Out-of-sequence thrusts and paleogeography of the Rhenodanubian Flysch Belt (Eastern Alps) revisited

The Oberstdorf nappe of the Western and the Laab nappe of the Eastern Rhenodanubian Flysch (ERF) were independently identified as out-of-sequence thrust units by facies studies (Mattern 1999) and zircon analyses (Trautwein et al. 2001a, b, c), respectively. A new look at both areas reveals mutual similarities and new evidence for the out-of-sequence concept. Paleocurrent and heavy mineral data make it possible to reconstruct the sediment influx directions. From the Barremian to the mid-Campanian, the western and eastern basin segments were fed with south-derived garnet and north-derived zircon/”ZTR” (i.e., zircon, tourmaline, and rutile). Because both out-of-sequence units are relatively rich in zircon/ZTR they must have occupied the northernmost basin position. In the Western Rhenodanubian Flysch segment, the Sigiswang nappe occupied the central and the Üntschen nappe the southernmost basin position. In the ERF segment the central basin is represented by the Greifenstein nappe and the southernmost basin by the Kahlenberg nappe. Both out-of-sequence units do not occur in the northernmost and tectonically lowest position in their respective nappe piles as they were thrust over the other nappes. The reconstructed basin positions of the thrust units are suggested by the observation of a gradient in heavy mineral content in the thrust units. This paleogeographic arrangement is least problematic and renders models with differently positioned thrust units, requiring debris-shedding intrabasinal ridges, as unnecessarily complicated. Instead, we suggest that gradual changes in heavy mineral composition existed in across-basin direction. Garnet may stem from the Central Gneiss Complex of the Tauern window and formerly exposed lateral equivalents, all representing the southern Mid-Penninic zone. We assign the Falknis/Tasna nappe and formerly exposed lateral equivalents to the northern Mid-Penninic zone which served as the zircon/ZTR source. Interpreting Ebbing’s (Ph.D. thesis, Freie Universität Berlin, pp 1-143, 2002; Fig. 6.10) density section, we suggest that Mid-Penninic crust exists beneath the Central Gneiss Complex. During the latest Cretaceous much garnet was also N-derived. This may reflect processes related to the consumption of the North Penninic basin.     

Calibration of the Albian/Cenomanian Boundary by Ammonite Biostratigraphy: U.S. Western Interior

Calibration of numerical ages to the geological time scale is a long scientific pursuit that requires the integration of multiple data sets. A case study of the Albian/Cenomanian stage boundary, also the Lower/Upper Cretaceous series boundary, illustrates the calibration process. The numerical age of this boundary has shifted from 96 Ma to 99 Ma over a time span of nearly fifty years. Re-calibration resulted first from improvements in radiometric dating, and later from inferences about ammonite phylogeny, and most recently from radiometric dates of newly discovered volcanic beds interbedded with diagnostic guide fossils. However, the calibration process continues with study of cosmopolitan dinoflagellates.     

Palaeogeographical implications of CretaceousBenthic Foraminifera recovered by the Deep Sea Drilling project in the Western South Atlantic ocean

Albian/Cenomanian benthic foraminiferal faunas recovered by the DSDP in the western South Atlantic Ocean (Leg 36) are described and analyzed from the palaeogeographic and palaeo-environmental points of view. In doing this the author compares Leg 36 assemblages in the western South Atlantic Ocean with coeval benthic foraminiferal faunas recovered in the eastern South Atlantic Ocean (Leg 40) and in the eastern Indian Ocean (Legs 26 and 27). The specific composition of these assemblages, except for Leg 27, is virtually the same. Consequently, they are considered to indicate the same depositional water depth at all relevant sites studied, whether located in the Angola Basin, the northern flank of the Walvis Ridge, the eastern margin of the Falkland Plateau or on the Naturaliste Plateau. All the assemblages indicate shallow environments around 100 m and not exceeding 300–400 m in the deepest parts, corresponding to the inner shelf and the inner part of the outer shelf. By contrast the foraminiferal associations of Leg 27 (especially Site 259) indicate a greater depth, of the order of 200–600 m (but not exceeding 1000 m) corresponding to upper slope of Sliter & Baker (1972) and Sliter (1972). These bathymetrical conclusions are in remarkable accord with those of Sliter (1976), based on planktic Foramini fera of Leg 36.Late Cretaceous (Campanian-Maastrichtian) material with benthic Foraminifera was limited to two positive samples; however, these faunas indicate much the same palaeo-environment as do the planktic ones analyzed by Sliter (1976).     

Biostratigraphical correlations of the calcareous nannofossil Marthasterites furcatus in the Bohemian Cretaceous Basin and Outer Flysch Carpathians,Czech Republic

The first occurrence (FO) of Marthasterites furcatus was correlated with the FOs of other nannofossils, inoceramid bivalves and foraminifers in the Bohemian Cretaceous Basin and Outer Flysch Carpathians. The correlation showed that the FO of M. furcatus was diachronous, becoming younger from east to west. In the Silesian Unit it appears in the lower Turonian in association with Eprolithus moratus (UC6b nannofossil Zone). In the Pavlovské vrchy klippes it appears in the upper middle Turonian together with Lithastrinus septenarius (UC9 Zone). In the Bohemian Cretaceous Basin, the FO of M. furcatus was observed in the lower upper Turonian just above the FO of Liliasterites angularis. The presence of M. furcatus in Turonian strata is scarce and discontinuous up to its sudden quantitative increase (represented by 5–27% in assemblages) below the FO of the inoceramid bivalve species Cremnoceramus waltersdorfensis and C. deformis erectus in the Turonian–Coniacian boundary interval. The top of the M. furcatus acme was recorded below the FO of Micula staurophora. The second quantitative rise of M. furcatus (12% in assemblage) was found in the lower lower Campanian of the Pavlovské vrchy klippes above the FO of Broinsonia parca parca in the UC14a Zone and the last occurrence of the planktonic foraminifer Whiteinella baltica. Above this second acme M. furcatus disappears. The significantly earlier appearance of M. furcatus in the Silesian Basin may be connected with a southeast-heading surface current from the North European epicontinental sea where the species appeared in the early Turonian too.     

The Lower Miocene volcaniclastic sedimentation in the Sicilian sector of the Maghrebian Flysch Basin: geodynamic implications

Abstract

Volcaniclastic debris-rich formations, characterising the Troina-Tusa Unit in the Sicilian Maghrebian Chain, are examined. The Troina-Tusa Unit terrains sedimented in the Maghrebian Flysch Basin, which, from Jurassic to Early Miocene, constituted the southernmost branch of the Western Tethys, located between Africa and the Mesomediterranean Terrane margins. New field, biostratigraphic and pétrographie data enable a reconstruction of the palaeogeographic and structural evolution of the Flysch Basin immediately before its deformation. All the studied formations transpired to be Burdigalian in age. The sandstone compositions, showing different source areas (magmatic arc, recycled orogen and continental block), indicate a provenance for the clastic material from a crystalline basement with an active volcanic arc, replaced by a remnant volcanic arc, which was rapidly completely eroded. The source area that has been considered is Sardinia, where Upper Oligocene -Aquitanian calc-alkaline volcanites are widespread, but the sedimentological characteristics and the Burdigalian age do not fit with this provenance. The Burdigalian calc-alkaline arc should be located on the internal side of the Troina-Tusa Basin, above the already stacked Peloritanian units. A migration of the volcanic activity, connected with the subduction plain roll-back, can be envisaged from the Sardinia Block to the Peloritanian Chain, this latter still docked to the Sardinia-Corsica massif. © 2002 Editions scientifiques et médicales Elsevier SAS. All rights reserved.     

Holocene reactivations of catastrophic complex flow-like landslides in the Flysch Carpathians (Czech Republic/Slovakia)

Complex flow-like landslides (CFLLs) are important geomorphic agents of Late Quaternary mountain evolution in the Flysch Belt of the Outer Western Carpathians. The CFLLs are characterised by the upper section of deep-seated, retrogressive landslide of structurally unfavourably oriented rocks and lower sections composed of earthflows originated due to liquefaction of material accumulated from the upper slopes. Radiocarbon dating of organic matter incorporated into landslide debris or related deposits suggests that most of the CFLLs collapsed repeatedly throughout the Holocene with typical recurrence intervals of approximately 1–2 ka. Catastrophic landslides that occurred during extreme hydrometeorological events in recent decades displayed evidence of Holocene activity. Most of the CFLLs dammed and steepened adjacent valleys. Our chronological dataset is biased by erosion of older landforms, but most of the dated reactivations correlate to regional increases in humidity identified by previous paleoenvironmetal studies.     

Calcareous nannoplankton, planktonic foraminiferal, and carbonate carbon isotope stratigraphy of the Cenomanian–Turonian boundary section in the Ultrahelvetic Zone (Eastern Alps, Upper Austria)

Ultrahelvetic units of the Eastern Alps were deposited on the distal European continental margin of the (Alpine) Tethys. The Rehkogelgraben section (“Buntmergelserie”, Ultrahelvetic unit, Upper Austria) comprises a 5 m thick succession of upper Cenomanian marl-limestone cycles overlain by a black shale interval composed of three black shale layers and carbonate-free claystones, followed by lower Turonian white to light grey marly limestones with thin marl layers. The main biostratigraphic events in the section are the last occurrence of Rotalipora and the first occurrences of Helvetoglobotruncana helvetica and Quadrum gartneri. The thickest black shale horizon has a TOC content of about 5%, with predominantly marine organic matter of kerogen type II. Vitrinite reflectance and Rock-Eval parameter T_max (<424 °C) indicate low maturity. HI values range from 261 to 362 mg HC/g TOC. δ¹³C values of bulk rock carbonates display the well documented positive shift around the black shale interval, allowing correlation of the Rehkogelgraben section with other sections such as the Global Boundary Stratotype Section and Point (GSSP) succession at Pueblo, USA, and reference sections at Eastbourne, UK, and Gubbio, Italy. Sediment accumulation rates at Rehkogelgraben (average 2.5 mm/ka) are significantly lower than those at Pueblo and Eastbourne.     

Palynostratigraphy and palynofacies indications of depositional environments and source potential for hydrocarbons: the mid Cretaceous Nahr Umr and lower Mauddud formations, Iraq

Palynomorphs recovered from core and cuttings samples from five boreholes in the East Baghdad Oilfield indicate a mid Albian–early Cenomanian age-range for the Nahr Umr Formation and the lower part of the overlying Mauddud Formation. Two palynomorph zones and four types of palynofacies have been identified. The latter are interpreted to indicate delta-top swamp and marsh, silty–muddy deltaic, inner silty and carbonate-rich platform, and limestone-platform environments. The palynofacies of the two types of platform accumulations suggest that these are potential sources of biogenic methane and condensates, and may yield more liquid hydrocarbons in areas where the formations are at greater depths than within the region studied.     

Foraminiferal Biostratigraphy of the Mobarak Formation (Lower Carboniferous) in Kiyasar Area,SE Sari,Northern Iran

The Mobarak Formation is near the town of Kiyasar in the south-east of Sari city, northern Iran. This formation conformably overlies the Geirud Formation (Upper Devonian). The lower part of the Mobarak Formation consisting of shales and thin- to medium-bedded limestone toward the top of these sequences changes into alternations of dark limestone and interbedded gray to black shales. Weathered yellow thick-bedded shales are observed at the top of the section. This formation is covered unconformably by sandstones attributed to the Dorud Formation (Lower Permian). The thickness of the formation in this region is 250 m. Four rock units have been recognized in this section. Foraminiferal biostratigraphy shows that the age of the Mobarak Formation in the Kiaysar region ranges from Lower Tournaisian to Early Middle Visean. The foraminifer Zones FAZ1 and FAZ2 are correlated with the Lower Tournaisian and Upper Tournaisian, whereas Zones FAZ3 and FAZ4 correlate with the Visean. Affinities exist between specimens recorded in the Kiyasar section with species known from other regions in eastern and Central Alborz, but there are important differences in their appearance.     

Stable isotope analysis of the Cenomanian–Turonian (Late Cretaceous) oceanic anoxic event in the Crimea

Carbon and oxygen isotope data from Cenomanian–Turonian sediments from the southwest of the Crimea are presented. The sediments consist of limestones, marls and organic-rich claystones, the latter with total organic carbon values up to 2.6 wt. %, representing Oceanic Anoxic Event 2. A shift to more negative δ¹⁸O values through the uppermost Cenomanian into the lowermost Turonian may be the result of warming; however, petrographic analysis shows that the samples have undergone a degree of diagenetic alteration. The carbon isotope data reveal a positive excursion from 2.7‰ to a peak of 4.3‰ at the Cenomanian/Turonian boundary; values then decrease in the early Turonian. This excursion is comparable to those of other Cenomanian–Turonian sections, such as those seen in the Anglo-Paris Basin, and is thought to be due to global changes in the oceanic carbon reservoir. On this curve are a number of negative δ¹³C excursions, just below the Cenomanian/Turonian boundary. It is suggested that these negative excursions are associated with the uptake of light carbon derived from the oxidation and deterioration of organic material during localised exposure of the sediments to oxic or meteoric diagenetic conditions, possibly during sea-level fluctuations.     

Inoceramid bivalves and biostratigraphy of the upper Albian and lower Cenomanian of the United States Western Interior Basin

Inoceramid bivalves of the upper Albian and lower Cenomanian of the United States Western Interior are revised, Eleven species-level taxa and three genera are described. Two new species, Gnesioceramus mowriensis, characterizing the Mowry Shale of the early, but not the earliest, Cenomanian, and Posidonioceramus merewetheri, of the lower Cenomanian, and on new genus, Posidonioceramus, are recognised. The Western Interior inoceramid species from this interval are strongly endemic and are not good tools for long-distance correlations, although they are very effective in regional dating.In terms of the inoceramid biostratigraphy, middle and upper parts of the upper Albian can be referred to the Gnesioceramus Biozone, represented by G. comancheanus (Cragin) and G. bellvuensis (Reeside). These taxa are endemic to the Western Interior and some adjacent areas (Gulf Coast; Greenland?), but are closely allied to the cosmopolitan species, Gnesioceramus anglicus (Woods). At approximately the Albian-Cenomanian boundary, the endemic clade of ‘Inoceramus’ nahwisi appears, now referred to the newly erected Posidonioceramus, resulting in a distinct P. nahwisi biozone. This zone corresponds to the lower part of the ammonite Neogastroplites’ stratigraphic range. Gnesioceramids re-appear in the early Cenomanian. Close to base of the Cenomanian, for the first in the Western Interior, the genus Inoceramus, represented by Inoceramus irenensis Warren and Stelck, 1958, apparently immigrated into the Western Interior Basin.The Western Interior inoceramids do not allow for direct correlation to chronostratigraphic standard subdivision. The Albian-Cenomanian boundary, as earlier recognized on geochronologic correlations and confirmed, to some extent, based on ammonites, may approximately be located close to the appearance level of the genus Posidonioceramus.     

Garnet zoning and the identification of equilibrium mineral compositions in high-pressure–temperature granulites from the Moldanubian Zone, Austria

A detailed investigation of the compositional variation in garnet has been undertaken in a garnet–pyroxene‐bearing granulite from the high‐grade Gföhl Unit, Moldanubian Zone, Lower Austria. Textural observations, together with the interpretation of the preserved garnet chemistry, enables the recognition of both prograde core and peak metamorphic garnet mantle growth stages, an extremely rare feature in high‐P–T granulite facies rocks. Initial thermobarometric calculations undertaken across whole garnet zoning profiles show how correct interpretation of a zoning profile is essential if the maximum peak metamorphic P–T conditions are to be recovered. The effect of retrograde decompression‐ and cooling‐driven reactions on inclusion and host garnet compositions has also been assessed. The results indicate that caution should be exercised when utilizing inclusion and adjacent garnet compositions for the thermobarometric evaluation of peak metamorphic equilibration conditions. Peak P–T conditions were determined by the TWEEQU thermobarometric method, utilizing the core compositions of matrix phases combined with the interpreted high‐P–T garnet mantle composition, to give 15.6 kbar and 1090 °C, consistent with previously determined results for Moldanubian granulites. Similar high‐P–T estimates are also provided by a re‐evaluation of previously published results for a granulite sample from the same lithological unit, using a modified interpretation of garnet and plagioclase compositional data. The new estimates presented confirm the previously disputed idea that the Gföhl Unit underwent a high‐pressure granulite facies stage and is therefore distinctly different from the underlying tectonostratigraphic units. It is emphasized that any interpretation of the peak metamorphic conditions in high‐grade rocks must be based on detailed petrographic observations combined with a thorough understanding of the co‐existing equilibrium mineral compositions.     

Planktic Foraminiferal Biostratigraphy of the Cretaceous Oceanic Red Beds in Kangmar,Southern Tibet,China

The planktic foraminifera of the Chuangde Formation (Upper Cretaceous Oceanic Red Beds, CORBs) as exposed at Tianbadong section, Kangmar, southern Tibet has been firstly studied for a detailed for a detailed biostratigraphy elaboration. A rich and well-preserved planktic foraminifera were recovered from the Chuangde Formation of the Tianbadong section and the Globotruncanita elevata, Globotruncana ventricosa, Radotruncana calcarata, Globotruncanella havanensis, Globotruncana aegyptiaca, Gansserina gansseri and Abathomphalus mayaroensis zones have been recognized. The planktic foraminiferal assemblage points to an early Campanian to Maastrichitian age for the CORBs of the eastern North Tethyan Himalayan sub-belt, which also provides a better understanding of the shifting progress of the Indian Plate to the north and the evolution of the Neotethyan ocean. The lithostratigraphy of the Chuangde Formation of the Tianbadong section comprises two lithological sequences observed in ascending succession: a lower unit (the Shale Member) mainly composed of purple (cherry-red, violet-red) shales with interbedded siltstones and siliceous rocks; and an upper unit (the Limestone Member) of variegated limestones. The strata of the Chuangde Formation in the Tianbadong section are similar to CORBs in other parts of the northern Tethyan Himalaya area of Asia (Gyangze, Sa’gya, Sangdanlin, northern Zanskar, etc.). The fossil contents of the Chuangde Formation in the sections (CORBs) studied provide a means of correlation with the zonation schemes for those of the northern Tethyan Himalayan sub-belt and the Upper Cretaceous of the southern Tethyan Himalayan sub-belt. Paleogeographic reconstruction for the Late Cretaceous indicates that the Upper Cretaceous Chuangde Formation (CORBs) and correlatable strata in northern Zanskar were representative of slope to basinal deposits, which were situated in the northern Tethyan Belt. Correlatable Cretaceous strata in Spiti and Gamba situated in the southern Tethyan Belt in contrast were deposited in shelf environments along the Tethyan Himalayan passive margin. CORBs are most likely formed by the oxidation of Fe(II)-enriched, anoxic deep ocean water near the chemocline that separated the oxic oceanic surface from the anoxic.     

山东滩海地区下第三系生物地层与沉积环境初探

<正> 山东滩海地区位于胜利油气区东部沿海一带,自北向南依次为埕北凹陷、埕子口凸起及沾化凹陷东部的桩西、五号桩和孤东等地(图1)。多年来的石油地质勘探表明本区下第三系构造单元复杂,沉积类型多样,地层的超覆、剥失现象普遍,为地层油气藏     

新疆吐哈盆地连木沁构造带克拉玛依组生物地质特征

新疆吐哈盆地连木沁构造带,在连4-S井4215～4832m取样分析,该地层孢粉化石数量和属种较多,主要为苔癣、蕨类植物孢粉和裸子植物花粉,孢粉化石组合具有较清楚的时代地层意义,通过分析命名为Aratnspontes - Punctatispozites - Colpectopollis组合。根据组合主要分子的时限及其含量变化,以及与有关已知时代孢粉组合进行比对,可确认该地层地质时代为克拉玛依组。     

Shallow high-resolution seismics and reprocessing of industry profiles in southern Bavaria: The Molasse and the northern Alpine front

The purpose of this seismic investigation in the Upper Bavarian Miesbach area, as part of the international TRANSALP project, was to study the tectonic contact between the autochthonous Foreland Molasse and the allochthonous Folded Molasse marking the tectonic front of the Alpine orogen. Another specific target was the dip of the frontal emerging main thrust of the tectonic units Helveticum/Ultrahelveticum and Rhenodanubian Flysch overriding the Folded Molasse. Twelve seismic profiles obtained from the hydrocarbon industry were reprocessed. From the Foreland Molasse southward to the Autochthonous Molasse in the subsurface of the overthrust Folded Molasse conspicuous features such as steep normal faults at the Molasse base, S-directed thickening of Molasse sediments or sedimentary discordant base of Upper Marine Molasse can be recognized.Shallow high-resolution seismic measurements were conducted along two profiles across the tectonic contact between Foreland Molasse and Folded Molasse, as well as along a profile across the frontal emerging main thrust of the Helveticum/Ultrahelveticum and the Rhenodanubian Flysch. Geological structures could be identified in the top 300–500 ms two-way traveltime interval, which is hardly possible with the usual deep-seismic method. The method thus provides a bridge between deep-reflection seismics and surface geology.In contrast to the western Bavarian Molasse zone, the tectonic boundary between the Foreland Molasse and the Folded Molasse in the investigated area is not characterized by a large blind-thrust triangle zone but by a simple south-dipping thrust plane. Adjacent to the S follow several steeply south-dipping inverse Molasse thrust slices and the Miesbach syncline. The inverse thrust slices are interpreted as the overturned and sheared northern limb of a fault propagation fold, which linked the Folded Molasse to the Foreland Molasse during a final orogenic phase.The main thrust of the Helveticum/Ultrahelveticum and the Rhenodanubian Flysch are well imaged in the near-surface interval of the high-resolution reflection seismic data. In contrast to previously published results, these thrust planes show a gentle dip to the S from the surface down to at least 500–1000 m depth.     

Benthic foraminiferal assemblages of late Aptian-early Albian black shale intervals in the Vocontian Basin, SE France

Benthic foraminiferal assemblages were analyzed from three black shale intervals in the upper Aptain to lower Albian of the Vocontian Basin, SE France based on Q-mode principal component analyses. Variations in the distribution patterns of benthic foraminifera around these events suggest differences in the origin of the black shales. Differences between faunas of bioturbated marly and laminated black shale facies have been observed in the Niveau Paquier, Oceanic Anoxic Event (OAE) 1b and Niveau Leenhardt. Here, the faunal composition and plankton/benthos ratios suggest eutrophic conditions during the deposition of organic-rich sediments leading to black shales. No major variations have been observed in black shales of the upper Aptain Niveau Jacob. Benthic assemblages and low plankton/benthos ratios indicate mesotrophic conditions. Third order sea-level changes are believed to control mainly the origin of the investigated black shale levels.     

The stratigraphic and paleoenvironmental setting of Aptian OAE black shale deposits in the Pieniny Klippen Belt, Slovak Western Carpathians

During the Jurassic and Cretaceous, the Pieniny Klippen Belt units of the Outer Western Carpathians were situated on the edge of the Paleoeuropean shelf rimming the northermost margin of the Mediterranean Tethys. During the late early Aptian humid event, Lower Cretaceous pelagic carbonate (Maiolica) sedimentation was interrupted by terrigenous input as a consequence of the first major mid-Cretaceous climate perturbations. The fluctuation of radiolarian abundance indicated an expansion of the oxygen-minimum zone due to upwelling conditions and salinity changes. Foraminifera, radiolarians, non-calcareous dinocysts, and calcareous nannofossils encountered in the West Carpathian Rochovica section enable a comparison of the black shales of the upper lower Aptian Koňhora Formation with the well-known Selli Event. Subsequent anoxia patterns (depositional, productive, and stagnant) have taken part in the depositional regime. Early Aptian climate perturbations both in the Outer Western Carpathians, Swiss Prealps (situated in a similar position on the distal southern edge of the former Paleoeuropean shelf) and/or in other parts of the world are traceable with sedimentological, biological, and chemical proxies.     

Micropaleontological evidence for redox changes in the OAE3 interval of the US Western Interior: Global vs. local processes

The Coniacian-Santonian interval has been proposed as the youngest of the Cretaceous ocean anoxic events (OAE3), but this designation has long been debated. OAE3 is associated with a long-lasting (∼3 myr) succession of black shales from the central and South Atlantic, Caribbean region, and the North American Western Interior; in the Western Interior it is characterized by an abrupt increase in total organic carbon (TOC) and corresponding trace metal indicators for anoxia. However, the modern concept of OAEs is predicated on detection of global carbon cycle perturbations as recorded by substantial carbon isotope excursions (CIE), and the protracted Coniacian-Santonian black shale interval does not have a large CIE. A more conservative definition of OAE3 might limit the event to the modest positive carbon isotope excursion restricted to the upper Coniacian Scaphites depressus Ammonite Zone. Trace metal proxies suggest that oxygen levels abruptly declined prior to the onset of this CIE in the Western Interior Sea (WIS), but it is unknown whether regional anoxic conditions were confined to sediments/pore waters, or how anoxia may have affected the biota. In an effort to characterize the oxygenation history of the WIS and to better understand the nature of the hypothesized OAE3, we present micropaleontological evidence of declining oxygen in bottom waters prior to the event using benthic foraminifera, which are sensitive to dissolved oxygen. Changes in benthic foraminiferal abundances suggest a decline in oxygen at least 1-myr prior to the CIE (including a nadir immediately below the start of the excursion), improving bottom water oxygen during the CIE, and re-establishment of persistent anoxia following the isotope excursion. Anoxia endured for nearly 3 myr in the central seaway, showing some signs of recovery toward the top of the Niobrara Formation. Our findings suggest that declining oxygen concentrations in the seaway eventually reached a tipping point, after which dissolved oxygen quickly dropped to zero.The late Coniacian CIE is an exception to the trend of declining oxygen in the WIS, and part of a larger pattern in the oxygenation history of the Niobrara Formation which suggests that it does not adhere to standard black shale models. Transgressive periods, including the Fort Hays Limestone and the lower limestone unit of the Smoky Hill Shale (which corresponds to the CIE) are relatively oxic, while periods of highstand (i.e., most of the Smoky Hill) correspond to deteriorating oxygen conditions. This contrasts with the standard black shale model for sea level and oxygen, where transgressions typically correlate with maximum TOC enrichment, interpreted to result from both sediment condensation and oxygen deficiency. The association of global carbon burial/anoxia (as indicated by carbon isotopes) with a regional increase in oxygen and decrease in organic matter preservation is reminiscent of the Cenomanian-Turonian Greenhorn Limestone, which contains OAE2. In both cases, the facies are not typical black shales, but instead have appreciable carbonate content. Western Interior redox trends support the rejection of the original concept of a protracted Coniacian-Santonian OAE3 because it is not a distinct “event.” Increasing local oxygen during the late Coniacian CIE also argues against a narrower OAE designation for this event, because the excursion can't be tied to anoxia here or anywhere else it has been described. Nevertheless, the Late Coniacian Event (as we prefer to call this CIE) still represents an important perturbation of the global carbon cycle. This is emblematic of the shift away from widespread, discrete anoxic events during the ongoing paleoceanographic reorganization of the Late Cretaceous, even as large carbon cycle perturbations continued.     

Characteristics of three recent earthquake sequences in the Taupo Volcanic Zone, New Zealand

We have analysed three recent earthquake sequences in the northern part of the Taupo Volcanic Zone. A 1998 sequence at Haroharo with a largest event of M_L 4.8, and a 2004 sequence near Lake Rotoehu (largest event M_L 5.4), had normal b-values, and displayed an aftershock decay pattern, with most of the activity within the first few days. In contrast, a 2005 sequence a few tens of kilometres away at Matata (largest event M_L 4.1), had very different characteristics, with a slow development and decay, no tendency for enhanced seismicity after the larger events, and a very high b-value.The focal mechanisms of the Rotoehu and Matata events are normal, and have stress patterns consistent with the geodetically observed extension of the Taupo Volcanic Zone in a northwest–southeast direction. The extensive recent volcanism in the Okataina Volcanic Centre does not seem to have affected the stress pattern in this area.The Rotoehu sequence showed a strong resemblance, particularly in the time distribution of events, to the well-known swarm activity in the Vogtland region on the German/Czech border, in which larger events were followed by a burst of seismicity, as in a normal aftershock sequence. Some of the arguments that have been advanced to explain the Vogtland swarm as seismicity induced by fluid injection apply to Rotoehu, but there is no direct evidence of fluid involvement. The Matata sequence appears to have a continuing trigger mechanism, either a slow injection of fluid, or a slow slip event, in an environment in which opening pore spaces prevent high overpressures developing. The Matata sequence occurred close to the area of the 1987 M_L 6.3 Edgecumbe Earthquake, so exhibiting two extremes of seismic temporal pattern, namely mainshock–aftershock and a swarm with many events of similar magnitude, within a small area.