Tracing multiple sources of sediments using trace element and Nd isotope geochemistry: provenance of the Mesozoic succession in the Kutch Basin, western India

Abstract

An integrated approach involving Sr–Nd isotope, trace and rare earth element analyses tracks multiple sources of the Mesozoic sediments of the Kutch Basin at the western continental margin of India. High (⁸⁷Sr/⁸⁶Sr)_t (ratio at time of deposition), negative ε_Nd and high concentrations of large-ion lithophile elements (LILEs) indicate the upper continental source. Ratios of Nb/Ta and Zr/Hf suggest sedimentary and felsic igneous sources of sediments. The moderate to high concentration of La, Th and Sc, light rare earth elements (LREE-) enrichment, weak negative Eu anomalies and the relationship between ε_Nd(0) and Th/Sc indicate the dominantly felsic composition of source rocks. However, low contents of Th, low values of (⁸⁷Sr/⁸⁶Sr)_t and depleted mantle model age T_DM < 1600 Ma indicate input from a younger mafic source. Increasing concentrations of Zr, Hf and Nd isotopes and a gradual increase in mean T_DM from the older to the younger formations indicate erosional unroofing at the source terrain. The increasing (⁸⁷Sr/⁸⁶Sr)_t through time relates to increased weathering of the source rock. The overwhelmingly southwesterly palaeocurrent direction of current-generated sedimentary structures, and the mean T_DM ages trace suggest source areas of the Kutch Basin to Precambrian rocks in the north and NE of this basin. The T_DM ages highlight the dominance of late Palaeoproterozoic source rocks. Nd isotope composition indicates that Proterozoic rocks of Marwar Supergroup and Erinpura Granite, in particular, served as main sediment contributors for the Mesozoic sediments in Kutch. We therefore conclude that the Mesozoic sediments in the Kutch Basin are predominantly of late Palaeoproterozoic age with lesser inputs from rocks of early Mesoproterozoic and early Palaeoproterozoic age.

1. Introduction

Sedimentary successions in pericratonic rift basins preserve the evolutionary history of adjacent cratons and orogenic belts (Dickinson & Suczek, 1979; Dickinson, 1988). Provenance interpretations of these sedimentary successions contribute to the understanding of tectonic setting, climate, extent of weathering and drainage patterns during the time of deposition (Nesbitt & Young, 1982; Algeo & Maynard, 2004; Tribovillard et al. 2006; Hofer et al. 2013; Verma & Armstrong-Altrin, 2016; Armstrong-Altrin et al. 2019). However, temporal provenance shifts often remain untraceable because of their effects being masked by simultaneous sediment supply from multiple sources. This can be resolved only when mineralogical and geochemical variations in a sedimentary formation are correlated not only to probable sources but also to time. Due to their limited mobility during weathering and transportation, many trace elements, including rare earth elements (REEs), present in the clastic sedimentary rocks are useful in tracking dispersal of sediments (McLennan et al. 1983; Bhatia & Crook, 1986; Armstrong-Altrin & Verma, 2005; Armstrong-Altrin et al. 2013, 2018; George & Ray, 2017; Ramos-Vázquez & Armstrong-Altrin, 2019). The concentrations of trace elements and Sr and Nd isotopic composition provide information about the chemical composition and age of mantle derivation (or duration of crustal residence) of the source rocks. The integrated approach of using trace-element content, Nd isotope model ages and Sr isotope ratios is therefore likely to resolve secular shifts in the sedimentary source. The result may further enlighten us about the related plate tectonic setting.

The c. 3000 m thick Mesozoic succession in the Kutch Basin, western India is taken as a test case here. The choice is prompted by the fact that the secular shift in sediment contributing source has already been suggested for this succession based on petrographic modal analysis and major-element composition (Chaudhuri et al. 2020). However, the present approach moves forwards to the compositional make-up of the source rocks of specific time ranges. The main objective of this work is to determine the lithology and age of the source rock of Mesozoic sediments in Kutch. For this purpose, we use geochemical (trace elements) and isotopic (Sr–Nd) fingerprinting.

2. Geological setting

During the Late Jurassic Period, after the break-up of eastern Gondwana from its western counterpart, the earlier-formed Kutch Basin remained attached to the Indian subcontinent. Madagascar remained with western India until 88–90 Ma (Storey et al. 1995; Torsvik et al. 1998) while Seychelles split at c. 63 Ma (Collier et al. 2008). The Kutch Basin is a proven petroliferous basin at the western continental margin of India formed by the reactivation of primordial faults along the Aravalli–Delhi fold belt during the Gondwanaland break-up (Biswas, 1982, 1987, 2005). During the syn-rift to early post-rift stage, the Kutch Basin accumulated Upper Triassic – Lower Cretaceous mixed siliciclastic and carbonate sediments of thickness c. 3000 m (Biswas, 1982, 1987). The post-rift Cenozoic succession consists of mixed carbonate siliciclastic intervals (Biswas, 1981; Banerjee et al. 2012 a, b; Saraswati et al. 2018). The Kutch Basin remained surrounded by Nagar Parkar Igneous Suite to the north, Bhilwara, Aravalli and Delhi Supergroups to the NE, Dharwar Supergroup to the south and Central Indian Tectonic Zone (CITZ) to the east. The Aravalli highlands to the east and the Nagar Parkar Ridge to the north are traditionally considered as source areas of the Mesozoic sediments in the Kutch Basin (Ahmad & Bhat, 2006; Ramakrishnan & Vaidyanadhan, 2008; Ahmad et al. 2014; Valdiya, 2015). The E–W-trending faults result in a series of uplifts exposing the Mesozoic sections in Island Belt Uplift (comprising Patcham, Khadir, Bela and Chorad islands), Wagad Uplift and Kutch Mainland Uplift (Biswas, 1980, 2005) (Fig. 1).

Fig. 1. Geological map of Kutch mainland showing extents of Cenozoic and Mesozoic outcrops (after Biswas, 1977, 1981). Mesozoic succession of the Kutch Basin, western India (after Biswas, 1977, 1981).

The Mesozoic stratigraphy of the Kutch Mainland Uplift comprises Jhurio, Jhumara, Jhuran and Bhuj formations in ascending order of succession overlying the basement rocks, separated by a basal granite–cobble conglomerate (Biswas & Deshpande, 1968; Biswas, 1987) (Fig. 1). The marine Jhurio Formation (Bathonian–Callovian) rests unconformably on the Precambrian basement and mainly comprises limestone and minor shale. The overlying Jhumara Formation (Oxfordian) consists of argillaceous sediments at the base, and limestone and minor sandstone beds at the top (Biswas, 2005). The shallow-marine Jhuran Formation (Kimmeridgian–Tithonian), unconformably overlying the Jhumara Formation, consists primarily of sandstone–shale alternations and it is divided into three constituent members based on three coarsening-upwards cycles of depositions (Arora et al. 2015, 2017). The youngest Bhuj Formation (Valanginian–Albian), consisting exclusively of sandstone and shale, was deposited in fluvio-deltaic conditions (Biswas, 1991). Several workers reported a predominantly southwesterly palaeocurrent pattern for the entire Mesozoic sequence (Biswas, 1991, 1993, 2005; Mandal et al. 2016; Arora et al. 2017; Desai & Biswas, 2018).

3. Methods

Samples for the present study were collected from different locations in the Kutch Mainland Uplift, namely Zara, Nirona, Palara, Bhuj, Yaksh, Rukmavati, Gangeshwar and Tapkeshwar. The majority of the collected samples from the oldest Jhurio Formation contain a significantly high amount of calcareous fragments and were therefore not included in the current study. Besides, pore-filling and replacive carbonate cements are abundant within sandstones in Jhumara, Jhuran and Bhuj formations, whereas they are absent from the associated shales in these formations (Chaudhuri et al. 2018). We have therefore mainly selected shale samples from Jhumara, Jhuran and Bhuj formations along with two sandstone samples from the Bhuj Formation because of the negligible amounts of carbonate cementation in them. In total, 15 samples from Jhumara Formation, 53 samples from Jhuran Formation and 17 samples from Bhuj Formation were analysed for the present investigation. The Jhuran Formation is considerably thick and is mapped by previous workers up to the Member level in the Kutch Mainland. A large number of studied samples therefore belong to the Jhuran Formation. For trace-element and REE concentrations, c. 50 mg of each sample powder was used to prepare sample solutions with 5 mL of 1 ng mL^{–1 103}Rh solution added as an internal standard. From this stock solution, 5 mL was diluted to 50 mL using deionized water and analysed at CSIR-NGRI, Hyderabad, using a high-resolution inductively coupled plasma mass spectrometer (HR-ICP-MS) (Nu Instruments Attom, UK). Chinese standard reference material GSR-5 was used to check the accuracy and precision of measurements. Some of the trace-element data (sample series JP, NP and BP) were generated at the Physical Research Laboratory, Ahmedabad, India using a Thermo X-Series Q-ICP-MS. For this, carbonate and organic matter were removed from powdered samples before being dissolved in HF-HNO₃. Analyses were carried out in 2% HNO₃ sample solutions and BHVO-2 standard (from USGS) was used for calibration as well as for checking the accuracy and precision of measurements. Reproducibility at 2σ level was ≤3% for REEs and ≤6% for all other trace elements (Chatterjee & Ray, 2017, 2018).

For Sr–Nd isotopic ratio analyses at the Physical Research Laboratory, Ahmedabad, India, the samples were dissolved following the standard HF-HNO₃-HCl dissolution protocol for silicate rocks (e.g. Awasthi et al. 2010). Sr was separated from other REEs by cation exchange column chromatography while Nd was separated from other REEs using Ln-specific resin from Eichrom with dilute HCl (0.18 N) as elutant (Dickin, 2000; Awasthi et al. 2010). ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd were measured using a Thermo Neptune multi-collector (MC) ICP-MS (Awasthi et al. 2014). The measured ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios were corrected for mass fractionation using ⁸⁶Sr/⁸⁸Sr of 0.1194 and ¹⁴⁶Nd/¹⁴⁴Nd of 0.7219. Average measured ¹⁴³Nd/¹⁴⁴Nd for an internal laboratory standard (Merck Nd) was 0.511705 ± 27 (2σ, n = 56). The average ¹⁴³Nd/¹⁴⁴Nd for BHVO-2, measured regularly during our analyses, is 0.512967 ± 0.000008 (n = 10; ±0.2 in ε_Nd units at 2σ). Further details of analytical protocols and data presentation for comparison are provided in Chatterjee & Ray (2017, 2018).

4. Results

4.a. Trace-element composition

Trace-element concentrations of samples from Jhumara, Jhuran and Bhuj formations are presented in Tables 1–5. Concentrations of most trace elements, especially that of large-ion lithophile elements (LILEs), are higher in these samples compared with the average shale composition (Wedepohl, 1971), except for Ni and Sc. The Lower Member of the Jhuran Formation possesses the highest average ∑REE of c. 317 ppm. The Upper Continental Crust (UCC) normalized trace-element concentrations in these samples are either enriched, depleted or UCC-equivalent (Fig. 2). Ba, U, Pb and Sr exhibit prominent depletion with increasing Sr depletion in younger formations. Th shows enrichment for the entire Mesozoic record. However, Nb and Ta show enrichment. The Lower Jhuran sediments show an increase in Zr and Hf, whose magnitude diminishes towards the top of the succession (Fig. 2). The Nb/Ta versus Zr/Hf of all the samples from the basin show two clusters, one group showing higher Nb/Ta and lower Zr/Hf compared with the other (Fig. 3).

Table 1. Trace-element concentrations of samples from Jhumara Formation. CN – chondrite-normalized

Table 2. Trace-element concentrations of samples from Lower Member, Jhuran Formation. CN – chondrite-normalized

Table 3. Trace-element concentrations of samples from Middle Member, Jhuran Formation. CN – chondrite-normalized

Table 4. Trace-element concentrations of samples from Upper Member, Jhuran Formation. CN – chondrite-normalized

Table 5. Trace-element concentrations of samples from Bhuj Formation. CN – chondrite-normalized

Fig. 2. Upper Continental Crust (UCC-) normalized trace-element patterns for samples from various formations, arranged in stratigraphic order, of the Mesozoic Kutch Basin. Normalizing values are from Rudnick & Gao (2003).

Fig. 3. Nb/Ta versus Zr/Hf plot for samples from the Mesozoic Kutch Basin.

Chondrite-normalized REE patterns of Jhumara, Jhuran and Bhuj samples show broadly similar characteristics, with a prominently LREE-enriched pattern, negative Eu anomaly and positive Gd anomaly (Fig. 4). These patterns broadly overlap with those of UCC and Post-Archean Australian Shale (PAAS). Weak negative Eu anomalies, Eu/Eu* = Eu/(Sm_CN*Nd_CN)^1/2 (where the subscript ‘CN’ indicates chondrite-normalized) in Jhumara, Jhuran and Bhuj samples have average values of 0.65, 0.65 and 0.61, respectively. The chondrite-normalized REE patterns for shale samples from the Jhuran Formation reveal three distinct bands for its three Lower, Middle and Upper members (Fig. 4). The samples from the Lower Member exhibit consistently high ∑REE contents, whereas those of the Upper Member show distinctly low ∑REE content. Nearly half of the samples from the Jhumara Formation exhibit REE patterns similar to those of the Upper Member of the Jhuran Formation. Samples from all three formations exhibit a low La/Th ratio (1.59–3.01 ppm); those from the Bhuj Formation exhibit the highest average (2.60). In a cross-plot of Th versus Sc, the samples from the Jhuran Formation exhibit the maximum spread of data points (Fig. 5). Most samples from Jhuran and Bhuj formations and nearly half of the samples from the Jhumara Formation bear felsic signature, while a few samples from the Jhuran (belonging to the Upper and Middle members) and Bhuj formations and most samples from the Jhumara Formation plot within the field for intermediate igneous rocks (Fig. 5) (Cullers, 2002).

Fig. 4. Composite log of the Jhumara, Jhuran and Bhuj formations (adapted from Biswas, 2005; Fursich et al. 2005; Mandal et al. 2016). Chondrite-normalized REE patterns for Jhumara (lower), Jhuran (middle) and Bhuj (upper) are placed to the right of the log. Solid lines: LM – Lower Member; MM – Middle Member; UM – Upper Member. Dashed lines: MORB – mid-ocean-ridge basalt; NASC – North American Shale Composite; PAAS – Post Archean Australian Shale. Chondrite meteorite values from Boynton (1984). NASC, PAAS and MORB values from Taylor & McLennan (1985).

Fig. 5. Source-rock discrimination based on Th versus Sc plot (Cullers, 2002) for shale samples from Jhumara, Jhuran and Bhuj formations. Abbreviations as for Figure 4.

Average Sc/Cr ratios for samples from Jhumara, Jhuran and Bhuj formations are 0.13, 0.12 and 0.13 respectively. In a cross-plot of La/Th versus Hf, most samples plot in the field marked for passive margin sources, but a few samples occupy the field of acidic arc sources (Fig. 6). Samples from the Lower Member of Jhuran Formation and the Bhuj Formation exhibit distinctly higher concentrations of Hf compared with samples from other formations.

Fig. 6. Tectonic setting discrimination based on La/Th versus Hf (Floyd & Leveridge, 1987) for shale samples from Jhumara, Jhuran and Bhuj formations. Abbreviations as for Figure 4.

4.b. Isotope composition

Samples from Jhumara, Jhuran and Bhuj formations bear continental crustal signatures. The value of (⁸⁷Sr/⁸⁶Sr)_t is similar in all three formations; samples from the Bhuj Formation have the highest (⁸⁷Sr/⁸⁶Sr)_t ranging over 0.73–0.76, followed by Jhuran Formation (0.72–0.75) and Jhumara Formation (0.72–0.73) (Fig. 7). All samples exhibit overlapping but negative ε_Nd(0) and ε_Nd(t) values, suggesting derivation from LREE-enriched mantle. Samples from the Jhumara Formation and Lower and Middle members of the Jhuran Formation exhibit high values of ε_Nd(t), while those from the Upper Member of the Jhuran Formation and the Bhuj Formation demonstrate relatively low ε_Nd(t) values (Fig. 7a). In a cross-plot of ε_Nd(0) versus Th/Sc, samples from Jhumara, Jhuran and Bhuj formation indicate the dominance of felsic components with values similar to those of upper crust (Fig. 8). The fractionation factor f _Sm/Nd values vary from −0.37 to −0.49, −0.31 to −0.50 and −0.40 to −0.46 for the Jhumara, Jhuran and Bhuj samples, respectively. Figure 9 shows temporal variations in ε_Nd(0), depleted mantle model age (T _DM) and ε_Nd(t) in the succession. The marked decrease of ε_Nd(0) and ε_Nd(t) in samples from the Bhuj Formation is accompanied by an increase in T _DM. The T _DM age calculated from the measured data range over 1560–2170 Ma, 1430–2220 Ma and 1760–2320 Ma for the Jhumara, Jhuran and Bhuj formations, respectively (Table 6). The average T _DM for the analysed samples increases through 1570, 1680 and 1800 Ma from Jhumara through Jhuran and Bhuj formations with T _DM mode at 1800 Ma (Fig. 10). In a cross-plot of f _Sm/Nd versus ε_Nd(0)_, Jhumara, Jhuran and Bhuj samples plot within the early Proterozoic upper crustal rocks (> 1.6 Ga) and are in agreement with the values of T _DM (Fig. 11).

Fig. 7. (a) ε_Nd(t) and (b) T _DM versus (⁸⁷Sr/⁸⁶Sr)_t plot for shale samples from Jhumara, Jhuran and Bhuj formations. Abbreviations as for Figure 4.

Fig. 8. Source-rock discrimination based on ε_Nd versus Th/Sc plot (McLennan et al. 1993) for shale samples from Jhumara, Jhuran and Bhuj Formation. Abbreviations as for Figure 4.

Fig. 9. Variations in ε_Nd(0), T _DM(Ga) and ε_Nd(t) across Jhumara, Jhuran and Bhuj formations. Abbreviations as for Figure 4.

Table 6. Sm–Nd isotope data for samples from Jhumara, Jhuran and Bhuj formations

Note: Subscripts m and t indicate the ratios measured and at the time of deposition, respectively. Initial ratios were calculated at the age of deposition, given in brackets. Sm and Nd concentrations were measured by Q-ICP-MS at Physical Research Laboratory, Ahmedabad, India. Depleted mid-ocean-ridge basalt mantle values used for T _DM calculations: ¹⁴³Nd/¹⁴⁴Nd = 0.513114 and ¹⁴⁷Sm/¹⁴⁴Nd = 0.222 (Michard et al. 1985).

Fig. 10. Histogram of T _DM distribution for the sediments in the Mesozoic Kutch Basin.

Fig. 11. Plot of f _Sm/Nd versus ε_Nd(0) (modified after McLennan et al. 1993) for shale samples from Jhumara, Jhuran and Bhuj formations. Abbreviations as for Figure 4.

5. Discussion

Both trace-element analysis and Sr–Nd isotopic composition of sediments in the Mesozoic Kutch Basin point to their derivation primarily from upper continental sources. This is reflected in the enriched LILE and LREE, (⁸⁷Sr/⁸⁶Sr)_t > 0.71, ε_Nd(t) < −10 and negative f _Sm/Nd (Condie, 1993). The same is reflected in the T _DM distribution of the sediments (Fig. 12). T _DM mode at 1800 Ma is related to one of the major crust-forming episodes on the Earth (Condie, 2001; Condie & Aster, 2010). The insignificant change in ε_Nd(t) from the Jhumara Formation to the Middle Member of the Jhuran Formation suggests a negligible shift in sediment sources. The low Th (Fig. 5), lowest (⁸⁷Sr/⁸⁶Sr)_t and average T _DM age of 1570 Ma indicate sediment inputs from a juvenile mafic source for the oldest Jhumara Formation. The basin possibly received sediments from young orogenic belt(s) during the initial phase. Importantly, the influence of such a sediment source diminishes through time, with felsic (granitic) source progressively dominating from the bottom to the top of the Mesozoic succession. The concentration of trace elements such as Th and Sc, the LREE-enriched chondrite normalized patterns and the negative Eu anomaly suggest the dominance of felsic composition at source for Jhumara, Jhuran and Bhuj formations. The high content of Th (average, 26.4 ppm) and high ∑REE in samples from the Lower Member of the Jhuran Formation are possibly related to the high content of monazite in the samples as reported by Chaudhuri et al. (2018) (Table 2). Low Sc/Cr ratios and the cross-plot of La/Th versus Hf indicate a passive-margin setting (Bhatia & Crook, 1986; Floyd & Leveridge, 1987) (Fig. 6).

Fig. 12. Average T _DM versus average ε_Nd(t) plot for Mesozoic sediments in the Kutch Basin compared with those of potential sources in Rajasthan. Error bars for the source points are 3σ. Data sources: George & Ray (2017) and Shukla et al. (2019).

The depletion of Ba, U, Pb and Sr observed in all the formations (Fig. 2) are possibly linked to the weathering of the source region (cf. Price et al. 1991). The magnitude of Sr depletion increases from the bottom to the top of the succession, which could be attributed to higher weathering in the source region as a function of time (i.e. the younger formations received more sediments from highly weathered sources). The highly weathered nature of the source possibly corresponds to the progressive tectonic stability of the basin from syn-rift to post-rift. The two clusters in Nb/Ta versus Zr/Hf cross-plot suggest multiple weathering or depositional histories (Fig. 3). The high Nb/Ta (low Zr/Hf) most likely represents highly recycled sediments, that is, derivation from sedimentary source rocks; the low Nb/Ta could be attributed to derivation from felsic igneous rocks.

The Nd isotopic composition of the Bhuj Formation indicates predominant sediment derivation from crustal sources of early Proterozoic age (Figs 7, 8, 10–12). T _DM ages indicate the dominance of source rocks of late Palaeoproterozoic age (1700–1800 Ma), with subordinate contributions from rocks of early Mesoproterozoic (1400–1600 Ma) and early Palaeoproterozoic (2100–2400 Ma) ages (Fig. 10). The mode of T _DM is c. 1800 ± 200 Ma.

Considering the overwhelming southwesterly slope of the basin (Biswas, 1991, 2005; Arora et al. 2015, 2017; Mandal et al. 2016; Desai & Biswas, 2018), the possible rocks which could have sourced these sediments include Nagar Parkar Igneous Suite exposed in the Nagar Parkar Ridge; Banded Gneissic Complex; Aravalli, Bhilwara, Delhi and Marwar supergroups; Erinpura Granite; and Malani volcanic rocks exposed in the Aravalli highlands (Fig. 13). The Nd isotopic composition of Mesozoic sediments in the Kutch Basin and their T _DM ages overlap with those of the Proterozoic Marwar Supergroup and the Erinpura Granites (Fig. 12), suggesting these rocks were the major source of sediments to the basin. The mafic juvenile component, especially in the Jhumara Formation, possibly derives from the Nagar Parker Igneous Suite in the north, which contains mafic magmatic rocks within a largely granitic terrain (e.g. Khan et al. 2012, 2017; Jan et al. 2017; de Wall et al. 2018; Rehman et al. 2018). This indicates the existence of southerly drainage during the initial phase of the basin. Subsequently, the palaeoslope became southwesterly because of the seawards tilting of the basin. Although there is substantial similarity in the source of the Middle Jurassic syn-rift sediments and the Lower Cretaceous post-rift sediments, trace-element concentrations, their ratios and Nd isotopic compositions reveal subtle variations in source characteristics of younger sediments. The increasing Hf concentration in samples from Jhuran and Bhuj formations exhibiting older sediment components suggest erosional unroofing at the source (Fig. 6). Increasing mean T _DM ages exhibited by Jhumara, Jhuran and Bhuj samples further supports this interpretation.

Fig. 13. Schematic diagram of palaeodrainage pattern in the Early Cretaceous Kutch Basin and possible provenance areas.

This study indicates the dominance of felsic source rocks for the entire Mesozoic rock record. Integrating results from trace-element and Sr–Nd systematics (low Th, low (⁸⁷Sr/⁸⁶Sr)_t and T _DM < 1600 Ma) highlights additional juvenile mafic source rocks in the Jhumara Formation. The concentration of Hf indicates older source rocks in younger Jhuran and Bhuj formations. Finally, ε_Nd(t) and T _DM ages, along with the established palaeoslope, provide a more reliable correlation with the existing rocks at source area. This confirms the applicability of trace elements and Nd isotope geochemistry in tracing multiple source rocks.

6. Conclusions

Concentrations of trace elements (Th, Sc) and their ratios (Nb/Ta and Zr/Hf) indicate that multiple sources, including both igneous and sedimentary rocks, contribute sediments to Jhumara, Jhuran and Bhuj formations of the Mesozoic Kutch Basin. High (⁸⁷Sr/⁸⁶Sr)_t, negative ε_Nd and LREE enrichment indicate enriched crustal source of sediments. Although the felsic source rocks dominate, sediments in the Jhumara Formation exhibit inputs from a juvenile mafic source.

T _DM ages indicate that rocks of late Palaeoproterozoic age (1700–1800 Ma) are the dominant sediment contributors, as well as those of early Mesoproterozoic (1400–1600 Ma) and early Palaeoproterozoic (2100–2400 Ma) ages.

Concentrations of Hf indicates the dominance of older inputs in younger sediments of Jhuran and Bhuj formations. The increasing mean T _DM from bottom to top, namely 1570, 1680 and 1800 Ma for Jhumara, Jhuran and Bhuj formations, respectively, corroborates sediments from older rocks in younger formations, suggesting erosional unroofing of source rocks. Average T _DM of 1800 Ma coincides with one of the major crust-forming events.

The increasing (⁸⁷Sr/⁸⁶Sr)_t from the bottom to the top of the Mesozoic succession relates to increased weathering of the source rock, possibly linked to the increasing tectonic stability of the basin.

Considering the southwesterly palaeoslope of this basin and the mean T _DM ages, rocks of the Marwar Supergroup and Erinpura Granite north and NE of the Kutch Basin constitute the main sediment source. However, minor amount of sediments are derived from the Palaeoproterozoic Banded Gneissic Complex II, Bhilwara Supergroup and Aravalli Supergroup and the Mesoproterozoic Delhi Supergroup. The mafic juvenile component in the sediments of Jhumara Formation is likely to have derived from the Nagar Parkar Igneous Suite to the north.