Early Albian marine environments in Madagascar: An integrated approach based on oxygen,carbon and strontium isotopic data

New palaeotemperature reconstructions have been obtained on the basis of oxygen isotopic analysis of 178 aragonitic shell samples taken from specimens of three ammonoid orders (and some corresponding families): Phylloceratida (Phylloceratidae), Lytoceratida (Tetragonitidae) and Ammonitida (Oppeliidae, Desmoceratidae, Silesitidae, Cleoniceratidae and Douvilleiceratidae). Those obtained from aragonite shells, secreted in the lower epipelagic and in the middle mesopelagic zones during coolest season (winter), range from 15.4 to 16.8 °C, and from 11.8 to 12.0 °C, respectively. Presumed spring/autumn palaeotemperatures obtained from aragonite shells, secreted apparently in the upper and lower epipelagic, upper and middle mesopelagic zones, are somewhat higher. Presumed summer palaeotemperatures, calculated apparently for the upper and lower epipelagic, and upper mesopelagic zones range from 19.4 to 21.7 °C, from 17.7 to 19.4 °C, and from 14.4 to 16.1 °C, respectively. The predominant part of investigated ammonoids from Madagascar inhabited the epipelagic zone, but some phylloceratid, tetragonitid and silesitid ammonoids preferred deeper, cooler conditions (upper-middle mesopelagic zone). The study supports the hypothesis that Madagascar was located in middle latitudes within the tropical-subtropical climatic zone during the early Albian. Available carbon and strontium isotope data allow us to assume a more or less expressed carbon and strontium isotope stratification of the water column in this region in the early Albian. On the basis of the stable isotope data, following partly Lukeneder (2015), two large ethological groups can be recognised mainly in mid-aged and adult ammonoids. Some ammonoids (group 1) preferred apparently mesopelagic conditions, and to a lesser degree the epipelagic zone, being mainly cool-requiring animals. However, a significant part of the isotopically investigated ammonoids (group 2) preferred, on the contrary, only epipelagic conditions, being mainly thermophilic dwellers.     

Isotopic analysis of belemnites and brachiopods from the Cretaceous (Albian) Hunstanton Red Chalk Formation (Hunstanton,Norfolk, UK)

Cretaceous brachiopods (Moutonithyris dutempleana) and belemnites (Neohibolites minimus) from the (Albian) Hunstanton Red Chalk Formation (Hunstanton, UK) were isotopically analysed with the aim of identifying palaeoecological and palaeotemperature trends. Shell preservation was assessed via thin section petrography and geochemical analyses. Oxygen isotopic compositions (and corresponding temperature interpretations) of well-preserved belemnites are similar in comparison to the brachiopod shells. Assuming calcite precipitation in isotopic equilibrium, they are interpreted to have occupied the same or similar warm (15–19 °C) shallow marine environment. Further, these findings indicate that the belemnites mineralised in relatively warm waters and not in deep and cool waters as suggested for some belemnite species. The isotope data are thus inconsistent with the belemnites being associated with a cool water pulse, contrasting with events associated with the Cenomanian chalks. A difference δ¹³C between the belemnites and brachiopods is interpreted to originate from differences in metabolic rates.     

Oxygen isotope evolution of biogenic calcite and apatite during the Middle and Late Devonian

Oxygen isotope ratios of well-preserved brachiopod calcite and conodont apatite were used to reconstruct the palaeotemperature history of the Middle and Late Devonian. By assuming an oxygen isotopic composition of –1 V-SMOW for Devonian seawater, the oxygen isotope values of Eifelian and early Givetian brachiopods and conodonts give average palaeotemperatures ranging from 22 to 25 °C. Late Givetian and Frasnian palaeotemperatures calculated from ¹⁸O values of conodont apatite are close to 25 °C in the early Frasnian and increase to 32 °C in the latest Frasnian and early Famennian. Oxygen isotope ratios of late Givetian and Frasnian brachiopods are significantly lower than equilibrium values calculated from conodont apatite ¹⁸O values and give unrealistically warm temperatures ranging from 30 to 40 °C. Diagenetic recrystallization of shell calcite, different habitats of conodonts and brachiopods, as well as non-equilibrium fractionation processes during the precipitation of brachiopod calcite cannot explain the ¹⁸O depletion of brachiopod calcite. Moreover, the ¹⁸O depletion of brachiopod calcite with respect to equilibrium ¹⁸O values calculated from conodont apatite is too large to be explained by a change in seawater pH that might have influenced the oxygen isotopic composition of brachiopod calcite. The realistic palaeotemperatures derived from ¹⁸O _apatite may suggest that biogenic apatite records the oxygen isotopic composition and palaeotemperature of Palaeozoic oceans more faithfully than brachiopod calcite, and do not support the hypothesis that the ¹⁸O/¹⁶O ratio of Devonian seawater was significantly different from that of the modern ocean.     

Cenomanian palaeotemperatures derived from the oxygen isotopic composition of brachiopods and belemnites: evaluation of Cretaceous palaeotemperature proxies

Sixty low-magnesium-calcite samples from Cenomanian articulate brachiopods, belemnites and oysters from the epicontinental shelf sea of Europe were geochemically and microscopically studied in order to evaluate their preservation and potential as carriers of palaeoenvironmental information. The sampled localities in northern Spain, Germany and southern England cover the transition between subtropical (25-30°N) and temperate (33-38°N) climates. Mean Cenomanian salinity-adjusted palaeotemperatures of diagenetically unaltered terebratulid and rhynchonellid brachiopods are 25.5ǃ.3 °C in Spain and 19.4ǃ.9 °C in southern England. The resulting low-to-mid-latitude meridional temperature gradient of ~0.7 °C per degree latitude is similar to the gradient today and suggests modern heat transport values for Cenomanian low latitudes. Oxygen isotopic composition of unaltered specimens of the Upper Cenomanian belemnite Praeactinocamax plenus (mean: 0.2‰) is enriched in ¹⁸O by 1‰ in comparison to brachiopod shells. Correspondingly, Upper Cenomanian palaeotemperatures derived from belemnite calcite (~13.0ǃ.3 °C) underestimate modelled mid-latitude sea surface temperatures by ~6 °C. Since P. plenus occurs as Boreal pulse fauna during a short interval in the Late Cenomanian, its heavy oxygen isotopic composition can be attributed either to migration from a cooler and/or deeper water mass or to unknown vital effects.     

A lithostratigraphic revision and palaeoenvironmental assessment of the Cretaceous System exposed in the onshore Cauvery Basin, southern India

The exposed Cretaceous shelf succession of the Cauvery Basin, southeastern India, has provided a world-class record of mid and Late Cretaceous invertebrates, documented in a substantial literature. However, the lithostratigraphy of the succession has been little studied and previously subject to a range of nomenclature. It is revised here, on the basis of intensive regional mapping, to stabilize the definition and nomenclature of lithostratigraphic units. The Uttattur Group is restricted in outcrop to the Ariyalur district and divided into the Arogypapurum Formation (new; Albian), Dalmiapuram Formation (late Albian), and Karai Formation (late Albian–early Turonian) for which the Odiyam and Kunnam Members are recognized. The Trichinopoly Group follows unconformably and is also restricted in outcrop to the Ariyalur district. It is divided into the Kulakkalnattam Formation (Turonian) and Anaipadi Formation (late Turonian–Coniacian). The Ariyalur Group is more widely distributed. In the Ariyalur district, the Sillikkudi Formation (Santonian–Campanian) and its Kilpaluvari Member, the Kallakurichchi Formation (early Maastrichtian), the Kallamedu Formation (mid and Late Maastrichtian) and the Niniyur Formation (Danian) are recognized. The sequence in the Vriddhachalam area consists of the Parur and Patti formations (Campanian), Mattur Formation (late Campanian–earliest Maastrichtian) and Aladi Formation (Maastrichtian). For the Pondicherry district, the Valudavur and Mettuveli formations (Maastrichtian) and Kasur and Manaveli formations (Paleocene) comprise the succession. The interpreted depositional environments for the succession in the Ariyalur district indicate four eustatic cycles in the mid and Late Cretaceous and earliest Tertiary: late Albian–early Turonian, late Turonian–Santonian, Campanian, Maastrichtian, and Paleocene. Overall the Cauvery Basin sequence is arenaceous and relatively labile in terms of framework grain composition, and contrasts with the pelitic assemblage developed on the west Australian margin from which eastern India separated in the Early Cretaceous (Valanginian). The difference is ascribed to palaeoclimate as controlled by palaeolatitude. For the Late Cretaceous, the Cauvery Basin drifted north on the Indian plate from 40 to 30°S. This zone is inferred to constitute Southern Hemisphere horse latitudes for Late Cretaceous time, characterized by an arid climate, physical weathering and the production of labile sands. By contrast, the west Australian margin of matching tectonic history remained in a high palaeolatitude (>40°S) throughout the Late Cretaceous, experiencing a pluvial climate, the dominance of chemical weathering and the production of clays.     

Carbon isotope records of the early Albian oceanic anoxic event (OAE) 1b from eastern Tethys (southern Tibet,China)

The early Albian Oceanic Anoxic Event (OAE), i.e., OAE1b, is well documented in western Tethys and in the primary North Atlantic Ocean, but has not yet been reported from eastern Tethys. In this paper, we present bulk carbon isotope data of hemipelagites to examine if it was recorded in eastern Tethys. Samples were taken from the upper Chuangdepu Member (nannofossil zone CC8) of the lower Gyabula (former Shadui) Formation at the Bangbu section, Qonggyai, southern Tibet of China. The δ¹³C values mainly range from −0.6‰ to 1.8‰ with a maximum of 1.87‰ and a minimum of −0.69‰. Three stages of carbon isotope evolution were distinguished with three boundaries. By the constraint of the stratigraphic sequence and nannofossil biostratigraphic zone CC8, the rapid δ¹³C change and correlation with western Tethys and Atlantic Ocean together suggest that these three boundaries of the carbon isotope evolution probably correspond to three subevents of the early Albian OAE1b, and the subevent levels of upper Kilian, Paquier, and Leenhardt are recorded in eastern Tethys (southern Tibet). The fact that the amount of δ¹³C shift is less by ∼1.5–2.0‰ in eastern Tethys than in western Tethys and Atlantic Ocean is interpreted as a result of possible cool sea surface (∼14–16 °C) of the southeastern Tethys (northern Indian passive margin of Greater India), which was probably located in a medium–high latitude during the Albian, leading to low primary productivity. The recognition of OAE-1b from Tethys Himalaya can improve our understanding of the Tethys and global paleoclimatic and paleoceanographic changes during the mid-Cretaceous.     

An approach to estimate Lower Jurassic seawater oxygen‐isotope composition using δ18O and Mg/Ca ratios of belemnite calcites (Early Pliensbachian,northern Spain)

Palaeotemperature estimates from the oxygen‐isotope compositions of belemnites have been hampered by not knowing ancient seawater isotope compositions well enough. We have tackled this problem using Mg/Ca as a proxy for temperature and here, we present a ~2 Ma record of paired Mg/Ca and δ¹⁸O measurements of Jurassic (Early Pliensbachian) belemnites from the Asturian basin as a palaeo‐proxy of seawater oxygen‐isotope composition. From the combined use of the two approaches, we suggest a δ¹⁸O_w composition of about ?0.1‰ for the Jamesoni–Ibex zones. This value may have been increased by about 0.6‰ during the Davoei Zone due to the effect of waters with a different δ¹⁸O_w composition. These findings illustrate the inaccuracy of using a globally homogeneous ice‐free value of δ¹⁸O_w = ?1‰ for δ¹⁸O_carb‐based palaeotemperature reconstructions. Our data suggest that previous palaeotemperatures calculated in the region from δ¹⁸O values of belemnites may have been underestimated as the seawater oxygen isotopic composition could have been higher.     

Late Cretaceous ophiolite obduction and Paleocene India-Asia collision in the westernmost Himalaya

Abstract

Collision of the Kohistan island arc with Asia at ~100 Ma resulted in N-S compression within the Neo-Tethys at a spreading center north of the Indo-Pakistani craton. Subsequent India-Asia convergence converted the Neo-Tethyan spreading center into a short-lived subduction zone. The hanging wall of the subduction zone became the Waziristan, Khost and Jalalabad igneous complexes. During the Santonian- Campanian (late Cretaceous), thrusting of the NW IndoPakistani craton beneath Albian oceanic crust and a Cenomanian volcano-sedimentary complex, generated an ophiolite-radiolarite belt. Ophiolite obduction resulted in tectonic loading and flexural subsidence of the NW Indian margin and sub-CCD deposition of shelf-derived olistostromes and turbidites in the foredeep. Campanian-Maastriehtian calci- clastic and siliciclastic sediment gravity flows derived from both margins filled the foredeep as a huge allochthon of Triassic-Jurassic rise and slope strata was thrust ahead of the ophiolites onto the Indo-Pakistani craton. Shallow to intermediate marine strata covered the foredeep during the late Maastrichtian. As ophiolite obduction neared completion during the Maastrichtian, the majority of India-Asia convergence was accommodated along the southern margin of Asia. During the Paleocene, India was thrust beneath a second allochthon that included open marine middle Maastrichtian colored mélange which represents the Asian Makran-Indus-Tsangpo accretionary prism. Latérites that formed on the eroded ophiolites and structurally higher colored mélange during the Paleocene wei’e unconformably overlapped by upper Paleocene and Middle Eocene shallow marine limestone and shale that delineate distinct episodes of Paleocene collisional and Early Eocene post-collisional deformation.     

Albian oceanic anoxic events in northern Tunisia: Biostratigraphic and geochemical insights

Albian pelagic successions of the Nebeur area in northwestern Tunisia consist of radiolarian-bearing and organic-rich black shale beds, which represent the lower part of the Fahdene Formation. The carbonate content of the organic-rich beds ranges between 40 and 48%. Total organic carbon (TOC) analyses via Rock Eval pyrolysis yielded values ranging between 0.7 and 2.8% and a mixed marine/terrestrial origin. T_max values vary between 424 and 450 °C, indicative of submature to mature organic matter. High resolution planktic foraminiferal and radiolarian biostratigraphy suggest that the black shales beds span the mid- to late Albian, confined to the middle part of the Ticinella primula zone, upper Biticinella breggiensis zone and lower appeninica + buxtorfi zone. Episodes of organic-rich deposition in the “Tunisian Trough” are interpreted as being the sedimentary record of the global oceanic anoxic events OAE1b, c, and d respectively. Age-diagnostic radiolarian assemblages recovered from late Albian organic-rich black shales lie within the UA13–UA14 boundary biochronozones. The abundance of radiolarian and calcispheres (i.e. pithonella) within the black shales suggests high productivity periods and eutrophic conditions probably triggered by upwelling currents.     

Southern Granulite Terrain, South of the Palghat-Cauvery Shear Zone: Implications for India-Madagascar Connection

The present paper correlates the southern Madgascar terrain, south of the Ranotsara shear with the granulite terrain of southern India, occurring south of the Palghat-Cauvery (P-C) shear zone. Both the terrains have witnessed high temperature to ultra high temperature granulite metamorphism at 550 Ma and are traversed by shear zones and deep crustal faults. The 550 Ma old granulite terrains of Madagascar and southern India have similar lithologies, in particular, sapphirine bearing pelitic assemblages. Graphite deposits and gem occurrences are common to both these terrains. The 550 Ma old southern granulite terrain of southern India comprises of different blocks, the Madurai and the Kerala Khondalite belt, but all the blocks have similar lithologies with pelite—calc silicate rocks inter-banded with two pyroxene granulite bodies. These lithologies occur amidst an essentially charnockitic terrain. The protolith ages of the southern granulite terrain, south of the P-C shear zone ranges between 2400–2100 Ma. The terrain as a whole has witnessed the 550 Ma old granulite event. The granulite metamorphism took place under temperatures of 800–1000°C and at pressures of 9.5 to 5 Kbar.The source of heat for the high temperature granulite event of the southern Madagascar terrain has been linked to advective heat transfer along mantle deep faults. The source for the high temperature granulite metamorphism for the southern granulite terrain may be attributed to high temperature carbonatite and alkaline intrusives in an extensional setting which followed an initial crustal thickening.Many workers have linked Madagascar to southern India by connecting the Ranotsara shear either to the P-C shear zone or to the Achankovil shear zone, further south. The important factor is the lithologies of the Madagascar terrain, south of Ranotsara shear zone and the 550 Ma. old southern Indian granulite terrain are similar in many aspects. It will be more appropriate to link the Ranotsara shear to the curvilinear lineament bounding the Anaimalai-Kodaikanal ranges and which merges with the southern margin of the P-C shear zone.However, north of the Ranotsara shear/fault, the northern Madagascar terrain comprises of a dominant Itremo sequence (< 1850 Ma) and 780 Ma old calc-alkaline intrusives. The latter have similarities with that of Aravallis and the Sirohi, Malani sequences occurring further north east. The Rajasthan terrain has witnessed igneous intrusive activity at 1000–800 Ma. If we can broaden the area of investigations and include the above areas, the Madagascar-India connection can be better understood.     

The Middle to Upper Jurassic stable isotope record of Madagascar: Linking temperature changes with plate tectonics during the break-up of Gondwana

Stable isotope (δ¹⁸O, δ¹³C) analyses were performed on well preserved belemnites, oysters, and rhynchonellid brachiopods from the Middle to Upper Jurassic of the Morondava Basin in southern Madagascar. Both brachiopods and oysters indicate similar average temperatures of 18.7 to 19.3 °C in the Early Callovian, followed by a temperature decrease towards the Middle Oxfordian (13.9 °C) and a minimum in the Early Kimmeridgian (12.3 °C). In contrast, belemnites from the Oxfordian show lower average temperatures of 10.0 °C, which is likely caused by specific conditions for these organisms (e.g., different fractionation or life habits). Additionally, three oysters from the Upper Oxfordian and Lower Kimmeridgian were used for high-resolution stable isotope analyses. The data show seasonal fluctuations of >6 °C around averages between 14.4 and 14.7 °C. Latitudinal temperature gradients for the Callovian and Kimmeridgian are similar to today at the examined low latitudes of the southern hemisphere. The observed cooling of around 5 °C from the Callovian to the Oxfordian/Kimmeridgian can be attributed to a concurrent southward drift of Madagascar during the break-up of Gondwana. Thus, the study underlines the importance of considering palaeogeography in interpreting stable isotope data as well as the potential of detecting and timing palaeogeographic events by using stable isotope analyses.     

The Mesozoic ostracod genus Arculicythere Grékoff: further evidence for the southern Gondwana seaway

This paper demonstrates that Arculicythere Grékoff is a widespread taxon in the uppermost Upper Jurassic and Lower Cretaceous of Gondwana. It occurs in Madagascar, India, Israel, South Africa, the Falklands Plateau, Argentina and Australia. The earliest record is from the Upper Tithonian of Madagascar but the most profuse occurrences are in the Albian, when the genus was very widespread around Gondwana. Its distribution seems to be associated with a major southern Gondwana seaway, and the genus provides additional proof of the existence of this corridor. Unlike another endemic gondwanine genus, Majungaella Grékoff, which ranged from earlier in the Jurassic but extended into the Neogene in the Antarctic, or Rostrocytheridea Dingle that survived into the Campanian of the Antarctic, Arculicythere seems to have become extinct in the Albian.     

The first finds of cretaceous belemnites from the Magellan Rise, Pacific Ocean

The occurrence of belemnites in Mesozoic sediments of the Pacific guyots is established for the first time (rostra Dimitobelidae gen. et sp. indet. from the late Campanian-Maastrichtian detrital limestone of the DVGI Guyot, Belemnitella? sp. from oolitic limestone of the Gelendzhik Guyot, which are presumably of the Santonian-Maastrichtian age, and Belemnitidae? gen. et sp. indet. from the Maastrichtian oolitic limestone of the Butakov Guyot, the Magellan Rise). In recent years, fossil cephalopods important in stratigraphic and paleobiogeographic aspects have been found at five guyots of that rise. New data on fossil invertebrates from the study region suggest breaks in the sedimentation here at the terminal Maastrichtian, Paleogene, and initial Neogene time. Possible limits of vertical migration in the tropical Pacific are estimated for the Late Cretaceous belemnites based on preliminary results of the oxygen isotope analysis.     

Chronology of upper Quaternary offshore successions from the southeastern Mediterranean Sea,Israel

Pleistocene and Holocene transgressions advancing over the shelf that was exposed during glacial maxima drowned any continental and shallow marine sediments deposited during low sea level stands. To complement records from sequences exposed on land, core material from the shallow continental shelf is needed to reconstruct climatic and sea level fluctuations. Two cores drilled offshore Ashqelon off the southern Mediterranean coast of Israel, in a water depth of 10 and 25 m, were analyzed. Sedimentary facies and faunal analyses indicate that most of the sediments were deposited in nearshore environments, with only short intervals of continental episodes. Luminescence dating of alkali feldspar and quartz, as well as ¹⁴C ages of mollusks, date the cores to marine oxygen isotopic stages 6–1, between ∼140 and 5 ka. Comparison between the dating methods shows that most alkali feldspar ages agree with independent sea level and sedimentological constraints while quartz ages are overestimated.     

Isotopic and chemical intra-shell variations in low-Mg calcite of rudist bivalves (Mollusca-Hippuritacea): disequilibrium fractionations and late Cretaceous seasonality

 Isotopic (δ¹³C, δ¹⁸O) and elemental (Mg, Sr, Mn, Fe) compositions were analysed in sclerochronological profiles of several shells of late Cretaceous rudist bivalves from Greece, Turkey, Somalia and the Arabian Peninsula. The preservation of original compositions of low-Mg calcite of outer shell layers is indicated by constant and high Sr, generally low Fe and Mn, and the preservation of fibrous-prismatic ultrastructures. Cyclic variations in δ¹⁸O and Mg are interpreted to reflect seasonal temperature/salinity cycles and, thus, annual growth increments. In shells of Torreites, amplitudes of correlated δ¹³C and δ¹⁸O cycles cannot be related to reasonable palaeotemperatures or salinity. This isotopic pattern reflects vital fractionations of an extent which is unknown from modern bivalves. In contrast, almost identical ranges and amplitudes of δ¹⁸O cycles are observed in 13 shells of five species from Santonian-Campanian localities in central Greece and northern Turkey, suggesting that seasonal variations in environmental conditions were recorded without significant vital fractionations. The effect of seasonal salinity changes on δ¹⁸O of the shells is evaluated, and mean palaeotemperatures are constrained within the range of 30–32.5  °C. The annual range of temperature was estimated to be 7  °C, assuming a constant salinity. This agrees with other isotopic proxies of Late Cretaceous palaeotemperatures, and with global circulation models which predict higher low-latitude sea-surface temperatures than the present ones. Received: 12 February 1998 / Accepted: 24 May 1999     

A 11,000 yr palaeotemperature reconstruction from the southern boreal zone in Finland

The ecotone between the boreo-nemoral (hemiboreal) and the southern boreal vegetation zones constitutes the northern distributional limit of a number of thermophilous tree species in northern Europe and is, to a large extent, controlled by climatic conditions. We present a quantitative annual mean temperature reconstruction from a high-resolution pollen stratigraphy in southern boreal Finland, using a pollen-climate calibration model with a cross-validated prediction error of 0.9°C. Our model reconstructs low but steadily rising annual mean temperature from 10,700 to 9000 cal yr BP. At 8000–4500 cal yr BP reconstructed annual mean temperature reaches a period of highest values (Holocene thermal maximum) with particularly high temperatures (2.0–1.5°C higher than at present) at 8000–5800 cal yr BP. From 4500 cal yr BP to the present-day, reconstructed annual mean temperature gradually decreases by ca 1.5°C. Comparison of present results with palaeotemperature records from the Greenland ice cores, notably with the NorthGRIP δ¹⁸O record, shows marked similarities, suggesting parallel large-scale Holocene temperature trends between the North Atlantic and North European regions. The verification of the occurrence, timing, and nature of the short-term temperature fluctuations during the Holocene in the southern boreal zone in Europe requires replicate, high-resolution climate reconstructions from the region.     

Gondwana to Asia: Plate tectonics,paleogeography and the biological connectivity of the Indian sub-continent from the Middle Jurassic through latest Eocene (166–35 Ma)

Using the most up-to-the-date information available, we present a considerably revised plate tectonic and paleogeographic model for the Indian Ocean bordering continents, from Gondwana's Middle Jurassic break-up through to India's collision with Asia in the middle Cenozoic. The landmass framework is then used to explore the sometimes complex and occasionally counter-intuitive patterns that have been observed in the fossil and extant biological records of India, Madagascar, Africa and eastern Eurasia, as well those of the more distal continents.Although the paleogeographic model confirms the traditional view that India became progressively more isolated from the major landmasses during the Cretaceous and Paleocene, it is likely that at various times minor physiographic features (principally ocean islands) provided causeways and/or stepping-stone trails along which land animals could have migrated to/from the sub-continent. Aside from a likely link (albeit broken by several marine gaps) to Africa for much of this time (it is notable, that the present-day/recent biota of Madagascar indicates that the ancestors of five land-mammal orders, plus bats, crossed the > 400-km-wide Mozambique Channel at different times in the Cenozoic), it is possible that the Kerguelen Plateau connected India and Australia–Antarctica in the mid-Cretaceous (approximately 115–90 Ma). Later, the Seychelles–Mascarene Plateau and nearby elevated sea-floor areas could have allowed faunas to pass between southern India and Madagascar in the Late Cretaceous, from around 85–65 Ma, with an early Cenozoic extension to this path forming as a result of the Reunion hot-spot trace islands growing on the ocean floor to the SSW of India. The modelling also suggests that India's northward passage towards Asia, with eventual collision at 35 Ma, involved the NE corner of the sub-continent making a glancing contact with Sumatra, followed by Burma from ~ 57 Ma (late Paleocene) onwards, a scenario which is compatible with the fossil record indicating that India–Asia faunal exchanges began occurring at about this time. Finally, we contend that a number of biologically-based direct terrestrial migration routes that have been proposed for last 15 m.y. of the Cretaceous (Asia to India; Antarctica to Madagascar and/or India) can probably be dismissed because the marine barriers, likely varying from > 1000 up to 2500 km, were simply too wide.     

Depositional age,provenance and metamorphic age of metasedimentary rocks from southern Madagascar

Southern Madagascar is the core of a > 1 million km² Gondwanan metasedimentary belt that forms much of the southern East African Orogen of eastern Africa, Madagascar, southern India and Sri Lanka. Here the Vohibory Series yielded U–Pb isotopic data from detrital zircon cores that indicate that it was deposited in the latest Tonian to late Cryogenian (between ~ 900 and 640 Ma). The deposition of the Graphite and Androyen Series protoliths is poorly constrained to between the late Palaeoproterozoic and the Cambrian (~ 1830–530 Ma). The Vohibory Series protoliths were sourced from very restricted-aged sources with a maximum age range between 910 and 760 Ma. The Androyen and Graphite Series protoliths were sourced from Palaeoproterozoic rocks ranging in age between 2300 and 1800 Ma. The best evidence of the timing of metamorphism in the Vohibory Series is a weighted mean ²⁰⁶Pb/²³⁸U age of 642 ± 8 Ma from 3 analyses of zircon from sample M03-01. A considerably younger ²⁰⁶Pb/²³⁸U metamorphic age of 531 ± 7 Ma is produced from 10 analyses of zircon from sample M03-28 in the Androyen Series. This ~ 110 Ma difference in age is correlated with the early East African Orogeny affecting the west of Madagascar along with its type area in East Africa, whereas the Cambrian Malagasy Orogeny affected the east of Madagascar and southern India during the final suturing of the Mozambique Ocean.     

Upper Albian OAE 1d event in the Chihuahua Trough,New Mexico,U.S.A.

Oceanic anoxic events are clues to ocean processes and are correlation datums. In North America only OAE 1a and 2 are well documented. Based on a low-resolution sampling program, a multi-proxy geochemical approach constrained by a biostratigraphic framework was utilized to identify OAE 1d in the upper part of the upper Albian Mesilla Valley Formation near El Paso, Texas. Chronostratigraphic and biostratigraphic evidence indicate that the OAE 1d event in the Mesilla Valley section is located in the lower part of the upper Albian–Cenomanian Ovoidinium verrucosum zone, which correlates with the uppermost Albian Parathalmanninella appenninica and Stoliczkaia dispar zones. The chronostratigraphic age of the geochemical event in the Mesilla Valley Formation is uppermost Albian (97.39–97.30 Ma).The classic geochemical signatures for OAEs are enriched total organic carbon (TOC) concentrations and coupled positive δ¹³C excursions. OAE 1d at this location records TOC values ranging from 0.25 to 0.69 wt.% throughout the Mesilla Valley Formation, where TOC increases during the OAE (21.0–40.0 m) to more than 0.40 wt.%. Interestingly, the organic matter in the Mesilla Valley is dominantly type III, which indicates a pervasive terrigenous source. Although marine organic matter is abundant from the base into the middle of the proposed OAE interval, it is progressively replaced by terrestrial material above the OAE section during progradation. The δ¹³C_organic values record a positive δ¹³C shift of +1.6‰ from −26.41 to −24.80‰ across the stratigraphic interval from 21.0 to 40.0 m, which correlates with OAE 1d.Mn and Fe geochemistry suggest the depositional conditions of the Mesilla Valley Formation were dominated by anoxic and possibly Fe-rich bottom waters, specifically during the time period associated with the OAE 1d event. This interpretation is supported by the presence of Fe enrichment recorded by Fe_Total/Al and Fe_{Highly Reactive}/Fe_T with the lack of Fe_pyrite/Fe_{Highly Reactive} associated with Mn depletion.