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Paleoseismology has been making an important contribution to understanding the Alpine Fault and the hazard it poses to society. However, evidence of past earthquakes comes from a wide variety of sources and publication of the evidence has been somewhat fragmented. Here, we review physical evidence for past large to great earthquakes on the Alpine Fault to summarise current understanding, illustrate progress and highlight future directions. Paleoseismic evidence has been derived from tree disturbance, landscape features and trenches across the fault. These records have been supplemented and extended back in time with sedimentary evidence of Alpine Fault earthquakes from fault-proximal lakes and wetlands. In this review, we update radiocarbon analyses using recent calibration curves and modern Bayesian statistical methods where necessary to enable comparison between on-fault, fault-proximal and off-fault earthquake records. Over recent decades, Alpine Fault paleoseismology has progressed from playing an important role in demonstrating that large surface-rupturing earthquakes occur, to enabling estimates of earthquake recurrence behaviour, shaking intensities, rupture extents, landscape response durations and likelihood of the next earthquake. [ABSTRACT FROM AUTHOR]

Investigations of modern coseismic ground surface deformation where fault rupture is absent typically rely on remote sensing techniques. We used monitoring of salt marsh vegetation and substrate for 3 years after the 22 February 2011 Christchurch earthquake (MW 6.2) to document the biological response to vertical deformation, to provide estimates of the amount of uplift and subsidence and ground-truth remote sensing data. Comparison of vegetation-derived vertical deformation with estimates from remote-sensing techniques (Light Detection and Ranging, Global Positioning System and Differential Interferometric Synthetic Aperture Radar) shows good agreement at sites where several decimetres of vertical movement occurred, and less agreement where smaller amounts of vertical movement occurred and/or where vegetation-monitoring sites were affected by differential movement of artificial structures such as roads and breakwaters. Biological and sedimentological changes observed in salt marshes around the Avon–Heathcote Estuary/Ihutai (AHEI) as a result of the 22 February 2011 Christchurch earthquake are likely to be preserved as subtle geological signatures in restricted locations around the AHEI. [ABSTRACT FROM AUTHOR]

The Hikurangi subduction margin, where the Pacific Plate subducts beneath the North Island of New Zealand, poses a major seismic and tsunami hazard to the New Zealand region, but its seismic and tsunami potential is largely unknown because of New Zealand's short (< 170 years) historical record of seismicity. This article discusses the implications of results from GPS, paleoseismology, and tsunami modeling studies for understanding Hikurangi subduction earthquake and tsunami potential. Paleoseismic and geodetic data indicate that earthquakes of MW 8.0 and larger are certainly plausible at the Hikurangi margin. Paleoseismic evidence for large megathrust earthquakes beneath Hawke Bay in central Hikurangi demonstrates that large seismic slip may occur within an area that currently slips in episodic slow slip events. This result has important implications for seismic hazards at subduction margins elsewhere. Strong similarities between the subduction zones of the Hikurangi margin and the Japan Trench suggest that a giant MW 9.0 earthquake similar to the 2011 Tohoku-Oki earthquake may be possible for the Hikurangi margin. Such an event would generate a large tsunami that would inundate much of the east coast of the North Island. Understanding of the earthquake potential of the Hikurangi megathrust is only in its infancy, and we recommend a number of studies to increase knowledge. [ABSTRACT FROM AUTHOR]

The scarcity of long geological records of major earthquakes, on different types of faults, makes testing hypotheses of regular versus random or clustered earthquake recurrence behavior difficult. We provide a fault-proximal major earthquake record spanning 8000 years on the strike-slip Alpine Fault in New Zealand. Cyclic stratigraphy at Hokuri Creek suggests that the fault ruptured to the surface 24 times, and event ages yield a 0.33 coefficient of variation in recurrence interval. We associate this near-regular earthquake recurrence with a geometrically simple strike-slip fault, with high slip rate, accommodating a high proportion of plate boundary motion that works in isolation from other faults. We propose that it is valid to apply time-dependent earthquake recurrence models for seismic hazard estimation to similar faults worldwide. [ABSTRACT FROM AUTHOR]

Abstract: A high-resolution record of lacustrine environments spanning ca. 30–9calkaBP was obtained from Onepoto maar, northern North Island, New Zealand. The multi-proxy record of environmental change is constrained by tephrochronology and AMS 14C ages and provides evidence for episodes of rapid environmental change during the Last Glacial Coldest Period (LGCP: 28.5–18calkaBP) and Late Glacial–Interglacial Transition (LGIT) from northern New Zealand. The Onepoto pollen record indicates that the LGCP was cold, dry and windy in the Auckland region with vegetation dominated by herbs and grasses in a beech forest mosaic. At the same time the diatom record indicates oligotrophic conditions with low lakes levels and turbulence whilst cladocerans indicate low water temperatures. The inference of cold, dry and windy conditions during the LGCP is supported by geochemical evidence for increased sediment influx, charcoal and CO2 limiting conditions for terrestrial macrophytes. Rapid climate amelioration and forest expansion after ca. 18calkaBP corresponds with reduced sediment influx, diatom and cladoceran-inferred higher lake levels indicating increasing moisture availability and temperature. Diatom flora indicates that an oligotrophic, circumneutral lake was becoming established during the LGIT but conditions were still variable. Between ca. 13.8 and 12.5calkaBP two brief drier and possibly cooler episodes are apparent (ca. 13.8–13.2 and 13–12.5calkaBP) followed by a warm phase combined with generally stable high lake levels between ca. 12.5 and 10.5calkaBP. Subsequently the lake water chemistry became more alkaline and eutrophic, possibly because sea level had risen high enough by this time to influence ground water chemistry. [Copyright &y& Elsevier]

Stratigraphic investigations of three coastal waterbodies in southeastern Tasmania reveal major paleoenvironmental phases related to sea level change and anomalous deposits consistent with tsunami inundation. Twenty-two short sediment cores were examined for their sedimentology and fossil diatom, foraminifera and macrofossil assemblages; nine radiocarbon ages were obtained. Despite diverse Holocene histories at each site, four common phases of Holocene paleoenvironmental evolution can be distinguished. In Phase I (pre-8000 yr BP) terrestrial environments existed. During Phase II (8000–6500 yr BP) ponded freshwater environments formed behind transgressive coastal barriers. In Phase III (6500–2000 yr BP) the sites were subject to varying degrees of marine influence, resulting in environments ranging from current-swept tidal inlets to sheltered brackish-marine lagoons. In Phase IV (2000 yr BP to present) there was a decrease in marine influence, one site changed to a freshwater wetland environment while the other two changed to ephemeral salt pans. This study suggests that postglacial sea level rise culminated after c. 7300 cal. yr BP in southeastern Tasmania and that there was probably a late-Holocene fall in sea level. These paleoenvironmental histories provide a framework within which to identify anomalous deposits and assess them for likely causes. Five anomalous deposits are identified, three of which are considered likely to have been deposited by tsunami occurring at c. 4000 cal. yr BP, c. 2000 cal. yr BP and <2000 cal. yr BP, although deposition by large storms cannot be ruled out. [ABSTRACT FROM AUTHOR]

Abstract: Diatom microfossils preserved in 38 core top samples from offshore of eastern New Zealand are examined to develop the first offshore modern analogue dataset for diatoms in New Zealand waters. The sample set consists of seven, approximately E–W trending depth transects with samples from the continental shelf, slope and abyssal plain between latitudes 33° and 54°S. The identification of terrestrial and coastal species in open marine core top samples indicates that offshore transport of diatom microfossils occurs to an extent that could be useful for sediment provenance studies or at least to enable improved identification of transported versus in-situ deposition on the continental shelf. Cluster analysis and ordination indicate that the Chatham Rise and/or the overlying Subtropical Front are the most significant bathymetric/oceanographic features in the dataset as this location shows up as a major barrier or transition zone in terms of diatom distribution. The strongest environmental control on diatom distribution is the north–south sea surface temperature gradient. A statistically strong relationship (r 2 =0.81; RMSEP=1.57) exists between diatom abundance and sea surface temperature making diatoms ideal for quantitative reconstruction of past sea surface temperatures in future paleoclimate studies. [Copyright &y& Elsevier]

Abstract: Paleoenvironmental reconstructions of three coastal waterbodies in Wellington, New Zealand, reveal that sites were isolated from the sea within the last 7500 years through coseismic uplift and barrier growth. Evidence for coseismic uplift consists of distinct transitions in diatom assemblages representing large changes in relative sea-level or water-table level, commonly in association with sedimentological evidence for catchment disturbance or marine influx. Transitions are abrupt, laterally extensive and synchronous within each waterbody. Amount of change across transition horizons is assessed using quantitative estimates of paleosalinity and waterbody type as proxies for relative sea-level change. Seven transitions involve large paleoenvironmental changes and provide evidence for earthquakes occurring at approximately 5100, 3200 (recorded at two sites), 2300 (recorded at two sites), 1000cal years BP and 1855AD. Five other transitions involve smaller paleoenvironmental changes and are considered to be consistent with effects of earthquakes but do not provide independent evidence for earthquake occurrence. These smaller transitions occur at approximately 6800, 3600, 2200, 1000 (coincident with a large transition) and 500cal years BP. The data refine ages and provide information about the extent and effects of past large earthquakes in the region. These are the first paleoecologically derived earthquake signatures for Wellington and they contribute to the sparse collection worldwide of off-fault sedimentary earthquake records for predominantly strike-slip faults. [Copyright &y& Elsevier]

Fossil foraminifera and diatoms are used to identify sudden, probably earthquake-related, elevational changes in three Holocene sedimentary sequences from the high-tidal fringes of Ohiwa Harbour, eastern Bay of Plenty, New Zealand. Modern analogue calibration sets of faunal and floral census data are used to estimate palaeosalinities and palaeotidal elevations that help quantify seismic-related, vertical displacements. Age models for the three vibracored sequences are built on a combination of tephrostratigraphy and radiocarbon dating.A new index, the land elevation record (LER), is introduced to graphically portray earthquake-related vertical land displacements on a time-depth diagram. Also plotted are elements used to calculate LER, such as the indicative depth estimated from microfossils, inferred sediment compaction, and the New Zealand Holocene palaeo-sea-level curve.All three Ohiwa cores, spread over 3 km of coast, contain both freshwater and intertidal sediments. A prominent erosional contact between freshwater peat or soil and overlying intertidal mud, records a major subsidence event in each core of c. 2 m, dated at ca 2600 cal years BP. The deepest core (7.4 m) indicates that this is the only substantial vertical displacement event to have occurred in the last 8 ka. A small subsidence event (ca 0.3–0.7 m) is indicated close to the top of one core, but is not present in the other two sites. This may be the result of a local land subsidence during the poorly known Taneatua Earthquake of 1866.There is no historic human record of earthquake displacements around Ohiwa, but mid-Pleistocene, interglacial, marine sediments have been uplifted 10–60 m in several identified fault blocks. Our study provides conclusive evidence of at least 2 m of earthquake-related, subsidence during the Holocene, with a recurrence time of major earthquakes of ca 5 ka. [Copyright &y& Elsevier]

At Table Cape, Mahia Peninsula, North Island, New Zealand, four marine terraces have been uplifted coseismically during the past 3500 years. Detailed facies assessment of the terrace coverbed sequence coupled with identification of modern analogues on the active shore platform were used to infer the process of marine terrace formation and to estimate the timing and amount of past uplift events (earthquakes). The modern platform can be subdivided into seven depositional zones: subtidal, outer platform, intertidal sand pockets, inner platform, high-tide, mid-storm, and storm beach. Terrace coverbeds were characterised from two trenches excavated across the full width of the uplifted terrace sequence. Off-lapping packages of high tidal, mid-storm, and storm beach sediments were most common. Outer platform sediments occurred only rarely near the base of some uplifted shore platforms. Overlying the marine sediments were near-horizontal terrestrial deposits of airfall tephra (on the two highest terraces), subsoil, topsoil, rare wedges of colluvial sediment (slopewash) shed from terrace risers, and an anomalous deposit possibly emplaced by a tsunami. Fifty-one radiocarbon ages, obtained from molluscs in the marine coverbeds, showed a general pattern of seaward-younging across the coastal plain and across each terrace and a less pronounced pattern of decreasing age upward in each coverbed sequence. The distinctive stepped geomorphology of the terraces, the facies and age structure of the terrace deposits and historical earthquake causation of similar terraces elsewhere in New Zealand provided the data to invoke an earthquake-driven model for terrace formation. Marine terrace development following an uplift event involved rapid cutting of a new intertidal shore platform and generally regressive deposition of high-tide to storm beach deposits. Following further uplift, the platform became a geomorphic terrace (above marine influence) and was then mantled by terrestrial sediments. On the two highest terraces at Table Cape, airfall tephras mantling the marine coverbeds provided a minimum age for terrace uplift. The youngest radiocarbon ages from high-tide deposits high in the stratigraphy and near the seaward edge of each terrace provided the best estimates for the timing of uplift. Based on the new radiocarbon ages and the constraining airfall tephra ages, we revised the earthquake ages to 3530–3350, 1810–1730, 1560–1300 and 300–100 cal. YBP. Associated best estimates of the coseismic uplift amounts were 2.1, 1.4, 1.8, and 3.1 m respectively, once we accounted for eustatic sea level changes through the late Holocene. [ABSTRACT FROM AUTHOR]

Abstract: A sequence of fluvio-estuarine sediments exposed beneath the highest Holocene marine terrace at Pakarae, North Island, New Zealand, records the early-mid Holocene infilling of the Pakarae valley. This sequence was developed on an active, coseismically uplifting coastline and provides a valuable comparison to widely used facies models for estuaries, which were developed exclusively from stable coastal settings. We describe eight sedimentary sections, distributed along a 220 m stretch of riverbank and present twelve new radiocarbon ages. Sedimentology and benthic foraminifera are used to divide the sequence into eight bio-lithofacies. These units are grouped into four paleoenvironmental facies associations: barrier, estuarine, estuary-head delta and floodplain. We compare the distribution of the Pakarae paleoenvironmental facies associations to those in models of incised valley infill sequence models and case studies of infilled valleys. These data allow us to present new contributions to the development of a facies model for the sedimentary infilling of an incised valley system that was experiencing coseismic uplift synchronous with deposition. We suggest the distinctive characteristics of such a model would include (1) part, or all, of the transgressive and lowstand sequences may now lie above modern sea level, (2) the transgressive sedimentary sequence is typically condensed relative to the coeval amount of eustatic sea level (SL) rise that occurred during that period, and (3) evidence of relative SL falls, such as transitions from estuarine to fluvial environments, despite conditions of rapid and continuous eustatic SL rise. [Copyright &y& Elsevier]

Abstract: The coastal geomorphology of the northeastern Raukumara Peninsula, New Zealand, is examined with the aim of determining the mechanisms of Holocene coastal uplift. Elevation and coverbed stratigraphic data from previously interpreted coseismic marine terraces at Horoera and Waipapa indicate that, despite the surface morphology, there is no evidence that these terraces are of marine or coseismic origin. Early Holocene transgressive marine deposits at Hicks Bay indicate significant differences between the thickness of preserved intertidal infill sediments and the amount of space created by eustatic sea level rise, therefore uplift did occur during early Holocene evolution of the estuary. The palaeoecology and stratigraphy of the sequence shows no evidence of sudden land elevation changes. Beach ridge sequences at Te Araroa slope gradually toward the present day coast with no evidence of coseismic steps. The evolution of the beach ridges was probably controlled by sediment supply in the context of a background continuous uplift rate. No individual dataset uniquely resolves the uplift mechanism. However, from the integration of all evidence we conclude that Holocene coastal uplift of this region has been driven by a gradual, aseismic mechanism. An important implication of this is that tectonic uplift mechanisms do vary along the East Coast of the North Island. This contrasts with conclusions of previous studies, which have inferred Holocene coastal uplift along the length of the margin was achieved by coseismic events. This is the first global example of aseismic processes accommodating uplift at rates of >1mmyr−1 adjacent to a subduction zone and it provides a valuable comparison to subduction zones dominated by great earthquakes. [Copyright &y& Elsevier]

The Hikurangi subduction margin, New Zealand, has not produced large subduction earthquakes within the short written historic period (~180 years) and the potential of the plate interface to host large (M > 7) to great (M > 8) earthquakes and tsunamis is poorly constrained. The geological record of past subduction earthquakes offers a method for assessing the location, frequency and approximate magnitude of subduction earthquakes to underpin seismic and tsunami hazard assessments. We review evidence of Holocene coseismic coastal deformation and tsunamis at 22 locations along the margin. A consistent approach to radiocarbon age modelling is used and earthquake and tsunami evidence is ranked using a systematic assessment of the quality of age control and the certainty that the event in question is an earthquake. To identify possible subduction earthquakes, we use temporal correlation of earthquakes, combined with the type of earthquake evidence, likely primary fault source and the earthquake certainty ranking. We identify 10 past possible subduction earthquakes over the past 7000 years along the Hikurangi margin. The last subduction earthquake occurred at 520–470 years BP in the southern Hikurangi margin and the strongest evidence for a full margin rupture is at 870–815 years BP. There are no apparent persistent rupture patches, suggesting segmentation of the margin is not strong. In the southern margin, the type of geological deformation preserved generally matches that expected due to rupture of the interseismically locked portion of the subduction interface but the southern termination of past subduction ruptures remains unresolved. The pattern of geological deformation on the central margin suggests that the region of the interface that currently hosts slow slip events also undergoes rupture in large earthquakes, demonstrating different modes of slip behaviour occur on the central Hikurangi margin. Evidence for subduction earthquakes on the northern margin has not been identified because deformation signals from upper plate faults dominate the geological record. Large uncertainties remain in regard to evidence of past subduction earthquakes on the Hikurangi margin, with the greatest challenges presented by temporal correlation of earthquake evidence when working within the uncertainties of radiocarbon ages, and the presence of upper plate faults capable of producing deformation and tsunamis similar to that expected for subduction earthquakes. However, areas of priority research such as improving the paleotsunami record and integration of submarine turbidite records should produce significant advances in the future. • We review - past coseismic coastal deformation on the Hikurangi subduction margin. • Along-margin temporal correlations are used to identify past subduction earthquakes. • Upper plate faults introduce uncertainty in earthquake source interpretation. • We identify ten possible subduction earthquakes in the past 7000 years. [ABSTRACT FROM AUTHOR]

Sudden changes in microfossils and lithologies in Holocene sediments of a former tidal inlet on the Hikurangi subduction margin provide evidence of 10 large earthquakes. Studies were focused in three former embayments where intertidal shelly sediment interfingers with freshwater and salt-marsh peat. Paleoelevation histories were reconstructed using the modern analogue technique with foraminiferal assemblages. Land elevation record analysis indicates 8-9 m of mid- to late Holocene tectonic subsidence occurred prior to 1.5 m of uplift during the A.D. 1931 Hawkes Bay earthquake. Chronologies of displacement events were constrained using 50 radiocarbon dates and three widespread air-fall tephras. We infer the following earthquakes: earthquake 1: 7.3-7.0 ka (-1.1 ± 0.3 m), earthquake 2: 5.6-5.1 ka (+0.4 ± 0.4 m), earthquake 3: 5.2-4.9 ka (-0.5 ± 0.5 m), earthquake 4: 4.4-3.8 ka (-0.6 ± 0.5 m), earthquake 5: 2.8-2.4 ka (-0.9 ± 0.5 m), earthquake 6: 1.73-1.70 ka (-1.0 ± 0.3 m), earthquake 7: 1.5-1.3 ka (-0.7 ± 0.5 m), earthquake 8: 1.04-0.89 ka (-1.2 ± 0.4 m), earthquake 9: 0.60-0.44 ka (-0.8 ± 0.6 m), and earthquake 10: A.D. 1931 (+1.5 ± 0.3 m). A further 1.6-2.6 m of subsidence could have occurred by gradual aseismic slip or in smaller earthquakes. The age ranges of four of the recognized earthquakes (earthquakes 1, 6, 8, and 9) overlap with other documented displacement events onshore along 250-600 km of the Hikurangi subduction margin, and with turbidites offshore 100-300 km to the north. These four are considered strong candidates for large subduction-interface earthquakes. The other five inferred earthquakes are less strongly correlated with along-margin displacement events and offshore turbidites. These could have been caused by upper-plate fault ruptures (like historic earthquake 10), but subduction-interface sources cannot be ruled out. This evidence for repeated coseismic vertical deformation suggests large coseismic slip on a part of the subduction interface beneath Hawkes Bay that is currently dominated by aseismic creep processes, such as transient slow-slip events. This clearly indicates multiple slip processes are possible in a single location on a subduction interface. [ABSTRACT FROM AUTHOR]

Three paleo-embayments on the southwest side of the uplifted Ahuriri Inlet, Hawkes Bay, contain complex interfingering sequences of Holocene terrestrial and saltmarsh peat and intertidal shelly sand and mud. We use 295 foraminiferal samples from 45 short cores (up to 8 m deep) to reconstruct the paleoenvironmental history of the bays. We infer that the strongest influence on their paleoenvironmental history was 8–10 m of net tectonic subsidence since 7.3 ka, which provided the accommodation space for sediment deposition prior to the c. 1.5 m of uplift in the AD 1931 Hawkes Bay Earthquake. Much of the subsidence appears to have occurred in eight large co-seismic events (0.4–2 kyr recurrence time) which caused marine transgressions of varying amounts into each bay. Sea-level changes (eustatic and isostatic) have been a secondary driver over the middle–late Holocene with an interval (c. 2.6–1.7 ka) of widespread erosion or slow sedimentation, caused by a sea-level fall of c. 1 m following the middle Holocene highstand. The interval of fastest sedimentation and maximum marine transgression occurred within the last 1 kyr and was driven by increased tectonic subsidence, rising sea level and enhanced compaction of thicker sequences of Holocene sediment, particularly peat. The supply of fluvial mud and cliff-eroded sand was the main, relatively constant source of clastic sediment. Airfall and reworking of three pumiceous tephras had a minimal impact on the paleoenvironments of the bays. [ABSTRACT FROM PUBLISHER]

The authors discuss the study "Lidar reveals uniform Alpine fault offsets and bimodal plate boundary rupture behavior, New Zealand," by Gregory P. De Pascale, Mark C. Quigley and Tim R. H. Davies, published online on March 17, 2014 by "Geology." Topics addressed include the occurrence of partial fault ruptures in New Zealand's Alpine fault (AF) near Whataroa, the lack of evidence for bimodal rupture behavior, and the occurrence of moderate to large earthquakes in the historical record.

Foraminiferal faunas in 29 short cores (maximum depth 7 m) of estuarine and coastal wetland sediment were used to reconstruct the middle–late Holocene (last 7 ka) elevational history on the southern shores of Poverty Bay, North Island, New Zealand. This coast is on the southwest side of a rapidly subsiding area beneath western Poverty Bay. Modern Analogue Technique paleo-elevation estimates based on fossil foraminiferal faunas indicate that the four study areas have gradual late Holocene (<3.5 ka) subsidence rates that increase from the southwest (mean c. 0.5 m ka–1) to northeast (mean c. 1.0 m ka–1). Only two rapid, possibly co-seismic, vertical displacement events are recognised: (1) c. 1.2 m of subsidence at 5.7 ± 0.4 ka (cal yr BP), which may have been generated by a subduction interface earthquake centred offshore and recorded in other published studies in northern Hawkes Bay, c. 35 km to the south; and (2) c. 1 m of uplift (relative sea-level fall) at c. 4.5 ± 0.3 ka, which might have been generated by rupture on an offshore upper plate fault that also uplifted coastal terraces at Pakarae and Mahia, 40 km to the north and south of the study area, or by rupture on the subduction interface penetrating beneath Poverty Bay. No sudden displacement events are recognised during the last 4 ka although subsidence, possibly aseismic, has continued. [ABSTRACT FROM AUTHOR]

The shallow tidal Wairau coastal lagoons, New Zealand, are in a prime location for investigating the relative roles of tectonic and eustatic sea level on their palaeogeographic evolution. The Wairau lagoons are unique in New Zealand for their wide seasonal and tidal salinity range, from hyposaline (10-20 psu) to hypersaline (35-54 psu). Foraminiferal and ostracod associations are recognised, using Q-mode cluster analysis, living in and around these lagoons and detrended canonical correspondence analysis (DCCA) shows that their distributions are strongly correlated with tidal elevation and salinity. Analyses of the modern analogue faunal data combined with Holocene microfaunal data from five 2.5-9 m deep cores enables direct palaeoenvironmental interpretation of the fossil faunas and elucidation of the lagoons' palaeogeographic evolution. The area was inundated by rising eustatic sea level from 8.5 ka onwards, forming a fully marine, sheltered, subtidal bay. Sediment supply outpaced local tectonic subsidence and the bay filled with mud, shallowing to intertidal by 4.5-3.5 ka, still with an open mouth to the sea. Since then sediment supply has kept pace with 3-4 m of inferred tectonic subsidence. At ∼1.5 ka the calcareous-dominated foraminiferal faunas suddenly changed to agglutinate-dominated faunas, indicating a switch to a semi-closed lagoon linked to the Wairau River estuary, with highly varied salinity like today. We infer this was caused by northwards extension of the Wairau Boulder Bank across the bay's mouth in response to a sharp eustatic sea-level fall after 2 ka. Sediment supply switched to fluvially derived sand which built a flood-delta into the lagoon dividing it into three water bodies. Relative sea-level rise in the last 600 years from earthquake-related compaction (ad 1855) and accelerating eustatic rise (0.6 m) has resulted in increased marginal erosion of the lagoons and their re-amalgamation into one linked water body. [ABSTRACT FROM AUTHOR]

Abstract: This paper provides the first solid evidence in support of a century-old hypothesis that the mountainous Marlborough Sounds region in central New Zealand is subsiding. More recent hypotheses suggest that this may be a result of southward migration of a slab of subducted Pacific Plate causing flexural downwarping of the overlying crust in the vicinity of the transition between subduction and strike-slip on the Pacific-Australian plate boundary. The proxy evidence for gradual Holocene subsidence comes from micropaleontological study of seven intertidal sediment cores from the inner Marlborough Sounds (at Havelock, Mahau Sound and Shakespeare Bay). Quantitative estimates (using Modern Analogue Technique) of former tidal elevations based on fossil foraminiferal faunas provide evidence of tectonic (not compaction-related) subsidence in all cores. Estimates of subsidence rates for individual cores vary within the range 0.2–2.4mka−1. The wide variation within subsidence rate estimates are related to a combination of the accuracy limits of radiocarbon dates, elevation estimates, and particularly our poor knowledge of the New Zealand Holocene sea-level curve. The most consistent subsidence rate at all three sites for the mid-late Holocene (last 6–7ka) is ∼0.7–0.8mka−1. This rate is consistent with the average subsidence rate in the adjacent 4-km thick Wanganui sedimentary basin for the last 5myr. Subsidence is inferred to have migrated southwards from the Wanganui Basin to impinge on the inner Marlborough Sounds in just the last 100–200ka. [Copyright &y& Elsevier]

Abstract: A tephra-bearing lake sequence from near Ormond, New Zealand, provided the opportunity to conduct a multi-proxy paleoenvironmental analysis within the Mid-Pleistocene time period. A 10.5-m-thick section was measured and analysed for pollen, spores, diatoms, macrofossils, and tephra geochemistry. Palynological assemblages in the lower 4m of the section indicate an ameliorating temperate climate and increased humidity. The upper 6.5m is dominated by diatomite that did not yield sufficient palynomorphs for study. The source vegetation was distal lowland mixed broadleaf podocarp forest, swamp forest from ca. 2.5–4.0m, and proximal scrubland with sporadic forest encroachment. Abundant freshwater algae in the samples suggest that any brackish influence in the lower part of the section was minor. Marine dinoflagellates found in the basal pollen samples could be mostly recycled. Diatomite samples were overwhelmingly dominated by a freshwater but mildly salt-tolerant diatom. We interpret the section as representing a shallow coastal lowland lake that intermittently had access to the sea. The chronology of the section is based on a single glass-ITPFT age of 0.62±0.09Ma from a tephra interbed (T8) in the lower part of the section. In addition, the lowermost tephra in the sequence (T1) is geochemically correlated to AT-485, preserved in the marine record east of New Zealand, with an astronomically tuned age of 0.7163Ma. This chronology places the basal portion of the Ormond section within the Brunhes normal Chron with sequence deposition occurring during either the OIS 18/17 or 16/15 transitions. However, paleomagnetic data indicate a clear reverse polarity from an equivalent stratigraphic position and at this stage it is difficult to reconcile this age discrepancy. [Copyright &y& Elsevier]

Abstract: Foraminiferal and diatom assemblages in 11 cores (3–7.5m deep) of Holocene sediment from brackish marine Ahuriri Inlet in southern Hawke''s Bay, New Zealand, provide a record of 8.5m of subsidence followed by 1.5m of uplift in the last 7200cal years, in a region overlying the subduction zone between the Australian and Pacific Plates. Modern Analogue Technique was used to estimate paleotidal elevation of the 97 richest foraminiferal assemblages. The most precise estimates are for high-tidal salt marsh assemblages cored in marginal settings in the north and south of the former inlet. The least precise estimates are from low-tidal and subtidal assemblages from cores in the middle of the inlet. These paleoelevation estimates combined with sediment thicknesses, age determinations (from tephrostratigraphy and radiocarbon dates), the New Zealand Holocene sea level curve, and estimates of compaction, identify the Holocene land elevation changes and earthquake-displacement events in each core. The following major, earthquake-related displacements are inferred: ca 7000calyrBP (>−0.6m displacement); ca 5800calyrBP (>−0.5m; ca 4200calyr BP (ca −1.5m); ca 3000calyrBP (−1.4 to −1.8m); ca 1600calyrBP (ca −1.7m); ca 600calyrBP (ca −1m); 1931AD Napier Earthquake (+1.5m). Further smaller events involving regional subsidence or earthquake-shake compaction are indicated during the 7000–3000yr BP interval, but cannot be identified precisely. The six (possibly subduction interface) subsidence events in the last 7000 years have had a return time of 1000–1400 years. Identified displacement events have a range of sedimentary expressions, from an eroded and burrowed hiatus surface, to an abrupt lithologic switch from mud to sand, or peat to shelly mud, or in some places no change in sediment character whatsoever. [Copyright &y& Elsevier]