Unit/
Subunit |
Sediment
type |
Stratification
|
Bedforms
|
Soft sediment deformation
|
Grain
size |
Size grading
|
Sorting
|
Components
|
Basalt glass/clast vesicularity
|
Cement
|
Comments
|
|---|---|---|---|---|---|---|---|---|---|---|---|
| 2, 4a | Calcareous interbeds | Laminated | Massive to cross-bedded | Bioturbated at top | Silt to fine sand | Ca = 75%, Cl = 10%, Do = 5%, BGS = 10% |
Unit 4a contains nannofossils. | ||||
| 4j, 7a, 15, 7b, 10, 12, 22a, and 27 | Vitric and volcaniclastic siltstone-sandstone | Laminated to thin bedded | Plane bedded (massive and cross-stratified beds; internal erosion surfaces) | Loading structures on bedding planes; slump disturbed bedding and microfaults in Unit 4j | Silt to medium sand | Reverse and normal graded beds | Good to moderate | Mixture of basalt glass fragments, carbonate, and siliciclastic material | Carbonate and zeolite? | Units 7b, 10, and 27 contain nannofossils. | |
| 4b, 4d, 4e, 4i, 4k, and 4m | Resedimented basalt tuff | Laminated to thin bedded | Plane bedded, with intercalated massive, graded or cross-stratified beds | Very fine to medium ash | Normal, symmetric, or reverse | Moderate (good to poor) | VBG/BGS = 85%-95%, Cy = 5%-10%, L = 0%-10% |
Typically highly vesicular | Carbonate or zeolite | Units 4d and 4e may have been emplaced as density currents. | |
| 4c, 4f, 4g, 4h, and 25 | Basalt tuff (scoria fall deposit) | Medium to thick bedded | Massive to graded beds | Fine to coarse ash | Normal | Good to moderate | VBG = >90%, Cy = <10% |
40% to >70% | Zeolite | Deposit contains highly vesicular and delicate reticulite-like clasts. Bedded tephra fall deposited in water. | |
| 7c, 7d, 17, and 31a | Basalt hyaloclastite tuff | Thin to medium bedded | Massive or graded beds with rare cross-stratified beds | Very fine to very coarse ash | Normal | Poor | BGS = 60%-90%, Cy = 5%-20%, L = 5%-20% |
Non- to poorly vesicular | Carbonate | These deposits comprise non- to poorly vesicular, angular, splinterlike clasts identical to those in hyaloclastite tuffs formed by quenched fragmentation. Unit 17 contains nannofossils. | |
| 4l, 9, and 22b | Basalt-lapillistone/lapilli tuff | None or thick bedded | Massive to graded beds | Fine to medium lapilli | Normal | Moderate | VBG = 95%, L = 5% |
40% to >70% | Zeolite or carbonate | Subaerial scoria fall deposits. Unit 22b contains ballistic lava blocks and armored lapilli. | |
| 13 | Breccia: plagioclase-basalt hyaloclastite breccia | None | Massive | Breccia | None | Very poor | BG = 50%, L = 50% |
Carbonate | 10- to 125-mm plagioclase-basalt lithic blocks in a lapilli matrix consisting of plagioclase-basalt glass and lithic fragments. Lithology is identical to the underlying lava. | ||
| 28 | Breccia: volcaniclastic breccia | None | Massive | Breccia | None | Very poor | L = 50%, Ca = 50% |
Carbonate | Matrix supported; 50- to 100-mm basalt lava lobes and lithic blocks in calcareous mud matrix (peperite-like association). Lithology is identical to the underlying lava. |
Note: Ca = carbonate, Cl = clay, Do = dolomite, BGS = basalt glass shards, VBG = vesicular basalt glass fragments (tephra or scoria clasts), Cy = crystal fragments, L = lithic fragments, BG = splinter-shaped basalt glass fragments.