| Abstract: | Rainfall at the site of Union City, California, during early Holocene time appears to have been about half that of today, 470 mm/yr. We base this conclusion on detailed descriptions and particle-size analyses of 12 soil profiles and 1:20 scale logs of the fluvial stratigraphy in two 100-m-long, 5-m-deep excavations dug perpendicular to the axis of an alluvial fan along the Hayward fault. Subsidence and right-lateral movement along the fault allowed an offset stream to produce a nearly continuous alluvial record documented by 35 14C ages on detrital charcoal. Bk (calcitic) horizons in paleosols developed in the fan suggest that a relatively dry climatic period occurred from 10 to 7 ka (calendar-corrected ages). The pedogenic calcite exists primarily as vertically oriented filaments and fine, cavernous nodules formed at ped intersections. Soils and paleosols formed before 10 ka or since 7 ka did not have Bk horizons. Bk horizons that were buried suddenly at 7 ka were overlain by leached zones averaging 41 ?? 3 cm thick - about half the current depth of leaching. |
| Genre: | Article |
| ProdID: | 70021551 |
| Citation Author: | Borchardt, G.; Lienkaemper, J. J. |
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| Citation End Page: | 918 |
| Citation Issue: | 6 |
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| Citation Language: | English |
| Citation Larger Work Title: | Bulletin of the Geological Society of America |
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| Citation Number Of Pages: | 13 |
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| Citation Search Results Text: | Pedogenic calcite as evidence for an early Holocene dry period in the San Francisco Bay area, California; 1999; Article; Journal; Bulletin of the Geological Society of America; Borchardt, G.; Lienkaemper, J. J. |
| Citation Start Page: | 906 |
| Citation Volume: | 111 |
| Citation Year: | 1999 |
| Type: | citation/reference |
| Text: | Pedogenic calcite as evidence for an early Holocene dry period in the San Francisco Bay area, California; 1999; Article; Journal; Bulletin of the Geological Society of America; Borchardt, G.; Lienkaemper, J. J. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| Date Other: | Fri, 1 Jan 1999 00:00 -0600 |
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