Geology topics

Loyd D. Keigwin

Publications and source records attributed to Loyd D. Keigwin.

4 recordsLinked to original sources

USGS2005

Catastrophic meltwater discharge down the Hudson Valley: A potential trigger for the Intra-Allerød cold period

Glacial freshwater discharge to the Atlantic Ocean during deglaciation may have inhibited oceanic thermohaline circulation, and is often postulated to have driven climatic fluctuations. Yet attributing meltwater-discharge events to particular climate oscillations is problematic, because the location, timing, and amount of meltwater discharge are often poorly constrained. We present evidence from the Hudson Valley and the northeastern U.S. continental margin that establishes the timing of the catastrophic draining of Glacial Lake Iroquois, which breached the moraine dam at the Narrows in New York City, eroded glacial lake sediments in the Hudson Valley, and deposited large sediment lobes on the New York and New Jersey continental shelf ca. 13,350 yr B.P. Excess 14 C in Cariaco Basin sediments indicates a slowing in thermohaline circulation and heat transport to the North Atlantic at that time, and both marine and terrestrial paleoclimate proxy records around the North Atlantic show a short-lived (<400 yr) cold event (Intra-Allerød cold period) that began ca. 13,350 yr B.P. The meltwater discharge out the Hudson Valley may have played an important role in triggering the Intra-Allerød cold period by diminishing thermohaline circulation.

Geology↗

USGS1994

Lake-level history of Lake Michigan for the past 12,000 years: the record from deep lacustrine sediments

Collection and analysis of an extensive set of seismic-reflection profiles and cores from southern Lake Michigan have provided new data that document the history of the lake basin for the past 12,000 years. Analyses of the seismic data, together with radiocarbon dating, magnetic, sedimentologic, isotopic, and paleontologic studies of core samples, have allowed us to reconstruct lake-level changes during this recent part of the lake's history. The post-glacial history of lake-level changes in the Lake Michigan basin begins about 11.2 ka with the fall from the high Calumet level, caused by the retreat of the Two Rivers glacier, which had blocked the northern outlet of the lake. This lake-level fall was temporarily reversed by a major influx of water from glacial Lake Agassiz (about 10.6 ka), during which deposition of the distinctive gray Wilmette Bed of the Lake Michigan Formation interrupted deposition of red glaciolacustrine sediment. Lake level then continued to fall, culminating in the opening of the North Bay outlet at about 10.3 ka. During the resulting Chippewa low phase, lake level was about 80 m lower than it is today in the southern basin of Lake Michigan. The rise of the early Holocene lake level, controlled primarily by isostatic rebound of the North Bay outlet, resulted in a prominent, planar, transgressive unconformity that eroded most of the shoreline features below present lake level. Superimposed on this overall rise in lake level, a second influx of water from Lake Agassiz temporarily raised lake levels an unknown amount about 9.1 ka. At about 7 ka, lake level may have fallen below the level of the outlet because of sharply drier climate. Sometime between 6 and 5 ka, the character of the lake changed dramatically, probably due mostly to climatic causes, becoming highly undersaturated with respect to calcium carbonate and returning primary control of lake level to the isostatically rising North Bay outlet. Post-Nipissing (about 5 ka) lake level has fallen about 6 m due to erosion of the Port Huron outlet, a trend around which occurred relatively small (± ∼2 m), short-term fluctuations controlled mainly by climatic changes. These cyclic fluctuations are reflected in the sed-imentological and sediment-magnetic properties of the sediments.

Indiana, Illinois, Michigan, Wisconsin↗

USGS1994

Lake Michigan's late Quaternary limnological and climate history from ostracode, oxygen isotope, and magnetic susceptibility

The limnology of Lake Michigan has changed dramatically since the late Pleistocene in response to the expansion and contraction of continental glaciers, to differential isostatic rebound, and to climate change. The lake sediment's stratigraphic trends, magnetic susceptibility, δ 18 O, and ostracode species abundance ratios provide criteria to identify the lake's response to glacial ice and to differential isostatic rebound. The latter phenomena dominate the lake's late Pleistocene and early Holocene history. The lake's hydrological budget provides the primary linkage between the lake and climate, particularly effective moisture. Dissolved salts were stored in the lake's water column when the lake's output shifted toward evaporation, but were flushed when output shifted toward outflow. The lake's salt storage history may be interpreted from some ostracode, δ 18 O, and magnetic susceptibility records found in sediment cores. Climate change influenced the entire lake's limnological history, but became the primary limnological driver from about the middle-Holocene to the present. The complex limnological history of Lake Michigan resulted in substantial changes in the ostracode species assemblages; from about 12,000 ka to about 5,500 ka, five ostracode intervals can be identified. These ostracode intervals provide a within-lake biostratigraphy and a stratigraphic reference for reconstruction of the paleoenvironmental dynamics of the lake.

Indiana, Illinois, Michigan, Wisconsin↗

USGS1985

Foraminiferal, lithic, and isotopic changes across four major unconformities at Deep Sea Drilling Project Site 548, Goban Spur

Sediment samples taken at close intervals across four major unconformities (middle Miocene/upper Miocene, lower Oligocene/upper Oligocene, lower Eocene/upper Eocene, lower Paleocene/upper Paleocene) at DSDP-IPOD Site 548, Goban Spur, reveal that coeval biostratigraphic gaps, sediment discontinuities, and seismic unconformities coincide with postulated low stands of sea level. Foraminiferal, lithic, and isotopic analyses demonstrate that environments began to shift prior to periods of marine erosion, and that sedimentation resumed in the form of turbidites derived from nearby upper-slope sources. The unconformities appear to have developed where a water-mass boundary intersected the continental slope, rhythmically crossing the drill site in concert with sea-level rise and fall.

Atlantic Ocean, Goban Spur↗