LOCAL INITIATION OF WALKER LANE TECTONISM PRIOR TO 3.6MA RECORDED IN NEOGENE SEDIMENTS AT HONEY LAKE BASIN, NORTHEASTERN CALIFORNIA

Pliocene lacustrine sedimentary rocks are exposed in the overlap between the Honey Lake and Warm Springs faults in the southwestern part of Honey Lake, at the northern end of the Walker Lane. These rocks are characterized by lacustrine facies comprising diatomaceous claystone interbedded with graded sandstone beds and tephras, and containing debris flows with intraformational megablocks. Facies associations are interpreted as lacustrine turbidite-fan systems, ranging from slope through basin floor. A 5 m thick debris flow with sand and mud megablocks overlies levee facies associations. Decimeter- to meter-scale scours atop the debris flow indicate lowering of base level and fan abandonment. Thick hemipelagic sediments overlie the debris flow and fan system, indicating lake deepening. A sequence boundary can be placed between fan and hemipelagic facies associations; age of the boundary is about 3.6Ma based on tephra correlation and the rate of sediment accumulation. The sedimentary record (i.e. generation of debris flow, fan abandonment and subaerial erosion) suggests basin extension or uplift around 3.6Ma, probably due to seismicity along the Honey Lake - Warm Springs fault zone. This Neogene sedimentary section in the western Honey Lake basin records a four-part history. Early basin initiation was due to either extension or transtension. However, before 3.6Ma the western part of the basin was subject to local transpression along the Warm Springs fault zone, resulting in uplift and local erosion of basin sediments. This represents a youngest possible age for the beginning of strike-slip Walker Lane-style faulting in the area. At about 3.6Ma relative lake level dropped, due either to local uplift, rearrangement of lake depocenter, or climate change. Immediately thereafter the western basin subsided and flooded. Finally, the area was uplifted, exhumed and deformed by several sets of local strike-slip faults in a restraining bend of the Honey Lake fault, active today.