Suwannee Strait Research Articles

Reading the sediment archive of the Eastern Campeche Bank (southern Gulf of Mexico): from the aftermath of the Chicxulub impact to Loop Current variability

This is the first high-resolution seismic study showing how the Chicxulub impact shaped the eastern slope of the Campeche Bank in the south-eastern Gulf of Mexico. The induced shock wave fractured Cretaceous strata causing the collapse of the upper slope and shelf over a length of ca. 200 km. Failed material was either transported downslope or remained in parts on the accommodation space created by the collapsed. In the Cenozoic, the East Campeche Plastered Drift developed within the created accommodation space, controlled by the inflowing surface current from the Caribbean, which forms the Loop Current. The internal reflection configuration of the drift shows that the closure of the Suwannee Strait in the Late Oligocene and the closure of the CAS in the Mid to Late Miocene controlled the variability of the southern Loop Current in time. Since the Loop Current transports heat and moisture from the western Atlantic warm water pool into the North Atlantic and further to NW Europe by the Gulf Stream, the drift represents an archive for controlling factors that influenced climate of the northern hemisphere. This first high-resolution seismic reflection study from the eastern Campeche Bank expands the understanding of destructive processes that a meteorite impact induces into the earth system. Furthermore, these data document that the East Campeche Plastered Drift bears the potential to understand the link between the climate variability of the northern hemisphere and oceanic processes in the equatorial western Atlantic.

Delineation of post-KPg carbonate slope deposits as a sedimentary record of the Paleogene linkage of De Soto Canyon and Suwannee Strait, northern Gulf of Mexico

Seismicity generated from the Chicxulub impact has been postulated as the cause for the dramatic alteration of basin margin morphology and catastrophic movement of sediments in the Gulf of Mexico (GOM). Immediately following the impact, the formation of the Cretaceous-Paleogene boundary deposit (KPBD) was widespread and caused considerable erosion as portions of the Florida Escarpment collapsed, inducing sediment failure on the northern Florida Platform and formation of the ancestral De Soto Canyon. Overlying the more prominent KPBD existed a distinct, younger, post-Cretaceous/Paleogene carbonate slope deposit (CSD) confined within the De Soto Canyon bathymetric feature. Presence of this discrete unit provided insight into the post-impact history of De Soto Canyon and its long-duration connection to the Suwannee Strait, which linked the GOM with the Atlantic Ocean for almost 40 ma. We have postulated that the bathymetric low of the De Soto Canyon acted as a conduit for west to east sediment movement from nearby carbonate-dominated shorelines into the canyon in episodic sediment transport events from the Danian to the earliest Miocene. Closure of the Suwannee Strait, due to sediment infilling, terminated deposition of the De Soto Canyon CSD. This was followed by major siliciclastic influx as the paleo-Tennessee drainage system began to enter the Mississippi Canyon area.

Cretaceous to Recent Rifting in the Gulf of Mexico Basin

ABSTRACT There is evidence in, and, around the periphery of the northern Gulf of Mexico Basin that indicate the basin was formed by tectonic plate readjustment. This rifting started in the late Early Cretaceous and is continuing today. Over 40 articles of evidence support Gulf rifting. A geologic model for this type basin formation is also presented. Evidence of rifting includes: Arcuate linear magnetic signatures, recorded across the northern Gulf of Mexico, outline possible plate movement. Reflection and refraction data along with deep well control revealed a deep basement ridge and valley system in the northern Gulf that matches closely the above linear magnetic trend. Radiating from the DeSoto Canyon high is a triple juncture system formed by the Cretaceous Shelf Edge, West Florida Escarpment and Suwannee Strait. The Trans-Mexico neovolcanic belt is offset by a right-lateral transform fault resulting from plate readjustment. The possible connection of the New Madrid and Middleton Place-Summerville earthquake zones to this rift system. Plate readjustment created compressional forces that caused a series of east-west trending mountain ranges in Guatemala, Honduras and Nicaragua along with Caribbean seamounts. Sea floor spreading in the Cayman Trench that could be results of, and/or part of, initiation of plate movement. The northern Gulf's Exterior Basin salt mass, along with its confining basin, are possibly the results of plate movement. This tectonic model has implications for future petroleum exploration that will be discussed.

Eocene echinoids, the Suwannee Strait, and biogeographic taphonomy

Faunal similarity among regions is often used as a means of identifying regions of endemism in fossil faunas. At least two large-scale taphonomic effects can affect apparent faunal similarity: stratigraphic and facies mismatching. In stratigraphic mismatching, an unconformity represents removal of most or all of a complete assemblage zone in one region, and the constituent taxa are mistakenly interpreted as having never inhabited that region. In facies mismatching, environmental differences between two regions (possibly unrecognized) cause the inference of a barrier that never existed. The two types of mismatching can work in concert if a facies was originally represented in a single stratigraphic interval that has been completely removed from one region. Analysis of faunal similarity via multivariate analysis of individual localities, coupled with comparison of the regions as single samples, may indicate mismatching if the results differ significantly.We view these two problems as part of a suite of taphonomic effects that are not evident in paleobiological analyses of smaller geographic scope. First, there is ambiguity in the notion of “barrier,” even when a candidate is obvious. Second, barriers in paleobiogeography are often hidden and must be inferred from their effects rather than observed. Third, stratigraphic and facies mismatching produce effects on regional faunas similar to those produced by barriers. Anyone using barriers to explain faunal disruptions should address these three points.Upper Eocene faunas of central Florida seem taxonomically distinct from those of the remainder of the Gulf Coastal Plain. This has historically been attributed to a known paleogeographic feature, the Suwannee Strait, which acts as a barrier. The amount of dissimilarity of the echinoid faunas is greater than the amount predicted as a result of sampling problems. Comparison of the results of multivariate and whole-region analyses suggests that mismatching of the two faunas, rather than a true barrier, causes the distinction. Principally facies, but also strata are mismatched. Early Late Eocene faunas inhabited terrigenous sands to the north of the strait and carbonate sands to the south and show the highest distinctiveness. Middle Late Eocene faunas inhabited primarily carbonate sands to the south and both carbonate sands and muds to the north. Overall similarity is higher for both local and regional analyses, and the faunas of northern sands are more similar to those of the southern region than to the northern mud faunas. Overall similarity across the strait is highest in the late Late Eocene strata when both regions had carbonate mud and sand facies. The faunas exhibit greater similarity within facies than they do within regions. Upper Late Eocene strata are poorly preserved north of the strait because of post-Eocene erosion.

Evolution of a deep-water carbonate platform: Upper Cretaceous to Pleistocene sedimentary environments on the west Florida margin

Deep-water carbonates have been accumulating on the west Florida margin since the early Late Cretaceous, although the depositional style and sediment types have changed through time. Seven coreholes drilled by EXXON record the establishment of two gently-dipping aggradational ramps, the first in the Late Cretaceous to Oligocene, and the second in the middle to late Miocene to the present. These dominantly pelagic depositional environments followed episodes of downslope transport of shallow-water grains, diluting background pelagic sedimentation and producing progradational ramps that built seaward. This study traces the evolution of the deep-water west Florida sedimentary systems, and contrasts the older aggradational ramp, characterized by both foraminiferal and radiolarian oozes as well as volcanic ash, with the late Neogene ramp whose biogenic components are mainly foraminifera and coccoliths. The cycles of progradation, separated by periods of ramp aggradation, developed as eustasy interacted with prolonged subsidence of the margin (early Late Cretaceous), as well as oceanographic changes caused by closure of the Suwannee Strait (late Oligocene to early Miocene) and of the Isthmus of Panama (middle to late Miocene). The major transitions in environments recorded in the west Florida ramp platform thus resulted from the superposition of climatic, tectonic, and oceanographic events on global sea level changes.

Late Eocene Echinoid Biofacies of Florida

Combining the substrate preferences of Jacksonian (late Eocene) echinoid species of Florida (Carter et al., 1989) with their geographic distributions (Carter, 1987a) allows construction of biofacies maps reflecting the spatial distribution of carbonate mud-rich and carbonate sand-rich sediments in the Ocala Group of Florida. Both cluster analysis and interpretation of individual localities suggest a consistently sandy bottom over most of the shelf in the early Jacksonian, with a north-south gradient developing during the middle and late Jacksonian. In the middle Ocala, some mud-tolerant species are present in the northern part of the Florida peninsula, toward the Suwannee Strait, and the middle Ocala of the western panhandle is dominated by mud-tolerant species. In the upper Ocala, most localities contain a significant proportion of mud-dwelling species, and the northward prevalence of mud-tolerant assemblages is even more pronounced, with those assemblages closer to the Suwannee Strait entirely dominated by mud-dwellers. These data suggest that the Ocala Bank of Cheetham (1963) was more of a northward sloping carbonate ramp than a carbonate shelf.

Paleogene Echinoid Distributions in the Atlantic and Gulf Coastal Plains

Cluster analyses of echinoid distribution data for Paleogene stages in the Coastal Plains of eastern North America suggest provincial distributions for some stages. In only one case (New Jersey versus the Gulf Coast in the Sabinian) is this interpretable as climatically controlled endemism. The Suwannee Strait in southwestern Georgia and northwestern Florida may have acted as a barrier to echinoid dispersal between central Florida and the rest of the Gulf Coast during the Eocene. However, preliminary results suggest that stratigraphic andlor ecological differences between the two regions better explain the observed distinction. Most of the apparent faunal differences suggested for other stages can best be attributed to facies differences or subtle age differences among the regions. We should expect stratigraphic mismatching of strata between provinces to be a particularly tricky problem in older rocks (especially the Paleozoic) for which temporal resolution is worse; paleobiogeographic studies of Paleozoic rocks should explicitly address this problem. The Gulf Coast region (south Georgia, south Alabama, the panhandle of Florida and westward to east Texas) was one province throughout the Paleogene. Through the Vicksburgian an east-west gradient in diversity existed within the region. By the Chickasawhayan this gradient, and the apparent facies differences controlling it, had disappeared. The Carolinas represent a distinct province at least throughout the Eocene, probably because of their depositional setting as deep-water carbonates. Central Florida was faunally distinct during the Eocene (no older exposures are known from Florida), but by the late Oligocene this distinction no longer existed.

Paleoecology and Paleogeography of an Extensive Rhodolith Facies from the Lower Oligocene of South Georgia and North Florida

An extensive areal occurrence of Lower Oligocene rhodolith limestone has been observed in cores and outcrops extending nearly 290 km along NE-SW trend from south-central Georgia to the Florida Panhandle. Maximum observed thickness of the limestone is 30 m. Such tremendous accumulation of fossil rhodoliths has not been previously described in the literature. The boundaries of the rhodolith facies coincide with the edges of the Suwannee Strait, Cretaceous to Neogene paleobathymetric low, and may be used in subsurface mapping to delimit the edge of the Strait. Most of the rhodoliths are Archaeolithothamnium with mean diameter of 5 cm and most (95%) are spherical (compact) in shape. Rhodolith shape plus their internal laminar growth pattern indicate exposure to high-energy environments, resulting in frequent movement of the algae. The occurrence of Archaeolithothamnium, along with the red alga Lithoporella and dasycladacean alga, suggest moderate to shallow water depth. Rhodoliths overwhelmingly dominated the marine biotic community because the coarse, mobile substrate they produced precluded the development of more diverse faunal assemblage. Species that did live within the rhodolith facies had specific adaptations for survival on such substrate including the ability to encrust (corals and ectoprocts), bore (Lithophaga), live interstitially (Lima), and ease of mobility (scallops, echinoids). INTRODUCTION The purpose of this paper is to show how the interpretation of outcrops and cores containing Oligocene age rhodoliths has aided in determining the position of buried seaway known as the Suwannee Strait. To make this determination, we first described an unusually large areal occurrence of an Oligocene rhodolith facies, and then determined the paleoecological implications of the rhodoliths, associated fauna, and sedimentary facies examined in outcrop and core. Using modern rhodolith deposits as guide, we inferred the position of the Suwannee Strait. The Strait has been described by Applin and Applin (1944) as a channel or trough extending southwestward across Georgia through the Tallahassee area of Florida to the Gulf of Mexico. Although the seaway existed from the Late Cretaceous (Hull, 1962) to Eocene (Chen, 1965; McKinney, 1984), the exact location of the Strait during the Tertiary has been matter of debate. Reports concerning coralline algal nodules, named rhodolites by Bosellini and Ginsburg (1971), can be found in the literature beginning in the late nineteenth century. Early studies (KjelLman, 1883; Foslie, 1894) dealt mostly with the descriptive and taxonomic aspect of these algae that grow as detached, individual, primary nodules. More recent work has been directed towards the ecological relationships of rhodoliths. To this end, several investigators (Logan, et al., 1969; Bosellini and Ginsburg, 1971; Adey and Macintyre, 1973; Focke and Gebelein, 1978; Bosence, 1985) have observed the nodules in Recent environments, thereby providing basic information for paleoenvironmental interpretations. Data from these studies have been used by others (Siesser, 1972; Toomey, 1975; Orszag-Sperber, Poignant, andPoisson, 1977; Pal and Dutta, 1979; Bourrouilh-le-Jan, 1979) to describe environmental conditions of ancient rhodolith-bearing strata. Two significant problems are encountered when attempting paleoenvironmental statements based on the presence of certain algal form. Because classification is based on cell and reproductive structures observed in thin section, identification of the genus can be quite difficult where replacement or dolomitization has taken place. Also, because most of the rhodolith genera have wide, overlapping ranges of ecological tolerances; depth zonation, light penetration, wave energy, and water temperatures cannot be sharply delineated. As result of these difficulties Adey and Macintyre (1973) state that in paleoecological studies many erroneous or

Shallow seismic stratigraphy and post-Albian geologic history of the northern and central Blake Plateau

Interpretation of >4,700 km of high-resolution, seismic-reflection profiles from the northern and central Blake Plateau was used to reconstruct the geologic history of this continental margin sector since Albian time. Beneath the northern Blake Plateau, a basal Albian sequence is overlain by three progradational sequences inferred to be Turonian-Coniacian, Santonian, and Campanian-Maastrichtian in age. Their clinoform patterns and external geometry suggest that these sequences consist of clastic sediment derived from a source to the west. The position of the seaward terminus of these sequences shifted by as much as 50 km during the Late Cretaceous, presumably in response to variations in the input of clastic sediment. To the south, the progradational units grade into thinner, blanketlike deposits interpreted as being deep-water sediments that accumulated in a slowly subsiding basin. By latest Cretaceous time, sediment was introduced to the inshore reaches of this deep-water basin apparently by a powerful, easterly flowing current sweeping through the Suwannee Strait of southern Georgia and northern Florida. Three thin, but mappable, units of Paleocene, Eocene-Oligocene, and post-Oligocene age comprise the Cenozoic section. Drill-hole data indicate that they consist principally of deep-water foraminiferal oozes and limestones. The dominant geologic agent during the Cenozoic was the Gulf Stream, the flow axis of which shifted periodically across the Plateau in response to global sea-level fluctuations. This powerful current influenced the location and development of the Florida-Hatteras Shelf and Slope, controlled facies distribution, and scoured the surface of the Blake Plateau, thereby producing an abbreviated sedimentary section containing numerous unconformities. The persistence of Gulf Stream erosion during the Cenozoic, in conjunction with crustal subsidence, transformed the distal edge of this continental margin sector into a deep-water, sediment-starved environment, the Blake Plateau.

A scenario of Mesozoic-Cenozoic ocean circulation over the Blake Plateau and its environs

After the continental breakup of North America, Africa, and Europe, a sluggish, wind-driven circulation gyre probably formed in the juvenile North Atlantic basin. Surface flow in the western Atlantic Ocean during the Early Cretaceous likely was northward along the seaward edge of an extensive reef that flourished offshore of North America. Sometime during the Late Cretaceous, the surface circulation in the Gulf of Mexico had evolved into a clockwise rotary pattern as the exchange of water with the Pacific Ocean diminished. By latest Cretaceous time, a vigorous easterly current flowed through the Suwannee Strait of southern Georgia and northern Florida, injecting copious amounts of water and sediment into the western Blake Plateau basin. This flow pattern apparently persisted into Paleocene time. During late Paleocene and early Eocene time, strong northerly flow through the Straits of Florida and across the Blake Plateau was established. This represented the onset of Gulf Stream circulation over the Blake Plateau. The position of the Gulf Stream shifted repeatedly across the northern and central plateau during the Tertiary and Quaternary Periods. The westernmost track was located along the inner Blake Plateau parallel to the Florida-Hatteras Slope; the easternmost track was 500 m lower, bathymetrically, and crossed the central plateau and continental slope just north of the Blake Spur. The Gulf Stream apparently shifted in response to changes in water depth on the Blake Plateau that accompanied global fluctuations of sea level. During rises of sea level, the Gulf Stream drifted westward until it impinged on the Florida-Hatteras Slope and Outer Shelf. During lowerings of sea level, the Gulf Stream was deflected progressively eastward across the central plateau by the Charleston Bump, a prominent bathymetric bulge of the northern Blake Plateau.

Shaler's Line and Suwannee Strait, Florida and Georgia: GEOLOGICAL NOTES

The approximate crest of the Central Georgia uplift was determined from the Florida border northward into Georgia for about 45 mi on the basis of the sediment-size ratio of Miocene phosphorite matrices. A large breaching of the Central Georgia uplift was indicated by isopleths of the same ratios where the Suwannee Strait and Shaler's line coincide as they cross the uplift. Also indicated was possible left-lateral movement along Shaler's line.

Structure Beneath Continental Shelf, Northeastern Gulf of Mexico

Data from 47 reversed seismic refraction profiles in the northeastern Gulf of Mexico are presented in the form of four east-west and two north-south cross sections. Where possible, correlations are drawn between velocity layers encountered offshore and well data from various oil wells drilled on the Florida mainland. The Peninsular arch of Florida is shown to exhibit a lobe-like extension on its western limb, affecting the attitude of the pre-Cretaceous basement rocks. Under the eastern part of the extreme northeastern Gulf of Mexico, interpretation of the seismic records is complicated by the presence of strata with lower seismic velocities than the material above. Evidence is presented that these strata lie somewhere near the top of the Upper Cretaceous. The subsurface eology beneath the continental shelf in this area generally parallels that of northern Florida, exhibiting the lateral dual facies relationship of clastic sediments in the west grading to carbonates in the east. Evidence points to the possible existence of scattered reefal deposits in the Upper Cretaceous along the extrapolated axis of the Suwannee strait.

Cretaceous Suwannee Strait, Georgia and Florida: GEOLOGICAL NOTES

The Suwannee strait is an elongate negative structure in southern Georgia and northeastern Florida. Upper Cretaceous rocks are abnormally thin within the strait. This thinness, generally attributed to post-Cretaceous erosion, can be explained as the result of differential sedimentation during Late Cretaceous time, when the strait separated the coastal plain from the carbonate reefs and banks of the Florida Peninsula.