# Multidisciplinary study on the stratigraphy of the upper Cretaceous-Paleogene successions in the western Tajik Basin, Uzbekistan

Hassan Khozyem, Thierry Adatte, Marie-Françoise Brunet, Massimo Chiaradia, Gerta Keller, Nicolas Thibault, Irina Sidorova, Bakhtiar Nurtaev, Uygar Karabeyoglu, Jorge Spangenberg, et al.

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Hassan Khozyem, Thierry Adatte, Marie-Françoise Brunet, Massimo Chiaradia, Gerta Keller, et al. Multidisciplinary study on the stratigraphy of the upper Cretaceous-Paleogene successions in the western Tajik Basin, Uzbekistan. Journal of Asian Earth Sciences, 2024, 267, 10.1016/j.jseaes.2024.106137. insu-04604304

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Multidisciplinary study on the stratigraphy of the upper Cretaceous-Paleogene successions in the western Tajik Basin, Uzbekistan

Hassan Khozyem, Thierry Adatte, Marie-Françoise Brunet, Massimo Chiaradia, Gerta Keller, Nicolas Thibault, Irina Sidorova, Bakhtiar Nurtaev, Uygar Karabeyoglu, Jorge Spangenberg, Sébastien Castelltort

PII: S1367-9120(24)00132-9

DOI: https://doi.org/10.1016/j.jseaes.2024.106137

Reference: JAES 106137

To appear in: *Journal of Asian Earth Sciences*

Received Date: 24 May 2023

Revised Date: 24 March 2024

Accepted Date: 30 March 2024

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Please cite this article as: Khozyem, H., Adatte, T., Brunet, M-F., Chiaradia, M., Keller, G., Thibault, N., Sidorova, I., Nurtaev, B., Karabeyoglu, U., Spangenberg, J., Castelltort, S., Multidisciplinary study on the stratigraphy of the upper Cretaceous-Paleogene successions in the western Tajik Basin, Uzbekistan, *Journal of Asian Earth Sciences* (2024), doi: https://doi.org/10.1016/j.jseaes.2024.106137

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Multidisciplinary study on the stratigraphy of the Upper Cretaceous-Paleogene successions in the western Tajik Basin, Uzbekistan

Hassan Khozyem<fnref n="1" />ᵃ,ᵇ*, Thierry Adatte<fnref n="2" />, Marie-Françoise Brunet<fnref n="3" />, <fnref n="4" />, Massimo Chiaradia<fnref n="5" />, Gerta Keller<fnref n="6" />, Nicolas Thibault<fnref n="7" />, Irina Sidorova<fnref n="8" />, Bakhtiar Nurtaev<fnref n="8" />, Uygar Karabeyoglu<fnref n="2" />, Jorge Spangenberg<fnref n="9" />, Sébastien Castellort<fnref n="5" />

**Highlights**

- The Upper Cretaceous-Paleogene stratigraphy of the western Tajik Basin sequence.

- Dating the western Tajik Basin using Sr-isotope and biostratigraphy.

- Emplacement of the OAE2 and PETM within the western Tajik Basin sequence.

- Deciphering the major and minor sea level cycles in the western Tajik Basin sequence.

<footnote n="1">¹ªGeology Department, Faculty of Science, Aswan University, 81528-Aswan, Egypt.</footnote>

<footnote n="1">¹ᵇNational Research Institute of Astronomy and Geophysics (NRIAG), Helwan, Egypt.</footnote>

<footnote n="2">²Institute of Earth Sciences, ISTE, Geopolis, Université de Lausanne, 1015 Lausanne, Switzerland.</footnote>

<footnote n="3">³Sorbonne Universités, UPMC Univ. Paris 06, UMR 7193, Institut des Sciences de la Terre Paris (iSTeP), F-75005 Paris, France.</footnote>

<footnote n="4">⁴CNRS, UMR 7193, Institut des Sciences de la Terre Paris (ISTEP), F-75005 Paris, France.</footnote>

<footnote n="5">⁵Département des Sciences de la Terre, Université de Genève, Rue des Maraîchers 13, 1205 Genève, Switzerland.</footnote>

<footnote n="6">⁶Department of Geosciences, Princeton University, Princeton, NJ 08544, USA.</footnote>

<footnote n="7">⁷Institute for Geosciences and Natural Resource Management, University of Copenhagen, Øster Voldgade 10, DK-1350 Københavns K., Denmark.</footnote>

<footnote n="8">⁸Institute of Geology and Geophysics of the Academy of Science of Republic Uzbekistan, Olimlar 49, 100041 Tashkent, Uzbekistan.</footnote>

<footnote n="9">⁹Institute of Earth Surface Dynamics (IDYST), Geopolis, University of Lausanne, 1015 Lausanne, Switzerland.</footnote>

<footnote>*corresponding author: hkhozyem@gmail.com, h.m.khozyem@aswu.edu.eg</footnote>
**Abstract**

The Tajik-Afghan Basin is a large basin in Central Asia, whose sediments document the area's long tectonic and climatic history from the Paleozoic to the present. However, the sedimentary characteristics and stratigraphy of these successions remain poorly understood. The study of this basin is critical for understanding the depositional conditions that prevailed during the transformation of this area from a part of the Western Oceanic Tethys to a more restricted Para-Tethys. In the southwestern corner of the Tajik Depression, a well-exposed sedimentary sequence associated with a large anticlinal limb was sampled. The authors proposed a new age model based on a combination of biostratigraphic data from planktic foraminifera, calcareous nannofossils, and strontium chemostratigraphy ($^{87}$Sr/$^{86}$Sr). The lower part of the studied section is of the upper Cenomanian age (95.5 Ma), while the upper part is assigned to the early Oligocene age (34.05 Ma). The carbon isotope profile shows several excursions linked to major paleoenvironmental events including the Oceanic Anoxic Event 2 (OAE2) and the Paleocene-Eocene Thermal Maximum (PETM). The latter is revealed in the study area for the first time. New sedimentological observations and interpretations of the depositional environments and sea-level cycles are provided. The deposition in the Aktash area occurred between upper coastal lagoonal and transitional environments before fully transitioning to continental environments in the Neogene. The stratigraphic record in Aktash is divided into large-scale progradation/ retrogradation cycles that can be tentatively linked to global sea-level signals.

**Keywords:** Tajik Basin, carbon isotope profile, strontium age dating, sequence stratigraphy. Cretaceous to Paleogene

**1. Introduction**

Several sedimentary basins have formed in the Central Asia region, including the South Caspian Basin in the west (as a corridor to Europe), the Amu Darya Basin, the Afghan-Tajik Basin, the Fergana Basin, the Junggar Basin, the Tarim Basin, and the Maskhel Basin. These basins have their special importance for gas and oil exploration and production (Orudgeva, 1990). The deposition in these basins started from the Jurassic to the Paleogene and extended occasionally to the Neogene (Clarke, 1994; Ulmishek and Masters, 1993). Throughout the geologic time, the formation of sedimentary basins has been associated primarily with orogenic events. One of the best examples of these basins is the Central Asia Basin (CAB; Audet & Bürgmann 2011; De Grave et al. 2012; Zanchetta et al. 2013; Yang et al. 2017). The CAB was influenced by the Precambrian-Paleozoic orogen and accretion of the Cimmerian blocks during the Mesozoic and its rejuvenation.

The Afghan-Tajik Basin is one of the most important foreland basins in the Central Asia region. This basin is surrounded by the Pamir Mountains from the east, the Tian Shan Mountains from the north and west, and the Hindu Kush from the south (Burtman and Molnar, 1993). The Afghan-Tajik Basin has more than 3 km thick sedimentary deposits that are considered as a pre-orogenic sequence of Jurassic - Neogene age (Nikolaev, 2002). These sediments were deposited under the influence of several tectonic events. The multiple tectonic mechanisms indicate that different
depositional regimes developed within a cratonic basin, a passive margin, a peripheral back-arc foreland basin, and a retro-arc foreland basin (Burtman and Molnar, 1993; Burtman, 2000; Bratash, et al, 1970; Carrapa et al, 2015; Chapman et al, 2019; Chatelain et al, 1980; Fuersich et al, 2015; Nikolaev, 2002; Leith, 1985; Zonenshain, 1990; Sengor, 1984; Tapponnier et al, 1981; Tevelev and Georgievskii, 2012; Ulmishek, 2004; Varentsov et al, 1977).

The indicated depositional environments provide important information about the deposition processes in the epicontinental areas at the transition boundaries between the western Tethys Ocean, Para-Tethys areas, and eastern continental Asia. In particular, extreme faulting is evident in the sedimentological records and stratigraphic successions of such basins. Moreover, this structural setting is important for understanding the transmission of climatic and tectonic signals through sedimentary systems (Castelltort and Van Den Driessche, 2003, Romans et al., 2016). The ecological and geological records in this setting have particular importance in understanding the interactions between global and secular climate signals. These interactions are due to the progressive closure of the Tethyan Ocean and the rise of Alpine relief, as well as their effects on the vertical motions of the lithosphere (e.g., Molnar, 1990).

Several major global climatic events have disrupted the Mesozoic and Cenozoic. Extreme perturbations in sedimentological and geochemical records are indicated within the stratigraphic successions. Amongst them are the Cenomanian-Turonian oceanic anoxic event (OAE 2) (Bralower, 1988; Coccioni et al., 1995; Erba, 2004; Faucheret et al., 2017; Gräfe, 2005; Kuhnt, 1992; Luciani and Cobianchi, 1999; Paul et al., 1999; Scopelliti et al., 2004), the Santonian–Campanian Boundary Event (SCBE) (Jarvis et al., 2002, 2006) the mid-Campanian Event (MCE) (Jarvis et al., 2002, 2006, Thibault et al., 2012a), the late Campanian Event (LCE) (Jarvis et al., 2002, 2006, Voigt et al., 2012, Thibault et al., 2012a, 2012b), and the end of Cretaceous mass extinction (Cretaceous/Paleogene boundary, K/Pg; 66.043 ± 0.011 Ma; Renne et al., 2013). During the Paleocene and early Eocene, several hyperthermal events took place to represent the greenhouse world. The best examples of these events are the Paleocene Eocene Thermal Maximum (PETM; ~56 Ma; Alegret et al., 2009; Berggren and Ouda 2003; Kennett and Stott, 1991; Khozyem et al., 2013, 2014; Ouda et al., 2013; Sluijs et al., 2006; Zachos et al., 2003), and the Eocene Thermal Maximum 2 and 3 (ETM2 & 3; Galeotti et al., 2019).

In the present manuscript, we aim to present preliminary data on the sedimentary record and geochemical evolution of the Cretaceous - Paleogene sequence at the western margin of the Tajik Depression (the fold belt in the southwestern Gissar Mountains, Uzbekistan). We try briefly to interpret the paleoenvironment and provide the first complete isotope record on the Mesozoic-Cenozoic successions in this area. The numerical strontium isotope ages combined with carbon isotopes and biostratigraphy provide important information about the general stratigraphy of the area. Moreover, we attempt to locate the position of some important environmental and climatic events such as the stratigraphic position of the Oceanic Anoxic Event 2 (OAE2) and the Paleocene Eocene thermal maximum event (PETM) within the traditional local stratigraphic subdivisions.

## 2. Geological setting

### 2.1. Geology of Tajik Depression
The Tajik Depression is located between the southwestern Tien Shan and the Pamir Mountains, west of the western Himalayan syntaxis (Fig. 1A). The depression extends from Uzbekistan in the west to Tajikistan in the east and Afghanistan in the south. The sedimentary sequence has post-Triassic to Pleistocene age and is subjected to a complex tectonic and climatic history. The depression itself is bounded from the west by the Kugitang (mega-) anticline (Fig. 1B&C), in which the Precambrian basement rocks are exposed at its core. The Mesozoic-Cenozoic sedimentary cover of the Afghan-Tajik is represented by a classic fold belt formed during the Miocene to Pliocene (Gagala et al., 2014). The present study focuses on a part of the Tajik Depression near the village of Aktash, about 70 km west of the city of Termez, Uzbekistan (Fig. 1A).

The Mesozoic - Neogene deposits are exposed along river canyons and on the slopes of the relatively cylindrical segment of the Aktash-Surkhantau marginal anticline (Figs. 1B&C; Tevelev and Georgievskii, 2012). The Aktash-Surkhantau anticline is striking NE-SW for more than 100 km and lies between the thick-walled basement overthrust blocks of the Kugitang anticline to the west and the large-walled regional Surkhandarya syncline to the east.

During the subduction and northwest closer of the Paleo-Tethys Ocean (Fig. 2), the Permian and Triassic rifts formed along the southern margin of Eurasia including the study area (e.g., Abdullah et al., 2008; Brookfield and Hashmat 2001; Ulmishek, 2004). This rift basin is filled with clastic deposits in the period from the Upper Triassic to the Upper Jurassic. These clastic sediments were deposited as erosional products of the Eo-Cimmerian belt formed during the closure of the Paleo-Tethys Ocean, and the collision of the Cimmerian blocks with Eurasia (Sengoer, 1979; 1984). The reactivation of the old extensional events formed during the Jurassic led to the return of marine conditions through the Bathonian in the Afghan-Tajik Basin (Fuersich et al., 2014). The paleogeographic arrangement of landmasses and oceans at the beginning of the depositional period of the sequence under investigation (middle Cretaceous and middle Eocene) is shown in Figure 2. The Afghan-Tajik basin was already in an epicontinental setting during the middle Cretaceous and generally opened southward to the Neo-Tethyan Ocean. During this time, the black shales were deposited in the North and South Atlantic and the epicontinental areas of Laurasia and Asia. This indicates the marine depositional environment for the lower part of the Afghan-Tajik sedimentary sequence (Gavrelove et al., 2003; Wagreich, 2012). Such depositional conditions prevailed until the middle Eocene when the Afghan-Tajik depression was a restricted marine and/or marginal sea, opened westward and surrounded by uplifted masses. The transition from marine to terrestrial took place at the margin of the Para-Tethys during the Oligocene-Miocene (Woutersen et al., 2023).

Several models have been proposed to explain the formation of the Tajik Basin (Burtman, 2000; Burtman and Molnar, 1993; Ingersoll, 2012; Nikolaev, 2002; Schneider et al., 2013; Ulmishek, 2004). During the Pre- and Late Cretaceous, thermal expansion and subsidence occurred (Leith, 1982; 1985), resulting in crustal extension and the formation of a south-trending passive marginal basin (Leith, 1985). Then, the passive marginal basin abruptly thinned during the Cretaceous time due to displacement of the Tethyan overthrust belt (Chapman et al., 2017; Hamburger et al., 1992), and a retro-arc foreland basin formed associated with northward subduction of the Tethyan seafloor (Chapman et al., 2019). The crustal extension sustained the thermal subsidence during the Jurassic to the early Miocene (Burtman and Molnar, 1993), and the Late Cretaceous to the early Paleogene basin extension. The lithospheric stretching extended through the late Paleogene to the
Miocene, with a high subsidence rate in the foreland basin followed by a flexural foreland phase that began in the middle Eocene (Chapman et al., 2019).

Events associated with basin formation from the late Jurassic through the Paleocene-Eocene can be summarized as long-term subsidence, shallow marine carbonate deposition, and continental deposition. The sedimentary basin opened westward to the margin of the Great Caucasus-South Caspian Basin, then to the Para-Tethys Ocean (e.g., Barrier and Vrielynck, 2008; Ulmishek 2004). At the beginning of the late Eocene, thick wedges of continental clastic of typical foreland basins were deposited. They are generally associated with flexure due to the topographic growth of the Pamirs and Hindu Kush (Nikolaev; 2002; Thomas et al., 1994). In particular, the Mesozoic and Cenozoic series have been deformed into classic fold and overthrust belts. The fold axis is perpendicular to the direction of relative movement between the Pamir and Tien Shan Mountains (Fig. 1C; Leith and Alvarez, 1985; Nikolaev, 2002).

## 2.2. Lithostratigraphy of the study section

The study section is located on the flank of the Aktash anticline (see Fig. 1), where the Cretaceous-Neogene sequences are continuously exposed (Thomas et al., 1994). The anticline core consists of resistant limestones, followed by a continuous series of the Upper Cretaceous marine shales and limestones (Fig. 3). The Paleocene Bukhara Limestone Formation marks the beginning of the Paleogene. The Suzak Shale is a thin interval of gray-green, shallow-marine shales alternating with limestones. This formation is the first of the upper Paleocene and lower Eocene formations that conformably overlie the Bukhara Formation.

The Eocene Alai Formation is the uppermost marine formation of the Eocene (according to the map of Shaiakubov et al., 1980). The rest of the sequence consists entirely of red strata, with color variations indicating possible climatic signals. According to the geologic map presented here (Fig. 1), the entire Oligocene is absent in this area, and the first red bed (Shurysai Fm.) begins in the lower Miocene. However, according to Nikolaev (2002), the same formation begins in the upper Oligocene, and all subsequent formations are offset by half a step (Figs. 1 and 3). The entire sedimentary sequence is then unconformably covered by the Quaternary gravels. Two significant unconformities are displayed in the sequence (Shaiakubov et al., 1980): the first is between the Cretaceous and Paleocene, and the second is between the middle upper Eocene (possibly Bartonian) and the overlying red beds of lower Miocene age (Fig. 1C). These unconformities are marked in the field by sharp lithologic transitions but show no significant angular relationships. Formations marked on the geologic map were identified in the field based on the correlation of our study section on satellite imagery and the geologic map (Fig. 1B).

Synthetic names of the Late Cretaceous - Paleogene sedimentary formations at the western margin of the Tajik Depression (Fig. 3) were taken from the geologic map of the Gissar region (Shaiakubov et al., 1980), and adapted for the study area. The spelling of formation names was translated from Russian or taken from the relevant literature (e.g., Bukhara and Alai; Leith and Alvarez, 1985). The Cenozoic red beds are referred to as the Shurysai, Baldzhuan, Khingou, and Tavildara formations (Nikolaev, 2002). However, there is no consensus on the spelling of these formation names. In the Aktash section, the basal part consists of hard massive limestones that
may be dated as the Cenomanian to Turonian (Figs. 1; 4). These Middle to Upper Cretaceous sediments are described in the literature as predominant carbonate rocks representing marine facies (Klett and Steinshouer, 2006; Nikolaev, 2002). In general, the Upper Cretaceous rocks in the Tajik Basin represent the first transgressive-regressive cycles of the Para-Tethys Sea that connected the Tarim and Tajik Basins (Bosboom et al., 2017).

The Upper Cretaceous rocks consist mainly of dark gray to green shale of marine origin and limestone (Djalilov, 1971), range in thickness from 500 to 750 m in the central Tajik Basin, to more than 1 km in the Pamir Mountains (Burtman, 2000). Marine deposits continued until the Maastrichtian with short regression cycles characterized by several lagoons and continental interbeds (Klett and Steinshouer, 2006; Nikolaev, 2002). The Maastrichtian sequence ends with a regional unconformity (Nikolaev, 2002; Shaiakubov et al., 1980), and is overlain by the Bukhara Formation (Figs. 1C and 5). The Paleogene sediments resemble those of the Upper Cretaceous and consist of shallow-marine limestone with minor evaporites and marl (Davidzonet al., 1982). The thickness of the Paleocene limestones is less than 300 m, represented by the Bukhara Formation which is a thick interval of carbonate rocks with regional extent (Nikolaev, 2002; Ulmishek, 2004). This formation documents deposition in a shallow marine carbonate environment. Anhydrite amalgamation, dolomite, and limestone indicate arid climatic conditions. The Bukhara Formation is generally assigned to the Middle and Upper Paleocene because a major part of the entire Lower Paleocene (Danian) was eroded by the Middle Paleocene erosion (Ulmishek, 2004). This criterion is essential for identifying and documenting the K-T boundary in this area and emphasizes the need for further stratigraphic study (Burtman, 2000; Nikolaev, 2002).

The Suzak Shale (Figs. 1C and 6) is immediately adjacent to the Bukhara Formation and is an important formation frequently mentioned in the literature for its considerable organic carbon content (Klett and Steinshouer, 2006; Nikolaev, 2002). Klett and Steinshouer (2006) stated that the "lower Eocene Suzak" formation is "widespread throughout Central Asia" and consists of ~50-200 m thick mudstones with abundant organic material, which is likely a source of petroleum in the Afghan-Tajik Depression. They also indicated the presence of combustible bituminous mudstone (0.2 to 1.6 m thick). Phosphorites and pyrite are found in the lower half of this formation. Although the formation is assigned to the lower Eocene, the geologic map suggests the presence of the upper Paleocene at the base of the Suzak Shale, likely being a preserver of the PETM interval. Tevelev and Georgievskii (2012) noted that the Suzak Shale is remarkably continuous and homogeneous over much of the southwestern Gissar Mountains. They attributed this observation to the record of an "episode of unusual tectonic quiescence" in the otherwise active area. The Alai-Turkestan interval follows the Suzak Shale and marks the beginning of general regression facies that eventually led to the deposition of the overlying Neogene red beds. The Eocene series consists of shales and siltstones with carbonates and marl (Ulmishek, 2004), partially absent in some places. These series were deposited in a shallow marine shelf of the Turan Sea (an epicontinental sea; Fig. 2) that was a part of the early Para-Tethys, retreated in the late Eocene, and eventually declined in the Oligocene. The Oligocene sediments overlie the Eocene succession with a regional or a slight angular unconformity (Bosboom et al., 2011).

The relative stability of the continental plate during the Paleogene, and the removal of the crustal uplift zones resulted in a decrease in the thickness of this interval, which is a maximum of one to two hundred meters in the considered area (Ulmishek, 2004). According to the geological map (Fig. 1), the Alai formation occupies the upper Ypresian, the Lutetian, and part of the
Bartonian with an erosional unconformity at the top. The entire Oligocene to the subsequent lower Miocene red bed Formation is found above. This interpretation differs from the stratigraphic framework outlined in Nikolaev, (2002), in which the Suzak and Alai Fms. form a "subgroup" of "marine clay, sandstone, limestone, and marl" of the "Eocene-Oligocene" age (Fig. 3).

To clarify the view of Nikolaev (2002), the authors contrast his scheme of stratigraphic assignments with the geologic map represented in the columns of Figure 3. It is noted that the presence of much smaller gaps in his scheme than those of the geologic map at the transition between the Alai-Turkestan and Shurysai strata (Ulmishek, 2004; Klett and Steinshouer, 2006). This unconformity thus marks the onset of the Neogene deformation in the Amu Darya and Tajik-Afghan basins. Regarding Burakhek's (1934), the remained red layer represents the Baldzhuan Formation of the upper Oligocene and lower Miocene, the Khingou and Tavildara Formations of the middle and upper Miocene, and the Karanak and Polizak formations of the Pliocene. These discrepancies in stratigraphic assignment mean that there is no consensus for the age of the Red Bed.

## 3. Material and methods

During the fieldwork in Aktash, Uzbekistan, samples were taken at high and medium resolution. In sections having significant organic-rich intervals such as the Cenomanian-Turonian and Paleocene-Eocene intervals, lithologic description and sampling were conducted at 10- to 50 cm intervals to maximize the potential detection of isotopic excursions. In the other Cretaceous-Eocene and Oligocene sequence, sampling distances were increased to 0.5 to 5 m. The described measured sequence from the Cenomanian to the base of the red beds is ~1000 m thick. The overlying continental red beds are ~3800 m thick and were not sampled or described in detail.

### 3.1. Calcareous nannofossils

Forty-three samples from the Upper Cretaceous were prepared for analysis of calcareous nannofossils using the method described in Thibault et al. (2012). The study focused on the presence or absence of species, and apparent changes in abundance are estimated from a few observed specimens (+) to many (+++). The state of preservation is on average very poor, and many specimens are completely devoid of nannofossils. The modes of preservation of calcareous nannofossils were examined using Roth's (1983) visual criteria for etching and overgrowth. Three categories are distinguished: a. nearly barren (NB), when only one or two solution-resistant species with few specimens are present in the samples; b. very poor (VP), when several species could be identified (Plat-1). However, most observed specimens could not be identified to species level; and c. poor (P) when more than four species could be identified to species level with certainty.

### 3.2. Planktonic foraminifera

For foraminifera analysis, 100 g of sediment per sample was prepared using the standard method and washed through 63 µm and 38 µm sieves to obtain small species (Keller et al., 1995). Biostratigraphic analysis was performed on fractions less than 63 µm in size, and standard biozonation was established. The planktic foraminifera was analyzed at the University of Princeton, United States (plate-2).

### 3.3. Strontium isotope analyses
Strontium analyses of molluscan shells (bivalves and gastropods) were performed at the Department of Earth Sciences, University of Geneva. The shells were first analyzed under cathodoluminescence to detect possible diagenetic overprinting (Plate-3), then 50 mg of carbonate was extracted from the best-preserved part of the shell using a microdrill and processed into a powder. About 10 and 30 mg of pure carbonate were dissolved in 2.2 M acetic acid. The solution was centrifuged, the supernatant was pipetted off, dried on a hot plate, and converted to nitrate with a few drops of 14 M HNO₃. Sr was separated from the matrix using Sr-spec resin columns, loaded onto individual Re-filaments with Ta-oxide solution, and then measured at a pyrometer-controlled temperature of 1470 °C in static mode on a Thermo-Triton thermal ionization mass spectrometer using the virtual amplifier design to compensate for gain calibration biases between amplifiers. The ⁸⁷Sr/⁸⁶Sr values are internally corrected for fractionation, using an ⁸⁸Sr/⁸⁶Sr value of 8.375209. The raw values are further corrected for external fractionation by a value of +0.034‰ determined by repeated measurements of the SRM987 standard (⁸⁷Sr/⁸⁶Sr = 0.710248). The external reproducibility of the ⁸⁷Sr/⁸⁶Sr ratio for the SRM987 standard is 6 ppm.

### 3.4. Isotopic analyses of organic carbon

Isotopic analyses of organic carbon from kerogen-extracted material were performed at the Institute of Earth Surface Dynamics, University of Lausanne. The organic matter was separated from the samples by HCl treatment. The separated OM was rinsed several times with ultrapure water and dried (40°C; 16h). The dried materials were analyzed for carbon isotopes by flash combustion in a Carlo Erba 1108 elemental analyzer connected to a Thermo Fisher Scientific Delta V isotope ratio mass spectrometer operated in continuous helium flow mode via a Conflo III split interface. The δ¹³C org values were reported relative to VPDB. Calibration and evaluation of isotopic analysis reproducibility and accuracy were performed using replicate analyses of laboratory standard materials and international reference materials. The reproducibility was better than 0.1‰ (1 σ).

## 4. Results and discussion

### 4.1. Age model based on calcareous nannofossils and planktic foraminifera.

The age model for the Cretaceous interval is based on the nannofossils biostratigraphy (Supplementary Data File 1; Fig. 7; Plate -1). Unfortunately, the examined assemblage's preservation is generally very poor. The occurrence of nannofossil biozonal markers is very inconsistent. It often relies on findings in only one or two samples, adding considerable uncertainty to the preliminary biostratigraphy. Nonetheless, the nannofossil assemblage contains many species typical of the Boreal Intermediate, comparable to the Upper Cretaceous of the English Chalk (Burnett, 1998; Hampton et al., 2007). The results of determination and biostratigraphic interpretation are presented in supplementary data file 1. The interval from Samples OKE21 through OKE19 is rich in *Tranolithus orionatus*, *Zeughrabdotus erectus*, *Biscutum constans*, and *Eprolithus floralis*. The bloom of the first two species with high fecundity is characteristic of the Oceanic Anoxic Event 2 (Fig. 7; Plate-1; Bralower, 1988; Erba, 2004; Melinte-Dobrinescu et al., 2013). Sample OKE19 also contains a few specimens of *Quadrum intermedium*, whose first occurrence (FO) marks the base of the late Cenomanian UC5c subzone (Burnett, 1998). Most specimens above this interval are devoid of calcareous nannofossils. However, the presence of large amounts of organic matter in the OKE8 slides through OKE10 combined with the significant
positive $\delta^{13}$C$_{org}$ excursion between samples OKE10 and OKE16 is evidence of typical late Cenomanian age (Fig. 7; Plate-1). The FO of *Quadrum gartneri* in sample OKC13 marks the base of UC7. This bio-horizon is considered an early Turonian event in Burnett's (1998) scheme and has indeed been detected in sections of the Western Interior (Corbett and Watkins, 2014; Tsikos et al., 2004) and Germany (Linnert et al., 2010) slightly above the Cenomanian-Turonian boundary. An earlier FO of *Q. gartneri* in the late Cenomanian has been recorded in Tunisia (Nederbragt and Fiorentino, 1999), Gubbio, Italy (Tsikos et al., 2004), and the Equatorial Atlantic (Hardas and Mutterlose, 2007). Therefore, the exact location of the Cenomanian/Turonian boundary remains uncertain. The FO of *Eiffelithus eximius* in sample OKC17 marks the base of zone UC8. The FO of *Micula decussata* (synonym of *M. staurophora* by some authors) in sample OKC45 marks the base of zone UC10 and attests to an early Coniacian age. *Reinhardtites anthophorus* in samples OKC50 and OKB114 is further evidence of Zone UC10, as this species first appears in the middle of UC10 (Burnett, 1998). No other standard biostratigraphic markers for the interval from the Coniacian to Santonian are found in samples OKC50 through OKB75. However, the interval between Samples OKB114 and OKB105 contains an assemblage rich in *Helicolithus trabeculatus* with abundant *Eprolithus* spp. such features are characteristic of nannofossil assemblages from the Coniacian to the earliest Santonian. In addition, *Helicolithus tectufissus* is noted in samples OKB111 and OKB105. This rare species has been described from the Coniacian/Santonian boundary of the Ten Mile Creek section in the western interior (Blair and Watkins, 2009). Its presence here could support a possible assignment of the interval between OKB 111 and OKB 105 to the Coniacian/Santonian boundary transition. The interval between samples OKB 99 and OKB 75 is poor in nannofossils. The FO of *Broinsonia parca* in sample OKB 67 marks the base of UC14, and therefore the last interval below it can be assigned to zones UC12-13 from the Santonian to the lower Campanian. The LOs of *Eiffelithus eximius*, *Broinsonia parca*, *Reinhardtites levis*, and *Tranolithus orionatus* are found in the same sample, OKB26, suggesting that the top of the upper Campanian zone (UC15) defined by the LO of *E. eximius*. The placement of LO of *E. eximius* at this level also indicates that much of the lower Maastrichtian is missing, as *T. orionatus* and *R. levis* mark the top of zones UC17 and UC18 of the lower Maastrichtian, respectively. The Presence of *Micula murus* in sample OKB18 attests to the upper Maastrichtian subzone UC20bTP. The upper Maastrichtian age is confirmed by the simultaneous presence of several prominent representatives of *Arkhangelskiella cymbiformis* (*A. cymbiformis* var. *W. sensu*, Thibault, 2010), which was first distributed in this age interval (Thibault, 2010). The interval between OKB18 and OKB10 is therefore assigned to the upper Maastrichtian.

The Paleogene stratigraphy is determined based on planktonic foraminifera (Plate-2). The lower part of the Paleogene, beginning with OKB10 to OKB1 (Bukhara Formation), is a barren interval. In the transition interval from the limestone of the Bukhara Formation to the Suzak Shale (samples from OK9 to OK11) planktonic foraminifera are poorly preserved. However, the presence of *G. pseudomenardii* and other species: *Acarinina mckannai*, *A. nitida*, *A. subsphaerica*, *Subbotina velascoensis*, *S. triangularis*, *Igorina albeari*, *I. tadjikistanensis* indicates zone P4 a and b. Presence of well abundant planktic foraminifera assemblage, *A. subsphaerica*, *S. velascoensis*, *S. triangularis*, *S. patagonica*, *M. apanthesma*, *A. esnaensis*, *I. pusilla*, *Morozovella aequa*, *A. esnehensis*, *A. esnaensis*, *A. soldadoensis*, *A. coalingensis*, *A. mckannai*, *A. nitida*, *Chiloguembelina trindidadensis*, *G. pseudomenardii*, *G. chapmanni*, *A. subsphaerica*, *S. triangularis*, *M. apanthesma*, with rare *I. pusilla*, *A. soldadoensis*, *Chiloguembelina trindidadensis* (samples from OK12 to OK61) above the previous interval refer to zone P4c. Two poorly preserved pyritized and phosphatized bivalve intervals are observed within zone P4c. The first is
near sample OK25, and the second is at the top of the same interval. Sample OK 61 contains gypsum, pyritized moulds, few planktons, with good benthos.

Zone P5 is placed within samples from OK62 to OK85. The recorded assemblages are well preserved and contain (LO) *A. mckannai* and are dominated by mostly small subbotinids: *S. velasocensis*, *S. hornibrooki*, *S. patagonica*, *S. triangularis*, *A. coalingensis*, *A. subspharica*, *A. esnaensis*, *A. nidita*. This zone is characterized by several changes where the planktonic fauna is poorly preserved shows signs of dissolution and is predominantly benthic and rarely planktonic (samples from OK63 to OK71). The OK70 and OK71 samples contain small benthic fauna, gypsum, pyrite framboids, and a few planktonic species (*I. pusilla* and *A. esnaensis*). Samples OK85 and OK86a have abundant pyrite framboids and rusty red forams with rare planktic species (*A. sibaiyaensis*, *S. triloculinoides*, *A. nitida*, *A. apanthesma*, *I. pusilla*, and *A. esnehensis*).

Based on the above observations, the authors can determine the temporal boundary intervals of the study section as follows:

### 4.1.1. Cretaceous age model (calcareous nannofossils; Plate-1):

a. From the base of the section to sample OKC1, the upper Cenomanian age is proposed (UC5c/UC6), followed by a barren/hiatus interval from samples OKC2 to OKC11.

b. Samples from OKC12 to OKC30 (zone UC7 to the middle of zone UC8/9) assign the Turonian age.

c. Samples from OKC31 to OKB106 (from the middle of UC8/9 to the middle of UC11 zones) are Coniacian in age.

d. Samples from OKB105 to OKB90 (from middle UC11 to lower third of UC12/13 zones) have Santonian age.

e. Samples from OKB91 to OKB68, zones (from the second third of UC12/13 zone to its top) are of the lower Campanian age.

f. Samples from OKB67 to OKB26 (UC14 and UC15 zones) are determined to be middle to upper Campanian in age.

g. The UC16 zone is absent, which could be due to uplift and nondeposition or erosion.

h. Samples from OKB25 to OKB18 (UC17/18 zone) represent the lower Maastrichtian age.

i. The UC19 zone is absent due to uplift and nondeposition or erosion.

j. Samples from OKB17 to OKB7 (UC20b-d zones); are of the upper Maastrichtian (Fig. 7).

### 4.1.2. Paleogene age model (planktic foraminifera; Plate-2):

a. The Bukhara Formation may be associated with foraminiferal zones P1, P2, and P3.
b. Samples from OK9 to OK13, (P4a and b zones) represent the late Danian to late Selandian age.

c. Samples from OK14 to OK50 (zone P4c) are of the late Selandian to late Thanetian age.

d. Samples from OK50 to OK86a (zone P5) indicate the uppermost Thanetian.

## 4.2. Strontium isotope stratigraphy

Strontium isotope analysis focused on 13 samples of molluscan shells. The measurements of strontium isotope ratios are carried out with high technical quality (high signal and reproducibility). The age-to-ratio data from McArthur et al., (2001) calibrated to the geologic time scales (Gradstein et al., 2012, 2020) is used to assign the numerical ages (Fig. 7 and Table 1). Because multiple ages are possible when the marine Sr lineage records identical isotopic values multiple times. The interpretation and age decision are based on the following criteria: 1) the relative stratigraphic position of the samples, and 2) the biostratigraphic interpretation of both nannofossils and planktic foraminifera. The higher weight has been given to stratigraphic ages determined from nannofossils and planktic foraminifera (Fig. 7), despite possible uncertainties in the timing and synchrony of their worldwide occurrence.

Starting from the base of the studied section, OKC1, our first sample at the surface of resistant limestone of Tiubegatan to Muzrabat has an ⁸⁷Sr/⁸⁶Sr ratio of 0.707407, refer to the Lower to Middle Cretaceous age (Figs. 7 and 8). Plotting of these samples on the standard curve could lead to misinterpretation of the ages, Hauterivian, Aptian, Albian, or Cenomanian. However, according to the geologic map (Fig.1), this sample should belong to the upper part of the Lower Cretaceous (Cenomanian to Turonian). Thus, in the absence of other information, the age of 95.81 Ma could be inferred from the Cenomanian. The presence of *Rhagodiscus reniformis*, *Staurolithites laffitei*, *Staurolithites* sp. below sample OKC1 (OKEs), and *Quadrum gartneri* in sample OKC13, indicate the Turonian age upon the geologic time scale (2012), thus the upper Cenomanian is confirmed for this interval. The authors cannot exclude the possibility that OKC1 has a much younger age (86.58 Ma), so both ages are marked as "possible" in Table 2. Regarding the nannofossils stratigraphy, the authors suggest an upper Cenomanian age for OKC1. Immediately above OKC1 (sample OKB112) the proposed age is either the Turonian or the Coniacian. Sample OKB112 has the ⁸⁷Sr/⁸⁶Sr ratio of 0.707342471, suggesting either the age of 89±0.2 Ma or 93.1±0.2 Ma. In correlation with the nannofossils biozone, *Helicolithus tectufissus*, and *Helicolithus trabeculatus* sample OKB112 is retained to the Coniacian, and 89±0.2 Ma is recommended age calibrated with the geologic time scale (2012, 2020). In particular, considering a Cenomanian age of 95.5 Ma for OKC1, samples OKB48 and OKB57, which yield Santonian ages of 84.38 Ma and 84.45 Ma, respectively, also appear to be too old (Table 1). Sample OKB50, on the other hand, yields a biostratigraphically consistent age of 82.79 Ma, which is consistent with middle to upper Campanian biostratigraphy. Sample OK9 was taken at the base of the Suzak Shale, i.e., above the Bukhara Formation, which is generally assigned to the Paleocene in age due to its stratigraphic position. Therefore, the authors reject the Maastrichtian age of 67.05 Ma (too old) and the Oligocene age of 33.87 Ma (too young) for this sample. Instead, the late Danian age (62.25±1.9 Ma) is considered, which very well correlates with the planktic foraminifera zonation (Fig. 7) and is consistent with local geology knowledge.
For the rest of the samples between OK9 and OKA18, in the absence of nannofossils, the age assignment is inferred from 1) the stratigraphic position of the samples, 2) the strict age assignment of samples OK9 (see above) and OKA18, which delimit the interval, and 3) presence of planktic foraminifera. This helps to correlate the age obtained from biostratigraphy with the $^{87}$Sr/$^{86}$Sr age. Sample OKA18 is from the youngest mollusc in the sequence. Based on its ratio, it intersects the very steep late Eocene/Oligocene part of the marine Sr isotope record line and yields an age of 34.35 Ma, i.e., coincident with a very Late Eocene (Priabonian). There is no reason to consider the possibility of the Paleocene or Upper Cretaceous age for OKA18. Only sample OKA2 has a fluctuating age, either too old (57.68) or too young (34.46 Ma), and therefore is not considered further in this study. In contrast, sample OK14 has an indeterminate age between 38.14 Ma and 48.64 Ma due to the shape of the marine Sr record, with no conflicts with samples above or below it. Sample OK109, with an age of 54.82 Ma is remarkably consistent with the identification of the PETM event (55.8 Ma–see corresponding section below).

Despite the considerable uncertainties in the biostratigraphic interpretation of the calcareous nannofossils and planktic foraminifera, it is well correlated and compatible with the numerical $^{87}$Sr/$^{86}$Sr age (Fig. 7). Due to this consistency, the authors can conclude that the base of the studied section is of Upper Cretaceous age (late Cenomanian) and the upper part is assigned to the upper Eocene (Priabonian) to the early Pliocene (Figs. 7 and 8) followed by the Oligocene and Miocene deposits.

### 4.3. Carbon isotope stratigraphy and global correlations.

Disruptions in the planetary carbon cycle have left distinct traces in the Upper Cretaceous and Paleogene carbon isotope records. However, the magnitude and shape of carbon isotope curves vary from one event to another, and from place to other. Such isotopic stratigraphy remains extremely useful for identifying and correlating different events worldwide (Sluijs and Dickens, 2012).

About 72 carbon isotope events have been determined from the Cenomanian to the Campanian in the English Chalk successions (Jarvis et al., 2006). The determined events can be recognized in contemporaneous sections worldwide (Takashima et al., 2010; Voigt et al., 2007; Wendler et al., 2009). Based on previously published isotopic profiles of the English Chalk successions and other sections covering the interval from the Upper Cretaceous to the Paleogene. Several of these were adopted in correlation with the Aktash sequence (Figs. 9 and 10).

In the Aktash sedimentary sequence, eight organic carbon isotopic excursions (CIEs) are recognized along the isotope curve through the present study (Figs. 9 and 10). Three of them are positive excursions and the rest represent negative CIEs. They start from the base by closed double positive $\delta^{13}C_{org}$ shifts of 2.9 (OKE8) and 0.7‰ (OKE2). Based on their stratigraphic position below sample OKC1 that correlated to UC5c/UC6, and the age assigned to this double peak is 95.5 Ma, these two isotopic excursions are linked to the late Cenomanian age. Lithologically, is characterized by a transition from the hard ground raised beach of the latest Cenomanian to the black shale of the Early Turonian. The late Cenomanian isotopic excursion therefore, correlates very well with the Cenomanian-Turonian oceanic anoxic event 2 (OAE2) as recorded worldwide (English chalk isotope curve; Jarvis et al., 2006; Western Interior composite isotope curve; Joo and Sagman, 2014; the GTA 2012 curve; Fig. 9).
The second $\delta^{13}C_{\text{org}}$ - CIE corresponds to the interval between OKC31 to OKC41 with a negative isotopic excursion (-1.8 ‰) and coincides with the middle of UC8/9 (the upper Turonian) to the top of the UC8/9 zone (lower Coniacian). Therefore, the CIE observed in this interval may represent the transition interval from Turonian to Coniacian. This isotopic excursion may be referred to as a Hitch Wood and/or late Turonian event (English chalk isotope compilation curve; Jarvis et al., 2006; Fig. 9). A smaller peak shift in $\delta^{13}C_{\text{org}}$ observed between the first and second excursions. Based on its stratigraphic position, it is possibly linked to the Round-Down interval associated with the English chalk isotope compilation curve (Fig. 9).

The third $\delta^{13}C_{\text{org}}$ - CIE is a positive gradual shift in organic carbon isotopic values (2,3‰). This shift extends from OKB102 to OKB90, coincides with the lower part of the UC12/13 zone, and covers the interval from the middle to upper Santonian. Carbon isotope values return to the observed background in the transition interval from the Santonian to the lower Campanian. This gradual positive spik in $\delta^{13}C_{\text{org}}$ is well correlated to the Santonian-Campanian boundary event (SCBE; Jarvis et al., 2006; Iran; Razmjooei et al., 2020; northern Germany; Voigt et al., 2010; Italy; Sprovieri et al., 2013; Sabatino et al., 2018; Thibault et al., 2016; Voigt et al., 2010), indicates that this peak has global significance.

Along the transition interval from the lower to middle Campanian, the fourth $\delta^{13}C_{\text{org}}$ - CIE occurs, correlating with the uppermost UC12/13 and the lower UC14/15. This $\delta^{13}C_{\text{org}}$ - CIE represents a positive shift in $\delta^{13}C_{\text{org}}$ values (2.8‰; OKB74 to OKB63) and can be correlated with the middle Campanian event (Fig. 9). The transition interval from the middle to upper Campanian corresponds to a minor negative shift in $\delta^{13}C_{\text{org}}$ and can be defined as a BUCE event correlating with the reference intercepts and GTE -2012 (Figs. 7 and 9).

The transition from the middle-late Campanian to the lower Maastrichtian has been defined within the interval from the UC14-UC15 to the UC17/18 zones (zone UC16 is missing). A gradual negative $\delta^{13}C_{\text{org}}$ - CIE characterizes this interval, which occurs between samples OKB34 and OKB23, and reaches its minimum value at sample OKB29 (-26.6‰). Above this interval and through the upper Maastrichtian (zone UC20b-d), the $\delta^{13}C_{\text{org}}$ values fluctuate; and reach their minimum at sample OKB11 (-27.7‰). The observed negative shift in this interval is related to the Campanian-Maastrichtian boundary event (CMBE) as observed worldwide (Figs. 7 and 9). The Cretaceous-Tertiary transition is characterized by an eroded surface.

No $\delta^{13}C_{\text{org}}$ data are produced from samples OKB10 to OK1 in this manuscript (Bukhara Formation). The lower Danian Bukhara Formation (Sample OK9) has an age of 62.25 ± 1.9Ma and gives an age of the upper Danian for the base of the Suzak Shale. The obtained numerical age is consistent with the planktic foraminifera (P4a & b zone).

In the Paleogene, one hundred and thirty-six samples of the Suzak Shale were analyzed for organic matter carbon isotope content. The resulting $\delta^{13}C_{\text{org}}$ curve (Fig. 9) is evident and helpful in constraining the chronostratigraphy of this interval at the Aktash sequence

Between samples OK1 and OK86a, the $\delta^{13}C_{\text{org}}$ is relatively constant and lies within a narrow values range of approximately -23.2‰ and -25.2‰. Above sample OK86a ($\delta^{13}C_{\text{org}}$ - CIE No. 6; Fig. 9), the laminated organic-rich shales (average TOC is 23.7%; see supplementary data file 2) show a significant shift to more negative values of ca. -28‰ (OK94). The observed negative shift
of ca. -3‰ indicates the global negative CIE typically for the Paleocene-Eocene thermal maximum event (PETM; McInerney and Wing, 2011). The absolute values and magnitude of CIE found here in organic content are similar to the range recorded in the other representative sections (Westerhold et al., 2009; McInerney and Wing, 2011; Barnet et al., 2019; Figs. 7 and 10). The discovery of this event in the Aktash sequence is consistent with sedimentological observations in the region. Other studies have documented the presence of the PETM immediately above the Paleocene Bukhara Formation elsewhere in the region. This may be due to the intensive weathering of the uppermost Paleocene (Bolle et al., 2000; Gavrilov et al., 2003).

The $\delta^{13}C_{org}$ - CIE of the PETM is followed by two negative CIEs (Nos. 7 and 8; Fig. 10) located between samples OK109 and OKA4 (54.82 Ma and 52.48 Ma, respectively). They are significantly related to ETM2 and ETM3 events. The $\delta^{13}C_{org}$ values are about -27.7‰ and 27.3‰, respectively (Barnet et al., 2019; McInerney and Wing, 2011; Westerhold et al., 2009). The uppermost carbon isotope shift may be related to the Ypres-Lutetian boundary event.

## 4.4. Depositional environments.

The studied sequence can be divided into three main intervals. These three intervals are stratigraphically ordered as the Upper Cretaceous shale (from the base of the sequence to the bottom of Bukhara Fm), the Paleocene Bukhara Formation, and the Paleocene-Eocene interval.

### 4.4.1. *Upper Cretaceous Shale*

Most of the sequence from the base to the bottom of the Bukhara Fm consists of monotonous gray-green-brown shales, marls, and siltstones with limited fossil content and sedimentary structures (Fig. 4). The base of the section is formed of a hard ground surface well-sorted grainstone and packstone with abundant borrows, large forms of unbroken gastropods, and karstic infills (Fig. 4A, B, C and E).

This hard ground surface is followed by several meters (OKC2 to OKC8) of greenish muddy bioclastic wackestone, karst fills, borrow concretions, and metric low-angle crossbreds (Fig. 4F). Above this, an interval of particularly dark shales and marls (Fig. 4H), more or less monotonous up to the base of the Bukhara Formation.

This monotony is interrupted by several tens of centimetres of resistant limestone layers breaking the sequence into repetitive packages tens of meters thick. The first of these carbonate layers contains large ammonite shells within the interval of sample OKB112 (Fig. 4G). The other resistant carbonate layers that punctuate the sequence are generally mollusc-dominated bioclastic layers with several decimetres to a meter thick (Fig. 4I). The bivalves are well preserved and generally unbroken, with abundant brings in their shells, but also not in a live position. Occasionally, small (cm) unbroken ammonites can be observed in these layers. Toward the end of the Upper Cretaceous interval; well-sorted siltstone and fine sandstone layers occur, 5 to 20 cm thick, with the presence of small-scale hummocky cross-bedding and ripples (Fig. 4). The combination of first-order lithology, macrofauna, and structures observed in this sequence is consistent to the published works (e.g. Ulimishek, 2004), referring to deposition in the shallow-marine carbonate-clastic shelf.
The monotonic shales and marls can be interpreted as deposits below the storm wave base (lower offshore). The bioclastic carbonates consist of mixed shallow-water species of pelagic ammonite with perforated and complete shells. They are interpreted as storm soils deposited during a period of sea-level low as observed by the presence of a bioturbated surface, without platform upwelling. The fine-grained sandstones and siltstones characterized by hummocky cross-stratification (HCS), indicate the upper-offshore conditions above the storm-wave base. At the base of this sequence, an emersion is inferred from the abundance of lending and karst features. Given the magnitude of sea level fluctuations during the Upper Cretaceous (Kominz et al., 2008), and the lack of obvious emersion features except at the base of the sequence, suggest that the paleo-water depth of these deposits must have exceeded 50 meters (upper-offshore). Given the epicontinental context, the water depth of the lower offshore must have been 100 meters or more.

### 4.4.2. Bukhara Formation of Paleocene age

The Bukhara Formation sharply overlies the Upper Cretaceous sequence (Figs. 5 & 7). A bright, prominent, and resistant carbonate member (about 120 m thick) stands out in the landscape and is the most notable structural marker between the fine-grained sequences below and above it (Fig. 5). The Bukhara Formation consists of brecciated limestones and dolomites with dolomite-evaporite amalgamation. A rare occurrence of oolitic facies characterizes the upper part of the Bukhara Fm. Faunal content is rare and constitutes indeterminate foraminifera (OKB11, Fig. 5). Nautilids are found at the bottom of the Bukhara Fm. (OKB10; Fig. 5). Beyond that, no other hydrodynamic indicators are observed, except for some weak symmetrical wave ripples immediately above the Nautilids level (inset OKB9; Fig. 5). In the Aktash sequence, it is difficult to identify subgroups within the Bukhara Complex, as named by Knepel (2010) in the Eastern Tajik Depression. In the present work, the lithology and colour of the Bukhara Formation (Shaiakubov et al., 1980), with the presence of evaporites, oolites, rare ripples, and intraformational breccias; suggest the deposition within a shallow carbonate platform in a relatively arid climate.

It is possible that the platform was externally deformed, which could also account for the brecciation that occurred in some layers. Nevertheless, the extensive lateral persistence of these facies at the basin level suggests regional climate control imposed over shallow topography and perhaps even and/or a period of relatively quiet tectonism. However, the observation of a Nautilus at the base of an isolated basin suggests a connection to open marine conditions in the late Upper Cretaceous. Further up, the existence of some wave ripples, oolites, and evaporites suggests deposition above the fair-weather wave base and possibly a lagoon.

### 4.4.3 Paleocene-Eocene Formations (Suzak and Alai)

The shale sequence is mainly consisting of variegated shales and marls (Figs. 6 and 7). The carbonate alternation is rare and generally lacks nannofossils. A distinct resistive layer (Alai Bed) separates the interval into the underlying Suzak Shale and the overlying Alai Formation. The Suzak Shale is a sequence of very drab grey, bluish marls and siltstones about 100 m thick, and is graded upward into marly limestones characterized by the presence of different size oyster shells (up to 15-20 cm in size). Two remarkable layers are observed in this sequence. The first is a thin organic-bearing layer (5 to 30 cm) of very dark laminated black shales (samples OK85-86; average TOC is 23.7%; Fig. 6) sandwiched between two marl levels. The organic-bearing layer has a similar grain
size to the preceding and succeeding marls. It is not readily visible everywhere because of mass deterioration and creeping marl slope cover. However, one can note a subtle colour change on the slopes indicating the presence of this dark layer.

As mentioned above, this remarkable layer in the Aktash shale sequence is an expression of the Paleocene-Eocene thermal maximum (PETM) event. In general, the Paleocene-Eocene interval is characterized by a fine-grained limited texture, absence of nannofossils, and rare mollusca. The disappearance of large gypsum beds relative to the underlying Bukhara Fm. indicates a deeper depositional environment. Although the oysters have not yet been identified, their remarkable size and stratigraphic position lead us to suspect that they may be similar or related species to those observed in the assemblages of Lan and Wei (1995), and Lan (1997) in the coeval Late Eocene Kalatar and Wulagen Formation at Aertashi in the Tarim Basin (Bosboon et al., 2011). If this is true, the paleoecological preferences of these bivalves confirm an environment characterized by warm, shallow water above the storm wave base (Bosboon et al., 2011). The absence of typical alternation of shale and sandy storm layers indicates a restricted environment that may likely be protected from the influence of open ocean storms. The presence of organic-rich level (up to 31%) suggests exceptionally eutrophic conditions at the Paleocene-Eocene boundary (Khozyem et al., 2013; Schulte et al., 2011), consistent with a limited shallow epicontinental environment. In geographic and geologic continuity with the study area, an example of such an environment is located in the northwestern part of the modern Caspian Sea (Mamaev, 2002). The preservation of such an extensive organic-rich interval at PETM raises questions about the effects of climate warming on landscape evolution in this area relative to other areas worldwide (Chen et al, 2018; Foreman et al, 2012; Schmitz and Pujalte, 2007; Vimpere et al, 2023). The sequence presented here requires further studies and may also hold interesting clues for understanding the mechanisms of carbon sequestration and climate recovery after the PETM (Lyons et al., 2019).

The second marker layer is the Alai Bed. This bed is a resistant bioclastic sandstone that defines the top of the Suzak Shale and the base of the Alai Formation (Fig. 6). The Alai Bed is a coarsening upward sequence with several shell-rich intervals (small and large mollusca species), an abrupt erosional surface is placed at its top, forming the base of a very coarse cross-bedded sandstone (2-m-thick). In addition, numerous pierced basal pebbles are found at the erosional surface. A fine-grained mixed carbonate-sandstone interval overlies the Alai sandstone bed. Finally, the remains Alai Formation sequence formed of grey-greenish marls and silty marl intercalations (about 30 m thick). On the top of this interval, the marls merge into a paleosol with variegated and mottled clays (1m thick) that terminate below the base of the succeeding Shurysai Formation.

In summary, the fine-grained sequence may represent high-elevation upper-offshore conditions. On the other hand, the bioclastic strata and siliceous sandstones represent lower shore, lagoonal, and transitional conditions given the amplitude of sea level fluctuations in the Eocene (e.g., Kominz et al., 2008). The Paleo-water depths must have ranged from 0 to 50 m, with a single prominent unconformity in this succession.

## 5. Cycles of Sea level changes

The study section shows an evolution of first-order depositional environments, that can be divided into several large-scale packages bounded by major sequence stratigraphic surfaces (Fig. 11). Although this work focuses on a 1D section, it is emphasized that these packages and their
bounding surfaces are of potential chronostratigraphic importance to the basin. The shallowing-
upward successions are "progradation" in the broadest sense of shifting facies belts in the basin
area while deepening successions are referred to as "retrogradation". The term "unconformities"
or "sequence boundaries" is used for erosional surfaces that mark basin-ward in depositional
environments and represent a break for relative continuous shallowing recorded within a
progradation trend. Finally, the term "maximum flood plain (MFS)" is used to refer to a horizon
of maximum paleo-water depth that marks the transition between increasing and decreasing water
depth. As discussed above, maximum inundation interval or level is often used in place of surface
area; because identifying a single distinct surface area is complicated by the generally very fine-
grained nature of the sequence. Trends in flattening and deepening (progradation-retrogradation)
are shown in Figure 11, lateral to the column of our interpretation of the depositional environments.
The main stratigraphic features of the succession can be summarized as follows:

5.1. First major sea progradation in the Tjubegatan Formation Baldzhuvon Group: the Cenomanian - Turonian.

The age of the Tjubegatan Formation correlates with the base of the Baldzhuvon Group in the Tajik Basin (Chapman et al., 2019; Dzhalilov et al., 1982). The first shallowing upward interval extends from the base of the section to the top of the resistant limestone of the upper Cenomanian and lower Turonian age (Fig. 11). The top of the resistant limestone is a distinct erosional surface with karst features and perforations. It marks a transition between open marine limestones below and shallow marine shoreface wackstones and packstones above. The recorded erosion surface is a regional feature that can be traced through the Central Asia basins (i.e., Trim and Tajik basins; Chapman et al., 2019; Dzhalilov et al., 1982; Kaya et al., 2019). It is classified as a regional unconformity surface. Two minor (local) progradation/retrogradation cycles are noted in this interval.

5.2. First major marine intrusion in the Muzrabat Formation: The Santonian - lower Campanian.

As mentioned before, the maximum flooding level is described as "levels" rather than surfaces
because their position within a very fine-grained sequence does not allow the identification of a
single, localized surface. However, this can sometimes be done based on sedimentological and
paleontological criteria on hard surfaces. This level is localized within the transition from the
Santonian to the lower Campanian (Muzrabat Formation or Hasarakbolo; Chapman et al., 2019;
ca. OKB90; Fig. 11). The shale interval marks the end of the transgressive trend that occurs after
emersion at the base of the sequence. It is an interval of particularly dark shales within a very fine-
grained sequence. In addition to lithology, a maximum water depth at this level can also be inferred
from the deepening trend observed below (increasing proportion of pelagic – ammonoid fauna)
and the shallowing-upward trend observed above (increasing abundance of bioclastic storm beds).

The long-term progradation/retrogradation cycle covers most of the Upper Cretaceous sediment
in the Aktash sequence (from the Turonian to the upper Maastrichtian). Several minor
shallowing/deepening cycles were locally observed. The frequency of these cycles increased
toward the end of the Cretaceous, with sharp transgression pulses (Fig. 11). At the top of the Upper
Cretaceous sequence; a sharp surface of massive shallow-water limestone-evaporite assemblages
of the Bukhara Formation occurred (Fig. 11). This surface appears to has a regional extent along
the Afghan-Tajik, Tajik, and Tarim basins (Chapman et al., 2019; Kaya et al., 2019; Shaiakubov
et al., 1980) and even in adjacent countries (i.e., Turkmenistan and Tajikistan; Brookfield and Hashmat, 2001; Hosseinyar et al., 2019; and Iran; Wilmsen et al., 2015). However, neither significant scouring nor angular unconformities are observed.

### 5.3. Second major sea prograding in the upper Bukhara and Suzak Formation: The Danian-Selandian.

The contact surface between the massive shallow-water limestone-evaporite assemblage of the Bukhara Formation and the overlying Suzak shale Formation is characterized by an abrupt change in sediment types from limestone to mudstone (ca. OK1; Fig. 11). It is coincident with a significant progradation level starting from the lowermost part of the Bukhara Formation. This progradation interval has been observed in both long- and short-term progradation/retrogradation cycles in the Tajik Basin (Nurek section; Kaya et al., 2019). Therefore, this surface can be considered an important sequence boundary.

### 5.4. Second major marine intrusion in the Suzak Formation: The Paleocene-Eocene boundary.

In the Paleocene-Eocene interval, the authors inferred a maximum flooding level within the marls and shales that followed the organic-rich PETM interval. These marls and shales preceded a return to shallower environments characterized by increased oyster beds. Both the long- and short-term progradation/retrogradation cycles are congruent. This may be due to the global environmental perturbation that accompanied the Paleocene-Eocene Thermal Maximum (PETM). At the top of the Suzak Shale Formation and the base of the Alai Formation (Alai Bed), the coarsest facies of the entire succession are observed. This facies contains drilled-out, large-sized (15 cm) pebbles at the base of a sharp-edged coarse sandstone with shell debris. It represents mixed shallow fluvio-marine conditions on an erosional surface overlying open marine deposits. Below this, a significant shoreline shifts, and thus a significant unconformity is present. Given the succession of facies associations and the sharp-edged contact, the Alai bed is interpreted here as a sharp-edged shoreline surface (Plint, 1988). The Alai marker bed is laterally extensive and is mentioned as far north as the Peter-the-First Range (Leith & Alvarez, 1985), suggesting both a very significant event and a very shallow topographic gradient. This event corresponds to the Eocene-Oligocene Sea level decline. The very shallow topography, with poorly developed drainage systems in the surrounding relief, would have prevented the development of large interior valleys, and instead favored the preservation of a regressive surface of marine erosion (Catuneanu, 2002) and associated sharp-edged shorelines.

A fourth, insignificant but conspicuous surface is located at the sharp contact between the fluviatile sandstones and paleosols of the upper Red Beds Member to the base of the Shurysai Formation. This surface is of less stratigraphic importance than the others described above. Although it is very prominent in the field because of the unique colour and facies change, it represents a developmental continuum rather than a shift of the depositional belts toward the basin. Although the Paleocene-Eocene interval of Suzak and Alai is generally marine, the uppermost part of the Alai Formation, as described above, exhibits an increasingly shallow succession, marked at the end by Paleo-Solar features. Consequently, the sandy limestones with burrows and root marks at the base of the Shurysai naturally follow the Alai Formation in a generally shallowing-upward trend, with no significant break at the transition.
## 6. Conclusions

The Aktash section in southern Uzbekistan at the tip of the Tian Shan and Gissar mountain ranges, as part of the Afghan-Tajik Basin, began to develop during the Mesozoic and continued to develop during the Paleogene. Based on absolute and relative age dating, the lower part of the sedimentary sequence is fixed to the late Cenomanian and the upper part to the Late Eocene. Several climatic and paleoenvironmental events can be recognized by their isotopic and sedimentological signatures throughout the study period. The most prominent climatic and environmental changes are the Oceanic Anoxic Event (OAE2) in the Cenomanian-Turonian and the Paleocene-Eocene Thermal Maximum event (PETM), identified based on biostratigraphy and organic carbon isotope profiles. Based on sedimentological facies analyses, several long- and short-term progradation/retrogradation cycles are identified. These cycles are partially correlated with the global sea level curve and in some intervals associated with local events. The distinct transition from the Paleogene marine sediments studied in this work to the upper Late Paleogene (?) to Neogene continental red beds, which have not been studied, remains to be investigated but is most likely related to the retreat of the Turan Sea and the aridification of Central Asia (Bosboom et al., 2011 and 2017).

### Authorship contribution statements

**Hassan Khozyem:** Fieldwork, data collection, analyses, illustration and interpretation, writing; **Thierry Adatte:** Fieldwork, analyses, interpretation; **Marie-Françoise Brunet:** Funding acquisition and project conceptualization; **Massimo Chiaradia:** Strontium analyses and interpretation; **Gerta Keller:** Foraminifera analysis and interpretations; **Nicolas Thibault:** Nannofossil analyses and interpretation; **Irina Sidorova:** Field logistics; **Bakhtiar Nurtaev:** Local supervision and support; **Jorge Spangenberg:** Geochemical analyses and interpretation; **Sébastien Castelltort:** Funding, fieldwork, data collection, interpretation, principal investigator and overall supervision.

### Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

### Acknowledgments

We acknowledge Eric Barrier, the DARIUS program (Sorbonne Universities), and their sponsors for providing the funding for this study.

### Declaration of generative AI and AI-assisted technologies in the writing process

During the preparation of this work, the author(s) used [Insta Text] to [improve writing and decrease orthographic and grammatical errors]. After using this tool/service, the author(s) reviewed and edited the content as needed and take(s) full responsibility for the content of the publication.

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## Figure Captions

**Fig. 1:** A. Location map of Uzbekistan showing the position of the study area, B. Satellite image (Google Earth©) of the Aktash anticline and the main lithological formations from the literature. C. Geological map of the study area traced from the 1:100,000 geological map of the Gissar region (after Shaiakubov et al., 1980) with a color key and labels showing the stratigraphic assignments of the local formations. The thick black segments represent the position of the various sections that were measured and sampled in the field. Schematic cross-section A-A' shows the structure of the folded strata and the location of the sampled sections.
**Fig. 2:** Paleogeography map for 90-80Ma. Uplifted continental masses and shallow marine platforms are from Blakey (2008). Colored outlines represent plate boundaries reconstructed using Gplate software and database (Mueller et al., 2008). The names of the major paleogeographic units are from the Paleomap Project (Scotese n.d.). The three white circles surrounding the study area in the lower panel (Middle Eocene) indicate other existing sections with observation and description of PETM marker beds. From left to right, these are the sections of Torengly in Turkmenistan (Gavrilov et al., 2003), Aktumsuk in the Aral region of Uzbekistan (Bolle et al., 2000), and Kurpai in Tajikistan (Gavrilov et al., 2003).

**Fig. 3:** Upper Cretaceous-Paleogene stratigraphy of the western Tajik Depression correlated with formation nomenclature in the region (Amu Darya Basin, Turkmenistan, Tajikistan, and Central Asia (after Bosboom et al, 2017; Burtman, 2000; Chapman et al., 2019; Hosseinyar et al., 2019; Klett and Steinshouer, 2006; Klocke et al., 2017; Shaiakubov et al. 1980) and the lithostratigraphy of the studied section.

**Fig. 4:** Sedimentological section of the Upper Cretaceous succession in the Aktash area together with field record of sedimentological observations. A) Field photographs showing the possible Cenomanian/Turonian boundary; B) Field photographs showing the surface of the upper Cenomanian sequence boundary (karst); C) The perforation surface of the Cenomanian - Turonian sequence boundary; D) Field photo showing general view of the Campanian-Maastrichtian boundary, the position of KTP hiatus interval, and base of early Danian Bukhara Formation; E) Large scale gastropod (hardground of uppermost Cenomanian platform); F) Bioclastic interval between uppermost Coniacian and black shales; G) Large ammonite in shelf shale below OKB120. H) Bioclastic (molluscs) storm bed (OKB47); I) Thin tempestites with small-scale, hummocky cross-bedding (near OKB30).

**Fig. 5:** Detailed sedimentological section through the Paleocene Bukhara Formation. The field image shows the basal part of the Bukhara Formation with indeterminate foraminifera (OKB11), Nautilids (OKB10), and some weak symmetrical wavy ripples (OKB9).

**Fig. 6:** Detailed sedimentological section of the Paleocene-Eocene interval above Bukhara, showing the Alai and Suzak formations in the field and the transition to the Rotliegend Molasse. The numbers from 1 to 6 from represent the TOC-rich interval of the PETM.

**Fig. 7:** lithostratigraphic representation of the proposed age model constructed in the current study based on $^{87}$Sr/$^{86}$Sr, calcareous nannofossils, and planktic foraminifera.

**Fig. 8:** Intersection between the best-fit line of the marine $^{87}$Sr/$^{86}$Sr isotope curve (LOWESS version 3, (McArthur et al., 2001) and $^{87}$Sr/$^{86}$Sr ratios measured in samples from Aktash. The ages are calibrated according to Gradstien (2004, 2020). The red and blue lines delimit the 95% confidence interval.

**Fig. 9:** Correlation plot of the Aktash section isotope curve and the published global carbon isotope datasets for the Upper Cretaceous. 1) Shahneshin section, Iran, central Zagros (Razmjooei et al., 2020), 2) Gubbio composite section, Italy (Sabatino et al., 2018; Sprovieri et al., 2013; Thibault et al., 2016; Voigt et al., 2010), 3) English Cretaceous reference curve (Jarvis et al., 2006) and correlation with the 2012 Geologic Time Scale carbon isotope compilation. Middle Maastrichtian
event (MMN), Campanian-Maastrichtian boundary event (CMBE), Late Campanian event (LCE), Med Campanian event (MCD), Santonian Campanian Boundary event (SMCE), Late Turonian event (LTE), Oceanic anoxic event (OAE2)

**Fig. 10:** Correlation plot of the Aktash section isotope curve and published global carbon isotope records through the Paleogene (data compilation after GTS 2012; Westerhold., 2008; Barnet et al., 2019; Anagnostou et al., 2020).

**Fig. 11:** Long and short-term transgression/regression cycles calculated in the Aktash section correlated with the global sea level curve (modified after Miller et al., 2005) along with the paleogeographic map through the time interval from the upper Cenomanian to upper Eocene (Scotese et al., 2013a, 2013b)

**Table title:**

**Table 1:** $^{87}$Sr/$^{86}$Sr ratios of mollusc samples from Aktash (see stratigraphic position Fig.8). The coloring of the cells indicates whether the numerical age calibration of a given isotope ratio yields an age that is too young (green), too old (orange), or possible (gray) concerning the stratigraphic position and nannofossil content. The plus-minus sign indicates the uncertainty associated with age calibration using the Lowess model.

<table><caption>Table 1:</caption><thead><tr><th>Sample No</th><th><sup>87</sup>Sr/<sup>86</sup>Sr</th><th>Age1</th><th>Age 2</th><th>Age 3</th><th>Age 4</th></tr></thead><tbody><tr><td>OKA18</td><td>0.707804283</td><td>34.35±0.2</td><td></td><td></td><td></td></tr><tr><td>OKA14</td><td>0.707727239</td><td>38.45-40.10-41.70</td><td>47.8</td><td>52.82</td><td></td></tr><tr><td>OKA 6</td><td>0.707711821</td><td>48.5</td><td>52.25</td><td></td><td></td></tr></tbody></table>
<table><tr><td>OKA 5</td><td>0.707713381</td><td>48.4</td><td>51.35</td><td></td><td></td></tr><tr><td>OKA 4</td><td>0.7077235</td><td>38.75/39.00-41.4/41.5</td><td>48.00</td><td>52.95</td><td></td></tr><tr><td>OKA 2</td><td>0.707787934</td><td>34.75</td><td>57.9</td><td></td><td></td></tr><tr><td>OK 109</td><td>0.707754547</td><td>36.80</td><td>42.6</td><td>46.45</td><td>54.82</td></tr><tr><td>OK 9</td><td>0.707812942</td><td>34.175</td><td>62.25±1.9</td><td>68.1±0.3</td><td></td></tr><tr><td>OKB 48</td><td>0.707458502</td><td>84.30±0.3 (model A)</td><td></td><td></td><td></td></tr><tr><td>OKB 50</td><td>0.707486029</td><td>82.25±0.3 (model B)</td><td></td><td></td><td></td></tr><tr><td>OKB 57</td><td>0.707457732</td><td>84.10±0.3 (model B)</td><td></td><td></td><td></td></tr><tr><td>OKB 112</td><td>0.707342471</td><td>89±0.2</td><td>93.1±0.2</td><td></td><td></td></tr><tr><td>OKC 1</td><td>0.707406746</td><td>86.95</td><td>95.50</td><td></td><td></td></tr></table>

Plates

**Plate 1:** Selected calcareous nannofossil taxa from upper Cretaceous interval of Aktash section (Uzbekistan), scale bar =5 µm. 1- *Ascidian spicule*. 2- *A. cymbiformis* var.NT. 3- *B. matalosa*. 4- *B. parca* parca. 5-*B. signata*. 6-*B. constans*. 7-*Biscutum* sp. 8- *C. ehrenbergii*. 9- *C. cf. C. sculptus*. 10- *E. digitatus*. 11-- *E. eximius*. 12- *E. floralis*. 13- *E. moratus*. 14- *E. octopetalis*. 15- *E. octopetalis*. 16-*E. rarus*. 17- *G. coxalliae*. 18- *G. segmentatum*. 19- *G. coronadventis*. 20- *H. trabeculatus*. 21- *H. compactus*. 22- *L. grillii*. 23- *L. armilla*. 24- *M. cubiformis*. 25- *M. staurophora*. 26- *N. dislocates*. 27- *P. cretacea*. 28- *Q. gartneri*. 29- *R. anthophorus*. 30- *R. levis*. 31- *R. splendens*. 32- *T. orionatus*. 33- *Z. bicrescenticus*. 34- *Z. biperforatus*. 35- *Z. noeliae*.
**Plate 2:** Selected planktic foraminifera taxa from upper Paleocene/Eocene interval of Aktash section (Uzbekistan), scale bar =100 µm. (1a, b) *Acarinina sibaiyaensis*, (2a, b, c, d) *Acarinina esnehensis*, (3) *Acarinina angulosa*, (4a, b) *Acarinina pentacamerata*, (5) *Acarinina aspensis*, (6) *Acarinina pseudotopilensis*, (7) *Acarinina esnaensis*, (8) *Chiloguembelina trindidadensis*, (9) *Morozovella formosa*, (10) *Morozovella crater*, (11) *Premurica lozanio*, (12) *Subbotina patagonica*, (13) *Subbotina yeguaensis*, (14) *Subbotin roesnaensis*.

**Plate 3:**

Transmitted light images compared to cathodoluminescence properties of different paragenetic phases of the molluscan shells (bivalves and gastropods), to examine its suitability of for the strontium isotope analysis. Photos (1 – 6) represent the accepted samples for strontium isotope analysis based on the original calcite shells from orange to dark orange. Photos (7-10) represent the rejected samples for strontium isotope analysis due to its late diagenetic features (Recrystallization).
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**Authorship contribution statements**

**Hassan Khozyem:** Fieldwork, data collection, analyses, illustration and interpretation, writing; **Thierry Adatte:** Fieldwork, analyses, interpretation; **Marie-Françoise Brunet:** Funding acquisition and project conceptualization; **Massimo Chiaradia:** Strontium analyses and interpretation; **Gerta Keller:** Foraminifera analysis and interpretations; **Nicolas Thibault:** Nannofossil analyses and interpretation; **Irina Sidorova:** Field logistics; **Bakhtiar Nurtaev:** Local supervision and support; **Jorge Spangenberg:** Geochemical analyses and interpretation; **Sébastien Castelltort:** Funding, field work, data collection, interpretation, principal investigator and overall supervision.

We the undersigned declare that this manuscript is original, has not been published before and is not
currently being considered for publication elsewhere.

We confirm that the manuscript has been read and approved by all named authors and that there are no
other persons who satisfied the criteria for authorship but are not listed. We further confirm that the order
of authors listed in the manuscript has been approved by all of us.

We understand that the Corresponding Author is the sole contact for the Editorial process. He/she is
responsible for communicating with the other authors about progress, submissions of revisions and final
approval of proofs.

Signed by the corresponding author:

<figure><img src="image_64.png" /><figcaption>Hassan M. Khozyem</figcaption></figure>

**Declaration of interests**

[x] The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

[ ] The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
<figure><img src="image_65.png" /></figure>