摘要:

The stratigraphically and biostratigraphically most complete Cretaceous‐Tertiary (K‐T) boundary succession yet identified in New Zealand occurs in bathyal limestones of the Mead Hill Formation at Flaxbourne River, coastal Marlborough. It is one of three New Zealand K‐T sections with a well‐delineated “fireball” layer, containing anomalous iridium, soot particles, and fullerenes, and it contains a highly fossiliferous latest Cretaceous marl unit, not seen in other sections, immediately underlying the K‐T boundary clay. The c. 50 m thick Flaxbourne section is the only New Zealand locality known with an essentially complete sequence of earliest Paleocene foraminiferal zones. These include (K‐T boundary is zero datum):Guembelitria cretaceaZone (P0), 0.0–0.07 m;Parvularugoglobigerina eugubinaZone (P?), 0.07–0.24 m;P. eugubina‐Subbotina triloculinoidesSubzone (P1a), 0.24–0.40 m;S. trilo‐culinoides‐Globanomalina compressa/Praemurica inconstansSubzone (P1b), 0.40–0.50 m; andGlobanomalina compressa/Praemurica inconstans‐Praemurica uncinataSubzone (P1c), 0.50–11.5 m. Strata from 11.5 m to the highest exposed beds at c. 38 m are classified as undifferentiated Paleocene. Cretaceous planktic “survivor taxa” occur up to 0.40 m but are replaced rapidly above Zone P0 by Paleocene taxa.

ISSN:0028-8306    

DOI:10.1080/00288306.2000.9514867

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Carbon isotopic studies from marine organic matter of the Permian‐Triassic Maitai Group, New Zealand, reveal a significant δ13Corgshift toward more negative values within the Little Ben Sandstone Formation. These isotopic data chemostratigraphically define the previously debated position of the Permian‐Triassic boundary in the Maitai Group. The Permian‐Triassic record of the Maitai Group is also important because of its high paleolatitudinal setting and the deposition at intermediate depths in the ocean (c. 400 m) within a volcanic arc‐related basin. Marine Permian‐Triassic strata deposited at water depths deeper than shelf areas are rare. High latitude Permian‐Triassic boundary sections document a significantly larger isotopic offset across the boundary compared with lower latitude settings.

ISSN:0028-8306    

DOI:10.1080/00288306.2000.9514868

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A relatively rich, previously unknown fauna of Ammonitina is described from the Bajocian of southwest Auckland. The great majority are Sphaeroceratidae. TheChondrocerasfauna has yieldedC. orbignyanumandC. (Defonticeras)cf.oblatum,clearly indicating the Humphriesianum Chron. Also associated is the bivalve indexRetroceramus inconditus.The superjacent fauna of Waikatoceratinae (n. subfam.) is almost exclusively endemic to New Zealand, withWaikatoceras crassum, W. hudsoni, Opuatia circularis, O. inflata,andO. challinorin. genn. et spp. Accessory taxa includeChondrocerascf.orbignyanum,andToxamblyitesaff.densicostatus,previously known only from the upper Lower Bajocian of Europe and North Africa. However, stratigraphic evidence together with the bivalve indexRetroceramus marwickiclearly date the Waikatoceratinae fauna as mostly post‐Humphriesianum Chron (i.e., early Late Bajocian). The presence ofToxamblyitesin this fauna suggests that its range was one chron longer in the Southwest Pacific than in Eurafrica—unless the fragmented specimens were reworked, which is considered unlikely.

ISSN:0028-8306    

DOI:10.1080/00288306.2000.9514869

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The systematics and affinities of species that have previously been assigned to the terebratelloid brachiopod genusStethothyrisThomson, 1918, are reappraised and the taxonomic composition of the Subfamily Stethothyridinae is re‐evaluated. Only the type species(S. uttleyi)is retained within the genusStethothyris.The remainder are now distributed among the new genera,Erihadrosia (E. epsilon)from New Zealand, andEpacrothyris (E. pectoralis, E. sufflata)from Australia, andAliquantulaRichardson, 1991 (A. insolita, A. tapirina).One new species (Epacrothyris rennisonae)from the Abel Head Formation, Northwest Nelson, New Zealand, is described. All butErihadrosiaare included in the Subfamily Stethothyridinae.

ISSN:0028-8306    

DOI:10.1080/00288306.2000.9514870

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Calc‐alkaline basic volcanic rocks in a c. 600 m thick sequence of Miocene age, the Valle Nevado stratified sequence (VNSS), have been affected by very low grade metamorphism characterised by mineral assemblages of the zeolite facies. Metastable conditions prevailed, most of the igneous minerals being wholly or partially preserved. The main metamorphic phases are mafic phyllosilicates and zeolites of calco‐sodic and calcic composition. The intensity of the metamorphism was controlled by depth and by hydrothermal activity related to volcanic centres.

ISSN:0028-8306    

DOI:10.1080/00288306.2000.9514871

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The 0.89 Ma Tikorangi Ignimbrite (revised name) is a mixed andesite‐rhyolite ignimbrite preserved within a localised area of the Matahana Basin on the western side of the Taupo Volcanic Zone, New Zealand. The source of the ignimbrite is poorly constrained, but the location and limited maximum pumice and lithic data available suggest that the ignimbrite was emplaced by a pyroclastic flow erupted from within the Kapenga caldera complex. The ignimbrite is the oldest exposed unit sourced from the complex and offers a window into the early history of the Taupo Volcanic Zone.

ISSN:0028-8306    

DOI:10.1080/00288306.2000.9514872

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

“Sandy black” ignimbrites within the Taupo Volcanic Zone, New Zealand, are often incorrectly correlated. One of these ignimbrites was considered to be the lateral equivalent of the Kaingaroa Ignimbrite, but an integrated study of field geology, lithic componentry, mineralogy, and geochemistry of juvenile pumices has shown the ignimbrite is a separate unit, here termed the Kawerau Ignimbrite, with a source in the southern part of the Okataina caldera complex. The ignimbrite comprises two subunits that locally grade into each other: a lower partially welded “sandy black” ignimbrite and an upper tan‐buff pumice‐poor ignimbrite. Mineralogy and whole‐rock pumice geochemistry indicate significant compositional variation with two magma types: a high‐silica rhyolite (type A) and a dacite (type B). Both magma types show anomalously high Zr, Zn, and Hf, with type‐B pumice having similar values to weakly peralkaline rhyolites. The study highlights the importance of integrating all study methods before correlating units of apparent similar lithology.

ISSN:0028-8306    

DOI:10.1080/00288306.2000.9514873

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

On 25 September 1995, phreatomagmatic explosions through Crater Lake at Ruapehu volcano, New Zealand, generated a closely spaced sequence of lahars. From direct observations of the flows and timely description of their deposits, we infer these debris flows transformed to hyperconcentrated streamflows not by dilution with incorporated water they overran, as previously proposed. Rather, the described debris flows diluted by selective deposition of their coarse clasts as they thinned and decelerated while spreading >700 m laterally over the Whangaehu fan. Deposits recording this transformation are veneering (<100 mm thick) layers of muddy sandy gravel interspersed with many boulders and cobbles. Downstream of their transformation to hyperconcentrated streamflows, ephemeral near‐channel deposits indicate the flows were vertically stratified. A new depositional model for these hyperconcentrated streamflows includes a basal, coarse, sediment‐concentrated “channel flow” that emplaced transitory near‐channel sediment wedges. The near‐channel sediment was bouldery, massive, and poorly sorted, like debris‐flow deposits elsewhere in the Whangaehu catchment. The upper and marginal parts of the lahars (the surface layer) were diluted, finer hyperconcentrated flows that left voluminous overbank deposits. The overbank sediment is poorly sorted gravelly sand, with some degree of horizontal bedding, like other hyperconcentrated flow deposits elsewhere in the catchment. The rapid erosion of channel‐flow deposits within days to months of the events indicates that geologic records will only preserve lateral‐flow deposits of such lahars. Hence, long after an event, interpretation of hyperconcentrated streamflow mechanisms from geologic deposits can be misleading without the near‐channel record.

ISSN:0028-8306    

DOI:10.1080/00288306.2000.9514874

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0028-8306    

DOI:10.1080/00288306.2000.9514875

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor