| Unit | Description |
|---|---|
| PR | Mottled clay and silt with some sand, sparse carbonate nodules, and occasional pebbles. This unit is defined as a mixed zone resulting from root bioturbation and agricultural tilling. The unit extends across the upper 10-20 cm of both walls of the trench exposure. Color: 2.5Y 4/2 (gray/brown) |
| MSEUD | Mottled mix of clay, silt, sand and some pebbles. The uppermost unit beneath the present day sag expression. The unit is undifferentiated because of heavy mixing due to bioturbation of both burrows and to a greater extent roots within the sag pond. Color varies. |
| MSE1 | Very fine sand and silt with pedogenic clay development. MSE1 is only exposed to the northeast of fault zone 1 and is the lowest unit exposed in that portion of the trench. It is tabular with a slight down warping towards fault zone 1. The unit is consistent in composition across the exposure. It is capped by a thin, 2-8 cm, clay layer containing sparse charcoal. Color: 5Y 4/2 (brownish grey) |
| MSE2 | Fine silt that is dissected by multiple sand and gravel paleochannels of the Little Cholame Creek and/or the offset stream channel. MSE 2 is found to the northeast of fault zone 1 and is warped downward by fault zone 1. Channel deposits vary in size from sand to cobbles. Cobbles were sub-rounded to rounded and included mafic clasts of Franciscan origin and sandstones including quartz arenites and greywackes with weathering rinds. Large pebbles included arkosic sandstones, Franciscan, gabbros, and marble. Smaller pebbles consisted of granite, chert, and quartz. Color: 5Y 4/2(brownish gray) |
| MSE3 | Thick clayey sand and silt containing small carbonate nodules. MSE3 has a lower mixing interface with MSE2 containing some small pebbles from MSE2. The unit is thinned and folded down into fault zone 1 and is not continuous across the fault zone. Near fault zone 1 the unit can be divided into subunits based upon an obvious variation in color and clay content. Color: 7.5YR 7/1 (light grey) |
| MSE4 | Organic rich clayey silt, some small carbonate nodules, locally bioturbated by burrows. MSE 4 is folded downward, thinned and discontinued across fault zone 1. Color: 7.5YR 5/1 (dark brown/grey) |
| MSE5 | Silty fine sand, which is apparently down warped and dropped by fault zone 1. MSE5 is siltier to the northeast of fault zone 1. Color: 5Y 7/2 |
| MSE6 | Brown gray clay, 10YR 4/1, to the southwest of fault zone 1. |
| MSE7 | Organic rich unit of mottled clay and silt with widespread carbonate nodules. Down dropped and thickens over fault zone one indicating deposition was coincident with deformation along fault zone 1. MSE 6 and MSE7 could be lumped into one thickening unit across fault zone 1, but has been separated here based upon clay content (MSE 6 is more clay rich). Alternatively, with much more logging time, the units could be broken into many smaller subunits representing on lapping sag pond deposition as the sag subsided tectonically. Color: 10YR 4/1 (mottled brown and grey) |
| MSE8 | Clayey silt deposited over fault zone 1 and thickens towards fault zone 2 where it is truncated. Top of unit is clay with discontinuous charcoal, probably an in situ burn. Color: 7.5YR 6/1 (light grey/brown) |
| MSE9 | Thin sandy silt, thickens from fault zone 1 to fault zone 2 where it is truncated. Some root bioturbation within sag. Color: 5YR 6/2 (tan/gray) |
| MSE10 | Dark, organic rich, silty clay, which, thickens from fault zone 1 to fault zone 2 where it is truncated. Charcoal is abundant. Color: 10YR 6/1 (gray/green) |
| MSE11 | Thin layer of tan silty sand, overlain by undifferentiated MSEUD so this could be an influx of sand related to local deposition within the sag or it could be Little Cholame Creek over bank deposit. Truncated by fault zone 2. Color: 7.5 YR 6/2 (tan) |
| MSE12 | Lowest unit exposed between fault zone 2 and 4, and only on the northwest wall. Silty clay tilted down towards fault zone 3/sag pond. Color: 10YR 4/1 (brown/gray/green) |
| MSE13 | Silty clay tilted down towards fault zone 3. Color: 5YR 5/2 (pale brown) |
| MSE14 | Clayey sand and silt. Tilted down towards fault zone 3. Color: 10YR 4/2 (brown) |
| MSE15 | Organic rich clay. Deformed by splay of fault zone 2 on southeast wall and tilted down towards fault zone 3. Color: 10YR 5/2 (dark brown) |
| MSE16 | Clayey silty sand that becomes more clayey as it is tilted down towards fault zone 3. Is also deformed by splay of fault zone 2 on southeast wall. Color: 2.5Y 4/2 (light brown) |
| MSE17 | Clayey sandy silt that is tilted and down faulted by fault zone 3. Color: 5Y 2.5/2 (brownish grey) |
| MSE18 | Fine silty clayey sand. It is folded and down warped by fault zone 3. Color: 7.5YR 4/2 (brown) |
| MSE19 | Mottled layer of dark clay with intermixed silt that becomes thinner and more homogeneous dark clay as it is faulted and down warped by fault zone 3. Color: 10R 4/2 (red/brown) |
| MSE20 | Silty clayey very fine sand is deformed across fault zone 3, consistent with the units below. Truncated by fault zone 4. Color: 2.5Y 4/2 (yellowish brown) |
| MSE21 | Clayey sandy silt, which becomes more clayey towards fault zone 3. Separated from MSE20 by a thin clay band containing sparse charcoal (a possible burn horizon). Faulted down by fault zone 3 in the same manner as units below. Truncated by fault zone 4. Color: 2.5Y 5/2 (orange/brown) |
| MSE22 | Silty clay, which is darker and more organic right towards the bottom of the exposure. Some charcoal present, near bottom of current sag depression. Truncated by fault zone 4. Color: 5GY 4/1 (gray brown) |
| MSE23 | Dark green clay, sag deposit. Truncated by fault zone 4. Color: 5GY 4/1 (green brown) |
| MSE24 | Upper distinguishable unit of current sag pond. Some charcoal, mottled clay and silt, truncated by fault zone 4. Color varies. |
| MSWUD | Heavily burrowed and bioturbated, lumped as one unit because of its current state, but once consisted of silts, sands and gravels. This southwest side of the sag pond is much drier than the northeast side, allowing more burrow related bioturbation. Tan, gray, and brown. |
| MSW1 | Dark silty sandy clay, lowest of the southwestern units. Tilted down towards fault zone 4. Color: 7.5YR 4/3 (dark brown) |
| MSW2 | Fine silty sand that is bioturbated to the southwest, tilted down towards fault zone 4. Color: 10YR 4/3 (tan) |
| MSW3 | Clayey sandy silt between laminated burn horizon (MSW4) and sand (MSW2), discontinuous because of bioturbation. Tilted down towards fault zone 4. Color: 5YR 4/4 (brown grey) |
| MSW4 | Laminated silty clay with laminated charcoal. Tilted towards fault zone 4. Discontinuous because of bioturbation. Color:10YR 6/4 (gray brown) |
| MSW5 | Fine to coarse sand with some small pebbles, heavily bioturbated towards the southwest and cannot be traced across entire exposure. Tilted towards fault zone 4. Color: 5YR 3/4 (brown) |
| MSW6 | Dark clayey silt that grades to brown as it is bioturbated towards the southwest. Tilted, sheared and faulted by fault zone 4. Color: 2.5YR 2.5/2 (dark grey) |
| MSW7 | Brown sandy silt is apparently warped down into fault zone 4 and faulted several times. Color: 2.5Y 4/2 (brown) |
[Back]