Vintage 2-D (two-dimensional) seismic reflection surveys from the sparsely explored Mentelle Basin (western Australian margin) have been reprocessed and integrated with a recent high-quality 2-D ...seismic survey and stratigraphic borehole data. Interpretation of these data sets allows the internal geometry of the Mentelle Basin fill and depositional history to be reanalysed and new insights into its formation revealed. Basin stratigraphy can be subdivided into several seismically defined megasequences separated by major unconformities related to both breakup between India-Madagascar and Australia-Antarctica in the Valanginian-Late Hauterivian and tectonically-driven switches in deposition through the Albian. Resting on the Valanginian-Late Hauterivian breakup unconformity are several kilometre-scale mounded structures that formed during Late Jurassic to Early Cretaceous extension. These have previously been interpreted as volcanic edifices although direct evidence of volcanic feeder systems is lacking. An alternative interpretation is that these features may be carbonate build-ups. The latter interpretation carries significant climatic ramifications since carbonate build-ups would have formed at high palaeolatitude, ~60° S. Soon after breakup, initial subsidence resulted in a shallow marine environment and deposition of Barremian-Aptian silty-sandy mudstones. As subsidence continued, thick successions of Albian ferruginous black clays were deposited. Internally, seismic megasequences composed of successions of black clays show previously unresolved unconformities, onlapping and downlapping packages, which reflect a complex depositional, rifting and subsidence history at odds with their previous interpretation as open marine sediments. Southwestwards migration of the Kerguelen hotspot led to thermal contraction and subsidence to the present day water depth (~3000 m). This was accompanied by Turonian-Santonian deposition of massive chalk beds, which are unconformably overlain by pelagic Palaeocene-Holocene sediments. This substantial unconformity is related to the diachronous breakup and onset of slow spreading between Australia and Antarctica, which may have led to the reactivation and inversion of basement faults and was followed by rapid seafloor spreading from the Middle Eocene to the present.
Vintage 2-D (two dimensional) seismic reflection surveys from the sparsely explored Mentelle Basin (western Australian margin) have been re-processed and integrated with recent high quality seismic ...survey, and stratigraphic borehole data. Interpretation of these data sets allows the internal geometry of the Mentelle Basin fill and depositional history to be reanalysed with a greater degree of confidence. Basin stratigraphy can be subdivided into several seismically defined megasequences, separated by major unconformities related to both the Valanginian breakup between India-Madagascar and Australia-Antarctica, and tectonically-driven switches in deposition through the Albian. Resting on the Valanginian unconformity are several kilometre-scale mounded structures that formed during late Jurassic to early Cretaceous extension. These have previously been interpreted as volcanic edifices, although direct evidence of volcanic feeder systems is lacking. An alternative interpretation is that these features may be carbonate build-ups. The latter interpretation carries significant climatic ramifications, since carbonate build-ups would have formed at high palaeolatitude, ~60° S. Soon after breakup, initial subsidence resulted in a shallow marine environment and Barremian-Aptian silty-sandy mudstones were deposited. As subsidence continued, thick Albian ferruginous black clays were deposited. Internally, black clay megasequences show previously unresolved unconformities, onlapping and downlapping packages, which reflect a complex depositional, rifting and subsidence history, at odds with their previous interpretation as open marine sediments. Southwestwards migration of the Kerguelen hotspot led to thermal contraction and subsidence to the present day water depth (~3000 m). This was accompanied by Turonian-Santonian deposition of massive chalk beds, which are unconformably overlain by pelagic Palaeocene-Holocene sediments. This substantial unconformity is related to the diachronous breakup and onset of slow spreading between Australia and Antarctica, which may have led to the reactivation and inversion of basement faults, followed by rapid seafloor spreading from the middle Eocene to the present.
Earlier studies had shown significant differences in sorption of nine pesticides in soils collected from two landuses (native vegetation and market gardens), which could not be explained on the basis ...of organic carbon content alone. Consequently it was hypothesised that the differences in sorption behaviour between the two landuses may be due to variation in the chemistry of the organic carbon. In this study the relationship between sorption behaviour of the nine chemicals and soil organic carbon chemistry, as determined by solid-state
13C NMR spectroscopy, was investigated. No significant differences were found between the two landuses in the distribution of the four main spectral regions of the
13C NMR spectra of soil OC, except for the carbonyl fraction (165–220
ppm), which may reflect the low OC content of the soils from both landuses. For all chemicals, except prometryne, the most significant (
P
<
0.01 or
P
<
0.001) relationship between
K
d values and types of OC was found with the aromatic (110–165
ppm) or the alkyl (0–45
ppm) fraction. A comparison was made of the variability of
K
d values normalized over OC (i.e.
K
oc), alkyl, aromatic and alkyl
+
aromatic fractions. Expressing
K
d values for all chemicals, except azinphos methyl, in soils under native vegetation as
K
alkyl or
K
aromatic greatly decreased the variability compared with the
K
oc value. However in the cultivated soils only the sorption coefficients for DEA, DIA and fenamiphos showed a decrease in variability when expressed as
K
alkyl or
K
aromatic. This reflected the stronger relationship between sorption coefficients and the alkyl and aromatic fraction of soil OC in soils from native vegetation compared with those determined from the market garden soils. The different relationships between sorption coefficients and types of OC of the two landuses also suggests that the type of aromatic and alkyl carbon under the two landuses is different and NMR characterisation of the OC was not sufficient to distinguish these differences.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
Earlier studies had shown significant differences in sorption of nine pesticides in soils collected from two landuses (native vegetation and market gardens), which could not be explained on the basis ...of organic carbon content alone. Consequently it was hypothesised that the differences in sorption behaviour between the two landuses may be due to variation in the chemistry of the organic carbon. In this study the relationship between sorption behaviour of the nine chemicals and soil organic carbon chemistry, as determined by solid-state (13)C NMR spectroscopy, was investigated. No significant differences were found between the two landuses in the distribution of the four main spectral regions of the (13)C NMR spectra of soil OC, except for the carbonyl fraction (165-220ppm), which may reflect the low OC content of the soils from both landuses. For all chemicals, except prometryne, the most significant (P<0.01 or P<0.001) relationship between K(d) values and types of OC was found with the aromatic (110-165ppm) or the alkyl (0-45ppm) fraction. A comparison was made of the variability of K(d) values normalized over OC (i.e. K(oc)), alkyl, aromatic and alkyl+aromatic fractions. Expressing K(d) values for all chemicals, except azinphos methyl, in soils under native vegetation as K(alkyl) or K(aromatic) greatly decreased the variability compared with the K(oc) value. However in the cultivated soils only the sorption coefficients for DEA, DIA and fenamiphos showed a decrease in variability when expressed as K(alkyl) or K(aromatic). This reflected the stronger relationship between sorption coefficients and the alkyl and aromatic fraction of soil OC in soils from native vegetation compared with those determined from the market garden soils. The different relationships between sorption coefficients and types of OC of the two landuses also suggests that the type of aromatic and alkyl carbon under the two landuses is different and NMR characterisation of the OC was not sufficient to distinguish these differences.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
We present the first carbon- and oxygen-isotope records from the Valanginian-earliest Hauterivian interval of the South Carpathians (Romania). Stable isotopic curves have been generated from three ...sections in the Bucegi Mountains. The carbon-isotope values fluctuate around 2.1L' to 2.7L' within the late Early Valanginian, and 1.1 L' to 1.7L' within the Late Valanginian-earliest Hauterivian. The total organic carbon (loss on ignition method - LOI) content fluctuate between 1.6% to 2.8% within the late Early Valanginian, and 0.6% to 3.3% within the Late Valanginian-earliest Hauterivian. With limited sites recording Valanginian organic-rich black shale deposition, the positive carbon-isotope excursion has been interpreted to represent an increase in organic matter storage, related to high surface water productivity. The abundance of the nanno-fossils Biscutum constans, Discorhabdus rotatorius, Zeugrhabdotus erectus, and Dia-zomatolithus lehmanii suggest higher fertility episodes, cooler surface waters, and eu-trophic environments. The presence of conical and trochospiral inflated foraminiferal specimens is interpreted as an indicator of epifaunal to shallow infaunal deposit feeders, that were more tolerant of low oxygen conditions. Moreover, dysaerobic conditions of the sea floor are suggested by the dominant presence of small Spirillina among the benthic foraminiferal assemblage. High fertility could be related to an excess in pCO2 levels, globally linked to the Parana-Etendeka continental floods basalts and to increased rates of oceanic crust production during the Gondwana breakup.
