Basin Research - Volume 4, Issue 1, 1992

Interpretation of seismic reflection data have led to a new model of the development of the Queen Charlotte Basin. New multi‐channel data collected in 1988 and an extensive network of unpublished older single‐ and multi‐channel profiles from industry image a complex network of sub‐basins. Structural styles vary along the axis of the basin from broadly spaced mainly N‐trending sub‐basins in Queen Charlotte Sound, to closely spaced NW‐trending sub‐basins in Hecate Strait, to an E‐W en echelon belt of sub‐basins in Dixon Entrance. Transtensional tectonics dominated in the Miocene and transpression dominated in the Pliocene except in Queen Charlotte Sound. The data we present prove that the origin of the basin is extensional and its most recent deformation is compressive.

Evidence for the strike‐slip origin of tectonism includes along‐axis variations in structures, simultaneous extension and compression in adjacent sub‐basins, lack of correlations across faults, and mixed normal and reverse faults within structures. We infer that the Pacific‐North America plate boundary has been west of the Queen Charlotte Islands since the Miocene when relative plate motions have been dominantly strike‐slip. The formation and development of the Queen Charlotte Basin is the result of distributed shear; by which a small percentage of the plate motion has been taken up in a network of faults across the continental margin. As this region of crust deforms it interacts with neighbouring rigid crust resulting in extension dominating in the south of the basin and compression in the north. Continental crust adjacent to some transform plate boundaries can be sheared over a wide region; the network of basins in southwestern California is a good analogue for the Queen Charlotte Basin.

The Betic Cordillera (Southern Spain) acquired its present configuration during the Neogene. The formation, evolution and total or partial destruction of Neogene sedimentary basins were highly controlled by the geodynamic situations and the positions of the basins in the Betic Cordillera.

It is impossible to reconstruct the geometry of basins formed during the Early and Middle Miocene, concurrently with the westward drift of the Internal Zones, because in many cases only small outcrops remain. The basins formed on the mobile substratum (the Internal Zones) are characterized by a sedimentary infill made up of synorogenic deposits, which were intensely deformed towards the end of the Middle Miocene, and which were heavily eroded before the beginning of the Late Miocene. In the External Zones, deposition mainly took place in the North Betic Strait, an area across which there was wide communication between the Atlantic and the Mediterranean, which received huge olistostromic masses in its more mobile sector (the foredeep basin), and which evolved differently in its eastern and western sectors.

The palaeogeography of the Cordillera changed radically at the beginning of the Late Miocene, when the westward drift of the Internal Zones ceased. During this time the North Betic Strait disappeared and, in what had been its northwestern half approximately, the Guadalquivir Basin became individualized. This basin, which was located between the Betic Chain and the emerged Hercynian Massif, acquired a structure similar to that of the present basin and its extension was also similar to that of the present Neogene outcrops.

Intramontane basins became individualized in the recently formed and progressively emerged mountain chain, reaching a development and size in this Cordillera much greater than in other Alpine chains. These basins are characterized by their thick infills, which are unconformable on the folded and deformed substratum, and which can be subdivided according to the different movements of the fault sets that controlled their evolution.

The Calabrian‐Peloritan Arc (southern Italy) represents a fragment of the European margin, thrusted onto the Apennines and Maghrebides during the Europe‐Apulia collision in the late Early Miocene. A reconstruction of the pre‐Middle Miocene tectono‐sedimentary evolution of the southern part of the Calabrian‐Peloritan Arc (CPA) is presented, based on a detailed analysis of the Stilo‐Capo ďOrlando Formation (SCO Fm). Deposition of the SCO Fm occurred in a series of mixed‐mode piggy‐back basins. Basin evolution was controlled by two intersecting fault systems. A NW‐SE oriented system delimited a series of sub‐basins and fixed the position of feeder channels and submarine canyons, whereas a NE‐SW oriented system controlled the axial dispersal of coarse‐grained sediments within each of the sub‐basins. From base to top, sedimentary environments change from terrestrial and lagoonal to upper bathyal over a timespan of approximately 12 Myr (late Early Oligocene‐late Early Miocene). During this interval, extensional tectonic activity alternated with oblique backthrusting events, related to dextral transpression along the NW‐SE oriented faults. This produced a characteristic pulsating pattern of basin evolution.

Oligocene‐Early Miocene evolution of the W. Mediterranean basin was dominated by ‘roll back’ of the Neotethyan oceanic lithosphere. Considerable extension in the overriding European Plate gave rise to the formation of a back arc‐thrust system. The initial stages of Calabrian Basin evolution are remarkably similar to the evolution of rift basins in the back arc (Sardinia). The Calabrian basins, which are inferred to have originated as thin‐skinned pull‐apart basins, were subsequently incorporated into the Apennines‐Maghrebides accretionary wedge by out‐of‐sequence thrusting, and became decoupled from the back arc. Periodic restabilization of the accretionary wedge, resulting in an alternation of backthrusting and listric normal faulting, provides an explanation for the structural evolution of these mixed‐mode basins. The basins of the southern part of the CPA may be termed ‘spanner’ or ‘looper’ basins, in view of their characteristic pulsating structural evolution, superimposed upon their migration toward the foreland. This new term adequately accounts for the occurrence of tectonic inversions in long‐lived piggy‐back basins, as expected in the light of the dynamics of accretionary wedges.

Book reviewed in this article:

Antarctica as an Exploration Frontier–Hydrocarbon Potential, Geology and Hazards:Bill St John (ed.)

American Association of Petroleum Geologists, Tulsa, 1990.

The Integration of Geology, Geophysics, Petrophysics and Petroleum Engineering in Reservoir Delineation, Description and Management:Principal conference convenor, Robert Sneider; Association editor, Susan Longacre

Proceedings of the 1 st ARCHIE Conference, October 22–25, Houston, Texas, USA, 441 pp., colour and B & W figures. (Sponsored jointly by the American Association of Petroleum Geologists, the Society of Exploration Geophysicists, the Society of Petroleum Engineers and the Society of Professional Well Log Analysts.)

Lacustrine Fades Analysis:P. Anadón, LI. Cabrera, K. Kelts (eds)

Blackwell Scientific Publications, Oxford, 1991.