Geology topics

F. Serra

Publications and source records attributed to F. Serra.

3 recordsLinked to original sources

USGS2001

Vertical tectonics in northern Escanaba Trough as recorded by thick late Quaternary turbidites

Escanaba Trough, the southernmost segment of the Gorda Ridge, is filled by as much as 500 m of late Quaternary turbidite and hemipelagic sediment. Coring at Deep Sea Drilling Project Site 35 and Ocean Drilling Program (ODP) Sites 1037 and 1038 together with 4.5-kHz deep-tow and 3.5-kHz surface-ship seismic reflection profiles enable a distinct pattern of reflections to be mapped throughout Escanaba Trough in the upper part of this sediment fill. The uppermost 80 m of turbidite sediment, which includes at least 11 turbidity current events, were deposited in <7 kyr. Nine of these turbidites are found throughout Escanaba Trough at water depths >3200 m. The turbidity currents were trapped upon entering Escanaba Trough, resulting in all of the sediment in suspension in the flows being deposited. The thickness of the turbidite layers reflects both the flow thickness and the vertical grain concentration within the flow that deposited the layer. Variations in the turbidite thickness with respect to water depth can be used to estimate the degree of relative vertical movement within the floor of Escanaba Trough. In the area of hydrothermal activity near ODP Site 1038, uplift of as much as 140 m has occurred over the past 8 kyr.

California↗

USGS2000

Turbidite megabeds in an Oceanic Rift Valley recording jokulhlaups of late Pleistocene glacial lakes of the western United States

Escanaba Trough is the southernmost segment of the Gorda Ridge and is filled by sandy turbidites locally exceeding 500 m in thickness. New results from Ocean Drilling Program (ODP) Sites 1037 and 1038 that include accelerator mass spectrometry (AMS) 14C dates and revised petrographic evaluation of the sediment provenance, combined with high-resolution seismic-reflection profiles, provide a lithostratigraphic framework for the turbidite deposits. Three fining-upward units of sandy turbidites from the upper 365 m at ODP Site 1037 can be correlated with sediment recovered at ODP Site 1038 and Deep Sea Drilling Program (DSDP) Site 35. Six AMS 14C ages in the upper 317 m of the sequence at Site 1037 indicate that average deposition rates exceeded 10 m/k.yr. between 32 and 11 ka, with nearly instantaneous deposition of one ~60-m interval of sand. Petrography of the sand beds is consistent with a Columbia River source for the entire sedimentary sequence in Escanaba Trough. High-resolution acoustic stratigraphy shows that the turbidites in the upper 60 m at Site 1037 provide a characteristic sequence of key reflectors that occurs across the floor of the entire Escanaba Trough. Recent mapping of turbidite systems in the northeast Pacific Ocean suggests that the turbidity currents reached the Escanaba Trough along an 1100-km-long pathway from the Columbia River to the west flank of the Gorda Ridge. The age of the upper fining-upward unit of sandy turbidites appears to correspond to the latest Wisconsinan outburst of glacial Lake Missoula. Many of the outbursts, or jokulhlaups, from the glacial lakes probably continued flowing as hyperpycnally generated turbidity currents on entering the sea at the mouth of the Columbia River.

Journal of Geology↗

USGS1999

Deep-sea sedimentary record of the late Wisconsin cataclysmic floods from the Columbia River

New results from Ocean Drilling Program Site 1037 and U.S. Geological Survey high-resolution seismic-reflection profiles confirm the great thickness, fast deposition rate, distant source, and convolute path of turbidites that fill the Escanaba Trough, the rift valley of the southernmost segment of the Gorda Ridge. Accelerator mass spectrometry 14 C measurements provide the first direct dating of the Escanaba Trough turbidites, demonstrating an average deposition rate faster than 10 m/k.y. between 32 and 11 ka and as fast as 15 m/k.y. during the oxygen isotope stage 2 lowstand. In the upper 60 m of sediment, the petrology of turbidite sand beds, which are as much as 12 m thick, show that the dominant source for the turbidites is from the Columbia River, which is more than 800 km to the north, rather than from the much closer rivers of northern California. New high-resolution seismic-reflection profiles show that, except for areas of very recent volcanism, the entire Escanaba Trough below 3200 m water depth is floored by the turbidite sequence that was cored in the upper 60 m at Site 1037B. The ages of the upper 120 m of turbidites correspond with the ages of channeled scabland deposits associated with latest Quaternary jokulhlaups from glacial Lake Missoula. The age and source characteristics suggest that these megaturbidite beds in Escanaba Trough are most likely deposits formed by hyperpycnally generated turbidity currents as the largest of the Lake Missoula floods entered the sea.

Geology↗