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Turbidite Ichnology in Baja California, Mexico

on . Posted in General Ichnology

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My research is focussed upon using trace fossils to help understand depositional environments in deep water turbidites. The Rosario Formation in Baja California, Mexico, are an excellent case study, because the depositional environments, architecture, stratigraphy and evolution of these channel turbidite rocks have been studied by members of the “Slopes 2 Consortium” (www.turbidites.org) for several years, and I have been working in the field with other members of this research team. Surprisingly, the trace fossils within this system have not been studied in detail until now, and as with other turbidite systems, they have not been studied systematically across the range of depositional environments present in these settings.

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Trace fossils are widely used in palaeoenvironmental interpretation, facies models and reservoir characterization, but this approach mostly been applied to shallow marine rocks, such as those from the continental shelf, shoreface and deltaic settings. Trace fossils from deep marine environments have not typically been used in these kinds of high resolution palaeoenvironmental studies – although preliminary research suggests that trace fossils are likely to be equally useful in these applications.

I have just returned from my second month-long field session down in Baja California (May 2010), where I have been working on identifying trace fossil assemblages that are diagnostic for different palaeoenvironments. These palaeoenvironments are subject to different conditions such as Oxygen concentration, current energy, sedimentation rate and nutrient supply. Different environments are consequently inhabited by contrasting benthic communities and these are reflected in the trace fossil assemblages within the rocks. The archetypal view is that almost the entire deep marine realm is characterized by trace fossils of the Nereites ichnofacies. In contrast, my work in the Rosario Formation has shown that it is possible to recognize trace fossils and assemblages that can be used to identify different parts within this complex channel-turbidite system. These include axial and confined parts of the channel, overbank and terrace deposits, internal levees and major confining levees.

The work in Baja has been a whole new experience compared with fieldwork I have done elsewhere. Firstly, it’s remote: Some localities are hours away from a paved road, which still be hours away from a proper town. It’s also a long, long way from a hospital or emergency facilities. There’s also no cell phone signals, and obviously no wi-fi internet or other communications, so you need to make sure the satellite phone is well charged. It’s also really dirty: Deserts and semi-arid regions are dusty and sandy and being an ichnologist means you often have to dig and hammer to get at your samples. Oh, and you only get to shower once a week. Thirdly, the wildlife: As well as your usual bees, wasps and biting flies, there are giant centipedes, scorpions, rattlesnakes and the ominous sounding tarantula hawk to contend with. Fourthly, the beauty: Once you get over the fact that the place first appears barren, brown and dusty, you can really start to appreciate that it is a stunning location to do fieldwork. Camping for weeks at a time among the cacti and coyotes can be hard work, but is compensated by camping in such a fantastic setting, with what is always a fun and lively international group of geologists. The most recent work this May was really productive and successful with lots of good data collected. It looks like I’m also going to have to head back in the autumn for another look at the Rosario Formation, and I’m sure I can find some excuses for another visit after that!

 

Rich Callow