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Thin-section analysis of lithified paleosols from Dagshai Formation of the HimalayanForeland: Identification of paleopedogenic features and diagenetic overprinting andimplications for paleoenvironmental reconstruction☆

P. Srivastava a,⁎, D. Sauer b

a Department of Geology, University of Delhi, Delhi 110 007, Indiab Institute of Geography, Dresden University of Technology, Helmholtzstr. 10, D-01069 Dresden, Germany

a b s t r a c ta r t i c l e i n f o

Keywords:Himalayan ForelandPaleosolsOligoceneBurial diagenesisMicromorphology

In the present study we report micromorphology of diagenetically altered paleosols (~31 Ma old) from DagshaiFormation, Himalayan Foreland. The fluvial sequence exposed along the Koshaliya River, NW Himalaya, containsfour types of paleosols with decreasing abundance of well-developed paleosols from basal to upper part of theDagshai Formation. Burial diagenesis (at ~7.5 kmdepth) caused compaction (54–78% current thickness comparedto pre-burial thickness) and cementation of the paleosols, accompanied by internal reorganization of groundmasswithin peds, staining of pedwallswith iron oxide, plugging of voids, disruption of textural pedofeatures, fracturingof large mineral grains and nodules, coarsening of pedogenic calcite crystals, redoximorphic features, andmineralization of root channels. Despite diagenetic alteration, evidence of paleopedogenic processes is stillwell-preserved in these fossil soils in the form of microstructures, b-fabrics, pedogenic calcite, bioturbation,and textural pedofeatures. Thin-section analysis helped to distinguish pedogenic and diagenetic features oflithified paleosols and to infer the paleoenvironment of the Dagshai paleosols. The paleopedological charac-teristics of the fossil soils suggest humid to sub-humid conditions during their formation in early Oligocene.The paleoclimate inferred here is consistent with prevalence of tropical paleovegetation (cf. Ficus L.) reportedfrom Dagshai sediments.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

Pre-Quaternary paleosols that are found in thick sedimentarysequences require a cautious approach to unravel the ancient soil-forming processes because of overprinting caused by burial diagenesis(Lander et al., 1991; Nesbitt and Young, 1989; Nordt et al., 2012;Retallack, 1991; Sheldon and Retallack, 2001). Major controlling factorsduring diagenetic alteration of the paleosols include interactionof ground water with weathered profile and changes in temperatureand pressure (Nesbitt and Young, 1989). Burial diagenesis results incompaction, cementation, and disequilibriumbetweenminerals formedduring pedogenesis and conditions after burial (Nesbitt and Young,1989). Diagenetic overprinting may make it difficult to recognize andproperly interpret the paleosols (Bronger and Catt, 1989; Johnson andWatson-Stegner, 1987; McCarthy et al., 1998, 1999; Nordt et al., 2012;Retallack, 1991). However, micromorphological investigation of suchpaleosols can resolve the complexity caused by diagenetic overprintingby detailed description of pedogenic and diagenetic features and at thesame time enable organizing them into a sequential order of pedogenic

and geological events (Bronger and Heinkele, 1989; Fedoroff et al.,2010; McCarthy et al., 1998).

In view of the potential of micromorphological analysis for identifyingsoil-forming processes, we have undertaken a detailed micromorpho-logical study of the fossil soils of the Dagshai Formation (31.6 ± 3.9 Mato 30.3 ± 3.9 Ma) representing the period immediately after transitionfrom marine (Subathu Formation) to continental (Dagshai Formation)sedimentation in the Himalayan Foreland. The goal of the present studyis to reconstruct the paleopedogenesis of the fossil soils of the DagshaiFormation that could provide valuable additional knowledge on tectonics,paleoclimate, sedimentology, geochronology, and paleoecology of thisfluvial record from the Himalayan Foreland (Bera et al., 2008; Bhatia,2000; Kumar et al., 2008; Najman et al., 2004; Raiverman et al, 1983;Ravikant et al., 2011; Sahini et al., 1983).

2. Geological setting

The outer part of the Himalayan range in the south is marked by anactive foreland basin that resulted from thrust loading and subsidencewith synorogenic sedimentation from the hinterland (Burbank et al.,1996; Raiverman et al., 1983). It is bounded by the Main BoundaryThrust in the north and the vast Indo-Gangetic Plains in the south(Burbank et al., 1996; Parkash et al., 1980; Raiverman et al., 1983).

Catena 112 (2014) 86–98

☆ This paper is dedicated to the late Nicolas Fedoroff, an exceptional micromorphologistand palaeopedologist and a great person.⁎ Corresponding author. Tel.: +91 27667073.

E-mail address: [email protected] (P. Srivastava).

0341-8162/$ – see front matter © 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.catena.2013.08.008

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The terrestrial sedimentary record preserved in the foreland is related tohinterland tectonics, mirroring the exhumation history of the hinter-land, southward propagation of the thrust sheets, and progressiveshift of the provenance (Ravikant et al., 2011). The synorogenic sedi-ments in the marine Subathu sub-basin representing the basal partof the foreland sedimentary sequencewere sourced frommixed Tethyanand Lesser Himalayan rocks in the North and Cratonic rock of the Indianshield from the South (Ravikant et al., 2011). The overlying continentalDagshai Formation consisting of red mudstone and white/gray sand-stone deposited bymeandering rivers indicates drastic changes in depo-sitional environment and progressive shift of the provenance (Bera et al.,2008; Bhatia and Bhargava, 2006; Najman, 2006; Ravikant et al., 2011).A recent study of detrital zircon (U–Pb age and Hf isotopy) from the

Himalayan Foreland demonstrated that the sediments of the DagshaiFormation were derived from exhumed Tethyan Himalaya and aremarked by very low-grademetamorphic detritus (Ravikant et al., 2011).

The Subathu successions (Fig. 1) in the Himalayan Foreland repre-sent the last phase of marine sedimentation during Paleocene–Eocene(Bera et al., 2008, 2010a; DeCelles and Giles, 1996; Najman, 2006;Ravikant et al., 2011). It is overlain by fluvial sediments of the Dagshaiand Kasauli Formations with a hiatus of possibly considerable dura-tion (Bhatia and Bhargava, 2006; Najman, 2007; Najman et al.,1993, 1994, 2004). Based on benthic foraminifera providing a con-tinuous biochronological record across the Subathu and Dagshaiformations, the Subathu-Dagshai transition was assigned to an ageof 44 Ma (Bhatia and Bhargava, 2006; Mathur, 1978). The hiatus

Fig. 1. (a) Location of Dagshai basin in the Himalayan Foreland, (b) geological map of the Dagshai basin (after Raiverman, 1979 and Raiverman et al., 1983), and location of the 18 loggedsections (D1 to D18) along the Koshaliya River in the Dagshai Formation (c).

87P. Srivastava, D. Sauer / Catena 112 (2014) 86–98


between marine (Subathu Fm.) and continental (Dagshai Fm.)sedimentation is also supported by sedimentary facies analysis(Kumar et. al., 2008; Sangode et al., 2005). The depositional agesto the lowermost and uppermost parts of the Dagshai Formationhas been dated to 31.6 ± 3.9 Ma and 30.3 ± 3.9 Ma, respectively,by detrital-zircon fission-track (ZFT) analysis (Jain et al., 2009).

Fluvial sediments of the Dagshai basin experienced burial by7.0–7.5 km thick sediments during the deposition of the Kasauli Forma-tion and Siwalik Group, followed by thrusting along theMain BoundaryFault during Neogene (Karunakaran and Rao, 1976). Based on a geo-thermal gradient of ~20 °C km−1 for the Siwalik basin, this correspondsto a minimum temperature of ~140 °C after the burial of the DagshaiFormation (Mugnier et al., 1995). The post-burial conditions estimatedhere are in agreement with illite crystallinity, vitrinite reflectance, andcolor of spores of the Dagshai Formation (Najman et al., 1997, 2004).

3. Methods

We distinguished pedogenic and diagenetic micromorphologicalcharacteristics of the fossil soils of Dagshai Formation to infer thepaleoenvironmental conditions during pedogenesis in the oldest terres-trial landscapes in the Himalayan Foreland. Eighteen sections exposedalong the Koshaliya River close to the Kalka-Shimla highway (latitude:N30° 49′ 54.2″ to N30° 49′ 54.7″, longitude: E76° 58′ 07″ to E76° 58′07″), comprising the entire fluvial succession of the Dagshai Formation(Fig. 1c), were described, recording themacromorphological character-istics of the paleosols (Soil Survey Staff, 1999). Sixty-five paleosolhorizons were identified in the 18 sections. They were examined forcolor, structure, texture, Fe/Mn concentration and depletion features,pedogenic CaCO3 (PC) and non-pedogenic CaCO3 (NPC), and character-ized asmaster horizons according to USDA Standards (Soil Survey Staff,1999, 2006). PC and NPC were distinguished according to the criteriadefined by Srivastava et al. (2002), i.e. impure nodules of micrite withdiffuse boundaries for PC and, on the other hand, coarsely crystallinecalcite with sharp boundaries for NPC. The paleosol horizons of usually50–100 cm thickness were sampled at 20–30 cm intervals for detailedthin-section analyses. 65 thin-sections (4 × 6 cm) of the fossil soilsfrom the 18 sections were made following Murphy (1986) anddescribed under the petrographic microscope following the guide-lines by Stoops (2003). The degree of pedogenic development wasassessed on the basis of maturity of the paleopedogenic features

following criteria established for macro- and micro-morphologicalfeatures (Birkeland, 1999; Bullock et al., 1985). Accordingly well-developed, moderately-developed, and weakly-developed paleosolsare marked by strongly to poorly expressed pedofeatures similar tothose in modern polygenetic soils and Late Quaternary paleosols ofthe Gangetic Plains (Kumar et al., 1996; Srivastava and Parkash,2002; Srivastava et al., 1994, 2010). The guidelines of Nesbitt andYoung (1989) and Retallack (1991) were used to resolve the over-print of paleopedological features by burial diagenesis. The procedureestablished by Sheldon and Retallack (2001) was applied to reconstructthe pre-burial thickness of the fossil soils.

4. Results

4.1. Major types of paleosol–sediment sequences

The entire fluvial sequence of the Dagshai Formation exposed alongthe Koshaliya River is characterized by mudstone–sandstone beds withformation of ferruginous paleosols in mudstones. Field characteristics,bulk rock geochemistry, and stable isotope geochemistry of these fossilsoils have been described elsewhere (Srivastava et al., 2013). On thebasis of field descriptions, four types of paleosol–sediment sequencesare recognized in the Dagshai Formation, named Type A, B, C, andD from bottom to top of the entire formation (Table 1). The fourpaleosol–sediment sequences described here follow an approachsimilar to pedofacies described from overbank deposits to denote later-ally contiguous bodies of sedimentary rock that differ in their containedlaterally contiguous paleosols as a result of their distance (during for-mation) from areas of relatively high sediment accumulation (Bownand Kraus, 1987). Paleosols constitute on average a proportion of 65–75% of the paleosol–sediment sequence in Type A, 50–60% in Type B,25–30% in Type C and b15% in Type D sequences (Srivastava et al.,2013). Grey sandstone constitutes the remaining lithological part inthese sequences, becoming more abundant from bottom to top (i.e.from Type A to Type D paleosol–sediment sequences) of the DagshaiFormation. A brief description of the typical features of the four typesof the paleosol sequences is given below.

The Type A paleosol–sediment sequence, encased in cross-beddedgray sandstone in the lower part of the Dagshai Formation, comprisesthree to four well-developed paleosols (exposed in sections D1–D5and D7; Figs. 2–3). The lower boundary of the Type A sequence is

Table 1Major types of paleosol–sediment sequences of Dagshai Formation.

Type of paleosol–sediment sequenceand stratigraphic position(in brackets: sections representing that type)

Typical paleopedofeatures andfrequency of paleosols

Degree of development Comparable soils/paleosols(after Srivastava et al., 1994, 2010)

Type-A(e.g. D1, D2, D3, D4, D5, D7)lowermost part of Dagshai Formation(100 m–150 m)

Thick B horizon (N1 m), well-developed peds,illuvial features (N1%), rhizoliths,mottles and pedogenic carbonate3–4 well-developed and fewweakly-developed paleosols

Strong/well-developed QGH4–5 soils with strongly developedpedofeatures formed in 10–8 ka time

Type-B(D6, D10, D12, D13, D15)lower middle part of Dagshai Formation(150 m–220 m)

B horizon (0.7–0.5 m), moderately-developed peds,illuvial features (b1%), rhizoliths, mottlesand pedogenic carbonate1–2 moderately developed and few weaklydeveloped paleosols

Moderate development QGH3 soils with moderatelydeveloped pedofeatures formedin 2.5–5 ka time

Type-C(D8, D9, D14)upper middle part of Dagshai Formation(160 m–210 m)

B horizon (0.3–0.2 m), poorly-developed peds,few rhizoliths, mottles, pedogenic carbonate,and few thin clay pedofeatures1–2 weakly-moderately developed paleosolswith dominance of mudstone

Weak/poor development QGH2 soils with weakly developedpedofeatures (0.5–2.5 ka)

Type-D(D11, D14, D18)upper part of Dagshai Formation(190 m–240 m)

Dominance of sedimentary features withoutany prominent B horizon, but occasionally fewrhizoliths and mottles

Sediments with little orno pedogenic activity

QGH1 soils with little or nopedogenic activity (b0.5 ka)

88 P. Srivastava, D. Sauer / Catena 112 (2014) 86–98


defined by an erosional surface with numerous pedorelicts in contactwith lithic sandstone (Fig. 3a). The well-developed paleosols of theType A sequence are dusky-red, have silty texture and exhibit numerousfilled and bleached root channels (Fig. 3a, Table 2). The bleached rootchannels occur as elongate tubular features (2–20 mm wide)branching out down to 2 m in depth and are marked by grey coreand red or reddish-brown rims (Fig. 3a). Most of these paleosolshave blocky structure but some of the horizons are also marked by platyand wedge shaped peds with pedogenic slickensides (Table 2, Fig. 3b).Within Type A paleosol sequence few poorly-developed paleosols alsoalternate with well-developed paleosols. Type B paleosol–sedimentsequences occurringmainly in themiddle parts of the Dagshai Formationshow less (1–2) well-developed paleosols in comparison with Type A(exposed in sections D6, D10, D12–13, and D15; Fig. 4a, b). Furtherupwards only sequences with moderately developed paleosols (exposedin sections D8–9 and D14) occur and are defined as Type C paleosol–sediment sequences (Fig. 5a). The uppermost part of the Dagshai Forma-tion is characterized by the dominance of sediments with little or nopedogenic overprint and only a few weakly to very weakly developedpaleosols; these sequences are termed Type D sequences (exposed insections D11, D14, and D18; Fig. 5b). The types of macroscopic featuresin the moderately to poorly developed paleosols are similar to those in

well-developed paleosols but the degree of development is relativelyless in comparison.

4.2. Micromorphology of the paleosols

Type A:Micromorphology of the lowermost part of the Dagshai For-mation, exposed in theD2 section (~4 m), shows three distinct paleosolunits with well-developed paleopedofeatures (Fig. 3a; Table 2). The top~1.1 m (Table 2; D2/2–D2/5 thin sections) of this paleo-pedocomplex ismarked by well-developed subangular blocky structure, silty texture,cross-striated b-fabrics, clay illuviation, pedogenic carbonate nodules(PC) of micrite, iron oxide impregnation features, and numerous filledand iron-depleted root channels. Diagenetic influence in this paleosolunit occurs as: (i) internal reorganization of the groundmass, compac-tion, and hypocoatings of iron-oxide along pedwalls (Fig. 3b), wherebyinternal organization of the groundmass is characterized by somewhatcircular fabric and iron remobilization, but still retaining the shapeof the peds (Fig. 3b), (ii) overprinting of illuvial iron-rich clay and finesilty-clayey coatings and intercalations, in the form of disruption andloss of orientation of these features (Fig. 3c), (iii) remobilization of ironoxide resulting in cementation by thin iron coatings on coarse grainsconsisting of sand sized quartz, mica and lithic fragments, (iv) formation

Fig. 2. Sedimentological details along the stratigraphic section measured in the study area (after Kumar et al., 2008) and correlating paleosol–sediment sections (D1 to D18). Details offour types (A–D) of paleosol sequences in terms of degree of soil development (poorly, moderately, and well-developed) bounded by sandstone. The log of the representative measuredsections (Type A: D2; Type B: D10; Type C: D9; Type D: D17) also includes key-pedofeatures of the diagnostic horizons. Age of Dagshai Formation after Jain et al. (2009).



of stagnic color pattern around root channels, showing an organicmatter-rich iron oxide core followed by a rim of iron-depletion andthen hypocoating of iron oxide along the walls (Fig. 3d); the rootchannels are in addition marked by infillings of dense micrite andmineral grains with pedorelicts (Fig. 3e, f), (v) coarsening of pedogeniccarbonate (PC)which originally consisted of densemicrite and spheruliticcalcite to equigranular sparry calcite up to 10–20% (Fig. 3g, h).

Micromorphological characteristics of this upper paleosol of thepaleo-pedocomplex in section D2 correspond to Bt and Btk horizonsof an Alfisol. Illuvial clay and pedogenic carbonate nodules occur indifferentmicro-areas of the same horizon (cf. Btk) with no overprintingrelationship. The underlying paleosol (Table 2, thin sections D2/6–D2/11)shows wedge-shaped peds, poro-striated and parallel-striated b-fabric,along with flattened and elongated nodules of micrite (Fig. 3i).

Below this vertic horizon a paleosol with Inceptisol-like features occurswith paleopedofeatures and diagenetic features similar to those in theupper paleosol–sediment sequences (Fig. 2). Contact of this paleosolwith the underlying sandstone is marked by an erosional surface(Fig. 3a). The erosional surface is marked by a ~0.5 m–1.0 m thick layercontaining numerous subangular to angular gravel sized lithorelicts andpedorelicts (Fig. 3a). Thin-sections of paleosols of the D5 section (~5 m,still lower part of Dagshai Formation) show micromorphologicalpaleopedofeatures and diagenetic features similar to D2 paleosols inaddition to remobilization and precipitation of cryptocrystalline silica(Table 2; Fig. 3j).

Type B: The middle part of the Dagshai Formation represented byD10, D12, and D15 sections is marked by 1–2 well-developed paleosols(Table 1, Figs. 2, 4a–b). Micromorphological characteristics of these

Fig. 3. Type-A paleosols: (a) profile photograph of section D2 with diagnostic paleosol horizons (scale: each black/white bar = 0.5 m); (b) thin-section characteristics of Bt1 horizon ofsection D2 showingwell-developed blocky pedswith iron oxide hypocoatings (marked by arrow); (c) yellowish brown thick illuvial clay coating along a channel in Bt1 horizon of sectionD5; (d) depletion feature after degradation of root with remains of organic matter in the core in Bss horizon of section D2; (e) large root channel infilling in Bw horizon of section D2comprising pedorelicts and groundmass (marked by arrow); (f) detail of the pedorelicts shown in “d”; (g) pedogenic calcium carbonate nodule consisting of impure micritewith 10–15% coarsening due to re-crystallisation in Bw horizon of section D2; (h) dense spindle-shaped calcium carbonate crystals forming spherulites after bacterial actionin Btk1 horizon of section D2; (i) poro-striated and parallel-striated b-fabric, and elongated pedogenic calcium carbonate nodules in Bss horizon of section D2; (j) remobilisationand precipitation of cryptocrystalline silica cement (marked by arrow) in Bw horizon of section D5.



Table 2Micromorphological and diagenetic features of the lithified paleosols of Dagshai Formation.

Dagshai Fm. Paleosolhorizon

Micro-structure

Texture Groundmass

b-fabric Coating PC NPC Ironoxide

Rizoliths Diagenetic featuresS. no Depth(m)

D17/1 A 0.3 • • • − − − • • •••Mudstone, embayed quartz grains, iron reduction,

cementation: micrite & iron oxide, illitization after

feldspar and other clay minerals, 20−30% re-

crystallization of micrite

D17/2 Bw 0.5 •• •• •• − • • − • •••D17/3 BC1 0.9 • •• •• ••••• − • − •• ••D17/4 BC2 1.2 • •• •• ••••• − • − •• ••D17/5 BC3 1.6 • •• •• ••••• − • − •• ••D16/1 C 0.3 • • ••• • − − • − −

Sandstone, sutured contacts, cementation by micrite,

iron oxide, & silica, illitization, bending of mica

flakes

D16/2 C 0.6 • • ••• • − − • − −D16/3 C 0.9 • • ••• • − − • − −

D15/1 Bw 0.3 •• ••• •••• •••• • •• •• ••• •••Mudstone, remobilisation of peds groundmass, iron

oxide hypocoatings on ped walls, 10−20% coarsening

of micrite, stress related argillans, illitization

D15/2 Bss1 0.6 ••• ••• •••• •••• •• •• •• •• •••D15/3 Bss2 0.9 ••• •••• •••• •••• •• • •• •• •••

D12/1 A 0.3 ••• ••• •••• •••• • ••• •• •• ••Mudstone with erosional surface, pedorelicts,

flattening of peds & nodules of micrite, iron oxide

coating on ped walls, remobilization of groundmass

& liquefaction due to pore fluid pressure, remnant

laminations, iron reduction around decomposed

(incomplete) roots, 5−10% coarsening of micrite,

illitezation

D12/2 Bss 0.6 ••• ••• •••• •••• • ••• •• •• ••D12/3 Bssk 0.9 ••• ••• •••• •••• • •••• •• •• ••D12/4 Bss 1.2 ••• ••• •••• •••• • •• • • •D12/5 Bwk1 1.5 ••• ••• •••• •••• • • •• •• •D12/6 Bwk2 1.8 ••• ••• •• ••• • • •• •• •D12/7 BC 2.1 • ••• − − − − − − −

D11/1 A 0.3 • • • − − − • •• ••Mudstone, gleying and remobilization of iron oxide,

fracturing and sutured contacts, illitizationD11/2 Bw1 0.6 •• •• •• ••• • − • ••• ••D11/3 Bw2 0.9 •• ••• •• ••• • − • ••• ••

D10/1 A 0.2 • • • − •• − • ••• ••Mudstone, remobilization of groundmass &

liquefaction due to pore fluid pressure, fracturing

andsutured contacts, illitization, gleying, darkening/

blackening of organic matter, iron oxide coating on

ped walls

D10/2 Bt1 0.5 •• •• •• •• ••• − • ••• ••D10/3 Bt2 0.7 •• ••• •• •• ••• − • ••• ••D10/4 Bt3 0.9 ••• ••• •• •• ••• − • ••• ••D10/5 Bw1 1.1 •• • • • •• − • ••• ••D10/6 Bw2 1.3 •• • • • • • • ••• ••D10/7 BC 1.5 • • • − •• − • ••• • •

D9/1 A 0.3 •• • • − • • •• ••• ••Mudstone, remobilization of groundmass & ped

walls coated by iron oxide, iron reduction due to

burial, calcretisation of root channels, illitezation,

10−20% coarsening of micrite

D9/2 Bt 0.5 •• • • • ••• • • ••• ••D9/3 Bw 0.8 •• • • ••• ••• •• • ••• ••D9/4 BC 1.2 • • • • − ••• • ••• •

D5/1 AC 0.3 •• ••• ••• • − − • • •••Mudstone, iron reduction due to burial and

calcretisation of root channels, remobilization of

groundmass & ped walls with hypocoatings of iron

oxide, liquefaction due to pore fluid pressure,

flattening of peds & nodules of micrite,

remobilisation of silica and precipitation of

cryptocrystalline quartz, fracturing and sutured

contacts, darkening/blackening of organic matter,

10−20% coarsening of micrite

D5/2 Bt1 0.5 •• • • •• •• − • •• •••D5/3 Bt2 0.9 •• • •• •• •• • •• ••• ••D5/4 Bwk1 1.2 •• • •• • • •••• •• ••• ••D5/5 Bwk2 1.5 •• •• •• • • •••• • ••• ••D5/6 A 1.8 •• •• •• • − •••• • ••• ••D5/7 Bwk3 200 •• •• •• •• • •• • ••• ••D5/8 Bw 2.3 •• •• •• • • − − ••• ••D5/9 Bw 2.5 •• •• •• • • − − ••• ••D5/10 Bw 3.0 •• •• •• • • ••• • ••• •D5/11 Bt 3.3 •• •• •• •• •• • • ••• ••D5/12 Bwk4 3.8 •• •• •• •• •• •• • ••• ••D5/13 Bwk5 4.0 •• •• •• •• •• ••• • ••• •D5/14 Bw 4.3 • • • − − • • •• ••D5/15 Bt 4.5 •• • • • •• • • •• ••D5/16 Bw 5.1 • • • − • • • •• •D5/17 BC 5.3 • • • − − − − •• −D2/1 C 0.3 • • ••• • − − • − −

Sandstone at top and bottom of the paleosol in

mudstone, erosional surface with pedorelicts,

reduction of and iron and remobilization along roots,

calcretisation of root channels, thin platy structure

and slickensides, remobilisation of groundmass in

peds, hypocoating of ped walls, large pedotubular

infillings, 10−20% re-crystallization of micrite as

spherulitic calcite, equigranular microsparite,

flattening of micritic nodules and stress argillans,

darkening/blackening of organic matter, fracturing

and sutured contacts, planar voids

D2/2a Bt1 0.5 •• ••• •••• ••• ••• • • •• ••D2/2b Bt2 0.7 •• ••• •••• ••• ••• • • •• ••D2/3 Btk1 0.9 •• •• •• •• ••• ••• • •• ••D2/4 Btk2 1.1 •• ••• •••• ••• •••• • •• • •• ••D2/5 Bw 1.4 •• ••• •••• ••• •• • • •• ••D2/6 Bss 1.8 ••• ••• •••• •••• • •• • • ••D2/7 Bssk1 2.0 ••• ••• ••••• •••• • •••• • • ••D2/8 Bssk2 2.4 •••• •• •• •• • ••• • • •D2/9 Bw 2.6 •• ••• •••• •••• − ••• • • ••D2/10 Bssk3 2.8 ••• ••• ••••• •••• • •••• • • ••D2/11 Bssk4 3.0 ••• ••• ••••• •••• • •••• • • ••D2/12 BC 3.2 • •• •• • − • • • −D2/13 Bw 3.4 •• • •• • • • • • ••D2/14 Bw 3.6 •• • •• • • • • • ••D2/15 Bw 3.8 •• • •• • • ••• • • •D2/16 BC 4.2 • • • − − − • − −

Index Microstructure

(MS)

Texture Ground

mass (c/f)

b-fabric Coatings Pedogenic

CaCO3 (PC)

Non-pedogenic

CaCO3 (NPC)

Iron oxide Rhizoliths

Sandstone Massive: • Subang. blocky: ••

Ang. blocky: •••Platy: ••••

Granular: •••••

Sand: • Sandy loam: ••

Silty: ••• Silty loam: ••••

Clay: •••••

80/20: •60/40: ••

50/50: ••• 40/60: ••••

30/70: •••••

Undifferentiated: •Stipple speckled: ••

Cross striated: ••• Reticulate striated: ••••

Parallel striated: •••••

Few discontinuous: • (<1%)Few thin continuous: •• (<1%)

Few thick continuous: ••• (~>1%)Common thick cont.: •••• (>1%)

Coatings + papules: ••••• (<1%)

<5%: • 5−10%: ••

10−20%: •••20−30%: ••••

30−40%: •••••

<5%: • 5−10%: ••

10−20%: •••20−30%: ••••

30−40%: •••••

Few mottles: •Common m. ••

Few conc: •••Comm conc ••••

Conc + hc: •••••

<5%: • 5−10%: ••

10−15%: •••15−20%: ••••

>20%: •••••

Mudstone

D2 Paleosol

section



paleosols correspond to moderately to strongly developed Bt, Bss, andBw horizons of Alfisol-, Vertisol-, and Inceptisol-like paleosols (Table 1and 2). Their micromorphology is marked by strong pedality, speckledto striated b-fabrics, iron-oxide mottles and concretions, filled rootchannels with stagnic color pattern and hypocoatings of iron-rich siltyclay, textural pedofeatures, and pedogenic calcium carbonate (10–15%) in deeper parts of the paleosols (Table 2; Fig. 4e–k). Diagenetic fea-tures observed are similar to those in Type-A paleosols, includingflatten-ing of peds, iron oxide hypocoatings, coarsening of micrite up to 20%,sutured contact of quartz grains, and illitization (Table 2; Fig. 4d, f–h).In addition, clayey intercalations occurring as vertical or oblique emana-tions protruding from folded laminations as pore fluid escape featuresare also commonly observed (Fig. 4c; Table 2).

Type C: Soil-sediment sequences exposed in sections D8, D9, andD14 also belong to the middle part of Dagshai Formation but aremarked by predominance of only moderate to weak soil develop-ment; no well-developed paleosols like in Type A and B paleosol–sediment sequences occur (Table 1, Fig. 5a). Micromorphologyof the paleosol (~1.2 m) in section D9 shows weak to moderatedevelopment of subangular blocky peds, stipple-speckled and cross-

striated b-fabric, rhizocretions, iron-rich clay coatings and inter-calations, and pedogenic calcium carbonate that becomes moreabundant in the lower horizons (Table 2; Fig. 5c–e). Diageneticfeatures observed are similar to those in Type-A paleosols(Table 2; Fig. 5c–e).

Type D: Paleosol–sediment sequences occurring in the upper partsof Dagshai Formation (sections D11, D16, D17, and D18) are character-ized by only sporadic occurrence of any pedogenic alteration and aredominated bymudstone and sandstone with no evidence of pedogene-sis (Fig. 5b). Micromorphological characteristics of the paleosols insections D11, D16, and D17 confirm their low degree of development(Table 2). Important diagenetic features include sutured contacts,cementation by micrite, iron oxide, and silica, bending of mica flakes,and illitization in sandstones. The mudstones showing weakly devel-oped pedofeatures are marked by diagenetic features similar to thosein Type A, B, and C paleosols (Fig. 5g–h).

The c/f-related distribution pattern of all studied paleosols isporphyric (c/f: 30/70–40/60 applying a 20 μm limit; Figs. 3c, f, 4h, 5c)as most of the paleosols developed in mudstones. The coarse fractionis dominated by sand-sized quartz grains showing effects of burial

Fig. 4. Type-B paleosols: (a) exposure of well-developed paleosol in section D10; (b) paleosol in section D10 showing bleached root channel extending for ~1.5 m; (c) thin-section detailsof Bss horizon of section D12 showing clayey intercalations interpreted as liquefaction feature (arrow); (d) detail of clayey intercalations showing bow-shaped fabric consisting of alter-nating laminations of coarse and fine groundmass (arrow); (e) peds with hypocoatings of SOM-rich iron oxide in Bss horizon of section D12 (arrow); (f) fragmented pedogenic micriticcalcite nodule in Bwk1 horizon of section D12; (g) pedogenic micritic calcite nodule showing coarsening of ~10% of its areal extent due to re-crystallisation; (h) yellowish brown illuvialclay in Bt1 horizon of section D10; (i) globular concretion of iron oxide and cross-striated b-fabric in Bss horizon of section D15; (j) part of a root with iron-oxide rich silty-clay coatingalong the wall of the root channel in Bt horizon of section D10; (k) organic matter impregnation after root degradation in Bt horizon of section D10.



such as fragmentation and sutured contacts (Fig. 5f). The most domi-nant b-fabrics are cross- and grano-striations; parallel, speckled andundifferentiated b-fabrics are less common. Textural paleopedofeaturesoccur commonly inmoderately to strongly developed paleosols, such asyellowish brown clay to iron rich silty clay (i) coatings, (ii) infillings,(iii) intercalations, and (iv) papules (Figs. 3c, 4h, Table 2). Illuvial featuresare more common in Type A and B paleosols occurring in the lower andmiddle parts of the Dagshai Formation, whereas little or no illuvialpedofeatures occur in Type C and D paleosols in the upper parts (cf.Table 2). Pedogenic carbonates occurring as dense micritic nodules aremore commonly observed in Type A and B paleosols in comparisonwith paleosols in upper part of Dagshai Formation (Table 2).

5. Discussion

5.1. Diagenetic influence on Dagshai paleosols

Macro- and micromorphological characteristics of the Dagshaipaleosols correspond to modern Entisols, Inceptisols, Alfisols andVertisols. In order to estimate the diagenetic compaction of the

paleosols, the procedure established by Sheldon and Retallack (2001)was applied:

C ¼ −Si= Fo=eDK

� �–1

h i

whereC is the original fraction of original thickness, Si is the initial solidity,Fo is the initial porosity, K is a curve fitting constant, and D is the burialthickness (km). For a burial thickness of 7.5 km, the original thicknessof the paleosols was calculated by using a K-factor of 0.17 for Entisols,0.27 for Inceptisols, 0.35 for Alfisols, and 0.12 for Vertisols. Values appliedfor initial solidity and initial porosity were 0.62 and 0.38 for Entisols, 0.51and 0.49 for Inceptisols, 0.65 and 0.35 for Alfisols, and 0.69 and 0.31 forVertisols (Sheldon and Retallack, 2001). These input variables resultedin compaction (C) factors of 0.69 for Entisols, 0.54 for Inceptisols, 0.73forAlfisols, and0.78 for Vertisols. These compaction factors suggest differ-ential compaction ranging from 54% to 78% of pre-burial thickness ofthese paleosols. Despite the severe compaction estimated for the Dagshaipaleosols caused by 7.5 km burial, most of the paleopedogenic character-istics are still well-preserved, although overprinted by additional diage-netic features. Nevertheless, much of the paleopedogenic history could

a Moderately-developed paleosol D9

A

b

c d e

g h f 100µm

100µm 100µm

500µm 100µm

100µm

Bt

Bw

BC

Poorly-developed paleosol D17

A

Bw

BC1

BC2

BC3

Fig. 5. Type C and D paleosols: (a) paleosol exposed in section D9 with moderately developed pedofeatures; (b) paleosol exposed in section D17 with poorly developedpedofeatures; (c) burial-redoximorphic feature and degradation of organic matter in Bw horizon of section D9 (arrow); (d) iron oxide hypocoating on ped walls in BC horizonof section D9; (e) burial-redoximorphic feature and digitate organic matter residue after a root in Bw horizon of section D11; (f) sutured contact of coarse fraction in sandy Bwhorizon of section D17 (arrow); (g) bending of muscovite and sutured contact between mineral grains in sandstone of section D16; (h) bending of a large muscovite grain andsutured contact between mineral grains in sandstone of section D16.



be revealed by detailed macro-, and micromorphological analyses(Fedoroff et al., 2010; Lander et al., 1991; McCarthy et al., 1998).

Pedality varies fromwell-developed blocky and platy peds in Type Ato very weakly-developed blocky peds in Type D paleosols of theDagshai Formation. The peds outlined by iron oxide hypocoatingsoccur as discrete features that developed during early Oligocenepedogenesis (Figs. 3b, i, 4e, 5d). It is concluded that impregnationof the ped walls with iron oxide, caused by remobilization of ironoxide and internal reorganization of the groundmass after burial, ledto stabilization and hence preservation of 50–60% of the peds in thefossil soils of the Dagshai basin. This is in agreement with the observa-tion of pedality in paleosols with deep burial diagenesis formMid-Tertiary sediments of China and Lower Cretaceous Mill Creeksediments of Canada (Lander et al., 1991;McCarthy et al., 1998). Preser-vation of the peds during burial diagenesis of the Dagshai paleosols isadditionally supported by their behaviour that is more akin to sand-stone rather than mudstone and thus facilitates preservation of struc-tural elements in paleosols (Retallack, 1993; Sheldon and Retallack,2001). During burial peds get packed more closely with increased con-tact area between peds similar to repacking of sand grains in sand-stones. This process is reflected in closely packed peds and flatteningof the peds observed in the Dagshai paleosols (cf. Figs. 3b, 4e).

The remaining 30–40% of the thin-sections shows nearly completeobliteration of the paleosolswith predominance of complexly folded lam-inations and clayey intercalations, representing pore fluid escape dykesthat appear similar to liquefaction features (0.5 to 1.5 cm; Fig. 4c–d).The clayey intercalations occur as vertical or oblique emanations fromthe folded laminationswith bow shaped fabrics (Fig. 4c). The features ob-served here can be explained by diagenetic processes that may influenceclayey sediments such as: (1) mechanical compaction, which is mainlycontrolled by effective stress and sediment (matrix and grains) strengthand compressibility, resulting mainly in volume change due to porosityreduction; and (2) chemical diagenesis, which involves mineral dissolu-tion and precipitation (Nygård et al., 2004). The clayey intercalationsare interpreted as diagenetic liquefaction caused by overpressure duringshallow (b1 km)burialwhenmud tends to undergomechanical compac-tion as the dominant process (Hurst, 2011). During deep burial chemicaldiagenesis (temperature dependent) exertsmore control on diagenesis ofthemudrock (Broichhausen et al., 2005;Matthews et al., 2000). Interplayof both processes during burial causes reduction of porosity initially from60–70% to 10–20% at 7–8 km depth following conventional exponentialporosity reduction and compaction (Compton, 1991). Mechanical com-paction produces anisotropic rearrangement of clay particles and oncechemical diagenesis has taken place, chemical cementation preservesthe micro-structure of the paleosols with only minor alteration evenunder very high stress (Nygård et al., 2004). This could explain preser-vation of peds together with pore fluid escape features in thesefossil soils. The diagenetic liquefaction described here is in agree-ment with postdepositional sediment mobilization within mud-stone rich successions described by Davies et al. (2006), occurringduring shallow burial due to pore fluid expulsion and overpressurebuildup.

Textural pedofeatures in paleosols are among the most diagnosticfeatures providing evidence of pedogenesis under humid conditions(Fedoroff et al., 2010; McCarthy et al., 1998; McSweeney andFastovsky, 1987; Retallack and Wright, 1990; Sheldon, 2005). The tex-tural paleopedofeatures in paleosols of Dagshai Fm. indicate substantialilluviation and formation of argillic horizons under humid and well-drained conditions. Burial diagenesis resulted in remobilisation of thegroundmass and overprinted illuvial features leading to: (i) loss of pre-ferred orientation and contorted appearance, and (ii) compaction anddisruption of the clay pedofeatures (cf. Figs. 3c, 4h), which is in agree-ment with disruption of textural pedofeatures caused by compactionas described by Kemp (1985). It is assumed that much of the disruptionof illuvial pedofeatures occurred during mechanical compaction undershallow burial. Disruption of textural pedofeatures in Dagshai paleosols

due to burial diagenesis is similar to that reported from early Eocenepaleosols of Mill Creek Formation in Canada which also experienceddeep burial (temperature ~150 °C) (McCarthy et al., 1998).

Pedogenic calcium carbonate is more abundant (25–30%) in thelower than in the upper parts (nil to 5%) of the Dagshai Formation(Table 2). The pedogenic carbonate is predominantlymicritic, occurringas nodules with diffuse boundaries (Figs. 3g, 4f–g), with only 10–15% ofequigranular sparite that possibly re-crystallized due to diagenesis. Thissuggests preservation of pedogenic carbonate nodules with densemicrite despite ~7 km burial. However, some of the nodules are markedby disruption/fragmentation. Preservation of the pedogenic carbonatenoduleswith densemicrite is similar to those of peds, suggesting that, de-spite burial diagenesis, the pedogenic carbonate nodules could stillprovide paleoenvironmental information. The stable isotope compo-sition of the pedogenic carbonates of the Dagshai paleosols confirmstheir paleoenvironmental potential (Bera et al., 2010b; Srivastavaet al., 2013). llitization is another common diagenetic feature recordedin most of the thin sections (Table, 2; Figs. 4h, k, 5g, h). It is suggestedthat during deep burial interplay of raised temperature and percolatingpore fluids or groundwater acting on the groundmass of the paleosolsresulted in illitization and cementation of the paleosols (Nesbitt andYoung, 1989). This interpretation is in agreement with chemical diagene-sis (temperature dependent) of themudrocks resulting in precipitation ofnewminerals such as illite as described by several authors (Broichhausenet al., 2005; Matthews et al., 2000; Nygård et al., 2004; Sandler et al.,2012).

It is critical to understand the role of diagenesis related to red colorand iron oxide features (Blodgett et al., 1993; Retallack, 1991). Ironoxide features of the Dagshai paleosols (mottling and concretions)show disruption and remobilization of the iron possibly due to burialdiagenesis. XRD studies of the Dagshai paleosols show a mixture ofhematite and goethite with predominance of hematite, suggestingthat the iron oxide features and red color of these paleosols is ofpedogenic origin because diagenesis should have affected all forms ofiron oxides in a similarway rather than producing amixture of hematiteand goethite (Kraus and Hasiotis, 2006; PiPujol and Buurman, 1994).Petrological studies of the sediments from Dagshai Fm. also confirmthat burial diagenesis did not cause complete alteration of these sedi-ments because lithic fragments of very low-grade metamorphism(Chaudhri, 1975; Najman and Garzanti, 2000) and significant propor-tions of smectitic clays (Raiverman, 2002; Raiverman and Suresh,1997) are well preserved. Based on these different independent obser-vations it is concluded that the red color of these ferruginous paleosolsis mainly a result of the prevailing paleoenvironmental conditions,and that burial diagenesis caused only partial iron remobilization andprecipitation. It is the characteristic color of tropical and subtropicalsoils (Kampf and Schwertmann, 1982), and is attributed to oxidizingconditions in the presence of abundant vegetation in well-drained con-ditions (Kraus and Hasiotis, 2006; Macedo and Bryant, 1987; PiPujoland Buurman, 1994). In general, these paleosols lack discrete organiccompounds, but in some thin-sections former plant residues arerecorded as disseminated opaque, dark-colored fragments (~100–200 μm) and as digitate pseudomorphs after plant residues (cf.Figs. 3d, e, 4k). This observation is in agreement with the record of or-ganic compounds reported from lithified paleosols elsewhere (Landeret al., 1991; McCarthy et al., 1998; Nordt et al., 2012). Total organic car-bon (TOC) contents of the Dagshai paleosols range from 0.4 to 1.9%,which is comparable to modern ferruginous tropical soils of southernIndia (Chandran et al., 2005). Darkening of the opaque fragments ofthe organic matter found in the groundmass of these paleosols is attrib-uted to coalification during deep burial (Boggs, 2006).

Iron-depleted filled root channels are themost diagnostic character-istics of the Dagshai paleosols. They are vertically oriented, orthogonalto bedding plane, downward tapering and branching (cf. Figs. 3a, 4b,5a–b; Table 2), and are interpreted as the fossil root traces of woodyvegetation prevailing during the formation of the paleosols in the



Dagshai basin during early Oligocene. The bleached root channels rarelyshowanymorphological disruption, indicating resistance (similar to thepeds) during mechanical compaction at shallow burial (b1 km).However, duringdeepburial itwas influencedby the followingprocesses:(i) central cores were infilled by groundmass and pedorelicts; (ii) ironoxide, calcium carbonate, and clay minerals formed cementations; (iii)rarely preserved organic residues were coalified; (iv) iron-depletionzones around the central core and iron-oxide hypocoatings formedalong the walls (cf. Figs. 3d, 4j–k, 5c, e). The diagenetic influence on roottraces of woody vegetation in the Dagshai paleosols is similar to thosedescribed from ferruginous paleosols that experienced deep burial else-where (Hasiotis, 2004; Hiller et al., 2007; Kraus and Hasiotis, 2006;McCarthy et al., 1998; Smith et al., 2008).

5.2. Paleoenvironmental reconstruction based on thin-section analysis ofthe fossil soils

Despite diagenetic alteration micromorphological evidence ofimportant soil-forming processes is still discernible in these fossil

soils. For example, the well-developed paleosols showing Bt, Btk,Bss, and Bssk horizons are marked by strong pedality, cross- andparallel-striated b-fabrics, bioturbation, mineral weathering,rhizocretions, ferruginous nodules/concretions, and pedogenic car-bonates (e.g. D2, D5, D10 in Type-A and Type B, Table 2). The texturalpedofeatures occurring as thick-ferruginous silty-clay coatings and in-tercalations of silty-clay (e.g. Fig. 3c, 4h) suggest large scale illuviationand formation of the Bt horizons in these paleosols under well-drained and humid conditions (Chandran et al., 2005; Srivastava et al.,2009).

Pedogenic calcium carbonate accumulations with dominance ofimpure micrite observed in these fossil soils are similar to pedogeniccarbonates of Late Quaternary paleosols and Holocene soils of theHimalayan Foreland (Srivastava et al., 2002, 2007, 2009, 2010). Theyare interpreted as pedogenic features of warm and dry periods withloss of pCO2 from sub-soils. This is in agreement with the formation ofpedogenic carbonates in paleosols to dry periods of seasonal climates(Breecker et al., 2009). The presence of spherulitic calcite (cf. Table 1)points to the role of microorganisms in calcium carbonate precipitation

Fig. 6. Scheme of chronological sequence of event-process-response of Dagshai paleosols related to (i) paleopedogenesis; (ii) shallow burial diagenesis; (iii) deep burial diagenesis.



in these fossil soils (Verrecchia et al., 1995). The present observation ofspherulitic calcite in Dagshai paleosols is in agreementwith earlierfind-ings of bacterial precipitation of calcite in Paleogene sediments of theHimalayan Foreland during its paleolatitudinal position in tropics(Singh et al., 2007), which is also in agreement with spherulitic calciteprecipitation in tropical soils reported by Braissant et al. (2003). Thepresence of clay coatings along with pedogenic carbonates supportsthe possibility of seasonality during paleosol formation in the Dagshaisub-basin with humid to subhumid conditions. Wedge-shaped pedsand strongly developed poro-striated and parallel-striated b-fabric inBss horizons of these fossil soils suggest shrinking and expansion ofswelling-clays in a seasonal, subhumid climate (Pal et al., 2001;Srivastava et al., 2002; Wilding and Tessier, 1988), which is supportedby the presence of smectite-rich clays reported from sediments of theDagshai Formation (Raiverman, 2002; Raiverman and Suresh, 1997).The shrink-swell features of these paleosols are similar to those inLate Quaternary paleosols of interfluves from the Gangetic Plains thatformed in subhumid to semiarid climatic conditions (Pal et al., 2012;Srivastava et al., 2010).

Despite diagenetic alteration, former root channels are stillmorphologically well-expressed in these fossil soils, characterizedby iron-depleted inner core and iron oxide precipitation alongthe channel walls. The same morphology of root traces wasdescribed from well-drained ferruginous paleosols elsewhere(Hasiotis, 2004; Hiller et al., 2007; Kraus and Hasiotis, 2006;Smith et al., 2008). The presence of these features in the Dagshaipaleosols indicates dominance of woodland vegetation with thickroots (~20–30 mm wide) extending over 2 m. This interpretationis supported by fossil leaf imprints of Ficus L. in fluvial sequencesof the Dagshai Formation, which is an evergreen to occasionallydeciduous, moderate to large tree distributed over humid-tropicalregions (Mathur et al., 1996; Srivastava et al., 2011). This interpre-tation is also supported by tropical paleovegetation recorded inOligocene fluvial sediments in the NW and NE Himalaya with itspaleolatitudinal position at 10–15°North (Martin et al., 2011;Srivastava et al., 2012). The paleolatitudinal position (~18°North)of Dagshai sub-basin during early Oligocene time confirms tropicalconditions during the formation of paleosols.

The paleoenvironmental interpretation on the basis of micromor-phological analysis is also in agreementwith bulk geochemistry and sta-ble isotopic composition of the pedogenic carbonates from Dagshaipaleosols (Srivastava et al., 2013). The geochemical composition ofthese paleosols suggests moderate-high degree of weathering, as indi-cated by leaching of bases and concentration of Al, Ti and Fe. The ratioof Al2O3/SiO2 shows higher values for Bt/Btk horizons in comparisonwith BC/Bw horizons suggesting the formation and translocation of ped-ogenic clay that have been confirmed bymicromorphological study. Thechemical index of alteration (CIA-K) that can be used as ameasure of in-tensity of chemical weathering (Maynard, 1992; Nesbitt and Young,1989; Sheldon et al., 2002) ranges from 73 to 89 for Bw/Bt/Bss hori-zons of Dagshai paleosols. The paleoprecipitation estimate basedon CIA-K values provides MAP ranging from 947 mm to 1287 mm,suggesting humid conditions that could have caused intense chemi-cal weathering during soil formation in the Dagshai basin (Srivastavaet al., 2013). Stable isotope composition of pedogenic carbonatesduring burial diagenesis is marked by additional depletion of δ18Ovalues up to −10‰, making it difficult to interpret, but δ13C of thepedogenic carbonate remains unaltered and represents the originalpaleoenvironmental conditions (Bera et al., 2010b; Cerling, 1991;Leier et al., 2009). The δ13C values for pedogenic carbonates ofDagshai paleosols range from−9.4‰ to−11.3‰, supporting that trop-ical paleovegetationwas dominated by C3 typewoodland (Srivastava etal., 2013). The C3 type of paleovegetation recorded in the carbon isoto-pic signature of pedogenic carbonates of the Dagshai paleosols is inagreement with the global paleovegetation record of C3 type duringearly Oligocene (Alroy et al., 2000; Cerling, 1992; Zachos et al., 2001).

6. Conclusions

Based on thin section analysis of lithified paleosols, this study distin-guished micromorphological characteristics reflecting soil-formingprocesses and effects of subsequent burial diagenesis (~7.5 km,140 °C) in Dagshai paleosols of the Himalayan Foreland. A sequential/hierarchical order of major paleopedogenic and diagenetic processescould be established through this study (Fig. 6). Paleopedogenic charac-teristics identified in this study include structural elements, texturalpedofeatures, mottling, biogenic features, bleached root channel traces,pedogenic calcium carbonate accumulations, and swell-shrink features.Formation of these pedogenic features was followed bymechanical dis-ruption under shallow burial that caused compaction,flattening of peds,loss of porosity and partial liquefaction. Subsequent deeper burialresulted in chemical alteration, including cementation, mineral dissolu-tion and re-precipitation, coarsening of micrite, and coalification. Thepaleoenvironmental conditions inferred based on paleopedogenic pro-cesses in Dagshai Fm. are characterized as seasonal subhumid tohumid tropical with good drainage during early Oligocene.

Acknowledgements

We thank INSA-DFG bilateral exchange programme that allowed thefirst author P. Srivastava to visit Germany for threeweeks and study thin-sections of the Dagshai paleosols together with D. Sauer. We are deeplyindebted to Prof. Nicolas Fedoroff for his critical comments that greatlyimproved this article. We are also thankful to two anonymous reviewersfor their constructive suggestions to improve the manuscript. We thankour colleagues for the helpful discussions during thework at Hohenheimand Delhi Universities.

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