Mud Debris Research Articles

Permafrost Carbon and CO2 Pathways Differ at Contrasting Coastal Erosion Sites in the Canadian Arctic

Warming air and sea temperatures, longer open-water seasons and sea-level rise collectively promote the erosion of permafrost coasts in the Arctic, which profoundly impacts organic matter pathways. Although estimates on organic carbon (OC) fluxes from erosion exist for some parts of the Arctic, little is known about how much OC is transformed into greenhouse gases (GHGs). In this study we investigated two different coastal erosion scenarios on Qikiqtaruk – Herschel Island (Canada) and estimate the potential for GHG formation. We distinguished between adelayedrelease represented bymud debrisdraining a coastal thermoerosional feature and adirectrelease represented bycliff debrisat a low collapsing bluff. Carbon dioxide (CO2) production was measured during incubations at 4°C under aerobic conditions for two months and were modeled for four months and a full year. Our incubation results show thatmud debrisandcliff debrislost a considerable amount of OC as CO2(2.5 ± 0.2 and 1.6 ± 0.3% of OC, respectively). Although relative OC losses were highest in mineralmud debris, higher initial OC content and fresh organic matter incliff debrisresulted in a ∼three times higher cumulative CO2release (4.0 ± 0.9 compared to 1.4 ± 0.1 mg CO2gdw–1), which was further increased by the addition of seawater. After four months, modeled OC losses were 4.9 ± 0.1 and 3.2 ± 0.3% in set-ups without seawater and 14.3 ± 0.1 and 7.3 ± 0.8% in set-ups with seawater. The results indicate that adelayedrelease may support substantial cycling of OC at relatively low CO2production rates during long transit timesonshoreduring the Arctic warm season. By contrast,directerosion may result in a single CO2pulse and less substantial OC cyclingonshoreas transfer times are short. Once eroded sediments are deposited in thenearshore, highest OC losses can be expected. We conclude that the release of CO2from eroding permafrost coasts varies considerably between erosion types and residence timeonshore. We emphasize the importance of a more comprehensive understanding of OC degradation during the coastal erosion process to improve thawed carbon trajectories and models.

Stratum development characteristics and sedimentary evolution model of the second member of Shuangyang formation in Moliqing area, Yitong Fault Basin

During the Second Member of Shuangyang Formation of Moliqing fault in the Yitong Basin, northeast of China, the intermittent transportation and rapid accumulation of nearshore gravity flows make the facies belts of fan apron narrow and changefully. Lacking stable contrastive maker layers, while the several tectonic events such as strike slip, transtension and compression occurring in the later period make the stratigraphic distribution of this area more complex. For these reasons, the research on stratigraphic correlation and the distribution of sedimentary facies are extremely difficult. To solve the above problems, this paper proposes the following solutions: (1) This paper assists to achieve the stratigraphic cycle analysis through logging data entropy spectrum analysis, on which basis and combining with the core data, seismic interfaces and geological markers to achieve the division and correlation of small layers of single sand body; (2) By analyzing the coarse clastic sedimentary system, we research the coarse clastic glutenite sediments of Shuangyang Formation in Moliqing fault from the fluid properties and fluid type conversion so as to clearly understand the vertical sequences and horizontal distribution characteristics analysis of core facies as well as deduce the fluid type of supply source and the characteristics of sediments. The results show that: (1) The sequence development is dominated by tectonic movements, and the strata can be divided into 5 middle-term cycles and 25 short-term cycles adopting T-R mode; (2) studies suggest that because the fluid property of supply source occurs cyclical changes under the condition of multiple sources, and the fluid shows alternation and conversion between gravity flow and traction flow under the control of particular ancient landform, therefore, the sediments of researched area form a mixed sedimentary system of gravity flow and traction flow. On the basis of source characteristics and sedimentary characteristics analysis, this paper proposed the sedimentary type of continental facies slope apron, which is divided into three sub-facies: proximal, middle and distal sub-facies. Among them, proximal sub-facies mainly develop the slop channel sedimentation dominated by mud debris flow deposits, central sub-facies develop the superposition channel microfacies dominated by mix depositions of gravity flow and traction flow and the leading edge microfacies of fan dominated by traction flow, while the distal sub-facies is mainly based on the thin sheet sand body and gravity flow slump depositions.

RECURRENCE QUANTIFICATION ANALYSIS OF BOREHOLE TEMPERATURES: EVIDENCE OF FLUID CONVECTION

To describe intra-hole fluid convection, fine-scale temperature-time variations were monitored at 25 depth levels within a 50 m long interval (80—130 m depth) in a slim experimental borehole in Sporilov (the Czech Republic). High-resolution temperature data were sampled with a 15 sec time interval for 1.6 up to 2.7 days. The time series obtained were from 10 000 to 16 000 data points. In the upper part of the investigated depth interval, the temperature time series showed a complex oscillation pattern with amplitudes of up to 45 mK (milliKelvin). This variation pattern is alternated with a "quiet" regime below 110 m depth, where temperature oscillations fall within 4–10 mK range. Convection produced temperature signal was studied by means of recurrence plots and their quantification analysis. This method was proven to be effective to detect transitions in system dynamics. The analysis confirmed a relevant deterministic part in the measured signal (quasi-periodic skeleton) and enabled to quantify the periodic—periodic and periodic—chaotic transitions in the borehole convection dynamics. Thermal dynamics is richer and cooler at shallower depths. The results were confirmed with temperature time series registered at the bottom hole, where the probe penetrated into soft mud debris, which prevented convection, and restricted heat transport to a pure conduction.

Sequence of instability processes triggered by heavy rainfall in the northern Italy

Northern Italy is a geomorphologically heterogeneous region: high mountains, wide valleys, gentle hills and a large plain form a very varied landscape and influence the temperate climate of the area. The Alps region has harsh winters and moderately warm summers with abundant rainfall. The Po Plain has harsh winters with long periods of subfreezing temperatures and warm sultry summers, with rainfall more common in winter. Geomorphic instability processes are very common. Almost every year, landslides, mud flows and debris flows in the Alpine areas and flooding in the Po flood plain cause severe damage to structures and infrastructure and often claim human lives. Analyses of major events that have struck northern Italy over the last 35 years have provided numerous useful data for the recognition of various rainfall-triggering processes and their sequence of development in relation to the intensity and duration of rainfall. Findings acquired during and after these events emphasise that the quantity and typology of instability processes triggered by rainfall are related not only to an area's morphological and geological characteristics but also to intense rainfall distribution during meteorological disturbances. Moreover, critical rainfall thresholds can vary from place to place in relation to the climatic and geomorphological conditions of the area. Once the threshold has been exceeded, which is about 10% of the local mean annual rainfall (MAR), the instability processes on the slopes and along the hydrographic networks follow a sequence that can be reconstructed in three different phases. In the first phase, the initial instability processes that can usually be observed are soil slips on steep slopes, mud–debris flows in small basins of less than 20 km 2 in area, while discharge increases substantially in larger stream basins of up to 500 km 2. In continuous precipitation, in the second phase, first mud–debris flows can be triggered also in basins larger than 20 km 2 in area. Tributaries swell the main stream, which is already in a critical condition. The violent flow causes severe problems mainly along valley bottoms of rivers with basins up to 2000 km 2 in area. First bedrock landslides can occur, reaching a considerable area density, with volumes from a few hundred up to about one to two million cubic meters. In continuous precipitation, in the third phase, basins of more than 2000 km 2 in area reach their first critical stage. River-bed morphology is extensively modified, with erosional and depositional processes which can locally undermine the stability of structures and infrastructures. Waters overflow levees, flooding villages and towns to various widths and depths and sometimes claiming casualties. Some days after an intense rainfall period, large landslides involving the bedrock can still take place. These processes usually cause the movement of very large rock masses. The total duration of rainfall usually has a greater effect on these landslides than does the number of short periods of very intensive precipitation. This sequence cannot be divided into separate phases when the events occur simultaneously because of the presence of intense rainfall pulses and the generation of very diffuse surface runoff. Such situations usually happen during short-lasting heavy summer rainstorms or in late spring, when snow melt combines with intense rainfall. The three-phase sequence has been identified in three severe events that are analysed in this paper: Valtellina (Lombardy) in 1987, Tanaro Valley (Piedmont) in 1994 and Aosta Valley in 2000; but this sequence has also been observed during other events that occurred in northern Italy: in Piedmont in 1968, 1977, 1978, 1993 and 2000; in Lombardy in 1983 and 1992; in the Aosta Valley in 1993.

Mechanisms of mud extrusion on the Mediterranean Ridge Accretionary Complex

Drilling two mud domes on the Mediterranean Ridge during ODP Leg 160 has demonstrated that the eruption of mud breccia began at least 1.5 Ma ago. An evolution through extrusive building of a cone, followed by successive eruptions of clast-bearing mud debris flows and subsequent subsidence can be deduced for both domes. Results from permeability and shear strength tests, grain size analyses, sedimentary textures, and clast provenance provide clues concerning the mechanism of mud volcanism. The collision of Africa with Eurasia resulted in backthrusting of the evaporite-dominated accretionary wedge against a rigid backstop. This allowed egress of overpressured fluid-rich mud of presumed Messinian age from the decollement, although many of the clasts may have originated from the overlying accretionary wedge.

Offshore and onshore liquefaction at Moss Landing spit, central California—Result of the October 17,1989, Loma Prieta earthquake

As a result of the October 17, 1989, Loma Prieta (Santa Cruz Mountains, California) earthquake, liquefaction of the fluvial, estuarine, eolian, and beach sediments under a sand spit destroyed the Moss Landing Marine Laboratories and damaged other structures and utilities. Initial studies suggested that the liquefaction was a local phenomenon. More detailed offshore investigations, however, indicate that it occurred over a large area (maximum 8 km{sup 2}) during or shortly after the earthquake with movement of unconsolidated sediment toward and into the head of Monterey submarine canyon. This conclusion is supported by side-scan sonographs, high-resolution seismic-reflection and bathymetric profiles, onshore and sea-floor photographs, and underwater video tapes. Many distinct lobate features were identified on the shallow shelf. These features almost certainly were the result of the October 17 earthquake; they were subsequently destroyed by winter storms. In addition, fresh slump scars and recently dislodged mud debris were found on the upper, southern wall of Monterey submarine canyon.