title: Stratigraphy and sedimentology of Pliocene strata in the forearc basin (Waikoau and Waikari River catchments), northern Hawke's Bay

authors: Graafhuis, Rhys B.

subjects: Sediments

abstract: An area of over 250 km² in northern Hawke's Bay has been geologically mapped at a scale of 1:50 000, and over 1350 m of Pliocene sedimentary section described and interpreted in the Waikoau and Waikari River catchments. Two new formations and 13 members have been defined, and two formations redefined. The strata show little structural deformation
and form a shallow to moderately dipping (5°- 25°) succession on the uplifted limb of the Hawke's Bay Monocline. The rocks are of Pliocene age, ranging from Opoitian to Nukumaruan. The formations show rapid changes in thickness and lithology along strike from the southwest to the northeast, which is oblique to the depositional paleoslope.
Coarse-grained lithologies such as conglomerates and limestones typically become finergrained, less continuous and thinner towards the northeast.

In ascending order the new formations ( except where redefined) are: Titiokura Formation, Rangiora Formation, Matahorua Formation (redefined) and Waipunga Formation
(redefined). Titiokura Formation is dominated by calcareous siliciclastic sandstone and sandy limestone. The Rangiora Formation and Waipunga Formations are siliciclastic
sandstone and siltstone dominated. Matahorua Formation is dominated by siliciclastic sandstone and greywacke conglomerate.

Lithofacies analysis has been applied to the strata to establish the deposition paleoenvironments. Four lithofacies associations (siltstone, sandstone, conglomerate and
limestone) and 13 lithofacies have been identified. Interpreted bathymetric ranges for the siltstone association ranges from inner to outer shelf. The sandstone association is
characterised by massive to tabular cross-bedded sandstone interpreted to have been deposited on a shoreface to innershelf setting; storm current and tidally emplaced
tempestites and tidalities were deposited on the lower-shoreface to mid shelf; massive to horizontally bedded sandstone and silty beds were deposited on the inner-mid shelf.
Conglomerate associations are characterised by non-marine greywacke conglomerates deposited on a broad braidplain. Sandstone, siltstone and pumice conglomerate all within a
calcareous sandy matrix, are interpreted to have been deposited in tidal channels or on a beachface. The limestone association is characterised thick successions (10 - 50 m) of
sandy coquina that probably formed on the inner shelf possibly on a structural high as carbonate source areas. Thinner correlative units (50 cm - 6 m) of trough cross-bedded
sandy coquina accumulated in inner-mid shelf environments, having been reworked across the shelf from the carbonate source areas.

The successions in the four stratigraphic formations have been interpreted within a sequence stratigraphic framework and 25 sequences have been identified. Interpretation of
sequence boundaries is based on observed unconformities between lithologies, inferred unconformities between lithologies of differing paleoenvironments, and correlative
conformities.

Four typical sequence stratigraphic motifs have been interpreted from these formations. Each motif comprises three or four systems tracts: trangressive (TST), highstand (HST),
regressive (RST) and lowstand system tracts (LST). Motif 1 is representative of the Titiokura Formation, and consists of sandstone and mud drapes (TST and HST), with 
sandstone grading up into limestone (RST) having unconformable tops. Motif 2 is represent by the Rangiora Formation. This formation is comprised of thick successions
(100 m +) of interbedded sandstone and siltstone (TST), siltstone (HST), and siltstone coarsening up into sandstone (RST). The boundary on top of the RST sandstone is typically
unconformable. Motif 3 occurs in the Matahorua Formation. Siltstone or sandstone (TST), sandstone (HST), and interbedded siltstone and sandstone (RST) coarsen up into
greywacke conglomerate (LST). The sequence boundary usually lies within the top of the conglomerate between the coarse massive part and finer bedded conglomerate commonly having a heterogeneous silty-sand matrix; rarely the sequence boundary is at the vert top of the conglomerate unit. Motif 4 is represented by the Waipunga Formation. It is characterized by thin successions (10 m) of interbedded siltstone and sandstone (TST, HST) coarsening upward into sandstone (HST).

The stratigraphic evolution of each of these motifs has been interpreted within the context of an across shelf profile. Evolution of the motifs during a sea-level transgression, is
generally one of limestone deposition near the highstand shoreline. Thinly bedded tidalities, parasequences and massive sandstone with a weak backlap shellbed occur basinward in the TST. Limestone deposition near the highstand shoreline, and siltstone and thickly bedded tidalities basinward, characterise deposition during a sea-level highstand. Erosion and reworking of sediments basinwards during falling sea level conditions result in the formation of erosional sequence boundaries and the accumulation of a regressive sediment
wedge (RST). Sea-level lowstands are characterised by the deposition by greywacke conglomerate on a non-marine braidplain.

The Pliocene sedimentary succession on the western limb of the Hawke's Bay Monocline is interpreted as having been deposited in a steadily subsiding seaway (forearc basin) with uplift on its western margin. Strong storm and tidal currents reworked sediment from shallow into deeper water across a shelf. The siliciclastic sediment was sourced from
erosion in the hinterland. The compressive component within the plate boundary zone in North Island, increased around 2-3 Ma, resulting in uplift of the Axial Ranges, which
became a major sediment source. Sea-level fluctuations throughout the deposition of the sedimentary succession in the study area resulted in the development of cyclothems. The
periodicity of the cycles appears to increase from the Opoitian to the Nukumaruan, for which 6th order (41 ka) cyclicity is inferred. The bathymetric range of the cyclothems also
appears to increase from the Opoitian to Nukumaruan.

text: Stratigraphy and sedimentology of Pliocene strata in the forearc basin (Waikoau and Waikari River catchments), northern Hawke's Bay An area of over 250 km² in northern Hawke's Bay has been geologically mapped at a scale of 1:50 000, and over 1350 m of Pliocene sedimentary section described and interpreted in the Waikoau and Waikari River catchments. Two new formations and 13 members have been defined, and two formations redefined. The strata show little structural deformation
and form a shallow to moderately dipping (5°- 25°) succession on the uplifted limb of the Hawke's Bay Monocline. The rocks are of Pliocene age, ranging from Opoitian to Nukumaruan. The formations show rapid changes in thickness and lithology along strike from the southwest to the northeast, which is oblique to the depositional paleoslope.
Coarse-grained lithologies such as conglomerates and limestones typically become finergrained, less continuous and thinner towards the northeast.

In ascending order the new formations ( except where redefined) are: Titiokura Formation, Rangiora Formation, Matahorua Formation (redefined) and Waipunga Formation
(redefined). Titiokura Formation is dominated by calcareous siliciclastic sandstone and sandy limestone. The Rangiora Formation and Waipunga Formations are siliciclastic
sandstone and siltstone dominated. Matahorua Formation is dominated by siliciclastic sandstone and greywacke conglomerate.

Lithofacies analysis has been applied to the strata to establish the deposition paleoenvironments. Four lithofacies associations (siltstone, sandstone, conglomerate and
limestone) and 13 lithofacies have been identified. Interpreted bathymetric ranges for the siltstone association ranges from inner to outer shelf. The sandstone association is
characterised by massive to tabular cross-bedded sandstone interpreted to have been deposited on a shoreface to innershelf setting; storm current and tidally emplaced
tempestites and tidalities were deposited on the lower-shoreface to mid shelf; massive to horizontally bedded sandstone and silty beds were deposited on the inner-mid shelf.
Conglomerate associations are characterised by non-marine greywacke conglomerates deposited on a broad braidplain. Sandstone, siltstone and pumice conglomerate all within a
calcareous sandy matrix, are interpreted to have been deposited in tidal channels or on a beachface. The limestone association is characterised thick successions (10 - 50 m) of
sandy coquina that probably formed on the inner shelf possibly on a structural high as carbonate source areas. Thinner correlative units (50 cm - 6 m) of trough cross-bedded
sandy coquina accumulated in inner-mid shelf environments, having been reworked across the shelf from the carbonate source areas.

The successions in the four stratigraphic formations have been interpreted within a sequence stratigraphic framework and 25 sequences have been identified. Interpretation of
sequence boundaries is based on observed unconformities between lithologies, inferred unconformities between lithologies of differing paleoenvironments, and correlative
conformities.

Four typical sequence stratigraphic motifs have been interpreted from these formations. Each motif comprises three or four systems tracts: trangressive (TST), highstand (HST),
regressive (RST) and lowstand system tracts (LST). Motif 1 is representative of the Titiokura Formation, and consists of sandstone and mud drapes (TST and HST), with 
sandstone grading up into limestone (RST) having unconformable tops. Motif 2 is represent by the Rangiora Formation. This formation is comprised of thick successions
(100 m +) of interbedded sandstone and siltstone (TST), siltstone (HST), and siltstone coarsening up into sandstone (RST). The boundary on top of the RST sandstone is typically
unconformable. Motif 3 occurs in the Matahorua Formation. Siltstone or sandstone (TST), sandstone (HST), and interbedded siltstone and sandstone (RST) coarsen up into
greywacke conglomerate (LST). The sequence boundary usually lies within the top of the conglomerate between the coarse massive part and finer bedded conglomerate commonly having a heterogeneous silty-sand matrix; rarely the sequence boundary is at the vert top of the conglomerate unit. Motif 4 is represented by the Waipunga Formation. It is characterized by thin successions (10 m) of interbedded siltstone and sandstone (TST, HST) coarsening upward into sandstone (HST).

The stratigraphic evolution of each of these motifs has been interpreted within the context of an across shelf profile. Evolution of the motifs during a sea-level transgression, is
generally one of limestone deposition near the highstand shoreline. Thinly bedded tidalities, parasequences and massive sandstone with a weak backlap shellbed occur basinward in the TST. Limestone deposition near the highstand shoreline, and siltstone and thickly bedded tidalities basinward, characterise deposition during a sea-level highstand. Erosion and reworking of sediments basinwards during falling sea level conditions result in the formation of erosional sequence boundaries and the accumulation of a regressive sediment
wedge (RST). Sea-level lowstands are characterised by the deposition by greywacke conglomerate on a non-marine braidplain.

The Pliocene sedimentary succession on the western limb of the Hawke's Bay Monocline is interpreted as having been deposited in a steadily subsiding seaway (forearc basin) with uplift on its western margin. Strong storm and tidal currents reworked sediment from shallow into deeper water across a shelf. The siliciclastic sediment was sourced from
erosion in the hinterland. The compressive component within the plate boundary zone in North Island, increased around 2-3 Ma, resulting in uplift of the Axial Ranges, which
became a major sediment source. Sea-level fluctuations throughout the deposition of the sedimentary succession in the study area resulted in the development of cyclothems. The
periodicity of the cycles appears to increase from the Opoitian to the Nukumaruan, for which 6th order (41 ka) cyclicity is inferred. The bathymetric range of the cyclothems also
appears to increase from the Opoitian to Nukumaruan.

year: 2001

title: Phylogeography of New Zealand’s coastal benthos

authors: Ross, Philip M.

subjects: genetic differentiation

abstract: During the past 30 years, 42 molecular studies have been undertaken in New Zealand to examine the phylogeography of coastal benthic invertebrates and plants. Here, we identify generalities and/or patterns that have emerged from this research and consider the processes implicated in generating genetic structure within populations. Studies have used various molecular markers and examined taxonomic groups with a range of life histories and dispersal strategies. Genetic disjunctions have been identified at multiple locations, with the most frequently observed division occurring between northern and southern populations at the top of the South Island. Although upwelling has been implicated as a cause of this disjunction, oceanographic evidence is lacking and alternative hypotheses exist. A significant negative correlation between larval duration and genetic differentiation (r2 = 0.39, P < 0.001, n = 29) across all studies suggests that larval duration might be used as a proxy for dispersal potential. However, among taxa with short larval durations (<10 days) there was greater variability in genetic differentiation than among taxa with longer pelagic periods. This variability implies that when larval duration is short, other factors may determine dispersal and connectivity among populations. Although there has been little congruence between the phylogeographic data and recognised biogeographic regions, recent research has resolved population subdivision at finer spatial scales corresponding more closely with existing biogeographic classifications. The use of fast-evolving and ecologically significant molecular markers in hypothesis-driven research could further improve our ability to detect population subdivision and identify the processes structuring marine ecosystems.

text: Phylogeography of New Zealand’s coastal benthos During the past 30 years, 42 molecular studies have been undertaken in New Zealand to examine the phylogeography of coastal benthic invertebrates and plants. Here, we identify generalities and/or patterns that have emerged from this research and consider the processes implicated in generating genetic structure within populations. Studies have used various molecular markers and examined taxonomic groups with a range of life histories and dispersal strategies. Genetic disjunctions have been identified at multiple locations, with the most frequently observed division occurring between northern and southern populations at the top of the South Island. Although upwelling has been implicated as a cause of this disjunction, oceanographic evidence is lacking and alternative hypotheses exist. A significant negative correlation between larval duration and genetic differentiation (r2 = 0.39, P < 0.001, n = 29) across all studies suggests that larval duration might be used as a proxy for dispersal potential. However, among taxa with short larval durations (<10 days) there was greater variability in genetic differentiation than among taxa with longer pelagic periods. This variability implies that when larval duration is short, other factors may determine dispersal and connectivity among populations. Although there has been little congruence between the phylogeographic data and recognised biogeographic regions, recent research has resolved population subdivision at finer spatial scales corresponding more closely with existing biogeographic classifications. The use of fast-evolving and ecologically significant molecular markers in hypothesis-driven research could further improve our ability to detect population subdivision and identify the processes structuring marine ecosystems.

year: 2009

title: 'Kōrero Tuku Iho': Reconfiguring Oral History and Oral Tradition

authors: Mahuika, Nepia

subjects: History

abstract: The studies of oral history and oral tradition each have their own distinctive bodies of literature and preferred methodologies, yet share significant overlaps that make them difficult to differentiate. For many indigenous peoples, oral histories and traditions are key to their their past, present, and future lives, and are rarely considered separate. This thesis examines the differences and similarities between the studies of oral history and oral tradition. It explores how these areas of research converge and diverge in form, politics, practice, and theory, and the extent to which they resonate within a specific ‘indigenous’ context and community.
The thesis draws on the life narrative interviews of four generations of Ngāti Porou descendents, the second largest tribal group in New Zealand, whose home boundaries extend from Potikirua in the north to Te Toka-a-Taiau in the south on the East Coast of the North Island. Drawing on these voices, this study offers a commentary on the form and nature of oral traditions and histories from an indigenous perspective, and explores the ways they converge and depart from ‘international’ understandings. An exploration of these intersections offers insights to the ways oral history and oral traditions might be reconsidered as distinctive fields of study. Reconfigured through an indigenous frame of reference, this thesis challenges scholars of both oral history and oral tradition to expand their conceptions. Likewise, it urges indigenous scholars to consider more deeply the work of oral historians and oral traditionalists to further enhance their scholarship. Moreover, this thesis revisits the intellectual and conceptual territory that names and claims oral history and oral tradition, and invites all those who work in these areas to develop a more extensive comprehension of the interconnections that exist between each area of study.

text: 'Kōrero Tuku Iho': Reconfiguring Oral History and Oral Tradition The studies of oral history and oral tradition each have their own distinctive bodies of literature and preferred methodologies, yet share significant overlaps that make them difficult to differentiate. For many indigenous peoples, oral histories and traditions are key to their their past, present, and future lives, and are rarely considered separate. This thesis examines the differences and similarities between the studies of oral history and oral tradition. It explores how these areas of research converge and diverge in form, politics, practice, and theory, and the extent to which they resonate within a specific ‘indigenous’ context and community.
The thesis draws on the life narrative interviews of four generations of Ngāti Porou descendents, the second largest tribal group in New Zealand, whose home boundaries extend from Potikirua in the north to Te Toka-a-Taiau in the south on the East Coast of the North Island. Drawing on these voices, this study offers a commentary on the form and nature of oral traditions and histories from an indigenous perspective, and explores the ways they converge and depart from ‘international’ understandings. An exploration of these intersections offers insights to the ways oral history and oral traditions might be reconsidered as distinctive fields of study. Reconfigured through an indigenous frame of reference, this thesis challenges scholars of both oral history and oral tradition to expand their conceptions. Likewise, it urges indigenous scholars to consider more deeply the work of oral historians and oral traditionalists to further enhance their scholarship. Moreover, this thesis revisits the intellectual and conceptual territory that names and claims oral history and oral tradition, and invites all those who work in these areas to develop a more extensive comprehension of the interconnections that exist between each area of study.

year: 2012