journal of paleontology
1
volume 87 ■ Number 1 ■ JANUARY 2013 ■ ISSN 0022-3360
1
Patricia Vickers-Rich, Andrey Yu. Ivantsov, Peter W. Trusler, Guy M. Narbonne, Mike Hall,
Siobhan A. Wilson, Carolyn Greentree, Mikhail A. Fedonkin, David A. Elliott, Karl H. Hoffmann,
and Gabi I. C. Schneider
Reconstructing Rangea: new discoveries from the Ediacaran of southern Namibia
16 James C. Brower
Paleoecology of echinoderm assemblages from the Upper Ordovician (Katian) Dunleith Formation of northern
Iowa and southern Minnesota
44Rimma R. Khodjanyazova and Vladimir I. Davydov
Late Moscovian fusulinids from the “N” Formation (Donets Basin, Ukraine)
69Timothy P. Topper, Christian B. Skovsted, David A. T. Harper, and Per Ahlberg
A bradoriid and brachiopod dominated shelly fauna from the Furongian (Cambrian) of Västergötland, Sweden
84 Henning Scholz and Matthias Glaubrecht
Shell and operculum taphonomy of the bithyniid gastropod Gabbiella in the Pleistocene Turkana Basin, north
Kenya
91
Dermeval Aparecido Do Carmo, João Carlos Coimbra, Robin Charles Whatley,
Lucas Silveira Antonietto, and Raphael Teixeira De Paiva Citon
Taxonomy of limnic Ostracoda from the Alagamar Formation, middle–upper Aptian, Potiguar Basin,
northeastern Brazil
105Thomas Saucede, Alain Bonnot, Didier Marchand, and Philippe Courville
A revision of the rare genus Cyclolampas (Echinoidea) using morphometrics with description of a new species
from the upper Callovian of Burgundy (France)
151 Washington Jones, Andrés Rinderknecht, Rafael Migotto, and R. Ernesto Blanco
Body mass estimations and paleobiological inferences on a new species of large Caracara (Aves, Falconidae)
from the late Pleistocene of Uruguay
159Michał Zatoń, Paul D. Taylor, and Olev Vinn
Early Triassic (Spathian) post-extinction microconchids from western Pangea
166 Jeffrey R. Thompson, William I. Ausich, and Legrand Smith
Echinoderms from the Lower Devonian (Emsian) of Bolivia (Malvinokaffric Realm)
■ Pages 1–176
147 Phil R. Bell, Federico Fanti, John Acorn, and Robin S. Sissons
Fossil mayfly larvae (Ephemeroptera, cf. Heptageniidae) from the Late Cretaceous Wapiti Formation, Alberta,
Canada
■No 1
123 Vladimir N. Makarkin and S. Bruce Archibald
A diverse new assemblage of green lacewings (Insecta, Neuroptera, Chrysopidae) from the early Eocene
Okanagan Highlands, western North America
Volume 87
Journal of Paleontology
Taxonomic Note
■
176 David M. Rohr, Jirí Frýda, and Robert B. Blodgett
Alaskodiscus, a new name for the Ordovician bellerophontoidean gastropod Alaskadiscus Rohr, Frýda and
Blodgett, 2003
JANUARY 2013
vol 87 No 1 JANUARY 2013 The Paleontological Society
Journal of Paleontology, 87(1), 2013, p. 1–15
Copyright Ó 2013, The Paleontological Society
0022-3360/13/000187-0001$03.00
RECONSTRUCTING RANGEA: NEW DISCOVERIES FROM THE EDIACARAN
OF SOUTHERN NAMIBIA
PATRICIA VICKERS-RICH,1 ANDREY YU. IVANTSOV,2 PETER W. TRUSLER,1 GUY M. NARBONNE,3 MIKE
HALL,1 SIOBHAN A. WILSON,1 CAROLYN GREENTREE,1 MIKHAIL A. FEDONKIN,2 DAVID A. ELLIOTT,1
KARL H. HOFFMANN,4 AND GABI I. C. SCHNEIDER4
1
School of Geosciences, Monash University, Clayton, Vic. 3800, Australia, ,[email protected].; 2Paleontological Institute, Russian Academy of
Sciences, Profsoyuznaya ul. 123, Moscow 117997, Russia, , mfedon@paleo. ru.; 3Department of Geological Sciences and Geological Engineering,
Queens University, Kingston, Ontario, Canada, ,[email protected].; and 4Namibian Geological Survey, Ministry of Mines and Energy,
Windhoek, Namibia, ,[email protected].
ABSTRACT—Rangea is the type genus of the Rangeomorpha, an extinct clade near the base of the evolutionary tree of large,
complex organisms which prospered during the late Neoproterozoic. It represents an iconic Ediacaran taxon, but the
relatively few specimens previously known significantly hindered an accurate reconstruction. Discovery of more than 100
specimens of Rangea in two gutter casts recovered from Farm Aar in southern Namibia significantly expands this data set,
and the well preserved internal and external features on these specimens permit new interpretations of Rangea morphology
and lifestyle. Internal structures of Rangea consist of a hexaradial axial bulb that passes into an axial stalk extending the
length of the fossil. The axial bulb is typically filled with sediment, which becomes increasingly loosely packed and porous
distally, with the end of the stalk typically preserved as an empty, cylindrical cone. This length of the axial structure forms
the structural foundation for six vanes arranged radially around the axis, with each vane consisting of a bilaminar sheet
composed of a repetitive pattern of elements exhibiting at least three orders of self-similar branching. Rangea was probably
an epibenthic frond that rested upright on the sea bottom, and all known fossil specimens were transported prior to their
final burial in storm deposits.
Ediacaran fossil localities (Xiao and Laflamme, 2009). This
taxon is not known from Newfoundland, and the single
specimen reported from the Flinders Ranges of South Australia
(Gehling, 1991, pl. 3, fig. 1) was subsequently referred to the
genus Beothukis Brasier and Antcliffe, 2009 due to the presence
of primary elements that consistently show only one side of the
rangeomorph structure (Narbonne et al., 2009). The relatively
small number of quite variable specimens of Rangea has
significantly impeded determination of its life habit and threedimensional reconstruction, leading to the many different
interpretations noted above.
Two sedimentary concentrations totaling more than 100
complete and partial specimens of Rangea are herein reported
from Farm Aar in southern Namibia (Fig. 1). The original
discovery was from float (Vickers-Rich, 2007, fig. 116), with
additional discoveries of float and abundant in situ material
made by the authors over the following years. Fossils were
excavated under permits from the National Heritage Council of
Namibia, and specimens are deposited with the Geological
Survey of Namibia, National Earth Science Museum (NESM) in
Windhoek. These new specimens increase the Rangea dataset by
a factor of five and exhibit a unique style of preservation that
permits some investigative preparation, revealing previously
unknown internal features and significantly enhancing our
understanding of Rangea and its place in the early evolution
of complex macroscopic life.
INTRODUCTION
T
EDIACARAN frond Rangea Gürich, 1930 was the first large
and complex Precambrian fossil named and described
anywhere in the world, and remains an iconic image of the
Ediacara biota. Rangea is a centimeter- to decimeter-scale frond
consisting of several ‘vanes’ or ‘petaloids’ (sensu Jenkins, 1985;
Laflamme and Narbonne, 2008a, 2008b) that radiate from the
axis with each vane consisting of a sheet of elements composed
of a repetitive pattern of self-similar branches. In the century
since its original discovery in 1908, Rangea has been studied by
many Ediacaran researchers but remains enigmatic. Estimates of
the number of vanes in Rangea have ranged from two (Gürich,
1930, 1933; Richter, 1955) to three (Grazhdankin and Seilacher,
2005) or three pairs (Pflüg, 1972) to four (Dzik, 2002) to five
(Pflüg, 1970; Jenkins, 1985) and possibly six (Pflüg, 1972).
Rangea is normally reconstructed as an epibenthic frond
(Richter, 1955; Pflüg, 1970; Jenkins, 1985; Dzik, 2002;
Laflamme et al., 2009) but was interpreted as living infaunally
by Grazhdankin and Seilacher (2005). Early interpretations of
Rangea regarded it as representing a primitive example of living
radial phyla, either Ctenophora (Gürich, 1930, 1933) or Cnidaria
(Richter, 1955), but with rare exceptions (Jenkins, 1985; Dzik,
2002) most modern workers regard Rangea and other rangeomorphs as members of an extinct clade in the early evolution of
complex multicellular life (Pflüg, 1972; Seilacher, 1992, 2007;
Narbonne, 2004; Brasier and Antcliffe, 2004; Gehling and
Narbonne, 2007; Xiao and Laflamme, 2009; Erwin et al., 2011).
The first Rangea specimens were collected from Namibia
early in the twentieth century (Germs, 1972, 1973) and were
later formally described by Gürich (1930, 1933). All of the
relatively few (,21) Rangea specimens collected in Namibia
before 2004 were found as float by either herders or mapping
geologists and later turned over to paleontologists for study. A
few specimens of Rangea have also been described from the
White Sea in Russia (Grazhdankin, 2004; Grazhdankin and
Seilacher, 2005), but the genus is not known from any other
HE
GEOLOGICAL AND ENVIRONMENTAL SETTING
The Nama Group is a 3-km thick succession of generally flatlying, fine-grained siliciclastic and carbonate strata that nonconformably overlie Mesoproterozoic basement in southern
Namibia (Fig. 2.1). Nama Group strata were deposited and
slightly deformed in a foreland basin that developed during
collision of the Damara and Gariep structural belts in the late
Ediacaran and early Cambrian, and have been divided into three
sub-groups reflecting this progressive orogenesis (Germs, 1983;
1
2
JOURNAL OF PALEONTOLOGY, V. 87, NO. 1, 2013
FIGURE 1—Location of the newly discovered Rangea specimens on Farm
Aar, Namibia.
Grotzinger and Miller, 2008). The Kuibis Subgroup consists of
up to 200 m of mature siliciclastics and carbonates representing
cratonogenic and early foreland basin deposits. The overlying
1200-m thick Schwarzrand Subgroup mainly consists of distal
flysch and carbonates deposited in shallow-marine environments. The Nomtsas Formation capping the Schwarzrand
Subgroup and the overlying Fish River Subgroup are made up
of shallow marine and non-marine molasse reflecting fill of a
foreland basin. The Kuibis and Schwarzrand subgroups contain
abundant Ediacara-type fossil impressions and remains, with
carbon-isotope stratigraphy and precise U-Pb dates of 547–541
Ma derived from volcanic ash beds providing further support for
a late Ediacaran age, whereas the unconformably overlying
Nomtsas Formation hosts Cambrian-type trace fossils and has
yielded an early Cambrian radiometric date of 538 Ma (Germs,
1972; Grotzinger et al., 1995; Narbonne et al., 1997; Abelson et
al., 2012; Schmitz, 2012; Narbonne et al., 2012).
The newly discovered specimens of Rangea reported in this
paper occur in the upper part of the Kliphoek Member of the
Dabis Formation within the Kuibis Subgroup (Fig. 2.1, 2.2).
This unit, particularly the lower part, has previously yielded
abundant Ediacara-type fossil impressions, including those of
Pteridinium, Ernietta, Nemiana and, less commonly, Rangea at
multiple levels throughout the member (Germs, 1972; Saylor et
al., 1995). The Kliphoek and the overlying Mooifontein
limestone collectively form a single depositional sequence (K2
of Saylor et al., 1995, 1998; Grotzinger and Miller, 2008). In
southern Namibia, the top of K2 is erosionally overlain by the
basal strata of the Schwarzrand Group, but additional sequences
are present in the upper Kuibis Subgroup north of the Osis Arch.
The overlying sequence (K3) contains a volcanic ash that has
FIGURE 2—Stratigraphic setting of the newly discovered Rangea specimens
on Farm Aar, Namibia: 1, complete Nama Group stratigraphy in the Witputs
Sub-basin, asterisk indicates date correlated from Zaris Sub-basin; 2,
stratigraphy on Farm Aar, showing stratigraphic units and fossil
occurrences; ZFM¼Zaris Formation. Revised U/Pb dates from Schmitz
(2012).
yielded a precise U-Pb date of 548.861 Ma (Grotzinger et al.,
1995; Saylor et al., 1998, 2005), subsequently revised to
547.3260.65 Ma (Schmitz, 2012; Narbonne et al., 2012),
providing a minimum age for the Rangea fossils in the present
study.
Saylor et al. (1995, 1998) and Grotzinger and Miller (2008)
described the environmental succession of the Kliphoek and
Mooifontein members. Desiccation cracks or other evidence of
emergence are strikingly absent from both the Kliphoek and
Mooifontein members, and imply subaqueous deposition
throughout the entire sequence. Basal Kliphoek strata below
the fossiliferous levels are lowstand deposits consisting of
mainly thick-bedded, coarse-grained quartzarenites with abundant meter-scale trough cross-bedding. Deposition may have
occurred in a sandy braided fluvial or more likely in a highenergy nearshore or deltaic setting. The upper 70 cm of the
continuous sandstone within the lower part of the Kliphoek
Member consists mainly of fine-grained quartzarenite with
syneresis cracks and/or sandstone injection structures, currentand combined-flow-ripplemarks, and hummocky cross-stratification. These strata contain abundant impressions of Pteridinium and Ernietta and a single specimen of Rangea. Above this
sandstone, the upper part of the Kliphoek Member, which
contains the new fossil occurrence in addition to previously
reported specimens of Pteridinium, Ernietta, and Nemiana,
VICKERS-RICH ET AL.—RECONSTRUCTING RANGEA
consists of transgressive gray-green shale and siltstone with
sporadic interbeds of very fine- to fine-grained, centimeter-scale
sandstone event beds that are laterally discontinuous over
decameter scales. Sandstone event beds are erosionally based.
The lower part of each event bed consists of parallel-laminated
sandstone reflecting upper-flow regime plane beds, which is
overtopped by sandstone exhibiting hummocky cross-stratification, wave ripples, or combined-flow ripples. Centimeter-scale
rip-up clasts of shale and/or microbialite also occur commonly
in the upper half of these event beds. These features are
diagnostic of storm beds modified by wave processes during the
waning flow stage, and imply deposition slightly below fairweather wave-base on a muddy ramp (Myrow, 1992; Myrow
and Southard, 1996; Plint, 2010). Shallow-water limestones with
hummocky and swaley cross-stratification, intraclastic textures,
and microbial textures first appear approximately 3 m above the
new Rangea occurrence (Fig. 2.2). Laminated carbonates,
locally containing cross-bedded ooids and the shelly fossil
Cloudina, dominate the overlying Mooifontein Member and
imply shallow-water deposition during highstand conditions to
the top of the K2 sequence.
In summary, these data imply that the Rangea specimens of
this study were preserved in a muddy mid-ramp setting just
below normal wave-base, an environment with gentle wave and
current action and periodic disturbance by major storms. These
features also imply that the sea bottom was probably within the
photic zone. This environmental interpretation is broadly similar
to that postulated for other Ediacaran fossil occurrences in the
Kuibis (Grazhdankin and Seilacher, 2002, 2005; Bouougri et al.,
2011) and Schwarzrand (Narbonne et al., 1997) subgroups of
Namibia and many others worldwide (Grazhdankin, 2004).
NEW RANGEA OCCURRENCE
A concentration of more than 100 specimens of Rangea was
discovered along the dirt track leading from Highway B4 to
Farm Aar 16, approximately 8 km east of Aus in south-western
Namibia (locality 1 in Fig. 1). The original discovery was in
float dislodged during road maintenance (Vickers-Rich, 2007,
fig. 116), which led to the location of abundant in situ material
as well as further float specimens during the following years. In
situ specimens were collected from a flat-bottomed gutter cast
with its top located 35–40 cm above the upper boundary of the
continuous sandstones of the lower Kliphoek Member (Fig. 2.2).
A larger, but less fossiliferous concentration was discovered in a
similar gutter cast at the same stratigraphic level 2.6 km to the
south-west (locality 2 in Fig. 1).
The fossiliferous gutter casts are gentle- to steep-sided (20–
758 slopes), mainly flat-bottomed, 35–100 cm wide and 5–10 cm
deep (Fig. 3). The walls and floor of these gutter casts are
locally adorned with tool marks, oriented broadly parallel with
its axis. The highly sinuous nature of the gutter casts and the
absence of flutes or other directional indicators, however,
preclude accurate determination of the direction of flow. Rangea
site 1 occurred in a gutter cast 38–55 cm wide with an exposed
length of 1.2 m and a maximum depth of 10 cm, oriented at 120/
3008Az. (Fig. 3.1, 3.2). Rangea site 2 was a complex of at least
two partially overlapping and cross-cutting, flat-bottomed gutter
casts (Fig. 3.3, 3.4) The largest is a sinuous channel at least 3.7
m long (incomplete at the east end), which is 35–45 cm wide
and 7 cm deep in its central region but flares to more than a
meter in width at either end with a maximum thickness of 5 cm
in the widened section. It partly overlaps and partly cuts a
similar but smaller channel at least 33 cm wide trending 045/
2258Az. Each gutter exhibits a bipartite fill similar to that of the
storm event beds in the section (Fig. 3.2). The lower half
3
consists of unfossiliferous, finely laminated, fine-grained quartz
sandstone, which is confined to the gutter cast. This is abruptly
overlain by very fine-grained quartz sandstone with low angle
hummocks and swales that fills the gutter casts and occasionally
steps beyond the erosional margins of the underlying channel,
giving the fossiliferous lenses a somewhat irregular shape in
plan view.
Thin intraclasts of mudstone and/or microbial sheets, cmscale smooth and striated baglike fossils, and specimens of
Rangea occur abundantly within these hummocky crossstratified caps (Fig. 3.1, 3.3, 3.4). The Rangea specimens show
a consistent orientation in a vertical sense, with the frond axis
nearly horizontal and all edges slightly bowed upwards to form
a convex-down, boat-shaped profile (Figs. 4.1–4.4, 5.2), a
profile that is typical of Rangea specimens worldwide
(Grazhdankin and Seilacher, 2005).
RECONSTRUCTING RANGEA MORPHOLOGY
Virtually all previously described specimens of Rangea show
only a leafy petalodium, and consequently, the nature of the
base of Rangea and its internal organization, have been largely
unknown and quite controversial. Jenkins (1985, figs. 2c, 4b)
and Dzik (2002, fig. 2B) regarded a single specimen
(NESMF338-5; previously illustrated by Pflüg, 1970, fig. 6B
and pl. 34.5) as showing evidence for a sand-filled axial stalk
above a bulbous base, and incorporated these features in their
somewhat different reconstructions of Rangea as an attached
frond. However, Grazhdankin and Seilacher (2005) regarded
these features in NESMF338-5 as ‘‘fortuitous’’ and reconstructed Rangea as consisting only of a leafy petalodium that grew in
the sediment.
The frondose petalodium of the new specimens from Farm
Aar is remarkably similar to the flattened (‘forma plana’ of
Gürich, 1933) specimens of Rangea described by previous
authors. Uniquely, however, most of the new specimens exhibit
a hexaradial, bulb-like structure located proximally within the
Rangea frond that continues as a gently tapering cone axially
throughout the entire length of the Rangea frond (Figs. 4.3–4.6,
5.1–5.5, 6, 7, 8). These features are only rarely and
controversially represented in previously described specimens
of Rangea, and provide critical information for reconstructing
the morphology and lifestyle of this previously enigmatic
Ediacaran fossil.
Most organic materials in the two fossiliferous gutter casts
were replaced by or coated with a thin layer of pyrite variably
preserved as pyrite ‘‘death masks’’ (Gehling, 1999), and other
minerals that represent weathering products of pyrite: goethite
and other Fe-oxyhydroxide minerals (i.e., ‘‘limonite’’) and
jarosite ([KFe3þ3(SO4)2(OH)6]). The identification of jarosite
was confirmed using powder X-ray diffraction (XRD). Jarosite
is a common oxidative weathering product of pyrite (Jambor and
Blowes, 1998; Lottermoser, 2010) in the presence of K-bearing
silicate minerals such as micas and K-feldspars (Bladh, 1982),
which are abundant in the Farm Aar samples (Figs. 5.1, 6.1).
These early diagenetic pyritic replacements/coatings of the
organic material of Rangea provide a mineralogical contrast
between the fossils and the sedimentary rock in which they are
entombed that further enhances recognition and study of the
newly discovered Rangea specimens from Farm Aar. A
reconstruction of Rangea is presented in Figure 9.
Axial bulb and stalk.—In contrast with previously published
specimens of Rangea, most of which consist entirely of the
petalodium, effectively all specimens in this study show a three
dimensional axial structure made up of a proximal axial bulb that
grades distally into a conical stalk tapering to the tip of the
4
JOURNAL OF PALEONTOLOGY, V. 87, NO. 1, 2013
FIGURE 3—Outline diagrams of fossiliferous channel deposits from Farm Aar in south-western Namibia: 1, top view of a specimen block sequence from
Channel 1 showing the horizontal distribution of fossils excavated from within the deposit and registered against the flow pattern (gray lines) as cast by the lower
channel sediment unit, line of transverse section A–B, with specimen block numbers (F638–641) referring to the National Earth Science Museum (NSEM)
VICKERS-RICH ET AL.—RECONSTRUCTING RANGEA
5
FIGURE 4—Rangea schneiderhoehni (Gürich, 1930) preservation form. 1, 2, the boat-shaped preservation expressed in part and counter-part specimens: 1,
upper view of concave down NESMF631-b, lower part; 2, lower view of convex down NESMF631-a, upper counter-part; 3, bottom view showing variety of
preservation and exposure levels in three specimens of NESMF628; 4, outline diagram of NESMF628, original discovery specimen from Farm Aar, near Channel
1, specimens 1–3, vanes shaded light gray, marginal tubes shaded mid-gray, axial fill shaded dark gray; 5, oblique profile view of NESMF628, specimens 1–3
proximal regions; 6, outline diagram of NESMF628, specimens 1–3 proximal regions, vanes shaded light gray, marginal traces shaded mid-gray, axial fill shaded
dark gray. All scale bars¼1 cm. Abbreviations: as¼axial stalk; av¼axial volume; em¼element midline; mt¼marginal tube.
collection in Windhoek, scale bar¼10 cm; 2, reconstructed transverse section A–B across three blocks of Channel 1, lower sediment unit dark gray, upper
sediment unit light gray, scale bar¼10 cm; 3, photograph of the excavated central part of Channel 2, arrow indicates excavated Rangea specimen NESMF659-b,
scale bar¼50 cm; 4, outline of Site 2 Channel showing the horizontal distribution of fossils excavated from within the deposit and registered against the flow
pattern (gray lines) as cast on the base of the channel, arrow indicates Rangea specimen NESMF659, scale bar¼50 cm.
6
JOURNAL OF PALEONTOLOGY, V. 87, NO. 1, 2013
FIGURE 5—Channel 1, Farm Aar, southern Namibia: 1, Rangea specimen and other fossil material NSEMF642-c showing jarosite coating; 2, profile of
NESMF641-b with specimen NESMF641-c confined to the upper channel unit, immediately above the boundary (arrowed) of the lower unit; 3, block
VICKERS-RICH ET AL.—RECONSTRUCTING RANGEA
specimen (Figs. 4.3–4.6, 5.2–5.5, 6.1–6.4, 7, 8.1–8.3). The
proximal axial bulb is internally cast with sandstone which is
lithologically dissimilar to the very fine-grained sandstone
entombing the fossils, but is compositionally, texturally, and
diagenetically similar to the fine-grained sandstone layer which
forms the basal fill of the gutter cast several millimeters to
centimeters below the fossils (Fig. 5.3–5.6). This axial fill
becomes increasingly loosely packed and porous along the stalk
towards the distal taper, which typically is preserved as an open
void (Figs. 4.3–4.6, 6.1–6.4, 7.3, 7.4). This may well have been
soft tissue or liquid-filled in life. The frondose part of Rangea is
partially flattened, but the axial region has generally been
preserved fully dimensional, with minimal distortion despite the
absence of axial fill by sandstone in the distal parts of the
specimen. This geometrical relationship is maintained even in
specimens in which the sandstone-filled axial bulb is stratigraphically higher than the open cylindrical stalk (Figs. 6.1–6.4,
7.1–7.4), implying that a sandstone-filled axial bulb and an
organic-filled axial stalk may have been primary features of the
specimens from Farm Aar.
The axial bulb is lobate, with consistent hexaradial symmetry
(Fig. 7.5–7.7). Undeformed bulbs whose axes lie perpendicular to
bedding invariably exhibit six major lobes defined by shallow
longitudinal creases, with each major lobe further divided by a
fainter longitudinal crease that imparts a secondary hexaradial
pattern. The confluence of the six major lobes at the proximal
pole of the bulb commonly exhibits an axial node 4–10 mm
(average 5 mm) in diameter, the function of which is unresolved
(Figs. 6.3, 6.4, 7.3, 7.6. 8.5).
The hexaradial axial bulb at the base of a conical stalk has not
previously been described from any specimen of Rangea
worldwide, and represents an important contribution of the new
specimens herein described. The smooth ‘‘ovate mass of
sediment’’ in specimen NESMF338-5 that Jenkins (1985)
interpreted as a possible holdfast and Dzik (2002) termed a
‘‘basal bulb’’ lacks hexaradial symmetry and lies proximal to the
rangeomorph frondose elements and a badly cracked and nearly
unrecognizable internal axial structure. This smooth ball may be
an indistinct and badly preserved example of the hexaradial bulb
or may be a fortuitous juxtaposition of different features as
inferred by Grazhdankin and Seilacher (2005). Similarly, there is
a featureless ovoid structure abutting the axial bulb of
NESMF636-f (Fig. 7.6). Neither NESM F338-5 nor any other
previously figured specimen of Rangea shows the hexaradial
sandstone bulb that is so prevalent in the specimens of Rangea
from Farm Aar.
The hexaradial axial bulb passes distally into a conical axial
stalk (Figs. 5.2, 6.1–6.4, 6.7, 6.8, 7, 8.1, 8.3) with a circular crosssection and a gently distal taper. This axial stalk is evident in
essentially every specimen of Rangea at Farm Aar but is not
obvious in previously described specimens noted in the literature,
which exhibit more traditional Rangea preservation. In these
previously known specimens, the axial stalk may be indiscernible
(e.g., Jenkins, 1985, fig. 2A, 2E1) or represented by a flattened
triangular region (the ‘‘median zone of flattening’’ of Jenkins,
1985), which may (Jenkins, 1985, fig. 2D) or may not (Jenkins,
7
1985, fig. 2A) exhibit rangeomorph branching on the surface.
Other authors have figured this triangular feature without
comment. We infer that a conical axial stalk was present beneath
the frondose rangeomorph structure in all of these specimens but
was partially collapsed in swollen (‘forma turgida’ of Gürich,
1933) specimens and completely collapsed in flattened (‘forma
plana’ of Gürich, 1933) specimens of Rangea.
Internal casts of the axial stalk imply that it was originally
circular in cross-section and lay horizontal to the bedding plane in
this preservation (Figs. 5.2, 6.7, 6.8), with its proximal portion
curving upwards towards the axial bulb (Figs. 5.2–5.5, 6.1–6.4,
7.1–7.7). The highest level of the bulb is consistently higher than
the stalk. The flexure between the horizontal stalk and the vertical
bulb is marked with crescentic ridges that are arranged in an
alternating series on each side of the shallow creases. Where the
axial cast is upwardly curved at the ‘neck’ of the bulb, the
longitudinal markings are strongly evident on the ‘outer’
curvature and the transverse crescents weakly so, but these form
a more wrinkled surface on the ‘inner’ curvature. This implies
that the flexure is not natural and more likely is a result of
distortion of a flexible structure, probably a depositional or post
mortem feature of collapse, compaction or contraction.
Petalodium.—The axial bulb and stalk are entirely internal
features that were completely surrounded by the petalodium of
Rangea—a radial arrangement of elongate, semiovate vanes with
each vane exhibiting the self-similar branching diagnostic of
rangeomorph architecture (Figs. 4.3, 4.4, 6.1, 6.2, 7.1, 7.2, 8.1–
8.3, 9). The preserved appearance of the Rangea petalodium has
been well described by all previous authors (Gürich, 1930;
Richter, 1955; Pflüg, 1970; Germs, 1973; Jenkins, 1985; Dzik,
2002, Grazhdankin and Seilacher, 2005), although their structural
interpretations vary. Rangea shows at least four orders of selfsimilar branching that we label in ascending order from the
largest (most visible) to the finest scale following the pattern
illustrated by Narbonne et al. (2009, fig. 2). The highest-level
(primary) element consists of a bifoliate ovate sheet extending the
entire length of the fossil, with its midline corresponding to the
major groove on the underlying hexaradial axial bulb (Figs. 7.5–
7.7, 8.4, 8.5, 9). This midline serves as the origin for an array of
alternating major and subsidiary branches, estimated to number
18–22 for each series (Figs. 4.3, 4.4, 6.1, 6.2, 7.1, 7.2, 9) that
together constitute the second order series. Each second order
branch is centimeter-scale and consists of a series of millimeterscale secondary branches alternating along each side of its
midline. Only three orders of branching are visible in most
Rangea specimens, but Pflüg (1970) described a possible fourth
order branching in one specimen. This is similar to the
rangeomorph fossils of Newfoundland, which typically show
two orders of branching, centimeter-scale and millimeter-scale,
but reveal up to four orders of self-similar branching in the best
preserved specimens from Spaniard’s Bay (Narbonne, 2004;
Narbonne et al., 2009).
Grazhdankin and Seilacher (2005) recognized an alternating
pattern of major and minor second order elements of Rangea and
inferred an interdigitation of these branches to produce both sides
of the vanes. We concur with their observation of the alternating
size of primary branches but differ in our interpretation of the
NESMF643 vertically sectioned transverse to channel showing various specimens (arrowed) within the upper channel unit; 4, detail of Rangea specimen in block
NSEMF643 (arrow on right in 3), shown in thin section under raking natural light (slightly oblique to specimen axis); 5, outline of thin section in 4, fill shaded
dark for solid granular sediment, light shading for finer degraded sediment, jarosite layers in black lines, fill laminations in brown lines; 6, thin sections from
NESMF643 photographed with raking natural light, showing shallow gradation zone between lower and upper sediment units (marked by double arrow) and
unidentified sectioned specimen enclosing fill different from surrounding upper channel sediment unit (arrowed). All scale bars¼1 cm. Abbreviations: ab¼axial
bulb; af¼axial fill; as¼axial stalk; mt¼marginal tube.
8
JOURNAL OF PALEONTOLOGY, V. 87, NO. 1, 2013
FIGURE 6—Specimen NESMF643-b1, Farm Aar, Channel 1, with thin sections and line drawings illustrating external and internal structure: 1, lower surface
showing axial shaft flexed upwards (into matrix) at its proximal end, region of exposed axial fill proximal to the distal two-thirds of the shaft length is covered by
VICKERS-RICH ET AL.—RECONSTRUCTING RANGEA
three-dimensional architectural structure. Fossil remains of
Rangea now show concave relief of the primary branches (Fig.
8.4). The reconstruction (Fig. 9) shows the concave relief restored
to a convex-out architecture by analogy with other rangeomorphs.
Details of the architecture of Rangea from Farm Aar and
elsewhere are currently under study and will be presented
separately. In the interim, the architecture in Figure 9 is shown
generically as consisting of a self-similar series of convex-out
lobes on both sides of each vane, consistent with previous
interpretations of Rangea and other rangeomorphs (Pflüg, 1970;
Jenkins, 1985; Seilacher, 1992; Dzik, 2002; Narbonne, 2004;
Brasier and Antcliffe, 2004; Grazhdankin and Seilacher, 2005;
Gehling and Narbonne, 2007; Flude and Narbonne, 2008,
Narbonne et al., 2009; Laflamme et al., 2009).
Where the outer edge of a Rangea vane can be observed in plan
view, it is typically represented by a sharp marginal ridge (Fig.
4.3, 4.4; see also Jenkins, 1985, fig. 2A, 2B; Grazhdankin and
Seilacher, 2005, fig. 6b; Bouougri et al., 2011, fig. 4G). Variable
preservation of this margin in different specimens from Farm Aar
implies that it was a cylinder that extended the length of each
vane (Figs. 5.4, 5.5, 6.1–6.4, 6.7, 6.8, 7.1–7.4, 8, 9). Where this
marginal tube was sand-filled, it is cylindrical with a ridged
ornamentation, but the marginal ridge could also be deflated and
appear as a gutter-shaped feature.
Gürich (1930, 1933) and Richter (1955) regarded Rangea as
bifoliate, based on limited material available at the time, but all
subsequent authors agree that Rangea is multifoliate (sensu
Laflamme and Narbonne, 2008a, 2008b), consisting of three or
more vanes that join length-wise along their inner edge and
radiate outwards from this axis. In most specimens the vanes were
folded flat upon each other during burial, with the multifoliate
nature visible mainly through partial overlap of underlying vanes.
As a consequence, the number of vanes in the Rangea petalodium
has been difficult to determine with certainty. Based on specimen
NESMF-540 and other material, Pflüg (1970) and Jenkins (1985)
suggested that there was evidence for five or more vanes. Pflüg
(1972) provided three reconstruction modes for Rangea, one of
which was pentameral and two showing differing arrangements of
three pairs of branching structures, implying six vanes. Dzik
(2002) recognized four vanes, and Grazhdankin and Seilacher
(2005) regarded Rangea as consisting of only three vanes, a
pattern also seen in the erniettomorph Pteridinium (Pflüg, 1970;
Grazhdankin and Seilacher, 2002; Elliott et al., 2011). Five vanes
are visible in several of the new specimens from Farm Aar,
supporting the views of Pflüg and Jenkins that Rangea is highly
multifoliate. Cross-sections of five vanes are preserved with
equidistant spacing allowing for a sixth (Fig. 6.7, 6.8). Evidence
from the bases of other specimens solidly demonstrates the
presence of six vanes, each emanating from one of the major
lobes of the axial bulb and extending up the side of the axial
column (Fig. 8). This association between the six vanes that
characterize the external Rangea petalodium and the six lobes of
its internal axial bulb provides a firm basis for reconstructing the
three-dimensional morphology of Rangea.
9
Reconstruction.—The morphologic features and relationships
described above permit a reconstruction that appears to be
applicable to the 100þ specimens of Rangea recovered from Farm
Aar and other specimens of Rangea worldwide (Fig. 9). This
analysis supports and augments aspects of Rangea morphology
proposed by previous workers, rules out some other past
interpretations, and, most importantly, permits integration of
some formerly disparate views into a unified reconstruction of the
Rangea organism.
The sandstone-filled hexaradial axial bulb present in most of
the specimens from Farm Aar had not been previously reported in
any specimens of Rangea, and represents a unique contribution to
understanding Rangea morphology. Reconstruction of this
structure and the axial stalk to which it was attached (Fig. 9)
strongly supports Dzik’s (2002) view that the Rangea anatomy
enveloped a voluminous and persistent axial space, which
traversed the length of the organism and was integral to its
construction. It is also consistent with Pflüg (1970) and Jenkins
(1985) that the Rangea frond was highly multifoliate, and
specifically suggests that it had six vanes, which correspond to
the hexaradial symmetry in its axial bulb, with the edge of the
vane inserting into each of the clefts in this bulb. The Farm Aar
specimens exhibit at least three orders of self-similar branching,
consistent with the descriptions and illustrations of Gürich (1930,
1933), Richter (1955), and all subsequent workers.
RECONSTRUCTING RANGEA LIFESTYLE AND TAPHONOMY
The new specimens of Rangea from Farm Aar are similar to
all previously figured specimens of Rangea in being oriented
sub-horizontally within or on the surface of sandstone beds.
Bouougri et al. (2011, fig. 4H) figured a specimen they
suggested was embedded vertically within the sediment, but
this interpretation is not evident from their figure, which indeed
appears to be preservation on a bedding plane. Most previous
authors have interpreted this horizontal orientation of Rangea as
representing transported and felled specimens of epibenthic
fronds (Jenkins, 1985; Dzik, 2002), but Grazhdankin and
Seilacher (2005) reinterpreted the present-day horizontal
orientation of Rangea as reflecting in situ specimens that lived
infaunally.
The Farm Aar specimens of Rangea are scattered through the
uppermost 25 mm of hummocky cross-stratified, fine-grained
sandstone, which caps the mainly fine-grained storm deposits
filling two storm-cut gutter casts (Figs. 3, 5.3, 5.6). Some of the
specimens from Farm Aar are aligned parallel with each other
(Fig. 4.3), but most show no preferred orientation in a horizontal
sense (Fig. 3.1, 3.4), implying that, unlike the unimodally
oriented fronds of Mistaken Point in Newfoundland (Seilacher,
1999; Wood et al., 2003), these Rangea specimens were not
tethered to the seafloor during their final deposition. In contrast
with the lack of orientation in a horizontal sense, there is a
strong orientation in a vertical sense, with all specimens
oriented convex-down, a boat-shaped orientation also typical
of other Namibian preservations of Rangea (Grazhdankin and
an element midline cast in negative relief; note the partial collapse of the specimen where the axial space fill is absent distally; a single vane is present on left,
two vanes with marginal traces are preserved on right; 2, outlined dorsal surface with lines of section for 3–8, axial shaft of adjacent Rangea specimen arrowed;
3, axial section A–B photographed with raking natural light; 4, outline of axial section A–B, axial shaft fill shaded dark for solid granular sediment, light shading
for finer degraded sediment, proximal node of axial bulb bracketed; 5, lateral section C–D photographed with raking natural light showing thick region of vane
preservation along the ventral surface; 6, outline of lateral section C–D showing flattened structure of vanes 4 and 5; 7, transverse section E–F photographed with
raking natural light; 8, outline of transverse section E–F with five vanes and the position of a sixth vane indicated, axial shaft fill shaded dark for solid granular
sediment, light shading for finer degraded sediment. All scale bars¼1 cm. Abbreviations: ab¼axial bulb; af¼axial fill; as¼axial stalk; av¼axial volume;
em¼element midline; mpb¼major primary branch; mt¼marginal tube; nab¼proximal node of axial bulb; spb¼subsidiary primary branch; v¼vane.
10
JOURNAL OF PALEONTOLOGY, V. 87, NO. 1, 2013
FIGURE 7—Rangea axial bulb and stalk morphology, Farm Aar, Channel 1: 1, lower surface of Rangea NSEMF643-b3; 2, outlined lower surface of Rangea
NSEMF643-b3 showing line of axial section G–H; 3, Rangea NSEMF643-b3 thin section G–H photographed with raking natural light; 4, outline of Rangea
VICKERS-RICH ET AL.—RECONSTRUCTING RANGEA
Seilacher, 2005) and Pteridinium (Grazhdankin and Seilacher,
2002). This combination of a strong orientation in a vertical
sense but little or no preferred orientation horizontally was
regarded by Grazhdankin and Seilacher (2005) as indicative of
an infaunal habit, but is also consistent with deposition of
transported, untethered specimens of Rangea during a storm
event, with the upturned edges reflecting water escaping upward
while sediment settled downward from suspension (Fig. 10).
Axial bulbs of Rangea from the channels are filled with finegrained sandstone that is similar in all regards to the sandstone
fill in the bottom of the gutter cast a few millimeters to
centimeters below the fossil, effectively ruling out the
possibility that this fill represents either a purely biochemical
precipitate or a later infiltration of sand after burial. Faint
laminations parallel with the base of the axial bulb imply that
sandstone fill of the bulb occurred while the frond was in a
vertical orientation (Figs. 5.5, 7.4), before dislocation and
subsequent deposition in a horizontal orientation. The sandstone
fill in the proximal part of the axial stalk becomes increasingly
loosely packed, porous and pyritic/jarositic distally passing into
a hollow cone which tapers to the distal end of the fossil.
Sandstone fills the axial bulb and also thinly lines the axial stalk
(Figs. 6.3, 6.4, 7.3, 7.4). The sand-filled axial bulb is presently
connected to, but stratigraphically higher than, the open stalk.
Despite this orientation there is no evidence that loose sand
flowed from the bulb into the stalk, nor is there any sign of
compaction of the stalk during burial. This implies that sand
filled the axial bulb very early, either during life or immediately
after death, while the stalk was still filled with stiff organic
material preventing both the flow of the loose sand fill during
burial and collapse of the stalk during burial. It is likely that the
open stalk was then filled with an early diagenetic mineral,
which preserved its form through subsequent burial compaction
and mild orogenesis and was then removed in the modern
weathering environment to yield the open stalk visible today.
It is tempting to conclude that sand was packed in the bottom
part of Rangea during life especially since the presence of a
sand-filled bulb overlain by a hollow axial stalk would provide
increased stability on the seafloor, much like a child’s toy with a
weighted base to keep it upright, an explanation that has
previously been applied to some Ediacaran and Cambrian taxa
interpreted as soft-bodied cnidarians (Seilacher, 1992; Savazzi,
2007).
Several unrelated protistan and animalian groups in modern
seas have convergently evolved the ability to incorporate sand
grains into their bodies for structural support and/or ballast, and
these may usefully serve as constructional (albeit not phylogenetic) analogues for sand-grain incorporation in Rangea.
Xenophyophores are giant, deep-sea protists that commonly
agglutinate sediment tests, presumably as structural support of
their delicate cytoplasm. Species variously incorporate additional sediment in the form of internally secreted fecal pellets
and by the selective ingestion of mineral grains from the
substrate into the cytoplasm as an internal skeleton (Tendal,
1972; Gooday et al., 2011). This process is also seen in juvenile
sand dollars, which selectively ingest sand grains from the
11
substrate and use these as a weight-belt for increased stability in
shifting substrates (Chia, 1973; Seilacher, 1979; Mooi and
Chen, 1996). We note further that the ‘‘Zoantharia’’ build a
stolon, mat or other support with sediment particles and debris
(Haywick and Mueller, 1997; Reimer et al., 2010). Many
sponges do the same and also attract other organisms within
their tissues, preferably those capable of secreting calcareous
skeletons (Cerrano et al., 2007; E. Savazzi, personal commun.,
2012). According to this model, Rangea from Farm Aar would
have derived sand ballast during deposition of the fine-grained
sand in the lower part of the gutter or from similar sediments
elsewhere and lived as upright, epibenthic fronds with their
bases resting on or slightly buried in the sediment (Fig. 10.1).
This interpretation implies that the rangeomorph elements near
the base of Rangea (Fig. 9) may have had a structural as well as
food-gathering function, a view consistent with rangeomorph
elements covering the bottom side of Fractofusus (Gehling and
Narbonne, 2007) and surrounding the holdfast of Bradgatia
(Flude and Narbonne, 2008, fig. 4) from Newfoundland.
Additionally, the expansion of the marginal tubes surrounding
the proximal bulb may well have provided further support. The
presence of sand ballast is also consistent with the concentration
of Rangea specimens in gutter casts and their extreme scarcity
in otherwise indistinguishable storm beds throughout the
succession. Specimens were likely transported and deposited
horizontally during the final storm event, producing a concaveup (boat-shaped) profile due to their settling out of a sedimentrich suspension at the end of a storm event (Fig. 10.3). Evidence
for only limited alignment of Rangea fossils supports our view
that the fronds were untethered and implies that the waning
stages of the storm were characterized by oscillatory/turbulent
conditions rather than unidirectional flow. Distal vanes collapsed during burial, but the presence of potentially more
resistant proximal vanes and the greater thickness of the axial
bulb as opposed to the axial stalk likely resulted in flexure and
rotation of this bulb during burial to produce the fossil form
preserved today (Fig. 10.6, 10.7).
Other interpretations of the life habit of Rangea have also
been proposed. An early interpretation of the Ediacaran fossils
from Namibia as ‘‘polyps with a float structure for buoyancy in
the water column’’ (Brasier, 1979) is consistent with our
reconstruction (Fig. 9) but is not consistent with the taphonomy
of the fossils, especially the ubiquitous presence of a sandstonefilled axial bulb. Interpretation of Rangea as a sessile infaunal
organism (Grazhdankin and Seilacher, 2005) was invoked to
explain the consistent boat-shaped (convex-down) relief of
Rangea and Pteridinium in the absence of evidence for any axial
or basal supporting structure for an epibenthic life style. The
additional morphological attributes revealed by these new
specimens and the restriction of Rangea to preservation within
sediments deposited during the waning phases of storms do not
support this interpretation. Because all Rangea preservations to
date represent transported organisms, evidence for sediment
displacement during growth has not been found or can be
expected from these deposits. Modeling implying that the selfsimilar (rangeomorph) architecture of Rangea was specifically
NSEMF643-b3 thin section G–H; 5, excavated axial bulb F640-b, upper, profile and lower view, top to bottom, respectively; 6, upper view of NESMF636-f with
axial node arrowed, profile view of NESMF636-f with deposition fragment NESMF636-e attached at position of arrow, lower view of NESM F636-f, top to
bottom, respectively; 7, partially excavated axial bulb NESMF641-e, upper, profile and lower view, top to bottom, respectively. All scale bars¼1 cm.
Abbreviations: ab¼axial bulb; af¼axial fill; as¼axial stalk; av¼axial volume; em¼element midline; mpb¼major primary branch; mt¼marginal tube; nab¼proximal
node of axial bulb; spb¼subsidiary primary branch; v¼vane.
12
JOURNAL OF PALEONTOLOGY, V. 87, NO. 1, 2013
FIGURE 8—Rangea axial bulb, marginal tube morphology and symmetry, Farm Aar: 1, Rangea NESM F635-c lower (ventral) view, scale bar¼1 cm; 2, Rangea
NESMF635-c, upper (dorsal) view, scale bar¼1 cm; 3, outline of Rangea NESMF635-c in dorsal view showing proximal preservation of marginal traces
represented as translucent white, superimposed on a flipped outline of the lower view shaded mid-gray with axial region shaded dark gray, scale bar¼1 cm; 4,
diagrammatic transverse section at axial bulb of Rangea showing architecture and symmetry postulated from major confined regions of sediment fill (stippled)
and major traces of jarosite (black lines); 5, diagrammatic proximal view of Rangea architecture and symmetry postulated from molded surfaces of marginal
tubes and axial bulb.
adapted for extracting nutrients from the water column
(Laflamme et al., 2009) makes interpretation of Rangea as an
infaunal organism even more unlikely. While neither pelagic nor
infaunal models for Rangea can be strictly ruled out, the new
specimens from Farm Aar are most consistent with the
traditional interpretation of Rangea as an epibenthic frond
(Jenkins, 1985), with the significant proviso that no holdfast is
preserved which might have tethered Rangea to the bottom
during life. Our view that Rangea was an untethered epibenthic
frond further implies that virtually all Rangea are likely to have
been transported at least a short distance before their final burial
during the waning stages of storm activity.
CONCLUSIONS
Rangea was the first complex Ediacaran fossil described
anywhere in the world (Gürich, 1930, 1933), and over the
subsequent 80 years its reconstruction has been analyzed by
some of the key workers in Ediacaran paleontology. All of these
workers made important discoveries that elucidated critical
aspects of the complex architecture and construction that
characterize Rangea. Pflüg (1970) first recognized its highly
multifoliate nature and the constraints this placed on Rangea
reconstructions. Germs (1973) described the flexibility of the
Rangea vanes in life, and Jenkins (1985) described features that
permitted reconstruction as an epibenthic frond. Dzik (2002)
VICKERS-RICH ET AL.—RECONSTRUCTING RANGEA
13
morphology; S. Morton for photography; P. Komarower for
editorial assistance; D. Gelt for drafting; R. Trusler and M.
Anderson for IT assistance with graphics; M. A. Zakrevskaya
(Paleontological Institute, RAS) for Russian translation; and C.
Williams, along with students N. Fournie, C. Wemmers, O.
Trusler and M. Meyers for field and laboratory assistance. Thanks
to the Hoffmann family and Hotel Christophe for accommodation
over many years; the National Geographic Society and the
International Geosciences Program (IGCP) of UNESCO for
grants supporting the field work that led to the discovery of the
Rangea specimens, as did the Natural Sciences and Engineering
Research Council of Canada (NSERC) and Queen’s University.
Material was collected under permits from the National Heritage
Council of Namibia: Permit 4 of 2004, 11 of 2006, 18 of 2008, 13
of 2009 and 6 of 2011, and resides in the Geological Survey of
Namibia, Ministry of Mines and Energy collections in Windhoek.
Thanks to our families for listening to our endless debates, in
particular G. Trusler and T. Rich.
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FIGURE 9—Hypothetical life reconstruction of Rangea shown partly cut
away to reveal the architecture of the body form as deduced from the
preservation on specimens from Farm Aar, Namibia.
recognized an axial region within Rangea, and Grazhdankin and
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axial bulb and axial stalk over which the six vanes of frondose
elements of Rangea were draped. This is not the end of the
analyses, and new discoveries and new techniques will continue
to yield exciting insights into this iconic Ediacaran taxon.
ACKNOWLEDGMENTS
Many people over the years have helped us bring this research
paper to fruition: staff at the Geological Survey of Namibia,
especially K. Mhopjeni, H. Mocke, U. Schrieber and E. Grobler;
owners of Farm Aar, B. Boehm-Erni and the late B. Boehm, along
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FIGURE 10—Taphonomic scenario of the Rangea accumulations on Farm Aar, Namibia: 1, living Rangea community; 2, storm-dislodged Rangea transported
by suspension in a sediment-water mixture flow; 3, burial of Rangea in erosion gutter during waning stages of storm, arrows indicate slowing flow and
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ACCEPTED 20 SEPTEMBER 2012
and water expulsion; 5, detail, sediment sorting during settling and compaction, Rangea specimens begin to decay and deform, with early diagenetic pyrite
coating or replacing the Rangea biomaterials, arrows indicate sediment compaction and water expulsion; 6, detail, sediment fully compacted and lithified, pyrite
biofilms altering to jarosite, arrows indicate compaction pressure; 7, detail, molded surfaces of Rangea at the same stratigraphic level revealed in part and
counterpart relief, arrows indicate forced parting.