Maastricht Reconstructing the Ecosystem from the South of the Netherlands and Belgium at the End of the Cretaceous Period

The prehistoric sea of Maastricht Reconstructing the ecosystem from the South of the Netherlands and Belgium at the end of the cretaceous period 1 Table of contents: Title paper 1 Table of contents 2 Introduction Chapter 1: What is the geological structure of the Maastricht formation? Chapter 2: What was the environment like during the deposition of the Maastricht formation? Chapter 3: What organisms lived in the Maastricht seas? Chapter 4. How did the Maastricht seas change over the course of their existence? Main question: what did the ecosystem cretaceous seas of Maastricht look like? Introduction Many people are familiar with at least some animals from the mesozoic era, the ‘’era of reptiles’’, especially the dinosaurs. What most do not know is just how rich the fossil record is in the right places, and that our own country has very rich fossil-bearing layers in south Limburg. The tunnels and caves in the Limburg marl are fairly well known, but the fossil findings from the chalk are not something most people are aware of. Over the course of more than two centuries scientists and amateurs alike have collected and described tens of thousands of fossils, which when pieced together can paint an extremely vivid idea of an extinct ecosystem. While a great number of people have written an impressive volume of literature about the fossils from the chalk of south Limburg, no-one has taken the task of assembling much of it and trying to create and describe the ecosystem it represented, everything from the diverse crustacean fauna to some of the largest marine predators. In this work I will attempt to describe the fauna, flora and environment of the Maastricht formation in depth, including as much literature as I can find on the subject. The fossils of the Maastricht formation, and other chalk layers in the same area, are a valuable source of information about life at the end of the mesozoic era, which ended with the most famous mass extinction, known for ending the dinosaurs among much of other life. 2 What is the geological structure of the Maastricht formation? The Maastricht formation is not a single unit, and there are chalk layers above and below it. The base of the chalk layers is situated on top of a much older layer, carboniferous in age of the Limburg group. The Aachen formation is situated on top of this base, and is late santonian in age (~83-84 million years old). On top of the Aachen formation is the Vaals formation, which spans the campanian age 83.6 to 72.1 million years ago. The Gulpen formation covers the Vaals formation in some areas, while in others outcrops the Vaals formation continues slightly farther up and touches the Kunrade formation. The Kunrade formation has been considered as part of the Maastricht formation by Umbgrove (1926) first, and nowadays is most often considered part of this formation. In this work I also go by this interpretation, but I will still provide information regarding the Kunrade formation in the layers where it is contemporary to the coeval Maastricht formation for additional completeness. The Gulpen formation does not overlap with the overlying Maastricht formation. This formation spans from the late campanian to the late maastrichtian age. The Maastricht formation completes the latest part of the late maastrichtian age as the terminal part of the cretaceous. There unit above the Maastricht formation is the Houthem formation, which was deposited in the early paleocene epoch in the recovering world after the K-pg extinction event. The Maastricht formation is far from a homogenous layer itself, and consists of six layers with several hardground horizons between them and intervals. The members are from oldest to youngest: Valkenburg, Gronsveld, Schiepersberg, Emael, Nekum, Meerssen. Between the members are horizons that represent the transitions between the members. The lower members of the Maastricht formation (Valkenburg, Gronsveld, Schiepersberg member) are only represented in the north east of the area, to the south east they are replaced by the Kunrade limestone facies, now recognized as a separate formation because the different members of the Maastricht formation cannot be recognized in it. There is no question however that the Kunrade formation was coeval to the lower Maastricht formation and represented its more littoral equivalent, so it is still an important chalk formation to consider when talking about the Maastricht formation. Alternating hardgrounds are characteristic of most of the chalk sequence in the Maastricht area: a consolidated base indicating a period of more erosion than deposition, after which the sediment gets progressively finer upwards, and then a new hardground. These are called fining upward cycles and reflect important changes through time with changing. Zijlstra (1995) noted that these cycles reflect precession related cycles of storm intensity, with the storms reaching peak intensity at hardground intervals, where netto deposition was zero or negative. This allowed the layer to be intensely bioturbated and eventually cemented and lithified. Then the cycle begins anew with very low storm intensity allowing chalk to be deposited with no netto loss. The chalk gets finer as the cycle advances and then a new period of intense storms begins, creating a new opportunity for hardgrounds to form, though sometimes the hardgrounds are only partially formed or eroded afterwards. Hardgrounds 3 Lichtenberg horizon At the border between the Gulpen and Maastricht formation is the Lichtenberg horizon, an aberrant stratigraphic layer that is between a few millimeters and 20 cm thick. This horizon was deposited under conditions distinct from the strata under and above it, and is readily recognizable by the composition. The Lichtenberg horizon is a conglomerate composed chiefly of bioclasts (fossils and fossil fragments), little pieces of chalk, and glauconite pellets (a mineral associated with marine deposition under low oxygen levels). The layer is greatly bioturbated by digging organisms, indicating high levels of biotic activity. The absence of siltstone, sandstone and clay suggests that this layer was likely not deposited very close to the coast, just like the overlying Valkenburg member. The depositional environment was clearly very different from the Valkenburg member however, which consists of a mostly homogenous layer of cream-coloured chalk, indicating a tranquil environment that was less severely bioturbated and not significantly under the influence of storm waves as has been suggested to be the case for the Lichtenberg horizon. The Lichtenberg horizon has a very high fossil content and is therefore a popular target for fossil collectors, though the remains can often be quite eroded due to the high energy depositional environment. Valkenburg member The Valkenburg member of the Maastricht formation is the most basal chalk package of the Maastricht formation , and varies in thickness between 2.5 and 45 m, with the thickness clearly increasing to the east, while decreasing to the west. The chalk varies in colour from yellow-grey in colour to a whitish yellow and the chalk material varies from very fine grained to relatively coarse grained. Towards the east the Valkenburg member transitions into the adjacent Kunrade formation, which was previously considered as part of the Maastricht formation. The Valkenburg member is relatively thin in the west (2-3 m thick) but can reach up to 35 m in the Valkenburg outcrop, which is where the changes through the Valkenburg member are best observed. The lower part of the Valkenburg member is more glauconitic than the upper part and contains are relatively lower amount of calcium carbonate and flint nodules. The lowest part is a fossil-grit layer of the Valkenburg formation is deposited right on top of the Lichtenberg horizon and is characterized by coarse grained sand with relatively pyrite, glauconite and phosphate contents. Horizon of St. Pieter This is a thin undulating hardground with thin fossil hash lenses above it. The chemical composition is similar to the horizon of Lichtenberg and indicates this too was deposited in a period of high energy conditions. Gronsveld member: The Gronsveld member consists almost entirely of calcium carbonate (~92 - 97%). This calcium carbonate content goes through several cycles, with at the base of each cycle a more glauconitic, phosphatic and pyritic sand and fossil hash containing layer which gradually transitions in a more pure 97% chalk content, then the cycle starts again. A higher chalk percentage indicates 4 less terrestrial influence and thus the Gronsveld member was not deposited very close to the coastline. Around 5 to 10% of the volume of the member consist of flint nodules, and to the west there are several clear flint nodule layers indicating long lasting erosion. The member is up to 14.4 m thick but there are areas where it is almost entirely absent, presumably due to higher erosional rates. Schiepersberg member: The Schiepersberg member is calcarenitic chalk packet usually between 3 and 6 m thick, though it is absent in the south (Eben Emael area). In most of the Schiepersberg member there are prominent layers of large flint nodules, though towards the east these layers disarticulate and the flint nodules become more randomly scattered. Like other members this member is deposited on an irregular hardened layer, and has several fossil grit layers in the lower part. Romontbos horizon: The Romontbos horizon is the transition between the Schiepersberg and Emael members, a cemented layer with a fossil grit layer on top. This member is absent in the Eben-Emael area, but instead the flint layer below is especially well developped indicating it was deposited but subsequently eroded. Emael member: The Emael member itself is divided in two distinct lithological units, the lower and upper part separated by the horizon of Lava. The lower part is characterized by sometimes large horizontal pipe-shaped flint nodules formed by burrows, presumably by thalassinidean crustaceans such as Protocallianassa faujasi and Schlueteria heterodon.The lower part is between 2.5 and 7 m thick depending on the location.

Load more