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.
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 |
| Google Analytic Metrics | Metrics page |