Growing up in a fossiliferous area in Westphalia, north Germany, I have been digging for fossils for most of my life. There were many outcrops in the vicinity of our home and I got rich practical experience of where to find which fossils. It’s a truism, especially in palaeontology, that you need to be patient to be successful. Some fossils are rare and only a systematic approach will uncover them. Early on I started to collect in a scientific way, progressing bed-by-bed and documenting what I did. However, although already an experienced collector, I did not experience how randomly fossils can be scattered in the individual geological units before starting my PhD.
My fieldwork in the Late Cretaceous of Lengerich and Brochterbeck, Westphalia, included archaeological-style methods, systematically unearthing several square metres of finely bedded marlstones, an elementary method in antiquarian studies that is still little used in modern palaeontology. However, the most astounding observation I made was based on an even more primitive method. My work area included mainly limestone–marlstone couplets that were deposited on the ground of an epicontinental sea, way off the former coastline, and probably related to Milankovitch cyclicity (e.g. Gale et al. 1999). Single beds appear completely uniform within the outcrop, with no beds pinching out or showing any irregularities in facies and lithology. This lithologically boring succession with mostly unattractive fossils — often poorly preserved as internal mould — was never systematically collected bed-by-bed. But simply hammering off as much material as possible for each single bed revealed staggering results. (Of course, one needs permission and restraint for this sort of collecting.)
One part of the story is that extensive collecting did reveal a remarkably rich fauna with many new species for the region and for the strata; for example, the first belemnites — usually very rare in this stage in Germany. A more prominent result, at least from my point of view, was the dispersal of fossils. It was notably heterogeneous, most fossils did not occur singly but in clusters. Some clusters contained fossils of the same groups (e.g. only echinoderms or brachiopods), some represented a mixture of different invertebrates. The nature of associations was obvious for only a couple of clusters: body chambers of ammonites were a shelter for organisms randomly washed in — a phenomenon described in many other strata and known as sheltered preservation (e.g. Maeda & Seilacher 1996). The majority of clusters were accumulated either by bottom current (the mixed invertebrates), probably in small depressions on the sea floor, or represented small benthic in vivo associations (the monospecific assemblages).
What does this tell us?
- Even the most uniform and lithologically homogenous strata are not uniform in their fossil content. One could argue that my example focuses on a shelf environment that underwent dynamic processes, but it is true even for deep-sea sediments that are believed to be very stable. Deep-sea cores of various international drilling programs often reveal finds of whale bones or shark teeth even though these represent a minute amount of material from each single bed.
- The quality of basic field data is key for the understanding of palaeoenvironments. Even as a ‘computer palaeontologist’ — a term used by Dolf Seilacher to tease students — high-quality palaeontological data are the result of hands-on business. It needs a lot of rock-smashing and concretion busting — simple and exhausting but academically useful — for some basic results, with the welcome side-effect of clearing your mind.
Gale, A S, J Young, N Shackleton, S Crowhurst, and D Wray (1999). Orbital tuning of Cenomanian marly chalk successions: Towards a Milankovitch time-scale for the Late Cretaceous. Philosophical Transactions: Mathematical, Physical and Engineering Sciences 357, 1815–1829, DOI 10.1098/rsta.1999.0402.
Maeda, H and A Seilacher (1996). Ammonoid taphonomy. In: Landman NH, K Tanabe, R Davis (eds) Ammonoid Paleobiology. Topics in Geobiology. Plenum Press, New York. 543–578, DOI 10.1007/978-1-4757-9153-2_14.