J. J. Lienkaemper G. Borchardt 1999 <div id="15009462" class="article-section-wrapper js-article-section js-content-section " data-section-parent-id="0"><p>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<span>&nbsp;</span>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.</p></div> application/pdf 10.1130/0016-7606(1999)111<0906:PCAEFA>2.3.CO;2 en Geological Society of America Pedogenic calcite as evidence for an early Holocene dry period in the San Francisco Bay area, California article