Evidence for early Pliocene and late Miocene transgressions in southern Patagonia (Argentina): 87Sr/86Sr ages of the pectinid “Chlamys” actinodes (Sowerby)

Numerical ages based on ⁸⁷Sr/⁸⁶Sr dating of calcitic shells belonging to the pectinid “Chlamys” actinodes (Sowerby) document the only late Miocene (Tortonian) sea flooding event in the Austral Basin at Cabo Buentiempo (8.95 ± 0.82 Ma, 2 s.e.), and provide evidence of the first documented early Pliocene (Zanclean) transgression in Argentina recorded at Cañadón Darwin (5.15 ± 0.18 Ma, 2 s.e., Austral Basin) and at Terraces of Cerro Laciar (5.10 ± 0.21 Ma, 2 s.e.), southern San Jorge Basin). The sedimentary rocks deposited during the Tortonian are correlated with the youngest beds deposited by the “Entrerriense Sea” that covered northern Patagonia. The Zanclean marine episode is correlated with the long-term cycle represented in the Southern Hemisphere by the flooding events recorded in Cockburn and James Ross Islands (Antarctica) and in North-Central Chile.     

Late Oligocene Kangaroo Well Local Fauna from the Ulta Limestone (new name), and climate of the Miocene oscillation across central Australia

The Late Oligocene Kangaroo Well Local Fauna from the Ulta Limestone (new name), northwestern Lake Eyre Basin correlates best with vertebrate assemblages from the Etadunna, Namba and Wipajiri Formations of the central Lake Eyre Basin, and from the Carl Creek Limestone (Karumba Basin) of northwestern Queensland. The biochronologically informative marsupials, Neohelos tirarensis (Diprotodontidae, Zygomaturinae), Marlu sp. cf. M. kutjamarpensis and Pildra sp. cf. P.magnus (Pseudocheiridae), and Ektopodon ulta sp. nov. (Ektopodontidae), indicate that the Kangaroo Well Local Fauna may be slightly older than the Kutjamarpu Local Fauna (Wipajiri Formation) and slightly younger than the Ngama Local Fauna (zone D of the Etadunna Formation) of Late Oligocene age. A new species of primitive ?Wynyardiidae, Ayekaye jaredi sp. nov., is described, and the nomenclature of two extinct gastropods, Glyptophysa rodingae (McMichael) and Cupedora Iloydi (McMichael) (new combinations), the type localities of which are in the Ulta Limestone, is revised in line with current taxonomy. The Ulta Limestone, an alluvial calclithite composed primarily of caliche fabrics, and its correlatives were deposited during the Miocene oscillation climatic event. Palaeoclimatic modelling using sedimentological data, crocodilians and extant analogs of fossil terrestrial gastropods indicates that the average annual temperature at Kangaroo Well during the Late Oligocene was probably between 14 and 20°C, while mean annual rainfall was probably <600 mm. Similar associations from central parts of the Lake Eyre Basin, from Riversleigh, northwestern Queensland, and from Bullock Creek, north‐central Northern Territory, indicate that such conditions were widespread during depositional phases of the Miocene oscillation. Palaeoclimatic indicators do not support the presence of widespread closed forests in northwestern Queensland and across the inland of the Northern Territory and South Australia during the Miocene oscillation.     

Palaeo‐oceanographical significance of Miocene deep‐sea ostracoda from the Kingfish 8 well,Gippsland Basin,southeastern Australia

In the latest Early to Middle Miocene section of the Kingfish 8 well, offshore Gippsland Basin, the characteristically deep‐marine ostracod genus Zabythocypris is a conspicuous component of ostracod assemblages dominated by species of the genera Argilloecia, Krithe and Parakrithe. The taphonomy and taxonomic composition of the assemblages suggests that they accumulated in an upper bathyal environment (500–1000 m water depth) occurring in a lower continental slope setting. Supporting evidence for these deep‐marine ostracod assemblages occurring near the upper limit of their palaeobathymetrical range is the broadly coincident occurrence of the deep‐marine taxa Legitimocythere sp. and Neonesidea whatleyi Warne, in what would otherwise be considered an outer‐shelf (120–160 m) ostracod fauna at Fossil Beach, Mornington. Ostracod occurrences indicative of dysaerobic sea‐floor conditions in the Kingfish 8 well and Fossil Beach sections, when considered together, appear to record a shallowing of the oceanic oxygen‐minimum zone during the latest Early Miocene to earliest Middle Miocene transgressive phase of southeast Australia.     

The structure and stratigraphy of deepwater Sarawak,Malaysia: Implications for tectonic evolution

The structural-stratigraphic history of the North Luconia Province, Sarawak deepwater area, is related to the tectonic history of the South China Sea. The Sarawak Basin initiated as a foreland basin as a result of the collision of the Luconia continental block with Sarawak (Sarawak Orogeny). The foreland basin was later overridden by and buried under the prograding Oligocene-Recent shelf-slope system. The basin had evolved through a deep foreland basin (‘flysch’) phase during late Eocene–Oligocene times, followed by post-Oligocene (‘molasse’) phase of shallow marine shelf progradation to present day.Seismic interpretation reveals a regional Early Miocene Unconformity (EMU) separating pre-Oligocene to Miocene rifted basement from overlying undeformed Upper Miocene–Pliocene bathyal sediments. Seismic, well data and subsidence analysis indicate that the EMU was caused by relative uplift and predominantly submarine erosion between ∼19 and 17 Ma ago. The subsidence history suggests a rift-like subsidence pattern, probably with a foreland basin overprint during the last 10 Ma. Modelling results indicate that the EMU represents a major hiatus in the sedimentation history, with an estimated 500–2600 m of missing section, equivalent to a time gap of 8–10 Ma. The EMU is known to extend over the entire NW Borneo margin and is probably related to the Sabah Orogeny which marks the cessation of sea-floor spreading in the South China Sea and collision of Dangerous Grounds block with Sabah.Gravity modelling indicates a thinned continental crust underneath the Sarawak shelf and slope and supports the seismic and well data interpretation. There is a probable presence of an overthrust wedge beneath the Sarawak shelf, which could be interpreted as a sliver of the Rajang Group accretionary prism. Alternatively, magmatic underplating beneath the Sarawak shelf could equally explain the free-air gravity anomaly. The Sarawak basin was part of a remnant ocean basin that was closed by oblique collision along the NW Borneo margin. The closure started in the Late Eocene in Sarawak and moved progressively northeastwards into Sabah until the Middle Miocene. The present-day NW Sabah margin may be a useful analogue for the Oligocene–Miocene Sarawak foreland basin.     

Capybaras (Rodentia,Hydrochoeridae, Hydrochoerinae) and their bearing in the calibration of the late Miocene–Pliocene sequences of South America

Fossil capybaras were long regarded as composed of numerous taxa, each one endemic to a particular area, a scenario completely different from the one shown by the living species. The interpretation of the record according to new criteria of ontogenetic change has demonstrated that they are useful for biocorrelation because their members have short biochrons with wide geographic distribution. The levels with capybaras of each locality would represent a short lapse within the bearing lithostratigraphic units. In turn, they would also represent short intervals within the temporal extension proposed for each Stage/Age or SALMA. All the late Miocene–Pliocene records of capybaras were analyzed and a chronological scheme was built mainly for Argentina, where records are most abundant. Numerical ages and magnetostratigraphic studies contribute to correlate this scheme with the global time scale. The Chasicoan SALMA would be correlated with part of the Tortonian Stage/Age; the Huayquerian SALMA with the late Tortonian-Messinian, and it could even extend to the earliest Zanclean. The Montehermosan SALMA would be restricted to the Zanclean. The Chapadmalalan SALMA would be correlated with the late Zanclean-early Piacenzian.     

The age of the oceanic accretionary wedge and onset of continental collision in the Sicilian Maghrebian Chain

New biostratigraphic data from the formations unconformably lying above the tectonic units resulting from the Flysch Basin Domain (FBD) in the Sicilian Maghrebids are here reported. The FBD constituted a southern branch of the western Tethys, separating during the Jurassic to Paleogene a Mesomediterranean Microplate from the African Plate.

The age of the youngest sediments involved in the nappes and that of the unconformable terrains deposited in thrust-top basins on these tectonic units, allow to define both the age of deformation of the oceanic realm and the onset of the continental collision. The deformation migrated from internal to external areas of FBD starting from the latest Burdigalian-Langhian to Serravallian. Therefore, the previously proposed Eocene-Oligocene mesoalpine deformation of the Maghrebian FBD cannot be supported. The continental collision started during the Serravallian and it was accomplished in the late Tortonian, when clastic deposits sealed the boundaries of the tectonic units originated from all the paleogeographic domains of the Maghrebian Chain.

The steps of the tectonic evolution in the Sicilian Maghrebids are now very well constrained and the proposed tectonic evolution may be extended to the whole Maghrebian Chain, as far as to the western Betic Cordilleras and to the southern Apennines, where most of the tectonic events show highly similar features and ages.     

The Precambrian rocks

Bauxite deposits in Gippsland are small, low in grade, and buried under a thick cover of Tertiary sands. Occurring at various stratigraphic levels in the Thorpdale volcanic sequence, they are also texturally and compositionally primitive and hence now presumably fossilised. Although broadly comparable with deposits in Tasmania and New England, they show few obvious analogies with other Australian bauxites. Profile studies reveal a somewhat erratic vertical mineralogical zonation which can, at least in part, be accounted for by assuming a degree of post‐bauxitisation planation so that some profiles are now truncated. Some profiles show gibbsite increasing with depth and at least in the Boolarra profile this has significant genetic implications. Here, during submergence of the lateritic surface, rising carbonated connate waters precipitated scarbroite and this, with subsequent renewed leaching, decomposed initially to form nordstrandite, and finally gibbsite.