Late Paleocene Thermal Maximum Research Articles

PALEOENVIRONMENTAL RECORDS OF INFLUENCE OF GAS HYDRATE-DERIVED METHANE ON CLIMATE OF THE LATE QUATERNARY

Gas hydrate serves as the largest reservoir in the global carbon cycle. It may release lots of methane into water column and atmosphere due to the global warming and/or sea level falling,which greatly affects climate and environment. Since Dickens et al. proposed the hypothesis that massive methane releasing from gas hydrate is one of the most important reasons of the Latest Paleocene Thermal Maximum (LPTM) in 1995,great research effort has been focused on the evolution of gas hydrate in geological history. A series of climate fluctuations have occurred since the late Quaternary,and scientists have found paleoenvironmental records of carbon isotope negative excursions in Santa Barbara basin,Guaymas basin,Lake Baikal,Greenland Sea,Peru,East Greenland continental shelf,Papua New Guinea,and South China Sea,which are related to the gas hydrate-derived methane. In this study,we compile these records to provide valuable information for future studies of dynamic evolution of gas hydrate.

Mixed carbonate–siliciclastic sequence stratigraphy of a Paleogene transition zone continental shelf, southeastern USA

The sequence stratigraphy and facies of the Paleogene in the subsurface of the Albemarle Basin, North Carolina was defined using 1600 thin sections of plastic impregnated well cuttings from 24 wells, wireline logs, biostratigraphic data, and seismic data. The facies formed in the transition zone between warm subtropical and temperate conditions on a swell-wave dominated, open shelf exposed to major boundary current activity. The shelf has a distinctive seismic profile consisting of a shallow inner shelf, inner-shelf break, deep shelf (depths in excess of 200 m), and the continental slope. The inner shelf was characterized by distinctive quartz sand and sandy mollusk facies inshore, passing seaward into a broad, wave-swept abrasional shelf, and then into storm-influenced bryozoan–echinoderm limestones to depths of several tens of meters. Argillaceous lime mud (marl) deposition was widespread across the deep shelf, extending onto the inner-shelf during major highstands. Sediment thickness trends were controlled by greater differential subsidence of crustal blocks within the Albemarle Basin, which considerably modified but did not obliterate the effects of eustatic sea level changes in this passive margin setting. Five supersequences were identified on seismic and in wells, each consisting of multiple regionally identifiable sequences. The Paleocene supersequence is dominated by widespread marl deposition, reflecting shelf flooding into the Late Paleocene thermal maximum. This warming corresponds with widespread inner-shelf skeletal carbonate deposition from the Late Paleocene through the Middle Eocene. The two Eocene supersequences identified are dominated by bryozoan–echinoderm-rich carbonates that formed a seismically definable sediment buildup 50 km wide by 100 m thick across the deepest inner-shelf during the Lower to early Middle Eocene. Middle to Upper Eocene supersequence highstand sequences indicate increased progradation and greater mixing of shelf carbonates with nearshore siliciclastics, likely in response to lowering sea-levels and cooling climate. The two Oligocene supersequences identified are dominated by coarse siliciclastic sand that is heavily admixed with mollusk-foraminifer-dominated carbonates. Rapid flooding, followed by extensive progradation of shallow shelf sediments in Oligocene sequences reflects continued eustatic lowering driven by the onset of icehouse climatic conditions. Increased incision and reworking of deep shelf sediments during Oligocene supersequence highstands resulted from increased ancestral Gulf Stream boundary current activity during icehouse times. Key elements controlling facies distribution through time include significant wave energy, which controls the width and distribution of inner-shelf facies belts through the degree of water bottom abrasion and winnowing. Boundary currents also are capable of large-scale reworking of deep shelf sediment; they also provide a mechanism for widespread inner-shelf hardground development during major transgressions. In addition, boundary currents play a major role in stabilizing local climate by buffering seasonal temperature variations, directly influencing which carbonate grain producers can thrive in this transition zone setting.

LPTM（the Late Paleocene thermal maximum）における炭素循環

LPTM（the Late Paleocene thermal maximum）における炭素循環

堆積学におけるガスハイドレート科学の展望

GAS HYDRATES-A HUGE CARBON SINK OF SHALLOW GEOSPHERE:Findings of gas hydrates in marine sediments in late 20th century have made a strong impact on the study of carbon cycle and global changes as well as on the exploration for energy resources. Gas hydrates are crystalline materials composed of cages of water molecules that surround low-molecular-weight gas such as methane, ethane, propane, carbon dioxide, and etc. Naturally occurring gas hydrates are mostly composed of methane and water, then called as methane hydrate, but often referred as gas hydrates (e. g., Lancelot and Ewing, 1972; Shipley et al., 1978).Recent geological and geophysical surveys for natural gas hydrates have revealed that the upper few hundred meters of the deep sea sediments of continental margins are often associated with laterally extensive gas hydrate deposits that underlain by free gas zone. Methane Hydrate Exploration Project of METI-JNOC (1995-) identified and recovered gas hydrate saturated sands from the Nankai Trough (e. g., Matsumoto, 2000). The pore saturation of the sands reaches up to 80%. The total carbon mass stored in modern gas hydrates is estimated to be 7, 500 to 15, 000 Gt (Gt=1015g), which is -25% of the total DIC in the ocean, -104 times the amount of methane carbon in the atmosphere, and comparable to the conventional fossil fuel reserves (e. g., Kvenvolden, 1988, 1993). Methane of marine gas hydrates is mostly originated from microbial methanogenesis and is therefore extremely depleted in 13C (δ13C=-60 to -90%0 PDB).Gas hydrates are stable at low temperature and high-pressure conditions with certain amounts of gas and water. Therefore, gas hydrates in marine sediments is sensitive to even a little change in the relative sea level, bottom water temperatures, and geothermal gradients. The modeling of carbon cycle and global change must take into account the presence of gas hydrates in marine sediments and the consequences of the dissociation and possible release of large amount of methane carbon into the ocean-atmosphere system.δ13C OF MARINE CARBONATES AND GAS HYDRATE INDUCED EVENTS:Stratigraphic boundary events with mass extinction are often associated with abrupt negative excursion in δ13C of marine carbonates. Extensive depletion in 13C in the shallow oceans had been explained in two ways; a mass extinction and reduced primary productivity-photosynthesis (Hsu et al., 1985; Hsu and McKenzie, 1990) and an oceanic overturning and consequent upwelling of anoxic bottom waters (e. g., Hoffman et al., 1991). Large releases of isotopically light carbon are also interpreted to have come from massive dissociation of gas hydrates (e. g., Dickens et al., 1995; Matsumoto, 1995; Kennett et al., 2000).The “Latest Paleocene Thermal Maximum” (LPTM) ca. 55Ma is a typical example of “gas hydrate induced” boundary event. LPTM was characterized by a 4 to 6°C rise in deep ocean water temperature (Kennett and Scott, 1991), coincided with major extinction of benthic foraminifers (Kaiho, 1994) and negative carbon isotopic excursion (Δδ13C=-2 to -3‰). Early Paleogene was a period of general warmth, and futhermore a sharp temperature increase is recorded within a short interval of ca. 55Ma. High-resolution isotope records indicate that the main drop and gradual return in δ13C spanned less than 10, 000 years and 200, 000 years, respectively (e. g., Bains et al., 1999). The timing and magnitude of the δ13C excursion across LPTM are best explained by gas hydrate hypothesis. General increase of bottom waters, probably caused by recorded igneous activities, finally triggered thermal dissociation of marine gas hydrates and release of large amount of 13C-depleted methane to the ocean (e. g.,

Comment

Research Article| May 01, 2003 Comment Wuchang Wei Wuchang Wei 1Scripps Institution of Oceanography, University of California, San Diego, California 92093-0244, USA Search for other works by this author on: GSW Google Scholar Geology (2003) 31 (5): 467–468. https://doi.org/10.1130/0091-7613(2003)031<0467:PTSMEF>2.0.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Wuchang Wei; Comment. Geology 2003;; 31 (5): 467–468. doi: https://doi.org/10.1130/0091-7613(2003)031<0467:PTSMEF>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Jolley et al. (2002) presented two very interesting points: (1) the late Paleocene thermal maximum (LPTM) has an age between 57.5 and 60.54 Ma (vs. 54.98 Ma in the current time scale of Cande and Kent [1995] and Berggren et al. [1995]), and thus the current time scale is too young by up to 5 m.y. for the late Paleocene, and (2) the LPTM correlates with and was most likely caused by the early phase of widespread North Atlantic volcanism. Both points are of broad interest in geosciences because the geological time scale is probably the most important standard... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

A methane fuse for the Cambrian explosion: carbon cycles and true polar wander

The dramatic diversification of animal groups known as the Cambrian Explosion (evolution’s ‘Big Bang’) remains an unsolved puzzle in Earth Science. The Vendian–Cambrian interval is characterized by anomalously high rates of apparent plate motion, interpreted as True Polar Wander (TPW), and by more than a dozen large, high-frequency perturbations in carbon isotopes that dwarf all others observed through the past 65 million years. We suggest that these biological, tectonic, and geochemical events are intimately related in the following fashion. First, tropical continental margins and shelf-slopes which formed during fragmentation of the supercontinent Rodinia accumulated massive quantities of isotopically-light organic carbon during Late Neoproterozoic time, as indicated by strikingly heavy isotope ratios in inorganic carbon during interglacial intervals. Second, an initial phase of Vendian TPW moved these organic-rich deposits to high latitude, where conditions favored trapping biogenic methane in layers of gas hydrate and perhaps permafrost. Continued sedimentation during Late Vendian time added additional hydrate/gas storage volume and stabilized underlying units until the geothermal gradient moved them out of the clathrate stability field, building up deep reservoirs of highly pressurized methane. Finally, a burst of TPW brought these deposits back to the Tropics, where they gradually warmed and were subjected to regional-scale thermohaline eddy variation and related sedimentation regime changes. Responding to the stochastic character of such changes, each reservoir reached a critical failure point independently at times throughout the Cambrian. By analogy with the Late Paleocene Thermal Maximum event, these methane deposits yield transient, greenhouse-induced pulses of global warming when they erupt. Temperature correlates powerfully with biodiversity; the biochemical kinetics of metabolism at higher temperature decrease generation time and maintain relatively rich and dense invertebrate populations. Repeated thermal pulses along with progressive disruption and alteration of global ocean circulation patterns by TPW could cause the increase in diversity that accompanied the radiation of metazoans. We suggest that a methane ‘fuse’ ignited the Cambrian Evolutionary Explosion.

New paleomagnetic pole and magnetostratigraphy of Faroe Islands flood volcanics, North Atlantic igneous province

A paleomagnetic sampling was carried out along four sections (altogether 86 lava flows, 548 samples) in the North Atlantic Igneous Province outcropping in Faroe Islands, Denmark. The four polarity zones in the 700-m-thick exposed part of the Faroes lower formation can be correlated with the geomagnetic polarity time scale as C26n–C25r–C25n–C24r. The seven lava flows erupted during C25n indicate a very low eruption rate in the upper part of the Faroes lower formation of ∼1/70 kyr. The Faroes middle and upper formations (composite thickness ∼2300 m) are all reversely magnetized corresponding to C24r. The eruption rate at the onset of middle formation volcanism was very high as evidenced by several thick lava sequences recording essentially spot readings of the paleomagnetic field. The shift in eruption rate between the Faroes lower and middle formations and evidence that onset of the Faroes middle formation volcanism took place in C24r are of particular importance, placing onset of middle formation volcanism in close temporal relation to North Atlantic continental break-up and the late Paleocene thermal maximum. After grouping flows recording the same field directions, we obtained 43 independent readings of the paleomagnetic field, yielding a paleomagnetic pole with coordinates 71.4°N, 154.7°E ( A 95=6.0°, K=14, N=43); age 55–58 Ma. The pole is supported by a positive reversal test. Paleosecular variation, estimated as the angular standard deviation of the virtual geomagnetic pole distribution 21.7°+3.9°/−2.8°, is close to expected for the given age and paleolatitude. Our new Faroes paleomagnetic pole is statistically different from the majority of previously published poles from the British and Faroes igneous provinces, and we suggest that these older data should be used with care.

Paleogene time scale miscalibration: Evidence from the dating of the North Atlantic igneous province

Igneous activity in the North Atlantic igneous province began with the arrival of the proto-Iceland plume beneath the lithosphere in early Cenozoic time. Sediments between and equivalent to the oldest lavas contain an influx of a diagnostic pollen flora, an influx of the dinocyst Apectodinium, a benthic foraminiferal extinction, nannofossil zone NP9, and a carbon isotope excursion associated with the late Paleocene thermal maximum (LPTM). Lavas immediately overlying the LPTM strata (54.98 Ma on the current time scale), yield U-Pb and Ar-Ar isotopic dates between 57.5 and 60.54 Ma, highlighting a dating discrepancy of up to 5 m.y. Recognition of this disparity, as well as our biostratigraphical correlation, places the LPTM within the early phase of widespread northeast Atlantic margin basaltic volcanism. A later volcanic phase, equivalent to the seaward-dipping reflector series, terminates at 54 Ma. The onset of 60 Ma basaltic volcanism can be linked to ocean water mass perturbations, and the release of ocean-floor methane hydrates thought responsible for the LPTM.

Effect of seafloor temperature and pressure variations on methane flux from a gas hydrate layer: Comparison between current and late Paleocene climate conditions

We investigate the response of a methane hydrate layer in marine sediments to cyclic seafloor perturbations of temperature and pressure in order to determine the change in seafloor methane flux resulting from gas hydrate dissociation or accumulation. By using a one‐dimensional model describing mass, energy, and methane transport through porous sediments we show that seafloor pressure changes have negligible effect on methane transport to the seafloor. The effect of seafloor temperature perturbations is more pronounced than that of pressure. With an initial seafloor temperature of 3°C, which corresponds to current conditions on Earth, a +4°C seafloor temperature perturbation occurring over 104 years does not significantly effect methane transport. Thus such a perturbation is not likely to have a significant impact on the current global climate or to give rise to an event such as the δ13C excursion during the late Paleocene thermal maximum (LPTM). If the initial seafloor temperature is assumed to be 11°C, which corresponds to the conditions of the late Paleocene, a +4°C temperature perturbation over a period of 104 years could result in complete dissociation of methane hydrate layers situated at water depths around 1200 m. In this case, the calculations show that the change in methane flux might be able to explain the δ13C excursion of marine carbonate fossils during the LPTM. This result is weakened because the simplifications in the model tend to yield overestimates of the change of methane flux. The principal point is that strong coupling between methane transport and seafloor temperature occurs because significant hydrate accumulation and dissociation take place near the seafloor only when the seafloor temperature is relatively high. This was the case during the late Paleocene, but it is not the case at present.

The potential volume of oceanic methane hydrates with variable external conditions

Gas hydrate abundance in marine sediment depends on gas concentration and the available pore space within certain stability limits. Potentially, gas hydrates can occur between the seafloor and a locus of subbottom depths where geothermal gradients intersect gas–gas hydrate-pore water equilibrium curves. Perpendicular to a given continental margin, the lens shaped area between these two bounding surfaces ( A sl) varies according to seven basic parameters: gas composition, water activity ( a w), bottom water temperature ( T b), geothermal gradient ( G), slope depth ( z slb), slope gradient ( Z) and sea level relative to the shelf break ( z 0). Assuming pure CH 4 gas, ∼35 km 2 of sediment can host gas hydrate across an average continental margin at a Pleistocene lowstand ( a w =0.981, T b=0 °C, G=0 °C; z slb=4000 m; Z=0.04; z 0=0). However, this potential area would decrease with smaller a w, higher T b, greater G, shallower z slb, steeper Z and lower z 0, and increase with opposite external conditions. Of the basic parameters, temperature ( T b and G) and bathymetry ( z slb and Z) can particularly influence the distribution of gas hydrate on continental slopes. A hydrothermal gradient with e.g. surface temperatures> T b will also decrease A sl, although minimally, especially if T b is warm. The sum of parallel cross-sectional areas along a margin combined with porosity ( φ) gives the potential volume of gas hydrate ( V). Assuming ∼200,000 km of continental margin with a φ of 50%, ∼3.5×10 6 km 3 of pore space can contain gas hydrates, at present-day, a volume that compares favorably with previous estimates (1.2 to 6.4×10 6 km 3) although underlying approaches differ fundamentally. Since the Triassic, V Glob probably has increased significantly because T b has cooled while total margin length has grown. This trend was likely punctuated by at least one major decrease (nominally 1.5 to 0.7×10 6 km 3) when T b suddenly rose by ∼5 °C during the latest Paleocene thermal maximum (LPTM). A prominent global negative δ 13C excursion across the LPTM may signify massive release of CH 4 associated with this theoretical drop in V Glob.

Identification of a Waipawa Formation equivalent in the upper Te Uri Member of the Whangai Formation ‐ implications for depositional history and age

Stable isotopes and biomarkers have identified a unit with similar organic geochemistry to the Waipawa Formation, in the upper Te Uri Member of the Whangai Formation, exposed in the Akitio River, at Tawanui, southern Hawke's Bay, New Zealand. At Tawanui, the uppermost greensand of the Te Uri Member contains a large positive 813C isotopic excursion from ‐27.0%o to ‐20%e and an increase in total organic carbon from 0.1% to 1.0%. Biomarker analyses demonstrate a similar C30 sterane fingerprint to other deposits of the Waipawa Formation. We propose that the uppermost greensand of the Te Uri Member at Tawanui is a condensed stratigraphic equivalent of the Waipawa Formation at nearby Angora Stream and other East Coast Basin localities. This correlation demonstrates that Waipawa Formation is middle Teurian (middle Paleocene) and precedes the late Paleocene thermal maximum event by c. 5 m.y. The likely upwelling event that resulted in deposition of the Waipawa Formation was geographically widespread but probably restricted to the outer shelf/upper slope. In places, biogenic activity prevented the preservation of organic carbon in equivalent condensed stratigraphic intervals. Localised restriction of upwelling and black shale deposition may be demonstrated by the occurrence of a thick black shale at Angora Stream only c. 10 km from the coeval greensands at Tawanui. Alternatively, Oligocene‐Miocene east‐west shortening and structural reorganisation in the East Coast Basin may have juxtaposed facies that were originally many tens of kilometres apart. Our correlation also implies that the Te Uri Member is diachronous. It may have been on the outermost shelf to upper slope during lowstand conditions, where it is oldest, to higher on the shelf during transgression and highstand conditions.

An osmium isotope excursion associated with the Late Paleocene thermal maximum: Evidence of intensified chemical weathering

In the latest Paleocene an abrupt shift to more negative δ13C values has been documented at numerous marine and terrestrial sites [Bralower et al., 1997; Cramer et al., 1999; Kaiho et al., 1996; Kennett and Stott, 1991; Koch et al., 1992; Stott et al., 1996; Thomas and Shackleton, 1996; Zachos et al., 1993]. This carbon isotope event (CIE) is coincident with oxygen isotope data that indicate warming of surface waters at high latitudes of nearly 4°–6°C [Kennett and Stott, 1991] and more moderate warming in the subtropics [Thomas et al., 1999]. Here we report 187Os/188Os isotope records from the North Atlantic and Indian Oceans which demonstrate a &gt;10% increase in the 187Os/188Os ratio of seawater coincident with the late Paleocene CIE. This excursion to higher 187Os/188Os ratios is consistent with a global increase in weathering rates. The inference of increased chemical weathering during this interval of unusual warmth is significant because it provides empirical evidence supporting the operation of a feedback between chemical weathering rates and warm global climate, which acts to stabilize Earth's climate [Walker et al., 1981]. Estimates of the duration of late Paleocene CIE [Bains et al., 1999; Bralower et al., 1997; Norris and Röhl, 1999; Röhl et al., 2000] in conjunction with the Os isotope data imply that intensified chemical weathering in response to warm, humid climates can occur on timescales of 104–105 years. This interpretation requires that the late Paleocene thermal maximum Os isotope excursion be produced mainly by increased Os flux to the ocean rather than a transient excursion to higher 187Os/188Os ratios in river runoff. Although we argue that the former is more likely than the latter, we cannot rule out significant changes in the 187Os/188Os ratio of rivers.

Did the Late Paleocene thermal maximum affect the evolution of larger foraminifers? Evidence from calcareous plankton of the Campo Section (Pyrenees, Spain)

The larger foraminifer turnover (LFT), which marks the base of the Ilerdian stage, may be related to the Late Paleocene Thermal Maximum (LPTM), or be at least nearly coeval with that climatic event. Thus, the impact of the LPTM may have been greater than hitherto realised, having also affected mid-latitude shallow-marine biota. This conclusion has been reached after a re-study of the calcareous plankton of the uppermost Paleocene and lowermost Eocene interval of the Campo section in the central southern Pyrenees. Campo is an important reference section because it contains larger foraminifers, planktic foraminifers and calcareous nannofossils, and their co-occurrence was used to intercalibrate their respective zonal schemes. Previous studies at Campo placed the onset of planktic foraminiferal Zone P5 near the base of the Ilerdian, and the calcareous nannofossil NP9/NP10 chronal boundary (sensu Bybell, L.M., Self-Trail, J.M., 1995. Evolutionary, biostratigraphic and taxonomic study of calcareous nannofossils from a continuous Paleocene/Eocene boundary section in New Jersey. US Geol. Surv. Prof. Pap. 1554, pp. 1–36) not less than 150 m above the Ilerdian lower limit. By these estimates, the LPTM (known to have occurred in the middle part of Zone P5 and just before the NP9/NP10 boundary) would be an event much younger than the LFT. However, our reexamination of planktic foraminifers suggests that the base of the Ilerdian is probably situated at the middle of Zone P5 (a possibility proposed by Hillebrandt in 1965, but denied by later authors). For instance, Morozovella occlusa has been found for the first time in the Campo section. Its Last Appearance Datum (LAD), which in the Pyrenees was approximately coeval with that of Morozovella velascoensis (event used to place the top of Zone P5), has been identified in beds situated less than 70 m above the base of the Ilerdian. Such thickness represents a time span of a similar magnitude as the one which separated the LPTM and the LAD of M. occlusa in the deep-water hemipelagic succession of the Basque Basin, in the western Pyrenees. Autochthonous calcareous nannofossils are neither abundant nor well preserved in most of the studied interval, with Rhomboaster bramlettei (the marker of the base of Zone NP10) being extremely rare in lower and middle Ilerdian beds, a fact that makes it very difficult to fix the position of the NP9/NP10 boundary in the Campo section. However, the bases of zones NP9 and NP11 have been located, and they support the zonation with planktic foraminifers. These new data suggest that the LFT and the LPTM may have been coeval or nearly so, a possibility reinforced by correlation with sections of the Basque Basin. Specialists of larger benthic foraminifers can easily delineate the LFT in shallow water carbonate successions of the Tethys domain, and they propose to place the Paleocene/Eocene boundary at the base of the Ilerdian stage. On the other hand, the deep benthic extinction event (BEE) is a major global biotic turnover in the bathyal and abyssal realms, while the ∂13C excursion (CIE) is an excellent tool for correlation between marine and terrestrial records. Therefore, the synchrony or near synchrony postulated here between the LFT, BEE and CIE (all of them probably related to the LPTM) would argue strongly in favour of these events as the criterion to officially redefine the Paleocene/Eocene boundary.

Global dinoflagellate event associated with the late Paleocene thermal maximum

The late Paleocene thermal maximum, or LPTM (ca. 55 Ma), represents a geologically brief time interval (∼220 k.y.) characterized by profound global warming and associated environmental change. The LPTM is marked by a prominent negative carbon isotope excursion (CIE) interpreted to reflect a massive and abrupt input of 12 C-enriched carbon to the ocean-atmosphere reservoir, possibly as a result of catastrophic gas-hydrate release, on time scales equivalent to present-day rates of anthropogenic carbon input. The LPTM corresponds to important changes in the global distribution of biota, including mass extinction of marine benthic organisms. The dinoflagellate cyst record indicates that surface- dwelling marine plankton in marginal seas also underwent significant perturbations during the LPTM. We report on the dramatic response of representatives of the genus Apectodinium from two upper Paleocene–lower Eocene sections in the Southern (New Zealand) and Northern (Austria) Hemispheres, where the dinoflagellate records are directly correlated with the CIE, benthic foraminifera extinction event, and calcareous nannofossil zonation. The results indicate that the inception of Apectodinium -dominated assemblages appears to be synchronous on a global scale, and that the event is precisely coincident with the beginning of the LPTM. Apectodinium markedly declined in abundance near the end of the LPTM. This Apectodinium event may be associated with (1) exceptionally high global sea-surface temperatures and/or (2) a significant increase in marginal-marine surface-water productivity. Such a globally synchronous acme of dinoflagellate cysts is unprecedented within the dinoflagellate cyst fossil record.

Evidence for Late Jurassic release of methane from gas hydrate

Four Late Jurassic carbonate successions deposited in the Tethys-Atlantic Ocean record a negative carbon isotope excursion of at least 2‰. The excursion is present in both organic and carbonate carbon records and is comparable in magnitude and duration to isotopic changes during the late Paleocene thermal maximum. Our results indicate that during the Late Jurassic, long considered a warm greenhouse time, additional greenhouse gas was input to the atmosphere by a sudden release of methane from buried gas hydrate. A potential triggering mechanism may have been the opening of an oceanic gateway through the early Atlantic between the ancient Tethys and Pacific Oceans.

High concentrations of greenhouse gases and polar stratospheric clouds: A possible solution to high-latitude faunal migration at the latest Paleocene thermal maximum

High concentrations of greenhouse gases and polar stratospheric clouds: A possible solution to high-latitude faunal migration at the latest Paleocene thermal maximum

New chronology for the late Paleocene thermal maximum and its environmental implications

New chronology for the late Paleocene thermal maximum and its environmental implications

The Paleocene-Eocene transition in the marginal northeastern Tethys (Kazakhstan and Uzbekistan)

We studied two sections that accumulated during the Paleocene–Eocene transition in shelf waters in the northeastern Tethys. Stable carbon isotopic compositions of marine and terrestrial biomarkers are consistent with a 13C depletion in the oceanic and atmospheric carbon dioxide pools during the Late Paleocene Thermal Maximum (LPTM; Subzone P5b). The 2–3‰ negative δ 13C excursion in planktic foraminifera coincides with minimum δ 18O values, an incursion of transient subtropical planktic foraminiferal fauna, and the occurrence of an organic-rich sapropelite unit in Uzbekistan, which accumulated at the onset of a transgressive event. Biomarker distributions and hydrogen indices indicate that marine algae and bacteria were the major organic matter sources. During the Late Paleocene (Subzones P4 and P5a), the marginal northeastern Tethys experienced a temperate to warm climate with wet and arid seasons. Most likely, warm and humid climate initiated during the LPTM (Subzone P5b) and subsequently extended during the Eocene (Zone P6) onto adjacent land areas of the marginal northeastern Tethys.

Late Paleocene event chronology; unconformities, not diachrony

Abstract The chronology of the events associated with the late Paleocene thermal maximum (LPTM, Chron C24r) has been established through the construction of a composite reference section that involved chemomagnetobiostratigraphic correlations and assumed minimum diachrony of biostratigraphic events. On this basis, discrepancies between correlations in different sections were explained by inferred unconformities. However, diachrony between distant sections cannot be ruled out. We report here on two geographically close sections drilled onshore New Jersey that yield different records of chemomagnetobiostratigraphic correlations in the interval representing Chron C24r. Because of their proximity ( approximately 40 km apart), diachrony of biostratigraphic events between the two sections can be ruled out. In contrast, the marked lithologic disconformities in the sections explain well the different records of events. We thus conclude that the current relative chronology for Chron C24r is firmly based and that the upper Paleocene-lower Eocene stratigraphic record yields multiple unconformities, with Subzone NP9b rarely sampled. We examine the implications that undeciphered unconformities may have on the identification of proxies for paleoceanographic reconstruction, in particular with regard to the identification of the carbon isotope excursion (CIE) that reflects a dramatic latest Paleocene disturbance of the carbon cycle. We propose biostratigraphic means (short-lived calcareous nannoplankton and planktonic foraminifera taxa) that permit the unequivocal identification of the CIE not only in the oceanic realm but also in neritic settings.

Evidence for subtropical warming during the late Paleocene thermal maximum—New insights from DSDP Site 527

Evidence for subtropical warming during the late Paleocene thermal maximum—New insights from DSDP Site 527