Dinosaur coprolites from the Late Cretaceous (Maastrichtian) Lameta Formation of India: isotopic and other markers suggesting a C3plant diet

A single locality of the Late Cretaceous (Maastrichtian) Lameta Formation at Pisdura in Central India has yielded a large number of coprolites attributed to titanosaurian dinosaurs. Internally the coprolites are dark grey and contain abundant plant tissues and other organic materials. The plant tissues are mostly of gymnospermous origin. In addition, remains of bacterial colonies, fungal spores and algae are seen in the macerated fraction under scanning electron microscope. The dark grey appearance is probably attributable to fine-grained organic matter within voids in tracheids or xylem. The average ¹³C/¹²C ratio of the organic matter in the coprolites is -24‰ (relative to PDB) suggesting that plants of C₃type were the main diet of their producers. A comparison of δ¹⁵N value (about 4‰ w.r.t. air) of the coprolites with that of faecal matter of modern herbivores and carnivores suggests that gut fermentation may not have been an active mechanism in the digestion process of titanosaurs.     

Felsic tuff from Rutland Island — A pyroclastic flow deposit in Miocene-sediments of Andaman-Java subduction complex

The bedded felsic tuff exposed in Rutland Island, Andaman, consists of two facies:

An overview on geochemistry of Proterozoic massif-type anorthosites and associated rocks

A critical study of 311 published WR chemical analyses, isotopic and mineral chemistry of anorthosites and associated rocks from eight Proterozoic massif anorthosite complexes of India, North America and Norway indicates marked similarities in mineralogy and chemistry among similar rock types. The anorthosite and mafic-leucomafic rocks (e.g., leuconorite, leucogabbro, leucotroctolite, anorthositic gabbro, gabbroic anorthosite, etc.) constituting the major part of the massifs are characterized by higher Na₂O + K₂O, Al₂O₃, SiO₂, Mg# and Sr contents, low in plagioclase incompatible elements and REE with positive Eu anomalies. Their δ ¹⁸O‰ (5.7–7.5), initial ⁸⁷Sr/⁸⁶Sr (0.7034–0.7066) and ɛ _Nd values (+1.14 to +5.5) suggest a depleted mantle origin. The Fe-rich dioritic rocks occurring at the margin of massifs have isotopic, chemical and mineral composition more close to anorthosite-mafic-leucomafic rocks. However, there is a gradual decrease in plagioclase content, An content of plagioclase and X_Mg of orthopyroxene, and an increase in mafic silicates, oxide minerals content, plagioclase incompatible elements and REE from anorthosite-mafic-leucomafic rocks to Fe-rich dioritic rocks. The Fe-rich dioritic rocks are interpreted as residual melt from mantle derived high-Al gabbro melt, which produced the anorthosite and mafic-leucomafic rocks. Mineralogically and chemically, the K-rich felsic rocks are distinct from anorthosite-mafic-leucomafic-Fe-rich dioritic suite. They have higher δ ¹⁸O values (6.8–10.8‰) and initial ⁸⁷Sr/⁸⁶Sr (0.7067–0.7104). By contrast, the K-rich felsic suites are products of melting of crustal precursors.     

Petrogenetic implications of ophiolitic chromite from Rutland Island, Andaman—a boninitic parentage in supra-subduction setting

Chromites occurring in different modes have been characterized from ophiolites of Rutland Island, a part of Burma-Andaman-Java subduction complex in the Bay of Bengal. Chromite mainly occurs as massive chromitite pods in mantle ultramafic tectonite and as thin massive chromitite bands together with minor disseminations in crustal ultramafic cumulate. Other than pods chromite also appears as: (a) anhedral restitic grains, (b) strings occurring as exsolved phases and as (c) symplectitic intergrowth with orthopyroxene in mantle tectonite. The chromites occurring as massive chromitite pods and bands contain high Cr (Cr#—73 to 80). Restitic chromite grains in mantle ultramafics are high-Mg (Mg#—58), high-Al (Al₂O₃—34 wt.%) and intermediate-Cr (Cr#—37) chromites. The bivariant plots of TiO₂ wt.% vs 100Cr#, Mg# vs Cr# and Cr-Al-Fe³⁺ ternary discrimination diagram show that the massive and disseminated chromites fall in the boninitic field. The (Al₂O₃)_melt and (FeO/MgO)_melt values for the massive chromitites are estimated as 10 wt.% to 11 wt.% and 0.67–1.78 respectively, corroborating a boninitic parentage. Massive chromitite on Fe²⁺/Fe³⁺ vs Al₂O₃ wt.% and TiO₂ wt.% vs Al₂O₃ wt.% plots occupy mainly the field of supra-subduction zone peridotites. High-Mg olivine (Fo_91?93), high-Mg orthopyroxene (En_～90) and high-Cr chromites of Rutland ophiolite are all supportive of boninitic source at supra-subduction zone setting. ⁵⁷Fe Mössbauer study of chromite of beach placer shows that chromites occur in partly inverse spinel structure with iron distribution as Fe³⁺(A)Fe²⁺(A)Fe²⁺(B) which might be a result of oxidation. The olivine-spinel geothermometry shows 650–700°C re-equilibration temperature which is much lower than near crystallization temperature (950–1,050°C) derived from orthopyroxene-clinopyroxene assemblage. At supra-subduction setting an oxidizing hydrous fluid derived from subducting slab might have a major influence during the formation of Rutland ophiolite in this part of Burma-Java subduction complex.     

Some regional indicators of the Tertiary–Quaternary geodynamics in the paleocoastal part of the Bengal basin (India)

Sedimentary processes in the paleocoastal part of the Bengal basin that occured in the Tertiary and Quaternary have been addressed. Three indicators were used: sedimentary bedding forms, microstructure of the sediment, and trace fossils. Various forms of sedimentary structures developed under the influence of dynamic geomorphic processes in the study area in the Quaternary. The microstructure analysis of the sedimentary materials was made by two methods: microphotography and Digital Color Analysis (DCA). The microstructure analysis shows that the geomorphic process remained very dynamic in the Quaternary, influencing the form, thickness, and mineral composition of the sediment strata. The enrichment of the sediments in heavy minerals evidences either oscillating or combined flow sedimentation, while under stable conditions light-mineral deposition took place. The digital data of microfabric study by the DCA method also show that larger particles deposited in the oscillating or high-flow environment and evidence a greater amount of heavy minerals like ferruginous materials. Trace fossils found in the sediments of this area also strongly support the concept that the environment remained dynamic during the Tertiary and Quaternary. The Late Tertiary deposition shows that, during these periods, the sediments were transported from tide-dominated marine coast with low flow energy, which is typical of hot and humid conditions. From Late Tertiary to Early Quaternary, the macrotidal coast became mesotidal (wave-dominated). The second phase is the Middle Pleistocene, when the environment was stable, favoring the continuous deposition of finer particles under low- to medium-flow energy conditions. The third phase, the Recent, is marked by the shoreline shift and modification of the environment. In the Early–Middle Holocene, the shoreline started to shift, which modified the geomorphic conditions of this place from coastal to estuarine and, finally, inland fluvial.     

Gravitational instability of interstellar magnetic clouds

The gravitational instability of a nonrotating isothermal gaseous disk permeated by a uniform frozen-in magnetic field is investigated using a fourth-order perturbation technique. From the results it is found that the disk is stable whenn/B ₀ < (4/3³ G)^–1/2, wheren andB are the column density of the disk and unperturbed magnetic field, respectively, andG is the gravitational constant. The disk is gravitationally unstable only whenn/B ₀ > (4/3³ G)^–1/2.     

An Appraisal of the 2001 Bhuj Earthquake (Mw 7.7, India) Source Zone: Fractal Dimension and b Value Mapping of the Aftershock Sequence

We examined seismic characteristics, b value and fractal dimension of the aftershock sequence of the January 26, 2001 Bhuj earthquake (Mw 7.7) that occurred in the Kutch failed rift basin, western margin of the Stable Continental Region (SCR) of India. A total of about 2,000 events (M?≥?2.0) were recorded within two and a half months, immediately after the main shock. Some 795 events were precisely relocated by simultaneous inversion. These relocated events are used for mapping the frequency-magnitude relation (b value) and fractal correlation dimension (Dc) to understand the seismic characteristics of the aftershocks and the source zone of the main shock. The surface maps of the b value and Dc reveal two distinct tectonic arms or zones of the V-shaped aftershock area, western zone and eastern zone. The b value is relatively higher (~1.6) in the western zone compared to a lower value (~1.4) in the eastern zone. The Dc map also shows a higher value (1.2–1.35) in the western zone compared to a lower Dc (0.80–1.15) in the eastern zone; this implies a positive correlation between Dc and b value. Two cross sections, E–W and N–S, are examined. The E–W sections show similar characteristics, higher b value and higher Dc in the western zone and lower in the eastern zone with depth. The N–S sections across the fault zones, however, show unique features; it imaged both the b and Dc characteristics convincingly to identify two known faults, the Kutch Mainland fault and the South Wagad fault (SWF), one stepping over the other with a seismogenic source zone at depth (20–35?km). The source zone at depth is imaged with a relatively lower b and higher Dc at the ‘fault end’ of the SWF showing a negative correlation. These observations, corroborated with the seismic tomography as well as with the proposed geological/tectonic model, shed a new light to our understanding on seismogenesis of the largest SCR earthquake in India in the recent years.     

Evidence for the thrust emplacement of the ‘Lesser Himalaya’ Chur granite,Himachal Pradesh

Numerous peraluminous and porphyritic granitic bodies and augen gneisses of granitic compositions occur in the nappe sequences of the Lower Himalaya. They are Proterozoic-to-lower Paleozoic in age and have been grouped into the ‘Lesser Himalaya granite belt’. The mode of emplacement and tectonic significance of these granites are as yet uncertain but they are generally considered to be sheet-like intrusions into the surrounding rocks. The small and isolated granite body (the Chur granite) that crops out around the Chur peak in the Himachal Himalaya is one of the more famous of these granites. Several lines of evidence have been adduced to show that the Chur granite has a thrust (the Chur thrust) contact with the underlying metasedimentary sequence (locally called the Jutogh Group). The Chur granite with restricted occurrence at the highest topographic and structural levels represents an erosional remnant of a much larger sub-horizontal thrust sheet. The contact relations between the country rocks and many of the other granite and granitic augen gneisses in the Lesser Himalaya belt are apparently similar to that of the Chur granite suggesting that at least some of them may also represent thrust sheets.     

CCD photometry inVRI bands of the galactic cluster NGC 2818

bdAbstract The open cluster NGC 2818 containing a planetary nebula has been observed inVRI bands using the CCD system at prime focus of the 2.3-metre Vainu Bappu Telescope. The study extending to starsV ∼ 21 magnitude establishes the distance modulus as(m-M) ₀ = 12.9 ±0.1 for the cluster. Based on the fitting of theoretical isochrones computed for solar metallicity, an age of 5(±1) × 10₈ years has been assigned to the cluster. Association of the planetary nebula with the cluster indicates that the progenitor mass of the planetary nebula on the main sequence is ≥2.5M_⊙ Based on observations obtained with the Vainu Bappu Telescope.