The aromatization and isomerization of hydro carbons and the thermal and subsidence history of the Nova Scotia margin

1985 ◽  
Vol 315 (1531) ◽  
pp. 203-232 ◽  
Keyword(s):  
Nova Scotia ◽  
Geothermal Gradient ◽  
Temperature History ◽  
Burial History ◽  
Generation Zone ◽  
Oil Generation ◽  
Model Predictions ◽  
History Of ◽  
Reaction Constants ◽  
Oil Source

The temperature and burial histories of the sediments deposited on the continental margin off Nova Scotia have been modelled. A good match between predicted and observed present-day bottom-hole temperatures is only achieved when the thermal conductivities of sediments are derived from laboratory measurements of representative samples; values commonly quoted in the literature predict too low a geothermal gradient. The temperature history is used to predict the extents of geochemical reactions involving steroid hydrocarbons together with previously derived reaction constants. The reaction extents were measured on 33 samples. In general, agreement between observations and predictions is good. The reactions in some samples, however, appear to have progressed anomalously far for their depths. This is thought to be the result of impregnation of these sediments with oil, which has migrated from depth. The good general agreement between model predictions and observations encourages extrapolation of the model to areas of no sample control, and the reconstruction of the temperature and burial history of the margin. Tentative reconstruction of oil generation from the principal oil source rock of the region may also be attempted. The top of the oil-generation zone currently lies 4 km below the shallow regions of the continental shelf. Model predictions suggest that the Verrill Canyon formation and its equivalents are mature but that younger sediments are not. Maturation of deeper regions of the Verrill Canyon started in the Early Cretaceous, but significant volumes of sediment only entered the oil-generation zone during the Tertiary.

Maturation thermique et histoire de l'enfouissement et de la génération des hydrocarbures du bassin de l'archipel de Mingan et de l'île d'Anticosti, Canada

1990 ◽  
Vol 27 (6) ◽  
pp. 731-741 ◽  
Author(s):  
Rudolf Bertrand
Keyword(s):  
Carbonate Platform ◽  
Burial History ◽  
Upper Ordovician ◽  
Southeastern Part ◽  
Middle Ordovician ◽  
Oil Generation ◽  
Wide Range ◽  
History Of ◽  
Anticosti Island ◽  
Depth Of Burial

Carbonate platform sequences of Anticosti Island and the Mingan Archipelago are Early Ordovician to Early Silurian in age. With the exception of the Macasty Formation, the sequences are impoverished in dispersed organic matter, which is chiefly composed of zooclasts. Zooclast reflectances suggest that the Upper Ordovician and Silurian sequences outcropping on Anticosti Island are entirely in the oil window but that the Lower to Middle Ordovician beds of the Mingan Archipelago and their stratigraphic equivalents in the subsurface of most of Anticosti Island belong to the condensate zone. Only the deeper sequences of the southwestern sector of Anticosti Island are in the diagenetic dry-gas zone. The maximum depth of burial of sequences below now-eroded Silurian to Devonian strata increases from 2.3 km on southwestern Anticosti Island to 4.5 km in the Mingan Archipelago. A late upwarp of the Precambrian basement likely allowed deeper erosion of the Paleozoic strata in the vicinity of the Mingan Archipelago than on Anticosti Island. Differential erosion resulted in a southwestern tilting of equal maturation surfaces. The Macasty Formation, the only source rock of the basin (total organic carbon generally > 3.5%, shows a wide range of thermal maturation levels (potential oil window to diagenetic dry gas). It can be inferred from the burial history of Anticosti Island sequences that oil generation began later but continued for a longer period of geologic time in the northeastern part than in the southeastern part of the island. Oil generation was entirely pre-Acadian in the southern and western parts of Anticosti Island, but pre- and post-Acadian in the northern and eastern parts.

Thermal diagenesis in the Swiss molasse basin: implications for oil generation

1982 ◽  
Vol 19 (2) ◽  
pp. 328-342 ◽  
Author(s):  
F. Monnier
Keyword(s):  
Organic Matter ◽  
Clay Mineral ◽  
Maximum Level ◽  
Hydrocarbon Generation ◽  
Molasse Basin ◽  
Burial History ◽  
Oil Generation ◽  
History Of ◽  
Mixed Layers ◽  
Mineral Transformations

Clay mineral transformations during burial are indicators of the degree of diagenesis of sediments. Diagenetic zonations in numerous wells of the Swiss molasse basin are defined by the disappearance of smectite and (or) the appearance of either corrensite or irregular 2:1 mixed layers. The maximum level attained in the thickest molasse sections corresponds to organic matter maturation suitable for hydrocarbon generation. Reconstructed on the basis of the clay mineral transformation data, a burial history of the basin is proposed.

Timing of fluorite mineralization and exhumation events in the east Central Alborz Mountains, northern Iran: constraints from fluorite (U–Th)/He thermochronometry

2021 ◽  
pp. 1-17
Author(s):  
Behnam Shafiei Bafti ◽  
István Dunkl ◽  
Saeed Madanipour
Keyword(s):  
Thermal Relaxation ◽  
Geothermal Gradient ◽  
Source Rocks ◽  
Lower Amount ◽  
Mining District ◽  
Northern Iran ◽  
East Central ◽  
Central Alborz ◽  
Ore Mineralization ◽  
History Of

Abstract The recently developed fluorite (U–Th)/He thermochronology (FHe) technique was applied to date fluorite mineralization and elucidate the exhumation history of the Mazandaran Fluorspar Mining District (MFMD) located in the east Central Alborz Mountains, Iran. A total of 32 fluorite single-crystal samples from four Middle Triassic carbonate-hosted fluorite deposits were dated. The presented FHe ages range between c. 85 Ma (age of fluorite mineralization) and c. 20 Ma (erosional cooling during the exhumation of the Alborz Mountains). The Late Cretaceous FHe ages (i.e. 84.5 ± 3.6, 78.8 ± 4.4 and 72.3 ± 3.5 Ma) are interpreted as the age of mineralization and confirm an epigenetic origin for ore mineralization in the MFMD, likely a result of prolonged hydrothermal circulation of basinal brines through potential source rocks. Most FHe ages scatter around the Eocene Epoch (55.4 ± 3.9 to 33.1 ± 1.7 Ma), recording an important cooling event after heating by regional magmatism in an extensional tectonic regime. Cooling of the heated fluorites, as a result of thermal relaxation in response to geothermal gradient re-equilibration after the end of magmatism, or exhumation cooling during extensional tectonics characterized by lower amount of erosion are most probably the causes of the recorded Eocene FHe cooling ages. Oligocene–Miocene FHe ages (i.e. 27.6 ± 1.4 to 19.5 ± 1.1 Ma) are related to the accelerated uplift of the whole Alborz Mountains, possibly as a result of the initial collision between the Afro-Arabian and Eurasian plates further to the south.

Eighteenth-Century Sierra Leone English

1999 ◽  
Vol 20 (1) ◽  
pp. 1-34 ◽  
Author(s):  
Michael Montgomery
Keyword(s):  
Eighteenth Century ◽  
African American ◽  
Nova Scotia ◽  
African Americans ◽  
Sierra Leone ◽  
American English ◽  
African American English ◽  
History Of ◽  
Nova Scotian

This essay examines the language of an expatriate community as found in letters and petitions written by African Americans who migrated to Sierra Leone by way of Nova Scotia in 1792. These documents provide some of the earliest first-hand evidence of African American English and contribute to debates about the history of that variety. The paper compares selected grammatical features in that variety to modern-day African Nova Scotian English for insights to the history of African American English and develops a case for the principled use of manuscript documents for reconstructing earlier stages of colloquial English.

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