RKC Newsletter #2, March, 2014. This is the second of a series of “newsletters” talking about sequence stratigraphic “things-of-interest”.

My main audience that I am sending this to are those who have attended my well and seismic sequence stratigraphic schools, or who are clients.

If you have any “issues” with these please contact me and also if you have something that you want to show to others, or ask “what is this?” in a public forum, then please feel free to send it to me and I can post it.

Please contact me (robkirkconsultants@bigpond.com) if you do not want to receive this-probably it will come once a month.

The subject matter for these articles will be similar to that in my schools with updates and anything new that I have come across, or corrections for where I got something wrong!

The first two will look at models and then we will look at different environments such as fans, fluvial etc.

Models 2.

This Newsletter continues on from the previous one on Geological Models. The reason we are using these models is to understand the distribution of different environments and, hopefully, of reservoirs and seals-Figure 15. Whichever model we use it has to be able to work in all environments from alluvial fans in the mountains to the marine abyss.

Figure 15. The cause of sequences is often debated. Many authors believe that they are produced by Milankovitch cycles. These high frequency events are related to changes in the Earth’s orbital parameters (precession, eccentricity and tilt) and affect the amount of solar energy hitting the Earth. There is a lot of confidence in this mechanism when studying young rocks such as in the deep water Gulf of Mexico-Figure 16 (Haq et al, 1987).

Figure 16. Here we see many third order cycles with sudden sea level fall at the basal SB due to global cooling and ice formation-blue arrows. Then there is gradual global warming, ice melts and sea level rises. Some authors query whether this mechanism is present throughout geological history. Nevertheless we nearly always see cycles of some sort so there is a regular mechanism (s) for causing these cycles. Biostratigraphers are vital for sequence stratigraphy-both in determining ages and also environments. Figure 17 from Bob Morley (Palynova-pers. com.) shows some bio-data from the Tertiary of SE Asia that helped build a useful model with well data in the Malay Basin. The Exxon model is shown (systems tracts only) in the lower part of his figure.

I was working the seismic and well log facies and Bob was working the biofacies and independently we came up with low stand units etc.

Figure 17. When starting the model work on a job I will work the well data on its own for a while and then, independently, work the seismic for a while to see which data set best displays the model. Then integrate the two data sets. Figure 18 shows a second order model on seismic from SE Asia. This is based on seismic amplitude, continuity and geometry (but is backed up with well data). Such 2nd order cycles are made up of several 3rd order “sequences” which appear to be stacking “in phase” with the 2nd order cycle. Sometimes you will have to develop your model with well data only, or seismic data only.

Figure 18. Figure 19 shows a model developed on well data only. Note that the setting of these wells is to the left side of the Exxon model as there is little marine basin developed.

Figure 19.

Note in this figure that we have HST deltas that are coeval to fluvial rocks. This is seen in most basins, so when linking well data do not always link the deltas to the deltas! Figure 20 from Utah (courtesy of Ward Abbott) shows near-seismic scale outcrop (from a plane) of prograding deltas laterally changing landward in to point bars (meandering rivers).

Figure 20. The location of your block has a bearing on how easy it may be to develop your model-Figure 21.

Figure 21.

If your permit is in deep water you may never see deltas or fluvial, or prograding, or shelf edges-and your sequence may seem to be all low stand. If you are in a landward setting you may only ever see fluvial/alluvial rocks with almost no seismic geometries. Find whatever paleogeography maps you have to see where your block sits. So far we have been discussing the Exxon Type 1 SB where the shelf edge is exposed when base level falls. If it is not exposed, such as in a ramp setting, then we may have a Type 2 SB-Figure 22. The “SMST” is a shelf margin systems tract, or shelf margin wedge.

Figure 22. It can be difficult determining what sits on the SB in such a setting and often we have to think about low stand deltas (“pgc”) or shelf margin wedges which are the Type 2 equivalent. Try to interpret Figure 23-upper. I always mark the shelf edges/breaks where the flat shelf changes in to deeper water prograding. Note on this line that we have two shelf breaks but we cannot have two coeval deep-shallow transitions. In such cases think of Type 2 boundaries-as shown in Figure 23-lower.

Figure 23. All these previous model discussions generally apply to non-tectonically active margins. When we have high frequency tectonics then we may need to modify the Exxon model-as Ward Abbott has done in Figure 24 where he has drawn four sequences.

Figure 24. Abbott worked in the field in California and Alaska where active tectonics occurred during deposition. Note on this model the location of fans-often in “mid-cycle”. Basically turbidites may be shed in to the basin at any time in an active cycle, but especially in the tectonic HST. The Exxon model requires an SB beneath the fans whereas the Abbott model does not. Note the first Abbott sequence on the figure above-the “rift basin”. These are common in many basins-such as in China, Brazil, southern Australia, Indonesia and New Zealand. Figure 25 shows a seismic rift basin.

Figure 25. These tectonic features should not (normally) be affected by marine base level changes-being solely tectonic. There is usually an active fault on one side of the asymmetric basin-as shown above with alluvial fans and fan deltas. The basal SB usually has some shallow water-fluvial rocks on it before the lake shales are developed. The lake usually fills with varying amounts of lacustrine deltas and fluvial rocks and the lake may be shallow or deep and may, or may not, have a lacustrine source rock. Figure 26 shows an image from the main outcrop-study area for rifts-the Ridge Basin near Los Angeles, USA. Here we can see seismic scale prograding deep water rocks, overlain by deltas and fluvial units.

Figure 26.

Figure 27 shows a simple carbonate version of the Exxon model by Rick Sarg.

Figure 27. Note the presence of siliciclastic LST fans in this model. This is the same as in the Exxon model and we see it in several basins. It is rare to see a productive fan made of carbonates. Figure 28 shows Abbott’s carbonate models. He has not really addressed the LST in these models. Note that the TST can have a siliciclastic unit (bts) on the SB or a carbonate equivalent (“ramp limestone”). The HST may have reefs but often has platform facies comprised of carbonate sands and muds. These platforms may grade landward to evaporites/ siliciclastics-as seen in the second order Gulf of Mexico cycle of Figure 29 (carbonates are blue and siliciclastics are yellow)-Mancini (2001).

Figure 28.

Figure 29. Figure 30 also shows this interleaving of carbonates (left well) with siliciclastics (right well)-on seismic from NW Australia.

Figure 30. Carbonates sometimes exhibit large platforms or atolls out in the marine setting because carbonates can grow very fast and cement up very quickly when base level rises fast. Carbonates seem to be simple when worked on seismic but usually are very complex to understand once you have a development, due to the prevalence of multiple types of later diagenesis. It is usually difficult to understand the porosity and permeability and we often have to get to the petrographic level before we can. Figure 31, by John Sangree (1990), shows a simple distribution of carbonate facies in a TST and HST shelf setting. Note the different packing terms.

Figure 31. Figure 32, from Van Buchem et al, 2002, shows a carbonate sequence, interpreted using the Exxon model, constructed from outcrops in Oman.

Figure 32.

Figure 33 from the Canning Basin of Western Australia shows a single Devonian carbonate sequence with associated LST and HST palaeogeography sketches made from seismic and well data. This exploration used the Exxon model of Sarg where the basin floor fan was siliciclastic but the rest of the sequence was sealing

carbonate. Figure 33. In later Newsletters I will discuss the different environments in more detail and also talk about seismic facies mapping, palaeogeography mapping and pitfalls. References: Abbott, W.O (1991) Operational Seismic Stratigraphy. Occidental Petroleum course, Grand Canyon, February. Adamson, K., Lang, S., Marshall, N. et al, (2013),

Understanding the late Triassic Mungaroo and Brigadier deltas of the northern Carnarvon Basin, NWS, Australia, in West Australian Basins Symposium Proceedings.

Armentrout, J.(1993) Integrated Stratigraphic Analysis –SEPM Short Course, New Orleans, 23-25 April. Bruhn, C., (1998), Deepwater Reservoirs from the Eastern

Brazilian Rift and Passive Margin Basin, AAPG

International Conference, Rio de Janeiro, Brazil. Course No. 6, Petroleum Geology of Rift and Passive Margin Turbidite Systems: Brazilian and Worldwide Examples.

Catuneanu, O., et al, (2010), Sequence stratigraphy: common ground after three decades of development, First Break, 28, pp. 21-34.

Catuneanu, O. & Zecchin, M., (2013), High resolution sequence stratigraphy of clastic shelves II: controls on sequence development, Marine and Petroleum Geology 39, pp. 26-38.

Embry, A., (2002), Trensgressibve-regressive sequence stratigraphy, 22nd Annual GCSSEPM Foundation Research Conference.

Embry A., Johannessen, E., Owen, D., Beauchamp, B., Gianolla, P., (2007), Sequence stratigraphy as a “concrete” stratigraphic discipline, report of the ISSC task group on sequence stratigraphy.

Embry, A., (2010), Correlating siliciclastic successions with sequence stratigraphy, SEPM Special Publication, No. 94, pp. 35-53.

Haq, B.V., Hardenbol, J. (1987) Chronology of fluctuating sea level since & Vail, P.R. the Triassic (250 million years ago to present): Science, Vol. 235, pp. 1156-1167.

Mancini, E., Badali, M., Puckett, T., Llinas, J., Parcell, W., (2001), Mesozoic carbonate petroleum systems in the NE Gulf of Mexico area. In: GCSSEPM Foundation, 21st Annual Research Conference, Houston, Dec 2-5, 2001.

Sangree, J. (1990) Sequence Stratigraphy School (In-house BHPP). AMF Workshop Course 5114/90. September 17-19, 1990 Melbourne.

Sarg, J. F. (1988) Carbonate sequence stratigraphy. In: Sea-Level Change - an Integrated Approach: SEPM Special Publication No. 42. Ed. Van Wagoner, J.C.

Vail, P.R. & Womardt, W.W 1990. Well log-seismic sequence stratigraphy. A new tool for exploration in the 90’s. pp. 379-

388. GCSSEPM Foundation. 11th Annual Research Conference. Program and abstracts, December 2, 1990. Van Buchem, F., Razin, P., et al, (2002), Stratigraphic

Organization of Carbonate Ramps and Organic Rich Intrashelf Basins, Natih Formation of Northern Oman, AAPG Bulletin Vol. 86, No. 1, pp 21-53.

White, D. (1990) Assessing oil and gas plays in facies-cycle wedges. AAPG Bulletin, Vol 64, pp 1158-1178.

Zecchin, M. & Catuneanu, O., (2012), High resolution sequence stratigraphy of clastic shelves I: units and bounding surfaces, Marine and Petroleum Geology 39, pp. 1-25.

In this next section we will start the Ten Commandments

of Stratigraphy (by Frank Brown-tongue slightly in cheek at times!)

These were supplied by Gerhard Brink. THE 10 (Actually ~ 100!) STRATIGRAPHIC COMMANDMENTS:

THOU SHALTS AND SHALT NOTS

FOR SILICICLASTIC ROCKS-Frank Brown.*

In stratigraphy, valid methods and concepts must be based on “reading” the rocks, but nothing is written on stone tablets! Ideas and concepts rapidly change, slowly evolve, or are (by professional consensus) eventually discarded. Some stratigraphic ideas persist despite subsequent evidence to the contrary. They then become “myths,” and we all know that myths never die! Such “geologic” myths tend to survive for decades after they

were proven incorrect or were modified to fit with current evolving and growing sedimentary evidence. Inflexibility or unwillingness to study objectively and to test honestly and personally new ideas describes some scientists in all fields. However, don’t geologists seem to cling longer, with more tenacity and with greater perseverance to questionable ideas? Rhetoric, preconceived ideas, “gut feelings,” and “I just don’t believe it,” are not substitutes for both intensive and extensive hands-on analysis of real comprehensive data sets. And then “let the chips fall where they may!”

I. Thou shalt not believe that (a) water depth maps based on benthic microfossils are valid, except for episodes of maximum flooding. They reflect inferred water depths (e.g., outer and middle neritic) during the deposition of marine-condensed sections comprising high organic content and high species diversity and abundance of microfossils. Such bathymetric maps are totally invalid for sediments deposited between floods! And absence of fossils does not necessarily prove “continental” environments. (b) Thou shalt believe that deposition on and transport of sediment across submerged shelves must involve shoreline progradation, lowstand entrenched river transport, or rarely, density flow via relict submarine canyons. (c) Thou shalt not believe that sand-rich, commonly deltaic and/or shoreface and associated deposits that exhibit extensive, sheet-like distribution have been deposited on submerged shelves below maximum storm wave base. Such sandstone “sheets” or blankets are internally highly diachronous but homotaxial (“a similarity of arrangement, as of geologic strata or fossil assemblages that have the same relative position but are not necessarily contemporaneous”-rk)

, and become younger in a basin ward direction. (d) Thou shalt remember that microfossil biozones may represent long periods of time. Consequently, it is possible that at least two high frequency maximum flooding surfaces (= fossiliferous marine condensed sections or flooding surfaces) may exist within the same biozone! If, therefore, micropaleontologists correlate species directly to species only, they may be correlating the same species within two entirely different horizons! This practice leads to major chronostratigraphic miscorrelations!

Commandment II next issue.

What-is-this #1?

If you have an interesting seismic feature (or even well log) that you want to “share” on this site, or get help with it then please send it in to me.