Fan Deposits Research Articles

Intense and quick land relief transformation in the Little Ice Age: The age of accumulative fan deposits in Serteyka River Valley (Western East European Plain)

In the rich of archaeological sites dated from the late Palaeolithic to the Modern Period region of the Serteyka River, deposits of an extensive accumulative fan were studied in detail. In the lower sector of the present-day Serteyka River valley, the strict chronology and depositional conditions of an extensive accumulative fan deposits were studied in detail. An important part of the project has been also: a checking of usefulness of luminescence, radiocarbon and lead methods of dating in determination of the age of inorganic deposits accumulation The 14C, optically stimulated luminescence (OSL), and 210Pb dating methods were used to determine the fan's deposition age. Then, we discussed the depositional conditions of the accumulative fan by the textural, geochemical, and palaeoecological analysis.The use of 14C and 210Pb methods of dating allows for elaboration of a reliable model of the evolution of slope processes occurring from the 2nd half of 17th c. AD to 2nd half of 19th c. AD (i.e. during the younger part of the Little Ice Age). It was a period of human induced deforestation, as confirmed by the first results of palaeobotanical analyses. In addition, four OSL dates have been obtained, but the acquired age significantly exceeded previous expectations. Three dates indicate the Neolithic period, and a chronological inversion of OSL dates can be seen. This may be due to incomplete bleaching of the sand grains during transport, which indicates that the material being transported had a relatively large volume. The lower deluvium of the accumulation fan is formed by the drainage of hydrated sediment (mudflows).Summarizing, slope sediments can be extremely difficult material for absolute dating. This may be due to the redeposition of the material, the hiatuses in deposition and incomplete bleaching of quartz grains. In the case of 14C (AMS) dating, the dependence is on the presence of plant macroremains within the studied material. In the case of slope deposits, there is a very high probability of the redeposition of organic material. Lead dating, on the other hand, has a small chronological range. Moreover, the dating of inorganic sediments with this method poses many problems, including of a methodological nature. In the tested accumulative fan, as a result of insufficient grain whitening and the short chronological range of the 210Pb method, the 14C method was the main analysis determining the age of inorganic sediments.

Deep-water sedimentation processes on a glaciated margin: The Foula Wedge trough mouth fan, West of Shetland

Trough Mouth Fans (TMF) are sedimentary depocenters located at glaciated continental margins and consist predominantly of glacigenic debris flow deposits. The Foula wedge is a Pleistocene TMF accumulated offshore West of Shetland over the Northeast Atlantic margin. This study presents an analysis of a 3D seismic reflection dataset imaging the distal Foula wedge basin fan deposits between 1010 and 1100 m water depth, directly downslope from a gully system which was active untill the end of the last deglaciation. Results reveal, in unprecedented detail, the basal surface of this fan system and its internal complex architecture. Features typical of both debris flow deposits and turbidites are identified, including a basin channel network with linear and diverging erosional features forming distinctive terminal lobes, stacked and backstepping. The study links the seafloor morphology of the basin fan with its subsurface geomorphology, showing connection with the downslope gully system to the east. It presents evidence for a complex distal depositional system on glaciated margins, characterised by heterogeneous sediment delivery processes and deposits. A conceptual evolution model is proposed, with a glacigenic debris flow-dominated TMF at the LGM, subsequently influenced by meltwater discharges, with deposition occurring as a function of the shelf margin and slope paleo-morphology, slope substrate composition, interaction of downslope and along slope processes and ice-margin dynamics.

Alluvial fan aggradation in low relief, humid‐temperate landscapes, Uwharrie National Forest, North Carolina Piedmont

AbstractWe describe the soils, stratigraphy, distribution and ages of alluvial fans in the North Carolina Piedmont to understand factors contributing to their formation in this low relief, humid‐temperate setting. We find that those contributing factors (i.e., contributing source basin area and rock type; and climate) parallel, but do not precisely mimic those of arid and semi‐arid climate fans. Digital elevation model (DEM) and field observations revealed that about 25% of 209 mapped basin outlets contain alluvial fans. Fans are all < 0.01 km2 in area, with a contributing basin area threshold of ~0.1km2 above which fans are not commonly observed. Fans issuing from basins underlain by more easily weatherable and erodible argillites are generally larger than those that contain more resistant rhyolites. Radiocarbon dates of fan sediments are dominantly late Holocene (13 ages < 3000 ka; two ages between 7000–10,000 ka), with notably no late‐Pleistocene aged fans. We thus infer that fan aggradation is predicated on watershed characteristics – and climates – that favor high sediment supply to discharge ratios. Detailed soil and sediment descriptions from pits located on 15 fans reveal that approximately half exhibit cumulic over‐thickened soil profiles forming dominantly in sheetflood deposits, providing evidence of ongoing, relatively slow deposition. Low iron ratios measured from those fan soils suggests recycling of more developed soils from basin hillslopes. Occasional matrix‐supported debris flow deposits in some fans provide evidence of much less common, rapid (0.5–1 m) fan accumulation. While acknowledging a paucity of detailed climate records in the Piedmont precludes identifying precise mechanistic relationships, our mapping, soils and sedimentologic data suggest that climates favoring modest hillslope erosion without extreme runoff lead to periods of fan aggradation in this transport‐limited landscape. Overall, this work documents significant rock‐type modulated, climate‐driven Holocene landscape evolution in the south‐eastern US Piedmont predating legacy sediment erosion and deposition that has gone largely underappreciated.

Copula-Based Probabilistic Approaches for Predicting Debris-Flow Runout Distances in the Wenchuan Earthquake Zone

After the Wenchuan earthquake, frequent debris-flow disasters caused catastrophic damage to the infrastructures and inhabitants in the downstream. It is very important to properly determine the runout distances of debris flows to delineate potential hazard areas for the postearthquake mitigation work design and effective risk management. However, this is a difficult task due to the high variability and uncertainty of debris flows. This paper developed copula-based probabilistic approaches for predicting the runout distances of debris flows on depositional fans. The proposed approaches integrate the debris flow’s maximum runout distance (L), debris-flow volume (VD), and catchment internal relief (H) into a three-dimensional copula-based probabilistic model. A probabilistic model of debris flows in the Wenchuan earthquake zone was developed based on the field investigation data of 133 channelized debris-flow events. The developed model is able to predict the possible maximum runout distances for a specific hazard level. The proposed approaches were validated using an independent field investigation dataset of debris flows. Results show that the proposed approaches properly estimate the maximum runout distances of debris flows in the Wenchuan earthquake zone for a specific probability level of 0.88.

Modern Dryland Source-to-Sink System Segments and Coupling Relationships from Digital Elevation Model Analysis: A Case Study from the Mongolian Altai

Source-to-sink (S2S) systems have represented a major area of research in recent years; however, few modern S2S system analyses have been applied to typical dryland uplifts/mountains. A modern lacustrine sedimentary system is widely developed in the Great Lakes Basin of western Mongolia, and the Jargalant Nuruu in the Mongolian Altai is a suitable natural laboratory for modern dryland S2S system analysis. In this study, the multi-order S2S system of the Jargalant Nuruu was applied based on a digital elevation model (DEM) and Google Earth database analysis. The Jargalant Nuruu system is subdivided into three second-order sub-S2S systems of the eastern, western, and southern parts (S2S-E, S2S-W, and S2S-S, respectively) and 35 third-order sub-S2S systems (E1–E18, W1–W9, and S1–S8) according to the slope gradients, altitude, and hydrographic net of the Jargalant Nuruu recognized by DEM data, integrated with the quantitative recognition of the topographic drainage divide and structural patterns of the uplift margin. The three second-order S2S systems correspond to three various S2S system coupling models. The S2S-E is characterized by a steep slope gradient system (average 15.61°) with small-scale dominantly alluvial fan deposits (average 4.56 km2). S2S-W is represented by a gentle slope gradient system (average 10.24°) with large-scale dominated fan-shaped lobes (average 30.04 km2). S2S-S, in contrast, is a transformation zone system with transitional features between the two former types. Four major potential controlling factors for the difference in sub-S2S systems are summarized here, including tectonic activity, bedrock properties in the source area, morphology from source to sink, and climatic conditions. The landforms, sedimentary characteristics, and their differences in these sub-S2S systems are the result of the comprehensive influence and control of these multiple factors. This case study could serve as a useful reference for characterizing the sedimentary features of a modern or even ancient S2S system in other regions.

Effect of Solid Volume Concentration on Rheological Properties of Chengdu Clay Slurry

The determination of rheological model about the debris flow is the basis of the simulation of mud flow impact distance and sedimentary fan. By using a mcr301 rheometer, rheological experiments of Chengdu clay slurry with different solid volume concentrations were carried out and the effect of solid volume concentration on shear stress were analyzed. Then the rheological process of Chengdu clay slurry with different solid volume concentration was fitted on the basis of the power law model, the Bingham model and the H–B model. The conclusions are drawn as follows: Chengdu clay mud is a typical shear-thinning non-Newtonian body. The influence of solid concentration on the flow curve is different. When the solid volume concentration is not less than 34% and the shear rate is less than 1.0 s−1, the shear stress increases rapidly as the shear rate increases. Meanwhile, when the shear rate is greater than 1.0 s−1 the shear stress decreases with the increase in the shear rate. When the solid volume concentration is less than 31.6% and the shear rate is less than 1.0 s−1, the shear stress increases with the increase in the shear rate, while when the shear rate is more than 1.0 s−1, the shear stress is less affected by shear rate. In the range of low shear rate (less than 1.0 s−1), the increase amplitude of shear stress (slope of semi logarithmic coordinate flow curve) increases as the solid volume content increases. The flow curve of Chengdu clay mud can be reflected in the whole process by using the Herschel and Bulkley model. It is the best mathematical model to fit the rheological process of Chengdu clay mud. According to the above results, the effect of solid volume concentration on the yield stress of the H–B model is analyzed.

Lithospheric-mantle modification beneath the thick sedimentary fan of Bay of Bengal: Inference from the 3D gravity model

A lithospheric density structure of the Bay of Bengal (BoB), which includes the thickest sedimentary layers deposited after continental rifting, is determined from constrained 3D/2D gravity modeling, to understand intricate tectonics processes of the region. The results suggest lateral density variation in the sub-crustal lithospheric mantle and high-density upper mantle is found beneath the thick sedimentary region of BoB. The present density model also predicts the thick lithosphere beneath the huge pile of sediments. The dense and thick lithospheric mantle results are supported by global tomographic and other geophysical results. It is also noticed that the dense mantle and thick sedimentary region have high elastic strength. We propose that the density and strength of the lithospheric mantle in the northern BoB are increased with age and sedimentation since rifting. The cause of density changes in the mantle is indistinct and could occur due to numerous reasons such as the transformation of mantle material catalyzed by a change in pressure and temperature conditions, or mantle flow.

The Evolution of Ancient Fluvial Systems in Memnonia Sulci, Mars: Impact Crater Damming, Aggradation, and a Large Water Body on the Dichotomy?

AbstractThere is conflicting evidence for an ancient ocean which occupied the northern hemispheric basin on Mars. Along different regions of the dichotomy boundary, sediment fans have been interpreted as either forming into a large water body or a series of smaller paleolake basins. Here, we investigate fluvial systems in the Memnonia Sulci region of Mars, set along the dichotomy, which comprise erosional valley networks, paleolake basins, inverted channel systems, and sediment fans. We focus our analysis on the evolution of the upslope catchment and characterizing the ancient environment of a large, downslope basin, bound by the topographic dichotomy and the Medusae Fosse Formation. The catchment fluvial systems comprise highly degraded valley networks and show a complex history of incision and filling, influenced by paleolake basin overflow, impact crater damming, aggradation, and possibly a downstream water body. The morphology of the sediment fans is consistent with either fluvial fans or deltas and they form at discrete elevations, rather than a common elevation plane. Our analysis is consistent with the sediment fans forming into a series of paleolake basins set along the dichotomy, rather than into a large inner sea or ocean‐sized water body. The fluvial systems were likely active between the mid Noachian and early Hesperian periods. Our results demonstrate the complex, multi‐phase evolution of fluvial systems on ancient Mars and highlight the importance of regional and local studies when characterizing ancient regions of the dichotomy.

Provenance of Late Cretaceous accretionary complex within the Yarlung–Zangpo suture zone, Bainang, southern Tibet: Implications for the subduction–accretion of the Neo-Tethyan ocean

Accretionary complexes offer important source of information for studying the subduction history and source-to-sink system and neighboring terranes. In this study, we conducted field mapping, detrital zircon U–Pb age and trace element analyses, and electronic microprobe composition analysis of detrital Cr-spinel in sandstones from the Cretaceous Bainang accretionary complex in the central part of the Yarlung–Zangpo suture zone (YZSZ). The Bainang accretionary complex is located in a structural window that is mainly composed of Xigaze ophiolite, Late Triassic–Early Cretaceous radiolarite chert with a Late Cretaceous hemipelagic siliceous shale matrix, and Late Cretaceous sandstone. The obtained detrital zircon geochronological dataset confirms two spectra. Detrital zircons from the Canggasaba and Lianxiang sections are dominated by Precambrian grains with subordinate numbers of Mesozoic grains clustering at 243–178, 164–117, and 109–91 Ma, consistent with the mélange and trench-fill Rongmawa Formation, and all the trace elements of the Mesozoic grains match continental arc affinity. Provenance analysis suggests that detritus in these sections was mainly derived from the eastern part of the Gangdese arc and the central–northern Lhasa terrane. These results confirm the existence of the ancestral Lhasa River that transports sediments from the eastern Lhasa terrane to the subduction zone and further westward along the east–west axial system parallel to the trench. Conversely, the Qiajiu section is mainly dominated by Mesozoic detrital zircon grains, representing submarine fan deposits that were sourced from the adjacent Gangdese arc and transported through a local north–south-flowing river system. Detrital Cr-spinel compositions and detrital zircon trace elements from the Qiajiu section also revealed the contribution of ophiolites. Considering the abundance of Eurasia-affinity detrital zircons, this study supports the single subduction model that was developed along the southern margin of the Lhasa terrane.

Climate-tectonic imprints on the Late Quaternary Ravi River Valley Terraces of the Chamba region in the NW Himalaya

• The present manuscript provides pristine OSL ages of the Ravi River Valley terraces, a tributary of the Indus River. • Aggradation events were mainly induced by climate, whereas the incisions phases were governed by both tectonic and climate. • Synchronous incision phases in Hinterland (Ravi River) and Indus plain suggest akin Late Quaternary climatic conditions. • Unlike Ganga River system, Ravi River system does not show any time lag for incision between the hinterland and the plain. • The first report on reactivation age (46 ka) of the MBT and the Chamba Thrust in NW Himalaya. An attempt has been made to reconstruct the landform evolution in monsoon-dominated the Ravi River Valley (a major tributary of the Indus River), Chamba Nappe, Lesser Himalaya based on detailed field mapping, supported by the Optically Stimulated Luminescence (OSL) dates. In the upper Ravi River Valley sediments are generated by glaciation-paraglaciation processes and accumulated in terraces and alluvial fan deposits in lower reaches north of the Main Central Thrust during deglaciation and periods of intensified monsoonal phases. Field study and OSL dating demonstrate aggradation of river terraces and debris-flow terraces occurred in two major phases: 73–46 ka and 39–23 ka and at least six minor phases between <23 ka and 7 ka. The incision was initiated shortly after 7 ka and ascribed to the decrease in overall monsoon intensity and simultaneous reduction in sediment flux. The first phase (73–46 ka) of aggradation was regional and occurred in a pre-existing river valley, whereas the later phases (39 ka onward) occurred as cut-and-fill and degraded terraces. The incision of the first major phase (220 m thick) accelerated between ∼46 ka and 39 ka due to reactivation of the Chamba Thrust and the Main Boundary Thrust (MBT). The study suggests that the fluvial dynamics and aggradation phases in the Ravi River Valley were regulated by monsoon variability, whereas both tectonic activity and climatic variables governed the incision of these deposits. The contemporaneous aggradation and incision in the hinterland and the Indo-Gangetic plains suggest that the Late Quaternary climate variability was the main factor in the evolution of fluvial landforms.

Flood Hazards in Erbil City Kurdistan Region Iraq, 2021: A Case Study

Erbil city is constructed in a flat plain with moderate gradient increasing northwards, the plain is dissected by tens of ephemeral wadis. The maximum elevation in the high lands NE of Erbil city is 1062 m (a.s.l.), whereas the elevation of the center of Erbil city is 420 m (a.s.l.). The average gradient from the highest part to the center of the city is 2.15%, increasing towards northeast to reach 4.79%. The mean annual rainfall is 365 mm, while the average monthly rainfall is about 24.42 mm. The site of the city is mainly covered by alluvial fan sediments. Towards northeast, however, the exposures of the Bia Hassan Formation, which consists of alternation of conglomerate and claystone cover considerable areas (82 km2) and form the high lands NE of Erbil city. The exposed rocks are thick claystone alternating with coarse conglomerate. Two very heavy torrential rain events have caused flash floods in Erbil city on 30th October and 17th December 2021. The rainfall intensities were 52 mm/day and 60 mm/day, respectively, causing destructive floods. The most affected areas were Zirin (north of Erbil) and Dara Too (northeast of Erbil), respectively, with very heavy property damages and tens of fatalities. The main reasons for the floods were the partially constructed embankments of the 150 m ring-road, and the urban development within large and wide drainage basins. Different climate data were used for the purpose of this article, with field checks.

Geochemistry and paleogeography of the Rajang Group, Northwest Borneo, Malaysia

The Late Cretaceous to Late Eocene Rajang Group in Borneo is one of the world's largest deep-sea sedimentary fans. The volume of the Rajang Group cannot be explained by erosion of the Schwaner Mountains in SW Borneo and the Malay Peninsula. To identify other contributing sources, this study examined the provenance history of the Rajang Group and the overlying Tatau Formation. A combination of bulk rock geochemistry, zircon morphological analysis and U–Pb geochronology is used to better constrain the provenance of the Rajang Group. Bulk rock Nd data, supported by detrital zircon data indicates that a late Mesozoic magmatic belt include the Schwaner Mountains was an important source before the Paleocene, after which sediment supply was dominated by older crustal sources, consistent with the Malay Peninsula. The increased contribution from older crustal material is considered to be the consequence of collapse of the magmatic arc and collision between Australian microcontinental fragment(s) and the southern margin of Sundaland. Paleocene river systems that flowed through the Malay Peninsula, transported large amounts of sediments to the marine basins including the deep-sea Rajang Group. A strong signal of sediment recycling for the Tatau Formation indicates uplift and denudation of lower Rajang Group in Late Eocene.

Controls on submarine canyon morphology along a convergent tectonic margin. The Southern Caribbean of Colombia

Submarine canyons are major conduits for sediment transfer from continental shelf to deep marine environments. Mass failures and faults play a key role in the initiation and evolution of submarine canyons along convergent tectonic margins, in addition to continental sediment supply. Here we analyze high-resolution bathymetry and seismic data from the Colombian southern Caribbean to investigate the controls on submarine canyon morphology along a convergent tectonic margin. We propose three end-member types of canyons: Type I canyons have a direct connection to a major river associated with high sediment supply. These canyons are highly erosive and cut topographic barriers created by tectonic deformation. Type II canyons are associated with faults at the canyon's head, where the location, orientation, and sinuosity are controlled by fault strike. Also, the presence of faults is related to an increase in the occurrence of mass failures from the steep canyon borders, increasing the depth and width asymmetry. Finally, Type III canyons evolve toward the continental shelf edge through retrogressive mass failures. These mass failures produce erosional scars that merge downslope to create submarine canyons in early stages of development, which later evolve to wider but shallow canyons due to the progressive basinward merging. We argue that the morphology of each canyon type is controlled by the interaction between continental sediment supply, mass failures, shelf width, and fault occurrence. We also demonstrate that seafloor topography influences the size of submarine fan deposits at the mouths of canyons. We identified large fan deposits (>650 km2) on the continental rise, whereas in piggyback sub-basins we found smaller fans (<60 km2). Our analysis of downdip canyon morphology and associated deposits can be used to predict the development of submarine canyons and associated fans in convergent tectonic margins worldwide.

Seismicity and landform development of the dextral Kalabagh Fault Zone, Pakistan: Implications from morphotectonics and paleoseismology

The Kalabagh Fault Zone in the western Sub-Himalayas is a dextral strike slip fault zone that exhibits a push-up block in the stepover zone of the two fault segments. The inception of the push-up block occurred along the restraining faults that form two morphotectonic bends along the mountain front at Zaluch and in the South of Thathi. The landform was further developed by en-echelon fold and thrust sequence up to Khairabad in the North and Ghundi village in the South. The aseismically moving fault zone has experienced earthquakes during late Quaternary forming surface expressions in the West of the push-up block at Khairabad, Larkakki and Ghundi. The Khairabad and Ghundi sections are the active tectonic fronts of the stepover zone. Displacements caused by these seismic activities has deformed Quaternary sediments creating stream deflections, surface ruptures, pressure ridges, uplifted sediments at the mountain front, foreland ridges and uplifted alluvial fan. Offsets in the late Quaternary sediments indicate the Kalabagh Fault is active and seismic events of Mw ≥ 6 has formed these ground effects. Furthermore, stratigraphic correlations of fluvial sediments indicate the Indus River has been flowing in the NS direction along the northern segment of the Kalabagh Fault. Uplift of the push-up block in the Kalabagh Fault Zone and subsequent deposition of the alluvial fans has caused westward diversion of the Indus River.

Hypotheses for Triton's plumes: New analyses and future remote sensing tests

At least two active plumes were observed on Neptune's moon Triton during the Voyager 2 flyby in 1989. Models for Triton's plumes have previously been grouped into five hypotheses, two of which are primarily atmospheric phenomena and are generally considered unlikely, and three of which include eruptive processes and are plausible. These hypotheses are compared, including new arguments, such as comparisons based on current understanding of Mars, Enceladus, and Pluto. An eruption model based on a solar-powered, solid-state greenhouse effect was previously considered the leading hypothesis for Triton's plumes, in part due to the proximity of the plumes to the subsolar latitude during the Voyager 2 flyby and the distribution of Triton's fans that are putatively deposits from former plumes. The other two eruption hypotheses are powered by internal heat, not solar insolation. Based on new analyses of the ostensible relation between the latitude of the subsolar point on Triton and the geographic locations of the plumes and fans, we argue that neither the locations of the plumes nor fans are strong evidence in favor of the solar-powered hypothesis. We conclude that all three eruption hypotheses should be considered further. Five tests are presented that could be implemented with remote sensing observations from future spacecraft to confidently distinguish among the eruption hypotheses for Triton's plumes. The five tests are based on the: (1) composition and thickness of Triton's southern hemisphere terrains, (2) composition of fan deposits, (3) distribution of active plumes, (4) distribution of fans, and (5) surface temperature at the locations of plumes and/or fans. The tests are independent, but complementary, and implementable with a single flyby mission such as the Trident mission concept. We note that, in the case of the solar-driven hypothesis, the 2030s and 2040s may be the last chance for approximately a century to observe actively erupting plumes on Triton.

Geophysical Reconnaissance for Siting Dryland Critical-Zone Monitoring Experiments in Southern New Mexico, USA

A dryland critical-zone observatory is planned on a piedmont setting of the Jornada Experimental Range northeast of Las Cruces, New Mexico, near a ∼10-yr eddy flux covariance tower and vegetation monitoring experiment and a 2-yr old water-uptake rainfall infiltration experiment. We carried out several geophysical surveys to help select sites that minimize geologic complexity for follow up hydrologic and biogeochemical studies that will be conducted by other researchers. First, we conducted a review of regional topography, gravity, and magnetics prior to a site visit and then collected reconnaissance magnetic and electromagnetic data to aid in planning more detailed geophysical site characterization surveys. Our initial topographic analysis using 1/3 arc-second digital elevation models (DEMs) showed the proposed area had an out-of-equilibrium curvature pointing to active erosion and possible faulting. Short-wavelength step-like topographic anomalies in the DEMs were confirmed in LiDAR elevations, and are consistent with erosionally resistant soil horizons in the old alluvial fan deposits. Comparison of 2-D density and susceptibility models based on nearby (3-8 km) hydrostratigraphic studies established that the observed regional gravity and magnetic anomalies were larger than could be modeled with the 2-D structural constraints, and established the station spacing our reconnaissance surveys would require to sample shallow soil variations. Our first site visit confirmed the general fault locations and we identified three outcropping caliche horizons distinct to alluvial channel, proximal splay and distal splay deposits in a several hundred-meter traverse that are consistent with the short-wavelength topographic features. In order to plan additional seismic, radar, gravity, and electrical surveys within a region of such high potential variability, we collected magnetic field and magnetic susceptibility measurements along two profiles at 10-50 m spacing. We found anomalies consistent with two projected faults, as well as other bedrock structures, a result significantly more complex than prior regional hydrostratigraphic mapping had suggested. We also conducted a more limited 0.5 km long ground conductivity survey with 5 m spacing that traversed the rainfall infiltration experiment site and found anomalies that aligned with one of the projected faults. The results showed deep (&gt;6 m) 50 mS/m (milliSiemens/meter) values, indicating moister soils, on the footwall side, dropping to 20 mS/m after crossing the fault, consistent with previous observations that normal faults in the Rio Grande Valley asymmetrically influence fluid flow.

The Oligocene‐Miocene Guadalope‐Matarranya Fan, Spain, as an Analog for Long‐Lived, Ridge‐Bearing Megafans on Mars

AbstractNumerous sedimentary fans on Mars have been studied to better understand the early martian hydrological system. Of particular interest is to estimate the duration of fluvial activity from alluvial fan size by dividing deposit volume by bankfull sediment flux. However, such a calculation requires an intermittency factor—a parameter relating sediment discharge from channel‐filling (bankfull) floods to the long‐term mean sediment discharge—which is poorly constrained. Here, we investigated fluvial fan deposits from the Oligocene–Miocene Caspe Formation, Spain, as an analog to fans on Mars because it has exhumed channel belts that create sinuous ridges in the modern topography, similar to those observed on Mars that are used for paleohydraulics. We made measurements of the thicknesses of dune and bar cross sets within exhumed channel belts at nine field sites to reconstruct bankfull channel depth (∼1.4 m) and bankfull sediment flux (∼0.48 m3/s). We estimated total bed‐material sediment volume of the fan (362 km3) from stratigraphic thickness, the area containing exhumed channel belts, porosity and sand fraction. Combined with previous constraints on depositional timespan (∼6 Myr), we calculated a sediment‐transport intermittency factor of 0.004 (range: 0.0004–0.04). Our approach can be applied to Mars by using remote sensing measurements of fluvial ridge morphology, which indicates the possibility of long depositional timespans exceeding millions of years for martian fans.

A 3D geological model of a structurally complex relationships of sedimentary Facies and Petrophysical Parameters for the late Miocene Mount Messenger Formation in the Kaimiro-Ngatoro field, Taranaki Basin, New Zealand

The present study investigates the reservoir characteristics of the Mount Messenger Formation of Kaimiro-Ngatoro Field which was deposited in deep-water environment. A 3D seismic dataset, core data and well data from the Kaimiro-Ngatoro Field were utilized to identify lithofacies, sedimentary structures, stratigraphic units, depositional environments and to construct 3D geological models. Five different lithologies of sandstone, sandy siltstone, siltstone, claystone and mudstone are identified from core photographs, and also Bouma sequence divisions are also observed. Based on log character Mount Messenger Formation is divided into two stratigraphic units slope fans and basin floor fans; core analysis suggests that basin floor fans show better reservoir qualities compared to slope fan deposits. Seismic interpretation indicates 2 horizons and 11 faults, majority of faults have throw less than 10 m, and most of the faults have high angle dips of 70–80°. The Kaimiro and Ngatoro Fields are separated by a major Inglewood fault. Variance attribute helped to interpret faults, and other seismic attributes such as root-mean-square amplitude, envelope and generalized spectral decomposition also helped to detect hydrocarbons. The lithofacies model was constructed by using sequential simulation indicator algorithm, and the petrophysical models were constructed using sequential Gaussian simulation algorithm. The petrophysical parameters determined from the models comprised of up to ≥ 25% porosity, permeability up to around 600mD, hydrocarbon saturation up to 60%, net to gross varies from 0 to 100%, majority of shale volumes are around 15–20%, the study interval mostly consists of macropores with some megapores and 4 hydraulic flow units. This study best characterizes the deep-water turbidite reservoir in New Zealand.

Sedimentary Sequence, Evolution Model and Petroleum Geological Significance of Forced Regression: A Case Study of the Miocene Zhujiang Formation of the Pearl River Mouth Basin in the Northern South China Sea

Using 2D/3D seismic data and a large number of drilling and logging data and applying sequence stratigraphy, seismic sedimentology, and petroleum geology concepts, the characteristics of the sedimentary sequence of the forced regression have been analysed, the migration trajectory of the coastline have been reconstructed, the evolution model of the forced regression have been presented, and the significance for petroleum geology of the forced regressive sandbodies have been discussed. The falling stage systems tract (FSST) of the Zhujiang Formation present offlap high-angle oblique foreset reflection structure in the seismic profiles of the depositional trends and turbidite fan deposits with strong amplitude mound reflection structure are developed in the downdip direction of its front. The trajectory of migration of the shoreline shows a terraced downtrend in the direction of basin. The FSST is characterized by the shelf-edge delta without topset beds. The FSST was formed in the fall of relative sea-level. Five sets of foreset beds controlled by high-frequency relative eustatic were developed, therefore ordinal regressive overlap can be observed for the five sets of shelf-edge deltas in the depositional trends. The favourable reservoirs which were located close to the upper boundary of the falling stage systems tract and the basal surface of forced regression are sandbodies of the shelf-edge delta front and wave-dominated shoreface sands and the sandbodies of the turbidite fan. Those sandbodies favour the formation of lithologic oil–gas reservoirs by means of good trap sealing conditions, excellent oil–gas reserving performance, and effective oil source communication of fracture system.

Sequence stratigraphy and sedimentary characteristics of the shelf-edge delta and slope fan systems in the Late Oligocene, Baiyun Sag, Pearl River Mouth Basin, China

The Pearl River Mouth Basin in the South China Sea is one of the most important offshore petroliferous basins in China. Specifically, the shelf-edge delta and slope fan systems in the deepwater area of the Baiyun Sag have been regarded as the most important objects for hydrocarbon exploration, and the sequence stratigraphic structure, sedimentary evolution, and “source to sink” relationship between them is an important basis for predicting favorable areas for hydrocarbon exploration. In this study, the sequence stratigraphic structure and sedimentary system of the Late Oligocene Zhuhai Formation in the Baiyun Sag of the Pearl River Mouth Basin were studied based on a comprehensive dataset that integrated seismic, logging, and core data. A total of four third-order sequences were determined in the second-order composite sequence (CS3) according to nature of unconformities. Within each third-order sequence, the characteristics of different sedimentary systems were successfully identified. Within CS3-1 and CS3-2 the transgressive systems tracts (TST) are relatively thick, and the highstand systems tracts (HST) encompass mainly the outer-shelf deltaic deposits with thin foresets. As for CS3-3 and CS3-4, the lowstand systems tract (LST) and falling-stage systems tracts (FSST) are dominated by shelf-edge deltas and slope fans deposits, whereas the TST are very thin. The depositional evolution and “source to sink” relationship between the shelf-edge deltas and associated slope fans are revealed as follows: there are mainly three stages of shelf-edge deltas, and their sedimentary paleo-water depths were 794.9 m, 822.6 m, and 556.8 m, with progradation angles of 8.5°, 7.7°, and 5.7°, respectively; the thick delta front (200–500 m) and slump deposit are the main identification features of the shelf-edge delta. During the period of LST, although the progradation angle of the shelf-edge delta was the largest, there were few slope fans or only mud-rich slope fan deposits in the front of the delta due to the influence of relative sea-level rise, and during the period of FSST, the slump and redeposition of the delta front sand bodies provided the sand source for the formation of the slope fans, thus forming the sand-rich fans. Moreover, according to the root mean square amplitude slices and 3D seismic profile, it was found that the slope fans in this area are directly related to the development of the channels between the deltas and slope fans; generally, the larger and denser the channel, the larger the slope fan area.