New Zealand Journal of Geology and Geophysics
ISSN: 0028-8306 (Print) 1175-8791 (Online) Journal homepage: http://www.tandfonline.com/loi/tnzg20
Description and interpretation of a fossil beetle assemblage from marine isotope stage 6 from Banks Peninsula, New Zealand M. J. Marra To cite this article: M. J. Marra (2003) Description and interpretation of a fossil beetle assemblage from marine isotope stage 6 from Banks Peninsula, New Zealand, New Zealand Journal of Geology and Geophysics, 46:4, 523-528, DOI: 10.1080/00288306.2003.9515026 To link to this article: http://dx.doi.org/10.1080/00288306.2003.9515026
Published online: 21 Sep 2010.
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New Zealand Journal of Geology & Geophysics, 2003, Vol. 46 : 5 2 3 - 5 2 8 0028-8306/03/4604-0523 $7.00/0 © The Royal Society of N e w Zealand 2003
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Description and interpretation of a fossil beetle assemblage from marine isotope stage 6 from Banks Peninsula, New Zealand
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M. J. MARRA Department of Geological Sciences University of Canterbury Private Bag 4800 Christchurch, New Zealand email:
[email protected] Abstract A penultimate glaciation-age beetle fauna is described from a core record from Banks Peninsula, South Island, New Zealand. A total of 19 beetle species belonging to 5 families was recorded. The fossil beetles indicate a forest environment of montane affinity but in a coastal setting. The assemblage is dominated by phytophagous species, mainly weevils, associated with forest habitats. The beetle fauna includes Rhicnobelus metallicus, which is a forest canopy species; forest floor and swamp forest taxa; and Cecyropa modesta, which is specific to coastal dune systems. Fossil seeds were also identified. They include species from salt marsh and tidal flats, indicating an estuarine setting, which suggests that the beetle remains were washed into an estuary from an adjacent forest. The fossil beetle assemblage indicates cooler than modern conditions but not full glacial. This interpretation is consistent with the regional pollen record for this interval. Keywords fossil beetles; paleoclimate; environmental reconstruction; paleoecology; penultimate glaciation
This paper describes and interprets the beetle fossil assemblage from the organic deposit in Unit D at a core depth of between —41.10 and -40.70 m. SITE DESCRIPTION Banks Peninsula is located on the east coast of the South Island of New Zealand (Fig. 1). The peninsula is c. 1200 km2 in area and composed of Miocene volcanic peaks and lava flows (Weaver et al. 1990). The volcanoes are heavily eroded and steep sided, and valleys between the paleoflows contain thick sediment fills from marine and terrestrial sources. Gebbies Valley is one of these basalt-bounded valleys on the southwestern flank of the peninsula, and is the site of this study. Climate on the peninsula is varied. The lowland climate is cool temperate. Elevations above 750 m are subalpine. The present-day vegetation consists of hill pastureland with patches of scrub and native forest (Burrows 1994). Before human occupation, indigenous forest covered most the peninsula. The valley floors and lower slopes were vegetated in podocarp forest dominated by Dacrycarpus dacrydioides and Podocarpus totara. The elevated areas were dominated by Podocarpus hallii. Nothofagus fusca grew on southern, elevated areas, and coastal gullies included frost-sensitive Rhopalostylis sapida (Soons et al. 2002). Now the forest is limited to numerous small patches, the largest of which are c. 150 ha (Burrows 1994).
INTRODUCTION In 1996, a 200 000 yr core record spanning 3 glacial/ interglacial cycles was extracted from Gebbies Valley, Banks Peninsula (Fig. 1). A number of techniques were employed to interpret the core record, including sedimentology, pollen, diatom, and phytolith analyses, all of which are reported in Shulmeister et al. (1999) and Soons et al. (2002). An organicrich (peaty) unit was identified between —48.25 and -40.27 m (Unit D in Shulmeister et al. 1999). This unit contained visible beetle fragments. Thermoluminescence provided an age of 136 ± 10 ka, which places it in marine isotope stage (MIS) 6 (Shulmeister et al. 1999). The interpreted depositional environment is a back barrier, freshwater setting in a low forest-shrubland dominated landscape. The interpreted climatic conditions for this time were interstadial rather than pleniglacial (Shulmeister et al. 1999; Soons et al. 2002). The presence of insect fossils provided an opportunity to examine the MIS 6 paleoenvironment from a different perspective.
G02036; Online publication date 13 November 2003 Received 12 July 2002; accepted 28 July 2003
METHODS Insect fossils were extracted from c. 1 kg of organic silty material from Unit D. The sediment was washed through a 300 µm sieve, and fossil insect remains were extracted by kerosene flotation method described in Elias (1994), picked under a binocular microscope and mounted on microfaunal slides. Fossil identification was made by comparisons with modern specimens deposited at the New Zealand Arthropod Collection (NZAC), Mt Albert Research Centre, Auckland.
RESULTS A total of 19 beetle species belonging to 5 families were extracted and identified (Table 1). The assemblage, most of which are weevil species, was dominated by phytophagous species associated with forest habitats (Fig. 2). Although a number of seeds and fruit were also extracted, only three seeds were identified (Table 2). The beetle forest fauna included the weevil Rhicnobelus metallicus (Belidae) that is found on Dacrydium cupressinum, Phyllocladus alpinus, Ph. Trichomanoides, and Podocarpus totara (Kuschel 2003). Rhicnobelus metallicus is found in the canopy of the host trees from lowland to c. 1500 m a.s.l.
New Zealand Journal of Geology and Geophysics, 2003, Vol. 46 Fig. 1 Location of Gebbies Valley core site.
Ffank.n Peninsula.
l-.l
Valley core site
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Iflknn
The larvae live in sound, dead branches, and the adults feed on new growth of host trees (Kuschel pers. comm. 2000). Although only a fragment of a wing case belonging to Rhicnobelus metallicus was found, it is identifiable by characteristic transverse wrinkles (Fig. 3A). The forest floor
fauna included weevils Mandalotus irritus and Nestrius sp., which inhabit the litter and feed on small ground plants and seeds. The larvae of both species feed on roots of small plants. Several other weevils belonging to Cryptorhynchini (Fig. 3FH) were also included in the forest floor fauna. These taxa
Table 1 Taxonomic list of fossils from the Gebbies Valley core at -41.10 to -40.70 m. Coleoptera Carabidae Undet. sp. 1 Undet. sp. 2 Staphylinidae Bledius sp. 1 Aleocharinae sp. 1 Byrrhidae Epichorius sp. 1 Anobiidae Sphinditeles sp. 1 Curculionidae Belidae Rhicnobelus metallicus (Pascoe) Entiminae Cecyropa modesta (Fabricius) Mandalotus irritus (Pascoe) Nestrius sp. 1 Curculionidae: Erirhinini Baeosomus sp. 1 Curculioninae: Cryptorhynchini Microcryptorhybchus perpusillus (Pascoe) Scelodlichus sp. 1 Genus species 1 Genus species 2 Genus species 3 Genus species 4 Genus species 5 Cossininae Eucossonus setiger (Sharp)
#
Part
Habitat
Reference Identification/ecology
1 1
e e,p
7 7
NZAC NZAC
1 1
e e
Beach Forest floor?
NZAC NZAC
1
e
Moss
NZAC
1
P
Forest
Auckland Museum
1
e
Canopy
G. Kuschel
3 2 1
h h P
Sand dunes Forest floor litter Forest floor litter
G. Kuschel G. Kuschel G. Kuschel
1
e
Moss mats
G. Kuschel
2 1 1 1 1 1 1
e,p P e P h h h
Various hosts Forest floor litter Forest floor Forest floor Forest floor Forest floor Forest floor
G. G. G. G. G. G. G.
1
e
Cordyline
G. Kuschel
NZAC = New Zealand Arthropod Collection: identifications confirmed by R. Leschen. # = Minimum number of individuals from fossil elements. e = elytron; p = prothorax; h = head.
Kuschel Kuschel Kuschel Kuschel Kuschel Kuschel Kuschel
525
Marra—Fossil beetles, Banks Peninsula
i
1
-i
Coastal-open 5
r
15%
It
Forest
Iltt
PALEOENVIRONMENTAL RECONSTRUCTION
•3
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Fig. 2 Composition of assemblage by habitat type and function.
occupy dead wood habitats. Scelodolichus sp. 1 (Curculionidae) was also present. The adults of these weevils feed on algae and small lichens growing on litter, and the larvae are found in dead twigs on the forest floor (Kuschel pers. comm. 2000). Spinditeles sp. 1 (Anobiidae) was probably a member of the forest fauna. This genus is rare in collections, and little is known of its ecology, but larvae of most anobiids are wood or bark borers (Klimaszewski & Watt 1997). A forest margin weevil Irenimus compressus (Curculionidae) was also present. Larvae of Irenimus compressus live well down in the soil, feeding on rootlets, and the adults live on leaves on various dicotyledonous hosts (Kuschel pers. comm. 2000). Eucossonus setiger (Curculionidae) is a weevil strictly tied to Cordyline (cabbage tree) and indicates a swampy environment nearby. Species associated with moss habitats were present in the assemblage and include Baeosomus (Curculionidae) (Fig. 3E) and Epichorius (Byrrhidae) (Fig. 3B). Both adults and larvae of Baeosomus live on moss mats and feed on mosses, particularly mosses of the Polytrichaceae family (Kuschel pers. comm. 2000). Although Baeosomus occurs from lowland to alpine environments, only the lowland species have uneven elytral tubercles (Kuschel pers. comm. 2001); thus, the fossils were identified as the lowland type. Epichorius larvae are found living on and feeding from moss in damp habitats (Klimaszewski & Watt 1997). The open habitat fauna included the rove beetle (Staphylinidae) Bledius sp. 1 (Fig. 3C) and the weevil (Curculionidae) Cecyropa modesta (Fig. 3D). Bledius indicates the presence of a beach (either freshwater or marine) environment nearby (Klimaszewski et al. 1996). Cecyropa modesta occupies sand dune habitats and also indicates a coastal environment. The
Table 2
adults of this species feed on dune plants and the larvae live deep in the sand feeding off plant roots (Kuschel pers. comm. 2000). No freshwater aquatic beetles were found. The identified fossil seeds were Suaeda sp. (probably S. novae zealandiae), which inhabits estuarine margins within the tidal range, and species of Cyperaceae/Juncaceae, which may also be from salt marsh communities. Chenopodium seeds, probably C. glaucum, were identified. This is a common coastal herb that inhabits salt marshes, coastal sands, and mudflats.
In summary, the fossil beetle assemblage indicates a forest environment on the margin of an estuary or swampy area in a coastal setting. Although the interpreted paleoenvironment by Shulmeister et al. (1999) is freshwater (either lagoon or swamp) behind a coastal barrier, the beetle fossil and seed data presented here suggest the environment was estuarine, although there is also evidence of a nearby freshwater swamp environment. The preferred interpretation is that the paleoenvironment was estuarine with the freshwater taxa arriving from the freshwater-dominated zone at the head of the estuary. The freshwater/aquatic fauna is absent from the fossil assemblage and this also suggests Unit D was deposited in an estuarine environment. Although the absence of freshwater taxa is not evidence of the absence of a freshwater aquatic paleoenvironment, given the richness, abundance, and preservation quality of the insect fossils in Unit D, and that New Zealand has a diverse freshwater aquatic and riparian beetle fauna, it is not unreasonable to expect some evidence of a freshwater aquatic environment in the fossil beetle assemblage were such an environment present. Although this analysis is restricted by the amount of core material available for fossil extraction, the fossil beetles still provide a unique perspective into the environment toward the end of MIS 6. This is in part because the beetle fauna is particularly well known from the area with several published natural histories and inventories (Wakefield 1873; Speight etal. 1927; Knox 1969; Johns 1986). Only three of the fossils listed in Table 1 (Rhicnobelus metallicus, Eucossonus setiger, and Cecyropa modesta) are present today in Banks Peninsula (although the two undetermined carabids, Nestrius sp. 1 and Bledius sp. 1, could also be present). There is no record of
Epichorius, Spinditeles, Mandalotus, Baeosomus, Microcryptorhynchus, or Scelodolichus occurring in the modern Banks Peninsula fauna. The absence of these beetles in the modern record may be a result of destruction of widespread forest on Banks Peninsula over the past 150 yr (Speight et al. 1927). However, numerous forest patches still remain and provide the forest habitat for Spinditeles,
Seeds recovered from Gebbies Valley core.
Taxon
Number of seeds
Habitat
4 6 14
Salt marsh, within the tidal range Coastal, salt marsh, tidal flats Saltmarsh or freshwater swamps
Suaeda sp. Chenopodium sp. Cyperaceae/Juncaceae Seed identification by C.Webb.
New Zealand Journal of Geology and Geophysics, 2003, Vol. 46
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Fig. 3 Selection of Coleoptera and seed fossils. A, Rhicnobelus metallicus (Belidae) elytron fragment. B, Epichorius sp. (Byrrhidae) elytron. C, Bledius sp. (Staphylinidae) elytron. D, Cecyropa modesta (Curculionidae) head. E, Baeosomus sp. (Curculionidae) elytron. F, Cryptorhynchini sp. 1 (Curculionidae) head. G, Cryptorhynchini sp. 2 (Curculionidae) elytron. H, Cryptorhynchini sp. 3 (Curculionidae) elytron. I, Chenopodium sp. (seed). J, Cyperaceae sp. (seed).
Scak bare = 1 mm
Mandalotus, Microcryptorhynchus, and Scelodolichus. Moreover, as Epichorius and Baeosomus are not forest taxa, the loss of forest habitat is not likely to be the reason for their absence in the modern Banks Peninsula fauna. Therefore, although the modern vegetation has been altered, the difference between the fossil beetle fauna and modern beetle fauna may well be the result of different environmental conditions at MIS 6. Climate reconstruction is difficult with this small dataset. The interpretation from the pollen data (Shulmeister et al. 1999) describes coastal-montane vegetation dominated by secondary trees and shrubs, which is not typical of glaciation grass and shrub vegetation in New Zealand during MIS 6 (e.g., Bussell 1990; Mildenhall 1995). The beetle fossils are also a mixture of montane and coastal species. The altitudinal distribution limit of Rhicnobelus metallicus at 1500 m places a limit on the cold end of the range. Sphinditeles and Epichorius are rare and little is known of their ecologies and distribution. However, the fossil Sphinditeles matches
modern examples collected from Dunedin, and Epichorius matches modern examples from montane habitats at c. 450 m in the Old Man and Dunstan Ranges, both of which suggest cooler conditions. Based on the montane beetle fauna, and using a simple environmental lapse (0.55 ± 0.05°C per 100 m), the lowering of the montane zone by c. 450 m to a sea-level position equates to a temperature depression of c. 2-3 °C. However, this paleotemperature reconstruction needs to be treated with caution as the interpretation is based only on phytophagus beetles rather than the preferred climate indicators (predator or scavenger beetles) that provide reliable and precise paleotemperature estimates (e.g., Coope 1977; Elias et al. 1999). Therefore, there is a risk that the fossil beetles used in this reconstruction relied on plants, and these plants may not have been "in step" with the climate. Conditions may also have been drier. Mandolotus and Nestrius are associated with low-rainfall areas (Kuschel pers. comm. 2000) and usually occur in drier regions in New Zealand. The dry conditions on the peninsula at MIS 6 were
527
Marra—Fossil beetles, Banks Peninsula ACKNOWLEDGMENTS
For supervision of this PhD research and for comments of this paper, thanks are due to J. Shulmeister (University of Canterbury) and to R. Leschen (Landcare Research). For assistance with identifications, I thank R. Leschen (general Coleoptera) and G. Kuschel (Curculionidae). For distribution and biological information, I thank S. Thorpe and J. Nunn. Thanks to C. Webb for the identification of seeds. I also thank the reviewers of this paper, S. Elias and G. Kuschel. This research was funded by scholarships from Fulbright and Victoria University of Wellington and partly supported through the PGSF through contract VICX0010. Thanks to A. Ashworth (North Dakota State University) for training in this field of research.
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