Barrow Hill And Tansey Green

Also within

West Midlands County

Condition (Natural England)

Geology & landscape

Geological Feature: Igneous Intrusion · Geological Period: Carboniferous · Rock Type: Basalt

Landscape processes: Fluvial, Volcanic / Igneous

Description

Description Barrow Hill and Tansey Green SSSI is a nationally important site which forms part of a network of sites in central England and the Welsh Borders, important for demonstrating igneous activity during the Carboniferous Period. Barrow Hill and Tansey Green is notably distinct as it comprises a vent agglomerate mixture of dolerite, volcanic ash and small blocks of Coal Measures rocks that demonstrates extrusive explosive activity, whereas the other sites are intrusions with no evidence of having reached the surface. The Tansey Green section demonstrates the surface expression of the volcanic activity as ash fall and surge deposits. The lower now buried ash fall deposits contain the oldest known anatomically preserved conifer like stems, internationally important in the understanding of the evolution of gymnosperms. General description The Barrow Hill complex which lies about three kilometres west of Dudley is one of numerous small outcrops of igneous rocks of Carboniferous Westphalian Series age distributed across the West Midlands. The site is notable as it demonstrates explosive volcanic activity whereas all the other outcrops are intrusions with no evidence of having reached the surface. The majority of the site east of the dismantled railway line is within the Barrow Hill Local Nature Reserve. The site reveals a complex inter relationship between agglomerates of a volcanic vent located at Barrow Hill and its associated volcanic deposits at Tansey Green Claypit. The volcanic deposits occur interbedded with alluvial mudstones and sandstones of the Etruria Marl Formation which underlies most of the area. The Etruria Formation is assigned to the Bolsovian Stage approximately 311 million years old. The vent appears to have been at or near to the ground surface at the time, penetrating wet and largely unconsolidated sediments. The interaction of the hot gaseous magma with groundwater resulted in explosive activity which produced dykes of sedimentary and igneous material. Barrow Hill has been interpreted as a major volcanic centre, with basalt pipe, sills and dykes intruded more or less coevally with the agglomerates. The surface expression of the activity is seen as ash fall deposits, surge deposits and thick breccias similar to the agglomerate seen in the vent. The first volcanic material erupted from the vent is interpreted as ash fall that accumulated rapidly in an alluvial flood plain environment. The ash fall has entombed the oldest anatomically preserved conifer stems found to date. Temperatures were sufficient to char the conifer stems, removing the outer cuticle bark layer. The excellent preservation of the wood, pith and xylem make these stems of considerable importance in the understanding of the evolution of gymnosperms and provides information on environmental constraints on plant growth during the late Carboniferous Period.