Search for: All records

We have been studying the stratigraphy of core LWB 4-5 taken in 2001 in the Hudson River 1.5 km north of the transit of the Peekskill meteorite in October 1992. We measured magnetic susceptibility and elemental composition at 1 cm intervals down to 50 cm and then at 5 cm intervals down to 108 cm. Magnetic susceptibilities are unusually high (above 20 cgs units) from 12-19 cm and again at 31 cm. The level at 31 cm contains mm-sized fragments of Fe oxide. X-Ray Fluorescence spectroscopy revealed high Ni/Cr levels concentrated from 9-11 cm and again below 97 cm. We found tektite-like spheroids, dumbbells and teardrops from 8-15 cm depth. They are glasses and they contain appreciable K, consistent with an origin as true tektites but we have not identified the source. Overall, we interpret the high susceptibility, high Ni/Cr and possibly tektite bearing layer as a resulting from the fall of one of the bodies postulated to have fallen with the Peekskill meteorite in 1992. A 1992 age for the top of the Peekskill layer at 8-9 cm depth is consistent with a uniform sedimentation rate in the core and the occurrence of the base of modern Pb at 97 cm depth. From previous work on cores from Central Park Lake, the base of modern Pb represents the year 1880 A.D. We also found other prominent horizons whose ages fit a linear sedimentation rate model. We found a step change in As/Pb ratio whose inferred age matches 1988, the year when Pb and Cu arsenide were banned as pesticides. Our core exhibits peaks in Ca and Sr content and a minor susceptibility peak at 17.5 depth that may represent the 1980 "Great Catskill Toilet Flush" Hudson River flood event. The Catskills contain abundant marine limestone that could serve as a source for Ca and Sr. A prominent susceptibility peak at 37.5 cm could represent a flood in 1955. We also found a peak in Pb at 50 cm depth whose inferred age matches that of the cessation of incinerator burning in 1938. 137Cs and 210Pb ages are in progress and may be available by the time of the meeting. The high Pb and As levels in parts of LWB 4-5 are supported by examination of the coarse fraction. We found two bright orange grains, both with carbon rich coatings. One grain analyses on the X-ray analyzer of an SEM as 8%C, 70% Pb, 17%As and 2% Cu. The second grain analyzes as 10% C, 43% Pb, 1% Ca, 2% P, 27% As, 4% Fe, 2% Ni, 1% Si, and 6% Zn. All analyses are in wt.% on an oxygen free basis. 

We have been studying the stratigraphy of core LWB4-1 taken in 2001 in the Hudson River about 100 meters north of the calculated transit path of the Peekskill meteorite in October 1992. We measured magnetic susceptibility at 1cm intervals from 0 -70 cm depth and found a layer with a magnetic susceptibility of 11 cgs units at 6 cm depth. This is the highest susceptibility in the top 40 cm of the core. Scanning X-Ray Fluorescence spectroscopy revealed the high susceptibility layer at 6 cm depth is part of a 3 cm interval with a high Ni/Cr ratio, but the depth of the peak in the Ni/Cr ratio is poorly resolved due to measurement error. We plan to dry and homogenize discreet samples for analysis on bench top XRF to reduce Ni and Cr error. Based on our identification of the base of modern Pb at 68 cm depth, the top 40 cm of the core covers the time interval from 2001 to 1930. From previous work on Central Park Lake, the base of modern Pb represents the year 1880 A.D. A uniform sedimentation rate model is supported a peak in Pb and As at 8 cm depth. The peak might represent the 1988 ban on the use of Pb arsenide and the start of use of DDT as a pesticide. We found a second peak in Pb at 37.5cm potentially from 1938, the date at which incineration was banned in New York City. We found a third peak in Pb at 50.5cm that might be from World War I around 1914. We found two deeper susceptibility peaks of 12 cgs at 43 cm and 8 cgs at 59 cm. These peaks could represent major Hudson River floods in 1927 and 1903. 137Cs and 210Pb 210 dating are in progress and will help us to determine if our age model is correct. Also, our core exhibits a distinct increase in Ca content starting at 18-25 cm depth and increasing towards the top of the core. This increase could be due to increased erosion, anthropogenic inputs or increased dissolution of CaCO3 rich rocks. We are measuring CaCO3 in the core to better determine the origin of this increase of Ca.