UPPER MANZANILLA FORMATION AT FISHING POND VILLAGE FIELDTRIP GUIDE

Transcription

1 UPPER MANZANILLA FORMATION AT FISHING POND VILLAGE FIELDTRIP GUIDE Saturday 10 th March 2012 Trip Leader: Georgia Huggins

2 INTRODUCTION MANZANILLA Formation Author of name: WARING (G.A.) (1926.). The geology of the Island of Trinidad B.W.I The Jon Hopkins Univ., studies in Geology no 7, p. 59 Type locality: The eastern coast of Trinidad from Manzanilla Bay northwards to Fishing Pond (north of Point Paloma) Thickness: About 6,300feet The upper contact is defined by a MFS containing the thick dark grey shale, shell beds, transgressive lag and erosion (lower part of the Springvale Formation), while the lower contact is subjective and is thought to be an unconformable surface above the mid Miocene Brasso/ Tamana Formation. Geographically the formation is found along the north flack of the Central Range and extends from the east coast westward into Venezuela in the Gulf of Paria. The formation is characterized by predominantly blue-black silty clays, abundant glauconite nodules, iron stained sands and by the silts with lignitic beds, fine sand and conglomerates. The Manzanilla has been traditionally subdivided into three members: the San Jose Calcareous Silt, the Montserrat Glauconitic Sandstone and the Telemaque Sandstone. The type section for the Telemaque Sandstone is at the Telemaque River north of the old Brasso Railway Station but with time cut faces have deteriorated. Better exposures are found just south of the Fishing Pond area along the coastline. Outcrops consist of fine to medium heterolithic deltaic sands with strong tidal signitures, organic rich tidal plain and estuary silts and mud, lignite and bright red paleosol beds. Fossils vary in abundance and consist of mainly Ophiomorpha, Thalassinoides, Planolites, Skolithos and Chondrites burrows. The assemblage indicates environmental stress possibly associated with areas of saline and fresh water mixing.

3 5 OUTCROP LOCATION Fig. 1 Location map for the Upper Manzanilla Formation at Fishing Pond Village. Stops for this field trip indicated on the map at right. Fig. 2 Lith- log of the Fishing Pond section of the Manzanilla Fm with the stops for this field trip indicated.

4 STRATIGRAPHY The Manzanilla Formation is traditionally broken up into three parts based on lithology (Kugler, 1956; Carr-Brown and Frampton, 1979 and Radovsky and Iqbal, 1985). We will be looking at the Telemaque Mbr, the upper part of the Manzanilla dominated by tidal sandstones, siltstones and mudstones. According to Schumm (1972) most rivers carry between 85 to 95 % of mud in suspension with the majority of this mud deposited in the marine environment as mud drapes through suspension settling. When fresh water enters the marine environment from the river this mud flocculates creating mud drapes and shale horizons interbedded with courser sediment. The alternating layers of sandstone, siltstone and mudstone of the Telemaque Mbr reflect variations in the discharge of hypopycnal and hyperpycnal flows from a branch of the paleo-orinoco river into the Trinidad area. Fig. 3 The position of the Manzanilla Fm. in Trinidad stratigraphy after Kugler, 1956; Carr-Brown and Frampton, 1979; Elrich et al., 1993, Geetan and Archie, 1995 and Babb, T e l e m a q u e Mont S a n J o s e Fig. 4 The sequence stratigraphic division of the Manzanilla Fm based on current work (Huggins, 2007)

5 LOCATION 1 Glauconite rich fine sands and silts (Montserrat Member) contain pebble to clast-sized iron rich nodules. This bed is the most distal facies at Fishing Pond and represents the first instance of deltaic encroachment. The siderite nodules could be the result of depositional processes or because of chemical processes occurring in the rock during diagenesis. LOCATION 2 These beds form up to 17m-thick units of very fine to finegrained, iron- rich sandstone beds alternating with grey shale and siltstones. There is a slight coarsening upward trend sandstone individual beds thicken to 12cm and become wavy bedded. Bioturbation is scarce with only limited Ophiomorpha and Chondrites. Paleocurrent directions are to the east, northeast and south. LOCATION 3 These deposits represent the most proximal facies found in the Manzanilla Formation. Common features include thick lignite beds and baked paleosols. The lignite beds vary in thickness from 1 cm up to 1m with soft sediment deformation common at the bed boundaries (arrow). Paleosols contain a large amount of iron as observed by their bright red colour. Plant fragments and leaf imprints have been found (Carr-Brown and Frampton, 1979). LOCATION 4 At this location trough cross bedded, channelized sandstones form multi-storey channel bodies consisting of well sorted medium to coarse-grained trough cross bedded sandstones up to 15m thick. These incise into the finer grained heterolithic beds and sandstones of the coarsening upward deltaic facies. In the larger channels 1 to 5m-high compound-dune bedsets separated by minor erosional surfaces, are also present.

6 Figure 5 Snapshots through the development of the delta. The Fishing Pond section occurs during stage 3 when progradation of the delta was at its maximum and stage 4 basin wide transgression and drowning. (Huggins, 2007)

7 Date: 10th March 2012 Outcrop: Telemaque Mbr. Manzanilla Formation Location: Fishing Pond Village AREA WHAT TO LOOK OUT FOR WHAT TO DO Wet ground Slips and falls HAZARD ASSESSMENT Be careful while walking especially in areas that have leaf litter F O R E S T Fallen trees and exposed roots Tripping hazard Tree branches and spikes Insects Wasps, bees and mosquitoes Swampy ground Look around while walking and slowly cross over fallen trees Keep to the centre of the pathway and observe other persons to ensure they don't get scratched by branches or tree spikes Tell the trip leader if you are allergic to wasps and bees. Wear insect repellent and keep applying during the trip. Cross carefully following the trip leader and try not to fall in B E A C H Soft un-compacted sand Tripping hazard Sun Heat stroke Insects Flies and Sandflies Falling outcrop (and coconuts) Fatigue Look around for depressions and disturbed sand that could indicate possible soft areas and avoid them. Walk on wet compacted sand Continually take small mouthfuls of water throughout the trip even when not thirsty. Wear a hat and sunscreen. Wear insect repellent and keep applying during the trip. Look up at outcrop and assess if its safe the approach. Use the helmets provided by trip leader. Don't stand under coconut trees Tell the trip leader if you need a break, are getting cramps or feel dizzy.

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