Increase In Subsidence Research Articles

Cratonic Platform and Foredeep Response to Plate Margin Convergence: Devonian through Mississippian Subsidence History in Western Montana and East-Central Idaho: ABSTRACT

Devonian and Mississippian sedimentary rocks of western Montana and east-central Idaho were deposited on a cratonic platform that faced a northern extension of the Antler foredeep. Subsidence analyses of this sequence and isopach maps illustrate regional patterns of subsidence related to convergence along the western North American plate margin. Tectonic stresses affected deposition on platform areas which were hundreds of kilometers inboard from the ancient continental margin. Wavelengths of paleostructural elements, tectonic inversion of these structures (i.e., transition of a paleohigh into a depocenter), and time scales involved in the inversion process cannot be attributed solely to flexure or to vertical displacements by in-plane stresses but suggest reactivation of Precambrian structural trends. Late Devonian (Frasnian) platform sedimentation began during a brief interval of increased subsidence across western Montana. This interval of increased platform subsidence is greater than a Late Devonian eustatic sea level rise (determined from subsidence analyses of Devonian strata from stable cratonic areas) and suggests some tectonic event must have influenced subsidence in Montana. Thin uppermost Devonian Strata contain numerous unconformities that may be related to flexure of the platform plus eustatic sea level fluctuations. Rapid subsidence across Montana during the Early Mississippian (Kinderhookian) resulted in a condensedmore » platform sequence, which is overlain by deep water shaly carbonates. Rapid subsidence continued into the Osagean then slowed, allowing progradation of carbonate platform facies across Montana. A regional karst surface on top of the Meramecian platform coincides with conglomerate deposition and increased subsidence rates in the foredeep; unconformity durations on the platform also increase to the east.« less

Sedimentation, sea-level change, and tectonics on an early Pleistocene continental shelf, northern California

Research Article| October 01, 1989 Sedimentation, sea-level change, and tectonics on an early Pleistocene continental shelf, northern California ELANA L. LEITHOLD; ELANA L. LEITHOLD 1Department of Geological Sciences, University of Washington AJ-20, Seattle, Washington 98195 Search for other works by this author on: GSW Google Scholar JOANNE BOURGEOIS JOANNE BOURGEOIS 1Department of Geological Sciences, University of Washington AJ-20, Seattle, Washington 98195 Search for other works by this author on: GSW Google Scholar Author and Article Information ELANA L. LEITHOLD 1Department of Geological Sciences, University of Washington AJ-20, Seattle, Washington 98195 JOANNE BOURGEOIS 1Department of Geological Sciences, University of Washington AJ-20, Seattle, Washington 98195 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1989) 101 (10): 1209–1224. https://doi.org/10.1130/0016-7606(1989)101<1209:SSLCAT>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation ELANA L. LEITHOLD, JOANNE BOURGEOIS; Sedimentation, sea-level change, and tectonics on an early Pleistocene continental shelf, northern California. GSA Bulletin 1989;; 101 (10): 1209–1224. doi: https://doi.org/10.1130/0016-7606(1989)101<1209:SSLCAT>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Rio Dell Formation was deposited in a tectonically active area during a time of fluctuating eustatic sea-level. Detailed interpretation of Rio Dell shelf sediments, facilitated by comparison to the nearby, analogous, modern Eel River shelf, has proved a vital tool for decoding the record of these influences. Understanding of the nature and relative roles of processes on the modern and ancient shelf, including those associated with storms and with river floods, not only allows for detailed paleobathymetric reconstruction of the ancient sequence, but also for recognition of relatively subtle effects of syndepositional tectonism.Shelf sediments of the Rio Dell Formation comprise four depositional sequences bounded by thin, submarine condensed sections. The condensed sections formed during periods of rapid, probably largely eustatic, sea-level rise. The sequences each record progradation of the shelf, predominantly during sea-level highstands. Paleobathymetric reconstruction provides the basis for interpretation of the magnitude of local, relative sea-level changes within and between the sequences.Subsidence of the Rio Dell shelf apparently played a role in recorded local sea-level fluctuations, as did eustasy. Subsidence ("geohistory") analysis of the sequence indicates that the shelf was subsiding throughout its existence, due not only to sediment loading but also due to tectonism. The analysis points to a period of rapid shelf subsidence, accompanied by onland uplift, between about 1.3 and 1.2 Ma.An increase in subsidence rates after about 1.3 Ma apparently caused an increase in Rio Dell shelf gradient, which changed the balance between flood and storm processes on the middle shelf. Increased shelf inclination evidently resulted in restriction of storm-wave reworking to a narrower zone extending from the shoreline, whereas distance from shoreline to the shelf area most influenced by river-flood deposition remained unchanged. The resultant increased segregation of flood and storm effects caused a fining of background grain-size distributions at mid-shelf sites. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Review and computer modelling of the Brent Group stratigraphy

Summary The depositional history of the Brent Delta system can be analysed on three different levels: (i) the individual formations and their facies distribution, used for the interpretation of the depositional processes; (ii) the vertical succession of formations in each well, indicating the temporal changes in environment; (iii) the two- or three-dimensional array of sequences illustrating both the temporal and spatial variations within the delta system. The Brent Group is essentially one regressive-transgressive megacycle. The regressive part comprises the Rannoch and Etive Formations (delta front) and the lower Ness Formation (delta plain), and the transgressive system contains the Tarbert Formation (delta front) and the (upper) Ness Formation (delta plain). With the aid of a computer program, the succession geometry can be analysed in terms of the relative importance of sediment supply, eustasy and tectonics. The change from regressive to transgressive conditions was probably initiated by an increase in subsidence rates, whereas regressive pulses in the overall transgressive Tarbert Formation can be explained in part by eustatic sea-level falls.

Three-Dimensional Reconstruction of an Evolving Fluvial System: Chinle Formation, Northeastern Arizona: ABSTRACT

Exceptional three-dimensional (3-D) exposures of the Triassic Chinle Formation in northeastern Arizona allow detailed architectural analyses of a complex fluvial system. Lateral profiling, element analysis , and hierarchy of bounding surfaces demonstrate deposition in both low- and high-sinuosity channel systems. Two conglomerate bodies, the Shinarump and the Sonsela, were deposited in low-sinuosity, valley-confined systems as indicated by internal sequences of sedimentary structures and geometry of the macroforms. Stacked channel sequences consist of in-channel sandy bed forms separated from large, in-channel, downstream-accreting sandy macroforms (up to 5 m thick by 50 m long) bounded by fourth-order surfaces. Within localized channels, conglomerate bar complexes (up to 10 m thick by 150 m long) record downstream and oblique accreting macroforms bound both laterally and vertically by in-channel elements. Architectural features in the Chinle reflect intrabasinal as well as extrabasinal controls on sedimentation. Major changes in stream sinuosity are largely controlled by gradient changes associated with increased subsidence rates with time.

Carbonate Buildup Development Within a Passive-Margin Setting: Upper Jurassic of Lusitanian Basin, Portugal, and Comparable Carbonates from Eastern North American Seaboard: ABSTRACT

Several carbonate buildups occur within the Upper Jurassic of the Lusitanian basin, Portugal. Their development can be related either to halokinetics or reactivation of basement fault blocks. In most places, the buildups contain only minor volumes of recognizable biogenic framework. The basement-controlled buildups, which have shelf profiles, are relatively thin (200-500 m), show great lateral facies variation, and are predominantly micritic with only thin grainstone and packstone sequences. The salt-controlled buildups, which have a ramp or distally steepened ramp profile, are relatively thick (500-1000 m or more), show little lateral facies variation, and contain thick sequences of grainstones and packstones. Increased subsidence rates during the early Kimmeridgian resulted in the drowning of many of the buildups, followed by an influx of clastics throughout most of the Lusitanian basin. In the southern, clastic-starved part of the basin, however, a prograding carbonate ramp sequence passively filled the newly deepened basin. This buildup is micrite dominated, containing only minor volumes of recognizable biogenic framework. Upper Jurassic carbonate buildups are also known from offshore Morocco and beneath the eastern North American continental shelf. A series of prograding clinoforms occurs in the Baltimore Canyon area, for example, which show similar thicknesses and grainstone-dominated composition tomore » the salt-controlled buildups of the Lusitanian basin. Salt movement probably did not influence the Baltimore Canyon buildups; comparable, uniform subsidence histories may explain their similarity to the Portuguese occurrences.« less

Mechanism of subsidence of ancient cratonic rift basins

Cratonic basins commonly occur over ancient rift zones. These inactive rift basins are recognizable by a positive linear Bouguer gravity anomaly that may correspond to the axial gravity high found in modern rift valleys. Many of these basins undergo discrete periods of increased subsidence rates, or reactivations, long after the mass excess responsible for the linear gravity high was emplaced. Furthermore, the reactivation of many cratonic basins occurs simultaneously with large-scale compressional tectonics. It is suggested that the driving force for subsidence is the isostatically uncompensated ancient mass excess. The subsidence of these basins is modelled by a lithospheric flexure model with a nonlinear Maxwell viscoelastic rheology. Solutions to this model indicate that basins may experience a low subsidence rate throughout geologic time. The subsidence of a basin will stop only when isostatic compensation of the mass excess is achieved. Since ancient rift mass excesses may be uncompensated over long geologic time intervals, the early thermal and structural evolution of rifts may not significantly influence later basin subsidence. The models suggest that basins may be reactivated by any mechanism which lowers the effective viscosity of the lithospheric material, allowing the uncompensated basin to settle toward an isostatic-compensation depth faster than normal. Since viscosity is a strong function of temperature, reactivation by a world-wide increase in heat flow is suggested as a possible mechanism for the synchroneity of basin subsidence throughout a continent. An increase of 15% in the geothermal gradient, for example (from 16.5°–18.9°K/km), will cause about a 5% increase in subsidence. This increase in heat flow, however, seems unlikely of producing by itself the magnitude of basin subsidence during a reactivation phase that is observed in the geologic record where up to 100% increase in subsidence might occur. Since the rheology of the lithosphere is nonlinear, effective viscosity is also a strong nonlinear function of stress. The presence of a regional compressive stress during periods of tectonism of 1.1 · 10 8 Pa (about 2.8% of the buckling strength of the lithosphere) produces a short period of reactivated subsidence (≅ 10 5 yr). During the reactivated subsidence, the newly-imposed regional stress relaxes sufficiently in the lower lithosphere to restore the effective viscosity to values similar to that before reactivation. This suggests that reactivated subsidence caused by regional compression can be maintained as long as the stress level remains high in the lower lithosphere. This may be accomplished by an intermittent application of the regional stress over time.

THE PERMIAN LOWER EVAPORITES OF FORDON IN YORKSHIRE

Summary In the Fordon No. 1 borehole, sunk by the D’Arcy Exploration Company to a depth of 7559 feet near Scarborough, the Permian succession contains 1387 feet of evaporites. This paper describes and discusses the Lower Evaporites in detail. These are 1069 feet in thickness, and the petrography of each of the main ten subzones they contain is described. The major constituents are dolomite, anhydrite, polyhalite, kieserite and halite. Minor constituents include magnesite, glauberite, celestine, aphthitalite, pyrite, sulphoborite, sulphur and talc. Glauberite and sulphoborite are new to Britain. The origin of the rocks is discussed in relation to experimental work on salt systems. The ten subzones can be placed in three cycles of sedimentation, each ended by a relatively sudden increase in rate of subsidence, the middle cycle consisting of two sub-cycles. The upper and lower cycles are relatively simple, consisting mainly of halite and anhydrite, but the middle cycle is more complex, and contains rocks unlike any so far recorded from this country. On textural evidence it is concluded that, whereas gypsum was a primary mineral of the upper and lower cycles, the calcium sulphate of the middle cycle was deposited as anhydrite. The latter has been replaced by polyhalite on a large scale, and it is believed that this change was penecontemporaneous, and released enough calcium for the formation of a large amount of primary polyhalite. The later succession has therefore been considerably modified, and some of the polyhalite and kieserite-bearing subzones may represent the potash-free magnesium sulphate and kainite zones of the experimental succession. There is evidence of a considerable number of replacements. Most of the major ones are probably penecontemporaneous. Others are post-consolidation effects, probably due to rise of temperature and pressure during burial. Some, like those involving glauberite, have probably been effected by solutions rising from a lower cycle; others have been effected by downward or sideways moving solutions from the same or a higher cycle. Some replacements are later than movement and recrystallization of halite under pressure. A count of rhythmic layers in the middle cycle gives information on rates of deposition and suggests that this cycle may have been deposited in about 25000 years. The Fordon Lower Evaporite succession is compared with that in other parts of Yorkshire. The Fordon evidence favours Lotze’s correlation of the Lower Evaporites of Yorkshire with the Middle Zechstein of Germany.

Stratigraphic Evidence for Tectonic and Current Control of Upper Devonian Reef Sedimentation, Duhamel Area, Alberta, Canada

In the Duhamel area of central Alberta, the Upper Devonian section under study comprises in ascending order: (1) Cooking Lake formation, (2) basal calcilutite of the Duvernay formation, (3) Leduc reef, and (4) Ireton formation. In off-reef sections, the Duvernay consists of basal calcilutites and argillaceous beds overlain by bioclastic limestones and an upper sequence of brown and black shales and calcilutites, overlain by the Ireton formation. The Cooking Lake formation is composed mainly of pelletoid (pseudo-oolitic) calcarenites and calcilutites formed probably by precipitation on a widespread bank. Calcarenites were concentrated along the western side of an interpreted shoal, the margin of which trended north to north-northeast approximately along the locus of later Leduc reef growth at Duhamel. The basal Duvernay calcilutite unit is less than 10 feet thick above the Cooking Lake shoal, but increases in thickness abruptly to 50 feet directly west of the shoal margin. It is interpreted that these facies and thickness changes occurred along a tectonic hinge line caused by possible fault movement in the Precambrian basement that determined the locus of later Leduc reef growth. Leduc reef growth at Duhamel commenced essentially after the basal Duvernay calcilutite was deposited. Earliest or incipient patch-reef growth was confined to the relatively positive eastern side of the hinge line during latest Cooking Lake sedimentation. However, with differential subsidence along the aforementioned hinge line, the reefs grew laterally westward, overlapping the thickest section of basal Duvernay calcilutites, and the subsequent main reef buildup occurred on the interpreted downwarped, western side of the hinge line. The bioclastic limestone unit of the Duvernay increases in thickness toward reefs, suggesting a derivasion by erosion of actively growing reefs. The thickness distribution of bioclastic deposits indicates dominant currents from the northeast that transported a greater amount of debris to the southwestern (leeward) side of the reefs; however, thicker deposits at the southeast may have resulted from longshore current transport southward along the fore-reef side. During upper Duvernay deposition, increased subsidence resulted in mainly vertical reef growth and reduction in amount of reef erosion; only calcium carbonate and argillaceous muds accumulated more than one mile away from the reef locus. The muds were deposited in relatively deep water, resulting in dark bituminous and partly laminated rocks with a sparse benthonic fauna. Brown and black shales accumulated in greater amounts in the more protected and stagnant waters southwest (leeward) of the reefs, and only in minor amounts as far as 10 miles north and east of the Duhamel reef front. In lower Ireton time, further increase in subsidence rate removed the restricting effects of the biohermal reefs and gray-brown and green-gray calcareous shales and calcilutites were deposited in off-reef areas. Reef growth was probably terminated during lower or middle Ireton deposition. Facies and isolith maps of pertinent units in the Cooking Lake and Duvernay formations may be used as an effective new tool in the search for petroleum-bearing Leduc reefs in central Alberta.