Changes In Subsidence Rates Research Articles

The orogenic effects on forebulge evolution: A case study from Cenozoic deposits in the Salento Peninsula, Italy

The Salento Peninsula is a part of the larger Apulia Carbonate Platform, one of the carbonate platforms that have developed along the southern margin of the Tethys Ocean since the Triassic, above the Adria microplate. This peninsula represents the culmination of a lithospheric anticline formed due to the subduction of the Adria Plate beneath two mountain belts migrating in opposite directions: the Dinarides-Albanides-Hellenides (DAH) chain, moving from NE to SW, and the southern Apennines (SA) chain, moving from SW to NE. Consequently, the Salento Peninsula represents the foreland sector of these two mountain belts, whose different migration rates, deeply influenced the carbonate sedimentation and paleogeographic evolution of this area over the last 60 Myr. In our study field analysis, a database of 350 wells, and 90 seismic lines calibrated with 3 exploration wells were employed to characterize the physical stratigraphy and depositional setting of the Salento Peninsula and define its paleogeographic evolution during the Paleogene and Neogene. Our results suggest that temporal variations in sedimentation rates and types as well as the reduced thickness (maximum 200 m) of the Cenozoic stratigraphic succession in the internal sectors and both along the Adriatic and Ionian margins of the Salento Peninsula are directly or indirectly linked to the migration rates of the DAH and SA chains. These migration rates played a role in determining changes in subsidence rates, the occurrence of soft-sediment deformation, and the influx of Plio-Pleistocene fine-grained terrigenous sediments, especially along the Ionian margin. Although the investigated succession exhibits a reduced thickness, it comprises several lithostratigraphic units bounded by unconformity surfaces. Within these units, a stack of complete and incomplete simple and composite high- and low-rank depositional sequences has been recognized. Our data suggest that these units are the result of a multifold cyclicity, reflecting the close interaction between eustatic sea-level changes and the tectonic setting of the area.

The role of fluvial and tidal currents on coal accumulation in a mixed‐energy deltaic setting: Pinghu Formation, Xihu Depression, East China Sea Shelf Basin

ABSTRACTThe Eocene Pinghu Formation in the Xihu Depression of the East China Sea Shelf preserves mixed‐process deltaic deposits and contains a large number of thin coal seams. This study improves the prediction of coal seam occurrences based on facies distribution and stratigraphic architecture models of deltaic deposits, using core and wireline log datasets. Sedimentological analysis reveals four facies associations, which represent delta plain (including distributary channels and interdistributary bays), delta front, prodelta and tidal flat. These facies associations reflect and preserve the interaction of fluvial and marine processes. Delta‐plain and delta‐front deposits record progressively greater tidal influences when traced southward. Well‐log correlations show that coal‐forming mires on the tide‐influenced lower delta plain were relatively favourable for peat accumulation because the stability of the tidal channels led to a stable platform for peat accumulation on the lower delta plain. The temporal and spatial distribution of coal seams is a function of both autogenic and allogenic responses to forcing. Increased probability of frequent changes in subsidence rates and sea‐level in an active tectonic setting and erosion by channels resulted in thin single‐layer coal seams (mostly 0.5 to 1.0 m). Autogenic processes (for example, delta growth and delta lobe switching) played a significant role in the areal distribution, lateral variation in thickness (ranging from 3 to 71 m) and large cumulative thicknesses (up to 71 m) of coal seams. A general vertical decrease in coal seam thickness likely records a cooling palaeoclimate during deposition of the Pinghu Formation. By comparing delta plain processes to favourable environments of peat accumulation in modern systems with favourable mineralogical, chemical and physical conditions, it can be concluded that: (i) relatively few and discontinuous coal seams developed on the tide‐dominated delta plain generated; (ii) laterally discontinuous and ribbon‐shaped coal seams developed in tide‐influenced deltas; whereas (iii) coal seams formed in river‐dominated deltaic environments have better lateral continuity.

Investigation of the Cretaceous total petroleum system using wireline logs, core, and geochemical data in Bahrah Field, Northern Basin, Kuwait

We used wireline logs, seismic, core data, fluid analysis, and geochemical data to investigate the total petroleum system in the Cretaceous period. Also, we used thin sections and fluid analysis throughout the investigation. Python’s 1-D backstripping technique was used to determine the abrupt changes in subsidence rates and their effect on the reservoir’s quality. The results defined that the potential reservoirs include, from top to bottom, Mauddud, Upper Burgan, Lower Zubair, and Ratawi Limestone. The reservoir facies reflect different environments between the carbonate ramp (Mauddud, Ratawi Limestone, and Minagish reservoirs), delta plain (Zubair reservoir), and margin shelf (Burgan reservoir), and its quality is graded from Mauddud to Ratawi Limestone from top to bottom. The field lies up-dip under Kuwait Bay and represents the continuation of super-giant Greater Burgan Field. It filled with the spilled oil from the down-dip Raudhatain and Sabriyah fields through a structural saddle. Two major tectonic events subsided the deposited sediments by 0.25 mm/year, besides three minor events; however, these events did not affect all Cretaceous reservoirs but only according to their deposition times. Furthermore, according to burial history, thermal maturity, and reservoirs’ fluid geochemical analysis, the Sulaiy (Makhoul) and Minagish formations are likely the primary sources for all Cretaceous reservoirs.

Lacustrine source rock deposition in response to co-evolution of environments and organisms controlled by tectonic subsidence and climate, Bohai Bay Basin, China

Three Paleogene syn-rift intervals from the Bohai Bay Basin, the most petroliferous basin in China, were analyzed with sedimentological and geochemical techniques to characterize the lateral source rock heterogeneities, to reveal the environmental and ecological changes through geologic time and to construct depositional models for lacustrine source rocks under different tectonic and climatic conditions. The third (Es 3) and first (Es 1) members of the Eocene Shahejie Formation and the Oligocene Dongying Formation (Ed) display widely variable total organic carbon contents, hydrogen indices and visual kerogen compositions, suggesting changes in organic facies from deep to marginal sediments. Carefully selected deep-lake facies samples from any interval, however, display fairly uniform biomarker composition. These three intervals have distinctly different biomarker assemblages, which indicate weakly alkaline, freshwater lakes with a moderately deep thermocline during Es 3 deposition, alkaline-saline lakes with shallow chemocline during Es 1 deposition and acidic, freshwater lakes with deep, unstable thermocline during the deposition of the Dongying Formation. Such environmental changes corresponded to changes in subsidence rate and paleoclimate, from rapid subsidence and wet climate during Es 3 deposition, through slow subsidence and arid climate during Es 1 deposition to rapid subsidence and wet climate during Ed deposition and resulted in synchronous changes in terrigenous organic matter input, phytoplankton community and primary productivity. The co-evolution of environments and organisms controlled by tectonic subsidence and climate accounted for the deposition and distribution of high quality lacustrine source rocks with distinctly different geochemical characteristics. Most rift basins experienced changes in subsidence rates and possibly changes in climates during their syn-rift evolutions. The models constructed in this paper may have important implications for source rock prediction in other lacustrine rift basins.

Upper Devonian to Lower Mississippian conodont biostratigraphy of uppermost Wabamun Group and Palliser Formation to lowermost Banff and Lodgepole formations, southern Alberta and southeastern British Columbia, Canada: Implications for correlations and sequence stratigraphy

Research Article| December 01, 2010 Upper Devonian to Lower Mississippian conodont biostratigraphy of uppermost Wabamun Group and Palliser Formation to lowermost Banff and Lodgepole formations, southern Alberta and southeastern British Columbia, Canada: Implications for correlations and sequence stratigraphy David I. Johnston; David I. Johnston 103 - 3017 Blakiston Drive NW, Calgary, AB T2L 1L7, johnstda@shaw.ca Search for other works by this author on: GSW Google Scholar Charles M. Henderson; Charles M. Henderson Department of Geoscience, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, charles.henderson@ucalgary.ca Search for other works by this author on: GSW Google Scholar Michael J. Schmidt Michael J. Schmidt ConocoPhillips Canada, 401 9th Avenue SW, Calgary, AB T2P 2H7, Mike.J.Schmidt@conocophillips.com Search for other works by this author on: GSW Google Scholar Bulletin of Canadian Petroleum Geology (2010) 58 (4): 295–341. https://doi.org/10.2113/gscpgbull.58.4.295 Article history received: 23 Sep 2009 accepted: 02 Nov 2010 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation David I. Johnston, Charles M. Henderson, Michael J. Schmidt; Upper Devonian to Lower Mississippian conodont biostratigraphy of uppermost Wabamun Group and Palliser Formation to lowermost Banff and Lodgepole formations, southern Alberta and southeastern British Columbia, Canada: Implications for correlations and sequence stratigraphy. Bulletin of Canadian Petroleum Geology 2010;; 58 (4): 295–341. doi: https://doi.org/10.2113/gscpgbull.58.4.295 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 SocietyBulletin of Canadian Petroleum Geology Search Advanced Search Abstract Biostratigraphic analysis of conodont faunas from the Upper Devonian Wabamun Group, the Upper Devonian to Lower Mississippian Exshaw Formation and the Lower Mississippian Banff Formation in southern Alberta has shown that significant hiatuses may exist within the Late Devonian Big Valley and equivalent upper Costigan Member of the Palliser Formation and within the Early Mississippian lower Banff and Lodgepole formations. Minor hiatuses occur in the Late Devonian to Early Mississippian Exshaw Formation between the lower and upper members and between the equivalent lower black shale and middle sandstone members of the Bakken Formation. All of these hiatuses are interpreted to have been the result of forced regression due to uplifts. Biostratigraphic data and stratigraphic evidence derived from mapping suggest an erosional high existed at about the position of the Fifth Meridian in southwestern Alberta, as indicated by the repeated removal of Upper Devonian to Lower Mississippian strata in this area. The only other tectonic elements that may have influenced sedimentation and distribution patterns of these strata are possible deep-seated basement faults beneath the position of the Early Cretaceous Cutbank channel and the Sweetgrass Arch.The lower part of the Big Valley Formation and upper Costigan Member may represent one major episode of deposition, whereas the upper part of these units, the Exshaw Formation and the lower and middle members of the Bakken Formation appear to represent another depositional event. At least two depositional events may be represented in the lower Banff and Lodgepole formations in the study area. The depositional events and hiatuses documented in the study area generally correlate with similar events in western North America and globally. However, discordance between events in our study area and elsewhere probably reflect the masking effect of local tectonism. Correspondingly, one transgressive-regressive sequence may be recognized in the lower part of the Big Valley and upper Costigan Member. The upper part of these units, the Exshaw Formation and the lower and middle members of the Bakken Formation are interpreted as a single transgressive-regressive sequence, contrary to previous interpretations. One complete sequence and a portion of another are recognized in the lower Banff and Lodgepole formations.Many of the unconformities may be linked to Antler orogenesis, which also would have affected subsidence rates. Changes in subsidence rates interacting with eustatic sea level changes produced the stratigraphic framework and distribution of units observed in the study area. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Controls on clastic sequence geometries in a shallow‐marine, transtensional basin: the Bohemian Cretaceous Basin, Czech Republic

AbstractThe Bohemian Cretaceous Basin combines features of a shallow‐water (mostly < 100 m) epicontinental seaway formed during a global transgression with those of a tectonically active, transtensional setting. The basin formed under a greenhouse climate and was affected by strong axial currents. Dense well‐log coverage, combined with locally high‐quality exposures and biostratigraphic control, make it possible to examine in three dimensions the geometries of genetic sequences and interpret their controlling variables. Sand‐dominated deltas formed sequences at several spatial scales that reflect nested transgressive–regressive cycles with durations ranging from tens of thousands of years to millions of years. Progradation directions and distances, thicknesses and internal geometry of the individual sequences were controlled primarily by intrabasinal faulting, basin‐scale changes in subsidence rate, eustatic fluctuations and localized bathymetric changes due to successive filling of the basin. Along‐strike change in sediment input from different parts of the source area and a short‐lived uplift of a secondary clastic source provided additional controls on the sequence geometry. Efficient hypopycnal transport combined with redeposition of fine clastics in shallow water promoted development of steep slopes of sand‐dominated deltas while preventing downlap of muddy clinoforms; most of the suspended load became deposited downcurrent in subhorizontal or gently dipping bottomsets. Long‐term accommodation rates were low during the Early to Middle Turonian, with minor intrabasinal faulting, but became accelerated in the Late Turonian and Early Coniacian. This acceleration was caused at least partly by increased subsidence rate accompanied by structural partitioning of the depocentre and partly compensated by increased sediment input indicating increased uplift rates in the Western Sudetic Island source area. This event probably reflected an increase in the regional strain rate in Central Europe. The succession of two major flooding events in the Early Turonian and late Early Coniacian, separated by a low‐accommodation interval in the Middle Turonian, shows a close similarity to published estimates of long‐term eustatic curves. However, the eustatic component of accommodation rate in the Bohemian Late Turonian and Coniacian is difficult to separate from accelerated subsidence. In several cases, evidence for short‐term (100 kyr scale) forced regressions, independent of basinal structural activity, suggests small‐scale eustatic falls at rates which, as presently understood, cannot be explained other than by a glacio‐eustatic mechanism.

Long-term fluvial archives in Hungary: response of the Danube and Tisza rivers to tectonic movements and climatic changes during the Quaternary: a review and new synthesis

The paper discusses the Quaternary evolution of the Danube and Tisza rivers and their main tributaries in the context of evolution of the entire Pannonian Basin, which is Europe's largest intramontane basin, within the Alp–Carpathian orogen. The palaeo-drainage reconstruction of the Pannonian Basin for the pre-Quaternary period is outlined in connection with the gradual regression of Lake Pannon since the Late Miocene. Deltas of rivers that entered the basin from the northwest and northeast were gradually transformed into extended alluvial plains; thus, the earliest possible ancestor of the Danube coming southeastwards from the Alps could be as old as Late Miocene. By the Pliocene the whole Lake Pannon was infilled. The former extensional basin formation was replaced by a compresional stress field, which resulted in an uplift of the marginal flanks and late-stage subsidence anomalies. The increasing relief led to the formation of the Quaternary drainage pattern. The actively subsiding young basins were filled by fluvial sediments, transported by the Danube and Tisza river systems from the uplifting mountains. Between the subsiding regions of the Little and Great Plains, the Danube has formed an antecedent valley with terrace staircases between the uplifting sections of the Transdanubian Range and the North Midmountains. The formation of the terraces is attributed to periodic climate changes during the Pleistocene combined with differences in the uplift rate. The paper gives a complex overview of the classical chronology of the six terraces based on various data sources: mostly dating of loess/paleosol sequences, travertines, aeolian sand, and tephra strata overlying the fluvial sediments, complemented by scattered vertebrate faunal data and archaeological evidence directly from the terrace sediments.The Quaternary drainage pattern evolution of the Great Plain, with a strong tectonic control, is discussed in detail. Rivers originating from the uplifting marginal areas were drawn towards the subsiding depressions which served as local base level. Changes in subsidence rates in space and time throughout the Quaternary resulted in the evolution of a complex drainage pattern. A special emphasis is placed on the Late Pleistocene–Holocene development of the Middle–Tisza region and the Körös basin, where the Berettyó–Körös Rivers form an eastern tributary system of the Tisza River. A comparative evaluation of these two areas is especially relevant, as they provide insights into large-scale Late Pleistocene avulsion of the Tisza River. OSL dating, complemented with inferred transport directions determined from heavy mineral analysis of fluvial sediments in the Körös basin, has revealed an ancient large meandering river system that can be identified with the palaeo-Tisza, which was flowing along a tectonically controlled depression during the Late Pleniglacial. Successions in the Middle Tisza region have allowed differentiation between the older channels of the palaeo-Bodrog River and the Sajó–Hernád alluvial fan and the younger meander belts of the new course of the Tisza. In the Tisza system, changes in river style (braided to various scales of meandering) show correspondence to millennial-scale climate changes of the last 25ka, while in the Körös basin the effects of tectonics are overprinted onto the regional climatic signals.

FLOODPLAIN DEPOSITS AND SOIL CLASSIFICATION: THE PREDICTION OF CHANNEL SAND DISTRIBUTION WITHIN THE TRIASSIC ARGILOGRESEUX INFERIEUR, BERKINE BASIN, ALGERIA

Middle to Late Triassic fluvio‐lacustrine sandstones referred to as the Trias Argilo‐Grèseux Inférieur (TAG‐I) are an important hydrocarbon reservoir in the Algerian Berkine Basin. Three depositional sequences have been identified within the TAG‐I and a fourth sequence overlies it, forming part of the “Trias Argilo‐Carbonaté”. Subtle changes in the style of sedimentation through these sequences have been identified and are attributed to periodic rises in base‐level together with changes in subsidence rate and climate, leading to basinward, progradational shifts of the fluvial systems. The palaeoclimate changed from semi‐arid to sub‐humid with seasonal wetting and drying, as indicated by the evolved style of the deposition, the abundance of vegetation and the nature of associated palaeosols. Four main types of palaeosol profile have been identified and consist of green/grey, red, and red/brown to purple palaeosols together with green/grey to red pedogenically modified mudstones, depending on the level of maturity.The presence of sphaerosiderites in green palaeosols is a clear indication of the occurrence of wetland conditions. Palaeosol development and maturity are useful aids to stratigraphic correlation and as an indication of the proximity of reservoir channel sandstones. With improved prediction of the sandbodies’location, better models of reservoir distribution can be made leading to an enhanced field development plan

The northern Upper Rhine Graben: basin geometry and early syn-rift tectono-sedimentary evolution

A large-scale transfer zone subdivides the northern parts of the Upper Rhine Graben into a northern and a southern sub-basin. These sub-basins display the geometry of asymmetric half-grabens with opposing tilt directions. The transfer zone connects the western master fault of the northern half-graben with the eastern master fault of the southern half-graben. In the northern Upper Rhine Graben early syn-rift sedimentation (Late Priabonian to Late Rupelian) was controlled by the tectonically induced subsidence of these half-grabens (autogenetic), as well as by regional third-order sea level variations (allogenetic). Within the graben, lateral changes in subsidence rates (in dip and strike direction of fault blocks) controlled the development of accommodation space and thus, sediment thickness and facies. Furthermore, a low-displacement segment along the western border fault acted as a sediment entry point. Tectonics controlled the distribution of early syn-rift deposits and the palaeogeography of the northern Upper Rhine Graben.

Fluvial, evaporitic and shallow-marine facies architecture, depositional evolution and cyclicity in the Sivas Basin (Lower to Middle Miocene), Central Turkey

Lower to Middle Miocene rocks in the Karayün region of the Sivas Basin are represented by the Agilkaya and Egribucak Formations, forming a 4 km thick continuous section. Each formation is subdivided into three members, representing similar lithofacies. The lower members are made up of fluvial sheet-sandstone and red mudstone that migrated laterally on a flood basin within a semi-arid fan system. The middle members are composed of bedded to massive gypsum and red-green mudstone of a coastal and/or continental sabkha environment. They are intercalated with lagoonal dolomitic limestone and bituminous shale in the Agilkaya Formation and fluvial red-pink sandstone–red mudstone in the Egribucak Formation. The upper members are made up of shallow-marine fossiliferous mudstone and sandy limestone. Rapid vertical and horizontal facies changes in both formations reflect the locally subsiding nature of this molassic basin. The overall section can be also subdivided into three orders of fining-upward cycles. Type I cycles correspond to the Agilkaya and Egribucak Formations (each around 2 km thick) and indicate two long-term transgressive phases, controlled by tectono-eustatic factors. Type II cycles (140 m thick on average) are formed by alternations of fluvial sheet-sandstone and red mudstone capped by up to 50 m thick red flood basin mudstone. A 400 ka period Milankovitch cyclicity related to astronomical climatic fluctuations is suggested as a governing mechanism, although subsidence cannot be excluded. The existence of laterally persistent, fluvial sheet-sandstone overlain by red mudstone that forms fining-upward Type III cycles (10 m thick on average) is attributed to changes in subsidence rate. Rhythmic alternations between gypsum beds and red-green mudstone and/or dolomitic limestone and bituminous shale, observed in the middle members, might be related to minor periodical climatic changes rather than to tectonics.

Basin formation at a contractional bend of a large transcurrent fault: Plio-Pleistocene subsidence of the Kobe and northern Osaka Basins, Japan

The basin formation process at a contractional bend of a large transcurrent fault is studied here from the viewpoint of extensive subsidence history. The Kobe and northern Osaka Basins in southwest Japan are located at the easternmost left-stepping bend of the dextral Median Tectonic Line (MTL), a fault system activated throughout the Quaternary. Many subordinate faults in these basins accommodate compressive stress, whereas differential vertical motion of fault-bounded blocks results in complex sedimentation patterns within the basins. We compiled stratigraphic information of the Late Pliocene to Pleistocene Osaka Group using core samples of 19 drill holes distributed in the study area. On the basis of magnetostratigraphy, tephrochronology and paleoenvironmental analysis, 15 datum horizons of transgression, which are recognized as bases of marine clays (Ma −1 to 13), in cores are assigned to the oxygen isotope events. An interval accumulation rate between two successive horizons represents a cycle of eustatic sea level changes, and thus provides us with an indicator of tectonic subsidence rate. Subsidence curves and temporal changes in subsidence rates at the drill holes visualize differential subsidence in detail. The northern Osaka Basin is divided into western and eastern depocenters and the central N–S Uemachi Basement high, which grew rapidly during the Ma 7/8 interval (ca. 550 kyr), whereas the subsidence pattern in the Kobe Basin is controlled by constant vertical displacements on the NE–SW Wada-misaki Fault. An interbasinal tectonic episode of sharp decline in subsidence is also detected in the Ma 5/6 interval (ca. 670 kyr), coinciding with the Mantidani Unconformity in the Osaka Group.

Evidence for a synchronous circum‐Iberian subsidence event and its relation to the African‐Iberian plate convergence in the Late Cretaceous

Subsidence curves from Mesozoic sedimentary basins at the southern Iberian margin (Betic Cordilleras) display pronounced changes in subsidence rates around 85 Ma (chron 34, Late Cretaceous, Santonian to earliest Campanian). The subsidence events correlate with changes in the bulk and clay mineral composition in these basins, as well as with an Eoalpine high‐pressure metamorphic event in the western Mediterranean region. The synchroneity with subsidence events observed in basins around the Iberian microplate suggests a causal relationship with the regional plate tectonic setting. We propose that the circum‐Iberian subsidence event was largely controlled by the convergence and incipient collision of the Iberian microplate with Africa.

Provenance of the upper Miocene Modelo Formation and subsidence analysis of the Los Angeles basin, southern California: Implications for paleotectonic and paleogeographic reconstructions

The Los Angeles basin has undergone three stages of development related to complex plate interactions within the evolving San Andreas transform system: transrotation (16–12 Ma), transtension (12–6 Ma), and transpression (6–0 Ma). Timing of these stages correlates with microplate-capture events along the continental margin, and is expressed in changes in subsidence rates and provenance within the Los Angeles basin. The Modelo Formation and related units were deposited in the northern part of the Los Angeles basin at bathyal depths during late Miocene time. The northern Los Angeles basin was segmented into three subbasins, in each of which coarse sediment was deposited as submarine fans (Puente, Tarzana, and Simi). A fourth fan system (Piru) formed in the Ventura basin, just north of the Los Angeles basin. The Puente, Tarzana, and Piru fans were derived from the San Gabriel block, which consists primarily of crystalline basement and lesser volcanic and sedimentary components. Sandstone within the Puente fan reflects unroofing of the central and eastern San Gabriel block. The Tarzana fan was derived primarily from the central San Gabriel block, and the Piru fan was derived primarily from the western San Gabriel block, which is distinctly characterized by Ca-rich plagioclase derived from Proterozoic anorthosite and related bodies. The lack of Ca-rich plagioclase in the other fans eliminates the western San Gabriel block as a possible source area, and confirms differentiation of the Ventura basin from the Los Angeles basin by late Miocene time. The Simi fan was derived from locally uplifted Cretaceous and Paleogene strata; sandstone composition reflects the recycling of these sediments. Subsidence and provenance analyses are consistent with the following paleogeographic and paleotectonic reconstruction. Beginning at approximately 16 Ma, transrotation of the Western Transverse Ranges induced extension and thermal subsidence of the Los Angeles basin area. A second pulse of extension and thermal subsidence occurred when motion began along the San Gabriel fault at 12 Ma. Right slip of 60–70 km occurred along the San Gabriel fault, which produced transtension in the Los Angeles basin area and deposition of the Puente, Tarzana, Simi, and Piru fan systems. At 6 Ma, transform motion was transferred to the San Andreas fault; transpression has dominated the Los Angeles basin since 6 Ma, including rapid uplift, flexural subsidence due to tectonic loading, and rapid sedimentary filling. The rapid subsidence and filling and the sudden switch between transtension and transpression in the Los Angeles basin are typical of strike-slip basins in general. However, initiation of the Los Angeles basin by transrotation reflects the uncommon process of microplate capture along the rapidly evolving California margin.

Evolution of Miocene fluvial environments, eastern Potwar plateau, northern Pakistan

ABSTRACTThe Miocene‐Pliocene Siwalik Group records changing fluvial environments in the Himalayan foreland basin. The Nagri and Dhok Pathan Formations of this Group in the eastern Potwar Plateau, northern Pakistan, comprise relatively thick (tens of metres) sandstone bodies and mudstones that contain thinner sandstone bodies (metres thick) and palaeosols. Thick sandstone bodies extend for kilometres normal to palaeoflow, and are composed of large‐scale stratasets (storeys) stacked laterally and vertically adjacent to each other. Sandstone bodies represent single or superimposed braided‐channel belts, and large‐scale stratasets represent channel bars and fills. Channel belts had widths of km, bankfull discharges on the order of 103 cumecs and braiding parameter up to about 3. Individual channel segments had bankfull widths, maximum depths, and slopes on the order of 102 m, 101 m and 10−4 respectively, and sinuosities around 1‐1. These rivers are comparable to many of those flowing over the megafans of the modern Indo‐Gangetic basin, and a similar depositional setting is likely. Thin sandstone bodies within mudstone sequences extend laterally for on the order of 102 m and have lobe, wedge, sheet and channel‐form geometries: they represent crevasse splays, levees and floodplain channels. Mudstones are relatively bioturbated/disrupted and represent mainly floodbasin and lacustrine deposition. Mudstones and sandstones are extremely disrupted in places, showing evidence of prolonged pedogenesis. These ‘mature’ palaeosols are m thick and extend laterally for km. Lateral and vertical variations in the nature of their horizons apparently depend mainly on deposition rate.The 500 m‐thick Nagri Formation has a greater proportion and thicker sandstone bodies than the overlying 700 m‐thick Dhok Pathan Formation. The thick sandstone bodies and their large‐scale stratasets thicken and coarsen through the Nagri Formation, then thin and fine at the base of the Dhok Pathan Formation. Compacted deposition rates increase with sandstone proportion (0‐53 mm/year for Nagri, 0‐24 mm/year for Dhok Pathan), and palaeosols are not as well developed where deposition rates are high. Within both formations there are 100 m‐scale variations (representing on the order of 105 years) in the proportion and thickness of thick sandstone bodies, and tens‐of‐m‐scale alternations of thick sandstone bodies and mudstone‐sandstone strata that represent on the order of 104 years. Formation‐scale stratal variations extend across the Potwar Plateau for at least 100 km, although they may be diachronous: however, 100‐m and smaller scale variations can only be traced laterally for up to tens of km.Alluvial architecture models indicate that increases in the proportion and thickness of thick sandstone bodies can be explained by increasing channel‐belt sizes (mainly), average deposition rate and avulsion frequency on a megafan comparable in size to modern examples. 100‐m‐scale variations in thick sandstone‐body proportion and thickness could result from ‘regional’ shifts in the position of major channels, possibly associated with ‘fan lobes’on a single megafan or with separate megafans. However, such variations could also be related to local changes in subsidence rate or changes in sediment supply to the megafan system.Formation‐scale and 100‐m‐scale stratal variations are probably associated with interelated changes in tectonic uplift, sediment supply and basin subsidence. Increased rates of hinterland uplift, sediment supply and basin subsidence, recorded by the Nagri Formation, may have resulted in diversion of a relatively large river to the area. Alternatively, changing river sizes and sediment supply rates may be related to climate changes affecting the hinterland (possibly linked to tectonic uplift). Climate during deposition of the Siwalik Group was monsoonal. Although the deposits contain no direct evidence for climate change, independent evidence indicates global cooling throughout the Miocene, and the possibility of glacial periods (e.g. around 10‐8 Ma, corresponding to base of Nagri Formation). If the higher Himalayas were periodically glaciated, a mechanism would exist for varying sediment supply to megafans on time scales of 104‐105 years. Although eustatic sea‐level changes are related to global climatic change, they are not directly related to Siwalik stratigraphic changes, because the shoreline was many 100 km away during the Miocene.

Downstream Changes In Alluvial Architecture: An Exploration of Controls on Channel-stacking Patterns

ABSTRACT Various, but related, models have been proposed to explain the architectural arrangement of channel stacking patterns in avulsion-dominated alluvial sequences. The early models published by Leeder, Allen, and Bridge (LAB) addressed the role of changes in sedimentation rate (a proxy for subsidence rate) as a control on stacking patterns. The models decouple avulsion frequency from sedimentation rates, resulting in an inverse relationship between stacking density (or interconnectedness) and sedimentation rates. A key element missing from these models is the likely dependence of avulsion frequency on local sedimentation rate within the active channel belt. We consider a simple model whereby avulsion takes place only when a minimum, critical, relief is developed between a channel bank and the adjacent flood plain. If avulsion frequency increases at rates slower than the increase in sedimentation rate, then stacking density increases with decreasing sedimentation rate, similar to that predicted by the LAB models. However, if avulsion frequency increases linearly with sedimentation rate, then there is no change in stacking pattern with changes in sedimentation rate. If avulsion frequency increases faster than sedimentation rates, as seen in some data sets, then stacking patterns become more dense with increasing sedimentation rates, a result that is the exact opposite of that predicted by the LAB models. Therefore sensitive dependence on the relationship between avulsion frequency and sedimentation rate calls into question the veracity of some previous interpretations of re ative subsidence made in alluvial architecture studies. We provide an alternative, simple geometric model that links changes in subsidence rate to downstream rate of change in stacking pattern as seen in three dimensions within sedimentary basins. Other controls that are considered include: the geometry of subsidence; whether avulsions take place locally along a river or regionally affect the basin; whether local sedimentation rate or flow depth controls the thickness of sand bodies; and the exact relationship between avulsion frequency and sedimentation rate. The primary result of the model is that subsidence strongly influences the rate at which alluvial architecture changes in the downstream direction, but other controls dictate whether the stacking pattern becomes more dense or less dense downstream. Hence, we suggest that subsidence e erts an influence on stacking patterns not necessarily evident in individual vertical sections, but may be recorded in three dimensions as downstream changes in alluvial architecture. Unfortunately any model of alluvial architecture in avulsion-dominated sequences is limited by our lack of understanding of the processes controlling avulsion. As a result any model of alluvial stacking patterns is at best a working hypothesis that should not be taken as proof of changes in tectonic subsidence rates or sea-level changes.

INFLUENCE OF PLATE TECTONIC RE-ORGANISATIONS AND TECTONIC SUBSIDENCE ON THE MESOZOIC STRATIGRAPHY OF NORTHWESTERN AND SOUTHEASTERN AUSTRALIA: IMPLICATIONS FOR SEQUENCE STRATIGRAPHIC ANALYSIS

Determining and predicting the interplay of plate tectonic events, subsidence, flexure and depositional systems is important in frontier exploration, play concept development, and maturation modelling. A circum-Australian plate tectonic model is here tied to an internally consistent global plate tectonic model to determine the timing and orientation of changes in the lithospheric stress regime induced by plate tectonic changes. One-and three-dimensional geohistory results for the Otway Basin and North West Shelf/Exmouth Plateau are presented, based on an integrated sequence stratigraphic framework. These geohistory results compare the timing and types of changes in subsidence rate to the changes in lithospheric stress due to plate tectonic changes. Changes in tectonic subsidence rate appear to be discrete events related to plate tectonic changes; subsidence events bound major transgressive-regressive facies cycle packages ('supersequences') in a basin. The recognition of sequence system tracts and especially system tract boundaries within a 'supersequence' is enhanced or diminished by processes occurring only during certain phases of the supersequences. Recognition of lowstand systems tracts and sequence boundaries is improved due to erosion during the regressive phase of the supersequence. Conversely, during the transgressive phase of the supersequence, transgressive and highstand system tracts are emphasised and recognition of flooding surfaces improved. Good reservoir sands form during enhanced lowstands, while good source and sealing shales form during enhanced transgressions.In the southeastern Australian Otway Basin, every perturbation of the tectonic subsidence rate during the Late Cretaceous can be correlated directly to a local and/or global plate tectonic event, and each supersequence is bounded by tectonic events. In the North West Shelf/Exmouth Plateau region of Western Australia, the situation is complicated during the Berriasian by uncompensated f lexural load effects related to the rapid formation and filling of multiple Barrow Delta depocentres. Two supersequences correlate to tectonic events, while one supersequence is bounded by a f lexural subsidence event unrelated to regional or global plate tectonic events. Hence not all perturbations of the tectonic subsidence curve are related to tectonic events, and not all supersequences are bound by tectonic events. Without three-dimensional geohistory techniques, it is impossible to isolate the flexural load effects from the effects of plate tectonic events.

Neogene Evolution of the North New Guinea Basin, Papua New Guinea: New Constraints from Seismic and Subsidence Analysis and Implications for Hydrocarbon Exploration: ABSTRACT

The present-day North New Guinea basin is a Plio-Pleistocene successor basin that formed subsequent to accretion of the Finisterre volcanic arc to the Australian Plate. The Ramu, Sepik, and Piore infrabasins formed in a forearc setting relative to the continental Maramuni magmatic arc. The evolution of these infrabasins was strongly influenced by accretion of the composite Torricelli-Prince Alexander terrane to the Australian Plate. Regional reflection seismic data and tectonic subsidence-subsidence rate calculations for seven wells drilled in the North New Guinea basin reveal a complex history. The timing and magnitude of subsidence and changes in subsidence rates differ between each of the Miocene infrabasins. A diachronous middle to late Miocene unconformity generally truncates infrabasin sequences. The Nopan No. 1 in the Sepik basin, however, has a complete middle Miocene to Pleistocene sedimentary record. This well records late Miocene negative subsidence rates documenting that the Nopan anticline grew as erosion occurred elsewhere in the region. This circumstance suggests that the major, sequence-bounding unconformity results from regional uplift and deformation, rather than changes in global sea level. The Plio-Pleistocene evolution of the North New Guinea basin has two profound implications regarding hydrocarbon exploration. First, the late Pliocene structural inversion of parts ofmore » the basin hinders stratigraphic and facies correlation inferred from the present setting. The recognition of basin inversion is particularly important in the Piore basin for predicting the distribution of potential reservoir facies in the Miocene carbonates. Second, the subsidence data suggest that although potential source rocks may be thermally within the oil window, these rocks may not have had sufficient time to mature owing to their recent burial.« less

Oceanic transform structures and the development of Atlantic continental margin sedimentary basins—a review

Atlantic sedimentary basins are classified into 3 types: (1) tensional rift basins (simple elongate basins and fracture zone end basins), (2) sheared margin basins (fracture zone parallel and fracture ridge dammed basins), and (3) taphrogenic basins. During the early phase of ocean opening, wrench tectonics occur ams offset continential margins, producing splay faulting relative to some transform directions; this influences the formation of fracture zones end and fracture zone parallel basins. Dammed basins develop against fracture zone ridges along large offset sheared margins. In taphrogenic basins of southern S America extant fracture zones follow Palaeozoic lines of weakness across the continent. Basement structures influence the location of some transform directions, particularly in the equatorial Atlantic, and there is some evidence to suggest a link between changes in subsidence rates and the shift in location of poles of opening on sedimentation rates. The asymmetry of basin development on opposing sides of the Atlantic is partially ascribed to the grain of the coastal geology and partly to differential subsidence rates caused by anomalous or asymmetric development of the adjacent ocean floor.