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Palaeoworld 23 (2014) 50–68

Trace fossils analysis of fluvial to open marine transitional sediments:xample from the Upper Devonian (Geirud Formation), Central Alborz, Iran

M. Sharafi a,∗, A. Mahboubi a, R. Moussavi-Harami a, H. Mosaddegh b, M.H.M. Gharaie a

a Department of Geology, Ferdowsi University of Mashhad, Iranb Department of Geology, Kharazmi University, Iran

Received 27 November 2012; received in revised form 26 August 2013; accepted 17 October 2013Available online 31 October 2013

bstract

This study integrates ichnological and sedimentological data to interpret depositional environments of the mixed siliciclastic-carbonate fluvial toarine sediments of the Geirud Formation (Upper Devonian) in the central Alborz, northern Iran. Lithofacies analysis shows that these sediments

re deposited in fluvial, tidal, shoreface, and shelf environments. Fluvial and tidal deposits are characterized by the presence of bi- to multi-irectional cross beddings, reverse directional current ripples, low angle cross beddings, and herringbone cross beddings, with a few scatteredkolithos and Palaeophycus. Shoreface sediments, accumulated in a storm-influenced setting, are characterized by a preferentially interfacend low diversity Cruziana ichnoassemblage (Rhizocorallium, Thalassinoides, Palaeophycus, Chondrites, and Ophiomorpha). In contrast to theuvial-tidal assemblage, the storm-influenced shelf sediments display a highly diversified, mixture of dwelling and feeding forms (Arenicolites,rotovirgularia, Diplocraterion, Palaeophycus, Thalassinoides, Chondrites, and Helminthopsis), reflecting the presence of adequate food resourcesoth in substrate and water column under normal salinity conditions. A fluvial-shelf replacement of the weakly to scarcely bioturbated sedimentsy the Rhizocorallium-Thalassinoides suite (Cruziana) – Chondrites-Helminthopsis (distal Cruziana) suite from the lower to upper parts of the

uccession clearly indicates an overall deepening upward in the Geirud Formation. In contrast to the lower part, generally of restricted environment,he upper part of the succession mainly shows open marine conditions. Ichnofabric development is controlled primarily by depositional conditions,.g., bottom water oxygenation, sediment type, food abundance, and hydrodynamic level, which all exert control on substrate colonization style.

2013 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS. All rights reserved.

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eywords: Fluvial-marine transition; Trace fossil; Devonian; Geirud Formation

. Introduction

The Upper Devonian Geirud Formation in the Central Alborzf the northern Iran consists of mixed siliciclastic-carbonate sed-ments. These sediments represent an overall deepening-upwarduccession that was accumulated on a gently sloping continentalamp on the northern continental margin of the Gondwana land-ass (Fig. 1). The most tide-dominated estuarine deposits were

ccumulated in the fluvial to marine transition zone. The transi-ion zone between terrestrial (river) environments and the open-

arine shelf represents one of the most profound spatial changes

n depositional condition. A monotonic seaward increase inalinity from fresh through brackish to fully marine on the shelfharacterizes estuaries. The brackish water conditions in the

∗ Corresponding author. Tel.: +98 09379760885.E-mail address: sharafi2262@gmail.com (M. Sharafi).

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871-174X/$ – see front matter © 2013 Elsevier B.V. and Nanjing Institute of Geolottp://dx.doi.org/10.1016/j.palwor.2013.10.004

ositional environment

ransition zone, accompanied by the high turbidity and phys-cally harsh conditions, produce a biologically stressed envi-onment, in which bioturbation is generally not pervasive. Thechnofossil assemblage in this zone is characterized by the lowiversity of ichnogenera and small size of the individual burrows.his transition zone is characterized by remarkable changes in

ate and direction of sediment movement, which is unidirectionalnd continuous to seasonal or flashy in the river, mutually evasiveransport pathways in tidal settings to episodic and either coastarallel in shelf settings. In general, these zones display a simpleecrease in energy level as water depth increase (Dalrymple andhoi, 2007). As a result of this monotonic trend in energy level,

here is a predictable correlation between water depth and facies.ertical trend is represented by a coarsening upward succession

hat passes from mudstones or thin-bedded limestone (offshore

r shelf), through deposits with thin, discrete sandstone bedsith ripples and hummocky cross beddings (HCS) (offshore

ransition), into amalgamated sandstones with HCS (lower to

gy and Palaeontology, CAS. All rights reserved.

M. Sharafi et al. / Palaeoworld 23 (2014) 50–68 51

Fig. 1. (A) Map of Iran showing the nine geological-structural zones (modified from Stöcklin, 1968). (B) Generalized palaeogeography of the Upper Devonianof the north Gondwana and the southern shore of the Palaeo-Tethys Ocean, displaying the passive margin of the north Gondwana (thickened gray line) and thenorthward drift of the Tarim (TM) and Pamir (Pr) continents (modified from Golonka, 2007; Bagheri and Stampfli, 2008). AL: Alborz; LU: Lut block; Pr: Pamir;S on ofv

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S: Sanandaj-Sirjan; TM: Tarim. The area in red is a rift zone. (For interpretatiersion of this article.)

iddle shoreface) and eventually into sandstones with abun-ant HCS and planar to trough cross bedding (upper shoreface)e.g., Walker and Plint, 1992). Ichnological analysis has become

valuable tool in basin analysis, especially for recognizing

nd interpreting genetically related sedimentary packages (e.g.,ovar et al., 2007). The primary controls on the distributionf different burrowing behaviors and lifestyle of the existing

c(e

the references to colour in this figure legend, the reader is referred to the web

auna and the trace markers in the marine realm are widely con-idered to be nutrient supply, hydrodynamic energy (Seilacher,967), salinity (Pemberton and Wightman, 1992), rate of sed-mentation (Pollard et al., 1993), oxygenation of the water

olumn (Bromley and Ekdale, 1984), substrate consistencyMacEachern and Burton, 2000), and water turbidity (Gingrast al., 2008). These factors also control diversity, abundance,

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nd preservation of trace fossils and body fossils as well asevelopment of the ichnofabrics in the sedimentary successions.inally, ichnological data are integrated with sedimentologicaleatures such as sedimentary structures and bedding geometry tonterpret the sedimentary process and the depositional systems.he ichnofabric analysis method reflects a bottom-up approach,omparable to conventional facies analysis. Sedimentary fab-ic and ichnofabric are studied simultaneously on a bed-by-bedasis (see Taylor and Goldring, 1993; Taylor et al., 2003), andnclude routine quantification of the intensity of bioturbationnd documentation of cross-cutting relationships recorded on anchnofabric logging sheet (Taylor and Goldring, 1993) and sum-arized on an ichnofabric constituent diagram. In this manner, it

s possible to document one or more ichnofabrics present within single sedimentary facies. In some cases, sets of related ich-ofabrics may also be compared to a Seilacherian ichnofacies.

This research is the first attempt to establish a connectionetween ichnological characteristics and environmental condi-ions during deposition of the Geirud Formation. The objectivesf this paper are: (1) to describe the distribution and diversityf trace and body fossils in the Geirud Formation and (2) to usentegrated ichnological and sedimentological data to interprethe depositional environment of the Geirud Formation.

. Geological setting and stratigraphy

The E-W trending Alborz Mountains (Alborz zone) is onef the geological-structural zones (Stöcklin, 1968) in the north-rn Iran (Fig. 1). This zone is sub-divided into the east, central,nd west parts and the study area is located in the central part.he Geirud Formation crops out mainly at the Touyeh Dar-ar section, which is situated in the southwest of Damghanity. Geographical coordinates of the Touyeh Darvar section is6◦00′ N and 53◦52′ E (about 40 km southwest from Damghanity) (Fig. 2). The Devonian successions of Iran are mostlyxposed and widespread in the eastern and central Alborznd Central Iran (Wendt et al., 2005). In the central Alborz,he Devonian successions consist of the Geirud Formation. Inhe study area, the Geirud Formation disconformably overlieshe marine shale of the Milla Formation (Ordovician) and isonformably overlain by the black limestone of the Mobarakormation (Lower Carboniferous). A major hiatus is presentetween the Milla and Geirud formations and extends fromhe Late Ordovician to Early–Middle Devonian time, possi-ly equivalent to the Caledonian orogeny (Ghavidel-Syooki,995). On the basis of brachipods (Bozorgnia, 1964), paly-omorphs (Ghavidel-Syooki, 1995), and goniatites (Dashtban,995) biostratigraphy, the age of the Geirud Formation is Lateevonian (Frasnian–Famennian). During the Late Devonian,

ran was located in the northern margin of Gondwana, along theouthern shore of the Palaeo-Tethys Ocean (Fig. 1) (Golonka,007; Bagheri and Stampfli, 2008). The Gondwanan affinitiesf Iran are clearly indicated by Silurian ostracods (Hairapetian

t al., 2011), Early Ordovician and Late Devonian (Geirud For-ation) palynomorphs (Ghavidel-Syooki, 1995). Furthermore,adimi (2007) recognized structural evidence for the Pan-frican orogeny in the Precambrian basement of Central Iran

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rld 23 (2014) 50–68

hat supports the peri-Gondwanan setting of Iran (Hairapetiant al., 2011).

. Materials and methods

This study focused on a measured section in the Centrallborz in northern Iran (Fig. 2). One hundred and twenty

hin sections were examined to identify fine-scale physicalharacteristics (mineralogical composition and fossil contents).ithology, grain-size, and sedimentary structures were recordednd lithofacies entitled according to the lithofacies codes ofiall (1985, 2006). Both sedimentological and trace fossils fea-

ures were examined on fresh and weathered surfaces in theeld. Degree of bioturbation is assessed according to Taylor andoldring (1993) and is done with using of comparative charts.he bioturbation index (BI), in which a descriptive grade isssigned to the degree of bioturbation, aims to relate the degreef bioturbation to the preservation of primary bedding featuresTaylor and Gawthorpe, 1993). In this scheme, a BI is defined,anging from 0 (no bioturbation) to 6 (complete bioturbation,otal biogenic homogenization of sediments).

. Sedimentology

.1. Description

The Geirud Formation in the study area is about 137 m thickFigs. 3 and 4) and can be subdivided into four groups that areelated to four major environments.

The lowermost part of the succession (up to 25 m above thease of the formation) is characterized not only by abundant ofi- to multi-directional cross beddings (lithofacies Sp), reverseirectional current ripples (lithofacies Cr), and low angle crosseddings (lithofacies Sl), but also by massive to parallel lami-ated sandstone (lithofacies Shl), herringbone cross bedded andaminated green mudstone with intercalated siltstone and fineandstone (Fm) (heterolithic deposits). This package is cappedy large oscillation ripple marks with straight and partly bifur-ated ripple crests (Fig. 5A–D). Sandstones are white to gray,ade of medium- to fine- and rounded to sub-angular grains withoderate sorting. Sparse bioclasts consist of bivalves, trilobites,

rinoids, and ostracods (Fig. 5E). Bioturbation is low to absentBI is 0–1).

The next major interval (25–39 m) consists of red to pink andassive to laminated mudstone, medium- to fine-grained sand-

tone with moderately to poorly sorted sub-rounded to angularrains, and gravelly deposits. Sharp-based trough cross bedslithofacies St) and cross beds (lithofacies Sp) with reverse dipirection are present (Fig. 5F). Individual units show a finingpward cycle from conglomerate to conglomeratic sandstone athe base (as scour fills) to medium- to fine-grained trough crossedded sandstone (Fig. 5G, H). They have erosive, concave-p bases (channel-like shape) normally cutting into underlying

udstone (Fig. 6A). The BI is also low (0–1). Above this

ackage (39–70 m), sedimentary deposits are displayed by whiteo gray, medium- to fine-grained sandstone with sub-rounded toub-angular grains and moderate to poor sorting, and laminated

M. Sharafi et al. / Palaeoworld 23 (2014) 50–68 53

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ig. 2. (A) Location map and the studied section of the Geirud Formation in nhe studied section, based on: sheet No. 676 of 1:100,000 map of Kiyasar (Said

reen mudstone. Planar cross bedding (tubular to tangential)lithofacies Sp) (Fig. 6B), horizontal lamination (lithofacieshl), and massive sandstone (Sm) are predominant in this partf the formation. Current ripple laminations locally indicate bi-irectional dip direction with thin mud drape in reactivationurfaces. Bioclasts (mainly brachiopods, bivalves and crinoids)n this part become more common with respect to lower pack-ges. These bioclasts are commonly highly fragmented and showonvex-up orientation that were accumulated as sharp-based lag

oncentrations, grading upward into horizontal laminated sand-tone (Fig. 6C). The BI is low to absent (0–1), although highegree of bioturbation (BI is 3–4) is locally observed.

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ran. (B) Simplified geological map of the Tuyeh-Darvar area, with location ofAkbarpour, 1992).

The following part of the section is marked by a generalncrease in carbonate sediments, with abundant brachiopodsnd crinoids as well as goniatites, tabulate and rugose corals,ryozoans, and ostracods and a simultaneous decrease of silici-lastic materials.

Above 70 m, the section is composed of thin to thick bed-ed, black limestone with brachiopods, goniatites, and tabulatend rugose corals (5 m thick) (Fig. 6D). The overlying succes-ion (from 75 to 92 m) consists of thickening upward cycles,

haracterized by alternations of laminated gray-black mud-tone and thin-bedded sandstone at the base, grading upwardnto thin to thick bedded sandstone. Trough cross bedded

54 M. Sharafi et al. / Palaeoworld 23 (2014) 50–68

istribu

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Fig. 3. Composite sedimentary log and trace fossil d

andstone and sandy limestone (Fig. 6E), HCS, horizontal lam-nation, and tempestite sediments (Fig. 6F) are common inhis part. Skeletal elements include abundant brachiopods as

ell as crinoids, bivalves and ostracods, dominantly display-

ng high fragmentation and abrasion (Fig. 6E). Trace fossilsound are Rhizocorallium jenense, Rhizocorallium irregulare,

lgt

tion of the Geirud Formation. See Fig. 4 for legend.

halassinoides isp., Palaeophycus heberti, Palaeophycus tubu-aris, Palaeophycus striatus, and Chondrites isp.

The uppermost part consists of gray to black, thin-bedded

imestone (Fig. 6G, H) with abundant brachiopods, crinoids andoniatites, tabulate and rugose corals, bivalves, bryozoans, gas-ropods, trilobites, and ostracods, intercalated with thin-bedded

M. Sharafi et al. / Palaeoworld 23 (2014) 50–68 55

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lack shale. Biogenic structures consist of Thalassinoides isp.,alaeophycus tubularis, Chondrites isp. Chondrites targionii,hondrites intricatus, Chondrites bollensis, Helminthopsis isp.,rotovirgularia isp., Arenicolites isp., and Diplocraterion isp.

.2. Interpretation

Abundant bi- to multi-directional planar and herringboneross bedding, oscillation wave ripples, reverse direction crossamination and reactivation surfaces in the lower part of theection (0–25 m and 39–70 m) suggest tidal currents controlledeposition on a tide-dominated coast (Dalrymple et al., 1992;omatsu, 1999; Nouidar and Chellai, 2001; Dalrymple andhoi, 2007; Fabuel-Perez et al., 2009; Dashtgard et al., 2010;ehrmann et al., 2010). Development of mutually-opposed

ross bedding with local development of herringbone cross bed-ing suggests current reversals under ebb-flood tidal fluctuationsBhattacharya and Bhattacharya, 2006, 2010). Laminated greenudstones with intercalated thin bedded siltstone and sand-

tone are interpreted as tidal flat deposits during a period oflack water and sea level rise respectively (Shanley et al., 1992;ouidar and Chellai, 2001). Low bioturbation with vertical ororizontal lifestyle and body fossils suggests stressed, brack-sh biotopes, which is consistent with estuarine setting wherehifting substrate and fluctuations in turbidity and salinity areommon (Frey and Howard, 1986; Nouidar and Chellai, 2001;uatois et al., 2002; Gingras et al., in press). Laterally dis-ontinued sharp-based lag concentration grading upward intoorizontal laminated (waning phase) sandstone is interpreted as

torm deposits.

Red to pink, massive to laminated mudstone, medium-finerained sandstone (25–39 m) and gravelly deposits imply fluvialystem. This interpretation is supported by erosive, concave-up

s

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ogical structures, body fossils and abbreviations in Fig. 3.

ases (channel-like shape) (Fig. 6A) which normally cut intonderlying red mudstones (Fabuel-Perez et al., 2009). Channelsommonly cut into mud-dominated sediments and show basalrosional scour surfaces that are filled by conglomerate (or grav-lly sandstone) (Fig. 5H), which was formed as a consequence ofapid deposition of poorly-sorted bed load (Fabuel-Perez et al.,009). Bi-directional cross beds are interpreted to show a tide-nfluenced channel river (Longhitano et al., 2012; Bhattacharyat al., in press). Massive to laminated red mudstone is interpreteds overbank sediments deposited in a river channel floodplainnvironment.

The following part of the section represents a transition fromidal-fluvial to more normal marine conditions characterizedy the occurrence of the first bioclastic limestone (with abun-ant brachiopods as well as crinoids at 70 m) and reefoidalacies with solitary corals and colonies of tabulate corals (e.g.,avosites, Syringopora) (Fig. 6D), goniatites, crinoids, bivalves,rachiopods and ostracods.

Upward, between 75 and 92 m, HCS and storm deposits (tem-estites) as well as trough cross beds all indicate medium-highnergy conditions in middle shoreface environments mainlybove fair-weather wave-base (Walker and Plint, 1992; Urozand Steel, 2008; Sharafi et al., 2012, 2013). Abraded and frag-ented shell remains (Fürsich and Pandey, 2003) indicate a

tressed environment with moderate to high energy. The contentsf the shell remains (brachiopods and crinoids) and ichnoassem-lage indicate normal marine conditions (Fürsich and Pandey,003; Malpas et al., 2005). Alternation of green laminated mud-tone and thin bedded sandstone with horizontal lamination inhis part of the Geirud Formation reveals lower shoreface depo-

ition.

Thin-bedded black limestone with intercalated black shalen the uppermost part of the section is deposited in a shelf

56 M. Sharafi et al. / Palaeoworld 23 (2014) 50–68

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nvironment, occasionally affected by storm waves. This inter-retation is supported by a large number of typical shelfrganisms and biogenic structures (see the following section)ound in these strata (e.g., brachiopods, crinoids, trilobites,ivalves, goniatites, corals, and bryozoans) (Fürsich and Pandey,003; Wehrmann et al., 2010; Sharafi et al., 2012). Further-ore, the black shale reflects phases of stability with respect

o hydrodynamic energy, siliciclastic input, and water depth.

. Results

.1. Trace fossil analysis

The definitions of the ichnofabrics within this geneticallyelated succession are based on previous studies (e.g., Taylor,991; Taylor and Goldring, 1993; Fürsich, 1998; Zonneveldt al., 2001; Buatois et al., 2002; Taylor et al., 2003; Tovar et al.,007; Dashtgard et al., 2010; Sharafi et al., 2012). Environmen-al interpretation is based on sedimentology, facies analysis, andrace fossil diversity (Taylor and Goldring, 1993; Taylor et al.,003). In this study, six trace fossil suites are identified (Table 1).he vertical succession of these suites has been used herein

o indicate environmental changes within a shallow marineetting.

.1.1. Skolithos suite (Fig. 7A)Description: Skolithos isp. (1–2 mm in diameter) and sub-

ertical Palaeophycus isp. are the only trace fossils within thisuite. Skolithos burrows are locally observed within white toray, thin- to thick-bedded sandstone with abundant primaryedimentary structures such as bi- to multi-directional cross bed-ing (Fig. 5B–D), herringbone cross bedding (Fig. 5A), reverseirectional cross-lamination and horizontal lamination. The BIs 0–1. Burrow fills of the Skolithos are of the same compositions the background sediments but are visible because of their ten-ency to be weathered out. Sparse bioclasts consist of bivalves,stracods, trilobites, and crinoids. This suite is observed only inhe lowermost part of the Geirud Formation (Fig. 3).

Environmental interpretation: This suite is resulted fromhe biological activity of the burrowing organisms operating in aidal environment, above fair weather wave base, with high sed-mentation rates. Low diversity of trace and body fossils alongith presence of Skolithos is normally indicative of a high energy

etting (Zonneveld et al., 2001; Malpas et al., 2005). Sedimen-ary structures such as bi- to multi-directional cross bedding,

erringbone cross bedding and cross lamination with reverse dipirection as well as low diversity of trace and body fossils arendicative of deposition in a stressful brackish water condition,ominated by deposition from traction current and frequent tidal

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ig. 5. (A–E) Sedimentary structures and petrography features in the tidal deposits. (B) Multi-directional cross bedding (arrows refer to the mutual current directions). (Cross beddings with reverse dip direction (arrows). (E) Fine grain, well-sorted sandsto

ight). (F–H) Sedimentary structures and petrography features in the fluvial deposits.

G) Medium grain, medium sorted sandstone (XPL: cross polarized light). (H) Channtratigraphical position of the images.)

rld 23 (2014) 50–68 57

eworking with high current velocities (Zonneveld et al., 2001;uatois et al., 2002; Dashtgard et al., 2010). Vertical burrowsrevail as in the classic Skolithos ichnofacies model of Seilacher1967).

.1.2. Rhizocorallium-Thalassinoides suite (Fig. 7B–E)Description: This suite is up to 2 m thick and consists of

arallel bedding, preferentially interstratified, Rhizocoralliumenense, Rhizocorallium irregulare, and Thalassinoides isp. inellowish fine- to medium-grained sandstone intercalated withaminated gray to black mudstone. Spreiten structures includehizocorallium jenense and Rhizocorallium irregulare. Rhi-ocorallium jenense has 5–7 cm burrows diameter and tubeiameter 1.1–1.5 cm. Rhizocorallium irregulare has 5–12 cmurrows diameter and tube diameter 1.5–2.5 cm. The Thalassi-oides occurs as positive hyporelief and Y- to T-shaped branchesFig. 7D). Rhizocorallium and Thalassinoides are filled with theame materials as the background sediments in terms of colornd composition. Other trace fossils present in this suite arealaeophycus tubularis with burrow diameter of 0.5–1 cm andhondrites isp. (0.3–0.7 cm in diameter) (Fig. 7E). Thalassi-oides is occasionally cross-cutting the Palaeophycus burrowsnd is cross-cut by large Rhizocorallium systems. The BI inhis suite is 3–5. Predominantly, horizontal lamination (at thease of each sedimentary cycle) as well as HCS and other tem-estite structures (Fig. 6F) are the major sedimentary structuresresent in this suite. The bioclastics contents of Rhizocorallium-halassinoides suite consist of bivalves, brachiopods, crinoids,nd ostracods. This suite is observed in the middle part of theeirud Formation (Fig. 3).Environmental interpretation: The increase in ichnodi-

ersity and bioturbation along with a decrease in sedimentarytructures suggests a low-energy, nutrient-rich, lower shorefacenvironment with a low sedimentation rate under normal marineonditions (Uchman and Kremnayr, 2004; Malpas et al., 2005;guirre et al., 2010). According to Buatois et al. (2002), the ichn-diversity of the proximal lower shoreface is low and feedingraces of deposit feeder are common. The high degree of biotur-ation results from the activity of the climax, resident infaunaBuatois et al., 2002). The ichnoassemblage is dominated byodinichnia, suggesting Cruziana ichnofacies (Fürsich, 1998;uatois et al., 2002). Although the Cruziana ichnofacies is usu-lly characterized by a wide variety of behavioral patterns, theominance of traces of deposit-feeders may be due to the gener-lly low-energy hydrodynamic regime, in which food particles

end to accumulate on the sea floor rather than being kept in sus-ension (Fürsich, 1998; Buatois et al., 2002; Dashtgard et al.,010; Sharafi et al., 2012). The water at the sediment-water inter-ace is fully oxygenated. According to Dashtgard et al. (2010),

A) Planar (lower) and herringbone (upper) cross beddings in white sandstone.) Large wave ripple with straight, partly bifurcated ripple crests (arrows). (D)ne with a few skeletal elements (Bi: bivalve; C: crinoids; XPL: cross polarized

(F) Bi-directional cross bedding (arrows refer to the mutual current directions).el with scoured surface, which is filled with gravelly sandstone. (See Fig. 3 for

58 M. Sharafi et al. / Palaeoworld 23 (2014) 50–68

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t the storm affected shoreface, the lower shoreface is dominatedy intensely bioturbated sand and the burrows include hori-ontal deposit-feeder structures and interface deposit-feedingraces (Fig. 7C). The resultant trace fossil suite corresponds toroximal expressions of the Cruziana ichnofacies (MacEachernnd Bann, 2008). A lower shoreface environment interpreta-ion is supported by predominantly horizontal laminated, thinedded sandstone with intermittent laminated mudstone withccasional HCS in tempestite deposits and an increase inioclasts.

.1.3. Palaeophycus-Thalassinoides suite (Fig. 7F–H)Description: This suite consists predominantly of simple

nd branched structures like Palaeophycus and Thalassinoides.alaeophycus is thinly-lined, horizontal to slightly inclined,nd 0.5–1.5 cm in diameter, including Palaeophycus tubularisnd Palaeophycus heberti. Thalassinoides isp. is Y- and T-haped branches and inclined to bedding. There are also rareccurrences of Palaeophycus striatus, branched Chondrites isp.0.3–0.5 cm in diameter) and bivalve resting traces (cubichnia)s well as escape traces (fugichnia) (Fig. 7H). Palaeophy-us is commonly cross-cut by Thalassinoides structures. TheI is 2–5. This suite also shows a preferentially interfaceurrow preservation (Fig. 7G), although other forms of preser-ation are also observed. This suite occurs in 0.5–3 m thick,ellowish, moderate- to well-sorted fine- to medium-grainedandstone with trough cross bedding and HCS, horizontal andipple cross-lamination along with abundant tempestite depositsFigs. 6E, 7H). The bioclastic contents of Palaeophycus-halassinoides suite consist predominantly of fragmented andbraded (Fig. 6F) bivalves, brachiopods, crinoids as well asstracods. This suite is observed in the middle part of the for-ation (Fig. 3).Environmental interpretation: This suite is a mix of

uspension (Palaeophycus tubularis, fugichnia) and depositChondrites, Thalassinoides) feeder traces. Sedimentary struc-ures (e.g., St, HCS, Cr) indicate an environment dominatedy deposition from traction currents, frequent wave reworking,nd intermittent strong currents in a high energy, middle-upperhoreface environment (Malpas et al., 2005; Uroza and Steel,008; Dashtgard et al., 2010). This interpretation is supportedy predominantly fragmented and abraded bioclast elements.hese lines of evidence, taken together with the low diversity of

race fossils, indicate a stressed environment with only a fewaxa capable of exploiting the nutrient resources (Zonneveld

t al., 2001; Malpas et al., 2005; Gibert and Goldring, 2007).bundant tempestite deposits as well as HCS and associated

scape trace (fugichnia) show a storm-influenced shorefacenvironment (Dashtgard et al., 2010). According to Dashtgard

isr

ig. 6. (A) Channel-like sandstone body in the fluvial deposits. (B) Tabular crossoncentration, interpreted as storm deposits (tempestites), capped by horizontal lamolony of tabulate corals (Syringopora) in the black limestone (patch reef). (E) Sharp-

n the lower shoreface. (F) Laterally discontinuous, sharp-based sand bed interpretedn the uppermost part of the Geirud Formation. (H) Well-preserved skeletal elementsimestone. (See Fig. 3 for stratigraphical position of the images.)

rld 23 (2014) 50–68 59

t al. (2010), as storm influences sediment deposition, the pro-ortion of unburrowed or only slightly burrowed sand bedsncreases and the number and thickness of interbedded tem-estites increase landwards. In this situation, tops of storm bedsay be bioturbated with a suite of mainly vertical dwellings and

eposit-feeding (Thalassinoides) structures representing ini-ial opportunistic colonization following the storm (Pembertont al., 2001). This ichnoassemblage corresponds to the proximalruziana ichnofacies.

.1.4. Protovirgularia-Palaeophycus suite (Fig. 8A, B)Description: This suite consists of simple to slightly

urved, positive hyporelief, Protovirgularia isp. with diam-ters of 0.5–2.5 cm and simple to slightly curved, positiveyporelief, thinly-lined and horizontal Palaeophycus tubularis,.5–1.5 cm in diameter. Horizontal, positive hyporelief, Y-haped branched structures of Thalassinoides isp. (0.5–1 cmn diameter) are also present. Thalassinoides is occasionallyross-cutting the Palaeophycus or Protovirgularia burrows.he BI in this ichnofabric is 3–6. This suite occurs in

hin-bedded, black limestone with abundant brachiopods andrinoids as well as trilobites, solitary corals, goniatites, bry-zoans and ostracods with intercalated black shale. Therachiopod fauna is well preserved (Fig. 8C) and consists ofoth articulated and disarticulated shells. The Protovirgularia-alaeophycus suite overlies the Palaeophycus-Thalassinoidesuite and passes upward to the Arenicolites-Diplocraterionuite.

Environmental interpretation: This suite results from pro-esses operating in a marine environment, below storm wavease with a low sedimentation rate and high hard part carbonateroduction, given the high BI and good state of fossil preser-ation (Malpas et al., 2005; Parras and Casadio, 2005; Fürsicht al., 2009; Sharafi et al., 2012, 2013). The low diversity ofrace fossils, thin-bedded black limestone abundant in marineauna (e.g., brachiopods, crinoids, trilobites) intercalated withlack shale, and rare terrigenous material are indicative of aow energy setting. This suggests deposition in a deeper partf the basin within the shelf zone. The water at the sediment-ater interface was fully oxygenated, nutrient-rich, justified byreferentially horizontal traces (Zonneveld et al., 2001; Parrasnd Casadio, 2005). This suite corresponds to the Cruzianachnofacies.

.1.5. Arenicolites-Diplocraterion suite (Fig. 8D, E)

Description: This suite is characterized by Arenicolites

sp., Diplocraterion isp., and Palaeophycus tubularis withcarce Thalassinoides isp. Arenicolites isp. is 2.5–4 cm in bur-ow diameter and tube diameter ranges from 0.5 to 1.2 cm.

bedding in the tidal deposits. (C) Laterally discontinuous, sharp-based lagination (Hl), the waning phase, and planar cross bed (Sp), successively. (D)based trough cross bedded limestone with highly fragmented skeletal elements

as storm-deposits in the middle shoreface. (G) Thin-bedded, black limestone with a very high percentage of conjoined specimens in the thin-bedded, black

60

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Table 1Summary of the suites associated with the Geirud Formation (see sedimentology section for abbreviations).Suite Description Thickness (m) Trace fossils BI Body fossils Sedimentary structures Processes Environmental interpretation

Skolithos Predominantly vertical to subvertical,Skolithos and slightly inclinedPalaeophycus isp. in white to gray,sparse bioclastic, fine- tomedium-grained sandstone

Skolithos isp., Pa. isp. 0–1 Scarce, predominantly fragmentedand abraded bivalves, ostracods,trilobites and echinoderms

Sp, Cr, herring-bone, waveripple, St and scour surface

High energy, high-sedimentationrate, softground substrate

Shallow marine above.Fair-weather wave base:tide-dominated estuarine

Rhizocorallium-Thalassinoides

Predominantly horizontal, large, large,positive hyporelief and epirelief,Rhizocorallium and Thalassinoideswith high abraded and rounded shelldebris in buff to yellowish, fine- tomedium-grained sandstone

0.5–2 Rh. jenense, Rh. irregulare, Th.isp., Pa. tubularis and Ch. isp.

3–5 Predominantly fragmentedbrachiopods, echinoderms,bivalves and ostracods

St, Cr, Hl, HCS and tempestite Medium sedimentation rate,production related, softgroundsubstrate

Below Pa-Th suite. Shallowmarine moderately low energybetween FWWB and SWWB:lower shoreface

Palaeophycus-Thalassinoides

Predominantly horizontal, positivehyporelief, Palaeophycus andThalassinoides in high abraded androunded shell debris in yellowish, fine-to medium-grained sandstone

1–3 Pa. tubularis, Pa. heberti, Pa.striatus, Th. isp., Ch. isp.

2–5 Predominantly fragmentedbrachipods, echinoderms, bivalvesand ostracods

St, Hl, HCS and tempestite High energy, high-sedimentationrate, softground substrate

Above Rh-Th suite and belowPr-Pa suite. Shallow marine,moderate-high energy betweenFWWB and SWWB:middle-upper shoreface

Protovirgularia-Palaeophycus

Horizontal, simple to slight meanderingburrow structures in gray-black,thin-bedded limestone

Pr. isp., Pa. tubularis, Th. isp. 3–6 Predominantly well preservedbrachiopods, goniatites as well asechinoderms, bivalves, bryozoans,corals, trilobites and ostracods

Absent Low sedimentation rates,production related, highbioturbation rate, low energydeeper water

Above Pa-Th suite and belowAr-Di suite. Open marine, lowenergy below SWWB: shelf

Arenicolites-Diplocraterion

Vertical to horizontal, burrow structuresin gray-black, thin-bedded limestone

Ar. isp., Di. isp., Pa. tubularis, Th.isp.

2–4 Fragmented and completebrachiopods, goniatites,echinoderms as well as bivalves,bryozoans, corals, trilobites andostracods

Tempestite Low sedimentation rates,production related, highbioturbation rate, low energydeeper water, occasionallystorm-affected

Above Pr-Pa suite and belowCh-Hel suite. Open marine, lowenergy below SWWB:occasionally storm-affected shelf

Chondrites-Helminthopsis

Predominantly horizontal, branched,positive hyporelief and epirelief, simpleto meandering burrow structures ingray-black, thin-bedded limestone

Ch. targionii, Ch. isp., Ch.intricatus, Ch. bollensis, Hel. isp.,Ar. isp., Di. isp., Pa. tubularis, Th.isp.

4–6 Predominantly well preservedbrachiopods, goniatites, corals aswell as bivalves, bryozoans,echinoderms, trilobites andostracods

Tempestite Low sedimentation rates,production related, highbioturbation rate, low energydeeper water, occasionallystorm-affected

Above Ar-Di suite. Open marine,low energy below SWWB:occasionally storm-affected shelf

M. Sharafi et al. / Palaeoworld 23 (2014) 50–68 61

Fig. 7. (A) Skolithos suite (arrows) in the tidal deposits (Cr: cross lamination). (B–E) Rhizocorallium-Thalassinoides suite in the lower shoreface. (B) Rhizocoralliumirregular at the lower plane view. (C) Rhizocorallium jenense (note the interface nature of these trace fossils) (upper plane view). (D) Thalassinoides isp. at thelower plane view. (E) Chondrites isp. (F and G) Palaeophycus-Thalassinoides suite in the middle shoreface, note the preferentially interface structures, because ofadaptation of the trace markers in storm-influenced conditions (Hl: Horizontal lamination related to waning phase of the storm event). The white arrow refers to abivalve resting trace. (H) Amalgamated storm deposits showing the three phases of storm events, with scarce vertical trace fossils (fu: fugichnia). P.h.: Palaeophycusheberti; Ps: Palaeophycus striatus; Pt: Palaeophycus tubularis; Rh.ir.: Rhizocorallium irregulare; Th: Thalassinoides. (See Fig. 3 for stratigraphical position of theimages.)

62 M. Sharafi et al. / Palaeoworld 23 (2014) 50–68

Fig. 8. (A and B) Protovirgularia-Palaeophycus suite with preferentially positive hyporelief structures in the thin-bedded, black limestone. (C) Well-preservedskeletal elements with a very high percentage of conjoined specimens associated with Protovirgularia-Palaeophycus suite in the thin-bedded, black limestone. (D andE) Arenicolites-Diplocraterion suite (lower plane view). (F–H) Chondrites-Helminthopsis suite (upper plane view). (F) Helminthopsis isp. (G) Chondrites bollensis.(H) Chondrites isp. Ar: Arenicolites isp.; Di: Diplocraterion isp.; Pt: Palaeophycus tubularis; Pr: Protovirgularia isp. (See Fig. 3 for stratigraphical position of theimages.)

M. Sharafi et al. / Palaeoworld 23 (2014) 50–68 63

F r plan(

DtwllavritH

achpSloS

caeows

5

miCilfig

ig. 9. (A–D) Chondrites-Helminthopsis suite. (A) Chondrites intricatus (uppelower plane view). (D) Diplocraterion isp.

iplocraterion isp. has a burrow diameter of 0.7–1 cm and aube diameter of 1.5–2 cm. Palaeophycus tubularis is thinlyalled, with simple burrows, horizontal and positive hypore-

ief. The BI is 2–4. This suite occurs in thin-bedded, blackimestone with brachiopods, crinoids, bryozoans, bivalves, goni-tites, tabulate and rugose corals, and gastropods, showingarious degrees of fragmentation and abrasion. Sharp-based,andomly oriented lag concentrations are locally observedn this suite. The Arenicolites-Diplocraterion suite overlieshe Protovirgularia-Palaeophycus suite and is overlain by theelminthopsis-Chondrites suite.Environmental interpretation: Decrease in diversity and

bundance of the trace fossils as well as dominance of the verti-al traces of suspension-feeders suggests generally high-energyydrodynamic regime and the unstable substrate, in which foodarticles tend to be kept in suspension (Dashtgard et al., 2010;harafi et al., 2012). However, the horizontal, positive hypore-

ief structures of Palaeophycus tubularis record short phasesf a stable substrate condition (Fürsich and Pandey, 1999).torm-influenced shelf deposits are shown by sharp-walled lag

HtHl

e view). (B) Chondrites targionii (upper plane view). (C) Thalassinoides isp.

oncentrations (tempestite deposits) with mainly fragmentednd disarticulated skeletal elements (Miller, 2007; Dashtgardt al., 2010; Sharafi et al., 2013). High diversity and abundancef the skeletal elements suggest a normal marine environmentith respect to the salinity, water circulation, and light etc. This

uite corresponds to the Cruziana ichnofacies.

.1.6. Chondrites-Helminthopsis suite (Figs. 8F–H, 9A–D)Description: This suite consists predominantly of epirelief,

eandering Helminthopsis isp. parallel to bedding, 0.1–0.3 mmn diameter, and branched Chondrites isp., Chondrites targionii,hondrites intricatus, and Chondrites bollensis of 0.1–0.4 cm

n diameter. It also has Palaeophycus isp. and scarce Arenico-ites isp., Diplocraterion isp. and Thalassinoides isp. Burrowlls of Chondrites are different in composition from the back-round sediments. Millimeter scale Chondrites is cross-cutting

elminthopsis, and Thalassinoides is occasionally cross-cutting

he Palaeophycus burrows. The BI in this suite is 4-6. Theelminthopsis-Chondrites suite occurs in thin-bedded, black

imestone (Fig. 6G) containing brachiopods, crinoids, tabulate

6 aeoworld 23 (2014) 50–68

atcps

tasebbic(wcdT

6

mcmlaomophmroMtaafitwbsimmlms

(snPs

Fig. 10. Sharpe-based lag concentration associated with Chondrites-Hs

ssaCdhmif2S

mRhddbsnftdmo1tdts2os

4 M. Sharafi et al. / Pal

nd rugose corals, bivalves, goniatites, bryozoans, and gas-ropods, intercalated with black shale. Sharp based, mostlyonvex-up, and fining-upward lag concentrations are locallyresent in this suite (Fig. 10). The Helminthopsis-Chondritesuite overlies the Arenicolites-Diplocraterion suite.

Environmental interpretation: High degree of bioturba-ion, low diversity of trace fossils, thin-bedded black limestone,nd abundant normal marine fauna are indicative of a low energyetting below storm wave base (Malpas et al., 2005; Wehrmannt al., 2010). This suggests deposition in the deeper part of theasin, occasionally affected by storm, characterized by sharp-ased, convex-up oriented lag concentrations. Helminthopsis isnterpreted as a pascichnion, made by grazing deposit-feedersolonizing on a soft substrate (Miller, 2007). According to Fu1991), some forms of Chondrites represent chemosymbiosisithin a dysoxic to anoxic substrate, supported by the black

olor of the limestone beds and intercalated black shale. Excepturing storm deposition, the environment was relatively quiet.his suite corresponds to the distal Cruziana ichnofacies.

. Discussion

As stated before, the feeding manner and lifestyle of tracearkers in a special setting of sedimentary environment are

ontrolled by depositional setting (which controls the sedi-entary factors, such as sedimentation rates, hydrodynamic

evel and nature of substrate) and ecological elements, suchs salinity, water turbulence, circulation, light, bottom waterxygenation, and food abundance. Furthermore, these environ-ental factors affected the distribution, diversity, and abundance

f trace fossils and body fossils that emanated finally from theirreservation nature (e.g., horizontal vs. vertical, epirelief vs.yporelief, suspension feeding vs. deposit feeding traces, frag-ented vs. complete, and chaotic vs. oriented fossils), their

elationship with the sedimentary surfaces and developmentf trace fossil assemblages in the sedimentary successions.oreover, one or a few factors can diminish the effects of

he other factors. For example, hydrodynamic level in a suit-ble condition of light, water circulation, and salinity can cause

special lifestyle and feeding manner of trace markers thatnally are recorded on preservation nature of trace fossils. In

his respect, distribution of trace fossil assemblages integratesith sedimentological features (e.g., sedimentary structures andedding geometry) to interpret sedimentary process and depo-itional systems of the Geirud Formation, which is depositedn various environments consisting of fluvial-estuary to openarine environments (Fig. 11). Trace fossils of the Geirud For-ation are controlled mainly by salinity and hydrodynamic

evel as well as water circulation, food abundance, and sedi-ent supply that are the most effective factors in the coastal

ettings.High energy, shallow water environments such as tidal

0–25 m and 39–70 m) and fluvial environments, with high

edimentation rates, are represented by a low diversity ich-oassemblage with only low abundance of Skolithos andalaeophycus (Fig. 11). Scarce occurrences of bioturbationtructures and highly fragmented body fossils are suggestive of

(scc

elminthopsis suite, interpreted as storm deposits. Note the mostly convex-uphell orientation (arrows) and fining upward trend.

tressed brackish biotopes, which are consistent with estuarineettings where substrate shifting and fluctuations in turbiditynd salinity are common (Frey and Howard, 1986; Nouidar andhellai, 2001; Buatois et al., 2002). This ichnoassemblage isominated by traces of suspension-feeders. In a substrate withigh sedimentation rates, the redox boundary will encompassost of the organic materials, and resources quickly become

naccessible, resulting in preferentially vertical suspension-eeding lifestyle (Zonneveld et al., 2001; Dashtgard et al.,010). Vertical burrows that prevail is an example of the classickolithos ichnofacies of Seilacher (1967).

Medium to high energy, storm-influenced shoreface environ-ent (between 75 and 92 m) contains Rhizocorallium jenense,hizocorallium irregulare, Thalassinoides isp., Palaeophycuseberti, Palaeophycus tubularis, Palaeophycus striatus, Chon-rites isp., and escape traces (fugichnia). This ichnoassemblageisplays a preferentially interface structure (Fig. 12), and maye due to adaptations of the trace markers to a storm-influencedhoreface environment. In such dynamic system that is recog-ized by abundant tempestite deposits and HCS as well as highlyragmented and abraded skeletal elements, concentrated withinhe tempestite sediments, the trace fossils were produced mainlyuring the relatively quiet interstorm phases and are restrictedainly to the sediment surfaces; therefore they can form before

r after the deposition with respect to the tempestite (Fürsich,998). In this relation, a three-stage model of development ofhe ichnoassemblages can be recognized (Fig. 12A). Duringeposition of the storm-influenced sandstone bed, with HCS andempestite deposits, burrows are characterized by a few escapetructures (fugichnia) (stage 1, Fig. 12A). In the next step (stage, Fig. 12B), under fair weather condition and with a slowdownr halt in sedimentation rate on the sea floor (minor omissiontage), the sediment surface is colonized by many trace markerscolonization window, the period of time which is feasible for

uccessful colonization of the substrate is extended to includehemical (oxygen, salinity), trophic as well as physical (wave,urrent energy) windows) (e.g., Thalassinoides, Palaeophycus

M. Sharafi et al. / Palaeoworld 23 (2014) 50–68 65

F ution,t

aSzpsPff

osbiedfc(ftTDdHaubAd

eieseoalt

snavs

stCtdGtFta

ig. 11. Summary diagram of the depositional processes, environmental distribext for explanations. See Fig. 4 for legend to symbols and abbreviations.

nd Chondrites) that are preserved mainly as epirelief structures.tarting with a new storm phase (stage 3, Fig. 12C), the hori-ontal trace fossils at the top of the lower sandstone bed werereserved as convex hyporelief at the lower plane of new sand-tone bed. This ichnoassemblage is a mix of suspension (e.g.,alaeophycus, fugichnia) and deposit (e.g., Rhizocorallium)eeder traces, corresponding to the Skolithos-Cruziana ichno-acies.

With an increase in distance of the shore and establishmentf a fully marine condition (e.g., light, water circulation, andalinity) along with a decrease in hydrodynamic level and tur-ulence in a shelf setting, the trace fossils show an increasen diversity, abundance, and the lifestyle. Moreover, skeletallements in this setting shows an increase in diversity and abun-ance, characterized by various taphonomic features such asragmented and oriented (related to minor active phases and con-entrated within tempestite sediments) vs. complete and chaoticrelated to fair weather condition) (Figs. 8C, 10). The trace fossilauna found in the storm-influenced shelf environment of lowo intermediate energy in carbonate substrates is indicated byhalassinoides isp., Palaeophycus tubularis, Arenicolites isp.,iplocraterion isp., Protovirgularia isp., Chondrites isp. Chon-rites targionii, Chondrites intricatus, and Helminthopsis isp.igh diversity of trace and body fossils reflect the presence of

dequate food resources in both substrate and water columnnder normal salinity conditions (Fig. 11). The ichnoassem-

lage shows preferentially positive hyporelief structures (exceptrenicolites isp., Diplocraterion isp., Chondrites) along withominance of the complete and chaotic oriented fossils (Sharafi

d2a

trace fossils, and general characteristics of suites in the Geirud Formation. See

t al., 2013), reflecting predominantly low energy, low sed-mentation rate and stable substrate conditions in the shelfnvironment (Fürsich, 1998; Zonneveld et al., 2001), occa-ionally affected by storm currents. According to Zonneveldt al. (2001), in substrates with the low sedimentation rates,rganic material will be concentrated near the sediment surface,nd organisms will preferentially exhibit an interface-feedingifestyle. This ichnoassemblage is dominated by deposit-feederraces and corresponds to the Cruziana ichnofacies.

Thalassinoides is common and abundant and occurs in alluites except the Skolithos suite. This indicates that the orga-isms that excavate these burrows are generally not restricted tony particular environment and can construct fodinichnia in aariety of substrate types and water depths in the normal marineetting.

The vertical suite succession, displayed by a fluvial-helf replacement of the weakly bioturbated sediments byhe Rhizocorallium-Thalassinoides ichnofabric (Cruziana) –hondrites-Helminthopsis (distal Cruziana) suite from lower

o upper succession, clearly shows an overall increase in waterepth and decrease in energy level during deposition of theeirud Formation. The most important regional factors that con-

rolled deposition and the vertical facies trends of the Geirudormation in the studied area can be tectonic subsidence along

he east-west running longitudinal faults (Sharafi et al., 2013) inssociation with a general eustatic sea level rise that happened

uring the Late Devonian time in a global scale (Wendt et al.,005). The sea level rise caused flooding of large parts of Irannd deposition of increasingly marine deposits (Wendt et al.,

66 M. Sharafi et al. / Palaeowo

Fig. 12. Sequential development of the colonization window of the storm-influenced shoreface deposits in the Geirud Formation. (A) Stage 1: depositionof the storm-influenced sandstone bed with HCS and a few escape structures(fu: fugichnia). (B) In the next step (stage 2), under fair weather condition anda slowdown or halt in sedimentation rate toward the top of bed (minor omissionstage), the upper plane of the sandstone bed is colonized by many trace markers(colonization window) (e.g., Thalassinoides, Palaeophycus and Chondrites) thatare preserved mainly as concave epirelief structures (R: resting trace). (C) Withonset of the new storm phase (stage 3), the casts of the trace fossils at the top ofthe lower sandstone bed filled by storm-induced sediments of this new phase andthe trace fossils preserved as convex hyporelief at the lower plane of the newsi

2dAist(ptm

(msdtttD

7

ilmsD

catcbc

fspPmHas

bbDso

issd

ioc

A

helps. We acknowledge Department of Geology, Ferdowsi Uni-

andstone bed. Ch: Chondrites; Ps: Palaeophycus striatus; Pa: Palaeophycussp.; Rh: Rhizocorallium; Th: Thalassinoides.

005). Tectonic subsidence and sea level rise created accommo-ation space for deposition of the siliciclastic-carbonates in thelborz Basin, Iran. During this time Iranian plate was located

n the northern continental margin of the Gondwana along theouthern shore of the Palaeo-Tethys Ocean and a tractional sys-em was established in this part of the super continent (Fig. 1)Golonka, 2007; Bagheri and Stampfli, 2008). The same exam-

le of the coastal to shelf transition successions is recorded inhe Taurides Basin, Turkey, which was located at the northern

argin of the Gondwana landmass during the Devonian time

vMt

rld 23 (2014) 50–68

Wehrmann et al., 2010). Despite some differences in their sedi-entary sequences (e.g., thickness and a few sub-environments

uch as sabkha and lagoon that can be related to their localepositional setting) (Wehrmann et al., 2010) with respect tohe Alborz Basin, they show similarity in the depositional sys-ems and vertical facies trends, and thus display same large-scalerends along the southern shore of the Palaeo-Tethys during theevonian time.

. Conclusions

The vertical succession of suites reflects lateral changesn depositional environments from tidal (Skolithos suite),ower shoreface (Rhizocorallium-Thalassinoides ichnofabric),

iddle-upper shoreface (Palaeophycus-Thalassinoidesuite), to shelf (Protovirgularia-Palaeophycus, Arenicolites-iplocraterion and Chondrites-Helminthopsis suites).Tidal environment is characterized by a low diversity of verti-

al to sub-vertical trace fossils (Skolithos and Palaeophycus) and low BI, indicating a high energy condition with high sedimen-ation rates. Sedimentary structures in this part of the formationonsist of bi- to multi-directional planar cross bedding, herring-one cross bedding, oscillation wave ripple, reverse directionross-lamination, and reactivation surfaces.

Lower to middle shoreface shows medium diversity of traceossils, displayed by a diversity of horizontal and vertical toub-vertical structures attributable to a variety of crustaceans,olychaetes and bivalves (Rhizocorallium, Thalassinoides,alaeophycus, Chondrites and escape traces (fugichnia)). Sedi-entary structures in this part of the Geirud Formation consist ofCS and horizontal lamination within tempestite sandstone with

sharp basal lag concentration, displaying storm-influencedhoreface deposits.

Shelf deposits in the Geirud Formation are characterizedy high diversity of trace fossils and high degree of biotur-ation (Thalassinoides, Palaeophycus tubularis, Arenicolites,iplocraterion, Protovirgularia, Chondrites, and Helminthop-

is) with a few sharp-basal lag concentrations, showingccasionally storm-influenced conditions.

A fluvial-shelf replacement from the weakly bioturbated sed-ments (Skolithos suite) to the Rhizocorallium-Thalassinoidesuite (Cruziana) – Chondrites-Helminthopsis (distal Cruziana)uite from lower to upper succession clearly shows an overalleepening-upward within succession of the Geirud Formation.

The main controls on development of ichnofabricsnclude the nature of relict sediment, salinity, bottom waterxygenation, food abundance, energy level, water clarity, andhanges in sediment supply.

cknowledgments

We are grateful to Franz Fürsich (Erlangen, Germany) for his

ersity of Mashhad for its support during the course of this study.ahmoud Ashouri and Mahmoud Sadegh Zadeh are thanked for

heir fieldwork assistance. We thank Renata Guimarães Netto

aeowo

am

R

A

B

B

B

B

B

B

B

D

D

D

D

F

F

F

F

F

F

F

G

G

G

G

G

H

K

L

M

M

M

M

M

MN

N

P

P

P

P

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nd an anonymous reviewer for their constructive reviews of theanuscript.

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