ABSTRACT The fauna of the Lower Cambrian is far from fully understood, as is the environment of that epoch. Some of the most crucial moments in the history of evolution takes place during this epoch; the Cambrian explosion and the appearance of ecosystems as we know them. That makes it an important period to investigate. Doing so, the Lower Cambrian offers a lot of problems, one of which is that body fossils are seldom preserved. That has often left us with trace fossils to create an image of the Lower Cambrian life, but also some bedrock features such as ripple marks. The main purpose of this work has been to investigate the possibilities of relating the wave lengths and forms of recent wave-generated ripples to fossil ones, and also to evaluate the methods for that kind of comparison. In this case the ripple marks belong to about 520 million year old sandstone formations at the shore of Trolmens strand (Kinnekulle area) and the mine Centralgruvan (Kvarntorp, Kumla). In total eighteen ripple trains from the Lower Cambrian were compared to the recent ripples in the shallow waters of Persbols strand and a somewhat steeper offshore area of Herrängen, northern and southern lake Skagern respectively. After measuring the ripples several methods were used to find a practical and accurate procedure for the Persbols strand area. The conclusion is that, depending on depth and water transparency, a combination of methods should be used. Closest to the shore it was possible to take photos along the entire section from above water level, but because of the water depth further from the shore the aim of measuring the entire distance had to be abandoned. Instead, measurements should be taken with an adequate frequency, in this case every other meter up to one hundred meter from the shore line. As a result of the measured recent ripples three different zones have been distinguished. One is situated 0-3 m from the shore line, or also a water depth down to 20 cm. The ripples in this area have wavelengths between one and four cm. and are asymmetrical, in some cases transforming to symmetrical in the outer part of the zone. It is only in this area, and some very shallow parts outside this zone, catenary ripples can be found. They are built up in the meter closest to the shore. The second zone is situated approximately 3-80 m from the shore, or in areas of 20-80 cm water depth. The wave lengths grow from some 4 to 8 cm as the water depth increases. The ripple form is symmetrical, with the exception of some areas on the lake side of sand banks. Also, ripples with short crests and long throughs seems to dominate this zone. Further out from the shore, more than 80 m, or in waters deeper than 80-100 cm, a third zone appears. The wave lengths are about 10 cm and, without any exceptions, the ripples are, symmetrical. None of the largescale fossil ripple marks were located due to the fact that no measurements further than 100 m from the shore were made. The methods used here will make it possible to determine the environment of formation of the ripple marks, at least within 100 m from the shore, to the degree considered necessary for investigations in Earth science. Furthermore, the depth of water has appeared to be just as an important factor as the distance to the shore.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:kau-879 |
| Date | January 2007 |
| Creators | Ringholm, Patrik |
| Publisher | Karlstads universitet, Institutionen för natur och miljö |
| Source Sets | DiVA Archive at Upsalla University |
| Language | Swedish |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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