Maastrichtian-Danian in the SW Zagros Fold-Thrust Belt (S Iran): Integrated Planktonic Foraminiferal Biostratigraphy and Gamma-Ray Spectrometry

Maastrichtian-Danian in the SW Zagros fold-thrust belt

ABDOLREZA Moghaddasi, HOSSEIN Vaziri-Moghaddam *, ALI Seyrafian

Department of Geology, Faculty of Science, University of Isfahan, P.O. Box: 81746-73441, Isfahan, Iran

Abstract: In this study, the Maastrichtian-Danian boundary was measured and sampled, in two stratigraphic sections, north and south flanks of Dehnow anticline in Coastal Fars, Southern Iran. Also this boundary was investigated in drilled exploratory well- 1 in the same region. The lithology of Maastrichtian-Danian deposits consists of glauconitic, phosphatic argillaceous limestones and marlstones. 30 genera and 77 species of planktonic foraminifera have been determined. The recognized biozones are Gansserina gansseri Interval Zone, and Contusotruncana contusa Interval Zone which indicates latest Campanian to middle Maastrichtian age for upper part of the Gurpi Formation and Eoglobigerina edita (P1) Partial-range Zone, Praemurica uncinata (P2) Lowest-occurrence Zone, Morozovella angulata (P3) Lowest-occurrence Zone, and Globanomalina psudomenardii (P4) Taxon-range Zone representing Danian to Thanetian age for lower part of Pabdeh Formation. Due to lack of Abathomphalus mayaroensis Interval Zone, Pseudoguembelina hariaensis Interval Zone, Pseudotextularia elegans Interval Zone, Plummerita hantkeninoides Interval Zone, Guembelitria cretacea (P0) Partial-range Zone and Parvularugoglobigerina eugubina (Pα) Total- range Zone, there is a paraconformity between Maastrichtian–Danian boundary in the studied area and this hiatus encompasses the late Maastrichtian until earliest Danian age. Danian deposits of the study area contain reworked glauconitized macrofossils, planktonic and benthonic foraminifera of Cretaceous. The obtained surface gamma-ray spectrometry logs are resemble to exploratory well-1 gamma-ray wireline log.

Keywords: Maastrichtian-Danian, Biostratigraphy, Planktonic foraminifera, Gamma-ray spectrometry, Zagros, Iran

*Corresponding author: E-mail: [email protected] and [email protected]

1 Introduction

One of the five largest events in the earth history is the Cretaceous/Paleogene (K/Pg) boundary which is the second most important event on the Earth (Sepkoski, 1996) which coincides 66 million years ago (Ogg et al., 2012, 2016). This event caused to mass extinction by which 64 to 85 % of all species of marine and terrestrial organisms were extinct (Sepkoski, 1996; MacLeod et al., 1997). There are many hypothesis invoked for this event including extraterrestrial bolide impacts and positive iridium anomaly by Alvarez (Alvarez et al., 1980; Smit, 1990), multiple impact (Mullen, 2004), volcanism (Decan Traps flood basalt (Duncan and Pyle, 1988)), CO2 poisoning (MacLean, 1985), O2 suffocation (Landis et., al. 1993 in Keller, 1996; Hengst et al., 1996), reproduction failure (McLean 1991, 1994 in Keller 1996), sea-level fluctuations and climate changes (Hallam, 1989), supernova (Ellis and Schramm, 1995), and multiple event causes (Keller et al., 2001). The K/Pg boundary was defined at the base of the boundary clay at a section near El Kef, Tunisia (Keller, 1998b, Keller et al., 1995; Molina et al., 2006, 2009). The other sections described in Aïn Settara and Ellès in Tunisia (Arenillas et al., 2000; Karoui-Yaakoub, 2002; Molina et al., 2009), Agost, Caravaca and Zumaya in SE Spain (Canudo et al., 1991; Pardo et al., 1996; Molina et al., 2004, 2009), Bidart in France (Gallala et al., 2009; Molina et al., 2006, 2009), El Mulato and Bochil in Mexico (Molina et al. 2009) and Poty in Brazil (Albertão et al. 1993, 1994; Stinnesbeck and Keller, 1996; Koutsoukos, 2005, 2006).

This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1111/1755-6724. 14292.

This article is protected by copyright. All rights reserved. The K/Pg boundary is continuous only in Danial section in Iran (Beiranvand and Ghasemi-Nejad, 2013; Beiranvand et al., 2013; Beiranvand et al., 2014 a, b) whereas is not continuous in our studied area. There are few detailed geological studies in Maastrichtian-Danian deposits of south Iran, therefore the aims of the present study are 1. Detailed micropaleontological study by means of planktonic foraminifera and correlation with worldwide biozonation, 2. Checking this boundary by gamma-ray spectrometry in surface sections and correlation with subsurface data, 3. Lithostratigraphical revision on the formations deposited during at this time span.

2 Geological setting

The studied area crops out in Zagros Fold-Thrust Belt (ZFTB) and it extends within the Alpine-Himalayan orogenic belt for 2000 km between the Central Iran microcontinent (Takin, 1972) and the northwestern Iranian plate in the NE and the Arabian plate in the SW (Koyi et al, 2008). This fold-thrust belt formed as a result of subduction of the Neo-Tethyan Ocean beneath Iran and late Miocene continent-continent collision between Iran and Arabia (Takin, 1972; Stöcklin, 1974; Alavi, 1980, 1994, 2004; Berberian and Kings, 1981; Koyi et al., 2008; Jahani, et al., 2009; Agard et al., 2005, 2011; Motamedi et al, 2012). The ZFTB is one of the largest and most active foreland basin systems on the earth being well-known for oil and gas reservoirs, salt diapirs and anticlines (Pirouz, et al., 2015, 2016). Two-thirds of proven oil reserves and one-third of world’s gas reserves hosted by ZFTB (Beydoun et al., 1992). The structural evolution of depositional history of ZFTB is as follow: a stable platform condition and block faulting in Paleozoic, rifting phase during Permo-Triassic, passive continental margin with northeast sea floor spreading and subduction in Late Triassic–Late Cretaceous (Turonian), ophiolite obduction in Late Cretaceous (Coniacian-Santonian), developing foreland basin in Late Cretaceous (Campanian)–Miocene, folding and shortening during Mio-Pliocene (Jahani et al., 2005; Motamedi et al, 2012). During the K/Pg boundary the ZFTB was situated at the southern Neo-Tethys Ocean (Fig. 1).

Fig. 1. Paleogeographic position of Zagros fold and thrust belt during Cretaceous/Paleogene boundary (66 Ma) (redrawn and modified from MacLeod and Keller, 1991b).

The ZFTB has been divided into a number of different tectonic zones bounded by either structural or depositional discontinuities in various locations, which show a separate geological history. The Zagros Imbricate Zone, Simply Folded Belt and Mesopotamian Foreland Basin are the main zones. The external fold belt (Simply Folded Belt) of the Zagros basin consists two salients – the Lurestan salient and Fars salient separated by the Dezful embayment (Stöcklin, 1968 b; Setudehnia, 1978; Motiei, 1995; Berberian, 1995). The Fars salient is divided into three subzones, based on changes in folding geometry and depositional history (Motiei, 1993). The northern part is Interior Fars, the middle is the Subcoastal Fars, and southern part is the Coastal

This article is protected by copyright. All rights reserved. Fars (Setudehnia, 1978; Motiei, 1995; Berberian, 1995). Due to the local unconformities and growth strata units, folding was initiated since early Paleocene in the inner part of the Fars Province (High Zagros and Interior Fars) and propagated toward the Coastal Fars area onward (Gharabeigli, 2014). The studied area situated in Coastal Fars, comprises two stratigraphic section in Dehnow anticline and one drilled exploratory well-1 in the same region. There are two important faults in the studied area (Fig. 2). The first one is Razak fault which was introduced by Barzegar (1994) and is considered as a basement north-south trending strike- slip fault. Its main activity was during Paleozoic, however it was reactivated later (Barzegar, 1994; Hessami et al, 2001; Hessami and Tabassi, 2006). The second one is Zagros Frontal Fault (ZFF) which was introduced by Berberian (1995) and situated between Dehnow and Khalfani anticlines. It is also considered as a basement east- west trending fault and its main activity was from post Miocene. There is no surface impression of ZFF in the eastern part of studied area.

Fig. 2. Geological location map of the studied area in Coastal Fars (redrawn and modified from NIOC, 1975).

3 Previous study

The type sections of Gurpi and Pabdeh formations introduced by James and Wynd (1965) in Tang-e Pabdeh are located on the southwestern flank of the southeastern plunge of Kuh-e Pabdeh just north of the Lali oil field in Dezful embayment. The Gurpi Formation comprises 320 m of dark bluish grey, marine marlstones and shales with subordinate marly limestones. The Emam Hasan Limestone Member is present in Lurestan salient and Khuzestan and Lopha limestone informal member is present only in Lurestan salient. In Lurestan salient the upper contact of Gurpi Formation is placed at the junction of dark grey shales of the Gurpi Formation with the sandy, silty, purple shales of lowermost Pabdeh Formation. The Pabdeh Formation comprises 798 m low-weathering grey shales and thin argillaceous limestones. The purple shale informal member at the base of Pabdeh Formation was defined by James and Wynd (1965). In parts of Dezful embayment and Lurestan salient, the Gurpi and Pabdeh formations acts as a source rocks (Ala et al., 1980; Bordenave and Burwood, 1990; Bordenave and Huc, 1995; Bordenave and Hegre, 2010).The Gurpi Formation can be considered as a cap rock in Dezful embayment (Bordenave and Burwood, 1990, Bordenave and Huc, 1995, Bordenave and Hegre, 2010).

This article is protected by copyright. All rights reserved. The first biozonation in ZFTB was introduced by Wynd (1965). For the upper Maastrichtian deposits of the Gurpi Formation two biozones are as follow: Globotruncana stuarti–Pseudotextularia varians assemblage zone in Lurestan, Fars salients and Khuzestan, and Abathomphalus mayaroensis occurrences only in the Lurestan salient was proposed. For the Danian deposits, one biozone as a name Globorotalia-Globigerina-Globigerina daubjergensis assemblage zone was introduced in Lurestan and somehow in Khuzestan which based on lithostrartigraphy it was assigned to the Gurpi Formation. According to James and Wynd (1965), Wynd (1965), and Setudehnia (1977) the Danian deposits are absent in Fars salient. Sampo (1969) introduced Globotruncana stuarti– Bolivina incrassate Zone for the Maastrichtian and Globigerina daubjergensis Zone for Danian of ZFTB. Hamrang (1975) based on planktonic foraminifera work on K/T boundary of some sections and exploratory wells in west of Kermanshah, in Lurestan salient and compared with established zonation in Trinidad. Kalantari (1986, 1992) reported some planktonic foraminifera of the Gurpi and Pabdeh formations from stratotype and other localities. Vaziri Moghaddam (2002) introduced Globotruncanita stuarti Zone VI and Gansserina gansseri Zone VII from the Gurpi Formation from Sarvestan area, SE of Shiraz city, demonstrated the early to middle Maastrichtian age and mentioned the upper Maastrichtian deposits missed. Darvishzad et al. (2007) based on planktonic foraminifera indicated the Gurpi–Pabdeh boundary in Kabirkuh section in Lurestan salient is continuous. Parvaneh-Nejad Shirazi et al. (2013) work on biostratigraphy and paleoecology of Gurpi Formation based on planktonic to benthonic ratio (P/B) at Shiraz area. Fereydoonpour et al. (2014) based on planktonic foraminifera assigned the early Santonian– early Maastrichtian age for Gurpi Formation at Deh Dasht area. The latest biozonation on K/Pg boundary in Danial section situated in Izeh zone represented the Gurpi-Pabdeh formations boundary is conformable (Beiranvand and Ghasemi-Nejad, 2013; Beiranvand et al., 2013; Beiranvand et al., 2014 a, b).

4 Materials and methods

Two outcrops of the Gurpi Formation in contact with of the Pabdeh Formation were selected in order to follow previous researches (i.e Perrier, 1976; Genevraye, 1977) along examining Gavbast geological quadrangle map scale 1:100,000 (Jahani et al., 2004); Eshkanan, Gavbandi geological quadrangle maps scale 1: 50,000 (James, 1960). Two stratigraphic sections were measured and sampled in north and south flanks of Dehnow anticline using Jacob staff. Each section was measured and sampled perpendicular to strike of layer regarding true dips of strata. In the field, the hard part of the stratigraphic sections such as limestones were cleaned from surface contamination by paint-brush and the top of each sample marked by a marker pen to detect the top of layer and oriented samples were collected. For soft layers such as marlstones and shales, surface was cleaned by trowel, then was dug at least 25 cm depth, to attain fresh bed and afterwards cleaned by paint-brush. They were separately sampled to avoid any possible contamination. The interval of sampling was 30 cm before and after K/Pg boundary and closer 10 cm at intervals across this boundary. The accumulative thickness of dense sampling was 6.2 m and 5.5 m in north and south flank of Dehnow anticline respectively. The interval of samples in drilled exploratory well-1 was 2 m. The cutting samples at the Maastrichtian-Danian boundary were selected and the lithology of this interval was determined under corvascope, thin sections of cuttings under polarizing microscope and petrophysical log interpretation. Two or three thin sections of hard samples of stratigraphic sections were prepared along the top layer which was marked by an arrow then micropaleontological and petrographic investigations were carried out by using a Leica DM LP polarizing microscope equipped with Nikon Ds-Fi1 camera. Loose samples were separated for micropaleontological analysis following the procedure mentioned in Lirer (2000). The samples were sieved with four sieve, 80 mesh (178μm), 120 mesh (125μm), 230 mesh (63μm) and 325 mesh (44μm). The abundance of foraminiferal species is defined following Nishi et al. (2003), rare (1-2), few (3-5), common (6-10), and abundant (>10). The preservation of washed planktonic foraminifera were moderate and poor at K/Pg boundary. With regarding Signor–Lipps effect (MacLeod, 1996; MacLeod et al., 1997) a blind test has been done at K/Pg boundary (Keller et al., 1995; Molina et al., 2006). Planktonic foraminifera were hand-picked by using a Zeiss Stemi SV 11 stereo zoom microscope and then put into three cells slides. The samples have been checked and photographed by TE Scan model VEGA II Scanning Electron Microscope (SEM) in Razi Metallurgical Research Center (RMRC) in Tehran. All the samples, thin sections, picked slides and stubs of SEM presented in this paper are stored in the collection of Paleontological Laboratory warehouse of National Iranian Oil Company, Exploration Directorate, Tehran, Iran and labelled as ARMO 940-1130, ARMO 1316- 1406 and KHL 642-692. In each sampling point the natural radioactivity comprising uranium (U), potassium (K), and thorium (Th), and dose rate (total gamma-ray) was measured by portable gamma-ray spectrometer made by GF Instruments. The method and procedure was based on the user manual of instrument and also followed the Fiet and Gorin (2000). Calibration and test of the instrument has been done according to above mentioned references. The count time was regarded one minute after numerous checking. The detector of gamma-ray instrument was placed in planar surface of limestones and cleaned surface of soft lithology and remained stable during measuring.

This article is protected by copyright. All rights reserved. The gamma-ray obtained raw data, drawn by Geolog software for creation of gamma-ray log. These logs interpreted by CycloLog software and correlated with exploratory well-1, adjacent to the surface sections in the Coastal Fars.

5 Lithostrartigraphy

In the studied area, the lithostratigraphic description of upper part of Gurpi Formation and lower part of Pabdeh Formation are as follow:

5.1 North flank of Dehnow anticline (Tang-e Gabrzar section) The Tang-e Gabr ar section situated at 5 Km east of Eshkanan town (Fig 2) The elevation of measured section is 500 m above mean sea level and the base of section coordination is: geographic long 53 38 48 64 E, lat 27 10 13.23 N (UTM 0762265 E, 3008070 N) and the top of section coordination is as follow: geographic long 53 38 50 04 E, lat 27 10 15 78 N (UTM 0762301 E, 3008149 N) These coordinates situated in one 39 of UTM/UPS. In this stratigraphic section (Fig. 3a), the upper part of Gurpi Formation consists of thick bedded, low weathered, grey to bluish grey, yellowish grey, argillaceous limestones (planktonic foram wackestones and packstones) at the lower part and low weathered, grey to dark grey, bluish grey, nodular, bioturbated argillaceous limestones (planktonic foram wackestones and packstones) in middle part and dark grey, greenish grey, strongly bioturbated (Planolites isp.), nodular, glauconitic and phosphatic limestones (planktonic foram packstones) somehow argillaceous near to top of section. There are glauconitic and phosphatic layers at the top of the Gurpi Formation with 35 m thickness. The upper contact of the Gurpi Formation is placed at the junction of very thin bedded low weathered glauconitic, phosphatic foliated argillaceous limestones (planktonic foram wackestones and packstones) (Fig. 3b) and grey to dark grey, bluish marlstones of the lowermost of the Pabdeh Formation. In continuation to the top of Pabdeh Formation, thin bedded greenish, bluish cherty nodular limestones (Fig. 3c) with trace fossils such as Planolites isp. are present. At the base of Pabdeh Formation (Fig. 4a) there are abundant glauconitic and phosphatic nodules (Fig. 4b) and reworked glauconitized macrofossils such as cephalopods (Eutrephoceras sp. (Fig. 4c)), bivalves and sponges. At the continuation in this section, the Pabdeh Formation passes into a mixed Jahrum-Pabdeh facies assigned to Eocene age (James and Wynd, 1965) which was not investigated

. Fig. 3. Field photos of north flank of Dehnow anticline (Tang-e Gabrzar section). (a) The panorama of Gurpi-Pabdeh formations boundary (view to east); (b) The Gurpi-Pabdeh formations contact shows dense sampling; (c) The cherty limestones above the base of Pabdeh Formation (arrow shows chert nodule).

Fig. 4. Close view of Pabdeh-Gurpi formations boundary in north flank of Dehnow anticline (Tang-e Gabrzar section). (a) The contact of Gurpi-Pabdeh formations at Tang-e Gabrzar stratigraphic section (view to east); (b) The glauconite pointed with the worn gloves finger in marlstones at the base of Pabdeh Formation; (c) Reworked glauconitized cephalopd (Eutrephoceras sp.) in marlstones at the base of Pabdeh Formation.

5.2 South flank of Dehnow anticline (Tang-e Bonab section) This section situated at 2 Km north of Bouchir town (Fig. 2). The elevation is 349 m above mean sea level and the base of section coordination is as follow: geographic long 53 44 06 7 E; lat 27 02 43 09 N (UTM 0771332 E, 2994427 N) and the top of section coordination is as follow: geographic long 53 38 44 04 E; lat 27 02 40 0 N (UTM 0771252 E, 2994302 N). These coordinates situated in zone 39 R of UTM/UPS. In this stratigraphic section (Fig. 5a), the upper part of Gurpi Formation consists of thick bedded of low weathered greenish grey argillaceous limestones, partly ridge forming at the lower part and dark greenish grey, nodular and glauconitic and phosphatic, bioturbated (Planolites isp.) (Fig. 5b) argillaceous limestones (planktonic foram packstones) partly ridge forming at the top of Gurpi Formation.

Fig. 5. Field photos of south flank of Dehnow anticline (Tang-e Bonab section). (a) The panorama of Gurpi-Pabdeh formations exposed in Tang-e Bonab stratigraphic section (view to north); (b) Trace fossil Planolites isp. at the top of Gurpi Formation ; (c) The base of Pabdeh Formation (d); Measuring of surface gamma-ray with portable gamma-ray surveyor.

The base of Pabdeh Formation (Fig. 5c) comprises of low weathered fissile glauconitic and phosphatic argillaceous limestones (planktonic foram wackestones and packstones) and in continuation cherty nodular, grey tiny to medium bedded argillaceous limestones (planktonic foram wackestones). Also in each sampling point the surface gamma-ray was measured by handheld gamma-ray spectrometer (Fig. 5b).

5.3 Lithostratigraphic revision of the Gurpi–Pabdeh formations boundary According to James and Wynd (1965) and Setudehnia (1977), throughout Lurestan and Khuzestan the base of Pabdeh Formation is placed at the bottom of purple shale informal member but in Fars salient the purple shale generally is not present, and they regarded the cherty limestones as the base of Pabdeh Formation. In the studied sections, 5 meters below the cherty limestones, an interval about 2 meters of very thin bedded bioturbated greenish grey marlstones containing reworked macrofossil with abundant glauconitic and phosphatic nodules is present, which we recommend as the base of Pabdeh Formation (Fig. 4).

5.4 The exploratory (wild cat) well-1 In this well the upper part of Gurpi Formation consists of argillaceous glauconitic and phosphatic limestones (planktonic foram wackestones and packstones) and marlstones. The lower part of Pabdeh Formation comprises argillaceous glauconitic and phosphatic limestones (planktonic foram wackestones).

6 Planktonic foraminiferal biostratigraphy

The planktonic foraminifera were investigated on thin-sections and washed samples. Generic classification, descriptions, stratigraphic ranges, and determinations of Maastrichtian, Danian planktonic foraminifera follows Postuma (1971), Robaszynski et al. (1984), Caron (1987), Toumarkine and Luterbacher (1987), Loeblich and Tappan (1964, 1988), Sartorio and Venturini (1988), Sliter (1989, 1999), Nederbragt (1989, 1991), Berggren and Norris (1997), Olsson et al. (1999), Premoli Silva and Sliter (1995, 2002), Premoli Silva et al. (2003), Premoli Silva and Verga (2004), Keller et al. (1995), Li and Keller (1998b) and mikrotax site (Huber et al., 2016). The Cretaceous biozonation was after Li and Keller (1998a, b), Li et al. (1999), and Coccioni and Premoli Silva (2015). For Paleocene biozonation the Berggren and Miller (1988), Berggren and Pearson (2005), Wade et al. (2011), and Coccioni et al. (2016) have been used. The recognized biozones compared with old biozonation which was proposed by Wynd (1965) in ZFTB.

6.1 The Maastrichtian biozones

This article is protected by copyright. All rights reserved. We enumerate here the recognized Maastrichtian biozones in upper part of Gurpi Formation in two stratigraphic sections and exploratory well-1 (Figs. 6, 7, 9-13).

Fig. 6. Stratigraphical distribution of Maastrichtian-Danian planktonic foraminifera in north flank of Dehnow anticline (Tang-e Gabrzar section).

Fig. 7. The Gurpi Formation planktonic foraminiferal index-species in Tang-e Gabrzar section. (a) Globotruncana bulloides Volger, 1941, Sample no. ARMO 970; (b) Contusotruncana fornicata (Plummer, 1931), 985; (c) Globotruncanita stuarti (de Lapparent, 1918), 988; (d) Globotruncanita pettersi (Gandolfi, 1955), 1010; (e) Contusotruncana contusa (Cushman, 1926), 1020; (f) Pseudotextularia elegans (Rzehak, 1891), 1035; (g) Planoheterohelix globulosa (Ehrenberg, 1840), 1047; (h) Pseudoguembelina excolata (Cushman, 1926), 1048; (i) Trinitella scotti Brönnimann, 1952, 1058; (j) Globotruncanella petaloidea (Gandolfi, 1955), 1062; (k) Globotruncanita conica (White, 1928), 1064; (l)

This article is protected by copyright. All rights reserved. Globotruncana aegyptiaca var. gagnebini Nakkady, 1951, 1067; (m) Globotruncanita angulata (Tilev, 1951), 1070; (n) Contusotruncana walfischensis Todd, 1970, 1076; (o) Gansserina gansseri (Bolli, 1951), 1076.

6.1.1 Gansserina gansseri Interval Zone (Coccioni and Premoli Silva, 2015)

Definition: Interval from the lowest occurrence (LO) of the zonal marker to the LO of Contusotruncana contusa. Age: Latest Campanian – early Maastrichtian. Remark: This zone is equivalent to the CF7 zone of Li and Keller (1998a, b) The aim of this study is to detect the exact K/Pg boundary, hence the first occurrence (FO) of this biozone is not recognized. The composition of the assemblage of planktonic foraminifera in this biozone is as follow: Gansserina gansseri (Bolli, 1951), Pseudoguembelina excolata (Cushman, 1926), Globotruncanita conica (White, 1928), Gt. stuarti (de Lapparent, 1918), Gt. stuartiformis (Dalbiez, 1955), Globotruncana aegyptiaca Nakkady, 1950, G. orientalis El Naggar, 1966, G. rosetta (Carsey, 1926), G. bulloides Volger, 1941, G. lapparenti Brotzen, 1936, G. linneiana (d'Orbigny, 1839), G. falsostuarti Sigal, 1952, Globotruncanella havanensis (Voorwijk, 1937), Ge. minuta Caron & Gonzalez Donoso, 1984, Rugoglobigerina hexacamerata Brönnimann, 1952, Ru. rugosa (Plummer, 1926), Archaeoglobigerina blowi Pessagno, 1967, Ag. cretacea (d'Orbigny, 1840), Muricohedbergella monmouthensis (Olsson, 1960), Mu. holmdelensis Olsson, 1964, Contusotruncana plummerae (Gandolfi, 1955), Macroglobigerinelloides alvarezi (Eternod Olvera, 1959), Mg. prairiehillensis (Pessagno, 1967), Contusotruncana fornicata (Plummer, 1931), Planoheterohelix globulosa (Ehrenberg, 1840), Pseudotextularia elegans (Rzehak, 1891), and benthonic foraminifera.

6.1.2 Contusotruncana contusa Interval Zone (Coccioni and Premoli Silva, 2015) Definition: Interval from the LO of the zonal marker to the LO of Abathomphalus mayaroensis. Age: Middle Maastrichtian. Remark: This zone is equivalent to the CF6 zone of Li and Keller (1998a, b). The LO of Abathomphalus mayaroensis is not recognized. The assemblage of planktonic foraminifera in this biozone are as follow: Contusotruncana contusa (Cushman, 1926), C. patelliformis (Gandolfi, 1955), C. walfischensis (Todd, 1970), Macroglobigerinelloides alvarezi (Eternod Olvera, 1959), Mg. subcarinatus (Brönnimann, 1952), Globotruncana arca (Cushman, 1926), G. orientalis El Naggar, 1966, G. rosetta (Carsey, 1926), G. ventricosa White, 1928, G. insignis Gandolfi, 1955, G. bulloides Volger, 1941, G. lapparenti Brotzen, 1936, G. linneiana (d'Orbigny, 1839), G. falsostuarti Sigal, 1952, G.hilli Pessagno, 1967, G. aegyptiaca Nakkady, 1950, Globotruncanita stuarti (de Lapparent, 1918), Gt. stuartiformis (Dalbiez, 1955), Gt. angulata (Tilev, 1951), Gt. pettersi (Gandolfi, 1955), Planoheterohelix globulosa (Ehrenberg, 1840), Rugoglobigerina rugosa (Plummer, 1926), Ru. pennyi Brönnimann, 1952, Pseudotextularia elegans (Rzehak, 1891), Pt. nuttalli (Voorwijk, 1937), Trinitella scotti Brönnimann, 1952, Globotruncanella havanensis (Voorwijk, 1937), Ge. petaloidea (Gandolfi, 1955), Muricohedbergella monmouthensis (Olsson, 1960), Mu. holmdelensis Olsson, 1964, Gansserina gansseri (Bolli, 1951), Pseudoguembelina costulata (Cushman, 1938), and benthonic foraminifera such as Neoflabellina delicatissma Plummer, 1927. These are associated with shark teeth (Cretolamna sp.), echinoderm and bivalve fragments. The uppermost part of Gurpi Formation in the studied area assigned to the middle Maastrichtian age. It should be mentioned we did not detect this Zone in exploratory well-1 which seemingly could be due to excessive cutting sampling interval (2 m). The Globotruncana stuarti – Pseudotextularia varians assemblage zone of Wynd (1965) regarded as equivalent of above mentioned two biozones of Coccioni and Premoli Silva (2015).

6.2 The Danian biozones We enumerate here the Danian biozones which were recognized at the base of Pabdeh Formation in two stratigraphic sections and exploratory well-1 (Figs. 6, 8, 9-13).

Fig. 8. The Pabdeh Formation planktonic foraminiferal index-species in Tang-e Gabrzar section. (a) Abundant glauconite (green color) and phosphate (brown color) with Danian planktonic foraminifera, Sample no. ARMO 1079; (b) Subbotina trivialis Subbotina, 1953, 1079; (c) Globoconusa daubjergensis (Brönnimann, 1953), 1079; (d) Subbotina triloculinoides (Plummer, 1926) inside the phosphate particle, 1079; (e) Reworked Globotruncanita pettersi (Gandolfi, 1955) at K/Pg boundary, 1079; (f) Parasubbotina pseudobulloides (Plummer, 1926), 1080; (g) Globanomalina archaeocompressa (Blow, 1979), 1080; (h) Praemurica inconstans (Subbotina, 1953), 1084; (i) Praemurica uncinata (Bolli, 1957), 1085; (j) Globanomalina pseudomenardii (Bolli, 1957), 1101; (k) Igorina albaeri (Cushman and Bemudez, 1949), 1102; (l) Morozovella

This article is protected by copyright. All rights reserved. velascoensis (Cushman, 1925), 1110; (m) Morozovella praeangulata (Blow, 1979), 1113; (n) Globanomalina chapmani (Parr, 1938), 1121; (o) Morozovella conicotruncata (Subbotina, 1947), 1121.

Fig. 9. The SEM photos of Gurpi (a-i) and Pabdeh (j-o) formations in Tang-e Gabrzar section. (a) Globotruncanita stuartiformis (Dalbiez, 1955), Sample no. ARMO 944; (b) Globotruncanita stuarti (de Lapparent, 1918), 944; (c) Globotruncana insignis Gandolfi, 1955, 1004; (d) Neoflabellina delicatissima Plummer, 1927, 1014; (e) Globotruncana bulloides Volger, 1941, 1014; (f) Rugoglobigerina

This article is protected by copyright. All rights reserved. rugosa (Plummer, 1926), 1024; (g) Contusotruncana fornicata (Plummer, 1931), 1054; (h) Heterohelix globulosa (Ehrenberg, 1840), 1054; (i) Cretolamna sp., 1077; (j) Eoglobigerina eobulloides Morozova, 1959, 1079; (k) Praemurica inconstans (Subbotina, 1953), 1079; (l) Subbotina triloculinoides (Plummer, 1926), 1087; (m) Praemurica pseudoinconstans (Blow, 1979), 1087; (n) Enlarged wall of previous photo, 1087; (o) Otodus sp., 1123.

Fig. 10. Stratigraphical distribution of Maastrichtian–Danian planktonic foraminifera in south flank of Dehnow anticline (Tang-e Bonab section).

Fig. 11. The Gurpi-Pabdeh formations planktonic foraminiferal index-species in Tang-e Bonab section. (a) Contusotruncana contusa (Cushman, 1926), Sample no. ARMO 1320; (b) Rugoglobigerina hexacamerata Brönnimann, 1952, 1326; (c) Globotruncana neotricarinata Petrizzo, Falzoni, & Premoli Silva, 2011, 1330; (d) Gansserina gansseri (Bolli, 1951), 1332; (e) Globotruncanita stuarti (de Lapparent, 1918), 1336; (f) Glauconite filled the chambers of Macroglobigerinelloides alvarezi (Eternod Olvera, 1959), 1345; (g) Globotruncanita pettersi (Gandolfi, 1955), 1345; (h) Reworked Globotruncana stuartiformis (Dalbiez, 1955) besides the glauconite at K/Pg boundary, 1358; (i) Globoconusa daubjergensis (Brönnimann, 1953), 1361; (j) Gansserina gansseri (Bolli, 1951), 1362; (k) Eoglobigerina fringa (Subbotina, 1947), 1364; (l) Globanomalina compressa

This article is protected by copyright. All rights reserved. (Plummer, 1926), 1371; (m) Morrozovella angulata (White, 1928), 1386; (n) Igorina tadjikistanensis (Bykova, 1953), 1391; (o) Globanomalina pseudomenardii (Bolli, 1957), 1400.

Fig. 12. Stratigraphical distribution of Maastrichtian–Danian planktonic foraminifera in the exploratory well-1.

Fig. 13. The Gurpi (a-f) and Pabdeh (g-l) formations planktonic foraminiferal index-species in the exploratory well-1. (a) Globotruncana bulloides Volger, 1941, Sample depth (in meters) - KHL 680; (b) Globotruncanita angulata (Tilev, 1951), 677; (c) Macroglobigerinelloides subcarinatus (Brönnimann, 1952), 675; (d) Globotruncana falsostuarti Sigal, 1952, 675; (e) Macroglobigerinelloides prairiehillensis (Pessagno, 1967), 670; (f) Globotruncanita stuarti (de Lapparent, 1918), 668; (g) Reworked Globotruncana sp., 655; (h) Globoconusa daubjergensis (Brönnimann, 1953), 655; (i) Eoglobigerina eobulloides Morozova, 1959, 655; (j) Small globigerinids, 655; (k) Subbotina triloculinoides (Plummer, 1926), 644; (l) Morozovella angulata (White, 1928), 642.

6.2.1 Eoglobigerina edita Partial-range Zone (P1) (Berggren and Pearson, 2005; Wade et al., 2011) Definition: Partial range of the nominate taxon between the HO of Parvularugoglobigerina eugubina and the LO of Praemurica uncinata. Age: Early Paleocene (Danian). The assemblage of planktonic foraminifera in this biozone are as follow: Globoconusa daubjergensis (Brönnimann, 1953), Subbotina triloculinoides (Plummer, 1926), Parasubbotina pseudobulloides (Plummer, 1926), Praemurica inconstans (Subbotina, 1953), Praemurica pseudoinconstans (Blow, 1979), Globanomalina archaeocompressa (Blow, 1979), and Globanomalina compressa (Plummer, 1926). We could not separate the subzones, including P1 a, b and c in the studied area.

This article is protected by copyright. All rights reserved. 6.2.2 Praemurica uncinata Lowest-occurrence Zone (P2) (Berggren and Pearson, 2005; Wade et al., 2011) Definition: Biostratigraphic interval between the LO of Praemurica uncinata and the LO of Morozovella angulata. Age: Early Paleocene (Danian). The assemblage of planktonic foraminifera in this biozone are as follow: Praemurica uncinata (Bolli, 1957), Parasubbotina pseudobulloides (Plummer, 1926), Chiloguembelina sp. Loeblich and Tappan, 1956.

6.2.3 Morozovella angulata Lowest-occurrence Zone (P3) (Berggren and Pearson, 2005; Wade et al., 2011) Definition: Biostratigraphic interval between the LO of Morozovella angulata and the LO of Globanomalina pseudomenardii. Age: Early-middle Paleocene (Danian-Selandian). The assemblage planktonic foraminifera in this biozone are as follow: Morozovella angulata (White, 1928), Igorina albeari (Cushman and Bermudez, 1949), Igorina pusilla (Bolli, 1957). We could not separate the P3 subzones including P3a and b in the studied area. The Globorotalia – Globigerina – Globigerina daubjergensis assemblage zone of Wynd (1965) is the equivalent of above mentioned biozones of Wade et al. (2011) for Danian age.

6.3 The Selandian-Thanetian biozone Globanomalina psudomenardii Taxon-range Zone (P4) (Berggren and Pearson, 2005; Wade et al., 2011) Definition: Biostratigraphic interval characterized by the total range of the nominate taxon Globanomalina pseudomenardii. Age: Middle-late Paleocene (Selandian-Thanetian). The assemblage planktonic foraminifera in this biozone are as follow: Subbotina triloculinoides (Plummer, 1926), Parasubbotina pseudobulloides (Plummer, 1926), Praemurica inconstans (Subbotina, 1953), Acarinina decepta Martin, 1943, Morozovella aequa (Cushman and Renz, 1942), Subbotina eocaena Guembel, 1868, Igorina tadjikistanensis (Bykova, 1953), Globanomalina pseudomenardii (Bolli, 1957), Morozovella velascoensis (Cushman, 1925), Igorina albaeri (Cushman and Bemudez, 1949), Globanomalina ehrenbergi (Bolli, 1957), Igorina pusilla (Bolli, 1957), Subbotina velascoensis (Cushman, 1925), Morozovella conicotruncata (Subbotina, 1947), Morozovella apanthesma (Loeblich and Tappan 1957), Morozovella angulata (White, 1928), Globanomalina chapmani (Parr, 1938), Morozovella acuta (Toulmin, 1941), Morozovella acutispira (Bolli and Cita, 1960), Morozovella subbotinae (Morozova, 1939). We could not separate the P4 subzones including P3a, b and c in the studied area. The Globorotalia velascoensis - G. psudomenardii assemblage zone of Wynd (1965) is the equivalent of above mentioned biozones of Wade et al. (2011) for Selandian-Thanetian age.

6.4 Comparison of proposed biozonation with other localities The Maastrichtian–Danian boundary at El Kef section in Tunisia (Arenillas et al., 2004; Molina et al., 2006, 2009), tropical and subtropical realm (Berggren and Pearson, 2005; Wade et al., 2011), Gubbio section in Italy (Coccioni and Premoli Silva, 2015; Coccioni et al., 2016), Danial section in Izeh zone (Beiranvand and Ghasemi- Nejad, 2013; Beiranvand et al., 2014b) and Kabirkuh section in Lurestan salient (Darvishzad et al., 2007) are conformable but in Lali (Beiranvand et al., 2014b) and our studied area, this boundary is unconformable. In Jordan (Farouk et al., 2014) and most places in Iraq (Sharbazheri et al., 2009) a hiatus occurred at this boundary, while it is conformable in Sirwan Valley, northeastern Iraq (Sharbazheri et al., 2009) (Fig. 14). There is also an unconformity in shallow platform setting at Maastrichtian-Danian boundary in southern Persian Gulf countries (Alsharhan et al., 1991; Sharland et al., 2004).

Fig. 14. Comparison of Maastrichtian-Danian planktonic foraminiferal biozonations of studied area with the other biozonations schemes.

7 Gamma-ray spectrometry and CycloLog interpretation

The portable gamma-ray spectrometer measures the complete spectrum, from which it evaluates the cps (count per second) values in ROIs (region of interests) and calculates the concentrations of elements K (%), U (ppm), Th

This article is protected by copyright. All rights reserved. (ppm) (Ellis, 1987; Ellis and Singer, 2008). The total gamma-ray (nGy/h) (nano Gray/hour) was calculated from measured concentrations of K, U, and Th according to the IAEA recommendations (IAEA, 1976, 2003). The total gamma-ray measuring unit in exploratory wells is API (American Petroleum Institute) and the API unit calculated by the equation (Herron and Herron, 1996, 1998). In spite of the fact that, there are differences between the units of surface gamma-ray and wireline log, we correlate the general trends of total gamma-ray with each other. The measured data by gamma-ray spectrometer was plotted with Geolog software and it interpreted by CycloLog software. The CycloLog software creates the INPEFA (Integrated Prediction Error Filter Analysis) log based on gamma-ray log. The INPEFA is cumulative difference between the predicted log values and actual log values (ENRES, 2015). The prediction error filter analysis is indicative of stratigraphic continuity; large errors indicate significant breaks in the succession (Nio et al., 2005). Utilizing it can result in noticeable improvements in resolution compared to conventional biostratigraphy. The INPEFA shows the positive breaks (PB) (to the right) are related to sequence boundaries while negative breaks (NB) (to the left) correspond to maximum flooding surfaces (Nio et al., 2005; De Jong et al., 2006).

7.1 Gamma-ray spectrometry of north flank of Dehnow anticline (Tang-e Gabrzar section) Due to importance, only the measured values with 10 cm interval in Maastrichtian-Danian boundary are shown in table 1, however discussion are given for the whole section (see below).

Table 1 The 10 cm interval in-situ measured parameter by portable gamma-ray spectrometer from Maastrichtian - Danian boundary in north flank of Dehnow anticline (Tang-e Gabrzar section). Profile Dead- Dose Sample Station ROI-K ROI-U ROI-Th ROI-Tot K eU eTh K/Pg time Rate No. (m) (cps) (cps) (cps) (cps) (%) (ppm) (ppm) boundary (%) (nGy/h) ARMO

1 43.5 0.34 2.48 1.08 0.25 859.25 0.26 2.49 0.45 18.6 1058 1 43.8 0.34 2.45 1.15 0.47 862.52 0.22 2.29 2.17 21.25 1059 2 43.9 0.34 2.43 1.47 0.43 861.67 0.1 3.47 1.83 25.65 1060 2 44 0.34 2.75 1.3 0.37 863 0.27 3.02 1.34 23.94 1061 2 44.1 0.34 2.28 1.42 0.22 856.25 0.08 3.73 0.1 22.48 1062 2 44.2 0.35 2.9 1.5 0.32 867.72 0.25 3.82 0.89 27.16 1063 2 44.3 0.35 3.38 1.55 0.32 871.72 0.39 4 0.88 29.95 1064 2 44.4 0.35 3.58 1.78 0.27 864.5 0.37 4.92 0.43 33.88 1065 2 44.5 0.34 3.1 1.45 0.27 867.37 0.33 3.74 0.5 26.84 1066 2 44.6 0.34 2.75 1.5 0.35 866.62 0.2 3.76 1.16 26.8 1067 2 44.7 0.34 3.18 1.4 0.3 868.52 0.37 3.5 0.78 26.72 1068 2 44.8 0.34 2.92 1.35 0.33 864.38 0.3 3.26 1.06 25.12 1069 2 44.9 0.35 3.1 1.47 0.3 869.17 0.32 3.74 0.77 27.37 1070 2 45 0.35 3.17 1.53 0.22 863.67 0.33 4.14 0.08 27.96 1071 2 45.1 0.35 3.22 1.42 0.47 867.32 0.37 3.23 2.12 28.48 1072 2 45.2 0.35 3.53 2.02 0.33 874.35 0.28 5.61 0.91 37.72 1073 2 45.3 0.35 3.28 1.65 0.4 866.52 0.32 4.18 1.53 31.71 1074 2 45.4 0.37 6.18 3.67 0.38 902.77 0.57 11.32 0.95 74.05 1075 2 45.5 0.42 9.32 5.48 0.78 961.67 0.95 16.92 3.78 117.82 1076 2 45.6 0.44 11.23 7.72 0.7 993.9 0.81 24.95 2.61 158.71 1077 2 45.7 0.4 8.77 5.47 0.63 959.17 0.78 17.16 2.57 114.01 1078 2 45.8 0.4 8.67 4.93 0.75 942.52 0.92 15.05 3.63 106.55 1079 2 45.9 0.39 7.75 4.35 0.63 933.85 0.83 13.23 2.82 92.97 1080 2 46 0.38 6.92 3.75 0.63 920.1 0.77 11.12 2.95 80.46 1081 2 46.1 0.37 6.07 3.27 0.58 911.7 0.66 9.51 2.65 69.21 1082 2 46.2 0.36 5.15 2.7 0.53 888.23 0.56 7.62 2.38 56.44 1083 2 46.3 0.36 4.8 2.3 0.5 894.47 0.58 6.27 2.2 48.69 1084 2 46.4 0.36 4.7 2.05 0.48 888.13 0.63 5.43 2.12 44.38 1085 2 46.5 0.36 4.62 1.97 0.48 886.07 0.64 5.13 2.14 42.78 1086 2 46.6 0.36 3.85 1.78 0.45 877 0.45 4.55 1.91 36.52 1087 2 46.7 0.35 3.62 1.73 0.45 869.92 0.39 4.38 1.92 34.78 1088 2 46.8 0.35 4.12 1.8 0.32 878.05 0.54 4.88 0.83 36.79 1089 2 46.9 0.36 4.15 1.73 0.53 876 0.56 4.21 2.59 37.72 1090 2 47 0.35 3.77 1.63 0.67 870.15 0.47 3.6 3.68 35.7 1091 2 47.1 0.35 3.7 1.32 0.47 875.37 0.56 2.88 2.15 29.02 1092 2 47.2 0.35 3.63 1.28 0.57 869.22 0.55 2.56 2.96 29.07 1093 2 47.3 0.35 3.58 0.95 0.4 867.9 0.65 1.72 1.69 22.48 1094 2 47.4 0.35 3.73 1.18 0.4 871.83 0.62 2.54 1.64 26.61 1095 2 47.5 0.35 3.85 1 0.33 873.35 0.72 2.03 1.15 23.81 1096 2 47.6 0.35 4.05 1.2 0.55 879.88 0.71 2.3 2.85 29.44 1097 2 47.7 0.35 4.17 1.15 0.52 884.48 0.77 2.19 2.59 28.91 1098 2 47.8 0.35 4.5 1.17 0.73 873.35 0.86 1.82 4.33 32.35 1099 2 47.9 0.35 4.5 1.55 0.37 876.28 0.74 3.9 1.3 35.07 1100 2 48 0.35 4.03 1.15 0.53 883.32 0.72 2.16 2.72 28.48 1101 2 48.1 0.35 4.2 1.18 0.57 882.83 0.76 2.21 2.99 29.96 1102 2 48.2 0.35 4.08 1.25 0.67 876.6 0.7 2.25 3.77 31.29 1103 2 48.3 0.35 3.93 1.35 0.55 866.92 0.62 2.83 2.81 31.19 1104

This article is protected by copyright. All rights reserved. 2 48.4 0.35 3.83 1.15 0.33 866.95 0.67 2.55 1.11 25.99 1105 2 48.5 0.35 3.72 1.3 0.45 872.33 0.57 2.85 2.02 28.71 1106 2 48.6 0.35 3.5 1.35 0.45 869.93 0.49 3.03 2 28.54 1107 2 48.7 0.35 4.1 1.15 0.38 875.55 0.75 2.46 1.52 27.52 1108 2 48.8 0.35 3.8 1.33 0.38 877.67 0.59 3.1 1.47 29.01 1109 2 48.9 0.35 4.22 1.32 0.5 874.67 0.73 2.81 2.42 31.48 1110 2 49 0.35 4.6 1.72 0.38 878.55 0.72 4.45 1.39 38.13 1111 2 49.1 0.35 4.4 1.62 0.58 882.08 0.68 3.7 3.02 37.44 1112 2 49.2 0.35 4.17 1.47 0.4 875.98 0.66 3.54 1.58 32.69 1113 2 49.3 0.35 4.47 1.87 0.48 880.82 0.62 4.78 2.16 40.64 1114 2 49.4 0.36 4.18 1.67 0.62 885.75 0.59 3.81 3.28 37.55 1115 2 49.5 0.36 4.55 1.62 0.63 885.33 0.73 3.6 3.43 38.48 1116 2 49.6 0.35 4.37 1.62 0.47 878.55 0.67 3.93 2.08 36.33 1117 2 49.7 0.36 4.77 1.6 0.67 881.58 0.8 3.48 3.7 39.42 1118 2 49.8 0.35 4.78 1.82 0.6 878.27 0.73 4.37 3.11 42.19 1119 2 49.9 0.36 4.55 1.93 0.62 884.05 0.62 4.75 3.22 43.09 1120 3 50 0.35 3.5 1.47 0.48 873.25 0.45 3.37 2.24 30.57 1121 3 50.3 0.36 4.85 2.1 0.48 887.33 0.67 5.6 2.11 45.76 1122

7.1.1 Total gamma-ray (Dose rate) The total gamma-ray values display wide changes. The lowest value is 17.21 nGy/h in sample no. ARMO 1015 in Gurpi Formation and the highest value is 158.71 nGy/h in sample no. ARMO 1077 which situated at the base of Pabdeh Formation (Danian age).

7.1.2 Uranium (U) The curve of U concentration is similar to that of total gamma-ray. The lowest value of U concentration observed in sample no. ARMO 955 of Gurpi Formation with 1 .2 ppm and the highest values is 24.95 ppm in sample no. ARMO 1077 which situated at the base of Pabdeh Formation (Danian age) same as the uranium curve.

7. 1. 3 Thorium (Th) The Th concentration curve has a regular trend. The lowest value in the Gurpi Formation 0 ppm in sample no. ARMO 1042 and the highest value in the Pabdeh Formation is 4.33 ppm in sample no. 1099.

7.1.4 Potassium (K) The K values curve shows the lowest concentrations 0.37 % in sample no. ARMO 940 and the highest is 1.05 % in sample no. 1024 of Gurpi Formation.

The CycloLog curves in north flank of Dehnow anticline (Tang-e Gabrzar section) includes the long term Dynamic INPEFA-GR at the thickness 45.5 m has been reached to high GR value at the Gurpi-Pabdeh formations boundary and the short term of D-INPEFA-GR_3 (light blue color curve) has a negative trend (coarsening upward), and D-INPEF-GR_4 (light green curve) shows positive trend (fining upward) (Fig. 15). This boundary was also confirmed by biostratigraphical results

Fig. 15. The INPEFAs computed for Maastrichtian-Danian in north flank of Dehnow anticline (Tang-e Gabrzar section). Refer to the text

7.2 Gamma-ray spectrometry of south flank of Dehnow anticline (Tang-e Bonab section) Due to importance, only the measured values with 10 cm interval in Maastrichtian-Danian boundary are shown in table 2, while the whole section is discussed below:

This article is protected by copyright. All rights reserved. Table 2 The 10 cm interval in-situ measured parameter by portable gamma-ray spectrometer from Maastrichtian -Danian boundary in south flank of Dehnow anticline (Tang-e Bonab section). Profile Dead- Dose Sample Station ROI-K ROI-U ROI-Th ROI-Tot K eU eTh K/Pg time Rate No. (m) (cps) (cps) (cps) (cps) (%) (ppm) (ppm) boundary (%) (nGy/h) ARMO 1 8.7 0.35 2.98 1.7 0.33 870.72 0.21 4.49 0.98 30.65 1345 1 9 0.36 3.75 1.98 0.35 871.57 0.36 5.46 1.05 38.27 1346 1 9.1 0.36 3.63 1.93 0.32 880 0.34 5.35 0.8 36.75 1347 1 9.2 0.36 3.67 2.37 0.53 889.98 0.19 6.44 2.44 45.18 1348 1 9.3 0.35 3.72 1.88 0.48 883.92 0.37 4.84 2.15 37.73 1349 1 9.4 0.35 3.38 1.83 0.47 867.58 0.29 4.7 2.02 35.43 1350 1 9.5 0.36 4.08 1.97 0.53 872.77 0.46 5.03 2.54 40.94 1351 1 9.6 0.35 3.43 1.95 0.38 871.82 0.27 5.27 1.33 36.71 1352 1 9.7 0.36 3.98 2.02 0.63 880.83 0.41 5.01 3.33 42.09 1353 1 9.8 0.36 4.78 2.83 0.42 893.87 0.4 8.32 1.4 55.93 1354 1 9.9 0.4 8.25 4.62 0.68 949.45 0.9 14.07 3.17 99.5 1355 1 10 0.41 9 5.47 0.8 964.45 0.85 16.83 3.91 116.37 1356 1 10.1 0.43 10.5 6.42 0.63 982.6 1.02 20.5 2.37 135.57 1357 1 10.2 0.44 11.43 6.53 0.72 1003.25 1.27 20.75 3.02 141.94 1358 1 10.3 0.44 10.98 7.28 0.93 1000.88 0.87 22.96 4.58 153.08 1359 1 10.4 0.43 11.17 7.05 0.75 989.03 1.01 22.5 3.16 148.84 1360 1 10.5 0.38 6.33 3.68 0.57 918.53 0.6 11.01 2.43 76.45 1361 1 10.6 0.36 4.9 2.42 0.48 901.85 0.57 6.72 2.04 50.72 1362 1 10.7 0.35 3.97 2.05 0.45 876.12 0.4 5.49 1.85 41.01 1363 1 10.8 0.35 3.78 2.33 0.47 886.03 0.24 6.46 1.91 44.62 1364 1 10.9 0.35 3.6 1.48 0.58 875.87 0.47 3.23 3.05 32.06 1365 1 11 0.35 3.18 1.28 0.37 874.98 0.41 2.96 1.35 25.52 1366 1 11.1 0.35 3.3 1.43 0.38 861.98 0.4 3.45 1.45 28.4 1367 1 11.2 0.35 3.6 1.38 0.5 871.93 0.51 3.05 2.4 29.88 1368 1 11.3 0.35 3.78 1.5 0.37 877.67 0.53 3.72 1.3 31.3 1369 1 11.4 0.35 3.15 1.37 0.42 877.12 0.37 3.15 1.73 27.04 1370 1 11.5 0.35 4.12 1.3 0.43 878.7 0.7 2.88 1.89 30.26 1371 1 11.6 0.35 3.7 1.3 0.55 874.07 0.56 2.65 2.82 29.46 1372 1 11.7 0.36 3.78 1.38 0.57 883.65 0.56 2.91 2.94 31.2 1373 1 11.8 0.35 3.58 1.37 0.32 869.05 0.51 3.35 0.93 28.04 1374 1 11.9 0.35 4.03 1.1 0.5 875.43 0.74 2.05 2.47 27.46 1375 1 12 0.35 3.62 1.17 0.42 871.12 0.59 2.45 1.78 26.01 1376 1 12.1 0.35 3.88 1.2 0.5 869.05 0.66 2.4 2.44 28.32 1377 1 12.2 0.35 3.85 1.32 0.55 875.6 0.61 2.71 2.82 30.34 1378 1 12.3 0.35 4.17 1.4 0.58 878.58 0.68 2.94 3.07 33.2 1379 1 12.4 0.35 3.53 1.1 0.43 878.98 0.58 2.18 1.93 24.8 1380 1 12.5 0.35 3.97 1.07 0.55 863.07 0.73 1.83 2.88 27.09 1381 1 12.6 0.35 3.52 1.1 0.48 862.95 0.57 2.08 2.33 25.14 1382 1 12.7 0.34 3.7 1.05 0.57 865.02 0.65 1.74 3.01 25.85 1383 1 12.8 0.35 3.35 1.03 0.68 867.55 0.53 1.45 3.95 25.08 1384 1 12.9 0.35 4.02 0.83 0.68 867.37 0.82 0.75 4 24.9 1385 1 13 0.35 4.05 1.2 0.65 870.62 0.7 2.1 3.65 30.26 1386 1 13.1 0.35 4.68 1.22 0.5 868.82 0.91 2.46 2.45 31.95 1387 1 13.2 0.35 4.08 1.03 0.68 867.88 0.77 1.45 3.96 28.18 1388 1 13.3 0.35 4.13 1.32 0.5 863.65 0.7 2.81 2.42 31.13 1389 1 13.4 0.34 3.82 1.35 0.5 862.98 0.59 2.93 2.41 30.29 1390 1 13.5 0.34 3.82 1.45 0.33 863.88 0.56 3.61 1.04 30.41 1391 1 13.6 0.34 3.45 1.12 0.42 857.53 0.55 2.27 1.79 24.56 1392 1 13.7 0.35 4.17 1.62 0.5 868.85 0.61 3.87 2.35 35.77 1393 1 13.8 0.35 4.12 1.75 0.62 879.62 0.54 4.11 3.26 38.52 1394 1 13.9 0.36 4.57 1.67 0.57 878.53 0.72 3.91 2.88 38.75 1395 1 14 0.36 4.23 1.72 0.6 881.73 0.59 4.02 3.13 38.37 1396 1 14.1 0.35 4.43 1.82 0.58 876.45 0.62 4.41 2.98 40.58 1397 1 14.2 0.36 4.55 1.87 0.62 884.43 0.64 4.52 3.23 42.09 1398 1 14.3 0.36 4.82 1.53 0.5 882.45 0.85 3.57 2.37 37.26 1399 1 14.4 0.35 4.78 1.57 0.53 880.08 0.82 3.63 2.63 37.89 1400 1 14.5 0.35 5.07 1.63 0.67 889.33 0.88 3.6 3.69 41.19 1401 1 14.6 0.35 4.5 1.55 0.58 883.25 0.73 3.47 3.04 36.86 1402 1 14.7 0.35 4.32 1.73 0.6 871.7 0.61 4.08 3.13 38.97 1403 7.2.1 Total gamma-ray The total gamma-ray values are 19.39 nGy/h in sample nos. ARMO 1329, 1339 at the base of section and increases to 153.08 nGy/h in sample no. ARMO 1359 at Maastrichtian-Danian boundary.

7.2.2 Uranium (U) The curve of U concentration follows the trend of total gamma-ray. The minimum U concentration is observed in sample no. ARMO 1329 of Gurpi Formation with 2.2 ppm value and the maximum 22.96 ppm in sample no. ARMO 1359 at Maastrichtian-Danian boundary.

This article is protected by copyright. All rights reserved. 7.2.3 Thorium (Th) The Th concentration curve has a regular trend. The lowest value is 0 ppm in the Gurpi Formation in sample no. ARMO 1318 and the highest value in the Pabdeh Formation is 4.58 ppm in sample no. 1359.

7.2.4 Potassium (K) The K values are rather stable. The lowest concentrations is 0.17 % in sample no. ARMO 1335 and the highest is 1.27 % in sample no. 1358 of Gurpi Formation.

The CycloLog curves in south flank of Dehnow anticline (Tang-e Bonab section) includes the long term of D- INPEFA_GR at the thickness 10.3 m has been reached to high GR value and the short term of D-INPEFA-GR_1 (blue color curve) just below the Gurpi-Pabdeh formations boundary represents a negative trend (coarsening upward), and D-INPEFGR_2 (green color curve); while indicates a positive trend above this boundary (fining upward) (Fig. 16).

Fig. 16. The INPEFAs computed for the Maastrichtian-Danian in south flank of Dehnow anticline (Tang-e Bonab section). Refer to the text

7.3 Gamma-ray log and CycloLog in exploratory well-1 In exploratory well-1 composite, at depth 659 m the CycloLog long term of D-INPEFA_GR at the Maastrichtian- Danian boundary has highest GR value. The short term of D-INPEFA-GR_3 (light blue color curve) below the boundary shows a negative trend (coarsening upward), and short term D-INPEFGR_4 (green curve) above this boundary reveals a positive trend (fining upward trend) (Fig 17).

Fig. 17. The exploratory well-1 long-term INPEFA curve and short-term INPEFAs curves computed for Maastrichtian-Danian. Refer to the text

7.4 Gamma-ray and CycloLog correlation The correlation were made between three sections, in which the Maastrichtian–Danian boundary was considered as a datum (Fig. 18). There is a good similarity between the long-term INPEFA curve and short-term INPEFAs curves of exploratory well-1 and measured stratigraphic sections.

Fig. 18. The correlation panel of the Maastrichtian-Danian boundary from south to north in the studied area.

8 Discussion

From biostratigraphic point of view the following biozones, Gansserina gansseri Interval Zone (Coccioni and Premoli Silva, 2015) equivalent of CF7 (Li and Keller, 1998a, b), and Contutruncana contusa Interval Zone (Coccioni and Premoli Silva, 2015) equivalent of CF6 (Li and Keller, 1998a, b) have been detected and indicating latest Campanian to middle Maastrichtian age for upper part of Gurpi Formation in the studied area. The

This article is protected by copyright. All rights reserved. Eoglobigerina edita Partial-range Zone (P1), Praemurica uncinata Lowest-occurrence Zone (P2), and Morozovella angulata Lowest-occurrence Zone (P3) (Berggren and Pearson, 2005; Wade et al., 2011) have been detected representing early Danian age for the Lower part of Pabdeh Formation. We did not identify the Abathomphalus mayaroensis Zone (Coccioni and Premoli Silva, 2015), Pseudoguembelina hariaensis Interval Zone (Coccioni and Premoli Silva, 2015) equivalent of CF3 zone of Li and Keller (1998a, b), Pseudotextularia elegans Interval Zone (Coccioni and Premoli Silva, 2015) equivalent of Psudoguembelina palpebra (CF2) zone of Li and Keller (1998 b), Plummerita hatkeninoides Interval Zone (Coccioni and Premoli Silva, 2015) equivalent of CF1 zone of Li and Keller (1998a, b); Li et al.(1999), Guembelitria cretacea (P0) Partial-range Zone and Parvularugoglobigerina eugubina (Pα) Total-range zone (Wade et al., 2011), consequently there is a hiatus between the Maastrichtian- Danian, encompasses late Maastrichtian and earliest Danian age. There are reworked fauna from Maastrichtian deposits of Gurpi Formation in Danian deposits of Pabdeh Formation in all three sections. In Tang-e Gabrzar section the Globotruncanita pettersi (Gandolfi, 1955) can be seen in the Danian deposits (Fig. 8e) and in Tang-e Bonab section, the reworked planktonic foraminifera are Globotruncanita stuartiformis (Dalbiez, 1955) (Fig. 11h), Gansserina gansseri (Bolli, 1951), Macroglobigerinelloides alvarezi (Eternod Olvera, 1959) and Planoheterohelix globulosa (Ehrenberg, 1840). Also the Maastrichtian reworked planktonic foraminifera (globotruncanids) present in phosphate nodules associated by Danian planktonic foraminifera (Globoconusa daubjergensis (Brönnimann, 1953)) in exploratory well-1 in the same chips (depth 659 m) (Fig. 13g). There is also an extensive bioturbation (Planolites isp.) at the Maastrichtian-Danian (Gurpi-Pabdeh formations) boundary. From lithological point of view the glaucony is one of the most sensitive indicators of low sedimentation rate in marine environments and it is commonly associated with hardgrounds indicating depth between 50m to 500m (Amorosi, 1997). It is also associated with transgressive deposits (Banerjee et al., 2016 b). The presence of phosphates characterized the anoxic conditions (Berra et al., 2007). In the studied area the color of glauconite grains under PPL of microscope is green to dark green hence their maturity is “evolved” to “highly evolved” (sensu Odin and Matter, 1981) These grains are “bad sorted” and some chambers of planktonic foraminifera are filled by glauconite and phosphate (Fig.11 F), which imply their autochthonous origin (Amorosi, 1997; Berra et al., 2007; Banerjee et al., 2016 a, b). The gamma-ray spectrometry of surface sections represents maximum value of total gamma-ray at the Maastrichtian-Danian boundary. In Tang-e Gabrzar section the total gamma-ray value is 158.71 nGy/h and in Tang- e Bonab section it is 153.08 nGy/h. The highest total gamma-ray value coincides to highest U concentration value. This can be a good key for separating of Maastrichtian-Danian boundary. Also the long term and short term D- INPEFAs of CycloLog confirmed this boundary in surface sections and exploratory well. According to Keller (1996) the K/Pg global sections which situated in continental shelf, represents an unconformity; whereas it is continuous in shelf-slop zone e.g. El Kef in Tunisia, Agost in Spain. The sections are situated in slope to bathyal zones due to drowning shows an unconformity (Fig. 19). The above mentioned biostratigraphical and lithological evidences of interruption in deposition reveals that the depositional depth of K/Pg boundary in studied area, was situated in slope to bathyal zones which can be deducted a hardground with paraconformity between Maastrichtian–Danian (Fig. 19).

Fig. 19. Depositional depths of K/Pg boundary sections in the world and the position of Coastal Fars of Zagros (redrawn and modified from Keller (1996)).

9 Conclusions

Based on the detailed micropaleontological, lithological and gamma-ray log data on two stratigraphic sections in Dehnow anticline and on the cutting samples of the drilled sequence of exploratory well-1 in Coastal Fars, the following points have been concluded: 1. The planktonic foraminiferal studies suggest the middle Maastrichtian and early Danian ages for the uppermost part of Gurpi and lowermost of Pabdeh formations respectively. 2. Due to recognized biozones, there is a hiatus between Maastrichtian-Danian, which encompasses late Maastrichtian to earliest Danian age. 3. The lithostratigraphic boundary of Gurpi and Pabdeh formations coincide on bioturbated grey marlstones layer. This layer comprises reworked Maastrichtian planktonic foraminifera and glauconitized macrofossils from older deposits. We recommend this layer as a formations boundary in Coastal Fars. 4. The lack of many biozones, highly bioturbation, and presence of glauconite (filled chambers of planktonic foraminifera) and phosphate at the K/Pg boundary are evidences of paraconformity and hardground.

5. The high total gamma-ray value of surface gamma-ray at the Maastrichtian-Danian boundary, could be used for differentiating the Gurpi and Pabdeh formations. Also CycloLog positive break at this boundary confirms the presence of an unconformity.

Acknowledgements

The authors would like to thank the University of Isfahan for providing financial supports. The writers also indebted to the management of the Exploration Directorate of National Iranian Oil Company (NIOC-EXP) for supporting field trips and permission to publish this paper as a part of PhD thesis of the first author. We gratefully acknowledge NIOC-EXP geologists for assistance in the field work. We wish to express our sincere gratitude to Dr. Maria Rose Petrizzo from the University of Milan, Milan, Italy for reviewing an earlier version of this manuscript. Our thanks also go to Prof. Dr. Kazem Seyed-Emami from University of Tehran, Tehran, Iran for determining the cephalopod. We are grateful to Mrs. Solmaz Saeeidi-Manesh PhD candidate from the University of Tabriz, Tabriz, Iran for linguistic editing of the manuscript. The manuscript text benefited from an editorial corrections by Dr. Hassan Mohseni from Bu-Ali Sina University, Hamadan, Iran. Authors are thankful to the anonymous reviewers for their constructive criticisms and useful suggestions on the manuscript.

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Table 1 The 10 cm interval in-situ measured parameter by portable gamma-ray spectrometer from Maastrichtian-Danian boundary in north flank of Dehnow anticline (Tang-e Gabrzar section).

Table 2 The 10 cm interval in-situ measured parameter by portable gamma-ray spectrometer from Maastrichtian-Danian boundary in south flank of Dehnow anticline (Tang-e Bonab section).

About the first author: ABDOLREZA Moghaddasi, male, born in 1968 in Oroumiyeh City, Western Azarbaijan Province, Iran; currently PhD candidate of University of Isfahan in field of Stratigraphy and Paleontology; BSc of Geology from Kharazmi University (Tehran); MSc of Stratigraphy and Paleontology from University of Tehran; His interests are foraminifera micropaleontology and biostratigraphy. E-mail: [email protected]; phone: +982182703528; mobile: +989122134480

This article is protected by copyright. All rights reserved. About the corresponding author HOSSEIN Vaziri-Moghaddam, male, born in 1965 in Isfahan city, Isfahan Province, Iran; currently Professor of University of Isfahan; BSc of Geology from University of Isfahan; MSc of Stratigraphy and Paleontology from University of Tehran; PhD from University of Liverpool in field of foraminiferal biostratigraphy. He is now interested in the study of foraminiferal biostratigraphy and sequence stratigraphy. E-mail: [email protected] and [email protected]; phone: +983137932160; mobile: +989133289745