Sequence Stratigraphy of the South Texas Oligocene: Understanding the Relationship Between Shale Tectonismand Lowstand DepositionR. Trevio, L.F. Brown, R. Loucks, and U. Hammes

Bureau of Economic GeologyJackson School of GeosciencesThe University of Texas at Austin

A New Depositional Model for the Frio / Vicksburg

OverviewLocation

South Texas Growth-Faulted Subbasins

Stratigraphy Structure Interplay

Dynamic Model

Exploration Potential

Location Map

Seismic Line in Corpus Christi Bay

Schematic representation - successive growth-faulted intraslope subbasins

Organization of sands(after Mitchum and Van Wagoner, 1991)

Related to the interaction of:Origin of Growth-Faulted Subbasins- gravity tectonics, - relative sea-level changes, - and sediment supply.

Wireline-log sequence stratigraphyBasin-floor fans

Wireline-log sequence stratigraphySlope fans

Wireline-log sequence stratigraphyLowstand prograding wedge

Wireline-log sequence stratigraphyLowstand prograding wedge

Organization of sands

Early Lowstand Systems TractDepositional systems after Galloway et al., 1982

Schematic representation of successive growth-faulted intraslope subbasins

Dynamic Depositional Model

Offshelf Lowstands overload slope

Growth-faulted subbasins younger basinward

Similar log facies, different subbasins = different time

Deep Potential Conclusions

AcknowledgementsWestern Geco Seismic

Sabco

IBC (now Boss Exploration)

STARR PROGRAMState of TexasAdvanced Resource Recovery

Organization of sands(after Mitchum, 1991)

Organization: Seismic view

Schematic representation of successive growth-faulted intraslope subbasins

Regional dip cross section using S5 logs Paleo control

Isochron map of lowstand prograding wedgesSediment input (incised valleys) axes

Isopach map of lowstand prograding wedges

Isopach map of lowstand incised-valley fills

Cross section of incised-valley fills (lowstand)

Wireline-log sequence stratigraphyLowstand incised-valley fill, transgressive, and highstand systems tracts

Wireline-log sequence stratigraphyLowstand incised-valley fill, transgressive, and highstand systems tracts

Red Fish BayS5-Benchmark Chart

Section of Red Fish Bay S5-Benchmark Charts

Regional correlations of sandsSo, how do you correlate between subbasins?

Regional dip cross section using S5 logs

Site-Specific Sequence-Stratigraphic Section Benchmark Charts (S5 Benchmark Charts)Composite logs with Sequence stratigraphyadditional data summarize subbasin geology

Promote accurate correlations

Stage in development and filling of growth-faulted intraslope subbasins: Stage 1

Stage in development and filling of growth-faulted intraslope subbasins: Stage 2

Stage in development and filling of growth-faulted intraslope subbasins: Stage 3

Stage in development and filling of growth-faulted intraslope subbasins: Stage 4

Stage in development and filling of growth-faulted intraslope subbasins: Stage 5

Stage in development and filling of growth-faulted intraslope subbasins: Stage 6

Stage in development and filling of growth-faulted intraslope subbasins: Stage 7

Schematic representation of successive shifting LST depocenters

Schematic representation of successive shifting LST depocenters

Schematic representation of successive shifting LST depocenters

Schematic representation of successive shifting LST depocenters

Schematic representation of successive shifting LST depocenters

Thank colleauges, Bureau, Acknowledge STARR.

High falutin titlenow the real title

and their use for chronostratigraphic correlations in growth faulted basins.

A seismic line showing a typical growth fault and a growth-faulted subbasin on the downthrown side. From Mitchum & Van Wagoner paper in Sedimentary geologyDifference is the presence of the growth fault and the shale mass (in gray)All together they are called an off-shelf lowstand. Plan view of an early LST along S. Texas Oligocene coast. Note:Slope fans over-loading the slope w/ shale ridges formingIncised valleys funneling input to shelf edge (previously submerged in green)IVs often incise near juncture of adjacent older growth faults due to differential loading.Lets look at the development of a typical subbasin. And generate the growth faulted subbasinsAlmost intuitive, but has consequences for regional correlations because,Repetition of facies from one basin to the next (younger) one = nonetheless temporal distinctness. PW is just beginning to prograde over the SF complex.The next series of slides is intended to show the non-linear nature of the subbasins emplacement. The sequence model cross section is not intended to imply dip-alignment. Due to differential loading.