Integrated stratigraphy of the Waitakian-Otaian Stage boundary stratotype, Early Miocene, New Zealand

The base of the type section of the Otaian Stage at Bluecliffs, South Canterbury, is recognised as the stratotype for the boundary between the Waitakian and Otaian Stages. Principal problems with the boundary are the restriction of existing bioevent proxies to shelf and upper slope environments and its uncertain age. These topics are addressed by a multidisplinary study of a 125 m section about the boundary, which examines its lithostratigraphy, depositional setting, biostratigraphy, correlation, and geochronology. The lower siltstone lithofacies (0-38.5 m) was deposited at upper bathyal depths (200-600 m) in a marginal basin which was partially sheltered from fully oceanic circulation by a submarine high and islands. The site was covered by cool-temperate water and was probably adjacent to the Subtropical Convergence. This unit is succeeded by the banded lithofacies (38.5-106 m) and the upper siltstone lithofacies (basal 19 m studied). Paleodepth probably declined up-sequence, but deposition at shelf depths is not definitely indicated. A cyclic pattern of abundance spikes in benthic and planktonic foraminifera commences 9 m above base and extends to 73 m in the banded lithofacies. Oxygen isotope excursions (up to 2.08%) in Euuvigerina miozea and Cibicides novozelandicus are greatest within the interval containing the abundance spikes. The stage boundary occurs in the banded lithofacies at the highest abundance spike (73 m). Although condensed intervals might affect the completeness of the section, they are not associated with sedimentary discontinuities, and we consider that the section is suitable as a biostratigraphic reference. Spores, pollens, dinoflagellates, calcareous nannofossils, foraminifera, bryozoans, and ostracods are preserved near the boundary, but molluscs principally occur higher, in the shallower upper siltstone lithofacies. Siliceous microfossils are rare. There is considerable scope for further biostratigraphic research. The primary event marking the boundary at 73 m is the appearance of the benthic foraminifer Ehrenbergina marwicki. This is a distinctive and widely distributed event but is restricted to shelf and upper bathyal environments. Supplementary events in planktonic foraminifera and calcareous nannofossils were researched. Highest occurrences of Globigerina brazieri and G. euapertura are recorded at 47 and 58 m. There is a marked decline in relative abundance of Paragloborotalia spp. at 62 m. Helicosphaera carteri becomes more abundant than H. euphratis between 56 and 87 m. These events are not exact proxies for the boundary but they may usefully indicate proximity to it. They occur in the interval of prominent spikes in foraminiferal abundance. The Waitakian-Otaian boundary is dated at 21.7 Ma by strontium isotopes. Stable primary remanence could not be determined in a pilot paleomagnetic study of Bluecliffs specimens. However, specimens trended towards reversed polarity, and remagnetisation great circle analysis will allow directions to be calculated in future collections

Environmental Forcings of Paleogene Southern Ocean Dinoflagellate Biogeography

Despite warm polar climates and low meridional temperature gradients, a number of different high-latitude plankton assemblages were, to varying extents, dominated by endemic species during most of the Paleogene. To better understand the evolution of Paleogene plankton endemism in the high southern latitudes, we investigate the spatiotemporal distribution of the fossil remains of dinoflagellates, i.e., organic-walled cysts (dinocysts), and their response to changes in regional sea surface temperature (SST). We show that Paleocene and early Eocene (∼65–50 Ma) Southern Ocean dinocyst assemblages were largely cosmopolitan in nature but that a distinct switch from cosmopolitan-dominated to endemic-dominated assemblages (the so-called “transantarctic flora”) occurred around the early-middle Eocene boundary (∼50 Ma). The spatial distribution and relative abundance patterns of this transantarctic flora correspond well with surface water circulation patterns as reconstructed through general circulation model experiments throughout the Eocene. We quantitatively compare dinocyst assemblages with previously published TEX86–based SST reconstructions through the early and middle Eocene from a key locality in the southwest Pacific Ocean, ODP Leg 189 Site 1172 on the East Tasman Plateau. We conclude that the middle Eocene onset of the proliferation of the transantarctic flora is not linearly correlated with regional SST records and that only after the transantarctic flora became fully established later in the middle Eocene, possibly triggered by large-scale changes in surface-ocean nutrient availability, were abundances of endemic dinocysts modulated by regional SST variations

Miocene foraminifera from the Finniss Clay and Cadell Marl, western Murray Basin: taxonomic and taphonomic contrasts and their environmental significance.

Sandwiched between Miocene limestones of the Mannum Formation and Morgan Limestone in the western Murray Basin, the Finniss Clay and Cadell Marl contain different foraminiferal faunas with varying taphonomic grades. At the Mannum Pumping Station section, the Finniss Clay fauna has a low diversity, frequent shallow-water forms, and a poor taphonomic grade. In what was the deeper part of the basin at Waikerie, a diverse fauna with well-preserved small species is recorded in sediments equivalent to the Finniss Clay. In contrast, the Cadell Marl from various localities comprises a well-preserved and diverse biofacies with both shallow and deeper water taxa. These contrasts suggest different depositional environments: shallower and warm during deposition of the Finniss Clay and nutrient-rich, dysaerobic and deeper water during deposition of the Cadell Marl. The shallowing event indicated by faunas from the Finniss Clay was due to falling sea level close to the early/middle Miocene boundary, whereas the Cadell fauna appears to reflect the global carbon buildup at the peak of the Monterey carbon excursion during the Miocene climatic optimum, about 16 million years ago. © 1999 Association of Australasian Palaeontologists.Li, Qianyu McGowran, Bria

Climatically driven macroevolutionary patterns in the size of marine diatoms over the Cenozoic

Numerous taxonomic groups exhibit an evolutionary trajectory in cell or body size. The size structure of marine phytoplankton communities strongly affects food web structure and organic carbon export into the ocean interior, yet macroevolutionary patterns in the size structure of phytoplankton communities have not been previously investigated. We constructed a database of the size of the silica frustule of the dominant fossilized marine planktonic diatom species over the Cenozoic. We found that the minimum and maximum sizes of the diatom frustule have expanded in concert with increasing species diversity. In contrast, the mean area of the diatom frustule is highly correlated with oceanic temperature gradients inferred from the δ(18)O of foraminiferal calcite, consistent with the hypothesis that climatically induced changes in oceanic mixing have altered nutrient availability in the euphotic zone and driven macroevolutionary shifts in the size of marine pelagic diatoms through the Cenozoic

Cenozoic environmenal shifts and foraminiferal evolution

The dense record of Cenozoic foraminifera simultaneously supplies a mosaic of biostratigraphy, a rich field for evolutionary studies and the vehicles for geochemical environmental proxies. Four groups are discussed: the larger foraminifera on the warm-water shelves and platforms, the planktonics, the deep-sea faunas and the southern-extratropical benthics. The environmental trajectory from greenhouse in the later Cretaceous and earlier Paleogene to icehouse in the Neogene is not smooth but punctuated, and there are two particularly critical intervals, later Eocene and early-middle Miocene. The foraminiferal record is not smooth but chunky at 107 years’ scale. There are several good examples of two powerful synchroneities, one being between the faunas of the different realms and the other between the fossil record and the physical-environmental record.Brian McGowra

Cenozoic stratigraphic succession in southeastern Australia

Strata of Cenozolc age occur around the southern margin of Australia as thin and discontinuous outcrops, interpolated and fleshed out by economic exploration onshore and offshore. The neritic strata fall into four sequences or allostratigraphic packages of (I) Paleocene - Early Eocene, (II) Middle Eocene - Early Oligocene, (III) Late Oligocene - Middle Miocene, and (IV) Late Miocene - Holocene age: A four-part pattern that can be seen also in the flanking pelagic and terrestrial realms including regolith deep weathering. Problems of correlation and age determination (predominantly biostratigraphic) have included biogeographical constraints (endemism in neritic molluscs and terrestrial palynomorphs, mid-latitude assemblages in calcareous plankton), and slow progress in magnetostratigraphy and chemostratigraphy. Sequence I largely repeats the Cretaceous siliciclastic-coal, marginal-marine facies (carbonate-poor, with marine and non-marine palynomorphs and agglutinated foraminifers) punctuated by marine Ingressions with microfaunas and sparse macrofaunas, Sequence II contains the first carbonates in the region since the Palaeozoic and the most extensive coals of the Cenozoic anywhere. Sequence III contains the most extensive neritic carbonates and the lost major coals. Sequence IV is more strongly siliciclastic than the two preceding. Each of these four second-order entities (107 years duration) comprises third-order packages each with an unconformity and marine transgression. These packages hold true right along the southern Australian margin in the sense that the hiatuses and transgression do not display significant diachroneity at the relevant timescales (105-106 years). Recognised, delimited and correlated independently of the putatively global Exxon sequences, they are remarkably consistent with the latter, thereby providing a significant regional test. There are two widespread emphases on southern Australian geohistory and biohistory: (1 to regard the regional story as part of the global story of accreting continents, an expiring Tethys, and an episodically cooling planet, and (II) a somewhat contrary emphasis, with the region being a special case of rapid longitudinal motion towards the equator. Both emphases are plausible with the former being the more heuristic. The stratigraphic record is strongly punctuated, the four sequences being separated by both tectonic and climatic events. Thus: the sequence I/II gap involved extensive plate-tectonic reorganisation and a new spreading regime from cc 43 Ma, coevally with early growth of Antarctic ice, in the II/III gap, deformation in marginal basins is coeval with a global low in cooling, large ice sheet and falling sea-level to ca 30 Ma; and the III/IV gap is marked by widespread cessation or contraction of stratal accumulation and withdrawal of thermophilic taxa coevally with the major expansion at ca 14 Ma of the Antarctic ice sheet, onset of intense canyon cutting, and plate-wide basin inversion