David W. Haig

A late early Albian marine transgressive pulse over northeastern Australia, precursor to epeiric basin anoxia: foraminiferal evidence

Abstract A major transgressive pulse occurred during the late early Albian in the western Papuan Basin, and totally changed the character of foraminiferal faunas in the basin, from impoverished agglutinated-dominated assemblages to diverse calcareous assemblages. A similar change is reflected in coeval deposits of other basins on the northeastern margin of the Australian continent (Laura Basin and northern Carpentaria Basin), and to a lesser extent in the intracratonic Eromanga and Surat Basins. This pulse preceded the condensed section of the Toolebuc Formation in the Eromanga Basin (of late middle Albian to early late Albian age), and succeeded deposition of the first radiolarian-rich units (late Aptian) in all basins. A rapid marine regression took place in the western Papuan Basin immediately after the latest Albian (95 Ma), and reflected the final retreat of marine conditions in the intracratonic basins to the south. Foraminiferal biofacies indicate that the late early Albian transgressive pulse resulted in peak sea levels in all basins; between 200 m and 500 m deep along the northern edge of the Cretaceous continent (northern Papuan Basin), decreasing to about 150 m in the northern Carpentaria Basin and the Laura Basin, and to 50–100 m in the southeastern Carpentaria Basin, northeastern Eromanga Basin, and southwestern Eromanga Basin, and to around 50 m in the Surat Basin. The change in bathymetry during the transgressive pulse was greatest in the northern marginal basins (possibly a deepening of over 100 m), and decreased to the southeast (about 10–20 m) where increased sand deposition occurred. Although the transgressive pulse bought slightly more saline and more oxygenated bottom water far into the basin, a barrier still existed in bottom waters across the central Carpentaria Basin between slightly brackish, dysaerobic conditions to the south and normal marine conditions to the north. After peak sea level was reached, bottom-water circulation within the southern Carpentaria and Eromanga sea decreased and this was accompanied by a decrease in sediment influx. During the late middle Albian through early late Albian anoxic conditions existed in central parts of the epeiric basins and a condensed section of black shales represented by the Toolebuc Formation was deposited. The late early Albian sea-level rise was partly controlled by eustatism, but may also have been influenced in different areas by varying amounts of continental uplift and subsidence associated with tectonism in the volcanic arc along the eastern Australian margin. The transgressive pulse broadly coincides with Albian transgressions reported widely from passive margins and epeiric basins elsewhere, but precise correlation is difficult. The consistently high sea level during the middle and early late Albian and the regression at the end of the Albian are out-of-phase with events on other continents and probably resulted from increasing tectonism along the eastern continental margin.

Carbonate pelagites in the post-Gondwana succession (Cretaceous – Neogene) of East Timor

In East Timor the upper parts of the Permian to Middle Jurassic Gondwana Megasequence are structurally juxtaposed against indurated carbonate pelagites of Early Cretaceous (Aptian) to early Late Miocene age. The pelagites probably represent a thin (several hundred metres thick) succession that was deposited at middle to lower bathyal water depths unconformably above the Gondwana succession after continental breakup. The widespread occurrence of pelagites, lack of turbidites at least in the post-Albian succession, association with upper parts of the Gondwana Megasequence and with Upper Jurassic shales of Australian affinity, and stratigraphic correspondence with adjacent Australian basins suggest that these sediments were deposited on a middle bathyal continental terrace similar to the present-day Exmouth Plateau. Evidence of chaotic soft-sediment mixing affecting units as young as early Late Miocene and analogy to present-day coeval successions on undeformed continental terraces suggest that the carbonate pelagites were friable chalk or ooze prior to deformation. Cementation, stylolitisation, and vein formation took place after the early Late Miocene (i.e. after 10.9 – 9.8 Ma GTS2004). Overlying the deformed succession is the Pliocene – Pleistocene Viqueque Megasequence (planktonic foraminiferal Zones N18 – N23) with a thin basal unit of friable chalk (30 m thick in the type area) that was deposited at middle to lower bathyal water depths similar to the older carbonate pelagites. The basal chalk ranges from zone N18 through N20 (Early to Middle Pliocene) and suggests a quiet tectonic interval, although the first indication of distal turbiditic deposition, presumably to the north, lies in the 4.2 – 3.35 Ma GTS2004 interval. Proximal turbidite deposition commenced at around 3.35 Ma GTS2004 with clasts sourced from an emerging Timor island to the north. The basal unit of the Viqueque Megasequence together with the older carbonate pelagite succession suggests that a middle bathyal continental terrace setting continued in this region, at least on the southern side of Timor, from the Cretaceous – Paleogene to the Late Miocene and Early Pliocene. The soft-sediment mixing, probably induced by tectonism, in the deformed pelagites, and the Bobonaro Mélange beneath the relatively undeformed type section of the Viqueque Megasequence suggest that during part of the Late Miocene (9.8 – 5.6 Ma GTS2004), tectonic mobilisation of sedimentary units took place, and mud volcanoes erupted on the seafloor. The Timor highlands were emergent from about 3.35 Ma GTS2004 (Middle Pliocene) as the deformation front moved from the north. The Timor Trough developed as a gentle downwarp from a pre-existing continental terrace that had been located in the middle bathyal zone since the late Early Cretaceous.

FORAMINIFERA AND THEIR HABITATS WITHIN A COOL-WATER CARBONATE SUCCESSION FOLLOWING GLACIATION, EARLY PERMIAN (SAKMARIAN), WESTERN AUSTRALIA

One of the best-developed carbonate successions of the Lower Permian in eastern Gondwana is the Callytharra Formation, deposited above glacially influenced sediments in a narrow elongate rift basin far from the open ocean. This formation and the underlying Carrandibby Formation provide evidence for faunal changes that accompanied the melting of the Sakmarian Gondwanan ice sheets. Diverse smaller benthic foraminifera including organic-cemented agglutinated, hyaline, and porcelaneous calcitic forms, accompany a heterozoan macrofauna (mainly bryozoans, crinoids and brachiopods). Fusulinid foraminifera and calcareous algae are absent. Seven foraminiferal assemblage zones subdivide the succession and parallel changes in associated macrofauna and lithofacies. Environmental changes determined from the succession include (1) a transition from nearshore, low-energy, low-salinity, cool waters to higher-energy, normal-marine waters supporting bryozoan, crinoidal and non-skeletal-macroalgal meadows; and (2) a transition from well-oxygenated, shallow-water, sandy substrates to deeper-water, less-oxygenated, muddy substrates. Faunal comparisons suggest that at paleolatitudes higher than 45°S, in widely separated interior basins in eastern Gondwana, a change from low-diversity, siliceous-agglutinated to high-diversity, Calcitornella -rich, foraminiferal assemblages took place during the Sakmarian. This change may have been associated with a reduction in melt-water influx into the interior basins from retreating Gondwanan ice sheets. The warming was insufficient to allow colonization of the shallow seas by fusulinids and calcareous algae, which only ranged as far south as 45°S paleolatitude.

Mid-Cretaceous calcareous and siliceous microfossils from the basal Gearle Siltstone, Giralia Anticline, Southern Carnarvon Basin

A diverse assemblage of foraminifera, radiolaria, and calcareous nannoplankton is recorded from basal beds of the Gearle Silstone in its type area. The calcareous nannofossils place the strata within the temperate-latitude CC8a Subzone and the Southern Ocean Sollasites falklandensis Subzone; the planktonic foraminifera indicate that the beds belong to the Hedbergella planispira Zone of the Australian region. The biozones suggest an early Albian age (later than the earliest Albian). Abundant calcareous and siliceous plankton and the Marssonella Association of benthonic foraminifera indicate normal-marine depositional conditions in a water depth of about 100 m. The transition from Windalia Radiolarite to Gearle Siltstone may reflect a marine transgressive pulse that reactivated bottom-water circulation and facilitated a significant increase in the calcareous biogenic component of the sediment. Deposition of the basal Gearle Siltstone was coincident with a major increase in bathymetry in the Papuan, Laura, C...

Palaeobathymetric zonation of foraminifera from lower Permian shale deposits of a high-latitude southern interior sea ☆

Abstract Foraminifera are documented from the type section of the Quinnanie Shale in order to interpret their bathymetric distributions in a shallow high-latitude interior sea during the Kungurian. The marine setting was a narrow elongate half-graben (Merlinleigh Sub-Basin of the Southern Carnarvon Basin) in the Western Australian portion of eastern Gondwana. The Quinnanie Shale is part of the Byro Group of formations that display pronounced shale–sand cyclicity recording frequent changes in bathymetry. The type section of the Quinnanie Shale shows an overall progradational pattern in lithofacies, and consists of five ‘cycles’, each culminating in a prominent sandstone bed. Foraminifera are abundant in the shale and are almost entirely siliceous (organic-cemented) agglutinated types that probably dominated the original fauna of the interior sea. Hierarchical cluster analysis of samples taken every meter through the 162-m-thick type section is used to distinguish ten biofacies, each defined by a different set of dominant agglutinated species. Although biofacies frequently change up-section, there is an overall trend that is related to the progradational trend suggested by the lithofacies. Based on comparisons between lithofacies and biofacies, a palaeobathymetric zonation is established for the foraminifera. This zonation, the sparse macrofauna, and the lithofacies suggest that the interior sea was stratified in terms of salinity and dissolved oxygen levels, and the water was generally hyposaline. Most of the agglutinated foraminiferal species have analogous morphotypes present in modern confined estuaries and interior seas and this points to great conservatism in the evolutionary and ecological development of this component of interior-sea faunas. Aaptotoichus quinnaniensis sp. nov., an organic-cemented agglutinated foraminifer, is described from the Quinnanie Shale type section.

Latest Miocene to Early Pliocene bathymetric cycles related to tectonism, Puri Anticline, Papuan Basin, Papua New Guinea

Strata on the northern limb of the Puri Anticline record four main cycles of bathymetric change from bathyal to neritic water depths in the time interval from 6.15 ± 0.35 Ma to 4.7 ± 0.5 Ma (CK95 chronometric scale). The studied 2000 m‐thick section extends from the uppermost Puri Limestone through the Orubadi Formation to the lowermost Era Formation, and includes planktonic foraminiferal zones N17B and N18. Within the Papuan Foreland Basin, in the Puri Anticline region, a proximal foredeep with water depths in the middle bathyal zone was present from 8.5 Ma or older to about 5.8 Ma (CK95). A rapid decrease in water depth of greater than 1000 m took place between about 5.8 Ma and 5.3 Ma with effective accumulation of about 270 m of mudstone (at present‐day compacted thickness). This progradational phase of cycle 1 reflects the first major episode of compressional deformation causing uplift within the frontal part of the present‐day Papuan Fold Belt during the Late Miocene and Pliocene. The progradational ...

Foraminiferal evidence for inner neritic deposition of Lower Cretaceous (Upper Aptian) radiolarian-rich black shales on the Western Australian margin

Diverse foraminifera, Lingula-like brachiopods and the geological setting indicate that Aptian radiolarian-rich black shales forming the Windalia Radiolarite were deposited at water depths probably less than 40 m in the Southern Carnarvon Basin. Elsewhere in Australia, coeval radiolarian-rich deposits are widespread in other western-margin basins and in vast interior basins. The organic-rich mudstones containing the radiolaria include the foraminiferal Ammobaculites Association, a sparse benthic macrofauna and kerogens of mainly terrestrial plant origin. The deposits suggest that there was substantial high-nutrient freshwater input into the epeiric seas as well as high levels of dissolved silica resulting from marine flooding of a mature silicate-rich landscape bordered on the eastern and western continental margins by large volcanic provinces. The widespread presence of organic-rich muds through the broad, shallow Southern Carnarvon Basin and through the coeval interior basins suggests that regional geomorphology controlled the distribution of eutrophic facies in the Australian Aptian rather than any global expansion of the oceanic oxygen minimum zone. The foraminiferal assemblage from the Windalia Radiolarite consists of calcareous hyaline benthic types (diverse Lagenida as well as abundant Lingulogavelinella, Epistomina and Coryphostoma) and organic-cemented agglutinated species (including common Ammobaculites humei, Haplophragmoides–Recurvoides spp., and Verneuilinoides howchini). Planktonic foraminifera are very rare and present only in the northern, more open part of the basin.

A restraining bend in a young collisional margin: Mount Mundo Perdido, East Timor

Mount Mundo Perdido, a 1750 m-high, steep-sided massif situated in the Viqueque district of East Timor, comprises approximately 30 km2 of complexly juxtaposed rocks deriving from both sides of the collisional plate boundary between the Australian Plate and the Banda Arc. Lithologies include Triassic–Jurassic interior-rift basin deposits, Cretaceous–Oligocene pelagites of Australian passive margin origin, neritic Oligocene–Miocene limestones and volcanics of Asiatic affinity, and Pliocene–Pleistocene synorogenic deposits. Detailed structural mapping shows Mount Mundo Perdido to be dominated by recent, high angle, oblique-slip and strike-slip faults that have been active into the Pleistocene and control the present-day topography. The fault architecture and stratigraphic distribution in the study area are comparable to pop-up structures developed at restraining bends, in this case within an east–west oriented zone of sinistral strike-slip. Our observations, supported by comparisons to scaled sandbox models and to similar pop-up structures developed in strike-slip systems elsewhere in the world, suggest that plate boundary-parallel strike-slip deformation is an integral part of the kinematics within the collisional zone between the Australian and Eurasian/Pacific plates in the Timor region.

Latest Carboniferous (late Gzhelian) fusulinids from Timor Leste and their paleobiogeographic affinities

Abstract An uppermost Gzhelian bioherm discovered in the central highlands of Timor Leste contains abundant foraminifera belonging to 17 genera. Representatives of the families Biseriamminidae, Biwaellidae, Bradyinidae, Cornuspiridae, Lasiodiscidae, Palaeotextulariidae, Pseudotaxidae, Ozawainellidae, Schubertellidae, Schwagerinidae, Staffellidae and Textrataxidae are present, including 21 species referred to known types and 12 species left in open nomenclature. Two new Schwagerina species are described: Schwagerina timorensis new species, and Schwagerina maubissensis new species. The assemblage belongs to the uppermost Gzhelian Schwagerina robusta–Ultradaixina bosbytauensis Zone although a possible lowest Asselian correlation cannot be excluded (the name Ultradaixina is controversial and sometimes synonymized as Bosbytauella. The case to resolve this issue has been submitted to the Bulletin of Zoological Nomenclature). The bioherm is the oldest carbonate unit so far recorded from the Maubisse Formation and the oldest sedimentary unit biostratigraphically dated in Timor. This discovery has implications for the latest Carboniferous–earliest Permian climate history of Timor that lay in the northern part of the north-south East Gondwana rift system along which the western margin of Australia later developed. The highest peak in fusulinid diversity within the Pennsylvanian–Cisuralian interval and a major marine transgression documented in many regions in Northern Pangaea took place during the latest Gzhelian to earliest Asselian and evidence for this is now extended to southern Pangaea. Cluster analysis, using the Jaccard similarity index at species level, of late Gzhelian fusulinids from 16 regions has been performed. This shows that the Timor fauna is most closely related to faunas from South China and the Changning-Menlian region of Yunnan (China). The assemblages here are distinct from those of three biogeographic regions (Arctic, Uralo-Asian and Irano-Taurids) recognized within the Tropical belt.

Middle Eocene Foraminifera from the type Giralia Calcarenite, Gascoyne Platform, Southern Carnarvon Basin, Western Australia

Foraminifea from the type section of the Giralia Calcarenite indicate an upper zone P12 correlation and a Middle Eocene age (probably within the interval 41.5–40.5 Ma, BKSA95 time scale). The type Giralia Calcarenite is considered to represent one sequence (with maximum thickness of 40–50 m preserved on the Gascoyne Platform) and to reflect late transgressive and early highstand deposition about a maximum flooding event. Initial retrogradation of the shoreline produced a maximum water depth of about 50 m at the type locality (5–6 m above base of stratigraphic section). The formation may correlate with shallow marine deposits found elsewhere in the Southern Carnarvon Basin (e.g. Eocene limestones at Yaringa and Red Bluff, and the Merlinleigh Sandstone), and correlates with Middle Eocene transgressive units in the Perth, Eucla, Great Australian Bight and Otway Basins.