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Article

Shallow-Marine Late Thanetian Lockhart Limestone from the Hazara Basin, Pakistan: Insights into Foraminiferal Biostratigraphy and Microfacies Analysis

by
Muneeb Ahmad
1,
Urooba Farman Tanoli
1,
Muhammad Umar
1,
Tofeeq Ahmad
1,2,3 and
Alaa Ahmed
2,3,*
1
Department of Earth Sciences, The University of Haripur, Haripur 22620, Pakistan
2
Geosciences Department, United Arab Emirates University, Al Ain 15551, United Arab Emirates
3
National Water and Energy Center, United Arab Emirates University, Al Ain 15551, United Arab Emirates
*
Author to whom correspondence should be addressed.
Geosciences 2025, 15(2), 63; https://doi.org/10.3390/geosciences15020063
Submission received: 31 December 2024 / Revised: 8 February 2025 / Accepted: 10 February 2025 / Published: 13 February 2025
(This article belongs to the Section Sedimentology, Stratigraphy and Palaeontology)
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Abstract

:
The Palaeocene Lockhart Formation, a carbonate-rich succession abundant in Larger Benthic Foraminifera, represents a significant potential hydrocarbon reservoir extending throughout the Kohat, Potwar and Hazara basins of Pakistan. This study examines two stratigraphic sections of the Lockhart Formation in the Hazara Basin—Bagran and Karhaki—providing crucial insights into its biostratigraphy and microfacies analysis. The formation comprises medium- to fine-grained limestone with shale intercalations, exhibiting argillaceous to compacted textures. Biostratigraphic analysis revealed a diverse assemblage of Larger Benthic Foraminifera, with 23 species identified across 9 genera, including Miscellanea miscella, Lockhartia haimei, Lockhartia conditi and Ranikothalia sindensis. These fossils indicate deposition within Shallow Benthic Zone (SBZ) 4 during the Late Thanetian, suggesting a dynamic palaeoenvironment. Seven distinct microfacies types were identified: bioclastic mudstone, mixed bioclastic wackestone, miliolidal bioclastic wackestone, foraminiferal wackestone–packstone, foraminiferal wackestone, foraminiferal packstone and bioclastic foraminiferal packstone. These microfacies indicate varied depositional settings, from shallow subtidal and lagoonal to shallow restricted and open marine environments, spanning inner ramp to distal mid-ramp conditions. This research advances our understanding of Late Thanetian depositional environments within the Lockhart Limestone, with implications for regional sedimentology, palaeogeographic reconstruction and reservoir characterisation.

1. Introduction

During the Palaeocene Epoch, significant basins of Pakistan—including the Upper Indus Basin (UIB), Lower Indus Basin (LIB) and Balochistan Basin (BB)—accumulated sedimentary sequences predominantly comprising limestones, marls, shales, sandstones and conglomerates. These deposits are entirely marine in origin, with the exception of the fluviatile Bara Formation in the LIB [1]. The UIB, encompassing the Kohat, Potwar and Hazara basins, contains well-preserved Palaeocene successions, including the Hangu Formation, Lockhart Limestone and Patala Formation [2].
The Palaeocene rocks of these basins have been extensively studied by numerous researchers [3,4,5]. The Lockhart Limestone, in particular, has attracted considerable attention and has undergone several nomenclatural revisions. Ref. [6] initially described these rocks as the base of the “Hill Limestone” formation. Subsequently, ref. [7] introduced the term “Nummulitic series”, whilst [8] later modified this to “Khairabad Limestone”. Ref. [9] proposed the name “Tarkhobi Limestone”, and [10] later designated it the “Mari Limestone”. To address the confusion arising from these various nomenclatures, the Stratigraphic Committee of Pakistan formally standardised the name as “Lockhart Limestone”, with its type locality designated at Fort Lockhart [1].
In the Hazara Basin (HB), the Lockhart Limestone is extensively developed, varying from pale to dark grey in colour and containing shale interbeds [11]. Whilst the formation averages 60 m in thickness throughout the Kohat and Potwar basins, it thickens northward into the UIB and HB, reaching between 80 and 242 m [10,11]. The formation exhibits a conformable upper contact with the Patala Formation and an unconformable lower contact with the Kawagarh Formation [12]. Previous studies have focused primarily on the formation’s general lithofacies, depositional environments and palaeontological aspects [1,5,10,13,14,15,16,17]. The Lockhart Limestone contains a diverse fossil assemblage, including algae, small corals, echinoids, molluscs and foraminifera. Notable foraminiferal genera include Lockhartia, Ranikothalia, Miscellanea, Discocyclina, Alveolina and Rotalia [5,18,19]. Age-diagnostic fossils have confirmed a Palaeocene age for the formation [4,5,20].
Despite its economic significance, the Palaeocene succession in the HB remains poorly documented. The region holds considerable potential for hydrocarbon exploration, particularly within the Lockhart Limestone, which is known for its reservoir potential in other basins of Pakistan. Dense vegetation cover, complex structural geology and limited accessibility have hindered detailed investigation, with previous studies largely restricted to broad-scale mapping and basic lithological and palaeontological assessments of the Palaeocene succession [1,5,10,13,21]. This research aims to provide a comprehensive petrographic analysis of the Lockhart Limestone, focusing on its biostratigraphic analysis, microfacies interpretation, depositional environments and age determination. By integrating these aspects, the study intends to establish a stratigraphic framework that enables both local and regional correlation across different regions of the Neo-Tethys, enhancing understanding of the Late Palaeocene carbonate systems in the Hazara Basin.

2. Tectonic Framework and Regional Stratigraphy

The Hazara Basin (HB), situated within the Hazara Fold and Thrust Belt of the Lesser Himalaya, has been the subject of extensive research owing to its complex tectonic history. Located within the active Himalayan belt, the region has undergone significant deformation. The east–west-trending basin is bounded by the Main Boundary Thrust (MBT) to the south and the Panjal Thrust (PT) to the north (Figure 1). The ongoing Indian–Eurasian plate convergence generates southward-directed stresses, which are accommodated by various shear zones along the Himalayan Front. The MBT is primarily responsible for deformation in southern Hazara (Lesser Himalaya), where it has thrust Precambrian to Cenozoic sequences northward over younger strata [22].
The southern Hazara comprises a broad band of foreland sedimentary successions enclosed by metamorphosed hinterland to the north [23]. The area exhibits intense deformation, characterised by overturned folds and thrust faults. The southeasterly dipping exposed strata reflect the compressional forces generated during the Indian–Eurasian plate collision. The HB preserves evidence of diverse depositional and tectonic events. Numerous researchers have investigated its stratigraphic framework [1,10,12,23,24,25,26,27,28,29,30]. Notably, ref. [12] documented environments ranging from deep marine to fluvial settings, based on parameters such as lithological composition, sedimentary structures, fossil assemblages and geochemical indicators, including trace element analysis and redox-sensitive proxies. Whilst the basin contains strata from Precambrian to Holocene age, the study area exposes only Late Jurassic to Middle Eocene sequences (Figure 2).
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Figure 1. Generalised map of Pakistan, highlighting significant tectonic events and the study area, after [31].
Figure 1. Generalised map of Pakistan, highlighting significant tectonic events and the study area, after [31].
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3. Study Area

The study area lies within the Hazara Range of the HB, near Haripur, Pakistan (Figure 1). The Hazara Range, situated in the northeastern Himalayan foreland, formed during the Eocene as a result of Indian–Eurasian plate convergence [32]. The HB preserves a well-exposed Palaeocene succession comprising, in ascending order, the Hangu Formation, Lockhart Formation and Patala Formation [5,12,21,23,33]. The Lockhart Limestone developed extensively throughout the Haripur–Abbottabad depositional province and adjacent areas of the Hazara Basin, where it predominantly comprises limestone with shale and marl intercalations.
For this study, two lithostratigraphic sections were selected for detailed petrographic and palaeontological analysis: the Bagran and Karhaki sections. The Bagran section (33°48′22″ N, 73°02′34″ E) is exposed along the Grand Trunk Road at Jabbri, approximately 13 km northeast of Khanpur city. Here, the Palaeogene succession includes the Lockhart Limestone, Patala Formation and Margala Hill Limestone. The Lockhart Limestone maintains a conformable upper contact with the Patala Formation, whilst its lower contact remains unexposed (Figure 3A). The limestone exhibits uniform, medium to thick bedding throughout, with thin intercalated shale layers. The measured thickness of the formation at this locality is 54 m (Figure 4).
The Karhaki section (33°56′17″ N, 73°09′17″ E), located along the Lora–Jabbri Road, about 22 km east of Haripur city, exposes a well-preserved Palaeogene sequence comprising the Late Palaeocene Lockhart Limestone, Latest Palaeocene–Early Eocene Patala Formation and Early Eocene Margala Hill Limestone. At Bagran, the lower contact of the Lockhart Limestone is not exposed, whilst its upper boundary corresponds to the Patala Formation (Figure 3B). At this locality, the Lockhart Limestone consists of thinly to thickly bedded fossiliferous argillaceous limestone with thin to thick shale and marl intercalations. The formation attains a thickness of 96.6 m (Figure 5).

4. Materials and Methods

A total of forty-two samples were collected for thin section preparation and petrographic analysis: twenty-two from the Bagran section and twenty from the Karhaki section. Thin sections were prepared at the Pearl Minerals prospecting facility in Haripur, Pakistan, and analysed using an Optika B-380 petrographic microscope, manufactured by OPTIKA Srl. from Ponteranica, Italy, at the Department of Earth Sciences, University of Haripur. Microphotographs of significant features were captured using an Optika Proview digital camera mounted on the microscope. Limestone classification followed Dunham’s [34] scheme, based on petrographic analysis of orthochem and allochem percentages. The microfacies analysis was based on visual estimation of micrite, cement, allochems and depositional texture based on Flügel’s [35] classification. Allochem types were subsequently identified to determine depositional sub-environments.
Age-diagnostic Larger Benthic Foraminifera (LBF) species were identified using the established taxonomic literature [4,36,37,38,39,40,41,42,43,44,45,46]. A biozonation scheme was developed using key species and assemblages, with ages assigned through the correlation with zonation system established by Serra-Kiel et al. [42]. Depositional environment interpretations were refined through comparison with previous studies [5,14,20,21,47,48,49,50]. Maps were generated and digitised using ArcGIS 10.5 (ESRI), whilst CorelDRAW X7 (developed by Alludo, based in Ottawa, Canada) was employed to create lithologic logs, microfacies logs, biostratigraphic logs, correlation logs and depositional models for the Lockhart Limestone.

5. Results

5.1. Foraminiferal Biostratigraphy

The biostratigraphic study of the Lockhart Limestone utilised 42 samples for detailed petrography, revealing a significant assemblage of LBF. Twenty-three species of LBF were identified, belonging to the genera Lockhartia, Assilina, Miscellanea, Operculina, Ranikothalia, Orbitoclypeus, Discocyclina, Lakadongia and Idalina (Figure 6A–P). The stratigraphic distributions, taxonomic classifications and determined ages of these benthic foraminiferal species are shown in Figure 4 and Figure 5, whilst detailed microphotographs of the foraminiferal species identified in the Lockhart Limestone are described below.

5.2. Age Determination

The Lockhart Limestone in the studied sections contains numerous age-diagnostic fossils, including Miscellanea miscella, Assilina subspinosa, Lockhartia conditi, Lockhartia tipperi, Lockhartia haimei, Discocyclina ranikotensis, Ranikothalia sindensis, Ranikothalia sahnii and Assilina yvettae. This foraminiferal assemblage has also been documented by [10,17,18,20,50,51]. Hanif et al. [20] assigned a Lower Thanetian age to the Lockhart Limestone in the Upper Indus Basin based on larger foraminifera, specifically Miscellanea spp. and Ranikothalia spp., which dominate the assemblages and indicate Shallow Benthic Zones (SBZs) 4 and 5. Additional species, such as Lockhartia conditi, Lockhartia tipperi, Discocyclina ranikotensis, Alveolina sp., and Assilina sp., further support the biostratigraphic age determination. Whilst Sameeni et al. [17] proposed a Late Thanetian (SBZ-4) age for the formation in the HB based on the presence of age-diagnostic species such as Miscellanea miscella and Lockhartia haimei, which were consistently recorded throughout the formation, by correlating findings from the current study with previous research, we conclude that these species are restricted to SBZ-4 in the HB. The co-occurrence of L. haimei with M. miscella, R. sindensis, A. subspinosa and D. ranikotensis confirms an SBZ-4 (Late Thanetian) age for the Lockhart Limestone in this study (Figure 7).

5.3. Microfacies Analysis

Field investigations provided the basis for lithofacies description, whilst microscopic examination formed the foundation for carbonate rock microfacies characterisation. The fossil assemblage predominantly comprised Lockhartia spp., Ranikothalia spp., Assilina spp., Miliolid spp., Discocyclina spp., Miscellanea spp., Operculina spp. and algae. The microfacies of the Lockhart Limestone were classified according to Dunham’s [34] limestone classification scheme. Four microfacies were identified and interpreted in the Bagran section (Figure 8A–H) and three in the Karhaki section (Figure 9A–F).

5.3.1. Microfacies of the Lockhart Limestone (Bagran Section)

  • Bioclastic Mudstone Microfacies (MFLLB I)
Description: This microfacies comprises dark grey, thin- to medium-bedded limestone with thin shale intercalations. BMMF is 24% of the total thickness and is commonly observed in four thin sections (LLB-5 to LLB-7 and LLB-17), twice, at the 4 m and 45 m intervals (Figure 4). Characterised by a dominant mudstone texture, the micrite matrix accounts for 93% of the rock, with allochems representing the remaining 7%. These allochems include smaller benthic foraminifers, ostracods (which are also known to occur in freshwater, hypersaline and normal salinity environments), microbial structures and quartz grains (Figure 8A,B).
Interpretation: This microfacies represents a non-burrowed lime mudstone formed in a peritidal zone, consistent with Flügel’s RMF-19 classification. The low biota diversity can be attributed to deviations from normal salinity, high nutrients, potentially leading to eutrophic conditions, and/or reduced light availability, all of which likely suppressed the abundance of diverse carbonate-producing organisms and favoured microbial activity [40,52].
  • Mixed Bioclastic Wackestone Microfacies (MFLLB II)
Description: Characterised by light greyish fine-grained, thick-bedded, hard and fractured limestone units, this microfacies includes minor shale intercalations with prominent bedding. MFFLLB II comprises 42.5% of the total thickness and is observed in eight thin sections (LLB-11 to LLB-13, LLB-15 to LLB-16 and LLB-18 to LLB-20), thrice at the 26 m, 41 m and 47 m intervals (Figure 4). The composition features an 80% micrite matrix, with bioclasts comprising 10% of the rock. Biotic components include benthic foraminifera such as Miscellanea, Lockhartia, miliolids, and Textularia (6%), along with subordinate dasycladale algae (2%) and gastropods (2%) (Figure 8C,D).
Interpretation: The low diversity of biota, dominance of micrite matrix, and presence of small benthic foraminifera (miliolids and Textularia) indicate mesotrophic, low-energy conditions typical of a restricted lagoonal environment within the inner ramp. The occasional presence of symbiont-bearing large rotaliids (Miscellanea and Lockhartia) suggests brief influxes of organisms from more open areas within the ramp system, aligning with Flügel’s [35] RMF-20 classification.
  • Miliolidal Bioclastic Wackestone Microfacies (MFLLB III)
Description: This microfacies consists of dark greyish, thick-bedded, hard limestone beds with calcite veins. Shale intercalations are present at the base, with a compacted top and beds approximately 20–30 cm thick and exhibiting prominent bedding. MFLLB III is 7.5% of the total thickness and is observed in four thin sections (LLB-1 to LLB-4) at the 0 m to 4 m interval (Figure 4). The composition includes a 71% micrite matrix with occasional spar, miliolids (13%), bioclasts (11%) and minor components of algae, smaller benthic foraminifera and reworked grains (Figure 8E,F).
Interpretation: The low to moderate diversity of miliolids and smaller benthic foraminifera suggests mesotrophic, low- to moderate-energy conditions, indicating deposition in a shallow, restricted inner ramp setting, corresponding to Flügel’s [35] RMF-16.
  • Foraminiferal Wackestone–Packstone Microfacies (MFLLB IV)
Description: Featuring light greyish, thick- to medium-bedded, hard and fractured limestone with occasional calcite veins, this microfacies shows a complex composition. MFLLB IV is 26% of the total thickness and is observed in four thin sections (LLB-08 to LLB-10 and LLB-14), twice, at the 14 m and 38 m intervals (Figure 4). The matrix comprises 49.5% micrite with rare spar, planktonic foraminifera (20%), and benthic foraminifera including Lockhartia, Miscellanea, miliolids and Bigenerina (8%). Additional components include bioclasts (12.5%), subordinate dasycladale algae (6%), gastropods (2%) and ostracods (3%) (Figure 8G,H).
Interpretation: The abundance of foraminifera and bioclasts indicates high-energy conditions typical of foreshore depositional environments, corresponding to Flügel’s RMF-27 and interpreted as a fore-shoal setting within a middle ramp environment [53].

5.3.2. Microfacies of Lockhart Limestone (Karhaki Section)

  • Foraminiferal Wackestone Microfacies (MFLLK I)
Description: This microfacies comprises brownish-coloured fossiliferous limestone units with intercalated shale. The stratigraphic profile exhibits a lower part of compacted, thick-bedded limestone, a middle section dominated by shale with thin-bedded limestone, and an upper portion of sheared, weathered limestone with no obvious bedding. MFLLK I comprises 47.5% of the total thickness of the formation and is observed in eleven thin sections (LLK-02 to LLK-05, LLK-07 and LLK-17 to LLK-22, thrice, at the 4 m, 34 m, and 82 m intervals (Figure 5). Large benthic foraminifers occupy 28% of the rock, including diverse genera such as Miscellanea, Lockhartia, Discocyclina, Ranikothalia, Assilina, Operculina, and Nummulites. The micrite matrix accounts for 60%, with occasional spar complemented by 12% bioclasts (Figure 9A,B).
Interpretation: The high diversity of intermixed biota from the inner and middle ramps, coupled with rare dasycladale algae, suggests moderate-energy conditions and deposition in an open inner ramp environment, closely resembling Flügel’s [35] RMF-13 classification.
  • Foraminiferal Wackestone–Packstone Microfacies (MFLLK II)
Description: Characterised by brownish-coloured fossiliferous limestone in the lower part and argillaceous limestone beds with shale intercalations in the upper part, this microfacies presents a complex depositional environment. MFLLK II comprises 14.5% of the total thickness of the formation and is observed in four thin sections (LLK-06 and LLK-13 to LLK-15), twice, at the 29 m and 66 m intervals (Figure 5). Allochems constitute 56% of the microfacies, dominated by larger benthic foraminifera including Miscellanea, Lockhartia, Discocyclina, Assilina and Operculina. Bioclasts comprise 14% of the composition, with the matrix transitioning from 18% micrite in the lower part to 12% dolomite in the upper section (Figure 9C,D).
Interpretation: The discoidal larger benthic foraminifera indicate low-energy environments. The presence of M. miscella suggests shallow, warm waters [54], whilst Discocyclina hints at deep marine conditions. Operculina’s presence indicates lower mid-ramp settings between fair weather wave base (FWWB) and storm wave base (SWB) [55]. As a result, the occurrence of deep marine larger benthic foraminifera alongside shallow benthic foraminifera within a wackestone–packstone texture indicates proximal to middle mid-ramp settings.
  • Bioclastic Foraminiferal Packstone Microfacies (MFLLK III)
Description: This microfacies features brownish-grey, highly fossiliferous limestone with intercalated shale. The stratigraphic profile demonstrates a lower part with thin-bedded limestone and shale, a middle section of thick-bedded, highly fossiliferous limestone with minor shale, and an upper portion of fractured argillaceous limestone without distinct bedding. MFLLK III comprises 38% of the total thickness of the formation and is observed in seven thin sections (LLK-01, LLK-08 to LLK-12 and LLK-16), thrice, at the 0 m, 40 m and 75 m intervals (Figure 5). Allochems constitute 80% of the microfacies, with 20% bioclasts which are predominantly larger benthic foraminifera including Lockhartia, Miscellanea, Discocyclina, Ranikothalia, Assilina and Operculina. The matrix, mainly micrite, constitutes 20% of this submicrofacies in the lower part, whilst it transitions into the dolomite (6%) in the upper part (Figure 9E,F).
Interpretation: The presence of large, flattened Assilina species indicates deep oligotrophic high-energy environments [56,57], whilst Discocyclina and Operculina suggest low-energy and low-light environments [58]. The overall characteristics point to a shallow, open marine, high-energy depositional setting within middle–distal mid-ramp settings, effectively forming a foraminiferal shoal.

5.4. Depositional Environments

Based on the detailed microfacies analysis and interpretations above, the Lockhart Limestone in both the Bagran and Karhaki sections was deposited in a ramp-dominated depositional system, as evidenced by the absence of framework builders such as coralline algae or reef-building organisms. Detailed petrographic analysis revealed four depositional settings in the inner ramp and two major settings in the middle ramp (Figure 10, Table 1). The Lockhart Limestone at the Karhaki section was deposited in relatively deeper parts of the basin compared to the Bagran section.

6. Discussion

This research demonstrates that the Lockhart Limestone is extensively exposed throughout the HB in Pakistan. The accumulation and distribution of LBF indicate a cyclical pattern within the carbonate platform. The Lockhart Limestone in the study area is notably fossiliferous, containing a diverse assemblage of abundant and well-preserved LBF, which typically inhabit shallow marine environments [59]. The age-diagnostic fossils identified in the studied sections include Lockhartia tipperi, Miscellanea miscella, Lockhartia haimei, Lockhartia conditi, Ranikothalia sindensis, Assilina subspinosa, Discocyclina ranikotensis, Ranikothalia sahnii and Assilina yvettae. The presence of these fossils indicates a Late Thanetian SBZ-4 age for the Lockhart Limestone in the studied sections.

6.1. Local Correlation

Palaeocene carbonates across Pakistan are characteristically rich in LBF, making them chronostratigraphically significant. Various researchers have established local biozonations using the predefined shallow benthic zonation of [42]. This study elaborates the local correlations among Palaeocene carbonates exposed at different localities in Pakistan, based on the distribution patterns of age-diagnostic larger benthic foraminifera, utilising findings from several authors (Figure 11).
Based on the occurrence of LBF species, including Lockhartia haimei, Miscellanea miscella, Lockhartia conditi, Lockhartia tipperi, Ranikothalia sahnii, Ranikothalia sindensis, Operculina patalensis, Operculina salsa, Discocyclina ranikotensis, Assilina subspinosa, miliolids and Bigenerina, refs. [5,17] conducted biostratigraphic analyses of the Lockhart Limestone in the HB and assigned a Thanetian age (Late Palaeocene) to the formation. In the Azad Kashmir region, ref. [60] determined a Late Palaeocene age for the Lockhart Limestone based on the presence of LBF belonging to SBZ-4. In the Western Salt Range (UIB), refs. [20,40] suggested deposition during SBZ-3, based on the presence of benthic foraminifera species including Miscellanea yvettae, Miscellanea juliettae, Lockhartia haimei, Lockhartia tipperi, Lockhartia conditi, Ranikothalia sahnii, Ranikothalia sindensis, Fallotella alavensis, Coskinon rajkae, Laffitteina bibensis and Bolkarina aksarayi. The authors of [46] proposed a Late Thanetian (SBZ-4) age for the Lockhart Limestone in the Nammal Gorge section of the Western Salt Range.
In the Sulaiman Fold–Thrust Belt (LIB), refs. [40,61] confirmed the equivalence of the Late Palaeocene Dungan Formation to the Lockhart Limestone in the UIB, establishing the boundary between SBZ-3 and SBZ-4 using the first documented occurrence of Daviesina langhami, Miscellanea miscella and Discocyclina ranikotensis. Based on these findings, the Lockhart Limestone in the HB and UIB, and the Dungan Formation in the LIB are age-equivalent, spanning SBZ-3 to SBZ-4. According to [40], SBZ-3 is characterised by the presence of Vania anatolica, Miscellanea juliettae, Coskinon rajkae and Fallotella alavensis, whilst the boundary between SBZ-3 and SBZ-4 is marked by the first occurrence of Discocyclina ranikotensis, Daviesina langhami and Miscellanea miscella. Ref. [62] identified the first appearance of species from the genus Alveolina as marking the base of the Early Eocene (SBZ-5 and SBZ-6).

6.2. Regional Correlation

During the Palaeogene period, shallow-marine carbonate deposition was widespread across much of the Neo-Tethys region, preserving an extensive record of LBF. Researchers have identified age-diagnostic species from various regions of the Neo-Tethys, including R. sindensis, M. juliettae, L. haimei, M. miscella, D. ranikotensis and Kathina sp. These species have been utilised by numerous researchers to establish correlations between different units within the Neo-Tethys region [4,38,56,62,63,64,65,66,67]. This section will establish correlations between Palaeocene carbonate units across different regions of the Neo-Tethys, including present-day Pakistan, China, Iran and Saudi Arabia, based on documented age-diagnostic LBF.
The lower part of the Zongpu Formation in the Gamba Basin and the middle part of the Zhepure Formation in the Tingri Basin primarily comprise limestones containing abundant Late Palaeocene LBF. These include Lockhartia roeae, Lockhartia haimei, Discocyclina tenuis, Keramosphaerinopsis haydeni and Daviesina khatiyani of SBZ-3, and Aberisphaera gambanica, Rotalia cf. newboldi, Lockhartia conditi, Ranikothalia sindensis, Kathina nammalensis, Lakadongia and Daviesina langhami of SBZ-4 [68].
In the Kopet Dagh Basin, the Pestehligh Formation lies conformably on the Chehel-Kaman Formation and is overlain by the Khangiran Formation. The Chehel-Kaman Formation primarily comprises limestone and dolomite with subordinate shale and marls [66]. It contains a diverse assemblage of LBF, and the formation is dated to the Late Palaeocene (SBZ-3 to SBZ-4) based on the presence of diagnostic taxa, including Miscellanea juliettae, Lockhartia sp., Lockhartia haimei, Ranikothalia sindensis, Miscellanea miscella and Discocyclina sp.
In the Lorestan Basin, the Taleh Zang lime formation conformably overlies the Amiran Formation and has a conformable upper contact with the Kashkan Formation. The Taleh Zang lime formation predominantly comprises limestone with subordinate sandstone, and its lower portion contains a diverse assemblage of age-diagnostic benthic foraminifera, including Miscellanea miscella, Kathina sp., Glomalveolina primaeva, Distichoplax biserialis and Ranikothalia sindensis [69]. Based on these fossils, the formation has been dated to the Late Palaeocene (Thanetian).
The Rub al Khali Basin in southeast Saudi Arabia is characterised by the Umm er Radhuma Formation, a Palaeogene unit spanning the early Palaeocene to Early Eocene. The formation primarily comprises carbonates and has a conformable lower contact with the Cretaceous Aruma Formation [70,71]. It contains age-diagnostic fossils including Loxostoma applinae, Lockhartia tipperi, Miscellanea miscella, Lockhartia conditi, Siphogenerina eleganta and Bulimina semicostata, which have been studied for biostratigraphic dating. Based on the foraminiferal assemblages, the formation has been divided into a Late Palaeocene lower portion and an Early Eocene upper portion.
In northern Iraq, the Sinjar Formation conformably overlies the Kolosh Formation and has a conformable upper contact with the Gercus Formation. The Sinjar Formation has yielded Late Palaeocene to Early Eocene LBF, including Cuvillierina vallensis, Rotalia trochidiformis, Cibicides nammalensis, Miscellanea miscella, Idalina sinjarica, Discocyclina varians, Nummulites globulus, Spherogypsina globula, Cuvillierina sireli, Alveolina globosa, Orbitolites sp., Somalina sp., Ovulites sp., Assilina sp. and Cribogoesella sp. [72]. Based on these foraminiferal species, the lower portion of the formation has been assigned to the Late Palaeocene and the upper portion to the Early Eocene.

6.3. Depositional Settings

The Lockhart Limestone in the present study was deposited in inner–middle ramp settings of a distally steepened ramp, as evidenced by the gradual transition of facies and absence of reef barriers. Various researchers have studied the Lockhart Formation in the HB and proposed shallow-shelf (inner to outer shelf) carbonate environments, including [5] for the Jabbri section and [14] for the Touhidabad and Changlagali sections. Ref. [15] identified near-shore to middle-shelf settings for the Lockhart Limestone in the Shah Ala Ditta area, whilst [16] proposed fore-shoal to outer ramp settings in the Margala Hill Ranges (Figure 12).
In the Western Salt Range, the Lockhart Limestone accumulated in a carbonate ramp comprising three major depositional settings: the inner ramp lagoon, shoal and fore-shoal and open marine, as observed in the Dhok Kas, Nammal Gorge and Mari Indus (Kalabagh) sections [20]. Ref. [40] characterised the depositional environment of the Lockhart Limestone in two sections (Kotal Pass and Shakardara Well-1) as “Inner Ramp depositional setting”. Only the inner ramp facies of the present study show similarity to those previously documented in the UIB, suggesting that the Lockhart Limestone in the HB was deposited in deeper environments than in the UIB (Figure 13).
Chronologically, the Lockhart Formation in the UIB and HB correlates with part of the Dungan Formation in the Sulaiman Range [49]. The Dungan Formation in the Sulaiman Range comprises more than 90 percent planktonic foraminifera, indicating deposition in an open marine environment beyond the outer shelf [9,49,73]. In the Kirthar Range, the age-equivalent portion of the upper Ranikot Formation contains substantial planktonic foraminifera [47,48], indicating similar depositional conditions to the Sulaiman Range. The Lockhart Formation, Bagran section (this study), also contains planktonic foraminifera, albeit in lower proportions than the Dungan and Ranikot formations. Thus, we infer that the age-equivalent segments of the Dungan Formation and Ranikot Formation of the Indus Basin and HB were deposited in relatively deeper settings than the Lockhart Formation, likely bathyal environments, as indicated by smaller benthic foraminifera and high planktonic ratios [73].
Integration of our findings with published data indicates that the Lockhart Limestone in the HB and UIB was deposited in shallow carbonate platforms (ramp/shelf), with deeper deposition in the HB compared to the UIB. In the LIB, deposition occurred in deep marine and bathyal settings, as evidenced by high planktonic ratios. This variation in depositional environments likely reflects the morphological variation of the basin (carbonate platform) during the Palaeocene, which comprised a depositional high in the middle UIB surrounded by depositional lows in the north HB and south LIB (Figure 13).

7. Conclusions

This research investigated the sedimentology, biostratigraphy, depositional environments and diagenetic processes of the Lockhart Limestone in the eastern part of the HB. Two stratigraphic sections (Bagran and Karhaki) were systematically measured, sampled, documented and analysed for microfacies and fossil content. The main findings are as follows:
  • Petrographic analysis revealed seven distinct microfacies across both sections, characterised through visual estimation of micrite cement, allochems and depositional texture. These include bioclastic mudstone ((MFLLB I), mixed bioclastic wackestone (MFLLB II), miliolidal bioclastic wackestone (MFLLB III), foraminiferal wackestone–packstone (MFLLB IV), foraminiferal wackestone (MFLLK I), foraminiferal wackestone–packstone (MFLLK II) and bioclastic foraminiferal packstone (MFLLK III) microfacies.
  • The lithological characteristics, depositional texture, and allochem and orthochem components suggest deposition on a distally steepened carbonate ramp. The inner ramp is segregated into the shallowest subtidal, lagoonal, shallow restricted, and open inner ramp depositional settings characterised by the deposition of MFLLB I, MFLLB II, MFLLB III, and MFLLK I microfacies, respectively
  • The middle ramp consists of a proximal mid ramp, middle mid ramp and distal mid ramp, pervaded by MFLLB IV, MFLLK II and MFLLK III microfacies sequentially. The microfacies analysis indicates depositional environments ranging from proximal inner ramp to distal middle ramp within a distally steepened carbonate ramp.
  • The Lockhart Limestone is characterised by an abundance of Larger Benthic Foraminifera (LBF), which have been identified and reported up to the species level. Several age-diagnostic species were recognised, providing critical insights into the depositional age of the Lockhart Limestone. The index species include Miscellanea miscella, Lockhartia haimei, Ranikothalia sindensis, Discocyclina ranikotensis, Assilina subspinosa and Assilina yvettae. These species correspond to Shallow Benthic Zone SBZ-4, indicating a Late Thanetian age.
  • Future research should focus on conducting a comprehensive geochemical study to understand the region’s chemical characteristics. Detailed structural geological research must be carried out to examine the complex structural features of the area. Moreover, a thorough petrographic analysis of the formations near the study area should be performed to develop a better understanding of the geological formations in the Hazara region.

Author Contributions

Conceptualisation, M.A. and M.U.; methodology, M.A.; validation, M.U., T.A. and A.A.; investigation, M.A.; resources, M.A.; data curation, U.F.T.; writing—original draft preparation, M.A. and U.F.T.; writing—review and editing, U.F.T. and A.A.; visualisation, M.A. and U.F.T.; supervision, M.U. and T.A.; project administration, M.U. and T.A. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the United Arab Emirates University (funds no. 12S139 and 12S158).

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Acknowledgments

We extend our sincere gratitude to Azhar Khan for his invaluable assistance during the fieldwork. We also acknowledge the Department of Earth Sciences, University of Haripur for providing the laboratory facilities necessary for the petrographic studies. UAE University is also acknowledged to provide the required funding for research.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 2. Generalised stratigraphy of the study area in the Hazara Basin, Haripur, after [12].
Figure 2. Generalised stratigraphy of the study area in the Hazara Basin, Haripur, after [12].
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Figure 3. Geological map of (A) Bagran and (B) Karhaki section, after [10].
Figure 3. Geological map of (A) Bagran and (B) Karhaki section, after [10].
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Figure 4. Stratigraphic column, distribution of foraminifera, microfacies and depositional settings of Lockhart Limestone, Bagran section, Hazara Basin, Haripur.
Figure 4. Stratigraphic column, distribution of foraminifera, microfacies and depositional settings of Lockhart Limestone, Bagran section, Hazara Basin, Haripur.
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Figure 5. Stratigraphic column, distribution of foraminifera, microfacies and depositional settings of Lockhart Limestone, Karhaki section, Hazara Basin, Haripur.
Figure 5. Stratigraphic column, distribution of foraminifera, microfacies and depositional settings of Lockhart Limestone, Karhaki section, Hazara Basin, Haripur.
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Figure 6. Larger Benthic Foraminifera from both studied sections of the Lockhart Formation. (A) Lockhartia haimei, sample LLB-08; (B) Lockhartia conditi, sample LLK-02; (C) Lockhartia tipperi, sample LLK-04; (D) Miscellanea miscella, sample LLK-03.; (E) Ranikothalia sindensis, sample LLK-07; (F) Ranikothalia sahnii, sample LLK-07; (G) Assilina subspinosa, sample LLK-02; (H) Assilina yvettae, sample LLK-01; (I) Assilina laminosa, sample LLK-07; (J) Assilina granulosa, sample LLK-04; (K) Operculina salsa, sample LLK-01; (L) Operculina patalensis, sample LLK-08; (M) Discocyclina sp., sample LLK-08; (N) Orbitoclypeus sp., sample LLK-10; (O) Orthophragminid, sample LLK-08; (P) Idalina sinjarica, sample LLB-01.
Figure 6. Larger Benthic Foraminifera from both studied sections of the Lockhart Formation. (A) Lockhartia haimei, sample LLB-08; (B) Lockhartia conditi, sample LLK-02; (C) Lockhartia tipperi, sample LLK-04; (D) Miscellanea miscella, sample LLK-03.; (E) Ranikothalia sindensis, sample LLK-07; (F) Ranikothalia sahnii, sample LLK-07; (G) Assilina subspinosa, sample LLK-02; (H) Assilina yvettae, sample LLK-01; (I) Assilina laminosa, sample LLK-07; (J) Assilina granulosa, sample LLK-04; (K) Operculina salsa, sample LLK-01; (L) Operculina patalensis, sample LLK-08; (M) Discocyclina sp., sample LLK-08; (N) Orbitoclypeus sp., sample LLK-10; (O) Orthophragminid, sample LLK-08; (P) Idalina sinjarica, sample LLB-01.
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Figure 7. Stratigraphic and age range of different Larger Benthic Foraminifera species, adopted from [42] (Green bars indicate index species of the Thanetian age, while blue bars represent species from other ages as well).
Figure 7. Stratigraphic and age range of different Larger Benthic Foraminifera species, adopted from [42] (Green bars indicate index species of the Thanetian age, while blue bars represent species from other ages as well).
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Figure 8. Photomicrographs showing microfacies of the Bagran section in thin sections. (A,B) bioclastic mudstone microfacies (MFLLB I) showing Idalina sinjarica (Is), sample # 7 and 17; (C,D) mixed bioclastic wackestone microfacies (MFLLB II) showing Lockhartia sp. (Ls), Lockhartia haimei (Lh), recrystallised bioclast (Bc), Textularia (Tx), dasycladale algae (Dsy), sample # 12 and 20; (E,F) miliolidal bioclastic wackestone microfacies (MFLLB III) showing Idalina sinjarica (Is), Triloculina (Tl), Spiroloculina (Sl) and recrystallised bioclast (Bc), sample # 1 and 4; (G,H) foraminiferal bioclastic wackestone–packstone microfacies (MFLLB IV) showing dasycladale algae (Dsy), Miscellanea miscella (My), smaller rotaliid (Sr) and recrystallised bioclast (Bc), sample # 8 and 14.
Figure 8. Photomicrographs showing microfacies of the Bagran section in thin sections. (A,B) bioclastic mudstone microfacies (MFLLB I) showing Idalina sinjarica (Is), sample # 7 and 17; (C,D) mixed bioclastic wackestone microfacies (MFLLB II) showing Lockhartia sp. (Ls), Lockhartia haimei (Lh), recrystallised bioclast (Bc), Textularia (Tx), dasycladale algae (Dsy), sample # 12 and 20; (E,F) miliolidal bioclastic wackestone microfacies (MFLLB III) showing Idalina sinjarica (Is), Triloculina (Tl), Spiroloculina (Sl) and recrystallised bioclast (Bc), sample # 1 and 4; (G,H) foraminiferal bioclastic wackestone–packstone microfacies (MFLLB IV) showing dasycladale algae (Dsy), Miscellanea miscella (My), smaller rotaliid (Sr) and recrystallised bioclast (Bc), sample # 8 and 14.
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Figure 9. Photomicrographs showing microfacies of the Karhaki section in thin sections. (A,B) foraminiferal wackestone microfacies (MFLLK I) showing Miscellanea miscella (Ms), Lockhartia haimei (Loh), Operculina sp. (Op), bioclasts (Bc), Assilina subspinosa (As) and Nummulites sp. (Nm), sample # 4; (C,D) foraminiferal wackestone–packstone microfacies (MFLLK II) showing Operculina patalensis (Op), Discocyclina ranikotensis (Dc), Ranikothalia sindensis (Rk) and some bioclasts (Bc), sample # 13; (E,F) Bioclastic foraminiferal packstone microfacies (MFLLB III) showing Miscellanea miscella (Ms), Assilina subspinosa (As), Lockhartia conditi (Loc) and Discocyclina ranikotensis (Dc), sample # 1 and 16.
Figure 9. Photomicrographs showing microfacies of the Karhaki section in thin sections. (A,B) foraminiferal wackestone microfacies (MFLLK I) showing Miscellanea miscella (Ms), Lockhartia haimei (Loh), Operculina sp. (Op), bioclasts (Bc), Assilina subspinosa (As) and Nummulites sp. (Nm), sample # 4; (C,D) foraminiferal wackestone–packstone microfacies (MFLLK II) showing Operculina patalensis (Op), Discocyclina ranikotensis (Dc), Ranikothalia sindensis (Rk) and some bioclasts (Bc), sample # 13; (E,F) Bioclastic foraminiferal packstone microfacies (MFLLB III) showing Miscellanea miscella (Ms), Assilina subspinosa (As), Lockhartia conditi (Loc) and Discocyclina ranikotensis (Dc), sample # 1 and 16.
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Figure 10. Model showing depositional settings for microfacies of both the Bagran and Karhaki sections, Lockhart Limestone.
Figure 10. Model showing depositional settings for microfacies of both the Bagran and Karhaki sections, Lockhart Limestone.
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Figure 11. Biostratigraphic correlation between limestone of equivalent Palaeocene age exposed in the Hazara, Upper Indus and Lower Indus basins of Pakistan [5,20,42,50].
Figure 11. Biostratigraphic correlation between limestone of equivalent Palaeocene age exposed in the Hazara, Upper Indus and Lower Indus basins of Pakistan [5,20,42,50].
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Figure 12. Correlation between depositional environments of equivalent Palaeocene age limestones exposed in the Hazara, Upper Indus and Lower Indus –basins of Pakistan [14,20,50].
Figure 12. Correlation between depositional environments of equivalent Palaeocene age limestones exposed in the Hazara, Upper Indus and Lower Indus –basins of Pakistan [14,20,50].
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Figure 13. Depositional profile showing a comparison between depositional environments of the Lockhart Limestone and its age equivalents in different basins of Pakistan: Hazara Basin (yellow star), Upper Indus Basin (green star), and Lower Indus Basin (blue star).
Figure 13. Depositional profile showing a comparison between depositional environments of the Lockhart Limestone and its age equivalents in different basins of Pakistan: Hazara Basin (yellow star), Upper Indus Basin (green star), and Lower Indus Basin (blue star).
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Table 1. Depositional settings and associated microfacies of the Lockhart Limestone.
Table 1. Depositional settings and associated microfacies of the Lockhart Limestone.
RampDepositional SettingsCharacterisation
Inner RampPeritidal Facies BeltBioclastic Mudstone Microfacies (MFLLB I)
Lagoon Facies BeltMixed Bioclastic Wackestone Microfacies (MFLLB II)
Restricted Facies BeltMiliolidal Bioclastic Wackestone Microfacies (MFLLB III)
Shallow Open Inner Ramp
Facies Belt		Foraminiferal Wackestone
Microfacies (MFLLK I)
Middle RampProximal–Middle Mid Ramp
Facies Belt		Foraminiferal Wackestone–Packstone
Microfacies (MFLLB IV, MFLLK II)
Middle–Distal Mid Ramp Facies BeltBioclastic Foraminiferal Packstone Microfacies (MFLLK III)
Outer RampNo facies were observed or deposited on the outer ramp.
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MDPI and ACS Style

Ahmad, M.; Tanoli, U.F.; Umar, M.; Ahmad, T.; Ahmed, A. Shallow-Marine Late Thanetian Lockhart Limestone from the Hazara Basin, Pakistan: Insights into Foraminiferal Biostratigraphy and Microfacies Analysis. Geosciences 2025, 15, 63. https://doi.org/10.3390/geosciences15020063

AMA Style

Ahmad M, Tanoli UF, Umar M, Ahmad T, Ahmed A. Shallow-Marine Late Thanetian Lockhart Limestone from the Hazara Basin, Pakistan: Insights into Foraminiferal Biostratigraphy and Microfacies Analysis. Geosciences. 2025; 15(2):63. https://doi.org/10.3390/geosciences15020063

Chicago/Turabian Style

Ahmad, Muneeb, Urooba Farman Tanoli, Muhammad Umar, Tofeeq Ahmad, and Alaa Ahmed. 2025. "Shallow-Marine Late Thanetian Lockhart Limestone from the Hazara Basin, Pakistan: Insights into Foraminiferal Biostratigraphy and Microfacies Analysis" Geosciences 15, no. 2: 63. https://doi.org/10.3390/geosciences15020063

APA Style

Ahmad, M., Tanoli, U. F., Umar, M., Ahmad, T., & Ahmed, A. (2025). Shallow-Marine Late Thanetian Lockhart Limestone from the Hazara Basin, Pakistan: Insights into Foraminiferal Biostratigraphy and Microfacies Analysis. Geosciences, 15(2), 63. https://doi.org/10.3390/geosciences15020063

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