Pliocene Stratigraphy at Paredones Blancos: Significance of a Massive Crushed-Rhodolith Deposit on Isla Cerralvo, Baja California Sur (Mexico)

Petrographic study of a well-exposed submarine canyon fill sequence indicates that petrologic variation corresponds to changes in relative sea level. These changes are recorded as textural variation in the canyon fill: a basal coarse-grained unit capped by a middle fine-grained unit records a rise in sea level, and an upper coarse-grained unit records a temporary fall in sea level. These sea level fluctuations do not correlate with published eustatic sea level curves, although the temporary fall may be recorded on a regional (San Diego to San Carlos, 400 km) scale. Sandstone samples from the lower and upper coarse-grained units contain higher concentrations of volcanic rock fragments and plagioclase than the middle fine-grained unit, whereas the middle fine-grained unit contains higher concentrations of quartz and K-feldspar. Fluctuations in relative sea level may have been controlled by tectonic or magmatic events: (1) a tectonically controlled rise in relative sea level could have resulted in longer residence tie of the sediment in a nearshore environment, causing increased mechanical and chemical weathering of the least-resistant grains (i.e., plagioclase and volcanic fragments) relative to quartz and K-feldspar; or (2) a temporary lull in volcanism could have resulted in increased dissection of the arc and decreasedmore » sediment input due to lowered base level within the arc, resulting in a marine transgression and an increase in the concentration of quartz and K-feldspar in the sediment. The lack of significant alteration of the feldspar grains in the fine-grained unit relative to the coarse-grained units may favor the second hypothesis.« less

The middle dolomite unit of the Cambrian Metaline Formation in the Metaline district, Washington, was deposited in a low-energy, shallow-water environment. Deposition occurred as a complex mosaic of subtidal, intertidal, and supratidal environments in a restricted lagoonal and broad tidal-flat setting. Where primary depositional features have not been masked by intense diagenesis, the middle dolomite unit is characterized by seven distinctive lithofacies. The vertical succession of these lithofacies differs from locality to locality and is laterally discontinuous. The seven lithofacies and interpreted depositional environments are: (1) black, birdseye dolomite, deposited in the supratidal zone; (2) cryptalgalaminate dolobindstone, deposited in the upper intertidal and supratidal zones; (3) laminated, intraclastic dolofloatstone, deposited in the outer intertidal zone; (4) gray massive to mottled dolomite, deposited in the intertidal and subtidal zone; (5) intraclastic-oncolitic dolofloatstone, deposited as lag deposits in tidal-flat channels; (6) oncolitic dolofloatstone, deposited n shoal areas in the upper subtidal zone; and (7) lenticular-bedded dolomite, deposited in the subtidal zone. Changes in lithofacies over narrow vertical ranges were due more to changing hydrographic and sediment-supply conditions than to numerous minor eustatic sea level changes. Through time, however, there was a gradual rise in sea level, and subtidal sediments became dominant in the upper middle dolomite unit. The low-energy nature of the middle dolomite unit was the result of either a very long wave fetch, which extended across many kilometers of shallow water, or a remote barrier, which effectively reduced the hydrokinetic energy below that expected in open-marine conditions. End_of_Article - Last_Page 718------------

The modern stratigraphy of clastic continental margins is the result of the interaction between several geological processes acting on different time scales, among which sea level oscillations, sediment supply fluctuations and local tectonics are the main mechanisms. During the past three years my PhD was focused on understanding the impact of each of these process in the deposition of the central and northern Adriatic sedimentary successions, with the aim of reconstructing and quantifying the Late Quaternary eustatic fluctuations. In the last few decades, several Authors tried to quantify past eustatic fluctuations through the analysis of direct sea level indicators, among which drowned barrier-island deposits or coral reefs, or indirect methods, such as Oxygen isotope ratios (δ18O) or modeling simulations. Sea level curves, obtained from direct sea level indicators, record a composite signal, formed by the contribution of the global eustatic change and regional factors, as tectonic processes or glacial-isostatic rebound effects: the eustatic signal has to be obtained by removing the contribution of these other mechanisms. To obtain the most realistic sea level reconstructions it is important to quantify the tectonic regime of the central Adriatic margin. This result has been achieved integrating a numerical approach with the analysis of high-resolution seismic profiles. In detail, the subsidence trend obtained from the geohistory analysis and the backstripping of the borehole PRAD1.2 (the borehole PRAD1.2 is a 71 m continuous borehole drilled in -185 m of water depth, south of the Mid Adriatic Deep - MAD - during the European Project PROMESS 1, Profile Across Mediterranean Sedimentary Systems, Part 1), has been confirmed by the analysis of lowstand paleoshorelines and by benthic foraminifera associations investigated through the borehole. This work showed an evolution from inner-shelf environment, during Marine Isotopic Stage (MIS) 10, to upper-slope conditions, during MIS 2. Once the tectonic regime of the central Adriatic margin has been constrained, it is possible to investigate the impact of sea level and sediment supply fluctuations on the deposition of the Late Pleistocene-Holocene transgressive deposits. The Adriatic transgressive record (TST - Transgressive Systems Tract) is formed by three correlative sedimentary bodies, deposited in less then 14 kyr since the Last Glacial Maximum (LGM); in particular: along the central Adriatic shelf and in the adjacent slope basin the TST is formed by marine units, while along the northern Adriatic shelf the TST is represented by costal deposits in a backstepping configuration. The central Adriatic margin, characterized by a thick transgressive sedimentary succession, is the ideal site to investigate the impact of late Pleistocene climatic and eustatic fluctuations, among which Meltwater Pulses 1A and 1B and the Younger Dryas cold event. The central Adriatic TST is formed by a tripartite deposit bounded by two regional unconformities. In particular, the middle TST unit includes two prograding wedges, deposited in the interval between the two Meltwater Pulse events, as highlighted by several 14C age estimates, and likely recorded the Younger Dryas cold interval. Modeling simulations, obtained with the two coupled models HydroTrend 3.0 and 2D-Sedflux 1.0C (developed by the Community Surface Dynamics Modeling System - CSDMS), integrated by the analysis of high resolution seismic profiles and core samples, indicate that: 1 - the prograding middle TST unit, deposited during the Younger Dryas, was formed as a consequence of an increase in sediment flux, likely connected to a decline in vegetation cover in the catchment area due to the establishment of sub glacial arid conditions; 2 - the two-stage prograding geometry was the consequence of a sea level still-stand (or possibly a fall) during the Younger Dryas event. The northern Adriatic margin, characterized by a broad and gentle shelf (350 km wide with a low angle plunge of 0.02° to the SE), is the ideal site to quantify the timing of each steps of the post LGM sea level rise. The modern shelf is characterized by sandy deposits of barrier-island systems in a backstepping configuration, showing younger ages at progressively shallower depths, which recorded the step-wise nature of the last sea level rise. The age-depth model, obtained by dated samples of basal peat layers, is in good agreement with previous published sea level curves, and highlights the post-glacial eustatic trend. The interval corresponding to the Younger Dyas cold reversal, instead, is more complex: two coeval coastal deposits characterize the northern Adriatic shelf at very different water depths. Several explanations and different models can be attempted to explain this conundrum, but the problem remains still unsolved.

High-frequency sea level and sediment supply fluctuations during Termination I: An integrated sequence-stratigraphy and modeling approach from the Adriatic Sea (Central Mediterranean)

Evaluation of the effect of vegetation roots on the stability of rocky coastal cliffs is necessary to understand geomorphological, environmental and ecological changes in coastlines caused by sea-level rise (SLR). To better understand these topics, coastal cliffs with and without vegetation were investigated. Study cliffs were selected on Taketomi-jima Island and Kuro-shima Island, both in Okinawa, southwestern Japan, because their environmental settings are similar except for the vegetation cover: the islands are only 10 km away from each other and comprise uplifted coral limestone, with an elevation below 5 m. Pandanus odoratissimus (PO) covers the seaward edge of the top surface of the coastal cliffs in Taketomi-jima but is absent in Kuro-shima. Field investigations were conducted on both islands to map the distribution of blocks with the dimension of one side exceeding 1 m to obtain the parameters required for stability analysis. The results indicate that the actual coastal cliff elevation is higher in Taketomi-jima than that in Kuro-shima by approximately 1 m, which results in the presence of PO on the seaward edge of the coastal cliffs in Taketomi-jima and its absence in Kuro-shima. The PO root system likely reinforces the cliffs in Taketomi-jima because the stability analysis results revealed that these cliffs are unstable in terms of their dimensions. Therefore, the possible disappearance of PO in Taketomi-jima caused by an SLR of 1 m in the following several decades or hundred years can increase the apparent frequency of cliff collapses by approximately tenfold.

Sediment properties of lithologic units and their correlation within the lower delta plain of the Nakdong River Delta, southeast Korea

The following chapter is intended to provide a comprehensive field description of the Torridonian, replacing that given in the Geological Survey's NW Highlands memoir of 1907, and citing all relevant literature. Stratotypes and palaeocurrents are described, along with the section lines used to construct the regional stratigraphic sections (Figs 4&23), but detailed consideration of topics such as geochemistry, diagenesis, sediment source areas, palaeomagnetism and basin tectonics is contained in Chapters 2-5. for convenience the rocks are described under thirty-three compact subareas, most of which are shown on Plate 2. This plate also locates all figured maps and sections. The Directory starts with Cape Wrath and continues with sub-areas progressively farther south. The Geological Survey divided the Cape Wrath succession into three stratigraphic units, without definitely correlating any of them with the formations of the Torridon Group that they had established farther south (Peach et al. 1907, p. 292). They described the lowest unit (30 m thick) as coarse pebbly sandstone or basal conglomerate; the middle unit (300m thick) as coarse red sandstone with pebble bands, and the uppermost unit (75 m thick) as finegrained mottled purple and yellow sandstones. Remapping by Williams (1966a, 1969a, 2001) enabled him to subdivide the sequence stratigraphically into five main lithological units, which he called facies associations (FA) even though they always appear in the same order (cf. the definition of facies given on p. 2). Each successive facies is finer than the one below, as shown by the representative logs in Figure

The Tertiary Horse Spring Formation in southeast Nevada records the development of strike-slip and extensional tectonism that formed the Lake Mead left-lateral fault system. Stratigraphic, geochronologic, and mapping studies in the Virgin and south Virgin Mountains clarify the details of that evolution. Exposures of the Horse Spring Formation in the Virgin Mountains area consist of only its lower two members, in ascending order, the Rainbow Gardens and Thumb Members. The Horse Spring deposits are faulted and variably tilted by normal and oblique-slip faults. The Rainbow Gardens Member (ca. 26–18 Ma) was deposited in a broad shallow basin with positive areas to the northwest and southeast; facies changes are gradual and show no influence of active faulting. In contrast, complex facies relations in the Thumb Member are the result of deposition during complex mixed-mode deformation along kinematically linked strike-slip and extensional faults of the Lake Mead fault system, about 16–14 Ma. Tilting of Tertiary and older rocks about horizontal axes apparently occurred late in the extensional episode, at about 14 Ma or later. The Rainbow Gardens Member consists of three units that each represent separate pre-extensional depositional systems. The basal conglomerate is a braid plain or pediment deposited by northeast paleoflow. The middle unit is a mixture of tuffaceous fluvial and lacustrine deposits that are the result of a reversal of drainage to the southwest, into the Rainbow Gardens lake. The change in paleoflow direction is attributed to extensive volcanism to the north that blocked the earlier northeastward flow. The upper unit consists of pedogenically altered, palustrine carbonate rocks that formed during cessation of lacustrine deposition and waning of volcanic activity to the north. A previously unrecognized unconformity that records the onset of faulting separates the Rainbow Gardens Member from the overlying Thumb Member and can be traced throughout the Virgin Mountains area. The unconformity separates the underlying pedogenically altered carbonate rocks from overlying well-bedded lacustrine limestones. Locally the unconformity is marked by conglomerate and megabreccia deposits derived from the underlying Rainbow Gardens carbonate rocks across nearby fault scarps. Carbonate rocks above the unconformity grade laterally and vertically into lacustrine gypsum and fine-grained sandstone of the Thumb Member. These rocks in turn intertongue laterally and vertically with marginal lacustrine and alluvial fan facies. Abrupt influx of megabreccia and coarse conglomerate into lacustrine deposits occurred northward from both the Gold Butte and Lime Ridge faults. At approximately the same time, megabreccia and coarse conglomerate were shed Beard, L. S., 1996, Paleogeography of the Horse Spring Formation in relation to the Lake Mead fault system, Virgin Mountains, Nevada and Arizona, in Beratan, K. K., ed., Reconstructing the History of Basin and Range Extension Using Sedimentology and Stratigraphy: Boulder, Colorado, Geological Society of America Special Paper 303. 27 SP303-03.QXD 4•1•96 2:06 pm Page 27

The effects of particle size and inorganic mineral content on fines migration in fracturing proppant during coalbed methane production

ABSTRACTOil shale (OS) is a particularly promising alternative fossil fuel source. However, very different from coal, its inorganic mineral content is very high. The organic matters (mainly kerogen) are finely distributed in the inorganic minerals. Therefore, the minerals may affect the processing of OS, whose elucidation is critical to the choice of processing conditions. In this work, different minerals (SiO2, CaCO3, and Al2O3) were added to OS with different mass ratios of OS to mineral, respectively. Then, the thermogravimetric (TG) technique was employed to analyze the reaction behavior of these different OS/mineral mixtures in N2 and in air for studying the influence of minerals on the OS pyrolysis in N2 (i.e., retorting) and on the OS combustion in air. The results show that CaCO3 and Al2O3 have a promoting effect on both pyrolysis and combustion of OS, and they can decrease the reaction activation energy of both kinds of processes. However, SiO2 has an inhibitive effect and can increase the reaction activation energy for both kinds of processes. It is hoped that the present study can further increase the understanding toward the effect of different minerals on the OS reactions.

The shelf around Grand Cayman consists of two seaward-sloping terraces separated by a mid-shelf scarp . Except along the exposed windward margin where coral growth is dominant, the upper terrace (0-10 m bal) largely consists of a barren rocky pavement traversed by erosional furrows. Exposure related trends in the morphology and distribution of these erosional features, and the lack of coral growth , demonstrates that the terrace is the result of contemporary erosion during seasonal storms . The upper terrace is terminated by a mid-shelf scarp (10-20 m bal) that, in most areas, is partially to completely buried by modern carbonate deposits . Along narrow sections of the leeward shelf, the scarp is commonly exposed and displays an erosional intertidal notch at - 18.5 m. The lower terrace (12-40 mbsl) extends from the mid-shelf scarp to the shelf edge. Its surface is a modern reef-and- sediment wedge that thickens toward the shelf edge, reaching up to 40 m in thickness. These deposits are underlain by a seaward-sloping bedrock terrace (20-40 m bal). This buried terrace and the mid-shelf scarp, which are geomorphic equivalents of the upper terrace and coastal cliff, represent an earlier episode of marine planation when sea level was stabilized at a lower position. The contemporary erosional features of the upper -shelf terrace and the presence of identical terraces around recently uplifted islands demonstrates that the terraces on Grand Cayman were sculptured by marine erosion during the last deglacial sea-level rise. The lower terrace and the mid-shelf scarp were eroded during a slow-rise episode from 11- 7 ka and were subsequently drowned by an extremely rapid, 5 m rise-event at - 7 ka. Following this catastrophic event, which drowned fast -growing Acropora reefs in other areas of the Caribbean , sea-level stabilized and rose slowly to its present position , producing the upper terrace. This pronounced stepped pat tern in Holocene sea-level rise remains to be confirmed from outside the Caribbean-Atlantic reef province but is consistent with the stepped nature of pre-Holocene sea-level curves. The presence of seaward sloping terraces on many shelves around the world suggests that erosional terrace cutting is a common phenomenon during sea-level rise. In contrast, terraces in areas that have undergone relative sea-level fall are constructional in origin, produced entirely by reef accretion. This suggests that there is a genetic relationship between the sea-level cycle and terrace type: erosional terraces form during rise and constructional terraces during fall.

Facies patterns within the Pleistocene reef terraces along the Red Sea coast exhibit lateral changes over short distances. These changes reflect either transitions within the depositional environment or they are related to minor or major sea level fluctuations. On the basis of quantitative distributions of biota in the field as well as in thin section it is possible to establish and map these lateral patterns. Important biota are framebuilders and secondary reef encrusters (foraminifers, coralline algae). Frequency distributions of sessile foraminifera and scleractinians are strikingly similar to those of the recent environment within diagenetically unaltered terraces. The marine reef terraces occur in different elevated levels above the present sea level. Morphological steps are caused by onlap during different sea levels, by tectonics, or by erosion during transgression. Although several morphological steps exist which obscure the terrace stratigraphy, only three reef units can be distinguished. Each unit exhibits a lateral facies development, which begins at the shore, covering the whole lagoonal facies and ends at the upper reef slope. Besides this lateral facies pattern vertical patterns occur as well, showing a transgressive sequence in the youngest (lower) and oldest (upper) unit and a regressive one in the middle unit. In top quality outcrops, like wadi sections, it is possible to differentiate within the youngest reef unit between three onlaping reef cycles. Such cycles, however, can not be seen in the middle and oldest formations. The three reef cycles within the youngest unit and the three units as well, exhibit different degrees of diagenetic alterations, which are strongly reflected by a gradual reduction in the number of biota. This reduction may be best described as a process of “sieving”. Where these differences in diagenesis are recorded, they correspond to the age of the reef units. U/Th datations of the investigated terraces reveal an age for the youngest unit between 86,000 and 118,000 years B.P.. During this time three major sea level high stands have occurred, which explain the existence of the three reef cycles. The age of the middle formation is around 205,000 years, while the age for the oldest formation can only be assumed to fit in the time span between 290,000 and 340,000 years B.P.. All these data correspond to other published datations along the Red Sea coast.

Geo-archaeological studies along the Mediterranean coast of Israel and its seabed have revealed shipwrecks, anchorages, coastal installations and natural features that can act as markers to estimate the formation date and retreat rates of the coastal cliff of central Israel. The Sharon coastal ridge consists of alternating layers of kurkar (local term for aeolian carbonate-cemented, quartz sandstone) and poorly consolidated palaeosol deposits. The ridge was formed during the Late Pleistocene (about 70,000 to 10,000 yr. BP). At about 7,500 yr. BP, sea level reached the western edge of the present coastal ridge, currently located about 8 m below the present sea level, and a coastal cliff developed. Since then the cliff has continuously been eroded and retreated eastward by natural processes, as well as by anthropogenic impact. This article is an interdisciplinary geo-archaeological study of the extent and rates of retreat of the coastal cliff over the last 7,500 years. The findings suggest that overall the cliff has retreated about 730 m in this period, at an average rate of 9.7 cm/yr. However, the study shows that a considerably higher rate of cliff retreat occurred between about 7,500 and 3,900 yr. BP (about 650 m in about 3,600 years, at about 18 cm/yr). Sea level reached its present level at about 4,000 yr. BP (Middle Bronze Age) and has not changed significantly since. Since the Middle Bronze Age, the cliff has retreated about 80 m in 3,900 years (at about 2 cm/yr). Human activity and sea level rise during the last 100 years have significantly accelerated coastal erosion and cliff retreat.

This dataset contains spatial projections of coastal cliff retreat (and associated uncertainty) for future scenarios of sea-level rise (SLR) in Central California. Present-day cliff-edge positions used as the baseline for projections are also included. Projections were made using numerical models and field observations such as historical cliff retreat rate, nearshore slope, coastal cliff height, and mean annual wave power, as part of Coastal Storm Modeling System (CoSMoS). Read metadata and references carefully. Details: Cliff-retreat position projections and associated uncertainties are for scenarios of 0.25, 0.5, 0.75, 0.92, 1, 1.25, 1.5, 1.75, 2, 2.5, 3.0 and 5 meters of SLR. Projections were made at CoSMoS cross-shore transects (CST) spaced 100-200 m alongshore using a baseline sea-cliff edge from 2016 (included in the dataset). Within the zip file, there are two separate datasets available: 1) one that ignores coastal armoring, such as seawalls and revetments, and allows the cliff to retreat unimpeded (“Do Not Hold the Line”); and 2) another that assumes that current coastal armoring will be maintained and 100% effective at stopping future cliff erosion (Hold the Line). An ensemble of four numerical models synthesized from literature were used to make projections. All models relate breaking-wave height and period to cliff rock or unconsolidated sediment erosion. As sea level rises, waves break closer to the sea cliff, more wave energy impacts the cliffs, and cliff erosion rates accelerate. The final projections are a weighted average of all models (weighted by model performance), and the final uncertainties are proportional to 1) underlying uncertainties in the model input data, such as historical cliff retreat rates, and 2) the differences between individual model forecasts at each CST so that uncertainty is larger when the models do not agree. Uncertainty represents the 95% confidence level (two standard deviations about the mean projection). Model behavior also includes wave run-up and wave set-up that raises the water level during big-wave events. Please refer to Limber and others (2018) for more detailed information on the model and data sources.

Coastal erosion and coastal instability, threatens property, businesses and life. Because of the great concentration of natural resources in coastal zones, it is imperative that coastal change is well understood to allow for effective management and, where necessary, engineering intervention. The development of cliff erosion predictive models is mainly limited to geomorphological data because of the complex interactions between coupled processes acting in time and space result in large-scale variations. There have been few reliable process-response models of cliff recession published. These have been based on functional relationships between the dominant physical processes covering the shoreface, beach and cliff or bluff, avoiding the geotechnical retreat mechanisms and behaviour within the cliff. Under this procedure, the resulting simulations of cliffs of differing behaviour can produce identical annual retreat characteristics despite the potential responses to a changing environment being unequal.
 
 According to this inconvenience, a new process-response recession model has been developed. It incorporates the behavioural characteristics of coastal rock cliffs, the geology of which is dominated by overconsolidated clays and an associated protective talus wedge. This work brings together classic geotechnical stability analyses for rotational landslides called “Swedish” or “Fellenius” Method of slices among with collapse stability analysis for toppling mass failure. Once cliff material has fallen (landslide or toppling failure), colluvium formation at cliff foot is incorporated into the model using three different procedures, according to the geomechanical features of the weathered debris material. The first procedure is based on the friction angle for weathered materials; the second one is based on the angle of reach for landslides and the last one is based on field observations. The irregular recession cyclic pattern continues with the colluvium wedge erosion and the cliff profile steepening before a new failure occurs. Unlike previous models, the calibration parameter is restricted to account for hydrodynamic uncertainties from marine action and not includes the material strength. This new model introduces geotechnical parameters to evaluate the rock mass instability and failure through a safety factor, including RMR, cohesion, friction angle, uniaxial compressive strength of soil or rock mass of each geological component within the cliff, groundwater, etc. Among the capabilities of the model, it provides precise and stable responses to some of the inherent uncertainties in cliff or bluff recession processes, including those morphodynamics caused by different failure mechanisms, such as colluvium generation, groundwater influence, erosive tidal cycles and the cliff behaviour under changing climate conditions (i.e. sea level rise).
 
 In this work, the presented model is validated through profile evolution assessment at various locations of Holderness Coast, UK. The model reflects that the coastal oversteeping is a key factor of instability in coastal cliffs, accompanied by cliff height that determines the failure mechanism present in the study area. Higher sea levels would remove the previous failed material at the base of the cliff more quickly and cause the slope to become unstable more frequently. Sea level rise during this century produce an increasing erosion rates over soft cliffs. Additionally, higher groundwater level also produces an increase in the number and size of the slope failure. The results represent an important step-forward in linking material properties to the processes of cliff recession and the subsequent long-term response under changing environmental conditions.