Texas Cretaceous Sections

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Texas Cretaceous Sections

• A 50-1, Johnson City, Glen Rose Fm
• Section drawing
• Unit description
• Topographic Map
• A 109, Spring Branch, Cow Creek Fm.
• Section drawing
• Unit description
• Topographic Map
• A 108a, Spring Branch, Hensel Sand Glen Rose
  Fm.
• Section drawing
• Unit description
• Topographic map
• A 69e, Shoal Creek, Del Rio Buda Fm.
• Section drawing
• Unit description
• Topographic map
• A 149, Canyon Lake Glen Rose
• Discussion
• Topographic map

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Unit 8
Unit 7
Unit 6
Unit 5
Unit 4
Unit 3
Unit 2
Unit 1
Limestone
Exogyra layer
Shale
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Site A50-1 Unit Descriptions Unit
8 (14.28-14.52m) A 0.23m thick ledge forming
brown limestone (whats on top? Soil,
plants?). Unit 7 (13.40-14.28m) A 0.88m thick
brown limestone. It includes an 8cm thick tan
shale at top which forms a reentrant beneath the
overlying unit.. Unit 6 (12.62-13.40m) A 0.78m
thick recessive brown shale which forms a slight
reentrant beneath the overlying unit. Unit
5 (11.58-12.62m) A 1.04m thick brown (because
weathered?) shale capped by a 5cm limestone bed
immediately beneath the contact with the
overlying unit. A prominent echinoid bed (also
Loriola??, if you have nobody to determine it,
send me some photos how is the distribution? In
nests, or over the (paleo)surface?, also answer
for below) was noted at 12.0m above the base of
the section. Unit 4 (8.30-11.58m) A 3.28m thick
rubbly-bedded burrowed brown limestone. Clay
content increases moving upwards in the unit.
The upper part of the unit is very shaly (by eye
inspection?). A prominent echinoid (Loriola sp.)
bed noted at 9.0m above the base of the
section. Unit 3 (5.89-8.30m) A 2.41m thick
brown to tan fossiliferous (which other
taxa?)shale. This unit includes the upper E.
paupercula bed found at 6.85m above the base of
the section. Unit 2 (5.71-5.89m) A 0.18m thick
brown resistant ledge forming limestone bed.
Occurs as a single block (what does that mean?
Consistent over the entire outcrop? By the way,
what horizontal extension has the outcrop?
Brown-resistant sounds like ferruginous, might be
indicative of condensed horizon, no borings or
epifauna there?). Unit 1 (0.0-5.71m) A 5.71m
thick weakly calcareous blue shale (blue when
weathered or fresh?) with mollusks. This unit
includes the lower E. paupercula bed at 4.54m
above the base of the section .
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Topographic Map A 50-1
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Topographic Map A 140 Canyon Lake
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A109 Spring BranchCow Creek Formation
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Site A109 Unit Descriptions Unit 5b (3.66-4.14m)
A 0.48m thick bedded sandy limestone unit. This
unit is more massive bedded than unit 5a. Unit
5a (3.18-3.66m) A 0.48m thick sandy limestone
unit. Occurs as 8 beds of sub-equal
thickness. Unit 4 (2.08-3.18m) A 1.10m thick
tan sandy limestone unit. It is thinner bedded
than the underlying unit. Unit 3 (0.64-2.08m) A
1.44m thick massive bedded brownish-orange sandy
limestone. Unit 2b (0.36-0.64) A 0.28m thick
recessive pervasively burrowed limestone. Unit
takes on a honeycombed appearance when
weathered. Unit 2a (0.16-0.36m) A 0.20m thick
bed, same description as unit 2b. Unit
1 (0.0-0.16m) A 0.16m thick brownish-orange
sandy limestone unit.
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Site A108a Unit Descriptions Unit 7 (m) A soft
yellow (fresh) to red (weathered) nodular sandy
interval. Upper surface of unit marks the
contact with the Glen Rose Formation. NEED TO
REMEASURE THICKNESS!! Unit 6 (m) A red well
indurated sandstone layer. This unit is
resistant and forms a prominent ledge between
units 5 and 7. NEED TO REMEASURE
THICKNESS!! Unit 5 (2.27-?m) A soft cream
colored (fresh) to green (weathered) sandy
interval. NEED TO REMEASURE THICKNESS!! Unit
4 (1.48-2.27m) A 0.79m thick oyster bearing
sandy limestone interval. Unit contains numerous
specimens of Exogyra aquila. Unit 3 (0.94-1.48m)
A 0.54m thick covered interval. Unit
2 (0.30-0..94m) A 0.64m thick white
caliche. Unit 1 (0.0-0.30m) A 0.30m
yellow-green sandy clay. Interval underneath
this unit is covered.
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Topographic Map A 108a (same as 109)
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Site A69E Unit Descriptions Unit 4 (5.58-5.83m)
A 0.25m thick brown limestone. Unit is very
poorly exposed, being mostly covered or truncated
by the Holocene unconformity. Unit
3 (3.67-5.58m) A 1.91m thick brown limestone.
Occurs as 5 6 subequal beds. Unit is resistant
and forms a massive overhang above unit 2. Unit
2 (1.67-3.67m) A 2.0m thick blue-white (fresh)
to tan (weathered) fossiliferous wackestone.
Bedding is regular at base of unit, becomes
progressively more irregular towards the top of
the unit. Unit 1 (0.0-1.67m) A 1.67m thick
fossiliferous brown packstone. Base of unit is a
shell lag deposit just above the contact with the
underlying Del Rio Formation. Upper 7cm of the
unit is a shell hash, containing many
Texigryphaea roemeri and Exogyra clarki.
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Topographic Map A 69e Shoal Creek
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A 149Canyon Lake

• 
  This site was underwater during the
  January 2005 visit. This year the lake level is
  normal to low exposing the Exogyra layer at
  least 2 above lake level. We will attempt to
  find the Corbula layer but it is far above the
  collection zone. We tried last year with no
  success. We are unlikely to find it this year.
• Lower Glen Rose Formation

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Topographic Map A 109