Investigation of the manifestation of the Cretaceous High Arctic Large Igneous Province on Svalbard

Report on 2001 Field Expedition to Svalbard (July 29th to August 12th)

Participants:

Sponsors:

Purpose: Svalbard was located on the periphery of a Cretaceous age Large Igneous Province which relatively little is known about. The purpose is to better understand the timing, size, character and sedimentologic effects of this LIP. The basic approach is three pronged - stratigraphic and sedimentologic description of Cretaceous units with a focus on the Carolinefjellet Formation, thin section source terrain analysis, and establishment of the Nd isotope signature evolution of the sediments as the LIP developed, and of the magmatic suite exposed on Svalbard.

Sites investigated and sampled:

Reamurfjellet-Kolkdalen-Svedenborgfjellet, south shore of van Mijenfjorden: Here a section from the Ullaberget Member of the Rurikfjellet Formation up through the Helvetiafjellet and Carolinefjellet and into the basal Tertiary Firkanten sandstones was sampled at an interval of 10-20 m for thin section source terrane analysis and every hundred meters or so for Nd analysis (which required larger samples). Seven informal units from B to H were devised for the Carolinefjellet Formation, which is in excess of 600 m thick here, more than twice as thick as it is in the Longyear area. This section likely includes the bottom four informal members of the Carolinefjellet Fm. (Dalkjegla through Zillerberget, Dallmann, 1999). More detailed stratigraphic columns were measured for two of the informal units. Paleocurrent information was collected where available. Some of the Carolinefjellet informal units were mapped out using GPS. Exposures are excellent in this area, and there is virtually no part of stratigraphy that is not well exposed somewhere, including the more recessive, shalier portions.

Scanned portion of Norsk Polarinstitutt Turkart, Nordenskiold Land (1:200,000), showing sampling sites and place name localities.

Shoreline W of Maseneset: This was a diabase collection site. A sill some 20-25 m thick was sampled. The phenocrystic sill showed significant internal layering suggesting the passage of multiple magma pulses and/or gravity differentiation.

View to east along shore of camp and of the western ridge of Reamurfjellet where the Carolinefjellet Fm. was sampled. The upper most cliff-forming sandstone unit is the Tertiary Firkanten Formation.

Konusen - Carolinefjellet: This ostensibly is the general area of the type section for the Carolinefjellet Fm.. Along gullies and drainage along the southern slopes a continuous section of the Carolinefjellet Formation is exposed and was sampled at intervals of 10-20 meters, starting from exposures of the top of the underlying Helvetiafjellet Fm.. A sample of the overlying Tertiary sandstones was also collected.

Wimanfjellet-Konusen pass: Samples were taken here from sandstones of the Ullaberget Mbr. of the Rurikfjellet Formation up to the top of the Helvetiafjellet Formation. Significant facies changes can be seen in the section in the cliffs to the west.

Scanned portion of Norsk Polarinstitutt Turkart, Nordenskiold Land (1:200,000), showing sampling sites and place name localities.

Hyperinfossen and Diabasodden: Samples of the diabases were taken from the two different localities. Locally the diabase sill here is circa 50 m thick. Internal layering and boundaries again suggest multiple intrusion events. Cooling fractures could be identified and fracture orientations taken.

Gruvdalen: Some 250 meters of the Carolinefjellet Formation strata are well exposed in stream cut exposures. An overlying Tertiary sand was also sampled. The lower portion of the Carolinefjellet Formation is not exposed here. Three informal units were identified and were sampled at an interval of 10-25 m . Both a normal and reverse fault occur, but equivalent beds on both sides can be found. Detailed stratigraphic description of the lower unit was completed. It is hoped to complete a detailed description next year.

Slopes of Konusen and Carolinefjellet to the left where sampling of the Carolinefjellet Fm. was conducted. Cliff forming sandstones just beneath saddle between two peaks are the Firkanten Tertiary sandstones. Gullies just this side of the saddle are where samples were taken. A sand rich lower and shalier upper portion of the Carolinefjellet can be seen here. To the right is the Gruvdalen upper sandstone unit in the Carolinefjellet Fm.. These sands do not appear to be present at the northern site. Below is the sill at Hyperinfossen.

Summary results and subsequent work planned:

Approximately 100 samples were collected in all, with stratigraphic and GPS positions noted for each. An aggregate of over 1300 stratigraphic meters of section was sampled and described, as were three diabase sites. Over 200 m of detailed stratigraphic sections were measured and sedimentologic observations taken were possible.

While basement sources for the Helvetiafjellet could be identified in the field, no obvious volcanic input was noted in the field. Chert lithics, perhaps from the Kapp Starostin, were particularly common. Since the Helvetiafjellet has been described in some detail stratigraphically and sedimentologically we did not focus on this unit.

The focus was on the Carolinefjellet Formation strata. These are mostly shallow marine, wave dominated deposits, as reported in the literature. Fine grained sandstones volumetrically dominate most of the sequence. Perhaps 3 distinct sandstone populations can be recognized in the field on the basis of coloration and composition. More recessive slope forming units usually represent thinner bedded sands and silts, with mud-shale drapes and laminae. Significant shale dominated sections occur, but are relatively rare. A NE-SW trending shoreline with longshore drift to the SW can be inferred from sedimentary structures. Hummocky cross stratification, gutter casts, and conglomeratic lag storm beds all attest to the importance of storm events. Flooding surfaces on top of aggradational sequences can be recognized and are associated with siderite cementation and the development of concretion horizons. Rootlet horizons in some of the sands suggest proximal shoreline or emergent shoals. Trace fossils and coloration suggests waters were relatively well oxygenated, although several distinct anoxic horizons can be identified. Diplocraterion were especially common in some of the sandstone packets. Ammonite, bivalve and starfish fossils were found.

Glendolite concretions (?) at Gruvdalen to left and starfish fossil found at Svedenborgstupet to right.

Carolinefjellet stratigraphy in the Longyear and Kolkdalen areas are substantially different. Packets of sandstone are distinctly thicker and coarser grained at Kolkdalen. A simple Tertiary truncated layer cake stratigraphic architecture does not work for the Carolinefjellet. A wedge and onlap geometry may be more appropriate. Laterally most beds were discontinuous, with channel forms fairly common. Several meter thick sandstone packets are continuous for 100s of meters. The informal members identified for the Carolinefjellet Formation may not have island wide lateral continuity. There was not an overall transgressive or regressive pattern evident in even the more complete section at Kolkdalen. The picture instead was of a shallow marine system maintained by filling accommodation space made incrementally available.

Future work for next year: