Table 5.1.

Description and interpretation of sedimentary facies in the Par formation of Gwalior Group

Facies typeDescriptionInterpretationFacies thickness
Alluvial fan 1. Clast-supported boulder conglomerateMonomictic quartz gravels and boulders as a coherent mass; clasts poorly sorted and variably angular. Base often jagged as clasts penetrate into the substratum. Also present as ungraded matrix-infilled bedScree breccia or boulder lag from hyperconcentrated flood flows/megaflood flow boulder beds0.30–0.6 m
 2. Graded conglomerateGranule to pebble sized clasts; matrix or clast-supported with poorly sorted sand matrix having clay content <1%; Inverse to normal gradedHigh-density turbidity current; cohesionless debris flow. Reverse-graded units by sieve deposition0.12–0.4 m
 3. Sheet conglomerateClast supported; clasts generally bed parallel or imbricated with their intermediate axesHigh-energy tractive flow1.5–2.0 m
 4. Massive granular sandstoneModerately sorted medium- to coarse-grained sheet sandstone with dispersed granules; internally massive or plane laminated. Lateral pinching of bedHill-wash deposition. Rapid settling, possibly from grainflow or from upper flow regime tractive flow0.04–0.24 m
 5. Rhythmic granular pebbly and sandy planar coupletClast supported, poorly sorted coarse to very coarse granule/pebble in planar beds rhythmically interstratified with granule free medium to fine sand. Bedding planes sharp but non-erosionalSheetflow couplet deposited from upper flow regime flow(s) after heavy rainfall1.8–2.7 m
Braided alluvial system 6. Medium- to coarse-grained sheet sandstoneSheet-like beds with erosive to slightly concave basal surfaces. Beds internally massive, plane-laminated, cross-stratified. Incorporation of rip-up clastsBraided fluvial channels and distributary channels with gravel bars0.35–1.78 m
 7. Lensoidal conglomerateIntraformational with pebble/cobble sized clasts, frequently oversized, matrix supportedRapid deposition from heavily loaded flow, possibly of flash flood origin0.1–0.16 m
 8. Compound cross-stratified sandstones, often pebblyPoorly sorted sandstone. Smaller cross-strata (set thickness 2.2 cm) are trough shaped and oriented roughly in opposite direction to the large cross-strata. Pebbles preferentially concentrated at the base of large foresetsBar on the channel floor. Small dunes climbing the stoss of the bar0.15–0.2 m
 9. Tabular cross-stratified coarse- to medium-grained sandstoneCoarse- to medium-grained sandstone containing tabular cross-strata, locally with asymptotic toesTransverse bank attached bar, lateral accretion on bank or mid channel bars0.35–0.5 m
10. Rippled sandstoneThin bedded, lenticular in geometry, current ripples on bedding planeLower flow regime bed0.03–0.11 m
11. Siltstone–mudstoneInfrequently present demarcating boundaries of fining-upward cycles, laterally impersistent. Occasional presence of ripplesOverbank fines. River flood plain deposits0.01–0.03 m
Tidal bar-interbar12. Sandstone with cyclically rhythmic cross-stratificationFine- to medium-grained sandstone, locally turned muddy. Beds with unidirectional planar cross-sets with downcurrent decrease in foreset angle from c. 23° to c. 11°, periodically punctuated by steeper and erosive reactivation surfaces. Between two reactivation surface cross-bed geometry changes from concave-up – tabular form – gentle sigmoidal with concomitant variation in grain size. Double mud drape on cross-strataFull-vortex subtidal bar recording unsteady flow character. Tidal rhythms in successive packages defined by mud linings within the cross-sets. Intraset cyclic cross-laminal changes along with grain size, reveal repeated waxing and waning of the water flowUnits have laterally variable thicknesses; unit thickness ranges from 0.05 to 0.12 m
13. Interbedded shale-siltstoneAlternates with facies 12 with sharp/gradational contact. Siltstone beds are cross-stratified or plane laminated or rippled. Palaeocurrent direction diametrically opposite (180° apart) to that from facies 12Interbar sediment. Palaeocurrent reversal favours a tidal interpretation0.22–0.75 m
14. Fissile grey shaleOccurs at the topmost part of this association. Fissile, structure less. Occasional presence of massive siltstone laminaeDeep-water shelf below subtidal domain without any current/wave action0.6–1.25 m
Shoreface15. Well-sorted medium-grained tabular sandstoneTabular units of well-sorted sandstone; trough cross-stratification in chevron arrangement, low-angle planar lamination and rare tabular cross-stratification. Often contains rip-up mud clasts. Symmetrical ripples of Ripple Index (RI) <8 on bedding plane surfacesWave-dominated middle to upper shoreface sandstone. Planar laminations interrupted by rough cross-stratified wedges imply surf-swash transitionDecimetre- to metre-thick beds, isolated to amalgamated. Together with facies 16 forms stacked progradational cycles; increases upwards
16. Lenticular thin-bedded sandstone–shale alternationAlternates with facies 15. Silty to fine sandy lenticles interbedded with shale; symmetrical ripple forms, wavelength=12 cm, amplitude =0.8 cm, RI=15). Internally sandy lenticles massive or cross-laminated. sandstone: shale proportion varies from place to placeRelatively lower energy lower shoreface sedimentWithin individual progradational cycle relative abundance decreases upward