Palynology, age, correlation and paleoclimatology from JAPEX/JNOC/GSC Mallik 2L-38 gas hydrate research well and the significance for gas hydrates: a new approach
Authors: White J M 
Published: November 2010

The 1150 m deep JAPEX/JNOC/GSC Mallik 2L-38 research well was drilled in 1998 to investigate gas hydrate deposits previously identified in Mallik L-38. For the study of the palynostratigraphy and paleoclimatology of the Beaufort-Mackenzie Basin, Mallik 2L-38
provides an uncommon opportunity to analyse core and high quality cuttings that span a 480 m section of upper Paleogene sediment. A detailed, quantitative palynological analysis is reported herein and percentage diagrams are provided for each taxon. One hundred and twenty five taxa are
illustrated.
Recycling of palynomorphs from Cretaceous and older Paleogene strata can confuse age determination. A criterion proposed to evaluate recycling is an assessment of chaotic patterns versus coherent, explicable patterns. Relative abundance plots and statistical techniques are used to distinguish
between chaotic versus coherent patterns, hence evidence for and against recycling. These techniques do not produce a definitive assessment for any individual taxon, but demonstrate the coherence of the overall palynological record. It is concluded that the palynomorphs provide a biostratigraphic
record suitable for the determination of age and depositional environment of the rocks.
The proposed age and correlation for Mallik 2L-38 assigns the interval between 1150 m and a disconformity at 926.5 m to the Late Eocene, and the interval between that disconformity and the top of the cuttings at 670 m to the Oligocene and possibly earliest Miocene. It is concluded that some 1000 m
more sediment accumulated during the Eocene in Mallik 2L-38 than evinced by micropaleontology in adjacent Mallik L-38. This is because the foraminiferal top of the Haplophragmoides richardsensis zone in Mallik L-38 ends in a shallowing-upwards marine sequence, changing to a continental facies with
minor marine incursions, yielding an environment unsuitable for diagnostic foraminifera, but this continental environment was rich in pollen and spores. Placing these age interpretations beside the seismic sequence interpretations implies that the Kugmallit Sequence contains sediment of Late Eocene
age. This argues that the Richards and Kugmallit formations must be in part facies equivalents in the nearshore, although in the offshore Kugmallit overlies Richards.
Palynological correlation to the Caribou Hills is problematic, but the Mallik 2L-38 disconformity at 926.5 m may be equivalent to the Caribou Hills Embryophyte Zone 4b - 4c unconformity, or perhaps to some interval within CHE4c. In correlation to Adgo F-28, the Mallik 2L-38 disconformity at 926.5 m
probably correlates to the top of the Integricorpus zone.
Experimental proxies for paleoclimatic temperature are provided by four ratios of pollen taxa in an attempt to improve the age determinations by correlation to the North Atlantic foraminiferal delta 18O curve. Two ratios suggest that a cold climatic episode coincided with the deposition of sediment
at the top of the cored interval near 886 m in Mallik 2L-38, probably correlating with the basal Oligocene portion of the North Atlantic foraminiferal delta 18O curve. This suggests a relationship between this climatic event and the top of the gas hydrate hosting interval, which is most likely
explained by the climatic effect on sedimentation.
The taxonomy of triprojectate pollens, Integricorpus and Parviprojectus, are considered and it is proposed to provisionally adopt "Integricorpus sp. cf. I. reticulatus" for the reticulate form and retain usage of "Parviprojectus A" for the striate form. A new species of triprojectate pollen, named
Striatocorpus sweetii, is identified in Mallik 2L-38 in Late Eocene sediment.