Traps in continental sedimentary basins in China, tectonic and traps in foreland basins

The foreland basin has an asymmetrical structure, a lower depression near one side of the orogenic belt, and a large sedimentary thickness, characterized by the development of fold-thrust fault belts, and the strata are overlying and thinning towards the craton (Fig. 3-29), forming a wide and gentle slope, but the degree of tectonic transformation and deformation style are different in different foreland basins (Tables 3-7, 3-8), and the trap types are also different.

Fig.3-29 Schematic diagram of sedimentary facies distribution, tectonic style and trap in foreland basin.

Table 3-8 Typical foreland basin structures.

The structure of the foreland basin of Western Canada is relatively simple, but due to the change of deflection sedimentary thickness, there is salt dissolution and mountain erosion. There is a weak movement in the Precambrian base. These structures have no obvious control effect on oil and gas accumulation, so the main part of the Westland Foreland Basin except for the foothill zone is mainly sandstone stratigraphic traps, including stratigraphic pinching and unconventional deep basin hydrodynamic traps, and there is also a special stratigraphic trap——— shale source rock trap, which is at a medium maturity level, and mature oil is still remaining in the fractured shale.

The tectonic traps are basically limited to the foothills, which are thrust faults and fold traps, containing a large amount of natural gas reserves and a small amount of oil reserves.

The Neo-Tertiary-Quaternary deformation of the Zagros foreland basin formed a high-amplitude, wide concentric anticline, and developed the world's largest and most effective trap. The maximum anticline axis can reach 190 km and the amplitude can reach 6 10 km. Iraq's oil production has reached 10,108

The Kirkuk oilfield above t and the Bulgan oilfield in Kuwait are all large-scale anticline traps. The formation of large concentric folds is associated with the slippage of thick, relatively rigid carbonate layers along the lower Vholmz salt rocks. Where argillaceous sediments are thick and there is no salt, the folds are small and tightly closed, and the scale of oil and gas reserves is also small.

The fractures generated by the folding provide a channel for the upward migration of oil and gas from depth, and at the same time help to improve the reservoir.

The Oligocene-Miocene oil and gas traps in the foreland basin of East Venezuela are formed by normal faults and reverse faults, and the existence of these traps is conducive to the accumulation of large amounts of oil and gas in the Antelope.

The northern foreland basin of the north slope of Alaska is characterized by the uplift of the shoulder of the extensional rift, the structural development of the extrusion margin fault anticline in the south, the delta turbidite strata, lithologic traps and tectonic-stratigraphic traps on the northern front slope, and the large oil field of Prudhoe Bay is a sandstone overlying updipping stratigraphic trap.

The Rocky Mountain foreland basin in the United States is associated with gentle subduction, and the later modification form is unique. In the late evolution of foreland basins, basement detachment and basement fault uplift occurred due to the Laramie movement, and the foreland basin was dismembered into a series of sub-basins. Among them, the basin margin is mainly a tectonic trap, and in the flank of the gently dipping basin, it is mainly a stratigraphic trap and a composite trap composed of a low-amplitude tectonic nose and its wing stratigraphy and lithologic factors.

The Late Paleozoic pre-abyss of Ocheta in southwestern North America consists of seven subbasins separated by basal uplifts, each of which is a monocline that dips from the craton to the foreland thrust zone. Clastic stratigraphic traps are dominant, and deep-basin hydrodynamic traps also exist.

The northern margin of the basin includes Wolf Mountain, Wula Mountain, Daqing Mountain and Yinshan Mountain, and reaches the Jining-Hohhot area in the south, and its crystalline basement is composed of multiple sets of metamorphic rock series of the Middle and Neo-Archean. In the southern margin of the uplift area, strata in different eras since the Middle and Neoproterozoic have undergone stratigraphic thinning, extermination or lithofacies changes to the north, and most of them are high-lying uplift areas during the Late Triassic sedimentation, except for some areas of the Yimeng uplift that received sedimentation (Fig. 2-1). During the sedimentary period of the Yanchang Formation, the Yinshan paleocontinent constituted the northern boundary of the basin, which provided the main source for the Late Triassic sedimentary basin.

The Yinshan paleocontinent is composed of multiple sets of metamorphic rock systems from the Paleo, Middle Archean to the Proterozoic. Among them, the Jining Group of the Paleo-Archean and Middle Archean (a r1-2

It is dominated by deep metamorphic marble and granulite, and belongs to high amphibolite facies-granulite cypress; Neo-Archean Ula Mountains (a r3

The upper part is built of feldspar quartz sandstone-marble, and the lower part is built of amphiboboli-amphibolite-amphibole-amphibolite plagioclase gneiss, which is a high amphibolite facies. The lower part of the Paleoproterozoic Serten Mountains is composed of mixed lithified gneiss, mixed rocks and schists, the middle part is composed of residual porphyritic schist and greenschist, and the upper part is composed of hornblende plagioclase schist and hornblende. The upper part of the Paleoproterozoic is a two-way concave group, the lower part is greenschist facies, the middle part is marble and schist facies, and the upper part is schist and marble facies. The Lower Middle Proterozoic Zhartai Group is mainly composed of metamorphic conglomerate, quartz sandstone, quartzite, stromatolite-bearing crystalline limestone, dolomite, schist, phyllite, slate and medium mafic volcanic rocks. The Upper Middle Proterozoic Shinagan Group is unconformable to the Zhartai Group and is in pseudo-integrated contact with the Upper Cambrian strata. The Yinshan paleocontinent is adjacent to the basin margin, including the Yimeng uplift and the Inner Mongolia uplift to the north. It and the Alxa paleocontinent were uplifted for a long time in the geohistorical evolution, and most of them were high-lying paleouplift areas during the late Triassic subsidence, except for the Yimeng uplift part that received sedimentation.

The Inner Mongolia uplift is in the north of the Yimeng uplift, which is distributed horizontally in an east-west direction, and is composed of ancient metamorphic rocks of the Archean, Paleoproterozoic and Mesoproterozoic, with a thickness of tens of thousands of meters, and has been in an uplift state from the beginning of the Neoproterozoic to the Triassic, and only at the southern edge of the uplift there are scattered Cambrian-Ordovician and Carboniferous-Permian sedimentary distribution, constituting a huge paleocontinental area. In addition, there are Caledonian and Hercynian acid and mafic magmatic intrusions and volcanic eruptions in the uplift area, and there are more Mesozoic and Cenozoic small continental clastic basins developed above the uplift. The Yimeng uplift area in the south of the Inner Mongolia uplift has been basically in an uplift state since the Paleozoic Era, and the strata of various ages have thinned or been missing in this area, with a total sedimentary thickness of only 1 2 km.

Figure 2-1 Schematic diagram of the location of the stratigraphic extinction line or remnant boundary line of different ages in the northern margin of the Ordos Basin.

Throughout the formation and development of foreland basins, their evolution can be roughly divided into the early compound stone construction stage and the late molasse construction stage (Fig. 9-13).

Fig. 9-13 Evolution model from the passive continental margin of the craton to foreland basins (according to Lu et al., 1998).

Flysch formation stage: In the early stage of foreland basin formation, the lithosphere of the passive continental margin was bent and partially uplifted due to the load loading of the thrust overburden, resulting in foreland uplift and a deep and narrow foreland basin, and the overburden continuously provided abundant sources to the basin, so that the basin was filled with a huge set of terrigenous clastic compound stone accumulation. Due to the relative changes of sea level, tectonic thrust and deflective subsidence, the rhythm of complex stone sedimentation with multiple cycles is formed.

Molasses formation stage: In the late stage of the development of the foreland basin, with the continuation of extrusion and orogeny, the thrust overburden continued to advance, and the sedimentation rate in the basin was much greater than the lithospheric deflection and sinking rate, and the basin was in an overcompensated state, and the sediments from the orogenic belt began to cross the foreland uplift into the post-uplift basin, and transitioned to continental molasse sedimentation. The source of the foreland molar stone construction is mainly the weathering products of the active edge orogenic belt transported into the basin, and these materials are mainly transformed from the compound stone construction in the early orogenic period, so its source is the reforestation cyclic type.

The mill-drawn stone construction also has a multi-cycle structure, such as the Northern Alps mill-drawn stone construction, which consists of 4 cycles.