Stratigraphic Concepts

Demonstrating equivalency (genetic/) between strata ( units) • - organization of strata on the basis of their lithologic characteristics • - organization of strata on the basis of the they contain • - organization of strata on the basis of their magnetic characteristics • chemostratigraphy - organization of strata on the basis of their isotopic characteristics • seismic - organization of strata on the basis of their seismic characteristics

- time relationships • - depositional sequences, packages of strata bounded by

San Benito Gravels • Age? • Sedimentation Rate? S.R.=∆d/∆t • Episodic deposit.? – pause ? – ∆d=? ∆t=?

1 Absolute vs. Relative Time • Absolute time - set within the framework of geologic time – essential for reconstructing tectonic , paleoclimates, etc. • Relative time - time represented by the – essential for computing accumulation rates, etc. time time


depth depth ∆d

2 “Timing is everything”

(stratigraphy) is essential for understanding all history & hence earth system processes, – tectonic – climatic – biologic ().

Lithostratigraphy the study & organization of strata on the basis of lithologic characteristics • - type, color, composition, and grain size LITHOSTRATIGRAPHIC UNITS - bodies of rocks distinguished on the basis of observable lithologic characteristics – no connotation of age other than the – separated by contacts – - type section (most complete)

3 Fundamental Units*: n o i t • - collection of formations a m r o • Formation- lithologically distinctive unit f that is large enough in scale to be mapable (single lithology or regular alternation of ) C – e.g. Monterey Formation • Member - (subdivision of a formation) characteristics that distinguish it from other

parts of the formation B members? , – e.g. series of phosphatic-rich layers interfingering with dolomites/cherts Group I • Beds - subdivision of a member, smallest

unit Lithology *Only applied to land-based sedimentary C sections

Paleocene-Eocene Strata: Gulf & Atlantic Coast

4 -Eocene Strata: Gulf & Atlantic Coast


Wilson Lake

5 Paleocene-Eocene Strata: Gulf & Atlantic Coast Clayton Wilson Lake Gl-91

Purisma Santa Cruz MS



San Lorenzo

Butano SS


6 Contacts boundaries between units 1. plane or irregular surfaces 2. Conformable or unconformable

• Conformity (Conformable) - no physical evidence of non- – Abrupt – Gradational

• progressive - gradation Site 1263A - 13H S6 50.5 cm • intercalated - gradation is an Eocene inter-bedded interval Paleocene

7 Contacts • Unconformity (unconformable) - break or hiatus in deposition (erosional, non-deposition) current scour surface, or sub-aerial surface, slump or slide surfaces – Angular - younger atop eroded surface of tilted or folded rocks – Disconformity - parallel bedding planes, but erosional surface (channeled, paleosols, lag-gravel deposit) - uplift, sea-level regression • lithology may change – Paraconformity - same lithology above and below, non deposition or dissolution. • Can only be recognized by other stratigraphic techniques • Nonconformity - sedimentary / igneous or

Angul?ar UC



8 Recognition of Unconformities

• basal conglomerates • deeply weathered soils horizons • truncated bedding • clasts • burrowing or hardgrounds • channel deposits • truncated ranges (several lineages)

9 Lateral Contacts • pinch-out - progressive thinning of a • intertonguing - lateral splitting of units that pinch out independently – shoreline migrating back and forth • progressive lateral gradation

Stratigraphic completeness: hiatuses (diastems) - abundant in the rock record - – more frequent in high energy environments • Sedimentation rates high, but episodic (erosion common) • continental – non-deposition and erosion - uplift – episodic deposition - flooding • shallow marine depth time – Erosion - regressions (local, global) gap – non-deposition, wave erosion – deposition during storms • hemi-pelagic – slumps, turbidites represent episodic deposition • pelagic gap – sedimentation tends to be lower, but more continuous

10 ODP Site 1207, northwest Pacific • Drilling Objectives: – P/E Boundary – K/T Boundary – Aptian/Albian

ODP Site 1207, northwest Pacific


11 Relationships in Space and Time

Prograding Delta

12 Vertical and Lateral Successions of Strata:

• conformable and unconformable contacts divide sedimentary rocks into vertical successions. Walther’s law - to be conformable, vertically adjacent facies must reflect those facies which occur side by side • facies - a body of rock with some consistent characteristic • lithofacies - a consistent lithologic characteristic within a formation ( facies, evaporite facies)

Walther’s Law

Deepening upward Shallowing upward

13 Cyclic successions rhythmic sedimentation (repetitions of strata) • Temporal scales annual to m.y. • All environments pelagic - /marl delta - repeated coarsening upward cycles

Paleocene Scalia Rosa, Dolomites, Italy

14 Cycle Order (Scales)

Cycle Order Major sedimentary cycle durations as influenced by eustatic changes

Type Duration (m.y.) Cause 1st 200-400 Tectonic: formation and breakup of supercontinents 2nd 10-100 Mid-ocean ridge spreading changes - volume 3rd 1-10 Mid-ocean ridge spreading changes - volume 4th 0.2-0.5 Milankovitch glacioeustatic cycles

5th 0.01-0.2 Milankovitch glacioeustatic cycles

15 Cyclic successions

Causal Mechanisms: • Autocyclic - internal to the basin switching delta lobe, storm beds, floodplain – beds show limited lateral continuity Flood Plain Deposits, • Allocyclic - mainly external Paleocene-Eocene Bighorn Basin, WY to the basin climate, sealevel, tectonic movements in source area – beds may show extensive lateral continuity

U. Carboniferous, S Wales

Allocyclic Mechanisms

Milankovitch cycles - oscillations in earth's orbit primary periods: • 19, 23 ky - precession of the pole (wobble) • 41ky - obliquity (tilt) • 100, 410 ky - eccentricity Perihelion -147x106km Aphelion - 152x106km

16 Orbital cycles:Effect on Insolation • Eccentricity 95, 100, 120, 413 ky (2.3 m.y.) – Earth - sun distance 0.0 to 0.06 Effect on insolation: ca. 0.7 W/m2 uniform across latitudes • Tilt 41 ky (29, 54 ky,1.25 m.y.) – angle ~ 22.0-24.3° hotter summers / colder winters in both hemispheres Effect on insolation: up to 17 W/m2 at high latitudes • Precession 19, 23 ky – wobble - gravitational pull of sun on ’ equatorial bulge – elliptical precession hot summers/cold winters in one hemisphere, and cold summers/hot winters on the other. Effect on insolation: up to 40 W/m2

Ice-sheets (18 kya, present day)

17 Sea-level Change, 150 kya to present

Sea Level

120 meters

18 90 m

100 m ~10 km

Transgressions/Regressions Transgressions - shoreline moves landward Regressions - shoreline moves seaward 3 Causes: 1. Sea level - rise and fall 2. Tectonic - uplift / 3. Supply • eustatic changes – ice-volume (glacioeustatic), basin geometry Global signal • relative changes – Local subsidence/uplift or sediment supply Regional signal

19 Sea level Rise

sand silt mud


coastal onlap time lines

fining upward sequence

• Transgression – Sea level rise w/ no change in sediment supply • Stationary – Sea level rise w/ balanced by sediment supply • Regression – Sea level rise w/ large increase in sediment supply • all three produce coastal onlap because sea level is rising

Sea level rising (high sediment supply) regression

erosional surface coastal onlap

• Rising sealevel - coastal onlap, – regression

Top lap Regression

no onlap Sea level stationary

• Standstill of sealevel - no coastal onlap, but top-lap – regression

20 Coast Basin Section C Section A Section B

Lithofacies are time transgressive

Transgression (Deepnening) Regression (Shallowing)

Sea level Rise

21 Asymmetry of Transgressive and Regressive Cycles:

• Transgressive - classic fining non-marine marine non-marine marine upward? regression – Rare- fining upward less common than coarsening upward transgression

• Rapid rise in SL - erosion/non- Delta Progradation deposit during transgressive phase regression limestone (rapid) limestone – coastal and shallow marine deposits - shaly shale thin or non-existent (marine) transgression Rapid transgression – deposition mainly during regressive shale (sandy) phases channel sand disconfomity – e.g. delta progradation - Carboniferous Cyclothems

Carboniferous (299 to 359 Mya)

22 Carboniferous (299 to 359 Mya)

Cyclothems: Allocyclic vs. Autocyclic

Carboniferous , West Virginia

Correlation of Lithostratigraphic Units • Lateral Tracing • most direct method

• only where strata are continuously lithologic exposed similarity Key bed • Lithologic Similarity and Stratigraphic (ash) position • indirect method • correlation based on facies sequence • difficult to apply to cyclic successions • Event Stratigraphy • Marker beds • ash (bentonites) (e.g. Bishop Tuff, Long Caldera; 740 ky) • lava flows

23 Correlation of Lithostratigraphic Units Bishop Tuff • Long Valley Caldera • 740 ky

Lithologic Similarity and Stratigraphic position