Joseph F. Donoghue

Marine inundated archaeological sites and paleofluvial systems: examples from a karst-controlled continental shelf setting in Apalachee Bay, Northeastern Gulf of Mexico

Underwater geoarchaeological research in Apalachee Bay, in the northeastern Gulf of Mexico off northwest Florida, has enabled the reconstruction of portions of the karst-controlled paleodrainage system, the discovery of several inundated prehistoric archaeological sites, and the exposure of sediments accumulated during the drowning of the continental shelf. Diagnostic artifacts discovered at the sites included chipped stone tools and debitage indicating Paleoindian, Early Archaic, and Middle Archaic occupation. A geoarchaeological model using terrestrial analogs was used to locate and investigate inundated sites. Methods employed include seismic profiling, vibracoring, diver tow surveys, diver collection transects, and induction dredge excavations. We document evidence for sea-level rise, related environmental succession and site formation processes for indundated prehistoric sites in the Apalachee Bay region from approximately 8000 to 6000 yr B.P.

Plotting Equation for Gaussian Percentiles and a Spreadsheet Program for Generating Probability Plots: DISCUSSION

Balsillie et al. (2002) offer an equation for creating probability graphs. These are useful because the vertical axis is scaled in such a way that a sample with a Gaussian distribution plots in a straight line. Easy, computerized production of these graphs is clearly valuable, especially but not solely in studies of grain-size distributions, and the program is very convenient, given the widespread use of Excel. Moreover, the authors’ graphics are commendably aesthetic and publishable. The authors’ method involved splitting the distribution in half, because the cumulative % axis is scaled symmetrically around the 50th percentile, and then each half was fitted to a fifth-order transcendental polynomial. They note that few statistical packages allow creation of these sorts of probability plots, because the calculations are intractable. Theirs is an impressive achievement, and it leads to a short algorithm (albeit with a complex formula). Nonetheless, their approach takes a somewhat round-about and approximate route to a fairly simple problem. Simply put, in a probability plot the horizontal axis shows the parameter under investigation (here grain size, transformed to phi), and the vertical axis is really a linearly scaled Z-score axis that is, however, gridded and labeled with the corresponding cumulative probabilities in a Gaussian population. In other words, draw an axis of Z-score values; take the cumulative percents associated with the data points on the horizontal axis; and plot the Z scores that would relate to those cumulative percents in a Gaussian population (Fig. 1). Then draw grid lines at the Z scores that match desired Gaussian cumulative probabilities, and label them with those probabilities. The values can be obtained from a Z-score table, or they may be obtained from

Thermoluminescence of ZrSiO4 (zircon): A new dating method?

Zircon appears to be a suitable medium for thermoluminescence (TL) dating of sediments from the Quaternary. TL of zircon results predominantly from internal irradiation, due to the relatively high internal concentrations of α-emitting U and Th. The internal dose predominates over the external one that is caused by the surrounding geological layers and cosmic rays. Measurement of the TL buildup forms the basis for the development of a geochronometer, to measure the time elapsed since burial of the sediment by more recent layers. The separation and selection procedures, which are used to concentrate the high quality, transparent and colorless part of the zircon fraction of the sediments are an important part of the zircon TL measurements methodology. By improving the procedures, the colored (i.e. light absorbing) grains are excluded from the measurements. For all sand samples, the 3D TL spectra show Dy3+ peaks at low temperatures and Tb3+ bands at high temperatures. The Dy3+ peaks fade rapidly but we have found that after storage for 16 weeks in the dark, the peaks associated with Tb3+ are stable at room temperature for at least two years. Zircons were formed many millions to several billions years ago and therefore we suspected that the problems with zircons are related with ‘‘old’’ radiation damage. In this paper we will focus on two major problems of zircon dating: fading and zoning. We will show that if suitable procedures are used during the preparation stage and the dating experiments, these problems can be solved to a large extent.

Late Wisconsinan and Holocene depositional history, northeastern Gulf of Mexico

Abstract High-resolution seismic surveys and sedimentologic studies in the northeastern Gulf of Mexico reveal multiple late Quaternary fluvial erosion surfaces. The Apalachicola River, largest river in the northeastern Gulf, incised a network of large channels which today lie buried 5–40 m beneath the present-day inner shelf and the estuary of the modern river. An abundance of coastal and estuarine borehole data enables the seismic records to be quantified to yield paleohydrologic information. The paleohydrologic data show that the Apalachicola was a river of significantly higher discharge before the late Holocene, prior to migrating eastward to its present location. Available evidence indicates that the Apalachicola Delta began prograding in its present location at least 2000 years ago. Much of the near-surface sedimentologic and geomorphologic features of the inner shelf of the northeastern Gulf of Mexico, including perhaps the Florida Middle Ground reef tract, are the result of earlier episodes of migration and delta-building by the Apalachicola River.

Particle-borne radionuclides as tracers for sediment in the Susquehanna River and Chesapeake Bay

Abstract The Chesapeake Bay receives nearly 1 000 000 tonnes of sediment annually from its major tributary, the Susquehanna River. The pattern of deposition of this sediment affects the lifetime of the estuarine resource and the fate of any sediment-borne contaminants. Previous estimates of the extent to which Susquehanna River sediment is transported down the Chesapeake have differed considerably. By use of reactor-generated radionuclides adsorbed on the river sediment, a sediment budget has been compiled for the upper Chesapeake Bay and the reservoirs on the lower Susquehanna. Reservoirs impound nearly 1 400 000 tonnes of sediment annually behind the power dams on the lower Susquehanna River. Without the dams, sediment delivery to the upper bay would more than double. The uppermost Chesapeake Bay, within and above the turbidity maximum, retains virtually all of the fluvial sediment delivered to it. The result is an annual sedimentation rate of approximately 3 mm yr −1 in the upper bay, an infilling rate that is nearly equal to the regional rate of sea level rise.

Assessment of the suitability of zircons for thermoluminescence dating

Abstract A suit of zircon (ZrSiO 4 ) samples has been selected for experiments by thermoluminescence (TL) and by Laser Ablation ICP-MS to study the role of rare earth elements (REE). It is shown that the trace element composition results for the heavy REE (HREE) are consistent, and that zircons are HREE enriched. In all sediment samples used in this work, we found significant concentration of Dy and Tb, which are the important activators for luminescence in zircon. At low temperatures, emission peaks due to Dy 3+ are dominant in the 3D-TL spectra while at high temperatures the Dy 3+ peaks are absent and the TL spectrum is dominated by the 6-line-Tb 3+ signal.

Baseline sediment trace metals investigation: Steinhatchee River estuary, Florida, Northeast Gulf of Mexico

This Florida Geological Survey U.S. Department of the Interior, Minerals Manage ment Service Cooperative Study provides baseline data for major and trace metal concentrations in the sediments of the Steinhatchee River estuary. These data are intended to provide a benchmark for comparison with future metal concentration data measurements. The Steinhatchee River estuary is a relatively pristine bay located within the Big Bend Wildlife Management Area on the North Central Florida Gulf of Mexico coastline. The river flows 55 km through woodlands and planted pines before emptying into the Gulf at Deadman Harbor. Water quality in the estuary is excellent at present. There is minimal development within the watershed. The estuary is part of an extensive system of marshes that formed along the Florida Gulf coast during the Holocene marine transgression. Sediment accretion rate measurements range from 1.4 to 4.1 mm yr on the basis of lead-210 measurements. Seventy-nine short cores were collected from 66 sample loca...

Trends in Chesapeake Bay sedimentation rates during the late Holocene

Abstract Trends are discernible in the estimates of late Holocene rates of sedimentation and sea-level rise for the Chesapeake Bay. During most of the Holocene Epoch sedimentation rates and relative sea-level rise were equal, within the limits of measurement, at approximately 1 mm yr−1. Sedimentation rates measured over the past century, however, are nearly an order of magnitude higher, while the rate of relative sea-level rise for the Chesapeake Bay now averages 3.3 mm yr−1, as measured on long-term tide gauge records. When the acceleration in these rates occurred is uncertain, but it appears to have been confined to the past millennium, and probably to the past few centuries. The rapid sedimentation rates recorded during historic time may be a temporary disequilibrium that has resulted from a recent acceleration in the rate of relative sea-level rise.

Late Quaternary coastal and inner shelf stratigraphy, Apalachicola Delta region, Florida

Abstract Since the beginning of the Tertiary the sedimentology of the Gulf of Mexico Basin has been dominated by the depositional activity of the Mississippi River. The sedimentologic influence of the Mississippi diminishes with distance east or west of the Louisiana shelf, however. The Texas and northwest Florida shelf margins, for example, are characterized by a series of smaller deltas. In the inner and mid-shelf areas of these regions the near-surface sedimentary units include infilled stream channels and small deltas. Such features are commonly observed in sub-bottom seismic records from the middle and inner shelf of the northeastern Gulf, along the Apalachicola River coast of northwest Florida. The Apalachicola River is the principal source of clastic sediment to the northeastern Gulf of Mexico. During the late Holocene virtually all of the rivers sediment load has been deposited in the modern Apalachicola Delta and in the rivers estuary, Apalachicola Bay, which has been filling rapidly. During late Quaternary lowstands, prior to the development of the modern estuary, the river traversed the present-day inner and mid-shelf, incising a network of channels. Based on seismic records, many of these buried shelf channels were considerably larger than their modern counterparts. During lowstands the Apalachicola River also deposited coarse sediment on the shelf as deltaic and associated river-mouth sediments. These deposits comprise the modern near-surface sediments of the inner and middle shelf. An investigation of subsurface sedimentary features observed in seismic profiles provides details on the late Quaternary development of the northeastern Gulf of Mexico shelf. Seismic reflection profiles obtained on the inner and mid-shelf regions of northwest Florida reveal an approximately 50 m thickness of late Quaternary sediments, comprised of two and sometimes three discrete clastic sequences. Two lower fluvial sequences total as much as 40–50 m in thickness. A transgressive marine sand deposit overlies the older features in some places, varying in thickness from 0 to 5 m. Identification of seismic facies, combined with stratigraphic data from a suite of coastal boreholes, enables correlation of offshore seismic stratigraphic units with late Tertiary and Quaternary coastal stratigraphy.

Coastal Response to Storms and Sea-Level Rise: Santa Rosa Island, Northwest Florida, U.S.A.

ABSTRACT Kish, S.A. and Donoghue, J.F., 2013. Coastal response to storms and sea-level rise: Santa Rosa Island, northwest Florida, U.S.A.. In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 131–140, Coconut Creek (Florida), ISSN 0749-0208. The western panhandle coast of northwest Florida is wave dominated and microtidal. Major storms are infrequent but have a significant effect on coastal morphology. Santa Rosa Island, a 75-kilometer long barrier, is the major coastal feature of the region. The island is narrow, with an average width of 500 meters. During most of the historical period, prominent foredunes, ranging as high as 7 meters, have helped keep the islands sediment budget in near equilibrium. This investigation compiled and georeferenced nearly two dozen historical shoreline positions from surveys and aerial photos, dating from the 1850s to the present. Time intervals between shoreline positions ranged from 30 years to multiple datasets per year. The U.S. Geological Surveys Digital Shoreline Analysis System (DSAS) was used to analyze the shoreline data. Analysis of the dataset reveals that storms have heavily influenced shoreline position. Shoreline retreat during the period from 1851—present has averaged less than 1 meter per year. Periods of more rapid retreat have been associated with the occurrence of major storms. A six-decade period of relative quiescence during the mid-20th century resulted in modest advance of the islands coastline. A cluster of three major storms during the period 1995–2005 had a major impact on the morphology and stability of the island. Much of the foredune complex was lost and rates of coastal retreat increased significantly. The historical shoreline data therefore underscore the dominant influence of storm frequency and intensity in determining coastal change.