Dolomit v speleotemih iz Snežne jame V Snežni jami so bili odkriti obsežni speleotemi iz dolomita, aragonita in magnezita v obliki globularnih skorjastih tvorb, ki prekrivjao matično kamnino. Ogrodje skorij je zgrajeno iz razvejanih kristalnih skupkov aragonita, cementiranih z dolomitom, ki prekriva in deloma nadomešča aragonit. Dolomit se pojavlja v dveh teksturnih različkih: v obliki grobo zaobljenih do sferoidalnih kristalov, ki imajo pogosto fibrozno-radialno in/ali sferično notranjo zgradbo, ter v obliki mikrokristalnih agregatov. Magnezij, ki izvira iz raztopljene matične dolomitne kamnine, ima bistven vpliv na izločanje aragonita, dolomita in hidromagnezita. Izločanje dolomita je lahko spodbujeno s povišanim razmerjem Mg/Ca v raztopini, ki sledi izločanju kalcita ali aragonita, ali s povečanim izhlapevanjem zaradi cirkulacije zraka v jami v času, ko je bil jamski sistem s površjem povezan z več vertikalnimi prehodi in skozi nekdanji glavni vhod. Podobni pogoji verjetno obstajajo v mnogih jamah, vendar pa se dolomit v jamskih pogojih le redko izloča, zato v članku razpravljamo o mogočih drugačnih mehanizmih nasta janja dolomita-od izločanja pod mikrobnim vplivom do transformacije predhodnih mineralnih faz, kakršne bi lahko bile amorfne oblike Ca-Mg karbonatov ali hidromagnezit.
This work reviews the anthropogenic exploitation of small mammals during a crucial time span for the reconstruction of human behavior at the dawn of the Middle Upper Palaeolithic boundary in the Northern Mediterranean region. Data are sourced from faunal assemblages recovered in the final Mousterian levels of Grotta di Fumane (A5A6 complex) and the Late Mousterian levels of Riparo Tagliente (levels 35 and 36) and Grotta di San Bernardino (units II and IV), in the North of Italy. As a whole, these records mostly comprise ungulates, rather than bird and carnivore bones, and derive from primary accumulation processes more than from postdepositional activities or direct carnivore actions. Broadly, the taphonomic analyses reveal the presence of human modifications referable to different butchering activities on almost all of the ungulates. Small mammal bones are present throughout the late MP sequences in variable quantities, with canids and rodents represented in each of the assemblages. This work highlights new qualitative taphonomic records produced by humans within a large area that reveal Neandertals' exploitation of small mammals as game. At Grotta di Fumane, foxes have been butchered in order to exploit fur and meat. Similarly, at Grotta Maggiore di San Bernardino and Riparo Tagliente some large rodents bear cutmarks related to the same purposes. Krapina Cave is the only other Mousterian site containing evidence of small game exploitation (beaver and marmot) that is in close geographical proximity to the caves analyzed here.
Carbonate dissolution and precipitation are important geological processes whose rates often require quantification. In natural settings, these processes may be taking place at a slow rate, and thus, it may not be easily visible which of these processes is occurring. Alternatively, if the effects of precipitation/dissolution are visible, it may not be clear if they are still underway or an artefact of past conditions. Moreover, these two opposing processes may flip states depending on the environmental conditions, such as, on a seasonal basis. Here, we present the technical details and preliminary results of a method using carbonate tablets and Scanning Electron Microscopy (SEM) to evaluate which process (carbonate dissolution or precipitation) is occurring, using as an example, a cave environment. Our method involves making tablets by encasing blocks of carbonate rock into resin and polishing these to form a completely flat and smooth “zero surface”. These tablets are observed under SEM in exactly the same points both before and after exposure to the field environment, using a system of marking lines at specific locations on the resin. Our results show significant differences in the before and after images of the tablet surface after just six weeks in the cave. Furthermore, the use of the insoluble resin zero surface permits a comparison of the starting height with the new dissolved/precipitated surface that can be used to quantitatively estimate the rate of dissolution/precipitation happening at a field location in a relatively short time-frame (weeks/months). This method could be used in numerous natural and industrial settings to identify these processes that can be caused purely geochemically, but also through microbialmediation and physical weathering.
<p>Subglacial carbonate deposits have been exposed on the lee sides of small protuberances on a bare polished and striated limestone bedrock surface in the immediate vicinity of the retreating Triglav Glacier in southeastern Alps. They are fluted and furrowed crust-like deposits generally around 5 mm thick and characterized by brownish, greyish or yellowish colour. The deposits are generally around 0.5 cm in thickness and internally laminated. They offer a unique opportunity to gain additional knowledge of the past glacier&#8217;s behaviour and consequently the characteristics of the past climate which is essential to understand and predict future changes. Currently, the known extent and behaviour of the Triglav Glacier spans from the present to the Little Ice Age, the cool-climate anomaly between the Late Middle Ages and the mid-19th century, and is based on geomorphological remnants, historical records, and systematic monitoring. However, the preliminary uranium-thorium (U-Th) ages of the subglacial carbonates yielded considerably old ages: 23.62 ka &#177; 0.78 ka, 18.45 ka &#177; 0.70 ka and 12.72 ka &#177; 0.28 ka; the results indicate that these subglacial carbonate dates fall within the Last Glacial Maximum (LGM) and the Younger Dryas (YD).</p><p>The Triglav Glacier has generally been viewed as relict of the LIA, with discontinuous presence due to the Holocene Climatic Optimum, a period of high insolation and generally warmer climate between 11,000 and 5,000 years BP. Present chemical denudation rates of carbonate rocks in Alpine and temperate climate vary from ca. 0.009 to 0.140 mm/year. Taking the low and high extreme values for, e.g., 6 ka during the Holocene Climatic Optimum, the denudation in the Triglav area would be between 54 and 840 mm, so the exposed 5 mm thick subglacial carbonate would have already been denuded if exposed in the past. In addition, carbonate surfaces in periglacial areas are additionally exposed to frost weathering, promoting disintegration of depositional features. And lastly, glaciers cause pronounced erosion and in case of just a short-term retreat beyond the subglacial carbonates, the re-advance of the glacier would likely abrade the deposits. Therefore, had the subglacial carbonate deposits been exposed in the past, they should have been eroded by chemical denudation, frost weathering, or erosion at the onset of individual Holocene glacial expansion episodes, such as the LIA. May the presence of subglacial carbonates dated to the LGM and the YD at the Triglav Glacier suggest the continuous existence of the glacier throughout all but the latest Holocene?</p>
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