Pedogenic calcite as evidence for an early Holocene dry period in the San Francisco Bay area, California
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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.
Suggested Citation
Borchardt, G., and Lienkaemper, J.J., 1999, Pedogenic calcite as evidence for an early Holocene dry period in the San Francisco Bay area, California: Geological Society of America Bulletin, v. 111, no. 6, p. 906-918, https://doi.org/10.1130/0016-7606(1999)111<0906:PCAEFA>2.3.CO;2.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Pedogenic calcite as evidence for an early Holocene dry period in the San Francisco Bay area, California |
| Series title | Geological Society of America Bulletin |
| DOI | 10.1130/0016-7606(1999)111<0906:PCAEFA>2.3.CO;2 |
| Volume | 111 |
| Issue | 6 |
| Year Published | 1999 |
| Language | English |
| Publisher | Geological Society of America |
| Description | 13 p. |
| First page | 906 |
| Last page | 918 |
| Country | United States |
| State | California |
| Other Geospatial | San Francisco Bay area |