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WILLIAM R. EVITT
882 Cedro Way
Stanford, CA 94305
SARAH PIERCE DAMASSA
3 Ridge Street
Winchester, MA 01890
NAIRN R. ALBERT
6 Lavenida Drive
Orinda, CA 94563
(Reprint requests should be sent to the second author.)
Study of Palaeoperidinium pyrophorum and P. cretaceum leads to the conclusion that the principal fossilized wall in both species (here termed the exophragm) formed in an extrathecal position in intimate contact with the exterior surface of the theca. Specimens of P. pyrophorum from ten widespread Late Cretaceous and Paleocene localities and of P. cretaceum from the Early Cretaceous of Alaska were examined with light and scanning electron microscopy. An electronic technique for inverting an SEM image (i.e., exchanging light for dark pixels) and a manual microcasting technique provide support for this interpretation. In some specimens, the exophragm encloses a two-walled intrathecal cyst, like the conventional periphragm and endophragm of many fossil peridiniacean dinoflagellates. A minute but elaborately configured structure in a midventral position on the exophragm apparently includes the insertion points of the two flagella; it is illustrated with SEM stereopairs. Pillar-like projections produced where material of the developing cyst wall partially filled trichocyst pores of the theca are especially distinctive features on the interior surface of the exophragm. Comparable structures occur on the exterior of the periphragm in some species of other genera (e.g., Deflandrea, Subtilisphaera, Mikrocysta, and Phanerodinium), where they appear to have originated similarly; that is, from material that formed the periphragm. Such an interpretation accords with the intrathecal position generally attributed to the periphragm. However, the conclusion that the pillar-like structures interconnecting the two walls in still other dinoflagellates (e.g., certain species of Charlesdowniea, Chlamydophorella, Gardodinium, and Dinopterygium) are also trichocyst pore fillings has an unexpected implication: the outermost wall in many species of fossil dinoflagellates is an exophragm comparable to that in Palaeoperidinium. The further critical study of the exophragm that this interpretation invites may lead to a better understanding of homologies among cyst wall structures and to a more consistent descriptive terminology for cysts with multiple walls.
Concepts of the genus, Palaeoperidinium, and two species,
P. pyrophorum and P. cretaceum, are emended to accord
with observations in the SEM and the interpretation of their principal
wall as an exophragm. Nineteen other species18 listed as species
of Palaeoperidinium by Williams et al. (1998) and P.
eurypylum, which is reattributed herein to Palaeoperidinium
from Saeptodiniumare provisionally accepted in the genus
pending clarification of their characters in the SEM.
JAMES B. RIDING
British Geological Survey
Keyworth
Nottingham NG12 5GG
United Kingdom
j.riding@bgs.ac.uk
SUSAN L. MATTHEWS
Department of Geological Sciences
University College London
Gower Street
London WC1E 6BT
United Kingdom
NICHOLAS H. MILES
Robertson Research International Limited
Llanrhos
Llandudno
Gwynedd LL30 1SA
United Kingdom
nhm@robresint.co.uk
ANTON WOLFARD
Nederlandse Aardolie Maatschappij B.V.
XGS/33, Postbus 28000
9400 HH Assen
The Netherlands
a.wolfard@openmail.xgs31.namass.simis.com
A new morphologically distinct
polygonomorph acritarch, Metaridium
solidispinum sp. nov. occurs
in the Hauterivian-lowermost Barremian (Lower Cretaceous) strata
of eastern England and the southern North Sea Basin. This morphotype
is small and rectangular with a simple, long and solid process
emanating from each corner and a large pylome. This species is
persistent, relatively common and confined to the Hauterivian-lowermost
Barremian, and hence is deemed to be a reliable stratigraphic
marker. Metaridium solidispinum is, however, most characteristic
of the upper Hauterivian.
MIRTA E. QUATTROCCHIO
ANA M. BORROMEI CONICET
Departamento de Geología
Universidad Nacional del Sur
San Juan 670
8000 Bahía Blanca, Argentina
Pollen analysis from a sedimentary section in the valley of the
Sauce Grande River (southwestern Buenos Aires Province) and a
peat core from the Andorra Valley (southern Tierra del Fuego)
provides evidence for the apparent large-scale synchroneity of
major past vegetational changes and inferred climatic trends during
the late Pleistocene and Holocene in this region. Climate before
10,000 years B.P. was relatively cold and dry, both in southwestern
Buenos Aires Province and in southern Tierra del Fuego. A climatic
amelioration to warmer and wetter conditions during the late Pleistocene
and early Holocene is recorded in both regions. Late Holocene
climates show greater variability and they suggest the onset of
modern environmental conditions as represented by cool and wet
conditions in southern Tierra del Fuego, and by arid to semi-arid
conditions in southwestern Buenos Aires Province.
BAS VAN GEEL
Department of Palynology and Paleo/Actuo-ecology
The Netherlands Centre for Geo-ecological Research
Kruislaan 318
1098 SM Amsterdam
The Netherlands
E-mail: vangeel@bio.uva.nl
Microfossils of the form taxon Schizosporis reticulatus
might well be the resting eggs of rotifers related to the extant
species Hexarthra mira. Palynological records of this warmth-demanding
planktonic organism, which occurs in conditions of pH higher than
7, may help to reconstruct paleoenvironmental conditions.
JORUNN OS VIGRAN
IKU Petroleum Research
N-7034 Trondheim, Norway
(Present address: Hans Hagerups gt. 10
N-7012 Trondheim, Norway)
GUNN MANGERUD
IKU Petroleum Research
N-7034 Trondheim, Norway
(Present address: Norsk Hydro ASA
N-5020 Bergen, Norway)
ATLE MØRK
IKU Petroleum Research
N-7034 Trondheim, Norway
TOM BUGGE
IKU Petroleum Research
N-7034 Trondheim, Norway
(Present address: Saga Petroleum ASA
N-1301 Sandvika, Norway)
WOLFGANG WEITSCHAT
Geologisch-Paläontologisches Institut
Universität Hamburg
Bundesstrasse 55
D-20146 Hamburg, Germany
Material from shallow cores drilled through the uplifted and truncated deposits near the Svalis Dome in the Barents Sea contains Lower and Middle Triassic palynomorphs and ammonoids. Eight miospore assemblage zones have been established in this paper, and six of them are calibrated by ammonoids:
Svalis-1 is dated by ammonoids of the late Griesbachian commune Zone. The assemblage is recovered from the Havert Formation overlying the Permian limestone.
Svalis-2 is dated by ammonoids to the late Smithian tardus Zone. The deposits belong to the lower and middle parts of Klappmyss Formation. The unit represents the transgressive systems tract of a Smithian-early Spathian T-R Sequence.
Svalis-3 is recorded from the youngest part of Klappmyss Formation which is missing age conclusive faunal evidence. The palynological assemblage is correlated as early Spathian in age. The deposits represent the regressive systems tract of the Smithian-early Spathian T-R Sequence.
Svalis-4 is recovered from rocks deposited above the lowest part of the Steinkobbe Formation. Ammonoids of the subrobustus Zone date the deposits to the late Spathian. The main part of the unit represents the transgressive systems tract of the Spathian
Svalis-5 is recovered from a thin interval representing the middle part of the Steinkobbe Formation. Ammonoids restricted to the arkhipovi and evolutus zones date the assemblage as early Anisian. The deposits represent the lowest part of the lower-middle Anisian transgressive systems tract.
Svalis-6 is dated by ammonoids of the middle Anisian varium Zone. The assemblage is recovered from deposits representing the middle part of Steinkobbe Formation. The deposits comprise the upper part of a transgressive systems tract as well as the regres-sive systems tract of the lower-middle Anisian T-R sequence.
Svalis-7 is dated by ammonoids related to the late Anisian laqueatus Zone. The assemblage is recovered from the youngest part of Steinkobbe Formation, a unit which is interpreted as comprising the upper Anisian T-R sequence and the Ladinian transgressive systems tract above it.
Svalis-8 is recovered from deposits representing the middle part
of Snadd Formation. The deposits are dated as Ladinian on the
basis of palynological correlation. They represent the regressive
systems tract of the Ladinian T-R sequence.
HENRIK NØHR-HANSEN
The Geological Survey of Denmark and Greenland
Thoravej 8
DK-2400 Copenhagen NV
Denmark.
DAVID J. McINTYRE
3503 Underhill Drive N.W
Calgary, Alberta T2N 4E9
Canada
The dinoflagellate cyst assemblages from four Lower Cretaceous
sections from Melville Island, Axel Heiberg Island and Ellesmere
Island in the Northwest Territories, Canada are described. The
sections represent the upper part of the Isachsen Formation and
the Christopher Formation. The strata studied comprise a composite
stratigraphic section of approximately 1400 m of shale and siltstone
deposits. The study of 33 samples yielded 83 dinoflagellate cyst
species, which date the strata as late Barremian to early late
Albian. The flora discussed is correlative with assemblages described
from other parts of the arctic area. This study provides new and
detailed palynological information about the Lower Cretaceous
of the Arctic Islands. Comments are included on the morphology
and ranges of: Acanthaulax sp. aff. A.? tenuiceras,
Apteodinium sp. cf. A. maculatum ssp. grande,
Balmula sp. cf. B. tripenta, Batioladinium longicornutum,
Batioladinium shaftesburiense, Canningia reticulata,
Catastomocystis spinosa, Circulodinium sp. cf. C.
attadalicum, Conosphaeridium sp., Cribroperidinium
sp. aff. C. conopium, Fromea triquetra, Muderongia
pariata, Nyktericysta davisii, Nyktericysta?
vitrea, Nyktericysta sp., Pseudoceratium sp.
aff. P. toveae, Pseudoceratium sp., Rhombodella
paucispina, Senoniasphaera microreticulata, Vesperopsis
mayi and Vesperopsis nebulosa.
S. P. HORN
Department of Geography
University of Tennessee
Knoxville, TN 37996
JOHN C. RODGERS III
Department of Geography
University of Georgia
Athens, GA 30602
KENNETH H. ORVIS
Department of Geography
University of Tennessee
Knoxville, TN 37996
LISA A. NORTHROP*
Department of Geography
University of Tennessee
Knoxville, TN 37996
We investigated the potential of soil pollen analysis to provide information about recent land use and vegetation history in the lowland humid tropics. Our initial work at the La Selva Biological Station in Costa Rica revealed that pollen was surprisingly well preserved in mineral soil, with pollen concentrations in the upper 10 cm of our soil cores as high as values for some lake sediment samples. Pollen percentages in our initial core samples showed down-core variations that appeared to relate to what we knew about past episodes of forest clearance, pasture establishment, and secondary succession at our sampling sites.
We carried out further tests of soil pollen analysis by collecting
and analyzing additional soil cores from the La Selva Biological
Station. Based on these new results, we conclude that soil pollen
analysis in the lowland humid tropics does not hold the promise
suggested by our initial work. Most pollen in our soil cores may
be only a few decades old, and rapid downwash and/or bioturbation
may prevent the development of a stratigraphy at some sites. Poor
reproducibility at a scale of meters suggests that where a distinct
pollen stratigraphy exists, it may be highly localized, as soil
pollen profiles collected under tropical forest canopies may sample
very small areas. Alternatively, small (1-cc) samples may be unrepresentative
of soil horizons. A large number of samples will be needed in
either case to characterize the land use and vegetation history
of even a fairly small area. However, extreme locale-specificity
could be an advantage for detection of evidence of the past occurrence
of a particular plant taxon at a given location.
MARCO TONGIORGI
Dipartimento di Scienze della Terra
Università di Pisa
Via S. Maria 53
56126 Pisa
Italy
LEIMING YIN
Institute of Geology and Palaeontology
Academia Sinica
39 East Beijing Road (Chi-Ming-Ssu)
210008 Nanjing
People's Republic of China
ANNA DI MILIA
Dipartimento di Scienze della Terra
Università di Pisa
Via S. Maria 53
56126 Pisa
Italy
CRISTIANA RIBECAI
Dipartimento di Scienze della Terra
Università di Pisa
Via S. Maria 53
56126 Pisa
Italy
The lower part of the Dawan Formation (lower Arenig) from both
the Huanghuachang and the Daping sections (Yangtze Platform, Hubei
Province, South China) has yielded rich acritarch assemblages
dominated by the "cold water taxa" which are characteristic
of the high latitude Perigonwanan (or "Mediterranean")
Acritarch Paleoprovince. New findings show that the top of the
Dawan Formation (uppermost Arenig) is characterized by a very
different scenario. Here, elements of the Perigondwanan microflora
are missing, while the phytoplankton communities have typical
"Baltic" affinities. This change in the microfossil
composition within the Dawan Formation may be attributable to
a variety of different constraints, such as a modification in
the pattern of oceanic currents (influenced by changing paleogeography)
or sea level fluctuations (related to eustatic cycles).
KENNETH H. ORVIS
Department of Geography
University of Tennessee
Knoxville, Tennessee 37996-1420
Surface pollen samples collected along three transects that cross
the southern margin of the Sonoran Desert east of the Gulf of
California reflect regional vegetation gradients but also show
strong local variability, notably within the southern desert.
Chenopodiaceae-Amaranthaceae (Cheno-Am) and Gramineae pollen dominate
in tropical deciduous forest; Pinus and Quercus
in temperate-climate vegetation at high elevations; and Gramineae
and High-Spine Compositae in the central Sonoran Desert (>29·
N). The ERA group (composed largely of Euphorbiaceae, Rutaceae,
Anacardiaceae), Gramineae, Cheno-Am, and High-Spine Compositae
pollen inter-vary but dominate as a group in the southern desert;
Cheno-Am here may signal irrigated agriculture. Coastal sites
differ from the above, with Cheno-Am pollen strongly dominant
in saline conditions.
W. E. BOYD
C. J. LENTFER
Southern Cross University
Lismore, New South Wales
Australia
R. TORRENCE
Australian Museum
Sydney, New South Wales
Australia
The archaeology of prehistoric occupation of the island of Garua,
West New Britain, is beginning to provide a detailed picture of
human adaptation to a highly volatile environment in which periodic
catastrophic destruction of vegetation, soils and, presumably,
human habitation, is countered, apparently, by the human ability
to recolonise and adapt to changing circumstances. However, our
ability to fully identify these human responses is presently limited
by a lack of paleoenvironmental data. This wet tropical region
presents specific problems in obtaining and analysing such data.
In this case these problems are in part being overcome by the
use of fossil phytolith analysis. However, to put this technique
into use, several methodological issues have had to be addressed.
This paper considers several of these, describing experiments
testing preparation techniques, introducing key elements influencing
assemblage compositions in this environment, and outlining the
form of statistical analyses adapted and adopted to interrogate
the large multivariate data set. Results are described from tests
using modern analogue samples, which indicate promise in the ability
of the analytical techniques to identify and differentiate key
indicators of the complex and dynamic environment of prehistoric
West New Britain.