and

geopetal structures (Fig. 11c, e). Some of the aborted

stromatactis show a sequence of mud filling with different

compositions. The ceiling of these voids is often draped

with a thin coating of iron and/or manganese oxides

(Fig. 11d).

Aubrecht et al. (2009) discussed the origin of stroma-

tactis and documented that stromatactis results from

sponge taphonomy. Features of the red micritic limestone

with rhynchonellid brachiopods studied here such as the

presence of ‘‘floating’’ allochems (represented by skeleton

fragments of hexactinellid sponges), as well as sediment

aggregates surrounded by RFC (Fig. 12c), pores, and bor-

ings within RFC and the very abundant micropeloidal

fabrics and microbial crusts (Fig. 12e, f) of the host rock—

all of which are often observed in association with sponge

taphonomy (cf. Aubrecht et al. 2009)—indicate that for-

mation of stromatactis of the Romanian mound may have

been related to sponge taphonomy as well.

Echinodermal fragments and the brachiopod shells are

not affected by early dissolution. Shells and their fragments

often provided shelter porosity, which is filled with one or

multiple generations of cement or with geopetal mud and

cement (Fig. 5a). Sometimes the cementation of the shelter

pores started very early with radiaxial fibrous calcite fol-

lowed by later occlusion with blocky calcite (Fig. 11f), but

more often the cement was formed during burial diagenesis

with high manganese concentrations in the formation

waters as indicated by bright and dull luminescence

(Fig. 11g). Another effect of shallow burial diagenesis is

the silicification of bioclasts, like echinodermal debris and

some Foraminifera (Fig. 11h) in the upper layers of the

mud-mound. The silica probably derived from subjacent

layers where sponges were calcified.

Red pigmentation of limestones is often believed to be

linked to the presence of iron bacteria and fungi (e.g.,

Mamet and Preat 2006), which produce dispersed submi-

cronic crystals of hematite in the micrite matrix or more

localized coatings on internal surfaces. Many of the

microbial or sponge microborings in brachiopod shells or

echinodermal plates are completely filled with red micrite.

It is unclear if this pigmentation has a biotic or an abiotic

origin. However, the microbial bioerosion of calcitic

(Figs. 12d, 13a–c) and aragonitic shells is a very apparent

feature of the mud-mound facies. Present-day iron bacteria

have been described from poorly oxygenated microenvi-

ronments at the water–sediment contact (McLean et al.

1996). This kind of environment was probably also present

in stromatactis voids, where microorganisms might have

acted as complexing agents for a variety of metals such as

iron and manganese.

Stable isotopes

Samples for isotopic analysis were selected from the main

constituents of the stromatactis-bearing limestones: host-

rock micrite; brachiopod shells; early drusy cement; late

blocky spar. Carbon and oxygen stable isotopes have been

analyzed to reconstruct diagenetic processes and assess the

degree of alteration during diagenesis. The d18O values

vary from -2.3 to -0.5% and d13C values range from 0.8

to 2.6% (Table 1). Such isotope data indicate that car-

bonate precipitated from solutions with a composition like

contemporaneous seawater (cf. Veizer et al. 1999) without

significant alteration during burial diagenesis. The early

drusy cement is somewhat less 18O depleted than the other

phases (Fig. 14). This trend from an early cement to the

late blocky cement is one of progressive burial. The mi-

critic sediment, however, was apparently slightly more

affected by thermal overprint during the burial diagenesis,

which is often observed in micritic lithologies (e.g., Joa-

chimski and Buggisch 1999). This pattern is probably a

function of crystal size, as small crystal are more suscep-

tible to recrystallization.

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Facies

123

The paleoecological context

The brachiopod Lacunosella is the most common well-

preserved macrofossil in the stromatactis mud-mound and

therefore consideration of its paleoecology is relevant to

interpreting this unique association. Lacunosella ranges

from the Middle Jurassic to the Lower Cretaceous and is

therefore one of the longer-ranging brachiopod genera. As

a consequence of this longevity, it appears that Lacunosella

had at times both a broad geographic distribution and likely

inhabited a range of paleoenvironments given the potential

for diversification among its constituent species throughout

its stratigraphic range.

Khudolej and Prozorovskaya (1985) considered

Lacunosella to be one of a number of genera that charac-

terized a Mediterranean Province (west and central Tethys)

in the Late Jurassic. This association with a Mediterranean

Region or Subrealm continued into the Early Cretaceous

(Smirnova 1984, discussed in Mancenido 2002). Lacuno-

sella was considered one of several brachiopod genera that

characterize the northern margin of the Tethys in the

Tithonian (Sandy 1988). In another paleobiogeographical

analysis, Voros (1993) considered this genus to be repre-

sentative of the NW European province in the latest Juras-

sic. In terms of its paleoecological niche and bathymetry,

Lacunosella is considered to have lived in the sublittoral

zone (Ager 1965). Krobicki (1994) agreed with this view

and noted that Lacunosella is known from shallow-water

reef-like carbonates as well as olistoliths (in the Polish

Outer Carpathians; these latter occurrences do not neces-

sarily contradict the shallow-water association). The

co-occurrence of species of Lacunosella with sponges has

been noted and considered a common association for the

genus (e.g., Quenstedt 1868–1871; Wisniewska 1932; Ager

and Evamy 1963; Ager 1965). Childs (1969, p. 9) showed

that Lacunosella arolica (Oppel) occurs in marly facies at

various localities in the southern French Jura and considered

the paleoenvironment as sublittoral, muddy sea floors. The

author stated that Lacunosella arolica (Oppel) ‘‘is invari-

ably associated with sponges’’ and suggested that sponges

represented the necessary substrate for the fixation of the

brachiopods. Gradinaru and Barbulescu (1994) considered

that the co-occurrence of L. cracovinesis (Quenstedt) with

sponge-bearing build-ups may reflect a high affinity of this

species for space provided on the sponge build-ups from

Dobrogea (SE Romania). Barbulescu (in Dragastan et al.

1998) mentioned the high abundance of L. cracovinesis

(Quenstedt) from stromatolitic spongalgal facies from the

Casimcea Formation (Upper Oxfordian, Cechirgea Valley,

Central Dobrogea) and L. arolica (Oppel) associated with

small, lentiliform sponge-bearing build-ups from the

Casimcea Formation (Middle Oxfordian, Visterna Valley,

Central Dobrogea), the last build-ups representing small

thrombolytic mud-mounds dominated by hexactinellid

sponges (as noted by Herrmann 1996).

The association between the genus Lacunosella and

sponge facies (with high abundance of crinoids) during the

Oxfordian–Kimmeridgian interval was not simply fortu-

itous. Most probably there were some local environmental

parameters that justified such an association or more likely,

all these groups were well adapted to the mound environ-

ment. Some scenarios of mound formation postulate that

mounds grew in water masses that were particular rich in

nutrients (e.g., oxygen minimum zones, upwelling currents,

and internal waves, Stanton et al. 2000). If such a scenario

should apply, there might have been just a lot of food for

brachiopods, sponges, and crinoids in the water masses

where mounds were forming.

A preference of Lacunosella for relatively shallow water

is supported by a paleoecological study on brachiopods

from the Upper Oxfordian of Poland (Krawczynski 2008).

Specimens of Lacunosella with epifaunal thecideid bra-

chiopods were considered to be from a biohermal slope

where some specimens may have been in situ and some

transported down slope. The associated paleocommunity

(sponges and corals) was used to estimate that water depth

was not more than 100 m. Different water depths ranging

from 40 to 100 m have been estimated for Lacunosella-

sponge facies associations (Table 2). Oloriz et al. (2006)

suggested that the predominance of the Dictyida in the

sponge assemblages from the spongiolithic lithofacies

(Oxfordian–Kimmeridgian, External Prebetic units) points

to a mid-shelf environment with depths around 70 m or

even less. Leinfelder et al. (1994) and Pisera (1997) sug-

gested that the great amount of hexactinellid and lithistid

sponges could indicate rather deep waters, more than

100 m in depth.

A unique occurrence of Lacunosella with the terebra-

tulid Nucleata was discussed by Bujtor (2007) from the

Early Cretaceous (Valanginian) of Hungary. The brachio-

pods, along with other faunal elements, were from an iron

ore and manganese deposit. The depositional setting was

interpreted as a shallow-marine, nutrient-rich, submarine

volcanic area and was considered to have been related to an

upfaulted block or a hydrothermal vent. The unusual

Fig. 11 a Polished slab of a true stromatactis. b Radiaxial fibrous

cement inside a true stromatactis (FO2B1). c Early drusy and late

blocky cement inside an inhibited stromatactis with normal graded

sediment infill (FO1A0-1b). d Early sediment infill into an aborted

stromatactis void, which has the ceiling coated with a thin layer of

iron oxides (FO1F1). e Reverse grading into a stromatactis void,

which was first draped with micrite (FO1F2). f Shelter intraskeletal

pores displaying two generations of cement: radiaxial fibrous

inclusion-rich calcite followed by blocky inclusion-free calcite

(FO2B5). g CL image of a Lacunosella shell composed of non-

luminescent LMC and the adjacent shelter porosity filled with bright

to dull luminescent calcite. h Silicified echinodermal plate (FO1E)

b

Facies

123

occurrence of Lacunosella groenlandica in the Early Cre-

taceous (Valanginian) of Greenland (Owen 1976; Harper

et al. 2005) within red and yellow sandy mudstones is

considered to be part of a deeper-water [shelf] fauna with

some Tethyan affinities (Pygope for example). This high

latitude occurrence of Lacunosella and other taxa may have

been favored by the development of a proto Gulf Stream

during the opening of the Atlantic Ocean.

The studied mass-occurrence of brachiopods dominated

by Lacunosella in the stromatactis mud-mound would be

Fig. 12 a, b True stromatactis structures in red micritic crinoidal

limestone: a FO1B. b FO2B. c Skeleton fragments of hexactinellid

sponges, ‘‘floating’’ allochems and sediment islets surrounded by RFC

(FO2B1). d Micropeloidal fabrics (p), stromatactis, fragment of

brachiopod shell with marginal bioerosion, Fe-rich crusts (FO2B9).

e Micropeloidal fabrics (FO1A0). f Putative microbial crusts (FO1G)

Facies

123

consistent with moderately deep intrashelf settings (prob-

ably between 70–100 m) below wave-base on a deep ramp,

with a low to moderate energy environment and low rates

of sedimentation.

This is supported by the following observations:

• the high abundance of sessile epifaunal foraminifers,

brachiopods, crinoids, sponges, and serpulids (cf.

Oloriz et al. 2006);

• the general spectrum of the foraminiferal assemblage

dominated by Crescentiella, Globuligerina, Ammob-

aculites and epistominid forams (cf. Oloriz et al. 2006);

• the presence of Terebella lapilloides Munster (cf.

Oloriz et al. 2006);

• well-preserved pieces of fragile pelagic crinoids (Sac-

cocoma) alongside rare regular (Cidaridae) and irreg-

ular (Collyritidae) echinoids and very abundant crinoid

segments;

• moderate abundance of juvenile ammonites and a few

adult specimens assigned to the Perisphinctidae, Op-

pelidae, and Phylloceratidae (cf. Westermann 1996)

• the predominance of brachiopods with a thick shell

(Lacunosella) (cf. Fursich and Hurst 1974);

• the presence of hexactinellid sponges associated with

abundant microbial structures (cf. Oloriz et al. 2006).

Comparison with similar facies from Europe

The Kimmeridgian–Lower Tithonian mud-mound from

Fagul Oltului Valley is very similar to the coeval pink

micritic limestone of the Bohunice Limestone Formation

from Babina Klippe, Czorsztyn Unit, Pieniny Klippen Belt

(cf. Misik et al. 1994; Aubrecht et al. 2009). The microf-

acies of the latter is also represented by a biomicrite,

packstone to mudstone with Saccocoma–Globochaete mi-

crofacies, numerous juveniles ammonites, numerous

Foraminifera, fragments of brachiopods as well as bivalves,

ostracods, and rare echinoid spines. This limestone con-

tains the brachiopods Nucleata bouei (ZEJSZ.) and

Lacunosella aff. spoliata (SUESS), which agree with a

Kimmeridgian to Lower Tithonian age. The level with

Lacunosella is 4.5 m thick and contains stromatactis,

which is very similar to that of the sequence studied here.

Another similar Saccocoma facies has been described by

Fig. 13 a Bioerosion of the calcitic brachiopod shells: a (FO2B7), b (FO2B5), of the foraminifer test and of the echinoderm fragments:

c (FO2B8)

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123

Biskaborn (2009) from the Kimmeridgian of Grafenberg,

Middle Franconian Alb, Bavaria, in southern Germany.

The Fagul Oltului mud-mound shows similar patterns

like the small sponge mud-mound described by Hammes

(1995) from the Southern Franconian Alb (Germany). The

density and the size of organisms (brachiopods, crinoids,

echinoids, small ammonites, etc.) rapidly increase just

above the basal unit of the German mud-mound, but

abundance does not reach the levels of the Fagul Oltului

section. The basal facies of the Fagul Oltului mound doc-

uments the first stage of mound development. It is char-

acterized by pioneer communities represented by crinoids

and sponges (probably siliceous sponges), which were able

to colonize the initially soft surface. Monty (1995) showed

that already very small, local hard substrates such as cri-

noid ossicles can act as local pavements, which stabilize

the sediment surface and are required for the fixation of

brachiopods. This scenario is also feasible for the basal

facies of the Fagul Oltului mound. Most probably, such

hard substrates were also provided by microbial crusts or

taphonomically mineralized sponges. The second stage of

the mud-mound was the domination stage (sensu Hammes

1995), when the mound buildup was formed mainly by

sponge-bearing peloidal crusts and siliceous sponges.

Bryozoans, benthonic foraminifers, serpulid and aggluti-

nated worms also encrusted the abundant peloidal crusts in

addition to the sponges. But the distinctive characteristic of

the Fagul Oltului mud-mound is the mass-occurrence of the

rhynchonellid brachiopod Lacunosella. The development

of such large populations of brachiopods was probably

favored by numerous factors such as:

• the large extension of the peloidal crusts, abundance of

crinoid ossicles, reduced sedimentation rates, rapid

lithification all favoring the development of hard

substrates necessary for the settlement of metazoan

larvae;

• the high abundance of mineralized sponges especially

within the middle part of the mud-mound (FO1A-

FO1F2; FO2B1-FO2B10) is positively correlated with

brachiopod abundance, the dead (mineralized) sponges

providing very good hard substrates for larval settle-

ment of the brachiopods; most probably there were

successions of biocoenoses represented by sponge-

hardgrounds with brachiopods growing on top, since

we observed numerous stromatactis structures sur-

rounded by brachiopods;

• and an environment particular rich in nutrients, which

was possibly generated by local upwelling or internal

waves (cf. Stanton et al. 2000), typical of moderately

deep intrashelf settings (cf. Pratt 1995).

Conclusions

The studied Fagul Oltului section (Haghimas Mountains)

is remarkable for the rich Kimmeridgian brachiopod

Table 1 Carbon and oxygen isotope composition of different rock

components

Sample d13C (PDB) d18O (PDB) Lithology

FO2B1 2.55 -1.05 Early drusy cement

FO2B1 1.70 -1.36 Micrite

L4 1.1 1.97 -2.27 Micrite

L4 1.2 2.61 -0.53 Early drusy cement

L4 1.3 2.32 -1.18 Micrite


L4 1.5 2.27 -1.53 Late blocky cement





L4 2.1 2.26 -1.32 Micrite










L4 3.8 2.15 -1.88 Micrite

L4 3.9 2.10 -2.01 Micrite

L4 3.10 2.22 -1.29 Micrite


L4 4.2 0.80 -2.30 Micrite

L0 2.60 -1.18 Lacunosella shell

Fig. 14 Crossplot of carbon and oxygen isotope values (d18O vs.

d13C) of different constituents of the rock

Facies

123

assemblage within a red carbonate buildup, which is doc-

umented as a stromatactis mud-mound herein, making it

the first example of this type of deposit in the Eastern

Carpathian Mountains, Romania. The mound consists

dominantly of bioclastic wackestone and packstone with a

very rich macrofauna of superabundant brachiopods, cri-

noids, sponges, juvenile ammonites, and echinoids. Tens of

thousands of rhynchonellid brachiopods are well preserved,

still exhibiting their original shell. Most specimens are

articulated, neither decorticated nor eroded and found in

the life position. A wide range of shell sizes indicates

successive biocoenoses. Besides the brachiopods, the most

significant feature of the studied mud-mound is stroma-

tactis. The presence of skeleton fragments of hexactinellid

sponges along with other diagnostic features like sediment

aggregates surrounded by radiaxial fibrous calcite, pores,

and borings within radiaxial fibrous calcite and the very

abundant micropeloidal fabrics and microbial crusts sup-

port an origin of stromatactis related to the taphonomy of

sponges. The carbon and oxygen stable isotope composi-

tion of carbonate cements agrees with a formation from

marine waters. The mass-occurrence of brachiopods dom-

inated by the rhynchonellid Lacunosella is consistent with

a setting below wave-base on a deep ramp with low sedi-

mentation rates and only little reworking. The Fagul Olt-

ului mud-mound is one of only a few Kimmeridgian

stromatactis mud-mounds described to date.

Acknowledgments This article is dedicated to Professor Ion Preda,

who had an intimate knowledge on the geology of the Haghimas

Mountains. Many years ago he encouraged us to study the Lacuno-sella-rich strata from this area. Unfortunately, he could not see these

results. We would like to acknowledge Professor Ioan Bucur, member

of the Romanian Academy, for his important contribution in identi-

fying the microfauna and for valuable discussion concerning the

stratigraphical range of the studied section. We also thank the

reviewers Eberhard Gischler and Steffen Kiel for their critical com-

ments that considerably improved the manuscript, Professor Eugen

Gradinaru for valuable observations concerning the general geology

of the area, Marius Stoica for helping us during field work, and Mi-

haela Gradinaru for her contribution during field and laboratory work.

This work was supported by ANCS project number 3788/2007,

GEOBIOHAS PNII–PARTENERIATE in CTR 31-059/2007 and by

CNCSIS–UEFISCSU, project 1922 PNII–IDEI 1003/2008.

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an unusual brachiopod assemblage in a late jurassic ......iuliana laza˘r • cristina e. panaiotu...

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