Aztec Siltstone Research Articles

The dentition of Omalodontiformes, the order of unusual Devonian stem-chondrichthyans

The early chondrichthyan order Omalodontiformes from the late Early Devonian through to the Late Devonian is characterised by specific teeth. Unlike in most Devonian sharks, their bases are directed labially or are reduced and devoid of labial or lingual extensions. In this paper the complex history of investigation on the dermal skeleton of omalodontiforms is presented and the validity of the established taxa is revised. The dentition of an Emsian representative of this group, known from a single articulated specimen (NMBG 10127) and several isolated fin spines from Canada and previously, probably incorrectly, attributed to Doliodus, is distinctly heterodont. The nature of this heterodonty suggests that the two omalodontiform tooth-based genera described originally from the Middle/Upper Devonian Aztec Siltstone (Antarctica), viz. Portalodus and Anareodus, are in fact congeneric as their teeth represent different parts of the same jaw. Because the teeth of the Canadian specimen differ in important aspects from those of typical Doliodus and are generally similar to those of Portalodus, it probably should be placed in a new genus. Also, the validity of the distinction between Portalodus bradshawae and P. mannoliniae is considered questionable.

New insights into the origins and radiation of the mid-Palaeozoic Gondwanan stem tetrapods

ABSTRACTThe earliest tetrapodomorph fishes appear in Chinese deposits of Early Devonian age, and by the Middle Devonian they were widespread globally. Evidence for the earliest digitated tetrapods comes from largely uncontested Middle Devonian trackways and Late Devonian body fossils. The East Gondwana Provence (Australasia, Antarctica) fills vital gaps in the phylogenetic and biogeographic history of the tetrapods, with the Gondwanan clade Canowindididae exhibiting a high degree of endemism within the early part of the stem tetrapod radiation. New anatomical details of Koharalepis, from the Middle Devonian Aztec Siltstone of Antarctica, are elucidated from synchrotron scan data. These include the position of the orbit, the condition of the hyomandibular, the shape of the palate and arrangement of the vomerine fangs. Biogeographical and phylogenetic models of stem tetrapod origins and radiations are discussed.

New arthrodires (placoderm fishes) from the Aztec Siltstone (late Middle Devonian) of southern Victoria Land, Antarctica

A small collection of arthrodire remains is described from the Devonian Aztec Siltstone of southern Victoria Land, Antarctica. Barwickosteus antarcticus, gen. et sp. nov., is a small phlyctaeniid arthrodire probably closely related to Barrydalaspis from the Bokkeveld Group of South Africa. Grifftaylor antarcticus, gen. et sp. nov., is a generalised phlyctaeniid resembling Phlyctaenius and Neophlyctaenius. New specimens of Boomeraspis show that it had a high-spired trunk-armour with a median dorsal plate of similar proportions to Tiaraspis, Mithakaspis, Turrisaspis or Africanaspis. Other fragmentary median dorsal plates are provisionally referred to Turrisaspis and Mulgaspis. With these new taxa the vertebrate assemblage from the Aztec Siltstone comprises at least 37 genera and 50 species, making it one of the most diverse of Middle–Late Devonian age.

Depositional environment, stratigraphy, structure and paleobiology of the Hatchery Creek Group (Early–?Middle Devonian) near Wee Jasper, New South Wales

A revised depositional model of predominantly swampy rather than lacustrine conditions is proposed for the upper dark shales and mudstones (Corradigbee Formation) of the Hatchery Creek Group. The whole sequence is interpreted as a humid alluvial fan deposit, conformable on underlying limestones, with a total thickness of about 1800 m. Cyclic sedimentation probably resulted from climatic fluctuations much longer than seasonal events and may reflect Milankovitch cyclicity. The most recent Devonian time-scale calibrations indicate that much of the Hatchery Creek sequence could have been deposited during the Emsian, giving adequate time for subsequent folding during the Middle Devonian Tabberabberan episode. The Corradigbee Formation contains a unique fossil fish assemblage, not represented elsewhere in eastern Australia, but sharing features with Early Devonian faunas from Yunnan, China, and the Middle Devonian Aztec Siltstone fish fauna of Victoria Land, Antarctica. The first invertebrate fossils are recorded from the Hatchery Creek Group (freshwater gastropods, indeterminate arthropods). Abundant plant remains at some localities include lycopsids, some early leaf-like structures, and deep root systems preserved in paleosols, the earliest record of such features from Australia. The new data are inconsistent with Northern Hemisphere fossil evidence linked to a modelled dramatic drop in CO2 levels and rise in O2 during the Devonian Period, but comply with some other evidence that the first forests may have evolved somewhat earlier in East Gondwana than elsewhere.

Disarticulated acanthodian and chondrichthyan remains from the upper Middle Devonian Aztec Siltstone, southern Victoria Land, Antarctica

AbstractWell-preserved vertebrate microremains are abundant in the residues from a calcareous grey siltstone in thekarawakabiozone (?late Givetian) of the Aztec Siltstone at Mount Crean, Lashly Mountains, Antarctica. Acanthodians are represented by scales of acritolepidPechoralepis juozasisp. nov., climatiidNostolepissp. cf.N. gaujensisValiukevičius, diplacanthidMilesacanthus antarcticaYoung & Burrow, and an undetermined acanthodiform. The acanthodian assemblage resembles those from early Frasnian carbonates of central Iran. Chondrichthyan elements in the fauna include rare teeth ofAztecodus harmsenaeLong & Young andAntarctilamna priscaYoung, ctenacanthoid-type scales and branchial denticles which are possibly fromAntarctilamna, and scales of an indeterminate chondrichthyan. An isolated set of acanthodid acanthodiform jaws from the uppermost ‘phyllolepid’ biozone of the Aztec Siltstone at Mount Ritchie, Warren Range, Antarctica is also described.

Relationships of tristichopterids (osteolepiform lobe-finned fishes) from the Middle–Late Devonian of East Gondwana

Two well-preserved articulated tristichopterids are known from the Canowindra fossil fish locality (Frasnian) in central New South Wales: Mandageria Johanson & Ahlberg, 1997 and Cabonnichthys Ahlberg & Johanson, 1997. Two other large tristichopterids are Notorhizodon Young et al., 1992 from the Aztec Siltstone fauna of Antarctica (Givetian), and the Famennian Eusthenodon Jarvik, 1952, first described from East Greenland and recently identified in eastern Australia. Relationships of the East Gondwana tristichopterids were previously assessed as Notorhizodon [Platycephalichthys [Cabonnichthys [Mandageria [Eusthenodon]]]], with no endemic Gondwanan clade, and more basal tristichopterids (Tristichopterus, Eusthenopteron, Jarvikina) being Northern Hemisphere forms. This suggested that the group may have originated in Laurussia, with advanced tristichopterids later reaching Gondwana (Middle–Late Devonian). Reconsideration of evidence from structure of the palate and scale morphology suggests an alternative phylogeny, with an endemic Gondwanan clade (subfamily Mandageriidae nov.) comprising at least three genera: Cabonnichthys and Mandageria from Canowindra, an undescribed tristichopterid from Eden, NSW, and possibly Notorhizodon from Antarctica. Distinctive isolated scales of ‘mandageriid’ type are illustrated from the Antarctic Aztec Siltstone assemblage and contrasted with typical tristichopterid scales, including new examples illustrated from the Givetian Bunga beds, NSW. Biogeographic implications include a possible Gondwanan origin for tristichopterids.

A new basal actinopterygian fish from the Middle Devonian Aztec Siltstone of Antarctica

AbstractA new basal actinopterygian fish,Donnrosenia schaefferigen. et sp. nov., is described from the Middle Devonian (Givetian) Aztec Siltstone of southern Victoria Land, Antarctica.Donnroseniagen. nov. is characterized by the large parietals which are of almost equivalent size to the frontals, very small intertemporals, a small accessory operculum situated dorsally to the prominent anterodorsal process of the suboperculum, a deep dentary with anterior flexure, porous ornamentation on the clavicle, an elongate body form with macromeric squamation, an absence of paired fringing fulcra on the fins, and pectoral lepidotrichia which are unsegmented for much of their length. A phylogenetic analysis based on dermal skeletal features of Devonian actinopterygians indicates thatDonnroseniagen. nov. is the sister taxon toHowqualepisfrom the Middle Devonian of Victoria, Australia, and is embedded within a possible clade containing the actinopterygians from the Gogo Formation, Western Australia. This supports the concept of an endemic radiation of East Gondwanan actinopterygians, and reinforces the already strong biogeographical similarities between the Middle Devonian palaeofaunas of Australia and Antarctica.

GNATHOSTOME MICROREMAINS FROM THE LOWER DEVONIAN JAWF FORMATION, SAUDI ARABIA

Calcareous horizons in the Qasr and Hammamiyat members (Lower Devonian, ?Pragian and lower Emsian) of the Jawf Formation, northwestern Saudi Arabia, yielded a rich assemblage of microremains from acanthodian, placoderm, chondrichthyan, and sarcopterygian vertebrates. The most abundant elements are scales from acanthodians Nostolepis spp., Milesacanthus ancestralis n. sp., Canadalepis? sp., and Gomphonchus? fromensis, scales and dermal bone fragments from acanthothoracid and ?rhenanid placoderms, and teeth from onychodontids. Rarer occurrences include ?chondrichthyan scales of several different morphotypes, and petalichthid and ?ptyctodontid placoderm elements. The Qasr Member assemblage shows a close resemblance to slightly older faunas from the Lochkovian of Brittany and Spain. The Hammamiyat Member microvertebrate fauna shows closest affinity with that of the stratigraphically lower Qasr Member, with similarities also to coeval faunas from southeastern Australia, late Emsian/Eifelian faunas from west-central Europe, and the Givetian Aztec Siltstone fauna from Antarctica.

Phyllolepid placoderm fish remains from the Devonian Aztec Siltstone, southern Victoria Land, Antarctica

Phyllolepid placoderm remains from the Aztec Siltstone fish fauna are described as Austrophyllolepis quiltyi sp. nov., Austrophyllolepis cf. A. youngi, Placolepis tingeyi sp. nov., and phyllolepid indet. The new Antarctic species of two genera previously only known from Australia reinforce evidence from other fish taxa of close biogeographic affinity, as part of the eastern margin of Palaeozoic Gondwana. At least three genera and four species gives the Aztec Siltstone fish fauna the most diverse phyllolepid assemblage known, and probably the oldest documented so far (?late Middle Devonian). Specimens of Austrophyllolepis from the type locality at Mount Howitt, Victoria, are refigured for comparison with the Antarctic species. The order Phyllolepida is a key group for understanding Devonian vertebrate biogeography and palaeogeography, with a unique disjunct distribution in both time and space between the Southern and Northern hemispheres. Phyllolepids document one of the major dispersal events in early vertebrate history, which approximately coincided with the Frasnian–Famennian boundary mass extinction during the Late Devonian.

Early Forest Soils and Their Role in Devonian Global Change

A paleosol in the Middle Devonian Aztec Siltstone of Victoria Land, Antarctica, is the most ancient known soil of well-drained forest ecosystems. Clay enrichment and chemical weathering of subsurface horizons in this and other Devonian forested paleosols culminate a long-term increase initiated during the Silurian. From Silurian into Devonian time, red clayey calcareous paleosols show a greater volume of roots and a concomitant decline in the density of animal burrows. These trends parallel the decline in atmospheric carbon dioxide determined from isotopic records of pedogenic carbonate in these same paleosols. The drawdown of carbon dioxide began well before the Devonian appearance of coals, large logs, and diverse terrestrial plants and animals, and it did not correlate with temporal variation in volcanic or metamorphic activity. The early Paleozoic greenhouse may have been curbed by the evolution of rhizospheres with an increased ratio of primary to secondary production and by more effective silicate weathering during Silurian time.

New records of Devonian plants from southern Victoria Land, Antarctica

AbstractAn assemblage of fossil plants is here recorded from the Middle Devonian Beacon Heights Orthoquartzite and overlying Aztec Siltstone (Taylor Group), of the Cook Mountains and Skelton Névé regions, southern Victoria Land, Antarctica. The Beacon Heights Orthoquartzite exposed in the southern Cook Mountains yielded specimens of the lycopods Haplostigma lineare, Malanzania sp., and Archaeosigillaria sp. cf. A. caespitosa. The Aztec Siltstone flora contains Praeramunculus alternatiramus and H. lineare.

Crossopterygian fishes from the Devonian of Antarctica: systematics, relationships and biogeographic significance

Four new genera of osteolepiforms and a new rhizodontiform genus are described from the Middle-Late Devonian Aztec Siltstone (Beacon Supergroup) of Antarctica. Other indeterminate osteolepid, eusthenopterid and rhizodontid remains, and a single indeterminate porolepiform scale, are described from the same formation. Koharalepis jarviki n.gen., n.sp. is a large cosmine-covered osteolepiform with a broad flat head, two pairs of dermosphenotics, large extratemporals, a large postorbital in the cheek which does not reach the orbit, an elongate jugal, lachrymal separating the maxilla from the premaxilla at the jaw margin, and large anteriorly pointed median and triangular lateral extrascapulars. It is placed with Canowindra Thomson and Beelarongia Long in the new family Canowindridae. Platyethmoidia antarctica n.gen., n.sp. is a poorly known form with a very broad, flat fronto-ethmoidal shield with dorsomesially oriented slit-like nares, and a lower jaw with a deep articular region. It may be closely related to Gyroptychius? australis Young & Gorter. Mahalalepis resima n.gen., n.sp. is interpreted on the morphology of the fronto-ethmoidal shield as an early megalichthyid, and a new definition of this family is presented. Vorobjevaia dolonodon n.gen., n.sp. is a poorly known osteolepid with a distinctive jaw morphology. The rhizodontiform Notorhizodon mackelveyi n.gen., n.sp. was the largest fish in the Aztec fauna, attaining a length of over 3 m. It is characterised by elongate frontals and small dermosphenotics in the skull, Rhizodus-type tusks, and strong tooth flanges on the coronoid and dermopalatine series bones in the jaws. The braincase in a rhizodontiform is described for the first time, and in general morphology closely resembles that of Osteolepiformes. Notorhizodon resembles Screbinodus Andrews in dermal ornament and Barameda Long in skull pattern. All previously described crossopterygian material from the Aztec Siltstone is revised, and Gyroptychius antarcticus (Smith Woodward) is regarded as a nomen nudum. The stratigraphic distribution of rhipidistians in the Aztec Siltstone is summarised, and the biogeography and phylogenetic relationships of the new taxa discussed. The canowindrids were an endemic group of East Gondwana. The megalichthyids and rhizodontiforms may have originated in the East Gondwana Province during the Middle Devonian, but did not reach Euramerica until the uppermost Late Devonian. They flourished in the Carboniferous Period following the decline of the eusthenopterids and the initial radiation of tetrapods.

Thelodont scales from the Middle-Late Devonian Aztec Siltstone, southern Victoria Land, Antarctica

A new fossil agnathan, Turinia antarctica sp. nov., based on numerous isolated scales, comes from the lower fish-bearing beds of the Aztec Siltstone. Scales from moraine at Mount Suess, originally described as selachian or psammosteid heterostracan, are referred to the new species which shows close affinity with T. gondwana from Bolivia and T. cf. hutkensis from Iran. Reassessment of the biostratigraphy of Middle Devonian turiniid scales suggests that the lower part of the Aztec Siltstone may be of Eifelian age.

Fish-bearing Aztec Siltstone (Devonian) in the Cook Mountains, Antarctica

Abstract Outcrops of Aztec Siltstone (Taylor Group, Beacon Supergroup) have been discovered near MtHughes in the Cook Mountains, southern Victoria Land, Antarctica, over 100 km south of the nearest previously known exposures. The newly found Aztec Siltstonerests confonnably onHathertonSandstone, and has been dated as early Late Devonian (Frasnian) on the presence of phyllolepid placodenn fish.

The characterisation of the iron oxide phase in desert varnish from Antarctica using backscattered conversion electron and X-ray Mössbauer spectroscopy

The iron oxide phase in the desert varnish surface coatings on coarse- and fine-grained Ferrar dolerite, Aztec siltstone and orthoquartzite sandstone rocks from the Upper Taylor Valley area, McMurdo Dry Valley region, South Victoria Land, Antarctica, has been characterised using backscattered conversion electron and X-ray Mössbauer spectroscopy, and X-ray diffraction methods. The X-ray diffraction results show that, although visually the red-brown desert varnish layer extends some several millimetres into the rock, no crystalline or hydrous Fe-oxides could be detected. The conversion X-ray Mössbauer spectra show that at a depth of ∼ 20 μm the Fe 3+ Fe 2+ ratio is increased over that of the bulk rock, but there is still a dominant contribution from Fe 2+ iron in the primary ferromagnesian minerals, notably ortho- and clinopyroxenes. At shallower depths of up to ∼ 0.1 μm the conversion electron Mössbauer spectra show the Fe 3+ Fe 2+ ratio is further increased, but for the dolerites and siltstone this Fe 2+ contribution is still significant. These results suggest that the colour and extent of the desert varnish layer arises from the formation of a thin coating or staining, less than ∼ 0.1 μm thick, of hydrous Fe-oxides on the primary minerals at or near the surface of the rock. On the sandstone, where the Fe is derived from an external source, the oxide coating is precipitated from solution relatively quickly. This forms a very poorly ordered hydrated ferric oxide polymer. On the fine-grained dolerites where the diffusion and evaporation is slower due to the fine pore structure, a more ordered hydrous Fe-oxide polymer resembling ferrihydrite is found. On the coarse-grained dolerites and also the siltstone, the Fe-oxide phase is a slightly less ordered ferrihydrite-like material.

Paleoenvironmental interpretations and systematics of Devonian trace fossils from the Taylor Group (lower Beacon Supergroup), Antarctica

Abstract Trace fossils are varied and abundant in the otherwise unfossiliferous Taylor Group sandstones of the lower Beacon Supergroup. Twenty-four ichnotaxa are recognised, many previously unrecorded, and these have been grouped into 7 ichnocoenoses that occur successively from the basal Windy Gully Sandstone up into the Aztec Siltstone. The trace fossils suggest that the earliest Taylor Group sediments, the New Mountain Subgroup, is a marine transgressive sequence that progressively buried an irregular Kukri Erosion Surface and which eventually overwhelmed all basement highs by the end of Altar Mountain Sandstone deposition. Both the Windy Gully Sandstone and the New Mountain Sandstone are interpreted as the nearshore deposits of wide sandy tidal bays in which bioturbation by crustaceans was intense, while trough cross-bedded channel sands bear numerous trackways of large walking arthropods. The intervening Terra Cotta Siltstone is probably the deposit of a coastal lagoon with variable salinity and a fa...

Genesis of variegated redbeds in the fluvial Aztec Siltstone (late devonian), southern victoria land, Antarctica

The Aztec Siltstone (Late Devonian) formed in a meandering fluviatile environment and is a variegated redbed sequence consisting of red or drab overbank mudstones and drab channel sandstones, commonly arranged in fining-upwards cycles. The pigmentation in the red mudstones is caused by euhedral cryptocrystalline haematite which is dispersed throughout the matrix, masking the green colour of the underlying illitic and chloritic clays. Textural, mineralogical and chemical analyses suggest that the pigment formed in situ by dehydration and crystallization of a detrital, amorphous or poorly crystalline, yellow-brown ferric oxide precursor. The hydrated precursor apparently was derived from the weathering of iron silicates in a source area regolith, and transported in suspension with the Aztec alluvium, commonly by attachment onto surfaces of clay platelets. The association of the precursor with the clays is a contributing reason for the absence of red sandstones in the formation. Dehydration and crystallization of the yellow-brown ferric oxide to form the red haematite pigment occurred prior to deep burial of the host sediment. At least part of it occurred before burial, in an oxidising environment in well-drained and well-aerated overbank soils which were exposed for prolonged periods of time (4,000–10,000 years) under a hot and at least seasonally arid climate. Crystallization of the red pigment may have been completed during early diagenesis. Reducing conditions, induced by the presence of organic debris in the sediment and a relatively high water table, affected much of the deposit by removing the “free” hydrated ferric oxide, either partially or completely, from the in-channel sands, the low-lying and poorly drained overbank sediments, and the lacustrine sediments. This reduction was both a syndepositional and an early post-depositional process. Iron analyses indicate that, on average, the red mudstones are enriched in total iron (Fe) and Fe 3+ by 2%, all of which is attributable to the inherited “free” ferric oxide. There is no other significant difference in whole-rock mineralogy or major-element chemistry between the red and non-red mudstones.

Calcrete (caliche) palaeosols in fluvial redbeds of the Aztec siltstone (upper Devonian), Southern Victoria Land, Antarctica

Palaeosols in the Upper Devonian Aztec Siltstone of southern Victoria Land closely resemble pedocal ‘calcareous red earth’ and ‘red earth’ type modern soils and were formed on a low-relief surface under a hot and seasonally wet and dry, semi-arid climate. The Upper Devonian Aztec Siltstone of southern Victoria Land is interpreted as a fluviatile redbed sequence deposited on a broad, low-lying floodplain from high-sinuosity meandering streams which gave rise to characteristic fining-upwards sedimentary cycles. The fine-grained, fine-member portions of the cycles represent vertically accreted overbank sediment laid down on the interchannel floodbasin areas. With the development of relief, these sediments were subaerially exposed for extended periods (4000–10 000 years) during which time they underwent in-situ modification by pedogenic processes. This is evidenced by the common occurrence of carbonate nodules (calcrete), wavy bedding or pseudo-anticlines, colour mottling or gleying, and extensive bioturbation in these unbedded clay-rich sediments. Plant roots and associated plant fossils and spores are also present. The textural character of the fine-grained rocks is closely comparable to that of modern soils including a skel-lattisepic fabric with skew-planes. Mineralogical and detailed chemical analyses, including down-profile element variations, show that there was an in-situ reorganization of ‘soil plasma’ consequent on clay illuviation, translocation and deposition of carbonate, and mobilisation and segregation of iron oxide.

Stratigraphy and sedimentology of the Upper Devonian Aztec Siltstone, southern Victoria Land, Antarctica

Abstract The Aztec Siltstone is a redbed sequence deposited on a broad, low-lying alluvial plain during Late Devonian times in southern Victoria Land, Antarctica. It outcrops between the Mawson and Mulock Glaciers and is the uppermost formation of the Taylor Group, the lower of the two Beacon Supergroup subdivisions in southern Victoria Land. The formation consists largely of fine- to medium-grained, well sorted quartzarenite, greyish red (10R 4/2), grey (N5) and greenish grey (5G 6/1) siltstone and claystone. Minor lithologies include carbonaceous siltstone, limestone, and intraformational conglomerate. Conchostracans, fish fossils, plant fragments, and gypsum lenses are also present. Fining-upwards cycles with the characteristic channelling, intraformational conglomerate, crossstratification, and horizontal stratification are common in the formation and indicate deposition from shallow, high sinuosity (tortuous), meandering streams that migrated laterally across a broad alluvial plain. Laterally accreted channel, and vertically accreted overbank sediments are represented by sandstone and the finer-grained lithologies respectively. Levee and crevasse-splay deposits are also represented. Other floodbasin deposits include lacustrine sediments from pluvial ponds and ox-bow lakes and palustrinal sediments from the backswamps. Prolonged subaerial exposure of the overbank sediments gave rise to soil development in some, characterised by a compositional and textural similarity to modern soils, calcrete (caliche), vein networks, burrowing, and root horizons. Reddening of these deposits also took place during subaerial exposure, influenced by soil processes and a hot and seasonally wet and dry (savanna) climate. The hiatus, represented by soil development and reddening, was probably in the range 4000 to 10 000 years.

Stratigraphy of the Taylor and lower Victoria Groups (Beacon Supergroup) between the Mackay Glacier and Boomerang Range, Antarctica

Abstract The stratigraphy of the Taylor and basal Victoria Groups exposed over an area of 3500 km2 between the Boomerang Range and MacKay Glacier of southern Victoria Land is described, based upon data from 65 measured sections. The Taylor Group is of Devonian or older age and is at least 1400 m thick. It rests nonconformably, via the peneplained Kukri Erosion Surface, upon a crystalline basement complex of Ordovician and older rocks. The Taylor Group, composed largely of terrestrial quartzose sandstones. consists of the New Mountain Sandstone at the base, overlain by the Altar Mountain Formation, Arena Sandstone, Beacon Heights Orthoquartziite, and the Aztec Siltstone. The Terra Cotta Siltstone member of the New Mountain Sandstone, the Altar Mountain Formation, and the Aztec Siltstone contain cyclic red bed sequences. The New Mountain Sandstone is separated from the rest of the Taylor Group by the south and southwest trending Heimdall Erosion Surface. The diversity of the lower part of the Taylor Group contrasts with the homogenous and broadly equivalent Hatherton Sandstone and Alexandra Formation of the Beacon Supergroup elsewhere, suggesting paleogeographically distinct basins of sedimentation. The Permian to Triassic Victoria Group disconformably overlies the Taylor Group via the glacigene Maya Erosion Surface. Within the Victoria Group the basal Metschel Tillite is separated from the overlying Weller Coal Measures by the Pyramid Erosion Surface which in many localities has completely eroded the Metschel Tillite and cut down through the older Maya Erosion Surface.