Introduction to Geology of Paleozoic Rocks of Hook Head, South West Coast of County Wexford, Ireland

Introduction

The Late Cambrian the Booley Bay formation represents accumulation of deeper water slope sediments. These are part of the sedimentary fill that collected on a trailing margin that was part of the continental terrain that flanked the northern margin of Gondwana and later became the Avalonia continental fragment or microplate.
The Ordovician Caradocian andesitic lavas, silts and shales record of submarine sedimentary and volcanic fill. This accumulation was a response to the southward subduction of the Iapetus Ocean floor crust beneath Avalonia. This subduction caused the uplift and erosion of the Avalonian continental fragment and the deposition of the mix of sedimentary and volcanic Rocks that outcrop along the shore at Duncannon
The Devonian sediments of the Templeton conglomerate formation and Harry Lock formation are related to the collision of the continental terrains of Laurentia, Baltica and Avalonia. This collision caused the uplft associated with Acadian orogeny. The resulting relief was eroded and sediment was transported both east and west. The eastward movement of sediment resulted in the accumulation of the Old Red Sandstone continental siliciclastics that outcrop at Hook Head.
The Carboniferous marginal marine clastics of the Porter's Gate formation and the shelf slope to shallow water carbonates of the Hook Head formation represent the products the Variscan orogeny. This orogeny was a response to the collision of Gondwana with the continental mass formed by the previously welded fragments of Laurentia, Baltica and Avalonia. Initially this collision shed clastics eastward (the Porter's Gate formation) and then was followed by a period of crustal stability and carbonate accumulation (the Hook Head formation).

After the assemblage of maps and diagrams the galleries for the field trip are listed in same order that the outcrops of Hook Head were visited on this trip. You can access the appropriate gallery in the table below by clicking on the images to the right.

Geological diagrams and maps for the geology in the vicinity of Hook Head These are to help locate yourself in the field and are available in the gallery reached by clicking on the diagram to the right and are also on the pdf file that can be accessed by clicking on the pdf icon abovet.
Hook Head Lower Carboniferous shelf slope carbonates This first stop is located on the southwestern end of Hook Head adjacent to the lighthouse. The Lower Carboniferous shelf slope carbonates are largely formed of bioclastic packstones to wackestones. The Rocks are highly bioturbated exhibiting a Cruziana ichnofacies. bedding planes appear to be current or wave driven erosion surfaces. Sediment surfaces are often coated by fenestral bryozoans. There abundant crinoidal remains and other echinoidea fossils. Corals and brachiopods are common too. Small monoclinal like Variscan folds are common.
Hook Head Lower Carboniferous dolomitized carbonate grainstones This stop is located on the west side of Hook Head around half a mile from the lighthouse. The dolomites are largely grainstones. The Rocks are highly crossed Bedded with some bioturbation exhibiting a Scolithos ichnofacies, suggesting a nearshore beach or barrier facies. bedding planes are often draped by finer sediment.
Templetown Bay on west side of Hook Head Late Cambrian contact with overthrust and/or unconformable Devonian. Late Cambrian Cambrian Booley Bay formation is formed of thin Bedded fine quartz sands, silts and shales that show small scale slumping and current ripples within sharply defined continuous Beds. They show some evidence of Variscan structural deformation, including tight folding. The Devonian grades from low angle cross beds of conglomerate and coarse sands, to more steeply inclined cross Bedded sands with gravels floating in this matrix.
Sandeel Bay on east side of Hook Head Devonian Harry Lock formation represents the sediments of braided stream fill that grades from conglomeratic fill at the base of channels to coarse and finer cross Bedded sands. Some of the coarser fill is in channels incised into braided stream deposits in the form of bars and channels that are in turn interBedded locally with shale to siltstone overbank deposits!
Woarway Bay on east side of Hook Head Carboniferous Porter's Gate formation sandstones of near shore beach to barrier setting that grades coarse to finer cross Bedded sands and shales into carbonates. Some the carbonates are fossiliferous mudstones that are inter Bedded locally with shale to siltstone of an offshore shelf setting. These sediments were subjected to wave sorting and rippling!
Lumsdin's Bay on west side of Hook Head Carboniferous Porter's Gate formation sandstones of the near shore beach to barrier setting that grades coarse to finer cross Bedded sands and shales into carbonates. Some the carbonates are fossiliferous mudstones that are inter Bedded locally with shale to siltstone of an offshore shelf setting. These sediments were subjected to wave sorting and rippling! This section shows evidence of faulting which causes the section to be repeated!
Booley Bay near Duncannon on west side of Hook Head Late Cambrian Booley Bay formation is composed of fine grained sands and shales. These thin Bedded fine quartz sands, silts and shales show small scale slumping and locally current ripples. The thickness of the beds varies randomly around one centimenter to around ten centimeters, locally reaching no more than twenty centimeters. beds have sharply defined continuous surfaces and these beds are thought to have collected below wave base. bedding planes show evidence of Ediacaran like Ichno-Fossils occur as does elephant skin mottling which is thought related to microbial mat development. They show some evidence of Variscan structural deformation, including tight folding.
Duncannon Point and Strand on west side of Hook Head beneath the town of Duncannon Ordovician Caradocian Caradocian Rocks that include andesitic lavas, pillow lavas, ash and graptolitic shales and silts.