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1Department
of Geology and Petroleum Geology, University of Aberdeen, Aberdeen.
AB24 3UE.
1Department
of Geology and Petroleum Geology, University of Aberdeen, Aberdeen,
Scotland.
AB24 3UE.
Trenching
to bedrock combined with a ground magnetic survey over the margins of
the
northern half of the Rhynie basin show that the basin margins are
mostly fault
controlled. Four sets are
recognised: N-S, NE-SW, NW-SE and ENE-WSW. The first three sets include
faults
believed to have been active during sedimentation. The last set hosts
Permo-Carboniferous
dykes and may be of a similar age.
The
stratigraphic succession comprises three units, a lower mixed unit of
sandstones, shales, conglomerates and andesitic lava (>650m), a
middle unit
of laminated grey shale (c.250m) and an upper unit of laminated
sandstones and
shales (>200m).
Small
areas of chert float are found about 2 km east of the Rhynie SSSI and
are
interpreted as the surface expression of chert pods within the middle
shale
unit, which is believed to be the lateral equivalent of the shales
which host
the Rhynie cherts. The Windyfield cherts occur at a higher
stratigraphic level
within the upper unit. No further
centres of hydrothermal activity have been found in the northern half
of the
basin.
The beds are folded into a NE-SW trending syncline and refolded in the Rhynie area into a NW-SE trending anticline which, together with cross faults, control the distribution of the Rhynie cherts. The folding predates a Permo-Carboniferous dyke and may be related to compressive phases within a regional strike-slip system of late Caledonian age.
1Department
of Geology and Petroleum Geology, University of Aberdeen, Aberdeen,
Scotland.
AB24 3UE
2NERC
Isotopes Geosciences Laboratory, c/o BGS, Keyworth, Nottingham NG12 5GG
Whilst significant progress has been made
with
regards to our understanding of the Rhynie hot-spring system, both an
absolute
age for the hydrothermal activity and a definitive causal mechanism
have
remained elusive. High-precision U-Pb (TIMS) geochronology, as applied to key
igneous bodies, has the potential to resolve these outstanding problems.
In this contribution, we thus report new U-Pb mineral ages for an andesitic lava
(possessing a marginal peperitic facies where seen abutting sediments
lithologically and palynologically identical to those bearing the
Rhynie cherts)
and a suite of variably altered and mineralized intermediate-acidic intrusions present in the Rhynie
district. Published genetic models
for Rhynie require amendment.
1Department
of Earth Sciences, University of Cardiff, PO Box 914, Cardiff, CF10 3YE
Almost
90 years of investigation on the Rhynie Chert have added only one new
embryophyte sporophytic taxon (Trichopherophyton
teuchansii) to the five plants known to Kidston & Lang (Rhynia
gwynne-vaughanii, Aglaophyton major,
Asteroxylon mackiei, Horneophyton
lignieri and Nothia aphylla).
A further recent addition is Ventarura
lyonii from the Windyfield site. This
somewhat slow progress in adding to species diversity has been
compensated by
intriguing advances in disparity which have raised almost as many
questions as
such phenomenal preservation has solved. Sophistication
in growth pattern and in cell construction and arrangement is masked,
with one
exception, by simplicity in their axial, non-leafy architecture.
Detailed anatomical studies have permitted inferences on
palaeoeophysiology including quantification of their water relations,
while
stomatal frequencies have been used as atmospheric CO2
concentration
proxies. Spore dispersal mechanisms
have been deduced from sporangial wall construction.
Uncertainty still remains on the precise taxonomic
placement of Nothia,
Horneophyton and Aglaophyton. In all
cases more detailed information is needed on the ultrastructure of
water-conducting cells, including the apparent absence of discontinuous
secondary wall thickenings in Aglaophyton
which seemingly combines features of the hydroids of mosses with other
homoiohydric characters of tracheophytes. This
lack of conspecificity and arguably lack of congeners with coeval
Pragian
megafossils preserved in clastic rocks of the Old Red Sandstone
combined with
the unusual hot-spring setting of the ecosystem, provide evidence to
support the
contention that the Rhynie Chert assemblage may be a highly adapted one.
1
Forschungsstelle für Paläobotanik, Westfälische Wilhelms-Universität,
Hindenburgplatz 57, D-48143 Münster, Germany
2Department
of Geology and Petroleum Geology, University of Aberdeen, Aberdeen,
Scotland.
AB24 3UE.
The
Rhynie chert is not only of importance as one of the oldest
anatomically
preserved land floras, but also for the remarkable detail of
preservation and
for the occurrence of plants preserved in
situ. Seven land plant species are currently known from the Rhynie
chert and
the neighbouring Windyfield chert; five are common, one is rare and one
is only
known from the Windyfield chert. Several of these plants are now known
in great
detail.
Among
the most remarkable discoveries of the last decades are several
gametophytes
that have been described in the 1980s and early 1990s by Winfried Remy
and his
co-workers. They described two gametophytes with antheridia as Lyonophyton
rhyniensis and Kidstonophyton
discoides, and one gametophyte with archegonia as Langiophyton
mackiei. Based on similarities in tracheid structure
these can be related to three sporophytes, respectively Aglaophyton
major, Nothia
aphylla, and Horneophyton lignieri.
In
recent years more gametophytes showing various stages of development
have been
found. Moreover, several new types of gametophytes have been
encountered. With
the discovery of archegonia-bearing axes belonging to Aglaophyton
major, and antheridia-bearing gametophytes of Horneophyton
lignieri all essential stages of the life cycles of these two
plants are
known. One of the most spectacular finds is an in situ
gametophyte stand of Rhynia
gwynne-vaughanii with numerous antheridia- and archegonia-bearing
axes. Of
three of the Rhynie chert plants the alternation of generations can now
be fully
documented.
1Forschungsstelle
für Paläobotanik, Westfälische Wilhelms-Universität, Hindenburgplatz
57,
D-48143 Münster, Germany
Seven
species of land plants have been described from the Rhynie and
Windyfield
cherts. Of five of these, which are also preserved in in
situ stands, larger portions including basal parts are known. All
these
plants have a clonal growth and their basal parts served for anchorage
and
nutrition. Despite the relatively limited number of species, each of
these
plants shows specific morphological and histological adaptations of its
basal
parts to its substrate, varying from creeping rhizomatic axes, via
subterranean
tubers to deeper penetrating root-like axes.
Various
aspects of clonal growth and plant architecture will be discussed,
including the
ontogeny of the basal parts, and different of types of growth
strategies. Also
different histological adaptations of the basal parts to anchoring and
nutrition
will be shown. The basal parts of all five plant species are penetrated
by
glomacean fungi. Apparently these fungi were lining as endophytes
within the
intercellular spaces and did not harm their hosts, suggesting broad
adaptive
relations between soil fungi and these Rhynie chert plants.
1Institut für Geowissenschaften der Universität
Tübingen,
Sigwartstrasse 10, D-72076 Tübingen, Germany
1Centre
for Palynology, University of Sheffield, Dainton Building, Brookhill,
Sheffield,
England, S3 7HF
Spore
assemblages have been obtained from fine-grained horizons in cored
intervals
from throughout the Lower Devonian sequence of the Rhynie outlier. The
palynological preparations contain spores, phytodebris (cuticles,
tubular
structures, fungal hyphae) and fragments of arthropod cuticle.
Preservation
varies: it is generally excellent and the spores of relatively low
thermal
maturity, but in close proximity to lava and chert horizons thermal
maturity is
often high. All of the spore assemblages belong with the polygonalis-emsiensis
Spore Assemblage Biozone indicating a Pragian
age, and suggesting that the Rhynie deposits accumulated rapidly.
Comparisons
with coeval spore assemblages from southern Britain and the
Ardennes-Rhenish
region demonstrate regional differences. The Rhynie spore assemblages
are
generally of low diversity, with certain taxa, and indeed morphotypes
(e.g.
patinate spores), conspicuous by their paucity or total absence. This
probably
reflect differences between the flora of an inland intermontane basin
(Rhynie)
and the lowland floodplain (southern Britain). Detailed examination of in
situ spores preserved in the Rhynie chert plants permits
identification of
these spores in the dispersed spore assemblages. Analysis of the
occurrence and
distribution of these spores in dispersed spore assemblages (from
Rhynie and
elsewhere) is providing vital evidence regarding the ecology and
distribution of
the parent plants.
1Department
of Ecology and Evolutionary Biology, Natural History Museum and
Biodiversity
Research Center, University of Kansas, Lawrence, KS, USA
2
Forschungsstelle für Paläobotanik, Westfälische Wilhelms-Universität,
Hindenburgplatz 57, D-48143 Münster, Germany
It has
been hypothesised that fungi originated in the Precambrian based on
molecular
data; the earliest fossils, however, appear in the Ordovician.
Although these reports suggest that fungi have a long
evolutionary
history, none provides direct evidence for interactions with
microorganisms,
plants, or animals. The first unequivocal
evidence of fungal interactions with
plants occurs in the Early Devonian Rhynie Chert.
The exquisite preservation of this ecosystem provides a
unique
opportunity to document the morphology and life histories of fungi, and
to
decipher interactions with other organisms.
Continuing investigations of this aspect of the ecosystem
have identified
forms assignable to several major taxonomic groups (i.e.
Chytridiomycota,
Ascomycota, Zygomycota), as well as interactions including
saprophytism,
parasitism, and mutualism. Especially
significant are several forms of specific host responses to fungal
infection,
which indicate that Early Devonian plants had already evolved methods
of defence
that are identical to those of extant plants, and that the mechanisms
underlying
the establishment and sustenance of interactions between plants and
fungi were
well in place prior to the age of the Rhynie Chert.
1 Department
of Geology and Petroleum Geology, University of Aberdeen, Aberdeen,
Scotland,
AB34 3UE
2Laboratoire de
Paléontologie, Université de Montpellier
2, Place Eugène Batallion, Montpellier, France, F-34095
3 Forschungsstelle für Paläobotanik,
Westfälische
Wilhelms-Universität,
Hindenburgplatz 57, D-48143 Münster, Germany
A
diverse range of biota, representing both subaerial and subaqueous
ecosystems,
has been preserved in the Early Devonian Rhynie cherts, an ancient hot
spring
deposit in NE Scotland. A key element of the subaqueous ecosystem is
the
freshwater alga Palaeonitella cranii;
this relatively small, uncalcified charophyte has furcating branchlets
and
dactyls composed of allantoid cells. In the fertile part of the plant
antheridia
are found at every branching node, giving Palaeonitella
a nested appearance. Female gametangia have been observed
amongst P.
cranii thalli but are not seen in association with the antheridia
and it has
not been possible to determine the relationship between the two.
The crustaceans Castracollis
and Lepidocaris and the euthycarcinoid
Heterocrania are associated with Palaeonitella
and all are found in chert that formed as sinter in
freshwater pools.
Palaeonitella
cranii
is very similar in both structure and form to extant species belonging
to the
Nitelleae tribe of the Characeae. However, the reproductive organs,
although
undoubtedly those of charophytes, lack the diagnostic characteristics
that would
allow Palaeonitella to be assigned to
an established genera, either fossil or extant. Therefore, whilst P.
cranii can be considered an ancestor of the Nitelleae, its exact
taxonomic
position remains unclear.
1Department
of Geology &
Petroleum Geology, University of Aberdeen, Aberdeen, Scotland, AB24 3UE
The
Windyfield chert is located 700 meters north-east of the original
Rhynie chert
locality at Rhynie, Aberdeenshire. Originally identified by
concentrations of
surface float material, a drilling and trenching programme of the area
in 1997
revealed a chert ‘pod’ in situ
interbedded with fluvial/lacustrine sands and hydrothermally altered
shales.
This new material has allowed further insights into the nature of the
palaeoenvironments and palaeoecology of the Rhynie area during the
Early
Devonian.
Chert
morphotypes identified from float blocks and trench material range from
tabular
beds to lenticular pods displaying massive, nodular, laminated and
brecciated
textures. A suite of floral and faunal associations, when combined with
distinctive macro and microscopic chert textures, have been used to
interpret
depositional conditions. Palaeoenvironments ranged from terrestrial
laminated,
brecciated and vegetated sinter sheets to low temperature pools and
marginal
aquatic settings.
The
flora comprises six macro-land plant species, nematophytes, charophytes
and
various fungi and probable cyanobacteria. Arthropods include
lipostracan
branchiopods, a euthycarcinoid, trigonotarbid arachnids, centipedes,
eoarthropleurids and other enigmatic myriapods. Together the Windyfield
and
Rhynie cherts contain the most diverse associated fossil arthropod
fauna of
terrestrial and freshwater origin from rocks of comparable age anywhere
in the
world.
1Institut
für Systematische Zoologie, Museum für Naturkunde der
Humboldt-Universität zu
Berlin,
2Department
of Geology & Zoology, National Museums of Scotland, Chambers
Street,
Edinburgh, Scotland EH1 1JF
3Forschungsstelle
für Paläobotanik, Westfälische Wilhelms-Universität, Hindenburgplatz
57,
D-48143 Münster, Germany
A
harvestman (Arachnida: Opiliones) is described from the Early Devonian
(Pragian)
of the Rhynie Chert, Aberdeenshire, Scotland. This new genus and
species is the
oldest known harvestman and the fossil material includes both males and
females
preserving, respectively, a cuticular penis and ovipositor within the
opisthosoma. Both these structures are of essentially modern
appearance. The
Rhynie fossils also include a pair of large, branching trachea, again
with a
detailed morphology very similar to that of living taxa. This is the
oldest
record of arachnid tracheal respiration and strongly implies that the
Rhynie
harvestman was fully terrestrial. Based on its annulate, setose
ovipositor the
Rhynie fossils can be excluded from the extant clades Dyspnoi and
Laniatores in
which the ovipositor lacks annulations. The presence of median eyes and
long
legs argues against its inclusion in the extant clade Cyphopthalmi. Our
fossils
therefore represent either the extant clade Eupnoi or its putative
sister taxon.
This remarkable material is thus implicitly a crown-group harvestman
and is one
of the oldest known crown-group chelicerates. It also suggests an
extraordinary
degree of morphological stasis within the eupnoid line of the
Opiliones, with
the Devonian forms differing little in gross morphology – and perhaps
in
reproductive behaviour – from their modern counterparts.
1Department
of Geology & Zoology, National Museums of Scotland, Chambers
Street,
Edinburgh, Scotland, EH1 1JF
2Forschungsstelle
für Paläobotanik, Westfälische Wilhelms-Universität, Hindenburgplatz
57,
D-48143 Münster, Germany
Blocks
of Early Devonian (Pragian) Rhynie chert collected by Prof. Dr. W. Remy
in 1979
have yielded many examples of a new, unusual aquatic arthropod. The
small,
broadly ovoid test appears to be bivalved, but lacks the concentric
growth lines
of conchostracans. In transverse cross-section, the ventral surface
exhibits a
broadly “W”-shaped outline. A series of fine, setose appendages are
preserved positioned either side of the mid-line axis. In
well-preserved
examples, a ring-shaped internal structure is seen in this transverse
aspect. In
longitudinal cross-section, this structure is resolved into a segmented
tube
running axially. A small, anteriorly positioned rostrum is flanked
either side
by a pair of deep pits perhaps indicative of the sockets of antennal
appendages.
The arthropods are commonly found clustered together around plant axes,
comprising groups of up to 20 similarly sized individuals. The chert
texture
enclosing many individual specimens indicates a sub-aqueous
preservational
environment
The morphology of this new arthropod strongly suggests that it is a benthic cladoceran. This is significant as the record of the group only extends as far back as sub-fossil material from Recent lacustrine sediments. Examples of the same organism have recently been discovered in chert preparations from the nearby Windyfield site.
1Praxis
Critical Systems, 20 Manvers Street, Bath, BA1 1PX.
The fossils preserved in the Rhynie and Windyfield cherts include abundant and diverse coprolites. Coprolites of this age, known from Old Red Sandstone sedimentary rocks, are typically unvaried in morphology and content is largely dominated by plant spores. The assemblage preserved in the Rhynie chert differs; the coprolites are diverse in content and morphology and relatively few contain abundant plant spores. This assemblage of coprolites allows us some insight into the nature of Lower Devonian terrestrial food webs, indicating the presence of consumers differing in diet and life-habit. Modern relationships between faeces origin and character provide a key to interpretation, the faeces produced by soil-dwelling arthropods provide particularly useful analogues. Analysis of coprolite content and the available food provides further clues to their origin. They are concluded to be the product of at least four types of consumer including detritivores and herbivores. Spore-rich coprolites may suggest the presence of sporivory, however experimental results and fossil evidence reported in this paper suggest that they may be the product of detritivores.
1Geology
Department, National Museum and Galleries of Wales, Cardiff
Morphological
change during crystallisation masks the primary silica deposition
fabrics that
could reveal physicochemical conditions and processes active during
silica
permineralisation of fossil plants. Taphonomy experiments conducted in
Yellowstone hot springs and opal-A subfossils, however can provide
analogous
evidence of modern plant degradation and silicification.
In
experiments, high water temperatures and waterlogging reduced microbial
decomposition, promoting the retention of three-dimensional structure
even in
thin-walled parenchymatous cells. Silica in solution entered plants via
rhizomes, stomata and through the degrading epidermis/cuticle. Silica
permeated
parenchymatous cells within 30-days of immersion. Within plants, silica
polymerisation created cell wall lining films and intra-/intercellular
silica
sols (colloidal suspensions). Following 11-months, plants were
thoroughly silica
indurated. Inter- and intracellular silica deposition created a robust
silica
matrix that stabilised and replicated cell and tissue structure.
Silica fabrics in adjacent cells of similar function/structure displayed heterogeneity indicative of intraorganic microenvironments and fluctuating physicochemical conditions. Narrow particle size distributions suggest high levels of silica supersaturation and a single short-lived silica nucleation event, however, particle-aggregate cementation indicates low levels of supersaturation. Particle growth to the upper limit of colloidal stability and colloidal crystal structures indicate prolonged sol stability, whilst floc-like particle networks indicate localised sol instability.
1Geology
Department, Private Bag 92019, University of Auckland, Auckland, New
Zealand
Numerous
siliceous sinter deposits (Miocene-Recent) occur in the Taupo Volcanic
Zone,
Northland and Coromandel. They show
increases in structural ordering during diagenesis (noncrystalline
opal-A, to
paracrystalline opal-CT/opal-C, to microcrystalline quartz ± moganite),
progressive reductions in porosity and water content, and increases in
particle
density over ~30-40 kyrs. Microtextures
also change from solid opal-A spheres, to hollow spheres with minute
holes that
unfold into hexagonal platelets, which then gather into closely packed
opal-CT
bladed lepispheres. Further
diagenesis occurs along either fibrous or granular morphological
pathways.
Biotic/abiotic
inclusions are commonly well-preserved, except where patchy diagenesis
can
produce massive, mottled, quartzose sinter.
Consequently the aging of silica sinter recorded in the
North Island’s
thermal areas opens a series of taphonomic windows within a continuum
of
mineralogic-textural change. This
paleoenvironmental-diagenetic approach is useful for reconstructing
biosignals
in these and other extreme environments preserved in the geologic
record.
1Department
of Earth and Atmospheric Sciences,
University of Alberta, Edmonton, Canada, T6G 2E3
2Department
of Geological Sciences, University of Saskatchewan, Saskatoon, Canada,
S7N 5E2
3 US Geological Survey, 333 W. Nye Lane, Carson City, Nevada, U.S.A., 89706
The
geological and biological utility of silicified microbes relies largely
on the
validity of their taxonomic
Modern,
silica-precipitating hot springs, like those in New Zealand, are
natural
laboratories for assessing microbial silicification.
In those systems, some microbes are silicified while they
grow whereas
others have been replaced and encrusted by opal-A silica over several
decades. Their three-dimensional
preservation indicates that rapid
silicification occurred before decay had destroyed them.
Thus, many silicified microbes seem to be life-like
replicas of the
original microbes and therefore appear to preserve all the features
needed for
their identification. This, however, is
not the case.
The taxonomic identification of extant cyanobacteria, for
example, relies
on as many as 37 different features, most of which are not preserved by
silicification. Thus,
identification of silicified microbes must rely on a limited set of
morphological characteristics.
Our
incomplete understanding of how diagenesis affects microbes following
their
initial silicification further complicates the identification of
ancient
silicified microbes. The
identification of ancient silicified microbes, therefore, must be
undertaken
with great caution.
1Department
of Geological Sciences, University of Saskatchewan, Saskatoon, Canada,
S7N 5E2
2Department
of Earth and Atmospheric Sciences, University of Alberta, Edmonton,
Canada, T6G
2E3
3Department
of Geography, Hong Kong Baptist University, Kowloon Tong, Hong Kong,
China
Terraces
composed of siliceous sinter have formed downslope of geyser and hot
spring
vents at many major geothermal fields, including the Taupo Volcanic
Zone (New
Zealand), Yellowstone (Wyoming), and El Tatio (Chile).
The terraces are composed mainly of rimstone pools and rimstone dams, but they vary greatly in scale, morphology, and facies. Terrace growth commonly begins with opal-A precipitation at minor breaks of slope or upon obstacles, where fluids cool and evaporate. Terrace accretion and progradation are enhanced by positive feedback mechanisms. The factors that control terrace growth and its associated facies include original slope, chemical of composition of the outflow waters (especially amorphous silica saturation and pH), volume and temporal patterns of discharge, climate, and hydrostatic head. For example, where silica saturation is high and terrace growth is rapid, or where fluids are acidic or sulphurous, terrace surfaces commonly lack microbial mats even where waters are cool. Ornate geyserite or stratiform sinters may form. In contrast, thick bacterial mats may cover terrace surfaces where the outflow waters are neutral-alkaline and their silica saturation level is more moderate. Stromatolitic and intraclastic sinters form in the terrace pools. Such differences produce different fabrics in the terrace deposits that provide clues to the general nature of the spring system.
1Department of Plant and Soil Science, University
of Aberdeen,
Aberdeen, Scotland, AB24 3UU
2Department of Molecular and Cell Biology,
University of Aberdeen,
Aberdeen, Scotland, AB25 2ZD
3Department of Geology and Petroleum Geology, University of Aberdeen, Aberdeen, Scotland, AB24 3UE
The Rhynie system is
the oldest known
terrestrial hot spring system and contains within its sinters elevated
concentrations of gold, arsenic, antimony, tungsten and molybdenum.
These metal concentrations may be a result of inorganic
chemical
processes; however, there is also a possibility that microorganisms
played a
role in concentrating metals at the surface of the system.
1School of Earth Sciences, University of Leeds,
England
2IGNS, Wairakei Research Centre, Taupo, New Zealand
The silicification of microorganisms is a common occurrence in
active hot spring environments due to exposure
to geothermal waters supersaturated with respect to
amorphous opaline
silica. Such sites represent contemporary analogues for conditions
under which
microorganisms in ancient settings may have been fossilized. The role
microorganisms play in silica precipitation is not well defined and
previous
studies have focused on the morphological details and quality of
preservation,
both of which are influenced by microbial activity.
Although these studies provide useful information for a
better
understanding of the qualitative aspects of fossilization, they provide
no
insight into the mechanisms controlling microbially-mediated silica
accumulation
in environments such as modern hot springs or the ancient oceans.
1Department of Geology & Zoology, National Museums
of Scotland,
Chambers Street, Edinburgh, Scotland, EH1 1JF
2
Geology Department, National Museum & Galleries of Wales, Cardiff
3Department
of Geology and Petroleum Geology, University of Aberdeen, Aberdeen,
Scotland,
AB24 3UE
4
5225 Alkali Creek Rd., Billings, Montana, MT 59106-9511, USA
The
Norris Geyser Basin is arguably the most changeable and geothermally
active area
of Yellowstone National Park, Wyoming, USA. The basin consisting of
many
fumaroles, ‘frying pans’ (areas of sizzling ground), hot springs, hot
pools,
mud pots and geysers. Norris is predominantly an acid sulphate area
with many of
the geothermal features currently precipitating silica from solution.
We present
here the initial findings of a survey of the Norris Geyser Basin
deposits and
report a wide and varied fauna of arthropods preserved, and currently
preserving, within the siliceous sinters of the area. These include
dragonflies,
crickets, moths, spiders, beetles and hoverflies. To date, only three
of the
many hot springs in the area have yielded silicified fauna: Porkchop
geyser,
Opalescent spring and Medusa geyser. Subtly different preservational
mechanisms
are in operation at each locality, but the main controlling factors are
abnormally high dissolved silica values, frequent vent overspill and
the
presence of adhesive bacterial mats. The mode of preservation of these
arthropods has obvious implications for floral and faunal studies on
the fossil
sinter deposits of the Early Devonian Rhynie and Windyfield cherts,
Scotland,
and the Upper Devonian Drummond Basin cherts, Australia and comparisons
are
drawn with these sites.
1
Geology Department, National Museum & Galleries of Wales, Cardiff
2
5225 Alkali Creek Rd., Billings, Montana, MT 59106-9511, USA
In
Yellowstone, geothermally influenced wetlands (where hot spring fluids
mix with
abundant emergent-aquatic plants) are a major silicification
environment. Here,
plant preservation occurs at the cellular level, in growth position
(features
common to many Rhynie chert beds) as soil horizons become inundated by
rapidly
accreting opal-A sediments. Sediment remobilisation (scours) and
soft-sediment
deformation (slumps/desiccation cracks), features noted in the
Palaeozoic
Conway/Verbena geothermal system, Australia, where the vegetation also
locally
comprised wetland plants, are common.
Such
wetlands therefore have potential as analogues for Palaeozoic
environments of
silicification. However, most modern geothermal wetland sediments are
dominated
by diatom frustules, a biochemically precipitated silica source only
present
since the Late Jurassic.
A
recently discovered wetland, fed by geothermal run-off and dominated by
chemically precipitated opal-A sediment, may provide valuable evidence
of silica
deposition/silicification prior to the advent of the diatom
silica-sink. The
wetland contains plants and sedimentary structures directly comparable
to those
of more widespread diatomaceous wetlands. Over a 6-month period it
experienced
almost constant inundation by siliceous fluids, the development of
suspended
silica sols, and the colonisation, growth, senescence, partial
silicification
and burial of in situ wetland plants
as suspended silica was deposited.
1
Department of Palaeontology, Natural History Museum, Cromwell Road,
London, SW7
5BD, UK.
The
purpose of this poster presentation is to interest current and future
researchers in utilising the exceptionally large holdings of uncut
blocks of
Rhynie chert held at the NHM.
In
1963 and 1964 two trenches were dug at the Rhynie locality for the
International
Botanical Congress. The first trench (called 1A) was opened in the
‘lower
field’ in 1964. The other trench (called 2A) was opened in the ‘upper
field’ and remained open until 1964. This trench was almost exactly on
the
position of Tait’s No. 2 trench (opened circa 1912).
The
lithologies present in Trench 2A were recorded by Dr A.G. Lyon and Dr
W.
El-Saadawy, the results of which were recorded in a manuscript and
El-Saadawy’s
PhD thesis.
Whilst
these trenches were open, Dr John Pettit, Cedric Shute and Peter
Whybrow (all
from the NHM) collected several tons of highly fossiliferous material
from one
trench. These samples were collected at intervals of 1 foot (0.3m) for
the first
10 feet (3.05m) of the trench. Correlating these samples with the work
of Lyon
and El-Saadawy has led the author to conclude that the samples were
collected
from Trench 2A
1Department
of Geology & Petroleum Geology, University of Aberdeen, Aberdeen,
Scotland,
AB24 3UE
A new
crustacean is described from the Rhynie Chert. This discovery is the
first
unequivocal addition to the crustacean element of the fauna since the
discovery
of the enigmatic lipostracan Lepidocaris
rhyniensis.
The
material comprises complete individuals up to 8mm long plus fragmentary
remains.
The head is frequently detached from the body, and damage to the
anterior of the
thorax suggests most specimens are exuviae. The head region appears
domed with a
labrum and a pair of robust mandibles and long biramous antennae. A few
specimens exhibit what may be a detached and poorly preserved
cephalo-thoracic
shield. The trunk is multi-segmented, both thorax and abdomen
possessing similar
ring-like somites. The thorax variably comprises up to 26 segments. The
anterior
11 segments possess long homologous, phyllopodous appendages, the
remainder
variably possess 10 to 15 phyllopodous appendages with a disposition of
one per
somite. The abdomen comprises up to 28 apodous segments. The tail
comprises a
telson with two caudal furcae.
1Department
of Geology & Petroleum Geology, University of Aberdeen, Aberdeen,
Scotland,
AB24 3UE
2
Department of Geology & Zoology, National Museums of Scotland,
Chambers
Street, Edinburgh, Scotland, EH1 1JF
We
have created, with funding from the Joint Information Systems Committee
(JISC),
a web-based teaching and learning resource based on the Rhynie Chert
and its
flora and fauna. The resource is designed for use as an Honours level
palaeontology course, but has application for botanists, zoologists,
hot-spring
enthusiasts and interested amateurs.
The
data-base includes sections on History of Research, Geology of the
Rhynie area,
the biota, and comparisons with modern hot-spring environments. A
glossary and
extensive reference list is also included. An illustrated description
is given
for each of the major plants and animals so far described from the
chert.
A
‘teaching manual’ section gives ideas for tutors on course content and
assessment with suggested essay and examination question topics. This
particular
section will be password protected, tutors interested in accessing this
should
contact the authors.
The
learning resource may be accessed through the University of Aberdeen,
Department
of Geology and Petroleum Geology web site at www.abdn.ac.uk/rhynie
and
the authors would welcome suggestions for improvements and feedback
from tutors
using the course. The site will be updated as new material is described
in the
literature.
1. New
Brunswick Museum, 277 Douglas Avenue, Saint John, NB Canada E2K 1E5
2.
School of Geosciences, Monash University, Clayton, Victoria 3800, and
Queensland
Museum, S. Brisbane, Qld 4101, Australia
Early
Devonian (Pragian-Emsian) rocks from the Campbellton Formation indicate
early
complex terrestrial ecosystems resembling a modern land surface.
Modelling the
evolution of early vertebrates within these environments can
potentially aid
understanding of current problems (deforestation, land/water
degradation). A new
look at the Atholville beds exposes volcanic events inundating
vegetated coastal
plains. Sugarloaf Mountain was probably the source of ash and
fast-flowing
mudflows. Ostracodes, snails, eurypterids, plants, cephalaspids,
placoderms,
acanthodians, and chondrichthyans were killed in one devastating event,
leaving
a chaotic mess of remains and bedded rock chunks. This
geographically-limited
basal beds lahar formed almost instantaneously. Higher beds are
paler-coloured,
lagerstätten mudstones with well-preserved remains suggesting quieter
lagoonal
conditions. Large carapaces of euryperid Pterygotus
anglicus result from mass-moult ecdysius. The earliest known shark
with
tooth rows and a dental lamina, Doliodus,
also had paired fin spines, necessitating all acanthodian taxa based on
fin
spines to be examined including from comparative sites, e.g., in
Scotland.
Comparison of faunas suggests close geographic links between the
Midland Valley
and Avalon terranes as island arcs then among a range of terranes
scattered
across temperate to subtropical (mainly northern) palaeolatitudes.
Eurypterids,
plants, and vertebrates are closely comparable between Canada, Scotland
(and as
far 'east' as Podolia).
1Geological
Sciences Division, British Antarctic Survey, Cambridge CB3 0ET, UK
2
Scottish Universities Environmental Research Centre, Glasgow G75 0QF,
Scotland,
UK
Hydrothermal systems in eroded settings may be useful analogues in understanding the Rhynie system at depth. The South Shetland Islands volcanic arc (West Antarctica, ~ 62°S) contains an 80 km zone of propylitized volcanic rocks, with numerous silicic, sericitic, argillic and advanced-argillic occurrences. At Barton Peninsula, a terrestrial sequence of plant-bearing shales and basaltic lavas (49-44 Ma) contains massive chalcedonic-quartz, cherty veining and sericitic/propylitic alteration along ESE faults. Similar silicic clasts occur in nearby lapilli tuffs. Drusy quartz, calcite veins may represent feeders to the near-surface silicification. A deep, near neutral-pH geothermal system is suggested by anomalous Ag, Pb, Sb, Au, Te, Se, Zn, As, δ34S ~ -2 ‰ and 18Oqz of +4 to +7 ‰. The lavas and silicified zones were then brecciated and replaced by massive alunite (+ native S, pyrite) and pyrophyllite (+ pyrite, zunyite, diaspore) with anomalous Hg, Se, As, Bi, Au, Tl, Sb, Cu. Such advanced-argillic alteration is typical of magmatic volatiles (δ18O = +6 to +10 ‰) mixing with near-surface (<500 m) meteoric groundwaters (δ18O -8 ‰, D –55 ‰). δ34S alunite of +9 to +27 ‰ and pyrite of –20 to –5 ‰ indicate complex sulphur sources and kinetic processes. Barton Peninsula may be an analogue for Rhynie, 500m to 1 km below the land surface. Eocene plant communities in the South Shetland Islands arc may have been centred on active hot-spring systems.
1Department
of Geology and Petroleum Geology, University of Aberdeen, Aberdeen,
Scotland,
AB24 3UE
The
Rhynie Cherts represent the earliest known subaerial expression of a
hot-spring
system and preservation of the biota in the vicinity of the hot-springs
provides
a unique insight into Early Devonian terrestrial and freshwater
ecosystems. The
cherts occur within the Dryden Flags and Shales; a series of fluvial
overbank
and lacustrine sediments, deposited on an alluvial plain with small
lakes.
Three
boreholes drilled within the Rhynie SSSI intersected the Rhynie chert
in situ
allowing identification of up to 38 discrete chert beds. The floral
content,
organic and detrital textures, of each chert bed were used to attempt
correlation of the Chert beds and give an insight into lateral
variation.. Flora
and macroscopic chert textures were found to be of greatest use for
correlation.
It is
shown that over the 45-65 m distance covered by the boreholes general
correlation can be made of the chert-bearing unit, and also sandstone
and shale
units. However there is no bed-to-bed correlation of the cherts or
other
lithologies, neither is there a correlation in the sequences of plants
recorded.
1Department of Entomology, 4112 Plant Sciences Building, University of Maryland, College Park, MD 20742, USA
Much of our knowledge of Devonian arthropod faunas of the Old Red Sandstone continent is derived from two deposits, the Lower Devonian Rhynie Chert of Scotland and the Middle Devonian Panther Mountain Formation at Gilboa, New York State. At each of these localities, the arthropod fauna is preserved as organic cuticle, in chert and mudstone respectively. These faunas are comparable in composition to extant litter/soil faunas and are comprised of small detritivores (e.g. mites, collembolans, small arthropleurideans) and their predators (e.g. trigonotarbids, centipedes, pseudoscorpions). At each of these localities macro-arthropods are only represented by fragmentary remains, likely reflecting taphonomic biases. In contrast to Rhynie and Gilboa, the remaining known ORS terrestrial arthropods are macro-arthropods. Macro-arthropods have been found in three majors areas of the ORS: the Midland Valley of Scotland, the Maritime Provinces of Canada, and the Catskills of Pennsylvania and New York States. Arthropods from these localities consist almost exclusively of scorpions, millipedes and kampecarids, of which the millipede fauna (comprised of five genera in three orders) is best known.
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