Late Holocene Rates Research Articles

Holocene sea-level database from the Atlantic coast of Europe

High-quality relative sea-level (RSL) data reveal spatial and temporal variations in crustal movements during the Holocene, which are used for many applications, ranging from calibrating models of earth rheology and ice sheet reconstructions to the development of coastal lowlands and human occupation. Here, we present a Holocene RSL database for the Atlantic coast of Europe (ACE) and estimate rates of RSL change from the ACE database using a spatio-temporal empirical hierarchical model. The database contains 214 index points, which locate the RSL position in space and time, and 126 limiting dates, which constrain RSL to above or below a certain elevation at a specific point in time. The temporal distribution extends from present to ∼11.5 ka, with only 42 index points older than 7 ka. The spatial distribution spans 1700 km from French Flanders (France) to Algarve (Portugal), with more than half of the index points concentrated along the French coast.The ACE database shows RSL was below present during the Holocene. Rates of RSL change were highest during the early Holocene, ranging between 6.8 ± 0.5 mm yr−1 in middle Portugal and 6.3 ± 0.8 mm yr−1 in southern France from 10 to 7 ka. Mid-to late-Holocene rates decreased over time with rates ranging between 0.9 ± 0.4 mm yr−1 in middle France and 0.1 ± 0.5 mm yr−1 in middle Portugal from 4 ka to present. Comparison of the RSL data to output from a glacial-isostatic adjustment model suggests that deglaciation of the British-Irish and Fennoscandian Ice Sheets dominates the large-scale variability captured by the ACE database, which reflects a decreasing influence of the collapsing British-Irish and Fennoscandian peripheral forebulge that migrated from the northeast to the northwest after ∼4 ka.

Drivers of Holocene sea-level change in the Caribbean

Abstract We present a Holocene relative sea-level (RSL) database for the Caribbean region (5°N to 25°N and 55°W to 90°W) that consists of 499 sea-level index points and 238 limiting dates. The database was compiled from multiple sea-level indicators (mangrove peat, microbial mats, beach rock and acroporid and massive corals). We subdivided the database into 20 regions to investigate the influence of tectonics and glacial isostatic adjustment on RSL. We account for the local-scale processes of sediment compaction and tidal range change using the stratigraphic position (overburden thickness) of index points and paleotidal modeling, respectively. We use a spatio-temporal empirical hierarchical model to estimate RSL position and its rates of change in the Caribbean over 1-ka time slices. Because of meltwater input, the rates of RSL change were highest during the early Holocene, with a maximum of 10.9 ± 0.6 m/ka in Suriname and Guyana and minimum of 7.4 ± 0.7 m/ka in south Florida from 12 to 8 ka. Following complete deglaciation of the Laurentide Ice Sheet (LIS) by ∼7 ka, mid-to late-Holocene rates slowed to

Extreme multi-millennial slip rate variations on the Garlock fault, California: Strain super-cycles, potentially time-variable fault strength, and implications for system-level earthquake occurrence

Abstract Pronounced variations in fault slip rate revealed by new measurements along the Garlock fault have basic implications for understanding how faults store and release strain energy in large earthquakes. Specifically, dating of a series of 26.0 + 3.5 / − 2.5 m fault offsets with a newly developed infrared-stimulated luminescence method shows that the fault was slipping at > 14.0 + 2.2 / − 1.8 mm / yr , approximately twice as fast as the long-term average rate, during a previously documented cluster of four earthquakes 0.5–2.0 ka. This elevated late Holocene rate must be balanced by periods of slow or no slip such as that during the ca. 3300-yr-long seismic lull preceding the cluster. Moreover, whereas a comparison of paleoseismic data and stress modeling results suggests that individual Garlock earthquakes may be triggered by periods of rapid San Andreas fault slip or very large-slip events, the “on–off” behavior of the Garlock suggests a longer-term mechanism that may involve changes in the rate of elastic strain accumulation on the fault over millennial time scales. This inference is consistent with most models of the geodetic velocity field, which yield slip-deficit rates that are much slower than the average latest Pleistocene-early Holocene (post-8–13 ka) Garlock slip rate of 6.5 ± 1.5 mm / yr . These observations indicate the occurrence of millennia-long strain “super-cycles” on the Garlock fault that may be associated with temporal changes in elastic strain accumulation rate, which may in turn be controlled by variations in relative strength of the various faults in the Garlock-San Andreas-Eastern California Shear Zone fault system and/or changes in relative plate motion rates.

An updated database of Holocene relative sea level changes in NE Aegean Sea

The reconstruction of Holocene relative sea levels has several implications, ranging from the investigation of coastal vertical movements to the calibration of earth rheology models and ice sheet reconstructions. The North Eastern Aegean Sea is among the tectonically complex sectors of the Eastern Mediterranean, mainly influenced by the activity of the North Anatolian Fault. In this paper, we created a relative sea level (RSL) database by expanding upon the previous compilation with recently published geological and archaeological data. We reconstruct the RSL history in those Aegean coastal sectors located within the South Marmara microplate, a broad shear zone located between western Anatolia and central Greece and affected by dominant strike–slip faulting, at times combined with a normal component. Then, we compared it with the RSL histories obtained for the surrounding coastal sectors. The analysis of the database indicated that it is not possible to define a common Holocene RSL curve for the entire NE Aegean, as RSL history here is majorly influenced by changes in deformation patterns. In addition, data in our database are consistent with a continuous RSL rise in the last 6.0 ka BP in the whole NE Aegean Sea and cannot support the hypothesis of a mid-Holocene RSL highstand in the area. Finally, we present our best estimates of late Holocene rates of RSL prior to any possible acceleration during the twentieth century in the broad area of NE Aegean. Here we identified the fastest rising rate (∼0.9 mm a−1) in that sector whose active tectonic deformation is mainly controlled by the North Anatolian Fault activity.

Toward a consistent model for strain accrual and release for the New Madrid Seismic Zone, central United States

[1] At the heart of the conundrum of seismogenesis in the New Madrid Seismic Zone is the apparently substantial discrepancy between low strain rate and high recent seismic moment release. In this study we revisit the magnitudes of the four principal 1811–1812 earthquakes using intensity values determined from individual assessments from four experts. Using these values and the grid search method of Bakun and Wentworth (1997), we estimate magnitudes around 7.0 for all four events, values that are significantly lower than previously published magnitude estimates based on macroseismic intensities. We further show that the strain rate predicted from postglacial rebound is sufficient to produce a sequence with the moment release of one Mmax6.8 every 500 years, a rate that is much lower than previous estimates of late Holocene moment release. However, Mw6.8 is at the low end of the uncertainty range inferred from analysis of intensities for the largest 1811–1812 event. We show that Mw6.8 is also a reasonable value for the largest main shock given a plausible rupture scenario. One can also construct a range of consistent models that permit a somewhat higher Mmax, with a longer average recurrence rate. It is thus possible to reconcile predicted strain and seismic moment release rates with alternative models: one in which 1811–1812 sequences occur every 500 years, with the largest events being Mmax∼6.8, or one in which sequences occur, on average, less frequently, with Mmax of ∼7.0. Both models predict that the late Holocene rate of activity will continue for the next few to 10 thousand years.

Compaction of Holocene strata and the implications for relative sealevel change on the east coast of England

The contribution of compaction of Holocene strata to sea-level rise, shoreline erosion, and wetland loss is difficult to decipher because of a lack of long-term empirical data. We analyzed more than 360 radiocarbon-dated index points to constrain relative sea levels along the east coast of England during the Holocene and to provide estimates of sediment compaction. The isostatic effect of glacial rebound explains regional-scale differences in relative sea levels. Northeast England, the most northern study area, reveals a middle to late Holocene highstand, <1 m above present, ca. 3–4 kyr B.P., whereas the Tees Estuary, Humber Estuary, Lincolnshire Marshes, Fenlands, and North Norfolk each reveal sea-level histories of an upward trend during the Holocene. Within each area, sediment compaction explains the variation in elevation between sealevel reconstructions derived from index points taken from basal peat and those from peat intercalated within thick sequences of Holocene sediments. We find average compaction rates of 0.4 ± 0.3 mm yr−1 with higher values for the large estuaries. Rates of late Holocene relative sea-level changes, calculated from basal peats, range from −0.2 ± 0.1 mm yr−1 (i.e., sea-level fall) in northeast England to 0.8 ± 0.1 mm yr−1 in North Norfolk. Inclusion of intercalated index points overestimates late Holocene rates by 0.1–0.4 mm yr−1 because of the effects of sediment compaction.

Holocene coastal change in East Norfolk, UK: palaeoenvironmental data from Somerton and Winterton Holmes, near Horsey

We present palaeoenvironmental results from two cores, Winterton Holmes (GY2) and Somerton Holmes (GY3), south of Horsey, East Norfolk. The upper transgressive contact of the peat of cores GY2 and GY3 is dated to 2355–2742 cal. years bp and 2761–2949 cal. years bp, respectively. The litho- and biostratigraphical data show that both these peat contacts represent sea-level index points formed around mean high water spring tides during a positive tendency of sea-level movement, as saltmarsh indicators near the top of, and immediately above the peat show its deposition within intertidal environments. These sea-level index points when combined with other sea-level observations and predictions from East Norfolk, confirm an upward trend of Holocene relative sea-level change typical of an area at, or beyond, the margins of the last British ice sheet; rapid in the early Holocene then at a much reduced rate in the mid- and late Holocene. Late Holocene rates of relative uplift or subsidence are calculated for East Norfolk by subtracting a model of relative sea level from each index point and then calculating the best-fit linear trend. The late Holocene rate of relative sea-level rise (or land subsidence) is 0.67 ± 0.06 mm −1 which is c . 1 mm a −1 less than the twentieth-century mean sea-level trend estimated from Lowestoft tidal station, thus agreeing with the consensus of opinion that global sea levels have risen between 10 and 20 cm over the past century.

Relative sea-level rise across the Eastern Border fault (Branford, Connecticut): evidence against seismotectonic movements

Basal peat age–depth data from four salt-marsh sites located 500–1500 m south of the Eastern Border fault (EBF) near Branford, Connecticut, document an error envelope for the lower limit of relative mean high water (MHW) rise during the past 3300 yr. The long-term rate of relative lower-limit-MHW rise during the past 3000 yr (1.1 mm yr −1) corresponds with late Holocene rates of relative MHW rise found elsewhere in coastal Connecticut (0.9–1.2 mm yr −1). This result invalidates repeated claims that multiple seismotectonic lowering of a crustal block towards the south has occurred along a segment of the EBF near Branford shortly after 815 cal yr BC and during the past 1200 yr and calls for a non-tectonic interpretation of biostratigraphic evidence of local short-term sea-level variations.

An assessment of historic human impact on south-eastern Australian environmental systems, using late Holocene rates of environmental change

The late Holocene of south-eastern Australia was typified by stable climate, vegetation and sedimentary regimes, in relative equilibrium with Aboriginal land use and fire management. The arrival of Europeans, with the associated vegetation clearance, introduction of exotic plants and animals, notably for grazing and agriculture and a change in fire regimes, resulted in changes in vegetation and sedimentary patterns. Impacts varied in type and magnitude through the region and evidence of impacts that is preserved varies with sedimentary setting. Here we take a number of proxy measures of vegetation change, fire history, erosion and weathering from six sediment sections across south-eastern Australia and use an index to measure overall rate of change. This shows that the vegetation and environmental systems of south-eastern Australia have been very sensitive to human impact following European settlement.

Late-Quaternary Recharge Determined from Chloride in Shallow Groundwater in the Central Great Plains

An extensive suite of isotopic and geochemical tracers in groundwater has been used to provide hydrologic assessments of the hierarchy of flow systems in aquifers underlying the central Great Plains (southeastern Colorado and western Kansas) of the United States and to determine the late Pleistocene and Holocene paleotemperature and paleorecharge record. Hydrogeologic and geochemical tracer data permit classification of the samples into late Holocene, late Pleistocene–early Holocene, and much older Pleistocene groups. Paleorecharge rates calculated from the Cl concentration in the samples show that recharge rates were at least twice the late Holocene rate during late Pleistocene–early Holocene time, which is consistent with their relative depletion in 16O and D. Noble gas (Ne, Ar, Kr, Xe) temperature calculations confirm that these older samples represent a recharge environment approximately 5°C cooler than late Holocene values. These results are consistent with the global climate models that show a trend toward a warmer, more arid climate during the Holocene.

Spatial and Temporal Patterns of Late Holocene Rockfall Activity on a Norwegian Talus Slope: A Lichenometric and Simulation-Modeling Approach

Largest lichens (genus Rhizocarpon) were measured on 2800 boulders sampled systematically at 28 sites on a thin triangular talus. Sites with similar lichen-size frequency distributions were grouped and used to interpret the temporal and spatial patterns of rockfall supply. Most of the slope yields size-distributions of largest lichens that reflect the history of rockfall activity over at least the last 400 yr. A general increase in surface age diagonally downslope suggests boulders are supplied by rockfall rather than avalanching, with no evidence of postdepositional redistribution. At one corner of the talus foot the lichen-size distributions have reached equilibrium, suggesting negligible supply of boulders during the late Holocene. Sites at the apex of the talus are dominated by small lichens. Simulation modeling is used to reconstruct possible temporal patterns of debris supply to different parts of the talus, and competing models are tested by estimating the thickness of talus predicted to have accumulated during the Holocene. The normal rate of rockfall during the late Holocene is estimated to result in burial of about 4% of the talus surface each 25 yr. Rates of rockfall supply during the 18th century, the coldest phase of the Little Ice Age, are estimated to have been almost five times the normal late Holocene rate. Results are consistent with talus formation under periglacial conditions during the Holocene; a paraglacial origin is unnecessary.

Mud sedimentation on the continental shelf at an accretionary margin—Poverty Bay, New Zealand

Sediments on the continental shelf, atop the accretionary prism of the eastern North Island, are dominated by mud. This situation reflects a highly erodible provenance of soft Tertiary sediments, active tectonism, meteorological extremes, and, in historical times, changing land use. Off Poverty Bay, mud is supplied by the Waipaoa River, New Zealand's fourth largest river in terms of sediment supply. Under normal conditions, suspended sediment is dispersed as surface or hypopycnal plumes that have a net northeastward or southward dispersal along the shelf, mainly in response to the prevailing wind‐driven circulation. During extreme floods with return periods of 10 years or more, fluvial suspended sediment concentrations are probably high enough to form subsurface or hyperpycnal plumes that move and disperse under gravity and shelf currents. After the 100 year Cyclone Bola event of 1988, reef communities of the inner shelf were temporarily inundated by a fluid mud layer. Surficial sediments and 3.5 kHz seismic reflection profiles reveal that mud accumulates in a subsiding synclinal basin occupying the middle shelf. Offshelf dispersal is hindered by the growing Lachlan and Ariel Anticlines along the outer shelf. As a result, 20 km3 of mud has been deposited since c. 18 ka, of which 8 km3 accumulated since c. 8 ka. This late Holocene rate is nearly five times lower than the modern rate of mud supply, which equates with the marked increase in terrestrial erosion following European deforestation in the late nineteenth century.

Late Pleistocene and Holocene sea-level change in Greece and south-western Turkey: a separation of eustatic, isostatic and tectonic contributions

Sea-level change during Late Pleistocene and Holocene times is a combination of eustatic, isostatic and tectonic contributions. In the central Mediterranean Sea region of Greece and western Turkey, the isostatic components are important, due to the changing gravitational potential of the Earth, the readjustment of the crust upon the removal of the large ice sheets and the addition of the meltwater into the oceans, including the Mediterranean. Changes in relative sea-level due to these glacio-hydro-isostatic adjustments have reached amplitudes of 1 mm yr−1 during the last few thousand years. A model for the isostatic contribution to sea-level change, including the movement of shorelines due to the combined eustatic-isostatic changes, is developed, based on earth-model and ice-sheet parameters estimated from sea-level observations from other areas. Comparisons of this model with observations of sea-level change permit rates of vertical movement to be estimated for Late Holocene time. Allowance for the isostatic factors makes a significant difference to these rates. The plains of Argolis, Lakonia, Messinia and Navarine, in the southern Peloponnese, for example, appear to be tectonically stable on time-scales of a few thousand years and longer, consistent with the position of the Last Interglacial shoreline close to the present-day sea-level. The observations here, of a rising sea-level, are largely the consequence of the glacio-hydro isostasy and not of a long-term tectonic process. Crete as a whole is subject to tectonic uplift, but at variable rates, and forms part of an arcuate zone of uplift extending from Rhodes and Karpathos in the east to Kithera in the west at rates that locally exceed 4 mm yr−1. The southern shore of the Gulf of Corinthos is also subject to uplift at rates approaching 1.5 mm yr−1. These isostatically corrected estimates for the past few thousand years are in agreement with longer-term estimates based on the position of the Last Interglacial shoreline. Only on the Perachora Peninsula do the tectonic rates over these two time intervals appear to be in disagreement, with the Late Holocene rates being much higher than the long-term rates.

Holocene paleoseismicity of the Tunka fault, Baikal rift, Russia

The Tunka fault is a major normal‐oblique transform fault within the NNE trending Baikal rift that displays geomorphic evidence of recurrent Quaternary movement. A flight of six fanhead terraces of the Kyngarga River is displaced by several parallel faults and has scarps up to 32 m high at Arshan. The main fault zone is exposed in an abandoned gravel quarry about 1 km east of the Kyngarga River. Thirteen radiocarbon dates from the quarry, a shallow trench in a graben, and natural streamcuts constrain the timing of the latest two or three Holocene paleoearthquakes. The latest earthquake is bracketed by the 1024–1315 calendar years (cal. year) B.P. age of an unfaulted terrace and by the 1947–2179 cal. year B.P. age of a soil buried by scarp colluvium in the graben trench. The penultimate earthquake is also relatively well constrained, assuming that the displacement event slightly younger than 7091–7867 cal. year B.P. in the upper quarry exposure is the same as the fissuring event slightly older than 6733–7385 cal. year B.P. in the lower quarry exposure. Evidence for earlier event(s) between 9.2–12.7 ka depends on ambiguous stratigraphic evidence in the lower quarry exposure. On the basis of only the two well‐dated earthquakes, the recurrence interval at Arshan may range from 2.9 to 6.8 ka for earthquake displacements of at least 1.3 m or a slip rate of 0.19–0.44 mm/yr. Intermediate‐term (100 ka) and long‐term (circa 500 ka) slip rates computed from terrace age estimates and fault scarp heights are 0.08–0.16 mm/yr and 0.07–0.11 mm/yr, respectively, rates that are considerably lower than the late Holocene rate and the approximately 0.5 mm/yr that might be inferred from the tectonic geomorphology of the Tunka Range front.

Holocene sediment fluxes in the northeast Atlantic from 230Thexcess and radiocarbon measurements

Radiocarbon and 230Thexcess data from six NE Atlantic box cores are considered. The cores form a transect from the Porcupine Abyssal Plain over the East Thulean Rise to the southern end of Feni Drift. The chronology for the cores is established from bulk sediment carbonate radiocarbon data and reveals that sections exhibiting constant accumulation rates can be identified in all the cores, with rates of 3.0‐3.5 cm kyr−1 on the plain through the Holocene and late Holocene rates of 4.3–6.6 cm kyr−1 elsewhere. Five out of the six cores show accumulations of more 230Thexcess than is produced in the overlying water column, with the greatest inventories (up to 225% of production) in the cores from the rise and drift. A size fraction comparison between two cores from the plain and rise reveals that the higher overall accumulation rates and 230Thexcess inventories in the off‐plain cores are due to an increased fine (&lt;5 µm) component fraction, whereas the flux of coarser material is similar to that received on the plain. This suggests that the higher fluxes of materials observed are physically (rather than biogeochemically) driven and also that drift formation has been continuously active in the late Holocene. Sections of all the cores where regular accumulation is defined by the radiocarbon data are modeled first by a linear radiocarbon age/depth model and second by a constant rain (230Thexcess)0 model prorated for the observed core inventories. These modeling approaches yield historical mass accumulation rate estimates which are generally in reasonable agreement (±30%), but the differences observed appear to be well organized in time rather than random.

Trends in Chesapeake Bay sedimentation rates during the late Holocene

Trends are discernible in the estimates of late Holocene rates of sedimentation and sea-level rise for the Chesapeake Bay. During most of the Holocene Epoch sedimentation rates and relative sea-level rise were equal, within the limits of measurement, at approximately 1 mm yr−1. Sedimentation rates measured over the past century, however, are nearly an order of magnitude higher, while the rate of relative sea-level rise for the Chesapeake Bay now averages 3.3 mm yr−1, as measured on long-term tide gauge records. When the acceleration in these rates occurred is uncertain, but it appears to have been confined to the past millennium, and probably to the past few centuries. The rapid sedimentation rates recorded during historic time may be a temporary disequilibrium that has resulted from a recent acceleration in the rate of relative sea-level rise.