Major Northern Hemisphere Glaciation Research Articles

East Greenland Prograded Margin and Oceanic Composite Tectono-Sedimentary Element, offshore East Greenland

Abstract The East Greenland Prograded Margin and Oceanic Composite Tectono-Sedimentary Element (EGPMO CTSE) consists of the East Greenland Prograded Margin Tectonic-Sedimentary Element (TSE) and the East Greenland Oceanic (EGO) TSE located over continental and oceanic crust, respectively. The East Greenland Prograded Margin TSE (EGPM TSE) is made up of six segments, with their basal part deferring from Maastrichtian to Miocene in age. The variation reflects the different timing in transition from syn- to post-rift, controlled by the lateral migration of rifting and diachronic continental break-up in the northern North Atlantic. The post-rift history can be subdivided into a pre-break-up Maastrichtian–Paleocene post-rift phase developed entirely offshore NE Greenland and an earliest Eocene–Miocene syn- to post-break-up phase developed in the wake of progressive continental rupture. Finally, the CTSE started to develop as a unified body from Miocene time after the complete separation of Greenland from Eurasia and the Jan Mayen microcontinent. The EGO TSE has formed since the earliest Eocene commencement of seafloor spreading. The structural and depositional outline of the EGPMO CTSE depicts its tectonic history but also reflects phases of volcanism, denudation and intensified icehouse conditions since the middle Miocene that were triggered by the opening of the Fram Strait and the uplift of East Greenland. The first major northern hemisphere glaciations started in NE Greenland. Glaciations expanded southwards during the late Miocene as the Denmark Strait was transgressed and cold surface water from the high arctic started flowing along SE Greenland, cooling the region. The petroleum potential of the EGPM TSE is conceivably modest but a potential exists locally offshore northern NE Greenland where hydrocarbons sourced mainly from the Jurassic–Cretaceous section may have charged structures cored by Maastrichtian–Eocene sandstone reservoirs sealed by overlying marine mudstones.

Biomarker Evidence for an MIS M2 Glacial‐Pluvial in the Mojave Desert Before Warming and Drying in the Late Pliocene

AbstractAncient lake deposits in the Mojave Desert indicate that the water cycle in this currently dry place was radically different under past climates. Here we revisit a 700 m core drilled 55 years ago from Searles Valley, California, that recovered evidence for a lacustrine phase during the late Pliocene. We update the paleomagnetic age model and extract new biomarker evidence for climatic conditions from lacustrine deposits (3.373–2.706 Ma). The MBT′5Me temperature proxy detects present‐day conditions (21 ± 3°C, n = 2) initially, followed by warmer‐than‐present conditions (25 ± 3°C, n = 17) starting at 3.268 and ending at 2.734 Ma. Bacterial and archeal biomarkers reveal lake salinity increased after 3.268 Ma likely reflecting increased evaporation in response to higher temperatures. The δ13C values of plant waxes (−30.7 ± 1.4‰, n = 28) are consistent with local C3 taxa, likely expanded conifer woodlands during the pluvial with less C4 than the Pleistocene. δD values (−174 ± 5‰, n = 25) of plant waxes indicate precipitation δD values (−89 ± 5‰, n = 25) in the late Pliocene are within the same range as the late Pleistocene precipitation δD. Microbial biomarkers identify a deep, freshwater lake and a cooling that corresponds to the onset of major Northern Hemisphere glaciation at marine isotope stage marine isotope stages M2 (3.3 Ma). A more saline lake persisted for ∼0.6 Ma across the subsequent warmth of the late Pliocene (3.268–2.734 Ma) before the lake desiccated at the Pleistocene intensification of Northern Hemisphere Glaciation.

Nutrient availability in the North Pacific region not primarily driven by climate through the Quaternary

The subarctic North Pacific Ocean is a relatively understudied region in terms of palaeoclimate, limiting our understanding of how the region has both driven and responded to palaeoenvironmental events. Today, the subarctic North Pacific Ocean is marked by a year round stratified water column with a halocline at c. 300 m water depth. Previous studies at ODP Site 882 in the Northwest Pacific have suggested the stratified water column system developed at the onset of major Northern Hemisphere Glaciation (2.73 Ma). In addition to limiting the upwelling of carbon-rich deep waters and associated ventilation of CO2 to the atmosphere, the shift to a stratified state fundamentally altered oceanographic conditions and biogeochemical cycling across the region. Key questions remain over whether the region was permanently stratified for all of the Quaternary, or whether the changes in stratification/biogeochemical cycling altered over major climatic transitions such as the Mid-Pleistocene Transition (MPT), a process that would alter regional ocean-atmospheric carbon exchanges. We present new silicon and oxygen isotope data from diatoms (δ30Sidiatom and δ18Odiatom), alongside previously published data in order to test the mechanisms of biogeochemical cycling in the subarctic North Pacific Ocean between 2.85 Ma and 0.06 Ma, including influences from the wider region such as Glacial North Pacific Intermediate Water (GNPIW) originating in the Bering Sea. This has enabled us to reconstruct temporal changes in photic zone nutrient utilisation and silicic acid supply in the northwest subarctic Pacific Ocean through the progressive intensification of glacial-interglacial cycles through the Quaternary and over the MPT. We show that prior to the MPT climate does not appear to be a primary controller of nutrient availability in the North Pacific region, but that following the MPT, it has a greater influence, shown by the interrelationship with the upwelling index from the Bering Sea.

Mid-Pliocene global land monsoon from PlioMIP1 simulations

The mid-Piacenzian (Pliocene) warm period (approximately 3.3–3.0 Ma) monsoon not only provides us with a useful insight into the future monsoon under a warming scenario with high atmospheric CO2 concentration but is also hypothesized to play a key role in climate feedback through impact on the carbon cycle on a geological timescale. The monsoon evolution over time is one key to test this hypothesis. In this sense, we examine the mid-Piacenzian global land monsoon area (GLMA), precipitation (GLMP), and GLMP intensity (GLMPI) using all available model data from the Pliocene Model Intercomparison Project phase 1 (PlioMIP1). Relative to the pre-industrial period, both the GLMA and GLMP increase in the mid-Piacenzian and by an average of 7.3% and 5.8%, respectively. On a large scale, the increased GLMP comes mainly from northern Africa, Asia, and northern Australia. Quantitatively, it is the variation of GLMA, not of GLMPI, that makes a major contribution to the GLMP change. Further analysis reveals that anomalous inland water vapor transportation due to the reduced large-scale meridional thermal contrast in the mid-to-upper troposphere, together with the variation of vertical moisture advection and evaporation, explains most of the global land monsoon changes. A model–data comparison shows that the simulated monsoon precipitation variations are roughly consistent with the reconstructions in northern Africa, Asia, northern Australia, Central America, and eastern South America. Moreover, the intensified mid-Piacenzian Asian monsoon, which is supported by both simulations and reconstructions, or an overall intensified global land monsoon is hypothesized to contribute to the lowering of atmospheric CO2 concentration and the subsequent onset of the sustained major Northern Hemisphere glaciation.

Late Pliocene Marine pCO2 Reconstructions From the Subarctic Pacific Ocean

AbstractThe development of large ice sheets across the Northern Hemisphere during the late Pliocene and the emergence of the glacial‐interglacial cycles that punctuate the Quaternary mark a significant threshold in Earth's climate history. Although a number of different mechanisms have been proposed to initiate this cooling and the onset of major Northern Hemisphere glaciation, reductions in atmospheric concentrations of CO2 likely played a key role. The emergence of a stratified (halocline) water column in the subarctic northwest Pacific Ocean at 2.73 Ma has often been interpreted as an event which would have limited oceanic ventilation of CO2 to the atmosphere, thereby helping to cool the global climate system. Here diatom carbon isotopes (δ13Cdiatom) are used to reconstruct changes in regional carbon dynamics through this interval. Results show that the development of a salinity stratification did not fundamentally alter the net oceanic/atmospheric flux of CO2 in the subarctic northwest Pacific Ocean through the late Pliocene/early Quaternary. These results provide further insights into the long‐term controls on global carbon cycling and the role of the subarctic Pacific Ocean in instigating global climatic changes.

Expanded Florida reef development during the mid-Pliocene warm period

The coral fauna of the Tamiami Formation documents a northern expansion of reef development along the Florida Peninsula during the mid-Pliocene warm period (MPWP). Radiometric dating (U-Pb) of Solenastrea bournoni produced an age of 2.99±0.11Ma, constraining reef development to the MPWP and the peak of Plio-Pleistocene faunal turnover; subsequent to the final closure of the Central American Seaway (CAS) but prior to major Northern Hemisphere Glaciation (NHG). Coral faunal analyses are based on a total of 1614 coral specimens collected along a 165km stretch of the west Florida coast, and included rarefaction and detrended correspondence analysis (DCA). A total of 60 coral species occur within the Tamiami Formation, with faunal assemblages ranging from 42 to 87% extinct taxa. The Tamiami collections can be split into a southern “reef” assemblage with high diversity of stenotopic taxa and a northern “non-reef” assemblage with lower diversity eurytopic taxa. The southern reef assemblage contains framework buildups of the dominant tropical taxa Stylophora affinis, Orbicella annularis, and Acropora cervicornis. We interpret enhanced west Florida reef development during the middle Pliocene to be a product of more equitable sea surface temperatures, and reduced salinity fluctuations associated with higher sea levels. While mean sea surface temperature estimates based on oxygen isotopic analysis of the coral Solenastrea bournoni (25.3°C) are similar to present day values (26°C), a completely flooded southern Florida Platform in the Pliocene would be less prone to salinity fluctuations associated with coastal runoff and extreme cold-water events during winter storms. While higher latitude range shifts of tropical reef corals associated with current global climate change have been documented elsewhere in the world, we do not foresee the West Florida Shelf being conducive to significant range shifts in tropical coral taxa or reef development within the coming century.

Biogeochemical cycling in the Bering Sea over the onset of major Northern Hemisphere Glaciation

AbstractThe Bering Sea is one of the most biologically productive regions in the marine system and plays a key role in regulating the flow of waters to the Arctic Ocean and into the subarctic North Pacific Ocean. Cores from Integrated Ocean Drilling Program (IODP) Expedition 323 to the Bering Sea provide the first opportunity to obtain reconstructions from the region that extend back to the Pliocene. Previous research at Bowers Ridge, south Bering Sea, has revealed stable levels of siliceous productivity over the onset of major Northern Hemisphere Glaciation (NHG) (circa 2.85–2.73 Ma). However, diatom silica isotope records of oxygen (δ18Odiatom) and silicon (δ30Sidiatom) presented here demonstrate that this interval was associated with a progressive increase in the supply of silicic acid to the region, superimposed on shift to a more dynamic environment characterized by colder temperatures and increased sea ice. This concluded at 2.58 Ma with a sharp increase in diatom productivity, further increases in photic zone nutrient availability and a permanent shift to colder sea surface conditions. These transitions are suggested to reflect a gradually more intense nutrient leakage from the subarctic northwest Pacific Ocean, with increases in productivity further aided by increased sea ice‐ and wind‐driven mixing in the Bering Sea. In suggesting a linkage in biogeochemical cycling between the south Bering Sea and subarctic Northwest Pacific Ocean, mainly via the Kamchatka Strait, this work highlights the need to consider the interconnectivity of these two systems when future reconstructions are carried out in the region.

Millennial-Scale Interaction between Ice Sheets and Ocean Circulation during Marine Isotope Stage 100

Waxing/waning of the ice sheets and the associated change in thermohaline circulation have played an important role in global climate change since major continental ice sheets appeared in the northern hemisphere about 2.75 million years ago. In the earliest glacial stages, however, establishment of the linkage between ice sheet development and ocean circulation remain largely unclear. Here we show new high-resolution records of marine isotope stage 100 recovered from deep-sea sediments on the Gardar Drift, in the subpolar North Atlantic. Results of a wide range of analyses clearly reveal the influence of millennial-scale variability in iceberg discharge on ocean surface condition and bottom current variability in the subpolar North Atlantic during marine isotope stage 100. We identified eight events of ice-rafted debris, which occurred mostly with decreases in sea surface temperature and in current components indicating North Atlantic Deep Water. These decreases are interpreted by weakened deep water formation linked to iceberg discharge, similarly to observations from the last glacial period. Dolomite fraction of the ice-rafted events in early MIS 100 like the last glacial Heinrich events suggests massive collapse of the Laurentide ice sheet in North America. At the same time, our early glacial data suggest differences from the last glacial period: absence of 1470-year periodicity in the interactions between ice sheets and ocean, and northerly shift of the ice-rafted debris belt. Our high-resolution data largely improve the picture of ice-sheet/ocean interactions on millennial time scales in the early glacial period after major Northern Hemisphere glaciation.

Seismic geomorphological reconstructions of Plio-Pleistocene bottom current variability at Goban Spur

High-resolution single channel sparker reflection seismic data revealed the presence of large-scale sediment waves nearby DSDP Site 548, located on Goban Spur. They developed in a gentle terraced environment which contrasts with the canyon-incised Celtic margin, and the relatively smooth Porcupine Seabight to the north. Based upon the morphological characteristics of the observed seabed and buried sediment waves, energetic alongslope bottom currents are thought to be the driving mechanism for the sediment wave development. These currents are driven on their turn by an enhanced internal tide regime that could be attributed to the introduction of the Mediterranean Outflow Water. The DSDP Site 548 downhole geophysical data and the seismic stratigraphic analysis allowed the differentiation of three sequences that relate to evolutionary stages since the lower Pliocene. The sequences are bounded by local erosional events, associated with mass wasting events, which seem to occur roughly synchronously to major northern hemisphere glaciations, respectively during the Lower Pleistocene (~2.5 to 2.15Ma), and the Middle Pleistocene (~0.45Ma). The lower sequence (from ~4.5 to ~2.15Ma) shows no morphological evidence of bottom-current driven sedimentation. It is however settled over a smooth erosional surface which could indicate the introduction of the Mediterranean Outflow Water. The intermediate sequence is characterised by large-scale sediment waves that have gradually developed in close association with palaeo-seafloor irregularities. It is inferred that the sedimentation resumed with a relative bottom current energy increase. The youngest sequence recorded active sediment wave formation, similar to the previous sequence. Although the Goban Spur sediment waves cannot be regarded as contourite drifts as such, their stratigraphic evolution corresponds to other well-documented contourite depositional systems, influenced by the Mediterranean Outflow Water.

An integrated sequence stratigraphic and chronostratigraphic analysis of the Pliocene, Tiburon Basin succession, Mejillones Peninsula, Chile

We present new findings from Pliocene marine sediments from the Mejillones Peninsula Tiburon Basin of the northern Chile continental margin that provide constraints for the global sea level record. Sedimentologic and sequence stratigraphic studies reveal facies associations of a continental shelf setting. Textural variations indicate that coarsening and fining up of the succession are due to relative sea level rise and fall, respectively. Magnetostratigraphy was integrated with bio- and tephro- stratigraphic data to construct a record of high-resolution chronology. The age model constrains the Tiburon Basin lower section between 4.2 Ma and 2.8 Ma. The record is likely to be controlled in part by sea level change with orbital periodicities of obliquity (∼40 ka of frequency) and, between 3.2 Ma and 2.9 Ma a high-amplitude sea level fall is correlated to global climatic deterioration and the onset of major Northern Hemisphere glaciations.

The key role of global solid‐Earth processes in preconditioning Greenland's glaciation since the Pliocene

AbstractAfter >500 Ma of absence, major Northern Hemisphere glaciations appeared during the Plio‐Pleistocene, with Greenland leading other northern areas. Here, we propose that three major solid‐Earth processes underpinned build‐up of the Greenland ice‐sheet. First, a mantle‐plume pulse, responsible for the North Atlantic Igneous Province at ~60 Ma, regionally thinned the lithosphere. Younger plume pulses led to uplift, which accelerated at ~5 Ma, lifting the parts of the East Greenland margin closest to Iceland to elevations of more than 3 km above sea level. Second, plate‐tectonic reconstruction shows a ~6° northward component of Greenland motion relative to the mantle since ~60 Ma. Third, a concurrent northward rotation of the entire mantle and crust towards the pole, dubbed True Polar Wander (TPW), contributed an additional ~12° change in latitude. These global geodynamic processes preconditioned Greenland to sustain long‐term glaciation, emphasizing the role of solid‐Earth processes in driving long‐term global climatic transitions.

Late Pliocene variations of the Mediterranean outflow

Late Pliocene changes in the advection of Mediterranean Outflow Water (MOW) derivates were reconstructed at northeast Atlantic DSDP/ODP sites 548 and 982 and compared to records of WMDW at West Mediterranean Site 978. Neodymium isotope (eNd) values more positive than −10.5/−11 reflect diluted MOW derivates that spread almost continuously into the northeast Atlantic from 3.7 to 2.55 Ma, reaching Rockall Plateau Site 982 from 3.63 to 2.75 Ma. From 3.4 to 3.3 Ma average MOW temperature and salinity increased by 2°–4 °C and ~1 psu both at proximal Site 548 and distal Site 982. The rise implies a rise in flow strength, coeval with a long-term rise in both west Mediterranean Sea surface salinity by almost 2 psu and average bottom water salinity (BWS) by ~1 psu, despite inherent uncertainties in BWS estimates. The changes were linked with major Mediterranean aridification and a drop in African monsoon humidity. In contrast to model expectations, the rise in MOW salt discharge after 3.4 Ma did not translate into improved ventilation of North Atlantic Deep Water, since it possibly was too small to significantly influence Atlantic Meridional Overturning Circulation. Right after ~2.95 Ma, with the onset of major Northern Hemisphere Glaciation, long-term average bottom water temperature (BWT) and BWS at Site 548 dropped abruptly by ~5 °C and ~1–2 psu, in contrast to more distal Site 982, where BWT and BWS continued to oscillate at estimates of ~2 °C and 1.5–2.5 psu higher than today until ~2.6 Ma. We relate the small-scale changes both to a reduced MOW flow and to enhanced dilution by warmwaters of a strengthenedNorth Atlantic Current temporarily replacingMOWderivates at Rockall Plateau.

A major change in North Atlantic deep water circulation 1.6 million years ago

Abstract. The global ocean–climate system has been highly sensitive to the formation and advection of deep overflow water from the Nordic Seas as integral part of the Atlantic Meridional Overturning Circulation (AMOC) but its evolution over the Pliocene–Pleistocene global cooling is not fully understood. In particular, changes in the sources and mixing of prevailing deep waters that were involved in driving overturning throughout the Pliocene–Pleistocene climate transitions are not well constrained. Here we investigate the evolution of a substantial deep southward return overflow of the AMOC over the last 4 million years. We present new records of the bottom-water radiogenic neodymium isotope (ϵNd) variability obtained from three sediment cores (DSDP site 610 and ODP sites 980/981 and 900) at water depths between 2170 and 5050 m in the northeast Atlantic. We find that prior to the onset of major Northern Hemisphere glaciation (NHG) ∼3 million years ago (Ma), ϵNd values primarily oscillated between −9 and −11 at all sites, consistent with enhanced vertical mixing and weak stratification of the water masses during the warmer-than-today Pliocene period. From 2.7 Ma to ∼2.0 Ma, the ϵNd signatures of the water masses gradually became more distinct, which documents a significant advection of Nordic Seas overflow deep water coincident with the intensification of NHG. Most markedly, however, at ∼1.6 Ma the interglacial ϵNd signatures at sites 610 (2420 m water depth (w.d.)) and 980/981 (2170 m w.d.) synchronously and permanently shifted by 2 to 3 ϵNd units to less radiogenic values, respectively. Since then the difference between glacial and interglacial ϵNd values has been similar to the Late Quaternary at each site. A decrease of ∼2ϵNd units at 1.6 Ma was also recorded for the deepest water masses by site 900 (∼5050 m w.d.), which thereafter, however, evolved to more radiogenic values again until the present. This major ϵNd change across the 1.6 Ma transition reflects a significant reorganization of the overturning circulation in the northeast Atlantic paving the way for the more stratified water column with distinct water masses prevailing thereafter.

The transition on North America from the warm humid Pliocene to the glaciated Quaternary traced by eolian dust deposition at a benchmark North Atlantic Ocean drill site

We present Plio-Pleistocene records of sediment color, %CaCO3, foraminifer fragmentation, benthic carbon isotopes (δ13C) and radiogenic isotopes (Sr, Nd, Pb) of the terrigenous component from IODP Site U1313, a reoccupation of benchmark subtropical North Atlantic Ocean DSDP Site 607. We show that (inter)glacial cycles in sediment color and %CaCO3 pre-date major northern hemisphere glaciation and are unambiguously and consistently correlated to benthic oxygen isotopes back to 3.3 million years ago (Ma) and intermittently so probably back to the Miocene/Pliocene boundary. We show these lithological cycles to be driven by enhanced glacial fluxes of terrigenous material (eolian dust), not carbonate dissolution (the classic interpretation). Our radiogenic isotope data indicate a North American source for this dust (∼3.3–2.4 Ma) in keeping with the interpreted source of terrestrial plant wax-derived biomarkers deposited at Site U1313. Yet our data indicate a mid latitude provenance regardless of (inter)glacial state, a finding that is inconsistent with the biomarker-inferred importance of glaciogenic mechanisms of dust production and transport. Moreover, we find that the relation between the biomarker and lithogenic components of dust accumulation is distinctly non-linear. Both records show a jump in glacial rates of accumulation from Marine Isotope Stage, MIS, G6 (2.72 Ma) onwards but the amplitude of this signal is about 3–8 times greater for biomarkers than for dust and particularly extreme during MIS 100 (2.52 Ma). We conclude that North America shifted abruptly to a distinctly more arid glacial regime from MIS G6, but major shifts in glacial North American vegetation biomes and regional wind fields (exacerbated by the growth of a large Laurentide Ice Sheet during MIS 100) likely explain amplification of this signal in the biomarker records. Our findings are consistent with wetter-than-modern reconstructions of North American continental climate under the warm high CO2 conditions of the Early Pliocene but contrast with most model predictions for the response of the hydrological cycle to anthropogenic warming over the coming 50 years (poleward expansion of the subtropical dry zones).

An alternative suggestion for the Pliocene onset of major northern hemisphere glaciation based on the geochemical provenance of North Atlantic Ocean ice-rafted debris

The onset of abundant ice-rafted debris (IRD) deposition in the Nordic Seas and subpolar North Atlantic Ocean 2.72 millions of years ago (Ma) is thought to record the Pliocene onset of major northern hemisphere glaciation (NHG) due to a synchronous advance of North American Laurentide, Scandinavian and Greenland ice-sheets to their marine calving margins during marine isotope stage (MIS) G6. Numerous marine and terrestrial records from the Nordic Seas region indicate that extensive ice sheets on Greenland and Scandinavia increased IRD inputs to these seas from 2.72 Ma. The timing of ice-sheet expansion on North America as tracked by IRD deposition in the subpolar North Atlantic Ocean, however, is less clear because both Europe and North America are potential sources for icebergs in this region. Moreover, cosmogenic-dating of terrestrial tills on North America indicate that the Laurentide Ice Sheet did not extend to ∼39°N until 2.4 ± 0.14 Ma, at least 180 ka after the onset of major IRD deposition at 2.72 Ma. To address this problem, we present the first detailed analysis of the geochemical provenance of individual sand-sized IRD deposited in the subpolar North Atlantic Ocean between MIS G6 and 100 (∼2.72–2.52 Ma). IRD provenance is assessed using laser ablation lead (Pb) isotope analyses of single ice-rafted (>150 μm) feldspar grains. To track when an ice-rafting setting consistent with major NHG first occurred in the North Atlantic Ocean during the Pliocene intensification of NHG (iNHG), we investigate when the Pb-isotope composition (206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb) of feldspars deposited at DSDP Site 611 first resembles that determined for IRD deposited at this site during MIS 100 (2.52 Ma), the oldest glacial for which there exists convincing evidence for widespread glaciation of North America. Whilst Quaternary-magnitude IRD fluxes exist at Site 611 during glacials from 2.72 Ma, we find that the provenance of this IRD is not constant. Instead, we find that the Pb-isotope composition of IRD at our study site is not consistent with major NHG until MIS G2 (2.64 Ma). We hypothesise that IRD deposition in the North Atlantic Ocean prior to MIS G2 was dominated by iceberg calving from Greenland and Scandinavia. We further suggest that the grounding line of continental ice on Northeast America may not have extended onto the continental shelf and calved significant numbers of icebergs to the North Atlantic Ocean during glacials until 2.64 Ma.

Abrupt landscape change post–6 Ma on the central Great Plains, USA

The principal control on landscape evolution in the central Great Plains of the United States over the past 10 m.y. is a contentious subject. New sedimentary data collected from Late Miocene Ogallala Group and Pliocene Broadwater Formation of the Nebraskan Great Plains demonstrates a twofold increase in the median grain size (from 20 mm to >40 mm) exported from the Rocky Mountains across the Miocene-Pliocene boundary. Paleoslope reconstructions derived from these data support the tilting of the Miocene Ogallala Group after 6 Ma, but demonstrate that the transport slope of the lower part of the unconformably overlying Pliocene succession is identical to the present-day slope. These data allow us to constrain the timing of differential uplift in the Great Plains to between 6 and 3.7 m.y.; the wavelength and short duration of this tilting are best explained by the initiation of localized dynamic topography. Our results also suggest a threefold to fourfold increase in specific stream power at this time, meaning that Pliocene rivers draining the central Rockies were considerably more competent than their Miocene predecessors. Incision during this period was not continuous. A significant episode of aggradation from 3.7 to 2.5 Ma is best explained by high rates of sediment supply relating to the warm, wet mid-Pliocene climate optimum. The modern pattern of incision on the Great Plains occurred from 2.5 Ma, and not from the end of the Miocene as is sometimes supposed, reflecting the onset of major Northern Hemisphere glaciation.

Paleoceanographic significance of deep-sea benthic foraminiferal species diversity at southeastern Indian Ocean Hole 752A during the Neogene

Diversity parameters of Neogene deep-sea benthic foraminifera were measured at Ocean Drilling Program (ODP) Hole 752A, southeastern Indian Ocean (water depth of 1086.3m) using Information Function (H), Equitability (E), number of species (S) and Sander's rarefaction values. These parameters combined with population abundance of dominant benthic foraminifera (Bulimina macilenta, Nuttallides umbonifera, Cibicides wuellerstorfi, Cibicides lobatulus, Bolivina pusilla, Ehrenbergina carinata, Gavelinopsis lobatulus, Cassidulina laevigata, Globocassiulina subglobosa) reveal significant paleoceanographic changes in the southeastern Indian Ocean during the Neogene. The values of all the diversity parameters show a decrease from 25 to 23Ma and thereafter an increase with peak values at ~13.5Ma. The Late Oligocene to Earliest Miocene was an interval of more unstable conditions at Hole 752A dominated by species characteristic of low organic carbon, well-ventilated, carbonate corrosive high energy conditions. The highest values of diversity parameters coincide with the early Middle Miocene climatic optimum. All these parameters show a declining trend and gradual decrease from 13.5 to 4.5Ma coinciding with the major build up of ice sheets in the Antarctic region. Major increase in B. pusilla and E. carinata population during this time suggests high nutrient levels and low oxygen conditions at Hole 752A. This interval corresponds with the so-called “biogenic bloom” and an intense Oxygen Minimum Zone as observed throughout the Indo-Pacific region. Deep waters were warmer from 4.5 to 3Ma marked by an increase in species diversity values, coinciding with the early middle Pliocene warmth. The species diversity values abruptly decreased in the younger interval, contemporaneous with the major Northern Hemisphere glaciation. During this time species characteristics of high-energy bottom currents and relatively cold deep water were dominant.

Technical note: Late Pliocene age control and composite depths at ODP Site 982, revisited

Abstract. Ocean Drilling Program (ODP) Site 982 provided a key sediment section at Rockall Plateau for reconstructing northeast Atlantic paleoceanography and monitoring benthic δ18O stratigraphy over the late Pliocene to Quaternary onset of major Northern Hemisphere glaciation. A renewed hole-specific inspection of magnetostratigraphic reversals and the addition of epibenthic δ18O records for short Pliocene sections in holes 982A, B, and C, crossing core breaks in the δ18O record published for Hole 982B, now imply a major revision of composite core depths. After tuning to the orbitally tuned reference record LR04, the new composite δ18O record results in a hiatus, where the Kaena magnetic subchron might have been lost, and in a significant age reduction for all proxy records by 130 to 20 ky over the time span 3.2–2.7 million years ago (Ma). Our study demonstrates the general significance of reliable composite-depth scales and δ18O stratigraphies in ODP sediment records for generating ocean-wide correlations in paleoceanography. The new concept of age control makes the late Pliocene trends in SST (sea surface temperature) and atmospheric pCO2 at Site 982 more consistent with various paleoclimate trends published from elsewhere in the North Atlantic.

Clinker geochronology, the first glacial maximum, and landscape evolution in the northern Rockies

Clinker geochronology, the first glacial maximum, and landscape evolution in the northern Rockies

A well‐established Early–Middle Pleistocene marine sequence on south‐east Zakynthos island, western Greece: Magneto‐biostratigraphic constraints and palaeoclimatic implications

AbstractThe chronostratigraphy of a long, onshore Early–Middle Pleistocene marine sedimentary sequence on the south‐east part of Zakynthos island, Greece, is presented. Correlation of the succession with the isotope record of Ocean Drilling Program Site 963 reveals the combined influence of tectonics and eustacy in this area. The sequence is divided into three formations by two main unconformities that apparently relate to sea‐level lowstands associated with two major northern hemisphere glaciations, those of marine isotope stages (MIS) 22 and 12. The Zakynthos sequence in many ways is comparable with the Italian Valle di Manche section. Magnetostratigraphic and rock magnetic analyses, supported by biostratigraphy, document the position of the Matuyama/Brunhes Chron boundary (0.77 Ma), the top and base of the Jaramillo Subchron (0.99–1.07 Ma), the Cobb Mountain Subchron (1.173–1.185 Ma) and the top of the Olduvai Subchron (1.78 Ma). The underlying strata are constrained exclusively by detailed nannofossil biostratigraphy extending at least to the lowermost Pleistocene at around 2.54 Ma and therefore certainly incorporating the base of the Olduvai Subchron (1.95 Ma) and possibly the Gauss/Matuyama Chron boundary (2.58 Ma). In addition, a remarkable increase in sedimentation rate (from 3.2 and 28 cm ka−1 to 167 cm ka−1) and hence resolution above the Matuyama/Brunhes boundary (Middle Pleistocene) reveals one short‐lived magnetic excursion, possibly 17a (0.66 Ma), within the normal polarity Brunhes Chron. Copyright © 2011 John Wiley & Sons, Ltd.