摘要:

AbstractA 12 000 to 4000 yr BP pollen and tephra‐bearing profile from Auckland, New Zealand, provides insights into the vegetation history and evidence for early Holocene volcanic activity in this area centred on the Mount Wellington basaltic volcano. Possibly 500 yr separated initial scoriaceous ash deposition (ca. 9500 yr ago) and subsequent major lava flows (ca. 9000 yr ago) from Mount Wellington. The local vegelation, topography, and drainage patterns were substantially modified during this time, and damming by the lava flows resulted in the formation of Lake Waiatarua in a shallow valley head ca. 9000 yr ago. Diatom evidence indicates that this lake was initially deep (>5 m) but was shallowing around 4000 yr ago. In contrast to the Mount Wellington eruptions, tephra deposition resulting from distant rhyolitic volcanic activity of the central North Island and Mayor Island has had little effect on the Auckland vegetation during this time interval (12 000–4000 yr ago).Between ca. 12 000 and 10 000 yr ago, conifer‐angiosperm forest was the predominant vegetation cover on Auckland Isthmus, but during the early Holocene, forest dominated byMetrosiderosexpanded, probably on to fresh volcanic surfaces resulting from the Mount Wellington eruptions. At this time, swamp forest communities developed in Waiatarua valley basin, and included species indicative of moist, mild, relatively frost‐free climates. Some taxa show histories consistent with other records from the northern New Zealand region, including the rise ofAscarina lucidaca. 11 000 to 9000 yr ago, and its subsequent decline, and the expansion ofAgathis australis(kauri) forest communities from ca. 6000 yr ago. Taken together the history of local and regional vegetation points to a mild, moist and weakly seasonal early Holocene climate, which subsequently became drier with greater seasonal temperature e

ISSN:0267-8179    

DOI:10.1002/jqs.3390060302

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThis study examines the depletion of ferromagnesian silicate minerals from a sequence of thin, distal, mainly rhyolitic tephra layers of Holocene age preserved in an acid peat bog (Kopouatai), North Island, New Zealand. The rate of such depletion has been fast, as indicated by the complete loss of biotite from one tephra layer (Kaharoa Tephra), in which it is normally dominant, in only ca.770yr. Chemical dissolution is advocated as the likely cause for the depletion, with amphiboles and other mineral grains commonly showing etch pits, microcaves, and other characteristic surface solution features. Theoretical thermodynamic and kinetic models show a marked increase in the rate of dissolution of all ferromagnesian minerals under conditions of low pH (<4), but that where silica concentrations in solution are high the relative proportions of minerals remaining are unaffected. However, where concentrations of dissolved silica are low, as in most bog environments, the relative proportions of ferromagnesian minerals are affected as well as absolute amounts being decreased. Amphiboles are depleted relative to pyroxenes, consistent with kinetic studies.The results show that the identification and correlation of tephras on the basis of relative abundances of ferromagnesian minerals alone may be unreliable, and emphasise the need to use multiple criteria in such studies.

ISSN:0267-8179    

DOI:10.1002/jqs.3390060303

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractA pollen diagram from Lago di Martignano, a maar lake in central Italy, provides an 11000‐year record of vegetation and environment change. The earliest pollen spectra are dominated byArtemisiaand Gramineae, representing late glacial steppe vegetation typical of the Mediterranean region. Broad‐leaved forests were established by ca. 11 000 yr BP. AlthoughQuercusinitially dominated their canopy, a wide range of other mesophyllous trees were also present. Pollen values for sclerophyllous tree and shrub taxa characteristic of Mediterranean woodlands and scrub are initially low (40% of total land pollen at ca. 6700 yr BP, withOlea europaeathe single most abundant taxon. Human influence upon the vegetation only becomes significant somewhat after this peak, with progressive clearance of woodland and expansion of herbaceous communities.Castanea sativaandluglans regiapollen is recorded consistently from the beginning of the rise in pollen values for taxa characteristic of Mediterranean scrub communities. Pollen values for arable crops increase progressively after ca. 5500 yr BP, following the peak pollen values for taxa characteristic of Mediterranean scrub vegetation. Late glacial and Holocene climate changes have been complex in this region, with the present character of the climate developing only during the last millennium. Rates of change of pollen spectra peak during this per

ISSN:0267-8179    

DOI:10.1002/jqs.3390060304

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractArchaeological survey and palaeoenvironmental investigations in Coe Burn, Callaly Moor, Northumberland, have examined the chronology and nature of prehistoric and historic land‐use change in a small upland river catchment. These studies have revealed an intensively used landscape with evidence of late Neolithic to Bronze Age, medieval and post‐medieval land use and settlement. Two episodes of valley floor alluviation are identified and dated to the middle‐late Bronze Age and post‐medieval periods. Magnetic mineral and geochemical analyses of fine sediments from the older alluvial fill show it to contain a high proportion of topsoil, which is believed to have been produced by soil erosion resulting from Bronze Age tree clearance and cultivation. Deposition of the younger alluvial fill (post AD 1500) was associated with the inwash of relatively unweathered bedrock generated by coal mining in the catchment. It is demonstrated that by integrating archaeological field survey with off‐site palaeoenvironmental investigations a much fuller picture of human activity and land‐use change has emerged than otherwise would have been the case. Studies of this type may be particularly useful in other upland river catchments where archaeological survival is limi

ISSN:0267-8179    

DOI:10.1002/jqs.3390060305

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractBerry Head, a limestone headland in Torbay, southwest England, exhibits a series of subaerial marine erosion platforms and raised beaches spanning an altitude range of 97 m. Solution caves on the headland show preferred horizontal development at elevations that are correlated with the marine erosion platforms, and developed in a marine/freshwater mixing zone whose position was controlled by high sea‐level still‐stands. Corbridge Cave in Berry Head Quarry lies below the raised beaches in Torbay, and contains evidence of three marine transgressions in the form of fine‐grained marine ponding deposits with a marine microfauna. Uranium‐series dating of intercalated speleothems indicates that a transgression during oxygen isotope stage 5e reached an elevation of 5.8 m OD, while an earlier transgression (probably during stage 7) reached at least 7.2 m OD. These findings are used to constrain possible interpretations of the aminostratigraphy of raised beaches in Southwest Britain, and a correlation of the Unnamed Stage of Bowen, Sykes, Reeves, Miller, Andrews, Brew and Hare with oxygen isotope stage 5e is p

ISSN:0267-8179    

DOI:10.1002/jqs.3390060306

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe relative weathering of a sequence of five palaesols formed in different parent materials, including bedrock of phonolitic composition, is described and assessed. The three lower palaeosols (units 3–5) are considered to be of interglacial origin. The saprolite (unit 5), in phonolite, formed prior to deposition of the lower Brunhes‐age till, is considered to be as old as the Brunhes Matuyama boundary (0.73 myr). The other two palaeosols in this group (units 3 and 4), derived from loess and till, respectively, formed over middle to late Brunhes time under palaeoclimates that were wetter (and presumably warmer), and of sufficient leaching power to move clay, as well as organically complexed extractable Fe and Al. The palaeosols in unit 3 are more complex than the lower ones. Their upper and lower horizons have about the same chemical composition as the lowest two palaeosols, while the middle horizons are similar to the upper two palaeosols (units 1 and 2). Radiocarbon dates for unit 3 are considered to be too young to account for the strong weathering in the upper and lower horizons. This interpretation is supported by high D/L ratios of aspartic acid. Overlying sediments, emplaced by episodic colluvial (unit 2) and slope wash (unit 1) processes, are less weathered; the lower colluvial unit in this group was emplaced during the late stade of the last glaciation. The surface sediments were emplaced more recently during the same interval and weathered mainly during the post‐glacial period. Tentative correlations with core 82PCS18 from the Canary Basin show that upper unit 3 is probably equivalent to Isotope Stage 5e, lower unit 3 to Isotope Stage 7, unit 4 to Isotope Stage 8, and unit 5 to Isotope Stage 9. Units 1 and 2 are firmly correlated with Isotope St

ISSN:0267-8179    

DOI:10.1002/jqs.3390060307

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:0267-8179    

DOI:10.1002/jqs.3390060309

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:0267-8179    

DOI:10.1002/jqs.3390060310

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:0267-8179    

DOI:10.1002/jqs.3390060311

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

ISSN:0267-8179    

DOI:10.1002/jqs.3390060312

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY