Joseph I. Boyce

Architectural element analysis applied to glacial deposits: Internal geometry of a late Pleistocene till sheet, Ontario, Canada

Deposits left by continental ice sheets are characterized by sedimentological complexity and stratigraphic heterogeneity, but stratigraphic descriptions of such deposits, and resulting “first-generation” facies models, are still based primarily on one- or two-dimensional borehole or outcrop data. Reconstruction of depositional environments, hydrogeological investigations of Pleistocene glacial deposits, and hydrocarbon exploration in pre-Pleistocene glaciated basin fills require a more detailed understanding of the form and heterogeneity of lithofacies sequences in three dimensions. Architectural element analysis is used widely by sedimentologists for categorizing internal stratigraphic heterogeneity in sandstones, particularly those of fluvial origin. This paper demonstrates the first application of architectural element analysis to glacial deposits such as tills. Outcrop, borehole, and a broad range of subsurface geophysical data were collected from a thick (60 m) till sheet present across an 80 km 2 study area near Toronto, Canada. The till sheet is not homogeneous, but is composed of three distinct architectural elements and associated lithofacies, viz, diamict elements, interbeds of subglaciofluvial sediments, and glaciotectonically deformed zones. Application of architectural element analysis to these subglacial strata provides insights into the origin of drumlin bedforms and subglacial processes below the Laurentide Ice Sheet and creates a framework for understanding ground-water and contaminant movement in underlying aquifers.

The tsunami of 13 December A.D. 115 and the destruction of Herod the Great's harbor at Caesarea Maritima, Israel

Underwater geoarchaeological excavations on the shallow shelf (∼10 m depth) at Caesarea, Israel, have documented a tsunami that struck and damaged the ancient harbor at Caesarea. Talmudic sources record a tsunami that struck on 13 December A.D. 115, impacting Caesarea and Yavne. The tsunami was probably triggered by an earthquake that destroyed Antioch, and was generated somewhere on the Cyprian Arc fault system. The tsunami deposit consisted of an ∼0.5-m-thick bed of reverse-graded shells, coarse sand, pebbles, and pottery deposited over a large area outside of the harbor. The lower portion of the deposit was composed of angular shell fragments, and the upper portion of whole convex-up Glycymeris spp. shells. The sequence records tsunami downcutting (∼1 m) into shelf sands, with the return flow sorting and depositing angular shell fragments followed by oriented whole shells. Radiocarbon dating of articulated Glycymeris shells, and optically stimulated luminescence (OSL) dates, constrain the age of the deposit to between the first century B.C. and the second century A.D., and point to the tsunami of A.D. 115 as the most likely candidate for the event, and the probable cause of the harbor destruction.

Identifying tsunami deposits using bivalve shell taphonomy

On 28 November 1945, in the Makran trench off Pakistan, a large earthquake (8.1 Mw) produced a tsunami that struck the coast of Oman and left a taphonomically distinct shell bed in Sur Lagoon. The shell bed was thick (5–25 cm) and laterally extensive, covering a >1 km2 area. The shell assemblage from the deposit contained a mean of 59% for articulated bivalves of allochthonous offshore and subtidal species (e.g., Tellina palatam ) as well as a mean of 20% for lagoonal species, indicating large-scale erosion and transport. Taphonomic traits (e.g., articulation, rounding, fragment angularity) of all bivalve material >5.6 mm were quantified for eight sample horizons, and compared with a tsunamite from Caesarea, Israel. Some of the taphonomic characteristics between the shell beds from these two different depositional settings were similar, and three tsunamigenic specific traits were identified: (1) thickness and lateral extent of the shell deposit, (2) presence of allochthonous articulated bivalves out of life position, and (3) extensive angular fragmentation. These results show that tsunamis form shell accumulations and cannot be ignored when assessing shell bed origin for the geological record. When these three traits are collectively found, a tsunamigenic origin should be considered for the shell bed.

Basement-controlled faulting of Paleozoic strata in southern Ontario, Canada: new evidence from geophysical lineament mapping

Abstract Basement fault reactivation is now recognized as an important control on sedimentation and fault propagation in intracratonic basins. In southern Ontario, the basement consists of complexly structured mid-Proterozoic (ca. 1.2 Ga) crystalline rocks and metasedimentary rocks that are overlain by up to 1500 m of Paleozoic sedimentary strata. Reactivation of basement structures is suspected to control the location of Paleozoic fault and fracture systems, but evaluation has been hindered by a limited understanding of the regional structural characteristics of the buried basement. New aeromagnetic- and gravimetric-lineament mapping presented in this paper better resolves the location of basement discontinuities and provides further evidence for basement controls on the distribution of Paleozoic fault and fracture systems. Lineament mapping was facilitated by reprocessing and digital image enhancement (micro-levelling, regional residual separation, derivative filtering) of existing regional gravity and aeromagnetic datasets. Reprocessed images identify new details of the structural fabric of the basement below southern Ontario and delineate several previously unrecognized aeromagnetic and gravity lineaments and linear zones. Linear zones parallel the projected trends of mid-Proterozoic terrane boundaries identified by field mapping on the exposed shield to the north of the study area, and are interpreted as zones of shearing and basement faulting. Mapped aeromagnetic and gravity lineaments show similar trends to Paleozoic faults and fracture networks and broad zones of seismicity in southern Ontario. These new data support an ‘inheritance model’ for Paleozoic faulting, involving repeated reactivation and upward propagation of basement faults and fractures into overlying cover strata.

Acoustic architecture of glaciolacustrine sediments deformed during zonal stagnation of the Laurentide Ice Sheet; Mazinaw Lake, Ontario, Canada

Abstract In North America, the last (Laurentide) Ice Sheet retreated from much of the Canadian Shield by ‘zonal stagnation’. Masses of dead ice, severed from the main ice sheet by emerging bedrock highs, downwasted in situ within valleys and lake basins and were commonly buried by sediment. Consequently, the flat sediment floors of many valleys and lakes are now pitted by steep-sided, enclosed depressions (kettle basins) that record the melt of stagnant ice blocks and collapse of sediment. At Mazinaw Lake in eastern Ontario, Canada, high-resolution seismic reflection, magnetic and bathymetric surveys, integrated with onland outcrop and hammer seismic investigations, were conducted to identify the types of structural disturbance associated with the formation of kettle basins in glaciolacustrine sediments. Basins formed as a result of ice blocks being trapped within a regionally extensive proglacial lake (Glacial Lake Iroquois ∼12,500 to 11,400 years BP) that flooded eastern Ontario during deglaciation. Kettles occur within a thick (>30 m) succession of parallel, high-frequency acoustic facies consisting of rhythmically laminated (varved?) Iroquois silty-clays. Iroquois strata underlying and surrounding kettle basins show large-scale normal faults, fractures, rotational failures and incoherent chaotically bedded sediment formed by slumping and collapse. Mazinaw Lake lies along part of the Ottawa Graben and while neotectonic earthquake activity cannot be entirely dismissed, deformation is most likely to have occurred as a result of the rapid melt of buried ice blocks. Seismic data do not fully penetrate the entire basin sediment fill but the structure and topography of bedrock can be inferred from magnetometer data. The location and shape of buried ice masses was closely controlled by the graben-like form of the underlying bedrock surface.

Evidence for Holocene Marine Transgression and Shoreline Progradation Due to Barrier Development in Iskele, Bay of Izmir, Turkey

Abstract This study addresses the paleogeographic coastal evolution of the coastal plain in the environs of Iskele, Turkey. Eight sediment cores were collected along a north–south and east–west transect and analyzed to determine whether the coastal environment had changed in the recent past. The results illustrate that the coastal environment consisted of a transgressive systems tract, ending approximately 6000 BP and represented by marine transgression, flooding of incised river channels, and marsh development, followed by a high stand systems tract. Five major environmental facies were identified: terrestrial, wetland, lagoon, foreshore, and upper shoreface. The high stand systems tract was characterized by the development of a beach-barrier consecutive series of longshore transport-derived sandbars. These sandbars contributed to the creation and eventual isolation and terrestrial infilling of nearshore lagoons and wetlands. Sea-level indicators indicate rapid sea-level rise reaching a peak approximately 6000 YBP, followed by deceleration of sea-level rise and resulting shoreline progradation. The construction of a causeway connecting Karantina Island to the mainland approximately 2400 years ago has accelerated the process of progradation east of the causeway by decreasing the wave energy. Sediment that would have previously been transported further east is now deposited in the zone immediately east of the causeway.

Quartz flakes in lakes: Microdebitage evidence for submerged Great Lakes prehistoric (Late Paleoindian–Early Archaic) tool-making sites

Exploration for submerged prehistoric archaeological sites in the Great Lakes (North America) is a major challenge due to difficulties in locating scant cultural artifacts in lake-bottom sediments. Stone tool microfragments (microdebitage, 10 6 per tool) and more dispersed around tool-making sites, but have not been identified previously in an underwater context. To evaluate their use as a submerged site indicator, microdebitage analysis was conducted on five lake sediment cores from a shallow lagoon adjacent to a long-occupied prehistoric site (McIntyre site, Rice Lake, Ontario). We identified 155 microdebitage fragments within a distinctive muddy peat horizon (2–2.5 m depth) using light microscopy and scanning electron microscopy methods. The microdebitage consisted of angular to very angular quartz fragments (400–1000 μm) with characteristic conchoidal fractures and flake scars produced by mechanical percussion. The microdebitage horizon had a distinctive bimodal particle size peak and contained a low-diversity soil thecamoebian assemblage ( Phryaginella , Bullinularia sp.) indicative of a wetland environment that formed during an early Holocene shoreline transgression. Accelerator mass spectrometry 14 C dating of wood fragments yielded ages of 9470–8760 ± 50 yr B.P. (11,070–9560 cal [calibrated] yr B.P.), indicating a Late Paleoindian–Early Archaic age for the deposit. Results demonstrate that coring and microdebitage analysis are effective tools in the search for underwater prehistoric sites and can be employed more broadly in exploration of submerged landscapes in the Great Lakes basins.

High-resolution magnetic mapping of contaminated sediments in urbanized environments

The remediation of contaminated sediments in industrialized harbors and waterways is a growing environmental concern in North America. More than 100 marine ports and 42 inland harbors in the Great Lakes basins are currently listed by U.S. and Canadian regulatory agencies as having severe habitat and water-quality impairments due to bottom-sediment toxicity. Current approaches to remediation include sediment dredging and removal, capping with clean sediment, and in-situ treatment with oxidants.

Enhancement of magnetic data by logarithmic transformation

A common problem encountered when displaying magnetic data as a color image is that small amplitude variations, which may have geologic significance, might be lost due to the large dynamic range of the whole data set. The human eye is capable of distinguishing only a limited range of variations within the color spectrum. Enhancement of the low-amplitude features is usually achieved through some type of image transform.

Quantitative, nondestructive estimates of coarse root biomass in a temperate pine forest using 3‐D ground‐penetrating radar (GPR)

Coarse root biomass was estimated in a temperate pine forest using high-resolution (1-GHz) 3-D ground-penetrating radar (GPR). GPR survey grids were acquired across a 400-m2 area with varying line spacing (12.5 and 25 cm). Root volume and biomass were estimated directly from the 3-D radar volume using isometric surfaces calculated with the marching cubes algorithm. Empirical relations between GPR reflection amplitude and root diameter were determined for 14 root segments (0.1-10 cm diameter) reburied in a 6-m2 experimental test plot and surveyed at 5-25 cm line spacing under dry and wet soil conditions. Reburied roots >1.4 cm diameter were detectable as continuous root structures with 5 cm line separation. Reflection amplitudes were strongly controlled by soil moisture and decreased by ~40% with a two-fold increase in soil moisture. GPR line intervals of 12.5 and 25 cm produced discontinuous mapping of roots and GPR coarse root biomass estimates (0.92 kgCm-2) were lower than those obtained previously with a site-specific allometric equation due to non-detection of vertical roots and roots < 1.5 cm diameter. The results show that coarse root volume and biomass can be estimated directly from interpolated 3-D GPR volumes using a marching cubes approach but mapping of roots as continuous structures requires high inline sampling and line density (<5 cm). The results demonstrate that 3-D GPR is viable approach for estimating belowground carbon and for mapping tree root architecture. This methodology can be applied more broadly in other disciplines (e.g. archaeology, civil engineering) for buried structures.