Faunal/floral and isotopic responses to Milankovitch precession cycles and environmental changes in the upper Gulpen Formation (Upper Maastrichtian) at the CBR-Lixhe and ENCI-Maastricht bv quarries

Abstract

Two sections, just below the Nivelle Horizon in the upper Gulpen Formation (Upper Maastrichtian), and seven kilometres apart (CBR-Lixhe and ENCI-Maastricht bv quarries) have been analysed (samples every 5 cm) for dinocyst, pollen grains and bioclast contents as well as for carbon and oxygen isotopic composition, to obtain better insight into the influence of weathering on these sediments. The CBR section lies above groundwater level, while that at the ENCI quarry is some metres below. At the former quarry we recognised the influences of weathering (karst) nearby.At ENCI, palynological, bioclast and stable isotope results of the carbonate phase (mainly consisting of coccoliths) co-vary remarkably, displaying two cycles which may be interpreted tentatively as climatic fluctuations. The ∂18O curve varies roughly between −1.6‰ and −1.1‰ (on PDB scale), corresponding to a temperature change of about 2°C. Less negative values (i.e. cooler seawater) coincide with larger amounts of pollen of Normapolles and Triporates type assumed to represent temperate forest elements of a vegetation also containing tropical elements such as palms. Assuming the 5 cm sample intervals at ENCI to correspond to 1 ka, climatic maxima (and minima) may be 20–25 ka apart, obviously recalling Milankovitch precession cycles.These are independent of a sharp sedimentological change noted in the upper part of the lowest cycle (samples 42 to 24). Upwards of sample 42, bioclast contents increase and dinocysts, Spiniferites in particular, decrease significantly, corresponding to a marked shallowing. This turning point is also recorded in the ∂13C curve at ENCI. Bioclast percentages appear to follow composite trends that are influenced by both climatic and sedimentological conditions.

Belemnite-based strontium, carbon and oxygen isotope stratigraphy of the type area of the Maastrichtian Stage

“…In any case, the belemnite δ 13 C data show no trends or inflection patterns that relate to patterns observed in the δ 18 O or 87 Sr/ 86 Sr data, suggesting that different mechanisms control the carbon isotope system. Stable isotope patterns as observed here are not readily comparable to previously published stable isotope data of bulk carbonate samples from the Maastrichtian type area (Clauser, 1994;Felder et al, 2003). Particularly the oxygen isotope signal is difficult to reconcile between the three data sets.…”

“…Carbon isotope values of our data set and that of Clauser (1994) and Felder et al (2003) appear to be somewhat more consistent. All three records show comparable, relatively stable δ 13 C values through the Maastrichtian, which may suggest that the carbon isotope signal in bulk carbonate has not altered as much as the oxygen isotope signal.…”

A bioclast-based astronomical timescale for the Maastrichtian in the type area (southeast Netherlands, northeast Belgium) and stratigraphic implications: the legacy of P.J. Felder

“…Based on the present results, it is hypothesised that, at least in some of the sections studied, silica migrated, albeit to a limited extent, through the uppermost centimetres of the seafloor prior to the formation of the characteristic flint layers. Hence, as already proposed by Felder et al (2003), flint layers may potentially represent a secondary development and do not need to conform to primary deposition. This kind of silica migration would also easily allow the fusion of 'silica levels' such as proposed for the Lanaye Member, especially when depositional rates were relatively low.…”

“…This characteristic faunal change may be interpreted in favour of a rise in the local sea-water temperature or, alternatively, of an increased influence of tethyan faunal elements. By contrast, the results of a palynologic and oxygen isotope study of the upper Lixhe 3 and lowermost Lanaye Member with high resolution demonstrated a general cooling trend during this period (Felder et al, 2003). Altogether, these changes may reflect a palaeoceanographic reorganisation or, alternatively, a regional shift to a more restricted marginal-marine depositional environment in the Maastricht area resulting in lower δ 18 O values and less water exchange with the Boreal Chalk Sea of Denmark.…”

“…With the exception of Felder et al (2003), P.J. Felder did not follow up his approach relating bioclasts to Milankovitch cyclicity.…”