Glacial Beds Research Articles

Nilsen Plateau, Transantarctic Mountains, Antarctica: an update on the Gondwana stratigraphy and structure

ABSTRACT A revised and updated geological map of the Nilsen Plateau and a new geological map of the nearby Mt. Hassel-Mt. Bjaaland region are presented. The Gondwana succession, overlying pre-Devonian basement rocks, consists of Permian glacial beds, post-glacial shales and siltstones, deltaic sandstones, and coal measures succeeded by Triassic flood plain deposits. Jurassic dolerite sills intrude basement rocks and the Permo-Triassic beds. High-angle reverse faults displace Permian strata at the southern end of the range, and post-Jurassic normal faulting affected the whole range.

Paleoclimatic implications of a vascular plant from the lowermost Itararé Group

Plant fossils serve as critical proxies for interpreting past climates and environments, offering insights into the history of biosphere and climatic conditions. Here we describe a large tracheophyte cast, as well as the sedimentological settings in which it is preserved, expanding the paleobotanical database of the Itararé Group and contributing to the understanding of the LPIA in the Paraná Basin. This fossil occurs in Ponta Grossa, Paraná state, Brazil, within sedimentary levels interpreted as glacially dominated and deposited during the Late Paleozoic Ice Age (LPIA). The plant macrofossil is preserved as a cast, and the log is vertically oriented with a slight inclination in relation to the bedding plane. Taphonomic data indicate an allochthonous preservation, suggesting that the log was transported from inland areas to a plain before final burial. The identification of the tracheophyte cast within these glacial beds suggests that even in a dominantly glacial context, there were periods of episodic climatic amelioration. This finding implies that the climatic conditions during the Mississippian were not uniformly harsh, allowing the growth of vegetation as represented by the reported tracheophyta.

A combined tectono-climatic control on Holocene sedimentation in Ladakh Himalaya, India: Clues from Anisotropy of Magnetic Susceptibility (AMS) of lake sediments

Anisotropy of Magnetic Susceptibility (AMS) data from a ∼27.8 m thick soft sedimentary mud sequence (∼10.5–3.25 k yrs) from the Spituk Palaeolake Sequence (SPSS) of Holocene age, located in the northern bank of the Indus River in the Leh-Ladakh Himalaya, show effects of tectonic versus climate dynamics responsible for the Himalayan sedimentation. The sedimentary sequence, consisting of alternating of aeolian sand and glacio-fluvial mud flow deposits, has been subdivided into an older Last Glacier Phase I (LGP 1) and a younger Last Glacier Phase II (LGP 2), where the termination of each phase is marked by the occurrence of gravel beds of thickness ≤1 m, which were deposited due to glacial melting. The present AMS data along with previously published information on sedimentology confirm that the mudflow deposits of the LGP 1 and LGP 2 phases were deposited in a lacustrine environment under glacio-fluvial conditions. However, a weak fluvial flow towards NW and NE could have existed for the LGP 1 and LGP 2, respectively. The glacial beds terminating LGP 1 and LGP 2 appear to have formed by climatic warming and tectonic activity, respectively. Hence, the Holocene Himalayan sedimentation was influenced by both climatic and tectonic activities. However, the thickness of the gravel bed (∼0.8 m) terminating LGP 2 occupies only ∼ 2.8 vol % of the total studied thickness ∼28 m, of the SPSS in the present study, which indicated a lesser control of tectonism in the growth of the Himalaya in and around the study area.

Flowering Plants and Ferns of North Garhwal, Uttar Pradesh, India

The paper gives an account of the recent collection of flowering plants and ferns from the Garhwal Himalayas, made by the author during the years 1957 to 1959 in which nearly 1500 gatherings were made which on study yielded 738 species. The area covered by this study lies between 30° and 31° N., and 79° and 80° E., and includes the Alaknanda, Arwa, Bhyundar, Khiraun, Mandakini and Nandakini river valleys and their neighbouring glacial beds, mountain slopes and meadows ranging in altitude between 2000 and 4500 metres. Cypripedium elegans Reichb. f., a rare terrestrial orchid was collected for the first time in Western Himalayas.

Characterization of seismicity from different glacial bed types: machine learning classification of laboratory stick-slip acoustic emissions

Abstract Subglacial seismicity presents the opportunity to monitor inaccessible glacial beds at the epicentral location and time. Glaciers can be underlain by rock or till, a first order control on bed mechanics. Velocity-weakening, necessary for unstable slip, has been shown for each bed type, but is much stronger and evolves over more than an order of magnitude longer distances for till beds. Utilizing a de-stiffened double direct shear apparatus, we found conditions for instability at freezing temperatures and high slip rates for both bed types. During stick–slip stress-drops, we recorded acoustic emissions with piezoelectric transducers frozen into the ice. The two populations of event waveforms appear visually similar and overlap in their statistical features. We implemented a suite of supervised machine learning algorithms to classify the bed type of recorded waveforms and spectra, with prediction accuracy between 65–80%. The Random Forest Classifier is interpretable, showing the importance of initial oscillation peaks and higher frequency energy. Till beds have generally higher friction and resulting stress-drops, with more impulsive first arrivals and more high frequency content compared to rock emissions, but rock beds can produce many till-like events. Seismic signatures could enhance interpretation of bed conditions and mechanics from subglacial seismicity.

A magnetic fabric study of the origin of englacial debris bands at Fláajökull, Southeast Iceland

Two debris bands associated with an overdeepened basin in the terminus region of the Fláajökull glacier, Iceland, have been sampled for their ice and debris. Here the kinematics of deformation are investigated through anisotropy of magnetic susceptibly (AMS), microstructural analyses, and c-axis preferred orientations. Comparison of the crystallographic orientations of 180 grains and the AMS shape orientations of mineral inclusions in polycrystalline ice reveals a multi-maximum girdle oblique to the planar stratification and a record of near vertical triaxial ellipsoids. These two distinct fabrics can be attributed to both pure and simple shear suggesting a complex deformational history. In addition, AMS from an ice-free sediment ridge on the glacier surface indicates pure shear locally dominated strain. The physical properties of the debris bands, sedimentology and field observations suggest that they were sourced from the glacial bed and emplaced by highly pressurized water into localized fractures.

Onset of the late Paleozoic glaciation in the Lhasa terrane, Southern Tibet

The Late Paleozoic Ice Age is characterized by diverse stratigraphic records with extensive spatial-temporal distribution in the Gondwana. The Lhasa terrane located in northeastern Gondwana during the late Paleozoic developed successive glacial sedimentary records, but the depositional evidence, as well as age constraint for the onset of glaciation, is unknown. This paper provides the first full description of the basal glacial deposits in the Xainza area of Lhasa terrane, southern Tibet. Conodonts present in the carbonate overlying the glacial bed (1 m) dominantly consist of Declinognathodus intermedius, indicating that the initiation of the Late Paleozoic Ice Age in the Lhasa terrane took place in Bashkirian. Three facies associations were recognized: (i) tidal flat association (subtidal channel, bar, intertidal mixed flat), (ii) subglacial association (megaclasts and melt-out diamictite), and (iii) lonestone-bearing heterolithic association (grounding-line fan and iceberg). These facies associations are vertically arranged into a complete transgressive-retrogressive glacial succession. Ice movement direction reconstructed from the imbricated megaclasts, the concordant folds and the lateral distribution of subglacial deposits and glacial marine deposits is consistently from NNE to SSW. These characteristics suggest that the Bashkirian glaciation in the Lhasa terrane is irrelevant to western Australia, implying that these two blocks were separated during the Late Carboniferous.

Contrasting intensity of aragonite dissolution and dolomite cementation in glacial versus interglacial intervals of a subtropical carbonate succession

AbstractAragonite and high‐Mg calcite are abundant in modern, neritic carbonate systems but almost absent in their fossil counterparts. Dissolution of these metastable mineral phases commonly leaves no visible trace in the sedimentary record, compromising the derivation of palaeoenvironmental information from the rock record. The upper 25 m of Integrated Ocean Drilling Program (IODP) Site U1460 on the outer ramp of the western Australian Shelf were investigated to study shallow burial (tens of metres) marine diagenesis in organic‐carbon poor sediments using microscopic, total organic carbon, biomarkers and mineralogical analysis in combination with porewater geochemistry. Aragonite dissolution is negligible at the seafloor but intensifies ca 5 m below, even though bulk porewaters are supersaturated for aragonite. This apparent contradiction likely results from dissolution in undersaturated microenvironments. Aragonite dissolution below 5 to 6 m is on average more intense in interglacial compared to glacial intervals. The presence of disseminated framboidal pyrite and porewater results indicate that minor sulphate reduction is active at IODP Site U1460. Sulphate reduction is probably limited by the low organic matter content (ca 0.2%). It is well‐known from the literature that incipient sulphate reduction can lead to a drop in pH and consequently to carbonate dissolution. It is therefore assumed that the slightly higher concentration of organic matter in the interglacial intervals allowed increased aragonite dissolution during sulphate reduction compared to glacial beds. Low amounts of dolomite cement (<15%) start to form at the same depth (5 to 6 m) as aragonite dissolution intensifies. Dolomite formation and aragonite dissolution also show covariance on a metre‐scale below 5 to 6 m, indicating that a low carbonate saturation state might enhance dolomite formation. This mechanism provides an indirect link between dolomite formation, aragonite dissolution and orbital cycles. The outcome of this study, therefore, contributes to a better understanding of differential diagenesis in marine carbonates.

Deep ice drilling, bedrock coring and dust logging with the Rapid Access Ice Drill (RAID) at Minna Bluff, Antarctica

AbstractRapid Access Ice Drill is a new drilling technology capable of quickly accessing the glacial bed of Antarctic ice sheets, retrieving ice core and rock core samples, and providing boreholes for downhole logging of physical properties. Scientific goals include searching for old ice near the glacial bed and sampling subglacial bedrock. During field trials near McMurdo Station on a piedmont glacier at Minna Bluff in the 2019–20 austral summer, we successfully completed a ‘top-to-bottom’ operational sequence in three boreholes by (1) augering through firn, (2) creating a borehole packer seal in non-porous ice, (3) establishing fluid circulation, (4) quickly drilling a borehole in ice at penetration rates up to 1.2 m min−1, (5) acquiring a short ice core at depth, (6) penetrating the glacial bed at a depth of ~677 m, (7) recovering a 3.2 m core of ice, basal till and subglacial bedrock, (8) optically logging the borehole on wireline, (9) testing hydrofracture potential by overpressuring the borehole fluid and (10) operating in an environmentally benign yet rapid field mode. Minna Bluff testing, therefore, demonstrates the effectiveness of this integrated system to drill rapidly through thick ice and penetrate across the glacial bed to take cores of bedrock.

The importance of topography in the occurrence of glacial valleys in Belarus

The relief of the ice-sheet bed predetermines the location of the valleys both in vast regions and in local, relatively limited areas. The influence of the relief in a large region on the formation of valleys occurs in lowland, more dissected northern and western regions of Belarus. Here, the bedrock relief plays a key role in appearance the hollow-like Vidzovsky, Polotsk and Surazh glacial erosion depressions and in isolation of the elevations separating them. The distribution of these largest forms of glacial erosion is associated with the regional picture of the glacial ice flow in topographic depressions, increased erosion of the ice bed, which developed under the glacial streams and lobes of the Scandinavian ice sheet. The degree and character of the relief dissection, the size, surface slope and orientation of the depressions, river paleo-valleys, elevations, and escarps had a leading role in the location of valleys in local, relatively limited areas. Their significance for the formation of valleys was to determine the local picture of the glacial flow and the areas where stresses were concentrated at the bed and glacial erosion intensified. The formation of tunnel valleys was possible in depressions and in the dissected relief of the glacial bed, which contributed to the accumulation of meltwater, the formation of subglacial lakes, as well as the concentration of meltwater in the subglacial channels.

Influence of salt structures on the location of glacial valleys within the Pripyat Trough (Belarus)

It was found that glacial valleys in the Pripyat Trough are connected with the location of the halokinetic structures of the Upper-Famennian salt strata. Valleys were noticed over salt structures, which developed during the Quaternary. The most part of valleys is over salt diapires, pillows and swells, rarer they occur within synclinales and troughs. Within local anticlinales valleys focus mainly in its tops and limbs, which have incline down glacier. Within salt synclinales valleys lie over its axis and limbs, which are connected with adjacent anticlinales. The most typical regularities of the glacial valleys localization within the salt structures is their close connection with active fault systems. These faults propagate upwards from the tops and flanks of diapires across the Upper-Famennian and supra-salt overburden into the Quaternary, where underlie the valleys. The developing of salt structures and faults during the Narev and Dnieper glaciations created weakness zones in glacial bed that facilitated erosion by the glaciers and subglacial melt water.

CONDITIONS OF KAME FORMATION NEAR VILLAGE OF MASHIV (VOLHYNIAN POLISSIA)

Kames located in the Volhynian Polissya remain the most widespread and the least studied type of relict glacial landform. The article is focused on the specific conditions of kames creation within the peripheral parts of the Volhynian Polissya glacial bed elevation and their significant role in the formation of fissure net in the zones of deadened ice compression inherited from the stages of their inactivity. These compression zones were predetermined by the general planned configuration of the glacial bed landform climaxes. The presented reservoir is located to the north of the village of Mashiv and belongs to a complex of similar glacial accumulations crowed at the culmination of pre-glacial relief and placed at a considerable distance from the marginal formations of the maximum stage of the Dnieper glaciation. The morphological and geological structure of the form is analyzed to explain the conditions of its formation. It is revealed that its structure is dominated by fine-grained sediments; textural and structural features of them allow distinguishing two lithofacial complexes. The basis of the form is loamy sandy and sandy lake-ice deposits covered by a complex of fine-medium-grained sandy fluvioglacial sediments. The morphology of the form, its correlation with the elements of buried pre-glacial relief and the textural peculiarities of the described section deposits, allow to state that the accumulation of the material occurred within a semi-flowing or stagnant during certain periods basin filled with sediments of a small convey water-glacial outcasts; they were accumulated by activity of low energy melt water flows within the peripheral part of the ice glade. The glade was formed on the fracture zone line of the inactive (dead) ice, laid above the glacial bed landform climaxes. The textural and structural features of the form give reason to identify it as kame. Key words: Volhynian Polissia, deglaciation, kames, sedimentation, lithofacies analysis, glaciolacustrine and glaciofluvial sediments.

High-resolution landform assemblage along a buried glacio-erosive surface in the SW Barents Sea revealed by P-Cable 3D seismic data

The Quaternary sedimentary record in the Arctic captures a diverse and evolving range of landscapes reflecting climate changes. Here we study the geological landform assemblage of the Upper Regional Unconformity (URU) in the SW Barents Sea. The aims are (i) to characterize buried geological landforms on a meter-scale resolution, (ii) to understand their link with underlying structures, and (iii) to reconstruct paleo-ice-sheet dynamics and configurations. The data consist of a high-resolution three-dimensional (3D) P-Cable seismic cube with an extent of c. 200 km2 and an inline separation of 6 m. Dominant frequencies of c. 150 Hz allow to image landforms at URU with a vertical resolution of 1–5 m and a horizontal resolution of 3–6 m. We conduct detailed horizon-picking and seismic attribute analysis of the buried URU horizon. We identified four sets of mega-scale glacial lineations, and shear band ridges located to the west of a shear margin moraine. Other characteristic features include hill-hole pairs, transverse ridges, rhombohedral ridges and depressions, iceberg ploughmarks and pockmarks. Polygonal faults below URU and deeper faults have a strong effect on the location of structures observed on URU. Bedrock packages deformed down to 30 m below URU and up to 5 m-high transverse ridges at URU are imprints of glacio-tectonic activity. Deformed strata below URU indicate normal faulting superimposed by glaciotectonic deformation. The four sets of mega-scale glacial lineations indicate four streaming events with thawed glacial beds, with shear band ridges forming in the shearing zone during one of these streaming events. Hill-hole pairs and rhombohedral ridges are frozen-bed features which indicate a polythermal regime at the base of the Barents Sea Ice Sheet during multiple streaming phases. This study therefore shows that paleo-ice streams have been temporarily frozen to the ground in the SW Barents Sea, and that landforms evidencing this freezing are associated with underlying faults.

Two Metrics Describing the Causes of Seasonal and Spatial Changes in Subglacial Aqueous Chemistry

Seasonal change in surface melt input and spatial controls on the distribution of subglacial water can cause considerable variability in the aqueous chemistry of subglacial waters. Much of this variability has been interpreted in terms of a single variable: water residence time, with slow flow assumed to correlate with greater mineral dissolution and oxidative weathering. We synthesize data from a range of glacier and ice sheet settings to show that this approach does not adequately describe presently available data. Instead, we propose that two independent variables control spatial and seasonal changes in aqueous chemistry in subglacial settings: atmospheric gas abundance and sediment supply abundance. Where atmospheric gases are abundant, carbonation weathering is responsible for most of the subglacial chemical activity; where they become limited, oxidation weathering becomes more dominant. Where freshly comminuted sediment is abundant, easily dissolved minerals, especially calcite, have proportionally more influence on subglacial hydrochemistry; where sediment supply is limited, silicate minerals and less reactive carbonate minerals will increase in relative influence. In most settings, simple metrics of the abundance of SO42- and Ca2+ in the subglacial waters can characterize these two variables. In the data we synthesize, neither variable consistently correlates to the inferred water residence time, nor do the variables consistently correlate with each other. Spatial data show that point locations and small catchments on the glacial bed differ substantially from the integrated composition found at glacial outlets. The varied response in the subglacial aqueous chemistry to changing water residence times suggests complex control by a broad range of glaciological factors that affect water routing and subglacial sediment generation.

Basal Moraines: Communication 1. Essential Lithological Features

The facies complex of basal moraines with glaciodynamic structures (common basal moraines) dominates among deposits of the given genetic type. These moraines represent glacial diamictons of diverse structure and lithology. Some of their features are also typical of sediments of other genetic types. Therefore, a comprehensive study of glacial diamictons and their occurrence mode on the glacial bed (unconsolidated or consolidated) within large outcrops is methodically correct. Only such studies can unravel the wide range of specific features typical of common basal moraines.

Conditions of formation of kame near Zalissia village (Volyn Polissia)

This work is an attempt to explain the morphology and geological structure of glacial forms located within the frontal area of the first post maximal stage of Dnipro Glaciation near Zalissia (Volyn Polissia). We tried to explain their origin and conditions of formation. The research included morphological and morphometric methods and method of lithofacies analysis. Presented kames form isolated and semi-isolated hills. They mostly have an irregular shape, slightly elongated, subparallel of the ice frontal zones. The geological structure of the forms was studied in a large sand quarry and in several unrepresentative small outcrops of anthropogenic origin. They are located near the village of Zalissia. This research revealed that fine-grained sediments dominate in the geological structure of these forms. Texture and lithological features of the deposits of Zalissia section helped to identify a few lithofacies complexes in their composition. Thin horizontally layered glaciolacustrine sediments are lying at the base of the form. They are covered with the unsorted detrital deposits (diamicton). Mainly fine and middle sandy deposits of the fluvioglacial complex occur higher in the section. They are rhythmically constructed. Geological structure of section is finished by a layer of unsorted gravel and pebble ablative deposits with mainly sandy filler. Texture features of the deposits of this section make it possible to conclude that their accumulation took place in zones of increased fracture in the body of inactive, dead ice. Sedimentation was carried out in conditions of low-energy glaciofluvial streams and stagnant basins, occasionally interrupted by the accumulation of ablation masses. Such a combination of different deposits may indicate that the formation of this form could take place in the deepenings on the surface of the ice, possibly in large thawed patches, which reached the glacial bed. The thawed patches lay on the intersections of large cracks. The formation of cracks is a consequence of the uneven block movement of the ice masses in front of the barrier in the form of glacial bed elevation. Cracks had a constant tendency to expand as a result of increased ablation processes. These forms are identified as kames based on the detected sedimentological features. Key words: Volyn Polissia, kame, lithofacies analysis, sedimentation, glaciofluvial and glaciolacustrine deposits.

Basal (basic) moraines: Problem of the identification and principles of new classification

The existing concepts of moraine/till formation are discussed and the available factual data on this issue are analyzed. It is concluded that active glaciers from the transported mineral matter make up exclusively basal moraines on the river bed. The latter moraines, which are composed of material directly deposited from the glacier base on the substrate, represent glacial diamicts. It is believed that material in these deposits always acquire a semisolid-solid (“stiff”) state. We identified a new type of glacial deposits–“mitis” basal moraines, which include the recently defined low consolidated glacial diamicts. Consequently, basal moraines are divided into two facies associations: moraines with glaciodynamic structures (common “stiff” moraines) and “mitis” moraines (M-moraines). Deposits of these associations are formed in different thermal zones (areas) of the ice sheet bed. Moraines of the first facies association are formed in melt zones. Therefore, they are characterized by different lithologies and overconsolidation. The M-moraines formed on the thawed glacial bed are marked by massive structure and low (normal) consolidation. They are subdivided into the Barents Sea and Antarctic types.

Enrichment of Cryoconite Hole Anaerobes: Implications for the Subglacial Microbiome

Glaciers have recently been recognized as ecosystems comprised of several distinct habitats: a sunlit and oxygenated glacial surface, glacial ice, and a dark, mostly anoxic glacial bed. Surface meltwaters annually flood the subglacial sediments by means of drainage channels. Glacial surfaces host aquatic microhabitats called cryoconite holes, regarded as “hot spots” of microbial abundance and activity, largely contributing to the meltwaters’ bacterial diversity. This study presents an investigation of cryoconite hole anaerobes and discusses their possible impact on subglacial microbial communities, combining 16S rRNA gene fragment amplicon sequencing and the traditional enrichment culture technique. Cryoconite hole sediment harbored bacteria belonging mainly to the Proteobacteria (21%), Bacteroidetes (16%), Actinobacteria (14%), and Planctomycetes (6%) phyla. An 8-week incubation of those sediments in Postgate C medium for sulfate reducers in airtight bottles, emulating subglacial conditions, eliminated a great majority of dominant taxa, leading to enrichment of the Firmicutes (62%), Proteobacteria (14%), and Bacteroidetes (13%), which consisted of anaerobic genera like Clostridium, Psychrosinus, Paludibacter, and Acetobacterium. Enrichment of Pseudomonas spp. also occurred, suggesting it played a role as a dominant oxygen scavenger, providing a possible scenario for anaerobic niche establishment in subglacial habitats. To our knowledge, this is the first paper to provide insight into the diversity of the anaerobic part of the cryoconite hole microbial community and its potential to contribute to matter turnover in anoxic, subglacial sites.

Rapid Access Ice Drill: a new tool for exploration of the deep Antarctic ice sheets and subglacial geology

ABSTRACTA new Rapid Access Ice Drill (RAID) will penetrate the Antarctic ice sheets in order to create borehole observatories and take cores in deep ice, the glacial bed and bedrock below. RAID is a mobile drilling system to make multiple long, narrow boreholes in a single field season in Antarctica. RAID is based on a mineral exploration-type rotary rock-coring system using threaded drill pipe to cut through ice using reverse circulation of a non-freezing fluid for pressure-compensation, maintenance of temperature and removal of ice cuttings. Near the bottom of the ice sheet, a wireline latching assembly will enable rapid coring of ice, the glacial bed and bedrock below. Once complete, boreholes will be kept open with fluid, capped and available for future down-hole measurement of temperature gradient, heat flow, ice chronology and ice deformation. RAID is designed to penetrate up to 3300 m of ice and take cores in <200 hours, allowing completion of a borehole and coring in ~10 d at each site. Together, the rapid drilling capability and mobility of the system, along with ice-penetrating imaging methods, will provide a unique 3-D picture of interior and subglacial features of the Antarctic ice sheets.

Basal shear stress under alpine glaciers: insights from experiments using the iSOSIA and Elmer/Ice models

Abstract. Shear stress at the base of glaciers exerts a significant control on basal sliding and hence also glacial erosion in arctic and high-altitude areas. However, the inaccessible nature of glacial beds complicates empirical studies of basal shear stress, and little is therefore known of its spatial and temporal distribution. In this study we seek to improve our understanding of basal shear stress using a higher-order numerical ice model (iSOSIA). In order to test the validity of the higher-order model, we first compare the detailed distribution of basal shear stress in iSOSIA and in a three-dimensional full-Stokes model (Elmer/Ice). We find that iSOSIA and Elmer/Ice predict similar first-order stress and velocity patterns, and that differences are restricted to local variations at length scales of the order of the grid resolution. In addition, we find that subglacial shear stress is relatively uniform and insensitive to subtle changes in local topographic relief. Following the initial comparison studies, we use iSOSIA to investigate changes in basal shear stress as a result of landscape evolution by glacial erosion. The experiments with landscape evolution show that subglacial shear stress decreases as glacial erosion transforms preglacial V-shaped valleys into U-shaped troughs. These findings support the hypothesis that glacial erosion is most efficient in the early stages of glacial landscape development.