Using Dust and Pollen to sleuth the origin of lacustrine seismites

For quite some time (~7 years), I have been noticing that Holocene Dead Sea seismites frequently have a thin dark flat lying fine grained  layer of sediment on top. When I finally gained access to some electron microscopes at Cambridge University in 2013, I saw that these thin layers were very fine grained. After consultation with Dust Geologist Dr. Ken Pye, I came to the conclusion that they appeared to be proximal dust deposits. It was around that time that I realized that Dead Sea earthquakes probably kicked up dust clouds that then settled atop the seismite. An example of a dust cloud kicked up by an earthquake in Mexico is featured in my crowd funding pitch video (Jerusalem Quake Seasonality on Kickstarter ) and can be seen here (Mountain front dust clouds – Mexicali Quake of 2010 ). Christoph Gruetzner, who is also intrigued by the link between seismicity and dust, has accumulated a number of videos showing “dustquakes” on his YouTube channel[1].

Given the challenges in identifying a seismite as being caused by a historical earthquake versus a local slump of non-seismic origin, I thought examining these dust layers could have some utility. It would appear that a submarine slump would be much less likely to kick up a dust cloud and leave a topping dust layer. Further, since in the Dead Sea we have access to a historical earthquake record we have an opportunity to verify the overlying dust deposit as a seismite indicator which could then be used to sleuth older seismites in dry areas that lack a historical record (e.g. the Pleistocene Lisan formation in the Dead Sea[2], or the late Miocene in Spain[3] )

Further, I saw the opportunity to examine the pollen in these dust layers to both confirm the existence of localized dust cloud (as opposed to settling from a submarine slump) and to examine the seasonality of a seismite. For my Kickstarter campaign, the seasonality of the Jerusalem Quake (26-36 ACE) is a focus but there are other earthquakes of interest in this project. On the night of May 18 and the morning of May 19 in 363 ACE, there appears to have been an earthquake couplet. The earlier quake struck to the north of the Dead Sea. The latter event struck to the South. At En Gedi, there is a seismite which Migowski et. al. (2004) identified as being a result of an earthquake to the north of the Dead Sea which probably struck in the fall of 418 ACE[4]. However, my modeling work (based on Williams (2004)) indicated that the southern 363 ACE quake was a more likely candidate. It seemed like pollen was a way to resolve this conundrum especially after my colleague Dr. Suzanne Leroy published a technique in 2016 (Lopez-Merino et. al. 2016) which distinguished individual Dead Sea layers as being deposited in the Spring or the Fall based on the airborne pollen assemblages present in a given layer. The pollen atop a Fall (418 ACE) seismite should differ from the pollen atop a (May) 363 ACE seismite.
Hence, along with the Geomythology focus of examining the seasonality of the Jerusalem Quake, we will be testing two new hypotheses that will hopefully prove useful in Paleoseismology – particularly Paleoseismology of Lacustrine deposits in dry areas with active tectonics.

  1. Pollen atop the seismite layer can identify the seasonality
  2. Dust atop the seismite can help distinguish seismic vs. non seismic origin.

In historical earthquake research, the actual year of an earthquake is frequently in question. Multiple sources may use different calendar systems referring to different years when translated to our modern Gregorian calendar (see for example an earthquake in the Fall of 347 348 or 349 AD in Beirut[5]).  In some outcrops it can be difficult to distinguish between two different historical earthquakes (e.g. 363 ACE vs. 418/419 ACE).  In such cases, seasonality could be the key to understanding the source of the seismite.

Langgut, D., et al. (2016). “Resolving a historical earthquake date at Tel Yavneh (central Israel) using pollen seasonality.” Palynology 40(2): 145-159.

López-Merino, L., et al. (2016). “Using palynology to re-assess the Dead Sea laminated sediments – Indeed varves?” Quaternary Science Reviews 140: 49-66.

Migowski, C., et al. (2004). “Recurrence pattern of Holocene earthquakes along the Dead Sea transform revealed by varve-counting and Radiocarbon dating of lacustrine sediments.” Earth and Planetary Science Letters 222(1): 301-314.

Williams, J. B. (2004). Estimation of earthquake source parameters from soft sediment deformation layers present in Dead Sea muds. California State University – Long Beach. M.S. Civil Engineering.

 

[1] dustquakes

[2] Alsop, G. I. and S. Marco (2011). “Soft-sediment deformation within Seismogenic slumps of the Dead Sea Basin.” Journal of Structural Geology 33(4): 433-457.

[3] Rodrıguez-Pascua, M. A., et al. (2000). “Soft-sediment deformation structures interpreted as seismites in lacustrine sediments of the Prebetic Zone, SE Spain, and their potential use as indicators of earthquake magnitudes during the Late Miocene.” Sedimentary Geology 135(1–4): 117-135.

[4] Ambraseys, N. (2009). Earthquakes in the Mediterranean and Middle East: a multidisciplinary study of seismicity up to 1900. Cambridge, UK, Cambridge University Press.

[5] Ambraseys, N. (2009). Earthquakes in the Mediterranean and Middle East: a multidisciplinary study of seismicity up to 1900. Cambridge, UK, Cambridge University Press.

and

Guidoboni, E., et al. (1994). Catalogue of ancient earthquakes in the Mediterranean area up to the 10th century, Istituto nazionale di geofisica.

 

 

Anticipated Challenges

  • Proximity to Mountain Front – Dust layers appear to  be more likely when one is closer (En Gedi) to the mountain front than further away (Nahal Ze ‘elim) where wind conditions play a bigger role
  • Finding the seismite top – Particularly at En Gedi – Complex and successive deformation imprints appear to be present at En Gedi making it difficult to determine the seismite top. This appears to be because the En Gedi sediments possess greater sediment cohesion and have less of a tendency to create a seismite top suspension that resettles such as at Nahal Ze ‘elim. I think this is due to the greater salt content at En Gedi which is a deep water lacustrine facies as opposed to Nahal Ze ‘elim which are proximal and distal delta deposits.
  • The statistical nature of pollen – Lopez-Merino et. al. (2016) found their seasonality airborne pollen signal by only looking at undamaged and undegraded pollen grains assuming that the degraded grains were more likely a result of fluvial deposition which has a broader and less certain residence time distribution (i.e. poorer time resolution)
  • The basic plan for dealing with all of these challenges (which are substantial but not intractable) is lots of samples however I am anticipating new questions coming up which will probably require a second field trip.

 

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Jefferson Williams

Jefferson Williams is a Geologist, Geophysicist, and Engineer who is a specialist in the acoustic properties of sediments. He possesses Bachelor degrees in Geology and Mechanical Engineering as well as Master’s Degrees in Electrical and Civil Engineering. He started his career as a Field Seismologist and later branched into Borehole Geophysics. Since 1998, he has been conducting independent research in the Dead Sea on Historical Earthquakes and Geomythology. He is a member of SEG, SAG-AFTRA, and SPWLA.

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