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1

Sakuna-Schwartz, D., P. Feldens, K. Schwarzer, S. Khokiattiwong, and K. Stattegger. "Internal structure of event layers preserved on the Andaman Sea continental shelf, Thailand: tsunami vs. storm and flash-flood deposits." Natural Hazards and Earth System Sciences 15, no. 6 (June 12, 2015): 1181–99. http://dx.doi.org/10.5194/nhess-15-1181-2015.

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Abstract. Tsunami, storm and flash-flood event layers, which have been deposited over the last century on the shelf offshore Khao Lak (Thailand, Andaman Sea), are identified in sediment cores based on sedimentary structures, grain size compositions, Ti / Ca ratios and 210Pb activity. Individual offshore tsunami deposits are 12 to 30 cm in thickness and originate from the 2004 Indian Ocean Tsunami. They are characterized by (1) the appearance of sand layers enriched in shells and shell debris and (2) the appearance of mud and sand clasts. Storm deposits found in core depths between 5 and 82 cm could be attributed to recent storm events by using 210Pb profiles in conjunction with historical data of typhoons and tropical storms. Massive sand layers enriched in shells and shell debris characterize storm deposits. The last classified type of event layer represents reworked flash-flood deposits, which are characterized by a fining-upward sequence of muddy sediment. The most distinct difference between storm and tsunami deposits is the lack of mud and sand clasts, mud content and terrigenous material within storm deposits. Terrigenous material transported offshore during the tsunami backwash is therefore an important indicator to distinguish between storm and tsunami deposits in offshore environments.
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2

Sakuna-Schwartz, D., P. Feldens, K. Schwarzer, S. Khokiattiwong, and K. Stattegger. "Internal structure of event layers preserved on the Andaman Sea continental shelf, Thailand: tsunami vs. storm and flash flood deposits." Natural Hazards and Earth System Sciences Discussions 2, no. 12 (December 1, 2014): 7225–67. http://dx.doi.org/10.5194/nhessd-2-7225-2014.

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Abstract. Tsunami, storm and flash event layers, which have been deposited over the last century on the shelf offshore from Khao Lak (Thailand, Andaman Sea), are identified in sediment cores based on sedimentary structures, grain size compositions, Ti / Ca ratios and 210Pb activity. Individual offshore tsunami deposits are 12 to 30 cm in thickness and originate from the 2004 Indian Ocean tsunami. They are characterized by (1) the appearance of sand layers enriched in shells and shell debris, (2) cross lamination and (3) the appearance of rip-up clasts. Storm deposits found in core depths between 5 and 82 cm could be attributed to individual storm events by using 210Pb dating in conjunction with historical data of typhoons and tropical storms and could thus be securely differentiated from tsunami deposits. Massive sand layers enriched in shells and shell debris characterize the storm deposits. The last classified type of event layer represents flash floods, which is characterized by a fining-upward sequence of muddy sediment. The most distinct difference between the storm and tsunami deposits is the lack of rip-up clasts, mud, and terrigenous material within the storm deposits. Terrigenous material transported offshore during the tsunami backwash is therefore an important indicator to distinguish between offshore storm and tsunami deposits.
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3

Carey, Stephen P., John E. Sherwood, Megan Kay, Ian J. McNiven, and James M. Bowler. "The Moyjil site, south-west Victoria, Australia: stratigraphic and geomorphic context." Proceedings of the Royal Society of Victoria 130, no. 2 (2018): 14. http://dx.doi.org/10.1071/rs18004.

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Shelly deposits at Moyjil (Point Ritchie, Warrnambool), Victoria, together with ages determined from a variety of techniques, have long excited interest in the possibility of a preserved early human influence in far south-eastern Australia. This paper presents a detailed analysis of the stratigraphy of the host Bridgewater Formation (Pleistocene) at Moyjil and provides the context to the shelly deposits, evidence of fire and geochronological sampling. We have identified five superposed calcarenite–palaeosol units in the Bridgewater Formation, together with two prominent erosional surfaces that may have hosted intensive human activity. Part of the sequence is overlain by the Tower Hill Tuff, previously dated as 35 ka. Coastal marine erosion during the Last Interglacial highstand created a horizontal surface on which deposits of stones and shells subsequently accumulated. Parts of the erosional surface and some of the stones are blackened, perhaps by fire. The main shell deposit was formed by probable mass flow, and additional shelly remains are dispersed in the calcareous sand that buried the surface.
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4

Davies, David J., and Molly F. Miller. "Paleocommunity information retrieval vs. shell accumulation mode in Paleozoic carbonates: examples from the Lebanon Limestone (Middle Ordovician), Tennessee, U.S.A." Paleontological Society Special Publications 6 (1992): 81. http://dx.doi.org/10.1017/s2475262200006419.

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Compared to their terrigenous counterparts, carbonate shell accumulations have until recently been relatively little studied to determine either descriptive or genetic classifications of shell bed types, the preservation potential of each type, or their relative ability to preserve community-level information. A partial classification of Paleozoic carbonate shell-rich soft sediment accumulations is proposed using sedimentation patterns in the Lebanon limestone of the Stones River Group. Paleoecological information preserved therein is then contrasted by shell bed type. The Lebanon represents typical Ordovician shallow to moderate subtidal carbonate shelf deposits in outcrops flanking the Nashville Dome and peritidal deposits in the Sequatchie Anticline of Eastern Tennessee; shell beds alternate with shell poor sediments (micrites, wackestones and diagenetically enhanced dolomites and clay-rich partings).None of the analyzed shell beds was strictly biological in origin; most are sedimentological although >10% are combined sedimentological/diagenetic. While the majority are single simple shell beds, >20% are amalgamated. All are thin (1 shell to 15 cm) stringers that pinch and swell showing poor lateral continuity (outcrop scale, tens to hundreds of meters) likely enhanced by burial dissolution. These shell beds differ greatly in fabric (packing/sorting), clast composition, taphonomic signature, and intensity of time averaging; thus community information retrieval is biased in predictable patterns. Virtually no shell beds show common shell dissolution or encrustation from long-term sediment surface exposure or hardground formation. Five major categories of accumulation are herein proposed using a DESCRIPTIVE, non-genetic terminology modified from previous works of DJD, as well as a Genetic interpretation for each. These are easily distinguished in the field and are also discriminated by Q-mode cluster analysis.Categories include, in decreasing frequency of occurrence: 1. SHELL GRAVELS; Storm/“event” beds: Sharp bases; poorly sorted coarse basal bioclasts and/or intraclasts, often with no preferred orientation; clasts fine upward to comminuted shell material and micrite. Horizontal platy brachiopods often cap the beds. High diversity and a wide range in shell alteration is represented, from whole unaltered brachiopods to minor abraded fragments, indicating extreme time averaging and poor resolution of short-term community dynamics. 2. COMMINUTED SHELLY LS; Current/ripple concentrations: Small tidal channel fill and discrete ripple trough accumulations are composed of cross-stratified bioclastic deposits with local concentrations of rip-ups. Beds are not graded; typically clasts are abraded, rounded and concordant with cross-beds. Intense time averaging and mixing of discrete communities is inferred due to continual reworking in these background deposits. 3. SHELL/CEMENT LS; Early cementation beds: Intense early diagenetic alteration is inferred due to red discoloration and rapid intergranular cementation; some beds show diagenetic micritic rinds. Beds may be brecciated and show deep burial stylolitization cutting bioclasts and cement. They may represent zones of preferred early cementation rather than a change in shell accumulation rate. Many shells from some beds show little postmortem alteration; these units may preserve much of the original community structure. 4. DENSE SHELL PAVEMENTS; Subtidal surficial pavements: Single layers of shells, commonly concave down, overlie mudstones/wackestones with no basal erosion. No obrution deposits were noted. Bioclasts are typically disarticulated and reoriented, but are not substantially abraded, broken, or dissolved. Diversity is low. Only minor temporal and lateral community mixing with small environmental fluctuation is indicated. 5. VERTICALLY IMBRICATE SHELLY LS; High energy beach zones: Platy whole and major fragments of brachiopods are deposited in low diversity, high angle imbricate beds. Less postmortem reworking and time averaging is evident compared to types 1 and 2.Thus, the most common (physically reworked) shell bed types show the most intense loss of short-term paleocommunity information. There are surprisingly few insitu community pavements or obligate long-term accumulations. This pattern differs from some described Ordovician carbonates, which may contain common community beds or hardgrounds/hiatal accumulations. This implies a relatively low rate of net sediment accumulation on a shallow, periodically wave swept shelf, and no major flooding surfaces or other indications of significant sea level change. Delineation of the sequence stratigraphic position of these carbonates is enhanced from this type of integrated community/biostratinomic analysis.
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5

Corcoran, P. L., and L. N. Moore. "Subaqueous eruption and shallow-water reworking of a small-volume Surtseyan edifice at Kakanui, New Zealand." Canadian Journal of Earth Sciences 45, no. 12 (December 2008): 1469–85. http://dx.doi.org/10.1139/e08-068.

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Kakanui volcaniclastic deposits on the South Island of New Zealand are the remnants of two late Eocene to early Oligocene Surtseyan-type cones. Eruptive-dominated material of the (i) stratified tuff and lapilli tuff, and (ii) lapilli tuff breccia lithofacies and post-eruptive debris of the (iii) shell-rich tuff and lapilli tuff, and (iv) chaotic and cross-bedded tuff and lapilli tuff lithofacies compose the deposits. The 9–250 m thick stratified tuff and lapilli tuff contains grain-flow deposits originating from low-volume tephra jets and local thinning and fining upward sequences that formed from density currents during sustained uprush. The lapilli tuff breccia, up to 4.5 m thick, contains inward-dipping beds deposited via debris flows along inner-cone walls. Burrows and articulated shells in the 2–4 m thick shell-rich tuff and lapilli tuff indicate volcanic quiescence and low sedimentation rates, whereas shell fragments upsection signal increased wave and current activity. Burrows, pyrite concretions, and mudstone in the lower part of the 26 m thick chaotic tuff and lapilli tuff indicate suspension deposition and cessation in pyroclastic volcanism. High-angle trough cross-beds and limestone rip-up fragments upsection are consistent with wave-induced current reworking. The depositional model involves a Surtseyan-type eruption on a continental shelf, followed by colonization of organisms on the tops of planed-off cones. The Kakanui deposits comprise a cluster of cones constituting part of a late Eocene – early Oligocene monogenetic volcanic field. The Kakanui succession provides an opportunity to study deposits that form from explosive subaqueous pyroclastic eruptions and wave-dominated deposition and erosion.
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6

Meldahl, Keith H. "Origin of Shell Beds and Evolution of a Shelly Sand Spit, Bahia la Choya, Northern Gulf of California." Paleontological Society Special Publications 2 (1987): 189–99. http://dx.doi.org/10.1017/s2475262200004810.

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An actively prograding shelly sand spit forms the eastern margin of Bahia la Choya, northern Gulf of California. Shell-rich deposits exposed on the eastern side of the spit record previous phases of spit growth. Analysis and comparison of faunal composition, biofabric and shell preservation from the beach, estero mouth bar, and the fossil spit deposits suggest 3 major phases of spit evolution: (1) southward progradation of the spit tip/estero mouth bar (lower shell bed), (2) deposition of washover lobes during a major storm (upper shell bed), and (3) eolian accretion (spit crest). A 1300 ± 50 y.b.p. radiocarbon date on a bivalve shell from the storm shell bed provides a maximum age for the storm event.
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7

Vermeij, Geerat J. "The oyster enigma variations: a hypothesis of microbial calcification." Paleobiology 40, no. 1 (2014): 1–13. http://dx.doi.org/10.1666/13002.

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Oysters, whose inner shell layer contains chambers, vesicles, and sometimes chalky deposits, often have extraordinarily thick shells of large size, prompting the idea that there is something unusual about the process of shell fPormation in these and similarly structured bivalves with the oyster syndrome. I propose the hypothesis that calcifying microbes, especially sulfate-reducing bacteria growing on organic substrates in fluid-filled shell-wall chambers, are responsible for shell calcification away from the shell-secreting mantle of the host bivalve. Other phenomena, including the formation of cameral deposits in fossil cephalopods, the cementation of molluscs and barnacles to hard substrata, the formation of a calcified intriticalx on the shell's exterior, and cementation of objects by gastropods on the shell for camouflage, may also involve calcifying bacteria. Several lines of inquiry are suggested to test these hypotheses.
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8

Dattilo, Benjamin F., Carlton E. Brett, Cameron J. Tsujita, and Robert Fairhurst. "Sediment supply versus storm winnowing in the development of muddy and shelly interbeds from the Upper Ordovician of the Cincinnati region, USAThis article is one of a series of papers published in this Special Issue on the theme The dynamic reef and shelly communities of the Paleozoic. This Special is in honour of our colleague and friend Paul Copper." Canadian Journal of Earth Sciences 45, no. 2 (February 2008): 243–65. http://dx.doi.org/10.1139/e07-060.

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Shell-bed development can be a product of complex sedimentological and biological factors. The Upper Ordovician sediments near Cincinnati, Ohio constitute a succession of thinly interbedded shelly carbonates and mudrocks. Despite years of study, the development of Cincinnatian shell beds and metre-scale cycles has, until recently, been attributed solely to storm reworking. This “storm-winnowing model” treats shells as passive sedimentary clasts, ignoring other factors of shell-bed development. A recently proposed alternative is Brett and Algeo’s idea that these shell beds grew during long periods of normally low sedimentation, while most mud accumulated during brief periods of high sedimentation. Under this “episodic starvation model,” any storms would winnow pre-existing muds and shell beds alike. We tested both models in the Edenian–Maysvillian (early to mid Katian) strata of the Cincinnati region by compiling observations on their petrologic, taphonomic, and paleoecologic characteristics. The storm-winnowing model does not explain several observed features that the episodic starvation model does, including (i) storm-related sedimentary structures in mudrocks and limestones; (ii) lack of a sufficiently fossiliferous precursor deposit to winnow; (iii) deep-water faunas in grainstones; (iv) mixed taphonomic conditions of shell-bed fossils; (v) ubiquitous discontinuity surfaces; (vi) carbonate concretion horizons; (vii) unwinnowed shell beds; and (viii) micrite in packstones. Episodic starvation is a superior explanation because it explains all of these features and allows for the complex interplay of other environmental and biological factors that contribute to shell-bed growth. It may also be applicable to other deposits, previously interpreted as tempestites.
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9

Sparks, Darrell, and I. E. Yates. "Anatomy of Shuck Abscission in `Desirable' Pecan." Journal of the American Society for Horticultural Science 120, no. 5 (September 1995): 790–97. http://dx.doi.org/10.21273/jashs.120.5.790.

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Cellular changes associated with shuck dehiscence and markings deposited on pecan [Carya illinoinensis (Wangenh.) C. Koch] shells were examined by scanning electron and light microscopy. Fruit were sampled at three stages of maturity: 1) shuck and shell fused, 2) sutures separated (shuck opening), and 3) vascular system separated from shuck. Shuck dehiscence involved temporally regulated abscission events with shuck-shell, then shuck-suture, and finally shuck-vascular system separation. Abscission events occurred in a tissue zone common to and continuous among all three separation sites, even though segregated in time. Also, similar cell types and cellular changes were common to the three events. Thus, temporal segregation of abscission events was not due to differences in either tissue type or cellular modifications, but to maturation rate. Structures to become shell markings were single globules filling cells of the shuck inner tissue zone before shuck-shell separation. These globules were deposited on the shell at shuck-shell separation and were morphologically similar to deposits stuck to the dorsal shuck surface. Globules were partitioned differentially between the shuck and shell during shuck-shell separation. Thus, the inner zone of the shuck is an important tissue in pecan nut maturation; it functions as the site for dehiscence and provides markers for cultivar identification.
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10

Roy, Peter S. "Shell Hash Dating and Mixing Models for Palimpsest Marine Sediments." Radiocarbon 33, no. 3 (1991): 283–89. http://dx.doi.org/10.1017/s0033822200040303.

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The dating of palimpsest marine sediments using broken shell fragments (shell hash) is considered to be a necessary but unreliable technique because of the mixed age of the fragments. An analysis of geological mixing models and radiocarbon data on shell hash from sandy sediments on the southeast Australian coast and shelf are used to examine the possibility for simulating the depositional processes, and thus, to better understand the age structure of the deposits.
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11

Sherwood, John E., Ian J. McNiven, and Laurie Laurenson. "The Moyjil site, south-west Victoria, Australia: shells as evidence of the deposit’s origin." Proceedings of the Royal Society of Victoria 130, no. 2 (2018): 50. http://dx.doi.org/10.1071/rs18006.

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Characteristics of marine shellfish and other species found in a Last Interglacial (LIG) shell deposit at Point Ritchie (Moyjil) at Warrnambool in south-western Victoria have been compared to those from modern and LIG natural beach deposits, Holocene Aboriginal middens and modern Pacific Gull (Larus pacificus) middens. The research was aimed at determining whether properties such as shell speciation, size or taphonomy could identify the mechanism responsible for formation of the Moyjil deposit. Marine species found in the Moyjil deposit resemble those found in both Aboriginal and Pacific Gull middens and are non-discriminatory for the two types. Taphonomic properties such as wear and breakage pattern of opercula of the dominant species, Lunella undulata (syn. Turbo undulatus), are non-diagnostic because of post-depositional erosion and transport effects in the available specimens. The size of L. undulata opercula show clear bias toward larger individuals, in common with Aboriginal and seabird middens, when compared to natural shell deposits. Statistical analysis (ANOVA) of the size distributions shows a greater similarity of the Moyjil deposit to the two seabird middens than the two Aboriginal middens. Small individuals (operculum L. undulata as well as smaller shellfish species are absent from the seabird middens studied, but they are present in Aboriginal middens and in the Moyjil deposit. Overall, we conclude that shell properties alone are not sufficient to distinguish which predator collected the shellfish occurring in the deposit.
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12

FÜRSICH, FRANZ T., and YANHONG PAN. "Diagenesis of bivalves from Jurassic and Lower Cretaceous lacustrine deposits of northeastern China." Geological Magazine 153, no. 1 (June 4, 2015): 17–37. http://dx.doi.org/10.1017/s0016756815000242.

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AbstractIn contrast to the numerous excellently preserved arthropods, vertebrates and plants from the Mesozoic lacustrine fossil lagerstätten of northeastern China, which have calcium phosphate or organic skeletons, the preservation of taxa with a calcareous skeleton is fairly poor. Here we investigate, using a scanning electron microscope and energy dispersive X-ray spectrometer, the preservational modes of bivalves from the Jurassic Daohugou Fossil Beds of Inner Mongolia and the Lower Cretaceous Yixian Formation of eastern Liaoning. The Jurassic bivalve Ferganoconcha sibirica is preserved as strongly compressed composite moulds which contain remains of the organic periostracum. In the Yixian Formation, the bivalves Sphaerium anderssoni and Arguniella ventricosa occur as compacted internal, external or composite moulds or are preserved with a silicified shell, and rarely with a shell consisting of iron hydroxides, which had replaced pyrite during late diagenesis/weathering. Silicification produced partly fabric-replacive microcrystalline quartz and partly void-filling megaquartz crystals after the carbonate shell had been dissolved. Films of authigenic aluminosilicate minerals, partly secondarily silicified, cover the exterior and interior shell surfaces. Occasionally, early diagenetic pyrite crystals, now oxidized to iron hydroxides, filled shell cavities forming internal moulds and rarely replaced the bivalve shell. The poor preservation of the bivalves reflects the environment and water chemistry of these lakes, which were heavily influenced by volcanic processes. Frequent ash deposition and decomposition of volcanic glass particles created acidic and alkaline lake and interstitial waters, which led to early diagenetic formation of authigenic aluminosilicate minerals, ferruginous internal moulds, dissolution of shell carbonate and silicification of shells.
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13

Groenenberg, Dick S. J., Frank P. Wesselingh, Sanjeevi Rajagopal, Jeroen M. Jansen, Merijn M. Bos, Gerard van der Velde, Edmund Gittenberger, Bert W. Hoeksema, Harry Raad, and Herman Hummel. "On the identity of broad-shelled mussels (Mollusca, Bivalvia, Mytilus) from the Dutch delta region." Contributions to Zoology 80, no. 2 (March 18, 2011): 95–106. http://dx.doi.org/10.1163/18759866-08002001.

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Late Quaternary (Eemian) deposits of the Netherlands contain shells that resemble those of living Mytilus galloprovincialis. Similar broad-shelled mytilids also occur in estuaries of the southwestern Netherlands together with slender individuals typical of M. edulis. We sampled living mussels along a depth gradient in the Oosterschelde to a) investigate whether a relation exists between shell shape and depth, b) test if the broadshelled specimens might represent M. galloprovincialis (or a hybrid with M. edulis) and c) assess by inference if the Quaternary specimens might be attributed to M. galloprovincialis as well. In order to do so, we compared genetic (length polymorphism of Me 15/16, COIII sequences and AFLPs) and shellmorphological characteristics (juvenile L/W ratios and socalled Verduin parameters) of the same specimens. The obtained dataset indicates that all studied mussels from the Oosterschelde should be attributed to M. edulis, including those with broad shell outlines. No correlation of shell-morphology and depth-distribution was found. The worn and generally damaged state of the Eemian specimens precluded measurement of the Verduin parameters, while juvenile L/W ratios turned out not to be diagnostic. Therefore the shell characters examined in this study are insufficient to demonstrate the possible presence of M. galloprovincialis shells in Quaternary deposits of the Netherlands.
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14

Šimo, Vladimír, and Adam Tomašových. "Trace-fossil assemblages with a new ichnogenus in “spotted”." Geologica Carpathica 64, no. 5 (October 1, 2013): 355–74. http://dx.doi.org/10.2478/geoca-2013-0024.

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Abstract Highly-bioturbated “spotted” limestones and marls (Fleckenmergel-Fleckenkalk facies) of the Early Jurassic, which were deposited in broad and recurrent deep-shelf habitats of the Northern Tethys, are characterized by rare benthic carbonate-producing macroinvertebrates. To address this paradox, we analyse trace-fossil assemblages in a ~85 m-thick succession of Pliensbachian spotted deposits (Zliechov Basin, Western Carpathians). They are dominated by infaunal and semi-infaunal deposit-feeders, with 9 ichnogenera and pyritized tubes of the semi-infaunal foraminifer Bathysiphon, being dominated by Chondrites, Lamellaeichnus (new ichnogenus), and Teichichnus. Lamellaeichnus, represented by a horizontal basal cylindrical burrow and an upper row of stacked convex-up gutters, was produced by a mobile deposit-feeder inhabiting shallow tiers because it is crossed by most other trace fossils. We show that the spotty appearance of the deposits is generated by a mixture of (1) dark, organic-rich shallow- and deep-tier traces (TOC = 0.16-0.36), and (2) light grey, organic-poor mottled or structurless sediment (TOC = 0.09-0.22). The higher TOC in shallow-tier burrows of Lamellaeichnus demonstrates that uppermost sediment layers were affected by poor redox cycling. Such conditions imply a limited mixed-layer depth and inefficient nutrient recycling conditioned by hypoxic bottom-waters, allowed by poor circulation and high sedimentation rates in depocenters of the Zliechov Basin. Hypoxic conditions are further supported by (1) dominance of trace-fossils produced by infaunal deposit feeders, (2) high abundance of hypoxiatolerant agglutinated foraminifer Bathysiphon, and (3) high abundance of Chondrites with ~0.5 mm-sized branches. Oxygen-deficient bottom-conditions can thus simultaneously explain the rarity of benthic carbonate-producing macroinvertebrates and high standing abundance of tolerant soft-shell and agglutinated organisms in spotted deposits.
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15

Kaufman, Darrell, L. David Carter, Gifford H. Miller, G. Lang Farmer, and David A. Budd. "Strontium isotopic composition of Pliocene and Pleistocene molluscs from emerged marine deposits, North American Arctic." Canadian Journal of Earth Sciences 30, no. 3 (March 1, 1993): 519–34. http://dx.doi.org/10.1139/e93-041.

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High-precision strontium (Sr) isotopic measurements were obtained for 53 Pliocene and Pleistocene molluscan shells from emerged marine deposits around the coasts of Arctic North America to test whether such data can be used for chronostratigraphic purposes. 87Sr/86Sr ratios from Sr isotopic measurements on many marine fossils from Arctic Ocean borderland sites are broadly consistent with their expected values based on independent age control and on a comparison with the Sr isotopic evolution of seawater recorded in deep-sea cores. All 87Sr/86Sr ratios measured for shells from Middle and Late Pleistocene deposits are consistent with expected values, but only 9 of 22 ratios in shells from older deposits are consistent with independent age estimates. Aberrant 87Sr/86Sr ratios are consistently higher than expected. At Nome, Alaska, and Baffin Island, Canada, all 87Sr/86Sr ratios are higher than expected. Because these shells were formed along the Pacific Ocean and Atlantic Ocean margins, respectively, their high 87Sr/86Sr ratios cannot be attributed to possible differences in the Sr isotopic evolution of the Arctic Ocean relative to that of remainder of the world's oceans. Radiogenic Sr from proximal river-water input, or leaching of detritus within the shell matrix, may have changed the 87Sr/86Sr ratios by as much as about 5 × 10−5, but these mechanisms cannot account for the very high 87Sr/86Sr values (from 20 × 10−5 to 200 × 10−5 higher than those of modern seawater) measured for some shells. Alteration by diagenetic fluids rich in radiogenic Sr is the most plausible explanation for the aberrant results. Diagenesis is recognized petrographically in the most altered shells by micritic overprinting of the original shell microstructure; in addition, one shell enriched in 87Sr from Baffin Island exhibits a broad range (170 × 10−5) of 87Sr/86Sr ratios across the shell, and an oxygen isotopic gradient (l.6‰) that is greater than the expected primary variability. Although our data suggest that Sr isotopic data from young Arctic molluscan fossils may offer a viable dating method, criteria for screening altered shells must be devised before the technique can be considered a reliable chronostratigraphic tool.
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Bērziņš, Valdis, Ute Brinker, Christina Klein, Harald Lübke, John Meadows, Mudīte Rudzīte, Ulrich Schmölcke, Harald Stümpel, and Ilga Zagorska. "New research at Riņņukalns, a Neolithic freshwater shell midden in northern Latvia." Antiquity 88, no. 341 (August 26, 2014): 715–32. http://dx.doi.org/10.1017/s0003598x0005064x.

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The prehistoric shell middens of Atlantic Europe consist of marine molluscs, but the eastern Baltic did not have exploitable marine species. Here the sole recorded shell midden, at Riņņukalns in Latvia, is on an inland lake and is formed of massive dumps of freshwater shells. Recent excavations indicate that they are the product of a small number of seasonal events during the later fourth millennium BC. The thickness of the shell deposits suggests that this was a special multi-purpose residential site visited for seasonal aggregations by pottery-using hunter-gatherer communities on the northern margin of Neolithic Europe.
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17

Bailey, Geoff, and Elizabeth Rich. "Weipa Shell Mounds: Cultural or Natural Deposits?" Australian Archaeology 43, no. 1 (November 1, 1996): 53. http://dx.doi.org/10.1080/03122417.1996.12094422.

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18

Donato, S. V., E. G. Reinhardt, J. I. Boyce, R. Rothaus, and T. Vosmer. "Identifying tsunami deposits using bivalve shell taphonomy." Geology 36, no. 3 (2008): 199. http://dx.doi.org/10.1130/g24554a.1.

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19

FAULKNER, PATRICK. "Quantifying shell weight loss in archaeological deposits." Archaeology in Oceania 46, no. 3 (October 2011): 118–29. http://dx.doi.org/10.1002/j.1834-4453.2011.tb00106.x.

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20

Katupotha, Jinadasa, and N. P. Wijayananda. "Chronology of Inland Shell Deposits on the Southern Coast of Sri Lanka." Quaternary Research 32, no. 2 (September 1989): 222–28. http://dx.doi.org/10.1016/0033-5894(89)90078-1.

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AbstractExtensive patches of fossil shell deposits are found in many places along the rims of emerged coastal embayments and lagoon floors on the southern coast of Sri Lanka. Compositional and depositional sequences of fossil shells (Veneridae, Cerithidae, and Nassaridae) reveal that the bulk of the valves has been accumulated by three processes: (a) the shells have been piled up on the rims of emerged coastal embayments mainly by wave action; (b) following coastal progradation since the late Subboreal the shells possibly gathered on lagoon floors; and (c) the valves on the coastal hilly areas and dune areas were discarded by early human inhabitants in the course of their daily activities. Radiocarbon dates of fossil corals along the southwest and south coasts support this interpretation and indicate that mean sea level was at least 1 m higher than present in the middle Holocene. The fossil species may have lived in an intertidal zone of embayments and lagoons that extended 3 km or more inland form the present shore in the middle Holocene.
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Miller, Molly F., and David J. Davies. "Did shell layers negatively affect Ordovician soft-bodied infauna?" Paleontological Society Special Publications 6 (1992): 213. http://dx.doi.org/10.1017/s2475262200007735.

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What is the relationship, if any, between soft-bodied infaunal animals and shell accumulations? Do shell layers negatively affect infaunal animals and have they in the past? To determine whether this type of taphonomic inhibition may have operated in Ordovician infaunal communities, we evaluated extent of burrow penetration of shell-rich layers in shallow-water limestones of the Lebanon Formation, central Tennessee. Most of the analyzed shell layers, which are a few mm to 15 cm thick, are not cut by burrows. No burrows occur in shell layers in slabs containing 67% of the total area examined (5500 cm2), although burrows are common above and below the shell-rich layers.Most of the few shell-rich layers that are burrowed occur in wackestones in which skeletal fragements are arranged in a loose/dispersed fabric (Kidwell and Holland, 1991). Where burrow diameter is greater (1 cm) than maximum dimension of most shell fragments (2-4 mm), shells outline the burrow, suggesting that the animal pushed them aside during burrow construction. Where burrow diameter is less (2-3 mm) than length of shell fragments (0.5–2 cm), the burrows occur between the fragments, which show no signs of biogenic reorientation. In the single case where grainstone consisting of densely packed skeletal fragments (3–5 mm in longest dimension) is penetrated, burrow diameter (1 cm) exceeds fragment size.Shell layers penetrated by burrows originated variably as storm deposits, current winnowed accumulations, and dense shell pavements. No layers with vertically imbricated shells are burrowed; they probably were deposited in a high energy environment inimical to burrowers. With this exception there is little evidence that mode of origin of shell bed exerts strong control over subsequent penetration by burrowers.Although limited, these data suggest that Ordovician soft-bodied infaunal animals avoided burrowing through shell-rich layers. Those shell layers that were penetrated are loosely packed. Characteristically, in burrow-penetrated shell layers the ratio of fragment size: burrow size is either very low (animal pushed fragments aside) or very high (animal moved between shell fragments). Thus, abundance and character of shell-rich layers may have been an important factor controlling the composition and structure of Ordovician infaunal communities.
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22

Butts, Susan H. "Silicification." Paleontological Society Papers 20 (October 2014): 15–34. http://dx.doi.org/10.1017/s1089332600002783.

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Silicification is the replacement of original skeletal material accomplished through the concurrent dissolution of calcium carbonate and precipitation of silica. The processes is aided by the nucleation of silica to organic matter which surrounds the mineral crystallites within the shell. Factors that control silicification are those that influence the dissolution/precipitation process: shell mineralogy, shell ultrastructure (and, therefore, surface area), the amount and location of organic matter, and the character of the enclosing matrix. Silicification, like all types of fossilization, can produce taphonomic biases: it is far more common in Paleozoic than younger deposits, is more likely to occur in organisms with low-magnesium calcite shells, in carbonate sediments, and in environments with elevated dissolved silica.
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Burke, Chrissina C., Katie K. Tappan, Gavin B. Wisner, Julie A. Hoggarth, and Jaime J. Awe. "TO EAT, DISCARD, OR VENERATE: FAUNAL REMAINS AS PROXY FOR HUMAN BEHAVIORS IN LOWLAND MAYA PERI-ABANDONMENT DEPOSITS." Ancient Mesoamerica 31, no. 1 (2020): 127–37. http://dx.doi.org/10.1017/s0956536119000221.

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AbstractInterpreting middens, feasting events, ritual, or terminal deposits in the Maya world requires an evaluation of faunal remains. Maya archaeologists consistently evaluate other artifact classes, but often offer simply number of identified specimens values for skeletal elements recovered from these deposits. To further understand their archaeological significance, we analyzed faunal materials from deposits at the sites of Baking Pot and Xunantunich in the Upper Belize River Valley. We identified the species, bone elements, bone or shell artifacts, taphonomic signatures, and quantitative ratios recovered to test whether a deposit can be identified as a midden, part of a feasting ritual, terminal ritual, or other rituals significant to the Maya. Our analyses allow us to begin building a system for using faunal remains as a proxy for interpreting the significance of these deposits. In this paper, we present our results and hope to open the conversation for future evaluations of faunal remains in similar deposits.
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24

Sorokin, V. M., T. A. Yanina, and B. F. Romanyuk. "New finds of Karangat deposits in the eastern part of the Black Sea." Moscow University Bulletin. Series 4. Geology, no. 5 (December 17, 2022): 113–19. http://dx.doi.org/10.33623/0579-9406-2022-5-113-119.

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The sections of boreholes and sediment cores in the Taman shelf area and on the Caucasian continental slope, which uncovered shallow and deep-water facies of the interglacial Karangate horizon, were studied. The shallow-water sediments include clayey and sandy-shell varieties containing stenohaline marine molluscan fauna. Deep-water sediments are represented by sapropelic and coccolithic layers with a marine flora of diatom algae and coccolithophorids.
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25

Ma, Xueping, and Jed Day. "Revision of selected North American and Eurasian Late Devonian (Frasnian) species of Cyrtospirifer and Regelia (Brachiopoda)." Journal of Paleontology 77, no. 2 (March 2003): 267–92. http://dx.doi.org/10.1017/s0022336000043638.

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Study of the shell features of Givetian and Frasnian spiriferid brachiopods attributed to the genus Cyrtospirifer shows that the type species C. verneuili has micro-ornament consisting of fine concentric growth lines, radial capillae, with microspines arising from some capillae, spine bases appear to extend into the primary shell layer. Its dorsal interior features a pseudoseptum supporting the cardinalia. Micro-ornament of Cyrtospirifer varies widely and is a useful criterion for characterization of species of the genus. Most Frasnian species retained in the genus have micropustulate shells. Two late Givetian and Frasnian phylogenetic species groups of Cyrtospirifer are recognized based on similarities of shell form and external and internal shell features. Species of the verneuilisyringothyriformis group have transverse alate shells, and are the most abundant and widespread group in Frasnian deposits worldwide. The verneuiliformis group includes the oldest known species of Cyrtospirifer with narrow hinges and more inflated ventral valves where shell width is close to or equal to length. The oldest Cyrtospirifer originated in western Europe during the late Givetian, and subsequently migrated at different times during the Frasnian into other shelf areas of Eurasia, North America and China. The initial migration of Cyrtospirifer into tropical and subtropical shelf settings in North America coincided with the middle Frasnian eustatic sea level rise of Devonian Transgressive-Regressive (T-R) cycle IIc of Johnson and others. A second late Frasnian dispersal from western Canada to subtropical carbonate and clastic shelves in the southwestern and central U.S. coincided with the initial sea level rise of T-R cycle IId of Johnson and others. The Frasnian species Cyrtospirifer glaucus Crickmay, 1952a (middle Frasnian of western Canada) is the type species for Regelia Crickmay, 1952b, and is considered a valid genus, and is not a synonym of C. chemungensis (Conrad, 1842) as previously interpreted by some authors. Regelia differs from Cyrtospirifer in the absence of a delthyrial plate, complete in-filling of the delthyrial cavity by secondary shell material, its simpler rod-like teeth, and its fewer medial sinal shell plications. Species of Regelia are restricted to the middle to late Frasnian of North America.
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26

CZAJA, ALEXANDER, ALAN P. COVICH, THOMAS A. NEUBAUER, JOSÉ LUIS ESTRADA-RODRÍGUEZ, VERÓNICA ÁVILA-RODRÍGUEZ, and JORGE SÁENZ MATA. "A new freshwater snail genus and species (Gastropoda: Caenogastropoda, Cochliopidae) with extremely spinous shells from sub-recent spring deposits in northeastern Mexico." Zootaxa 5169, no. 5 (August 2, 2022): 472–80. http://dx.doi.org/10.11646/zootaxa.5169.5.5.

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A new monotypic genus of freshwater snail from late Holocene spring deposits in Viesca, Coahuila (Mexico), is described based on shell morphology. Spinopyrgus luismaedai n. gen. et n. sp. has two to three carinate shells with long and wide shovel-shaped spines, strong axial ridges and a pointed protoconch. All sculptural ornamentations on the teleoconch are part of the calcareous shell material and not projections of the periostracum. This combination of shell features and their almost “marine-like” appearance is unknown among North American recent and fossil freshwater snails. Because of its shell characteristics, we placed the new genus tentatively in the Cochliopidae. The springs of Viesca dried up in the second half of the 20th century so that any living occurrence of this species in neighboring areas is unlikely, rendering the new genus and species possibly extinct.
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LAZER, KAYLA, IAN P. STOUT, EDWARD L. SIMPSON, MICHAEL C. WIZEVICH, ABIGAL M. KEEBLER, and GRACE K. HETRICK. "PRESERVED MEMBRANE ON DINOSAUR EGGSHELL FRAGMENTS, UPPER JURASSIC MORRISON FORMATION, EASTERN UTAH." PALAIOS 38, no. 1 (January 27, 2023): 43–55. http://dx.doi.org/10.2110/palo.2022.002.

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ABSTRACT Dinosaur eggshell fragments, from the Upper Jurassic Brushy Basin Member of the Morrison Formation, Utah, were examined using Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive Spectroscopy, and Raman Spectroscopy. Analyses revealed that the mammillary tips on the shell interior contain carbonaceous residue. Comparison under the FESEM of these shells with modern bird shells, including some samples heated to diagenetic temperatures, indicate that the residue is degraded organic compounds (DOC). Bird egg membrane is composed of interlaced collagen fibers. Features observed on, and common to, modern bird and dinosaur egg fragments include: (1) irregular-shaped calcium carbonate grains “floating” in an organic matrix; (2) three-dimensional organic fiber matrix; (3) external calcium carbonate molds of fibers in the mammillary bodies; and in heated specimens, (4) carbonaceous residue with ovate to circular pores. However, unlike birds' eggs, the dinosaur eggs contain a calcium carbonate tube around fibrous organic material that emerges from the tube and spreads laterally in a ‘puddle-like' deposit. The sizes of circular organic matrix pores of the dinosaur egg fragments are significantly smaller than those in the bird shells. Gallus gallus domesticus eggshell membranes heated to diagenetic temperatures resulted in alteration of collagen fibers to gel-like substances. The organic matrix with ovate to circular pore openings and the puddle-like deposits in the dinosaur egg fragments are interpreted as the product of membrane thermal diagenesis. The recognition of carbonaceous residue of the shell membrane on dinosaur shell fragments opens newfound opportunities to explore DOC associated with fragmental dinosaur eggs.
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28

Kristina Hirst, K., Robert G. Thompson, and Katherine S. Walters. "Tracing the use of freshwater naiad shells as prehistoric implements through scanning electron microscopy and x-ray microanalysis." Proceedings, annual meeting, Electron Microscopy Society of America 48, no. 3 (August 12, 1990): 717. http://dx.doi.org/10.1017/s042482010016114x.

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Many freshwater naiad shells recovered from prehistoric Iowa archaeological sites have edges exhibiting patterns of use-wear. The ethnographic and ethnohistoric records contain accounts of the use of these shells in the removal of kernels from corn cobs. Recently, archaeologists have begun tracing use of stone implements through analysis of microscopic wear patterns and deposition of material such as opal phytoliths. Opal phytoliths are small silica bodies which plants deposit within and between some cells. Corn is among the plants which produce opal phytoliths in abundance. Experimentally created naiad shell implements were used to remove kernels from corn cobs. The deposits left on the edges of these implements were compared to those of prehistoric naiad shells thought to be utilized. Scanning electron microscopy (SEM) and x-ray microanalysis were utilized.The prehistoric and experimentally created edges were prepared for examination by cleaning and coating with carbon. Examination of the tools was performed with a Hitachi S-570 electron microscope equipped with a Kevex 8000 x-ray microanalyzer.
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29

Banjac, Nenad, Klaus Bandel, and Steffen Kiel. "Cassiopid gastropods from the cretaceous of Western Serbia." Annales g?ologiques de la Peninsule balkanique, no. 68 (2007): 61–71. http://dx.doi.org/10.2298/gabp0701061b.

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Three species of Cassiopidae (Cerithioidea, Gastropoda) are described from outcrops in the vicinity of the villages Rastiste and Mokra Gora in western Serbia. They occur in marly limestones of near shore shallow water deposits. Earlier micropaleontological investigations have indicated an Albian-Cenomanian age. The species encountered are related to those present in deposits of the European margin of the Tethys and closest relationships exist to those of the Armenian and Transcaucasian region. Our species can be placed in the genera Cassiope, Paraglauconia and Bicarinella. A new species Cassiope kotromanensis is erected. Assumptions about post-mortem shell transport and size sorting of gastropod shells were examined through statistical analysis.
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30

Thompson, Victor D., and C. Fred T. Andrus. "Evaluating Mobility, Monumentality, and Feasting at the Sapelo Island Shell Ring Complex." American Antiquity 76, no. 2 (April 2011): 315–43. http://dx.doi.org/10.7183/0002-7316.76.2.315.

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Two of the most salient anthropological questions regarding southeastern shell ring sites are related to the season(s) that they were occupied and whether or not the deposits represent monumental constructions and/or feasting remains. This paper addresses these questions through the analysis of growth band of clams (Mercenaria spp.) (N = 620) and stable oxygen isotope ratios of clam and oyster shells (Crassostrea virginica) (N = 58) at the Sapelo Island Shell Ring complex located on the Georgia coast, USA. The season of death and the samples' position in the shell matrix at Sapelo provide important information on the rate of shell deposition and the season(s) the site was occupied. These data support the view that at least some portion of the human population at Sapelo occupied the site year-round. Additionally, while it appears that two shell rings at the site formed through the gradual deposition and accumulation of daily subsistence, other areas evidence short term, large-scale, shellfish processing and may lend credence to the view that at some point shell rings become monuments, commemorating rituals and gatherings.
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31

Carter, Melissa, Ian Lilley, Sean Ulm, and Deborah Brian. "Mort Creek Site Complex, Curtis Coast: Site Report." Queensland Archaeological Research 11 (December 1, 1999): 85. http://dx.doi.org/10.25120/qar.11.1999.88.

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This paper reports the results of excavations conducted at the Mort Creek Site Complex, located in the Rodds Peninsula Section of Eurimbula National Park on the southern Curtis Coast, Central Queensland. Cultural and natural marine shell deposits were excavated and analysed as part of an investigation of natural and cultural site formation processes in the area. Analyses (including foraminifera studies) demonstrate a complex site formation history, with interfingering of cultural and natural shell deposits (cheniers) in some areas of the site. Radiocarbon dating indicates that Aboriginal occupation of the site was initiated before 2,000 cal BP, overlapping with dates obtained for natural chenier deposits.
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32

Al-Jaberi, Mohanad Hamid, Harith A. Al-Saad, Ghazi A. Hussain, and Hiba Khalid Lafta. "Study of Unio shells in the Quaternary deposits, southern Iraq." IOP Conference Series: Earth and Environmental Science 1087, no. 1 (October 1, 2022): 012020. http://dx.doi.org/10.1088/1755-1315/1087/1/012020.

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Abstract Shells are useful in evolutionary biology and paleobiology. Freshwater shells compose the main types of mollusks, and can use as a key for ecological variations. Shell samples in the present study were collected on the highway of Nasyriah city-Samawa city, southern Iraq. The study area contains a large accumulation of shells at 6-7m depths, especially at 7m depth. The main types of these shells are Unio, Corbicula, and Melanoides tuberculata. Unio was the most species common in the study area. Unio species were used to detect the paleoenvironment in Quaternary deposits, in southern Iraq. Calcite and aragonite are the common minerals in the Unio shells. According to the distribution and percentage of calcite and aragonite in the Unio shells, it was found the calcite at 6m is more than 7m, whereas the aragonite at 7m is highest compared to 6m. Under X-Ray Fluorescence analyzers, found that calcium oxide, silica, magnesium oxide, and phosphor oxide are the major oxides in the Unio shells, while Zn, Sr, Pb, and Rb are the main trace elements. Strontium (Sr) has a high concentration in the Unio shells at 7m than 6m, while magnesium (Mg) is found in a high concentration at 6m than 7m. According to trace and some of the major elements concentrations, the paleotemperature, paleosalinity, and water contamination of rivers at 6m are more than 7m, and the river water at 7m depth was fresh water with a high abundance of nutrients and climate was suitable to growth mollusks shells like Unio shells.
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Kim, Young Jun, Hyein Lee, Hee-Suk Chung, Youngku Sohn, and Choong Kyun Rhee. "PT-BI Co-Deposit Shell on AU Nanoparticle Core: High Performance and Long Durability for Formic Acid Oxidation." Catalysts 11, no. 9 (August 30, 2021): 1049. http://dx.doi.org/10.3390/catal11091049.

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This work presents the catalysts of Pt-Bi shells on Au nanoparticle cores and Pt overlayers on the Pt-Bi shells toward formic acid oxidation (FAO). Pt and Bi were co-deposited on Au nanoparticles (Au NP) via the irreversible adsorption method using a mixed precursor solution of Pt and Bi ions, and the amount of the co-deposits was controlled with the repetition of the deposition cycle. Rinsing of the co-adsorbed ionic layers of Pt and Bi with a H2SO4 solution selectively removed the Bi ions to leave Pt-rich and Bi-lean (<0.4 atomic %) co-deposits on Au NP (Pt-Bi/Au NP), conceptually similar to de-alloying. Additional Pt was deposited over Pt-Bi/Au NPs (Pt/Pt-Bi/Au NPs) to manipulate further the physicochemical properties of Pt-Bi/Au NPs. Transmission electron microscopy revealed the core–shell structures of Pt-Bi/Au NPs and Pt/Pt-Bi/Au NPs, whose shell thickness ranged from roughly four to six atomic layers. Moreover, the low crystallinity of the Pt-containing shells was confirmed with X-ray diffraction. Electrochemical studies showed that the surfaces of Pt-Bi/Au NPs were characterized by low hydrogen adsorption abilities, which increased after the deposition of additional Pt. Durability tests were carried out with 1000 voltammetric cycles between −0.26 and 0.4 V (versus Ag/AgCl) in a solution of 1.0 M HCOOH + 0.1 M H2SO4. The initial averaged FAO performance on Pt-Bi/Au NPs and Pt/Pt-Bi/Au NPs (0.11 ± 0.01 A/mg, normalized to the catalyst weight) was higher than that of a commercial Pt nanoparticle catalyst (Pt NP, 0.023 A/mg) by a factor of ~5, mainly due to enhancement of dehydrogenation and suppression of dehydration. The catalytic activity of Pt/Pt-Bi/Au NP (0.04 ± 0.01 A/mg) in the 1000th cycle was greater than that of Pt-Bi/Au NP (0.026 ± 0.003 A/mg) and that of Pt NP (0.006 A/mg). The reason for the higher durability was suggested to be the low mobility of surface Pt atoms on the investigated catalysts.
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34

Hutchinson, Ian. "Spatiotemporal Variation in ΔR on the West Coast of North America in the Late Holocene: Implications for Dating the Shells of Marine Mollusks." American Antiquity 85, no. 4 (August 12, 2020): 676–93. http://dx.doi.org/10.1017/aaq.2020.47.

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Radiocarbon ages on mollusk shells, which account for about half of the more than 8,000 dates from cultural deposits on the west coast of North America, need to be corrected for the local marine reservoir effect (ΔR) to yield true ages. Assays on “prebomb” shells show that ΔR increases poleward, echoing the age gradient in offshore waters. The meridional gradient in ΔR is not appreciably affected by the transition either from an upwelling regime to a downwelling regime north of 40°N–45°N or from a winter maximum-high alkalinity river discharge pattern to a summer maximum-low alkalinity pattern at the same latitude, probably because these changes are offset by increasing storminess and tidal energy in coastal areas. Mesoscale variations in ΔR along this gradient are attributable to contrasts in shore morphology and exposure. Data from 123 shell-wood pairs reveal similar patterns of temporal variation in ΔR in the late Holocene in the coastal ecoregions. The characteristic temporal pattern echoes phases of variable El Niño-Southern Oscillation (ENSO) activity. The high degree of variability in ΔR argues against the indiscriminate application of regionally uniform or trans-Holocene ΔR values and demands improvements in spatiotemporal resolution if shell is used to date cultural deposits.
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Wang, Wei-Wei, Yu Gu, Hao Yan, Kai-Xuan Li, Zhao-Bin Chen, Qi-Hui Wu, Christine Kranz, Jia-Wei Yan, and Bing-Wei Mao. "Formation sequence of solid electrolyte interphases and impacts on lithium deposition and dissolution on copper: an in situ atomic force microscopic study." Faraday Discussions 233 (2022): 190–205. http://dx.doi.org/10.1039/d1fd00043h.

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In situ AFM monitoring of the morphology evolution of Li deposits reveals that SEIs could be more influential on Li dissolution, and spatial integration of the SEI shell on Li deposits is important to maintain reversible deposition and dissolution cycles.
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36

Sharma, Komal, Nilesh Bhatt, Anil Dutt Shukla, Dae-Kyo Cheong, and Ashok Kumar Singhvi. "Optical dating of late Quaternary carbonate sequences of Saurashtra, western India." Quaternary Research 87, no. 1 (January 2017): 133–50. http://dx.doi.org/10.1017/qua.2016.12.

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AbstractBioclastic carbonate deposits that formed because of a combination of nearshore marine, fluvial, and aeolian processes, occur along the Saurashtra coast and in the adjacent interior regions of western India. Whether these carbonates formed by marine or aeolian processes has been debated for many decades. The presence of these deposits inland poses questions as to whether they are climate controlled or attributable to postdepositional tectonic uplift. In particular, the debate centres on chronologic issues including (1) appropriate sampling strategies and (2) the use of 230Th/234U and 14C ages on the bulk carbonates. Using traces (<1%) of quartz grains trapped in carbonate matrices, optically stimulated luminescence (OSL) dating of quartz grains, deposited along with the carbonate grains, provides ages for the most recent deposition events. The OSL ages range from >165 to 44 ka for the shell limestones, 75–17 ka for the fluvially reworked sheet deposits, and 80–11 ka for miliolites deposited by aeolian processes. These are younger than the 230Th/234U and 14C ages and suggest that the inland carbonate deposits were reworked from older carbonate sediments that were transported during more arid phases.
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37

Flessa, Karl W., Alan H. Cutler, and Keith H. Meldahl. "Time and taphonomy: quantitative estimates of time-averaging and stratigraphic disorder in a shallow marine habitat." Paleobiology 19, no. 2 (1993): 266–86. http://dx.doi.org/10.1017/s0094837300015918.

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We examined the radiocarbon age, taphonomic condition and stratigraphic position of shells of the venerid bivalveChionespp. from the tidal flats of Bahia la Choya, Sonora, Mexico. Shells in Bahia la Choya are time-averaged. Thirty shells yielded radiocarbon dates from modern (A.D. 1950 or younger) to 3569 years before present. The median calendar age of inner flat shells is 483 years; the median age of tidal channel shells is 427 years. We interpret such long shell survival to be the result of frequent shallow burial. Such burial retards bioerosion of shells.The taphonomic condition of shells varied with environment. Shells from the surface of the inner flats were better preserved than shells from the tidal channel. Shells are more likely to be physically worn and biologically degraded in the waters of the channel than on the quieter and more frequently exposed inner tidal flat. Taphonomic condition is an unreliable indicator of a shell's time-since-death. Poorly-preserved shells on the inner flats tended to be old, but in general shell condition was much more variable than shell age. A shell's condition is more likely the result of its total residence time on the surface than its time-since-death (surface time plus burial time).Two composite short (44 cm and 50 cm) cores revealed varying degrees of stratigraphic disorder (the departure from perfect correlation between relative stratigraphic position and relative age). One of eight shells in the inner flats core was disordered; four of nine shells in the tidal channel were disordered. The actual age range of surface shells approximates the age range of shells in cores. Stratigraphic disorder is a consequence of both time-averaging and physical and biogenic mixing.Time-averaging controls the degree of precision possible in paleoecological studies. Environmental changes and ecological phenomena occurring within a span of 3500 years would not be recognized in deposits like those of Bahia la Choya. Time-averaging and stratigraphic disorder also constrain the temporal resolution possible in microstratigraphic studies of evolution. The extent of time-averaging and stratigraphic disorder will dictate an appropriate sample interval. In order to prevent temporal overlap between successive samples in deposits like Bahia la Choya, sample spacing should not be less than approximately 0.5 m.
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Hausmann, Niklas, and Matthew Meredith-Williams. "Exploring Accumulation Rates of Shell Deposits Through Seasonality Data." Journal of Archaeological Method and Theory 24, no. 3 (May 6, 2016): 776–95. http://dx.doi.org/10.1007/s10816-016-9287-x.

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39

LEBEDEVA, I. V., M. I. FARFEL, D. Yu KONYASHIN, and M. M. BEREZIN. "EXPERIMENTAL STUDY OF SNOW LOAD DISTRIBUTION ON A SHELL OF THE GRAND SPORTS ARENA OF LUZHNIKI OLYMPIC COMPLEX." Bulletin of Science and Research Center of Construction 35, no. 4 (January 22, 2023): 40–61. http://dx.doi.org/10.37538/2224-9494-2022-4(35)-40-61.

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Introduction. The mechanism of the formation of snow deposits on the shell of the Luzhniki GSA and their redistribution in winter were established on the basis of the data obtained during the monitoring of the snow load for over 20 years.Aim. In this article, the mechanism of the formation of snow deposits and their distribution on the shell of the Luzhniki GSA were determined, along with the numerical values of the form factor μ characterizing the transition from the ground snow load to the snow load on the shell.Materials and methods. The measurements of the load and density of snow deposits on the shell of the Luzhniki GSA were carried out from 1998 to 2019. The obtained results were compared with the parallel measurements of ground snow load (GSL) in Luzhniki. In addition, the snow load, as well as statistical data analysis on the maximum annual values of the GSL, were analyzed using the hydrometeorological data of decadic snow surveys in Moscow, performed by the V.A. Mikhelson Meteorological Observatory following the dates of field measurements. The graphs of the repeatability of wind directions for the month preceding the observation dates were plotted.Results. The maximum values of the form factor μ for each section of the shell were obtained. The areas characterized by increased snow deposition on the shell during various periods of snow accumulation andthe dependence of their formation on wind speeds and directions in winter were revealed. Graphs depicting the distribution of snow load on the surface by observation years were plotted. It was established that the values of snow loads on the GSA shell during the observation period generally lay within the design values, except for local zones near the internal contour during the installation of the canopy.Conclusion. It was shown that the formation, accumulation, and redistribution of snow deposits on the shell comprise a complex and uneven process, varying from winter to winter. When selecting the analytical models of snow loads for calculating unique load-bearing structures, it is necessary to account for the most unfavorable wind flow directions, at which an uneven snow deposition pattern occurs, as well as the physical properties of the shell and field observations.
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Sherwood, John E., Jim M. Bowler, Stephen P. Carey, John Hellstrom, Ian J. McNiven, Colin V. Murray-Wallace, John R. Prescott, et al. "The Moyjil site, south-west Victoria, Australia: chronology." Proceedings of the Royal Society of Victoria 130, no. 2 (2018): 32. http://dx.doi.org/10.1071/rs18005.

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An unusual shell deposit at Moyjil (Point Ritchie), Warrnambool, in western Victoria, has previously been dated at 67±10 ka and has features suggesting a human origin. If human, the site would be one of Australia’s oldest, justifying a redetermination of age using amino acid racemisation (AAR) dating of Lunella undulata (syn. Turbo undulatus) opercula (the dominant shellfish present) and optically stimulated luminescence (OSL) of the host calcarenite. AAR dating of the shell bed and four Last Interglacial (LIG) beach deposits at Moyjil and Goose Lagoon, 30 km to the west, confirmed a LIG age. OSL analysis of the host sand revealed a complex mixing history, with a significant fraction (47%) of grains giving an early LIG age (120–125 ka) using a three-component mixing model. Shell deposition following the LIG sea-level maximum at 120–125 ka is consistent with stratigraphic evidence. A sand layer immediately below the shell deposit gave an age of ~240 ka (i.e. MIS 7) and appears to have been a source of older sand incorporated into the shell deposit. Younger ages (~60–80 ka) are due to bioturbation before calcrete finally sealed the deposit. Uranium/thorium methods were not applicable to L. undulata opercula or an otolith of the fish Argyrosomus hololepidotus because they failed to act as closed systems. A U–Th age of 103 ka for a calcrete sheet within the 240 ka sand indicates a later period of carbonate deposition. Calcium carbonate dripstone from a LIG wave-cut notch gave a U–Th age of 11–14 ka suggesting sediment cover created a cave-like environment at the notch at this time. The three dating techniques have collectively built a chronology spanning the periods before and after deposition of the shell bed, which occurred just after the LIG sea-level maximum (120–125 ka).
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41

Duffield, Seonaid, Jennifer Walkus, Elroy White, Iain McKechnie, Quentin Mackie, and Duncan McLaren. "Documenting 6,000 Years of Indigenous Fisheries and Settlement as Seen through Vibracore Sampling on the Central Coast of British Columbia, Canada." American Antiquity 87, no. 1 (November 8, 2021): 168–83. http://dx.doi.org/10.1017/aaq.2021.113.

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This article highlights the utility of vibracore technology to sample deep shell midden deposits on the Central Pacific Coast of British Columbia, Canada. Analysis of six core samples and 21 radiocarbon dates revealed that the archaeological deposits extended to a depth of 544 cm below surface and that occupation began approximately 6,000 years ago, continuing into the sixteenth century AD. Zooarchaeological identification of fine screened (2 mm) sediments shows that fish constitute 99.8% of identified vertebrate fauna, with a focus on herring (Clupea pallasii), salmon (Oncorhynchus sp.), rockfish (Sebastes sp.), and greenling (Hexagrammos sp.), followed by a variety of other fish taxa utilized throughout the occupation of this site. Despite a much smaller examined volume relative to conventional excavation, vibracoring was effective in recovering deep, stratigraphically intact, and adequate samples of zooarchaeological fisheries data as well as a considerable number of stone, bone, and shell artifacts (an estimated 550 artifacts per cubic meter of cultural sediments). These results show a persistent and sustainable ancient fishery through six millennia until the contact period. The field and laboratory methods described are especially conducive to sampling large and deep shell midden deposits repetitively.
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42

Parker, Wesley G., Yurena Yanes, Eduardo Mesa Hernández, Juan Carlos Hernández Marrero, Jorge Pais, and Donna Surge. "Scale of time-averaging in archaeological shell middens from the Canary Islands." Holocene 30, no. 2 (November 5, 2019): 258–71. http://dx.doi.org/10.1177/0959683619883020.

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Characterizing the degree of disturbance in archaeological deposits is critically important for archaeologists assessing foraging strategies, environmental conditions, or behavior patterns of ancient human groups. Qualitative techniques (e.g. micromorphology analysis) have previously been applied to assess the degree of disturbance (age-mixing) in archaeological sites; however, quantitative dating of material in the sites provides a more robust assessment of potential age-mixing. Unfortunately, because of budget constraints, archaeologists are frequently forced to rely on few quantitative age dates for an assemblage, thus obfuscating the signal of age-mixing of the deposit. The development of an affordable and rapid carbonate-target accelerator mass spectrometry (AMS) radiocarbon (14C) dating method provides a cost-effective way to retrieve more quantitative dates from carbonate material in archaeological assemblages to assess the degree of age-mixing in the deposit. This study tests this new technique and dates numerous harvested marine limpet shells from archaeological sites in the Canary Islands to determine whether there is multidecadal to multicentennial age-mixing. A total of 58 shells retrieved from six sites and three islands yielded uncalibrated radiocarbon ages ranging from 2265 ± 40 to 765 ± 35 BP, coinciding with the time of prehistoric human occupation in these islands. While most shells from the same stratum showed statistically equivalent ages, in some cases we detected age ranges that exceeded the imprecisions from analytical errors. This investigation is one of the first to quantitatively illustrate that shells retrieved from depth intervals without evident stratigraphic disturbance do not always contain contemporaneous remains and, therefore, dating each specimen is valuable for developing further paleoclimatic and paleoanthropological inferences. This study presents the first report of carbonate-target 14C ages from archaeological shell middens, and suggests that this novel radiocarbon methodology can be applied to these sites, thus allowing the generation of a more comprehensive chronology.
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43

Shepherd, SA, M. Avalos-Borja, and MO Quintanilla. "Toward a chronology of Haliotis fulgens, with a review of abalone shell microstructure." Marine and Freshwater Research 46, no. 3 (1995): 607. http://dx.doi.org/10.1071/mf9950607.

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The microstructure of the shell of the abalone Haliotis fulgens consists of alternate layers of aragonite and prismatic calcium with darker organic matrix (conchiolin) that are visible as rings when the shell is ground down at the spire. This abalone deposits about four prismatic layers in the first year and three layers each year thereafter at the site studied. Prismatic layers are laid down in about April, August and November, corresponding with sea temperature minima and maxima and with the spawning season. After about 3 years of age, prismatic layers at the spire of the shell begin to be lost through erosion of the outer layers of the shell. The first prismatic layers deposited are 5-10 �m across, and later layers successively increase in thickness to a maximum of about 80 �m. This property is used to estimate the rate of erosion of layers, which is about one per annum. When the rate of deposition and the rate of erosion are known for a locality, an estimate of the true age can be made. The findings are considered in relation to the microstructure of the abalone shell.
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44

Kluiving, S. J., L. R. Bartek, and F. M. van der Wateren. "Multi-scale analyses of subglacial and glaciomarine deposits from the Ross Sea continental shelf, Antarctica." Annals of Glaciology 28 (1999): 90–96. http://dx.doi.org/10.3189/172756499781822039.

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AbstractPiston cores collected from the Ross Sea continental shelf, Antarctica, were studied as part of a multi-scale analysis of glacial and glaciomarine stratigraphy and sedimentology. The objective of these analyses was to differentiate glaciomarine sediments from subglacially deformed tills. Results from analyses of microstructures, lithofacies and seafloor morphology indicate that glaciomarine and subglacially deformed sediments can be clearly distinguished and further characterized by variations in textural parameters. Overcompaction, as well as presence of stratification in sediments, are not considered critical criteria for distinguishing subglacial from glaciomarine deposits. Trough-shaped morphologies and fluted terrain strongly correlate with S-C and S-C-C- type shear-zone microstructures and indicate that subglacial deformation is an important process in these areas, confirming the presence of grounded ice on the shelf during formation of these landforms and deposits. Flat, smooth topographies, as well as (low-angle) slope environments, correspond to microfabrics which lack microscopic shear-zone geometries and contain dropstones, angular-sediment clasts, large-shell fragments and slight sorting in sandy layers, which imply ice-shelf or open-water conditions present during deposition.
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45

Ajayan, P. M., Ph Redlich, and M. Rühle. "Balance of graphite deposition and multishell carbon nanotube growth in the carbon arc discharge." Journal of Materials Research 12, no. 1 (January 1997): 244–52. http://dx.doi.org/10.1557/jmr.1997.0032.

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Except for atomistic models of individual carbon nanotube growth, there is still no precise understanding of the large scale deposition of carbon during the arc discharge. We study the microstructure of cathode deposits in detail using scanning electron microscopy, focusing on two distinct regimes found in the deposits having different large scale morphology. The shell grown circumferentially consists of extended graphite layers with preferred orientation, and the structure reveals close similarity to pyrolitic graphite. The core region is a porous assembly of nanotubes and nanoparticles. We conclude that closed nanostructures self-assemble from a dense carbon vapor, whereas pyrographitic shell grows by continuous deposition on exposed substrates.
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46

Lozouet, Pierre. "First record of the Caribbean genus Cittarium (Mollusca: Gastropoda: Trochidae) from the Oligocene of Europe and its paleobiogeographic implications." Journal of Paleontology 76, no. 4 (July 2002): 767–70. http://dx.doi.org/10.1017/s0022336000042037.

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The West Indian Top-shell, Cittarium pica (Linnaeus, 1758), is a very classic and common species of the Caribbean faunal province. Until now the only known fossil occurrence of Cittarium pica, and of the genus Cittarium, is from Pleistocene deposits restricted to the Caribbean province (Clench and Abbott, 1943). Despite the turbiniform shell, the monotypic genus Cittarium belongs to the family Trochidae and was assigned to the tribe Gibbilini Stoliczka, 1868 by Hickman and McLean (1990). This paper reports a new species of Cittarium and the only record outside the Caribbean province. More than twenty million years separate the single modern species of Cittarium and the new fossil species. All material collected is deposited in Museum national d'Histoire Naturelle, Paris (MNHN).
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47

Martias, Irsyad. "MODEL TRANSFORMASI SAMPAH CANGKANG KERANG DI PERMUKIMAN KAWASAN PESISIR WATUKARUNG, PACITAN: STUDI ETNOARKEOLOGI." Berkala Arkeologi 32, no. 1 (May 31, 2012): 65–82. http://dx.doi.org/10.30883/jba.v32i1.48.

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Ecofact is a key for investigating mode of adaptation. Ecofact that commonly found on archaeological sites especially on inhabited caves were shell deposits. Fundamentally, the formation of archaeological record was resulted from behavioral processes and transformational processes. However, the problem is that we can’t observe them, because those aspects had occurred in past time. Etnoarchaeological study can be used to solve those problems. Ethnoarchaeology studies have given contribution to interpret various aspects of human life of the past, starting from issues related to the technological and tools systems, subsistence, social systems, and processes of transformation. Therefore, this ethnoarchaeological research investigates behavioral system of coastal community who has collected, consumed, and discarded sea shells. The result of this research can be used as a model from formation processes of sea shell ecofact.
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48

Cannon, Aubrey. "Settlement and Sea-Levels on the Central Coast of British Columbia: Evidence from Shell Midden Cores." American Antiquity 65, no. 1 (January 2000): 67–77. http://dx.doi.org/10.2307/2694808.

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AbstractCoring of shell-midden sites provides a regional chronology of site settlement in the Namu vicinity on the central coast of British Columbia. Coring proved an accurate and cost-effective alternative to traditional test-excavation, and its application in only two short field seasons doubled the number of sites tested in this region. The dating of basal cultural deposits from the cores shows initial occupation of sites ranging from 10,000 to 800 B.P. These dates exhibit a strong linear relationship with the current elevation of deposits above average high tide, suggesting that the settlement history of known shell-midden sites in this region is strongly linked to gradual long-term decline in relative sea levels.
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49

Davis, Dylan S., Robert J. DiNapoli, Matthew C. Sanger, and Carl P. Lipo. "The Integration of Lidar and Legacy Datasets Provides Improved Explanations for the Spatial Patterning of Shell Rings in the American Southeast." Advances in Archaeological Practice 8, no. 4 (June 30, 2020): 361–75. http://dx.doi.org/10.1017/aap.2020.18.

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ABSTRACTArchaeologists have struggled to combine remotely sensed datasets with preexisting information for landscape-level analyses. In the American Southeast, for example, analyses of lidar data using automated feature extraction algorithms have led to the identification of over 40 potential new pre-European-contact Native American shell ring deposits in Beaufort County, South Carolina. Such datasets are vital for understanding settlement distributions, yet a comprehensive assessment requires remotely sensed and previously surveyed archaeological data. Here, we use legacy data and airborne lidar-derived information to conduct a series of point pattern analyses using spatial models that we designed to assess the factors that best explain the location of shell rings. The results reveal that ring deposit locations are highly clustered and best explained through a combination of environmental conditions such as distance to water and elevation as well as social factors.
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50

Majima, Ryuichi. "Life positions of fossil naticid opercula (Mollusca: Gastropoda)." Journal of Paleontology 61, no. 1 (January 1987): 62–65. http://dx.doi.org/10.1017/s0022336000028201.

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Two life positions of fossil naticid opercula are recognized in Pliocene deposits of Hokkaido, northern Japan. In one position, the operculum seals the aperture. In the other position, the operculum is pressed against the shell base adjacent to the aperture. The death position of the head-foot mass can be reconstructed from the two opercular positions, which coincide, respectively, to naticids that died with the head-foot mass retracted into the shell, and those that died with it entirely extended from the shell.
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