Nannostratigraphy and Palaeoecology of the Uppermost Mozduran Formation in the Jozak Section in West Kopet-Dagh (NE Iran)

doi:10.4236/ijg.2014.51003

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International Journal of Geosciences, 2014, 5, 12-19

Published Online Januar y 2014 (http://www.scirp.org/journal/ijg)

http://dx.doi.org/10.4236/ijg.2014.51003

Nannostratigr aphy an d P alaeoecolo gy of t he Uppermost

Mozduran Formation in the Jozak Section in West

Kopet-Dagh (NE Iran)

Mohammad Anvar Moheghy*, Fatemeh Hadavi

Department of Geology, Facult y of Science, Ferdowsi University of Mashhad, Mashhad, Iran

Email: *[email protected]

Received November 2, 2013; r evised D ecember 3, 2013; accep ted January 1, 201 4

Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original

and by SCIRP as a guardian.

ABSTRACT

This pa per disc usses t he bio stratigraphy and palaeoecology of calcareous nannofossils of the uppermost Mozdu-

ran Formation in the Jozak section in west Kopet-Dagh basin. The Mozduran Formation consists of white to

grey Limestone. In the stu died sectio ns, samples a re t aken and prepa red with smear slides. In the Jozak section,

17 species have been determined. Based on nannoplanktons and as a result of biostratigraphy studies, the nan-

nofossil standard zones (CC4) are identified. According to this zone, the age of the studied thickness is Early

Hauterivian in this section in west Ko pe t-Dagh basin. The presence of warm water indicators (Nannoconus,

Watznaueria , L ithraphidite s) suggests warm surface water conditions in the studied thickness. In the Jozak sec-

tion based on Nannoc o nus spp. , low fertility conditions a re suggested. The studied area is deposited in low to

middle latitudes and shallo w marine enviro nments.

KEYWORDS

Nannostratigraphy; Paleoecology; Mo z dur an; Shurije h; Kopet-Dagh; Iran

1. Introduction

Kopet-Dagh has a complete Cretaceous sedimentary

succession comprising marine shales, marly limestone

and subordinate sandstones. This sequence seems to

represent all stages of the Cretaceous [1].

The earliest paleontological studies of the Cretaceous

Formations o f the Kopet-Dagh and particularly Mozduran

Formation have been focused on the base on foraminifera.

The first comprehensive research on the calcareous

nannofossils of the Mozduran Formation in the east of

Kopet-Dagh in the Mozduran and Taherabad sections

was undertaken by Hadavi and Khodadadi [2].

Based on Calcareous nannofossils, the age of the

boundary between the Mozduran and Shurijeh Forma-

tions is Early Berriasian in the Mozduran section and

Late Valanginian in the Taherab ad section.

All of previous studies were inclusive study of whole

formation, but in the present study, for the first time, bi-

ostratigraphy and paleoecology of the uppermost Moz-

duran Formation in the Jozak section in west Kopet-

Dagh basin were discussed.

2. Geological Setting

The Mozduran Formation consists of shallow marine

dolomite and thin gypsum layers in the eastern part of

Kopeh-Dagh basi n, s ugges tin g that t he b asin i s sha llo wer

in the east than the west [3]. At Mozduran pass, the type

locality, the unit is about 500 m thick and overlies the

Moz duran For mation wit h an ap parent unc onfor mity and

is overlain by red clastic beds of Shurijeh Formation.

From the type locality southeastwards the thickness of

the Mozduran Formation decreases considerably and the

limestone and dolomites are replaced by sandstones, red

clastic rocks, and evaporites similar to the Shurijeh li-

*Corresponding author.

OPEN ACCESS IJG

M. A. MOHEGHY, F. HADAVI

thology [4].

The Shurijeh Formation consists of conspicuous red

beds, mainly sandstones and conglomerates; in more

northwestern outcrops the unit contains also some thin

gypsom layers and oolithic Limestone bands. Later, The

Shurijeh Formation was found to interfinger laterally

with the overlying Tirgan Formation northwest of the

Shurijeh type area. The thickness of the Shurijeh Forma-

tion varies from about 250 to 900 m [3].

The detailed observation of nannofossils gave us very

useful data, so this study is based on microscopic ana-

lyses of the calcareous nannoplanktons found in the

samples that were taken from the boundary between

Mozdur an and Shurijeh Format ions in west Kopet-Dagh

(Figure 1).

The thickness of the samples was 60 m in this section

and contained white to gre y Li mestone and brown to red

alternation of shale and sandstone (Figure 2).

Figure 1 . Geographical situation of studied section.

Figure 2 . Lithostrat igraphic column of t he bo undar y between Mozdur an and Shurij eh Fo rmations in t he Jozak s ection.

OPEN ACCESS IJG

M. A. MOHEGHY, F. HADAVI

3. Samples and Methods

A total of 13 samples from the boundary between Moz-

duran and Shurijeh Formations were collected. For cal-

careous nannofossils preparation, a small surface of the

sample was scraped with a razor blade (the razor used in

these preparations was washed with distilled water be-

tween samples) until a fresh surface was obtained, and

then, a small amou nt of sedimen t was mixed with a dr op

of distilled water and spread out evenly across a micro-

scope cover glass (we paid attention to the homogeneity

of the deposition so that calcareous nannofossils are

evenly distrib uted on the slide ); after this, susp ension has

dried up on a hot plate. The work area and the hot plate

that were used in making the smear slides were cleaned

using 10% HCl between sample preparations. This was

done to reduce the chance of contamination. The exami-

nation of nannofloras was performed by using a light

microscope at 1250× magnification. Digital images were

captured with a digital camera. All images were taken in

either cross polarized light (XP L) or plane p olar ized light

(PPL), they are shown on the (Plates 1-3). At first all

calcareous nannofossil specimens encountered were iden-

tified following the taxonomic schemes of several re-

nowne d a uthors [5-9] and then counted for the purpose of

palaeoecological studies. For counting in some purview,

all nannofossil species were counted. The percentage of

each species for drawing the diagrams was calculated

(Tables 1, 2).

4. Nannofossils Biostratigraphy and

Zonation

In the b oundar y between M ozdura n and Shurij eh For ma-

tions, biostratigraphic studies of calcareous nannofossils

have allowed the identification of calcareous nannofos-

Plate 1. All figures ×1250. (1): Nannoconus kamptneri, sample No. 5; (2): Zeugrha bdotus erect us, s a mpl e N o. 1; (3, 4): Nanno-

conus steinmannii, 3 sample No. 5, 4 sample No. 8; (5-7): Conusphaer a me xi c a na, 5 sample No. 3, 6 sample No. 7, 7 sample No.

10; (8, 9): Nannoconus dolomiticus, 8 sample No. 2, 9 sample No. 7; (10, 11): Watznaueria barnesae, 10 sample No. 1, 11 sam-

ple No. 1; (12): Assip et ra tereb rod entarius, sample No. 1; (13, 14): Didemnum minutum, 13 sample No. 1, 14 sample No. 4; (15):

Nannoconus kamptneri, sample No. 9; (16): Nannoconus sp. sample No. 1 2.

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M. A. MOHEGHY, F. HADAVI

Plate 2. All figures ×1250. (1-8): Lithraphidites bollii, 1 sample No. 2, 2 sample No. 5, 3 sample No. 9, 4 sample No. 6, 5 sample

No. 1, 6 sample No. 4, 7 sample No. 6, 8 sample No. 5; (9, 10): Nannoconus dolomiticus, 9 sample No. 5, 10 sample No. 2; (11,

12): Watznaueria biporta, 11 sample No. 1, 12 sample No. 1; (13): Tetralithus pseudotrifidus, sample No. 6; (14-16): Nannoco-

nus bucheri, 14 sample No. 6, 15 ample No. 4, 16 sample No. 11.

sils biozone CRETARHABDUS LORIEI (CC 4) in the

Jozak section with Early Hauterivian eage. This zone was

proposed by Sissingh [10]. The base of this zone is de-

fined as the first occurance (FO) of Cretarhabdus loriei

and the last occurance (LO) of Speetonia colligata de-

fines the top of the zone.

Remarks: The FO of Chiastozygus striatus is used in

the Boreal realm as a substitute marker for C. loriei. Sis-

singh suggested [10] a subdivision of CC 4 by the LO of

Biscutum sa lebrosum. T his has b ee n fou nd to b e an unre-

liable event, since B. salebrosum was found by several

authors in the Barremian and the Aptian/Albian. Perch-

Nielsen [11] suggested the FO of Eprolithus antiquus

and the LO of Cruciel lipsis cu villieri as additional events

to subdivide the Hauterivian in the Boreal realm. She

also used the LO of Chiastozygus striatus as a substitute

marker event for the top of CC 4. Thierstein [12] had

used the FO of Lithraphidites bollii and the LO of C.

cuvillieri for the subdivision of the Hauterivian in the

Tethyan realm. L. bollii was not found in the Boreal

realm.

In this boundary, Cretarhabdus loriei was ab se nt b ut L.

bollii is present, therefore according to Thierstein [12]

the age of the studied thicknes s is Early Hauterivian.

5. Nannofossils Diversity and Abundance

Abundant nannofossil assemblages and their occurrence

in shallow, ner itic settings in the Early Creta c e ous trop ic s

migration events into other eutrophic settings may have

occurred during periodic warming intervals [13].

In the uppermost Mozduran Formation, 17 species

were identified (Tables 1, 2). In spite of the indurated

lithology of the Mozduran and Shurijeh Formations,

Nannofloras are moderately preserved and relatively low

in diversity in this boundary. In these intervals, the low

nannofossil total abundances, and the poorly diversified

OPEN ACCESS IJG

M. A. MOHEGHY, F. HADAVI

Plate 3. All figur e s ×1250 . (1): Nannoconus colomii, 1 sample No. 3; (2-7): Calcicalathina alta, 2 sample No. 6, 2 sample No. 4, 3

sample No. 9, 4 sample No.10, 5 sa mple No. 12, 6 sample No. 2, 6 sample No.7; (8): Tetralithus cassianus, 8 samp le No. 3, (9,

10): Nannoconus bucheri, 9 sample No. 8, 10 sample No. 2; (11): Nannoconus dolomiticus, 11 sample No. 2; (12, 13): Lithra-

phidites bollii, 12 s ample No. 5, 1 3 sample No. 10; (14): Conusphaera Mexicana, 14 sample No. 5; (15): Didemnum m inutum, 15

sample No. 4; (15): Scapholithus fossilism, sample No. 6.

nannofossil assemblages are probably indicative of un-

favorable conditions in the water column [14]. The ab-

undance of all species does not follow a general pattern

as some species tend to increase or decline from base to

top. T he most c ommo n gene ra withi n the assemb lage a re

Nannoconus. In addition, Some species belonging to the

genera Watznaueria, Zeugrhabdotus, Tetralithus, Assi-

petra, Calcicalathina, Conusphaera and Lithraphid ites

are present in the assemblage but occurred only sporadi-

cally with relatively low percentage (Tables 1, 2).

6. Palaeoecology

Calcareous nannoplanktons are widespread in the recent

oceans, from coastal areas to open ocean settings. The

distribution of calcareous nannoplankton is intimately

linked to climatic zones and climate changes [15]. In the

present studies the following results obtained based on

the abundance species of calcareous nannofossils.

6.1. Fertility Indices

It has been demonstrated that calcareous nannofossil fer-

tility can play an important role in the reconstruction the

paleoenvironmental settings. Some nannofossil species

are good indicators of surface water fertility. Biscutum

spp. (mainly B. constans and B. ellipticum) and Zeugr-

habdotus s pp. (mainl y Z. erectus) are considered as indi-

cators of high surface water fertility in unstable envi-

ronments such as oceanic sites of upwellingor shelf areas

where trophic conditions may have been enhanced by

storm mixing or by runoff [16]. However, Biscutum

(mainly B. constans) is considered as an indicator of less

eutrophic conditions than Zeugrhabdotus spp. [17]. Cre-

tarhabdus spp., T. orionatus and Nannoconus spp. are

classified as indicators of low fertility conditions by dif-

OPEN ACCESS IJG

M. A. MOHEGHY, F. HADAVI

Table 1 . Ab unda n ce ta bl e of t h e re c og niz e d c al c are o us na n nof o ssi l s peci e s i n sample s fr o m t he u pper most Mozduran F or ma-

tion in the the Jozak section.

EARLY HAUTERIVIAN AGE

MOZDURAN SHURIJEH FORMATION

1 2 3 4 5 6 7 8 9 10 11 12 13 SAMPLE No.

12.50 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 As s i pe tra ter e b r o dentarius

0.00 16.64 0.00 14.28 18.00 20.02 35.20 0.00 25.50 40.20 26.00 0.00 52.70 Calcic alathina al ta

0.00 0.00 37.30 0.00 9.09 0.00 15.00 0.00 7.50 0.00 24.40 0.00 0.00 Conusphaera mexicana

12.50 0.00 0.00 28.57 0.00 0.00 20.00 0.00 17.20 0.00 0.00 0.00 0.00 Didemnum minutum

12.00 16.66 0.00 20.50 18.19 23.00 0.00 0.00 8.69 22.20 26.00 0.00 0.00 Lithraphidites bollii

0.00 16.60 0.00 36.65 0.00 10.44 0.00 55.20 18.36 0.00 0.00 53.30 0.00 Nannoconus bucheri

0.00 0.00 32.40 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Nannoconus colomii

0.00 50.10 0.00 0.00 17.18 0.00 29.80 0.00 10.80 21.00 0.00 0.00 0.00 Nannoconus dolomiticus

0.00 0.00 0.00 0.00 9.09 20.32 0.00 0.00 11.95 16.60 23.60 46.70 0.00 Nannoconus kamptneri

12.50 0.00 0.00 0.00 18.18 0.00 0.00 0.00 0.00 0.00 0.00 0.00 47.30

Nannoconus

sp.

0.00 0.00 0.00 0.00 0.00 14.11 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Scapholithus fossilis

0.00 0.00 0.00 0.00 10.27 0.00 0.00 44.80 0.00 0.00 0.00 0.00 0.00

Nannoconus steinmannii

0.00 0.00 30.30 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Tetralithus cassianus

0.00 0.00 0.00 0.00 0.00 12.11 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Tetralithus pseudotrifidus

10.50 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Watznaue ri a barnesa e

16.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Watznaue ri a biporta

24.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Zeugrhabdotus erectus

C. lorie i Nannofoss il event

CC4 Nannofossil zone

(Sissingh 1977)

Table 2. Di stri buti on of calc areous nanno fossils in the uppermost Mo zduran Formation fro m the Jo za k section.

EARLY HAUTERIVIAN AGE

MOZDURAN SHURIJEH FORMATION

CC4

ZONE Sissingh (1977)

1 2 3 4 5 6 7 8 9 10 11 12 13 SA MPLE No.

Assipetra terebrodentarius

Calc i c alathina al ta

Conus phaera mex icana

Didemnum minutum

Lithraphidites bollii

Nannoconus bucheri

Nannoconus colomii

Nannoconus dolomiticus

Nannoconus ka mptneri

Nannoconus sp.

Scapholithus fossilis

Nannoconus st einmann ii

Tetralithus cassianus

Tetralithus pseudotrifidus

Watznaueria barnesae

Watznaueria biporta

Z eugrhabdotu s erectus

OPEN ACCESS IJG

M. A. MOHEGHY, F. HADAVI

ferent authors [16,18]. Nannoconus spp. is the most ab-

unda nt nan nofo ssil gro up i n all sa mples exa mined i n this

study but Biscutum sp p. were absent and Zeugrhabdotus

spp. were very rare. According to abundance of nanno-

fossil assemblage in the Jozak section, were suggested

that the basin supported a restricted nannoflora, domi-

nated by shelf-adapted taxa with low fertility conditions

of surface waters.

6.2. Depth

The limiting role of water depth may be explained by a

number of interrelated neritic factors including environ-

mental stability, turbulence, transparency, salinity, and

nutrie nts or even wat er depth itself if the or ganism had a

benthic li fe-cycle stage [19]. The reasonably comprehen-

sive Early to Mid-Cretaceous biogeographic data suggest

there is now little doubt that the paleoecology of nanno-

conids was in some way related to water depth Nanno-

conus spp. has been interpreted as restricted to the lower

photic zone and to be controlled by fluctuations of the

depth of the nutricline [20]. Consequently, changes in

abundance of nannoconids and other coccoliths have

been used to reconstruct the fertility of surface waters

and nutria cline dynamics. High abundances of Nanno-

conus spp. may indicate a deep chlorop hyl l maximum

zone (DCM) with an increased productivity in the lower

photic zone [21]. Therefore, based on the high abun-

dances of Nannoconus spp., the Mozduran and Shurijeh

Formations were deposited in the relatively shallow ma-

rine environ ment .

6.3. Temperature and Latitudinal Distribution

Various species of Mesozoic calcareous nannofossils

have different temperature ranges [22] Cosmopolitan

taxa like Watznaueria barnesae covered a broad temper-

ature range, being common both in the low and the high

latitudes throughout most of the Mesozoic. Watznaueria

barnesae was common in tropical and subpolar regions

and may thus be viewed as a eurythermal taxon [23].

Other groups (e. g. Nannoconus, Conusphaera, Micula)

are most common in low latitudinal settings where they

were partly rock forming. Since they are rare in the Bo-

real Realm they have often been interpreted as Tethyan

warm water taxa [24]. Some cold water taxa (e. g. Ste-

phanolithion, Biscutum, Crucibis cuturn, Repagulum par-

videntatum, Seribiscutu m primitivurn, Sollasites falklan-

densis, Ceratolithin a , Kamptnerius, Nephrolithus) show

restricted palaeobiogeographic distribution patterns.

These taxa are most common only in the high latitudes

[25].

The diverse assemblages of the low latitudes are dom-

inated by Watznaueria spp., Rhagodiscus asper, Nanno-

conus spp., Micrantholithus spp. and Conusphaera spp.

These thermophile warm water taxa [17,26] indicate

relatively warm surface water temperatures of the trop-

ics and subtropic. These evidences suggest warm sur-

face water conditions and relatively low-middle latitude

in the up permost Mozd uran Formati on in the J ozak sec-

tion.

7. Comparison of Calcareous Nannofossils in

the West and East Kopet-Dagh

According to biostratigraphic studies, in the east Kopet-

Dagh, 19 species belonging to 12 genera of calcareous

nannofossils were recognized from the uppermost Moz-

duran Formation in the Mozduran section and 19 species

belo nging to 1 3 genera in the Taher abad sect ion. No ca l-

careous nannofossils were found in the lower part of the

Shurijeh Formation [2]. But In the Jozak section 17 nan-

noplanktonic species of 10genera were identified from

Mozduran and S hurijeh Fo rma tions (Tables 1, 2), unlike

the east Kopet-Dagh, Calcareous nannofossils existed in

the Shurijeh Formation in the west Kopet-Dagh, there-

fore, we conclude that environmental conditions in the

Mozduran and the Taherabad sections in the east of Ko-

pet-Dagh were better for calcareous preservation nanno-

fossils than t he west of Kopet-Dagh.

palaeoecological Comparison of the uppermost Moz-

duran Formation in the Jozak section in the west and

Mozduran and Taherabad sections in the east Kopet-

Dagh shows low fertility conditions, relatively low lati-

tude, warm water condition and shallow marine envi-

ronments. Based on Calcareous nannofossils, the upper-

most Mozduran Formation is assignable to Sissingh’s

(1977) [10] biozone CC1 (Early Berriasian) at the Moz-

duran section and to biozone CC3 (Late Valanginian) at

the Taherabad section in the east [2] and biozone CC4

(Early Hauterivian) at the Jozak section in the west, in-

dicating that the age of the top of the Mozduran Forma-

tion is diachronous across the basin and the uppermost

Mozduran Formation is younger from east to west in the

Kopeh-Dagh basin.

8. Conclusion

In this study, 17 species were identified in the boundary

between Mozduran and Shurijeh Formations in the Jozak

section. As the result of biostratigraphic studies, a bio-

zone is su gge sted whic h is eq uiva lent to CC4 o f Si ssing h

[10]. In the base of this zone, the age of studied thickness

is Early Hauterivian. Acc ording to the studies, the nanno-

fossil assemblages show mod erately preservation and the

abundant variation of species suggests that the Mozduran

and Shurijeh Formations were deposited in the relatively

shallow marine environments in low to middle latitudes

with warm surface water a nd low fertility cond itions.

OPEN ACCESS IJG

M. A. MOHEGHY, F. HADAVI

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