Michael J. Hannah

Orbitally induced oscillations in the East Antarctic ice sheet at the Oligocene/Miocene boundary

Between 34 and 15 million years (Myr) ago, when planetary temperatures were 3–4 °C warmer than at present and atmospheric CO2 concentrations were twice as high as today, the Antarctic ice sheets may have been unstable. Oxygen isotope records from deep-sea sediment cores suggest that during this time fluctuations in global temperatures and high-latitude continental ice volumes were influenced by orbital cycles. But it has hitherto not been possible to calibrate the inferred changes in ice volume with direct evidence for oscillations of the Antarctic ice sheets. Here we present sediment data from shallow marine cores in the western Ross Sea that exhibit well dated cyclic variations, and which link the extent of the East Antarctic ice sheet directly to orbital cycles during the Oligocene/Miocene transition (24.1–23.7 Myr ago). Three rapidly deposited glacimarine sequences are constrained to a period of less than 450 kyr by our age model, suggesting that orbital influences at the frequencies of obliquity (40 kyr) and eccentricity (125 kyr) controlled the oscillations of the ice margin at that time. An erosional hiatus covering 250 kyr provides direct evidence for a major episode of global cooling and ice-sheet expansion about 23.7 Myr ago, which had previously been inferred from oxygen isotope data (Mi1 event).

Palynomorphs from a sediment core reveal a sudden remarkably warm Antarctica during the middle Miocene

An exceptional triple palynological signal (unusually high abundance of marine, freshwater, and terrestrial palynomorphs) recovered from a core collected during the 2007 ANDRILL (Antarctic geologic drilling program) campaign in the Ross Sea, Antarctica, provides constraints for the Middle Miocene Climatic Optimum. Compared to elsewhere in the core, this signal comprises a 2000-fold increase in two species of dinoflagellate cysts, a synchronous five-fold increase in freshwater algae, and up to an 80-fold increase in terrestrial pollen, including a proliferation of woody plants. Together, these shifts in the palynological assemblages ca. 15.7 Ma ago represent a relatively short period of time during which Antarctica became abruptly much warmer. Land temperatures reached 10 °C (January mean), estimated annual sea-surface temperatures ranged from 0 to 11.5 °C, and increased freshwater input lowered the salinity during a short period of sea-ice reduction.

Identification and independence: morphometrics of Cenozoic New Zealand Spissatella and Eucrassatella (Bivalvia, Crassatellidae)

Abstract Fossil bivalve shells are well-suited for landmark/semilandmark morphometric analysis because they preserve both traces of the internal anatomy and the whole shell outline. Utilizing landmarks and semilandmarks, we have characterized internal and external shape variation in a monophyletic clade of Cenozoic New Zealand and Australian crassatellid bivalves, to test the contiguity in morphospace of species-level taxa and to quantitatively examine the “Concept of Independent Entities” of Yonge (1953). Thirteen species from two genera (Spissatella Finlay 1926 and Eucrassatella Iredale 1924) are investigated. Spissatella n. sp. C is confirmed as forming a contiguous group separate to S. trailli and S. clifdenensis. Shell outline and internal anatomy are found to covary in shape, refuting the “Concept of Independent Entities” in the study group.

Dinoflagellate biostratigraphy of the vertebrate fossil-bearing Maungataniwha Sandstone, northwest Hawke's Bay, New Zealand

Abstract Fossil organic-walled dinoflagellate cysts (dinocysts) have been used to constrain the age of the Maungataniwha Sandstone and associated phosphatic and calcareous concretions from the Mangahouanga Stream, northwest Hawkes Bay, New Zealand. These concretions often contain dinosaur and marine reptile fossils, including the mosasaur Moanasaurus mangahouangae, first discovered within the study area in a calcareous concretion. The Maungataniwha Sandstone contains low to moderately diverse dinocyst assemblages corresponding to the Vozzhennikovia spinulosa – Isabelidinium pellucidum zonal interval (lower to upper Haumurian). Recovered dinocyst assemblages from in situ concretions are similar to those from the surrounding sediments, suggesting that the concretions have grown in place. Calcareous float concretions containing the mosasaur Moanasaurus mangahouangae, as well as the two phosphatic concretions (one of which also contained a mosasaur fossil), are all of a lower Haumurian age. Plesiosaur fossil-bearing calcareous concretions exhibit a range of ages from lower to upper Haumurian (early Campanian to early Maastrichtian), spanning the age range of the Maungataniwha Sandstone section within the study area. The two dinosaur fossil-bearing calcareous concretions can only be dated as no younger than the middle upper Haumurian (early Maastrichtian).

The Taxonomy and Palaeobiogeography of Small Chorate Dinoflagellate Cysts from the Late Cretaceous to Quaternary of Antarctica

Small chorate dinoflagellate cysts are common in Upper Cretaceous to Quaternary sedimentary successions around the Antarctic margin. Taxonomic confusion surrounding dinoflagellate cysts and acritarchs of similar morphology throughout the southern high palaeolatitudes has hitherto limited investigation of their palaeoecological significance. This study aims to solve the taxonomic problems, and to allow a new assessment of dinoflagellate cyst acmes. A detailed morphological study of new material from the López de Bertodano Formation of Seymour Island, Antarctic Peninsula, is presented. These dinoflagellate cysts are identified as Impletosphaeridium clavus Wrenn & Hart 1988 emend. nov. Their gross morphology and their vast abundances in the James Ross Basin are strongly suggestive of dinoflagellate blooms. This scenario implies similarities to modern dinoflagellate cysts from the polar regions.

Torlessia mackayi and other foraminifera from the Torlesse Terrane, New Zealand

Abstract Fossils recovered from the Rolleston Range, Canterbury, are identified as belonging to the foraminiferal genus Hormosina. Comparison of the wall structure of these Hormosina and the common tube fossil Torlessia mackayi suggest that this too is a foraminifer rather than an annelid. Confirmation of this comes primarily from the discovery of several hundred specimens of T. mackayi in an outcrop near Sinclair Head, southwest Wellington. This has allowed a relatively broad range of variation within T. mackayi to be appreciated. A close comparison of this population with the foraminiferal genus Bathysiphon reveals that the two forms are almost identical. However, the presence of longitudinal striations on T. mackayi is sufficient to preclude incorporation of this species within Bathysiphon. Hence, the genus Torlessia is here transferred to the foraminiferal family Bathysiphonidae Avnimelech, 1952.

An occurrence of the tube fossil Torlessia mackayi Bather, 1906 from southwest Wellington, New Zealand

Abstract An outcrop of Upper Triassic Torlesse strata containing a spectacular occurrence of Torlessia mackayi Bather is documented from near Sinclair Head, southwest Wellington. Hundreds of well‐preserved specimens of this fossil, many of them large and complete, occur on some 10 m2 of a single bedding plane. Complete specimens range 30–70 mm in length, have medium to strong curvature, and are now flattened, although reconstructions suggest that the original form was tubular with diameters of 1.0–1.3 mm. The tube surface is ornamented with longitudinal striae. Some areas of the outcrop show prominent ripple marks, and the tubes of T. mackayi are aligned subparallel to the ripple crests, indicating postmortem transport from a nearby dense grouping of the organisms.

Anchors and snorkels: heterochrony, development and form in functionally constrained fossil crassatellid bivalves

Abstract. New growth rate estimates for nine species from three genera of New Zealand Crassatellidae (Mollusca: Bivalvia), combined with existing morphometric ontogenetic descriptions, allow identification of heterochronic processes in the evolution of these genera. Both paedomorphosis (progenesis and neoteny) and peramorphosis (hypermorphosis and acceleration) have occurred within the clade. Overall, morphological variability and response to environmental pressure in this nonsiphonate group is restricted by the interplay of anatomical and life habit constraints. Stability in the substrate, predator avoidance, sluggish burrowing speed, and inability to escape by deep burial are suggested as key drivers of, or constraints on, morphological change. Two groups of shell characters are identified: heavy, armored “anchors” and elongate “snorkels,” which combine juvenile and adult traits in shells of different sizes and ages, produced by heterochronic variation in developmental timing. Anchors and snorkels both represent different “solutions” to the problems of life as a nonsiphonate, infaunal bivalve.

Evolutionary Transition in the Late Neogene Planktonic Foraminiferal Genus Truncorotalia

Summary The fossil record provides empirical patterns of morphological change through time and is central to the study of the tempo and mode of evolution. Here we apply likelihood-based time-series analyses to the near-continuous fossil record of Neogene planktonic foraminifera and reveal a morphological shift along the Truncorotalia lineage. Based on a geometric morphometric dataset of 1,459 specimens, spanning 5.9–4.5 Ma, we recover a shift in the mode of evolution from a disparate latest Miocene morphospace to a highly constrained early Pliocene morphospace. Our recovered dynamics are consistent with those stipulated by Simpsons quantum evolution and Eldredge-Goulds punctuated equilibria and supports previous suppositions that even within a single lineage, evolutionary dynamics require a multi-parameter model framework to describe. We show that foraminiferal lineages are not necessarily gradual and can experience significant and rapid transitions along their evolutionary trajectories and reaffirm the utility of multivariate datasets for their future research.

New stratigraphic constraints on the late Miocene–early Pliocene tectonic development of the Aorangi Range, Wairarapa

ABSTRACT A revised stratigraphy is presented for the late Miocene–early Pliocene sedimentary rocks of the northern Aorangi Range, Wairarapa. Despite major differences in lithology, the Clay Creek Limestone and Bells Creek Mudstone are shown to be partially coeval, while the overlying Makara Greensand is shown to be a diachronous unit that ranges from late Miocene (Kapitean) to early Pliocene (Opoitian) age. This revised stratigraphy raises questions about the current classification of the Palliser and Onoke groups, and provides new insights into regional geological history. Previous seismic imaging studies have identified an episode of accelerated crustal shortening and deformation in the Wairarapa region near the Miocene–Pliocene boundary. The Clay Creek Limestone has proven to be a useful marker horizon for constraining the timing and style of this deformational episode, which is interpreted to have occurred prior to 7.2 Ma.