Quaternary Lecture 4- Reconstructing environmental change Flashcards
What can the past tell us?
- Natural variability in the environment
- Rates of change
- Spatial linkages (‘teleconnections’)
- Thresholds and feedbacks
- Empirical basis for modelling
- Context for, and evidence of, human impact
What has the quaternary been dominated by?
Ice ages
Repeated growth and decline of continental ice sheets
Enormous environmental change both close to, and distant from, the ice sheets (climate, sea-level, oceans)
What is stratigraphy?
Study of sediments and the sequence of events they record
What are 4 types of stratigraphy?
Lithostratigraphy
Biostratigraphy
Morphostratigraphy
Chronostratigraphy
What is lithostratigraphy?
Lithostratigraphy - ordering of sediment successions through observable variations in lithology – e.g. sedimentary structures, clast lithology.
What is biostratigraphy?
Biostratigraphy - ordering of sediment successions through the use of fossils
- e.g. pollen. Usually used for interglacials due to richer fauna & flora.
What is morphostratigraphy?
Morphostratigraphy – based on landforms (erosional or depositional). The
chronological subdivision of landforms in terms of their relative age based on
their surface form.
What is chronostratigraphy?
Chronostratigraphy - ordering of sediment successions through dated levels - e.g. use of radiocarbon dating.
What are sediments descriptions based on?
grain size, sorting, sedimentary structures, lateral variability, boundaries, secondary
structures
What are lithofacies?
The collective physical and organic characters found in any sedimentary rock which
indicate environment of deposition may be designated by using the term lithofacies
What are some principles of lithostratigraphy?
- Ordering of sediment successions by variations in lithology
➢ Principle of stratigraphic superposition
➢ Sediment found in cores or outcrops
➢ Sediments: clastic & biogenic
What are sedimentray lithofacies models?
Reconstruction of past depositional environments from sedimentary evidence.
What can sedimentary evidence tell us?
Modern analogues: If we study and understand modern sedimentray processes we can use sedimentary evidence to infer past processes
What are some principles of biostratigraphy?
Ordering of sediment successions through the use of fossils e.g. pollen. Usually used
for interglacials due to richer fauna & flora
Mainly based on faunal/floral fossil assemblages but also includes evidence of human presence
what are mammalian assemblage zones (biostratigraphy)?
Mammalian assemblage zones (MAZ) associated with different interglacials
E.g. – terraces of the Lower Thames (MIS 12 and younger) (Schreve et al., 2001; White et al.
2017)
The Lower Thames sequence has also provided evidence for early Human
evolution.
* Terrace sequence is also dated by independently by amino acid racemisation
(geochronology) and is an excellent example of morphostratigraphy
What are principles of morphostratigraphy?
Based on landforms (erosional or depositional). The chronological subdivision
of landforms in terms of their relative age based on their surface form.
* New frameworks for Quaternary morphostratigraphy (e.g.Candy et al., 2010;
Lee et al. 2018)
Our landscapes evolve in response to different phases (magnitude and frequency)
of climate forcing
What does proxy data tell us?
In paleoclimatology scientists use proxy data to reconstruct past climate
conditions. Such proxy data preserve the physical characteristics of a former
environment and can stand in for direct measurements.
What are the two types of proxy data?
- Flora and fauna
- Physical properties, organic proxies, geochemical proxies
Name examples of flora and fauna proxies.
Pollen, coleopteran, chironomids, diatoms; molluscs; ostracods
Name examples of Physical properties, organic proxies, geochemical proxies.
grain size; Magnetic susceptibility, bulk density, TOC, LOI, pigments, XRF, XRD
What is palynology?
the study of living and fossil pollen grains and plant spores
What are principles of palynology?
Reconstructing former vegetation cover from pollen grains in sediments
* Based on uniformitarian principles (‘present is the key to the past’)
* Identifies past variations in climate & differentiates similar events of different age
(e.g. interglacials)- Pollen zones
* Pollen grains are resistant to decay & are
well preserved & abundant in organic rich
sediments in bogs & lakes.
* Evidence generally comes from interglacial
records because such periods are richer in
organic material than glacials.
Discuss pollen records in the UK.
E.g. Loch Ashik, Isle of Skye, NW Scotland
* Lateglacial lithostratigraphic and pollen-stratigraphic sequence at Loch Ashik.
* The basal gravel, clay gyttja and gyttja deposits (base to c.523 cm) span the Lateglacial Interstadial (warming)
* The silty-clay sediments (523–508 cm) accumulated during the Loch Lomond Stadial (cold) . The black band in the middle of the Stadial unit is a visible layer of the Vedde Ash.
* The Holocene (warm) 508 cm upwards.
* Note the pollen fluctuation in response to severe cooling during the LLS
Discuss coleoptera and chironomids as proxies.
Insects = abundant & temperature sensitive – coleoptera (beetles) & chironomids
(midges) - concept of Mutual Climatic Range
* Exoskeletons are robust & preserve detail (chitin) & can thus be identified to species level.
* Beetles (coleoptera) are highly sensitive to their environment & thus can be used to
reconstruct palaeoclimate.
* Palaeoclimatic reconstructions are based upon modern distributions
