Palaeontological and sedimentological observations on nonmarine Lameta Formation (Upper Cretaceous) of Maharashtra, India: their palaeoecological and palaeoenvironmental significance

Palaeogeography, Palaeoclimatology,Palaeoecology, 105 ( 1993): 83-94

83

Elsevier Science Publishers B.V., Amsterdam

Palaeontological and sedimentological observations on nonmarine Lameta Formation (Upper Cretaceous) of Maharashtra, India: their palaeoecological and palaeoenvironmental significance D . M . M o h a b e y a, S . G . U d h o j i a a n d K . K . V e r m a b

'iPalaeontology Division, Gelogieal Survey of India, Seminary Hills, Nagpur 440 006, India bAlzo, Rajajipuram, Lucknow 226017, India (Received January 31, 1992; revised and accepted December 1, 1992)

ABSTRACT Mohabey, D.M., Udhoji, S.G. and Verma, K.K., 1993. Palaeontological and sedimentological observations on non-marine Lameta Formation (Upper Cretaceous) of Maharashtra, India: their palaeoecological and palaeoenvironmental significance. Palaeogeogr., Palaeoclimatol., Palaeoecol., 105: 83-94. The Lameta Formation (Upper Cretaceous) is exposed in parts of central and western India as detached outcrops and covers an area of nearly 5000 km 2. It generally rests on Precambrian and "Gondwana" rocks and is invariably capped by Deccan Trap volcanic flows. In the Nand and Dongargaon areas of the Chandrapur and Nagpur districts of Maharashtra, the Lameta Formation covers more than 400 km 2, attains a thickness of 20 m and is richly fossiliferous. The palaeontological and sedimentological observations strongly indicate alluvial-limnic environment for the deposition of the Lameta sediments under semi-arid conditions. Different lithofacies representing channel, overbank, paludal and lacustrine subenvironments have been identified. The biota represents terrestrial, semiaquatic and aquatic communities and is represented by dinosaurs, fishes, crocodiles, chelonia, gastropods, ostracodes, charophytes, coniferales and angiosperms. The biota appears to be mainly controlled by the different lithofacies, thereby suggesting strong palaeoecological and taphonomical control over their occurrence. Records of mass death of clupeids have been observed in many layers within the lacustrine clays. A nesting site of sauropods has been found near Pavna along with evidence of site-fidelity. A clutch with small oblong-shaped eggs of avian-like affinity has been also unearthed from this nesting site. The Lameta sediments were deposited in a freshwater environment that provided the preferred ecological niche for large-scale breeding and nesting of sauropods.

Introduction T h e L a m e t a s e d i m e n t s o f U p p e r C r e t a c e o u s age cover m o r e t h a n 5000 k m 2 as d e t a c h e d o u t c r o p s in p a r t s o f central a n d western India. A c o n s i d e r able p a r t o f the L a m e t a s e d i m e n t s is c o v e r e d by the D e c c a n T r a p volcanic suite. T h e s e d i m e n t s rest unconformably over the Precambrian and " G o n d w a n a " rocks. L a m e t a s e d i m e n t s are c o n v e n t i o n a l l y c o n s i d e r e d as fluvio-lacustrine d e p o s i t s (Hislop, 1859; M a t l e y , 1921; M e d l i c o t , 1872; Von H u e n e a n d M a t l e y , 1933; G u p t a a n d M u k h e r j i , 1938; Pascoe, 1964; B r o o k f i e l d a n d Sahni, 1987). H o w e v e r , in the last two decades, views have 0031-0182/93/$06.00

© 1993

e m e r g e d on the possible m a r i n e origin o f the L a m e t a sediments a r o u n d J a b a l p u r in M a d h y a Pradesh and Pisdura-Dongargaon in M a h a r a s h t r a . T h e m a r i n e i n t e r p r e t a t i o n is based on the presence o f algal-like structures, thalassin o i d b u r r o w s a n d g l a u c o n i t i c beds in the J a b a l p u r a r e a ( C h a n d a , 1963; C h a n d a a n d B h a t t a c h a r y a , 1966; Singh, 1981; Singh a n d Srivastava, 1981) a n d a few alleged m a r i n e fishes in the L a m e t a sediments o f the P i s d u r a D o n g a r g a o n areas. (Sahni, 1984 a n d Jain a n d Sahni, 1986). Recently, Brookfield a n d Sahni (1987) described L a m e t a sediments a r o u n d J a b a l p u r as d e p o s i t e d in an alluvial plain e n v i r o n m e n t u n d e r semi-arid c o n d i -

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84

tions. Tandon et al. (1990) have also described these sediments as fluvial and pedogenically modified semi-arid fan-palustrine flat system. The present finding by the authors do not lend support to the proposed marine origin of the Lameta sediments in the area. The concept of the existence of a "Trans-Deccan Strait" in peninsular India in Maestrichtian-Palaeocene time as envisaged by few workers (Sahni, 1984; Jain and Sahni, 1986) appears to be untenable. On the basis of Titanosaurus remains occurring in the Lameta sediments around Jabalpur, a Turonian age was assigned (Von Huene and Matley, 1933). However, the presence of tyrannosaurid and megalosaurid in the dinosaurian assemblage, prompted Chatterjee (1978) to assign a upper Cretaceous age to the sediments. Recent palynological studies have confirmed the Maestrichtian age for the Lameta sediments around Jabalpur (Dogra et al., 1988). A Maestrichtian age is also suggested for the Lameta sediments of Maharashtra on the basis of faunal and floral assemblages (Udhoji and Mohabey, 1991a,b). Under projects IGCP-216 (Global Bioevents in Earth History) and IGCP-245 (Nonmarine Cretaceous Correlation), the present authors have carried out systematic biostratigraphic and palaeoenvironmental studies of the Lameta Formation covering nearly 700 km 2 in the Nand, Pisdura and Dongargaon areas (Fig. 1 and 2) in Maharashtra (Mohabey and Udhoji, 1990; Udhoji and Mohabey, 1991a,b). Studies of the Lameta sediments in these regions has indicated an alluvial-limnic environment of deposition under semi-arid condition. Different lithofacies of overbank, channel, backswamp and lacustrine subenvironments have been identified. As the findings pertaining to Nand areas has already been described elsewhere (Mohabey and Udhoji, 1990), the scope of the present paper is confined to the Dongargaon area which includes the thickest Lameta section with significant lithofacies variation.

Geological setting The Lameta Formation of the DongargaonPavna area (Figs. 2 and 3) is nearly 20 m thick.

D.M. MOHABEY ET AL.

The Deccan Trap flows are associated with thin intertrappean sedimentary beds. The Lameta sediments are generally horizontal except for local warping in the Dongargaon hill section. The beds are generally exposed between 220 m and 240 m contours. The Lameta sequence comprises basal red and green silty clays that are overlain and overlapped by yellow, grey and green finely laminated clays intercalated with thin partings of claystone, limestone, marlite and occasional sandstone partings. In the upper parts of the sequence, the sandstones are cal-silcretised. Reworked caliche profiles and a palaeosol horizon have been identified within the sequence.

Lithology Clays form the dominant constituent of the Lameta lithotypes. The basal part of the sequence is generally represented by red and green silty clays associated with less frequently occuring sandstones of lateral and vertical accretional types. The thickness of these silty clays is limited to 6 m. These overlying and overlapping silty clays are finely laminated yellow, grey and green clays intercalated with claystone, marlite and limestone partings. The maximum thickness of these laminated clay is 7 m. In the northern part of the area, observed in the Pavna, Dhamni and Sagar sections (Figs. 2 and 3), the yellow laminated clays and the overlapping red silty clays are capped by sandstone beds calcretised in the upper parts. The Dongargaon Hill section represents nearly a complete section, except the calcretised sandstone unit which is better observed in the Dhamni-Pavna section.

(1) Dongargaon Hill section The Dongargaon Hill section (Fig. 3A,B) has an elevation of 264 m. It rests over rocks of the Kamthi Formation of Gondwana Group and are overlain by Deccan Trap flows. The contact between the Lameta Formation and the Deccan Traps is undulating and is indicative of the erosion of the Lameta sediments prior to the Deccan Trap eruption. The basal red silty clays are associated with sandy and pebbly lenses and are overlain by cream and yellow coloured laminated clays with thin intercalated and repeated bands of claystone,

NON-MARINE LAMETA FORMA] ION (UPPER CRETACEOUS) OF M A H A R A S H T R A ,

INDIA

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INDEX SOIL DECCAN T R A P / I N T E R T R A P P E A N S L A M E T A FM ( MAESTRICHTIAN )

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Key and geological map showing the Lameta Formation in parts of Chandrapur and Nagpur district, Maharashtra, India.

marlite and limestone. Thin fibrous calcite layers are also present. Small authegenic gypsum crystals are noticeably present within such clays. These yellow laminated clays become green mottled in

the upper parts and grade upwards into green laminated clays, which are carbonaceous and sapropelic in places. The frequency of occurrence of the intercalated bands within the clays decreases

86

D.M. MOHABEY

.:__~_ ..... ,_~,:,,__ . . . . . - -_ _-.-~.~.~..: . . - - - _ : - - : - - : _ -

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ioo

Fig. 2. Geological map and major Lameta fossil localities of Dongargaon-Pavna area, Chandrapur district, Maharashtra, India. upwards and are almost absent in the green clays. A thin (nearly 30 cm thick) but extensive, wave rippled laminated siltstone band is present in the green laminated clays. The green clays become non-laminated and silty upwards, and ascend into red silty and sandy non-laminated clays. A thin grey horizon with caliche features such as concretions, pedotubules, rhizolith, root-mottlings and burrows has been observed between the green and overlying red clays. This has been interpreted as a palaeosol horizon. A sandstone bed with medium to coarse grained, subangular to subrounded quartz is present in the upper parts of the red clays. The sandstone is rich in microvertebrates including fish teeth, scales and dinosaur eggshell fragments. A vesicular basalt flow caps the red clays. However, on the periphery of Dongargaon

hill, the Traps have also been observed to be resting over the yellow laminated clays. Broad warping is noticeable in the Lameta sequence here.

(2) Dhamni-Pavna Section In a nearly 6 m thick roadside section just southwest of Dhamni village, yellow and white, very fine laminated clays are present. Partings of giant septarian concretions having a diameter of more than 1 m are found within such clays. A rich assemblage of fresh-water ostracodes, gastropods and clupeid fishes is found in these clays. The basal clays are sandy, and are rich in pelecypods (Unio deccanensis). The clays are calcified in the upper parts and east of the village, are capped by non-laminated red silty clays. A thin but very

NON-MARINE LAMETA FORMATION (UPPER CRETACEOUS) OF MAHARASHTRA. INDIA

87

DONGARGAON HILL R.L.2e4m D

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_ ~

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Dinosaur bones

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Nodules, kankars

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Crocodilian bones

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calcite~ palaeosol

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DHAMNI

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White nodular cloy with kankars Marlite,l;olumnor

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Red clay silty and sandy ctoy

Gondwanas DM Mohabey and SG. Udhoji

Horizontal

Fig. 3. Gelogical sections across Dongargaon-Dhamni-Bijoli(A-B) and Pavna-Dhamni-Agar (C D), Dongargaon area, Chandrapur district, M.S. persistent calcrete horizon caps both the yellow laminated and red silty non-laminated clays. The thickness of this calcrete horizon increases northwards, where it attains a thickness of nearly 4 m. The calcretes show various stages of formation from the parent sandstones (Mohabey and Udhoji, 1990). Calcretisation features such as meniscus cement, micrite envelopes, micrite peloid, micritic rhinds and fenestral fabrics (Steel, 1973; Wright etal., 1988) are found within the calcrete. In the locality just north of Pavna, the laminated yellow and white clays, become earthy brown and grey coloured and are enriched in pelecypods (Unio deccanensis). These clays are capped by pebbly and gritty sandstone which is cal-silcretised in the upper parts. A nesting site with well preserved egg clutches (Fig. 4, f) of dinosaurs of probably sauropod affinity has been located within such calcretised sandstone (Mohabey, 1990a). The eggs are

spherical and have a nodose ornamentation. A clutch of small oblong-shaped eggs (Fig. 5, g) having polar and equatorial diameters of 5 cm and 2.5 cm respectively, has also been unearthed from this nesting site. The shells of such eggs are smooth and their microstructural characteristics indicate that they are non-dinosaurian. They appear to have an affinity towards avian-like eggshells. The eggshell microstructure is presently under study and the taxonomic identification remains to be confirmed. Check-list of fossils

The occurrence and the distribution of the fossils in the Lameta Formation is evidently significantly controlled by various lithologies. Based on taxonomic and taphonomic studies of the various fossils and lithological observations, palaeo-

88

D.M. MOHABEY ET AL.

Fig. 4 (a) Post-cranial remains of clupeid fish (No.134/CRP/89) from yellow laminated clays, Lameta Formation, Dhamni. (b) Partial remains of Pycnodus(No. 132/CRP/89) from limestone partings, Lameta Formation, Dongargaon. (c) Lepidotes body scale (No. 130/CRP/89) from claystone, Lameta Formation, Bhata]i. (d) Skull of Eoserranushislopi(No. 132/CRP/88) from yellow marl, Lameta Formation, Polgaon. (e) Mandible Lepisosteus indicus (No. 128/CRP/89) claystone Lameta Formation, Dongargaon. (f) Partial clutch of spherical sauropod eggs (No. 123/PAL/89) from calcretised sandstone, Lameta Formation, Pavna. (g) Partial clutch of oval-shaped avian-like egg (No. 127/PAL/CR/89) Loc. and horizon as in (f). environment of Lameta sediments can be inferred. Fossils found in the Lameta Formation include: Vertebrates (a) Skeletal remains of sauropod (Titanosaurus sp., Antarctosaurus sp.) and associated coprolites. Eggs (nearly complete to fragmentary) probably assignable to sauropods. (b) Crocodilian scutes (gen. sp. indet.) (c) Chelonian (Pelomedusidae) (d) Ayes (eggshells ? ). (e) F i s h e s - - n e a r complete to fragmentary remains of Lepidotes deccanensis, Lepisosteus indicus,

Flora (a) Charophytes-- Platychara perlata and Microchara sp. (b) Conifereles--Araucarites represented by clus(A.kutchiensis); ters of seeds and cones

Brachyphyllum. (c) M o n o c o t y l e d o n s - - B a s a l leaf impressions of smaller varieties of palm. (d) D i c o t y l e d o n s - - L e a f impressions of two types. Trace fossils Termitichnus (?)--Callie and gallery structure;

Trypanites, Planolites.

Pycnodont lametae, Eoserranus hislopi, Dasyatis, Phareodus, Nandidae and clupeids. Invertebrates (a) Gastropods--Lymnaea,

Melania, Paludina, Natica, Valvata, Bullinus (b) P e l e c y p o d s - - U n i o deccanensis, Corbicula. (c) O s t r a c o d e s - - Candoniella, Cypridopsis, Darwinula, Mongolianella, Metacypris, Cypridea, Cyprois

Litho-facies association and palaeoenvironment Based on the evidence described below, an alluvial-plain environment under semi-arid conditions has been inferred for the sediments. The various subenvironments (Fig. 4) identified within the alluvial system include:

N O N - M A R I N E LAMETA F O R M A T I O N I UPPER C R E T A C E O U S ) O F M A H A R A S H T R A , INDIA

89

Fig. 5 (al Cluster of Araucarites (No. 101/CRP/88) yellowmarl, Lameta Formation, Polgaon. (b) Charophyte (Plao,chara/ plant (No. 111 CRP/88). Locality and horizon same as in (a). (c) Araucarites seed (arrow) and a nest and gallerie structure of Termitichnus(?). Locality and horizon same as in (b). (No. 102/CRP/88). (d) Cluster of gastropod Melania (No. 133/CRP/88 ill yellow marl Lameta Formation, Alesur (Nand).

Overbank facies Lithology: Red and green silty clays often nonlaminated. Mottling occasionally observable at the contact between the lower green and upper red clays. Calcareous concretions in the clays. Texture and sedimentary structures: Clays and silts with commonly occurring dispersed detrital quartz grains and sandy streaks. Non-bedded. Rarely laminated. Local occurrences of mudcracks. Geometo, and association: Overbank facies occur in association with lenses and partings of channel related sandstones of both lateral and vertical accretional types. Mud-partings at places present within the sandstone. Paleosol horizon present within the clays. Fossils: Skeletal remains of sauropods (Titanosaurus sp. and Antarctosaurus sp.), associated with coprolites, occur occasionally as lag deposits over palaeosols (Mohabey and Udhoji, 1990) and more commonly as reworked, fragmented and weathered bones. Other less commonly

occurring fossils include dinosaurian eggshell fragments, stray fish teeth and scales of Lepisosteus indieus, Pycnodont lametae, Dasyatis and clupeids; Platychara and Microchara (rare and reworked types), Bullinus, Paludina and Natica. A palaesol horizon present within the clays is enriched in rhizoliths and pedotubules. The colour variation in the clays from the yellow and green in the lower parts to red in the upper parts with a green pink and red mottled zone at the transition zone, probably indicate leaching of red clays by downward percolation of the reducing water (Jerzykiewicz and Sweet, 1988). Occasional thin partings of grey marl enriched in charophytes may represent ponding of water in the overbank areas.

Channeljaeies Lithology: white to medium coarse grained, immature, often pebbly and gritty sandstone. Often loose and friable. Texture and sedimentao, structures: Variable rex-

90

D.M. MOHABEY ET AL.

ture. Poorly sorted with abundant fines. More commonly occurring as lensoid and thin persistent partings. Cross-stratification, occasional convoluted beddings, wave ripples, parting lineations and textured surface observable. U-shaped symmetrical channel-fill structure occasionally noticeable. Geometry and association: Upper contact gradational to overbank red and green clays. Lower contact sharp and rarely undulatary. Rarely sandstone partings present within the yellow laminated clays associated with marlite bands. Thin mud partings and films present within the sandstone. The sandstones also observed to be aggrading and overlapping both the non-laminated red silty clays of overbank type and yellow finely laminated clays of lacustrine type. Reworked caliche profiles comprising micrite peloids present within the sandstones. Such peloids also show size gradation and cross-bedding structure within the sandstone unit as observable in Sagar and Bijori sections. Small channel-fill structures are repeated both laterally and vertically, probably indicating lateral accretional type. Sandstone occurring in the upper parts of the sequence is calcretised in the upper parts as observable in Pavna and Sagar sections. Fossils: Dinosaurian egg clutches with wellpreserved eggs. The eggs are spherical and have a nodose ornamentation. A few small oblong eggs of doubtful avian affinity are also present. Reworked dinosaurian eggshell fragments fairly common within the sandstone in a few localities, including Pisdura and Dongargaon. Chelonian and crocodilian remains rare. Fish teeth and scales , including Lepisosteus indicus, Dasyatis, Pycnodus lametae, clupeids, common. Rare Platychara and Microchara and ostracodes Mongolianella, Candoniella also present. Trace fossils such as Trypanites, Diplocraterion are observable.

noticeable at Dongargaon and Bhatali. Becomes greenish in upper parts in few sections. Such green clays are at places carbonaceous as observed in Dongargaon section. The marlite and limestone partings occasionally contain ocherous nodules, altered pyrite and halite crystals. Thin (5-15 cm) partings of columnar and fibrous calcite layers occasionally present. Texture and sedimentary structures: Clay- and silt-sized, very finely laminated. Local mud-cracks. The intercalated partings of marlite and claystone occasionally show wave-ripple structure. Penecontemporaneous deformation structure such as convolute bedding in yellow clays noticeable at Bhatali. Geometry and association: Generally overlapped by flood-plain red and green silty clays. Occasional sandy intercalations represent detrital influx in the lake. Fossils: The lithofacies is dominated by fishes both in taxonomic diversity and abundance. Fishes include completely to partially preserved skeletal (Fig. 5, a-e) remains of teleosteans (clupeids) and ganoids (Lepidotes deccanensis. Lepisosteus indieus and Pycnodus lametae). In Dhamni, the complete skeletal remains of numerous clupeid fishes are found in layers within the yellow laminated clays. In this section they are associated with ostracodes (Cyprois) and gastropods (Viviparae). The Lepidotes, Lepisosteus and Pycnodus are generally found in the limestone, marlite and claystone partings intercalated with the yellow laminated clays, as observed in Dongargaon and Bhatali sections. The invertebrates are dominated by various ostracodes taxon including Candoniella, Cyprois and Mongolianella. These are often present as moulds and are crowded along different laminae. Pelecypods are dominantly represented by Unio

deccanensis. Lacustrine facies Swamp deposits Lithology: Very finely laminated yellow and white silty clays that are brown mottled along some laminae. Intercalated with repeated thin partings of limestone, marlite and claystone. Attains a thickness up to 8 m. Small authegenic gypsum crystals present in the lower parts of the clays as

Lithology: Thin bands of yellow and grey marl occasionally associated with white clays. Thickness never exceeding 1.5 m. Texture and sedimentary structures: Clay-sized fraction with rare thin calcitic stringers and fibrous

NON-MARINE LAMEIA F O R M A I I O N {UPPER CRETACEOUS) OF M A H , \ R A S H T R A , INDIA

calcite crusts. Characteristically unlaminated. Mudcracks and septerian nodules commonly present. Association and geometry: Deposits are small and haxe confined boundaries. Occur exclusively within the overbank red clays. Fossils: Charophytes (plants and gyrogonites of Platychara and rare Mieroehara) numerous. Associated with ostracodes (Candoniella in their various growth stages) and gastropods (Lymnaea, Pahutma and Melania). Disarticulated and partially articulated remains of fish Eoserranus hislopi numerous. Clusters of Arauearites, Brachyphyllum, and impressions of palm and dicot found in one locality (Polgaon).

Palaeoecology The various fossil assemblages have been assigned to lacustrine, fluvial and terrestrial palaeoenvironments. Lacustrine sediment is represented by the intercalating sequence of finely laminated clays, claystones, marlites and limestones that indicate fluctuating lake conditions. Various types of fish taxa were observed to have been dominating in such different litho-units of the lacustrine sequence. The clusters of completely preserved clupeids (as observable at Dhamni and Bhatali) occur as layers along with the different clay laminae occurring associated with ostracods ((),pridae) and gastropods (Vah,ata). Sediments are totally free of any carbonaceous matter and no bioturbation is observable in spite of the large population of ostracodes. The layers of completely preserved fishes indicate the settling of caracasses and their quick burial in lake bottoms, precluding any chance of scavenging. A mass mortality event for clupeids is inferred in this case which may be induced by deteriorating lake conditions probably due to increased alkalinity. The intercalated partings of the marlite and limestones within the laminated clay sequence as observable in the Bhatali and D o n g a r g a o n sections signify an increased alkalinity of the lake due to excessive evaporation induced by periodic dry cycles. Such partings exclusively host different taxa of fishes such as Pvcnodus larnetae, Lepisosteus indicus and Lepidotes sp. These fishes are also

91

nearly completely preserved, but disarticulated remains are also not uncommon. It is interesting to observe that the laminated lacustrine clays, which have enriched assemblage of fishes (clupeids), ostracodes (Cypridae) and gastropods (Valvata) are observed to be totally free of charophytes. In the Polgaon section in the Nand area. a thin (less than 1 m thick) marly clay horizon of a limited lateral extent is l\)und to be rich in lish remains exclusively of Eoserranus hislopi o1"varions sizes. These are found associated with a rich assemblage of ostracode Camhmiella and Chara represented by dominating Platychara perhlta and Microchara. Leaf whorls (Fig. 6, b) along with gyrogonites of Platyehara perlata are present. The ostracodes are found to occur within the sediments infilling the cavities in the fish remains. Fhis probably indicates that the ostracodes were scavenging on the dead caracasses of the fishes. The ostracodc and charophyte assemblage is also indicative of the slight alkalinity of the lake (Deckker, 1988: Elder and Smith. 1988; Lockley et al.. 1986). In addition in this marly horizon at Polgaon, plant remains are represented by coniferales such as clusters of Arauearites (Fig. 6, a) Brachyphylhm~ and angiosperms represented by monocots (palm leaf impressionsl and dicots (leaf impressions of Type A and B, genera and species indet.). It is worth observing that such plant remains are totally absent in similar and other types of litho-units in the area. This suggests that the vegetation grew around the water bodies. Numerous teeth of Dasvatis sp. are found in the sandstone beds of" Dongargaon and Pisdura. Such teeth are either absent or scarce in the lacustrine and overbank clays. It may be that these Dasvatis fishes (freshwater skates) were riverine in their habitat. The dinosaurian skeletal remains assignable to Titanosaurus sp. and Alllarclo,~'ato'zt.s sp. occur as (1) reworked, weathered and fragmented skeletal remains within channel sandstones and (2) lag deposits within pink and green mottled clays. In the latter case, the bones occur scattered over a palaeosol unit as found near Rajurvihri (Mohabe5 and Udhoji, 1990). Skeletal remains, such as vertebrae and limb-bones are l\)und to be coated by haematitic (caliche) glaebules (Bown and Kraus, 1981) and occur associated with coprolites, chelo-

92

D.M. MOHABEYET AL.

Palaeoenvironmental Interpretation of Lameta Formation %

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nian shell fragments and the gastropod Bullinus sp. Palaeosols have other features such as mottling, pedotubules, rhizoliths and bioturbation. The skeletal elements as found near Rajurvihri are assignable to Antarctosaurus sp. and appear to have been derived from a single animal and were scattered over a palaeosol unit. Dinosaur eggshells occur as (1) fragments in the sandstone and overbank clays and (2) as clutches of eggs within the calcretised sandstone. The former represents reworked eggshell fragments. The latter represents a nesting site near Pavna with many egg clutches of sauropods (Mohabey, 1990a). All the nesting sites located so far in the Lameta sediments in other parts of India like Gujrat (Mohabey, 1984, 1986, 1987; Mohabey and Mathur, 1989) and Madhya Pradesh (Mohabey, 1990a,b) are exclusively found in the sandstones. This has a significant bearing on the selection of the nesting sites by dinosaurs which preferred to nest on the overbank areas of the river that experienced seasonal climates, In the Kheda area in Gujarat, many nesting sites with well-preserved dinosaur egg clutches

were located in the Lameta Formation. A sizeable number of eggs are unhatched. Based on morphological and microstructural characteristics, the eggs have been classified into nine morphotypes (Mohabey, 1991). The taxonomic assignment (parentship) of such eggs is held-up for the lack of associated embryos and hatchlings. A partial skeleton of a juvenile sauropod has been unearthed from one of the egg clutches at Dhori Dungri nesting site (Mohabey, 1987; Lockley, 1989). This is the only record of a juvenile dinosaur find in India. At Pavna, the eggshells of similar morphotypes occur at two stratigraphic levels in the same section thereby indicating the site-fidelity amongst the dinosaurs (Mohabey, 1990a). Evidence of sitefidelity was also reported earlier from dinosaur nesting sites of the Kheda area in Gujarat (Mohabey, 1984, 1990b, 1991).

Concluding remarks On the basis of lithological and palaeontological observations in the area, it is concluded that the

NON-MARINE LAMETA FORMATION (UPPER CRETACEOUS) OF MAHARASHTRA, INDIA

Lameta sediments are deposited in an alluviallimnic environment. Subenvironments, such as channel, over-bank, back-swamp and lacustrine (Fig. 4) are present in the area with characteristic lithological and palaeontological signatures. The evidence of the increased alkalinity in the lakes and widespread calcretisation of the flood-plain sediments have been interpreted to be indicative of semi-arid conditions that prevailed during deposition of the Lameta sediments. Fishes such as clupeids, Pycnodus and Lepidotes are interpreted to be lake taxa, whereas Eoserranus appears to be more of a paludal inhabitant found in association with charophytes. The other fishes, specially Dasyati~ (fresh-water skates) and Lepisosteus, are probably riverine taxa. Mass death events of clupeids and Eoserranus may be due to increased alkalinity attributable to the excessive evaporation of the lake in the former and dessication of the back-swamp in the latter case. Numerous sauropod nesting sites are now known from the Lameta Formation of India (Mohabey, 1990b, 1991). The ,~13C values of the fossil eggshells (Sarkar et al., 1991) suggest that the dinosaurs were surviving on plants of C-3 type (conifers, small palms, dicot shrubs, etc.) The 6180 values suggest that they were drinking water from a variety of fresh-water sources and indicate that the prevailing climate was of a semi-arid type. Abundant higher plants grew around these waterbodies providing an ideal niche for the preferred habitat of sauropods in terminal Cretaceous time. The acme of their breeding and dense population was a prelude to their mass extinction. The biota indicates a terminal Cretaceous (Maestrichtian) age for the Lameta sediments. A part of this biota including dinosaurs, fishes, ostracodes, gastropods and charophytes recurr in the overlying Intertrappean beds associated with the Deccan volcanic suite. A Maestrichtian age is also indicated for these Inter-trappean beds. The K T B may lie above such Inter-trappean beds at a higher stratigraphic level in the Deccan volcanic suite. Skeletal remains of dinosaurs including partial semi-articulated remains of a sauropod are recorded from Intertrappean beds of Kutch in Gujarat (Ghevariya and Srikarni, 1990; Bajpai et al., 1990), Madhya Pradesh and Maharashtra (Mohabey and Udhoji,

93

1990). This shows that the initial Deccan volcanic eruption did not wipe out the dinosaurs completely, but few of them still struggled to survive onslought of environmental stress. Probably they migrated to safer areas away from the ill effects of volcanic eruptions and rehabilitated in the new area during the long pause between the two successive eruptions of flows. Evidently, the extinction is indicated to be a gradual affair rather than a catastrophic event. The repository of the material referred in the text is at the Geological Survey of India, Palaeontology Division, Central Region, Nagpur.

Acknowledgements The authors acknowledge their thanks to Shri B.C. Poddar, Deputy Director General, Central Region, for the fruitful discussions and the critical review of the manuscript and to the Director General, for the kind permission to publish the paper. Thanks are also due to Dr.S.S. Deshmukh, Director, for the helpful suggestions in improving upon the manuscript. The work benefited from the discussions with many of our colleagues. Preparation of the drawings by Shri Sk. Naveed and typing of the manuscript by Shri M.V. Vyawahare are also thankfully acknowledged.

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