Phosphatic precipitates associated with actinomycetes in speleothems from Grand Cayman, British West Indies

Calcitic speleothems from a cave located on the north central coast of Grand Cayman commonly include corrosion surfaces that developed when calcite precipitation ceased and corrosion mediated by condensates became the operative process. Dissolution features associated with these surfaces, including etched crystal surfaces, microcavities, and solution-widened boundaries between crystals, are commonly occupied by microbes and microbial mats that have been replaced by calcium phosphate and/or coated with calcium phosphate. No mineralized microbes were found in the calcite crystals that form the speleothems. The morphology of the mineralized hyphae (eight morphotypes) and spores (nine morphotypes) are indicative of actinomycetes, a group of microbes that are ideally adapted to life in oligotrophic cave environs. Superb preservation of the delicate hyphae, aerial hyphae, and delicate ornamentation on the hyphae and spores indicate that the microbes underwent rapid mineralized while close to their original life positions. Although these actinomycetes were extremely susceptible to replacement by calcium phosphate, there is no evidence that they directly or indirectly controlled precipitation. Nevertheless, the association between the P-rich precipitates and microbes shows that the use of phosphorus as a proxy for seasonal climate changes in paleoclimate analyses must be treated with caution.     

Recycled insular phosphates and coated grains: Case study from Little Cayman,British West Indies

Phosphatic limestones on the west end of Little Cayman, at an elevation of 3 to 4 m above sea level and ca 320 to 550 m inland of the coast, lie on top of a phytokarst surface that defines the upper boundary of the Pedro Castle Formation (Pliocene). These phosphatic limestones are formed of phosphatic lithoclasts, detrital phosphate grains, coated grains (glaebules), composite coated grains, biofragments and phosphate rafts that are held in a matrix that is formed of micrite, calcite cement, and non-crystalline masses formed of P, Al, Si and Fe. The phosphate in these limestones is primarily hydroxylapatite, whereas the overlying soils, found in some areas, are formed of hydroxylapatite, crandallite and minor amounts of boehemite, kaolinite and quartz. Textures in the lithoclasts and detrital phosphate grains indicate that they were derived from older insular phosphates that that were largely removed by mining in 1890 to 1895. The coated grains (glaebules) typically have nuclei formed of a detrital phosphate grains that are encased by non-crystalline cortical laminae that are composed primarily of Al with their variable red colour reflecting the variable Fe content. The phosphatic limestones developed in a low-lying coastal area where the guano produced by a large seabird colony that was close to or mixed with terra rossa and marine carbonates that were washed onshore during storms/hurricanes. The Al, Fe, Si and rare earth elements found in the phosphatic limestones came from the terra rossa. Critically, this study documents the complex depositional regimes and diagenetic processes that can exist at the interface of marine carbonates, coastal phosphates and terrestrial soils as sea-level fluctuations control phases of sediment accumulation that were periodically interrupted by periods of non-deposition.     

Highstands during Marine Isotope Stage 5: evidence from the Ironshore Formation of Grand Cayman,British West Indies

The Ironshore Formation on Grand Cayman is formed of six unconformity-bounded packages (units A–F). Units A, B, C, and D, known from the subsurface in the northeastern part of Grand Cayman, formed during Marine Isotope Stages (MIS) 11(?), 9, 7, and 5e, respectively. Unconformities at the tops of units A, B, and C are highlighted by terra rossa and/or calcrete layers. Strata in core obtained from wells drilled in George Town Harbour and exposed on the west part of Grand Cayman belong to unit D, and the newly defined units E and F. Corals from unit E yielded Th/U ages of ∼104 ka whereas conch shells from unit F gave ages of ∼84 ka. Unit E equates to MIS 5c whereas unit F developed during MIS 5a.Th/U dating of corals and conchs from the Ironshore Formation on the western part of Grand Cayman shows that unit D formed during the MIS 5e highstand whereas units E and F developed in association with highstands at 95–110 ka (MIS 5c) and 73–87 ka (MIS 5a). Unit E, ∼5 m thick in the offshore cores, is poorly represented in onshore exposures. Unit F, which unconformably overlies unit D at most localities, is formed largely of fossil-poor, cross-bedded ooid grainstones. The unconformity at the top of unit D, a marine erosional surface with up to 2.5 m relief, is not characterized by terra rossa or calcrete in the offshore cores or onshore exposures. Unit D formed with a highstand of +6 m asl, whereas units E and F developed when sea level was +2 to +5 asl and +3 to +6 m asl, respectively. Thus, the highstands associated with MIS 5e, 5c, and 5a were at similar elevations.     

Pleistocene trace fossils in the Ironshore Formation, Little Cayman, British West Indies

Oosparite grainstones of the Pleistocene Ironshore Formation, Little Cayman, British West Indies, contain the trace fossils Conichnus conicus, Ophiomorpha nodosa, and Planolites beverleyensis. The dominance of vertically-oriented trace fossils, complexity of cross-stratifications, coarseness of the sediment channel fill, and presence of several rudstone layers suggest deposition close to the seaward portion of lagoonal channels where higher energy conditions prevailed.     

Neogene echinoids from the Cayman Islands,West Indies: regional implications

The first fossil echinoids are recorded from the Cayman Islands. A regular echinoid, Arbacia? sp., the spatangoids Brissus sp. cf. B. oblongus Wright and Schizaster sp. cf. S. americanus (Clark), and the clypeasteroid Clypeaster sp. are from the Middle Miocene Cayman Formation. Test fragments of the mellitid clypeasteroid, Leodia sexiesperforata (Leske), are from the Late Pleistocene Ironshore Formation. Miocene echinoids are preserved as (mainly internal) moulds; hence, all species are left in open nomenclature because of uncertainties regarding test architecture. All Miocene taxa are recorded from single specimens apart from the 27 assigned to Brissus. Schizaster sp. cf. S. americanus (Clark) is compared to a species from the Oligocene of the south‐east USA. Brissus sp. cf. B. oblongus is close in gross morphology to a taxon from the Miocene of Malta. Leodia sexiesperforata is identified from fragments with confidence, being the only extant Antillean sand dollar with elongate ambulacral petals that is limited to carbonate substrates. The Miocene echinoids of Grand Cayman, although of limited diversity, are mainly comprised of genera common in comparable mid‐Cenozoic carbonate environments. Copyright © 2015 John Wiley & Sons, Ltd.     

Estimates of present-day erosion based on sediment transport in rivers: a case study in Taiwan

We discuss the present-day sediment transport by rivers, and hence the erosion rate in upstream basins, based on the example of Taiwan Rivers where large datasets are available. After data correction, the values of the suspended sediment load in the lower Kaoping River are nearly three times smaller than those from the literature. On the other hand, we add the bed load evaluated from numerical modelling, despite limitations from data and models. Whereas the contribution of the chemical denudation rate in Taiwan is minor, the bed load is significant and must be evaluated. We point out that biases in data collection may favour high values of suspended load data, and that large series of datasets are needed to reduce uncertainties and smooth the time variability effect. To cite this article: F.-C. Li et al., C. R. Geoscience 337 (2005).     

Composite methodology for interpreting sediment transport pathways from spatial trends in grain size: A case study of the Lithuanian coast

To achieve a more robust interpretation of sediment conditions and transport based on grain size, this study combines the perspectives of two different interpretation techniques that have been developed separately and applied in the literature: (i) ‘grain size trend analysis’ interprets changes between interrelated sampling sites assuming that sediment in the direction of transport should become either coarser, better sorted and more positively skewed, or finer, better sorted and more negatively skewed; and (ii) the ‘population anomalies’ method, which estimates the balance between erosion and accumulation processes at each sampling site based on individual site deviations compared with average values for grain‐size parameters in the area of interest. The simultaneous use of both approaches enables sedimentological conditions and transport alternatives to be distinguished. This improvement is necessary because site‐specific changes and general textural trends provide information that complements the strengths and weaknesses of each perspective. The methods are implemented here using two‐dimensional Geographic Information System tools and illustrated for the Lithuanian coast. Grain‐size characteristics of 712 surface samples of sandy sediments are used to interpret sediment transport pathways and predominant sedimentological conditions in the Lithuanian coastal zone. In general, coast‐parallel sediment transport dominates the entire investigation area, although wave‐induced movement perpendicular to the coastline is inferred in the shallow nearshore zone. The deepest areas offshore are characterized by sea floor erosion in the north, whereas an accumulation zone occurs in the relatively deep central part of the study area.     

Engineering-geological mapping of tropical soils for land-use planning and geotechnical purposes: A case study from Jamaica, West Indies

An area of a Tertiary and Cretaceous deposits, 100–310 m above sea level and on predominant 20–45°, highly dissected, concave slopes was investigated to assess its geotechnical characteristics and land use planning implications. Lithologies include turbidites, fluvial conglomerates, breccias, sandstones, mudrocks, carbonates, granodiorite, acid dykes, chloritized and epidotized volcanics, andesite and Holocene fluvial deposits. Bedrock is highly fractured and sheared, hydrothermally altered and highly weathered. Soils are quite variable, with a strong geological control on soil properties. Soils are generally sandy to gravely, with local silts and clays in mudrocks, within Holocene alluvium or in hydrothermally altered and sheared granodiorites. The soils are composed of 0.14–80.00% gravel; 5.36–62.50% sand, 2.33–50.55% silt, 0.17–51.50% clay, and total fine content between 2.50 and 94.50%, with natural moisture between 4 and 44% during the dry season, plastic limit between 6 and 35%, liquid limit between 19 and 83% and plasticity index between 1 and 59%. Sandy soils have residual friction angles between 19 and 39°, PI values less than 35% with cohesion between 1.00 and 5.27 KN/m² for cohesive samples. ASTM classification of soils include soil groups GC, GM, GW, GP, SP, SM, SC, SM, SC, ML, CL and CH.

Based on the characteristics of the terrain, the geotechnical and land use planning problems include high landslide frequency and susceptibility, soil erosion, fluvial and reservoir sedimentation, high debris flow hazard, cut slope failures, potentially expansive clays and silts, seepage erosion and soil piping, differential settlement in interlayered competent and incompetent lithologies, high solution erosion and potential subsidence over limestones, waste water disposal problems and groundwater pollution and seismic induced settlement and ground failures. These phenomena suggest that systematic site investigations should be conducted prior to the utilization of these areas for construction and development in order to minimize the deleterious effects resulting from ground failure.     

Historical trends in Chesapeake Bay dissolved oxygen based on benthic foraminifera from sediment cores

Environmentally sensitive benthic foraminifera (protists) from Chesapeake Bay were used as bioindicators to estimate the timing and degree of changes in dissolved oxygen (DO) over the past five centuries. Living foraminifers from 19 surface samples and fossil assemblages from 11 sediment cores dated by²¹⁰Pb,¹³⁷Cs,¹⁴C, and pollen stratigraphy were analyzed from the tidal portions of the Patuxent, Potomac, and Choptank Rivers and the main channel of the Chesapeake Bay.Ammonia parkinsoniana, a facultative anaerobe tolerant of periodic anoxic conditions, comprises an average of 74% of modern Chesapeake foraminiferal assemblages (DO-0.47 and 1.72 ml l⁻¹) compared to 0% to 15% of assemblages collected in the 1960s. Paleoecological analyses show thatA. parkinsoniana was absent prior to the late 17th century, increased to 10–25% relative frequency between approximately 1670–1720 and 1810–1900, and became the dominant (60–90%) benthic formaniferal species in channel environments beginning in the early 1970s. Since the 1970s, deformed tests ofA. parkinsoniana occur in all cores (10–20% ofAmmonia), suggesting unprecedented stressful benthic conditions. These cores indicate that prior to the late 17th century, there was limited oxygen depletion. During the past 200 years, decadal scale variability in oxygen depletion has occurred, as dysoxic (DO=0.1–1.0 ml l⁻¹), perhaps short-term anoxic (DO<0.1 ml l⁻¹) conditions developed. The most extensive (spatially and temporally) anoxic conditions were reached during the 1970s. Over decadal timescales, DO variability seems to be linked closely to climatological factors influencing river discharge; the unprecedented anoxia since the early 1970s is attributed mainly to high freshwater flow and to an increase in nutrient concentrations from the watershed.     

Interpreting flash flood palaeoflow parameters from antidunes and gravel lenses: An example from Montserrat,West Indies

The wavelength of stationary water‐surface waves and their associated antidune bedforms are related to the mean velocity and depth of formative flow. In past published sand‐bed flume experiments, it was found that lens structures were preserved during antidune growth and change, and the dimension of the lenses was empirically related to antidune wavelength, and thus could be used to estimate flow velocity and depth. This study is the first to compare observations of formative flow conditions and resulting sedimentary structures in a natural setting, testing the previously published relationship at a field‐scale. Trains of stationary and upstream migrating water‐surface waves were prevalent during the flash flood in October 2012 in the Belham Valley, Montserrat, West Indies. Wave positions and wavelengths were assessed at 900 sec intervals through the daylight hours of the event within a monitored reach. The wave data indicate flow depths up to 1·3 m and velocity up to 3·6 m sec^?1. Sedimentary structures formed by antidune growth and change were preserved in the event deposit. These structures include lenses of clast‐supported gravel and massive sand, with varying internal architecture. The lenses and associated low‐angle strata are comparable to sand‐bed structures formed from stationary and upstream migrating waves in flume experiments, confirming the diagnostic value of these structures. Using mean lens length in the event deposit underestimated peak flow conditions during the flood and implied that the lenses were preserved during waning flow.     

Soil and stream sediment based geochemical mapping: A case study in Goa

Geochemical mapping has been carried out in Goa using soil/laterite and stream sediment as media. The geochemical maps for U, Th, Nb and Ta show a conspicuous pattern in the NW part of Goa. The anomaly axis shows a NE-SW trend which is across the formational trend. The nickel and copper distribution around Usgaon area, east of Ponda, have indicated anomalous signature in the northern continuation of the Usgaon ultramafic complex.     

Void-filling deposits in karst terrains of isolated oceanic islands: a case study from Tertiary carbonates of the Cayman Islands

Caves, fossil mouldic cavities, sinkholes and solution-widened joints are common in the Cayman and Pedro Castle members of the Bluff Formation (Oligocene-Miocene) on Grand Cayman and Cayman Brac because they have been subjected to repeated periods of karst development over the last 30 million years. Many voids contain a diverse array of sediments and/or precipitates derived from marine or terrestrial environs, mineral aerosols, and groundwater. Exogenic sediment was transported to the cavities by oceanic storm waves, transgressive seas, runoff following tropical rain storms and/or in groundwater. At least three periods of deposition were responsible for the occlusion of voids in the Cayman and Pedro Castle members. Voids in the Cayman Member were initially filled or partly filled during the Late Oligocene and Early Miocene. This was terminated with the deposition of the Pedro Castle Member in the Middle Miocene. Subsequent exposure led to further karst development and void-filling sedimentation in both the Cayman and Pedro Castle members. Speleothems are notably absent. The void-filling deposits formed during these two periods, which were predominantly marine in origin, were pervasively dolomitized along with the host rock 2–5 million years ago. The third period of void-filling deposition, after dolomitization of the Bluff Formation, produced limestone, various types of breccia, terra rossa, speleothemic calcite and terrestrial oncoids. Most of these deposits formed since the Sangamon highstand 125 000 years ago. Voids in the present day karst are commonly filled or partly filled with unconsolidated sediments. Study of the Bluff Formation of Grand Cayman and Cayman Brac shows that karst terrains on isolated oceanic islands are characterized by complex successions of void-filling deposits that include speleothems and a variety of sediment types. The heterogenetic nature of these void-filling deposits is related to changes in sea level and climatic conditions through time.     

Ecological environment response of benthic foraminifera to heavy metals and human engineering: A case study from Jiaozhou Bay,China

The estuary and coastal zone are the key areas for socio-economic development,and they are also the important channels for pollutants transported to the sea.The construction of the Jiaozhou Bay Bridge changed the hydrodynamic condition of the bay,which made the self-purification capacity of the bay weakened and the pollution in the estuary and adjacent coastal zone become more serious.In this study,55 surface sediment samples were collected from the three seriously polluted estuaries and the adjacent coastal zone of Jiaozhou Bay to comprehensively study how the benthic foraminifera response to heavy metal pollution and human engineering,and to assess the ecological risks of the bay.A total of 80 species,belonging to 42 genera,were identified in this study.The results showed that Cu,Pb,Cr,Hg,Zn,and As had low to median ecological risks in the study area which would definitely affect the ecological system.The construction of the Jiaozhou Bay Bridge has resulted in pollutants accumulated at the river mouth of Loushan River,which has adverse effects on the survival and growth of benthic foraminifera.The lowest population density and diversity as well as the highest FAI(Foraminiferal Abnormality Index)and FMI(Foraminiferal Monitoring Index)occurred at Loushan River Estuary which indicated that the ecological environment of the northeastern part of Jiaozhou Bay(Loushan River Estuary)had been seriously damaged.Licun River and Haipo River estuaries and the adjacent coastal zone were slightly polluted and had low ecological risk.As a consequence,it suggested that the supervision of industrial and domestic waste discharge and the protection of the ecological environment in northeast Jiaozhou Bay should be paid more attention.     

基于沉积物物质来源的地下水化学特征分析:以北京市平原区为例

沉积物物质来源不同,其沉积环境和沉积特征不同,其地球化学特征、水动力体系和地下水循环响应不同。文中以北京市平原区为例,通过沉积物物质来源分析,研究浅层地下水化学分布特征。首先根据地下水系统分区进行取样和实验,采用矿物组合、风化强度及相关分析等多种方法综合分析北京市平原区沉积物的物质来源及其组合特征,多种方法分析结论一致,即北京平原区的主要物质来源:一是流经燕山山地花岗岩变质岩区的潮白河系统,一是流经西山山地石灰岩区的永定河系统;而两系统中、下部是多期物源多层交叠、纵横交错沉积形成的。其次在物源分析基础上通过水质分析研究两系统剖面上地下水水化学特征,即两系统剖面地下水化学类型主要为HCO3--Ca.Mg型水;但永定河系统的溶解性总固体、阴阳离子浓度均大于潮白河系统,这与两剖面所在系统物源分析的结果相吻合,即分析结果表明物源的沉积环境及沉积组合特征决定了系统的地下水化学特征。     

Heavy metals in the benthic foraminifera from the coastal lagoons,Red Sea,Egypt: indicators of anthropogenic impact on environment (case study)

Concentrations of Fe, Mn, Zn, Cu, Pb, Ni, and Cd were measured in several species and genera of Recent benthic foraminifera from three coastal lagoons, namely Abu-Shaar, Umm al-Huwaytat, and Marsa Shuni lagoons located along the Egyptian Red Sea coast. Spatially significant differences in the metal concentrations of benthic foraminifera were recorded among different sites. However, some foraminiferal species display deformation in their coiling, general shape of chambers and the apertures. Abu-Shaar and Umm al-Huwaytat lagoons are virtually influenced by anthropogenic activities while Marsa Shuni lagoon is affected by natural inputs. Benthic foraminifer shows high concentrations of Fe and Mn, especially in Umm al-Huwaytat lagoon. Foraminiferal black tests support this result and reflect selectivity for iron absorption. Among the metals analyzed, Cd, Pb, and Cu showed significant high concentrations in benthic foraminifera at the study areas. The anthropogenic activities and natural inputs are responsible for the abnormalities in benthic foraminifera. Therefore, benthic foraminifera can be used as a good indicator of the environmental changes.     

Structural geology controls on groundwater flow: Lembang Fault case study, West Java, Indonesia

Field evidence has shown that Lembang Fault (West Java, Indonesia) can act as a groundwater flow barrier. There are outcrops along the footwall comprising consolidated brecciated rock with very low permeability, springs and hot springs occurring along down-thrown hanging-wall rock adjacent to the fault, and a high permeability layer of old and young Tangkuban Parahu eruptive materials (hanging wall) juxtaposed against the low permeability of the older volcanic layer of Bukit Tunggul unit (footwall). Two different environmental tracers were utilized in the study: electrical conductivity measurement and stable isotope analysis. Hydraulic head was measured at some wells along the fault and water electrical conductivity measurements were carried out in a small catchment, the upper part of Cikapundung River basin, which is located just north of Bandung City. Water samples for stable isotope composition analysis were taken from 19 observation wells distributed randomly inside the basin. All analysis data lead to the recognition that Lembang Fault blocks the groundwater flow. No indication was found for water being recharged at higher elevation in the northern part of Bandung Basin, which means the recharged water in Mount Tangkuban Parahu area does not reach Bandung Plain.     

早期碳酸盐胶结作用对砂岩孔隙演化的影响——以塔里木盆地满加尔凹陷志留系砂岩为例

塔里木盆地满加尔凹陷志留系砂岩为无障壁的潮坪、滨岸及辫状河三角洲沉积的岩屑砂岩和岩屑质石英砂岩,对满北和满东、满南地区志留系砂岩成岩作用序次尤其是碳酸盐胶结的时间、方式和特征、物性的对比研究认为:砂岩中碳酸盐胶结的时间早晚对砂岩孔隙演化具有重要影响,满北地区志留系砂岩发育有大量早期泥晶碳酸盐胶结,显微镜下研究表明这种胶结作用发生在岩石受到充分压实之前,呈基底式胶结,岩石颗粒呈点接触或漂浮状分布于早期碳酸盐胶结物之中,这种胶结作用抑制了岩石后期的压实作用。尽管目前其埋藏达5 000～6 500 m,但其经历的压实作用并不强烈,粒间发育大量早期的碳酸盐胶结物,后来这些胶结物被溶蚀,形成了大量次生孔隙。而在满东和满南地区的志留系砂岩,碳酸盐胶结发生在岩石经过充分压实之后,晚期的碳酸盐胶结物仅分布于岩石经充分压实后的粒间孔隙中,含量较前者低,后期可供溶蚀的碳酸盐比前者少,因而溶蚀形成的次生孔隙有限。因此,尽管满东满南地区志留系埋藏比满北浅（3 700～5 000 m）,碳酸盐胶结物含量也低,也发育晚期碳酸盐胶结物的溶蚀,但岩石的压实作用比满北强,物性比满北低差。这主要与碳酸盐胶结的早晚有关,早期碳酸盐胶结对孔隙演化具有明显控制作用,有利于岩石孔隙的保存,为后来的溶蚀形成次生孔隙提供了条件。     

Petrographic and geochemical source-modeling of volcanic lithics from archaeological contexts: A case study from British Camp,San Juan Island,Washington

Classification and sourcing of vulcanic lithics is simplified through petrographic and geochemical analyses. In examining volcanic lithics, major element geochemistry is required for classification, trace element geochemistry is necessary for discrimination of materials from different sources, and rare earth elements are used in source-modeling. Materials such as those found in the debitage at the British Camp shell midden, San Juan Island (45SJ24), are ubiquitous in the Gulf of Georgia region of the Pacific Northwest. Previous archaeological reports over the past 100 years have classified this volcanic debitage as basalt and predicted a local source. Petrographic analyses of thin sections and geochemical analyses using ICP emission spectrometry have shown that these artifacts are formed of dacite rather than basalt. The analysis also shows that the major lithic material used for stone chipping during the entire temporal sequence at the British Camp site is invariably from the same distant source in the High Cascades, possibly as far as 200 km from the site. © 1996 John Wiley & Sons, Inc.