Middle Holocene Time Research Articles

High-Resolution Paleoclimatic Trends for the Holocene Identified Using Magnetic Susceptibility Data from Archaeological Excavations in Caves

A proxy paleoclimatic curve has been produced for the Holocene,c.9000–3500bp, from magnetic susceptibility (MS) measurements of sediment samples collected from two dated archaeological excavation trenches in Konispol Cave, Albania. The resulting MS data provide paleoclimate estimates that are in excellent agreement with independently published paleoclimatic trends for early–middle Holocene time. Basically, MS variations are attributed to variations in climate-controlled pedogenesis and the production of magnetic mineral phases, including maghemite, outside the cave. These soils are then washed, blown or tracked into the cave where they accumulate, creating the MS changes observed in the samples recovered. Low MS magnitudes indicate times of cooler/drier climate resulting from reduced pedogenesis, while warmer/wetter times yield higher pedogenetic rates and thus higher MS magnitudes. It is clear from the Konispol Cave results that some caves provide ideal, protected environments from which high-resolution, paleoclimatic records can be extracted. Composite sections from excavations within a single region can yield a relatively continuous, long-term climatic proxy that can be routinely correlated to artefacts recovered from these or other protected excavations within the same region.

Dune-dammed paleovalleys of the Nebraska Sand Hills: Intrinsic versus climatic controls on the accumulation of lake and marsh sediments

Although running water is the dominant geomorphic agent on Earth, eolian processes can gain ascendancy in regions where the climate is arid, vegetation is sparse, and abundant sand is available for transport. With climate change, the boundaries between fluvial-dominated and eolian-dominated areas may shift. Although there have been few reports in the North American literature of river systems blocked by dune sand, our work in the Nebraska Sand Hills provides evidence of multiple episodes of such blockage events. During prolonged arid intervals in latest Pleistocene and middle Holocene time, eolian dune sand blocked two large valley systems in western Nebraska. These blockages raised the water table of the High Plains aquifer as much as 25 m over an area of 7000 km2 and created over one thousand lakes. Wetlands far removed from the discharge points of the buried paleovalley system are strongly alkaline (exceeding 250 000 mg/L total dissolved solids [TDS]). Relatively fresh (280 mg/L TDS), flow-through lakes are present at the distal end of the system where the gradient of the water table is steep and the cross section of the buried valley is large. Anomalously thick marsh and lake sediments accumulated in deep paleovalleys upstream of dune dams near the southern margin of the Sand Hills. Our cores and radiocarbon dates from Blue and Crescent Lakes reveal their histories to be quite distinct from adjacent Swan Lake; these differences are best explained by multiple blockage events. Our work explains why lakes are most abundant in the driest part of the Sand Hills. It also provides another line of evidence for major dune activity in the Sand Hills region during Holocene time and shows that factors other than regional climate, specifically location, height, and hydraulic conductivity of dune dams, can control the rise and fall of the ground-water table and the chemistry of lakes.

Ages of Quaternary pluvial episodes determined by uranium-series and radiocarbon dating of lacustrine deposits of Eastern Sahara

Abstract As documented by radiocarbon dating and geoarchaeological investigations, the now hyperarid northwestern Sudan and southwestern Egypt experienced a period of greater effective moisture during early and middle Holocene time, about 10-5 ka. We have used the uranium-series technique to date lacustrine carbonates from Bir Tarfawi, Bir Sahara East, Wadi Hussein, Oyo Depression, and the Great Selima Sand Sheet localities. Results indicate five paleolakeforming episodes occurred at about 320-250, 240-190, 155-120, 90-65 and 10-5 ka. Four of these five pluvial episodes may be correlated with major interglacial stages 9, 7, 5e, and 1; the 90-65 ka episode may be correlated with substage 5c or 5a. Our results support the contention that past pluvial episodes in North Africa corresponded to the interglacial periods farther north. Ages of lacustrine carbonates from existing oases and from the sand sheet fail to indicate pluvial conditions between about 60 and 30 ka. Age results and field relationships suggest that the oldest lake- and ground-water-deposited carbonates were much more extensive than those of the younger period, and that carbonate of the latest wet periods were geographically localized within depressions and buried channels.

The volcanic, sedimentologic, and paleolimnologic history of the Crater Lake caldera floor, Oregon:Evidence for small caldera evolution

Apparent phreatic explosion craters, caldera-floor volcanic cones, and geothermal features outline a ring fracture zone along which Mount Mazama collapsed to form the Crater Lake caldera during its climactic eruption about 6,850 yr B.P. Within a few years, subaerial deposits infilled the phreatic craters and then formed a thick wedge (10-20 m) of mass flow deposits shed from caldera walls. Intense volcanic activity (phreatic explosions, subaerial flows, and hydrothermal venting) occurred during this early postcaldera stage, and a central platform of subaerial andesite flows and scoria formed on the caldera floor. Radiocarbon ages suggest that deposition of Iacustrine hemipelagic sediment began on the central platform about 150 yr after the caldera collapse. This is the minimum time to fill the lake halfway with water and cover the platform assuming present hydrologic conditions of precipitation and evaporation but with negligible leakage of lake water. Wizard Island formed during the final part of the 300-yr lake-filling period as shown by its (1) upper subaerial lava flows from 0 to -70 m below present water level and lower subaqueous lava flows from -70 to -500 m and by (2) lacustrine turbidite sand derived from Wizard Island that was deposited on the central platform about 350 yr after the caldera collapse. Pollen stratigraphy indicates that the warm and dry climate of middle Holocene time correlates with the early lake deposits. Diatom stratigraphy also suggests a more thermally stratified and phosphate-rich environment associated respectively with this climate and greater hydrothermal activity during the early lake history. Apparent coarse-grained and thick-bedded turbidites of the early lake beds were deposited throughout northwest, southwest, and eastern basins during the time that volcanic and seismic activity formed the subaqueous Wizard Island, Merriam Cone, and rhyodacite dome. The last known postcaldera volcanic activity produced a subaqueous rhyodacite ash bed and dome about 4,240 yr B.P. The late lake beds with base-of-slope aprons and thin, fine-grained basin-plain turbidites were deposited during the volcanically quiescent period of the past 4,000 yr. Deposits in Crater Lake and on similar caldera floors suggest that four stages characterize the postcaldera evolution of smaller (≤10 km in diameter) terrestrial caldera lake floors: (1) initial-stage caldera collapse forms the ring fracture zone that controls location of the main volcanic eruptive centers and sedimentary basin depocenters on the caldera floor; (2) early-stage subaerial sedimentation rapidly fills ring-fracture depressions and constructs basin-floor debris fans from calderawall landslides; (3) first-stage subaqueous sedimentation deposits thick flat-lying lake turbidites throughout basins, while a thin blanket of hemipelagic sediment covers volcanic edifices that continue to form concurrently with lake sedimentation; and (4) second-stage subaqueous sedimentation after the waning of major volcanic activity and the earlier periods of most rapid sedimentation develops small sili-ciclastic basin base-of-slope turbidite aprons and central basin plains. Renewed volcanic activity or lake destruction could cause part or all of the cycle to repeat.

Clastic sequences developed during late Quaternary glacio-eustatic sea-level fluctuations on a passive margin: Example from the inner continental shelf near Barnegat Inlet, New Jersey

Analysis of 100 km of seismic reflection (GEOPULSE) profiles from a 47-km 2 grid on the New Jersey low-mesotidal inner continental shelf near Barnegat Inlet reveals that the upper 30 m is composed of 3 unconformity-bounded units. Vibracores (1-6 m long) recovered from 12 sites contain several lithofacies, reflecting a variety of depositional environments that existed during late Quaternary glacioeustatic sea-level fluctuations on this slowly subsiding passive margin with low sediment supply. Environments include rivers during glacial and stadial lowstands of the sea, and a barrier island-lagoon complex, as well as pro-barrier ebb-tidal delta, shore-attached and -detached ridges, and below storm-wave-base shelf during interglacial or inter-stadial highstands. Following the last major interglacial (∼125 ka), sea level fell and rivers eroded a planar, seaward-dipping surface (R1) by early Wisconsinan time (∼70 ka). As sea level rose during the mid-Wisconsinan (∼55 ka), a barrier island system migrated to within 0.2-1.7 km of the modern barrier shoreline, leaving a 4- to 6-m-thick record (depositional sequence I). Maximum highstand of the mid- Wisconsinan sea level was 20 m below present. Sea level fell again during the late Wisconsinan (∼20 ka), and rivers again flowed across the exposed shelf, creating an unconformity (R2). A barrier/lagoonal system developed under rising sea level by at least early middle Holocene time, based on peats (8810 ± 170 yr B.P.) cored from -12 m. The mid-Wisconsinan (∼55 ka) barrier system was preserved under these early Holocene transgressive sediments (lower unit of depositional sequence II, lower transgressive tract). The modern barrier and inner continental shelf deposits (upper unit of depositional sequence II, upper transgressive tract) are relatively thin (average 3-4 m) pebbly sands overlying a prominent unconformity (a transgressive surface, R3) formed by marine erosion during the Holocene sea-level rise. Both the ebb-tidal delta and shore-attached linear sand ridges act as partial shields to wave and tidal- current erosion of the muddy sub-strate below R3. In the nearshore area, this shielding is creating a transgressive surface (marine unconformity) of relatively high relief (3-7 m).

Holocene history of the Bugaboo glacier, British Columbia

Sequences of tills, buried paleosols, wood, and tephra in moraines provide a fairly complete record of Holocene fluctuations of the Bugaboo glacier in British Columbia. The oldest till known to be exposed in the lateral moraines, apparently associated with an end moraine of the regionally known Crowfoot advance, is overlain by Mazama tephra, and is possibly early Holocene, but probably latest Pleistocene, in age. A paleosol incorporating the tephra and capping this till developed during early to middle Holocene time; it represents the warm and/or dry Altithermal interval. Subsequent (Neoglacial) advances deposited tills after 3.39 ka but before 3.07 ka, in the period ca. 2.5-1.9 ka, and in the period from ca. 0.9 ka to the nineteenth century. Recessional intervals are marked by paleosols and a former moraine gully, now filled. Results of the Bugaboo glacier study increase the resolution of known Neoglacial history in the Canadian Cordillera and generally demonstrate the usefulness of lateral-moraine stratigraphy.

Late Holocene Sea-Level Record in a Core from the Puget Lowland, Washington

AbstractDiatoms and lithological facies of an 8.45-m core collected from Shine swamp (47°52′20″N lat, 122°41′45″W long; about 2 m above the mean tide level) in the northern Puget Lowland reveal a rise in relative sea level during the past 6000 yr. A layer of fresh-water peat at a depth of 6.6-6.3 m (ca. 7000-5000 yr B.P.) indicates a low stand of the sea in early and middle Holocene time. About 5000 yr ago the rise in relative sea level resulted in accumulation of subtidal or lower intertidal clayey gyttja and gyttja which contain mainly marine and brackish-water diatoms (80–95%). By about 3500 yr B.P., the basin had shoaled to upper intertidal levels, and peat began to accumulate again while the sea continued its relative rise. During the period of this continuous peat growth, several alterations in fresh-water and marine/brackish-water diatom assemblages took place, indicating slight differences in the contemporaneous sea-level rise and vertical peat growth.

Holocene evolution of the northeastern corner of the Nile Delta

The constructive phase of the modern Nile Delta, as manifested in a 48-m section drilled east of the Suez Canal, commenced in very early Holocene times. Sands rich in marine fauna were deposited in the littoral zone and the shoreline was more than 20 km landward of its present-day position. Subsequently, clays and silts were dumped from the Nile distributaries and the marine faunal spectrum became very limited and brackish. Later in early and middle Holocene times the sediments deposited were rich in freshwater, delta-plain diatoms and pollen and in allochthonous fern spores from the tropics, indicating proximity of a distributary mouth. The middle part of the section (22.5-17.5 m) is very poor in faunal and floral remains; pollen grains from sabkha vegetation are abundant. The environment, which seems lagoonal and slightly hypersaline, is related to the sea regression in middle Holocene times. Euryhaline pelecypods, dating from about 3000 yr B.P., are abundant around the 8-m depth. Upward, there is an increase in pollen grains from sabkhas; the section is poor in diatoms and those present are mostly euryhaline and lagoonal. Allochthonous spores derived from the nearby Pelusiac Branch are abundant. Between 3000 and 2000 yr B.P. the constructive phase of the modern delta terminated and winnowed sands began accreting in front of the delta plain.

Significance of some geotechnical properties of continental slope and rise sediments off northeast Newfoundland

Shear strength measurements carried out on the 0–20 cm interval of continental slope and continental rise surficial sediments yielded mean values per station that ranged from 3.7 to 8.9 kPa. The factors controlling the bathymetric variation of sediment shear strength appear to be sediment texture (which is controlled locally by sediment spillover) on the upper slope, increased deposition of fines (silt- and clay-sized particles) from suspension and greater bioturbation activity on the middle slope, and bottom current sediment reworking on the base-of-slope and upper rise.Sediments deposited on the downslope side of the present presumed location of the Western Boundary Undercurrent (WBU) axis have comparatively high shear strength gradients that appear to denote the increased proportion of fine sediment deposition during early to middle Holocene time when the WBU axis may have been located further upslope than at present.

Maritime Hunter-Gatherers: Ecology and Prehistory [and Comments and Reply

In a recent discussion of prehistoric developments in coastal Peru, Osborn has drawn attention to the "uniqueness" of the Peruvian littoral in providing large amounts of nutrients to support locally high population densities and a base for the development of Peruvian civilization. This bounteous resource base is contrasted with that of other maritime environments, which are seen to be relatively unproductive. The present article takes issue with that viewpoint, arguing instead that the maritime and coastal environments occupied by humans are generally highly productive and have uniformly supported relatively dense populations of hunter-gatherers. Rather than arguing for the uniqueness of the Peruvian, Northwest Coast, or other situations where complex societies developed on a coastal base, it seems more profitable to develop a "midle-range" theory which will encompass these situations within the variability of maritime hunter-gatherers in general. To this end, I have suggested ten basic features that distinguish maritime-adapted populations (high resource biomass, high resource diversity, low resource seasonality, "unearned" resources, linear settlement patterns, sedentism, technological complexity, cooperative socioeconomic forms for resources explotation, lower dependency ratios, high population densities, and territoriality, interpopulation resource competition, and warfare). This in not an idle exercise, since without a general theory of maritime adaptation it is impossible to achieve and explanation of the origins of maritime adaptation. At minimum, such an explantion would have to encompass both the origins of maritime exploitation during the Upper Palaeolithic and the worldwide intensification of maritime exploitation, particularly shellfish collection, during middle Holocene times. Ecological factors, particularly climate and sea-level changes, offer the most parsimonious explanations for these observed worldwide trends.

Upper Quaternary peat deposits on the Atlantic inner shelf of the United States

Twenty-one upper Quaternary peat samples have been obtained from vibracores collected along the inner continental shelf of the Atlantic coast of the United States. Radiocarbon ages and pollen identifications from the peats, coupled with those from onshore borings and published data, provide additional information on the latest history of the Atlantic shelf. The radiocarbon ages cluster in two groups: early and middle Holocene time (10,000 to 5,000 B.P.) and late Pleistocene time (35,000 to 20,000 B.P.). Although ages and depths of the upper Pleistocene peats show some agreement with published graphs of changes in sea level, pollen data indicate that most of the peats formed in terrestrial environments and therefore may be unreliable as indicators of sea level. The Holocene peats were deposited in both marine and terrestrial environments. Correlation of the stratigraphic sequences in the cores containing peat with high-resolution seismic reflection profiles indicates a history of transgressive erosion on the inner shelf. Only remnants of carbonaceous sediments originally deposited in bogs, ponds, estuaries, and salt-marsh lagoons are present in the shallow subsurface on the inner shelf. These remnants, which are discontinuous and usually associated with erosional unconformities, provide evidence of regional marine planation of the shelf by the rising Holocene sea.

The Geological and Paleogeomorphological Evolution of a Spit System and Its Associated Coastal Environments: Cape Henlopen Spit, Delaware

ABSTRACT Cape Healopen is a simple spit located at the confluence of the large estuary, Delaware Bay, and the Atlantic Ocean on the northeast coast of the United States of America. Examination of surface and subsurface elements of the present and ancestral spit area and associated coastal environments over a sixty square kilometer area shows that Cape Henlopen was formerly a recurved spit building northward from an eroding Pleistocene headland. It has been possible to delineate the areal distribution of estuarine, spit, beach, nearshore-marine, dune, marsh, and lagoon environments of the spit complex from middle Holocene time to present based on data obtained from an intensive drilling program. As relative sea-level rise and coastal erosion continue, the upper portion of the stratigraphic record formed by the spit complex is being destroyed. The remainder is covered by a thin veneer of shallow marine sands and gravels. Vertical sedimentary sequences in the spit complex include regressive sequences in which coastal environments migrate over marine environments as well as transgressive sequences in which marine and barrier environments overlie lagoon and marsh environments.

On the Holocene History of Some Northern Great Basin Lagomorphs

Analysis of vertebrate faunas from archaeological sites in south-central Oregon's Fort Rock Basin supports the hypothesis that the common early Holocene jackrabbit in the northern Great Basin was Lepus townsendii , and that L. californicus did not become abundant in this area until middle Holocene times. The current range expansion of L. californicus at the expense of L. townsendii in the northern Great Basin and adjacent Plateau may, in part, represent the continuation of a process that began several thousand years ago. These faunas also document the presence of pikas ( Ochotona princeps ) in the Fort Rock Basin prior to, but not after, 7,000 years B.P. Pikas are absent from the area today; their disappearance here may have been due to the eruption of Mt. Mazama at, or just before, an episode of climatic change. These data support the argument that the distribution of boreal mammals on mountainous islands within the Great Basin can be accounted for by initial colonization followed by extinctions of geographically intermediate populations.