Determination of sulfite and manganese in sediments from the K/T boundary

The solid-state-physics technique of electron spin resonance (ESR) has been employed in an exploratory study of marine limestones and impact-related deposits from Cretaceous-Tertiary (KT) boundary sites including Spain (Sopelana and Caravaca), New Jersey (Bass River), the U.S. Atlantic continental margin (Blake Nose, ODP Leg 171B/1049/A), and several locations in Belize and southern Mexico within -600 km of the Chicxulub crater. The ESR spectra of SO3(1-) (a radiation-induced point defect involving a sulfite ion substitutional for CO3(2-) which has trapped a positive charge) and Mn(2+) in calcite were singled out for analysis because they are unambiguously interpretable and relatively easy to record. ESR signal strengths of calcite-related SO3(1-) and Mn(2+) have been studied as functions of stratigraphic position in whole-rock samples across the KT boundary at Sopelana, Caravaca, and Blake Nose. At all three of these sites, anomalies in SO3(1-) and/or Mn(2+) intensities are noted at the KT boundary relative to the corresponding background levels in the rocks above and below. At Caravaca, the SO3(1-) background itself is found to be lower by a factor of 2.7 in the first 30,000 years of the Tertiary relative to its steady-state value in the last 15,000 years of the Cretaceous, indicating either an abrupt and quasi-permanent change in ocean chemistry (or temperature) or extinction of the marine biota primarily responsible for fixing sulfite in the late Cretaceous limestones. An exponential decrease in the Mn(2+) concentration per unit mass calcite, [Mn(2+)], as the KT boundary at Caravaca is approached from below (1/e characteristic length =1.4 cm) is interpreted as a result of post-impact leaching of the seafloor. Absolute ESR quantitative analyses of proximal impact deposits from Belize and southern Mexico group naturally into three distinct fields in a twodimensional [SO3(1-)]-versus-[Mn(2+)] scatter plot. These fields contain (I) limestone ejecta clasts, (II) accretionary lapilli, and (III) a variety of SO3(1-) -depleted/Mn(2+) enriched impact deposits. Data for the investigated non-impact-related Cretaceous and Tertiary marine limestones (Spain and Blake Nose) fall outside of these three fields. With reference to thes enon-impact deposits, fields I, II, and III can be respectively characterized as Mn(2+) -depleted, SO3(1-) -enhanced, and SO3(1-) -depleted. It is proposed that (1) field I represents calcites from the Yucatin Platform, and that the Mn(2+) -depleted signature can be used as an indicator of primary Chicxulub ejecta in deep marine environments and (2) field II represents calcites that include a component formed in the vapor plume, either from condensation in the presence of CO2/SO3(1-) -rich vapors, or reactions between CaO and CO2/SO3 rich vapors, and that this SO3(1-) -enhanced signature can be used as an indicator of impact vapor plume deposits. Given these two propositions, the ESR data for the Blake Nose deposits are ascribed to the presence of basal coarse calcitic Chicxulub ejecta clasts, while the finer components that are increasingly represented toward the top are interpreted to contain high- SO3(1-) calcite from the vapor plume. The apparently-undisturbed Bass River deposit may contain even higher concentrations of vapor-plume calcite. None of the three components included in field III appear to be represented at distal, deep marine KT-boundary sites; this field may include several types of impact-related deposits of diverse origins and diagenetic histories.

Analyses of shocked quartz from the K-P boundary

The precise cause and timing of the Cretaceous-Paleocene (K-P) mass extinction 65 Ma ago remains a matter of debate. Many advocate that the extinction was caused by a meteorite impact at Chicxulub, Mexico, and a number of potential kill-mechanisms have been proposed for this. Although we now have good constraints on the size of this impact and chemistry of the target rocks, estimates of its environmental consequences are hindered by a lack of knowledge about the obliquity of this impact. An oblique impact is likely to have been far more catastrophic than a sub-vertical one, because greater volumes of volatiles would have been released into the atmosphere. The principal purpose of this study was to characterize shocked quartz within distal K-P ejecta, to investigate whether the quartz distribution carried a signature of the direction and angle of impact. Our analyses show that the total number, maximum and average size of shocked quartz grains all decrease gradually with paleodistance from Chicxulub. We do not find particularly high abundances in Pacific sites relative to Atlantic and European sites, as has been previously reported, and the size-distribution around Chicxulub is relatively symmetric. Ejecta samples at any one site display features that are indicative of a wide range of shock pressures, but the mean degree of shock increases with paleodistance. These shock- and size-distributions are both consistent with the K-P layer having been formed by a single impact at Chicxulub. One site in the South Atlantic contains quartz indicating an anomalously high average shock degree, that may be indicative of an oblique impact with an uprange direction to the southeast +/- 45°. The apparent continuous coverage of proximal ejecta in this quadrant of the crater, however, suggests a relatively high impact angle of >45°. We conclude that some of the more extreme predictions of the environmental consequences of a low-angle impact at Chicxulub are probably not applicable.

Dinoflagellate cysts abundance and events of ODP Hole 189-1168A sediments

Palynomorphs were studied in samples from Ocean Drilling Program (ODP) Leg 189, Hole 1168A (slope of the western margin of Tasmania; 2463 m water depth). Besides organic-walled dinoflagellate cysts (dinocysts), broad categories of other palynomorphs were quantified in terms of relative abundance. In this contribution, we provide an overview of the early late Eocene-Quaternary dinocyst distribution and illustrate main trends in palynomorph distribution. Dinocyst species throughout Hole 1168A are largely cosmopolitan with important contributions of typical low-latitude taxa and virtual absence of endemic Antarctic taxa. Dinocyst stratigraphic distribution broadly matches that known from the Northern Hemisphere and equatorial regions, although significant differences are noted. Selected potentially biochronostratigraphically useful events are summarized. The distribution of dinocysts in the middle-upper Miocene interval is rather patchy, probably due to prolonged exposure to oxygen. An important general aspect in the dinocyst assemblages is the near absence of Antarctic endemic species and the apparent influence of relatively warm waters throughout the succession at Site 1168. General palynomorph distribution indicates continued deepening from an initial shallow, even restricted, marine setting from late Eocene-Quaternary times. A curious massive influx of small skolochorate acritarchs is recorded throughout the late early-early middle Miocene; the significance of this signal is not yet understood. A general long-term oligotrophic nature of the surface waters influencing Site 1168 is suggested from the low abundance of (proto) peridinioid, presumably heterotrophic, species. The overall dinocyst distribution pattern corresponds to the long-term existence of a Leeuwin-like current influencing the region, including Site 1168, confirming results of earlier studies on other microfossil groups. The occasional influence of colder surface water conditions is, however, also apparent, notably during the late Pliocene-Quaternary, indicating the potential of high-resolution dinocyst analysis for future paleoceanographic studies.

Major oxides for tektites and for conglomerate clast of the Upper Eocene ejecta-bearing layer of ODP Hole 150-904A (Table 1)

Evidence for the Chesapeake Bay Crater as the source for New Jersey continental margin ejecta is provided by fine-grained tektites and coarse-grained unmelted ejecta. The Upper Eocene ejecta deposit, now demonstrated to be part of the North American strewn field, occurs on the New Jersey continental margin at Ocean Drilling Program (ODP) Sites 904 and 903. The mineralogy, major oxide composition of the ejecta materials, and biostratigraphic age of the enclosing sediments link the origin of these ejecta to the recently recognized Chesapeake Bay impact crater, located only 330 km away. Sediments associated with the ejecta provide information about the dynamics of impact events. The 35-cm-thick ejecta-bearing layer can be subdivided into three subunits that indicate a sequence of events. Bottom subunit III documents sediment failure and deposition of gravel-sized fragments, middle subunit II records deposition of abundant sand-sized ejecta by gravity settling, and upper subunit I contains a 12-cm-thick sedimentary deposit containing rare silt-sized tektites and evidence of waning currents. These events are interpreted by linking sediment deposition to seismic ground motion and subsequent tsunami waves triggered by both the Chesapeake Bay impact and slope failures.

Dinoflagellate abundance and events of ODP Site 189-1172 sediments

Palynomorphs were studied in samples from Ocean Drilling Program (ODP) Leg 189, Holes 1172A and 1172D (East Tasman Plateau; 2620 m water depth). Besides organic walled dinoflagellate cysts (dinocysts), broad categories of other palynomorphs were quantified in terms of relative abundance. In this contribution, we provide an overview of the dinocyst distribution from the Maastrichtian to lowermost Oligocene and Quaternary intervals and illustrate main trends in palynomorph distribution. The uppermost Cretaceous-lowermost Oligocene succession of Site 1172 has a confident biomagnetostratigraphy, enabling us to tie early Paleogene Southern Hemisphere dinocyst events to the geomagnetic polarity timescale for the first time. Dinocyst species from the Maastrichtian to earliest Oligocene at Site 1172 are largely endemic ("Transantarctic Flora") or bipolar; cosmopolitan taxa are present in the background as well. The Maastrichtian-early late Eocene dinocyst assemblages are indicative of shallow-marine to restricted marine, pro-deltaic conditions, closely tied to a massive siliciclastic sequence. By middle late Eocene times (~35.5 Ma), the siliciclastic sequence gave way to a thin glauconitic unit, considered to reflect the deepening of the Tasmanian Gateway. This transition coincides with the most prominent change in dinocyst associations of the Paleogene. The turnover is inferred to reflect a change from marginal marine to more offshore conditions, with increased winnowing and oxidation. Overlying pelagic carbonate ooze of middle early Oligocene and younger age is virtually barren of organic microfossils, although Quaternary assemblages have been recovered. This aspect is taken to reflect average low sedimentation rates and well-oxygenated water masses during most of the Oligocene and Neogene. The few palynologically productive samples from the Oligocene-Quaternary interval have a stronger cosmopolitan to subtropical signature, with warm-water species being common to abundant.

Abundance of planktic foraminiferal species in sediments at DSDP Sites 10-95, 77-536, and 77-540

Over most of the Gulf of Mexico and Caribbean a hiatus is present between the lower upper Maastrichtian and lowermost Tertiary deposits; sedimentation resumed ~200 ka (upper zone Pla) after the K-T boundary. Current-bedded volcaniclastic sedimentary rocks at Deep Sea Drilling Project (DSDP) Sites 536 and 540, which were previously interpreted as impact-generated megawave deposits of K-T boundary age, are biostratigraphically of pre-K-T boundary age and probably represent turbidite or gravity-How deposits. The top 10 to 20 cm of this deposit at Site 536 contains very rare Micula prinsii, the uppermost Maastrichtian index taxon, as well as low values of Ir (0.6 pbb) and rare Ni-rich spinels. These indicate possible reworking of sediments of K-T boundary age at the hiatus. Absence of continuous sediment accumulation across the K-T boundary in the 16 Gulf of Mexico and Caribbean sections examined prevents their providing evidence of impact-generated megawave deposits in this region. Our study indicates that the most complete trans-K-T stratigraphic records may be found in onshore marine sections of Mexico, Cuba, and Haiti. The stratigraphic records of these areas should be investigated further for evidence of impact deposits.

Seed dispersal characteristics to polar regions by means of visitors

Invasive alien species are among the primary causes of biodiversity change globally, with the risks thereof broadly understood for most regions of the world. They are similarly thought to be among the most significant conservation threats to Antarctica, especially as climate change proceeds in the region. However, no comprehensive, continent-wide evaluation of the risks to Antarctica posed by such species has been undertaken. Here we do so by sampling, identifying, and mapping the vascular plant propagules carried by all categories of visitors to Antarctica during the International Polar Year's first season (2007-2008) and assessing propagule establishment likelihood based on their identity and origins and on spatial variation in Antarctica's climate. For an evaluation of the situation in 2100, we use modeled climates based on the Intergovernmental Panel on Climate Change's Special Report on Emissions Scenarios Scenario A1B [Nakicenovic N, Swart R, eds (2000) Special Report on Emissions Scenarios: A Special Report of Working Group III of the Intergovernmental Panel on Climate Change (Cambridge University Press, Cambridge, UK)]. Visitors carrying seeds average 9.5 seeds per person, although as vectors, scientists carry greater propagule loads than tourists. Annual tourist numbers (~33,054) are higher than those of scientists (~7,085), thus tempering these differences in propagule load. Alien species establishment is currently most likely for the Western Antarctic Peninsula. Recent founder populations of several alien species in this area corroborate these findings. With climate change, risks will grow in the Antarctic Peninsula, Ross Sea, and East Antarctic coastal regions. Our evidence-based assessment demonstrates which parts of Antarctica are at growing risk from alien species that may become invasive and provides the means to mitigate this threat now and into the future as the continent's climate changes.