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David Bukry

Publications and source records attributed to David Bukry.

At least 19 recordsLinked to original sources
USGS2022

An 11,300 yr record of paleoclimatology and paleoceanography of the central California coast in a gravity core from Pioneer Seamount

Diatom, pollen, silicoflagellate, and biogenic opal analyses from a 155 cm-long gravity core from Pioneer Seamount, offshore Santa Cruz, California (PS1410-06 GC, latitude 37.3°N, longitude 123.4°W, water depth 2165 m) are compiled for the last ~11,300 years and compared with those of ODP 1019 and TN062-O550 from northern California. The relative abundance record of the subtropical diatom Fragilariopsis doliolus has similar bimodal Holocene patterns in all three cores, suggesting that sea surface temperatures (SST) were lower during the middle part of the Holocene than they were during the later and earlier parts. The relative abundance of coastal redwood ( Sequoia sempervirens ) pollen, a proxy for fog and coastal upwelling, displays stepwise increases in ODP 1019 and TN062-O550 between ~ 4000 and 3000 cal yr. BP, but its relative abundance in PS1410-06 GC increases gradually throughout the past 10,200 yr without any major steps. Similarly, biogenic silica (opal) displays stepwise increases at ~3600 and 2900 cal yr. BP in ODP 1019 and TN062-O550, respectively, whereas opal increases more gradually in PS1410-06 GC during the past 10,100 yr with relatively minor steps at ~3100 and ~2600 cal yr. BP. Together, coastal redwood and opal argue for a more gradual late Holocene increase in coastal upwelling along the coast of central California compared with that off northern California, where onshore-offshore gradients are more distinct.

California↗
USGS2018

High-resolution climate of the past ∼7300 years of coastal northernmost California: Results from diatoms, silicoflagellates, and pollen

Piston core TN062-O550, collected about 33 km offshore of Eureka, California, contains a high-resolution record of the climate and oceanography of coastal northernmost California during the past ∼7.34 kyr. Chronology established by nine AMS ages on a combination of planktic foraminifers, bivalve shell fragments, and wood yields a mean sedimentation rate of 103 cm kyr −1 . Marine proxies (diatoms and silicoflagellates) and pollen transported by the nearby Eel River reveal a stepwise development of both modern offshore surface water oceanography and coastal arboreal ecosystems. Beginning at ∼5.4 cal ka the relative abundance of coastal redwood pollen, a proxy for coastal fog, displays a two fold increase suggesting enhanced coastal upwelling. A decline in the relative contribution of subtropical diatoms at ∼5.0 cal ka implies cooling of sea surface temperatures (SSTs). At ∼3.6 cal ka an increase in the relative abundance of alder and oak at the expense of coastal redwood likely signals intensified riverine transport of pollen from inland environments. Cooler offshore SSTs and increased precipitation characterize the interval between ∼3.6 and 2.8 cal ka. A rapid, stepwise change in coastal climatology and oceanography occurs between ∼2.8 and 2.6 cal ka that suggests an enhanced expression of modern Pacific Decadal Oscillation-like (PDO) cycles. A three-fold increase in the relative abundance of the subtropical diatom Fragilariopsis doliolus at 2.8 cal ka appears to mark an abrupt warming of winter SSTs. Soon afterwards at 2.6 cal ka, a two fold increase in the relative abundance of coastal redwood pollen is suggestive of an abrupt intensification of spring upwelling. After ∼2.8 cal ka a sequence of cool-warm, PDO-like cycles occurs wherein cool cycles are characterized by relative abundance increases in coastal redwood pollen and decreased contributions of subtropical diatoms, whereas opposite proxy trends distinguish warm cycles.

California↗
USGS2018

A Holocene record of ocean productivity and upwelling from the northern California continental slope

The Holocene upwelling history of the northern California continental slope is examined using the high-resolution record of TN062-O550 (40.9°N, 124.6°W, 550 m water depth). This 7-m-long marine sediment core spans the last ∼7500 years, and we use it to test the hypothesis that marine productivity in the California Current System (CCS) driven by coastal upwelling has co-varied with Holocene millennial-scale warm intervals. A combination of biogenic sediment concentrations (opal, total organic C, and total N), stable isotopes (organic matter δ 13 C and bulk sedimentary δ 15 N), and key microfossil indicators of upwelling were used to test this hypothesis. The record of biogenic accumulation in TN062-O550 shows considerable Holocene variability despite being located within 50 km of the mouth of the Eel River, which is one of the largest sources of terrigenous sediment to the Northeast Pacific Ocean margin. A key time interval beginning at ∼2900 calibrated years before present (cal yr BP) indicates the onset of modern upwelling in the CCS, and this period also corresponds to the most intense period of upwelling in the last 7500 years. When these results are placed into a regional CCS context during the Holocene, it was found that the timing of upwelling intensification at TN062-O550 corresponds closely to that seen at nearby ODP Site 1019, as well as in the Santa Barbara Basin of southern California. Other CCS records with less refined age control show similar results, which suggest late Holocene upwelling intensification may be synchronous throughout the CCS. Based on the strong correspondence between the alkenone sea surface temperature record at ODP Site 1019 and the onset of late Holocene upwelling in northern California, we suggest that CCS warming may be conducive to upwelling intensification, though future changes are unclear as the mechanisms forcing SST variability may differ.

California↗
USGS2016

Holocene evolution of diatom and silicoflagellate paleoceanography in Slocum Arm, a fjord in southeastern Alaska

Diatom and silicoflagellate assemblages in cores EW0408-47JC, -47TC, -46MC (57° 34.5278′ N, 136° 3.7764′ W, 114 m water depth) taken from the outer portion of Slocum Arm, a post-glacial fjord in southeastern Alaska, reveal the paleoclimatic and paleoceanographic evolution of the eastern margin of the Gulf of Alaska (GoA) during the past 10,000 years. Between ~ 10 and 6.8 cal ka, periods of low salinity and cool water conditions alternated with brief intervals marked by the increased influx of oceanic, more saline and likely warmer waters. Increased surface water stability characterized by a middle Holocene interval between ~ 6.8 and 3.2 cal ka is typified by increased abundances of northeastern Pacific Thalassiosira spp. that are indicative of spring coastal blooms and decreased abundances of warm and higher salinity oceanic diatoms. At ~ 3.2 cal ka, an abrupt increase in both the relative contribution of oceanic diatoms and silicoflagellates suggestive of cooler upwelling conditions occurred in the -47JC record. A stepwise increase in alkenone sea surface temperature in northern GoA core EW0408-85JC and increase in southern sourced precipitation in the carbonate δ 18 O record of Jellybean Lake (Yukon) present evidence that this ~ 3.2 cal ka event coincided with the onset of enhanced positive Pacific Decadal Oscillation-like (PDO) conditions in the GoA. These positive PDO-like conditions persisted until ~ 1.0 cal ka and were followed by high amplitude fluctuations in the relative abundance of diatom and silicoflagellate assemblages.

Marine Micropaleontology↗
USGS2015

Paleoceanographic, and paleoclimatic constraints on the global Eocene diatom and silicoflagellate record

Eocene diatom and silicoflagellate biostratigraphy are summarized and correlated with the most recent geologic time scale as well as with the global oxygen isotope and eustatic sea level curves. The global distribution of Eocene diatom/silicoflagellate-bearing sediments varies considerably, reflecting changing oceanic gateways and paleoceanography with changing patterns that are punctuated by four major depositional events. Event 1 (~ 49 million years ago, Ma), at the end of the Early Eocene Climatic Optimum (EECO), saw the cessation of diatom/silicoflagellate deposition in epicontinental regions of the North Sea region and in the northern Russia and the onset of biosilica deposition in the Arctic. Event 2 (~ 46 Ma), which coincided with intensification of the Middle Eocene cooling trend, marked the widespread expansion of diatom/silicoflagellate deposition in both the North and South Atlantic. A shift of diatom/silicoflagellate deposition from the Atlantic to the Pacific began at Event 3, at the end of the Middle Eocene Climatic Optimum (MECO) (~ 40 Ma), that was likely tied to the initial opening of the Drake Passage between Antarctica and South America. Event 4 (~ 39 Ma) coincided with a major sea level fall and a widespread deep-sea hiatus in the latest Middle Eocene. Late Eocene diatom/silicoflagellate deposition became more concentrated in middle-to-high latitude regions and coastal upwelling regions, particularly in the Pacific Ocean. Tabulation of the first and last occurrences of 132 biostratigraphically-important diatoms suggests increased species turnover during the latest Paleocene to earliest Eocene that may be in part due to a monographic effect. An increasing rate of evolution of new diatom species between ~ 46 and 43 Ma and after ~ 40 Ma coincides respectively with the widespread expansion of diatom deposition in the Atlantic and with an increased pole-to-equator thermal gradient that witnessed the expansion of diatoms in high latitude oceans and coastal upwelling settings.

Palaeogeography, Palaeoclimatology, Palaeoecology↗
USGS2014

Response of diatom and silicoflagellate assemblages in the central Gulf of California to regional climate change during the past 55 kyrs

High-resolution studies of diatoms and silicoflagellates of the past 55 kyrs in cores MD02-2517/2515 from the central Gulf of California (GoC) reveal profound changes in GoC surface waters. Roperia tesselata , a diatom proxy for late winter–early spring upwelling, and Dictyocha stapedia , a subtropical silicoflagellate indicative of GoC sea surface temperatures (SSTs) > 24 °C, are common during the Holocene but rare during Marine Isotope Stage (MIS) 2 and most of MIS 3, a relationship that likely reflects a more northerly position of the North Pacific High (NPH) during the Holocene. In contrast during most of MIS 2 (~ 27–15 ka), the persistent presence of Distephanus speculum , a silicoflagellate associated with SSTs < 16°, suggests that cold, low salinity waters penetrated into the GoC, consistent with southward displacement of the NPH. During MIS 3 (~ 55–27 ka), increased dominance of Azpeitia nodulifera (diatom) implies that stratified, tropical waters were present year round, whereas silicoflagellate assemblages suggest that stratified tropical conditions alternated with more productive, upwelling conditions on millennial timescales. Reduced biosiliceous productivity during Heinrich events likely reflected a reduction in both surface water nutrient levels and in the strength of northwest winds due to a weakened and more southerly NPH. Conversely, enhanced biosiliceous productivity during MIS 3 interstadials was probably linked to heightened nutrient levels and a strengthened NPH. Abrupt relative abundance increases of the silicoflagellate, Dictyocha aculeata , approximate the termination of MIS3 Heinrich events and may signal times when nutrient-rich deep waters associated with the resumption of enhanced Atlantic Meridional Overturning Circulation penetrated into the central Gulf.

California↗
USGS2014

Geologic history of Siletzia, a large igneous province in the Oregon and Washington Coast Range: Correlation to the geomagnetic polarity time scale and implications for a long-lived Yellowstone hotspot

Siletzia is a basaltic Paleocene and Eocene large igneous province in coastal Oregon, Washington, and southern Vancouver Island that was accreted to North America in the early Eocene. New U-Pb magmatic, detrital zircon, and 40 Ar/ 39 Ar ages constrained by detailed field mapping, global nannoplankton zones, and magnetic polarities allow correlation of the volcanics with the 2012 geologic time scale. The data show that Siletzia was rapidly erupted 56–49 Ma, during the Chron 25–22 plate reorganization in the northeast Pacific basin. Accretion was completed between 51 and 49 Ma in Oregon, based on CP11 (CP—Coccolith Paleogene zone) coccoliths in strata overlying onlapping continental sediments. Magmatism continued in the northern Oregon Coast Range until ca. 46 Ma with the emplacement of a regional sill complex during or shortly after accretion. Isotopic signatures similar to early Columbia River basalts, the great crustal thickness of Siletzia in Oregon, rapid eruption, and timing of accretion are consistent with offshore formation as an oceanic plateau. Approximately 8 m.y. after accretion, margin parallel extension of the forearc, emplacement of regional dike swarms, and renewed magmatism of the Tillamook episode peaked at 41.6 Ma (CP zone 14a; Chron 19r). We examine the origin of Siletzia and consider the possible role of a long-lived Yellowstone hotspot using the reconstruction in GPlates, an open source plate model. In most hotspot reference frames, the Yellowstone hotspot (YHS) is on or near an inferred northeast-striking Kula-Farallon and/or Resurrection-Farallon ridge between 60 and 50 Ma. In this configuration, the YHS could have provided a 56–49 Ma source on the Farallon plate for Siletzia, which accreted to North America by 50 Ma. A sister plateau, the Eocene basalt basement of the Yakutat terrane, now in Alaska, formed contemporaneously on the adjacent Kula (or Resurrection) plate and accreted to coastal British Columbia at about the same time. Following accretion of Siletzia, the leading edge of North America overrode the YHS ca. 42 Ma. The voluminous high-Ti basaltic to alkalic magmatism of the 42–35 Ma Tillamook episode and extension in the forearc may be related to the encounter with an active YHS. Clockwise rotation of western Oregon about a pole in the backarc has since moved the Tillamook center and underlying Siletzia northward ∼250 km from the probable hotspot track on North America. In the reference frames we examined, the YHS arrives in the backarc ∼5 m.y. too early to match the 17 Ma magmatic flare-up commonly attributed to the YHS. We suggest that interaction with the subducting slab may have delayed arrival of the plume beneath the backarc.

Oregon, Vancouver, Washington↗
USGS2013

Response of diatoms and silicoflagellates to climate change in the Santa Barbara Basin during the past 250 years and the rise of the toxic diatom Pseudo-nitzschia australis

Diatoms and silicoflagellate assemblages were examined in two year-increments of varved samples spanning the interval from 1748 through 2007 in Santa Barbara Basin (SBB) box core SBBC0806 to determine the timing and impact of possible 20th century warming on several different components of the plankton. Diatoms (Thalassionema nitzschioides =TN) and silicoflagellates (Distephanus speculum s.l. =DS) indicative of cooler waters and a shallow thermocline begin to decline in the 1920s and persistently compose a lower percentage of the assemblage in the SBB by about 1940. Prior to 1940, TN constituted on average ~30% of the Chaetoceros-free diatom sediment assemblage and DS on average ~36% of the silicoflagellate assemblage. Between 1940 and 1996 these relative abundances were ~20% (TN) and ~8% (DS). These results are consistent with results from planktonic foraminifera and radiolarians that indicate an influence of 20th century warming on marine ecosystems before most scientific observations began. Cooling of surface waters coincident with the one of the strongest La Niña events of the 20th century (and a return to negative PDO conditions) in late 1998 brought about a return to pre-1940 values of these cool water taxa (TN ~31%, DS ~25%). However, this recent regional cooling appears to have been accompanied by profound changes in the diatom assemblage. Pseudo-nitzschia australis, and Pseudo-nitzschia multiseries, diatom species associated with domoic acid, a neurotoxin that causes shellfish poisoning and marine mammal deaths, rapidly became dominant in the SBB sediment record at the time of the regional cooling (1999) and increased substantially in numbers as a bloom-forming taxon (relative to Chaetoceros spores) in 2003. Prior to 2003 diatom blooms recorded in the SBB sediment record consisted predominantly of Chaetoceros spores and less commonly of Rhizosolenia-related species (Neocalyptrella robusta and R. setigera). Fecal pellets dominated by valves of P. australis, however, were particularly abundant in both the 2003 and 2006 samples, coincident with recorded incidents of domoic acid increase and widespread shellfish poisoning in the SBB.

Quaternary International↗
USGS2009

Paleoceanography of the Gulf of Alaska during the past 15,000 years: Results from diatoms, silicoflagellates, and geochemistry

High-resolution records of diatoms, silicoflagellates, and geochemistry covering the past 15,000 years were studied in three cores from the Gulf of Alaska (GOA). Core EW0408-85JC in an oceanic setting on the Kayak Slope displays a paleoceanographic record similar to that at several locations on the California margin during deglaciation. Biologic productivity as reconstructed using geochemical and microfossil proxies increased abruptly during the Bølling–Alleröd (Bø–Al) warm interval (14.7–12.9 cal ka), declined during the Younger Dryas (YD) cold interval (12.9 to 11.7 cal kyr BP), and rose again during the earliest Holocene. At this site, the record after ~ 11 cal kyr BP is dominated by oceanic diatoms and silicoflagellates, with geochemical proxies displaying more subtle variation. Cores EW0408-66JC in the Yakobi Sea Valley near Cross Sound and EW0408-11JC in the Gulf of Esquibel contain an expanded, composite record along the southeast Alaskan margin. Core 66JC contains a detailed record of the Bø–Al and YD. Diatoms and silicoflagellates indicate that coastal upwelling and biosiliceous productivity were strong during the Bø–Al but declined during the YD. Sea ice-related diatoms increased in abundance during the YD, indicating cooler, but less productive waters. The glacial to biogenic marine sediment transition in core 11JC occurs at 1280 cmbsf (centimeters below sea floor), probably representing rising sea level and deglaciation early in the Bø–Al. Freshwater and sea-ice related diatoms are common in the lower part of the core (Bø–Al and YD), but upwelling-related diatoms and silicoflagellates quickly increased in relative abundance up-core, dominating the record of the past 11,000 years. Low oxygen conditions in the bottom water as reconstructed using geochemical proxies (U and Mo concentration) were most intense between ~ 6.5 and 2.8 cal kyr BP, the beginning of which is coincident with increases in abundance of upwelling-related diatoms. The records from these three cores jointly thus made it possible to reconstruct paleoclimatic and paleoceanographic conditions at high northern Pacific latitudes during the last 15 kyr.

Alaska↗
USGS2008

Newly discovered Paleocene and Eocene rocks near Fairfield, California, and correlation with rocks in Vaca Valley and the so-called Martinez Formation or Stage

Discovery of a 3-foot thick sandstone bed with abundant Turritellid gastropods of late Paleocene age about 4 miles northeast of Fairfield and on the southwest flank of Cement Hill, Solano County provides an opportunity to reevaluate the relationships of lower Tertiary formations in this part of California. Cement Hill is named for travertine deposits in and on top of sandstone of Late Cretaceous age. In this report, the current study area where the Paleocene fossils were recently discovered is referred to as lower Cement Hill and is located in section 7 of the U.S. Geological Survey Fairfield North 7.5-minute quadrangle, Township 5 North, Range 1 West. Lower Cement Hill is about 23 miles north of the so-called Martinez 'formation' or stage area (Weaver and others, 1941) of late Paleocene age near Martinez. The Martinez 'formation' and stage have played a significant role in the development of early Tertiary stratigraphy in this part of California. The discovery of correlative rocks at Cement Hill was unsuspected and may be helpful in defining the extent of this so-called formation or stage. Coccolith identification and correlations are by David Bukry, foraminifer identifications and correlations by Alvin Almgren and Kristin McDougall, gastropod identification and correlation by LouElla Saul, and Radiolaria identifications and correlations are by Annika Sanfilippo.

California↗
USGS2007

Solar forcing of Gulf of California climate during the past 2000 yr suggested by diatoms and silicoflagellates

High-resolution records of the past 2000 yr are compared in a north–south transect (28° N to 24° N) of three cores from the eastern slopes of the Guaymas, Carmen, and Pescadero Basins of the Gulf of California (hereafter referred to as the “Gulf”). Evenly-spaced samples from the varved sediments in each core allow sample resolution ranging from ∼ 16 to ∼ 37 yr. Diatoms and silicoflagellates capture the seasonal variation between a late fall to early spring period of high biosiliceous productivity, that is driven by northwest winds, and a summer period of warmer, more stratified waters during which these winds slacken and/or reverse direction (monsoonal flow). As these winds decrease, tropical waters enter the Gulf and spread northward. Individual samples represent a composite of 7 to 23 yr of deposition and are assumed to record the relative dominance of the winter vs. summer floral components. Intervals of enhanced summer incursion of tropical waters, alternating with periods of increased late fall to early spring biosiliceous productivity are recorded in all three cores. Regularly spaced cycles (∼ 100 yr duration) of Octactis pulchra , a silicoflagellate proxy for lower SST and high productivity, and Azpeitia nodulifera , a tropical diatom, occur between ∼ A.D. 400 and ∼ 1700 in the more nearshore Carmen Basin core, NH01-21 (26.3° N), suggesting a possible solar influence on coastal upwelling. Cores BAM80 E-17 (27.9° N) and NH01-26 (24.3° N) contain longer-duration cycles of diatoms and silicoflagellates. The early part of Medieval Climate Anomaly (∼ A.D. 900 to 1200) is characterized by two periods of reduced productivity (warmer SST) with an intervening high productivity (cool) interval centered at ∼ A.D. 1050. Reduced productivity and higher SST also characterize the record of the last ∼ 100 to 200 yr in these cores. Solar variability appears to be driving productivity cycles, as intervals of increased radiocarbon production (sunspot minima) correlate with intervals of enhanced productivity. It is proposed that increased winter cooling of the atmosphere above southwest U.S. during sunspot minima causes intensification of the northwest winds that blow down the Gulf during the late fall to early spring, leading to intensified overturn of surface waters and enhanced productivity. A new silicoflagellate species, Dictyocha franshepardii Bukry, is described and illustrated.

California↗
USGS2005

Paleoceanographic history of the Guaymas Basin, Gulf of California, during the past 15,000 years based on diatoms, silicoflagellates, and biogenic sediments

High-resolution records of calcium carbonate, biogenic opal, diatoms, and silicoflagellates from western Guaymas Basin gravity core GGC55 and piston core JPC56 and eastern Guaymas Basin DSDP Site 480 reveal a complex paleoceanographic history of the central Gulf of California during the past 15,000 years. Prior to ∼ 6.2 ka, the eastern and western Guaymas Basin proxy records were remarkably similar. After conditions similar to those of today during the Bølling–Allerod, the Younger Dryas (YD) saw a major drop in diatom production, coincident with increased calcium carbonate and tropical microfossils suggestive of El Niño-like conditions. Biosiliceous productivity began increasing during the latter part of the YD, but it was only during the earliest Holocene (11.6 to 11.0 ka) that conditions similar to those of the Bølling–Allerod returned to the central Gulf. Between around 11.0 and 6.2 ka, tropical diatoms and silicoflagellates were virtually absent from the central Gulf, as relatively cooler and fresher surface waters resembling those of the modern northern Gulf were present in the central Gulf. Beginning at about 6.2 ka, tropical diatoms and silicoflagellates began increasing in the central Gulf, and coccoliths returned to western Gulf sediments. The onset of modern-day monsoon conditions in the American Southwest required the presence of warm SSTs in the northern Gulf, which probably did not occur until after about 5.4 ka, when tropical diatoms and silicoflagellates became relatively common in the central Gulf. Modern east–west contrasts, which arise from late winter–early spring coastal upwelling on the mainland side and lower diatom productivity on the western side of the Gulf, commenced between 6.2 and 5.4 ka, possibly due to a shift in the direction of late winter–early spring winds more towards the southeast, or down the axis of the Gulf. This proposed wind shift might have ultimately been due to a late Holocene strengthening of ENSO-like conditions in the eastern equatorial Pacific.

Gulf of California↗
USGS2005

Paleontology of the upper Eocene to quaternary postimpact section in the USGS-NASA Langley core, Hampton, Virginia

The USGS-NASA Langley corehole was drilled in 2000 in Hampton, Va. The core serves as a benchmark for the study of calcareous nannofossils, dinoflagellates, diatoms and silico flagellates, mollusks, ostracodes, planktonic foraminifera and bolboformids, and vertebrate remains in the upper Eocene, Oligocene, Miocene, and Pliocene sediments in southeastern Virginia. These sediments were deposited after the comet or asteroid impact that produced the Chesapeake Bay impact structure. The Chickahominy Formation was deposited rapidly in outer neritic to upper bathyal marine environments during the last 2 million years of the late Eocene. The Drummonds Corner beds are newly recognized in the Langley core. These beds appear to represent shallower water or more nearshore deposition than the underlying Chickahominy deposits. Paleontology indicates an age in the later part of the early Oligocene, with a sharp floral and faunal break between the Drummonds Corner beds and the underlying Chickahominy Formation. Late Oligocene sedimentation is represented by the Old Church Formation. The record of early and middle Miocene deposition in the Langley core is incomplete. The Calvert Formation records brief episodes of deposition in three members, which are separated by unconformities and are called the informal Newport News beds, the Plum Point Member, and the Calvert Beach Member. A second episode of rapid deposition at the Langley site is preserved as the upper Miocene St. Marys and Eastover Formations. The Eastover is overlain unconformably by the Yorktown Formation, which is both late early and early late Pliocene. The highest unit, the Tabb Formation (Pleistocene), was not studied paleontologically. Continued movement along faults and fractures of the crater and nearby region may have enhanced the contributions of older material into the various units filling the Chesapeake Bay impact crater, as suggested by the conspicuous reworking of microfossils in many of the samples from the upper Eocene and younger units in the USGS-NASA Langley core.

Virginia↗
USGS2001

Surface-geophysical characterization of ground-water systems of the Caloosahatchee River basin, southern Florida

The Caloosahatchee River Basin, located in southwestern Florida, includes about 1,200 square miles of land. The Caloosahatchee River receives water from Lake Okeechobee, runoff from the watershed, and seepage from the underlying ground-water systems; the river loses water through drainage to the Gulf of Mexico and withdrawals for public-water supply and agricultural and natural needs. Water-use demands in the Caloosahatchee River Basin have increased dramatically, and the Caloosahatchee could be further stressed if river water is used to accommodate restoration of the Everglades. Water managers and planners need to know how much water will be used within the river basin and how much water is contributed by Lake Okeechobee, runoff, and ground water. In this study, marine seismic-reflection and ground-penetrating radar techniques were used as a means to evaluate the potential for flow between the river and ground-water systems. Seven test coreholes were drilled to calibrate lithostratigraphic units, their stratal geometries, and estimated hydraulic conductivities to surface-geophysical profiles. A continuous marine seismic-reflection survey was conducted over the entire length of the Caloosahatchee River and extending into San Carlos Bay. Lithostratigraphic units that intersect the river bottom and their characteristic stratal geometries were identified. Results show that subhorizontal reflections assigned to the Tamiami Formation intersect the river bottom between Moore Haven and about 9 miles westward. Oblique and sigmoidal progradational reflections assigned to the upper Peace River Formation probably crop out at the floor of the river in the Ortona area between the western side of Lake Hicpochee and La Belle. These reflections image a regional-scale progradational deltaic depositional system containing quartz sands with low to moderate estimated hydraulic conductivities. In an approximate 6-mile length of the river between La Belle and Franklin Lock, deeper karstic collapse structures are postulated. These structures influence the geometries of parallel reflections that intersect the river channel. Here, reflections assigned to the Buckingham Limestone Member of the Tamiami Formation (a confining unit) and reflections assigned to the clastic zone of the sandstone aquifer likely crop out at the river bottom. Beneath these shallow reflections, relatively higher amplitude parallel reflections of the carbonate zone of the sandstone aquifer are well displayed in the seismic-reflection profiles. In San Carlos Bay, oblique progradational reflections assigned to the upper Peace River Formation are shown beneath the bay. Almost everywhere beneath the river, a diffuse ground-water flow system is in contact with the channel bottom. Ground-penetrating radar profiles of an area about 2 miles north of the depositional axis of the deltaic depositional system in the Ortona area show that progradational clinoforms imaged on seismic reflection profiles in the Caloosahatchee River are present within about 17 feet of the ground surface. Ground-penetrating radar profiles show southward dipping, oblique progradational reflections assigned to the upper Peace River Formation that are terminated at their tops by a toplapping or erosional discontinuity. These clinoformal reflections image clean quartz sand that is probably characterized by moderate hydraulic conductivity. This sand could be mapped using ground-penetrating radar methods.

Water-Resources Investigations Report↗