Vertical Stratigraphic Sections Research Articles

Debris-flow avulsion tendency estimated from boreholes or channel cuts

Debris fans are an important landform for human habitation and development in mountainous regions. While much research in debris flow runout has focused on quantifying recurrence intervals and volume predictions, less research has focused on predicting their paths, which is important to reduce hazards to life and property. This project uses a quantitative stratigraphy tool, the compensation index, to evaluate the likelihood of debris path alteration by avulsion. The compensation index is a quantitative measure of the strength of compensational stacking, which measures the tendency of flow events to preferentially fill topographic lows. A significant constraint on the use of the compensation index for debris-flow hazard analysis is the need for large natural exposures of fan stratigraphy and the difficulty of mapping flow boundaries. Therefore, a more readily available proxy for estimating the compensation index of debris fans is needed, such as vertical stratigraphic sections from borehole data or natural channel incisions. Data from four previous studies was used to correlate trends in unit thickness to the compensation index calculated using data generated from simulated boreholes along the measured cross-sections. It was found that the central tendency and coefficient of variation of unit thickness had moderate correlation to the compensation index, and therefore predictive capacity, in both submarine and subaerial debris fans. By contrast, the same data for fluvial channelized floodplains revealed no correlation to compensation index. Therefore, a limited number of vertical stratigraphic sections could provide a reasonable estimate of the compensation index, and therefore avulsion tendency, of a debris-flow deposit.

One catastrophic flood every millennium: Synchronicity of extreme floods and global warm periods in the multi-archive record of the Roman theatre of Guadix (Granada, SE Spain)

Past global changes are typically registered in both natural (e.g., geologic-geomorphological, atmospheric-climatic, hydrologic-glacial and biological) and cultural records (e.g., archaeological, historical and documentary sources). Nevertheless, there are few sites in the world where sedimentary and archaeological evidence combine to provide information about two or more past millennial climate changes. In this regard, the Roman city of Guadix (Granada, SE Spain) represents a singular location, whose Roman theatre (1st century CE), recently discovered in 2007, contains palaeo-flood evidences that can be related to the two latest global warm periods: the Roman and Medieval epochs.In this research, detailed geological analyses are carried out. These analyses consisted in careful descriptions of vertical stratigraphic sections (lithology, structures…) and lateral correlation panels; as well as fluvial facies models to interpret the sedimentary environments for each sequence. This sedimentological information was combined with the study of archaeological remains, radiocarbon dating and optically stimulated luminescence, and three major flood events have been identified: two of them dating back to the beginning of the 1st century CE (period of the Pax Romana Empire); and the other occurring at the end of the 12th century (Islamic Almohad period). Such extreme hydrological events were synchronous with two warm periods: the Roman Climatic Optimum and the Medieval Warm Period. This seems to suggest that the meteorological fluctuations associated to climate changes during warming periods (such as the current one associated with present-day climate change) very likely produce such extraordinary or extreme events, which can mobilise large amounts of solid load (sands, silts and clays) and trigger sudden changes in the configuration of the river system (channel avulsions, meander cut-offs and captures among tributaries) and alluvial fans (at tributary mouths).We believe that the documented observations provide an analogy for the current warming period. In this regard, flood risk management in the current city of Guadix, whose hazard and risk maps were drawn up according to the criteria of the European Flood Directive, should take into account: (i) the millennial recurrent character of catastrophic floods in Guadix, well above the 500-year return period officially considered; (ii) the importance of the mobilisation of solid load in flood hazard and risk, which can obstruct drains and reduce the capacity of channels and bridges; (iii) the geomorphological dynamics, capable of modifying the position of the channels and thus the delimitation of hazard and risk zones; (iv) the role of non-permanent tributaries of the Guadix River during storms and heavy rain, related to quasi-stationary convective cells. Only in this way, will flood hazard and risk maps be useful in territorial and urban planning, civil protection during emergencies and the reduction of damage from future catastrophic floods. The present study highlights how geoarchaeological and palaeo-environmental records can be a highly valuable source of data for the improvement of flood hazard assessments in the 21st Century.

Bedding Scale Correlation on Mars in Western Arabia Terra

AbstractLayered rocks in the Arabia Terra region of Mars preserve a record of the planet's ancient climate. However, the exact formation mechanism of these rhythmically layered deposits is currently unknown. We previously proposed two distinct regionally correlative units of the Arabia Terra layered deposits based on their bedding thicknesses, orientation, and morphology from High Resolution Imaging Science Experiment stereo observations. For this work, we selected two adjacent craters in Arabia Terra, Sera and Jiji, for further study to test the proposed stratigraphic correlation. We constructed vertical stratigraphic sections of the deposits from dip‐corrected bed thickness measurements and local stratigraphic correlations. We found that individual beds maintain a consistent thickness over kilometer scales but are somewhat variable at the basin scale. Each crater exhibited strata with a thinning‐upward trend that terminated at terraces with inconsistent bedding, possibly indicating an equilibrium elevation for the formation mechanism. We also identified a probable stratigraphic correlation between basins using the similarities in bedding characteristics and patterns of measurable differences in bed‐to‐bed thicknesses, indicating synchronous strata. The planar bedding and uniform thickness of the beds within the deposits are consistent with airfall deposition over a prolonged geologic period. This process likely occurred under comparably dry conditions relative to the previously proposed depositional and diagenetic formation mechanisms.

The interplay between cm- and m-scale geological and geomechanical heterogeneity in organic-rich mudstones: Implications for reservoir characterization of unconventional shale plays

In this study, the vertical and lateral geological and geomechanical heterogeneity of the Duvernay shale play of Western-Central Alberta (Canada) is investigated at two different scales (meter and centimeter) using an outcrop-based approach. Twenty-five hand samples from the Duvernay outcrop-equivalent Perdrix Formation were collected along one vertical stratigraphic section and analyzed for elemental composition and mechanical hardness. Data points were acquired at every node of a 1cm x 1cm grid built on the cut face of each sample. Results show that significant compositional and mechanical heterogeneity is present both when comparing different rock samples and when considering all the measurements taken within the same rock sample. Our study shows that intra-sample variation in chemical composition may exceed 20% on a relative basis, and intra-sample variation in mechanical hardness may exceed 50% on a relative basis. Multi-variate statistical models show that a positive relationship is observed between mechanical hardness and XRF Calcium content (carbonate proxy), while a negative relationship is observed between mechanical hardness and XRF Aluminum content (clay proxy). Our analysis shows that heterogeneity in the Perdrix Formation is facies-dependent: mudstones that are relatively lean in Calcium but rich in Silicon and Aluminum have up to twice the compositional and mechanical heterogeneity of facies that are relatively rich in Calcium and poor in in Silicon and Aluminum. Based on the analyzed data and published literature, we support the hypothesis that by decreasing the scale of investigation we increase the magnitude of heterogeneity that can be resolved when measuring organic-rich mudstone composition and mechanical hardness. This understanding can be applied to improve 3-D subsurface models, where upscaling often oversimplifies the reservoir and is unable to adequately resolve reservoir heterogeneity and its influence on reservoir potential and behaviour when undergoing hydraulic fracturing treatment.

Controlling role of Ta-d pumice on the coseismic landslides triggered by 2018 Hokkaido Eastern Iburi Earthquake

The 2018 Hokkaido Eastern Iburi Earthquake triggered massive landslides in the pyroclastic fall deposits. Most of them are shallow debris slides. Based on the field reconnaissance, the shallow debris slides were further categorized into three types: steep translational sliding, gentle translational sliding, and mobilization of V-shaped convergent sliding masses. The three types of shallow landslides were investigated in depth through longitudinal sections, vertical stratigraphic sections, and in situ hardness tests. All three types of shallow landslides were found to initiate from the liquefied failure of the weak Ta-d pumice layer and further evolve to the overall mobilization of the superimposed pyroclastic fall deposits along the liquefied sliding zone. To testify the controlling role and to study the shear behavior as well as the anti-liquefaction strength of the weak Ta-d pumice layer, a series of laboratory tests (basic physical tests and triaxial tests) were conducted on the soils around the sliding zone. The test results indicate that the medium sandy Ta-d pumice MS and the fragile Ta-d pumice CS have lower shear resistance and anti-liquefaction strength than other layers and they can be easily liquefied under intense ground motion. One paleosol layer underlying the Ta-d pumice shows low permeability and enables weathering and soil erosion of the Ta-d pumice, resulting in the widespread existence of the fragile and medium sandy pumice layers in Ta-d. In addition, the positive relationship between coseismic landslide density and Ta-d pumice thickness demonstrates the controlling role of the Ta-d on Iburi landslide occurrence from a macro perspective.

Using Carbon Isotope Equilibrium to Screen Pedogenic Carbonate Oxygen Isotopes: Implications for Paleoaltimetry and Paleotectonic Studies

Stable isotope compositions of pedogenic carbonates (δ13Ccarb, δ18Ocarb) are widely used in paleoenvironmental and paleoaltimetry studies. At the same time, both in vertical stratigraphic sections and in horizontal transects of single paleosols, significant variability in δ18Ocarb values is observed well in excess of what could reasonably be attributed to elevation changes. Herein, a new screening tool is proposed to establish which pedogenic carbonate δ18Ocarb compositions reflect formation in isotopic equilibrium with environmental conditions through the use of the co-occurring δ13Corg composition of carbonate-occluded or in profile organic matter, where Δ13C = δ13Ccarb – δ13Corg. Based upon 51 modern soils from monsoonal, continental, and Mediterranean moisture regimes, Δ13C = +15.6 ± 1.1‰ (1σ), which closely matches theoretical predictions for carbonates formed at carbon isotope equilibrium through Fickian diffusion. Examples from both disequilibrium and equilibrium cases in the geologic record are examined, and it is shown that previous δ18Ocarb records used to infer Cenozoic uplift in southwestern Montana do not provide any constraint on paleoelevation because >90% of the pedogenic carbonate isotopic compositions are out of equilibrium. Guidelines for future paleoaltimetry studies include collection of both vertical stratigraphic sections and lateral transects, of at least three nodules per horizon, petrographic screening of nodules for diagenesis, collection of at least one independent proxy for paleoclimate or paleovegetation, and screening δ18Ocarb values using Δ13C measured for each paleosol.

Palaeosol stratigraphy across the Permian–Triassic boundary, Bogda Mountains, NW China: Implications for palaeoenvironmental transition through earth's largest mass extinction

Upper Permian and Lower Triassic palaeosols from northeastern Tethyan localities exposed within the Bogda Mountains, NW China, provide a wealth of information regarding long-term palaeoclimatic and palaeoenvironmental variations. Wuchiapingian palaeosols are characterized by intense redoximorphy, accumulation of vascular plant matter, accumulation of clay minerals and Fe-oxides, slickensides, and clastic dikes, suggesting a soil moisture regime that ranged from perennially wet to distinctly seasonal in soil moisture budget. Changsinghian to early Induan palaeosols include subsurface accumulations of clay and carbonate as well as surficial accumulations of organic matter, indicative of sub-humid to sub-arid soil moisture and variable soil moisture regimes. Induan to Olenekian palaeosols contain pedogenic CaCO 3 accumulations and gypsum pseudomorphs, indicating a drier environment characterized by net soil moisture deficiency. Elemental composition of palaeosol matrix was used to estimate palaeoprecipitation through the chemical index of alteration minus Potassium (CIA-K) proxy. Estimates from various Wuchiapingian strata indicate relatively stable palaeoprecipitation. During the late Changsinghian and early Induan, palaeoprecipitation appears to have decreased from 1100 to 230 (± 180) mm/year over less than 100 m of vertical stratigraphic section. In the Induan and Olenekian, palaeoprecipitation appears much less stable than in Wuchiapingian, with values vacillating from 290 to 1014 mm/year. The transition to a relatively unstable precipitation state coincides generally with the Permian–Triassic boundary, and may reflect climatic disturbances associated with the end-Permian extinction event in addition to altered atmospheric circulation patterns resulting from regional tectonics, moisture availability, and expansion of the subtropical high pressure belt.

Validation of Hurst statistics: a predictive tool to discriminate turbiditic sub-environments in a confined basin

ABSTRACT Turbidite sequences within confined basins constitute important hydrocarbon reservoirs world-wide and, for this reason, the discrimination of sedimentary sub-environments based on an objective statistical method is of interest for pure and applied science. We investigated the potential use of the Hurst test as a statistical tool to discriminate sub-environments within geologically complex turbiditic units that fill a confined basin with well-exposed facies transitions and onlaps, at the scale of several stacked reservoirs (Cengio and Bric la Croce–Castelnuovo Turbidite Systems in the Tertiary Piedmont Basin, Oligocene, northern Italy). In vertical stratigraphic sections, the Hurst test determines the degree of clustering of low and high values of sedimentological variables, such as bed thickness, grain size and sand/mud ratio, which are dependent on sub-environments of deposition. We applied the Hurst test to depocentral and marginal sub-areas across the basin (parallel and perpendicular to the main palaeocurrent direction), documenting a different clustering of thick and thin beds, and of high and low values of the sand/mud ratio, in the depocentre–distal sector with respect to the onlap areas. A new field (onlap sub-environment) could thus be added to the classification diagram of turbidite settings based on the Hurst index. The Hurst phenomenon (clustering of high and low values of the selected variables) was also able to distinguish between proximal and distal (depocentral) lobe settings, and to recognize the fingerprint of the different depositional lobes (fully confined aggrading, prograding, backstepping). The map of turbidite sub-environments obtained by interpolation of the Hurst index is quite comparable to the field-observed facies map, providing impressive robust validation of the Hurst statistics. This method seems to represent a very promising predictive tool for subsurface studies of turbiditic oil fields based on core and log analyses.

North polar cap of Mars: Polar layered deposit characterization and identification of a fundamental climate signal

The record of recent climate change on Mars is encoded in the polar layered deposits within the north polar cap. Individual Mars Orbiter Camera (MOC) images of exposed layer sequences in cliffs and troughs provide the equivalent of high resolution “cores” through many sections in the upper part of the north polar layered terrain. In order to decode this record it is necessary 1) to quantitatively characterize the layers in individual “cores” and 2) to assess possible correlations between “cores” in vertical layered deposit sequences across the cap. We use two techniques commonly employed in paleoceanography for the study of deep‐sea sediment cores on Earth to establish the characteristics of layers in individual cores (Fourier analysis) and to determine the correlation between cores (curve‐shape matching algorithms). Application to “cores” (vertical sections) of the north polar layered terrain on Mars reveals several fundamental properties of north polar cap stratigraphy: 1) Fourier analysis of the layer vertical sequences reveals a characteristic and repetitive wavelength of ∼30 m thickness throughout the upper part (Zone 1) of all sequences analyzed. 2) Application of curve‐shape matching algorithms demonstrates that layers correlate across at least three quarters of the cap (∼6 × 105 km2) in the 13 images analyzed to date. 3) Assessment of geometric relationships shows that layers are not horizontal, but rather have an apparent dip of approximately 0.5 degrees. We interpret these results as follows: 1) The fundamental ∼30 m signal is interpreted as a climate signal that may correspond to a 51 kyr insolation cycle. 2) The lateral correlation and broad distribution of these layer sequences strongly imply that layer accumulation processes are widespread across the cap, rather than confined within a single trough or region. 3) Local to regional variability in individual layer thicknesses (and thus accumulation and sublimation rates) is typically less than a factor of 2.5, providing the ability to study regional trends, but often making it difficult to correlate visually the vertical sequences in individual cores. Finally, initial examination of layers located deeper in the stratigraphic sequence within the north polar cap than the ∼300 m thick Zone 1 provides evidence for a unit less than 100 m thick (Zone 2) in which the fundamental ∼30 m sequence is not detected. We interpret this as a deposit having formed during a recent high‐obliquity phase of Mars, during which time polar volatiles underwent mobilization and were transport equatorward, leaving a polar lag of dust‐rich material. The most recent “ice age” (∼0.5–2 Ma) offers a plausible candidate for this period of ice cap removal and lag deposit formation. An underlying Zone 3 (∼200 m) contains a dominant 35 m signal, and a lowermost Zone 4 (∼200 m) contains multiple signals but no dominant one. Together these four zones represent ∼800 m of vertical stratigraphic section, about one‐fourth of the total thickness of the cap. These findings support earlier interpretations that orbital parameter variations could cause significant erosion and possibly complete removal of the polar caps. The interpreted crater retention ages of the layered terrain are consistent with the correlations and vertical sequences described here, suggesting that the polar caps wax and wane throughout geological history, depending on the evolution of orbital parameters. Definition of the ∼30 m unit signal holds promise for determining 1) the detailed origin of individual layer types, 2) the nature of deposition and sublimation processes and their relation to insolation geometry across the polar cap, and 3) correlation with and comparison to the south polar layered terrain record.

SEQÜÊNCIAS E TRATOS DE SISTEMAS DEPOSICIONAIS DO GRUPO ITARARÉ, NORTE DO ESTADO DO PARANÁ

A representative vertical stratigraphic section about 800m thick was measured in outcrops of the Carboniferous-Permian Itarare Group in northern Parana State. Five depositional sequences bounded by disconformities were recognized and their facies associations described. The outcrop section shows good correction with well logs and the sequences may be traceable over 400 kilometers across the basin in a EW depositional strike section. The five sequences have the same basic stratigraphic signature, which represents the glaciomarine sedimentary response to advance and retreat of glaciers. Ideally, three successive facies associations would compose each sequence, but the lower and upper ones may be absent. The lower facies association occurs only in the two lowermost sequences and includes subglacial facies as tillites and boulder conglomerates (glacial maximum system tract). The subglacial facies are covered by conglomerates and sandstones, which in turn are overlain by diamictites, turbidites and finely laminated facies with dropstones, composing a typical retrogradational facies stacking resulting from deglaciation (deglaciation system tract). Lying directly over the disconformities when subglacial facies do not occur, the deglaciation facies association is present in all sequences and represents the bulk of the stratigraphic record of the Itarare Group. Fine-grained laminated facies represent the record of the maximum glacial retreat during interglacial periods and contain the maximum seawater-flooding surface of each sequence. Coarsening upward facies association may be present in the upper part of the sequences, interpreted as the sedimentary response to the beginning of new glacial advances (glacial advance system tract). This facies association could represent progradation in highstand system tracts, but coastal and continental facies were not observed in the studied area.

A pragmatic test of the early origin and fixation of gamma-ray spectrometric (U, Th) and magneto-susceptibility (Fe) patterns related to sedimentary cycle boundaries in pure platform limestones

In a pragmatic test conducted on vertical stratigraphic sections in Quaternary platform limestones of San Salvador Island, The Bahamas, gamma-ray spectrometric (GRS) and magnetosusceptibility (κ) data confirmed that characteristic geophysical patterns are coupled with depositional cycle boundaries. These geophysical patterns appear to develop in the early stages of diagenesis and are long lasting, because similar patterns are found both in the very young Bahamian limestones and in very old Devonian (Givetian-Frasnian) platform limestones of Moravia, Czech Republic. Because the Devonian limestones retain gamma ray and magnetic signatures similar to those seen in the Bahamian rocks, these signals are apparently resistant to changes that occur in later diagenetic alteration, including deep-burial diagenesis and 380 million years of rock-fluid interactions. Each sedimentary cycle on the Bahamian carbonate platform is marked by a terra rossa paleosol horizon that represents a lowstand emergent surface. The paleosol is typically characterized by a GRS-spike related to increased Th concentration. There is only a subtle downward infiltration of that GRS signal, but the Th signal may diffuse upward via sediment recycling. Two U-related GRS maxima are regularly developed within short distances below and above the cycle boundary. The lower anomaly reflects U enrichment in the sub-soil cementation zone, whereas the upper anomaly is related to increased U-content in the flooding beds of the next cycle. Such a combination of one Th-spike between two U-anomalies forms a distinctive tripartite GRS pattern.

Fingerprinting formation-waters using stable isotopes, Midale Area, Williston Basin, Canada

Hydrogen and oxygen isotope compositions of formation-waters from the Williston Basin are reported from produced waters and drill stem tests for a vertical stratigraphic section near Midale, Saskatchewan. These new data, in conjunction with data from the literature, show that Williston Basin formation-waters vary substantially in isotopic composition between aquifers in the stratigraphic section and within the same aquifer regionally. These large isotopic variations enable the use of H and O isotopes in Williston Basin formation-waters to fingerprint sources of contaminant water encountered during drilling and production of hydrocarbons.

Rare-earth element geochemistry of supergene manganese deposits from Groote Eylandt, Northern Territory, Australia

This study examines the rare-earth element (REE) geochemistry of manganese ores and associated rocks in the Mn-oxide deposit at Groote Eylandt in the Northern Territory of Australia. In vertical stratigraphic sections that have undergone lateritization, most REEs show a decrease with depth (except for Yb). Ce and Eu are the most mobile elements, exhibiting increasingly negative anomalies relative to the depletion of the others. Mineral normalization demonstrates that pyrolusite predominantly concentrates La, Ce, Eu, Nd, and Sm, and that goethite is strongly enriched in Gd. All other minerals are of minor importance in determining the REE composition of the bulk sample. The main laterite components show a distinct fractionation in the intermediate and heavy REEs. Kaolinite is depleted in the heavy REEs, whereas iron hydroxides are enriched in these elements. It is not yet possible to compare the REE composition of the ores directly with other deposits of similar origin and alteration history, because of a general lack of analytical data, but marine Mn-oxides from the Gulf of Bothnia (discoidal and flat concretions) display comparable REE patterns and concentrations. Also, similarities to diagenetic manganese oxide nodules are evident, which may indicate the existence of similar redox conditions during the formation of both deposits.

Depositional sequence analysis applied to Late Proterozoic Wilpena Group, Adelaide Geosyncline, South Australia

The initial application of depositional sequence analysis to selected stratigraphic sections through outcropping Late Proterozoic strata of the Adelaide Geosyncline in South Australia has identified major depositional sequences within the several‐kilometre‐thick Wilpena Group. Sharp facies shifts in vertical stratigraphic sections are proposed as actual sequence boundaries which, provided they are the result of eustatic sea level variations, may be key elements for future attempts at inter‐regional chronostratigraphic correlation. Two major sequence boundaries are identified, one at the base of the Nuccaleena Formation (boundary A) and a second at the top of the Brachina Subgroup (boundary B). These are attributed to significant basinward shifts in coastal onlap resulting in subaerial exposure and at least localized erosion, followed in each case by establishment of relatively deepwater environments. A somewhat different boundary (boundary C) is associated with an interval of diagenetic dolostone interbed...

Relict Nature of Sediments and Submarine Topography off Alligator Harbor, Florida: ABSTRACT

An offshore area south of Alligator Harbor, Florida, contains several linear offshore shoals separated by relatively flat-floored valleys. Eighty-six samples from End_Page 2037------------------------------ this area were analyzed for texture by standard laboratory technique. The simplest model of sediment distribution applicable is one of increased grain size and decreased sorting with increased water depth. The correlation of this pattern and other lithologic attributes with a vertical stratigraphic section from an onshore boring suggests that the sampled area represents a subaerially eroded surface in which there has been limited modification by marine processes during the most recent rise in sea level. This modification consists of movement of the finer fraction onto the shoals with minor return movement to some of the deeper channels. The deposition of finer sediments on these previous topographic highs may have accentuated the original (subaerial) relief. End_of_Article - Last_Page 2038------------