Birger Schmitz

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.

Abrupt increase in seasonal extreme precipitation at the Paleocene-Eocene boundary

A prominent increase in atmospheric CO, at the Paleocene-Eocene boundary, ca. 55 Ma, led to the warmest Earth of the Cenozoic for similar to 100 k.y. High-resolution studies of continental flood-plain sediment records across this boundary can provide crucial information on how the hydrological cycle responds to rapidly changing CO2. Here we show from continental records across the Paleocene-Eocene boundary in the Spanish Pyrenees, a subtropical paleosetting, that during the early, most intense phase of CO2 rise, normal, semiarid coastal plains with few river channels of 10-200 m width were abruptly replaced by a vast conglomeratic braid plain, covering at least 500 km(2) and most likely more than 2000 km(2). This braid plain is interpreted as the proximal parts of a megafan. Carbonate nodules in the megafan deposits attest to seasonally dry periods and together with megafan development imply a dramatic increase in seasonal rain and an increased intra-annual humidity gradient. The megafan formed over a few thousand years to similar to 10 k.y. directly after the Paleocene-Eocene boundary. Only repeated severe floods and rainstorms could have contributed the water energy required to transport the enormous amounts of large boulders and gravel of the megafan during this short time span. The findings represent evidence for considerable changes in regional hydrological cycles following greenhouse gas emissions. (Less)

A rain of ordinary chondritic meteorites in the early Ordovician

Forty fossil meteorites with a total original mass of V7.7 kg have been recovered in the first systematic search for fossil meteorites, pursued in an active quarry in Lower Ordovician (480 Ma) marine limestone in southern Sweden. The meteorites represent at least 12 different falls over a seafloor area of V6000 m 2 during 91.75 Myr, making the quarry one of the most meteorite dense areas known in the world. Geochemical analyses of relict chromite grains indicate that all or most of the meteorites are ordinary chondrites and probably L chondrites. Mechanisms for meteorite delivery from the asteroid belt to Earth were the same 480 Ma as today, however, the flux was one to two orders of magnitude higher, most likely reflecting the disruption of the L chondrite parent body at about that time. This is a major event in late solar-system history, which may also have led to an enhanced flux of asteroids to Earth during V30 Myr. fl 2001 Elsevier Science B.V. All rights reserved.

Sea-level, humidity, and land-erosion records across the initial Eocene thermal maximum from a continental-marine transect in northern Spain

In two continental sections in the Tremp basin, northern Spain, the initial Eocene thermal maximum (also known as the Paleocene-Eocene thermal maximum) is registered by an ∼6‰ fall in δ 1 3 C values in soil carbonate nodules. High-resolution correlations, using the δ 1 3 C excursion, can be made to nearby shelf and bathyal marine settings, allowing a detailed reconstruction of soil formation on land and transport of detritus to the sea during the initial Eocene thermal maximum. Soils that formed before and after the initial Eocene thermal maximum in the Tremp region reflect arid to semiarid conditions, with abundant evaporative minerals, whereas initial Eocene thermal maximum soils reflect seasonally wetter but generally dry conditions. During the initial Eocene thermal maximum, land erosion was intensified and accumulation rates of terrigenous detritus in the sea increased. This reflects both increased topographic relief associated with a prominent sea-level lowstand and enhanced seasonal precipitation over a dry landscape with sparse vegetation. Deeper erosion led to an increase in the flux of kaolinite from buried Mesozoic soils to the oceans. The association of the initial Eocene thermal maximum with a sea-level lowstand in northern Spain, as well as at other marginal North Atlantic sites, may reflect coeval large-scale magmatic activity in the northernmost Atlantic.

A benthic foraminiferal record of Paleocene sea level and trophic/redox conditions at Gebel Aweina, Egypt

We quantitatively analyzed benthic foraminiferal assemblages in order to reveal biotic and paleoenvironmental trends in the Paleocene section of Gebel Aweina, Egypt, on the southern Tethyan shelf. The first correspondence axis ranks taxa along an empirically derived bathymetric gradient, with neritic taxa (e.g., Discorbis duwi and Haplophragmoides walteri) opposed to bathyal taxa (e.g., Nuttallides truempyi and Gavelinella beccari(/ormis). The estimated paleodepth, as reflected by the various assemblages, was mostly ~ 200 m, but varied between ~ 50 m (P3a, NP4) and ~ 300 m (P4, N P8). The resultant four relative sea-level cycles appear to be at least of regional extent and may in part be eustatically controlled. The second correspondence axis reflects trends in trophic and redox development. Low-food, high-oxygen conditions prevailed during Biochrons Plc-P3b (NP4 NP5) and late P4 (NP8), when assemblages were mostly dominated by Cibicidoides spp. Most oligotrophic conditions coincided with maximum paleodepth. Intermediate trophic levels were established during middle P4 (NP6) and early P5 (NP9). From the level of the latest Paleocene benthic extinction event (BEE; middle P5 and NP9) onwards until Biochron P6a (NP10), assemblages dominated by buliminids marked increased trophic levels and reduced ventilation, probably resulting from enhanced surface productivity. Enhanced surface productivity along the southern Tethyan margin started during Biochron P4, and, at least on some shelves, intensified after the BEE. Increasing productivity during the latest Paleocene contrasts with global trends. This may be expected during climatic warming and an expanding trophic resource continuum, leading to regionally intensified eutrophy and oligotrophy. High productivity through upwelling along the southern Tethyan provides support for GCM predictions of intense wind-stress in this region during the warm late to latest Paleocene.

Gradual mass extinction, species survivorship, and long-term environmental changes across the Cretaceous-Tertiary boundary in high latitudes

Stable-isotope and planktic foraminiferal analyses across the Cretaceous/Tertiary (K/T) boundary transition at Nye Klov indicate longterm oceanic instability associated with global sea-level fluctuations, a gradual mass extinction, and decreased magnitude of the δ 13 C shift in high latitudes. Oceanic instability, which began at least 100 kyr before the K/T boundary and continued for about 300 kyr into the Tertiary, was accompanied by a gradual faunal turnover. The maximum sea-level lowstand during latest Maastrichtian is recorded about 75 cm below the K/T boundary. A sea-level rise first in evidence at 20 cm to 40 cm below the boundary continued into Zone P0 (boundary clay). This sea-level rise was accompanied by 2 °C of cooling in surface and bottom waters prior to the K/T boundary. δ 13 C values remained relatively stable up to 10 cm below the K/T boundary. A negative shift of 0.5 to 1.0 per mil occurred in the boundary clay in both planktic and benthic foraminifera. The surface to deep δ 13 C gradient remained nearly unchanged, in contrast to low latitudes, where this gradient is virtually eliminated. No sudden mass extinction occurred in this cosmopolitan, high-latitude fauna, and nearly all Cretaceous taxa thrived well into the Tertiary, when they gradually disappeared. Shallow seas, dominated by Cretaceous survivor taxa and a well-developed oxygen minimum zone, prevailed during the earliest Tertiary. Short-term sea-level lowstands are marked by hiatuses at the top of Zones P0 and P1a about 50 kyr and 230 kyr after the K/T boundary, respectively. Rising sea level reestablished normal marine conditions about 300 kyr to 350 kyr after the K/T boundary, coincident with the first post-K/T boundary recovery of the Tertiary fauna and extinction of Cretaceous survivors. During this time, high-latitude regions temporarily acted as centers of origin and dispersal for planktic foraminifera. Long-term oceanic instability, gradual faunal turnover, absence of a sudden mass extinction, and greatly diminished δ 13 C shift in high latitudes suggest that a K/T boundary bolide impact was not the primary cause for the K/T boundary faunal transition. Moreover, these data strongly imply that the destructive effects of the bolide impact would have been greatest in low latitudes and negligible in high latitudes.

Stable isotope and foraminiferal changes across the Cretaceous—Tertiary boundary at Stevns Klint, Denmark: Arguments for long-term oceanic instability before and after bolide-impact event

Abstract Stable isotope and planktic and benthic foraminiferal analyses of the K/T boundary transition at Stevens Klint, Denmark, indicate a 100–500 kyr long period of instability in oceanic bottom-water temperature and sea level. During the latest Maastrichtian (from 2.7 m below and up to the K/T boundary) bottom-water temperatures gradually cooled about 1.5°C as surface water temperatures remained constant. At the K/T boundary bottom water temperatures decreased additionally 3°C, and then returned to pre-boundary values just above the boundary interval. Coincident with the onset of the first temperature decrease there was a prominent sea-level fall, estimated between 50–100 m as observed in benthic and planktic foraminiferal assemblages as well as in a decreasing surface-to-bottom δ 13 C gradient. About 40 cm below the iridium-rich K/T boundary clay, sea level began to rise. Poor preservation of foraminifera above the K/T boundary allows only tentative interpretation of Danian events at Stevns Klint, however, sea level generally continued to rise interrupted by short sea level falls. Associated with the observed sea-level changes are three important hiatuses: At the contact between the white chalk and overlying grey-white bryozoan chalk about 2.7 m below the K/T boundary, at or near the top of the Fish Clay (Zone Pla, Parvularugoglobigerina eugubina missing) and at the contact of the Cerithium Limestone and overlying Bryozoan Limestone about 60 cm above the K/T boundary (part of Zone Plc missing). These unconformities are coeval with hiatuses observed in many continental shelf sections and indicate a global eustatic rather than regional isostatic response. Notable is that at Stevns Klint the episode of oceanic instability is registered over approximately the same stratigraphic interval in which supposed extraterrestrial amino acids occur, a circumstance that may indicate a connection. A gradual positive shift in δ 13 C is registered in both benthic and planktic foraminiferal assemblages in the upper Maastrichtian at Stevns Klint. The positive shift is followed by a prominent negative δ 13 C shift (1.3%) at the K/T boundary. An upper Maastrichtian positive δ 13 C excursion followed by a negative δ 13 C anomaly at or near the K/T boundary has previously been observed in deep-sea cores from the Pacific Ocean and the Weddell Sea, Antarctica, implying a global event. Previous suggestions of a relation between the uppermost Maastrichtian positive δ 13 C excursion and sea-level variation are not supported by the data for Stevns Klint.

High-resolution iridium, δ13C, δ18O, foraminifera and nannofossil profiles across the latest Paleocene benthic extinction event at Zumaya, Spain

In the expanded upper Paleocene-lower Eocene section (~ 30 m of Zone P5 sediments) at Zumaya, northern Spain, the highest occurrence of many late Paleocene deep-sea benthic foraminifera species (~40% extinction), coincides with a transition from marl to calcite-free clay. Our high-resolution studies (chemical elements, 613C, 6180, calcareous nannofossils, planktic and benthic foraminifera) show that below the marl-clay transition there is a 40-50 cm thick interval (corresponding to 10-20 kyr) containing a detailed record of a gradual succession of faunal and geochemical events culminating in the benthic extinctions. Planktic foraminiferal and nannofossil changes (e.g., the onset of demise in Fasciculithus genus) occur a few meters below the marl-clay transition. In the limestone 50 cm below the base of the clay, a prominent glauconite maximum indicates that sea-floor oxygenation suddenly decreased. Glauconite continues to be common until the onset of clay deposition. A whole-rock negative 613C shift (1.6%0), most likely reflecting an original sea-water trend, is gradually developed over the 40 cm of greenish brown marls immediately below the clay. At the base of these marls there is a small, significant iridium anomaly of 133 ppt Ir compared with an average background of 38 ppt. In the marls the demise of the Fasciculithus species accelerates, Gavelinella beccariiformis becomes extinct, and the abundance of Acarinina species begins to increase. The superjacent 4 m of clay is devoid of original calcite in its lower part and has a low calcareous content higher up. At calcareous levels in the clay an unusual planktic foraminifera fauna occurs, dominated by Acarinina species. When marl deposition returns, 613C gradually increases and then stabilizes at values about 0.5%o lower than before the isotopic excursion. The 613C excursion spans in total 5 m, probably corresponding to 200-400 kyr. The fasciculiths disappear shortly after the stabilization of 613C. Here we also present a whole-rock 6~3C profile through the entire Paleocene section at Zumaya. The profile is very similar to previous profiles registered in well preserved deep-sea material, suggesting that whole-rock 613C at Zumaya can be used for correlation.

First record of the Hirnantian (Upper Ordovician) delta C-13 excursion in the North American Midcontinent and its regional implications

The most prominent of the two major global delta C-13 excursions in the Ordovician, the Hirnantian delta C-13 excursion (HICE), which is previously recorded from the uppermost Ordovician in a few sections in Nevada, Quebec, Arctic Canada, Baltoscandia, Scotland and China, is documented for the first time from the North American Midcontinent. Samples through the Girardeau Limestone and Leemon Formation in Missouri and Illinois show elevated delta C-13 values of + 4 parts per thousand to + 5 parts per thousand. Although not determined precisely, the beginning of the HICE is likely to be in the upper part of the Orchard Creek Shale, and it ends in the upper Leemon Formation. Being extraordinarily useful chronostratigraphically, the presence of the HICE makes it possible to provide a firm dating of the study interval, whose age has long been controversial. Comparison between the study sections and coeval HICE sequences in North America and Europe show striking similarities, especially in sea-level history, indicating that major local lowstands reflect eustatic sea-level changes. A comparison with Hirnantian diamictite successions in North and South Africa and Argentina suggests that these lowstands correspond to two major Gondwanan glacial episodes. (Less)

The impact of Paleocene/Eocene boundary events on middle neritic benthic foraminiferal assemblages from Egypt

Abstract A 25 m upper Paleocene to lower Eocene marly sequence exposed at Gebel Duwi, (Quseir, Red Sea coast of Egypt) provides a good opportunity for studying Paleocene/Eocene (P/E) boundary stratigraphy and events. Various bio-, eco-, and isotope stratigraphic correlations accurately delineate the position of the P/E boundary (i.e. the level of stable isotopic excursions and deep-sea benthic extinctions) in the middle part of this section, within Zones P5 and NP9. In this paper the impact of P/E boundary environmental perturbations on benthic foraminiferal communities of the shallow Tethyan shelf is examined. Benthic foraminiferal assemblages from Gebel Duwi, characterized by large Frondicularia phosphatica and F. nakkadyi in addition to a number of other neritic taxa, but without any typical outer neritic-bathyal taxa, suggest middle neritic (75–100 m) deposition throughout the studied interval and only minor relative sea-level variations (perhaps some 10–20 m). Across the boundary sea-level appears to have been stable. Yet, a distinct faunal turnover marks the P/E boundary of this shallow site, which, in contrast to deep-sea records, is less abrupt, being preceded by a gradual diversity decrease starting some four meters below the boundary. Moreover, most exits are either local or just temporary and thus not true extinctions: many (Lazarus) taxa reappear at some point above the boundary, while all but one of the disappearing taxa are known from other lower Eocene neritic deposits in Egypt. In general, benthic foraminiferal assemblages display low diversities and high dominance values (notably Anomalinoides aegyptiacus: up to 74%), suggesting high levels of environmental stress at the sea-floor. In combination with occasionally very high P B ratios (up to 98%P), and generally laminated sediments, the character of the benthic assemblage points to a strong influence of recurrent dysoxia and/or anoxia. We suggest that these resulted from surface eutrophication by (intermittent) coastal upwelling and reduced ventilation of the bottom environment. Although these conditions prevailed during most of the time-interval studied, they were most severe during the latest Paleocene and early Eocene when eutrophication intensified, and the organic carbon flux to the sea-floor increased. Enhanced atmospheric contrasts between the Tethys seaway and the African continent, resulting in intensified longshore tradewinds, may have controlled these changes. At the P/E boundary the bottom environment became minimally ventilated, perhaps due to reduced oxygen advection from deeper waters. Three meters above the boundary a succession of increasingly diverse assemblages indicate a gradual decrease of environmental stress and a return to more normal conditions, although the organic carbon flux to the sea-floor remained high.