Accepted Manuscript
Benthic foraminifera as biostratigraphical and paleoecological indicators: an example from Oligo-Miocene deposits in the SW of Zagros basin, Iran
Asghar Roozpeykar, Iraj Maghfouri Moghaddam
PII: S1674-9871(15)00044-4 DOI: 10.1016/j.gsf.2015.03.005 Reference: GSF 355
To appear in: Geoscience Frontiers
Received Date: 29 September 2013 Revised Date: 26 February 2015 Accepted Date: 17 March 2015
Please cite this article as: Roozpeykar, A., Moghaddam, I.M., Benthic foraminifera as biostratigraphical and paleoecological indicators: an example from Oligo-Miocene deposits in the SW of Zagros basin, Iran, Geoscience Frontiers (2015), doi: 10.1016/j.gsf.2015.03.005.
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MANUSCRIPT
ACCEPTED ACCEPTED MANUSCRIPT
Benthic foraminifera as biostratigraphical and paleoecological indicators: an example from Oligo-Miocene deposits in the SW of Zagros basin, Iran
Asghar Roozpeykar*, Iraj Maghfouri Moghaddam
Department of Geology, Faculty of Sciences, University of Lorestan, Lorestan, Iran
* Corresponding author. Postal address: 7579111548-Janbazan Avenue-Dehdasht City-
Kohgiluyeh va Bouyer Ahmad Province-Iran;
Tel.: +989179428793; E-mail address: [email protected]
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Abstract
The Asmari Formation is a predominantly carbonate lithostratigraphic unit that outcrops in the Zagros Basin. Micropaleontological studies of the Asmari Formation in the Dehdasht area led to the identification of 51 species of foraminifera taxa. Among the foraminifera,
Nummulites cf. vascus, Operculin sp ., Opercolina complanata, Eulepidina dilatata,
Eulepina elephantine, Ditrupa sp., Miogypsina sp ., Elphidium sp . 14, and Borelis melo curdica are the most important. The Lepidocyclina-Operculina-Ditrupa assemblage zone represents the Rupelian–Chattian age. The Aquitanian age is also defined by co-occurrence of Miogypsina sp. and Elphidium sp. 14, and finally, the first occurrence of Borelis mello curdica represents the Burdigalian. Based on faunal assemblages, the following paleoenvironmental settings are determined for the deposition of the study section: (1) the deep, offshore settings in the aphotic zone dominatMANUSCRIPTed by pelagic and small benthic foraminifera; (2) the low energy, turbid and low light parts of the oligophotic zone characterized by large and flat lepidocyclinids ( Eulepidina ) and Nummulitidae; (3) the low turbidity, deeper part of the inner ramp dominated by Miogypsinoides , Neorotalia ,
Lepidocyclina , Operculina and Archias ; (4) the shallow, marginal marine environment exposed to salinity fluctuations (short-term salinity fluctuations or fully marine conditions) dominated by small benthic Foraminifera (Ammonia and Elphidium ); (5) highly translucent, shallowest part of the inner ramp dominated by representatives of Borelis , Meandropsina and PeneroplisACCEPTED. The biotic assemblages represent warm tropical waters with oligotrophic to slightly mesotrophic conditions. ACCEPTED MANUSCRIPT 3
Key words: Biostratigraphy; Asmari Formation; Iran; Oligo-Miocene; Oligotrophy;
Mesotrophy
1. Introduction
In most carbonate depositional environments, the bulk of sediment consists of skeletal fragments produced by different types of organisms with particular ecological requirements
(Meteu-Vicens et al., 2008). Oligocene carbonate platforms are characterized by the re- establishment of shallow water marine benthic communities following major change at the
Eocene/Oligocene boundary (e.g. Berggren and Prothero, 1992; Ivany et al., 2000;
Prothero, 2003). During the Neogene, large benthic foraminifera (LBF) were still active carbonate producers, though not as prolific as during the Eocene. Heterostegina,
Amphistegina, Cycloclypeus, and Lepidocyclina are common in packstones and grainstones of the late Oligocene through Miocene (e.g., ChaproMANUSCRIPTnière, 1984; Betzler, 1997; Hallock et al., 2006a). Coralline red algae increased in diver sity during the Oligocene (e.g., Manker and Carter, 1987; Buxton and Pedley, 1989; Pedley, 1998; Rasser and Piller, 2004), especially the shallow, warm-water lithophylloid and mastophoroid taxa, exhibiting their greatest species richness (Aguirre et al., 2000) and globally becoming dominant carbonate producers (Halfar and Mutti, 2005) during the early and middle Miocene. Larger foraminifera have arisen many times in the geological record from ordinary-sized ancestors
(Lee et al., 1979). Their appearance is often related to periods of global warming, relative drought, raisedACCEPTED sea levels, expansion of tropical and subtropical habitats, and reduced oceanic circulation (Hallock and Glenn, 1986). ACCEPTED MANUSCRIPT 4
The main factor limiting the latitudinal distribution of symbiont-bearing foraminifera is temperature (e.g. Hottinger 1983; Langer and Hottinger, 2000) because persistent temperatures below 14 °C in the winter months seem to hinder their survival. Larger foraminifera are thus restricted to the tropics with the exception of a few species that can also survive in the warm temperate zone (e.g. Betzler et al., 1997; Hohenegger et al., 2000;
Langer and Hottinger, 2000). Further factors influencing the distribution of larger foraminifera are light intensity, water energy and substrate conditions (Hottinger, 1988;
Bassi et al., 2007). LBF and corallinacean are the most important biotic assemblages in the
Asmari Formation. In the present work, we use the foraminiferal assemblages to determine the age of the Asmari Formation from the studied region and to interpret the paleoenviromental settings and paleoecological conditions. 2. Geological setting MANUSCRIPT The Zagros mountains are a fold and the thrust belt that extends from southeastern
Turkey through northern Syria and Iraq to western and southern Iran (Alavi, 2004). This orogenic belt is situated in the middle part of the Alpine Range. This belt is considered to be a passive eastern margin of the Arabian Shield (Stocklin, 1968; Farhoudi, 1978;
Berberian and King, 1981). The Zagros Basin was a part of the stable supercontinent of
Gondwana in the Paleozoic, became a passive margin during the Mesozoic, and then a convergent orogen in the Cenozoic (Bahroudi and Koyi, 2004). The Zagros mountains consists of threeACCEPTED zones: (1) the simply folded Zagros; (2) the imbricate thrust zone; (3) the Khozestan Plain (Motiei, 1993). Based on the sedimentary history and structural style,
Falcon (1961) divided the simply folded Zagros into several zones: Fars, Lurestan, the ACCEPTED MANUSCRIPT 5
Dezful Embayment, the Izeh Zone, the Abadan Plain, the thrust zone, the Bandar Abas
Hinterland and the complex structure with metamorphic rocks (Fig. 1A). The study area is located at the southwestern flank of the Kuh-e Siah Anticline, next to the Zargham Abad
Village, about 80 km northeast of Behbahan and 15 km north of Dehdasht. The section was measured in detail at 30°52 ΄ N and 50°38 ΄ E (Fig. 1B). The study area is located in the folded thrust zone of the Zagros Basin (Izeh Zone).
3. Materials and methods
Field observations were complemented with the petrographic examination of 157 thin sections for the identification of large benthic foraminifera and other skeletal components.
The supraspecific classification of foraminifera mainly follows Loeblich and Tappan
(1988) criteria. Large benthic foraminifera are photosymbiontic organisms (Leutenegger, 1984; Reiss and Hottinger, 1984) that require lightMANUSCRIPT, which restricts these taxa to live in the photic zone. Changes in foraminiferal assemblages can indicate fluctuations in light level, providing information valuable for interpretation of palaeoenvironments (Hallock and
Glenn, 1986; Hottinger, 1997; Hohenegger et al., 1999)
4. Results
The Asmari Formation outcrops with 318 m thickness in the study area, and consists of thin to thick bedded and massive limestones, nodular limestones, and rarely, marls.
Biogenic components are dominated by benthic foraminifera and coralline red algae. The existing benthicACCEPTED foraminifera correspond to agglutinated small foraminifera, porcellaneous and perforated larger benthic foraminifera (LBF) and smaller benthic foraminifera (SBF).
Coralline red algae are dominated by Lithothamnion sp., Lithophyllum sp., Mesophyllum ACCEPTED MANUSCRIPT 6
sp., Sporolithon sp., Lithoporella mellobesioides, Titanoderma sp. and Lithoporella sp.
Subordinate components are ostrea, pectinid bivalves, corals ( Porites sp., Favosites sp.,
Tarbellastraea sp., Thegioastraea sp. and Hydnophora sp.), gastropoda, bryozoan, ostracoda and echinoids. Ooid and peloid are the most common abiotic components. The
Asmari Formation overlies the Pabdeh Formation and is overlain by Gachsaran Formation.
4.1. Biostratigraphy
Planktonic foraminifera are rare in the Asmari Formation, making correlation with the planktonic zonation difficult. Therefore, biostratigraphic zonation is mainly based on the larger benthic foraminifera which are very abundant and have high diversity in the study section. The identified foraminifera fall into the following categories: LBF, smaller benthic foraminifera and pelagic foraminifera. The biostratigraphy of Asmari Formation was described by Wynd (1965), James and WyndMANUSCRIPT (1965) and reviewed by Adams and Bourgeois (1967). Adams and Bourgeois (1967) divided the Asmari Formation into three biozones (Fig. 2). Ehrenberg et al. (2007) and Laursen et al. (2009) applied strontium isotope dating to the Asmari Formation (Fig. 2). In order to date the age of Asmari
Formation, the present research used the results of Sr analysis.
It is worth noting that in older publications, such as those of Wynd (1965) and Adams and Bourgeois (1967), microfossils ascribed to the “Aquitanian ” may in fact refer to the late Oligocene, what we today call Chattian. Aside from these problems with the determination ACCEPTEDof chronostratigraphy of the foraminifera-based zones, facies are specific to particular zones, and thus they complicate the basin-wide stratigraphic correlations. One way to solve this dating problem is to calibrate the ranges of index fossils with an ACCEPTED MANUSCRIPT 7
independent dating method such as the Sr-isotope stratigraphy, which is not sensitive to depositional environments (Laursen et al., 2009).
From base to top, three foraminiferal assemblages were determined in the study area.
4.1.1. Assemblage I.
This assemblage begins at the basal part of the Asmari Formation and extends upward with a thickness of 141 m. The most important fauna are: Operculina complanata,
Operculina spp., Heterostegina spp. , Nummulites vascus, Eulepidina spp., Eulepidina elephantine, Nephrolepidina tournoueri, Spiroclypeus spp., Spiroclypeus blankenhorni and
Ditrupa. Additional species include Austrotilina howchini, A. asmariensis, Rotalia viennoti,
Miogypsinoides complanatus and Archaias sp.
These foraminifera correspond to the Lepidocyclina–Operculina–Ditrupa assemblage zone of Laursen et al. (2009). This zone ranges in age MANUSCRIPTfrom Rupelian to Chattian. 4.1.2. Assemblage II.
This assemblage was recorded from 141 to 214 m. Most of the fauna in this assemblage are Miogypsina sp., Elphidium sp. 14 , Peneroplis evolutus, Valvulinid sp., Spirolina sp.,
Schlumbergerina sp., Meandropsina iranica, Dendritina rangi, Austrotrillina sp.,
Austrotrillina asmaricus, Peneroplis sp., Peneroplis evolotus, Triloculina trigonula,
Discorbis sp., and Peneroplis thomasi.
These microfauna correspond to the Miogypsina-Elphidium sp., Peneroplis farsensis assemblage zoneACCEPTED of Laursen et al. (2009), and they indicate an Aquitanian age. ACCEPTED MANUSCRIPT 8
There are very fossil poor limestones from 214 to 234 m, in between the assemblage zone II and assemblage zone III. This has been named the “indeterminate zone” by Laursen et al. (2009), and it is mainly associated with the Aquitanian age.
4.1.3. Assemblage III.
This assemblage was recorded from 234 to 318 m. The most important foraminifera are:
Borelis mello curdica , Borelis sp., Peneroplis evolotus , Dendritina rangi, Meandropsina iranica , Discorbis sp. and Rotalia sp. The fauna association represents the Borelis mello curdica- B. melo melo assemblage zone of Laursen et al. (2009) which indicates a
Burdigalian age.
4.2. Comparison with other regions of Zagros Basin
The biostratigraphy of the Asmari Formation in various regions of the Zagros Basin has been proposed by many researchers. In this paper,MANUSCRIPT we compared the Asmari Formation in the study area with some sections in other regions of the Zagros Basin (Fig. 3). Vaziri-
Moghaddam et al. (2010) studied the depositional environment, biostratigraphy and the sequence stratigraphy of several sections in the NW of the Zagros Basin. In the Kabir Kuh section (southern Lurestan Basin), the Asmari Formation was deposited in the late
Oligocene (Chattian)–early Miocene (Aquitanian–Bourdigalian) age. In the Mamulan and
Sepid Dasht areas (central Lurestan Basin), the Asmari Formation was only in the
Bourdigalin age. Sadegi et al. (2009) reported that the Asmari Formation, southeastern of the Zagros foldedACCEPTED belt (Fars Province), was deposited in the Oligocene (Rupelin–Chattian) age. This age was also reported by Soltanian et al. (2011) for the Asmari Formation at the
Naura Anticine in Fars area. In these areas, the middle and upper parts of the Asmari ACCEPTED MANUSCRIPT 9
Formation were replaced by Gachsaran and Razak formations. In the Gachsaran area (Mish
Anticline), according to Van Buchem et al. (2010), the age of Asmari Formation is
Oligocene–early Miocene (Aquitanian–Burdigalian). Research results show that the age of the Asmari Formation changes from Oligocene (Rupelian–Chattian) to Oligocene–early
Miocene age from the SE to the middle parts of the Zagros Basin. In other words, the age of the Asmari Formation becomes younger from the SE to the middle parts of the basin. From the central parts to the NW of the basin, the age of the Asmari Formation changes from late
Oligocene–early Miocene to early Miocene (Burdigalian) age. These changes of the Asmari
Formation’s age are related to paleoenvironmental conditions.
During the Paleogene period, the Zagros Basin was completely covered by a transgressive sea (Fig. 4). In that time, three sub basins existed in the Zagros Basin: (1) Lurestan Province (northwestern parts), (2) KhuzestMANUSCRIPTan Province (central parts) and (3) Fars Province (southern parts). During the Paleocene–ear ly Eocene, the Sachun Formation was deposited in the coastal parts (western Fars Province), the Jahrum Formation in the shallow parts (eastern Fars Province), and the pelagic Pabdeh Formation in the deep parts of the basin. During the middle Eocene, the shallow platform parts emerged from water due to the
Pyrenean orogenic phase and the global sea level drop. The deposition of the Pabdeh
Formation continued only in the central parts. These conditions continued up to the late
Eocene–Oligocene in the northeastern and southern parts of the basin. As the sea level continued to fallACCEPTED during the early Oligocene, in the central parts of the basin the Asmari Formation was replaced by the Pabdeh Formation (Figs. 4 and 5). At the end of the late
Oligocene, the transgressive sea caused the remaining exposed regions to become ACCEPTED MANUSCRIPT 10
submerged. This, in turn, caused the deposition of the Asmari Formation in these regions although the northern parts of the basin were still exposed. These conditions continued for the northern parts up to the end of Aquitanian age. At the beginning of the Burdigalian, the transgressive sea caused the Asmari Formation to be deposited in every region of the
Zagros mountains (Motiei, 1993) (Figs. 4 and 5).
4.3. Paleoeecological interpretation
Foraminifera are the most abundant marine protozoa in the epipelagic and the upper mesopelagic realms. Because of the complexity and diversity of habitats, especially in the shallow benthic realm, foraminifera show high biodiversity resulting from their different ecological requirements (Barbieri et al., 2006).
Based on the type of distribution and paleoecological conditions, the faunas were grouped into five assemblages (Table 1, Figs. MANUSCRIPT 6 and 7). Assemblage 1 is dominated by planktonic foraminifera along with shallow water benthic foraminifera as Elphidium,
Rotalia and Textularia . Their rock texture is wackestone-packstone (Fig. 6A and B).
Assemblage 2 is represented by Lepidocyclinids with large and discoidal tests (Eulepidina ) and Nummulitids (Heterostegina sp., Nummulites cf. vascus, Spiroclypeus sp., Operculina complanata, Spiroclypeus blankenhorni, Operculina sp.). The LBF skeletons are mostly more than 3 cm in diameter. The texture is wackestone to packstone (Fig. 6C–F).
Assemblage 3 is characterized by co-occurrence of larger hyaline and imperforated forms (Fig. 7A–D).ACCEPTED Hyaline foraminifera were dominated by Miogypsinoides formosensis, Miogypsinoides complanatus, Lepidocyclina sp., Amphistegina sp., Operculina sp.,
Asterigerina sp., Miogypsina sp., Elphidium sp. 14., Sphaerogipsina sp., Discorbis sp., and ACCEPTED MANUSCRIPT 11
Neorotalia viennoti together with Neorotalia sp. Porcellaneous foraminifera were dominated by Austrotrillina howchini, Austrotrillina sp., Archaias sp., Planorbolina sp.,
Triloculina trigonola , Pyrgo sp., Triloculina tricarinata, Peneroplis evolutus, Peneroplis sp., Meandropsina iranica, Meandropsina sp. and Peneroplis thomasi .
Assemblage 4 is dominated by small benthic foraminifera (Fig. 7E and F). The diversity of fauna is very low in some samples, but it is very high in other samples.
Ammonia spp. and A. beccarii are the only biota elements in samples with low diversity.
The samples with high diversity fauna are characterized by Ammonia spp., A. beccarii,
Elphidium sp., Discorbis sp. and miliolids . Bryozoan, echinoids, mollusks and corallinacean are also present. Texture ranges from wackestone to packstone . Finally, assemblage 5 is characterized by larger imperforated foraminifera including (Fig. 7G and H): Dendritina rangi., Peneroplis evolutus, MANUSCRIPT Peneroplis sp., Meandropsina iranica, Meandropsina sp., Peneroplis thomasi, Borelis mello curdica, Borelis sp., Triloculina trigonola, Pyrgo sp., Triloculina tricarinata . Textularia sp., Discorbis sp., Spirolina sp.
Elphidim sp. is present but not common.
In Assemblage 1, abundant pelagic foraminifera represent a more pelagic, deep offshore environment (Mateu-Vicens et al., 2008). The absence of light-dependent biota such as corallinacea and LBF indicates that these fauna developed under aphotic conditions in an outer ramp setting (Pomar et al., 2004). The high muddy matrix indicates low turbulence water (NebelsickACCEPTED et al., 2000). Assemblage 2 is characterized by the dominance of large discoidal tests of Lepidocyclinids ( Eulepidina ) and Nummulitids. Fine silisiclastic particles are also present in the texture. The large sized lepidocyclinids and discoidal flat tests ACCEPTED MANUSCRIPT 12
(Eulepidina ) are typical for a low energy environment with a low light on the outer ramp
(Hallock, 1985; Hallock and Glenn, 1986). The predominance of large foraminifera may indicate a highly oligotrophic palaeoenvironment dominated by K-strategists (Bassi, 2005).
The sediments of Assemblage 3 suggest different degrees of water turbulence were involved in the creation of the packstone-grainstone texture. Abundance of larger benthic foraminifera suggests shallow, well-illuminated, warm, oligotrophic waters with suitable
Connell et al., 2012) and normal marine׳ substrate (Hottinger 1983; Murray 1991; O salinity. The mixture of large rotalids and the sea grass associated bioclasts (porcellaneous forms and small rotalids) indicates meso-euphotic conditions (Pomar et al. 2014). The grainstones represent a higher degree of turbulence with mobile substrate and fauna indicating well-lit conditions (Nebelsick et al., 2000), which is also shown by robust and thick tests of foraminifera (Fournier et al., 2004)MANUSCRIPT. In shallow waters, where light limitation is not problematic, LBF can produce thick tests, which protect the test from mechanical damage due to the increased hydrodynamic energy in shallow waters (Hohengger, 2000).
In Assemblage 4, the predominance of Ammonia and ostrea indicates a eutrophic environment with normal marine conditions that were only exposed to short-term salinity fluctuations (Reuter and Brachert, 2007). The presence of bryozoans together with microfossil assemblages with their relatively high diversity in some samples might suggest that the environmental conditions changed from unstable with salinity fluctuations to more stable conditionsACCEPTED and the normal salinity (Filipescu et al. 2014). The abundance of Ammonia and the occurrence of Textularia and heterotrophic organisms in the microfacies may indicate increased nutrient input (Sen Gupta 1999; Mateu-Vicens et al. 2008). The ACCEPTED MANUSCRIPT 13
dominance of porcellaneous larger foraminifera in Assemblage 5 indicates high-energy conditions in the well-lit, highly translucent, shallow part of the photic zone (Bassi and
Nebelsick, 2010). The low turbidity is ascribed to the high diversity of the porcelaneous foraminiferal fauna, which develops in meso-to-oligotrophic settings at a shallow depth
(Hallock, 1984, 1988; Reiss and Hottinger, 1984; Buxton and Pedley, 1989; Romero et al.,
2002; Barattolo et al,. 2007). The dominance of imperforate foraminiferal tests may indicate a slightly hypersaline depositional environment (Bandano et al., 2009). Based on the occurrence and morphology of foraminifera, our palaeoecological interpretation shows a gradient change from deep offshore, low energy conditions in aphotic zones dominated by planktonic foraminifera to a deep, turbid, low-light setting in the oligophotic zone dominated by Eulepidina (elephantine, dilatata , sp.) and Nummulitids (Heterostegina sp ., Operculina sp ., O. complanata., Spiroclypeus MANUSCRIPTsp., S. blankenhorni ). Following this, the conditions change again to deeper parts of the inner ramp dominated by Miogypsinoides complanatus, Neorotalia viennoti, Lepidocyclina sp., operculina sp . and Archaias sp., then to Assemblage 4 with a shallow, marginal marine environment exposed to salinity fluctuations (brackish or close marine value) dominated by small benthic foraminifera
(Ammonia spp. and Elphidium sp .), and finally to the near shore, well-lit, highly translucent, high energy conditions in an inner ramp setting dominated by Borelis mello curdica, Meandropsina iranica and Peneroplis evolotus (Fig. 8). 4.4. Paleolatitude,ACCEPTED Paleoclimate and Nutrient level The existence of aragonite components such as corals ( Porite s sp.) in the Chattian–
Aquitanian, ooids in the Aquitanian, and finally the persistent occurrence of lithoporella ACCEPTED MANUSCRIPT 14
melobesioides and lithoporella sp. in the red algal assemblages (Braga and Aguirre, 2001) of the Asmari Formation suggest that carbonate sedimentation took place in the warm waters of the tropical zone. According to the Oligo-Miocene paleogeographic maps developed by Heydari (2008), the Zagros mountains were located at about 29° N, confirming that the Asmari deposition took place in warm waters.
The Oligocene saw global climates show an initial cooling as a consequence of the formation of the first ice-sheets in Antarctica that persisted until the latest part of the
Oligocene, followed by a warming trend that reduced the extent of Antarctic ice (Zachos et al., 2001). This global climatic cooling and Antarctic glaciation influenced sedimentation worldwide during the middle Eocene to early Miocene that is documented in marine and terrestrial faunal and floral changes, seismic interpretations and oxygen and carbon isotope analyses (e.g. Miller et al., 1991, 2005; Prothero,MANUSCRIPT 1994; Abreu and Haddad, 1998; Clarke and Jenkyns, 1999; Zachos et al., 2001). The study section did not reveal the Oligocene cooling events.
Warmer global climates prevailed during the Miocene than those either of the preceding
Oligocene or of today. During this time, the modern pattern of ocean circulation was established and the mixing of warmer tropical water and cold polar water was greatly reduced. This led to well-defined climatic belts that stretch from Poles to Equator (Pomar and Hallock, 2008). During theACCEPTED Aquitanian, there is evidence for a cooling event (Miller et al., 2005). This cooling event caused the eustatic sea-level drops during the Aquitanian, which twice caused the isolation from the Neo-Tethys and led to the precipitation of subaqueous anhydrites ACCEPTED MANUSCRIPT 15
from the oversaturated seawater through evaporation in its centre (the ‘Basal Anhydrite’ and ‘Middle Anhydrite’). The faunal assemblage in the Aquitanian was influenced by this isolation from the open ocean, which caused an increase in the salinity of the intrashelf basin. The resultant specific environmental conditions led to a restricted, stressed environment: ooids, peloid and imperforate foraminifers became an important biotic and abiotic association in the depositional system (Van Buchem et al., 2010).
Zooxanthellate corals and LBF assemblages, such as Lepidocycina , Miogypsinoides ,
Operculina , Heterostegina, Borelis, Archaias of the Asmari Formation argue against high nutrients, as these assemblages thrive in oligotrophic (Langer and Hottinger, 2000) or possibly slightly mesotrophic (Halfar et al., 2004) waters.
5. Conclusions The large benthic foraminiferal assemblagesMANUSCRIPT are rich in the Asmari Formation. The most important faunas are Nummalites cf .vascus, Eulepidina elephantine, Archaias sp.,
Miogypsinoides complanatus, Spiroclypeus blankenhorni, Miogypsina sp., Elphidium sp .
14 and Borelis mello curdica. Based on the distribution of foraminifera assemblages, the
Asmari Formation in the studied section is Oligocene (Rupelian– Chattian)–early Miocene
(Aquitanian–Bourdigalin) in age. The biotic assemblages of the Asmari Formation suggest that carbonate sedimentation took place in tropical warm waters under oligotrophic or slightly mesotrophic conditions. The paleoenvironmental setting is interpreted as a shallow ramp environmentACCEPTED ranging from deep, offshore settings in the aphotic zone dominated by pelagic and smaller benthic foraminifera, to low-energy, turbid and low light conditions characterized by large and flat lepidocyclinids ( Eulepidina ) and Nummulitids, to the deeper ACCEPTED MANUSCRIPT 16
parts of the inner ramp dominated by Miogypsinoides , Neorotalia , Lepidocyclina ,
Operculina and Archias , to the shallow, marginal marine environment exposed to salinity fluctuations (brackish or hemirestrcted marine) dominated by small benthic foraminifera
(Ammonia and Elphidium ), and finally to well-lit, highly translucent shallow parts of the inner ramp dominated by Borelis , Meandropsina and Peneroplis.
6. Systematic Paleontology
6.1. Systematic of foraminifera
Larger foraminifera are the most important components of the Oligocene–early
Miocene succession. They allow the biostratigraphic subdivision of the studied section. A total number of 51 species of foraminifers taxa have been identified. These foraminifera correspond to agglutinated small foraminifera, porcellaneous and perforate larger benthic foraminifera (LBF) and smaller benthic foraminiferaMANUSCRIPT (SBF) (Figs. 9–11). Superfamily Asterigerinacea (dʼOrbigny, 1839)
Family Lepidocyclinidae (Scheffen, 1932)
Subfamily Lepidocyclininae (Scheffen, 1932)
Genus Lepidocyclina (Gumbel, 1870)
Eulepidina dilatata (Michelloti, 1861, Fig. 11J and H)
Remarks: Adams and Bourgeois (1967) as well as Laursen et al. (2009) reported two species of Eulepidina from the Asmari Formation within the Rupelian and Chattian. Description: ThisACCEPTED species of Eulepidina is characterized by the smaller size (<3 cm) and regular pillars between the chambers that become evenly distributed over the surface of the test. The other species is named dilatata (Michelotti), which is distinct from elephantine by ACCEPTED MANUSCRIPT 17
its too-large size and a size of more than 10 cm in diameter, and is characterized by giant embryon, extraordinarily large equatorial chamberlets and the general absence of regular pillars which penetrate to the surface.
Superfamily Asterigerinacea (dʼOrbigny, 1839)
Family Lepidocyclinidae (Scheffen, 1932)
Subfamily Lepidocyclininae (Scheffen, 1932)
Genus Lepidocyclina (Gumbel, 1870)
Lepidocyclina (Nephrolepidina ) tournoueri (Lemoine and Douvillé, 1904, Fig. 11C)
Remarks: Adams and Bourgeois (1967) as well as Laursen et al. (2009) recorded this from the late Rupelian and Chattian in the Asmari limestones.
Description: This species possesses a strongly biconvex test. The embryonic chambers consist of a protoconch and a deuteroconch withMANUSCRIPT relatively equal size and without any embrace. The lateral chambers have relatively large sizes, and the pillars between them are absolutely distinct and obvious.
Superfamily Nummulitacea (De Blainville, 1827)
Family Nummulitidae (De Blainville, 1827)
Genus Operculina (d’Orbigny, 1826)
Operculina complanata (Defrance, 1822, Fig. 11D)
Remarks: Adams and Bourgeois (1967) as well as Laursen et al. (2009) reported Operculina complanataACCEPTED from the Rupelian–Chattian age. It was also found by Bassi et al. (2007) in the upper Oligocene of the Venetain area, Northeast Italy. ACCEPTED MANUSCRIPT 18
Description : Test bilaterally symmetrical, evolute, planispiral, flattened; with little or no thickening at the poles. Its margins are always rounded and the septa are gently recurved.
Superfamily Nummulitacea (De Blainville, 1827)
Family Nummulitidae (De Blainville, 1827)
Genus Nummulites (Lamarck, 1804)
Nummulites vascus (Joly and Leymeraie, 1848, Fig. 10J)
Remarks: This species was reported from southwest of Iran by Adams and Bourgeois
(1967) and Larsen et al. (2009). It was also described by Bassi et al. (2007) in the upper
Oligocene of the Venetain area, Northeast Italy.
Description : The test is lenticular, wall calcareous hyaline, and planispirally coiled with four whorls. The thickness of wall and chambers are relatively equal. Superfamily Nummulitacea (De Blainville, 1827)MANUSCRIPT Family Nummulitidae (De Blainville, 1827)
Subfamily Cycloclypeinae
Genus Spiroclypeus (Douvalle, 1905)
Spiroclypeus blankenhorni (Henson, 1937, Fig. 11F and G)
Remarks: Adams and Bourgeois (1967) recorded Spiroclypeus blankenhorni from the
Aquitanian of Asmari Formation. But Ehrenberg et al. (2007) and Laursen et al. (2009) reported it from Chattian of the Asmari Formation. It was also described by Özcan et al. (2009) in the lowerACCEPTED Miocene of central Turkey. Description: This form is characteristically elongate-compressed, non reticulate, with relatively fine later chamberlets. ACCEPTED MANUSCRIPT 19
Genus Austrotrillina (Parr, 1942)
Genus Austrotrilina asmariensis (Adams, 1968, Fig. 9C)
Remark: Adams (1968) obtained the type specimens of A. asmariensis from the post- nummulititic Asmari Limestone. Adams and Bourgeois (1967) and Laursen et al. (2009) recorded this species from the Rupelian–Aquitanian. It was also described by Bassi et al.
(2007) in the upper Oligocene of the Venetain area, Northeast Italy.
Description : This species is characterized by its narrow, closely packed alveoles, which were present in a single series and did not bifurcate peripherally. Open chamber lumen, quinqueloculine nepionic stage consists of spherical proloculus followed by three chambers, and by later chambers arranged in triloculine manner. Nepionic stage walls are very thick and non alveolate. Superfamily Miliolacea (Ehrenberg, 1839) MANUSCRIPT Family Austrotrillinidae (Loeblich and Tappan, 1986)
Genus Austrotrillina (Parr, 1942)
Austrotrilina howchini (Schlumberger, 1893, Fig. 9B and M)
Remark: A. howchini was first described from the Tertiary of Australia. Adams and
Bourgeois (1967) and Laursen et al. (2009) reported this species from the Rupelian–
Aquitanian age of Asmari Formation.
Description: This species has chambers which are triangular in transverse section and also has alveoles whichACCEPTED bifurcate, trifurcate, the interior alveoles being divided peripherally into smaller alveolus.
Superfamily Alveolinacea (Ehrenberg, 1839) ACCEPTED MANUSCRIPT 20
Family Alveolinidae (Ehrenberg, 1839)
Genus Borelis (Montfort, 1808)
Borelis mello (Fichtel and Moll, 1798) curdica (Reichel, 1937, Fig. 10E)
Remark: This species was recorded by Adams and Bourgeois (1967) and Laursen et al.
(2009) from the Burdigalian of Asmari Formation.
Description : The test is small, porcelaneous and has spherical to subspherical shape with flattened Polar regions. The septulas of two surrounding chambers are seen alternatively small and large; therefore, the resulting chamberlets are alternatively small and large.
Superfamily Soritacea (Ehrenberg, 1839)
Family Peneroplidae (Schultze, 1854)
Genus Dendrita (d’Orbigny, 1826) MANUSCRIPT Dendritina rangi (d’Orbigny emend. Fornasini, 1904, Fig. 9D)
This species recorded by Adams and Bourgeois (1967) from Aquitanian–Burdigalian in
Asmari Formation.
Description : The test is lenticular, planispirally coiled and developed in umbilicus area. In equatorial section, the test is ovate to spherical, the number of whorls is 2.5–3 and the maximum chambers per whorl are 11–14. The septum is curved and is convex to the aperture. In theACCEPTED cross section, the test is elongated with a rounded- to actuated- periphery and the aperture is dendritic. The wall is calcareous and porcellaneous.
Superfamily Soritacea (Ehrenberg, 1839)
Family Peneroplidae (Schultze, 1854) ACCEPTED MANUSCRIPT 21
Genus Peneroplis (Montfort, 1808)
Peneroplis thomasi (Henson, 1950, Fig. 10L)
This species was recorded by Adams and Bourgeois (1967) from Rupelian to Aquitanian of
Asmari Formation.
The test is planispirally coiled in the early stage, which becomes opening in the next stage, and the height of chambers increases. In the cross section, the central part of test is picked and run shape.
Superfamily Rotaliacea (Ehrenberg, 1839)
Family Rotalidae (Ehrenberg, 1839)
Subfamily Rotalinae (Ehrenberg, 1839) Genus Rotalia (Lamarck, 1804) MANUSCRIPT Rotalia viennotti (Greig, 1935, Figs. 9N and 10A)
Adams and Bourgeois (1967) and Laursen et al. (2009) recorded this species from the
Rupelian to Aquitanian.
The test is unequally biconvex, and the ventral side is more convex. In the cross section, the test is trochospirally coiled and thickened, and the height of dorsal side is low and the margin is rounded. In the ventral side, the V-shaped plug is marked. In the equatorial section, the numberACCEPTED of whorl stages is low in a way that the maximum number of whorls becomes 3. The chambers are triangular, and the septum is multiple. The wall is calcareous and hyaline. ACCEPTED MANUSCRIPT 22
Superfamily Ataxophragmiacea (Schwager, 1877)
Family Valvulinidae (Berthelin, 1880)
Subfamily Valvulininae (Berthelin, 1880)
Genus Valvulina (d’Orbigny, 1826)
Valvulina sp. 1 (Adams and Bourgeois, 1967, Fig. 9O)
Remark: This species was recorded by Adams and Bourgeois (1967) from Rupelian–
Aquitanian of Asmari Formation.
The test is agglutinated. In the cross section, the test is conical, and in the equatorial section, it is close to spherical. This genus is characterized by its high spire, large size and regularly rounded growth pattern. The separated walls of chambers are thick and elongated from the margin to the central part of test. Superfamily Textulariacea (Ehrenberg, 1838) MANUSCRIPT Family Textularidae (Ehrenberg, 1838)
Subfamily Textulariinae (Ehrenberg, 1838)
Genus Bigenerina (d’Orbigny, 1826)
Bigenerina sp., Fig. 10C
Remarks: This species was reported from southwest of Iran by Adams and Bourgeois
(1967) from Rupelian to Burdigalian.
The test is agglutinated. In the cross section, the chambers are initially biserial, and then, they become uniserial.ACCEPTED The general shape of chambers is flat, and in margin, it is turgid. The number of chambers in biserial stage is 5–6 paired, and in the uniserial stage, it is 5–3.
Superfamily Textulariacea (Ehrenberg, 1838) ACCEPTED MANUSCRIPT 23
Family Textularidae (Ehrenberg, 1838)
Subfamily Textulariinae (Ehrenberg, 1838)
Genus Textularia (Defrance, 1824)
Textularia sp., Fig. 9E
Remarks: This species was reported from southwest of Iran by Adams and Bourgeois
(1967) from Rupelian to Burdigalian.
The test is agglutinated, biserial and the sutures are distinct. The number of chambers is 8 pairs, and the size of chambers gently increased. The aperture is like a slit, and it is placed in the aperture surface.
Superfamily Soritacea (Ehrenberg, 1839)
Family Peneroplidae (Schultze, 1854) Genus Meandropsina (Munier-Chalmas, 1882) MANUSCRIPT Meandropsina iranica (Henson, 1950, Fig. 11B)
This species was recorded by Larsen et al. (2009) from Chattian to Burdigalian of Asmari
Formation.
The test is porcellaneous. Chambers are numerous and tabular whose width and height gently increase towards the outside, 2 mm radial, and 26 chambers exist.
6.2. Systematic of coralline algae
Family CorallinaceaeACCEPTED (Lamouroux, 1812)
Subfamily Melobesioideae (Bizzozero, 1885)
Lithoporella melobesioides, Fig. 9K ACCEPTED MANUSCRIPT 24
This species is present from Chattian to Burdigalian of Asmari Formation.
This genus is characterised by its unistratose thallus with large palisade cells and multiple overgrowth of cell filaments.
Family Corallinaceae (Lamouroux, 1812)
Subfamily Melobesioideae (Bizzozero,1885)
Lithotamnion sp., Fig. 10D
This species was recorded from Rupelian to Burdigalian of the Asmari Formation.
Core filaments are non-coaxial. Cell fusions are present. The branched thallus with central core of filaments predominantly is bent towards the surface of the protuberance.
Family Corallinaceae (Lamouroux, 1812) Subfamily Lithophylloideae (Setchell, 1943) MANUSCRIPT Titanoderma sp., Fig. 9L
This species recorded from Chattian–Aquitanian in Asmari Formation.
This genus is characterised by its thallus with the palisade cells of the primigenous filament and tetra-bisporangial conceptacle with cylindrical pore canal.
Acknowledgement
We are thankful to Prof. Marco Brandano and Prof. David Bassi from Roma and Ferrara
Universities for their valuable suggestions and Kazem Sherafati for his help during field work. Also, thanksACCEPTED to Prof. Xiaoqiao Wan and Miss Lily Wang and to the reviewers for their constructive comments on this manuscript.
ACCEPTED MANUSCRIPT 25
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Table 1. Distinctive characteristics of fauna association and interpreted ecological conditions.
Figure Captions
Figure 1. (A) General map of Iran showing eight geologic provinces. The study area is located in Zagros Province (adopted from Heydari et al., 2003). (B) Subdivisions of the simply folded Zagros belt (after Falcon, 1961).
Figure 2. Comparison of biozonation of Adams and Bourgeois (1967), Laursen et al. (2009) and studied section. Figure 3. Corellation of Asmari Formation at MANUSCRIPT studied area with some sections in other regions of Zagros Basin.
Figure 4. Cenozoic stratigraphic correlation chart of the Zagros Basin (after Jams and
Wynd, 1965).
Figure 5. Correlation of depositional environments for Asmari Fm. in the studied area
(Khuzestan Province) with other areas of Zagros Basin. (a) Lurestan Province (adopted from Vaziri-Moghaddam et al., 2010), (b) Khuzestan Province (adopted from Van Buchem et al., 2010, with some modification) and (c) Fars Province. Figure 6. BiotaACCEPTED associations in Asmari Formation. (A and B) Assemblage 1, pelagic foraminifera and shallower benthic foraminifera in wackestone, packstone. (C–F) ACCEPTED MANUSCRIPT 39
Assemblage 2, Operculina, Spiroclypeus, Lepidocyclina, Amphistegina, Heterostegina in wackstone, packstone matrix.
Figure 7. Biota association in Asmari Formation. (A) Assemblage 3, Neorotalia,
Miogypsinioides, in grainstone matrix. (B–D) assemblage 4, Neorotalia, Miogypsinioides,
Operculina and Lepidocyclina , in wackestone-packstone matrix matrix. (E and F)
Assemblage 4 , small benthic foraminifera in wackestone-packstone matrix . (G and H)
Assemblage 5 , Borelis, Meandropsina, Dendritina, Peneroplis and miliolids in grinstone, packstone.
Figure 8. Lithology, biostratigraphy and vertical distribution of biota associations
(microfacies) for the Asmari Formation at the studied area.
Figure 9. Photomicrographs of some microfossils that recognized in studied area at Dehdasht area. (A) Austrotrilina sp., sampleMANUSCRIPT no.80; (B) Austrotrillina howchini (Schlumberger,1974), sample no.80; (C) Austrotrilina asmariensis (Adams, 1868), sample no.80; (D) Dendritina rangi (d’Orbigny, 1904) sample no.59; (E) Textularia sp., sample no.6; (F) Pyrgo sp., sample no.80; (G) Miogypsinoides formosensis (Yabe and Hanzava,
1928), sample no.36; (H) Miogypsina sp., sample no.70; (I) Planurbolina sp., sample no.21;
(J) Sphaerogypsina sp., sample no.27; (K) Lithoporella melobesioides (Foslie, 1909), sample no.124; (L) Titanoderm a sp., sample no.42; (M) Austrotrillina howchini
(Schlumberger, 1974), sample no.80; (N) Neorotalia viennoti (Greig, 1935), sample no.64; (O) Valvulinid ACCEPTED sp., sample no.80. Figure 10. Photomicrograph of some microfossils that recognized in study area at Dehdasht area. (A) Neorotalia viennoti (Greig, 1935), sample no.64; (B) Ditrupa sp., sample no.9; ACCEPTED MANUSCRIPT 40
(C) Bigenerina sp., sample no.67; (D) Lithotamnion sp., sample no.42; (E) Borellis mello
(Fichtel and Moll, 1798), curdica (Reichel, 1937) sample no.122; (F) Asterigerina sp., sample no.43; (G) Amphistegina sp., sample no.22; (H) Miogypsinoides deharti (Van Der
Vlerk, 1924), sample no.55; (I) Spirolina sp., sample no.99; (J) Nummulites cf. vascus (Joly and Leymerie , 1848), sample no.10; (K) Peneroplis sp., sample no.99; (L) Peneroplis thomasi (Henson, 1950), sample no.75.
Figure 11. Photomicrograph of some microfossils that recognized in study area at Dehdasht
area. (A) Marginopora sp., sample no.64; (B) Meandropsina iranica (Henson , 1950),
sample no.132; (C) Lepidocyclina (Nephrolepidina) tournori (Lemioln and Douville ,
1904), sample no. 22; (D) Operculina cf. complanata (Defrance, 1822), sample no.22; (E)
Quinqueloculina sp., sample no. 70; (F) Spiroclypeus blankenhorni (Henson , 1937), sample no. 22; (G) Spiroclypeus blankenhorniMANUSCRIPT (Henson , 1937), sample no. 22; (H) Eulepidina dilatata (Michelloti, 1861), sample no. 10; (I) Eulepidina sp., sample no.10;
(J) Eulepidina dilatata (Michelloti, 1861), sample no. 10.
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Table 1. Distinctive characteristics of fauna association and interpreted ecological conditions.
Facies Dominant components Subordinate components Paleoecological interpretation Pelagic foraminifera (50–60%) Serpulid, sponge spicule Calm, deep, offshore setting with Assemblage A small benthic foraminifera echinoid, bryozoa, mollusks aphotic condition in outer ramp (15–20%) (15–25%) to basin Eulepidina-Nepherolepidina Coralline red algae, bryozoans Low energy, turbid, low light Operculina, Heterostegina echinoid, mollusks, coral Assemblage B with oligophotic condition in Amphistegina, Spiroclypeus pelagic foraminifers middle-outer ramp (75–90%) (25 –10%) Coralline red algae, mollusks, Amphistegina, Dendritina , High energy, well lit, euphotic Assemblage C1 Miogypsinoides, Neorotalia echinoid, miliolid zone in inner ramp (75–85%) (15 –25%) Amphistegina, Dendritina Miogypsinoides, Operculina, Austrotrilina, Peneroplis Neorotalia, Archaias, miliolid Low energy, well lit, normal salinity, mollusks, bryozoans, coral Assemblage C2 coralline red algae, euphotic-mesophotic zone in echinoid, mollusks, Miogypsina Nepherolepidina in inner ramp (45 –30%) (55 –70%)
Ammonia beccarii, Ammonia Bryozoans, echinoid, Elphidium Low energy, well lit short-term spp, Assemblage D coralline red algae, miloilids salinity fluctuations or fully marine Mollusks (0 –80%) conditions in inner ramp (20 –100%) Borelis, Dendritina, Mollusks, Elphidium , Discorbis Well lit, highly translucent Peneroplis Assemblage E SpirolinaMANUSCRIPT shallowest part of the euphotic Meandropsina , miliolids (25 –15%) zone with hypersaline condition (75 –85%)
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Benthic foraminifera as biostratigraphical and paleoecological indicators: an example from Oligo-
Miocene deposits in the SW of Zagros basin, Iran
Asghar Roozpeykar*, Iraj Maghfouri Moghaddam
Department of Geology, Faculty of Sciences, University of Lorestan, Lorestan, Iran
* Corresponding author. Postal address: 7579111548-Janbazan Avenue-Dehdasht City-Kohgiluyeh va
Bouyer Ahmad Province-Iran;
Tel.: +989179428793; E-mail address: [email protected]
Highlights MANUSCRIPT Identification of 51 species of foraminifera.
Oligocene (Rupelian–Chattian)–early Miocene (Aquitanian–Burdigalian) age.
Warm tropical waters with oligotrophic to slightly mesotrophic conditions.
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