Sed Strat Week 13

biostrat and lithostrat

In a succession of beds, most of time is represented by…

surfaces that separate the beds (bedding planes; breaks in sedimentation over centuries). This amount of time is difficult to quantify.

Bioturbation intensity and surface exposure may provide clues

Evolution

Genetic changes in populations that live together and belong to the same species. Occur in response to environmental factors

Adaptations

Specialized features of animals and plants which perform one or more useful function (horns, teeth). Often mutations, where genes undergo structural change

Evolutionary divergence

Two or more species share a common ancestor but diverge at some point to favor different forms over the centuries

Homology

Presence of organs in 2 different groups of organisms that are the same in origin but perform different functions

Natural selection

Process in nature that parallels artificial selection in which different species gain adaptations, determining their survival

organisms do not revert to more primitive forms

Particulate inheritance

Genes retain their identities when being passed down to offspring. Dominant v. recessive genes

Species

Groups of interbreeding organisms that are separated from others

Linnean hierarchy

General term for ranks is “taxon” (taxa plural). Fundamental taxon rank is the “species”

similarities and differences in morphology define different species

Holotype

A single representative specimen against which other potential representatives of the species are compared

Genus

group of species that are closely related

Speciation

Geographic isolation of one population of the same species from the rest leads to evolutionary change, and thus the creation of a new species

Often appears to be a sudden event in the rock record

Phyletic transformation (phylogeny)

Change through time of a whole species that does not result in speciation

Phyletic extinction (pseudoextinction)

Ancestral species disappears, but not due to the death of the whole population. Result of changing forms

Phyletic gradualism

Idea that evolution is a steady, gradual process

Punctuated equilibria

Idea that evolution is not gradual but punctuated by periods of episodic change; rapid evolution occurs in bursts followed by hiatuses

Biozone

Fundamental unit of biostratigraphy. Defined by zone fossils and often interlinked w/ lithology, but not always

Interval biozone

defined by the occurrences within a succession of one or two taxa

Total range biozone

first appearance and the disappearance of a single taxon is used as the definition

Concurrent range biozone

uses two taxa with overlapping ranges, with the base defined by the appearance of one taxon and the top by the disappearance of the second one

Partial range biozone

Base is defined by the disappearance of one taxon and the top by the appearance of the second

Assemblage biozone

defined by at least three different taxa that may or may not be related

Acme biozone

An interval containing a statistically high proportion of a taxon may be used to define a biozone

Index fossil

An organism with hard parts that lived in all depositional environments and was abundant, with extensive evolutionary lineage

no such taxon has ever existed

Endemism

A highly specialized species being localized to only one area on earth, due to its mobility and geographical barriers

Small vs large organism fossils

Smaller organisms tend to be more numerous, so there are more of their fossils than large vertebrates. This is why microfossils (forams, diatoms, conodonts etc) are useful in the rock record

Regional tectonics

Uplift and subsidence are never on a global scale; always localized to a particular area of a continent

Allostratigraphy

records externally driven changes (Milankovitch cycles) in stratigraphic record

Autostratigraphy

records internally driven changes (localized cyclic processes) in stratigraphic record

Sequence stratigraphy

Origin of sedimentary strata is a direct result of relative sea level change

Drivers of transgression and regression

1. rate of eustacy

2. rate of regional tectonics

3. sedimentation rate (driven by climate)

Eustacy

Global sea level change

First order eustacy

200-400 my. Related to formation and breakup of supercontinents

Second order eustacy

10-100 my. Related to volume changes in mid-ocean spreading centers

Third order eustacy

1-10 my. Related to regional plate kinematics

Fourth-fifth order eustacy

0.01-1 my. Related to orbital forcing (Milankovitch)

Crustal age

image

Eustacy over time

HST are high stand tracts (SL is highest)

TST are transgressive system tracts (SL is rising)

LST are low stand tracts (SL is lowest)

Sequences

Large bodies of marine sediment that are relatively conformable, genetically related (active at one time), and linked to eustatic change. Usually bounded by unconformities

accumulation during TST, erosion during RST

Stratal terminations generated from seismic

image

Onlap (transgressive)

Bedding surfaces pinch out moving landward (upward fining/thinning)

Offlap (regressive)

Bedding surfaces punch out moving seaward (upward coarsening/thickening)

HST (highstand systems tract)

Sea level reaches its apex and transgression ends, right before regression begins.

Sedimentation rate slows down and sediment becomes ponded near-shore

FSST (falling stage systems tract)

Sea level drops with accumulating speed and forced regression begins.

Sedimentation rate near-stops and erosion begins. Sediment progrades out to sea (offlap)

LST (lowstand systems tract)

Sea level drop hits its minimum and regression slows down, transgression begins.

Sedimentation rate begins to increase again. Sediment begins to slowly prograde onshore

TST (transgressive systems tract)

Sea level rises rapidly and transgression speeds up.

Sedimentation rate increases rapidly and progrades quickly onshore (onlap)