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F Fasano - One of the best experts on this subject based on the ideXlab platform.
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the ricker hills Tillite provides evidence of oligocene warm based glaciation in victoria land antarctica
Global and Planetary Change, 2008Co-Authors: Carlo Baroni, F Fasano, Giovanna Giorgetti, Maria Cristina Salvatore, Cristiana RibecaiAbstract:Abstract The relationship between the Ricker Hills Tillite (RHT), which represents the northernmost outcrop of lithified continental glacial deposits in Victoria Land, is discussed with respect to the glacial landscape assemblage of the Ricker Hills, a nunatak at the internal border of the Transantarctic Mountains. A warm-based ice sheet deposited the Tillite and induced syn- to post-depositional glacial deformation under wet conditions both of the Tillite and of the bedrock. The thickness of the ice sheet on the nunatak is estimated to have been 600 m, at most. The area had been deeply eroded before deposition of the RHT as documented by the low elevation of Tillite outcrops located in overdeepened depressions of the nunatak. Micropaleontological analysis evidences only the presence of Permian to Jurassic palynomorphs. X-ray diffraction and SEM–EDS analyses of clay minerals in the RHT indicate continental chemical weathering under wet conditions after the RHT deposition. As documented by clay mineral assemblage variation in CRP drillholes, the progressive cooling of the Antarctic continent allowed chemical weathering in “warm” conditions until the Late Oligocene period in southern Victoria Land, leading to a chronological constrain for RHT deposition. Conservatively estimating the sea level to have been between the Tillite outcrops and the erosional trimline limiting horns in the Ricker Hills, at the time of RHT deposition, we suggest that the maximum uplift of the area would not have exceeded 900–1500 m since at least Late Oligocene.
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micromorphological evidence of warm based glacier deposition from the ricker hills Tillite victoria land antarctica
Quaternary Science Reviews, 2006Co-Authors: Carlo Baroni, F FasanoAbstract:Abstract Thin sections of impregnated samples were used for micromorphological analysis of the “Ricker Hills Tillite” in southern Victoria Land, Antarctica. The Tillite is composed of massive matrix-supported diamicton with a porphyric coarse/fine related distribution, low sorting, low rounding and medium to high angularity. Glacial deposits are completely represented by lodgement till. Phyllosilicate reorientation patterns (plasmic fabrics) are visible in most samples, especially associated skelsepic and lattisepic patterns. Syndepositional pervasive till shearing (glacially induced) is evidenced by clast alignments, shear planes, rotational structures and pressure shadows. Boudinage, ductile shear zones, and rotational structures are also widespread in the deformed bedrock. Water-escape structures are clearly evident in the Tillite and in the bedrock. Shear planes infilled by injection veins in lodgement till and at the till-bedrock interface testify to the presence of water during deposition. Secondary features like clay and silt coatings, sparite calcite, and oxidation products were found in all the examined outcrops. They formed under phreatic conditions due to saturated water circulation. A warm-based ice sheet was responsible for the deposition of the Tillite. Past ice-flow directions were similar to present ones.
Carlo Baroni - One of the best experts on this subject based on the ideXlab platform.
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the ricker hills Tillite provides evidence of oligocene warm based glaciation in victoria land antarctica
Global and Planetary Change, 2008Co-Authors: Carlo Baroni, F Fasano, Giovanna Giorgetti, Maria Cristina Salvatore, Cristiana RibecaiAbstract:Abstract The relationship between the Ricker Hills Tillite (RHT), which represents the northernmost outcrop of lithified continental glacial deposits in Victoria Land, is discussed with respect to the glacial landscape assemblage of the Ricker Hills, a nunatak at the internal border of the Transantarctic Mountains. A warm-based ice sheet deposited the Tillite and induced syn- to post-depositional glacial deformation under wet conditions both of the Tillite and of the bedrock. The thickness of the ice sheet on the nunatak is estimated to have been 600 m, at most. The area had been deeply eroded before deposition of the RHT as documented by the low elevation of Tillite outcrops located in overdeepened depressions of the nunatak. Micropaleontological analysis evidences only the presence of Permian to Jurassic palynomorphs. X-ray diffraction and SEM–EDS analyses of clay minerals in the RHT indicate continental chemical weathering under wet conditions after the RHT deposition. As documented by clay mineral assemblage variation in CRP drillholes, the progressive cooling of the Antarctic continent allowed chemical weathering in “warm” conditions until the Late Oligocene period in southern Victoria Land, leading to a chronological constrain for RHT deposition. Conservatively estimating the sea level to have been between the Tillite outcrops and the erosional trimline limiting horns in the Ricker Hills, at the time of RHT deposition, we suggest that the maximum uplift of the area would not have exceeded 900–1500 m since at least Late Oligocene.
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micromorphological evidence of warm based glacier deposition from the ricker hills Tillite victoria land antarctica
Quaternary Science Reviews, 2006Co-Authors: Carlo Baroni, F FasanoAbstract:Abstract Thin sections of impregnated samples were used for micromorphological analysis of the “Ricker Hills Tillite” in southern Victoria Land, Antarctica. The Tillite is composed of massive matrix-supported diamicton with a porphyric coarse/fine related distribution, low sorting, low rounding and medium to high angularity. Glacial deposits are completely represented by lodgement till. Phyllosilicate reorientation patterns (plasmic fabrics) are visible in most samples, especially associated skelsepic and lattisepic patterns. Syndepositional pervasive till shearing (glacially induced) is evidenced by clast alignments, shear planes, rotational structures and pressure shadows. Boudinage, ductile shear zones, and rotational structures are also widespread in the deformed bedrock. Water-escape structures are clearly evident in the Tillite and in the bedrock. Shear planes infilled by injection veins in lodgement till and at the till-bedrock interface testify to the presence of water during deposition. Secondary features like clay and silt coatings, sparite calcite, and oxidation products were found in all the examined outcrops. They formed under phreatic conditions due to saturated water circulation. A warm-based ice sheet was responsible for the deposition of the Tillite. Past ice-flow directions were similar to present ones.
Nicholas Eyles - One of the best experts on this subject based on the ideXlab platform.
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sedimentology of the neoproterozoic c 580 ma squantum Tillite boston basin usa mass flow deposition in a deep water arc basin lacking direct glacial influence
Sedimentary Geology, 2012Co-Authors: Shannon L Carto, Nicholas EylesAbstract:Abstract The Squantum ‘Tillite’ (c. 593–570 Ma) consists of thick (up to 215 m) massive and crudely-stratified diamictites conformably interbedded with subaqueously-deposited conglomerates and sandstones within a thick (~ 7 km) Boston Basin fill which is dominated by argillite turbidites. The Squantum Tillite was first interpreted as being glacigenic in origin in 1914 because of the presence of diamictites; argillites were interpreted as glaciolacustrine ‘varves’ with rare ice-rafted debris, and conglomerates as glaciofluvial outwash. More recently these have been shown to be the product of deep marine mass flow processes with no glacial influence, yet because of its age equivalence with the deep marine, glacially-influenced Gaskiers Formation, the Squantum Tillite is still seen by some as supporting evidence for a widespread ‘Snowball Earth’ event at c. 580 Ma. New sedimentological work confirms that conglomerate and sandstone facies are deep marine sediment gravity flows genetically related to massive (homogeneous) and crudely-stratified (heterogeneous) diamictites produced subaqueously by downslope mixing of gravel and cobbles with muddy facies. Rare horizons of ‘ice rafted debris’ in thin-bedded and laminated turbidite facies interbedded with thick debrites show a weak but positive correlation of lamina thickness with grain size, suggesting these facies are non-glacial co-genetic ‘debrite–turbidite’ couplets. A significant volcanic influence on sedimentation is identified from reworked lapilli tuff beds and reworked ash in turbidites. The depositional setting of the Squantum ‘Tillite’ appears to be that of a submarine slope/fan setting in an open marine volcanic arc basin receiving large volumes of poorly-sorted sediment on the mid-latitude active margin of Gondwana. No direct glacial influence is apparent.
Pascal Affaton - One of the best experts on this subject based on the ideXlab platform.
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chemostratigraphy of neoproterozoic cap carbonates from the volta basin west africa
Precambrian Research, 2004Co-Authors: Susannah M Porter, Andrew H Knoll, Pascal AffatonAbstract:Abstract The Neoproterozoic Era includes some of the most extreme ice ages in Earth history. The exact number of glaciations is unknown, although there were at least two events of global reach and possibly an equal number of lesser advances. Neoproterozoic glacial deposits in West Africa have proven particularly difficult to correlate with better constrained successions elsewhere. In most West African successions, only a single glaciogenic deposit is present, generally within a stratigraphic ‘Triad’of Tillite, carbonate, and bedded chert; the age of these deposits and their synchroneity across the craton remain controversial. We report isotopic data from carbonates that cap Tillites in the Volta Basin (Sud-Banboli Group). In the three sections measured, ∂ 13 C (‰ PDB) begins at ∼−2 to −3 and drops to −5 to −8, correlated with a drop in both ∂ 18 O and Mg/Ca. This pattern—both the drop in ∂ 13 C and its correlation with ∂ 18 O and lithology—has been observed in Neoproterozoic cap carbonates on other cratons, suggesting that it reflects primary depositional variations. In addition, the strong positive correlation among lithology, ∂ 13 C , and ∂ 18 O suggests that lithological variation may have exerted a principal control on isotopic variation, implying that the dolomite formed in isotopic equilibrium with seawater, as a primary precipitate or very early diagenetic replacement. This would require low levels of sulfate (estimated to be ∼1 mM or less), consistent with available S-isotopic data, the presence of barite crusts in association with some cap carbonates, and the conditions of seawater chemistry hypothesized in the aftermath of a ‘snowball Earth.’ The stratigraphic pattern of carbon isotope variation in the Volta Basin cap carbonates suggests that underlying Tillites are likely Marinoan (∼650–600 Ma) in age. This interpretation is supported by distinctive lithological characters observed in Volta Basin cap carbonates and accepted Marinoan correlatives. Tillites elsewhere on the craton have been assigned latest Proterozoic or Early Cambrian ages. Either the basis for these proposals requires reexamination, or West African Tillites record more than one glacial event.
M R A Thomson - One of the best experts on this subject based on the ideXlab platform.
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an early cambrian archaeocyath trilobite fauna in limestone erratics from the upper carboniferous fitzroy Tillite formation falkland islands
Earth and Environmental Science Transactions of The Royal Society of Edinburgh, 2011Co-Authors: P Stone, M R A Thomson, A W A RushtonAbstract:Rare clasts of limestone contained in the uppermost Carboniferous Fitzroy Tillite Formation of the Falkland Islands contain a rich Cambrian fauna of archaeocyaths together with a radiocyath and a few trilobites. Neither Cambrian strata nor limestone are present in the indigenous rock succession and the clasts are regarded as exotic erratics, introduced during the Permo- Carboniferous glaciation of southern Gondwana, prior to its Mesozoic break-up. Nineteen archaeocyath taxa have been identified, with seven (plus a radiocyath) occurring in a single clast. Trilobite identifications are less definitive, but they are compared to Yorkella and the Siberian genera Edelsteinaspis, Namanoia and Chondrinouyina. The archaeocyath fauna has an Australo-Antarctic character and the Transantarctic Mountains seem the most likely source for these unusual erratics. Most recent reconstructions of Gondwana rotate a Falklands microplate into a position between South Africa and East Antarctica. There, it is in proximity with the Eastern Cape Province, where Tillites within the Permo-Carboniferous Dwyka Group are correlatives of the Fitzroy Tillite Formation, and the 'Atlantic' end of the Transantarctic Mountains. The Dwyka Group Tillites also contain rare clasts of archaeocyathan limestone and the rotational reconstruction produces a continuity of the apparent ice-flow directions in South Africa and the Falkland Islands.
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archaeocyathan limestone blocks of likely antarctic origin in gondwanan Tillite from the falkland islands
Geological Society London Special Publications, 2005Co-Authors: P Stone, M R A ThomsonAbstract:Cambrian limestone clasts containing a rich, well-preserved archaeocyathan fauna have been recovered from the late Carboniferous Fitzroy Tillite Formation of the Falkland Islands. Since neither Cambrian strata nor limestone are present anywhere in the indigenous rock succession, the clasts are regarded as exotic erratics introduced during the Permo-Carboniferous Gondwana-wide glaciation. Most recent reconstructions of Gondwana rotate the Falklands into proximity with the Eastern Cape, South Africa and the Ellsworth Mountains, Antarctica. In both of these areas, Permo-Carboniferous diamictites correlated with the Fitzroy Tillite Formation also contain rare, exotic clasts of archaeocyathan limestone. The Transantarctic Mountains seem the most likely source for all of these unusual erratics. This interpretation sustains the requirement for substantial rotation of the Falklands microplate into Gondwana reconstructions and illustrates the extent of the late Carboniferous ice sheet. Apparent differences in the Tillite clast assemblages between East and West Falkland suggest variable provenance within the regional ice-flow regime.