Table 7 Brief descriptions and interpretation of facies types under the shoreface facies association (FA-5)

Facies 5A: Fossil-bearing sandstone

Fine- to medium-grained sandstone with local pebble layers; gastropods (Turritella) with bivalve (Cardium) near base; dominance of bivalves increases up-section; Gastropod shells often mutually oppositely oriented; symmetrical low-amplitude long wave-length ripples, ladder-back ripples and flat-topped ripples with bifurcated crest lines; near the upper part shells of the oyster Ostrea (height 4–10 cm) are abundant.

Association of Turritella and Cardium shells indicates shallow marine depositional conditions. The abundance of Turritella indicates well-oxygenated, nutrient-rich, warm water conditions (Malarkodi et al. 2009). Ostrea abundantly lives in bays and estuaries and/or in nearshore subtidal environments (Khosla and Sahni 2000). Small symmetrical ripples indicate wave activity in shallow waters (Bhattacharya and Jha 2014).

Facies 5B: Thalassinoides–Ophiomorpha-bearing thinly-laminated sandstone–mudstone

Red, thinly-laminated sandstone–mudstone alternations, with alternate bioturbated and non-bioturbated units; primary laminae disturbed by abundant large Thalassinoides and Ophiomorpha burrows; thin laminae in mudstone; small symmetrical ripple on sandstone beds.

Thick mudstone alternating with fine-grained sandstone indicates low-energy conditions (Reineck and Singh 1980); intense bioturbation (Thalassinoides and Ophiomorpha) indicates oxygenated, nutrient-rich shallow marine environments; small, symmetrical ripples indicate reworking by waves.

Facies 5C: Wave-ripple-bearing sandstone

Coarse-grained, moderately sorted sandstone with subrounded grains; thickness of beds 10–15 cm; flat-topped symmetrical ripples with continuous, bifurcated crests on sandstone beds; smaller ladder-back ripples in the troughs of the major ripples; chevron-shaped internal laminae with irregular bottom set.

Coarse grain size and symmetrical ripples with chevron laminae indicate moderate-energy wave conditions (Harms et al. 1975).

Facies 5D: Massive mudstone

Red, friable, thick (6–120 cm) mudstone, devoid of sedimentary structures; quartz, dark opaque minerals, and mica, with unaltered to partly-altered feldspar grains; well-developed near Sitapuri; bioturbation not observed; sharp contact with the overlying Nodular Limestone Formation.

Suspension fallout of fine sediments under very low energy conditions; absence of bioturbation indicates relatively anoxic conditions and an increased water depth.