Annual shell growth patterns of the three venerid bivalve species, Gafrarium pectinatum, Pitar citrinus, and Katelysia japonica were investigated based on the results of sclerochronological and stable oxygen isotope analyses of live-caught specimens from the intertidal zone of Iriomote Island, southern Ryukyu Archipelago. In the study area, these three species temporally stopped shell deposition, when sea surface temperature (SST) dropped to 23-26 degrees C, during the first three years. However, the shutdown temperature for shell growth increased slightly to higher than 26 degrees C after 6 years old for G. pectinatum combined with a shortening in the length of shell growing period. Seasonal changes in daily shell growth in these species were controlled mainly by SST and primary production. Shell delta O-18-derived summer temperatures recorded in the annual increments were higher by 3-5 degrees C than the highest SST records of the habitat. This data mismatch might be caused by an abrupt decrease in seawater delta O-18 values during the summer and fall typhoon seasons because of the influx of fresh water into the study area from nearby rivers. This study suggests that in the study area the annual shell growth patterns and shell delta O-18 values in the three species examined were controlled by mutually related biological and environmental factors such as ontogenetic age and seasonal changes in SST, salinity and primary production.

Photosymbiosis has played a key role in the diversification of foraminifera and their carbonate production throughout geologic history. However, identification of photosymbiosis in extinct taxa remains challenging, and even among the extant species the occurrence and functional relevance of photosymbiosis remain poorly constrained. Here, we investigate photosymbiosis in living planktonic foraminifera by measuring active chlorophyll fluorescence with fast repetition rate fluorometry. This method provides unequivocal evidence for the presence of photosynthetic capacity in individual foraminifera, and it allows us to characterize multiple features of symbiont photosynthesis including chlorophyll a (Chl a) content, potential photosynthetic activity (F-v/F-m), and light-absorption efficiency (sigma PSII). To obtain robust evidence for the occurrence and importance of photosymbiosis in modern planktonic foraminifera, we conducted measurements on 1266 individuals from 30 species of the families Globigerinidae, Hastigerinidae, Globorotaliidae, and Candeinidae. Among the studied species, 19 were recognized as symbiotic and 11 as non-symbiotic. Of these, six species were newly confirmed as symbiotic and five as non-symbiotic. Photosymbiotic species have been identified in all families except the Hastigerinidae. A significant positive correlation between test size and Chl a content, found in 16 species, is interpreted as symbiont abundance scaled to the growth of the host and is consistent with persistent possession of symbionts through the lifetime of the foraminifera. The remaining three symbiont-bearing species did not show such a relationship, and their (F-v/F-m) values were comparatively low, indicating that their symbionts do not grow once acquired from the environment. The objectively quantified photosymbiotic characteristics have been used to design a metric of photosymbiosis, which allows the studied species to be classified along a gradient of photosynthetic activity, providing a framework for future ecological and physiological investigations of planktonic foraminifera.

The CO2 concentration of air has increased over the last two centuries and recently surpassed 400 ppm. Carbon cycle models project CO2 concentrations of 720 to 1000 ppm for the IPCC intermediate scenario (RCP 6.0), resulting in an increase in global mean temperature of ~ 2.6 °C and a decrease in seawater pH of ~ 0.3. Together, global warming and ocean acidification are often referred to as the “evil twins” of climate change, potentially inducing severe threats in the near future. In this paper, our discussion is focused on the response of two major calcifiers, foraminifera and corals, which contribute much to the global carbonate burial rate. Photosymbiosis is regarded as an adaptive ecology for living in warm and oligotrophic oceans, especially for reef-building corals and larger reef-dwelling benthic foraminifera. As a consequence of global warming, bleaching may be a global threat to algal symbiont-bearing marine calcifying organisms under conditions of high temperature and light intensity. If CO2 is dissolved in seawater, the partial pressure of CO2 in seawater (pCO2) and dissolved inorganic carbon (DIC) increases while pH and the saturation state of carbonate minerals decreases without any change in total alkalinity. Generally, marine calcifying organisms show decreases in calcification rates in response to acidified seawater. However, the response often differs depending on situations, species, and life-cycle stage. Some benthic foraminifera showed a positive response to low pH conditions. The Acropora digitifera coral calcification of adult branches was not reduced markedly at higher pCO2 conditions, although calcification tended to decrease versus pCO2 in both aposymbiotic and symbiotic polyps. New analytical technologies help identify important constraints on calcification processes. Based upon Ca isotopes, the transport path of Ca2+ and the degree of its activity would predominantly control the carbonate precipitation rate. Visualization of the extracellular pH distribution shows that proton pumping produces the high internal pH and large internal–external pH gap in association with foraminiferal calcification. From the perspective of a long-term change in the Earth’s surface environment, foraminifera seem to be more adaptive and robust than corals in coping with ocean warming and acidification but it is necessary to further understand the mechanisms underlying variations in sensitivity to heat stress and acidified seawater for future prediction. Since CO2 is more soluble in lower temperature seawater, ocean acidification is more critical in the polar and high-latitude regions. Additionally, older deep-water has enhanced acidity owing to the addition of CO2 from the degradation of organic matter via a synergistic effect with high pressure. With current ocean acidification, pH and the saturation state of carbonate minerals are decreasing without any change in total alkalinity. However, in the Earth’s history, it is well known that alkalinity has fluctuated significantly. Therefore, it is necessary to quantitatively reconstruct alkalinity, which is another key factor determining the saturation state of carbonate minerals. The rapid release of anthropogenic CO2 (in the present day and at the Paleocene/Eocene boundary) induces severe ocean acidification, whereas in the Cretaceous, slow environmental change, even at high levels of pCO2, could raise alkalinity, thereby neutralizing ocean acidification. [Figure not available: see fulltext.]

Several foraminifers found in warm and low-nutrient ocean surface water have photosynthetic algae as endosymbionts (photosymbiosis). To understand the trophic interactions, we studied Globigerinoides sacculifer, a spinose planktic foraminifer that has a dinoflagellate endosymbiont. We controlled two nutritional factors, feeding and inorganic nutrients in the seawater. The growth of the host and the symbionts and the photophysiological parameters were monitored under four experimental conditions. The results demonstrated that the holobionts primarily relied on phagotrophy for growth. The foraminifers grew considerably, and the chlorophyll a content per foraminifer, which is an indicator of the symbiont population, increased in the fed groups, but not in the unfed groups. The nutrient-rich seawater used for some of the cultures made no difference in either the growth or photophysiology of the holobionts. These observations indicated that the symbionts mainly utilized metabolites from the hosts for photosynthesis rather than inorganic nutrients in the seawater. Additionally, we observed that the symbionts in the starved hosts maintained their photosynthetic capability for at least 12 days, and that the hosts maintained at least some symbionts until gametogenesis was achieved. This suggests that the hosts have to retain the symbionts as an energy source for reproduction. The symbionts may also play an indispensable role in the metabolic activities of the hosts including waste transport or essential compound synthesis. Overall, our results revealed a novel mode of photosymbiosis in planktic foraminifers which contrasts with that found in benthic photosymbiotic foraminifers and corals.

The stable carbon (delta C-13) and oxygen isotopes (delta O-18) of planktic foraminiferal tests have been widely used as proxies in paleoceanography and paleoclimatology. The ontogenetic isotopic profiles of foraminifers are also thought to record ecological information about species, such as changes in habitat depth and symbiotic relationships. However, isotopic profiles during "individual ontogeny" have rarely been examined. In this study, we report the ontogenetic isotopic information for three net-collected modern species, Globigerinoides sacculifer, Neogloboquadrina dutertrei, and Globorotalia inflata, together with several in situ oceanographic parameters of the water column in Sagami Bay, Japan (seawater temperature, salinity, nutrients, chlorophyll a content, delta C-13 of dissolved inorganic carbon [DIC], and delta O-18 of seawater). We examined the ontogenetic profiles of the foraminifers with chamber dissection and chamber-by-chamber analyses of delta C-13 and delta O-18 using a specially designed continuous-flow mass spectrometry system. The ontogenetic delta O-18 profiles showed overall O-18-enrichment in all three species, suggesting their ontogenetic migration toward deeper habitats. When these records were compared with the physicochemical profiles of the water column, all the ontogenetic records began within the uppermost thermocline or shallower, corresponding to the depth of relatively high chlorophyll content. Later in ontogeny, Gs. sacculifer and N. dutertrei migrated to the bottom of the level of maximum chlorophyll, whereas Gr. inflata descended to a depth of 200 m. The deviations of foraminiferal delta C-13 from the delta C-13 of DIC were largest in the juvenile stages, but were near zero at a test mass of ca. 10 mu g for all three species. Contrary to the subsequent asymptotic profiles of this deviation in N. dutertrei and Gr. inflata, Gs. sacculifer alone showed a subsequent increase, of up to +1.0%, reflecting its symbiotic relationship. We conclude that a certain ontogenetic test mass, in this case of around 10 mu g, can be assigned to a preferable size class of foraminifers from which to reconstruct the paleo-delta C-13 of DIC in the water column, regardless of the species ecology.

Photosymbiosis is an important ecological strategy that allows the host to thrive in oligotrophic environments, and the photosymbiosis of planktic foraminifers is no exception. Here, we present ontogenetic information about the photosymbiosis of planktic foraminifers that we obtained via analyses of the chlorophyll fluorescence [fast repetition rate (FRR) fluorometry] of symbiotic algae within the host We cultured two symbiont-bearing planktic foraminifers (Globigerinoides sacculifer and Globigerinella siphonifera Type II) until their natural death, and conducted FRR measurements on individual host algal consortia through the culture study. Time-series FRR analyses revealed no clear temporal trend in photophysiology but did reveale species specificity. The light absorption efficiency of the photosynthetic system was significantly higher in Gn. siphonifera than in Gs. saccubfer indicating higher potential to acclimate to low-light environment for Gn. siphonifera. In contrast to the physiology, the chlorophyll a content of foraminifer, a metric of the quantity of symbionts, showed conspicuous ontogenetic changes; the chlorophyll a content, initially less than 30 ng, reached a maximum of more than 140 ng, then it was all digested or lysed at the end of the host's ontogeny. The changes of symbiont biomass and relatively invariant photophysiology indicate dynamic rise and fall of potential photosynthesis of symbiont population during the host's life processes, not just the progressive increase of photosynthesis. Because photosynthesis of symbionts can alter the geochemical composition of the foraminiferal calcifying microenvironment, our results will also contribute to better understanding of the effect of photosynthesis on the foraminiferal tests that are important for paleoecological and paleoceanographic works. (C) 2015 Elsevier B.V. All rights reserved.

Evolution of photosymbiotic ecology is an important adaptation for planktic foraminifers that enhances the ecological advantage of living in oligotrophic oceans. Therefore, detecting photosymbiotic ecology in fossil species is one of the keys to understanding the paleobiodiversity dynamics of planktic foraminifers. Because foraminiferal tests record the ontogenetic history of ecological information in geochemical signatures, analyzing individual geochemical profiles with growth can reveal a species’ ecology. This study examined chamber-by-chamber stable isotopes (Î13C and Î18O) of foraminiferal individuals to identify photosymbiotic signals. We observed an ontogenetic Î13C increase of up to 2.4‰, accompanied by relatively stable, negative Î18O, in the symbiotic species Globigerinoides conglobatus and Globigerinoides sacculifer. In contrast, Î13C and Î18O showed significant positive correlation during ontogeny in the asymbiotic species Globorotalia truncatulinoides. These two ecological groups produce contrasting isotopic profiles, thereby allowing us to use our ontogenetic isotopic analyses of individual specimens to identify algal photosymbiosis in fossil foraminifers. The chamber-by-chamber isotope analyses with individual ontogeny have great advantages in analyzing rare species because only one individual is required to describe ontogenetic isotopic history. In addition to photosymbiotic identification, our methods hold great potential to provide new insight into species paleoecological studies such as the ontogenetic history of calcification depth.

Phospholipid-derived fatty acids (PLFA) and respiratory quinones (RQ) are microbial compounds that have been utilized as biomarkers to quantify bacterial biomass and to characterize microbial community structure in sediments, waters, and soils. While PLFAs have been widely used as quantitative bacterial biomarkers in marine sediments, applications of quinone analysis in marine sediments are very limited. In this study, we investigated the relation between both groups of bacterial biomarkers in a broad range of marine sediments from the intertidal zone to the deep sea. We found a good log-log correlation between concentrations of bacterial PLFA and RQ over several orders of magnitude. This relationship is probably due to metabolic variation in quinone concentrations in bacterial cells in different environments, whereas PLFA concentrations are relatively stable under different conditions. We also found a good agreement in the community structure classifications based on the bacterial PLFAs and RQs. These results strengthen the application of both compounds as quantitative bacterial biomarkers. Moreover, the bacterial PLFA- and RQ profiles revealed a comparable dissimilarity pattern of the sampled sediments, but with a higher level of dissimilarity for the RQs. This means that the quinone method has a higher resolution for resolving differences in bacterial community composition. Combining PLFA and quinone analysis as a complementary method is a good strategy to yield higher resolving power in bacterial community structure.

The Neodymium (Nd) isotope composition of fish remains has been widely used to track past changes in oceanic circulation. Although the number of published Nd isotope data for the Cretaceous has markedly increased in the last years, no consensus has been reached on the structure of the oceanic circulation and its evolution during the Late Cretaceous. Yet this period is characterised by major geodynamical and climatic changes and marked by the disappearance of global oceanic anoxic events in which changes in oceanic circulation modes may have played a significant role.
In this study we present the first record of Nd isotopic composition of fish remains from continental margin environments on the northwestern Pacific margin (Yezo Group in the Hokkaido area, Northern Japan) for the Late Cretaceous period. This record, interpreted in terms of Nd isotopic composition of local neritic seafloor seawater, is characterised by relatively radiogenic Nd isotope compositions and presents variations of several epsilon-units from the Turonian to the Campanian ranging from similar to-5.5 to similar to 0.5 epsilon-units, although most values remain in the similar to-1 to similar to-3 range. Conversely, the local detrital fraction remains more constant and around -4 e-units on the studied interval. This new set of seawater Nd data contains some of the most radiogenic values for the Cretaceous published yet. The more radiogenic seawater Nd isotope values compared to that of the sediments points to an input of radiogenic seawater in the studied area by surface currents during the Late Cretaceous. Similarly to the modern configuration, these radiogenic waters could have been conveyed in the studied area by a southward current comparable to the modern Oyashio current bathing the Hokkaido area. Our data are then consistent with the presence in the northern Pacific of highly radiogenic seawater, and support the northern and northwestern Pacific as a possible radiogenic source for the deep parts of the basin. As such this work represents a first step toward a better characterisation of the various end-members that could have contributed to the Nd isotopic signature of the deep-water masses filling the Cretaceous oceans. (C) 2013 Elsevier B.V. All rights reserved.

Deep-Earth convection can be understood by studying hotspot volcanoes that form where mantle plumes rise up and intersect the lithosphere, the Earth's rigid outer layer. Hotspots characteristically leave age-progressive trails of volcanoes and seamounts on top of oceanic lithosphere, which in turn allow us to decipher the motion of these plates relative to "fixed" deep-mantle plumes, and their (isotope) geochemistry provides insights into the long-term evolution of mantle source regions. However, it is strongly suggested that the Hawaiian mantle plume moved ~15° south between 80 and 50 million years ago. This raises a fundamental question about other hotspot systems in the Pacific, whether or not their mantle plumes experienced a similar amount and direction of motion. Integrated Ocean Drilling Program (IODP) Expedition 330 to the Louisville Seamounts showed that the Louisville hotspot in the South Pacific behaved in a different manner, as its mantle plume remained more or less fixed around 48°S latitude during that same time period. Our findings demonstrate that the Pacific hotspots move independently and that their trajectories may be controlled by differences in subduction zone geometry. Additionally, shipboard geochemistry data shows that, in contrast to Hawaiian volcanoes, the construction of the Louisville Seamounts doesn't involve a shield-building phase dominated by tholeiitic lavas, and trace elements confirm the rather homogenous nature of the Louisville mantle source. Both observations set Louisville apart from the Hawaiian-Emperor seamount trail, whereby the latter has been erupting abundant tholeiites (characteristically up to 95% in volume) and which exhibit a large variability in (isotope) geochemistry and their mantle source components.

Hotspots that form above upwelling plumes of hot material from the deep mantle typically leave narrow trails of volcanic seamounts as a tectonic plate moves over their location. These seamount trails are excellent recorders of Earth's deep processes and allow us to untangle ancient mantle plume motions. During ascent it is likely that mantle plumes are pushed away from their vertical upwelling trajectories by mantle convection forces. It has been proposed that a large-scale lateral displacement, termed the mantle wind, existed in the Pacific between about 80 and 50 million years ago, and shifted the Hawaiian mantle plume southwards by about 15 degrees of latitude. Here we use Ar-40/Ar-39 age dating and palaeomagnetic inclination data from four seamounts associated with the Louisville hotspot in the South Pacific Ocean to show that this hotspot has been relatively stable in terms of its location. Specifically, the Louisville hotspot-the southern hemisphere counterpart of Hawai'i-has remained within 3-5 degrees of its present-day latitude of about 51 degrees S between 70 and 50 million years ago. Although we cannot exclude a more significant southward motion before that time, we suggest that the Louisville and Hawaiian hotspots are moving independently, and not as part of a large-scale mantle wind in the Pacific.

Integrated Ocean Drilling Program Expedition 342 was designed to recover Paleogene sedimentary sequences with unusually high deposition rates across a wide range of water depths (Sites U1403-U1411). The drilling area is positioned to capture sedimentary and geochemical records of ocean chemistry and overturning circulation beneath the flow of the Deep Western Boundary Current in the northwest Atlantic Ocean. In addition, two operational days were dedicated to a sea trial of the Motion Decoupled Hydraulic Delivery System developmental tool (Site U1402).

The results of a calcareous nannofossil biostratigraphic investigation of the North Fork Cottonwood Creek section of the Budden Canyon Formation (BCF; Hauterivian-Turonian) in northern California are summarized using the Boreal - cosmopolitan Boreal Nannofossil Biostratigraphy (BC) - Upper Cretaceous Nannofossil Biostratigraphy (UC) nannofossil zonal schemes of Bown et al. and Burnett et al. Sixteen intervals, ranging from the BC15 to UC8 zones, were established in the section. Combined biostratigraphic and magnetostratigraphic studies suggest a Hauterivian to mid-Turonian age for the studied sequence. The Hauterivian-Barremian, Barremian-Aptian, Aptian-Albian, Albian-Cenomanian, and Cenomanian-Turonian stage boundaries were delineated near the top of the Ogo Member, below the Huling Sandstone Member, within the upper Chickabally Member, in the upper portion of the Bald Hills Member and within the Gas Point Member, respectively. Unconformities probably exist at the base of the Huling Sandstone Member and the upper part of the upper Chickabally Member. The nannofossil assemblage in the North Fork Cottonwood Creek suggests that the study area was under the influence of cold-water conditions during the Barremian to Lower Aptian interval, shifting to tropical/warm-water conditions during the Albian to Turonian interval as a result of the mid-Cretaceous global warming. Although oceanic anoxic events have not yet been reported in the BCF, preliminary total organic carbon, along with nannofossil data, suggest the presence of the global Cenomanian-Turonian boundary oceanic anoxic event 2.

The development of the climate during the Cretaceous greenhouse interval is reviewed based on geological and paleontological records, geochemical proxy records for paleotemperature and atmospheric carbon-dioxide concentration (pCO(2)), the production rate of oceanic crust, and the timing and scale of emplacement of large igneous provinces. Geological and paleontological evidence, and paleotemperature records indicate that the Early Cretaceous climate was relatively cool, possibly accompanied by the development of continental ice sheets. Subsequent warming reached a peak in the Turonian, when sea surface temperatures in equatorial and high-latitude regions exceeded 36 degrees C and 20 degrees C, respectively. The possibility of a maximum temperature above 36 degrees C at the equator is inconsistent with the cirrus cloud negative-feedback hypothesis proposed for the modern ocean, which may indicate that the hypothesis is not valid for an ice-free greenhouse system. Although elevated levels of pCO(2) are thought to be responsible for this extreme warming, the timing of the pCO(2) maxima differs from the timing of oceanic volcanic activity, which emitted massive amounts of CO, into the atmosphere, by similar to 30 m.y.: volcanic activity peaked at similar to 120 Ma, whereas pCO(2), temperature, and sea-level peaked at similar to 90 Ma, indicating that the abiotic Mesozoic marine revolution was not a simple, single event. Moreover, the occurrence of intermittent cooling during the Late Cretaceous, coupled with sea-ice development in the Arctic Ocean, suggests that the mid-Cretaceous greenhouse system was capable of producing not only extreme warmth but also seasonal freezing. Although the Mesozoic marine revolution is assumed to have been triggered by the general warming that occurred during the Cretaceous, a more precise analysis of the timing and magnitude of biotic events is required to understand the paleoecosystem of this greenhouse period.

The occurrence of Oceanic Anoxic Event 2 (OAE2) 94 million years ago is considered to be one of the largest carbon cycle perturbations in the Earth's history. The marked increase in the spatial extent of the anoxic conditions in the world's oceans associated with OAE2 resulted in the mass accumulation of organic-rich sediments. Although extensive oceanographic studies of OAE2 have been undertaken in the Atlantic Ocean, the Tethys Sea, and the epicontinental seas of Europe and America, little is known about OAE2 in the Pacific Ocean. Here, we present high-resolution carbon-isotope and degree of pyritization (DOP) data from marine sequences that formed along the continental margins of North America and Asia below the northeastern and northwestern Pacific Ocean. The predominance of low DOP values in these areas revealed that the continental margins of the Pacific Ocean were oxic for most of the OAE2 interval.

This study is based on Cenomanian sediments of Ocean Drilling Program (ODP) Sites 1258 and 1260 from Demerara Rise (Leg 207, western tropical Atlantic, off Suriname, similar to 1000 and similar to 500 m paleo-water depth, respectively). Studied sediments consist of laminated black shales with TOC values between 3 and 18% and include the Mid Cenomanian Event (MCE), a positive carbon isotope excursion predating the well-known Oceanic Anoxic Event 2 (OAE 2). Benthic foraminiferal assemblages of the continuously eutrophic environment at Demerara Rise are characterized by low diversities (<= 59 species per sample) and large fluctuations in abundances, indicating oxygen depletion and varying organic matter fluxes. Dominant species at both sites are Bolivina anambra, Gabonita levis, Gavelinella dakotensis, Neobulimina albertensis, Praebulimina prolixa, and Tappanina cf. lacinioso. Benthic foraminiferal assemblages across the MCE show a threefold pattern: (1) stable ecological conditions below the MCE interval indicated by relatively high oxygenation and fluctuating organic matter flux, (2) decreasing oxygenation and/or higher organic matter flux during the MCE with decreasing benthic foraminiferal numbers and diversities (Site 1258) and a dominance of opportunistic species (Site 1260), and (3) anoxic to slightly dysoxic bottom-water conditions above the MCE as indicated by very low diversities and abundances or even the absence of benthic foraminifera. Slightly dysoxic conditions prevailed until OAE 2 at Demerara Rise. A comparison with other Atlantic Ocean and Tethyan sections indicates that the MCE reflects a paleoceanographic turning point towards lower bottom-water oxygenation, at least in the proto-North Atlantic Ocean and in the Tethyan and Boreal Realms. This general trend towards lower oxygenation of bottom waters across the MCE is accompanied by ongoing climate warming in combination with rising sea-level and the development of vast shallow epicontinental seas during the Middle and Late Cenomanian. These changes are proposed to have favoured the formation of warm and saline waters that may have contributed to intermediate- and deep-water masses at least in the restricted proto-North Atlantic and Tethyan Ocean basins, poor oxygenation of the Late Cenomanian sediments, and the changes in benthic foraminiferal assemblages across the MCE. (C) 2009 Elsevier B.V. All rights reserved.

During the mid-Cretaceous period, the global subsurface oceans were relatively warm, but the origins of the high temperatures are debated. One hypothesis suggests that high sea levels and the continental configuration allowed high-salinity waters in low-latitude epicontinental shelf seas to sink and form deep-water masses(1-3). In another scenario, surface waters in high-latitude regions, the modern area of deep-water formation, were warmed through greenhouse forcing(4), which then propagated through deep-water circulation. Here, we use oxygen isotopes and Mg/Ca ratios from benthic foraminifera to reconstruct intermediate-water conditions in the tropical proto-Atlantic Ocean from 97 to 92Myr ago. According to our reconstruction, intermediate-water temperatures ranged between 20 and 25 degrees C, the warmest ever documented for depths of 500-1,000 m. Our record also reveals intervals of high-salinity conditions, which we suggest reflect an influx of saline water derived from epicontinental seas around the tropical proto-North Atlantic Ocean. Although derived from only one site, our data indicate the existence of warm, saline intermediate waters in this silled basin. This combination of warm saline intermediate waters and restricted palaeogeography probably acted as preconditioning factors for the prolonged period of anoxia and black-shale formation in the equatorial proto-North Atlantic Ocean during the Cretaceous period.

We investigate the coseismic vertical crustal movement along the northern and western coast of the Noto Peninsula caused by the Noto Hanto earthquake on March 25, 2007, from the distribution of supra-, mid- and infra-littoral organisms. The highest uplift of 44 cm is observed at Akakami and the maximum subsidence of 8 cm at Fukami. We construct a rectangular fault model with a uniform slip in elastic half-space using both the coseismic vertical displacement estimated from the distribution of these organisms and the coseismic crustal deformation obtained by GPS. The model shows a reverse fault with a right-lateral slip of 1.3 m in a 18.6 km x 14.5 km area. The seismic moment is 1.0 x 10(19) N m (M-W 6.6) using a rigidity of 30 GPa. The geometry of the source fault is consistent with the distribution of aftershocks and active faults, and the fault is restricted to the central area of the aftershock area. Relationships among the fault, the distribution of aftershocks, active faults, and geological blocks around the source area suggest that geological structures restrict the fault size of the earthquake. By considering an inclined altitudinal distribution of marine terraces and the coseismic vertical crustal deformation detected in this study, we estimate that the recurrence of earthquakes during the past 120 kyr would produce a vertical crustal deformation of similar to 12 m and the background tectonic uplift would reach similar to 28 m.

The mid-Cretaceous is widely considered the archetypal ice-free greenhouse interval in Earth history, with a thermal maximum around Cenomanian-Turonian boundary time (ca. 90 Ma). However, contemporaneous glaciations have been hypothesized based on sequence stratigraphic evidence for rapid sea-level oscillation and oxygen isotope excursions in records generated from carbonates of questionable preservation and/or of low resolution. We present new oxygen isotope records for the mid-Cenomanian Demerara Rise that are of much higher resolution than previously available, taken from both planktic and benthic foraminifers, and utilizing only extremely well preserved glassy foraminifers. Our records show no evidence of glaciation, calling into question the hypothesized ice sheets and rendering the origin of inferred rapid sea-level oscillations enigmatic. Simple mass-balance calculations demonstrate that this Cretaceous sea-level paradox is unlikely to be explained by hidden ice sheets existing below the limit of delta O-18 detection.

Oceanic anoxic event 2 ( OAE-2) occurring during the Cenomanian/Turonian ( C/T) transition is evident from a globally recognized positive stable carbon isotopic excursion and is thought to represent one of the most extreme carbon cycle perturbations of the last 100 Myr. However, the impact of this major perturbation on and interaction with global climate remains unclear. Here we report new high-resolution records of sea surface temperature ( SST) based on TEX86 and delta O-18 of excellently preserved planktic foraminifera and stable organic carbon isotopes across the C/T transition from black shales located offshore Suriname/French Guiana ( Demerara Rise, Ocean Drilling Program Leg 207 Site 1260) and offshore Senegal ( Cape Verde Basin, Deep Sea Drilling Project Leg 41 Site 367). At Site 1260, where both SST proxy records can be determined, a good match between conservative SST estimates from TEX86 and delta O-18 is observed. We find that late Cenomanian SSTs in the equatorial Atlantic Ocean ( >= 33 degrees C) were substantially warmer than today ( similar to 27 degrees-29 degrees C) and that the onset of OAE-2 coincided with a rapid shift to an even warmer ( similar to 35 degrees-36 degrees C) regime. Within the early stages of the OAE a marked ( similar to 4 degrees C) cooling to temperatures lower than pre-OAE conditions is observed. However, well before the termination of OAE-2 the warm regime was reestablished and persisted into the Turonian. Our findings corroborate the view that the C/T transition represents the onset of the interval of peak Cretaceous warmth. More importantly, they are consistent with the hypotheses that mid-Cretaceous warmth can be attributed to high levels of atmospheric carbon dioxide ( CO2) and that major OAEs were capable of triggering global cooling through the negative feedback effect of organic carbon-burial- led CO2 sequestration. Evidently, however, the factors that gave rise to the observed shift to a warmer climate regime at the onset of OAE-2 were sufficiently powerful that they were only briefly counterbalanced by the high rates of carbon burial attained during even the most extreme interval of organic carbon burial in the last 100 Myr.

Palaeotemperatures during the Albian-Coniacian in the northernmost Pacific have been determined on the basis of oxygen isotopic analysis of well-preserved brachiopod and molluscan shells from the Koryak Upland, Far East Russia. Those obtained from the calcitic brachiopod shells from the Albian range from 12.5 to 22.7 degrees C. The lower temperature level corresponds to winter seasons and the higher reflects summer temperatures. Probable winter isotopic palaeotemperatures, fluctuating from 10.9 to about 14.1 degrees C, were obtained from Coniacian bivalve shells. Presumed spring and autumn isotopic palaeotemperatures for the Coniacian, fluctuating from 14.1 to 17.7 degrees C, were obtained from rhynchonellid brachiopods and bivalves, all with calcitic shells, and aminonoids with aragonitic, shells. Presumed Summer isotopic palaeotemperatures varied between 18.5 degrees C to 22.4 degrees C. The new and previously published data suggest a short-term presence of polar ice during the Cretaceous (early Maastrichtian) only in the Southern Hemisphere on the Antarctic continent. Evidence pertaining to the Northern Hemisphere seems to suggest only occasional short-lived subfreezing conditions. These most probably occurred during polar winters in the early Valanginian, late Coniacian-early Santonian and early Maastrichtian. Temperatures in northern high latitudes during the course of even these winter seasons were probably not low enough for the formation of permanent sea ice. This may be a result of the lack of a continental massif in the North Pole area and a significant ameliorating effect of oceanic heat-transport poleward through the straits of Turgai and the Western Interior of North America. (c) 2005 Elsevier Ltd. All rights reserved.

Litho-. bio-. and chemostratigraphy of the Cretaceous forearc basin sediments exposed in Hokkaido, northern Japan allow a synthesis of the faunal, sedimentological, and environmental history of the north-west Pacific margin. Although the succession, named the Yezo Group, has yielded an abundant record of mid- to late Cretaceous invertebrates, monotonous lithologies of sandstone and mudstone, showing occasional lateral facies changes, have caused confusion regarding the lithostratigraphic nomenclature. Based on our wide areal mapping of the sequence, and analysis of litho- and biofacies, a new lithostratigraphic scheme for the Yezo Group is proposed. In ascending order, the scheme is Lis follows: the Soashibetsugawa Formation (Lower Aptian mudstone unit); the Shuparogawa Formation (Lower Aptian-lower Upper Albian sand stone-dominant turbidite unit); the Maruyama Formation (lower Upper Albian tuffaceous sandstone unit);, the Hikagenosawa Formation (Upper Albian-Middle Cenomanian mudstone-dominant unit) ; the Saku Formation (Middle Cenomanian-Upper Turonian sandstone-common turbidite unit); the Kashima Formation (Upper Turonian-Lower Campanian mudstone-dominant unit); and the Hakobuchi Formation (Lower Campanian-Paleocene shallow-marine sandstone-conglomerate unit). In addition, we designate two further lithostratic graphic units, the Mikasa Formation (Upper Albian-Turonian shallow-marine sandstone-dominated unit) and the Haborogawa Formation (Middle Turonian-Campanian shelf mudstone/sandstone unit), which correspond in age to the shallower facies of the Saku and Kashima formations, respectively.
Despite a lack of so-called "black shales", because of siliciclastic dilution, our Stratigraphic integration has revealed the horizons of oceanic anoxic events (OAEs) in the Yezo Group. The OAE1a horizon in the Soashibetsugawa Formation is characterized by a lack of foraminifers, macrofossils and bioturbation, and a prominent positive excursion of delta(13)C(org). A significant hiatus during the late Aptian and early Albian removed the OAE1b horizon. The OAE1c horizon in the Maruyama Formation shows a distinct negative excursion of delta(13)C(org), with a concomitant high productivity of racholarians. The OAE1d horizon in the middle part of the Hikagenosawa Formation consists of weakly laminated, pyrite-rich mudstone. Planktonic and calcareous benthic foraminifers are absent, whereas racholarians are abundant above the OAE1d horizon. The mid-Cenomanian event (MCE) horizon is identified at the top of the Hikagenosawa Formation. Stepwise extinction of calcareous benthic foraminifers and a decrease in radiolarian diversity become apparent above the MCE horizon. In the study area, the OAE2 horizon has been well documented, and is placed in the middle part of the Saku Formation. (C) 2004 Elsevier Ltd. All rights reserved.

The mudstone of the Yezo Group exposed in Central Hokkaido yields abundant microfossils of calcareous nannofossils, foraminifers, radiolarians and dinoflagellates. Benthic foraminifers consisting of both agglutinated and calcareous species occur abundantly and consistently throughout the sequence, while specimens of planktonic foraminifers are generally fewer than benthics in all samples. We recognized the following 13 planktonic foraminiferal zones assigned to the late Aptian to early Campanian in the Oyubari and Haboro-Kotanbetsu areas; (1) Globigerinelloides spp., (2) Ticinella primula, (3) Biticinella breggiensis, (4) Rotalipora subicinensis-Rotalipora ticinensis, (5) Rotalipora appenninica, (6) Rotalipora globotruncanoides, (7) Rotalipora cushmani (8), Whiteinella archaeocretacea (9) Helvetoglobotruncana helvetica, (10) Marginotruncana pseudolinneiana, (11) Marginotruncana sinuosa, (12) Contusotruncana fornicata, (13) Globotruncana arca. The Globigerinelloides spp. to H. helvetica Zones (late Aptian to early Turonian) can be correlated with standard zones in the Tethyan regions, whereas the assemblages from the M. pseudolinneiana to G. arca zones lack tropical zonal markers of Dicarinella concavata, D. asymetrica and Globotruncanita elevata in many studied sections. The scarcity or lack of tropical zonal species during the late Turonian to early Campanian suggests that the Oyubari and Haboro-Kotanbetsu regions in Hokkaido were located in the Transitional to Boreal biogeographical provinces. (C) 2002 Elsevier Science Ltd. All rights reserved.

Comparison of oxygen isotope data for exceptionally well preserved cooccurring plankton and benthos from the Campanian of Hokkaido, Japan, with nine species of ammonoids clearly indicates the demersal (nektobenthic) habitat of ammonoids; unlike Nautilus, the ammonoids studied did not engage in significant short-term vertical migrations in the water column. The new foraminiferal isotopic data suggest that sea-surface and sea-bottom temperatures were similar to26 and 18 degreesC, respectively, at 40degreesN in the Campanian northwestern Pacific. The temperatures were significantly warmer than those in the modern northwest Pacific. This finding provides the first reliable evidence for the warm Late Cretaceous mid-latitude North Pacific. Isotopic analyses of ammonoids show that the average calcification temperature of all ammonoid shells analyzed was similar to19 degreesC, comparable to those of cooccurring benthos. None of these ammonoids display calcification temperatures equivalent to those of planktonic foraminifers.

The Cretaceous deposits distributed in the Chikubetsu area, northwestern Hokkaido, are lithostratigraphically divided into the underlying Upper Yezo and the Hakobuchi Groups. They form an asymmetrical anticlinal structure, whose axis has a NNW-SSE trend and plunges to the NNW with an axial-plane fault. The Upper Yezo Group is subdivided into two formations, the underlying Middle Haborogawa Formation (over 450 m thick) and the Upper Haborogawa Formation (about 800 m). The former consists of mudstone, sandy mudstone and muddy sandstone with frequent intercalations of thin sandstone, while the latter of a coarsening upward sequence is composed of dark gray mudstone, bioturbated sandy mudstone and light gray muddy sandstone, and cross-bedded gray or bluish gray glauconitic sandstone in ascending order. The Hakobuchi Group is represented by the Pankezawa Formation (135-170 m thick), which is redefined in this study. It consists of dark gray mudstone, gray or bluish gray sandstone and parallel or cross laminated tuff in ascending order. The Upper Yezo Group is unconformably overlain by the Hakobuchi Group. Based on the stratigraphic distribution of ammonoids and inoceramids, the Middle Haborogawa Formation and the lower part of the Upper Haborogawa Formation are correlated to the Santonian, and the upper part of the Upper Haborogawa Formation and the Pankezawa Formation to the Campanian to the Maastrichtian. A time gap between the Upper Yezo Group and the Hakobuchi Group seems not to be large.

The occurrence of an Early Campanian planktonic foraminiferal assemblage consisting of Globotruncana arca, G. linneiana, Rosita fornicata and R. patelliformis is first reported from the Upper Haborogawa Formation exposed in the Haboro area, northwestern Hokkaido, Japan. This finding supports the previous interpretation that the Santonian/Campanian boundary can be placed at the basal part of Inoceramus (Platyceramus) japonicus Zone of the inoceramid biostratigraphy.