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Geology topics

Laurel M. Bybell

Publications and source records attributed to Laurel M. Bybell.

At least 37 records · Page 2Linked to original sources
USGS1997

Paleontology and physical stratigraphy of the USGS-Pregnall No. 1 core (DOR-208), Dorchester County, South Carolina

Pregnall No. 1, a 346-ft-deep corehole in northern Dorchester County, South Carolina, recovered sediments of late Paleocene, middle and late Eocene, and late Oligocene age. The core bottomed in the Chicora Member of the Williamsburg Formation (Black Mingo Group) of late Paleocene age (calcareous nannofossil Zones NP 7/8 (?) and NP 9). The Chicora (346 to 258 ft depth) consists of two contrasting lithologic units, a lower siliciclastic section of terrigenous sand, silt, and clay, and an upper carbonate section of moldic pelecypod limestone. The Chicora is overlain unconformably by the middle Eocene Moultrie Member of the Santee Limestone (Orangeburg Group). The Moultrie (258.0 to 189.4 ft) consists primarily of bryozoan-pelecypod-peloid packstones and grainstones, which are assigned to calcareous nannofossil Zone NP 16. Unconformably above the Moultrie are the locally shelly, microfossiliferous limestones of the Cross Member of the Santee Limestone (Orangeburg Group), which are assigned to middle Eocene Zone NP 17 and upper Eocene Zone NP 18. The Cross Member (189.4 to 90.9 ft) is unconformably overlain by a very thin, basal section of the upper Eocene Harleyville Formation (Cooper Group). The thin Harleyville section consists of fossiliferous limestone, primarily pelecypod-foraminifer-peloid packstones (90.9 to 85.8 ft), and is assigned to Zone NP 18, although samples from thicker Harleyville sections in the region typically are assigned to upper Eocene Zone NP 19/20. The Harleyville is overlain unconformably by the upper Oligocene Ashley Formation (Cooper Group). The Ashley Formation (85.8 to 30.0 ft) consists of a relatively homogeneous section of calcareous, microfossiliferous, silty and sandy clays assigned to Zones NP 24 and NP 25 (?). Neogene and (or) Quaternary deposits present in the upper 30 ft of the Pregnall section are assigned provisionally to an unnamed unit (30 to 22 ft) and to the Waccamaw Formation(?)(22 to 0 ft).

South Carolina↗
USGS1994

Paleogene stratigraphy of the Solomons Island, Maryland, corehole

The Solomons Island corehole was drilled in the hope of obtaining a continuous and more nearly complete section of upper Paleocene and lower Eocene strata than are found in the discontinuous and fragmentary sections in the outcrop belt to the west. Consultation with Harry Hansen (Maryland Geological Survey) on possible drilling sites that were within the limits of our equipment and funding led to the selection of Solomons Island. A strong factor in this selection was the stratigraphic information available from the nearby Lexington Park well (Hansen and Wilson, 1984). As anticipated, all Paleogene units previously reported in the Maryland and Virginia Coastal Plain, except for the upper Eocene Chickahominy Formation and the upper Oligocene Old Church Formation, were penetrated at Solomons Island. The upper part of the Solomons Island corehole also penetrated the Calvert Formation of Miocene age and the younger Lowland Deposit. Gibson and Andrews (1994) described the lithology and biostratigraphy of these Miocene sediments. This paper describes the lithologies of the Lower Cretaceous, Paleocene, and Eocene strata that were recovered from the Solomons Island corehole and gives a brief biostratigraphic and paleoenvironmental summary of the beds penetrated there.

Maryland↗
USGS1994

Sedimentary patterns across the Paleocene-Eocene boundary in the Atlantic and Gulf Coastal Plains of the United States

Fossiliferous clay and sand belonging to calcareous nannofossil Zones NP 9 (latest Paleocene) and NP 10 (earliest Eocene) are widespread in the US Gulf and Atlantic Coastal Plains. Although the thickness of Zone NP 9-NP 10 strata is several times greater in the eastern Gulf Coastal Plain than in the Atlantic Coastal Plain, the hiatus that usually is present between these two zones in inner neritic strata is of longer duration in the Gulf Coast. Although 6 sequences are found in Zones NP 10-NP 11 in both the Atlantic and Gulf Coastal Plains, the number of sequences in each NP zone differs in the 2 areas. There is continuous deposition across the Zone NP 9-NP 10 boundary only in the northern Atlantic Coastal Plain, where middle to outer neritic deposits record the presence of several latest Paleocene (upper Zone NP 9) events that occurred at approximately 55.2 Ma.

Atlantic Coastal Plain, Gulf Coastal Plain↗
USGS1992

Closure of the Isthmus of Panama: The near-shore marine record of Costa Rica and western Panama

The final closure of the Isthmus of Panama at ∼3.5 Ma divided the American tropical ocean into two separate and different oceanographic regions. Consequences for the marine biota were profound, but, hitherto, correlation of the Pacific and Caribbean coastal sections has not been precise enough to track biologic patterns. We present here a correlation of 31 sections from the Pacific and Caribbean coasts of Costa Rica and western Panama. Using calcareous nannofossils and planktonic foraminifera at both the tops and bottoms of each formation, we estimate that the Caribbean section ranges from 8.2 Ma to 1.7 Ma; and the Pacific sequence, from 3.6 Ma to <1.7 Ma. These intervals bracket postulated dates for final closure of the Isthmus and provide the first well-dated record of middle and late Pliocene faunas from the region. The Caribbean and Pacific sections include very different environments of deposition, yet there is sufficient overlap and diversity of habitats to permit meaningful biological comparisons. On the Caribbean side, formations tied together by the overlap of the upper Pliocene markers Sphenolithus abies and Pseudoemiliana lacunosa (3.5 Ma to 3.6 Ma) range from very shallow to shallow inner shelf (<200 m) and upper slope (200-800 m). The Pacific coast sections were mostly deposited in a trench slope environment, which is absent on the Caribbean side. These sections fortuitously include abundant thick intra-formational slumps containing shallow-water fauna more appropriate for biological comparison with the Caribbean biota. Similarly, the ∼1.9 Ma to 1.5 Ma interval, well constrained by various taxa, includes middle- to outer-shelf, and inner-shelf to upper-slope deposits on the Caribbean side, and marginal-marine to inner-shelf deposits on the Pacific coast. Using our new biostratigraphic framework to correlate previously poorly constrained mollusc collections, we show that evolutionary divergence of the Pacific and Caribbean near-shore marine faunas had occurred by 3.5 Ma. This strongly suggests that the Isthmus was effectively closed by this time.

GSA Bulletin↗
USGS1990

Eocene-Oligocene sea-level changes on the New Jersey coastal plain linked to the deep-sea record

We use magnetostratigraphy and Sr-isotope stratigraphy to improve stratigraphic control for the Eocene to Oligocene of the New Jersey coastal plain (ACGS4 borehole). Magnetostratigraphy in many cases is complicated in outcrop sections of shallow-water (<200 m paleodepth) sediments by low remanence and weathering; we minimize these problems by analyzing large samples obtained from the ACGS4 borehole and construct a firm magnetochronology for the early to middle Eocene. Sr-isotope stratigraphy confirms biostratigraphic evidence for a previously unknown uppermost Eocene to lowermost Oligocene unit and delineates a "middle" Oligocene hiatus that is unresolvabie using biostratigraphy alone. We recognize hiatuses and associated unconformities on the New Jersey margin near the lower Eocene/middle Eocene boundary, within the middle Eocene, and in the "middle" Oligocene and correlate these events with similar hiatuses observed in other continental-shelf, slope, and epicontinental settings. In addition, a hiatus probably occurred near the middle Eocene/upper Eocene boundary. We conclude that the interregional distribution of these Eocene-Oligocene hiatuses indicates a global cause: eustatic change.

New Jersey↗
USGS1988

Eocene to Miocene biostratigraphy of New Jersey core ACGS #4; implications for regional stratigraphy

Lower Eocene through probable upper Miocene sediments were recovered in a 945-foot core (ACGS #4) taken near Mays Landing, New Jersey. Calcareous nannofossils and planktic foraminifers are common to abundant in most of the lower part of the core. All standard calcareous nannofossil zones from lower Eocene Zone NP 12 through lower Oligocene Zone NP 21 are identified, and the midlatitude Eocene planktic foraminifer zones based on the Turborotalia cerroazulensis lineage are recognized. The Paleogene section of this core is unique for the New Jersey coastal plain because it includes a nearly continuous lower Eocene to lower Oligocene sequence of marine sediments. In contrast, previous analyses of this area indicate that a major unconformity is present between the middle Eocene and the Oligocene. A time versus depth plot controlled primarily by nannofossil zone boundaries shows that sediment accumulation rates during the early and middle Eocene were in the range of 6 to 15 feet per million years. During the late Eocene, accumulation rates were much higher, perhaps exceeding 70 feet per million years. The only clear hiatus detected in the Paleogene part of ACGS #4 on the basis of microfossils is between the early and (?)late Oligocene. However, hiatuses are suspected at the early-middle Eocene boundary and within the late Eocene. Occurrences of calcareous nannofossils and planktic foraminifers are documented, and a number of key taxa are illustrated.

New Jersey↗