The AAPG meeting in Houston next spring (April 2-5) is the centennial meeting, and should be a good one. In recent years, AAPG has organized the technical program into broad ‘themes’ rather than allowing specific session proposals, and then just grouped the submissions into sessions after the deadline. People have generally rebelled against this and just organized sessions with their colleagues in order to have coherent sessions. These are only sent out via email, however, and are hard to find. I wanted to collect all the emails I have been getting about different sessions, so here it is. If you have one to add, please make a comment below, and I will add it to the list.
If you want to submit an abstract to one of these ‘sessions’, just write your abstract in such a way that it incorporates the ideas in the proposal, and submit it to the theme listed (seems more complicated than it needs to be, doesn’t it?).
The abstract submission site is here. (deadline September 22).
Mixed Siliciclastic-Carbonate Systems (Submit to Theme 5).
Primary Convener: Jake Covault, UT/BEG
Session description: Mixed depositional systems are increasingly important deepwater exploration targets near the Atlantic continental margins and have been extensively studied in the Permian basin of West Texas and Southern New Mexico. Recent seafloor and shallow subsurface observations show that siliciclastic and carbonate deepwater depositional systems exhibit remarkably similar three-dimensional stratigraphic architectures associated with mass-transport, channel, levee, and lobe elements. However, questions remain regarding the long-term depositional processes and accumulation patterns of mixed systems. In particular, how do siliciclastic and carbonate systems interact to form stratigraphy in petroliferous sedimentary basins? We solicit contributions using outcrop, seafloor, and/or subsurface data to study the dynamics and controls of mixed deepwater systems.
Deep-marine sediment gravity flow deposits: new insights relevant to deep-water exploration and production (Submit to Theme 5).
Primary Conveners: Anna Pontén (Statoil) and Ian Kane (Univ. Manchester)
Session description: Sediment gravity flows are responsible for the transport and sorting of sediment from terrestrial and shallow marine environments to deep-marine basins. The resulting sedimentary accumulations are amongst the largest sedimentary bodies on earth, submarine fans. Owing to their size and large volumes of sand grade sediment within them, submarine fans represent significant, yet challenging, exploration targets. These potential reservoirs present challenges during exploration, owing to their often deep burial depth and deep-water setting resulting in poor seismic imaging and limited core calibration, and at the development and production stages owing to their complex internal heterogeneity distribution. Developing an understanding of the range of flow behavior, such as runout length, grain fractionation, erosion and flow transformation, and the subsequent character of their deposits enables prediction of lithofacies and likely reservoir qualities and stratigraphic compartmentalisation. In addition, the effects of burial diagenesis on the different facies types is non-uniform, and this may be considered in addition to the primary depositional reservoir property distribution. This session therefore seeks presentations that address the theme of relating flow processes to reservoir quality and to the sealing potential and distribution of stratigraphic baffles and barriers in deep-water settings.
Source-to-Sink Systems (Submit to Theme 5 or Theme 1).
Primary Conveners: Tor O. Sømme (Statoil), Lorena Moscardelli (Statoil), Vanessa Kertznus (Shell)
Session description: We welcome contributions that cover wide spatial and temporal scales of source-to-sink systems, using modern analogues, outcrops, subsurface data or modeling experiments. Source-to-sink analysis investigates relationships between sediment production, transport and deposition in the onshore and offshore domains of sediment routing systems. Understanding the stratigraphic record in these areas relies on an integrated understanding of how these sediment routing systems respond to allogenic forcing and autogenic processes at various spatial and temporal scales. Similarly, analysis of the stratigraphic record can reveal how ancient landscapes and sediment routing have changed through time in response to tectonic forcing and climate change. The recent interest in interdisciplinary source-to-sink studies have partly been driven by higher quantity and quality of seismic data, global cover of high resolution remote sensing data, as well as better geochronological tools, allowing higher resolution studies to be conducted both in modern and in deep-time settings. Being able to predict stratigraphic variability in source-to-sink systems is crucial for the hydrocarbon industry in order to define the distribution of reservoirs, sources and seals in the subsurface
Gulf of Mexico Regional Depositional and Structural Studies: Key to Deep-water Exploration (Submit to Theme 5)
Primary Conveners: John Snedden (UT Austin) and Paul Mann (Univ. Houston)
Session description: Regional studies in the greater Gulf of Mexico Basin have and continue to illuminate the complex depositional and tectonic history of this prolific hydrocarbon basin. Advances in our understanding of sedimentary processes from onshore to deep-water realms, the interplay of salt tectonics and deposition, and the transport pathways from mountain source to basin sink will be covered in this technical session. We expect presentations ranging from Mesozoic to Pleistocene, subsalt to Pleistocene fans, case studies of successes and insights from play tests that have extended the life of this remarkable habitat for oil and gas exploration. Papers about regional studies from the US, Mexico, and Cuba are welcome.
Modeling of Deepwater Systems: Understanding Reservoir Architecture and Predicting Reservoir Presence (Submit to Theme 5)
Primary Conveners: Anjali M. Fernandes (U-Conn), Peter Burgess (Univ. Liverpool), Zoltan Sylvester (Chevron)
Session description: The gradual shift in deepwater exploration and production to tackle reservoirs that display more challenging porosities and permeabilities requires a more realistic characterization of reservoir geometries and permeability heterogeneities. In this session, we will welcome abstracts that address this characterization problem across a range of spatial and temporal scales, from the dynamic construction and distribution of sand-rich reservoirs on continental margins, to the distribution and properties of individual architectural elements, to the details of grain size partitioning- and/or facies distribution. We solicit submissions that combine process analysis, measurement, and prediction, including but not limited to experimental, numerical, reduced complexity, or geostatistical modelling methods. We especially encourage submissions that bridge the gap between observations and models to better understand the impact of stratigraphic architecture on fluid flow through reservoirs.
I tweeted an image that got a lot of attention the other day and wanted to follow it up with a quick post describing the deposit. The back story is this: Lesli Wood, a submarine landslide expert, showed an image at a recent conference that is a spectacular example of a mass transport deposit (MTD), or more simply, a submarine landslide deposit. Landslides occur on land (example video), causing plenty of infrastructure damage and other problems. While they are difficult to view and visualize, landslides also occur on the seafloor, causing massive reorganization of the seafloor that can generate tsunamis. In fact, the Storegga slide that occurred offshore Norway about 6000 B.C. likely killed many Europeans.
Due to their volume and size, submarine landslides are usually characterized best with seismic reflection data – the map and cross section below from this paper by T.M. Alves. The map shows large blocks of rock that have been broken apart and transported downslope (from left to right) and the cross section shows what the internal character of those blocks are. Note the discordant nature of the blocks, very similar to the image above of the outcrop, with rocks in all directions.
Outcrops usually are too small or not well enough exposed to view these types of features, but the outcrops created by road making on the Boso Peninsula in Japan are definitely good enough. This paper by Yamamoto et al (download the paper here)describing these outcrops has a very nicely drawn diagram that demonstrates the deposit. There are probably two landslide deposits that are stacked here, with a turbidite separating them (grey layer in the middle of the diagram).
Here is another nice photo from a field symposium website showing a closeup of the deposit.
Callan Bentley over at Mountain Beltway just posted about Aden Crater, and I though i would share a few photos from Kilbourne Hole, a nearby maar volcanic crater. It’s only about 15 miles from my childhood home, and I went there quite a bit in high school, both for geology and just to get out into the desert (mainly to drink beer).
Geologically speaking, it is the crater that resulted from a magmato-phreatic explosion, or when, as Wikipedia says:
rising magma super-heats water-saturated earth, far enough below the surface that a high pressure can be contained. At some point, the pressure is too much, and a steam explosion occurs, throwing the earth out in a catastrophic event. Country rocks are fragmented and expelled in the atmosphere (together with fragments of the magma), eventually creating a deep crater, the bottom of which sits below the pre-eruptive ground surface.
For some nice images of other maars in action, go here. The main reason I like these features so much is that the ash cloud that the eruption produces (called a base surge) is a sediment gravity flow (just like a snow avalanche and a turbidity current). So, these are just really hot turbidity currents on land!
Looking on Google Earth at Kilbourne Hole and nearby Hunt Hole, you see one peculiar thing – there is a prominent ridge on the eastern side of the crater, but not the western side. This is thought to be due to westerly winds (i.e., winds out of the west blowing eastward) during the eruption that pushed most of the ash to the east. The wind in west Texas and southeastern New Mexico usually blows out of the west, and since this eruption only occurred ~25,000 years ago, I think that explanation makes good sense.
In the above photo, you can see the ridges on the eastern side of the crater, and I made a simple cross section showing the formation of the ridges and dunes from the explosion. Type in these coordinates in Google Earth to get you there – take a look at it yourself! 31°58’19.35″N, 106°57’45.23″W.
Looking north, you can see the right hand side (eastern) ridge is much higher than the western ridge. This is due to the wind blowing the exploded ash and bombs eastward. The crater is large – 2 x 3 km and 12 m deep – looks impressive from the ground:
One of the biggest attractions at Kilbourne Hole are the xenoliths full of beautiful green olivine – Callan has some nice photos here. However, we came to look at the base surge deposits on the rim of the crater, which formed when ash was falling after the explosion and piling up into big dunes and ridges on the eastern side of the crater. They are impressive, and quite thick:
In the above photo you can see many dune forms, which are all made of accretionary lapilli, which are basically sand-size ash clumps. If you want to learn more about these kinds of deposits, take a look at this thesis. A detailed photo of the lapilli is below.
Note that these deposits are normally graded (biggest grains on the bottom), as is common in many places where sediment gravity flows deposit sediment. Almost all turbidites are normally graded – see here and here for more info. And if you ever drive through the area, do yourself a favor and take a trip out to Kilbourne Hole (only takes 1 hour from downtown El Paso) – you’ll be glad you did.
Geologists are always taking multi-picture panoramas of outcrops and other geologically interesting phenomena, but then have to go back to the office and use photoediting software to stitch them together into a seamless image. The problem lies that the stitching is often imperfect due to photo overlap and the resultant images are hard to view on the computer because they are so large.
Gigapan (http://gigapan.com/) found a way to make this process better – you stick your camera into a small tripod mounted robot and tell it to take a large panorama (aka a gigapan), and then use Gigapan software to stitch it together and upload it onto the internet. The online viewer is pretty slick, and as you zoom in the resolution improves. In short, it is definitely the way to view large photographs interactively. You can even tag parts of a photo with a description of what is there.
Zoltan over at Hindered Settling introduced me to this whole Gigapan process (check out his Gigapan page too) , and we have taken many gigapans together. However, I wanted to try it on my own, so I took the robot out to the Guadalupe Mountains to test it out. My camera skills arent spectacular, so my first gigapan has a few vignetting issues, but it is still really cool. Since I was using a telephoto lens, this image is made up of 351 photos, resulting in almost a 3 gigapixel image!
This subject of the photo is a place called Slaughter Canyon, a prograding and aggrading Permian carbonate shelf margin. You can clearly see the progressively younger reef fronts moving from lower left to upper right. You can also see the very steep forereef slopes exposed just to the right of the cliffy, massive reef fronts – the one at far right is the best and longest slope, and gives an indication of the relief on this margin ( about 300 m). Here is a diagram showing the general morphology of that carbonate reef – if you could have walked around here in the Permian, this area may have looked somewhat similar to the modern coast near Oman, with dry desert on land and a carbonate reef in the shallow ocean.
The image below should link to the actual gigapan, but here is a link too. Be sure to push the full screen button and scroll around to see the full resolution. Enjoy!
After a long hiatus due to general craziness at work and at home, I am starting up the blog again with this call for a cool geology sign. The Ross Sandstone is a upper Carboniferous (Pennsylvanian) formation along the coast in western Ireland that is famous for its excellent turbidite channel and lobe exposures. See this page for more details. If you haven’t got the chance to go see those rocks and the beautiful countryside of the Emerald Isle, I highly suggest a trip.
In fact I will be there next week teaching a field trip, so maybe I will do a little day-by-day blogging about the rocks there. Stay tuned!
For a while now, the most popular page on my site has been this one, a photo of a Halloween pumpkin I carved to look like the Bouma sequence. It is the most popular because people are looking for information about the Bouma sequence, so it is time to do a real post on the Bouma sequence, with more detail about turbidite deposits and the turbidity currents that produce them.
Turbidity currents are a type of sediment gravity flow where turbulence is the dominant mechanism for grain support. A turbidity current that is more familiar to most people is a snow avalanche. A turbidity current is structured like the image below, with a head, body, and tail. In (A), grains are represented by the black dots – note that the coarser grains are located near the bed and towards the front of the flow. In (B) is a turbidity current produced in a laboratory experiment that shows the downslope evolution of the flow.
Turbidity currents in the world’s oceans produce spectacular seafloor architectures like canyons, channels, and lobes/fans, depending on the amount of erosion or deposition taking place at a particular location. The sedimentary architecture is influenced by many factors, including grain size and distribution, slope gradient, sediment supply, etc etc etc.
Turbidites are the products of deposition from a turbidity current. The simplest case is a current that is slowing down (waning) and entirely depositional (e.g. on a lobe). , a turbidity current produces the classical turbidite, which was famously described by Arnold Bouma in 1962 and interpreted by Roger Walker in 1965. The Bouma sequence, as it has become known, is the idealized sequence of sedimentary structures that represents the waning of a turbidity current as it passes over a single point. The five Bouma divisions are (in stratigraphic order):
Te – pelagic mud
Td – planar laminated mud produced from suspension settling
Tc – ripple or climbing ripple cross lamination
Tb – high velocity planar lamination
Ta – structureless (aka massive) division
An important concept reflected by these structures is that the energy (bed shear stress) is decreasing upwards as the current passes by, and this is also manifested in the normal grading of the bed – coarser at the base, finer at the top. This photo from the Mt Messenger Formation in New Zealand says a thousand words (this was published in a cool paper in Nature Geoscience):
Note the nice normal grading in the deposit (coarser stuff is slightly tannish in the Ta-Tb, then going to grey in the Tc, and finally to mud in the Td-Te). The squiggly yellow line in the photo is caused by the denser sand loading into the soft mud at the start of deposition. Notice that this loading repeats in the bed above, suggesting fairly high sedimentation rates.
The Bouma sequence can also be expressed in a cartoon fashion:
Many variations on the Bouna sequence are possible: it is common to lose the Ta in distal environments where there is not enough energy in the current, and in proximal settings, amalgamated Ta beds are common, where the rest of the sequence was either never deposited or eroded away.
The next post will focus on the processes of deposition of the Ta division and how the Bouma sequence relates to the ‘Lowe’ sequence, which is typically used to describe much coarser grained turbidites…
The blog has been quiet for a while, but here is one I had to share. This photo was taken about 35,000 feet above the Mississippi river near New Madrid, MO. New Madrid is famous for earthquakes in the early 1800s that altered the course of the river (see this ppt for an overview).
The reason I took this photo was not about the earthquakes, but about the large meander bend that is nearly at cutoff. Flow is from lower left to upper right, and this bend is only 1 river width away from becoming an oxbow lake. For a nice time lapse view of how this happens, click here. Given current channel migration rates (~50 m per year for undisturbed portions), this cutoff will occur within the next few years (unless the Amry Corps of Engineers chooses to fight the river and reinforce the banks). I suspect they have already done so (an intrepid reader could check the Google Earth time slider bar…)