Sil Ord

1
Refining The Geologic Time Scale An Integrated
Biostratigraphic Approach
1) Integrated biostratigraphy from the Trail
Creek Region, Idaho
Trail Creek Summit
Graptolites
Sil / Ord
Little Fall Creek, Idaho
Graptolites
The Phi Kappa Formation can be integrated into a
regional composite that represents one of the
biostratigraphically longest and most complete
exposures of Ordovician rocks in the world.
Conodonts
2
Refining The Geologic Time Scale An Integrated
Biostratigraphic Approach
2) MICROFOSSIL FAUNAL DIVERSITY DYNAMICS FROM THE
MIDDLE AND UPPER ORDOVICIAN ROCKS OF BALTOSCANDIA
Sample Composite Range Chart - Conodonts

• The Data
• 14 boreholes in Estonia, Latvia, Poland,
  and Scania, Sweden 5 outcrops in Scania (1) and
  the Siljan Region of Sweden (4).
• 103 Chitinozoan species 105 Conodont species
• 47 Graptolite species 200 Ostracode
  species
• 455 Total Taxa
• The CONOP9 Correlation Model
• Average positions of the Estonian Stage
• boundaries are horizontal red lines

Start of GICE
The CONOP9 Correlation Model
1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18 19
3
Year 2 Summary A) Trail Creek Idaho

• We collected samples from 3 sections in the
  Trail Creek Region. At the Little Fall Creek
  Section, we collected Cardiograptus morsus to
  Climacograptus bicornis Zone graptolites. Shale
  surfaces at 39.2 m contained the conodonts
  Periodon flabellum and Drepanodus sp. cf. D.
  arcuatus. Our collections at 201.5 meters yielded
  the conodonts Drepanodus sp., Periodon sp. cf. P.
  aculeatus, and the first recorded bedding plane
  assemblage of Pygodus serra. Nemagraptus gracilis
  was collected at 178 and 216.5 m, and occurred
  with the conodont species P. anserinus in the
  latter collection. Collections at 233 m contained
  C. bicornis and Amorphognathus tvaerensis.
• The Trail Creek Summit section is structurally
  complex but appears to be nearly continuous
  across the Late Ordovician. A thick package of
  fault-bounded, laminated calcisiltites are
  generally unfossiliferous, but appear
  lithologically similar to the Middle Ordovician
  rocks that crop out at Little Fall Creek. Hence,
  the summit section may contain a more complete
  sequence of Ordovician strata than previously
  known.
• The Trail Creek (creek) section is the type
  locality for the Paraorthograptus pacificus
  graptolite Zone. In addition to these latest
  Katian graptolites, we collected graptolites from
  the latest Sandbian and Early Katian. Graptolites
  of Early Katian (Ea1) were not previously known
  from the Trail Creek region. Thus, a composite of
  the Phi Kappa Formation in the Trail Creek region
  represents one of the longest and most complete
  exposures of Ordovician rocks in the world.The
  Phi Kappa Formation can be integrated into a
  regional composite that represents one of the
  biostratigraphically longest and most complete
  exposures of Ordovician rocks in the world.

4
B) Microfossil Faunal Dynamics from Baltoscandia

• CONOP9 is a powerful tool for high resolution
  stratigraphic correlation and allows
• for the use and comparison of many different
  types of data, but the correlation
• solution and range charts must be checked
  carefully.
• Chitinozoan diversity reaches a zenith in the
  Late Keila and then drops through
• the Oandu Stage, coincident with the GICE.
  Chitinozoan diversity then exhibits an
• overall gradual decline across the rest of
  the Ordovician.
• Conodonts have diversity peaks in the lower
  Uhaku and lower Kukruse Stages,
• and then decline gradually through the Late
  Ordovician.
• Ostracods diversify across the Late Keila and
  Oandu Stages, but this may be an
• artifact of our data.
• Overall, our study reveals a microfossil
  diversity declines in the Oandu Stage but
• to a lesser degree than the crisis
  described from the Rapla Core.