Rate Of Relative Sea-level Fall Research Articles

Late Holocene relative sea-level records from coral microatolls in Singapore

Late Holocene relative sea-level (RSL) data are important to understand the drivers of RSL change, but there is a lack of precise RSL records from the Sunda Shelf. Here, we produced a Late Holocene RSL reconstruction from coral microatolls in Singapore, demonstrating for the first time the utility of Diploastrea heliopora microatolls as sea-level indicators. We produced 12 sea-level index points and three marine limiting data with a precision of < ± 0.2 m (2σ) and < ± 26 years uncertainties (95% highest density region). The data show a RSL fall of 0.31 ± 0.18 m between 2.8 and 0.6 thousand years before present (kyr BP), at rates between − 0.1 ± 0.3 and − 0.2 ± 0.7 mm/year. Surface profiles of the fossil coral microatolls suggest fluctuations in the rate of RSL fall: (1) stable between 2.8 and 2.5 kyr BP; (2) rising at ~ 1.8 kyr BP; and (3) stable from 0.8 to 0.6 kyr BP. The microatoll record shows general agreement with published, high-quality RSL data within the Sunda Shelf. Comparison to a suite of glacial isostatic adjustment (GIA) models indicate preference for lower viscosities in the mantle. However, more high quality and precise Late Holocene RSL data are needed to further evaluate the drivers of RSL change in the region and better constrain GIA model parameters.

Late Holocene ice-mass changes recorded in a relative sea-level record from Joinville Island, Antarctica

AbstractRecent ice-mass loss driven by warming along the Antarctic Peninsula has resulted in rapid changes in uplift rates across the region. Are such events only a function of recent warming? If not, does the Earth response to such events last long enough to be preserved in Holocene records of relative sea level (RSL), and thus have a bearing on global-scale glacial isostatic adjustment (GIA) models (e.g. ICE-6G)? Answering such questions in Antarctica is hindered by the scarcity of RSL reconstructions within the region. Here, a new RSL reconstruction for Antarctica is presented based on beach ridges from Joinville Island on the Antarctic Peninsula. We find that RSL has fallen 4.9 ± 0.58 m over the past 3100 yr, and that the island experienced a significant increase in the rate of RSL fall from 1540 ± 125 cal. (calibrated) yr B.P. to 1320 ± 125 cal. yr B.P. This increase in the rate of RSL fall is likely due to the viscoelastic response of the solid Earth to terrestrial ice-mass loss from the Antarctic Peninsula, similar to the Earth response experienced after ice-mass loss following acceleration of glaciers behind the collapsed Larsen B ice shelf in 2002 C.E. Additionally, slower rates of beach-ridge progradation from 695 ± 190 cal. yr B.P. to 235 ± 175 cal. yr B.P. potentially reflect erosion of beach ridges from a RSL rise induced by a local glacial advance. The rapid response of the Earth to minor ice-mass changes recorded in the RSL record further supports recent assertions of a more responsive Earth to glacial unloading and at time scales relevant for GIA of Holocene and Pleistocene sea levels. Thus, current continental and global GIA models may not accurately capture the ice-mass changes of the Antarctic ice sheets at decadal and centennial time scales.

Late Holocene relative sea levels near Palmer Station, northern Antarctic Peninsula, strongly controlled by late Holocene ice-mass changes

Many studies of Holocene relative sea-level (RSL) changes across Antarctica assume that their reconstructions record uplift from glacial isostatic adjustment caused by the demise of the Last Glacial Maximum (LGM) ice sheets. However, recent analysis of GPS observations suggests that mantle viscosity beneath the Antarctic Peninsula is weaker than previously thought, which would imply that solid Earth motion is not controlled by post-LGM ice-sheet retreat but instead by late Holocene ice-mass changes. If this hypothesis is correct, one might expect to find Holocene RSL records that do not reflect a monotonic decrease in the rate of RSL fall but show variations in the rate of RSL change through the Holocene. We present a new record of late Holocene RSL change from Torgersen Island near Palmer Station in the western Antarctic Peninsula that shows an increase in the rate of relative sea-level fall from 3.0 ± 1.2 mm/yr to 5.1 ± 1.8 mm/yr during the late Holocene. Independent studies of the glacial history of the region provide evidence of ice-sheet changes over similar time scales that may be driving this change. When our RSL records are corrected for sea-surface height changes associated with glacial isostatic adjustment (GIA), the rate of post-0.79 ka land uplift at Torgersen Island, 5.3 ± 1.8 mm/yr, is much higher than the rate of uplift recorded at a nearby GPS site at Palmer Station prior to the Larsen B breakup in 2002 AD (1998-2002 AD; <0.1 mm/yr), but similar to the rates observed after 2002 AD (2002-2013 AD; 6–9 mm/yr). This substantial variation in uplift rates further supports the hypothesis that Holocene RSL rates of change are recording responses to late Holocene and recent changes in local ice loading rather than a post-LGM signal across portions of the Antarctic Peninsula. Thus middle-to-late Holocene RSL data may not be an effective tool for constraining the size of the LGM ice sheet across portions of the Antarctic Peninsula underlain by weaker mantle. In addition, current global-scale GIA models are unable to predict our observed changes in late Holocene RSL. Complexities in Earth structure and neoglacial history need to be taken into consideration in GIA models used for correcting modern satellite-based observations of ice-mass loss.

A Poor Relationship Between Sea Level and Deep-Water Sand Delivery

The most commonly cited control on delivery of sand to deep water is the rate of relative sea-level fall. The rapid rate of accommodation loss on the shelf causes sedimentation to shift basinward. Field and experimental numerical modeling studies have shown that deep-water sand delivery can occur during any stage of relative sea level position and across a large range of values of rate of relative sea-level change. However, these studies did not investigate the impact of sediment transport efficiency on the relationship between rate of relative sea-level change and deep-water sand delivery rate. We explore this relationship using a deterministic nonlinear diffusion-based numerical stratigraphic forward model. We vary across three orders of magnitude the diffusion coefficient value for marine settings, which controls sediment transport efficiency. We find that the rate of relative sea-level change can explain no more than 1% of the variability in deep-water sand delivery rates, regardless of sediment transport efficiency. Model results show a better correlation with relative sea level, with up to 55% of the variability in deep water sand delivery rates explained. The results presented here are consistent with studies of natural settings which suggest stochastic processes such as avulsion and slope failure, and interactions among such processes, may explain the remaining variance. Relative sea level is a better predictor of deep-water sand delivery than rate of relative sea-level change because it is the sea-level fall itself which promotes sand delivery, not the rate of the fall. We conclude that the poor relationship between sea level and sand delivery is not an artifact of the modeling parameters but is instead due to the inadequacy of relative sea level and the rate of relative sea-level change to fully describe the dimensional space in which depositional systems reside. Subsequently, sea level itself is unable to account for the interaction of multiple processes that contribute to sand delivery to deep water.

Mid-Holocene relative sea-level changes along Atlantic Patagonia: New data from Camarones, Chubut, Argentina

This paper concerns the relative sea-level changes associated with the Atlantic Patagonian coast derived from sea-level index points whose elevation was determined by a differential global position system (DGPS). Bioencrustations from outcrops located near Camarones, Chubut, Argentina, consist of autochthonous deposits characterized by Austromegabalanus psittacus (Molina, 1782), encrusting acervulinid foraminifera, coralline red algae and bryozoans. The association of the different organisms is interpreted as being associated with an intertidal environment, and they have been used as index points to establish the relative sea-level position. The main conclusion is that the relative sea-level between c. 7000 and 5300 cal. yr BP was in the range of c. 2–4 m a.s.l., with a mean value of c. 3.5 m a.s.l. Our data seem to support the existence of different rates of relative sea-level fall in different sectors of Atlantic Patagonia during the Holocene and highlight the importance of a more precise and accurate r...

Ice sheet retreat and glacio-isostatic adjustment in Lützow-Holm Bay, East Antarctica

The East Antarctic Ice Sheet has relatively few field data to constrain its past volume and contribution to global sea-level change since the Last Glacial Maximum. We provide new data on deglaciation history and develop new relative sea-level (RSL) curves along an 80 km transect (from Skallen to Skarsvnes, Langhovde and the Ongul Islands) in Lützow Holm Bay, East Antarctica. The geological constraints were compared with output from two Glacial Isostatic Adjustment (GIA) models. The minimum radiocarbon age for regional deglaciation is c. 11,240 cal. yr BP on West Ongul Island with progressively younger deglaciation ages approaching the main regional ice outflow at Shirase Glacier. Marked regional differences in the magnitude and timing of RSL change were observed. More in particular, in Skarvsnes a minimum marine limit of 32.7 m was inferred, which is c. 12.7 m higher than previously published evidence, and at least 15 m higher than that reported in the other three ice-free areas. Current GIA model predictions slightly underestimate the rate of Late Holocene RSL fall at Skallen, Langhovde, and West Ongul, but provide a reasonable fit to the reconstructed minimum marine limit at these sites. GIA model predictions are unable to provide an explanation for the shape of the reconstructed RSL curve at Skarvsnes. We consider a range of possible explanations for the Skarvsnes RSL data and favour an interpretation where the anomalously high marine limit and rate of RSL fall is due to reactivation of a local fault.

Holocene Relative Sea-Level Changes from Near-, Intermediate-, and Far-Field Locations

Holocene relative sea-level (RSL) records exhibit spatial and temporal variability that arises mainly from the interaction of eustatic (land ice volume and thermal expansion) and isostatic (glacio- and hydro-) factors. We fit RSL histories from near-, intermediate-, and far-field locations with noisy-input Gaussian process models to assess rates of RSL change. Records from near-field regions (e.g., Antarctica, Greenland, Canada, Sweden, and Scotland) reveal a complex pattern of RSL fall from a maximum marine limit due to the net effect of eustatic sea-level rise and glacio-isostatic uplift with rates of RSL fall as great as −69 ± 9 m/ka. Intermediate-field regions (e.g., mid-Atlantic and Pacific coasts of the USA, Netherlands, Southern France, St. Croix) display variable rates of RSL rise from the cumulative effect of eustatic and isostatic factors. Fast rates of RSL rise (up to 10 ± 1 m/ka) are found in the early Holocene in regions near the center of forebulge collapse. Far-field RSL records exhibit a mid-Holocene highstand, the timing (between 8 and 4 ka) and magnitude (between <1 and 6 m) of which varies among South America, Africa, Asia, and Oceania regions.

Middle- to late-Holocene relative sea-level changes at Puerto Deseado (Patagonia, Argentina)

Stratigraphic, morphologic and radiocarbon data from Puerto Deseado coastal area (Santa Cruz Province, Argentina) indicate that the Holocene coastline formed in response to the discontinuous aggradation of coarse gravely beaches since c. 6300 cal. yr BP related to a progressive falling of relative sea level. Beach ridge crests crudely approximate to the sea level showing at least three steps of aggradation and relative sea-level lowering. Two inactive abrasive notches at c. 7.9 and 3.4 m a.s.l. have recorded this sea-level trend, suggesting two important phases when sea level was stationary. This allows the estimation of a rate of relative sea-level fall in the last c. 3500 years of c. 1.8 mm/yr. Moreover, notches and morphological data indicate that the crest of the beach ridges exceeded the sea-level height by c. 2 ± 0.5 m. This value provides a reasonable regional estimate to be applied to produce comparable relative sea-level curve for Atlantic Patagonia coast.

Numerical Modeling of Falling-Stage Topset Aggradation: Implications for Distinguishing Between Forced and Unforced Regressions In the Geological Record

Abstract Distinguishing between forced and unforced regressive strata is important for identification of systems tracts, prediction of sediment bypass, and reconstruction of relative sea-level histories. Conventional sequence stratigraphic models distinguish between forced and unforced regressive strata through the presence of aggradational topset (no aggradation during forced regression) and style of shoreline trajectory (descending in forced regressive strata and flat to rising in unforced regressive strata). However, because present models contain implicit assumptions about sediment supply and the response of coastal-plain and fluvial deposystems to falling and rising relative sea level, it is probable that these two scenarios are an oversimplification of a more complex reality. This work investigates how topset aggradation might develop during relative sea-level fall using 1264 runs from a simple diffusional stratigraphic forward model. Topset aggradation is characterized for each model run by a topset/foreset volume ratio (t/f ratio). When topset strata are present the t/f ratio is > 0, when no topset strata are present the t/f ratio is zero. Multiple two-dimensional model runs (0.4 or 2 My duration, and constant sediment supply and discharge rates representative of medium-size river systems) suggest that sediment transport rate may be a key control on topset aggradation. Modeling a range of sediment transport rates for amplitudes of relative sea-level fall from 0 to 100 m shows that with relatively high rates of sediment transport, multiple model runs create strata with t/f ratios up to 0.08. Conversely, relatively low sediment transport rates lead to higher volumes of topset deposition reflected by t/f ratios ranging from 0.10 to 0.37. However, critically, high sediment transport with no relative sea-level fall leads to topset aggradation very similar to that resulting from low sediment transport and high-amplitude relative sea-level fall. This is an example of non-uniqueness, showing that topset aggradation can occur during falling relative sea level as well as steady to rising relative sea level, depending on rates of sediment transport. This result has been tested and verified with different rates of relative sea-level fall and with additional three-dimensional model runs, including runs in a different model. The results suggest that backstripped shoreline trajectories are likely to be a more reliable method of distinguishing forced from unforced regression, and that interpretation and prediction of sediment bypass history may be more complicated than current sequence stratigraphic models suggest.

Deltaic Infill of a Deglaciated Arctic Fjord, East Greenland: Sedimentary Facies and Sequence Stratigraphy

ABSTRACT The deltaic fill of a deglaciated side-entry fjord in western Jameson Land, East Greenland, shows the record of an interplay between regional and local controls, including climate and relative sea-level change, onshore and offshore topography, and sediment yield. A four-phase model is suggested for the delta development and fjord filling. At the deglaciation stage (phase 1), the newly flooded fjord floor primarily accumulated sediment from reworked glacial material. These deposits were relatively thin, and draped the uneven sea-floor topography. The subsequent onset of paraglacial delta sedimentation (phase 2) was characterized by a high meltwater runoff and extreme sediment yield, and corresponded to the highstand and gradual fall of relative sea level. A Gilbert-type delta with a short distributary plain formed at the head of the tributary fjord, which received a very high amount of fine-grained sediment. The stage of enhanced delta progradation (phase 3) was characterized by decreased sediment yield and runoff, and a rapid fall of relative sea level. Delta progradation was fast because of rapidly decreasing accommodation space, and a solitary river channel deeply incised the delta. The equilibrium stage (phase 4) spanned most of Holocene time and involved a lowered rate of relative sea-level fall. Seasonal runoff supplied limited amounts of sediment to the river mouth, and the delta front became increasingly reworked by wave action and longshore drift. The side-entry fjord, a small deglaciated valley invaded by the sea, was filled chiefly by highstand and regressive systems tracts, whereas relatively little sea-floor aggradation was associated with the transgressive systems tract. The stratigraphic pattern documented in this paper contrasts with the pattern usually reported from nonglaciated incised-valley systems, which are filled mainly by the transgressive systems tract, typically involving a retreating estuarine system. The pattern also differs from some large, gradually deglaciated fjord valleys containing thick, transgressive, glaciomarine deposits accumulated during glacier retreat. The study demonstrates the large variability of valley fills and illustrates the importance of topography, sediment supply, and climate as well as the style of deglaciation on the sediment filling of a fjord valley.

Unconformities within the Portlandian Stage of the Wessex Basin and their sequence-stratigraphical significance

Abstract At outcrop, the Portlandian Stage of the western Wessex Basin, southern England comprises a complex series of marine and non-marine carbonates deposited in moderate to shallow water depth, with the occasional development of siliciclastic deposits near to the basin margins. The strata record part of a marked overall long-term regression on which are superimposed four shorter term relative sea-level cycles. The base of each of these short-term cycles is marked by a major unconformity or its correlative conformity (sequence boundary) formed during the maximum rate of relative sea-level fall; these are denoted P1 to P4. The south Dorset exposures are each in slightly different tectonic settings within the Central Channel Sub-basin. The Isle of Purbeck sections are stratigraphically the most complete, but the sections on the Isle of Portland, previously assumed to be complete, contain at least two significant stratal gaps. The sections at Ringstead Bay and Dungy Head are thin, condensed and in part incomplete. Proximally, in the Vale of Wardour (Mere Sub-basin), Vale of Pewsey (Pewsey Sub-basin) and on the London Platform at Swindon, in Oxfordshire and in Buckinghamshire the succession becomes condensed, the major unconformities are frequently angular and there is at least one incised valley.

Mixed Siliciclastic-Carbonate Deposition in an Early Cambrian Oxygen-Stratified Basin, Chapel Island Formation, Southeastern Newfoundland

ABSTRACT The upper portion of member 3 and member 4 of the uppermost Precambrian (Vendian)-Lower Cambrian Chapel Island Formation represents a large-scale shoaling-up deposit dominated by shelf siliciclastic mudstone. Medium-scale, higher-order shoaling-up cycles at the top of member 3 and in member 4 are capped by peritidal limestones that contain a wide variety of stromatolitic buildups and algal mud mounds. Sedimentation took place in an oxygen-stratified basin with accumulation of gray dysaerobic mudstone offshore and green and red mudstone in shallower, more oxygenated waters. Biofacies models for dysaerobic basins can be applied to this sequence and help in understanding the distribution of trace fossils, skeletal fossils (shells and pyritic steinkerns), and diagenetic features. These da a are important for the understanding of the stratigraphic distribution of shelly fossils within this lowest Cambrian unit. A mixed carbonate-siliciclastic facies model is presented in which carbonate sediments formed in intertidal areas along the shoreline of a siliciclastic muddy shelf. The carbonate shoreline prograded during periods of increasing rate of relative sea-level fall or decreasing rate of relative sea-level rise. Restriction of carbonate sediments to the peritidal environment may have been due to a combination of higher rates of carbonate sediment production and accumulation in the peritidal zone, seaward dilution by siliciclastic mud, and a paleogeographic position near the latitudinal climatic extreme for carbonate production.

Sequence stratigraphy from “spot” outcrops—example from a carbonate-dominated setting: Devonian-Carboniferous transition, Dinant synclinorium (Belgium)

The application of sequence stratigraphy appears to be perfectly valid in isolated “spot” outcrops, which usually are badly exposed and located in areas of strong tectonic overprint. The case study presented here is in a carbonate-dominated setting at the northern edge of the Cornwall-Rhenish basin, during latest Devonian and earliest Carboniferous times. The approach taken involved the analysis of facies and vertical facies evolutions, in combination with detailed biostratigraphy. The subsequent deduction of deepening and shallowing events, and the understanding of the sedimentary response to these events in different palaeogeographical positions, are the basis for lateral correlation of facies sequences. A similar trend in the changes of deepenings and shallowings throughout the area, regardless of lateral facies differentiation, indicates a relationship between bathymetric changes and relative sea-level changes, that is independent of local differences in the sedimentation or subsidence rates. The studied stratigraphic interval, with its apparently “abrupt” changes in facies or lithology, is the sedimentary response to six, gradually changing trends in the rate of relative sea-level fall and rise. End-Devonian, offshore highstand deposits (1) are capped by an unconformity surface or by a surface of submarine erosion and nondeposition, representing a sequence boundary (2). The overlying lowstand unit consists of a basal (3) and an upper (4) part. The basal part contains an oolitic and crinoidal sand shoals, associated with a transgressive lag deposit in offshore position; the upper, main part is a prograding wedge of shallow-marine crinoidal sands, intercalated with increasingly deeper-water shaly facies (higher-order fluctuation). This lowstand unit was deposited during the initial, slow phase of relative sea-level rise. It levelled the topographic relief before the final drowning during the subsequent rapid (near the rise inflection point) relative sea-level rise (5). The associated offshore shales are the deepest facies recorded. They are capped by a prograding unit deposited during a relative highstand (6). The reconstruction of a relative sea-level curve and the subsequent determination of the bounding surfaces, is not only the key to understanding the Devonian-Carboniferous stratigraphy but also a tool for lateral correlation of “spot” outcrops.