Middle paleozoic waulsortian-type mud mounds in Southern Fergana (Southern Tien-Shan,commonwealth of independent states): The shallow-water atoll model

Summary Several Waulsortian-type mud mounds nearly 500 m thick and about 5 km long occur in the Middle Paleozoic carbonate section of the Aktur nappe in the mountains on the right bank of Isfara river. These buildups form a well developed barrier system that stretches along the South Ferganian carbonate platform margin and divides the carbonate complex into a fore-reef and a back-reef part. The time of the mounds' most active growth was from the Late Silurian (Ludlow) to the Middle Devonian (Eifel). Three main facies types can be recognized in the mud mounds: 1. micritic core facies, 2. sparitic flank facies and 3. loferitic capping facies. The central massive or crudely bedded part of the mounds consists of white or light grey clotted micrite. Macrofossils are rare. The sparitic flank facies in contrast consists of coarse and densely packed crinoidal wackestone-floatstones with some brachiopod shell debris. Solitary rugose corals, tabulate corals, stromato-poroids and fragments of mollusks are also abundant. The tops of the mounds are usually covered with loferitic pelmicrites or oolitic grainstone caps. Stromatactis-like structures are very rare and poorly developed in the South Ferganian mud mounds. However, almostin all such mounds horizons of calcitic breccias can be found. In order to explain all the features found in the Fergana mounds an ‘atoll-like’ model has been proposed which starts the evolution of the mud mounds with a small nucleus bioherm. The main stage of the evolution corresponds to an atoll-like structure developing on the surface of shallow water platforms. White clotted micrite of the mound core facies is interpreted as a accumulation of fine-grained sediment in an inner lagoon flanked by crinoidal bar deposits. The mound flank facies represents the atoll rim deposits from where the carbonate mud is derived. The capping loferitic facies is considered as tidal flat deposit that developed on top of the buildups during the last stage of its evolution. The knoll shape of the mounds is explained by the retreat of the atoll flanking crinoidal bars back into the inner lagoon during the rise in sea level. Stromatactis-like structures of small cavities filled with sparry calcite owe their existence to burrowing organisms. Calcitic breccias are interpreted as paleokarst collapse breccias. They indicate that the tops of the mud mound became subaerially exposed. Other evidence for a subaerial exposure can be seen in the occurrence of Variscian ‘black and white’ limestone gravel on the tops of some mud mounds. According toWard et al. (1970) these sediments were produced above the sea level at the edge of hypersaline lakes situated on islands.     

Late Paleozoic reef mounds of the Carnic Alps (Austria/Italy)

The Late Paleozoic (early Kasimovian-late Artinskian) sedimentary sequence of the Carnic Alps (Austria/Italy) is composed of cyclic, shallow-marine, mixed siliciclastic-carbonate sedimentary rocks. It contains different types of skeletal mounds in different stratigraphic levels. The oldest mounds occur at the base of the Auernig Group, within a transgressive sequence of the basal Meledis Formation. These mounds are small and built by auloporid corals. Algal mounds are developed in the Auernig Formation of the Auernig Group, forming biostromes, and Lower Pseudoschwagerina Limestone of the Rattendorf Group forming biostromes and bioherms. The dominant mound-forming organism of these mounds is the dasycladacean alga Anthracoporella spectabilis. In mounds of the Auernig Formation subordinately the ancestral corallinacean alga Archaeolithophyllum missouriense is present, whereas in mounds of the Lower Pseudoschwagerina Limestone a few calcisponges and phylloid algae occur locally at the base and on top of some Anthracoporella mounds. Mounds of the Auernig Formation formed during relative sea level highstands whereas mounds of the Lower Pseudoschwagerina Limestone formed during transgression. The depositional environment was in the shallow marine, low-turbulence photic zone, just below the active wave base and lacking siliciclastic influx. The algal mounds of the Carnic Alps differ significantly from all other algal mounds in composition, structure, zonation and diagenesis; the formation of the mounds cannot be explained by the model proposed by Wilson (1975). The largest mounds occur in the Trogkofel Limestone, they are composed of Tubiphytes/Archaeolithoporella boundstone, which shows some similarities to the “Tubiphytes thickets” of stage 2 of the massive Capitan reef complex of the Guadalupe Mountains of New Mexico/West Texas.     

Enhanced photosynthesis and flower production in a sagebrush morphotype associated with animal burrows

Two morphotypes of the evergreen shrub Artemisia tridentata Nutt. ssp. wyomingensis occur in the Shirley Basin of central Wyoming (USA), one of which was associated exclusively with Mima-like mounds generated by animal burrowing activity. Measured on a particularly dry year according to a 34-year precipitation record, plants growing on mounds (M) versus inter-mound locations (IM)were taller with greater leaf biomass and leaf area per unit ground area, and had over 90% of all inflorescences. As a result, the landscape consists of a patchy distribution of reproductive islands (~ 20-40 m^-2 in size) separated by a mean distance of ~ 30 m. In addition, greater photosynthesis per unit leaf area occurred for M plants when ephemeral leaves dominated total leaf area in spring and early summer, as well as during short time periods (< 3 days) following sporadic rainfall events in summer when only perennial leaves were present. As a result, estimated total annual carbon gain was 41% greater for M plants from May to mid-June, but was not significantly different from IM plants for the remainder of the season, resulting in a total summer carbon gain that was 14% greater in M plants. Stomatal and nonstomatal conductances to CO2 uptake were also greater for the ephemeral leaves of M plants, along with lower internal CO2 concentrations (193 ± 4 μl l^-1 vs. 209 ± 8 μl^-1, respectively). M plants also maintained higher xylem water potentials throughout most of the growth season (−1.1 ± 0.1 SD MPa in May, declining to −4.4 ± 0.3 SD MPa in August), along with higher water use efficiencies (photosynthesis/transpiration). M and IM soils did not differ significantly in total organic or nitrate contents, although leaf nitrogen content was higher in M plants when photosynthesis was also greater. Photosynthesis in M plants also responded more positively to afternoon showers greater than about 7 mm compared to IM plants. Thus, improved water and nutrient relations was associated with enhanced photosynthetic carbon gain in M plants, enabling greater flower production. Moreover, morphotypic plasticity coupled with the effects of animal burrows may have substantially increased sexual reproductive success in A. t. wyomingensis.     

Facies of Liassic sponge mounds, central High Atlas, Morocco

Summary Liassic sponge mounds of the central High Atlas (Rich area, northern Morocco) have a stratigraphic range from the Lower/Upper Sinemurian boundary interval up to the lower parts of the Lower Pliensbachian (Carixian). The base of Liassic sponge mounds consists of a transgressive discontinuity, i.e., a condensed section of microbioclastic wackestones with firm- and hardgrounds, ferruginous stromatolites, sponge spicules and ammonites. The top of Liassic sponge mounds is an irregular palaeorelief covered by cherty marl-limestone rhythmites, namely hemipelagic spicular wackestones with radiolaria. In the Rich area, section Foum Tillicht, the sponge mound succession has a total thickness of about 250 meters. Within this succession we distinguished between three mound intervals. The lower mound interval shows only small, meter-scale sponge mounds consisting of boundstones with lyssakine sponges, commensalicTerebella and the problematicumRadiomura. This interval forms a shallowing-upward sequence culminating in a bedded facies withTubiphytes, calcareous algae (Palaeodasycladus), sponge lithoclasts, coated grains, and thin rims of marine cement. The middle mound interval is aggradational with decametric mounds and distinct thrombolitic textures and reefal cavities. The mound assemblage here consists of hexactinellid sponges, lithistid demosponges, non-rigid demosponges,Radiomura, Serpula (Dorsoserpula), Terebella, encrusting bryozoa, and minor contributions by calcareous sponges, and excavating sponges (typeAka). Thrombolites are dendrolitic and may reach sizes of several tens of centimeters, similar to the maximum size of siliceous sponges. The upper mound interval appears retrogradational and geometries change upsection from mound shapes to flat lenses and level-bottom, biostromal sponge banks. The biotic assemblage is similar to that of the middle mound interval and there is no difference between mound and bank communities. The demise of sponge mounds is successive from regional spread in the Sinemurian to more localised spots in the Lower Pliensbachian. This reduction correlates with an increasing influence of pelagic conditions. At Foum Tillicht, sponge mounds lack any photic contribution and there is virtually no differentiation into subcommunities between mound surface and cavity dwelling organisms. There is some evidence that the heterotrophic food web of mound communities was sourced by oxygen minimum zone edge effects, namely microbial recycling of essential elements such as N and P. Basin geometry suggests a waterdepth of several 100's of meters, well below the photic zone and possibly only controlled by the depth range of the oxygen minimum zone. Palaeoceanographic conditions of well-stratified deeper water masses diminished gradually during widespread transgression across the Sinemurian to Pliensbachian boundary culminating in the Lower Pliensbachianibex ammonite zone.     

Growth history of Lower Mississippian Waulsortian mounds: Distribution,stratal patterns,and geometries,New Mexico

Summary The factors controlling the localization and growth of Lower Mississippian Waulsortian mounds have been difficult to establish because of limited exposure of individual mounds and mound-bearing platforms in western Europe, where the Waulsortian facies have been studied most intensively. Mounds on the Lower Mississippian homoclinal ramp of the Lake Valley Formation in the Sacramento Mountains, however, are exposed exceptionally well at platform, outcrop, and mound scales in an area roughly 5 km by 20 km, and provide the opportunity to better understand these aspects of Waulsortian mounds. Mounds occur in the northern 2/3 of the essentially continuous 32 km dip transect of the ramp. Mounds grew in an outer ramp setting below wave base, predominantly in the deeper part of the photic zone. Mounds range from broad composites of laterally back-stepping subunits on the shallow part of the ramp to taller and more vertically stacked composite structures down-ramp. The composite nature of the mounds is documented by distinct stratal units that have characteristic facies and geometries common to mounds throughout the transect. As a result, mound growth and form can be described in terms of several primary controlling parameters—submarine topography, water circulation (upwelling of nutrients and oxygen rich waters; oxygen deficient bottom waters), light penetration and the distribution of phototrophic microorganisms, and fluctuations in accommodation. Episodic mound growth is documented by diastems bounding the stratal units within the mounds as well as by the long-established useage of Alamogordo, Nunn, and Tierra Blanca phases of mound growth, correlative with the contemporaneous level-bottom units. However, mound growth that has been correlated with the level-bottom Nunn Member in reality took place during the late stage of deposition of the Alamogordo Member, and nondeposition or erosion occurred on the mounds during deposition of the Nunn Member. Mounds in the shallower (northern) part of the ramp grew primarily on the margins of a broad, low, intra-ramp topographic high, which had been defined previously from facies and isopach trends in underlying strata. Both the margins and the irregular topography of the high are reflected in the distribution, growth geometries, and facies patterns of the mounds, and by the facies and thickness trends of the strata enclosing the mounds. The siting of individual mounds on the shallower part of the ramp was controlled by local topography on and along the margins of the intra-ramp high. Mound growth along the margin began at or just behind local highs, retrograded onto the intra-ramp high, and then prograded onto the basinward side of the initial mound. The lesser height and more pronounced backstepping of mounds on the shallower part of the ramp, in contrast to mounds that grew more vertically and with less back-stepping down ramp suggest that growth and overall morphology were also controlled by accommodation.     

Soil translocation by pocket gophers in a Mima moundfield

Summary We measured soil translocation due to the tunneling of valley pocket gophers (Thomomys bottae) in a Mima moundfield at Miramar Mounds National Landmark, San Diego, California, from December, 1984 through December, 1985. We placed 1-l soil plugs containing 20 11-g iron pellets into pocket gopher tunnels at locations between mound tops and points about one mound radius beyond mound edges. After about 4–10 d, sites to which the marker-containing soil had been translocated were located with a metal detector and the horizontal and vertical displacements measured. Between 1 October and 15 May (the cooler, wetter portion of the year), pocket gophers removed an average of 63% of the experimental plugs and moved an average of 38% of the markers that we recovered. From 15 May through 1 October (the hotter, drier portion of the year), only 32% of plugs were cleared and 12% of the recovered markers were moved. On average, markers that were moved were displaced 41 cm moundward and 4.9 cm upward in elevation. The intensity of moundward translocation increased with distance from the mound center. At a distance of 0.5–1.0 mound radius beyond the edge of the mound, the moundward translocation tendency averaged 71 cm. The intensity of moundward translocation was also inversely related to maximum mound height. These observations provide strong support for the fossorial rodent hypothesis of Mima mound origin, and constitute a first step in development of a mathematical model of mound formation.     

Mud mounds: A polygenetic spectrum of fine-grained carbonate buildups

Summary This research report contains nine case studies (part II to X) dealing with Palaeozoic and Mesozoic mud mounds, microbial reefs, and modern zones of active micrite production, and two parts (I and XI) summarizing the major questions and results. The formation of different types ofin situ formed micrites (automicrites) in close association with siliceous sponges is documented in Devonian, Carboniferous, Triassic, Jurassic and Cretaceous mounds and suggests a common origin with a modern facies found within reef caves. Processes involved in the formation of autochthonous micrites comprise: (i) calcifying mucus enriched in Asp and Glu, this type presumably is linked to the formation of stromatolites, thrombolites and massive fabrics; (ii) protein-rich substances within confined spaces (e.g. microcavities) result in peloidal pockets, peloidal coatings and peloidal stromatolites, and (iii) decay of sponge soft tissues, presumably enriched with symbiotic bacteria, lead to the micropeloidal preservation of parts of former sponge bodies. As a consequence, there is strong evidence that the primary production of micrite in place represents the initial cause for buildup development. The mode of precipitation corresponds to biologically-induced, matrix-mediated mineralization which results in high-Mg-calcites, isotopically balanced with inorganic cements or equilibrium skeletal carbonates, respectively. If distinct automicritic fabrics are absent, the source or origin of micrite remains questionable. However, the co-occurring identifiable components are inadequate, by quantity and physiology, to explain the enhanced accumulation of fine-grained calcium carbonate. The stromatolite reefs from the Permian Zechstein Basin are regarded as reminiscent of ancestral (Precambrian) reef facies, considered the precursor of automicrite/sponge buildups. Automicrite/sponge buildups represent the basic Phanerozoic reef type. Analogous facies are still present within modern cryptic reef habitats, where the biocalcifying carbonate factory is restricted in space.     

一种地下啮齿动物土丘数量和分布调查的新方法

地下啮齿动物挖掘形成的土丘数量变化以及分布是其生态学研究的重要内容之一。传统的土丘数量和分布调查方法是计数法和填图法,存在工作量较大和误差较高等缺点。实时动态控制系统技术(RTK)是一种高精度的GPS测量方法,能够在野外实时得到厘米级的定位精度。本文以甘肃省天祝县抓喜秀龙乡高原鼢鼠(Eospalax baileyi)分布区为调查区域,利用RTK技术实现了高原鼢鼠土丘数量和分布情况调查,并结合Arc GIS软件实现了土丘数量及其相对种群密度变化的统计分析。RTK技术在研究其土丘空间分布特征、相对种群密度(以土丘数量代表)以及草地危害评估等方面具有很好的效果。此方法不仅可用于地下啮齿动物土丘数量和分布调查,还可用于地上啮齿动物洞口数量和分布的调查。