Precambrian Research 263 (2015) 1–18

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Precambrian Research

jo urnal homepage: www.elsevier.com/locate/precamres

Periglacial paleosols and Cryogenian paleoclimate near Adelaide,

South Australia

∗

Gregory J. Retallack , Brooklyn N. Gose, Jeffrey T. Osterhout

Department of Geological Sciences, University of Oregon, Eugene, OR 97403-1272, United States

a r t i c l e i n f o a b s t r a c t

Article history: Late Cryogenian deformation of the Reynella Siltstone near Hallett Cove, South Australia has been inter-

Received 12 September 2014

preted as shallow marine methane seeps, which were furthermore proposed to have played a role in

Received in revised form 13 February 2015

deglaciation from “Snowball Earth”. Re-examination and new analyses of these same outcrops confirms

Accepted 11 March 2015

an earlier interpretation of this intrastratal deformation as periglacial paleosols, which are evidence that

Available online 21 March 2015

even at maximum extent, late Cryogenian glaciers did not cover all continental lowlands, let alone the

world ocean. Known Miocene and Pliocene methane seeps of California examined for this study are very

Keywords:

different in their gray color, rounded nodules and clayey host rock, compared with red, highly deformed,

Cryogenian

Periglacial and silty to pebbly Reynella Siltstone of Hallett Cove. Stable isotopic composition of nodular carbonate

Paleosol in the Reynella Siltstone fails to show extreme carbon isotopic depletion or the meteoric oxygen lines

South Australia characteristic of known methane seeps and sphaerosideritic waterlogged paleosols, but instead shows

Snowball Earth covariance of carbon and oxygen isotopic composition comparable with that in pedogenic and subaerial

carbonate of well drained soils. Mass balance geochemical analyses show modest weathering compati-

ble with sand wedge structures and evaporitic pseudomorphs indicative of arid and frigid paleoclimate.

Outcrops of Reynella Siltstone near Hallett Cove represent frigid low latitude floodplains, not submarine

methane seeps nor global glaciation.

Published by Elsevier B.V.

1. Introduction the Elatina Formation near Hallett Cove has been interpreted as

evaporitic, oxidizing, supratidal and intertidal paleoenvironments

Coastal cliff exposures of the Reynella Siltstone Member of (Dyson and von der Borch, 1983; Alexander, 1984), including cal-

the Elatina Formation from Marino Rocks south to Hallett Cove, careous nodular and ice-deformed paleosols (Dyson and von der

near Adelaide, South Australia (Fig. 1), played an important role Borch, 1986; Williams, 1991), but more recently Kennedy et al.

in Neoproterozoic stratigraphy (Segnit, 1940), and remain impor- (2008) have interpreted nodules and deformation as submarine

tant to understanding the last widespread Snowball Earth episode methane seeps. The paleosol hypothesis did not consider methane,

of the Neoproterozoic (Kennedy et al., 2008; Shields, 2008). There and the methane hypothesis did not consider paleosols, so our

are beautifully preserved Permian tillites and striated pavements study provides comprehensive stratigraphic, petrographic and geo-

near Hallett Cove (Segnit, 1940), but other sea cliffs nearby have chemical data from multiple localities to test the alternatives of

been disappointing as evidence of Cryogenian glaciation because methane seeps or paleosols in the Reynella Siltstone Member of

they lack convincing Precambrian tillites like those known from the Elatina Formation.

the Flinders Ranges to the north (Mawson, 1940). The term Mari- Testing of these hypotheses has wider implications, because

noan, from nearby Marino Rocks is used in a chronostratigraphic methane seeps have been proposed as a source of greenhouse

sense to include late Cryogenian and Ediacaran (Fig. 2; Mawson and warming responsible for termination of the Elatina Glaciation and

Sprigg, 1950), but the terminal Cryogenian glacial advance during the Cryogenian Period (Kennedy et al., 2008; Shields, 2008). A soil

the Marinoan time-rock interval is best called the Elatina Glaciation rather than seep interpretation of these strata negates the idea of

(Mawson, 1939; Williams et al., 2008), and not “Marinoan glacia- methane-driven dramatic climatic warming after Snowball Earth,

tion” (Kennedy et al., 1998; Hoffmann et al., 2004). For many years and confirms lack of evidence for glacial moraines at Hallett Cove

(Mawson, 1940), thus limiting the seaward extent of Elatina Glacia-

tion from its mountain hinterland in the current Peake and Denison

∗ Range of South Australia (Lemon and Gostin, 1990; Retallack, 2011).

Corresponding author: Tel.: +1 5413464558; fax: +1 5413464692.

E-mail address: [email protected] (G.J. Retallack). Extensive Cryogenian equatorial oceans have been predicted by

http://dx.doi.org/10.1016/j.precamres.2015.03.002

0301-9268/Published by Elsevier B.V.

2 G.J. Retallack et al. / Precambrian Research 263 (2015) 1–18

some global circulation computer models (Hyde et al., 2000) and

biomarker evidence for continued photosynthesis (Olcott et al.,

2005). Equatorial seaways would have been important for the

survival of life (Runnegar, 2000) compared with total freezing of

lowlands and sea in snowball Earth scenarios of Hoffman et al.

(1998) and Hoffman and Schrag (2002). Our study reconsiders these

classical outcrops for evidence of methane seeps, glacial facies and

paleosols, and implications for the extent and termination of the

last Cryogenian glaciation.

2. Materials and methods

The Reynella Siltstone Member of the Elatina Formation was

observed in two outcrops (Fig. 1): sea cliffs near Hallett Cove

◦ ◦

(S35.06317 E138.50136 ), and the railway cuttings south of

◦ ◦

Kulpara (S34.12157 E138.033844 ). Also examined was drill

core of the Reynella Siltstone Member from Wokurna DDH

◦ ◦

6 (S33.7134463 E138.1411738 ), stored at Primary Industries

Research of South Australia (PIRSA), in the Adelaide suburb

of Glenside. At all locations paleosols were characterized, and

measurements taken of the depth to salts, thickness of salt accu-

mulation horizons and size of nodules (Supplementary information

Table S1). Other correlative sections examined for this work

include the Elatina Formation below basal Ediacaran stratotype

◦ ◦

monument on Enorama Creek (S31.33150 E138.63339 ), and the

Whyalla Sandstone and Cattle Grid Breccia (Williams and Tonkin,

◦

1985; Williams et al., 2008) in Mt Gunson Mine (S31.44278

◦

E137.135350 ) workings on July 5, 2007 (Figs. 1 and 2).

For comparison with putative methane seeps of Hallett Cove

(Kennedy et al., 2008), some undisputed Neogene methane

seeps were examined from California (Aiello et al., 2001; Aiello,

◦ ◦

Fig. 1. Location of Hallett Cove (A), Wokurna 6 bore (B) and Kulpara (B) in South 2005): near Santa Cruz (N36.949961 W122.04539 ), Jalama

◦ ◦

Australia. Beach (N34.51831 W120.50828 ), and Santa Barbara, California

(N34.408948◦ W119.856324◦).

Samples were collected for a variety of petrographic and

geochemical studies, which aimed to characterize mineral com-

position, grain size, major element and stable isotopic composition

Fig. 2. Cryogenian–Ediacaran stratigraphy and radiometric dating of Adelaide–Kulpara and neighboring regions of South Australia (after Ireland et al., 1998; Calver et al.,

2004, 2013; Kendall et al., 2009; Van Kranendonk et al., 2008; Williams et al., 2008; Fanning and Link, 2008; Mahan et al., 2010). Shaded units are red beds, and unshaded

unites are bluish and greenish gray.

G.J. Retallack et al. / Precambrian Research 263 (2015) 1–18 3

of these rocks. Petrographic thin sections were point counted (500 The rocks of Hallett Cove are gently folded in the Marino Anti-

points) for grain-size and mineral content, using a Swift® automatic cline, a Delamerian deformation dated by Rb–Sr dating of sericite in

point counter and stage (Supplementary information Tables S2–3). cleavage at 531 ± 32 Ma (Early Cambrian) in the overlying Brachina

The same specimens were analyzed for major elements using XRF, Formation (Turner et al., 1994; Preiss et al., 1995). Some 2300 m of

and for ferrous iron using Pratt titration (Supplementary informa- sedimentary cover culminating in the Bunyeroo Formation over-

tion Table S4), by ALS Chemex of Vancouver, BC against standard lies the Elatina Formation in Hallett Cove (Dyson, 2002). This

13

SY-4 (diorite gneiss from Bancroft, Ontario). Analyses of ␦ C and is compatible with high heat flow and lower greenschist facies

␦18

O in carbonate were made using a Finnegan MAT 253 mass metamorphism observed (Turner et al., 1994). The onset of brit-

spectrometer in Department of Geological Sciences, University of tle deformation near the Precambrian–Cambrian boundary (Preiss

Oregon, against Vienna PDB standard (Supplementary information et al., 1995) makes it unlikely that Hallett Cove included an addi-

Table S5). tional 1650 m of Ediacaran and 4852 m of Cambrian–Ordovician

Hydrolytic chemical reactions characteristic of soil formation overburden found in the Flinders Ranges to the north (Retallack,

were investigated by calculating gains and losses (mass transfer 2011).

of Brimhall et al., 1992) of elements in a soil at a given horizon

−3

( w,j in moles) from the bulk density of the soil (w in g cm ) and

4. New observations

−3

parent material (p in g cm ) and from the chemical concentra-

tion of the element in soils (C in weight %) and parent material

j,w 4.1. Field observations

(Cp,w in weight %). Also needed is changes in volume of soil during

weathering (strain of Brimhall et al. (1992), and estimated from an The upper Reynella Siltstone has pronounced intrastratal defor-

immobile element in soil (such as Ti used here) compared with par- mation in the cliff and rock platform below the Peera Street

ent material (εi,w as a fraction). The relevant Eqs. (1) and (2) are the staircase (Fig. 3A and B), and Martin Kennedy generously provided

basis for calculating divergence from parent material composition. us with Google Earth locations and numerous other images to guide

 

  our field observations, in addition to images published by Kennedy

w × Cj,w

et al. (2008) and Shields (2008). Of particular interest were features

= ε + − j,w i,w 1 1 (1)

p × Cj,p

identified as “branching pipes” and as a red “vertical cemented

 

chimney” (Kennedy et al., 2008; Shields, 2008). The chimney is

p × Cj,p

ε = illustrated here in side view (Fig. 3B), showing that it can be traced i,w − 1 (2)

w × Cj,w

3 m laterally as a three dimensional wedge-shaped structure 30 cm

above the hammer. Supposed “pipes” present circular cross sec-

3. Geological background tions illustrated here (Fig. 3F), but on sampling proved to be yellow

irregular to ellipsoidal nodules or clasts rather than pipes. They may

The Elatina Formation is Cryogenian in age by definition, have rounded to ellipsoidal sections, but lack an internal conduit.

because the stratotype basal Ediacaran (GSSP of Fig. 2) has been Kennedy et al. (2008, Fig. 1b) also illustrate wedge shaped struc-

placed at the base of the overlying Nuccaleena Formation in Eno- tures filled with sand and breccia, and these were confirmed as

rama Creek, South Australia (Knoll et al., 2006). Radiometric dating common polygonal patterns on the rock platform (Fig. 3F) and

in Namibia (Hoffmann et al., 2004), China (Condon et al., 2005), wedges in the cliff (Fig. 3A). The fill of wedge-shaped cracks is

and Tasmania (Calver et al., 2013) places the Ediacaran-Cryogenian not passive and horizontal, but vertical, and in places discontin-

boundary at about 635 Ma. The Nuccaleena Formation is present uous and deformed, as better illustrated in our scale mapping of

as three lenses within the Seacliff Sandstone, which overlies the the cliff (Fig. 4). Small examples of these structures were regarded

Reynella Siltstone Member of the Elatina Formation at Hallett Cove. as desiccation-cracks by Dyson and von der Borch (1983), but their

Another constraint on minimum age comes from the correlation by matrix is not clayey and their fill also vertical like that of the large

Gostin et al. (2010) of glacial dropstones in the Bunyeroo Forma- examples. The sand-granule fill of the cracks is identical to that of

tion with glaciation dated by U–Pb at 582 ± 4 Ma below the Croles beds which cap the red siltstone, and which are also folded upwards

Diamictite of Tasmania (Calver et al., 2004), and at 583.7 ± 0.5 Ma in into small sharp ridges, best seen in plan on the rock platform

the Gaskiers Formation of Newfoundland (Van Kranendonk et al., (Fig. 3E). Not all parts of the measured section shows such defor-

2008). mation, which is common at 4–11 m, 29 m, 90–91 m, and especially

The Reynella Siltstone Member in turn overlies the Marino prominent from 40 to 63 m (Fig. 5).

Arkose Member of the Wilmington Formation, which contains a Peloids in the sandy caps include clasts of micritic carbon-

detrital zircon dated by U–Pb at 657 ± 17 Ma (Ireland et al., 1998). ate identical with those of irregular shape and diffuse boundaries

A younger age for the base of the Elatina Formation comes from lower within the deformed beds (Figs. 6 and 7B–C). Thus car-

a Re–Os age of 643 ± 2.4 Ma for the Tindelphina Shale Member of bonate nodules were already formed in the pink siltstones before

the lowermost Tapley Hill Formation (Kendall et al., 2009), which is cracking and intrusion by the deformed cover sands (as also indi-

unconformably below both the Wilmington and Angepena Forma- cated by Kennedy et al., 2008). Folding of sandy horizons within

tions (Fig. 2). This date is incompatible with authigenic monazite red silty horizons is not consistent from one bed to the next, as

cement in the sandstone of the Enorama Formation dated using would be expected if this were a heterolithic, siltstone–sandstone

Th–U–Pb at 680 ± 23 Ma (Mahan et al., 2010), and also with a U–Pb sequence thrown into kink folds. These observations and continuity

date of 659 ± 6 Ma for a tuff low in the Wilyerpa Formation (Fanning of cover sands down into the wedges are evidence that wedging was

and Link, 2008). These inconsistencies are troubling, but allow the intrastratal and occurred between intervals of red silt deposition

late Cryogenian (∼635–640 Ma) age for the Elatina Glaciation pro- and alteration.

posed by Williams et al. (2008). Several sandstone beds have eroded margins like shallow pale-

Paleolatitude of deposition from chemical remnant magnetism ochannels (between arrows in Fig. 3G; 9, 17, 25, 28, 36 m levels

of ultrafine hematite in the Elatina Formation, supported by a fold of Fig. 5: see also Kennedy et al., 2008, Fig. 1b). These are

◦

test in the Flinders Ranges, was 6.5 ± 2.2 (Schmidt and Williams, filled with trough cross bedding, and low angle heterolithic cross

◦

1995; Williams et al., 2008). These measurements are currently 4 bedding, and oriented toward the south and southwest, like pale-

of latitude north of Hallett Cove, which was presumably also within ocurrents measured from trough cross-bedding and ripple marks

◦

12 of the equator at the time of deposition of the Elatina Formation. here by Alexander (1984). Undeformed red siltstones show both

4 G.J. Retallack et al. / Precambrian Research 263 (2015) 1–18

Fig. 3. Outcrops (A–G) at Hallett Cove, near Adelaide, South Australia and core (H and I) at Wokurna DDH 153 km to the northwest: (A) intrastratal deformation zone of upper

Reynella Siltstone Member (true-scale sketch is shown in Fig. 4); (B) oblique view of intrastratal deformation of upper Reynella Siltstone Member showing wedge shaped

deformation (at 50 m in Fig. 5; also illustrated by Shields, 2008, Fig. 1); (C) Viku paleosol and (D) its acicular sand crystals (both at 19 m in Fig. 5); (E) oblique view of uplifted

wedge of cover sand above Viku paleosol (19 m in Fig. 5); (F) plan view of drab polygons in Vani paleosol on rock platforms (43 m in Fig. 5); (G) shallow paleochannel of

sandstone and siltstone with lateral accretion sets (between arrows: at 18 m in Fig. 5); (H) Vani paleosol with small yellow nodules at 327 m (right) and Itala paleosol with

large yellow nodules at 326 m (left); (I) Wadni paleosol at 301.7 m. Hammers for scale (A–F), cliff 30 m tall (G) and core is 5 cm diameter (H and I).

asymmetric and oscillation ripples, both as isolated bedforms 2008). No hummocky bedding was found in the Elatina Formation,

(Fig. 3I) and in ripple drift sequences (Fig. 3H). There also are although it has been reported from the overlying Seacliff Sandstone

common varvelike graded beds, each 2–12 mm thick and graded and Brachina Formation at Hallett Cove (Dyson, 1983, 2002).

from silt to shale (Fig. 7A–C; Kennedy et al., 2008, Fig. 1e), like Acicular crystal casts are common at several stratigraphic lev-

those known elsewhere in the Elatina Formation (Williams et al., els (1–9 m, 14 m, 21–24 m, and 27 m in Fig. 5). The crystals are in

G.J. Retallack et al. / Precambrian Research 263 (2015) 1–18 5

Fig. 4. Scale diagram of intrastratal deformation, interpreted as successive periglacial sand wedges in the late Cryogenian Reynella Siltsone Member of the Elatina Formation

at Hallett Cove (interval 44–49 m of Fig. 5).

18

radiating arrays up to 2 cm in diameter (Fig. 3C) and full of chal- highly significant correlation of ␦ OPDB and CPDB from the same

cedony or clayey silt rather than the original mineral (Fig. 7D). samples, as demonstrated here for replacive-micritic nodular car-

2

Some are stout with interfacial angles and fishtail twins of gyp- bonate (Fig. 8, R = 0.54) and by Kennedy et al. (2008) for early

2

·

sum (CaSO4 nH2O: Dyson and von der Borch, 1983), but others calcite spar cements (R = 0.84) and pore-filling microcrystalline

2

are highly acicular and may have been other evaporite minerals dolomite (R = 0.71). In contrast, various undifferentiated carbo-

·

such as thenardite (Na2SO4) or mirabilite (Na2SO4 10H2O). The lat- nates of Kennedy et al. (2008) from this locality, but unknown

13

ter soda salts are suggested by high soda in chemical analyses of stratigraphic level, formed a cluster of mainly positive ␦ CPDB but

18

Viku and Vinarku paleosols, in which acicular crystals are common highly negative ␦ OPDB (Fig. 8).

(Fig. 6). The form of the crystals is not orthorhombic like barite

(BaSO4: Retallack and Kirby, 2007) and aragonite (CaCO3: Sumner,

4.4. Major element geochemistry

2002). Water soluble evaporite minerals were likely precursors to

the silicified crystal casts.

Major element chemical composition of Reynella Siltstone at

Hallett Cove shows evidence of salinization (high Na2O/K2O) and

4.2. Petrography

calcification (high CaO + MgO/Al2O3), but only modest chemical

weathering (low alumina/bases and Ba/Sr in Fig. 6). Some beds

In thin section, fine-grained red rocks of the Reynella Siltstone

(Vani cap, Viku and Wadni of Fig. 9) show lower titania than lower in

are surprisingly silty (Fig. 6). Clay is confined to thin seams that

the same bed as if they gained volume during formation, but other

form the tops of varve-like silty graded beds (Fig. 7A and E), like

beds have enriched titania, as if volume was lost during formation.

those described for the Elatina Formation by Williams et al. (2008).

The volume losses evidently included silica, alumina, iron, phos-

The clays are metamorphosed to lower greenschist facies like those

phorus, magnesium and soda, but conservation of potash (in Itala,

of the overlying Brachina Formation (Turner et al., 1994; Preiss

Vani, and Vinarku beds of Fig. 9). The gains in volume were primar-

et al., 1995), an observation incompatible with the identification

ily in cap sands and beds with abundant relict bedding, whereas

by Kennedy et al. (2006) of common (40%) dioctahedral smectite

silty parts of other beds lost volume (Itala, Vani and Vinarku beds

with structural disorder (SR 0.378 ± 0.14) within clay drapes to tidal

of Fig. 10).

laminae in the Reynella Siltstone.

Also surprising in thin section is lack of bedding, not only on the

cover sands (Fig. 7B and C), but also in some parts of the red silt- 4.5. Comparison with methane seeps

stones (Fig. 7A). The cover sands and wedge-shaped deformations

are a very poorly sorted jumble of quartz, feldspar, micrite clasts, For comparison, three seeps for natural gas of the late Miocene

and siltstone peloids. The massive siltstones, in contrast, are very Santa Cruz Mudstone (Fig. 11A and B) and Pliocene Pico (Fig. 11C

even grained and show abundant, irregular, subvertical disruptions and D) and Sisquoc Formations (Fig. 11E and F) were examined in

of bedding. coastal cliffs of California (Aiello et al., 2001; Aiello, 2005). These

well documented methane seeps have nodules with tubular con-

4.3. Stable isotopes duits, rimmed with bitumen. The nodules also are smooth and

light gray in color, and contrast with their dark gray shaley host

The isotopic composition of carbonate in the Reynella Siltstone rock, which shows fine laminations and ripple marks. Nodules also

at Hallett Cove shows an extreme range of compositions (Fig. 8): include local calcite veins. No breccias or wedge-shaped defor-

␦18 13

OPDB of −24.5 to +12.1‰ and ␦ CPDB of −8.6 to +7.3‰ (Kennedy mation was observed at any of these sites. We were unable to

et al., 2008). Furthermore, some phases of the carbonate show find an example of an intertidal methane seep, and documented

6 G.J. Retallack et al. / Precambrian Research 263 (2015) 1–18

Fig. 5. Measured section of paleosols in the late Cryogenian Reynella Siltstone Member of the Elatina Formation at Hallett Cove.

18 13

methane seeps are all subtidal marine (Aiello et al., 2001; Aiello, near zero for ␦ OPDB and highly variable and negative for ␦ CPDB.

2005; Formolo et al., 2004; Matsumoto, 1989) Four different sites within clathrate fields below the sea floor in the

Stable isotopic data on carbonate cements of these methane Gulf of Mexico were studied by Formolo et al. (2004) and another

seeps are provided by Aiello et al. (2001): they are invariant and four sea floor sites off South Carolina by Matsumoto (1989), with

G.J. Retallack et al. / Precambrian Research 263 (2015) 1–18 7

Fig. 6. Petrographic and geochemical data for paleosols in the late Cryogenian Reynella Siltstone Member of the Elatina Formation at Hallett Cove.

18

similar results, little within-site variation in ␦ OSMOW. Converted and wedge-shaped sandstone and breccia dikes in the cliff (Fig. 4).

to the PDB scale of Fig. 8 the Gulf of Mexico clathrate field carbon- Perhaps the Elatina Formation was originally gray and reddened

18

ate of Formolo et al. (2004) varied from −7.46 to +4.40‰ in ␦ OPDB by Neogene lateritization, as has been considered for other Neo-

13

and from −1.37 to −38.91 in ␦ CPDB. Three of the sites studied by proterozoic rocks of the Flinders ranges (Retallack, 2013), but we

Matsumoto (1989) were similar and varied from +6.1 to +0.3‰ in observed the same red colors and wedge-shaped dikes in the Elatina

18 13

␦

OPDB and from +3.5 to −31.8 in ␦ CPDB, but a third site (533) was Formation at a depth of 296–339 m in Wokurna 6 core (Fig. 3H and

18

unusually heavy for both isotopes: from +8.2 to +3.4‰ in ␦ OPDB I), below 136 m of unweathered gray Seacliff Sandstone. Further-

13

and from +12.8 to −19.2 in ␦ CPDB. more our observations (Fig. 3F) confirm those of Kennedy et al.

(2008, Fig. 1c), that red breccia clasts are found in gray matrix.

5. Alternative interpretations Finally, paleomagnetic fold tests of the Elatina Formation in the

Flinders Ranges (Schmidt and Williams, 1995) demonstrate oxi-

5.1. Methane seeps dation of matrix hematite or iron hydroxides between original

sedimentation and before burial diagenesis.

13 18

␦ ␦

Carbonate nodules, soft sediment deformation and brecciation The extreme range in both C and O isotopic composition

in the Elatina Formation at Hallett Cove has been attributed to and clear mixing lines of carbonates have been the main argument

methane seeps (Kennedy et al., 2008) on the grounds of field rela- for methane seep interpretation of the Reynella Siltstone Mem-

tionships and stable isotopic composition, and this idea is further ber at Hallett Cove (Kennedy et al., 2008), and these are compared

tested here with petrographic and geochemical data. with mixing lines from a variety of other environments in Fig. 8.

Our panel mapping (Fig. 4) and section measurements (Fig. 5) Neogene methane seep carbonates show vertical arrays of near-

18 13

␦ ␦

confirm that the deformation and nodules are strata concordant, constant O but highly variable C (Fig. 8F), and modern marine

13 18

␦ ␦

but we failed to find pipe-like or bitumen-lined tubular features limestones show near zero values for both C and O, displaced

18

␦

common in Neogene methane seeps documented here (Fig. 11) toward more negative values of O in Cambrian and Neopro-

and elsewhere (Matsumoto, 1989; Peckmann et al., 2002, 2007; terozoic limestones (Fig. 8E). In some ancient methane seeps, two

Formolo et al., 2004; Reitner et al., 2005). Known submarine parallel vertical arrays are seen: one from the active seep and its

methane seeps are all gray, unoxidized, nodular to veined shales associated fossils, and another in a petrographically distinct cement

and siltstones, lacking intraformational breccias (Aiello et al., 2001; formed during shallow burial (Peckmann et al., 2002). Different

Aiello, 2005; Formolo et al., 2004). Instead we found polygonal vertical arrays are seen from one methane seep to another on the

patterns of intraformational breccia on the rock platform (Fig. 3F) seafloor (Matsumoto, 1989; Formolo et al., 2004). Vertical arrays in

8 G.J. Retallack et al. / Precambrian Research 263 (2015) 1–18

Fig. 7. Photomicrographs of paleosols in the late Cryogenian Reynella Siltstone Member of the Elatina Formation at Hallett Cove: (A) filamentous bioturbation of lamination

in upper part of type Viku paleosol (21 m in Fig. 5A); (B) peloids in cover sand to Vani paleosol (46 m in Fig. 5A); (C) peloids in cover sand to Itala paleosol (47 m in Fig. 5A);

(D) acicular sand crystal disruption to bedding in Viku paleosol (m in Fig. 5A); (E) varvoid bedding in Itala paleosol (47 m in Fig. 5A). Specimen numbers in Condon Collection

of the Museum of Natural and Cultural History, University of Oregon are (A) R3879, (B) R3903, (C) S3896, (D) R3880, and (E) R3899.

13 18

crossplots of ␦ C and ␦ O are also well known from carbonate of a mixing line from marine carbonate clasts to soil crust (Fig. 8A).

methanogenic wetland paleosols (Ludvigson et al., 1998), Neither The range of values and covariance of stable isotopic compositions

marine limestone, nor methane seeps show significant mixing lines observed in the Reynella Siltstone at Hallett Cove are unknown in

2

(R < 0.2 in Fig. 8), but highly significant mixing lines are found in any marine rocks or sediments (Kennedy et al., 2008), but common

soils and soil crusts in which evaporative and other processes select in soils and paleosols (Fig. 8B).

18

‰ ␦

for mass of both isotopes simultaneously within CO2 or pedogenic Unusually heavy values of +1.3 to +12.1 OPDB and +2.4

13

‰ ␦

carbonate is formed on pre-existing carbonate (Knauth et al., 2003; to +7.3 CPDB from “dolomite cemented siltstone (authi-

Ufnar et al., 2008). Such a mixing line from pre-existing presumably genic microcrystalline pore-filling dolomite, often iron rich)” of

marine carbonate clasts to methanogenic carbonate is proposed by Kennedy et al. (2008), were not replicated in our own analyses

Kennedy et al. (2008), but does not fit the local data as closely as (Fig. 8A). Perhaps, as noted by Kennedy et al. (2008), such unusually

G.J. Retallack et al. / Precambrian Research 263 (2015) 1–18 9

Fig. 8. Distinct mixing lines of carbon and oxygen isotopic composition of carbonate in (A) in the late Cryogenian Reynella Siltstone Member of the Elatina Formation at

Hallett Cove derived for this study (closed circles), and by Kennedy et al. (2008: closed squares); (B) soil nodules (above Woodhouse lava flow, near Flagstaff, Arizona, from

Knauth et al., 2003; and in Yuanmou Basin, Yunnan, China, from Huang et al., 2005), (C) soil crusts on basalt (Sentinel Volcanic Field, Arizona, from Knauth et al., 2003),

(D) Quaternary marine limestone altered diagenetically by meteoric water (Key Largo, Florida, from Lohmann, 1988, and Clino Island, Bahamas, from Melim et al., 2004),

(E) unweathered marine limestone of Holocene (from Veizer et al., 2000) and Early Cambrian age (Ajax Limestone, South Australia, from Surge et al., 1997), and (F) marine

methane cold seep carbonate (Miocene, Santa Cruz Formation, Santa Cruz, California, from Aiello et al., 2001). Slope of linear regression (m) and coefficients of determination

2

(R ) for mixing lines show that carbon and oxygen isotopic composition is significantly correlated in soils and paleosols, but not in marine limestones or methane seeps.

13

positive values were produced during burial alteration several hun- +7.42 for ␦ CPDB (Quade et al., 2007). These unusually heavy stable

dred meters below the sea floor by fluids generated within the isotopic values will remain a puzzle until analyzed at micron scale.

zone of methane fermentation, as proposed by Matsumoto (1989). Finally the methane-seep-cemented marine beds should show

This may have been within the source rocks for dolomite grains, invariant mineral composition and chemical composition, and

which match marine isotopic composition (Fig. 8A and E). Meta- strain-tau values within the dilate-and-gain field. Some beds (Viku,

morphic alteration to low in the greenschist facies (Turner et al., Vani and Wadni of Fig. 6) show little mineral or chemical differen-

18

␦

1994; Preiss et al., 1995) typically creates lighter values of OPDB tiation, but others (Vinarku and Itala) show surficial gains of clay

13

␦

and CPDB (Algeo et al., 1992), so does not explain unusually and oxidized iron expected of Neoproterozoic paleosols (Retallack,

heavy values at Hallett Cove, although perhaps contributing to 2013). Dilate-and-gain of sedimentary additions were seen in cap-

the remarkable spread of isotopic values (Fig. 8A). Alternatively, ping sands of some beds, but most of the beds lost mass and

Knauth et al. (2003) have shown that comparable isotopic enrich- weatherable components in the collapse-and-loss field of soils and

ment is created by surface evaporation, and calcite soil coatings in paleosols (Fig. 9). Titanium used as a stable constituent is mainly

18

‰ ␦

the Atacama Desert of Chile reach values of +7.29 for OPDB and in ilmenite and other heavy minerals which fall to the base of

10 G.J. Retallack et al. / Precambrian Research 263 (2015) 1–18

Fig. 9. Mass balance geochemistry of paleosols in the Reynella Siltstone of South Australia, including estimates of strain from changes in an element assumed stable (Ti) and

elemental mass transfer with respect to an element assumed stable (Ti, following Brimhall et al., 1992). Zero strain and mass transfer is the parent material lower in the

profile: higher horizons deviate from that point due to soil formation or sedimentation as indicated in key to lower right.

sedimentary beds, but are enriched at the surface during soil for- 2000). Sand wedges have vertical bedding, unlike passively filled

mation which depletes the bed in weatherable components. The ice wedges (Williams, 1986). The largest sand wedges are in beds

analyzed beds of the Elatina Formation are unlike marine event with the largest calcareous nodules and the most disturbed bedding

beds in this respect, but also are not deeply weathered. These pet- (Fig. 2A), so that variation in size may be related to varied dura-

rographic and geochemical data can be added to stable isotopic tions of formation. The variation in size of the Reynella Siltstone

and field observations which falsify the methane seep hypothesis sand wedges matches both ice and sand wedges (Fig. 12B–C) of

of Kennedy et al. (2008). Holocene (Leffingwell, 1915; Black, 1976a,b; Gell, 1978; Washburn,

1980; Davis, 2001) and Pleistocene age (Black, 1976a; Washburn,

5.2. Paleosols 1980; Wayne, 1991; Dylik, 1994; French, 1996; Owen et al., 1998;

Davis, 2001; Van Vliet-Lanoë, 2010; Raffi and Stenni, 2011).

Intrastratal deformation of the Reynella Siltstone at Hallett Cove The fill and capping sands to layers include mildly deformed

(Fig. 4) is similar to periglacial sand wedge paleosols of the correl- soft-sediment clasts (Fig. 7B) similar to frozen granules transported

ative Whyalla Sandstone and Cattle Grid Breccia (Fig. 2) described in periglacial outwash (Van Vliet-Lanoë, 1985, 1998, 2010). These

by Williams and Tonkin (1985), Williams (1986), and Williams cap-sands and wedge fills are less geochemically weathered (base

et al. (2008). Polygonal networks of fissures (Fig. 3F) distinguish depleted) than associated red siltstones (Figs. 9 and 10). Cap-sands

these features from seismically induced sand volcanoes (Galli, may represent episodes of fluvioglacial outwash terminating the

Fig. 10. Depth functions of elemental mass transfer with respect to an element assumed stable (Ti, following Brimhall et al., 1992) for paleosols in the Reynella Silstone of

South Australia.

G.J. Retallack et al. / Precambrian Research 263 (2015) 1–18 11

Fig. 11. Neogene methane seeps from California: Santa Cruz Formation (late Miocene) near Santa Cruz (A and B), Sisquoc Formation (Pliocene) at Jalama Beach (C and D) and

Pico Formation (Pliocene) at Santa Barbara, California (E and F).

formation of the sand wedges, but also mildly deformed by subse- surface are characteristic of soils and paleosols (Gile et al., 1981;

quent sand wedges at higher stratigraphic levels (Fig. 4). Dan and Yaalon, 1982; Monger et al., 1991; Almohandis, 2002).

Periglacial sand wedges are one form of paleosol, but so are Both are replacive because they contain preexisting grains of

other features of the Reynella Siltstone at Hallett Cove. Replacive their matrix, and not displacive clear crystals of gypsum or cal-

spherulitic sand crystals (Fig. 7D) and micritic nodules (Fig. 6) cite common in marine nodules and evaporites (Shearman, 1978;

organized into horizons a fixed distance below the ancient land El Khoriby, 2005; Ziegenbalg et al., 2010). Crystal casts extend

12 G.J. Retallack et al. / Precambrian Research 263 (2015) 1–18

Fig. 12. Hypothetical development of periglacial paleosols from examples of varied development in the late Cryogenian Reynella Siltsone Member of the Elatina Formation

at Hallett Cove (A) and comparable dimensions of modern sand wedges (B).

beyond the spherulitic core of the aggregate (Figs. 3D and 7D), and redeposited clasts of red siltstone (Fig. 7B), a paleomagnetic fold

the micrite nodules are laterally linked into irregular aggregations test (Schmidt and Williams, 1995), and similar color of paleosols in

(Fig. 3F) as evidence that they formed in place, rather than as clasts the Elatina Formation at depths of 296–329 m in Wokurna DDH6

transported from formation elsewhere. drillcore (Fig. 3H and I).

2 18 13

Periglacial sand wedges and replacive evaporites and micrites Significant covariance (R = 0.54) between ␦ O and ␦ C is char-

are comparable with soil features which destroy original fine acteristic of paleosols, and its slope is low (0.13), perhaps reflecting

lamination of the Reynella Siltstone, with destruction of bedding low rates of paleoevaporation in a cold climate (Ufnar et al., 2008).

18

proportional to the size and abundance of the wedges, sand crys- Extremely enriched ␦ OPDB values of +6.96‰ at Hallett Cove are

tals and nodules. But there are other finer scale disruptions of found in highly evaporative soil crusts (Knauth et al., 2003; Quade

18

lamination giving rise to massive beds, and best appreciated on et al., 2007). Very low ␦ OPDB values (down to −22.5‰) are evi-

the scale of thin sections. Some of this homogenization of bed- dence of glacial meltwater or cold rain (Kennedy et al., 2008), but

18

ding is a system of cracks and brecciation at the tops of massive near zero ␦ O values may represent Proterozoic marine limestone

beds (Fig. 7C), as noted for the Hallett Cove locality by Dyson and fragments within the paleosols as silt-size grains of the parent loess

von der Borch (1983). Other bed tops have a system of filamen- (Fig. 7A and E).

tous disruptions of bedding spreading downward (Fig. 7A). The

small diameter, irregularity and ferruginization of these filamen- 6. Sedimentary interpretations

tous structures is most like structures made by soil microbes (Poelt

and Baumgärtner, 1964; Mihail and Bruhn, 2005; Garcia-Pichel and Sedimentary paleoenvironments of alluvial to tidal coastal flats

Wojciechowski, 2009). They are much thinner and irregular than are indicated for the Reynella Siltstone by primary sedimentary

fluid-escape structures or mud volcanoes, which tap into organic structures including bimodal paleocurrents (Alexander, 1984), her-

or fine grained lower layers not seen at Hallett Cove (Dionne, 1976; ringbone and flaser bedding and bundled lamination (Kennedy

Nichols et al., 1994). et al., 2008, Fig. 1e; Williams et al., 2008, Fig. 7a, b and d).

Geochemical differentiation within individual beds reflects typ- Compared with more complex bundling in Reynella Siltstone of

ical soil weathering: incongruent dissolution of feldspar and other the Flinders Ranges (Williams, 1991), bundling near Hallett Cove

weatherable minerals by carbonic acid to form clay and release includes proximal neap-spring tidal cycles representing 13.1 ± 0.1

2+ 2+ + +

nutrient cations (Ca , Mg , Na , K ). Modest progress of this lunar months/year, 400 ± 7 solar days/year and 21.9 ± 0.4 h/solar

hydrolysis reaction is revealed by increased clay and molar ratios day (Williams et al., 2008). Intertidal facies, shallow paleochannels

of alumina/bases toward the tops of profiles (Fig. 6). A more pre- with heterolithic fill of sandstone and siltstone (Fig. 3G between

cise demonstration of hydrolysis is revealed by calculating chemical arrows) and limestones are common in the lower 37 m of the mea-

losses and gains, as well as volume loss and gain to a stable con- sured section (Fig. 5), north along the seacliffs toward Marino Rocks.

stituent (Eqs. (1) and (2) above after Brimhall et al., 1992). The field These paleochannels not only contain heterolithic lateral accretion

of collapse of volume and loss of cations characteristic of soils is sets, but have steep cut banks (right hand arrow of Fig. 3G). Lat-

demonstrated by chemical analyses of paleosols in the Reynella For- eral accretion and cut banks are hallmarks of meandering streams,

mation, but the cap sandstones show subdued change or plot in the which Davies and Gibling (2010) argue are unknown before the

dilate and gain field characteristic of sediments (Fig. 9). Within-bed Silurian. This interval of the Reynella Siltstone is also where evap-

differences in red color comparable with those of ferruginization orite pseudomorphs are most common and indicate largely dry

of well drained paleosols and limited burial gleization (Retallack, supratidal coastal flats (Dyson and von der Borch, 1983). Meander-

1997) are revealed by variation in ferrous to ferric iron ratio (Fig. 6). ing intertidal channels are known from Proterozoic (Bengtson et al.,

This red color was acquired during the Cryogenian as revealed by 2007; Dehler et al., 2012) and Cambrian (Hereford, 1977; Cloyd

G.J. Retallack et al. / Precambrian Research 263 (2015) 1–18 13

et al., 1990) intertidal facies, and remain common on unvegetated, water stages in the original streams (Retallack, 2001, 2008). Local

low-relief, muddy, tidal flats today (Kleinhans et al., 2009). relief was thus no more than 3 m seen on some paleochannel cut

Tidal or lagoonal varve-like lamination (Fig. 7A and E) is less banks. Periglacial polygons (Fig. 4) and locally deformed outwash

common within the interval 37–65 m, where periglacial sand sands (Fig. 3E) would have given ground roughness with an ampli-

wedges are common, and paleochannels are still of trough cross- tude of about 20 cm.

bedded sand of a contrasting gray color to the intervening red

siltstones. From 65 to 92 m red color is found in three dis- 7.3. Former parent material

tinct facies: (1) siltstone paleosols, (2) siltstones with ripple

drift cross-lamination, and (3) trough cross-bedded paleochan- Parent materials to the paleosols were quartzofeldspathic and

nels. These parts of the sequence are similar to alluvial floodplain dolomitic silts and sands (Stevenson, 1972). The high proportion of

sequences: the drab paleochannel facies is comparable with the dolomitic silt seen in some levels (Fig. 6) may be eolian and derived

Ediacaran, Ediacara Member of South Australia (Retallack, 2013) from extensive marine dolostones exposed in the Peake and Deni-

and numerous Phanerozoic floodplain facies (Retallack, 2008; Mor- son Ranges (Retallack, 2011). Quartzofeldspathic silt grains also

rison and Straight Cliffs Formations of Retallack, 2009). Higher in are angular and randomly arranged, and may be loess distal to

the sequence both paleochannels and paleosols are red, compara- dune fields represented by the Whyalla Sandstone (Williams et al.,

ble with the Ediacaran Bonney Sandstone of South Australia (Drexel 2008). These silty parent materials contrast with sandy to gravelly

et al., 1993) and other Phanerozoic floodplain facies (Retallack, fluvioglacial outwash that forms caps to many of the beds (Fig. 6).

2001; Halgaito and Summerville Formations of Retallack, 2009).

7.4. Time for formation

7. Paleosol interpretations

Rates of ice and sand wedge growth in Antarctica ranged from

0.79 mm/yr in the 1960s (Black, 1973) to 0.04 mm/yr in the 1970s

7.1. Identification

(Black, 1982). Such wide disparity is problematic for understand-

ing rates and extrapolating age, though comparable with rates of

Individual beds of the Reynella Siltstone Member with deforma-

growth of such features in the northern hemisphere (Bockheim,

tional, petrographic and geochemical characteristics of paleosols

1995). From their width in paleosols of the Reynella Siltstone

fall into five repeated types, here given non-genetic pedotype

(Fig. 12B) the sand wedges would have formed in 10–72 years by

names from the Adnamatna aboriginal language (McEntee and

the fast rate and 200–1425 years by the slow rate.

McKenzie, 1992). These include Itala (crack in rock), Vani (flesh),

Longer estimates of time come from the formation of carbonate

Viku (eyebrow), Vinarku (gypsic alluvium), and Wadni (small).

nodules in the paleosols. In desert soils of New Mexico (Retallack,

The various pedotypes of the Reynella Siltstone at Hallett Cove

2005) diameter of carbonate nodules (S in cm) is related to soil age

can be identified within modern soil classifications (Table 1), such 2

(A in kyrs) by the following equation (R = 0.57; S.E. ± 1.8 kyr):

as those of the United States (Soil Survey Staff, 2010) and the Food

0.34

A = . S

and Agriculture Organization (1975, 1978), but the Australian clas- 3 92 (3)

sification does not seem to have closely comparable soils at present

This transfer function gives 16.5 ± 1.8 kyr for the type Itala pale-

(Isbell, 1996). The most similar Russian soils (units Bx6-3b of Food

osol and 6.6 ± 1.8 yr for the type Vani paleosol. An average duration

and Agriculture Organization, 1978), are Gelic Cambisols associated

with one standard deviation for 9 Itala paleosols is 16.2 ± 5.5 kyr

with Calcic Cambisols and Calcaric Regosols. Map unit Bx6-3b cov-

and for 20 Vani paleosols is 5.7 ± 3.0 kyr (Supplementary infor-

ers 10,816,000 ha in floodplain and headwaters of the Olenek River,

mation Table S1). These paleosols thus formed on Milankovitch

near Jerbogacon,ˇ Siberia, where climate is frigid and vegetation is

time scales, with long episodes of weathering followed by shorter

pine (Pinus sibirica)-larch (Larix dahurica) taiga forest. Comparable

episodes of frigid deformation. Sandy caps to the beds show little

Canadian soils (units Bx1-1a and Bx2-1b of Food and Agriculture

chemical weathering (Figs. 9 and 10), compared with the silty pale-

Organization, 1975) cover 6449,000 ha of marine sediments and

osols below with their carbonate nodules (Kennedy et al., 2008).

glacial outwash west of Hudson Bay and north of Churchill, where

Milankovitch precesssion cycles have been computed to have been

climate is frigid and vegetation is mixed spruce (Picea mariana)

19,462 years, and obliquity cycles 31,243 years at 640 million

taiga and tundra. Jerbogaconˇ has a mean annual temperature of

− ◦ years ago (by interpolation from table of Berger and Loutre, 1994).

6.7 C and mean annual precipitation of 323 mm, and for Churchill

◦ Wadni and Viku paleosols show little soil formation, and compa-

these values are −7.2 C and 435 mm (Müller, 1982). Such climate

rable Inceptisols and Entisols today represent millenia to centuries

may be comparable with that of these Cryogenian paleosols, but

of soil formation, even in Antarctica (Campbell and Claridge, 1987;

such vegetation cannot be inferred for paleosols from before the

Retallack et al., 2001).

advent of land plants.

7.5. Paleoclimate

7.2. Paleotopography

Sand wedge polygons form today under a well constrained set of

Tidal laminae (Fig. 7A and E) persist at least to 63 m in the mea- paleoclimatic controls: mean annual air temperatures of less than

− ◦ ◦

− − sured section (Fig. 5) and are evidence of a flat coastal plain to 12 to 20 C, mean coldest month temperature < 35 C, mean

◦

supratidal flats for the Reynella Siltstone. At these stratigraphic lev- warmest month temperature of +4 C, and mean annual precip-

els the sandstone paleochannels and lower levels of the paleosols itation <100 mm (Williams, 1986). Comparable paleoclimate has

are gray (Fig. 5), and ferrous iron is common (Fig. 6), but other parts been inferred for fossil sand wedges of the Cattle Grid Breccia and

of the paleosols are red and ferruginized (Fig. 6). Such alternation of lower Whyalla Sandstone of the Mount Gunson Mine on the Stuart

redox character can be attributed to persistently high water table in Shelf, and like those periglacial paleosols, the comparable features

a coastal plain, as for other comparable sequences of coastal pale- at Hallett Cove may record the coldest part of the Elatina Glaciation

osols (Retallack, 2008, 2013). These floodplains could not have been (Williams et al., 2008). Warmer, though still frigid, conditions are

permanently waterlogged, because brittle, frozen soil is required also evident from thufur mounds and shadow dunes in the overly-

for the formation of sand wedge polygons (Maloof et al., 2002). ing Nuccaleena Formation (Retallack, 2011). Under warmer frigid

Red paleochannels above 65 m (Fig. 5) reflect oxidation during low conditions, a variety of structures are formed including ice wedge

14 G.J. Retallack et al. / Precambrian Research 263 (2015) 1–18

Table 1

Pedotype definition and classification for the Elatina Formation.

Pedo-type Diagnosis Soil Survey Staff (2010) Food and Agriculture Australian (Isbell, 1996)

Organization (1975,1978)

Itala Drab yellowish gray sandy surface with deep wedge Haploturbel Gelic Cambisol Lithocalcic Calcarosol

like deformation(A) over red siltstone with large

calcareous nodules (Bk)

Vani Drab yellowish gray sandy surface with deep wedge Haploturbel Gelic Cambisol Lithocalcic Calcarosol

like deformation(A) over pink siltstone with small

calcareous nodules (Bk)

Vinarku Drab yellowish gray sandy surface (A) over diffuse Haplogypsid Gypsic Yermosol Hypersalic Rudosol

zone of calcified gypsum rosettes (By)

Viku Drab yellowish gray sandy surface (A) over dark red Haploxerept Eutric Cambisol Red-Orthic Tenosol

bedded silstone (Bw)

Wadni Ferruginized sitstone with cracking (A) over bedded Fluvent Fluvisol Stratic Rudosol

siltstone with wispy mottles (C)

polygons, periglacial involutions and thufur mounds (Young and no vegetation visible to the naked eye (Retallack, 2005; Retallack

Long, 1976; Krull, 1999; Retallack, 1999a,b, 2011, 2013). Ice wedges and Huang, 2010).

are best known from Greenland and Arctic Canada, which are mar- 0.0209Dy

P = 87.593e (6)

itime glacial climates, as opposed to the continental glacial climate

of modern Antarctica with sand wedges (Black, 1976a,b; Washburn, 2

P = . + . D − . D

137 24 6 45 k 0 013 k (7)

1980). Sand wedge polygons have also been reported from the

Both these proxies (Eqs. (6) and (7)) for paleoprecipitation

Lillfjället Formation of early Cryogenian age (Kumpulainen, 2011)

require decompaction of the paleosols, and in this case physical

and ice wedge polygons from Paleoproterozoic glacial deposits

constants for Aridisols (Eq. (7) after Sheldon and Retallack, 2001)

(Young and Long, 1976).

were used giving depth to salts in the in original soil (D ) from depth

Frigid paleotemperatures are supported by the pedogenic pale- s

in the current paleosol (D ) for a particular depth of burial (K in km).

othermometer of Óskarsson et al. (2009), based on frigid modern p

soils under tundra vegetation of Iceland. This linear regres- Dp

◦ Ds =    

sion between mean annual temperature (T in C) and chemical (8) 0.17K

−0.62/ 0.38/e − 1

index of weathering (I = 100 mAl2O3/(mAl2O3 + mCaO + mNa2O), in

2

molar proportions is given in the following equation (R = 0.81;

Arid paleoclimate was calculated by all three methods: mean

◦

S.E. = ±0.4 C):

annual precipitation of 357 ± 182 mm from chemical composition

and 158 ± 129 mm from depth to gypsum for type Viku paleosol,

T =

0.21I − 8.93 (4)

500 ± 182 mm from chemical composition and 162 ± 129 mm from

depth to gypsum for the type Vinarku paleosol, 275 ± 182 mm from

Results for the analyzed type profiles are mean annual tempera-

◦ ◦ chemical composition and 330 ± 149 mm from depth to micrite for

−

tures of 7.1 ± 0.4 C for the type Viku paleosol, −3.3 ± 0.4 C for the

◦ the type Vani paleosol, and 325 ± 182 mm from chemical compo-

type Vinarku paleosol, −6.6 ± 0.4 C for the type Vani paleosol, and

±

− ◦ sition and 314 149 mm from depth to micrite for the type Itala

4.8 ± 0.4 C for the type Itala paleosol. Other chemical paleother-

paleosol.

mometers of Gallagher and Sheldon (2013) and of Sheldon et al.

(2002) have a training set of modern temperate forested soils, and

◦ 7.6. Ancient life on land

yielded mean annual paleotemperatures in the range 7.2–10.7 C,

incompatible with evidence of sand wedge polygons (Fig. 4).

Phosphorus is depleted in some paleosols of the Reynella Silt-

Arid paleoclimate for the paleosols of the Reynella Siltstone

stone (Figs. 9 and 10), and experimental studies of modern soils

is supported by three distinct paleohyetometers. A chemical

have shown that only organic ligands can weather phosphorus to

transfer function of Sheldon et al. (2002) based on temperate

this extent from apatite in soils (Neaman et al., 2005). Another indi-

soils of North America uses chemical index of alteration with-

cation of microbial activity in these paleosols is molar depletion

out potash (R = 100 mAl2O3/(mAl2O3 + mCaO + mNa2O) in moles),

of alkali and alkaline earth oxides (CaO + MgO + Na2O + K2O) in the

which increases with mean annual precipitation (P in mm) in mod-

2 paleosols (Figs. 9 and 10) by CO2 from soil respiration (Retallack,

ern soils (R = 0.72; S.E. = ±182 mm), as follows: 1997).

0.0197R

P = Microtubular disruption of lamination in paleosols of the

221e (5)

Reynella Siltstone is sparse in lower parts of the profiles (Fig. 7E),

This formulation is based on the hydrolysis equation of weath- but totally disrupts lamination in the upper part of the profiles

ering, which enriches alumina at the expense of lime, magnesia, (Fig. 7A). These ptygmatically compressed, near-vertical tubules

␮

potash and soda. Magnesia is ignored because not significant for are 10–50 m in diameter. Similar features in modern soils are

most sedimentary rocks, and potash is excluded because it can produced by bundles of sheathed cyanobacteria, like modern

be enriched during deep burial alteration of sediments (Maynard, Microcoleus vaginatus (Garcia-Pichel and Wojciechowski, 2009),

1992). rhizomorphs of fungi, like those of honey mushroom, Armillaria

The other two other paleohyetometers come from depth to mellea (Mihail and Bruhn, 2005), or lichen rhizines like those of

salts in paleosols. Depth (Dy in cm) to gypsic (By) horizon in mod- bruised lichen, Toninia sedifolia (Poelt and Baumgärtner, 1964).

ern soils (Retallack and Huang, 2010) has found the relationship Although the exact nature of these microbes are unknown, commu-

2

of Eq. (6) with mean annual precipitation (P in mm: R = 0.63, nities of paleosols in the Reynella Siltstone may have been microbial

standard error ± 129 mm). Mean annual precipitation (P in mm) earths (Retallack, 2012), like those as known today from biological

is also related to depth to carbonate nodules (Dk in cm) accord- soil crusts (Belnap and Lange, 2003).

2

ing to Eq. (7) (R = 0.52; S.E. = ±147 mm). Both training sets include Life on land is known back at least 2200 million years (Retallack

many sparsely vegetated soils paleosols, including polar soils with et al., 2013), so evidence of microbes in paleosols of the Reynella

G.J. Retallack et al. / Precambrian Research 263 (2015) 1–18 15

Siltstone is unremarkable. Nor were these paleosols too cold to sup-

port life: comparable frigid soils in Antarctica today also have a rich

microbial community, as well as rotifers, nematodes, tardigrades,

mites and springtails (Cary et al., 2010). No megafossils were found

in the Reynella Siltstone, although they are known in other Cryo-

genian rocks. Compressions such as Aspidella, some 766 million

years old have been found on surfaces with old-elephant skin tex-

tures (Meert et al., 2011), like those of microbial earths (Retallack,

2012). Sponge-like skeletal remains such as Otavia, are known from

marine limestones up to 760 million years old (Maloof et al., 2010;

Brain et al., 2012).

8. Correlations and causes

Correlation of the Reynella Siltstone and Nuccaleena Formations

between Hallett Cove and the central Flinders Ranges is secure

because of identical lithologies in each area, connected by Kulpara

railway cutting and Wokurna core (Williams et al., 2008). These

formations are separated by a regional disconformity in the cen-

tral Flinders Ranges, but to the south by channel incision at the

base of the Seacliff Sandstone which includes stringers of Nuc-

caleena Formation (Dyson and von der Borch, 1986; Dyson, 2002).

These relationships are problematic for the idea that the Reynella

Siltstone includes methane seeps which terminated the last Cryo-

genian glacial advance (Kennedy et al., 2008). Instead of global

warming and sea level rise predicted by that view, the basal Sea-

cliff sandstone paleochannel incision records a local relative fall

Fig. 13. Conjectural reconstruction of paleosols and sedimentary paleoenvironment

of sea level (Dyson and von der Borch, 1994). Observations along

of the Reynella Siltstone near Adelaide.

this disconformity are also not supportive of the idea of a glacial

advance all the way to the sea in a global Snowball Earth (Hoffman

and Schrag, 2002), because several generations of observers (Segnit,

by Mawson (1940), Dyson (1983), Dyson and von der Borch (1983,

1940; Mawson, 1940; Williams et al., 2008) have failed to find

1986), Alexander (1984) and Williams (1991). This passive margin

evidence of dropped pebbles or moraines within the Seacliff Sand-

coast was well south of moraines of the Elatina Formation of the

stone. Trough cross bedding of the Seacliff Sandstone is evidence of

Flinders Ranges to the north (Lemon and Gostin, 1990; Retallack,

fluvial incision and fill (Dyson and von der Borch, 1994), at a time of

2011). An array of supratidal to alluvial paleosols in the Reynella

relative sea level fall during frigid conditions that created the sand

Siltstone includes Gelisols with sand wedge polygons formed near

wedge paleosols described here. Post-glacial marine transgression

Hallett Cove in an arid frigid continental paleoclimate like that

◦

was not until much later, as indicated by gray siltstones and hum-

of modern Antarctica (Fig. 13). Such cold conditions within 12

mocky cross bedding of the Brachina Formation (Dyson, 1983). The

of the equator during the late Cryogenian (∼635–640 Ma) peak of

disconformity between Seacliff Sandstone or Nuccaleena Forma-

the Elatina Glaciation (Williams et al., 2008) confirm the remark-

tion and the Elatina Formation is regional (Williams et al., 2008), but

able Neoproterozoic spread of glacial facies that has been termed

has nowhere yielded thick paleosols as evidence of longer duration

“Snowball Earth” (Hoffman and Li, 2009).

than other paleochannels within the Elatina Formation (Fig. 5).

Our reconstruction of the Reynella Siltstone Member of the

Elatina Formation from Marino Rocks to Hallett Cove confirms

9. Conclusions the conclusion of Mawson (1940) that these rocks contain neither

tillites nor fully marine deposits. Our reconstruction thus does not

The Reynella Siltstone Member of the Elatina Formation support extreme interpretations of a hard Snowball Earth, with

between Marino Rocks and Hallett Cove may have been deposited the whole ocean and all lowlands completely enveloped in ice

in coastal plains to intertidal flats (Fig. 13; Table 2), as envisaged (Hoffman et al., 1998; Hoffman and Schrag, 2002). Hallett Cove at

Table 2

Pedotype interpretative summary for the Elatina Formation.

Pedo-type Climate Organisms Topographic setting Parent material Time for formation

Itala Frigid arid (mean annual temperature Microbial soil crust Well drained Dolomitic and 10,000–20,000 years

◦

−4.8 ± 0.4 C; mean annual precipitation loess-alluvial terrace quartzo-feldspathic silt

314 ± 147 mm)

Vani Frigid arid (mean annual temperature Microbial soil crust Well drained Dolomitic and 3000–9000 years

◦

−6.6 ± 0.4 C; mean annual precipitation loess-alluvial terrace quartzo-feldspathic silt

330 ± 147 mm)

Vinarku Frigid arid (mean annual temperature Microbial soil crust Well drained supratidal Dolomitic and 100–1000 years

◦

−3.3 ± 0.4 C; mean annual precipitation flat quartzo-feldspathic silt

162 ± 129 mm)

Viku Frigid arid (mean annual temperature Early successional microbial loess plain Dolomitic and 100–1000 years

◦

−7.1 ± 0.4 C; mean annual precipitation soil crust quartzo-feldspathic

158 ± 129 mm) sand

Wadni Not diagnostic of climate Early successional microbial well drained supratidal Dolomitic and 10–100 years

soil crust flat quartzo-feldspathic silt

16 G.J. Retallack et al. / Precambrian Research 263 (2015) 1–18

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␦13 1127–1130.

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