Detrital zircon geochronology data, petrographic point count data and paleocurrent indicator data of Triassic turbidites in the Nanpanjiang Basin, South China

Triassic turbidites of the Nanpanjiang basin of south China represent the most expansive and voluminous siliciclastic turbidite accumulation in south China. The Nanpanjiang basin occurs at a critical junction between the southern margin of the south China plate and the Indochina, Siamo and Sibumasu plates to the south and southwest. The Triassic Yangtze carbonate shelf and isolated carbonated platforms in the basin have been extensively studied, but silicilastic turbidites in the basin have received relatively little attention. Deciphering the facies, paleocurrent indicators and provenance of the Triassic turbidites is important for several reasons: it promises to help resolve the timing of plate collisions along suture zones bordering the basin to the south and southwest, it will enable evaluation of which suture zones and Precambrian massifs were source areas, and it will allow an evaluation of the impact of the siliciclastic flux on carbonate platform evolution within the basin. Turbidites in the basin include the Early Triassic Shipao Formation and the Middle-Late Triassic Baifeng, Xinyuan, Lanmu Bianyang and Laishike formations. Each ranges upward of 700 m and the thickest is nearly 3 km. The turbidites contain very-fine sand in the northern part of the basin whereas the central and southern parts of the basin also commonly contain fine and rarely medium sand size. Coarser sand sizes occur where paleocurrents are from the south, and in this area some turbidites exhibit complete bouma sequences with graded A divisions. Successions contain numerous alternations between mud-rich and sand-rich intervals with thickness trends corresponding to proximal/ distal fan components. Spectacularly preserved sedimentary structures enable robust evaluation of turbidite systems and paleocurrent analyses. Analysis of paleocurrent measurements indicates two major directions of sediment fill. The northern part of the basin was sourced primarily by the Jiangnan massif in the northeast, and the central and southern parts of the basin were sourced primarily from suture zones and the Yunkai massif to the south and southeast respectively. Sandstones of the Lower Triassic Shipao Fm. have volcaniclastic composition including embayed quartz and glass shards. Middle Triassic sandstones are moderately mature, matrix-rich, lithic wackes. The average QFL ratio from all point count samples is 54.1/18.1/27.8% and the QmFLt ratio is 37.8/ 18.1/ 44.1%. Lithic fragments are dominantly claystone and siltstone clasts and metasedimentary clasts such as quartz mica tectonite. Volcanic lithics are rare. Most samples fall in the recycled orogen field of QmFLt plots, indicating a relatively quartz and lithic rich composition consistent with derivation from Precambrian massifs such as the Jiangnan, and Yunkai. A few samples from the southwest part of the basin fall into the dissected arc field, indicating a somewhat more lithic and feldspar-rich composition consistent with derivation from a suture zone Analysis of detrial zircon populations from 17 samples collected across the basin indicate: (1) Several samples contain zircons with concordant ages greater than 3000 Ma, (2) there are widespread peaks across the basin at 1800 Ma and 2500, (3) a widespread 900 Ma population, (3) a widespread population of zircons at 440 Ma, and (5) a larger population of younger zircons about 250 Ma in the southwestern part which is replaced to the north and northwest by a somewhat older population around 260-290 Ma. The 900 Ma provenance fits derivation from the Jiangnan Massif, the 2500, 1800, and 440 Ma provenance fits the Yunkai massif, and the 250 Ma is consistent with convergence and arc development in suture zones bordering the basin on the south or southwest. Early siliciclastic turbidite flux, proximal to source areas impacted carbonate platform evolution by infilling the basin, reducing accommodation space, stabilizing carbonate platform margins and promoting margin progradation. Late arrival, in areas far from source areas caused margin aggradation over a starved basin, development of high relief aggradational escarpments and unstable scalloped margins.

Geological and geochemical characteristics of the Tersang gold deposit, Malaysia: implications for genesis and gold exploration

The Central gold belt of peninsular Malaysia comprises a number of gold deposits located in the east of the N-S striking Bentong-Raub Suture Zone. The Tersang gold deposit is one of the gold deposits in the gold belt and hosted in sandstone, rhyolite and breccia units. The deposit has an inferred resource of 528,000 ounces of gold. The geochronology of the Tersang deposit has been newly constrained by LA ICP-MS U-Pb zircon dating. The maximum depositional age of the host sedimentary rocks ranges from Early Carboniferous to Early Permian (261.5 ± 4.9 Ma to 333.5 ± 2.5 Ma) for the host sandstone and Late Triassic for the rhyolite intrusion (218.8 ± 1.7 Ma). Textural characteristics of pyrite have revealed five types including (1) Euhedral to subhedral pyrite with internal fracturing and porous cores located in the sandstone layers (pyrite 1); (2) Anhedral pyrite overgrowths on pyrite 1 and disseminated in stage 1 vein (pyrite 2); (3) Fracture-filled or vein pyrite located in stages 1 and 2 vein (pyrite 3); (4) Euhedral pyrite with internal fractures also located in stage 2 vein (pyrite 4); and (5) Subhedral clean pyrite located in the rhyolite intrusion (pyrite 5). Based on pyrite mapping and spot analyses, two main stages of gold enrichment are documented from the Tersang gold deposit. Gold in sandstone-hosted pyrite 1 (mean 4.3 ppm) shows best correlation with Bi and Pb (as evidenced on pyrite maps). In addition, gold in pyrite 3 (mean 8 ppm) located in stage 2 vein shows a good correlation with As, Ag, Sb, Cu, Tl, and Pb. In terms of gold exploration, we suggest that elements such as As, Ag, Sb, Cu, Tl, Bi, and Pb associated with Au may serve as vectoring tools in gold exploration. Our new geological, structural, geochemical and isotopic data together with mineral paragenesis, pyrite chemistry and ore fluid characteristics indicate that the Tersang gold deposit is comparable to a sediment-hosted gold deposit. Our new genetic model suggests deposition of the Permo-Carboniferous sediments followed by intrusion of rhyolitic magma in the Late Triassic. At a later stage, gold mineralisation overprinted the rhyolite intrusion and the sandstone.

Mineralogy and age determination of sediment core D11957P

The Tore Seamount is a circular, volcano-like feature 100 km in diameter with its summit at 2200 m water depth and a small, 5000 m deep basin in its interior. It is situated approximately 300 km west of Lisbon and is surrounded by deep abyssal plains. This site with a standard pelagic stratigraphy is the southernmost point where the so-called Heinrich events have so far been recorded. A succession of alternating interglacial/glacial periods reveals a stratigraphic record back to the beginning of isotopic stage 7 (225 kyr). Climatic changes are identifiable by coherent variations in colour, carbonate content and distribution of ice-rafted detritus in the carbonate-free fraction. Inputs of ice-rafted quartz are well defined. Characteristics in common with other sites showing Heinrich layers include a high terrigenous to biogenic ratio, a dramatic decrease in the accumulation rate of foraminifera shells, an increase in dolomite abundance and the occurrence of polar foraminiferal species indicating southwards penetration of cold waters which lead us to consider a wider southeastern extent of the North Atlantic ice-rafted detritus belt than hitherto. If the presently accepted position of the Polar Front is maintained, icebergs must have been swept southwards from the southern boundary of the pack ice in a current merging into the ancestral Canary Current, bringing ice-rafted material to the Tore Seamount. The coincidence of reddish-feldspar, probably derived from the northern Appalachian Triassic red facies, with the transparent quartz suggests at least a partial Labrador source for all the Heinrich layers here, including HL 3. In comparison to other sites in the entire North Atlantic, two exceptions stand out: the absence of HL 5 and the low detritus to biogenics ratio for HL 3. The simultaneous occurrence of these two types of ice-rafted minerals is a new piece in the puzzle of the origin of Heinrich layers.

Chemical composition of basalts from the Atlantic Ocean

Basalt recovered beneath Jurassic sediments in the western Atlantic at Deep Sea Drilling Project sites 100 and 105 of leg 11 has petrographic features characteristic of water-quenched basalt extruded along modern ocean ridges. Site 100 basalt appears to represent two or three massive cooling units, and an extrusive emplacement is probable. Site 105 basalt is less altered and appears to be a compositionally homogeneous pillow lava sequence related to a single eruptive episode. Although the leg 11 basalts are much more closely related in time to the Triassic lavas and intrusives of eastern continental North America, their geochemical features are closely comparable to those of modern Mid-Atlantic Ridge basalts unrelated to postulated "mantle plume" activity. Projection of leg 11 sites back along accepted spreading "flow lines" to their presumed points of origin shows that these origins are also outside the influence of modern" plume" activity. Thus, these oldest Atlantic seafloor basalts provide no information on the time of initiation of these "plumes". The Triassic continental diabases show north to south compositional variations in Rb, Ba, La, and Sr which lie within the range of " plume "-related basalt on the Mid-Atlantic Ridge (20° - 40° N) This suggests that these diabases had mantle sources similar in composition to those beneath the present Mid-Atlantic Ridge. "Plumes" related to deep mantle sources may have contributed to the LIL-element enrichment in the Triassic diabase and may also have been instrumental in initiating the rifting of the North Atlantic. Systematically high values for K and Sr87/Sr86 in the Triassic diabases may reflect superimposed effects of crustal contamination in the Triassic magmas.

Abundance and preservation of radiolarian faunas of ODP Hole 122-761B (Table 1)

Sites 759 through 764 were drilled during Ocean Drilling Program Leg 122 on the Exmouth and Wombat plateaus off northwest Australia, eastern Indian Ocean. Radiolarian recovery was generally poor due to unsuitable lithofacies. A few Quaternary radiolarian faunas were recovered from most of the sites. Rare and poorly preserved Oligocene and Eocene radiolarian faunas were recovered from Holes 760A, 761B, 761C, and 762B. Poorly preserved Cretaceous radiolarians occur in samples from Holes 761B, 762C, 763B, and 763C. Chert intervals from Cores 122-761B-28X, 122-761C-5R, and 122-761C-6R contain moderately well-preserved Cretaceous radiolarian faunas (upper Albian, mid- to upper Cenomanian, and mid-Albian, respectively). Rare fragments of Upper Triassic radiolarians were recovered from sections in Holes 759B, 760B, and 764A. The only well-preserved pre-Quaternary radiolarians are in lower and upper Paleocene faunas (Bekoma campechensis Zone) recovered from Site 761, Sections 122-761B-16X-1 to 122-761C-19X-CC. The composition of these faunas differs somewhat from that of isolated coeval Paleocene faunas from Deep Sea Drilling Project sites in the Atlantic, Gulf of Mexico, tropical Pacific, eastern Indian Ocean, and near Spain and North Africa, as well as from several on-land sites in North America, Cuba, and the USSR.

Stable isotope composition of carbonate components of Rhaetian shallow-water limestones of the Wombat Plateau

Stable oxygen- and carbon-isotope ratios of Rhaetian (upper Triassic) limestone samples from the Wombat Plateau, northwest Australia, were measured to explore possible diagenetic pathways that the material underwent after deposition in a shallow-water environment, before plateau submergence in the Early Cretaceous. Host sediment isotopic values cluster near typical marine carbonate values (d18O ranging from -2.57 per mil to +1.78 per mil and d13C, from +2.45 per mil to +4.01 per mil). Isotopic values of equant clear calcite lining or filling rock pores also plot in the field of marine cements (d18O = +1.59 per mil to -2.24 per mil and d13C = +4.25 per mil to +2.57 per mil), while isotopic values for neomorphic calcites replacing skeletal (megalodontid shell) carbonate material show a wider scatter of oxygen and carbon values, d18O ranging from +2.73 per milo to -6.2 per mil and d13C, from +5.04 per mil to +1.22 per mil. Selective dissolution of metastable carbonate phases (aragonite?) and neomorphic replacement of skeletal material probably occurred in a meteoric phreatic environment, although replacement products (inclusion-rich microspar, clear neomorphic spar, etc.) retained the original marine isotopic signature because transformation probably occurred in a closed system dominated by the composition of the dissolving phases (high rock/water ratio). The precipitation of late-stage equant (low-Mg?) calcite cement in the pores occurred in the presence of normal marine waters, probably in a deep-water environment, after plateau drowning. Covariance of d18O and d13C toward negative values indeed suggests influence of meteorically modified fluids. However, none of the samples shows negative carbon values, excluding the persistence of organic-rich soils on subaerial karstic surfaces (Caribbean-style diagenesis). Petrographical and geochemical data are consistent with the sedimentological evidence of plateau drowning in post-Rhaetian times and with a submarine origin of the >70-m.y.-long Jurassic hiatus.

Sporomorphs and quantitative analysis of the Eocene record from IODP Hole 318-U1356A

The early Eocene epoch was characterized by extreme global warmth, which in terrestrial settings was characterized by an expansion of near-tropical vegetation belts into the high latitudes. During the middle to late Eocene, global cooling caused the retreat of tropical vegetation to lower latitudes. In high-latitude settings, near-tropical vegetation was replaced by temperate floras. This floral change has recently been traced as far south as Antarctica, where along the Wilkes Land margin paratropical forests thrived during the early Eocene and temperate Nothofagus forests developed during the middle Eocene. Here we provide both qualitative and quantitative palynological data for this floral turnover based on a sporomorph record recovered at Integrated Ocean Drilling Program (IODP) Site U1356 off the Wilkes Land margin. Following the nearest living relative concept and based on a comparison with modern vegetation types, we examine the structure and diversity patterns of the Eocene vegetation along the Wilkes Land margin. Our results indicate that the early Eocene forests along the Wilkes Land margin were characterized by a diverse canopy composed of plants that today occur in tropical settings; their richness pattern was similar to that of present-day forests from New Caledonia. The middle Eocene forests were characterized by a canopy dominated by Nothofagus and exhibited richness patterns similar to modern Nothofagus forests from New Zealand.

Carbonate content in lower Cretaceous sediments of ODP Hole 123-765C

Sediments recovered during Ocean Drilling Program (ODP) Leg 123 from the Argo Abyssal Plain (AAP) consist largely of turbidites derived from the adjacent Australian continental margin. The oldest abundant turbidites are Valanginian-Aptian in age and have a mixed (smarl) composition; they contain subequal amounts of calcareous and siliceous biogenic components, as well as clay and lesser quartz. Most are thin-bedded, fine sand- to mud-sized, and best described by Stow and Piper's model (1984) for fine-grained biogenic turbidites. Thicker (to 3 m), coarser-grained (medium-to-coarse sand-sized) turbidites fit Bouma's model (1962) for sandy turbidites; these generally are base-cut-out (BCDE, BDE) sequences, with B-division parallel lamination as the dominant structure. Parallel laminae most commonly concentrate quartz and/or calcispheres vs. lithic clasts or clay, but distinctive millimeter- to centimeter-thick, radiolarian-rich laminae occur in both fine- and coarse-grained Valanginian-Hauterivian turbidites. AAP turbidites were derived from relatively deep parts of the continental margin (outer shelf, slope, or rise) that lay below the photic zone, but above the calcite compensation depth (CCD). Biogenic components are largely pelagic (calcispheres, foraminifers, radiolarians, nannofossils); lesser benthic foraminifers are characteristic of deep-water (abyssal to bathyal) environments. Abundant nonbiogenic components are mostly clay and clay clasts; smectite is the dominant clay species, and indicates a volcanogenic provenance, most likely the Triassic-Jurassic volcanic suite exposed along the northern Exmouth Plateau. Lower Cretaceous smarl turbidites were generated during eustatic lowstands and may have reached the abyssal plain via Swan Canyon, a submarine canyon thought to have formed during the Late Jurassic. In contrast to younger AAP turbidites, however, Lower Cretaceous turbidites are relatively fine-grained and do not contain notably older reworked fossils. Early in its history, the northwest Australian margin provided mainly contemporaneous slope sediment to the AAP; marginal basins adjacent to the continent trapped most terrigenous detritus, and pronounced canyon incisement did not occur until Late Cretaceous and, especially, Cenozoic time.