Lithological Controls Research Articles

Controls on earthflow formation in the Teanaway River basin, central Washington State, USA

Abstract. Earthflows create landscape heterogeneity, increase local erosion rates, and heighten sediment loads in streams. These slow moving and fine-grained mass movements make up much of the Holocene erosion in the Teanaway River basin, central Cascade Range, Washington State, yet controls on earthflow activity and the resulting topographic impacts are unquantified. We mapped earthflows based on morphologic characteristics and relatively dated earthflow activity using a flow directional surface roughness metric called MADstd. The relative MADstd activity is supported by six radiocarbon ages, three lake sedimentation ages, and 16 cross-cutting relationships, indicating that MADstd is a useful tool to identify and relatively date earthflow activity, especially in heavily vegetated regions. Nearly all of the mapped earthflows are in the Teanaway and lower Roslyn formations, which comprise just 32.7 % of the study area. Earthflow aspect follows bedding planes in these units, demonstrating a strong lithologic control on earthflow location. Based on absolute ages and MADstd distributions, a quarter of the earthflows in the Teanaway Basin were active in the last few hundred years; the timing coincides with deforestation and increased land use in the Teanaway. Major tributaries initiate in earthflows and valley width is altered by earthflows that create wide valleys upstream and narrow constrictions within the earthflow zone. Although direct sediment delivery from earthflows brings fine sediment to the channel, stream power is sufficient to readily transport fines downstream. Based on our findings, over the Holocene – and particularly in the last few hundred years – lithologic-controlled earthflow erosion in the Teanaway basin has altered valley bottom connectivity and increased delivery of fine sediments to tributary channels.

Lithologic control on parameters of conceptual rainfall-runoff model and runoff characteristics: a case study of the Xinanjiang model

Lithologic control on parameters of conceptual rainfall-runoff model and runoff characteristics: a case study of the Xinanjiang model

Lithologic control on parameters of conceptual rainfall-runoff model and runoff characteristics: a case study of the Xinanjiang model

Lithologic control on parameters of conceptual rainfall-runoff model and runoff characteristics: a case study of the Xinanjiang model

Exploring the role of bedrock representation on plant transpiration response during dry periods at four forested sites in Europe

Abstract. Forest transpiration is controlled by the atmospheric water demand, potentially constrained by soil moisture availability, and regulated by plant physiological properties. During summer periods, soil moisture availability at sites with thin soils can be limited, forcing the plants to access moisture stored in the weathered bedrock. Land surface models (LSMs) have considerably evolved in the description of the physical processes related to vegetation water use, but the effects of bedrock position and water uptake from fractured bedrock have not received much attention. In this study, the Community Land Model version 5.0 (CLM 5) is implemented at four forested sites with relatively shallow bedrock and located across an environmental gradient in Europe. Three different bedrock configurations (i.e., default, deeper, and fractured) are applied to evaluate if the omission of water uptake from weathered bedrock could explain some model deficiencies with respect to the simulation of seasonal transpiration patterns. Sap flow measurements are used to benchmark the response of these three bedrock configurations. It was found that the simulated transpiration response of the default model configuration is strongly limited by soil moisture availability at sites with extended dry seasons. Under these climate conditions, the implementation of an alternative (i.e., deeper and fractured) bedrock configuration resulted in a better agreement between modeled and measured transpiration. At the site with a continental climate, the default model configuration accurately reproduced the magnitude and temporal patterns of the measured transpiration. The implementation of the alternative bedrock configurations at this site provided more realistic water potentials in plant tissues but negatively affected the modeled transpiration during the summer period. Finally, all three bedrock configurations did not show differences in terms of water potentials, fluxes, and performances on the more northern and colder site exhibiting a transition between oceanic and continental climate. Model performances at this site are low, with a clear overestimation of transpiration compared to sap flow data. The results of this study call for increased efforts into better representing lithological controls on plant water uptake in LSMs.

Lithological controls on fault damage zone development by coseismic tensile loading

During subshear earthquake rupture opposing sides of the fault experience transient impulses of tensile and compressive peak mean normal stresses exceeding the strength of the rock resulting in off-fault damage. This damage is expected to be influenced by lithology and occur preferably on the nominally tensile side of ruptures because rocks are weaker in tension than compression. Whereas the static tensile strength of many rocks is known, our capacity to relate parameters used to quantify brittle deformation in fault damage zones commonly measured in the field, including fracture density and fragment size, to earthquake rupture conditions is poor. This is due to a lack of experimental data relating tensile strength, fracture density, and fragment size to lithology under transient loading conditions. To relate brittle damage to coseismic tensile loading conditions, we use a modified sample configuration for a Split Hopkinson Pressure Bar (SHPB) designed to induce tensile rock fragmentation. Experiments cover a range of rock types including granite, diabase, welded tuff, and sandstone. All crystalline rocks fail predominantly via mode-I fracture, while sandstone fails through localized dilation bands, distributed pore space expansion, and less common mode-I fractures. Measurements of fracture density, fragment size, and porosity change are compared to tensile strength and strain rate at failure. We derive empirical relationships for (1) the transition from fracture to dilation banding as a function of initial porosity and (2) the strain rate dependence of tensile strength. These empirical relationships are used to estimate the rock strength during earthquake rupture on the side of the fault loaded under tension for comparison to predicted stress decay with distance from a fault to estimate the lithology dependent extent and nature of coseismic fault damage. Our experiments offer new insights into the lithological controls on the formation of asymmetric fault damage zones by dynamic rupture.

Morphometric Interpretation for Sub-Basin Management Planning and Practices in Hassan District, Karnataka India Using GIS and Remote Sensing

Classification and categorization of water basins is essential in sustainable growth, planning and management. Implementing the modern strategic techniques over a wider area needs huge resources and proper planning. Hence, morphometric analysis can be used as necessary tool for prioritizing sub- watersheds in the present study. The study area encompasses 265 sq. km, which is divided into nine sub-basins, specifically Bannur (W-1), Conimarur (W-2), Hampapura (W-3), Harohalli (W-4), Kaneyar (W-6), Konanuru (W-7), Saraguru (W-8), and Torenuru (W-9) ranging from 8 to 64 km2. The Survey of Indian toposheets and Digital Terrain Model are utilized to explain the drainage characteristics. The study reveals dendritic stream arrangement of fourth to fifth order. The density of drainage ranged between 1.03 to 1.32 km/km2, suggesting that the drainage texture was coarse to moderate, but low infiltration and high runoff. The change in stream length ratio over time implies that geomorphological progress is approaching its end. The bifurcation ratios range from 0.5 to 2.58, indicating that the region has good lithological control over the stream system and whole sub-watersheds are classified as "normal”. The form factor and circulatory ratio suggest elongated to circular sub-watersheds. Thus, the results of this analysis would be useful for the basin management planning and groundwater development. Keywords: Morphometry, Aerial Aspects, Linear aspects, Relief aspects, Hassan District

Correction to: Identifying the role of structural and lithological control of landslides using TOBIA and Weight of Evidence: case studies from Romania

Correction to: Identifying the role of structural and lithological control of landslides using TOBIA and Weight of Evidence: case studies from Romania

Lithological controls on arsenic accumulation in cultivated soils: observations from typical karst areas in Central Guizhou, Southwest China.

In this study, topsoil and soil profiles were collected from typical karst areas in central Guizhou to investigate the accumulation and bioavailability of As in cultivated soils. The parent material of the investigated soil is carbonate rock, but there is strong heterogeneity in the As concentrations of soils developed in the Permian and Triassic, with average concentrations of 18.31 and 40.35mg/kg, respectively. Additionally, the average As concentration of dolomite of the Anshun Formation (46.23mg/kg) is slightly higher than that of the limestone in the Daye Formation (31.96mg/kg) from the Triassic. Arsenic in the soil profiles of Triassic is also higher than that of the Permian and shows deep enrichment characteristics. Approximately 80% of the As exists as stable crystalline hydrous oxide-bound As and residual As fractions, and the bioavailability is very low.

Plate‐Rate Frictional Behavior of Sediment Inputs to the Hikurangi Subduction Margin: How Does Lithology Control Slow Slip Events?

AbstractThe northern Hikurangi subduction margin hosts slow slip events (SSEs), which are exceptionally shallow (<15 km). The sedimentary sequence on the incoming plate is therefore representative of the shallow fault material where the SSEs will take place once they enter the subduction zone. Knowledge about the frictional behavior of these sediments is required to know which lithologies are capable of hosting SSEs, and what mechanisms are causing them. Frictional behavior is material specific and depends on sliding velocity, but it is unknown how these natural sediments behave at plate‐rate velocities. We performed laboratory shearing experiments testing the major lithologies sampled during International Ocean Discovery Program (IODP) Expedition 375, at velocities ranging from the plate convergence rate at the Hikurangi margin (5 cm/year), up to those characteristics of the shallow SSEs (160 and 530 cm/year), under simulated in‐situ as well as standardized conditions. We find that the calcite‐rich pelagic sediments are relatively strong and display the velocity‐weakening frictional behavior required for slip events, whereas other lithologies are weaker and show velocity‐neutral to velocity‐strengthening friction. We observe spontaneous laboratory SSEs in the calcareous pelagic sediments, which show partial locking in between sliding events, consistent with the interpretation of SSEs within the spectrum of slow to fast earthquakes. For the Hikurangi margin, our results suggest that SSE occurrence requires the stronger carbonate‐rich unit to be incorporated into the plate‐boundary fault zone, which we suggest occurs because the rough incoming plate introduces geometrical complexity into the fault zone.

Lithologic controls on the mobility of Cd in mining-impacted watersheds revealed by stable Cd isotopes

Cd-rich wastes from open-pit mining can be transported into rivers, which are often followed by deposition in river sediments and/or further transfer into agricultural soils. The lithology of bedrock exerts a huge effect on physicochemical properties (e.g., buffering capacities, metal species, mineral phases, etc.) of the river system, thereby potentially impacting the Cd mobility in watersheds. However, to date, little is known about the microscopic processes (e.g., dissolution, adsorption, and precipitation) controlling the migration of Cd from mines to varied watersheds. This study, therefore, aims to determine the controlling factors on Cd mobilization in two mining-impacted watersheds with contrasting bedrock lithology using both Cd and Pb isotopes. The Pb isotope ratios of sediments and soils in both watersheds fall into a binary mixing model with two isotopically distinct sources, i.e., mining wastes and bedrock. These results indicate that mining activities are the main sources of Cd in sediments and soils. However, the Cd isotope ratios reveal different Cd migration processes between the two watersheds. In the siliceous watershed, the δ114/110Cd values of sediments decrease from -0.116‰ in the upper reach to -0.712‰ in the lower reach, with a concomitant increase in Cd concentration, which may result from Cd adsorption by goethite due to the increased pH. In contrast, in the calcareous watershed, the Cd isotope compositions of sediments (-0.345 to -0.276‰) and the pH of river water are nearly invariable, suggesting that the adsorption and release of Cd in sediments are limited. This may result from the strong pH buffering effect due to the presence of carbonate rocks. This study highlights the different fates of Cd in siliceous and calcareous watersheds and suggests that the development of Cd pollution control policies must consider regional lithology.

Lithological Control of Stream Chemistry in the Luquillo Mountains, Puerto Rico

Meteoric waters move along pathways in the subsurface that differ as a function of lithology because of the effects of chemical and physical weathering. To explore how this affects stream chemistry, we investigated watersheds around an igneous intrusion in the Luquillo Mountains (Puerto Rico). We analyzed streams on 1) unmetamorphosed country rock (volcaniclastic sedimentary strata, VC) surrounding an igneous intrusion, 2) the quartz-diorite intrusion (QD), and 3) the metamorphosed aureole rock (hornfels-facies volcaniclastics, HF). These lithologies differ physically and chemically but weather under the same tropical rain forest conditions. The sedimentary VC lithology is pervasively fractured while the massive QD and HF lithologies are relatively unfractured. However, the QD fractures during weathering to produce spheroidally-weathered corestones surrounded by cm-thick rindlets of increasingly weathered rock. Meteoric waters flow pervasively through the network of already-fractured VC rock and the spheroidally weathered rindlets on the QD, but only access a limited fraction of the HF, explaining why streams draining HF are the most dilute in the mountains. This results in various thicknesses of regolith from thick (VC) to moderate (QD) to thin or nonexistent (HF). The pervasive fractures allow groundwater to flow deeply through the VC and then return to the mainstem river (Río Mameyes) at lower elevations. These “rock waters” drive concentrations of rock-derived solutes (silica, base cations, sulfate, phosphate) higher in the lower reaches of the stream. Water also flows through weathering-induced fractures on the QD at high elevations where rindletted corestones are present in stacks, and this water flux dissolves plagioclase and hornblende and oxidizes biotite. This “QD rock water” is not generated at lower elevations in the Río Icacos watershed, where stacks of corestones are absent, and contributions to stream solutes derive from weathering of feldspar- and hornblende-depleted saprolite. The stream chemistry in the QD-dominated watershed (Río Icacos) thus varies from concentrated QD-rock water at channel heads below steep ridgelines toward more diluted “saprolite water” downstream. These observations emphasize the importance of lithology and fracture patterns in dictating water flowpaths, stream chemistry, and regolith development in headwater catchments.

Geological, fluid inclusion microthermometry and geochemical constraints on the ankeritic-sideritic iron deposits in the Delijan mining district, Malayer-Esfahan metallogenic belt, Iran

The Kahak, Raveh, and Khoreh stratabound sideritic-ankeritic iron deposits are located in the Malayer-Esfahan metallogenic belt (MEMB), Iran. Geological, geochemical, fluid inclusion and S isotope studies have been carried out on the Kahak, Raveh, and Khoreh deposits which are hosted by different types of Lower Cretaceous dolomite, sandstone, and tuff in the Delijan mining district (DMD). Ankerite and siderite ores display a strong lithological control and form stratabound stacked ore lenses hosted in different horizons by Kc2, Kcv, Kc3, and Km units. Economic orebodies are restricted to the hanging wall of the syn-sedimentary normal faults. Three ore types can be distinguished based on the petrographic studies: stringer zone ore facies, bedded ore facies, and massive-replacement ore facies. Ore minerals are predominantly ankerite, siderite, barite, chalcopyrite, sphalerite, galena, and pyrite. Ore mineralization in the Kahak, Raveh, and Khoreh deposits has emplaced in two stages. The fine-grained ore bands (stage 1) which are intricately interlayered with host rock beds, exhibit sedimentary textures such as lamina and bedding and indicate a syn-sedimentary origin. The coarser-grained stage 2 ores show massive and vein-veinlet textures that are considered to form by replacement during sub-seafloor fluid flow. Hydrothermal alteration minerals developed in the wall rock include dolomite, quartz, and calcite. A microthermometric study of fluid inclusions from the barite samples indicates homogenization temperatures between 162 and 210 °C. Salinities of ore-forming fluids range from 7.8 to 16.8 wt% NaCl eq. Fluid inclusion studies suggest that the ore-forming fluids were derived from basinal or formational brines. Fluid mixing (basinal brine and seawater) may have played an important role during Fe mineralization. Calculated δ34S values for the ore fluid vary between + 10.69 and + 31.98‰. Sulfur isotopic compositions suggest that the source of sulfur for barite was derived from seawater. These data show that the Kahak, Raveh, and Khoreh ankeritic-sideritic iron deposits are comparable with those of sub-seafloor carbonate-replacement SEDEX-type deposits.

Structural controls on coseismic rupture revealed by the 2020Mw 6.0 Jiashi earthquake (Kepingtag belt, SW Tian Shan, China)

SUMMARYThe Kepingtag (Kalpin) fold-and-thrust belt of the southern Chinese Tian Shan is characterized by active shortening and intense seismic activity. Geological cross-sections and seismic reflection profiles suggest thin-skinned, northward-dipping thrust sheets detached in an Upper Cambrian décollement. The 2020 January 19 Mw 6.0 Jiashi earthquake provides an opportunity to investigate how coseismic deformation is accommodated in this structural setting. Coseismic surface deformation resolved with Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) is centred on the back limb of the frontal Kepingtag anticline. Elastic dislocation modelling suggests that the causative fault is located at ∼7 km depth and dips ∼7° northward, consistent with the inferred position of the décollement. Our calibrated relocation of the main shock hypocentre is consistent with eastward, unilateral rupture of this fault. The narrow slip pattern (length ∼37 km but width only ∼9 km) implies that there is a strong structural or lithological control on the rupture extent, with updip slip propagation possibly halted by an abrupt change in dip angle where the Kepingtag thrust is inferred to branch off the décollement. A depth discrepancy between main shock slip constrained by InSAR and teleseismic waveform modelling (∼7 km) and well-relocated aftershocks (∼10–20 km) may suggest that faults within sediments above the décollement exhibit velocity-strengthening friction.

The chondrichthyan fossil record of the Florida Platform (Eocene–Pleistocene)

AbstractAs of September 2019, the Florida Museum of Natural History (FLMNH) had a curated collection of 117,449 chondrichthyan specimens from Florida, spanning the Eocene through the Pleistocene. Herein, I evaluate the completeness of the chondrichthyan fossil record from Florida based on the FLMNH collection, while analyzing patterns in taxonomic and ecomorphological diversity. At least 70 chondrichthyan taxa were recognized, representing 10 orders, 26 families, and 42 genera; of which, 20 taxa represent first occurrences from Florida. A sample of 107,698 specimens was organized into 12 time bins to analyze taxonomic and ecomorphological diversity, with an expectation that diversity patterns would correspond with global climate events (e.g., the Eocene–Oligocene transition and the middle Miocene climatic optimum). However, diversity patterns were obscured by pervasive sampling bias, attributable to variable collection methods, research prioritizations, and regional lithologic controls. Sampling is particularly poor for smaller specimens and older geologic units (e.g., the Paleogene). Despite incomplete sampling of the Florida chondrichthyan fossil record, there was an apparent turnover along the Atlantic and Gulf Coastal Plains from a lamniform- to carcharhiniform-dominated chondrichthyan fauna that occurred during the Eocene. This turnover corresponded with the extinction of many lamniform taxa with grasping-dominated dentition types (e.g., Brachycarcharias, Jaekelotodus, and Macrorhizodus). Selachian taxa that survived the late Eocene extinctions were predominantly represented by cutting-dominant dentition types. As cutting aids in the dismemberment of prey, this may reflect a macroevolutionary trend toward active predation and scavenging on larger prey, such as marine mammals, teleost fish, and other sharks.

Lithologic Controls on Geomorphic Evolution of the Central Western Ghats: An Example from the Aghnashini Catchment, Karnataka, India

Abstract In spite of the prolonged exposure and denudation (for >50 Ma), the catchments of the Western Ghats escarpment depict significant relief and rugged topography along the Indian passive margin. In this study, an endeavour has been made to comprehend the function of lithology in landscape dynamics of the Aghanashini catchment through quantitative geomorphology. Longitudinal profiles of this catchment demonstrate disequilibrium through anomalous high stream gradient index and normalized steepness index (ksn) that are related to topographic breaks. Correlation between lithology types and ksn inferred predominant lithologic control on drainage disequilibrium. Transformed coordinate (χ-plot) of the longitudinal profile explained the knickpoint dynamics in an extensive manner where the outcomes suggested river capture process, formation of steep gorge, and series of hanging waterfalls due to sudden change in boundary conditions. This study indicates strong lithologic control under the influence of intense precipitation on shifting knickpoints throughout the catchment area forcing to maintain the valley relief and hillslope angles responsible for rugged and high relief topography of Aghnashini catchment of the Western Ghats.

Westward migration of high-magma addition rate events in SE Tibet

Arc magmatism is an important process in the formation and evolution of the continental crust. Various arcs developed in the southern margin of Eurasian continent that recorded the final formation and growth of these micro-continent before the final India-Eurasia amalgamation. We have examined the often neglected Tengchong arc segment in southeastern Tibet using compiled zircon U-Pb-Hf and whole-rock geochemistry with GPS location and lithology control. The aim is to better understand the driving mechanism of spatial migration and temporal evolution of multi-stage high-MAR (magma addition rate) events and its role in formation and growth of Tengchong arc segment.Results indicate three magmatic “flare-ups” during east-to-west arc migration, from ~131–111 Ma (eastern), ~76–64 Ma (central), to ~55–49 Ma (western), during amalgamation of Lhasa-Tengchong and Qiangtang-Baoshan blocks and final collision of India-Asia plate following subduction of Neo-Tethys. Zircon Hf isotopes and geochemical analyses shows the significant increasing juvenile and/or mantle-derived materials and the range of isotopes also broaden during flare-ups, indicating the melting of diverse lithospheric and upper plate domains. Through comparison with geophysical parameters, these pulses are closely coupled with the arc migration along with changes of crustal thickness, but not correlated with angle and rates of convergence. The spatial arc migration of the multi-stage high-MAR events in Tengchong arc segment was potentially driven by slab steepening and break-off following the initial collision, and abrupt changes of subduction slab dynamics. These processes are well coupled with multi-stage interactions of crust-mantle and transitional Moho-depths.

Influence of structures and lithologies in the morphology and localization of Au–Ag mineralization at Martinetas deposit, Don Nicolas mine, Deseado Massif, Argentina

This work describes the structural and lithological controls that affect the distribution, orientation, and precipitation mechanism of mineralization in the Martinetas district, from the structural context and the analysis of the role played by the geological units that host the mineralization. Martinetas is a low sulfidation epithermal gold and silver mining district located in the northeastern sector of the Deseado Massif, Argentina. The district is characterized by numerous quartz veins, sheeted veinlets and breccias, developed in pyroclastic and volcanic rocks of the Bahia Laura Volcanic Complex.The analysis of fractures, faults and host rocks of the vein systems show that the main factors controlling the formation and distribution of the mineralization are the lithology, deformation style and fault kinematics. Their interplay led to positive feedback between the evolution of plane aperture through time, strain localization and the resulting mineralization. Vein orientations are indicative of a NE-SW extensional stress field at the time of hydrothermal fluid ascend, which favored fluid input and pervasive flow within the active fractures and the matrix of the geological units. Subsequently, cyclic channelized fluid flow during repeated fluid input caused extensive veining and numerous filling events. A link between hydrothermal organic matter and the presence of gold in the vein system has been recorded.Knowledge of the structural and lithological controls that set the structure and the distribution of higher grades ore shoots of the mineralization in the Martinetas district constitutes information of high value as an exploratory tool for the region.

New data on the palynostratigraphy and paleoenvironments of the late Miocene (Tortonian) Quifangondo Formation in the Cabo Ledo section, Kwanza Basin, Angola

A detailed palynostratigraphic and palynofacies analysis, associated with a lithological control, was carried out on eleven outcrop samples from the Quifangondo Formation in the Cabo Ledo (Petrofina) section, Kwanza Basin, Angola. The samples yield relatively diverse and well-preserved terrestrial and marine palynomorphs. A systematic analysis of the samples enables the identification of nine spore genera and 3 species, 20 pollen genera and 13 species, and 32 dinoflagellate cyst genera and 34 species. In addition, 10 genera of other aquatic palynomorphs, such as Chlorophyceae green algae, are identified. Dinoflagellate cysts and other aquatic palynomorphs typically dominate throughout the assemblages. In this section, a combined pollen - dinoflagellate cyst zonation is used to define two palynoassociations. The first palynoassociation is middle Tortonian in age and is characterized by the presence of the pollen grain Fenestrites spinosus and the first occurrence of the dinoflagellate cyst species Selenopemphix armageddonensis. Additionally, diverse Chlorophyceae green algae dominate most of this interval samples. The second palynoassociation is assigned to the late Tortonian and is characterized by a drastic decrease in Chlorophyceae green algae, as opposed to the gonyaulacales dinoflagellate cysts. The first occurrence of the pollen grain Fenestrites longispinosus marks the transition between the palynoassociations. Lithologically, the Cabo Ledo (Petrofina) section is dominated by a claystone with an increase in the silt and carbonate components towards the upper section. The lithological data, integrated with palynostratigraphy and palynofacies, suggests that the upper part of the Quifangondo Formation was mainly deposited in an inner to middle neritic environment characterized by dysoxic conditions punctuated by periods of terrestrial inflows. Such conditions typically result from seasonal fluctuations. The age and depositional environment of the upper Quifangondo Formation inferred from this new data allows a correlation with the other Quifangondo sequences previously studied by the authors. This multi-proxy approach is important for further stratigraphic analysis with other age-controlled lithostratigraphic units in the basin. Furthermore, the improvement of paleoenvironmental and depositional models for this unit is of great importance for cross-basin correlation and future petroleum exploration plays.

Petrophysical Facies and Inferences on Permeability at Brothers Volcano, Kermadec Arc, Using Downhole Images and Petrophysical Data

Abstract Downhole data and cores collected during International Ocean Discovery Program (IODP) Expedition 376 at Brothers volcano, Kermadec arc, provide unprecedented, in situ views of volcanic facies and fluid pathways in an actively forming volcanogenic massive sulfide (VMS) ore deposit. Brothers volcano is a submarine caldera with extensive sea-floor hydrothermal alteration. Downhole data were collected in two holes: Hole U1530A at the NW Caldera and Hole U1528D at the Upper Cone. Textural analysis of microresistivity images in Hole U1530A provides a continuous image facies record that greatly improves findings based upon sporadic and partial (18%) core recovery. Between 90 and 214 meters below sea floor (mbsf), the heterogeneous image facies with local pattern variations is consistent with the volcaniclastic facies interpreted from cores. Between 232 and 445 mbsf, a volcanic facies was not recognizable in cores because of overprinting alteration, apart from five intervals of coherent lava flows that were less altered. Based on the fairly constant petrophysical data, Vp-porosity relationship, and presence of five to six coherent image facies intervals on the microresistivity image, we propose that the apparent volcaniclastic textures observed on cores and microresistivity images beneath 232 mbsf are dominantly lava flows. The change from volcaniclastic to dominant lava flow facies occurs over a transition zone (214–232 mbsf) where all petrophysical properties gradually change. In Hole U1528D, cores and petrophysical data show a similar transition from deep coherent lava flows to shallower, largely volcaniclastic sequences at ~270 mbsf. Down to 232 mbsf in Hole U1530A and 360 mbsf in Hole U1528D, the overall first-order downward decrease in porosity is interpreted to be caused by compaction and increased alteration intensity. Volcanic facies and fractures exert a second-order local control on petrophysical properties. Beneath 232 mbsf in Hole U1530A, the prolonged hydrothermal activity is inferred to have diminished local petrophysical property variations within the proposed lava flow-dominated rock package. High downhole fluid temperatures in Hole U1528D contrast with the moderate temperatures in Hole U1530A. Permeable zones show a mix of structural (inferred fault in Hole U1530A) and lithological controls in both holes. Some low-permeability layers and/or lithological interfaces possibly focus fluids laterally in higher-permeability layers, which may act as a trap for metal-rich fluids to form stratabound massive sulfides and deposits. Matrix is likely too low in permeability to conduct fluids but provides perfect conditions for the storage of supersaline brines. In Hole U1530A, located near active vents at the sea floor, the relatively low fluid temperature and the alteration overprint of moderate temperature demonstrate the high spatial and temporal variations at Brothers volcano. The implications of the new stratigraphy and controls on permeability proposed here for Brothers volcano include a better understanding of the following: (1) submarine volcanic eruption sequences, (2) permeability in active submarine volcanoes, and (3) the formation of volcanogenic massive sulfide deposits on (and near) the sea floor.

Lithologic control of microbial-derived carbon in forest soils

Microbial necromass carbon (MNC) is an important contributor to soil organic carbon. The influence of lithology on MNC remains unclear. MNC is often regarded as a stable, uniform entity, but little consideration has been given to its unprotected and protected fractions. We measured MNC contents in particulate organic matter, which represents the unprotected fraction, and in mineral-associated organic matter, which represents the protected fraction, in forest soils over limestone and clastic rock across a climatic gradient in southwest China. Additionally, nearby croplands with long-term soil tillage were selected for comparison. On average, the contents of protected and unprotected MNC were 52–56% greater in forest soils over limestone compared to clastic rock. Both MNC fractions over clastic rock decreased with increasing the mean annual temperature (MAT), whereas only the unprotected fraction decreased with increasing the MAT over limestone. MNC was regulated by iron oxides and microbial biomass in clastic rock and by exchangeable calcium, iron oxides, and microbial biomass in limestone. However, long-term soil tillage minimized the influences of lithology on MNC. By extrapolating the data to the three provinces of southwest China based on the land-use conversion scenario, we estimated that the existing forestation (recovery and afforestation) has the potential to increase microbial-derived carbon by 17 Tg in topsoil (0–15 cm) over limestone and 11 Tg over clastic rock. The lithology-dependent drivers of microbial-derived carbon accumulation and stability should be considered to predict soil carbon dynamics and minimize carbon emissions under changing environments.