Origin and geochemical characterization of the glauconites in the Upper Cretaceous Lameta Formation, Narmada Basin, central India

This study presents geochemical characteristics of glauconites in estuarine deposits within the Maastrichtian Lameta Formation in central India. Resting conformably over the Bagh Group, the Lameta Formation consists of ~4-5 m thick arenaceous, argillaceous and calcareous green sandstones underlying the Deccan Traps. The sandstone is friable, medium-to coarse-grained, well-sorted and thoroughly crossstratified, and contains marine fossils. Detailed petrography, spectroscopy and mineral chemistry indicates unique chemical composition of glauconite with high KO, MgO, AlOand moderate TFeO. Glauconite is formed by the replacement of K-feldspars, initially as stringers in the cleavages and fractures of feldspars. Incipient glauconite subsequently evolves fully, appearing as pellets. Fully-evolved glauconite pellets often leave tiny relics of K-feldspar. XRD exhibits characteristic peak of 10A from basal(001)reflection of glauconite, indicating the "evolved" character. The KO content of glauconites in the Lameta Formation varies from 5.51% to 8.29%, corroborating the "evolved" to "highly-evolved" maturation stage.The TFeOcontent of glauconite varies from 12.56% to 18.90%. The PASS-normalized-REE patterns of glauconite exhibit a "hat-shape" confirming the authigenic origin of glauconites. The slightly-negative to slightly-positive Ce anomaly value and the moderate TFeOcontent of glauconite agree well with a suboxic,estuarine condition. The replacement of K-feldspar by the glauconite contributes towards the high KO content. Compositional evolution of glauconites in the Lameta Formation is similar to those observed in many Precambrian sedimentary sequences.

A New Species of Fossil <i>Mus</i>(Muridae, Mammalia) from the Late Quaternary Deposits of Narmada Valley, Central India

A new species of fossil Mus (Muridae, Rodentia) is described from the Pleistocene fluviatile deposits of the Narmada valley (Central India). The species, Mus narmadaensis sp. Nov., has a comparatively smaller lower molar which is characterized by a narrow molar with well connected cusps, small anterior expansion of lingual anteroconid, protoconid and metaconid, reduced posterior cingulum in addition to hypoconid and entoconid nearly at the same level. The large M3 has centrally placed bulbous hypoconid. Among the extant species, the present one is closest to M. shortridgei in having similarly placed protoconid and metaconid in M1 and a well developed hypoconid in M3.

印度纳尔玛达地区发现的粗壮智人化石及其与亚洲直立人的连续性

1999年,在印度西部的纳尔玛达(Narmada)河的一条支流——奥尔桑(Orsang)河谷发现了一具孤立的智人头骨,这对于了解印度人类进化历史和南亚直立人与最古老的亚洲智人(或AMH,解剖学上现代的人)之间的联系有着重要的意义。化石是在古老的河流沉积物中发现的。对主体沉积和颅内沉积物的红外光释光(IRSL)测年结果显示,其年代为3—5万年。然而,对化石的直接测年(放射性碳加速器质谱测年AMS)结果表明,其年代最小为4981—5579年前。头骨被归类为圆颅型智人。头骨上最引人注意的特征是颅外有亚洲直立人头后部很发达的角圆枕。头骨最宽处在下部(颞骨)如直立人,这样的情况从来不见于智人。这可能是由于乳突的气窦化而形成的。乳突上脊发育,从破损的眉间区(20mm)可以看到很宽的额窦。所有这些粗壮的特征都表明Orsang头骨和晚期亚洲直立人之间具有遗传连续性。

Palaeogeographic reconstruction of a fluvio-marine transitional system in Narmada rift basin, India——Implications on Late Cretaceous global sea-level rise

Rising sea-levels in tectonically active epicontinental basins often lead to varied depositional settings and palaeogeography, mostly influenced by the net accommodation resulting from mutual interference of the extent and nature of landward encroachment by the sea and the net sedimentation. The Cenomanian Nimar Sandstone Formation, Bagh Group, Narmada rift basin, uniquely portrays the effect of sea-level rise within an intra-cratonic setting and attributes to the corresponding palaeogeographic changes in west-central India. An integrated sedimentological–sequence-stratigraphic study of the broadly fining-upward Nimar Sandstone Formation(thickness~ 20–30 m) depicts the actual nature of changeover from a fluvial to a marine-dominated transitional depositional setting. Detailed sedimentological study reveals total seventeen facies, grouped in five facies associations, viz., the channel-fill facies association(FA-1), the overbank facies association(FA-2), the fluvial-dominated fluvio-tidal facies association(FA-3), the tide-dominated fluvio-tidal facies association(FA-4), and the shoreface facies association(FA-5). Overall facies architecture indicates a west-to-eastward marine encroachment, resulting in stacking of three distinct palaeo-depositional conditions:(i) an initial fluvial system with channel and overbank, changing into a tideinfluenced fluvial bay-head delta in the inner estuary, followed by(ii) marine encroachment leading to a tidedominated central estuary with inter-to sub-tidal settings, and finally,(iii) with further intense marine encroachments, a wave-reworked open shore condition in the outer estuary zone. The overall fining-up succession with a systematic change from fluvial to marine-dominated depositional systems points to a landward shift of the shoreline, signifying a major transgressive event correlated to the Cenomanian global sea-level rise. Characteristic stratal stacking patterns point to four coarsening-and fining-up hemicycles, embedded within the major transgressive succession. These high-frequency cycles attest to the varied interplay of sedimentation, tectonics and sea-level changes, and the resultant net accommodations. A palaeogeographic model is proposed based on the high-frequency transgressive–regressive hemicycles, which envisages the evolution of the depositional environments in relation to the Cenomanian eustatic rise in the intra-cratonic riftogenic fluvio-marine transitional basinal setup.

Tracking sources and paleotectonic settings of Mesozoic sandstones in interlinked rift basins of western India:An integrated approach using petrography and heavy mineral chemistry

Based on integration of field,petrographic and heavy mineral chemical data,this study highlights the source and tectonic setting of the Mesozoic sandstones of Kutch,Saurashtra,Narmada and Cambay basins at the western margin of India,formed by the progressive splitting of the eastern Gondwanaland.The Kutch Basin is dominated by arkosic sandstone,whereas Saurashtra,Narmada and Cambay basins show the predominance of sub-arkose and sub-litharenite.The modal analyses of framework grains in Kutch sandstones indicate basement uplift and transitional continent settings.In contrast,the sandstones of Saurashtra,Narmada and Cambay basins bear imprints of recycled orogenic and craton interior belts.The presence of abraded and detrital quartz overgrowth and rounded zircons in most sandstones reveal the recycling of sediments in these basins.Tourmaline and rutile mineral compositions constrain the possible lithology of source rocks.The tourmaline mineral chemistry(Ca-Fe_(tot)-Mg plot)suggests the derivation of sediments from various sources,including Li-poor granitoids associated with pegmatites,aplites,Ca-poor metapelites,metapsammites and quartz-tourmaline-rich granitic rocks.The compositions of rutile grains(Cr vs.Nb plot)in sandstones indicate metapelitic sources.The gamut of all mineral chemical data supports the predominance of sediment sources from quartzo-feldspathic rocks with minor inputs from mafic rocks.Based on available paleocurrent data and correlation of source compositions,we infer that the Mesozoic sediments of Kutch,Saurashtra,Narmada and Cambay basins were primarily sourced by various lithologies of the Aravalli Craton.The Narmada Basin possibly received additional sediment input from the Bundelkhand Craton.