Tectonics versus eustatic control on supersequences of the Zagros Mountains of Iran

At least 12 km of strata ranging in age from the latest Precambrian to the Recent are exposed in the Zagros Mountains of Iran. This sedimentary cover is characterized by distinct stratal packages separated by major unconformities forming twelve supersequences. They are informally named as: (1) Late Precambrian – Cambrian Hakhamanesh Supersequence, (2) Ordovician Kourosh Supersequence, (3) Silurian Camboojiyeh Supersequence, (4) Devonian Darioush Supersequence, (5) Mississippian – Pennsylvanian Khashayar Supersequence, (6) Permian – Triassic Ashk Supersequence, (7) Jurassic Farhad Supersequence, (8) Early Cretaceous Mehrdad Supersequence, (9) Late Cretaceous Ardavan Supersequence, (10) Paleocene – Oligocene Sassan Supersequence, (11) Oligocene – Miocene Ardeshir Supersequence, and (12) Miocene – Pleistocene Shapour Supersequence. These supersequences and their correlatives in neighboring areas have been used to infer tectonic events. The dominant interpretation has been that local or regional epeirogenic movements were responsible for the formation of these supersequences. Unconformities are considered as indications that epeirogenic movements associated with tectonic events affected the area. The present investigation provides an alternative to the established view of the Phanerozoic supersequences of the Zagros Mountains.

A good correlation exists between the lithofacies of supersequences in the Zagros Mountains and the second-order eustatic sea-level changes. Deposition of deep-water, marine shales occurred during periods of eustatic sea-level rise. Platform-wide unconformities coincided with eustatic sea-level lows. In fact, supersequences of the Zagros Mountains are nearly identical to those described from the North American Craton and the Russian Platform suggesting that these stratal packages are global. These observations suggest that supersequences of the Zagros Mountains formed by second order eustatic sea-level changes and not by local or regional epeirogenic movements.

Although tectonic events did not produce supersequences of the Zagros Mountains, they influenced regional lithofacies patterns through the formation of intrashelf depressions such as the Hormoz Salt Basin during the Precambrian and the Dezful Embayment and the Lorestan Basin during the Mesozoic. Tectonic events also affected sedimentation during the Tertiary collision of Arabia and the Central Iran microplate through uplift, erosion, and the formation of the Zagros Foreland Basin. The results of this investigation necessitate a re-evaluation of the role and the significance of pre-Tertiary tectonic events commonly used to interpret the geological evolution of the Zagros Mountains.     

Third-order depositional sequences controlled by synsedimentary extensional tectonics: evidence from Upper Triassic carbonates of the Carnian Prealps (NE Italy)

ABSTRACT The Upper Triassic platform-margin deposits of the Carnian Prealps fail to show the succession of the two global sea-level lowerings predicted for the Norian and Rhaetian by the Haq global sea-level curve. In both cases a relative sea-level rise occurs, a discrepancy that can be explained by an increase in tectonically controlled subsidence, a consequence of the plate-scale rifting in the NW Tethys Gulf preceding oceanic spreading in the Jurassic. Pulses of tectonic subsidence followed by relative quiescence are capable of generating depositional sequences similar in gross geometry and duration to the third-order eustatic cycles of Haq et al . The Late Triassic part of the Exxon global sea-level curve, partly derived from correlatable strata within the same palaeogeographical domain, is likely to reflect pulses of tectonically induced subsidence rather than eustatic sea-level changes.     

Rates of Holocene isostatic uplift and relative sea-level lowering of the Baltic in SW Finland based on studies of isolation contacts

Southwestern Finland was covered by the Weichselian ice sheet and experienced rapid glacio-isostatic rebound after early Holocene deglaciation. The present mean overall apparent uplift rate is of the order of 4-5 mm/yr, but immediately after deglaciation the rate of crustal rebound was several times higher. Concurrently with land uplift, relative sea level in the Baltic basin during the past more than 8000 years was also strongly affected by the eustatic changes in sea level. There is ample evidence from earlier studies that during the early Litorina Sea stage on the southeastern coast of Finland around 7000 yr BP (7800 cal. yr BP), the rise in sea level exceeded the rate of land uplift, resulting in a short-lived transgression. Because of a higher rate of uplift, the transgression was even more short-lived or of negligible magnitude in the southwestern part of coastal Finland, but even in this latter case a slowing down in the rate of regression can still be detected. We used evidence from isolation basins to obtain a set of 71 ¹⁴C dates, and over 30 new sea-level index points. The age-elevation data, obtained from lakes in two different areas and located between c. 64 m and 1.5 m above present sea level, display a high degree of internal consistency. This suggests that the dates are reliable, even though most of them were based on bulk sediment samples. The two relative sea-level curves confirm the established model of relatively gradually decreasing rates of relative sea-level lowering since c. 6100 yr BP (7000 cal. yr BP) and clearly indicate that the more northerly of the two study areas experienced the higher rate of glacio-isostatic recovery. In the southerly study area, changes in diatom assemblages and lithostratigraphy suggest that during the early Litorina Sea stage (8300-7600 cal. yr BP) eustatic sea-level rise exceeded land uplift for hundreds of years. Evidence for this transgression was discovered in a lake with a basin threshold at an elevation of 41 m above sea level, which is markedly higher than any previously known site with evidence for the Litorina transgression in Finland. We also discuss evidence for subsequent short-term fluctuations superimposed on the main trends of relative sea-level changes.     

Sea-level change, carbon cycling and palaeoclimate during the Late Cenomanian of northwest Europe; an integrated palaeoenvironmental analysis

A new high resolution sea-level curve for the Late Cenomanian M. geslinianum Zone has been generated using sequence stratigraphic analysis on transects through the margins of the Anglo-Paris Basin in the UK and Saxony Basin in Germany. Transgressive sediments that bury a rocky shoreline in the Dresden area have proved particularly useful in determining both the absolute amount of sea-level change and the rate of rise. After a brief fall at the base of the M. geslinianum Zone, sea level rose rapidly through the higher part of the zone, resulting in an overall short term eustatic rise of 22–28 m. Biostratigraphy and carbon isotope stratigraphy have enabled detailed correlations to be made between marginal locations and thick, relatively complete, basinal successions. The basinal successions at Eastbourne, UK, and Gröbern, Germany, provide both geochemical proxies for palaeoenvironmental change, including oxygen and carbon isotope records, and an orbital timescale graduated in precession and eccentricity cycles. Integration of the sea-level history with palaeoclimate evolution, palaeoceanography and changes in carbon cycling allows a detailed reconstruction of events during the Late Cenomanian. Orbital forcing on long eccentricity maxima provides the underlying drive for these changes, but amplification by tectonic events and feedback mechanisms augmented the orbital effects and made the Cenomanian/Turonian Boundary Event distinctive. In particular, variations in atmospheric CO₂ caused by oceanic drawdown and a brief period of intense volcanic outgassing resulted respectively in short term cooling and warming events. The magnitude and high rates (up to 1 m/1 kyr) of sea-level rise are diagnostic of glacioeustasy, however improbable this may appear at the height of the Cretaceous greenhouse.     

Facies sequences on a carbonate ramp: the Carboniferous Limestone of South Wales

During early Carboniferous times a major sea-level rise led to the development of an extensive carbonate ramp over what is now South Wales. Differential subsidence and sea-level changes resulted in distinctive facies sequences in the ramp succession and a model is offered which recognizes three distinct geomorpho-tectonic settings; inner, mid- and outer ramp. The inner ramp zone occurs in the more landward part of the province and was an area undergoing little or no subsidence. The sequence is dominated by oolitic grainstones and peritidal limestones representing shoal and back shoal environments. The peritidal units are transgressive deposits consisting of stacked asymmetrical shallowing-up cycles. The sequence contains many subaerial breaks and tectonic uplift resulted in base-level changes and fluvial incision. The mid-ramp zone sequence is intermediate in thickness between the inner and outer ramp successions and consists mainly of bioclastic limestones deposited below fairweather wave base. Sedimentation periodically exceeded sea-level rise and subsidence, and regressive (progradational) oolitic sand bodies developed, the thickest of which are stacked units with up to four individual sand bodies. Storm processes were of major importance in this setting. The outer ramp zone is represented by a thick sequence of muddy bioclastic limestones deposited below storm wave base and major Waulsortian reef-mounds also developed. None of the shallowing phases seen in the other ramp zones can be detected in this sequence. Subsidence and eustatic sea-level rise seem to have been the major controls on deposition but the recognition of eustatic sea-level falls is difficult. The detailed facies model for ramp carbonates presented here may be applicable elsewhere in the geological record.     

Eustatic control of late Quaternary sea-level change in the Arabian/Persian Gulf

Accurate sea-level reconstruction is critical in understanding the drivers of coastal evolution. Inliers of shallow marine limestone and aeolianite are exposed as zeugen (carbonate-capped erosional remnants) on the southern coast of the Arabian/Persian Gulf. These have generally been accepted as evidence of a eustatically driven, last-interglacial relative sea-level highstand preceded by a penultimate glacial-age lowstand. Instead, recent optically stimulated luminescence (OSL) dating suggests a last glacial age for these deposits, requiring > 100 m of uplift since the last glacial maximum in order to keep pace with eustatic sea-level rise and implying the need for a wholesale revision of tectonic, stratigraphic and sea-level histories of the Gulf. These two hypotheses have radically different implications for regional neotectonics and land–sea distribution histories. Here we test these hypotheses using OSL dating of the zeugen formations. These new ages are remarkably consistent with earlier interpretations of the formations being last interglacial or older in age, showing that tectonic movements are negligible and eustatic sea-level variations are responsible for local sea-level changes in the Gulf. The cause of the large age differences between recent studies is unclear, although it appears related to large differences in the measured accumulated dose in different OSL samples.     

塔里木盆地寒武-奥陶纪海平面升降变化规律研究

利用元素地球化学特征和地震几何构型特征,对塔里木盆地寒武-奥陶纪时期海平面升降变化规律进行了研究,建立了寒武-奥陶纪相对海平面变化曲线。研究发现,塔里木盆地寒武-奥陶纪可划分出3个一级旋回,8个二级旋回,17个三级旋回和多期高频震荡旋回。其中,寒武纪经历了3期二级旋回,早中奥陶世经历了2期旋回。相对于寒武纪,早奥陶世海平面升幅较大。晚奥陶世经历了3期二级旋回：第一期处于海平面低位期,幅度较小;后二期快速上升,直达最高水位状态。海平面相对升降变化控制着盆地的沉积充填和层序的形成演化,其旋回性与盆地沉积作用的旋回性相一致,并可通过沉积相的演变表现出来。     

Tectonic control on peritidal carbonate parasequence formation: an investigation using forward tectono-stratigraphic modelling

Studies of Quaternary extensional faults indicate that they have instantaneous amounts of throw (0·4 to 4 m), average slip rates (0·05 to 2·8 m kyr⁻¹) and frequency of recurrence (<40 000 years) accounting for the accommodation space required for the accumulation of peritidal carbonate parasequences (PCPs). Hangingwall sites and graben are characterized by fault down-dropping together with regional subsidence, and footwall sites and horsts by fault-related uplift alternating with periods of regional subsidence. The relative sea-level curves generated by these processes operating in a maritime rift setting are used as inputs to a forward stratigraphic modelling program SedTec2000 to simulate how fault-related changes in accommodation space can account for high-frequency PCP formation. Each instantaneous fault slip generates a flooding surface or aggradation in hangingwall and graben settings. High-frequency cycles in hangingwall sites are either symmetric (deepening then shallowing upward) or asymmetric (shallowing-upward). The major factor controlling cycle types is the balance between rates of carbonate accumulation and generation of accomodation space. High-frequency cycles in footwall sites and horsts comprise shallow subtidal facies, with no distinctive bathymetric trends, capped by erosional boundaries generated by footwall uplift. The modelled cycles are of the same thickness, with bathymetric trends and frequency to cycles commonly interpreted to be due to orbitally driven eustatic sea-level changes or autocyclic processes. These numerical experiments demonstrate that high-frequency PCPs can be generated by tectonic, fault-related processes, a hypothesis that is frequently discounted.     

Third-order depositional sequences reflecting Milankovitch cyclicity

The origin of third-order depositional sequences remains debatable, and in many cases it is not clear whether they were controlled by tectonic activity and/or by eustatic sea-level changes. In Oxfordian and Berriasian–Valanginian carbonate-dominated sections of Switzerland, France, Germany and Spain, high-resolution sequence-stratigraphic and cyclostratigraphic analyses show that the sedimentary record reflects Milankovitch cyclicity. Orbitally induced insolation changes translated into sea-level fluctuations, which in turn controlled accommodation changes. Beds and bedsets formed in rhythm with the precession and 100-kyr eccentricity cycles, whereas the 400-kyr eccentricity cycle contributed to the creation of major depositional sequences. Biostratigraphical data allow the correlation of many of the 400-kyr sequence boundaries with third-order sequence boundaries recognized in European basins. This implies that climatically controlled sea-level changes contributed to the formation of third-order sequences. Furthermore, this cyclostratigraphical approach improves the relative dating of stratigraphic intervals.     

Cretaceous to Eocene sea-level fluctuations on the New Jersey margin

The New Jersey margin contains an extensive record of Cretaceous to Eocene sea-level fluctuations. These events have been documented on the basis of sedimentology, benthic foraminiferal paleobathymetry (paleoslope), biostratigraphic recognition of unconformities and their associated hiatuses, and on seismic reflection records. The record of sea-level change for the New Jersey margin shows a long-term (second-order) rise beginning in the upper Albian that is punctuated by numerous third-order cycles of change in the Upper Cretaceous, Paleocene, and Eocene. The sequences deposited during these cycles that are most readily recognizable, are separated by type 1 unconformities. Sequences bracketed by one or two type 2 unconformities are more difficult to resolve, although many have been identified. Sequences shown on the cycle chart of Haq et al. (1987) of less than 1 Ma duration are the most difficult to recognize and many have not been identified in the New Jersey section.

Benthic foraminiferal paleoslope studies indicate that relative sea-level rise on the New Jersey margin varied on the order of 10–120 m above present sea level. Much of the preserved record in the coastal plain consists of sediments deposited during rising sea level. This has led to a stacked record of sea-level rise events separated by unconformities.     

Neotectonics, sea-level changes and biological evolution in the Fennoscandian Border Zone of the southern Kattegat Sea

Shallow seismic data and vibrocore information, sequence stratigraphic and faunal evidence have been used for documentation of Late Weichselian reactivation of faulting in the south central Kattegat, southern Scandinavia. The study area is situated on the Fennoscandian Border Zone, where tectonic activity has been recurrent since Early Palaeozoic time and still occurs, as shown by present earthquake activity. New data from the area south of the island of Anholt show that after deglaciation fast isostatic rebound resulted in reactivation of a NW-SE striking normal fault system. This tectonic episode is dated to a period starting shortly before 15.0 cal. ka BP and ending around 13.5 cal. ka BP, after regression had already reached a level of about 30 m b.s.l. The vertical displacement associated with the faulting was in the order of 20 m. More generally, the results support the previously reported late Weichselian sea-level highstand, which was followed by forced regression until the eustatic sea-level rise surpassed the rate of glacio-isostatic rebound in early Preboreal. Our findings further imply that drainage of the Baltic Ice Lake through the Øresund at c. 15 cal. ka BP (Bergsten & Nordberg 1992) may have been triggered by tectonic activity in this region.     

扬子东南大陆边缘晚元古代—早古生代层序地层和盆地动力演化

扬子东南大陆边缘晚元古代－早古生代层序地层和盆地动力演化刘宝珺，许效松，徐强（成都地质矿产研究所）扬子板块早古生代的形成和演化对中国古大陆的板块构造演化有重大意义，本文试图通过用新发展起来的露头层序地层方法和沉积盆地演化分析来阐明其变化规律。在扬子板...     

Foraminiferal depth palaeoecology of Late Pliocene shelf sequences and systems tracts, Wanganui Basin, New Zealand

High-resolution foraminiferal census of benthic taxa was undertaken on 113 closely spaced samples drawn from the Late Pliocene (ca. 2.6−1.7 Ma) cyclothemic marine strata of the Rangitikei Group, eastern Wanganui Basin, New Zealand. These strata comprise a ca. 1 km thick progradational stack of twenty, sixth-order, depositional sequences that accumulated in shelf and shoreline palaeoenvironments. The sequences are correlated with δ¹⁸O Stages 100−58, and each 41 ka glaciallinterglacial stage couplet is represented by an individual sequence comprising transgressive (TST), highstand (HST), and regressive (RST) systems tracts.

Statistical analysis of the census data identifies thirteen foraminiferal associations within the cyclothemic strata, that are grouped into seven depth- and lithology-related biofacies spanning the entire range of marginal marine to outer shelf palaeoenvironments. Foraminiferal palaeobathymetric analysis of the Rangitikei Group sequences reveals cyclical changes in water-depth of ca. 100–200 m amplitude with frequencies corresponding to the 41 ka obliquity orbital rhythm. Water-depth changes of this magnitude are consistent with a glacio-eustatic origin for the cyclothems, which correspond to an interval of Earth's history when successive continental glaciations of the Northern Hemisphere are known to have occurred. Furthermore the derived water-depth changes are also consistent with lithofacies and sequence stratigraphic inferences regarding palaeodepth of the sequences.

Individual sequences display a clear deepening-upward trend from shoreline to mid-shelf water-depths within TSTs. The level of resolution provided by the microfaunal analysis was insufficient to resolve the precise position of the maximum flooding surface (MFS) and its relationship to the downlap surface (DLS). However, the turn around from rising to falling relative sea level (maximum water-depth) corresponds to a < 5 m interval of section spanning the top of TSTs and lower portions of HST's. A progressive shoaling trend to shoreline and marginal marine environments is indicated for the overlying RSTs.

The amplitudes of water-depth changes for asymmetrical sequences, Rangitikei_nt motif (nondepositional transgression) (100–200 m), are somewhat greater than glacio-eustatic sea-level changes derived from the deep-sea δ¹⁸O record (50–100 m). This implies a significant subsidence contribution to relative sea-level changes. Notwithstanding the effect of subsidence and sedimentation on relative sea level, fluctuations in glacio-eustatic sea level are regarded as the primary factor controlling relative sea-level changes recorded in the Late Pliocene Wanganui Basin succession. Foraminifer-derived palaeobathymetric cycles within sequences display the same frequency, relative magnitude and symmetry as their correlative cycles on the δ¹⁸O sea-level curve.     

Facies Associations and Discontinuous Surfaces in the Syringothyris Limestone Formation of Tethyan Margin of Gondwana,Kashmir

The early Carboniferous sedimentation of the Tethyan Margin of Gondwana in the Kashmir Himalaya represents alternating siliciclastic - carbonate succession consisting of distinct stratigraphic sequences which are bounded by discontinuities. The discontinuities in the sedimentation are related to environmental changes in the form of subaerial exposure, subaqueous erosion, subaqueous omission or changes in texture and facies. These distinct surface zones or time significant boundaries can be correlated across the depositional platform. Low stand, high stand and transgressive sedimentation units in the lower and middle parts of early Carboniferous Syringothyris Limestone Formation in Banihal area have been recognised. This is explained by superposition of high frequency and low amplitude sea level fluctuations on a large-scale trend under greenhouse conditions during the early Carboniferous period. The facies associations present in the early Carboniferous succession of the Himalaya broadly represent intertidal (peritidal), shallow subtidal, deeper subtidal, off-shore-slope and deeper environments. Discontinuities that are interpreted as progradational, retrogradational and aggradational phases of sedimentation bound these facies associations. This formation represents continental margin depositional setting which is authenticated by deposition of siliciclastic sediments. This marginal depositional setting is greatly affected by numerous dynamic processes including tectonic and other active sea as well as continental processes. The records of all those processes in this formation reflect the eustatic changes in sea level. These periodic eustatic changes have generated the various discontinuities, stratigraphic sequences or systems tracts. Overall it appears that interplay of many processes such as sediment supply, thermal and tectonic activity, eustatic and climatic changes in the Kashmir Tethyan depositional basin generated these distinct depositional sequences during the early Carboniferous period.     

End-signature of deep-marine basin-fill, as a structurally confined low-gradient clastic system: the Middle Eocene Guaso system, South-central Spanish Pyrenees

The ca 300 m thick Guaso system is the youngest part of the ca 4 km thick deep-marine fill of the Middle Eocene Ainsa basin, Spanish Pyrenees. It is overlain by 150 to 200 m of fine-grained slope, prodelta and deltaic sediments. The ca 25 discrete deep-marine sandbodies within the Ainsa basin accumulated over ca 10 Myr, making eustasy the most likely control for coarse sand deposition (probably the ca 400 kyr Milankovitch mode). The first-order control on basin-scale accommodation, however, was tectonically-driven subsidence. Previously, the Guaso sandbodies were interpreted as linked to deep erosional, canyon-like features, but here it is argued that they are laterally extensive sandbodies, built by lateral-switching of 3 to 10 m deep erosional channels, and confined only by basin structure during deposition. The Guaso system represents the end of deep-marine deposition in a structurally-confined, delta-fed, low-gradient clastic system. The critical end-signature of deep-marine deposition was a phase of differential tectonic uplift above the underlying (Boltaña) thrust creating a narrower and shallower basin morphology, thus allowing sedimentation to create a low-gradient clastic system. Then, the next eustatic sea-level fall was insufficient to permit the cutting of canyons or deeply-incised slope channels, as had been the case earlier when the topographic relief between shelf and basin was at least several hundred metres greater. Such low-gradient clastic systems may characterize the end-signature for the infill of other shallowing-up deep-marine basins where a tectonic driver on subsidence is removed and/or differential uplift/subsidence leads to reduced sea floor gradients, leaving eustasy and sediment flux as the principal control on sediment supply.     

Contribution of regional climate drivers to future winter sea-level changes in the Baltic Sea estimated by statistical methods and simulations of climate models

A statistical downscaling approach is applied to the output of five different global climate model simulations driven by twenty-first century future scenarios of greenhouse gas concentrations. The contribution of sea-level pressure (SLP) and precipitation changes to regional future winter sea-level changes is estimated for four Baltic sea-level stations by establishing statistical relationships between sea level as predictand and large-scale climate fields as predictors. Using SLP as predictor for the central and eastern Baltic Sea level stations, three climate models lead to statistically significant twenty-first century future trends in the range of the order of 1–2 mm/year. Using precipitation as predictor for the stations in the southern Baltic coast all five models lead to statistically significant trends with a range of the order of 0.4 mm/year. These numbers are smaller, but of the order of magnitude as the predicted global sea-level rise.     

Mesocyclicity of Upper Triassic-Jurassic rocks in the Bureya Basin in the Far East of Russia: Their tectonics, eustasy, and sequence stratigraphy

The mesocyclicity of Upper Triassic-Jurassic rocks in the Bureya Basin located at that time at the paleocontinent margin was examined. The rock sections of this basin distinctly reflect the chronology of the eustatic sea-level fluctuations, which enabled us for the first time to construct a sequence stratigraphic model for this basin. Based on all the factors affecting the cyclicity, cycles of six orders (ranks) were recognized in the Bureya Basin for the Jurassic stage of its evolution. The tectonic factor predominates in the identification of the first three orders: the first-order cycle (the Alpian), the second-order cycles (the Indo-Sinian and Yanshanian), and the third-order cycles (the Late Indo-Sinian, Early Yanshanian, and Middle Yanshanian subcycles). The formation of the fourth-to sixth-order cycles was affected by not only the tectonic processes but also the eustatic sea-level fluctuations, the sediment supply??s volume, the sedimentary environment, and the climatic changes. Since the oil source rocks are formed during the maximal transgressions, the aleuropelitic strata of the fifth-order cycles (the Chagany, El??ga, Epikan, and Sinkal??tu formations along with the Khavagda Sequence) accumulated in the deepest parts of the basin are believed to be the most prospective objects.     

Late Pleistocene raised beaches of coastal Estremadura,central Portugal

We present new stratigraphic, sedimentological, and chronological data for a suite of tectonically raised beaches dating to Marine Isotope Stages 5, 4, and 3 along the Estremadura coast of west-central Portugal. The beach deposits are found in association with ancient tidal channels and coastal dunes, pollen bearing mud and peat, and Middle Paleolithic archaeological sites that confirm occupation of the coastal zone by Neanderthal populations. The significance of these deposits is discussed in terms of the archaeological record, the tectonic and geomorphic evolution of the coast, and correlation with reconstructions of global climate and eustatic sea-level change. Direct correlation between the Estremadura beach sections is complicated by the tectonic complexity of the area and the age of the beach deposits (which are near or beyond the limit of radiocarbon dating). Evidence from multiple sites dated by AMS radiocarbon and optical luminescence methods suggests broad synchroneity in relative sea-level changes along this coast during Marine Isotope Stage 3. Two beach complexes with luminescence and radiocarbon age control date to about 35 ka and 42 ka, recording a rise in relative sea level around the time of Heinrich Event 4 at 39 ka. Depending on assumptions about eustatic sea level at the time they were deposited, we estimate that these beaches have been uplifted at rates of 0.4–4.3 mm yr^?1 by the combined effects of tectonic, halokinetic, and isostatic processes. Uplift rates of 1–2 mm yr^?1 are likely if the beaches represent sea level stands at roughly 40 m below modern, as suggested by recent eustatic sea level reconstructions. Evidence from coastal bluffs and the interior of the study area indicates extensive colluvial, fluvial, and aeolian sedimentation beginning around 31 ka and continuing into the Holocene. These geomorphic adjustments are related to concomitant changes in climate and sea level, providing context that improves our understanding of Late Pleistocene landscape change and human occupation on the western Iberian margin.     

Sequence stratigraphy of the Dakota Formation (Cenomanian), southern Utah: interplay of eustasy and tectonics in a foreland basin

The Dakota Formation in southern Utah (Kaiparowits Plateau region) is a succession of fluvial through shallow-marine facies formed during the initial phase of filling of the Cretaceous foreland basin of the Sevier orogen. It records a number of relative sea-level fluctuations of different frequency and magnitude, controlled by both tectonic and eustatic processes during the Early to Late Cenomanian. The Dakota Formation is divided into eight units separated by regionally correlatable surfaces that formed in response to relative sea-level fluctuations. Units 1–6B represent, from bottom to top, valley-filling deposits of braided streams (unit 1), alluvial plain with anastomosed to meandering streams (2), tide-influenced fluvial and tide-dominated estuarine systems (3A and 3B), offshore to wave-dominated shoreface (4, 5 and 6A) and an estuarine incised valley fill (6A and 6B). The onset of flexural subsidence and deposition in the foredeep was preceded by eastward tilting of the basement strata, probably caused by forebulge migration during the Early Cretaceous, which resulted in the incision of a westward-deepening predepositional relief. The basal fluvial deposits of the Dakota Formation, filling the relief, reflect the onset of flexural subsidence and, possibly, a eustatic sea-level rise. Throughout the deposition of the Dakota Formation, flexure controlled the long-term, regional subsidence rate. Locally, reactivation of basement faults caused additional subsidence or minor uplift. Owing to a generally low subsidence rate, differential compaction locally influenced the degree of preservation of the Dakota units. Eustasy is believed to have been the main control on the high-frequency relative sea-level changes recorded in the Dakota. All surfaces that separate individual Dakota units are flooding surfaces, most of which are superimposed on sequence boundaries. Therefore, with the exception of unit 6B and, possibly, 3B, most of the Dakota units are interpreted as depositional sequences. Fluvial strata of units 1 and 2 are interpreted as low-frequency sequences; the coal zones at the base and within unit 2 may represent a response to higher frequency flooding events. Units 3A to 6B are interpreted as having formed in response to high-frequency relative sea-level fluctuations. Shallow-marine units 4, 5 and 6A, interpreted as parasequences by earlier authors, can be divided into facies-based systems tracts and show signs of subaerial exposure at their boundaries, which allows interpretation as high-frequency sequences. In general, the Dakota units are good examples of high-frequency sequences that can be misinterpreted as parasequences, especially in distal facies or in places where signs of subaerial erosion are missing or have been removed by subsequent transgressive erosion. Both low- and high-frequency sequences represented by the Dakota units are stacked in an overall retrogradational pattern, which reflects a long-term relative sea-level rise, punctuated by brief periods of relative sea-level fall. There is a relatively major fall near the end of the M. mosbyense Zone, whereas the base of the Tropic shale is characterized by a major flooding event at the base of the S. gracile Zone. A similar record of Cenomanian relative sea-level change in other regions, e.g. Europe or northern Africa, suggests that both high- and low-frequency relative sea-level changes were governed by eustasy. The high-frequency relative sea-level fluctuations of ≈100 kyr periodicity and ≈10–20 m magnitude, similar to those recorded in other Cenomanian successions in North America and Central Europe, were probably related to Milankovitch-band, climate-driven eustasy. Either minor glacioeustatic fluctuations, superimposed on the overall greenhouse climate of the mid-Cretaceous, or mechanisms, such as the fluctuations in groundwater volume on continents or thermal expansion and contraction of sea water, could have controlled the high-frequency eustatic fluctuations.