Linking early diagenesis and relative sea-level changes in ancient corals: a multiproxy approach from the Benassal Formation (Lower Cretaceous, Maestrat Basin, E Spain)

Geochemical characteristics of the Permian Changxing Formation reef dolomites, northeastern Sichuan Basin, China

Analysis and integration of data obtained in our field and laboratory investigations of 2008–2012 together with results of previous paleogeographic studies were conducted to reveal parameters and factors of the post-glacial changes in the relative sea-level on the Fildes Peninsula and the King George Island. Results of dating of organic material taken from cross-sections of Quaternary deposits, data on morphology of marine landforms as well as on bottom sediments in lakes were used to construct a curve of changes in the relative sea-level. Our research has shown that the rapid rise of relative sea level in the area (since the beginning of the Holocene) decelerated about 8000 years BP, achieving its maximum about 7000 years BP. This was followed by the fall of relative sea-level (the land elevation) by 18–20 m in total, and it was characterized by relatively high rate of fall during periods of 6000– 5000 years BP, 4000–2500 years BP, and during the last 1500 years; the rate decreased in 5000–4000 years BP and 2500– 1600 years BP. The changes in relative sea level in this region were determined by the following factors: the eustatic component of the global changes in sea-level and, possibly, oscillations in the global sea level of another nature; local parameters of the Last glacial maximum; a course of the Peninsula deglaciation; regional physical characteristics of the Earth's crust and the mantle substances; local tectonic processes, including the isostatic rebound. Since the beginning of the Holocene up to about 7000 years BP, the main contribution to changes of the relative sea-level in this area was made by the global eustatic factor. The subsequent fall of the relative sea-level (elevation of the Peninsula surface) proceeded under condition of reduced role of the eustatic factor and predominance of other factors.

Studies of the coastal sedimentary record have allowed both the reconstruction of relative sea-level changes and the determination of local rates and magnitudes of tectonic deformation, particularly in tectonically active areas. Despite their successful use elsewhere, studies of this type are much less common for the Mexican Pacific coast, which parallels the Cocos-North America subduction plate boundary. Stratigraphic, geochemical and microfossil data from sediments in Laguna Mitla, the Pacific coast of Guerrero, Mexico, document late-Holocene sea-level changes induced by tectonic activity in the Mexican subduction zone. Three major events are identified. First, the formation of the lagoon by c. 4630 yr BP, as indicated by a freshwater to brackish peat. Second, a relative sea-level rise, or land subsidence, as indicated by a shift from a freshwater marginal lagoon environment to a marine setting, preceded by a marine inundation represented by a sand unit (possibly a tsunami deposit), by c. 3400 yr BP. And finally, a return to lagoonal conditions indicating a drop in relative sea level or coastal uplift by c. 2300 yr BP. The Laguna Mitla stratigraphy indicates general coastal subsidence or relative sea level rise of c. 1 mm/yr. We argue that these relative sea-level (land-level) changes have been induced by tectonic activity associated with the Mexican megathrust. A plausible explanation for the 3400 yr BP marine inundation is probably a tsunami produced by a large seismic event accompanied by coastal subsidence. Discrete fining upward, fine to coarse, sand units with an erosional basal contact, medium to poor sorting, and clay/mud rip-up clasts; an increase in Na and Sr elemental concentrations, indicative of a marine origin; and the landward extent of the sands support a tsunamigenic source for these deposits. However, these apparent tsunami deposits require further study to determine their lateral extent and to assess whether they can be correlated from one site to another. This study demonstrates the applicability of a multiproxy sedimentary approach in interpreting relative sea-level (land-level) changes and to derive data on related earthquake and tsunami events in tropical coastal lagoons.

The Turonian-Coniacian Upper Ferron Sandstone Last Chance Delta was deposited along the western margin of the Western Interior Seaway as a wave-modified, river-dominated deltaic system. The Last Chance Delta was deposited during a slow relative sea-level rise whose rate of rise decreased with time. The sedimentation rate progressively decreased throughout the deposition of the Last Chance Delta. Architectural and sedimentological data for deltaic near-marine sandstones indicate that primary deltaic depositional style is directly correlated with degree of wave-modification, which is controlled by the ratio of sedimentation rate to the rate of relative change in sea level. The progradational parase-quence sets have a mean sandstone dip length/thickness aspect ratio of 788. The aggradational parasequence sets are shorter with a mean length/thickness of 520. The retrogradational parase-quence sets are shorter and thinner with a mean length/thickness of 397. River-dominated progradational parasequences have a mean length/thickness of 611, a mean width/thickness of 212, and a mean length/width of 1.9. River-dominated, wave-modified progradational parasequences have longer dip lengths and a higher length/thickness of 845. The aggradational parasequences have similar lengths as the wave-modified parasequences, with a mean length/thickness of 606. The retrogra-dational parasequences are short and thin, with a mean length/thickness of 793. Stream-mouth bar, reworked stream-mouth bar, and upper shoreface deposits show trends of length/thickness changing systematically with degree of wave-reworking, from a mean length/thickness of 479 (width/thickness = 256; length/width = 1.9) in river-dominated parasequences to 546 and 595 in reworked stream-mouth bar and upper shoreface deposits, respectively. Retrogradational parasequences have higher upper shoreface mean length/thickness aspect ratios of 649. Proximal delta-front, reworked proximal delta-front, and middle shoreface deposits show similar trends. River-dominated parasequences have mean proximal delta-front length/thickness of 425 (width/thickness = 472; length/width = 1.8) and reworked proximal delta-front and middle shoreface deposits have a mean length/thickness of 827 and 912, respectively. Retrogradational parasequences have a mean middle shoreface length/thickness of 807. Distal delta-front, reworked distal delta-front, and lower shoreface deposits also show similar trends. River-dominated parasequences have mean distal deltafront length/thickness ratios of 518 and reworked distal delta-front and lower shoreface deposits have mean length/thickness ratios of 819 and 2469, respectively. Retrogradational parasequences have a mean lower shoreface length/thickness of 981. Architectural and sedimentological data for fluvial channel-belt sandstones indicate that over-all geometry, internal architecture, and preserved sedimentary structures are directly correlated with sedimentation rate and rate of relative change in sea level. Internal channel belt architecture is controlled by the response of the river equilibrium profile to changes in relative sea level and shoreline position. Channel belts, from progradational parasequence sets, deposited during times of high sedimentation rate and moderate relative sea-level rise, are laterally restricted and multi-storied with channel-fill elements stacked vertically within the channel-belt boundaries. Fluvial channel belts in the upper delta plain have average width/thickness aspect ratios of 28.8; distributary channel belts located near the paleoshoreline have average aspect ratios of 19.0. Fluvial channel belts from aggradational parasequence sets deposited during times when sedimentation rate was approximately equal to the rate of relative sea-level rise are laterally extensive and multi-storied with channel-fill elements stacked laterally en-echelon. Fluvial channel belts in the upper delta plain have average width/thickness aspect ratios of 59.2; distributary channel belts, located near the paleoshoreline have a mean aspect ratio of 12.1. Channel belts from retrogradational parasequence sets deposited during times when sedimentation rate was less than the rate of relative sea-level rise are laterally extensive and sheet-like with average aspect ratios of 100.0. Their channel-fill elements generally stacked vertically within the channelbelt boundaries. Amalgamated, braided fluvial deposits occur within small high-gradient incised valleys developed during periods of 4th- and 5th-order relative falls in sea level. The preserved incisedvalley fluvial deposits, within the Last Chance Delta, range in width from 1.3–8.8 km (0.8–5.5 mi) and in thickness from 9–32 m (27–96 ft); the average width/thickness aspect ratio is 169.4 near the valley mouths and 644.1 at 10–17 km (6–11 mi) inland from the mouth.

In contrast to terrigenous margins, the stratigraphic response of carbonate platforms to relative sea level changes is influenced by carbonate productivity, dissolution, and diagenesis. Using seismic reflection and Ocean Drilling Program (ODP) drilling data from Broken Ridge, we assess the importance of these processes in controlling the stratigraphic response of a carbonate platform to relative sea level changes. Prior to middle Eocene rifting, Broken Ridge and Kerguelen-Heard Plateau constituted a large carbonate platform. ODP drilling data from the Kerguelen-Heard Plateau (Leg 120) and Broken Ridge (Leg 121) reveal that the carbonate platform had two major episodes of tectonic uplift. The early Maastrichtian uplift was confined to the southern section of the Kerguelen- eard Plateau (Sites 747, 748) and gently tilted the platform toward the north. The middle Eocene rift-induced uplift affected both Broken Ridge and the northern section of the Kerguelen-Heard Plateau (Sites 752-755). Watergun seismic reflection and drilling data indicate the following stratigraphic response of the platform to relative sea level changes. (1) Prograding clinoforms consisting of carbonate sediments were deposited during a long-term relative sea level rise. Submergence of the uplifted parts of the platform (southern Kerguelen-Heard Plateau) increased the area available for productivity allowing the carbonate sediment to prograde northward into the basin during the rise. (2) Onlapping sequences consisting of carbonate detritus were deposited in the basin during the middle Eocene relative sea level fall. The carbonate strata on Broken Ridge were uplifted to at least wavebase and eroded. The detritus was transported northward toward the basin and onlaps the preexisting strata. The approx mate volume balance between the sediment eroded from the crest of Broken Ridge and the onlapping sediments deposited along the northern slope suggests that mechanical erosion and transportation of carbonate sediment into the deep sea were important processes controlling the stratigraphy at Broken Ridge during the relative sea level fall. We propose that the stratagraphic response of Broken Ridge to the middle Eocene relative sea level fall is consistent with stratigraphic predictions based on terrigenous margins. However, during a relative sea level rise, biogenic carbonate production may allow carbonate sediment to prograde basinward despite the fact that water depths are increasing. Stratigraphic models based on terrigenous margins do not account for the increase in sediment supply along carbonate margins during a relative sea level rise, and thus require minor modification in order to predict the development of the prograding clinoforms.

Petrography, trace elements and oxygen and carbon isotopes of Gordon Group carbonates (Ordovician), Florentine Valley, Tasmania, Australia

Sequences in the Sikanni Formation in the frontier Liard Basin of northwestern Canada—evidence for high frequency late Albian relative sea-level changes

Relative sea level and wave energy changes recorded in a micro-tidal barrier in southern Brazil

The nature and impact of relative sea level rise on the coastal areas of Bangladesh: trend analysis and vulnerability assessment

Using seismic-reflection data and ODP drilling results collected from Broken Ridge we examine the stratigraphic response of a carbonate platform to relative sea-level changes. Interpretation of the seismic-reflection and drilling data indicates the following stratigraphic response of the platform to relative sea-level changes: prograding clinoforms comprising lower Maestrichtian to middle Eocene limestones and chalks were deposited during a long-term relative sea-level rise. High productivity allowed the carbonate sediment to prograde north into the basin during the rise. Onlapping sequences consisting of carbonate detritus were deposited along the northern slope of Broken Ridge in response to the middle Eocene rift-induced relative sea-level fall. The carbonate strata on Broken Ridge were uplifted to at least wave base during middle Eocene time and consequently eroded. The carbonate detritus was transported north into the basin and onlaps the preexisting slope of Broken Ridge. We propose that the stratigraphic response of Broken Ridge to the middle Eocene relative sea-level fall is consistent with stratigraphic predictions based on terrigenous margins. However, during a relative sea-level rise, biogenic carbonate production may allow carbonate sediment to prograde basinward despite the fact that water depths are increasing. Stratigraphic models based on terrigenous margins do not account for the increase in sediment supply along carbonate margins during a relative sea-level rise and thus require minor modification in order to predict the development of the prograding clinoforms.

I am writing this note in reference to one paragraph of a generally interesting report, “Changes in Relative Mean Sea Level’ [by the IAPSO Advisory Committee on Tides and Mean Sea Level], which appeared in the November 5, 1985 issue of Eos [p. 754]. In this paragraph the authors question the nature and even existence of the secular motion of the earth's rotation pole. The paragraph states that because of supposed extreme irregularities in the observed (ILS) motion, “it may even be that the entire apparent secular motion of the pole is an artifact of systematic efforts [this word should probably read ‘errors’] in the ILS” data.

We predict the decadal change in position of three American Samoa mangroves from analysis of a time series of remotely sensed imagery, a geographic information system, tide gauge data, and projections for change in sea-level relative to the mangrove surface. Accurate predictions of changes to coastal ecosystem boundaries, including in response to projected relative sea-level rise, enable advanced planning to minimize and offset anticipated losses and minimize social disruption and cost of reducing threats to coastal development and human safety. The observed mean landward migration of three mangroves' seaward margins over four decades was 25, 64, and 72 mma(-1), 12 to 37 times the observed relative sea-level rise rate. Two of the sites had clear trends in reductions in mangrove area, where there was a highly significant correlation between the change in position of the seaward mangrove margin and change in relative sea-level. Here it can be inferred that the force of sea-level rise relative to the mangrove surface is causing landward migration. Shoreline movement was variable at a third site and not significantly correlated with changing sea-level, where it is likely that forces other than change in relative sea-level are predominant. Currently, 16.5%, 23.4%, and 68.0% of the three mangroves' landward margins are obstructed by coastal development from natural landward migration. The three mangroves could experience as high as a 50.0% reduction in area by the year 2100. A 12% reduction in mangrove area by the year 2100 is possible in the Pacific islands region.

Geochemical constraints of hydrothermal alteration of dolostones: An example of Lower Cretaceous Qamchuqa Formation, Kurdistan Region, northern Iraq

Paleoenvironments and relative sea-level changes caused by regional tectonics during the last 4500 years in Kumihama Bay, northern Kyoto Prefecture, central Japan

Point analyses of natural calcite cements by SIMS confirm the earlier suggestions that 20 ppm Mn is required to activate luminescence, whereas Fe concentrations in excess of 1400 ppm quench it partly, independently of the Mn content. Below this Fe threshold, luminescence is bright at Mn concentrations in excess of 225 ppm. In the range 20-225 Mn, all types of luminescence--dull, luminescent, and nonluminescent--can occur. This undifferentiated domain is evident also from a compilation of literature data. The type of luminescence is not a simple function of Fe and Mn concentrations; other parameters influence CL. Sinc most diagenetic calcite cements have Fe and Mn concentrations that place them within the field of mixed cathodoluminescence, these results force reassessment of models that equate the type of luminescence with the redox state of the diagenetic environment.