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Musings over Sedimentary Basin Evolution: Discussion
Philosophical Transactions B
Abstract
Field geologists and explorationists are of necessity immersed in numerous very detailed surface and subsurface observations. They are often perplexed by the choice of relatively simple geophysical models that so elegantly explain the origin and evolution of sedimentary basins. Geophysicists, on the other hand, search for a simple theme to explain the origin of sedimentary basins and, much like managers, are often impatient with lengthy detailed geological discourse that often uses fancy jargon to hide the very real difficulty that geologists have in separating important evidence from mere encyclopaedic description. The following musings address the quality and limitations of geologic and geophysical evidence that may be used to evaluate the relative roles of stress, thermal effects and gravity loading, which have been so lucidly summarized by M. H. P. Bott in the preceding summary. The fine papers presented during this meeting, of course, have led to significant modifications of some of my earlier thoughts. Because these have been previously published elsewhere (Bally & Snelson 1980; Bally 1980), they are summarized here only for the convenience of the reader.
... Here, we refer to basins formed along Alpine continental collision sutures shortly after the culmination of the shortening (such as the Alboran, Aegean, Pannonian and Tyrrhenian basins in the Mediterranean region) as "episutural" basins (terminology after Bally et al., 1982). An important question is whether western-Pacific-type roll-back of subducting oceanic lithosphere remains a relevant mechanism to explain Mediterranean episutural basins. ...
The African affinity of the deformed Mesozoic continental margins surrounding the Adriatic Sea (a region known as Adria) was recognized in the 1920s. However, over the last several decades, the majority view of Mediterranean Mesozoic paleogeography has featured an ocean (Mesogea) that separated Adria and Africa in Mesozoic and early Cenozoic time. The presence of a Mesogea ocean has become an argument against the use of paleomagnetic data from Adria as a proxy for Africa, which has been central to the controversy surrounding alternative Permian configurations of Pangea (Pangea A or B). The rationale for Mesogea has been derived from the perceived need for oceanic lithosphere to feed Miocene to Recent subduction beneath the Tyrrhenian and Aegean seas, the apparent presence of Early Jurassic oceanic basement beneath the present-day Ionian Sea, and the presence of deep-water Permian and younger sedimentary rocks in Sicily. On the other hand, the presence of Mesogea is incompatible with the apparent continuity of Mesozoic sedimentary facies from North Africa and Sicily into Adria, and with increasingly well-documented consistency of paleomagnetic data from Adria and NW Africa. We argue that the subducting slabs beneath the Tyrrhenian and Aegean seas are delaminated continental-margin mantle lithosphere of Adria/Africa stripped of its sedimentary cover and most of its crustal basement by thrusting. We propose, rather than an early Mesozoic (Mesogea) ocean between Adria and Africa, a sinistral strike-slip fault system linked Atlantic spreading in the West to the Neo-Tethys in the East, during the Middle and Late Jurassic, and featured pull-apart basins that included the Ionian and Levant basins of the eastern Mediterranean. In our modelling, Adria moved with Iberia during initial opening of the Central Atlantic in the Early and Middle Jurassic (after 203 Ma until 170 Ma). From mid-Jurassic time (170 Ma), Adria began to break away from Iberia with onset of rifting in the Piemonte-Ligurian Ocean, and, as the rate of southeasterly motion of Adria relative to North America lagged that of Africa, the Ionian-Levant basins formed as pull-apart basins along a sinistral strike-slip fault system parallel to a small circle about the 170–154 Ma Euler stage pole for motion of Africa relative to Adria. From marine magnetic anomaly M25 time (154 Ma), Adria moved in synch with Africa and therefore pull-apart extension in the eastern Mediterranean came to a halt. The modeled opening of eastern Mediterranean pull-apart basins is consistent with the observed resemblance of Permian and younger paleomagnetic poles from Adria and NW Africa. The Atlantic Euler poles used to map these paleogeographic changes, when applied to Permian paleomagnetic poles from Adria, Africa, and elsewhere, support the existence of Pangea B in Early Permian time (280 Ma) with transformation to Pangea A by the Late Permian (260 Ma).
... The authigenic/synkinematic 1M d -IAA ages in the plots of Figures 6a and 6b indicate that illite-1M d formed during three younger thermotectonic events that can be interpreted as the result of multiple fault reactivation episodes since the Middle-Late Jurassic for both the Vallès-Penedès and Río Grío Faults (Figure 7). These ages and their interpretation are supported by the known Mesozoic-Cenozoic evolution of local intraplate basins of the Iberian Plate, which are excellent markers of the large-scale tectonic events of that time in the Iberian Plate (e.g., Bally, 1982; Figure 8a). (Jammes et al., 2010;Salas et al., 2001). ...
Large‐scale faults in the continental crust are significant features that control the evolution of sedimentary basins and intraplate mountain chains. Deciphering their evolution is a significant task because faults slip and reactivate in a variety of geological settings. In this work, clay gouges of two major orogen‐scale, long‐lived faults in northern Iberia, the Río Grío and Vallès‐Penedès Faults, were investigated by X‐ray diffraction and K‐Ar isotopic analysis. Illite polytype determinations of 44 subfractions (from <0.1 to 10 μm) allowed us to discriminate between authigenic/synkinematic illite crystals formed during faulting and detrital illite crystals inherited from the host rock. K‐Ar dating provided a detailed set of ages corresponding to key stages of the thermotectonic evolution of the Iberian Plate: (a) the Permian to Late Triassic extensional/transtensional activity associated to the emplacement of Late Variscan magmatic bodies and hydrothermal mineralizations, (b) the opening of the Central Atlantic Rift during Late Triassic‐Early Jurassic times, (c) the Late Jurassic‐Early Cretaceous rifting that led to the development of Mesozoic extensional/transtensional basins in northern Iberia, (d) the final stage of the anticlockwise rotation of the Iberian Plate with respect to Eurasia and the accommodation of the first Pyrenean compressional pulses in Campanian time, and (e) the positive inversion of Mesozoic extensional basins due to far‐field stresses associated with the Alpine orogeny during the Paleogene. The results highlight that thermotectonic conditions characterized by high‐geothermal gradients strongly favor fault movement and neoformation of clay minerals in fault gouges, regardless of the prevailing tectonic regime.
A comparison of transform margins that started their evolution as continental transforms shows differences in their tectonic style, which can be attributed to the variable kinematic adjustments they underwent during the post-breakup continental-oceanic stage of their development. Three end-member examples are presented in detail. The Cape Range transform fault zone (Western Australia) retained its strike-slip character during its entire continental-oceanic stage, as documented by the transform-perpendicular system of spreading-related magnetic stripe anomalies. The Coromandal transform fault zone (Eastern India) adjusted its kinematics to a transtensional one during its continental-oceanic stage, as indicated by the transform-oblique system of magnetic stripe anomalies and extensional component of movement indicated by a narrow zone of crustal thinning. The Romanche transform fault zone (Equatorial Africa) adjusted its kinematics to transpressional, as documented by the changing geometries of magnetic stripe anomalies and transpressional folding during its continental-oceanic development stage. Based on the recognition of the aforementioned adjustments, we suggest a new categorization of transforms into (1) those that experience transpressional adjustment, (2) those that experience transtensional adjustment and (3) those that do not experience any adjustment during their continental-oceanic development stage.
Supplementary material at https://doi.org/10.6084/m9.figshare.c.5762388
Serra, S. and Nelson, R.A., 1988. Clay modeling of rift asymmetry and associated structures. In: X. Le Pichon and J.R. Cochran (Editors), The Gulf of Suez and Red Sea Rifting. Tectonophysics, 153: 307-312. A clay model is used to simulate the development of half-graben of alternating asymmetry in a rift zone. The sense of asymmetry is determined by the spatial arrangement and movement pattern of plates below the clay. The plates can be thought of as analogous to low-angle detachment horizons below rifts. The change in half-graben asymmetry occurs across a "transfer zone" marked by a highly faulted anticlinal saddle whose axis is oblique to the rift trend.
During the Late Triassic-Middle Jurassic interval Iberia acted as a passive margin, where extensional or transtensional faulting, linked to the propagation of the Central Atlantic and the opening of the Ligurian Tethys, generated a NW and NE trending fault system that conditioned facies and thickness distribution. These faults also favored the implantation of mantle plumes and associated volcanism, giving rise to the evolution from a magma-poor passive margin, during the latest Triassic to the Pliensbachian, to a magma-rich passive margin, which developed from the Pliensbachian to the Bajocian. Progressive extensional faulting, that propagated from east to west reached a climax during the Toarcian, probably related to the onset of sea-floor spreading in the northern part of the Central Atlantic.
In the paper, the subduction of the South Caspian microplate beneath the continental lithosphere of Central Caspian is substantiated based on the GPS measurements, crustal density model, seismological data, and seismic section along the Elburs–Apsheron–Balkhan Sill regional profile. In this context, the geodynamical model is suggested for the formation and spatial distribution of the oil and gas fields in the South Caspian Basin (SCB). It is shown that the heterogeneous oil-and-gas saturation of the sedimentary section within the South Caspian Depression (SCD), which was revealed by the long-term prospecting and exploration works, is, according to the suggested model, controlled by the subduction zone. The developed geodynamical approach to the problem of the formation of hydrocarbon deposits in the South Caspian Basin calls for rethinking the strategy of further prospecting for hydrocarbons in this region.
The Gulf of Suez-Red Sea rift system exhibits superb outcrop examples of extensional transfer zones and displays the control of these zones on syntectonic and post-tectonic sedimentation. Hard and soft linkage transfer zones were identified at variable scales. Hard linkage transfer zones form inward and outward fault kinks whereas soft linkage transfer zones form relay ramps between overlapping rift-parallel faults. The two types of transfer zones invariably exerted fundamental control on the deposition of syn-and post-tectonic sediments, flow direction of drainage systems and locations of sediment entry points, as well as the intensity of erosion patterns of the structurally high sediment source areas. This study highlights the close relationship between the transfer zones and hydrocarbon accumulations in clastic syntectonic reservoirs in rift basins.
This paper provides an overview of the existing knowledge of transform margins including their dynamic development, kinematic development, structural architecture and thermal regime, together with the factors controlling these. This systematic knowledge is used for describing predictive models of various petroleum system concept elements such as source rock, seal rock and reservoir rock distribution, expulsion timing, trapping style and timing, and migration patterns. The paper then introduces individual contributions to this volume and their focus.
Supplementary material: Location table and map of specific transform examples, structural elements of the Romanche transform margin and glossary of terms used in this article is available at https://doi.org/10.6084/m9.figshare.c.3276407
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