Search

We present a compilation of the western Davis Strait region offshore southeastern Baffin Island, Nunavut, Canada with new subsurface geological structural details and observations regarding past hydrocarbon occurrences from scientific and commercial exploration. This consists of seismic mapping with archival data correlated with a filtered marine Bouguer anomaly gravity compilation and magnetic data sets covering northern Saglek Basin, the western part of the Lady Franklin Basin and the Ungava Fault Zone from south of Baffin Bay. A regional seismic horizon for mapping basin architecture comes from the top of the Paleogene volcanic syn-magmatic zone, where pervasive volcanic flows and intrusions are intermingled with the sedimentary section. The seismic depth map to the top of the regional volcanic seismic horizon shows pre-rift sedimentary basins having maximum depths of approximately 4–5 km flanking the shallower Ungava Fault Zone. Correlation of Bouguer anomaly gravity and magnetic data interpretations with the seismic mapping, indicate that over some areas true crystalline basement is deeper than can be determined by reflection seismic, as the base of the syn-magmatic section is not resolvable for seismic mapping. Extensive Paleogene mafic intrusives and extrusive basalts dominate the architecture of this volcanic rifted margin as seen by the dominant high amplitude magnetic anomalies associated with many deeper structures. The over 250 km long Davis Strait Fault is recognised as the key structural element of the Ungava Fault Zone (UFZ) and valley complex. The adjoining Davis Strait High maps on seismic as a continuous structure running the length of Davis Strait plunging southwards to a Bouguer gravity high feature that terminates the western end of the extinct Eocene spreading zone south of Davis Strait. This horn shaped structural feature establishes the presence of an accommodation zone with multiple faults and localised thrust faulting as required to fit the complex mechanics for strike-slip motion that occurs along the south end of this transform fault system. The revised marine Bouguer anomaly gravity data set also defines two new, near shore grabens east of Cumberland Sound, the southern Tariut Basin and the northern Imaqpik Basin, each extending over 100 km in length with sediment thicknesses of at least 4 km. These pre-rift basins most likely originate from the Paleozoic based on seafloor dredge and nearby shallow drill cores from previous studies. The hydrocarbon charge of a previously unexplained petroliferous shallow marine drill core that is adjacent the eastern edge of the Tariut Basin is attributed to Paleozoic source rocks that have undergone enhanced thermal maturation from sill intrusion associated with rifting. The Imaqpik Basin shows strong evidence of a hydrocarbon system from the proximity of clustered interpreted sea surface oil slicks, mapped from satellite radar images, and a local zone of anomalously high dissolved methane measured within the water column that originates from the seafloor immediately east of Cape Dyer at the northern limit of that basin. The overlying Cape Dyer flood basalt field extends from limited onshore exposures into the offshore and maps with magnetic data over an area of approximately 13,000 km2. This extrusive feature and it's implicit underlying intrusive components are likely the unconventional heat source for the anomalous enhanced thermal maturation of Paleozoic to Paleogene source rocks in these pre-rift basins that host this previously unrecognised petroleum system. • A 250 km length high angle transpressive fault, the Davis Strait Fault is recognised from gravity, magnetic and seismic data as defining the western side of the Davis Strait High. • The Ungava Fault Zone area of Davis Strait is geophysically mapped as a narrow sedimentary basin, of 2–4 km thickness, floored by widespread Paleogene volcanic rocks. • The Lady Franklin Basin is similarly mapped from the eastern side of the Davis Strait High and has a sedimentary section of at least 4 km thickness • The offshore extent of the Cape Dyer basalt field is mapped over an area of about 13,000 km2. • Two new pre Paleogene sedimentary basins, the southern Tariut and northern Imaqpik basins are of at least 4 to possibly 6 km thickness as mapped from marine Bouguer gravity and reflection seismic data. • Pervasive magmatism with wide scale sill development appears to be the primary thermal source for maturing source rocks, making this an unconventional petroleum system within this transform margin region. • The presence of radar imaged oil slick anomalies, hydrocarbon charged shallow rock cores and high amounts of dissolved water column methane near the seafloor likely all originate from this unconventional petroleum system. • Notable volcanic seismic features like SDR's and lava delta developments are seen only in the northern and southern ends of the Davis Strait transform margin. • Bouguer gravity data shows the western end of the extinct Eocene rift to have a distinct horn shape instead of the squared off edge that was previously surmised. • The transform margin consists of continental crust on both sides, with oceanic crustal pieces at either end of the fault zone. [ABSTRACT FROM AUTHOR]

We calculate the anomalous basement topography for the North Atlantic Ocean from 30° to 70°N latitude and from 0° to 70°W longitude at a resolution of roughly 6×6 km, using grids of total sediment thickness and observed and predicted sea-floor bathymetry to correct for the effects of isostatic sediment loading and lithospheric age. Plotting this residual topography for various plate reconstructions during opening of the North Atlantic, we delineate consistent patterns of basement highs related to variations in hotspot-related volcanism. In addition to Iceland and the Azores, we recognize three centers of excess volcanism at the mid-Atlantic ridge: the Milne Seamounts and Azores-Biscay Rise (∼75–40 Ma), the Southeast Newfoundland Ridge and Madeira-Tore Rise (∼130–110 Ma), and the East and West Thulean Rises (∼60–50 Ma). The duration of volcanic activity ranges from 8 to 10 m.y. (Thulean Rises) to 60 m.y. (Iceland) and thus it appears that both long- and short-lived hotspots coexist, even in relatively close proximity. In contrast, during the period 110–60 Ma we observe little excess volcanism during either continental breakup or seafloor spreading.We estimate isostatic crustal thickness from the anomalous basement depths, after first removing dynamic effects created by mantle flow. Maximum thicknesses of volcanic features, from 30 km beneath the Greenland–Iceland–Faeroe ridge to ∼15 km beneath the Azores-Biscay Rise, are broadly consistent with seismic data and predictions of decompression melting. Widths of volcanic features indicate that thickening primarily occurs within 100–200 km of hotspots except along continental margins that rifted at the time of the hotspot activity (i.e. East Greenland and the Hatton-Rockall Bank). We observe conjugate structures south of Greenland and Edoras Bank, where excess volcanism appears to have extended beyond the margin proper and into oceanic crust. Similar conjugate features appear in the Labrador Sea south of Davis Strait. Finally, we identify anomalous oceanic regions adjacent to some continental margins, where unusually low values of predicted crustal thickness suggest either additional variations in plate properties or non-isostatic effects within the mantle. [Copyright &y& Elsevier]