Foraminiferal Evidence of Late Holocene Sea-Level Change and Amerindian Site Distribution at Montague Harbour, British Columbia

Foraminiferal and sedimentological analysis of an underwater stratigraphie section from an Amerindian habitation site at Montague Harbour, British Columbia has further documented late Holocene sea level changes. It appears that part of the documented transgression was caused by tectonic subsidence of the area (Event 1 at approx. 3500 calendar years BP and Event 2 sometime before 1100 calendar years BP) and was recognized in the stratigraphie record by rapid environmental changes. The environmental changes caused by rapid shifts in water depth were recognized through sedimentological and foraminiferal evidence. The tectonic subsidence events, coupled with gentle late Holocene transgression, caused the breaching of Montague Harbour's northwestern channel. The breaching of the channel improved water circulation and increased salinity within the harbour. The salinity changes are reflected in the shift from a low salinity Cribroelphidium excavatum (Terquem, 1876) phenotype "clavata" dominated biofacies (1) at the base of the section to a higher salinity Buccella tenerrima (Bandy, 1950) and Elphidiella hannai (Cushman and Grant, 1927) dominated biofacies (2) at the top. These sea-level changes would have eventually forced local Amerindian settlements inland. The 14C dating of wood and shell, indicates that the recovery of archaeological remains of the Charles culture (ca.6500-3200 years BP) requires investigation in deeper waters.L'analyse des foraminifères et des sédiments d'une coupe stratigraphique sous-marine d'un habitat amérindien a permis d'accroître les connaissances sur les changements du niveau marin. Il semble qu'une partie de la transgression connue ait été causée par une subsidence de nature tectonique (1er épisode vers 3500 cal. BP et 2e épisode un peu avant 1100 cal. BP) qui a entraîné des changements environnementaux rapides consignés dans la stratigraphie. Les sédiments et les foraminifères ont en effet enregistré les changements rapides de la profondeur de l'eau. Les épisodes de subsidence, accompagnés par une transgression modérée à l'Holocène supérieur, ont provoqué la formation d'une brèche dans le chenal nord-ouest du Montague Harbour, qui a facilité la circulation des eaux et fait augmenter la salinité à l'intérieur du havre. Ce changement de salinité s'est manifesté par le remplacement du biofaciès (1) de faible salinité dominé par Cribroelphidium excavatum (Terquem, 1876) type « clavata », à la base de la coupe, par le biofaciès (2) de forte salinité dominé par Bucella tenerrima (Bandy, 1950) et Elphidiella hannai (Cushman et Grant, 1927) au sommet. Les changements du niveau marin ont forcé les Amérindiens à déménager vers l'intérieur. La datation au 14C sur bois et coquille montre que la récupération de vestiges archéologiques de la culture Charles (ca 6500-3200 BP) devra se faire en eaux plus profondes.Die Foraminiferen- und Sediment-Analyse eines stratigraphischen Unterwasserabschnitts von einer Indianer-Siedlung am Montague Harbour, British Columbia, hat weitere Belege ùber Meeresniveauwechsel im spàten Holozàn geliefert. Es scheint, daB ein Teil der dokumentierten Transgression durch tekton-ische Senkung des Gebiets verursacht wurde (Ereignis 1 urn circa 3500 Kalenderjahre v.u.Z. und Ereignis 2 irgendwann vor 1100 Kalenderjahren v.u.Z.) und in dem stratigraphischen Beleg durch rasche Umweltverànderungen kenntlich wurde. Die durch schnelle Wechsel der Wassertiefe verursachten Umweltverànderungen sind durch Sediment- und Foraminiferen-Belege aufgezeichnet worden. Die Episoden tektonischer Senkung verursachten zusammen mit einer sanften Transgression im spàten Holozàn die Bildung einer Bresche im nordwestlichen Kanal von Montague Harbour. Die Bresche im Kanal verbesserte die Wasserzirkulation und erhôhte den SaIzgehalt im Hafen. Die Verànderungen im Salzgehalt spiegeln sich im Wechsel von einer Biofazies (1) mit einem niedrigen Salzgehalt beherrscht von Cribroelphidium excavatum (Terquem, 1876) des Phânotypus "clavata" an der Basis des Schnittes, zu einer Biofazies (2) mit hôherem Salzgehalt, beherrscht von Bucella tenerrima (Bandy, 1950) und Elphidiella hannai (Cushman und Grant, 1927) an der Spitze. Diese Meeresniveau-Wechsel haben wohl die ôrtlichen indianischen Siedlungen gezwungen, landeinwàrts zu Ziehen. Die '4C-Datierung von HoIz und Muscheln zeigt, daB das Auffinden von archàologischen Spuren der Charles-Kultur (ca. 6500-3200 Jahre v.u.Z.) eine Suche in tieferen Wassern erfordert

Practical guidelines and recent advances in the Itrax XRF core-scanning procedure

XRF core scanning has evolved to become a standard analytical technique for the rapid assessment of elemental, density and textural variations in a wide range of sediments and other materials, with applications ranging from palaeoceanography, paleoclimatology, geology, and environmental forensics to environmental protection. In general, scanning provides rapid, non-destructive acquisition of elemental and textural variations at sub-millimetre resolution for a wide range of materials. Numerous procedural adaptations have been developed for the growing number of applications, such as analyses of unconsolidated, water-rich sediments, powdered soil samples, or resin bags. Here, practical expertise and guidance from the Itrax community, gained over 15 years, is presented that should provide insights for new and experienced users

Geomorphic and stratigraphic evidence for an unusual tsunami or storm a few centuries ago at Anegada, British Virgin Islands

© The Author(s), 2010. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Natural Hazards 63 (2012): 51-84, doi:10.1007/s11069-010-9622-6.Waters from the Atlantic Ocean washed southward across parts of Anegada, east-northeast of Puerto Rico, during a singular event a few centuries ago. The overwash, after crossing a fringing coral reef and 1.5 km of shallow subtidal flats, cut dozens of breaches through sandy beach ridges, deposited a sheet of sand and shell capped with lime mud, and created inland fields of cobbles and boulders. Most of the breaches extend tens to hundreds of meters perpendicular to a 2-km stretch of Anegada’s windward shore. Remnants of the breached ridges stand 3 m above modern sea level, and ridges seaward of the breaches rise 2.2–3.0 m high. The overwash probably exceeded those heights when cutting the breaches by overtopping and incision of the beach ridges. Much of the sand-and-shell sheet contains pink bioclastic sand that resembles, in grain size and composition, the sand of the breached ridges. This sand extends as much as 1.5 km to the south of the breached ridges. It tapers southward from a maximum thickness of 40 cm, decreases in estimated mean grain size from medium sand to very fine sand, and contains mud laminae in the south. The sand-and-shell sheet also contains mollusks—cerithid gastropods and the bivalve Anomalocardia—and angular limestone granules and pebbles. The mollusk shells and the lime-mud cap were probably derived from a marine pond that occupied much of Anegada’s interior at the time of overwash. The boulders and cobbles, nearly all composed of limestone, form fields that extend many tens of meters generally southward from limestone outcrops as much as 0.8 km from the nearest shore. Soon after the inferred overwash, the marine pond was replaced by hypersaline ponds that produce microbial mats and evaporite crusts. This environmental change, which has yet to be reversed, required restriction of a former inlet or inlets, the location of which was probably on the island’s south (lee) side. The inferred overwash may have caused restriction directly by washing sand into former inlets, or indirectly by reducing the tidal prism or supplying sand to post-overwash currents and waves. The overwash happened after A.D. 1650 if coeval with radiocarbon-dated leaves in the mud cap, and it probably happened before human settlement in the last decades of the 1700s. A prior overwash event is implied by an inland set of breaches. Hypothetically, the overwash in 1650–1800 resulted from the Antilles tsunami of 1690, the transatlantic Lisbon tsunami of 1755, a local tsunami not previously documented, or a storm whose effects exceeded those of Hurricane Donna, which was probably at category 3 as its eye passed 15 km to Anegada’s south in 1960.The work was supported in part by the Nuclear Regulatory Commission under its project N6480, a tsunami-hazard assessment for the eastern United States

Calcite raft geochemistry as a hydrological proxy for Holocene aquifer conditions in Hoyo Negro and Ich Balam (Sac Actun Cave System), Quintana Roo, Mexico

Two cores from calcite rafts deposits located in Cenote Ich Balam and Hoyo Negro were dated and analyzed for 87Sr/86Sr, δ18O, δ13C, Sr/Ca and Cl/Ca. The geochemical records show changing aquifer salinity spanning the last ∼ 8.5 cal kyrs BP and interrelationships with Holocene climate trends (wet and dry periods). During the wet mid-Holocene, the salinity of the meteoric Water Mass (WM; at 7.8–8.3 cal kyrs BP) was relatively high at 1.5–2.7 ppt and then became less saline (1.0–1.5 ppt) during the last ∼ 7000 yrs as climate became progressively drier. High salinity of the meteoric WM during the wet mid-Holocene is attributed to increased turbulent mixing between the meteoric and underlying marine WM. Increased precipitation, in terms of amount, frequency, and intensity (e.g. hurricanes) causes higher flow of meteoric water towards the coast and mixing at the halocline, a phenomenon recorded with recent instrumental monitoring of the aquifer. Conversely, during dry periods reduced precipitation and flow in the meteoric WM would result in lower salinity. Karst properties and Holocene sea-level rise also seem to have an effect on the aquifer. When the regionally extensive network of shallow cave passages (∼ 10–12 m water depth) are flooded at ∼ 8000 cal yrs BP, there is a rapid shift in salinity. This study demonstrates that calcite raft deposits can be used as paleo-environmental recorders documenting the effects of sea level and climate change on aquifer condition

Paleoindian ochre mines in the submerged caves of the Yucatán Peninsula, Quintana Roo, Mexico

Investigations in the now-submerged cave systems on the Yucatán Peninsula continue to yield evidence for human presence during the Pleistocene-Holocene transition. Skeletal remains are scattered throughout the caves of Quintana Roo, most representing individuals who died in situ. The reasons why they explored these underground environments have remained unclear. Here, we announce the discovery of the first subterranean ochre mine of Paleoindian age found in the Americas, offering compelling evidence for mining in three cave systems on the eastern Yucatán over a ~2000-year period between ~12 and 10 ka. The cave passages exhibit preserved evidence for ochre extraction pits, speleothem digging tools, shattered and piled flowstone debris, cairn navigational markers, and hearths yielding charcoal from highly resinous wood species. The sophistication and extent of the activities demonstrate a readiness to venture into the dark zones of the caves to prospect and collect what was evidently a highly valued mineral resource

The Influence of Morphology on Sinkhole Sedimentation at Little Salt Spring, Florida

Sedimentary processes are important for understanding sinkhole records of climate and sea-level change. This study examines Little Salt Spring (LSS), an hourglass-shaped sinkhole near the SW coast of Florida, to determine the influence of sinkhole morphology on sedimentation. An 8.27-m core recovered from LSS was subsampled at 2-cm intervals for particle-size, loss-on-ignition, and stable-isotope analyses (δ13C, δ15N, and C:N ratios). Nineteen radiocarbon dates provide chronology and sediment accumulation rates over the past approximately 13,500 cal. YBP. Particle size shows alternating periods of coarse and fine sediment from 6600 to 13,500 cal. YBP and coarser sediment from 0 to 6600 cal. YBP. Organic matter (OM) and carbonate content (CC) are initially low (<5%) but increase after about 10,000 cal. YBP to 60 and 15%, respectively. High C:N ratios (∼35), low δ15N (7.5‰), and low δ13C (-25‰) values were found between approximately 9000 and 13,500 cal. YBP but decreased afterward. Based on these sedimentary characteristics, sedimentation is classified into two phases. In Phase 1 (8000-13,500 cal. YBP), water level is low, with sedimentation dominated by input of allochthonous clastic sediment from surrounding areas. In Phase 2 (present-8000 cal. YBP), a higher water level and an increasingly sunlit open water area encouraged productivity, resulting in deposition of autochthonous, organic-rich sediment. Comparisons between the LSS site and an idealized model of sinkhole sedimentation forced solely by water level shows that both water level and karst basin physiography in LSS have influenced deposition

Foraminifera and testate amoebae (thecamoebians) in an anchialine cave: Surface distributions from Aktun Ha (Carwash) cave system, Mexico

Surface sediment samples from Aktun Ha (Carwash) cave system, Mexico, were analyzed for microfossils, carbonate isotopes, and organic matter content. Saline water flooded the cave during the Sangamon Interglacial highstand (124–119 kyr), hosting a marine assemblage dominated by saline foraminifera Bolivina sp. (73%) and Elphidium sp. (11‰) with a mean δ13C = 25.5‰ and a mean δ18O = 22.7‰. This assemblage was found distal to sinkholes (\u3e75 m upstream, \u3e150 m downstream) and in yellow-orange sediment (mean total organic carbon [TOC] = 3.6‰). Late Pleistocene (95-15 kyr) sea level fall reestablished vadose conditions in the cave, allowing for localized speleothem (flowstone) to seal in the marine assemblage. Holocene sea level rise completely reflooded the cave with freshwater by 6.5 kyr, providing a suitable habitat for a freshwater assemblage of living testate amoebae Centropyxis aculeata (~38‰), Arcella vulgaris (~10‰), and the foraminifer Ammonia tepida var. juvenile (~35‰), with a mean δ13C = 210.8‰ and a mean δ18O = 24.9‰ on the ostracod Cytheridella ilosvayi. This assemblage was found proximal to sinkholes (\u3c75 m upstream, \u3c150 m downstream) and in black to brown sediment (mean TOC = 17.5‰). Foraminifera and testate amoebae colonize aquatic cave environments, respond to physicochemical conditions in the cave similarly to other coastal settings, and thereby provide promise for the application of protists as proxies in flooded caves

Low-frequency storminess signal at Bermuda linked to cooling events in the North Atlantic region

Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 30 (2015): 52–76, doi:10.1002/2014PA002662.North Atlantic climate archives provide evidence for increased storm activity during the Little Ice Age (150 to 600 calibrated years (cal years) B.P.) and centered at 1700 and 3000 cal years B.P., typically in centennial-scale sedimentary records. Meteorological (tropical versus extratropical storms) and climate forcings of this signal remain poorly understood, although variability in the North Atlantic Oscillation (NAO) or Atlantic Meridional Overturning Circulation (AMOC) are frequently hypothesized to be involved. Here we present records of late Holocene storminess and coastal temperature change from a Bermudian submarine cave that is hydrographically circulated with the coastal ocean. Thermal variability in the cave is documented by stable oxygen isotope values of cave benthic foraminifera, which document a close linkage between regional temperature change and NAO phasing during the late Holocene. However, erosion of terrestrial sediment into the submarine cave provides a “storminess signal” that correlates with higher-latitude storminess archives and broader North Atlantic cooling events. Understanding the driver of this storminess signal will require higher-resolution storm records to disentangle the contribution of tropical versus extratropical cyclones and a better understanding of cyclone activity during hemispheric cooling periods. Most importantly, however, the signal in Bermuda appears more closely correlated with proxy-based evidence for subtle AMOC reductions than NAO phasing.Field support for this project was provided by the Williams and Nolan Families and the Walsingham Land Trust, and data support from the Bermuda Weather Service and R. Johnson (BIOS). Awards from the National Sciences and Engineering Research Council of Canada (Alexander Graham Bell CGS and Post-Doctoral Fellowship) and the inaugural Johanna M. Resig Fellowship from the Cushman Foundation for Foraminiferal Research provided primary research support, along with research grants from the Geologic Society of America, Cave Research Foundation, the Bermuda Zoological Society, WHOI Ocean and Climate Change Institute, and in part funded by the NSF Division of Ocean Sciences (Award #1519557).2015-08-1

Using marine deposits to understand terrestrial human environments: 6000-year old hyperpycnal flash-flood events and their implications

Offshore sedimentary deposits preserved in submarine canyons in southern Calabria, Italy, provide evidence for mid-Holocene (ca. 6000 BP) erosion and the transport of organic-rich floodplain sediments by flash-flood (hyperpycnal) flows from the San Pasquale River. Marine geophysical surveys (bathymetry, side-scan sonar) and diver reconnaissance revealed an unusual offshore peat deposit containing plant macrofossils representing local habitats, potentially reflecting human modified landscapes. The 20–30 cm thick organic deposit included a large tree trunk, well-preserved seeds, leaves, sticks and other delicate organics. Textural and microfossil (foraminifera) analysis of associated sediments (sands and muds) indicate that these deposits resulted from hyperpycnal flood events that were deposited as sediment gravity flows within gullies on the canyon margins. Whilst the value of studying in situ submerged prehistoric landscapes is well documented, we demonstrate that reworked floodplain deposits preserved in offshore environments can provide useful palaeoenvironmental information that may not be preserved in terrestrial settings. The botanic archive preserved in submarine flood deposits at San Pasquale affords a unique insight into the local environment in which people lived during the Final Neolithic.</p