Richard K. Olsson

Warm tropical sea surface temperatures in the Late Cretaceous and Eocene epochs

Climate models with increased levels of carbon dioxide predict that global warming causes heating in the tropics, but investigations of ancient climates based on palaeodata have generally indicated cool tropical temperatures during supposed greenhouse episodes. For example, in the Late Cretaceous and Eocene epochs there is abundant geological evidence for warm, mostly ice-free poles, but tropical sea surface temperatures are generally estimated to be only 15–23 °C, based on oxygen isotope palaeothermometry of surface-dwelling planktonic foraminifer shells. Here we question the validity of most such data on the grounds of poor preservation and diagenetic alteration. We present new data from exceptionally well preserved foraminifer shells extracted from impermeable clay-rich sediments, which indicate that for the intervals studied, tropical sea surface temperatures were at least 28–32 °C. These warm temperatures are more in line with our understanding of the geographical distributions of temperature-sensitive fossil organisms and the results of climate models with increased CO2 levels.

Late Cretaceous chronology of large, rapid sea-level changes: Glacioeustasy during the greenhouse world

We provide a record of global sea-level (eustatic) variations of the Late Cretaceous (99- 65 Ma) greenhouse world. Ocean Drilling Program Leg 174AX provided a record of 11- 14 Upper Cretaceous sequences in the New Jersey Coastal Plain that were dated by in- tegrating Sr isotopic stratigraphy and biostratigraphy. Backstripping yielded a Late Cre- taceous eustatic estimate for these sequences, taking into account sediment loading, com- paction, paleowater depth, and basin subsidence. We show that Late Cretaceous sea-level changes were large (.25 m) and rapid (K1 m.y.), suggesting a glacioeustatic control. Three large d 18 O increases are linked to sequence boundaries (others lack sufficient d 18 O data), consistent with a glacioeustatic cause and with the development of small (,10 6 km 3 ) ephemeral ice sheets in Antarctica. Our sequence boundaries correlate with sea-level falls recorded by Exxon Production Research and sections from northwest Europe and Russia, indicating a global cause, although the Exxon record differs from backstripped estimates in amplitude and shape.

Upper Cretaceous sequences and sea-level history, New Jersey Coastal Plain

We developed a Late Cretaceous sea- level estimate from Upper Cretaceous sequences at Bass River and Ancora, New Jersey (ODP [Ocean Drilling Program] Leg 174AX). We dated 11–14 sequences by integrating Sr isotope and biostratigraphy (age resolution ±0.5 m.y.) and then estimated paleoenvironmental changes within the sequences from lithofacies and biofacies analyses. Sequences generally shallow up-section from middle-neritic to inner-neritic paleodepths, as shown by the transition from thin basal glauconite shelf sands (transgressive systems tracts [TST]), to medial-prodelta silty clays (highstand systems tracts [HST]), and finally to upper–delta-front quartz sands (HST). Sea-level estimates obtained by backstripping (accounting for paleodepth variations, sediment loading, compaction, and basin subsidence) indicate that large (>25 m) and rapid (≪1 m.y.) sea-level variations occurred during the Late Cretaceous greenhouse world. The fact that the timing of Upper Cretaceous sequence boundaries in New Jersey is similar to the sea-level lowering records of Exxon Production Research Company (EPR), northwest European sections, and Russian platform outcrops points to a global cause. Because backstripping, seismicity, seismic stratigraphic data, and sediment-distribution patterns all indicate minimal tectonic effects on the New Jersey Coastal Plain, we interpret that we have isolated a eustatic signature. The only known mechanism that can explain such global changes— glacio-eustasy—is consistent with foraminiferal δ 18 O data. Either continental ice sheets paced sea-level changes during the Late Cretaceous, or our understanding of causal mechanisms for global sea-level change is fundamentally flawed. Comparison of our eustatic history with published ice-sheet models and Milankovitch predictions suggests that small (5–10 × 10 6 km 3 ), ephemeral, and areally restricted Antarctic ice sheets paced the Late Cretaceous global sea-level change. New Jersey and Russian eustatic estimates are typically one-half of the EPR amplitudes, though this difference varies through time, yielding markedly different eustatic curves. We conclude that New Jersey provides the best available estimate for Late Cretaceous sea-level variations.

Does ice drive early Maastrichtian eustasy

A large (30–40 m), rapid (≪1 m.y.), earliest Maastrichtian sea-level drop inferred from New Jersey sequence stratigraphic records correlates with synchronous δ18O increases in deep-water benthic and low-latitude surface-dwelling planktonic foraminifera. The coincidence of these events argues for the development of a moderate-sized ice sheet during the early Maastrichtian.

Effects of thermal discharges on the microstructural growth ofMercenaria mercenaria

The effects of thermal discharges from the Oyster Creek Nuclear Generating Station at Barnegat Bay, New Jersey, are recorded in the microstructural growth ofMercenaria mercenaria, a common coastal marine pelecypod. The analysis of the shell microstructure shows that this bivalve acts as an effective monitor of the environmental conditions existing in the marine waters adjacent to the power station. Many physiological and environmental events such as spawning, winter (freeze) shocks, summer (heat) shocks, thermal shocks, tidal cycles, and major storms are clearly recorded in the shell microstructure. The exact time of occurrence of these events can be determined by counting daily growth increments backwards from the outer shell margins of freshly killed individuals.Microstructural growth patterns reflected in Barnegat Bay specimens indicate that these pelecypods were affected mainly by temperature extremes, temperature variations, tides, type of substratum, and age. Growth patterns in specimens from areas surrounding Oyster Creek (affected by thermal effluent) are significantly different from those from other bay localities (unaffected by thermal effluent).Mercenaria mercenaria within approximately a 1.6km radius of Oyster Creek show a lower summer growth rate (10 percent to 25 percent lower) and a greater number of growth breaks (2 to 6 more per clam) than those away from the creek. The lower summer growth rates occur in bivalves subjected to the effluent because the added heat during the summer months causes water temperatures to exceed a critical threshold for optimum growth in the species. The greater number of growth breaks takes place, in turn, because many of the breaks (thermal shock breaks) are generated by rapidly fluctuating temperatures associated with abrupt shutdowns, massive load reductions and rapid renewal of operations following shutdowns or load reduction periods at the nuclear power station.In addition, the effluent may be upsetting natural spawning events in the clams when abrupt changes in power station operations overlap with spawning periods. In this respect, spawning may be precluded by sharp temperature changes which result in physiological shocks to the animal.

Ejecta layer at the Cretaceous-Tertiary boundary, Bass River, New Jersey (Ocean Drilling Program Leg 174AX)

A continuously cored borehole drilled at Bass River, New Jersey, recovered a Cretaceous-Tertiary (K-T) succession with a 6-cm-thick spherule layer immediately above the boundary. Below the spherule layer, the Cretaceous glauconitic clay is extensively burrowed and contains the uppermost Maastrichtian Micula prinsii calcareous nannofossil zone. Spherical impressions of spherules at the top of the Cretaceous indicate nearly instantaneous deposition of ejecta from the Chicxulub impact. The thickest ejecta layer shows clearly that a single impact occurred precisely at K-T boundary time. Above the spherule layer, the glauconitic clay contains the planktonic foraminiferal P0 and P-alpha Zones, indicating (1) a complete K-T succession and (2) continuous deposition interrupted only by fallout of the ejecta layer. Clay clasts within a 6 cm interval above the spherule layer contain Cretaceous microfossils and may be rip-up clasts from a tsunami or possibly a megastorm event. Extinction of the Cretaceous planktonic foraminifers and burrowing organisms occurs abruptly at the K-T boundary. Thus, the Bass River K-T succession unequivocally links the Chicxulub bolide impact to the mass extinctions at the end of the Mesozoic.

Controversies on the placement of Cretaceous-Paleogene boundary and the K/P mass extinction of planktonic foraminifera

Examination of recently reported K/P boundary sections indicates that the placement of the K/P boundary is based on equivocal criteria and that the boundary as placed is not synchronous. The conclusion that the K/P boundary in several U.S. Gulf Coast sections is complete and within a condensed section is simply the artifact of delineating the K/P boundary on disparate paleontologic datum planes and preservational bias of the microfossil assemblages. The upper slope and outer shelf sections at El Kef, Gredero, and Agost as well as the DSDP Site 577 section are continuous. The non-separation of Zone P0 at some deep sea sites is due to very low sedimentation rates and the short time interval of Zone P0

A paleoslope model of Campanian to lower Maestrichtian foraminifera in the North American basin and adjacent continental margin

Campanian to early Maestrichtian benthic foraminiferal assemblages of the New Jersey and Delaware coastal plain and the Baltimore Canyon Trough contain distinct bathymetric biofacies each occurring in adjacent settings to one another in a profile downdip toward the North American basin. The assemblages are interpreted as representing inner shelf to uppermost middle bathyal environments of deposition (10 to 500 m water depth). A unique biofacies which consists of predominantly arenaceous foraminifera in a lithology of dark lignitic shales is present in restricted intervals within the Baltimore Canyon region. This biofacies probably developed under oxygen deficient conditions in middle shelf to upper bathyal paleodepths. Within the North American basin, benthic foraminifers from Campanian to lower Maestrichtian sections at various DSDP sites indicate that deposition took place in middle bathyal to abyssal environments (500 m to more than 3000 m paleodepth). A complete paleoslope profile (shelf to abyssal) is identified within the North American basin and adjacent continental margin. The foraminiferal composition of this paleoslope is as follows:Gavelinella nelsoni, G. pinguis, Lenticulina pseudosecans, Cibicides harperi andPullenia americana characterize shore-face to inner shelf regions of 10 to 50 m water depth. Species that show maximum development in middle shelf environments (50 to 100 m water depth) includeClavulina trilatera, Hoeglundina supracretacea and nodosariids. In the outer shelf, 100–200 m water depth,Praebulimina carseyae, Gavelinella compressa, G. spissocostata, Coryphostoma plaitum andPullenia jarvisi predominate. The upper bathyal environment of 200–500 m water depth is characterized by species such asArenobulimina subspherica, Dorothia oxycona, Verneuilina dickinsonensis, n. sp.,Stensioina exculpta gracilis andGyroidinoides globosus. Pullenia cretacea, Gavelinella ammonoides, G. whitei, G. intermedia, Praebulimina reussi, P. cushmani, Pleurostomella subnodosa andStilostomella pseudoscripta are species common to the middle bathyal environment of 500 to 1500 m water depth. Species that characterize lower bathyal environments (1500 to 2500 m water depth) includeAragonia velascoensis, Reussella szajnochae, Osangularia utaturensis, Clavulina gabonica, Tritaxia aspera andSpiroplectammina dentata. Many of the middle and lower bathyal indicator species extend into the abyssal realm (2500 m water depth) where they are associated with more abundant species such asAragonia ouezzanensis, Reussella pseudospinulosa, Hyperammina elongata, Rhizammina indivisa andSaccammina complanata. The resulting paleoslope model allows a more critical evaluation of the role played by benthic foraminiferal species in shelf, slope and abyssal environments. It also enhances the accuracy of estimating paleobathymetry especially in shelf regions of the Campanian to early Maestrichtian.

An Exceptional Chronologic, Isotopic, and Clay Mineralogic Record of the Latest Paleocene Thermal Maximum, Bass River, NJ, ODP 174AX

A thick, apparently continuous section recording events of the latest Paleocene thermal maximum in a neritic setting was drilled at Bass River State Forest, New Jersey as part of ODP Leg 174AX [Miller, Sugarman, Browning et al., 1998]. Integrated nannofossil and magneto-stratigraphy provides a firm chronology supplemented by planktonic foraminiferal biostratigraphy. This chronologic study indicates that this neritic section rivals the best deep-sea sections in providing a complete record of late Paleocene climatic events. Carbon and oxygen isotopes measured on benthic foraminifera show a major (4.0% in carbon, 2.3% in oxygen) negative shift correlative with the global latest Paleocene carbon isotope excursion (CIE). A sharp increase in kaolinite content coincides with the isotope shift in the Bass River section, analogous to increases found in several other records. Carbon and oxygen isotopes remain low and kaolinite content remains high for the remainder of the depositional sequence above the CIE (32.5 ft, 9.9 m), which we estimate to represent 300-500 k.y. We interpret these data as indicative of an abrupt shift to a warmer and wetter climate along the North American mid-Atlantic coast, in concert with global events associated with the CIE.

PALEOBIOGEOGRAPHY OF PSEUDOTEXTULARIA ELEGANS DURING THE LATEST MAASTRICHTIAN GLOBAL WARMING EVENT

A latest Maastrichtian global warming event, which began approximately 450 k.y. and ended about 22 k.y. prior to the K/T boundary, is associated with the pole-ward migration of the warm-water planktonic foraminifer Pseudotextularia elegans. The warming event was apparently inititated by greenhouse warming due to the main outpouring of the Deccan Traps in India and is now well documented in the North and South Atlantic Oceans and in North America by the poleward migration of warm-water planktonic foraminifera and subtropical vegetation. A cooling trend ca 22 kyr prior to the K/T boundary caused marine δ18O values to return to climatic conditions recorded prior to the onset of warming and thus does not represent a significant change in long-term climate. Planktonic foraminifera responded by migration to the latest Maastrichtian global warming and cooling before their mass extinction at the K/T.