Earth Science Conservation Review
| Tircrevan Burn - Clay-with-Flints | |
| Site Type: | |
| Site Status: | ASSI |
| Council area: | |
| Grid Reference: | C70313220 |
| Google maps: | 55.13247,-6.89781 |
| Rocks | |
|---|---|
| Rock Age: | Cretaceous, Tertiary |
| Rock Type: | Chalk, Clay, Flint, Basalt |
| Interest | |
Summary of site:
Tircreven is a special place because of its earth science interest. The area provides access to an infrequently exposed deposit called the Clay-with-flints (CwF). This deposit is found between the Cretaceous white limestone below and the Palaeogene black basalt above, and spans a period of time of approximately 10 million years. Because of its location beneath the basalt, the CwF is usually only exposed at the edge of the Antrim Plateau.
The Cretaceous white limestone formed on the bottom of a sea floor around 75 million years ago, during a time when the island of Ireland was completely covered by a warm, clear, shallow sea. As the sea level eventually dropped, the resulting limestone was exposed and it underwent a long period of weathering. This would have led to the development of a landscape similar to that of the Burren in Co. Clare, with abundant limestone pavement and associated hollows and caves. The Cretaceous limestone contains abundant nodules and layers of flint, a silicarich material that does not dissolve in rainwater, unlike the limestone.
As weathering continued, it left behind the more robust flints that accumulated on the limestone landscape. At the beginning of the Palaeogene period, about 65 million years ago, volcanic activity began as a result of stretching and thinning of the Earth's crust when the North American and European tectonic plates pulled apart. The resulting lava flows covered much of Northern Ireland and preserved the top surface of the Cretaceous limestone, covering the CwF.
As its name suggests, the CwF is made up of two main components, namely flints, held together to a greater or lesser degree by clay. The colour of the clay varies greatly, as does the thickness of the deposit and its unique location between the Cretaceous white limestone and the Palaeogene black basalt is what makes it most interesting.
The origin of the CwF has been a subject of great debate amongst geologists. It was initially thought to be a result of weathering at the surface to produce the flint, combined with the residue left behind from the dissolution of the white limestone to produce the clay. Whilst this is correct in the case of the flint, the origin of the clay is much more doubtful. Another theory is that the clay component came from an explosive volcanic event that would have produced abundant volcanic material including ash. This would have occurred before the main basalts started forming. The most recent theory however indicates that the clay most likely came from localised mudflows that would have contained clays derived from the weathered basalts that would have been plentiful at the beginning of the Palaeogene period.
The Clay-with-Flints deposit represents a weathered residue formed sub-aerially, after the Cretaceous limestone had been uplifted from its original marine setting, but before the main Palaeogene basalts series had been erupted.
While such deposits are widespread below the basalts through much of Northern Ireland, uniquely at Tircreven, there are also fine-grained, organic-rich sediments above the flint-rich lower section. These are thought to have been deposited in a lacustrine environment. At the base of these sediments the lignite and lignitic clay appear to drape the uneven top surface of the Clay-with-Flints. The lignite and lignitic clay contain plant tissue, wood fragments and extremely sparse, low diversity miospore floras dominated by long ranging Cretaceous and Palaeogene spores and pollen. The palynofloras are indicative of low-lying swamp conditions with a cool temperate climate.
The Cretaceous white limestone formed on the bottom of a sea floor around 75 million years ago, during a time when the island of Ireland was completely covered by a warm, clear, shallow sea. As the sea level eventually dropped, the resulting limestone was exposed and it underwent a long period of weathering. This would have led to the development of a landscape similar to that of the Burren in Co. Clare, with abundant limestone pavement and associated hollows and caves. The Cretaceous limestone contains abundant nodules and layers of flint, a silicarich material that does not dissolve in rainwater, unlike the limestone.
As weathering continued, it left behind the more robust flints that accumulated on the limestone landscape. At the beginning of the Palaeogene period, about 65 million years ago, volcanic activity began as a result of stretching and thinning of the Earth's crust when the North American and European tectonic plates pulled apart. The resulting lava flows covered much of Northern Ireland and preserved the top surface of the Cretaceous limestone, covering the CwF.
As its name suggests, the CwF is made up of two main components, namely flints, held together to a greater or lesser degree by clay. The colour of the clay varies greatly, as does the thickness of the deposit and its unique location between the Cretaceous white limestone and the Palaeogene black basalt is what makes it most interesting.
The origin of the CwF has been a subject of great debate amongst geologists. It was initially thought to be a result of weathering at the surface to produce the flint, combined with the residue left behind from the dissolution of the white limestone to produce the clay. Whilst this is correct in the case of the flint, the origin of the clay is much more doubtful. Another theory is that the clay component came from an explosive volcanic event that would have produced abundant volcanic material including ash. This would have occurred before the main basalts started forming. The most recent theory however indicates that the clay most likely came from localised mudflows that would have contained clays derived from the weathered basalts that would have been plentiful at the beginning of the Palaeogene period.
The Clay-with-Flints deposit represents a weathered residue formed sub-aerially, after the Cretaceous limestone had been uplifted from its original marine setting, but before the main Palaeogene basalts series had been erupted.
While such deposits are widespread below the basalts through much of Northern Ireland, uniquely at Tircreven, there are also fine-grained, organic-rich sediments above the flint-rich lower section. These are thought to have been deposited in a lacustrine environment. At the base of these sediments the lignite and lignitic clay appear to drape the uneven top surface of the Clay-with-Flints. The lignite and lignitic clay contain plant tissue, wood fragments and extremely sparse, low diversity miospore floras dominated by long ranging Cretaceous and Palaeogene spores and pollen. The palynofloras are indicative of low-lying swamp conditions with a cool temperate climate.
| Enlander, I., Dempster, M. & Doughty, P., 2024. Tircrevan Burn - Clay-with-Flints, County , site summary. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/summary.php?item=1306. Accessed on 2024-12-26 |
| Previous Site | Next Site |