Cenozoic Seas

The View From Eastern North America

Edward J. Petuch

• Publisher: CRC Press
• Year: 2003
• ISBN:
  9781135501426
• Edition: 1
• Topic: Sciences biologiques
• Subtopic: Évolution

>The rich fossil record of the Atlantic and Gulf coastal plains of the United States is a gold mine for interested scientists. The last thirty million years of Earth history are superbly chronicled by a succession of fossil assemblages extending from the St. Lawrence River to Florida. Marine scientists, paleontologists, and systematic biologists al

Chapter 1. Paleoseas of Cenozoic Eastern North America

The Atlantic Coastal Plain and Gulf Coastal Plain regions of the eastern United States have long been known to contain vast, thick Cenozoic marine deposits. Being on the trailing edge of the North American Plate, the Gulf and Atlantic Coastal Plains have been almost continuously subject to structural downwarping, making them particularly sensitive to sea level fluctuations. This has allowed for the preservation of a virtually complete eustatic history of the area, a feature that is generally lost along leading plate edges. The sediments that accumulated along these downwarped, flooded continental margins also contain some of the richest and best preserved marine fossil beds found anywhere on Earth, enabling unprecedented insights into both the ancient marine ecosystems and the paleoceanography of the regions.

Unlike other trailing plate edges elsewhere, several large, open-ended basins formed along the Gulf and Atlantic Coastal Plains during the late Cenozoic (Oligocene-Pleistocene). These pericontinental basins were separated from each other by wide structural arches that had formed either during the Appalachian Orogeny or during some subsequent local reactivation or faulting event. Although traditionally referred to by geologists as “embayments” (Gibson, 1983; Ward, 1992), these pericontinental systems were far more complex than simple bays and represented true seas in the strict oceanographic sense. Like all seas, they were bodies of salt water, they were structurally bound on at least three sides, they occupied geologically discrete basins, they each contained their own distinct configurations of currents and water masses, and they contained their own distinctive endemic organisms and ecosystems. In this book, these late Cenozoic “embayments” will be accorded full paleosea status.

Depending on overall depth, geomorphological configuration, and rate of sedimentary infilling from deltas, each paleosea exhibited its own pattern of eustatic fluctuations and number of marine transgressive intervals. In the time interval from the early Oligocene to the late Pleistocene, some paleoseas had as many as ten large transgressive intervals, while others had as few as four. Some of the longer-lived paleoseas existed throughout this entire time, while others existed for only one or two epochs. In accordance with the standard paleoceanographic nomenclature used for epicontinental seas (Sloss, 1963), I here refer to the unconformity-bound transgressive intervals of marginal pale-oseas as “subseas.” These pericontinental subseas differed from epicontinental subseas in that they were influenced primarily by eustatic fluctuations and not by tectonics or oroge-ny.

As presently understood, the eastern North American paleoseas are divided into two distinct basinal groups, encompassing the Gulf basins and the Atlantic basins (Ward, 1985). Sedimentary deposition within these two groups differs greatly, with the Atlantic basins characteristically having thin marine transgressive units that are separated by numerous regressive unconformities and with the Gulf basins having much thicker, faster-growing units that are separated by fewer unconformities. These differences in sedimentary deposition reflect the erosional patterns of the Appalachian Mountains during the Neogene, when the bulk of the sediments was being deposited in the south and when giant deltaic environments existed along Alabama, northern Florida, and Georgia. In this

book, each separate marine sedimentary unit is considered to be a sea floor, or series of sea floors, within an individual subsea.

Geochronology and Geography of the Eastern American Paleoseas

By the beginning of the Oligocene, the eastern Gulf basinal systems contained only two paleoseas; the northern Choctaw Sea and the southern Okeechobean Sea. The Atlantic basinal systems were more complex and contained four paleoseas; the southern Charleston Sea, the central Albemarle Sea and Salisbury Sea, and the northern Raritan Sea. Included within the scope of this book, but not occupying a true structural basin, is a seventh paleosea, the far northern Champlain Sea. Formed by flooding due to isostatic depression caused by the great Wisconsinan continental ice sheet, the Champlain Sea was the only paleosea that was not eustatically controlled. Detailed overviews of the geomorphology, oceanography, and ecology of these seas and their subseas are given in the following chapters. The geochronology of the five main paleoseas, and their subsea intervals, is shown on Tables 1 and 2.

The Choctaw Sea

Named for the Choctawhatchee (“Choctaw River”) of northern Florida, this northeastern Gulf sea occupied a large area of the present-day Florida Panhandle, including the Choctawhatchee, Apalachicola, and Ochlockonee River deltas, and extended as far west as Okaloosa County and as far east as Taylor County. In its greatest development, the Choctaw Sea also extended inland as far north as Bainbridge, Georgia (Figures1, 3, and 5). Existing from the Rupelian Oligocene to the latest Piacenzian Pliocene, the Choctaw Sea encompassed six separate subseas. Based upon their marine faunas, these subseas can be further subdivided into two groups; the early subseas (Rupelian Oligocene to Serravallian Miocene; see Chapters 3 and 4) and the late subseas (Tortonian Miocene to Piacenzian Pliocene; see Chapters 5 and 6). Of the early subseas, the oldest, the Bainbridge Subsea (named for the fossil beds at Bainbridge, Georgia), existed during the early part of the Oligocene, from the Rupelian to the earliest Chattian Ages, and spanned the Suwannee Strait between Georgia and Florida (Figure 1). The Choctaw Sea basin dried out for most of the Chattian Age, but reflooded in the latest Chattian as the much smaller Chattahoochee Subsea (named for the Chattahoochee Formation of the Florida Panhandle). During Chattahoochee time, the Suwannee Strait closed off completely and Georgia connected to Florida as a single peninsula. By the early Aquitanian Miocene, this subsea disappeared and the basin remained dry until the beginning of the Burdigalian Miocene. At this time, the Chipola Subsea (named for the Chipola Formation of the Florida Panhandle and previously referred to as the “Chipola Sea” (Petuch, 1997)) flooded the area and persisted until the end of the Langhian Miocene (Figure 3).

After a short regressive period during the earliest Serravallian Miocene, the basin was reflooded during the early Serravallian Miocene to produce the first of the late subseas, the Walton Subsea (named for the fossil beds in Walton County, Florida Panhandle). The early Tortonian Age of the Miocene saw another regressive dry time within the Choctaw Sea basin. By the mid-Tortonian, however, a fifth transgressive flooding event produced the Alaqua Subsea (named for the fossil beds along Alaqua Creek, Walton County, Florida Panhandle). This subsea persisted until the mid-Messinian Miocene, when a major regressive period occurred. The basin remained dry throughout the late Messinian and the entire Zanclean Pliocene, only to be flooded in the Piacenzian Pliocene for a sixth and final time. This subsea, the Jackson Subsea (named for the Jackson Bluff Formation of the Florida Panhandle), was previously referred to as the “Jackson Sea” (Petuch, 1997) and existed only until the late Piacenzian Pliocene (Figure 5). For detailed discussions of the individual geo-morphologies and ecosystems of the Choctaw subseas, see Chapters 3, 4, 5, and 6.

Table 1. Oligocene and Miocene chronology of the five main eastern North American paleoseas, showing the chronological distributions of their subseas.

Table 2. Pliocene and Pleistocene chronology of the five main eastern North American paleoseas, showing the chronological distributions of their subseas.

The Okeechobean Sea

The other Gulf basin, the Okeechobean Sea (named for Lake Okeechobee, Florida; see Petuch, 1993; 1997), occupied the southern tip of Florida and extended from present-day Tampa, southward across the entire Everglades Basin, northward into the Kissimmee River Valley, and eastward to present-day Martin County (Figures 1, 3, 5, and 7). The longest-lived of all the eastern American paleoseas, the Okeechobean Sea existed from the early Oligocene to the late Pleistocene and encompassed eleven separate subseas. Like the Choctaw Sea, the Okeechobean Sea subseas can be subdivided into two groups, based upon their marine faunas; in this case, the early subseas (Rupelian Oligocene to Messinian Miocene; see Chapter 5) and the late subseas (Zanclean Pliocene to Sangamonian Pleistocene; see Chapters 6, 7, 8, 9). The oldest of the early subseas, the Dade Subsea (named for the fossil reefs in Dade County, Florida), represented the incipiency of the Okeechobean Sea and was contemporaneous with the Bainbridge Subsea of the Choctaw Sea (Rupelian-earliest Chattian Oligocene) (Figure 1). The Okeechobean Sea basin was emergent throughout most of the Chattian Age, flooding in the latest Chattian and developing into the Tampa Subsea (named for the fossil beds at Tampa, Florida). Contemporaneous with the Chattahoochee Subsea of the Choctaw Sea, the Tampa Subsea persisted into the early Aquitanian Miocene but dried out after that and remained emergent for the rest of the Aquitanian Age. The beginning of the Burdigalian Miocene saw the reflooding of the Okeechobean Sea basin and the establishment of the Arcadia Subsea (named for the Arcadia Formation of southern Florida). This subsea persisted until the Langhian-Serravallian boundary and was the exact contemporary of the Chipola Subsea. A short emergent interval during the early Serravallian Miocene gave way to a major transgressive flooding that ranged from the early Serravallian to the early Tortonian Miocene and produced the Polk Subsea (named for the fossil beds in Polk County, Florida). This subsea was contemporaneous with the Walton Subsea of the Choctaw Sea. After a short regressive period during the early to mid-Tortonian, the last of the early subseas, the Charlotte Subsea (named for the fossil beds in Charlotte County, Florida) flooded the area. This subsea was contemporaneous with both the Alaqua Subsea of the Choctaw Sea.

During the late Messinian Miocene, a major regression took place and the entire Okeechobean Sea basin was emergent. This was followed by a brief transgressional period during the early Zanclean Pliocene, producing the short-lived Murdock Subsea (named for the Murdock Station Formation of southwestern Florida). By late Zanclean time, the Okeechobean Sea basin was again emergent. This was soon reversed by a major trans-gressive event in the early Piacenzian Pliocene, establishing the large and complex Tamiami Subsea (named for the Tamiami Formation of southern Florida and previously referred to as the “Pinecrest Subsea” (Petuch, 1997)), an exact contemporary of the Jackson Subsea of the Choctaw Sea farther north (Figure 5). A series o...

Table of contents

• Cover Page
• Title Page
• Copyright Page
• Foreword
• Preface
• Acknowledgments
• Biography
• Chapter 1. Paleoseas of Cenozoic Eastern North America
• Chapter 2. Biogeography of the Eastern American Paleoseas
• Chapter 3. Oligocene and Earliest Miocene Seas
• Chapter 4. Early Miocene Seas
• Chapter 5. Middle and Late Miocene Seas
• Chapter 6. Early and Late Pliocene Seas
• Chapter 7. The Everglades Pseudoatoll
• Chapter 8. Latest Pliocene and Earliest Pleistocene Seas
• Chapter 9. Early and Late Pleistocene Seas
• Chapter 10. Biotic Patterns in Time and Space
• Systematic Appendix
• References