Geology Site Account

Site name: Warren Gorge (previously known as Warren Pit) (part of Chafford Gorges Nature Park)

Grid reference: TL 8329 3822

Brief description of site:

Site of geological interest showing rare periglacial features in the cliffs. Part of Chafford Gorges Nature Park. Geological interest is easily obscured by the growth of vegetation and should be controlled.

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Site description

Warren Pit has now been renamed Warren Gorge. A path leads down into the pit from Essex Wildlife Trusts new visitor centre which was opened in 2006. The centre provides information on the wildlife and geology of the area. The chalk cliffs are largely obscured by vegetation but a reasonable section through the Upper Chalk, capped by Thanet Sand, can be seen from the edge of the lake at the southern end of the quarry. Warren Gorge is linked to Lion Gorge, to the south, by a tunnel (now gated) under Warren Lane. Thames gravel can also be seen at the very top of the cliff. This is the 380,000 year old Orsett Heath Gravel which forms the highest and oldest of the terraces of the modern River Thames, now about 30 metres (100 feet) higher than the present river. In Chafford Hundred this gravel is also visible on the other side of Mill lane in Lion Pit, at the Sand Martin Cliff and in Mill Wood Sand Cliff.

At the north end of the pit is a fine exposure of coombe rock. This rock is evidence of the severe climate that existed in Essex towards the end of the last glacial stage, between 10,000 and 20,000 years ago, when the ground was permanently frozen (permafrost) with only the top metre or so thawing during each brief summer and freezing again the next autumn. Here, the Chalk was close to the surface and the constant freezing and thawing turned the top layer into a mass of saturated chalk rubble which was capable of slowly flowing down a slope like thick porridge to accumulate in valley bottoms. Now hardened into what is known as coombe rock it can be seen at the top of the cliffs beneath a layer of Thames gravel. The junction between the two is undulating and has been clearly affected by this freeze/thaw process. Unfortunately, at the time of writing (2007), this fine geological section is being rapidly obscured by the growth of vegetation, particularly Buddleia.

The Thames gravel at the north end of the pit is called Corbets Tey Gravel and at about 280,000 years old is from a middle terrace of the river and therefore younger than the Orsett Heath Gravel capping the cliffs at the south end of the pit. Very interestingly, both these gravels relate to a time when, locally, the Thames flowed westwards (see separate site entry for Davy Down Riverside Park, South Ockendon).

Warren Gorge is part of Chafford Gorges Nature Park and is managed by Essex Wildlife Trust.

Coombe rock overlain by Thames gravel (Corbets Tey Gravel) at the north end of Warren Gorge. Photo © G. Lucy