John C. Kraft

Sedimentary Facies Patterns and Geologic History of a Holocene Marine Transgression

Studies of Holocene sediments in coastal Delaware show complex sediment distribution patterns resulting from lateral and vertical movement of successive environments of deposition over a Pleistocene unconformity. These sediments are infilling a drowned topography with a local relief of 70 ft and possibly up to 125 ft eroded on highly variable Pleistocene sediments. Identification of the Pleistocene surface remains a problem. However, it may be recognizable at the unconformity as a soil zone or intermixture of firm marsh clay-silts with Pleistocene sands, as well as on the basis of radiocarbon dates. Larger depositional features forming around eroding Pleistocene headlands and infilling the estuaries include characteristic shoreline environments, such as spits, dunes, baymouth barriers, an intermeshing network of tidal deltas, nearshore marine erosional-depositional sands and gravels, and lagoons or estuaries with fringing Spartina, Distichlis, and Phragmites marshes, which form the westernmost edge of the transgressive units. The thickness and areal extent of the sedimentary bodies are to a large degree controlled by the morphology of the Pleistocene unconformity. A large portion of the Holocene sedimentary units is being eroded by the transgressing Atlantic Ocean. Cores of sediment under the shallow lagoons, such as Rehoboth, Indian River, and Assawoman Bays, and in the fringing marsh environment, show that the depositional units are thin, highly irregular in areal extent, extremely variable in thickness, and difficult to project. Sedimentary processes active in the shallow bays include shoreline marsh erosion and the formation of thin, possibly ephemeral, beach-dune washover complexes consisting of clean, well-sorted sand, with typical beach and washover sedimentary structures. These wash-over beaches are an anomaly completely surrounded by Spartina marshes on the landward side and extremely muddy sands grading into dark gray lagoonal muds on the bay side. It appears that distinctive sedimentary structures and sediment size-sorting relationships, such as those that characterize the larger, more common sedimentary units of the coastal area, may be formed in miniature at the very thin edge of transgression and may lead to considerable confusion in the interpretation of sediments of this type in the geologic record.

Influence of antecedent geology on stratigraphic preservation potential and evolution of Delaware's barrier systems

Electric shaver of reciprocal vibration type having improved vibration member for converting rotary motion of motor into reciprocal vibrating motion of inner cutter is provided. The member comprises an integral body of a driving plate part to be coupled on one side to the inner cutter, leg parts respectively extended from each end in directions of the reciprocal vibrating motion of the plate part and flexible only in said directions, a mounting base part coupled to extended ends of the leg parts for mounting the member to stationary part in shaver housing, and an arm-shaped connecting part extended from the other side of the plate part for directly connecting it to eccentric cam of the motor at free end of the connecting part and having a flexibility in directions perpendicular to the reciprocal vibrating directions of the plate part. Components of the rotary motion of the eccentric cam directly transmitted to the connecting part of the vibration member in said perpendicular directions are absorbed by the flexibility of the connecting part, whereby the driving plate part is vibrated only in the reciprocal vibrating directions as supported by the leg parts being flexible only in such directions.

Preservation potential of transgressive coastal lithosomes on the U.S. Atlantic shelf

Abstract Migration of coastal lithosomes across the continental shelf is a response to the latest Quaternary rise in sea level. Variable fractions of the transgressive sequence may be preserved, depending on pre-existing topography, depth of erosion, wave energy, sediment supply, erosion resistance, tidal range, and rate of relative sea-level change. Materials at greater depth in the stratigraphic column are more likely to be preserved. Sediment samples, seismic profiles, and bathymetric observations, indicate better preservation of shoreline elements on the outer shelf and more reworking on the inner shelf. This is hypothesized to be due primarily to the rate of sea-level rise. A relative sea-level curve for Delaware, obtained from radiocarbon dates on basal peats, rises smoothly from 25 m below present sea level 10,000 years B.P. The rate of rise decreases with time. Sea-level rise resulted in rates of coastal retreat of 20 m/yr 10,000 years B.P., 5 m/yr 5000 years B.P., and 1.5 m/yr at present. The long-term average rate of coastal retreat throughout the Holocene was 10 m/yr. In a conceptual model of constant volume of net erosion per unit length of coast, smaller depths of erosion are envisioned during the period of rapid coastal retreat early in the transgression, allowing a greater preservation potential. During the present slower rate of sea-level rise and coastal retreat, depths of erosion are greater, averaging 10 m off Delaware. In this situation there is a decreased potential for preservation of the coastal environmental lithosomes in a continuing transgression. Changes in factors such as wave climate, sediment supply, tidal range, and tectonics affect this simple model.

Holocene Relative Sea-Level Changes and Coastal Stratigraphic Units on the Northwest Flank of the Baltimore Canyon Trough Geosyncline

ABSTRACT A new local curve of relative sea-level change for the Delaware coastal area is based on 88 radiocarbon dates. The curve is smooth with relatively narrow potential limits of variation in amplitude. It has a somewhat steeper slope than published eustatic sea-level curves and other local relative sea-level curves. Holocene radiocarbon isochrons in Delaware marsh sections are horizontal. Interpretations strongly support the concept that Holocene sea level rose slowly and continuously relative to the Delaware coast; the favored hypothesis is that eustatic rise of sea level was responsible. No seaward tilting is indicated for the Delaware segment of the Atlantic coastal plain or inner shelf. However, radiocarbon-died shallow-water samples of comparable age suggest a strong seaward tilt of the outer continental shelf. The outer shelf over the Baltimore Canyon trough geosyncline has subsided approximately 40 m in the last 10,000 years.

Harbor areas at ancient Troy: Sedimentology and geomorphology complement Homer's Iliad

For at least two thousand years scholars have debated the location of Troy and the events and geographic features described in Homers Iliad . Geologic evidence is used to present a series of maps of the Trojan plain that show the geomorphic changes over the past six millennia. The geologic evidence correlates very well with the relevant Homeric geography.

Paleogeographic Reconstructions of Coastal Aegean Archaeological Sites

Many studies have been made of ancient Greek topography, some of the more recent ones based on modern techniques. However, most still ignore the subsurface dimension of coastal and other environments and hence fail to fully explain coastal and alluvial-colluvial processes, rates of change of geomorphology, and the effects of coastal change on humans. In this article subsurface geological analyses have been used to elucidate paleogeographic coastal settings of major archaeological sites around the Aegean Sea. Similar approaches could be applied in the Middle and Far East and elsewhere in the Mediterranean.

Holocene evolution of an estuarine coast and tidal wetlands

Modern facies-distribution patterns, extensive core data, and chronostratigraphic cross sections provide a detailed history of Holocene inundation within the Delaware Bay estuary and sedimentation in adjacent coastal environments. Flooding of the estuary occurred with rising sea level as the shoreline retreated northwest along a path determined by the pre-transgression topography. Simultaneous migration of an estuarine turbidity maximum depocenter provided the bulk of fine sediments which form the coastal Holocene section of the estuary. Prior to 10 Ka, the ancestral bay was predominantly a tidal river, and the turbidity maximum depocenter was located southeast of the modern bay mouth. By 10 Ka, lowlands adjacent to the ancestral channel of the Delaware River were flooded, forming localized tidal wetlands, and the depocenter had initiated high rates of fine-grained sedimentation near the present bay mouth. At that time, coastal Holocene strata began to onlap the interfluve highlands. By 8 Ka, the fine-grained depocenter had migrated northwest along the main channel of the Delaware River, although the widened mouths of tributary valleys continued to be active sites of sediment accumulation. Following the passage of the fine-grained depocenter, coarse-grained sediments accumulated along the coast in response to increased wind-wave activity. During the middle Holocene, portions of the estuarine coast began to resemble modern geomorphology, and washover barrier sands and headland beach sandy gravels accumulated along the southwest shore. The late Holocene was characterized by erosional truncation and submergence of aggraded coastal lithofacies and by planation of remnant highland areas. Knowledge of the eroded Holocene section is fragmentary. At present, continued sea-level rise is accompanied by deposition of tidally transported muds in coastal environments and deposition of sandy sediments in some offshore regions. An unconformity marks the base of the developing open estuarine sequence of coarse clastic lithofacies and denotes the end of coastal accumulations. Modeling of coastal-lithofacies transitions identifies specific lithofacies complexes in the Holocene stratigraphic section which were influential in the evolution of the coast. Development of the Holocene section of the estuary coast involved both constructive, or aggradational, and destructive, or erosional, phases.

Geomorphic Reconstructions in the Environs of Ancient Troy

Sea level rise, deltaic progradation, and floodplain aggradation have changed the landscape in the vicinity of ancient Troy during the past 10,000 years. With the waning of the last major world glaciation and resultant sea level rise and fluctuation, a marine embayment protruded nearly 10 kilometers south of the site of Troy at Hisarlik in the Troad of northwest Turkey. As the sea approached its present level approximately 6000 years ago, fluvial and marine deposition caused a northerly migration of the delta and floodplain of the Scamander and Simois Rivers past the site of Troy toward the present-day coast about 6 kilometers north of the site. In view of these major changes in morphology, interpretations of ancient geographies related to historical or historical-mythological settings must be changed. A number of paleogeographic maps have been reconstructed with the use of subsurface data that records the continuing landscape change since the first occupancy of the site at Troy 5000 years ago. These show that ancient Troy was located on an embayment of the sea. If the Trojan War occurred, then the axis of the battlefield and associated events must be relocated to the south and west of Troy.

Late Holocene Paleogeography of the Coastal Plain of the Gulf of Messenia, Greece, and Its Relationships to Archaeological Settings and Coastal Change

The coastal plain of the Pamisos River and five associated rivers at the head of the Gulf of Messenia in the southwestern Peloponnese includes middle through upper Holocene sedimentary-environment lithosomes of alluvial flood-plain deposits, channel sand, braided streams and deltas, bank swamps and marshes, dune fields, minor lagoons, beach-accretion ridges, and shallow-marine sediment. The areal distribution of these environments is in balance between the sediment supplied by the alluvial systems and their modification by coastal wave action. Questions remain about the importance of tectonic uplift and downwarp relative to sediment input and changes in eustatic sea level. Radiocarbon and pottery dates, drill cores, outcrops, and environmental studies have provided information for the development of a synthesis of paleogeographic change and its relationship to archaeological remains from the Neolithic period (middle Holocene) to the present. Examples include (1) a marine embayment extended into the area of the present Pamisos River flood plain near the town of Messini in middle late Holocene (Neolithic-Helladic) time, (2) rounded hills flanking the low-lying Karya River coastal plain were wave-cut cliffs in pre-Roman time, (3) the lower Karya River valley, now occupied by a braided stream, was a swampy lagoonal area, (4) major Early Helladic buildings at Akovitika were constructed along a shoreline, whereas the site is now surrounded by backswamp, and (5) the post-Roman delta–coastal plain of the Tsana River is now undergoing intense erosion. These types of paleogeographic analyses may prove of use to archaeologists in understanding the reasons for selection of habitation sites. They may also assist the modern occupants of the coastal area in coastal planning and in understanding rates and nature of coastal change at the head of the Messenian embayment.

Lateral and Vertical Facies Relations of Transgressive Barrier

Identification of transgressive barrier sequences in the stratigraphic record is important because preserved barriers are potential reservoirs of petroleum. The transgressive barrier complex on the Atlantic Coast of Delaware lies at the edge of the ongoing Holocene relative rise in sea level. The Delaware coastal zone is on the northwest flank of the subsiding Baltimore Canyon Trough geosyncline of the Atlantic continental shelf. Four major variants of a transgressive barrier complex in this area are (1) a spit-beachdune complex, (2) barrier overriding a coastal marsh, (3) beach against pre-Holocene highland, and (4) a barrier-tidal delta-lagoon system which includes a linear baymouth barrier and a lobate tidal delta. Characteristic vertical sequences in each of these var ants indicate that this barrier originated farther seaward and migrated landward to its present position. Coarse sediments overlying fine sediments, generally believed to be characteristic of regressive barriers, also are present in this transgressive example. Time lines clearly diverge and cross lithologic boundaries in both transgressive and regressive barrier sedimentary units. Hence, the transgressive or regressive nature of a preserved barrier sequence cannot be positively identified on the basis of characteristic shapes of geophysical logs or sedimentary sequences. Rather, projection of barrier trends must be based on a synthesis of barrier morphology, precise identification of elements of barrier stratigraphy, knowledge of time versus stratigraphic units and lateral and vertical s quences, and an understanding of sedimentary basin tectonics.